Macro- and microscopic properties of strontium doped indium oxide

NASA Astrophysics Data System (ADS)

Nikolaenko, Y. M.; Kuzovlev, Y. E.; Medvedev, Y. V.; Mezin, N. I.; Fasel, C.; Gurlo, A.; Schlicker, L.; Bayer, T. J. M.; Genenko, Y. A.

2014-07-01

Solid state synthesis and physical mechanisms of electrical conductivity variation in polycrystalline, strontium doped indium oxide In2O3:(SrO)x were investigated for materials with different doping levels at different temperatures (T = 20-300 °C) and ambient atmosphere content including humidity and low pressure. Gas sensing ability of these compounds as well as the sample resistance appeared to increase by 4 and 8 orders of the magnitude, respectively, with the doping level increase from zero up to x = 10%. The conductance variation due to doping is explained by two mechanisms: acceptor-like electrical activity of Sr as a point defect and appearance of an additional phase of SrIn2O4. An unusual property of high level (x = 10%) doped samples is a possibility of extraordinarily large and fast oxygen exchange with ambient atmosphere at not very high temperatures (100-200 °C). This peculiarity is explained by friable structure of crystallite surface. Friable structure provides relatively fast transition of samples from high to low resistive state at the expense of high conductance of the near surface layer of the grains. Microscopic study of the electro-diffusion process at the surface of oxygen deficient samples allowed estimation of the diffusion coefficient of oxygen vacancies in the friable surface layer at room temperature as 3 × 10-13 cm2/s, which is by one order of the magnitude smaller than that known for amorphous indium oxide films.

Shallow Heavily Doped n++ Germanium by Organo-Antimony Monolayer Doping.

PubMed

Alphazan, Thibault; Díaz Álvarez, Adrian; Martin, François; Grampeix, Helen; Enyedi, Virginie; Martinez, Eugénie; Rochat, Névine; Veillerot, Marc; Dewitte, Marc; Nys, Jean-Philippe; Berthe, Maxime; Stiévenard, Didier; Thieuleux, Chloé; Grandidier, Bruno

2017-06-14

Functionalization of Ge surfaces with the aim of incorporating specific dopant atoms to form high-quality junctions is of particular importance for the development of solid-state devices. In this study, we report the shallow doping of Ge wafers with a monolayer doping strategy that is based on the controlled grafting of Sb precursors and the subsequent diffusion of Sb into the wafer upon annealing. We also highlight the key role of citric acid in passivating the surface before its reaction with the Sb precursors and the benefit of a protective SiO 2 overlayer that enables an efficient incorporation of Sb dopants with a concentration higher than 10 20 cm -3 . Microscopic four-point probe measurements and photoconductivity experiments show the full electrical activation of the Sb dopants, giving rise to the formation of an n++ Sb-doped layer and an enhanced local field-effect passivation at the surface of the Ge wafer.

Remote p-type Doping in GaSb/InAs Core-shell Nanowires

PubMed Central

Ning, Feng; Tang, Li-Ming; Zhang, Yong; Chen, Ke-Qiu

2015-01-01

By performing first-principles calculation, we investigated the electronic properties of remotely p-type doping GaSb nanowire by a Zn-doped InAs shell. The results show that for bare zinc-blende (ZB) [111] GaSb/InAs core-shell nanowire the Zn p-type doped InAs shell donates free holes to the non-doped GaSb core nanowire without activation energy, significantly increasing the hole density and mobility of nanowire. For Zn doping in bare ZB [110] GaSb/InAs core-shell nanowire the hole states are compensated by surface states. We also studied the behaviors of remote p-type doing in two-dimensional (2D) GaSb/InAs heterogeneous slabs, and confirmed that the orientation of nanowire side facet is a key factor for achieving high efficient remote p-type doping. PMID:26028535

Exploring routes to tailor the physical and chemical properties of oxides via doping: an STM study

NASA Astrophysics Data System (ADS)

Nilius, Niklas

2015-08-01

Doping opens fascinating possibilities for tailoring the electronic, optical, magnetic, and chemical properties of oxides. The dopants perturb the intrinsic behavior of the material by generating charge centers for electron transfer into adsorbates, by inducing new energy levels for electronic and optical excitations, and by altering the surface morphology and hence the adsorption and reactivity pattern. Despite a vivid scientific interest, knowledge on doped oxides is limited when compared to semiconductors, which reflects the higher complexity and the insulating nature of many oxides. In fact, atomic-scale studies, aiming at a mechanistic understanding of dopant-related processes, are still scarce. In this article, we review our scanning tunneling microscopy (STM) experiments on thin, crystalline oxide films with a defined doping level. We demonstrate how the impurities alter the surface morphology and produce cationic/anionic vacancies in order to keep the system charge neutral. We discuss how individual dopants can be visualized in the lattice, even if they reside in subsurface layers. By means of STM-conductance and x-ray photoelectron spectroscopy, we determine the electronic impact of dopants, including the energies of their eigen states and local band-bending effects in the host oxide. Electronic transitions between dopant-induced gap states give rise to new optical modes, as detected with STM luminescence spectroscopy. From a chemical perspective, dopants are introduced to improve the redox potential of oxide materials. Electron transfer from Mo-donors, for example, alters the growth behavior of gold and activates O2 molecules on a wide-gap CaO surface. Such results demonstrate the enormous potential of doped oxides in heterogeneous catalysis. Our experiments address the issue of doping from a fundamental viewpoint, posing questions on the lattice position, charge state, and electron-transfer potential of the impurity ions. Whether doped oxides are suitable to catalyze surface reactions needs to be explored in more applied studies in the future.

Effects of single atom doping on the ultrafast electron dynamics of M1Au24(SR)18 (M = Pd, Pt) nanoclusters

NASA Astrophysics Data System (ADS)

Zhou, Meng; Qian, Huifeng; Sfeir, Matthew Y.; Nobusada, Katsuyuki; Jin, Rongchao

2016-03-01

Atomically precise, doped metal clusters are receiving wide research interest due to their synergistic properties dependent on the metal composition. To understand the electronic properties of doped clusters, it is highly desirable to probe the excited state behavior. Here, we report the ultrafast relaxation dynamics of doped M1@Au24(SR)18 (M = Pd, Pt; R = CH2CH2Ph) clusters using femtosecond visible and near infrared transient absorption spectroscopy. Three relaxation components are identified for both mono-doped clusters: (1) sub-picosecond relaxation within the M1Au12 core states; (2) core to shell relaxation in a few picoseconds; and (3) relaxation back to the ground state in more than one nanosecond. Despite similar relaxation pathways for the two doped nanoclusters, the coupling between the metal core and surface ligands is accelerated by over 30% in the case of the Pt dopant compared with the Pd dopant. Compared to Pd doping, the case of Pt doping leads to much more drastic changes in the steady state and transient absorption of the clusters, which indicates that the 5d orbitals of the Pt atom are more strongly mixed with Au 5d and 6s orbitals than the 4d orbitals of the Pd dopant. These results demonstrate that a single foreign atom can lead to entirely different excited state spectral features of the whole cluster compared to the parent Au25(SR)18 cluster. The detailed excited state dynamics of atomically precise Pd/Pt doped gold clusters help further understand their properties and benefit the development of energy-related applications.Atomically precise, doped metal clusters are receiving wide research interest due to their synergistic properties dependent on the metal composition. To understand the electronic properties of doped clusters, it is highly desirable to probe the excited state behavior. Here, we report the ultrafast relaxation dynamics of doped M1@Au24(SR)18 (M = Pd, Pt; R = CH2CH2Ph) clusters using femtosecond visible and near infrared transient absorption spectroscopy. Three relaxation components are identified for both mono-doped clusters: (1) sub-picosecond relaxation within the M1Au12 core states; (2) core to shell relaxation in a few picoseconds; and (3) relaxation back to the ground state in more than one nanosecond. Despite similar relaxation pathways for the two doped nanoclusters, the coupling between the metal core and surface ligands is accelerated by over 30% in the case of the Pt dopant compared with the Pd dopant. Compared to Pd doping, the case of Pt doping leads to much more drastic changes in the steady state and transient absorption of the clusters, which indicates that the 5d orbitals of the Pt atom are more strongly mixed with Au 5d and 6s orbitals than the 4d orbitals of the Pd dopant. These results demonstrate that a single foreign atom can lead to entirely different excited state spectral features of the whole cluster compared to the parent Au25(SR)18 cluster. The detailed excited state dynamics of atomically precise Pd/Pt doped gold clusters help further understand their properties and benefit the development of energy-related applications. Electronic supplementary information (ESI) available: The pump dependent transient absorption spectra and the corresponding global analysis results. See DOI: 10.1039/c6nr01008c

Scattering of low-energetic atoms and molecules from a boron-doped CVD diamond surface

NASA Astrophysics Data System (ADS)

Allenbach, M.; Neuland, M. B.; Riedo, A.; Wurz, P.

2018-01-01

For the detection of low energetic neutral atoms for the remote sensing of space plasmas, charge state conversion surfaces are used to ionize the neutrals for their subsequent measurement. We investigated a boron-doped Chemical Vapor Deposition (CVD) diamond sample for its suitability to serve as a conversion surface on future space missions, such as NASA's Interstellar Mapping and Acceleration Probe. For H and O atoms incident on conversion surface with energies ranging from 195 to 1000 eV and impact angles from 6° to 15° we measured the angular scattering distributions and the ionization yields. Atomic force microscope and laser ablation ionization mass spectrometry analyses were applied to further characterize the sample. Based on a figure-of-merit, which included the ionization yield and angular scatter distribution, the B-doped CVD surface was compared to other, previously characterized conversion surfaces, including e.g. an undoped CVD diamond with a metallized backside. For particle energies below 390 eV the performance of the B-doped CVD conversion surfaces is comparable to surfaces studied before. For higher energies the figure-of-merit indicates a superior performance. From our studies we conclude that the B-doped CVD diamond sample is well suited for its application on future space missions.

Enhancing the electrochemical performance of Li-rich layered oxide Li1.13Ni0.3Mn0.57O2 via WO3 doping and accompanying spontaneous surface phase formation

NASA Astrophysics Data System (ADS)

Huang, Jiajia; Liu, Haodong; Hu, Tao; Meng, Ying Shirley; Luo, Jian

2018-01-01

WO3 doping and accompanying spontaneous formation of a surface phase can substantially improve the discharge capacity, rate capability, and cycling stability of Co-free Li-rich layered oxide Li1.13Ni0.3Mn0.57O2 cathode material. X-ray photoelectron spectroscopy, in conjunction with ion sputtering, shows that W segregates to the particle surfaces, decreases the surface Ni/Mn ratio, and changes the surface valence state. High-resolution transmission electron microscopy further suggests that W segregation increases surface structural disorder. The spontaneous and simultaneous changes in the surface structure, composition, and valence state represent the formation of a surface phase (complexion) as the preferred surface thermodynamic state. Consequently, the averaged discharge capacity is increased by ∼13% from 251 to 284 mAh g-1 at a low rate of C/20 and by ∼200% from 30 to 90 mAh g-1 at a high rate of 40C, in comparison with an undoped specimen processed under identical conditions. Moreover, after 100 cycles at a charge/discharge rate of 1C, the WO3 doped specimen retained a discharge capacity of 188 mAh g-1, being 27% higher than that of the undoped specimen. In a broader context, this work exemplifies an opportunity of utilizing spontaneously-formed surface phases as a scalable and cost-effective method to improve materials properties.

Engineering Topological Surface State of Cr-doped Bi2Se3 under external electric field

NASA Astrophysics Data System (ADS)

Zhang, Jian-Min; Lian, Ruqian; Yang, Yanmin; Xu, Guigui; Zhong, Kehua; Huang, Zhigao

2017-03-01

External electric field control of topological surface states (SSs) is significant for the next generation of condensed matter research and topological quantum devices. Here, we present a first-principles study of the SSs in the magnetic topological insulator (MTI) Cr-doped Bi2Se3 under external electric field. The charge transfer, electric potential, band structure and magnetism of the pure and Cr doped Bi2Se3 film have been investigated. It is found that the competition between charge transfer and spin-orbit coupling (SOC) will lead to an electrically tunable band gap in Bi2Se3 film under external electric field. As Cr atom doped, the charge transfer of Bi2Se3 film under external electric field obviously decreases. Remarkably, the band gap of Cr doped Bi2Se3 film can be greatly engineered by the external electric field due to its special band structure. Furthermore, magnetic coupling of Cr-doped Bi2Se3 could be even mediated via the control of electric field. It is demonstrated that external electric field plays an important role on the electronic and magnetic properties of Cr-doped Bi2Se3 film. Our results may promote the development of electronic and spintronic applications of magnetic topological insulator.

Electronic structure of O-doped SiGe calculated by DFT + U method

NASA Astrophysics Data System (ADS)

Zhao, Zong-Yan; Yang, Wen; Yang, Pei-Zhi

2016-12-01

To more in depth understand the doping effects of oxygen on SiGe alloys, both the micro-structure and properties of O-doped SiGe (including: bulk, (001) surface, and (110) surface) are calculated by DFT + U method in the present work. The calculated results are as follows. (i) The (110) surface is the main exposing surface of SiGe, in which O impurity prefers to occupy the surface vacancy sites. (ii) For O interstitial doping on SiGe (110) surface, the existences of energy states caused by O doping in the band gap not only enhance the infrared light absorption, but also improve the behaviors of photo-generated carriers. (iii) The finding about decreased surface work function of O-doped SiGe (110) surface can confirm previous experimental observations. (iv) In all cases, O doing mainly induces the electronic structures near the band gap to vary, but is not directly involved in these variations. Therefore, these findings in the present work not only can provide further explanation and analysis for the corresponding underlying mechanism for some of the experimental findings reported in the literature, but also conduce to the development of μc-SiGe-based solar cells in the future. Project supported by the Natural Science Foundation of Yunnan Province, China (Grant No. 2015FB123), the 18th Yunnan Province Young Academic and Technical Leaders Reserve Talent Project, China (Grant No. 2015HB015), and the National Natural Science Foundation of China (Grant No. U1037604).

Computational study of dye adsorption onto Brookite TiO2 surfaces for the applications in dye sensitized solar cells

NASA Astrophysics Data System (ADS)

Maluta, N. E.; Dima, R. S.; Nemudzivhadi, H.; Maphanga, R. R.; Sankaran

2017-10-01

The theoretical and computational studies of dye sensitized solar cells (DSSCs) can contribute to a deeper understanding of these type of solar cells. In the current study the density functional theory (DFT) is used to understand the electronic properties of low index brookite (1 0 0) surface doped with ruthenium. The structural optimizations, band structure, and electronic density of states of doped and undoped titanium dioxide (TiO2) brookite surface was performed using the first-principles calculations based on DFT emplotying a plane-wave pseudopotential method. The generalized gradient approximation (GGA) was used in the scheme of Perdew-Burke-Ernzerhof (PBE) to describe the exchange-correlation functional. All calculations were carried out with CASTEP (Cambridge Sequential Total Energy Package) code in Materials Studio of Accelrys Inc. The two different doping methods employed in the current work are, doping by replacement and adsorption. The overlap among the Ruthenium (Ru) 3d, Titanium (Ti) 3d, and Oxygen (O) 2p states enhance photocatalytic activity in the visible light region. The adsorption method shows that an equilibrium position is reached for ruthenium element after optimization. All the methods show that the TiO2 brookite (1 0 0) surface reduces its band gap after been doped with the ruthenium element. From the two techniques used, the total energy of the doped structures show that they are energetically favorable, with the band gap being reduced to 0.263 eV compared to 2.376 eV of the pure system.

Sn-doped Bi 1.1Sb 0.9Te 2S bulk crystal topological insulator with excellent properties

DOE PAGES

S. K. Kushwaha; Pletikosic, I.; Liang, T.; ...

2016-04-27

A long-standing issue in topological insulator research has been to find a bulk single crystal material that provides a high quality platform for characterizing topological surface states without interference from bulk electronic states. This material would ideally be a bulk insulator, have a surface state Dirac point energy well isolated from the bulk valence and conduction bands, display quantum oscillations from the surface state electrons, and be growable as large, high quality bulk single crystals. Here we show that this materials obstacle is overcome by bulk crystals of lightly Sn-doped Bi 1.1Sb 0.9Te 2S grown by the Vertical Bridgeman method.more » We characterize Sn-BSTS via angle-resolved photoemission spectroscopy, scanning tunneling microscopy, transport studies, X-ray diffraction, and Raman scattering. We present this material as a high quality topological insulator that can be reliably grown as bulk single crystals and thus studied by many researchers interested in topological surface states.« less

Change of carrier density at the pseudogap critical point of a cuprate superconductor.

PubMed

Badoux, S; Tabis, W; Laliberté, F; Grissonnanche, G; Vignolle, B; Vignolles, D; Béard, J; Bonn, D A; Hardy, W N; Liang, R; Doiron-Leyraud, N; Taillefer, Louis; Proust, Cyril

2016-03-10

The pseudogap is a partial gap in the electronic density of states that opens in the normal (non-superconducting) state of cuprate superconductors and whose origin is a long-standing puzzle. Its connection to the Mott insulator phase at low doping (hole concentration, p) remains ambiguous and its relation to the charge order that reconstructs the Fermi surface at intermediate doping is still unclear. Here we use measurements of the Hall coefficient in magnetic fields up to 88 tesla to show that Fermi-surface reconstruction by charge order in the cuprate YBa2Cu3Oy ends sharply at a critical doping p = 0.16 that is distinctly lower than the pseudogap critical point p* = 0.19 (ref. 11). This shows that the pseudogap and charge order are separate phenomena. We find that the change in carrier density n from n = 1 + p in the conventional metal at high doping (ref. 12) to n = p at low doping (ref. 13) starts at the pseudogap critical point. This shows that the pseudogap and the antiferromagnetic Mott insulator are linked.

Topological nodal superconducting phases and topological phase transition in the hyperhoneycomb lattice

NASA Astrophysics Data System (ADS)

Bouhon, Adrien; Schmidt, Johann; Black-Schaffer, Annica M.

2018-03-01

We establish the topology of the spin-singlet superconducting states in the bare hyperhoneycomb lattice, and we derive analytically the full phase diagram using only symmetry and topology in combination with simple energy arguments. The phase diagram is dominated by two states preserving time-reversal symmetry. We find a line-nodal state dominating at low doping levels that is topologically nontrivial and exhibits surface Majorana flatbands, which we show perfectly match the bulk-boundary correspondence using the Berry phase approach. At higher doping levels, we find a fully gapped state with trivial topology. By analytically calculating the topological invariant of the nodal lines, we derive the critical point between the line-nodal and fully gapped states as a function of both pairing parameters and doping. We find that the line-nodal state is favored not only at lower doping levels but also if symmetry-allowed deformations of the lattice are present. Adding simple energy arguments, we establish that a fully gapped state with broken time-reversal symmetry likely appears covering the actual phase transition. We find this fully gapped state to be topologically trivial, while we find an additional point-nodal state at very low doing levels that also break time-reversal symmetry and has nontrivial topology with associated Fermi surface arcs. We eventually address the robustness of the phase diagram to generalized models also including adiabatic spin-orbit coupling, and we show how all but the point-nodal state are reasonably stable.

High spin state driven magnetism and thermoelectricity in Mn doped topological insulator Bi2Se3

NASA Astrophysics Data System (ADS)

Maurya, V. K.; Dong, C. L.; Chen, C. L.; Asokan, K.; Patnaik, S.

2018-06-01

We report on the synthesis, and structural - magnetic characterizations of Mn doped Bi2Se3 towards achieving a magnetically doped topological insulator. High quality single crystals of MnxBi2-xSe3 (x = 0, 0.03, 0.05, 0.1) are grown and analysed by X-ray diffraction (XRD), Low Energy Electron Diffraction (LEED), Scanning electron microscopy (SEM), and X-ray absorption near-edge structure spectroscopy (XANES). Magnetic properties of these samples under ZFC-FC protocol and isothermal magnetization confirm ferromagnetic correlation above x = 0.03 value. XANES measurements confirm that the dopant Mn is in Mn2+ state. This is further reconfirmed to be in high spin state by fitting magnetic data with Brillouin function for J = 5/2. Both Hall and Seebeck measurements indicate a sign change of charge carriers above x = 0.03 value of Mn doping. We propose Mn doped Bi2Se3 to be a potential candidate for electromagnetic and thermoelectric device applications involving topological surface states.

Structural, electronic and magnetic properties of carbon doped boron nitride nanowire: Ab initio study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jalilian, Jaafar, E-mail: JaafarJalilian@gmail.com; Kanjouri, Faramarz, E-mail: kanjouri@khu.ac.ir

2016-11-15

Using spin-polarized density functional theory calculations, we demonstrated that carbon doped boron nitride nanowire (C-doped BNNW) has diverse electronic and magnetic properties depending on position of carbon atoms and their percentages. Our results show that only when one carbon atom is situated on the edge of the nanowire, C-doped BNNW is transformed into half-metal. The calculated electronic structure of the C-doped BNNW suggests that doping carbon can induce localized edge states around the Fermi level, and the interaction among localized edge states leads to semiconductor to half-metal transition. Overall, the bond reconstruction causes of appearance of different electronic behavior suchmore » as semiconducting, half-metallicity, nonmagnetic metallic, and ferromagnetic metallic characters. The formation energy of the system shows that when a C atom is doped on surface boron site, system is more stable than the other positions of carbon impurity. Our calculations show that C-doped BNNW may offer unique opportunities for developing nanoscale spintronic materials.« less

Fully gapped superconductivity in In-doped topological crystalline insulator Pb 0.5Sn 0.5Te

DOE PAGES

Du, Guan; Gu, G. D.; Du, Zengyi; ...

2015-07-27

In this study, superconductors derived from topological insulators and topological crystalline insulators by chemical doping have long been considered to be candidates as topological superconductors. Pb 0.5Sn 0.5Te is a topological crystalline insulator with mirror symmetry protected surface states on (001)-, (011)-, and (111)-oriented surfaces. The superconductor (Pb 0.5Sn 0.5) 0.7In 0.3Te is produced by In doping in Pb 0.5Sn 0.5Te, and is thought to be a topological superconductor. Here we report scanning tunneling spectroscopy measurements of the superconducting state as well as the superconducting energy gap in (Pb 0.5Sn 0.5) 0.7In 0.3Te on a (001)-oriented surface. The spectrum canmore » be well fitted by an anisotropic s-wave gap function of Δ = 0.72 + 0.18cos4θ meV using Dynes model. The results show that the superconductor seems to be a fully gapped one without any in-gap states, in contradiction with the expectation of a topological superconductor.« less

Superconductivity across Lifshitz transition and anomalous insulating state in surface K-dosed (Li0.8Fe0.2OH)FeSe.

PubMed

Ren, Mingqiang; Yan, Yajun; Niu, Xiaohai; Tao, Ran; Hu, Die; Peng, Rui; Xie, Binping; Zhao, Jun; Zhang, Tong; Feng, Dong-Lai

2017-07-01

In iron-based superconductors, understanding the relation between superconductivity and electronic structure upon doping is crucial for exploring the pairing mechanism. Recently, it was found that, in iron selenide (FeSe), enhanced superconductivity ( T c of more than 40 K) can be achieved via electron doping, with the Fermi surface only comprising M-centered electron pockets. By using surface K dosing, scanning tunneling microscopy/spectroscopy, and angle-resolved photoemission spectroscopy, we studied the electronic structure and superconductivity of (Li 0.8 Fe 0.2 OH)FeSe in the deep electron-doped regime. We find that a Γ-centered electron band, which originally lies above the Fermi level ( E F ), can be continuously tuned to cross E F and contribute a new electron pocket at Γ. When this Lifshitz transition occurs, the superconductivity in the M-centered electron pocket is slightly suppressed, and a possible superconducting gap with a small size (up to ~5 meV) and a dome-like doping dependence is observed on the new Γ electron pocket. Upon further K dosing, the system eventually evolves into an insulating state. Our findings provide new clues to understand superconductivity versus Fermi surface topology and the correlation effect in FeSe-based superconductors.

Superconductivity across Lifshitz transition and anomalous insulating state in surface K–dosed (Li0.8Fe0.2OH)FeSe

PubMed Central

Ren, Mingqiang; Yan, Yajun; Niu, Xiaohai; Tao, Ran; Hu, Die; Peng, Rui; Xie, Binping; Zhao, Jun; Zhang, Tong; Feng, Dong-Lai

2017-01-01

In iron-based superconductors, understanding the relation between superconductivity and electronic structure upon doping is crucial for exploring the pairing mechanism. Recently, it was found that, in iron selenide (FeSe), enhanced superconductivity (Tc of more than 40 K) can be achieved via electron doping, with the Fermi surface only comprising M-centered electron pockets. By using surface K dosing, scanning tunneling microscopy/spectroscopy, and angle-resolved photoemission spectroscopy, we studied the electronic structure and superconductivity of (Li0.8Fe0.2OH)FeSe in the deep electron-doped regime. We find that a Γ-centered electron band, which originally lies above the Fermi level (EF), can be continuously tuned to cross EF and contribute a new electron pocket at Γ. When this Lifshitz transition occurs, the superconductivity in the M-centered electron pocket is slightly suppressed, and a possible superconducting gap with a small size (up to ~5 meV) and a dome-like doping dependence is observed on the new Γ electron pocket. Upon further K dosing, the system eventually evolves into an insulating state. Our findings provide new clues to understand superconductivity versus Fermi surface topology and the correlation effect in FeSe-based superconductors. PMID:28740865

Systematics of electronic and magnetic properties in the transition metal doped Sb2Te3 quantum anomalous Hall platform

NASA Astrophysics Data System (ADS)

Islam, M. F.; Canali, C. M.; Pertsova, A.; Balatsky, A.; Mahatha, S. K.; Carbone, C.; Barla, A.; Kokh, K. A.; Tereshchenko, O. E.; Jiménez, E.; Brookes, N. B.; Gargiani, P.; Valvidares, M.; Schatz, S.; Peixoto, T. R. F.; Bentmann, H.; Reinert, F.; Jung, J.; Bathon, T.; Fauth, K.; Bode, M.; Sessi, P.

2018-04-01

The quantum anomalous Hall effect (QAHE) has recently been reported to emerge in magnetically doped topological insulators. Although its general phenomenology is well established, the microscopic origin is far from being properly understood and controlled. Here, we report on a detailed and systematic investigation of transition metal (TM) doped Sb2Te3 . By combining density functional theory calculations with complementary experimental techniques, i.e., scanning tunneling microscopy, resonant photoemission, and x-ray magnetic circular dichroism, we provide a complete spectroscopic characterization of both electronic and magnetic properties. Our results reveal that the TM dopants not only affect the magnetic state of the host material, but also significantly alter the electronic structure by generating impurity-derived energy bands. Our findings demonstrate the existence of a delicate interplay between electronic and magnetic properties in TM doped topological insulators. In particular, we find that the fate of the topological surface states critically depends on the specific character of the TM impurity: while V- and Fe-doped Sb2Te3 display resonant impurity states in the vicinity of the Dirac point, Cr and Mn impurities leave the energy gap unaffected. The single-ion magnetic anisotropy energy and easy axis, which control the magnetic gap opening and its stability, are also found to be strongly TM impurity dependent and can vary from in plane to out of plane depending on the impurity and its distance from the surface. Overall, our results provide general guidelines for the realization of a robust QAHE in TM doped Sb2Te3 in the ferromagnetic state.

Role of associated defects in oxygen ion conduction and surface exchange reaction for epitaxial samaria-doped ceria thin films as catalytic coatings

DOE PAGES

Yang, Nan; Shi, Yanuo; Schweiger, Sebastian; ...

2016-05-18

Samaria-doped ceria (SDC) thin films are particularly important for energy and electronic applications such as micro-solid oxide fuel cells, electrolysers, sensors and memristors. In this paper we report a comparative study investigating ionic conductivity and surface reactions for well-grown epitaxial SDC films varying the samaria doping concentration. With increasing doping above 20 mol% of samaria, an enhancement in the defect association was observed by Raman spectroscopy. The role of such defect associates on the films` oxygen ion transport and exchange was investigated by electrochemical impedance spectroscopy and electrochemical strain microscopy (ESM). The measurements reveal that the ionic transport has amore » sharp maximum in ionic conductivity and drop in its activation energy down to 0.6 eV for 20 mol% doping. Increasing the doping concentration further up to 40 mol%, raises the activation energy substantially by a factor of two. We ascribe the sluggish transport kinetics to the "bulk" ionic-near ordering in case of the heavily doped epitaxial films. Analysis of the ESM first order reversal curve measurements indicate that these associated defects may have a beneficial role by lowering the activation of the oxygen exchange "surface" reaction for heavily doped 40 mol% of samaria. We reveal in a model experiment through a solid solution series of samaria doped ceria epitaxial films that the occurrence of associate defects in the bulk affects the surface charging state of the films to increase the exchange rates. Lastly, the implication of these findings are the design of coatings with tuned oxygen surface exchange by control of bulk associate clusters for future electro-catalytic applications.« less

Study on the adsorption properties of O{sub 3}, SO{sub 2}, and SO{sub 3} on B-doped graphene using DFT calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rad, Ali Shokuhi, E-mail: a.shokuhi@gmail.com; Shabestari, Sahand Sadeghi; Mohseni, Soheil

2016-05-15

We investigated the structure, adsorption, electronic states, and charge transfer of O{sub 3}, SO{sub 2} and SO{sub 3} molecules on the surface of a B-doped graphene using density functional theory (DFT). We found weak physisorption of SO{sub 2} (−10.9 kJ/mole, using B3LYP-D) and SO{sub 3} (−15.7 kJ/mole, using B3LYP-D) on the surface of B-doped graphene while there is strong chemisorption for O{sub 3} (−96.3 kJ/mole, using B3LYP-D ) on this surface. Our results suggest the potential of B-doped graphene as a selective sensor/adsorbent for O{sub 3} molecule. We noticed some change in hybridizing of boron from sp{sup 2} to sp{supmore » 3} upon adsorption of O{sub 3} which cases transformation of the adsorbent from 2D to 3D. - Graphical abstract: The electronic property of B-doped graphene is responsible to highly adsorption of O{sub 3} molecules while the adsorption of SO{sub 2} and SO{sub 3} molecules on this surface exhibits only a weak interaction. - Highlights: • B-doped graphene clearly is n-type semiconductor. • High negatively charge of C-atoms neighboring the boron dopant. • Chemisorption of O{sub 3} and physisorption of SO{sub 2} and SO{sub 3} on the surface of B-doped graphene.« less

Thermoelectric Properties of Topological Crystalline Insulator Nanowires

NASA Astrophysics Data System (ADS)

Xu, Enzhi

Bulk lead telluride (PbTe) and its alloy compounds are well-known thermoelectric materials for electric power generation. Tin telluride (SnTe) which has the same rock-salt crystalline structure as PbTe has recently been demonstrated to host unique topological surface states that may favor improved thermoelectric properties. In this thesis work, we studied the thermoelectric properties of single-crystalline nanowires of the SnTe family compounds, i.e. undoped SnTe, PbTe, (Sn,Pb)Te alloy, and In-doped SnTe, all of which were grown by a vapor transport approach. We measured the thermopower S, electrical conductivity sigma and thermal conductivity kappa on each individual nanowire over a temperature range of 25 - 300 K, from which the thermoelectric figures of merit ZTs were determined. In comparison to PbTe nanowires, SnTe and (Sn,Pb)Te has lower thermopower but significantly higher electrical conductivity. Both SnTe and (Sn,Pb)Te nanowires showed enhanced thermopower and suppressed thermal conductivity, compared to their bulk counterparts. The enhancement of thermopower may result from the existence of topological surface states, while the suppression of thermal conductivity may relate to the increased phonon-surface scattering in nanowires. Moreover, indium doping suppresses both electrical and thermal conductivities but enhances thermopower, yielding an improved figure of merit ZT. Our results highlight nanostructuring in combination with alloying or doping as an important approach to enhancing thermoelectric properties. In spite of excellent thermoelectric properties and robust topological surface states, we found that the nanowire surface is subject to fast oxidation. In particular, we demonstrated that exposure of In-doped SnTe nanowires to air leads to surface oxidation within only one minute. Transmission electron microscopy characterization suggests the amorphous nature of the surface, and X-ray photoelectron spectroscopy studies identify the oxide species on nanowire surface. We further developed an effective approach to removing surface oxides by means of argon ion sputtering.

Role of oxygen defects on the magnetic properties of ultra-small Sn1-xFexO2 nanoparticles

NASA Astrophysics Data System (ADS)

Dodge, Kelsey; Chess, Jordan; Eixenberger, Josh; Alanko, Gordon; Hanna, Charles B.; Punnoose, Alex

2013-05-01

Although the role of oxygen defects in the magnetism of metal oxide semiconductors has been widely discussed, it is been difficult to directly measure the oxygen defect concentration of samples to verify this. This work demonstrates a direct correlation between the photocatalytic activity of Sn1-xFexO2 nanoparticles and their magnetic properties. For this, a series of ˜2.6 nm sized, well characterized, single-phase Sn1-xFexO2 crystallites with x = 0-0.20 were synthesized using tin acetate, urea, and appropriate amounts of iron acetate. X-ray photoelectron spectroscopy confirmed the concentration and 3+ oxidation state of the doped Fe ions. The maximum magnetic moment/Fe ion, μ, of 1.6 × 10-4 μB observed for the 0.1% Fe doped sample is smaller than the expected spin-only contribution from either high or low spin Fe3+ ions, and μ decreases with increasing Fe concentration. This behavior cannot be explained by the existing models of magnetic exchange. Photocatalytic studies of pure and Fe-doped SnO2 were used to understand the roles of doped Fe3+ ions and of the oxygen vacancies and defects. The photocatalytic rate constant k also showed an increase when SnO2 nanoparticles were doped with low concentrations of Fe3+, reaching a maximum at 0.1% Fe, followed by a rapid decrease of k for further increase in Fe%. Fe doping presumably increases the concentration of oxygen vacancies, and both Fe3+ ions and oxygen vacancies act as electron acceptors to reduce e--h+ recombination and promote transfer of electrons (and/or holes) to the nanoparticle surface, where they participate in redox reactions. This electron transfer from the Fe3+ ions to local defect density of states at the nanoparticle surface could develop a magnetic moment at the surface states and leads to spontaneous ferromagnetic ordering of the surface shell under favorable conditions. However, at higher doping levels, the same Fe3+ ions might act as recombination centers causing a decrease of both k and magnetic moment μ.

Cobalt-doped ZnO nanocrystals: quantum confinement and surface effects from ab initio methods.

PubMed

Schoenhalz, Aline L; Dalpian, Gustavo M

2013-10-14

Cobalt-doped ZnO nanocrystals were studied through ab initio methods based on the Density Functional Theory. Both quantum confinement and surface effects were explicitly taken into account. When only quantum confinement effects are considered, Co atoms interact through a superexchange mechanism, stabilizing an antiferromagnetic ground state. Usually, this is the case for high quality nanoparticles with perfect surface saturation. When the surfaces were considered, a strong hybridization between the Co atoms and surfaces was observed, strongly changing their electronic and magnetic properties. Our results indicated that the surfaces might qualitatively change the properties of impurities in semiconductor nanocrystals.

Superconductivity in doped Dirac semimetals

NASA Astrophysics Data System (ADS)

Hashimoto, Tatsuki; Kobayashi, Shingo; Tanaka, Yukio; Sato, Masatoshi

2016-07-01

We theoretically study intrinsic superconductivity in doped Dirac semimetals. Dirac semimetals host bulk Dirac points, which are formed by doubly degenerate bands, so the Hamiltonian is described by a 4 ×4 matrix and six types of k -independent pair potentials are allowed by the Fermi-Dirac statistics. We show that the unique spin-orbit coupling leads to characteristic superconducting gap structures and d vectors on the Fermi surface and the electron-electron interaction between intra and interorbitals gives a novel phase diagram of superconductivity. It is found that when the interorbital attraction is dominant, an unconventional superconducting state with point nodes appears. To verify the experimental signature of possible superconducting states, we calculate the temperature dependence of bulk physical properties such as electronic specific heat and spin susceptibility and surface state. In the unconventional superconducting phase, either dispersive or flat Andreev bound states appear between point nodes, which leads to double peaks or a single peak in the surface density of states, respectively. As a result, possible superconducting states can be distinguished by combining bulk and surface measurements.

Stability of the antiferromagnetic state in the electron doped iridates

NASA Astrophysics Data System (ADS)

Bhowal, Sayantika; Moradi Kurdestany, Jamshid; Satpathy, Sashi

2018-06-01

Iridates such as Sr2IrO4 are of considerable interest owing to the formation of the Mott insulating state driven by a large spin–orbit coupling. However, in contrast to the expectation from the Nagaoka theorem that a single doped hole or electron destroys the anti-ferromagnetic (AFM) state of the half-filled Hubbard model in the large U limit, the anti-ferromagnetism persists in the doped Iridates for a large dopant concentration beyond half-filling. With a tight-binding description of the relevant states by the third-neighbor (t 1, t 2, t 3, U) Hubbard model on the square lattice, we examine the stability of the AFM state to the formation of a spin spiral state in the strong coupling limit. The third-neighbor interaction t 3 is important for the description of the Fermi surface of the electron doped system. A phase diagram in the parameter space is obtained for the regions of stability of the AFM state. Our results qualitatively explain the robustness of the AFM state in the electron doped iridate (such as Sr2‑x La x IrO4), observed in many experiments, where the AFM state continues to be stable until a critical dopant concentration.

A computational study on tuning the field emission and electronic properties of BN nanocones by impurity atom doping

NASA Astrophysics Data System (ADS)

Ahmadi, S.; Delir Kheirollahi Nezhad, P.; Hosseinian, A.; Vessally, E.

2018-06-01

We have inspected the effect of substituting a boron or nitrogen atom of a BN nanocone (BNNC) by two impurity atoms with lower and higher atomic numbers based on the density functional theory calculations. Our results explain the experimental observations in a molecular level. Orbital and partial density of states analyses show that the doping processes increase the electrical conductivity by creating new states within the gap of BNNC as follows: BeB > ON > CB > CN. The electron emission current from the surface of BNNC is improved after the CB and BeB dopings, and it is decreased by CN and ON dopings. The BeB and CN dopings make the BNNC a p-type semiconductor and the CB and ON dopings make it an n-type one in good agreement with the experimental results. The ON and BeB doping processes are suggested for the field emission current, and electrical conductivity enhancement, respectively.

Determination of the Si-conducting polymer interfacial properties using A-C impedance techniques

NASA Technical Reports Server (NTRS)

Nagasubramanian, G.; Di Stefano, Salvador; Moacanin, Jovan

1985-01-01

A study was made of the interfacial properties of poly(pyrrole) (PP) deposited electrochemically onto single crystal p-Si surfaces. The interfacial properties are dependent upon the counterions. The formation of 'quasi-ohmic' and 'nonohmic' contacts, respectively, of PP(ClO4) and PP films doped with other counterions (BF4 and para-toluene sulfonate) with p-Si, are explained in terms of the conductivity of these films and the flat band potential, V(fb), of PP relative to that of p-Si. The PP film seems to passivate or block intrinsic surface states present on the p-Si surface. The differences in the impedance behavior of para-toluene sulfonate doped and ClO4 doped PP are compared.

Fermi-surface-free superconductivity in underdoped (Bi,Pb)(Sr,La) 2CuO 6+δ (Bi2201)

DOE PAGES

Mistark, Peter; Hafiz, Hasnain; Markiewicz, Robert S.; ...

2015-06-18

Fermi-surface-free superconductivity arises when the superconducting order pulls down spectral weight from a band that is completely above the Fermi energy in the normal state. Here, we show that this can arise in hole-doped cuprates when a competing order causes a reconstruction of the Fermi surface. The change in Fermi surface topology is accompanied by a characteristic rise in the spectral weight. Finally, our results support the presence of a trisected superconducting dome, and suggest that superconductivity is responsible for stabilizing the (π,π) magnetic order at higher doping.

Effects of single atom doping on the ultrafast electron dynamics of M1Au24(SR)18 (M = Pd, Pt) nanoclusters.

PubMed

Zhou, Meng; Qian, Huifeng; Sfeir, Matthew Y; Nobusada, Katsuyuki; Jin, Rongchao

2016-04-07

Atomically precise, doped metal clusters are receiving wide research interest due to their synergistic properties dependent on the metal composition. To understand the electronic properties of doped clusters, it is highly desirable to probe the excited state behavior. Here, we report the ultrafast relaxation dynamics of doped M1@Au24(SR)18 (M = Pd, Pt; R = CH2CH2Ph) clusters using femtosecond visible and near infrared transient absorption spectroscopy. Three relaxation components are identified for both mono-doped clusters: (1) sub-picosecond relaxation within the M1Au12 core states; (2) core to shell relaxation in a few picoseconds; and (3) relaxation back to the ground state in more than one nanosecond. Despite similar relaxation pathways for the two doped nanoclusters, the coupling between the metal core and surface ligands is accelerated by over 30% in the case of the Pt dopant compared with the Pd dopant. Compared to Pd doping, the case of Pt doping leads to much more drastic changes in the steady state and transient absorption of the clusters, which indicates that the 5d orbitals of the Pt atom are more strongly mixed with Au 5d and 6s orbitals than the 4d orbitals of the Pd dopant. These results demonstrate that a single foreign atom can lead to entirely different excited state spectral features of the whole cluster compared to the parent Au25(SR)18 cluster. The detailed excited state dynamics of atomically precise Pd/Pt doped gold clusters help further understand their properties and benefit the development of energy-related applications.

Effects of single atom doping on the ultrafast electron dynamics of M 1Au 24(SR) 18 (M = Pd, Pt) nanoclusters

DOE PAGES

Zhou, Meng; Qian, Huifeng; Sfeir, Matthew Y.; ...

2016-02-29

Atomically precise, doped metal clusters are receiving wide research interest due to their synergistic properties dependent on the metal composition. To understand the electronic properties of doped clusters, it is highly desirable to probe the excited state behavior. Here, we report the ultrafast relaxation dynamics of doped M 1@Au 24(SR) 18 (M = Pd, Pt; R = CH 2CH 2Ph) clusters using femtosecond visible and near infrared transient absorption spectroscopy. Three relaxation components are identified for both mono-doped clusters: (1) sub-picosecond relaxation within the M 1Au 12 core states; (2) core to shell relaxation in a few picoseconds; and (3)more » relaxation back to the ground state in more than one nanosecond. Despite similar relaxation pathways for the two doped nanoclusters, the coupling between the metal core and surface ligands is accelerated by over 30% in the case of the Pt dopant compared with the Pd dopant. Compared to Pd doping, the case of Pt doping leads to much more drastic changes in the steady state and transient absorption of the clusters, which indicates that the 5d orbitals of the Pt atom are more strongly mixed with Au 5d and 6s orbitals than the 4d orbitals of the Pd dopant. These results demonstrate that a single foreign atom can lead to entirely different excited state spectral features of the whole cluster compared to the parent Au 25(SR) 18 cluster. As a result, the detailed excited state dynamics of atomically precise Pd/Pt doped gold clusters help further understand their properties and benefit the development of energy-related applications.« less

Theoretical studies of superconductivity in doped BaCoSO

NASA Astrophysics Data System (ADS)

Qin, Shengshan; Li, Yinxiang; Zhang, Qiang; Le, Congcong; Hu, Jiangping

2018-06-01

We investigate superconductivity that may exist in the doped BaCoSO, a multi-orbital Mott insulator with a strong antiferromagnetic ground state. The superconductivity is studied in both t-J type and Hubbard type multi-orbital models by mean field approach and random phase approximation (RPA) analysis. Even if there is no C 4 rotational symmetry, it is found that the system still carries a d-wave like pairing symmetry state with gapless nodes and sign changed superconducting order parameters on Fermi surfaces. The results are largely doping insensitive. In this superconducting state, the three {t_{{2_g}}} orbitals have very different superconducting form factors in momentum space. In particular, the intra-orbital pairing of the {d_{{x^2} - {y^2}}} orbital has an s-wave like pairing form factor. The two methods also predict very different pairing strength on different parts of Fermi surfaces. These results suggest that BaCoSO and related materials can be a new ground to test and establish fundamental principles for unconventional high temperature superconductivity.

Non-adiabatic molecular dynamics investigation of photoionization state formation and lifetime in Mn²⁺-doped ZnO quantum dots.

PubMed

Fischer, Sean A; Lingerfelt, David B; May, Joseph W; Li, Xiaosong

2014-09-07

The unique electronic structure of Mn(2+)-doped ZnO quantum dots gives rise to photoionization states that can be used to manipulate the magnetic state of the material and to generate zero-reabsorption luminescence. Fast formation and long non-radiative decay of this photoionization state is a necessary requirement for these important applications. In this work, surface hopping based non-adiabatic molecular dynamics are used to demonstrate the fast formation of a metal-to-ligand charge transfer state in a Mn(2+)-doped ZnO quantum dot. The formation occurs on an ultrafast timescale and is aided by the large density of states and significant mixing of the dopant Mn(2+) 3dt2 levels with the valence-band levels of the ZnO lattice. The non-radiative lifetime of the photoionization states is also investigated.

H 2 Desorption from MgH 2 Surfaces with Steps and Catalyst-Dopants

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reich, Jason M.; Wang, Lin-Lin; Johnson, Duane D.

2014-03-10

Light-metal hydrides, like MgH 2, remain under scrutiny as prototypes for reversible H-storage materials. For MgH 2, we assess hydrogen desorption/adsorption properties (enthalpy and kinetic barriers) for stepped, catalyst-doped surfaces occurring, e.g., from ball-milling in real samples. Employing density functional theory and simulated annealing in a slab model, we studied initial H 2 desorption from stepped surfaces with(out) titanium (Ti) catalytic dopant. Extensive simulated annealing studies were performed to find the dopant’s site preferences. For the most stable initial and final (possibly magnetic) states, nudged elastic band (NEB) calculations were performed to determine the H 2-desorption activation energy. We usedmore » a moment-transition NEB method to account for the dopant’s transition to the lowest-energy magnetic state at each image along the band. We identify a dopant-related surface-desorption mechanism that reloads via bulk H diffusion. While reproducing the observed bulk enthalpy of desorption, we find a decrease of 0.24 eV (a 14% reduction) in the activation energy on doped stepped surface; together with a 22% reduction on a doped flat surface, this brackets the assessed 18% reduction in kinetic barrier for ball-milled MgH 2 samples with low concentration of Ti from experiment.« less

Surface engineered two-dimensional and quasi-one-dimensional nanomaterials for electronic and optoelectronic devices

NASA Astrophysics Data System (ADS)

Du, Xiang

As the sizes of individual components in electronic and optoelectronic devices approach nano scale, the performance of the devices is often determined by surface properties due to their large surface-to-volume ratio. Surface phenomena have become one of the cornerstones in nanoelectronic industry. For this reason, research on the surface functionalization has been tremendous amount of growth over the past decades, and promises to be an increasingly important field in the future. Surface functionalization, as an effective technique to modify the surface properties of a material through a physical or chemical approach, exhibits great potential to solve the problems and challenges, and modulate the performance of nanomaterials based functional devices. Surface functionalization drives the developments and applications of modern electronic and optoelectronic devices fabricated by nanomaterials. In this thesis, I demonstrate two surface functionalization approaches, namely, surface transfer doping and H2 annealing, to effectively solve the problems and significantly enhance the performance of 2D (single structure black phosphorus (BP) and heterostructure graphene/Si Schottky junction), and quasi-1D (molybdenum trioxide (MoO 3) nanobelt) nanomaterials based functional devices, respectively. In situ photoelectron spectroscopy (PES) measurements were also carried out to explore the interfacial charge transfer occurring at the interface between the nanostructures and doping layers, and the gap states in MoO 3 thin films, which provides the underlying mechanism to understand and support our device measurement results. In the first part of this thesis, I will discuss the first surface functionalization approach, namely, surface transfer doping, to effectively modulate the ambipolar characteristics of 2D few-layer BP flakes based FETs. The ambipolar characteristics of BP transistors were effectively modulated through in situ surface functionalization with cesium carbonate (Cs2CO3) and MoO3, respectively. Cs2CO3 was found to strongly electron dope black phosphorus. The electron mobility of black phosphorus was significantly enhanced to ˜27 cm2V-1s-1 after 10 nm Cs2CO3 modification, indicating a greatly improved electron transport behavior. In contrast, MoO3 decoration demonstrated a giant hole doping effect. In situ PES characterization confirms the interfacial charge transfer between black phosphorus and doping layers. This doping can also modulate the Schottky junctions formed between metal contacts and black phosphorus flakes, and hence to enhance the responsivity of black phosphorus based photodetectors. These findings coupled with the tunable nature of the surface transfer doping scheme ensure black phosphorus as a promising candidate for further complementary logic electronics. Following the same surface transfer doping technique, I will demonstrate a remarkable performance enhancement of graphene/Si Schottky junction based self-powered photodetectors via surface modification with MoO3 thin film. It was found that the photocurrent responsivity of MoO3 doped graphene/Si photodetectors was highly increased under a wide spectrum of illuminated light from ultraviolet to near infrared. The current on-off ratio reached up to ˜104 under illumination of 500 nm light with intensity of ˜62 muWcm-2. More importantly, the external quantum efficiency of graphene/Si devices was significantly enhanced up to ˜80% by almost four times in the visible light region after MoO3 functionalization. The largely improved photodetecting performance originates from the increased Schottky barrier height at the graphene/Si interface as well as the reduced series resistance after MoO3 modification, which was further corroborated by the in situ PES and electrical transport characterizations. These observations promise a simple method to effectively modify the graphene/Si Schottky junction based self-powered photodetectors and thus significantly enhance their photodetecting performance. After discussion of the first surface functionalization method, next I will introduce the second approach which is H2 annealing, to greatly extend the photoresponse range of single MoO3 nanobelt based photodetector from UV to visible light by introducing substantial gap states. After annealing, the conductance of MoO3 nanobelt was largely enhanced; at the same time, the photodetector possessed wide visible spectrum response. As corroborated by in situ PES investigations, such strong wide spectrum photoresponse arises from the largely enriched oxygen vacancies and gap states in MoO3 nanobelt after H2 annealing. These results open up a new avenue to extend the wide bandgap metal oxide nanomaterials based optoelectronics devices with efficient visible light response through surface modification, i.e. the introduction of the high density of carefully engineered gap states.

Scanning Tunneling Microscopy/Spectroscopy study on Optimally Potassium Doped Single Crystal BaFe2 As 2

NASA Astrophysics Data System (ADS)

Ma, Jihua; Li, Ang; Zhang, Chenglin; Dai, Pengcheng; Pan, Shuheng

2011-03-01

The iron pnictide parent compound material can be brought into superconducting state by chemical doping. It is worthwhile to study and compare the hole- and electron-doped iron pnictides. Among the well-known family of AEFe 2 As 2 (AE=Ca, Sr, Ba), the scanning tunneling microscopy/spectroscopy study on hole-doped samples is insufficient. In this talk we will present high resolution STM/STS results on (001) surface of the optimally doped single crystal Ba 0.6 K0.4 Fe 2 As 2 (Tc ~ 37 K). With the data we will discuss the spatial variation of the superconducting energy gap.

The electronic structures and work functions of (100) surface of typical binary and doped REB6 single crystals

NASA Astrophysics Data System (ADS)

Liu, Hongliang; Zhang, Xin; Xiao, Yixin; Zhang, Jiuxing

2018-03-01

The density function theory been used to calculate the electronic structures of binary and doped rare earth hexaborides (REB6), which exhibits the large density of states (DOS) near Fermi level. The d orbital elections of RE element contribute the electronic states of election emission near the Fermi level, which imply that the REB6 (RE = La, Ce, Gd) with wide distribution of high density d orbital electrons could provide a lower work function and excellent emission properties. Doping RE elements into binary REB6 can adjust DOS and the position of the Fermi energy level. The calculated work functions of considered REB6 (100) surface show that the REB6 (RE = La, Ce, Gd) have lower work function and doping RE elements with active d orbital electrons can significantly reduce work function of binary REB6. The thermionic emission test results are basically accordant with the calculated value, proving the first principles calculation could provide a good theoretical guidance for the study of electron emission properties of REB6.

[Hydrothermal synthesis and luminescence of one-dimensional Mn(2+)-doped CdS nanocrystals].

PubMed

Yuan, Qiu-Li; Zhao, Jin-Tao; Nie, Qiu-Lin

2007-06-01

One-dimensional Mn(2+)-doped CdS nanocrystals were synthesized by the hydrothermal route. The products were characterized by SEM, EDS, XRD, TEM, HRTEM and PL, respectively. The results revealed that dopant Mn2+ completely substitutes Cd2+ in CdS nanocrystals, and the product was of good crystallite. Further more, a complete suppression of the emission from surface states at room temperature when doping with ions Mn2+ has been observed.

A uniform doping ultra-thin SOI LDMOS with accumulation-mode extended gate and back-side etching technology

NASA Astrophysics Data System (ADS)

Yan-Hui, Zhang; Jie, Wei; Chao, Yin; Qiao, Tan; Jian-Ping, Liu; Peng-Cheng, Li; Xiao-Rong, Luo

2016-02-01

A uniform doping ultra-thin silicon-on-insulator (SOI) lateral-double-diffused metal-oxide-semiconductor (LDMOS) with low specific on-resistance (Ron,sp) and high breakdown voltage (BV) is proposed and its mechanism is investigated. The proposed LDMOS features an accumulation-mode extended gate (AG) and back-side etching (BE). The extended gate consists of a P- region and two diodes in series. In the on-state with VGD > 0, an electron accumulation layer is formed along the drift region surface under the AG. It provides an ultra-low resistance current path along the whole drift region surface and thus the novel device obtains a low temperature distribution. The Ron,sp is nearly independent of the doping concentration of the drift region. In the off-state, the AG not only modulates the surface electric field distribution and improves the BV, but also brings in a charge compensation effect to further reduce the Ron,sp. Moreover, the BE avoids vertical premature breakdown to obtain high BV and allows a uniform doping in the drift region, which avoids the variable lateral doping (VLD) and the “hot-spot” caused by the VLD. Compared with the VLD SOI LDMOS, the proposed device simultaneously reduces the Ron,sp by 70.2% and increases the BV from 776 V to 818 V. Project supported by the National Natural Science Foundation of China (Grant Nos. 61176069 and 61376079).

Nematic order on the surface of a three-dimensional topological insulator

NASA Astrophysics Data System (ADS)

Lundgren, Rex; Yerzhakov, Hennadii; Maciejko, Joseph

2017-12-01

We study the spontaneous breaking of rotational symmetry in the helical surface state of three-dimensional topological insulators due to strong electron-electron interactions, focusing on time-reversal invariant nematic order. Owing to the strongly spin-orbit coupled nature of the surface state, the nematic order parameter is linear in the electron momentum and necessarily involves the electron spin, in contrast with spin-degenerate nematic Fermi liquids. For a chemical potential at the Dirac point (zero doping), we find a first-order phase transition at zero temperature between isotropic and nematic Dirac semimetals. This extends to a thermal phase transition that changes from first to second order at a finite-temperature tricritical point. At finite doping, we find a transition between isotropic and nematic helical Fermi liquids that is second order even at zero temperature. Focusing on finite doping, we discuss various observable consequences of nematic order, such as anisotropies in transport and the spin susceptibility, the partial breakdown of spin-momentum locking, collective modes and induced spin fluctuations, and non-Fermi-liquid behavior at the quantum critical point and in the nematic phase.

Study on photoemission surface of varied doping GaN photocathode

NASA Astrophysics Data System (ADS)

Qiao, Jianliang; Du, Ruijuan; Ding, Huan; Gao, Youtang; Chang, Benkang

2014-09-01

For varied doping GaN photocathode, from bulk to surface the doping concentrations are distributed from high to low. The varied doping GaN photocathode may produce directional inside electric field within the material, so the higher quantum efficiency can be obtained. The photoemission surface of varied doping GaN photocathode is very important to the high quantum efficiency, but the forming process of the surface state after Cs activation or Cs/O activation has been not known completely. Encircling the photoemission mechanism of varied GaN photocathode, considering the experiment phenomena during the activation and the successful activation results, the varied GaN photocathode surface model [GaN(Mg):Cs]:O-Cs after activation with cesium and oxygen was given. According to GaN photocathode activation process and the change of electronic affinity, the comparatively ideal NEA property can be achieved by Cs or Cs/O activation, and higher quantum efficiency can be obtained. The results show: The effective NEA characteristic of GaN can be gotten only by Cs. [GaN(Mg):Cs] dipoles form the first dipole layer, the positive end is toward the vacuum side. In the activation processing with Cs/O, the second dipole layer is formed by O-Cs dipoles, A O-Cs dipole includes one oxygen atom and two Cs atoms, and the positive end is also toward the vacuum side thus the escape of electrons can be promoted.

Effect of low Fe3+ doping on characteristics, sonocatalytic activity and reusability of TiO2 nanotubes catalysts for removal of Rhodamine B from water.

PubMed

Pang, Yean Ling; Abdullah, Ahmad Zuhairi

2012-10-15

Fe-doped titanium dioxide (TiO(2)) nanotubes were prepared using sol-gel followed by hydrothermal methods and characterized using various methods. The sonocatalytic activity was evaluated based on oxidation of Rhodamine B under ultrasonic irradiation. Iron ions (Fe(3+)) might incorporate into the lattice and intercalated in the interlayer spaces of TiO(2) nanotubes. The catalysts showed narrower band gap energies, higher specific surface areas, more active surface oxygen vacancies and significantly improved sonocatalytic activity. The optimum Fe doping at Fe:Ti=0.005 showed the highest sonocatalytic activity and exceeded that of un-doped TiO(2) nanotubes by a factor of 2.3 times. It was believed that Fe(3+) doping induced the formation of new states close to the valence band and conduction bands and accelerated the separation of charge carriers. Leached Fe(3+) could catalyze Fenton-like reaction and led to an increase in the hydroxyl radical (OH) generation. Fe-doped TiO(2) nanotubes could retain high degradation efficiency even after being reused for 4 cycles with minimal loss of Fe from the surface of the catalyst. Copyright © 2012 Elsevier B.V. All rights reserved.

Interfacial Engineered Polyaniline/Sulfur-Doped TiO2 Nanotube Arrays for Ultralong Cycle Lifetime Fiber-Shaped, Solid-State Supercapacitors.

PubMed

Li, Chun; Wang, Zhuanpei; Li, Shengwen; Cheng, Jianli; Zhang, Yanning; Zhou, Jingwen; Yang, Dan; Tong, Dong-Ge; Wang, Bin

2018-05-30

Fiber-shaped supercapacitors (FSCs) have great promises in wearable electronics applications. However, the limited specific surface area and inadequate structural stability caused by the weak interfacial interactions of the electrodes result in relatively low specific capacitance and unsatisfactory cycle lifetime. Herein, solid-state FSCs with high energy density and ultralong cycle lifetime based on polyaniline (PANI)/sulfur-doped TiO 2 nanotube arrays (PANI/S-TiO 2 ) are fabricated by interfacial engineering. The experimental results and ab initio calculations reveal that S doping can effectively promote the conductivity of titania nanotubes and increase the binding energy of PANI anchored on the electrode surface, leading to a much stronger binding of PANI on the surface of the electrode and excellent electrode structure stability. As a result, the FSCs using the PANI/S-TiO 2 electrodes deliver a high specific capacitance of 91.9 mF cm -2 , a capacitance retention of 93.78% after 12 000 charge-discharge cycles, and an areal energy density of 3.2 μW h cm -2 . Meanwhile, the all-solid-state FSC device retains its excellent flexibility and stable electrochemical capacitance even after bending 150 cycles. The enhanced performances of FSCs could be attributed to the large surface area, reduced ion diffusion path, improved electrical conductivity, and engineered interfacial interaction of the rationally designed electrodes.

Phosphorus Doping in Si Nanocrystals/SiO2 msultilayers and Light Emission with Wavelength compatible for Optical Telecommunication

PubMed Central

Lu, Peng; Mu, Weiwei; Xu, Jun; Zhang, Xiaowei; Zhang, Wenping; Li, Wei; Xu, Ling; Chen, Kunji

2016-01-01

Doping in semiconductors is a fundamental issue for developing high performance devices. However, the doping behavior in Si nanocrystals (Si NCs) has not been fully understood so far. In the present work, P-doped Si NCs/SiO2 multilayers are fabricated. As revealed by XPS and ESR measurements, P dopants will preferentially passivate the surface states of Si NCs. Meanwhile, low temperature ESR spectra indicate that some P dopants are incorporated into Si NCs substitutionally and the incorporated P impurities increase with the P doping concentration or annealing temperature increasing. Furthermore, a kind of defect states will be generated with high doping concentration or annealing temperature due to the damage of Si crystalline lattice. More interestingly, the incorporated P dopants can generate deep levels in the ultra-small sized (~2 nm) Si NCs, which will cause a new subband light emission with the wavelength compatible with the requirement of the optical telecommunication. The studies of P-doped Si NCs/SiO2 multilayers suggest that P doping plays an important role in the electronic structures and optoelectronic characteristics of Si NCs. PMID:26956425

The secret behind the success of doping nickel oxyhydroxide with iron.

PubMed

Fidelsky, Vicky; Toroker, Maytal Caspary

2017-03-15

Discovering better catalysts for water splitting is the holy grail of the renewable energy field. One of the most successful water oxidation catalysts is nickel oxyhydroxide (NiOOH), which is chemically active only as a result of doping with Fe. In order to shed light on how Fe improves efficiency, we perform Density Functional Theory +U (DFT+U) calculations of water oxidation reaction intermediates of Fe substitutional doped NiOOH. The results are analyzed while considering the presence of vacancies that we use as probes to test the effect of adding charge to the surface. We find that the smaller electronegativity of the Fe dopant relative to Ni allows the dopant to have several possible oxidation states with less energy penalty. As a result, the presence of vacancies which alters local oxidation states does not affect the low overpotential of Fe-doped NiOOH. We conclude that the secret to the success of doping NiOOH with iron is the ability of iron to easily change oxidation states, which is critical during the chemical reaction of water oxidation.

Controlling the Electronic Structure of Graphene Using Surface-adsorbate Interactions

DTIC Science & Technology

2015-07-21

substrate via n doping, with or without intercalation, suggests that the graphene-to-substrate interaction could be controlled dynamically. DOI : 10.1103...which form a Dirac cone and are degenerate at the Fermi level [1]. These states change in response to atoms adsorbed on top of graphene (doping) or when...coupling to the substrate is strong. In the case of graphene on metals, the energy of the Dirac cone can change as a result of interfacial doping, or

An All-Solid-State pH Sensor Employing Fluorine-Terminated Polycrystalline Boron-Doped Diamond as a pH-Insensitive Solution-Gate Field-Effect Transistor.

PubMed

Shintani, Yukihiro; Kobayashi, Mikinori; Kawarada, Hiroshi

2017-05-05

A fluorine-terminated polycrystalline boron-doped diamond surface is successfully employed as a pH-insensitive SGFET (solution-gate field-effect transistor) for an all-solid-state pH sensor. The fluorinated polycrystalline boron-doped diamond (BDD) channel possesses a pH-insensitivity of less than 3mV/pH compared with a pH-sensitive oxygenated channel. With differential FET (field-effect transistor) sensing, a sensitivity of 27 mv/pH was obtained in the pH range of 2-10; therefore, it demonstrated excellent performance for an all-solid-state pH sensor with a pH-sensitive oxygen-terminated polycrystalline BDD SGFET and a platinum quasi-reference electrode, respectively.

Study of microstructure and electroluminescence of zinc sulfide thin film

NASA Astrophysics Data System (ADS)

Zhao-hong, Liu; Yu-jiang, Wang; Mou-zhi, Chen; Zhen-xiang, Chen; Shu-nong, Sun; Mei-chun, Huang

1998-03-01

The electroluminscent zinc sulfide thin film doped with erbium, fabricated by thermal evaporation with two boats, are examined. The surface and internal electronic states of ZnS thin film are measured by means of x-ray diffraction and x-ray photoemission spectroscopy. The information on the relations between electroluminescent characteristics and internal electronic states of the film is obtained. And the effects of the microstructure of thin film doped with rare earth erbium on electroluminescence are discussed as well.

Negligible Electronic Interaction between Photoexcited Electron–Hole Pairs and Free Electrons in Phosphorus–Boron Co-Doped Silicon Nanocrystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Limpens, Rens; Fujii, Minoru; Neale, Nathan R.

Phosphorus (P) and boron (B) co-doped Si nanocrystals (NCs) have raised interest in the optoelectronic industry due to their electronic tunability, optimal carrier multiplication properties, and straightforward dispersibility in polar solvents. Yet a basic understanding of the interaction of photoexcited electron-hole (e-h) pairs with new physical features that are introduced by the co-doping process (free carriers, defect states, and surface chemistry) is missing. Here, we present the first study of the ultrafast carrier dynamics in SiO2-embedded P-B co-doped Si NC ensembles using induced absorption spectroscopy through a two-step approach. First, the induced absorption data show that the large fraction ofmore » the dopants residing on the NC surface slows down carrier relaxation dynamics within the first 20 ps relative to intrinsic (undoped) Si NCs, which we interpret as enhanced surface passivation. On longer time-scales (picosecond to nanosecond regime), we observe a speeding up of the carrier relaxation dynamics and ascribe it to doping-induced trap states. This argument is deduced from the second part of the study, where we investigate multiexciton interactions. From a stochastic modeling approach we show that localized carriers, which are introduced by the P or B dopants, have minor electronic interactions with the photoexcited e-h pairs. This is understood in light of the strong localization of the introduced carriers on their original P- or B-dopant atoms, due to the strong quantum confinement regime in these relatively small NCs (<6 nm).« less

Negligible Electronic Interaction between Photoexcited Electron-Hole Pairs and Free Electrons in Phosphorus-Boron Co-Doped Silicon Nanocrystals

DOE PAGES

Limpens, Rens; Neale, Nathan R; Fujii, Minoru; ...

2018-03-05

Phosphorus (P) and boron (B) co-doped Si nanocrystals (NCs) have raised interest in the optoelectronic industry due to their electronic tunability, optimal carrier multiplication properties, and straightforward dispersibility in polar solvents. Yet a basic understanding of the interaction of photoexcited electron-hole (e-h) pairs with new physical features that are introduced by the co-doping process (free carriers, defect states, and surface chemistry) is missing. Here, we present the first study of the ultrafast carrier dynamics in SiO2-embedded P-B co-doped Si NC ensembles using induced absorption spectroscopy through a two-step approach. First, the induced absorption data show that the large fraction ofmore » the dopants residing on the NC surface slows down carrier relaxation dynamics within the first 20 ps relative to intrinsic (undoped) Si NCs, which we interpret as enhanced surface passivation. On longer time-scales (picosecond to nanosecond regime), we observe a speeding up of the carrier relaxation dynamics and ascribe it to doping-induced trap states. This argument is deduced from the second part of the study, where we investigate multiexciton interactions. From a stochastic modeling approach we show that localized carriers, which are introduced by the P or B dopants, have minor electronic interactions with the photoexcited e-h pairs. This is understood in light of the strong localization of the introduced carriers on their original P- or B-dopant atoms, due to the strong quantum confinement regime in these relatively small NCs (<6 nm).« less

Negligible Electronic Interaction between Photoexcited Electron–Hole Pairs and Free Electrons in Phosphorus–Boron Co-Doped Silicon Nanocrystals

DOE PAGES

Limpens, Rens; Fujii, Minoru; Neale, Nathan R.; ...

2018-02-28

Phosphorus (P) and boron (B) co-doped Si nanocrystals (NCs) have raised interest in the optoelectronic industry due to their electronic tunability, optimal carrier multiplication properties, and straightforward dispersibility in polar solvents. Yet a basic understanding of the interaction of photoexcited electron-hole (e-h) pairs with new physical features that are introduced by the co-doping process (free carriers, defect states, and surface chemistry) is missing. Here, we present the first study of the ultrafast carrier dynamics in SiO2-embedded P-B co-doped Si NC ensembles using induced absorption spectroscopy through a two-step approach. First, the induced absorption data show that the large fraction ofmore » the dopants residing on the NC surface slows down carrier relaxation dynamics within the first 20 ps relative to intrinsic (undoped) Si NCs, which we interpret as enhanced surface passivation. On longer time-scales (picosecond to nanosecond regime), we observe a speeding up of the carrier relaxation dynamics and ascribe it to doping-induced trap states. This argument is deduced from the second part of the study, where we investigate multiexciton interactions. From a stochastic modeling approach we show that localized carriers, which are introduced by the P or B dopants, have minor electronic interactions with the photoexcited e-h pairs. This is understood in light of the strong localization of the introduced carriers on their original P- or B-dopant atoms, due to the strong quantum confinement regime in these relatively small NCs (<6 nm).« less

Adsorption of CO2 on Fe-doped graphene nano-ribbons: Investigation of transport properties

NASA Astrophysics Data System (ADS)

Othman, W.; Fahed, M.; Hatim, S.; Sherazi, A.; Berdiyorov, G.; Tit, N.

2017-07-01

Density functional theory combined with the non-equilibrium Green’s function formalism is used to study the conductance response of Fe-doped graphene nano-ribbons (GNRs) to CO2 gas adsorption. A single Fe atom is either adsorbed on GNR’s surface (aFe-graphene) or it substitutes the carbon atom (sFe-graphene). Metal atom doping reduces the electronic transmission of pristine graphene due to the localization of electronic states near the impurity site. Moreover, the aFe-graphene is found to be less sensitive to the CO2 molecule attachment as compared to the sFe-graphene system. These behaviours are not only consolidated but rather confirmed by calculating the IV characteristics from which both surface resistance and its sensitivity to the gas are estimated. Since the change in the conductivity is one of the main outputs of sensors, our findings will be useful in developing efficient graphene-based solid-state gas sensors.

Three energy scales in the superconducting state of hole-doped cuprates detected by electronic Raman scattering

DOE PAGES

Benhabib, S.; Gu, G. D.; Gallais, Y.; ...

2015-10-06

We explore by electronic Raman scattering the superconducting state of the Bi 2Sr 2CaCu 2O 8+δ (Bi-2212) crystal by performing a fine-tuned doping study. We find three distinct energy scales in A 1g, B 1g, and B 2g symmetries which show three distinct doping dependencies. Above p=0.22, the three energies merge; below p=0.12, the A 1g scale is no longer detectable, while the B 1g and B 2g scales become constant in energy. In between, the A 1g and B 1g scales increase monotonically with underdoping, while the B 2g one exhibits a maximum at p=0.16. The three superconducting energymore » scales appear to be a universal feature of hole-doped cuprates. Furthermore, we propose that the nontrivial doping dependencies of the three scales originate from the Fermi-surface changes and reveal competing orders inside the superconducting dome.« less

Upconversion improvement in KLaF4:Yb3+/Er3+ nanoparticles by doping Al3+ ions

NASA Astrophysics Data System (ADS)

Zhou, Haifang; Wang, Xiechun; Lai, Yunfeng; Cheng, Shuying; Zheng, Qiao; Yu, Jinlin

2017-10-01

Rare-earth ion-doped upconversion (UC) materials show great potential applications in optical and optoelectronic devices due to their novel optical properties. In this work, hexagonal KLaF4:Yb3+/Er3+ nanoparticles (NPs) were successfully synthesized by a hydrothermal method, and remarkably enhanced upconversion luminescence in green and red emission bands in KLaF4:Yb3+/Er3+ NPs has been achieved by doping Al3+ ions under 980 nm excitation. Compared to the aluminum-free KLaF4:Yb3+/Er3+ NPs sample, the UC fluorescence intensities of the green and red emissions of NPs doped with 10 at.% Al3+ ions were significantly enhanced by 5.9 and 7.3 times, respectively. Longer lifetimes of the doped samples were observed for the 4S3/2 state and 4F9/2 state. The underlying reason for the UC enhancement by doping Al3+ ions was mainly ascribed to distortion of the local symmetry around Er3+ ions and adsorption reduction of organic ligands on the surface of NPs. In addition, the influence of doping Al3+ ions on the structure and morphology of the NPs samples was also discussed.

Post-activation of in situ Bsbnd F codoped g-C3N4 for enhanced photocatalytic H2 evolution

NASA Astrophysics Data System (ADS)

Cui, Yanjuan; Wang, Hao; Yang, Chuanfeng; Li, Ming; Zhao, Yimeng; Chen, Fangyan

2018-05-01

Porous graphitic carbon nitride polymer (p-CN-BF) with enhanced photoproduction of H2 from water was prepared by a two-step treatment process including in-situ Boron and fluorine codoping using [Emim]BF4 as dopants followed by post-calcination in air. Several techniques were employed to characterize the modified structure and elucidate the doping state of B and F. It was shown that in-situ doping method is necessary for efficient doping of heteroatoms into the molecular composition of CN. The difference of doping state of B and F was that B doping primary existing in the inside skeleton of CN, but F doping merely presents in the surface layer. The inside doped B made for the enhanced visible light absorption and the production of uniform porous structure during post-sintering process. By the synergistic effect of Bsbnd F codoping and post-activation, p-CN-BF showed much enhanced photoelectron generation, transmission and separation, therefore, it performs high photocatalytic activity for H2 evolution (351 μmol h-1), which was 13 and 5 times higher than samples only modified by Bsbnd F codoping (CN-BF) or post-annealing (P-CN).

Surface States in the AlxGa1-xN Barrier in AlxGa1-xN/GaN Heterostructures

NASA Astrophysics Data System (ADS)

Liu, Jie; Shen, Bo; Wang, Mao-Jun; Zhou, Yu-Gang; Chen, Dun-Jun; Zhang, Rong; Shi, Yi; Zheng, You-Dou

2004-01-01

Frequency-dependent capacitance-voltage (C-V) measurements have been performed on modulation-doped Al0.22 Ga0.78N/GaN heterostructures to investigate the characteristics of the surface states in the AlxGa1-xN barrier. Numerical fittings based on the experimental data indicate that there are surface states with high density locating on the AlxGa1-xN barrier. The density of the surface states is about 1012 cm-2eV-1, and the time constant is about 1 mus. It is found that an insulating layer (Si3N4) between the metal contact and the surface of AlxGa1-xN can passivate the surface states effectively.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Xiaoguang; McGuire, Michael A.; Chen, Yong P.

Topological insulators, with characteristic topological surface states, have emerged as a new state of matter with rich potentials for both fundamental physics and device applications. However, the experimental detection of the surface transport has been hampered by the unavoidable extrinsic conductivity associated with the bulk crystals. Here we show that a four-probe transport spectroscopy in a multi-probe scanning tunneling microscopy system can be used to differentiate conductivities from the surface states and the coexisting bulk states in topological insulators. We derive a scaling relation of measured resistance with respect to varying inter-probe spacing for two interconnected conduction channels, which allowsmore » quantitative determination of conductivities from both channels. Using this method, we demonstrate the separation of 2D and 3D conduction in topological insulators by comparing the conductance scaling of Bi 2Se 3, Bi 2Te 2Se, and Sb-doped Bi 2Se 3 with that of a pure 2D conductance of graphene on SiC substrate. We also report the 2D conductance enhancement due to the surface doping effect in topological insulators. This technique can be applied to reveal 2D to 3D crossover of conductance in other complex systems.« less

Gigantic 2D laser-induced photovoltaic effect in magnetically doped topological insulators for surface zero-bias spin-polarized current generation

NASA Astrophysics Data System (ADS)

Shikin, A. M.; Voroshin, V. Yu; Rybkin, A. G.; Kokh, K. A.; Tereshchenko, O. E.; Ishida, Y.; Kimura, A.

2018-01-01

A new kind of 2D photovoltaic effect (PVE) with the generation of anomalously large surface photovoltage up to 210 meV in magnetically doped topological insulators (TIs) has been studied by the laser time-resolved pump-probe angle-resolved photoelectron spectroscopy. The PVE has maximal efficiency for TIs with high occupation of the upper Dirac cone (DC) states and the Dirac point located inside the fundamental energy gap. For TIs with low occupation of the upper DC states and the Dirac point located inside the valence band the generated surface photovoltage is significantly reduced. We have shown that the observed giant PVE is related to the laser-generated electron-hole asymmetry followed by accumulation of the photoexcited electrons at the surface. It is accompanied by the 2D relaxation process with the generation of zero-bias spin-polarized currents flowing along the topological surface states (TSSs) outside the laser beam spot. As a result, the spin-polarized current generates an effective in-plane magnetic field that is experimentally confirmed by the k II-shift of the DC relative to the bottom non-spin-polarized conduction band states. The realized 2D PVE can be considered as a source for the generation of zero-bias surface spin-polarized currents and the laser-induced local surface magnetization developed in such kind 2D TSS materials.

Self-energy behavior away from the Fermi surface in doped Mott insulators.

PubMed

Merino, J; Gunnarsson, O; Kotliar, G

2016-02-03

We analyze self-energies of electrons away from the Fermi surface in doped Mott insulators using the dynamical cluster approximation to the Hubbard model. For large onsite repulsion, U, and hole doping, the magnitude of the self-energy for imaginary frequencies at the top of the band ([Formula: see text]) is enhanced with respect to the self-energy magnitude at the bottom of the band ([Formula: see text]). The self-energy behavior at these two [Formula: see text]-points is switched for electron doping. Although the hybridization is much larger for (0, 0) than for [Formula: see text], we demonstrate that this is not the origin of this difference. Isolated clusters under a downward shift of the chemical potential, [Formula: see text], at half-filling reproduce the overall self-energy behavior at (0, 0) and [Formula: see text] found in low hole doped embedded clusters. This happens although there is no change in the electronic structure of the isolated clusters. Our analysis shows that a downward shift of the chemical potential which weakly hole dopes the Mott insulator can lead to a large enhancement of the [Formula: see text] self-energy for imaginary frequencies which is not associated with electronic correlation effects, even in embedded clusters. Interpretations of the strength of electronic correlations based on self-energies for imaginary frequencies are, in general, misleading for states away from the Fermi surface.

Preparation and surface characteristics of Re3W matrix scandate cathode: An experimental and theoretical study

NASA Astrophysics Data System (ADS)

Lai, Chen; Wang, Jinshu; Zhou, Fan; Liu, Wei; Hu, Peng; Wang, Changhao; Wang, Ruzhi; Miao, Naihua

2018-05-01

The Scandia doped thermionic cathodes have received great attention owing to their high electron emission density in past two decades. Here, Scandia doped Re3W matrix scandate (RS) cathodes are fabricated by using Sc2O3 doped Re3W powders that prepared by spray drying method. The micromorphology, surface composition and chemical states of RS cathode are investigated with various modern technologies. It reveals that the reduction temperature of RS powders is dramatically increased by Sc2O3. On the surface of RS cathode, a certain amount of Sc2O3 nanoparticles and barium salt submicron particles are observed. According to the in situ Auger electron spectroscopy analysis, the concentration ratio of Ba:Sc:O is determined to be 2.9:1.1:2.7. The X-ray photoelectron spectroscopy data indicates that low oxidation state of Sc is clearly observed in scandate cathodes. The high atomic ratio of Ba on RS cathode surface is suggested due to the high adsorption of Re3W to Ba. Moreover, RS cathode shows better adsorption to Sc by comparison with conventional tungsten matrix scandate cathode. For RS cathode, the main depletion of Sc is suggested to -OSc desorbing from RS cathode surface. RS cathode is expected to be an impressive thermionic cathode with good emission properties and ion anti-bombarding insensitivity.

Differentiation of surface and bulk conductivities in topological insulator via four-probe spectroscopy

DOE PAGES

Zhang, Xiaoguang; McGuire, Michael A.; Chen, Yong P.; ...

2016-03-08

Topological insulators, with characteristic topological surface states, have emerged as a new state of matter with rich potentials for both fundamental physics and device applications. However, the experimental detection of the surface transport has been hampered by the unavoidable extrinsic conductivity associated with the bulk crystals. Here we show that a four-probe transport spectroscopy in a multi-probe scanning tunneling microscopy system can be used to differentiate conductivities from the surface states and the coexisting bulk states in topological insulators. We derive a scaling relation of measured resistance with respect to varying inter-probe spacing for two interconnected conduction channels, which allowsmore » quantitative determination of conductivities from both channels. Using this method, we demonstrate the separation of 2D and 3D conduction in topological insulators by comparing the conductance scaling of Bi 2Se 3, Bi 2Te 2Se, and Sb-doped Bi 2Se 3 with that of a pure 2D conductance of graphene on SiC substrate. We also report the 2D conductance enhancement due to the surface doping effect in topological insulators. This technique can be applied to reveal 2D to 3D crossover of conductance in other complex systems.« less

Photo-assisted Kelvin probe force microscopy investigation of three dimensional GaN structures with various crystal facets, doping types, and wavelengths of illumination

NASA Astrophysics Data System (ADS)

Ali Deeb, Manal; Ledig, Johannes; Wei, Jiandong; Wang, Xue; Wehmann, Hergo-Heinrich; Waag, Andreas

2017-08-01

Three dimensional GaN structures with different crystal facets and doping types have been investigated employing the surface photo-voltage (SPV) method to monitor illumination-induced surface charge behavior using Kelvin probe force microscopy. Various photon energies near and below the GaN bandgap were used to modify the generation of electron-hole pairs and their motion under the influence of the electric field near the GaN surface. Fast and slow processes for Ga-polar c-planes on both Si-doped n-type as well as Mg-doped p-type GaN truncated pyramid micro-structures were found and their origin is discussed. The immediate positive (for n-type) and negative (for p-type) SPV response dominates at band-to-band and near-bandgap excitation, while only the slow process is present at sub-bandgap excitation. The SPV behavior for the semi-polar facets of the p-type GaN truncated pyramids has a similar characteristic to that on its c-plane, which indicates that it has a comparable band bending and no strong influence of the polarity-induced charges is detectable. The SPV behavior of the non-polar m-facets of the Si-doped n-type part of a transferred GaN column is similar to that of a clean c-plane GaN surface during illumination. However, the SPV is smaller in magnitude, which is attributed to intrinsic surface states of m-plane surfaces and their influence on the band bending. The SPV behavior of the non-polar m-facet of the slightly Mg-doped part of this GaN column is found to behave differently. Compared to c- and r-facets of p-type surfaces of GaN-light-emitting diode micro-structures, the m-plane is more chemically stable.

Controlling the dual mechanisms of oxide interface doping

NASA Astrophysics Data System (ADS)

Dai, Weitao; Cen, Cheng

The formation of two dimensional electron gas (2DEG) at LaAlO3/SrTiO3 interfaces involves multiple electronic and structural causes. The interplay between them makes the investigation of individual mechanism very challenging. Here we demonstrate the nanoscale selective control of two interface doping pathways: charge transfers from surface adsorbed protons and oxygen vacancies created in LaAlO3 layers. The selective control is achieved by combining intensive electric field generated by conducting AFM probe which controls both the creation/migration of oxygen vacancies and the surface proton density, with plasma assisted surface hydroxylation and solvent based proton solvation that act mainly on surface adsorbates. Robust nanoscale reversible metal-insulator transition was achieved at the interfaces with the LaAlO3 layer thicker than the critic thickness. Different combinations of the experimental methods and doping mechanisms enable highly flexible tuning of the 2DEG's carrier density, mobility and sensitivity to ambient environments. The reversible and independent controls of surface states and vacancies add to the fundamental material research capabilities and can benefit future exploration of designed 2DEG nanoelectronics.

Improved visible-light photocatalytic activity of TiO2 co-doped with copper and iodine

NASA Astrophysics Data System (ADS)

Dorraj, Masoumeh; Goh, Boon Tong; Sairi, Nor Asrina; Woi, Pei Meng; Basirun, Wan Jefrey

2018-05-01

Cu-I-co-doped TiO2 photocatalysts active to visible light absorption were prepared by hydrothermal method and calcined at various temperatures (350 °C, 450 °C, and 550 °C). The co-doped powders at 350 °C displayed the highest experimental Brunauer-Emmett-Teller surface area and lowest photoluminescence intensity, which demonstrated that a decrease in electron-hole recombination process. The synthesis of co-doped TiO2 was performed at this optimized temperature. In the co-doped sample, the Cu2+ doped TiO2 lattice created a major "red-shift" in the absorption edge due to the presence of the 3d Cu states, whereas the amount of red-shift from the I5+ doping in the TiO2 lattice was minor. Interestingly, the presence of Cu2+ species also boosted the reduction of I5+ ions to the lower multi-valance state I- in the TiO2 lattice by trapping the photogenerated electrons, which resulted in effective separation of the photogenerated charges. The Cu-I-co-doped TiO2 was able to degrade methyl orange dye under visible-light irradiation with improved photocatalytic activity compared with the single metal-doped TiO2 and pure TiO2 because of the strong visible light absorption and effective separation of photogenerated charges caused by the synergistic effects of Cu and I co-dopants.

Paramagnetic behavior of Co doped TiO{sub 2} nanocrystals controlled by self-purification mechanism

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anitha, B.; Khadar, M. Abdul, E-mail: mabdulkhadar@rediffmail.com; Banerjee, Alok

Doping in nanocrystals is a challenging process because of the self- purification mechanism which tends to segregate out the dopants resulting in a greater dopant concentration near the surface than at the interior of nanocrystals. In the present work nanocrystals of TiO{sub 2} doped with different atom % of Co were synthesized by peroxide gel method. XRD analysis confirmed the tetragonal anatase structure and HRTEM images showed the rod-like morphology of the samples. Raman modes of anatase phase of TiO{sub 2} along with weak intensity peaks of Co{sub 3}O{sub 4} for higher Co dopant concentrations were observed for the samples.more » EPR measurements revealed the presence of cobalt in +2 oxidation state in the TiO{sub 2} matrix. SQUID measurements indicated paramagnetic behavior of the Co doped TiO{sub 2} nanocrystals. The paramagnetic behavior is attributed to an increased concentration of Co{sup 2+} ions and an increased presence of Co{sub 3}O{sub 4} phase near the surface of the TiO{sub 2} nanocrystals due to self-purification mechanism. - Graphical abstract: Variation of the intensity ratios of XRD peaks as a function of atomic ratio of Co. Inset: variation of structure factor for (101) reflection as a function of atomic ratio of Co. Display Omitted - Highlights: • Co doped TiO{sub 2} nanocrystals were synthesized by peroxide gel method. • HRTEM images showed Co doped TiO{sub 2} nanocrystals to be rod-like. • EPR spectra showed +2 oxidation states for Co in the samples. • Co doped TiO{sub 2} nanocrystals showed paramagnetic behavior.« less

Electronic and Magnetic Properties of Ni-Doped Zinc-Blende ZnO: A First-Principles Study.

PubMed

Xue, Suqin; Zhang, Fuchun; Zhang, Shuili; Wang, Xiaoyang; Shao, Tingting

2018-04-26

The electronic structure, band structure, density of state, and magnetic properties of Ni-doped zinc-blende (ZB) ZnO are studied by using the first-principles method based on the spin-polarized density-functional theory. The calculated results show that Ni atoms can induce a stable ferromagnetic (FM) ground state in Ni-doped ZB ZnO. The magnetic moments mainly originate from the unpaired Ni 3 d orbitals, and the O 2 p orbitals contribute a little to the magnetic moments. The magnetic moment of a supercell including a single Ni atom is 0.79 μ B . The electronic structure shows that Ni-doped ZB ZnO is a half-metallic FM material. The strong spin-orbit coupling appears near the Fermi level and shows obvious asymmetry for spin-up and spin-down density of state, which indicates a significant hybrid effects from the Ni 3 d and O 2 p states. However, the coupling of the anti-ferromagnetic (AFM) state show metallic characteristic, the spin-up and spin-down energy levels pass through the Fermi surface. The magnetic moment of a single Ni atom is 0.74 μ B . Moreover, the results show that the Ni 3 d and O 2 p states have a strong p - d hybridization effect near the Fermi level and obtain a high stability. The above theoretical results demonstrate that Ni-doped zinc blende ZnO can be considered as a potential half-metal FM material and dilute magnetic semiconductors.

Simultaneous Conduction and Valence Band Quantization in Ultrashallow High-Density Doping Profiles in Semiconductors

NASA Astrophysics Data System (ADS)

Mazzola, F.; Wells, J. W.; Pakpour-Tabrizi, A. C.; Jackman, R. B.; Thiagarajan, B.; Hofmann, Ph.; Miwa, J. A.

2018-01-01

We demonstrate simultaneous quantization of conduction band (CB) and valence band (VB) states in silicon using ultrashallow, high-density, phosphorus doping profiles (so-called Si:P δ layers). We show that, in addition to the well-known quantization of CB states within the dopant plane, the confinement of VB-derived states between the subsurface P dopant layer and the Si surface gives rise to a simultaneous quantization of VB states in this narrow region. We also show that the VB quantization can be explained using a simple particle-in-a-box model, and that the number and energy separation of the quantized VB states depend on the depth of the P dopant layer beneath the Si surface. Since the quantized CB states do not show a strong dependence on the dopant depth (but rather on the dopant density), it is straightforward to exhibit control over the properties of the quantized CB and VB states independently of each other by choosing the dopant density and depth accordingly, thus offering new possibilities for engineering quantum matter.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vörös, Márton; Brawand, Nicholas P.; Galli, Giulia

Lead chalcogenide (PbX) nanoparticles are promising materials for solar energy conversion. However, the presence of trap states in their electronic gap limits their usability, and developing a universal strategy to remove trap states is a persistent challenge. Using calculations based on density functional theory, we show that hydrogen acts as an amphoteric impurity on PbX nanoparticle surfaces; hydrogen atoms may passivate defects arising from ligand imbalance or off-stoichiometric surface terminations irrespective of whether they originate from cation or anion excess. In addition, we show, using constrained density functional theory calculations, that hydrogen treatment of defective nanoparticles is also beneficial formore » charge transport in films. We also find that hydrogen adsorption on stoichiometric nanoparticles leads to electronic doping, preferentially n-type. Lastly, our findings suggest that postsynthesis hydrogen treatment of lead chalcogenide nanoparticle films is a viable approach to reduce electronic trap states or to dope well-passivated films.« less

Doping-induced spin-orbit splitting in Bi-doped ZnO nanowires

NASA Astrophysics Data System (ADS)

Aras, Mehmet; Güler-Kılıç, Sümeyra; Kılıç, ćetin

2017-04-01

Our predictions, based on density-functional calculations, reveal that surface doping of ZnO nanowires with Bi leads to a linear-in-k splitting of the conduction-band states, through spin-orbit interaction, due to the lowering of the symmetry in the presence of the dopant. This finding implies that spin polarization of the conduction electrons in Bi-doped ZnO nanowires could be controlled with applied electric (as opposed to magnetic) fields, making them candidate materials for spin-orbitronic applications. Our findings also show that the degree of spin splitting could be tuned by adjusting the dopant concentration. Defect calculations and ab initio molecular dynamics simulations indicate that stable doping configurations exhibiting the foregoing linear-in-k splitting could be realized under reasonable thermodynamic conditions.

Strong correlation effects on surfaces of topological insulators via holography

NASA Astrophysics Data System (ADS)

Seo, Yunseok; Song, Geunho; Sin, Sang-Jin

2017-07-01

We investigate the effects of strong correlation on the surface state of a topological insulator (TI). We argue that electrons in the regime of crossover from weak antilocalization to weak localization are strongly correlated, and calculate the magnetotransport coefficients of TIs using the gauge-gravity principle. Then, we examine the magnetoconductivity (MC) formula and find excellent agreement with the data of chrome-doped Bi2Te3 in the crossover regime. We also find that the cusplike peak in MC at low doping is absent, which is natural since quasiparticles disappear due to the strong correlation.

Synchrotron-Radiation Photoemission Study of Electronic Structures of a Cs-Doped Rubrene Surface

NASA Astrophysics Data System (ADS)

Cheng, Chiu-Ping; Lu, Meng-Han; Chu, Yu-Ya; Pi, Tun-Wen

Using synchrotron-radiation photoemission spectroscopy, we have studied the electronic structure of a cesium-doped rubrene thin film. The addition of cesium atoms causes the movement of the valence-band spectra and the change in line shapes at different concentration that can be separated into four different stages. In the first stage, the cesium atoms continuously diffuse into the substrate, and the Fermi level moves in the energy gap as a result of an electron transferred from the cesium to the rubrene. The second stage, in which the shifts of the spectra are interrupted, is characterized by the introduction of two in-gap states. When increasing doping of cesium into the third stage, the spectra move again; whereas, the line shapes maintain at the stoichiometric ratio of one. In the fourth stage, new in-gap states appear, which are the highest occupied molecular orbital (HOMO) and HOMO+1 states of (rubrene)2- anion.

An in situ vapour phase hydrothermal surface doping approach for fabrication of high performance Co3O4 electrocatalysts with an exceptionally high S-doped active surface.

PubMed

Tan, Zhijin; Liu, Porun; Zhang, Haimin; Wang, Yun; Al-Mamun, Mohammad; Yang, Hua Gui; Wang, Dan; Tang, Zhiyong; Zhao, Huijun

2015-04-04

A facile in situ vapour phase hydrothermal (VPH) surface doping approach has been developed for fabrication of high performance S-doped Co3O4 electrocatalysts with an unprecedentedly high surface S content (>47%). The demonstrated VPH doping approach could be useful for enrichment of surface active sites for other metal oxide electrocatalysts.

Chromium-induced ferromagnetism with perpendicular anisotropy in topological crystalline insulator SnTe (111) thin films

NASA Astrophysics Data System (ADS)

Wang, Fei; Zhang, Hongrui; Jiang, Jue; Zhao, Yi-Fan; Yu, Jia; Liu, Wei; Li, Da; Chan, Moses H. W.; Sun, Jirong; Zhang, Zhidong; Chang, Cui-Zu

2018-03-01

Topological crystalline insulator is a recently discovered topological phase of matter. It possesses multiple Dirac surface states, which are protected by the crystal symmetry. This is in contrast to the time-reversal symmetry that is operative in the well-known topological insulators. In the presence of a Zeeman field and/or strain, the multiple Dirac surface states are gapped. The high-Chern-number quantum anomalous Hall (QAH) state is predicted to emerge if the chemical potential resides in all the Zeeman gaps. Here, we use molecular-beam epitaxy to grow 12 double-layer (DL) pure and Cr-doped SnTe (111) thin film on heat-treated SrTi O3 (111) substrate using a quintuple layer of insulating (Bi0.2Sb0.8 ) 2T e3 topological insulator as a buffer film. The Hall traces of Cr-doped SnTe film at low temperatures display square hysteresis loops indicating long-range ferromagnetic order with perpendicular anisotropy. The Curie temperature of the 12 DL S n0.9C r0.1Te film is ˜110 K. Due to the chemical potential crossing the bulk valence bands, the anomalous Hall resistance of 12 DL S n0.9C r0.1Te film is substantially lower than the predicted quantized value (˜1 /4 h /e2 ). It is possible that with systematic tuning the chemical potential via chemical doping and electrical gating, the high-Chern-number QAH state can be realized in the Cr-doped SnTe (111) thin film.

Screening-Engineered Field-Effect Solar Cells

DTIC Science & Technology

2012-01-01

virtually any semiconductor, including the promising but hard-to- dope metal oxides, sulfides, and phosphides.3 Prototype SFPV devices have been...MIS interface. Unfortu- nately, MIS cells, though sporting impressive efficiencies,4−6 typically have short operating lifetimes due to surface state...instability at the MIS interface.7 Methods aimed at direct field- effect “ doping ” of semiconductors, in which the voltage is externally applied to a gate

Consequences of plasma oxidation and vacuum annealing on the chemical properties and electron accumulation of In2O3 surfaces

NASA Astrophysics Data System (ADS)

Berthold, Theresa; Rombach, Julius; Stauden, Thomas; Polyakov, Vladimir; Cimalla, Volker; Krischok, Stefan; Bierwagen, Oliver; Himmerlich, Marcel

2016-12-01

The influence of oxygen plasma treatments on the surface chemistry and electronic properties of unintentionally doped and Mg-doped In2O3(111) films grown by plasma-assisted molecular beam epitaxy or metal-organic chemical vapor deposition is studied by photoelectron spectroscopy. We evaluate the impact of semiconductor processing technology relevant treatments by an inductively coupled oxygen plasma on the electronic surface properties. In order to determine the underlying reaction processes and chemical changes during film surface-oxygen plasma interaction and to identify reasons for the induced electron depletion, in situ characterization was performed implementing a dielectric barrier discharge oxygen plasma as well as vacuum annealing. The strong depletion of the initial surface electron accumulation layer is identified to be caused by adsorption of reactive oxygen species, which induce an electron transfer from the semiconductor to localized adsorbate states. The chemical modification is found to be restricted to the topmost surface and adsorbate layers. The change in band bending mainly depends on the amount of attached oxygen adatoms and the film bulk electron concentration as confirmed by calculations of the influence of surface state density on the electron concentration and band edge profile using coupled Schrödinger-Poisson calculations. During plasma oxidation, hydrocarbon surface impurities are effectively removed and surface defect states, attributed to oxygen vacancies, vanish. The recurring surface electron accumulation after subsequent vacuum annealing can be consequently explained by surface oxygen vacancies.

Hydrogen treatment as a detergent of electronic trap states in lead chalcogenide nanoparticles

DOE PAGES

Vörös, Márton; Brawand, Nicholas P.; Galli, Giulia

2016-11-15

Lead chalcogenide (PbX) nanoparticles are promising materials for solar energy conversion. However, the presence of trap states in their electronic gap limits their usability, and developing a universal strategy to remove trap states is a persistent challenge. Using calculations based on density functional theory, we show that hydrogen acts as an amphoteric impurity on PbX nanoparticle surfaces; hydrogen atoms may passivate defects arising from ligand imbalance or off-stoichiometric surface terminations irrespective of whether they originate from cation or anion excess. In addition, we show, using constrained density functional theory calculations, that hydrogen treatment of defective nanoparticles is also beneficial formore » charge transport in films. We also find that hydrogen adsorption on stoichiometric nanoparticles leads to electronic doping, preferentially n-type. Lastly, our findings suggest that postsynthesis hydrogen treatment of lead chalcogenide nanoparticle films is a viable approach to reduce electronic trap states or to dope well-passivated films.« less

Correlation-Induced Self-Doping in the Iron-Pnictide Superconductor Ba2Ti2Fe2As4O

NASA Astrophysics Data System (ADS)

Ma, J.-Z.; van Roekeghem, A.; Richard, P.; Liu, Z.-H.; Miao, H.; Zeng, L.-K.; Xu, N.; Shi, M.; Cao, C.; He, J.-B.; Chen, G.-F.; Sun, Y.-L.; Cao, G.-H.; Wang, S.-C.; Biermann, S.; Qian, T.; Ding, H.

2014-12-01

The electronic structure of the iron-based superconductor Ba2Ti2Fe2As4O (Tconset=23.5 K ) has been investigated by using angle-resolved photoemission spectroscopy and combined local density approximation and dynamical mean field theory calculations. The electronic states near the Fermi level are dominated by both the Fe 3 d and Ti 3 d orbitals, indicating that the spacer layers separating different FeAs layers are also metallic. By counting the enclosed volumes of the Fermi surface sheets, we observe a large self-doping effect; i.e., 0.25 electrons per unit cell are transferred from the FeAs layer to the Ti2As2O layer, leaving the FeAs layer in a hole-doped state. This exotic behavior is successfully reproduced by our dynamical mean field calculations, in which the self-doping effect is attributed to the electronic correlations in the 3 d shells. Our work provides an alternative route of effective doping without element substitution for iron-based superconductors.

DFT calculation and experimental study on structural, optical and magnetic properties of Co-doped SrTiO3

NASA Astrophysics Data System (ADS)

Sikam, Pornsawan; Moontragoon, Pairot; Sararat, Chayanin; Karaphun, Attaphol; Swatsitang, Ekaphan; Pinitsoontorn, Supree; Thongbai, Prasit

2018-07-01

SrTiO3 (STO) is an attractive material that offers a wide range of technological applications, e.g., ferroelectricity, solar cell and photocatalysis. An application that the STO might be utilized is diluted magnetic semiconductors. Here, we would like to improve magnetic property of the STO by Ti site substitution using Co atoms. In this work, we present the structural, optical and magnetic properties of perfect and oxygen defect structures of STO and Co-doped SrTiO3 via experimental and theoretical aspects. In first-principles calculation, the structural properties, electronic band structure and magnetic properties of undoped STO and Co-doped STO supercells have been investigated by density functional theory using GGA with Hubbard model scheme (GGA+U) on Vienna Ab initio Simulation Package (VASP). In calculation detail, pure phase of STO with nanometer scale size of undoped STO and Co-doped STO have been synthesized using hydrothermal technique. The findings obtained from DFT computation reveal that the new states in gap between the valence band and conduction band of the STO were induced after Co atom was doped into the host structure. These impurity states narrow the band gap corresponding to experimental results. In addition, band splitting was observed on O defect and dopant systems, indicating that missing O and doping Co on STO could induce magnetization on none-magnetic material of STO. In case of synthesized powder, ferromagnetic behaviors are determined in the dopant system annealed in Ar. Additionally, another appreciated point of Co doping is that surface area of the STO is improved. Thus, it is expected that the surface activity, such as photocatalytic performance, of the STO will be enhanced. From all referred results, they introduce that the Co-doped STO might be a potential candidate to be a photocatalyst for the high photocatalytic performance under visible light radiation and the diluted magnetic semiconductor in spintronic devices.

Effect of counterions on the formation of ohmic contact between p-Si and poly(pyrrole) film - An ac impedance analysis

NASA Technical Reports Server (NTRS)

Nagsubramanian, G.; Distefano, S.; Moacanin, J.

1986-01-01

Conditions under which poly(pyrrole) (PP) films form ohmic contact with single-crystal p-Si are described. Counterions affect both the conductivity and flatband potential, V(FB), values of poly(pyrrole). While paratoluene-sulfonate-doped PP acts like a switch, the impedance behavior of PP films doped with ClO4(-), BF4(-), or PF6(-) allows evaluation of the V(FB) of these films. The formation of 'quasi-ohmic' and 'nonohmic' contacts, respectively, of PP (ClO4) and PP films doped with other counterions, with p-Si, are explained in terms of conductivity of these films and V(FB) of PP films with respect to that of p-Si. PP film seems to passivate or block intrinsic surface states present on p-Si surface.

Structural and electronic properties of graphene nanoflakes on Au(111) and Ag(111)

PubMed Central

Tesch, Julia; Leicht, Philipp; Blumenschein, Felix; Gragnaniello, Luca; Fonin, Mikhail; Marsoner Steinkasserer, Lukas Eugen; Paulus, Beate; Voloshina, Elena; Dedkov, Yuriy

2016-01-01

We investigate the electronic properties of graphene nanoflakes on Ag(111) and Au(111) surfaces by means of scanning tunneling microscopy and spectroscopy as well as density functional theory calculations. Quasiparticle interference mapping allows for the clear distinction of substrate-derived contributions in scattering and those originating from graphene nanoflakes. Our analysis shows that the parabolic dispersion of Au(111) and Ag(111) surface states remains unchanged with the band minimum shifted to higher energies for the regions of the metal surface covered by graphene, reflecting a rather weak interaction between graphene and the metal surface. The analysis of graphene-related scattering on single nanoflakes yields a linear dispersion relation E(k), with a slight p-doping for graphene/Au(111) and a larger n-doping for graphene/Ag(111). The obtained experimental data (doping level, band dispersions around EF, and Fermi velocity) are very well reproduced within DFT-D2/D3 approaches, which provide a detailed insight into the site-specific interaction between graphene and the underlying substrate. PMID:27002297

Morphology, composition and electrical properties of SnO{sub 2}:Cl thin films grown by atomic layer deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Hsyi-En, E-mail: sean@mail.stust.edu.tw; Wen, Chia-Hui; Hsu, Ching-Ming

2016-01-15

Chlorine doped SnO{sub 2} thin films were prepared using atomic layer deposition at temperatures between 300 and 450 °C using SnCl{sub 4} and H{sub 2}O as the reactants. Composition, structure, surface morphology, and electrical properties of the as-deposited films were examined. Results showed that the as-deposited SnO{sub 2} films all exhibited rutile structure with [O]/[Sn] ratios between 1.35 and 1.40. The electrical conductivity was found independent on [O]/[Sn] ratio but dependent on chlorine doping concentration, grain size, and surface morphology. The 300 °C-deposited film performed a higher electrical conductivity of 315 S/cm due to its higher chlorine doping level, larger grain size, andmore » smoother film surface. The existence of Sn{sup 2+} oxidation state was demonstrated to minimize the effects of chlorine on raising the electrical conductivity of films.« less

A strategy to improve the energy conversion efficiency and stability of quantum dot-sensitized solar cells using manganese-doped cadmium sulfide quantum dots.

PubMed

Gopi, Chandu V V M; Venkata-Haritha, M; Kim, Soo-Kyoung; Kim, Hee-Je

2015-01-14

This article describes the effect of manganese (Mn) doping in CdS to improve the photovoltaic performance of quantum dot sensitized solar cells (QDSSCs). The performances of the QDSSCs are examined in detail using a polysulfide electrolyte with a copper sulfide (CuS) counter electrode. Under the illumination of one sun (AM 1.5 G, 100 mW cm(-2)), 10 molar% Mn-doped CdS QDSSCs exhibit a power conversion efficiency (η) of 2.85%, which is higher than the value of 2.11% obtained with bare CdS. The improved photovoltaic performance is due to the impurities from Mn(2+) doping of CdS, which have an impact on the structure of the host material and decrease the surface roughness. The surface roughness and morphology of Mn-doped CdS nanoparticles can be characterised from atomic force microscopy images. Furthermore, the cell device based on the Mn-CdS electrode shows superior stability in the sulfide/polysulfide electrolyte in a working state for over 10 h, resulting in a highly reproducible performance, which is a serious challenge for the Mn-doped solar cell. Our finding provides an effective method for the fabrication of Mn-doped CdS QDs, which can pave the way to further improve the efficiency of future QDSSCs.

In Situ One-Step Synthesis of Hierarchical Nitrogen-Doped Porous Carbon for High Performance Supercapacitors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jeon, Ju Won; Sharma, Ronish; Meduri, Praveen

2014-04-30

Electrochemical performance of the existing state-of-the art capacitors is not very high, key scientific barrier is that its charge storage mechanism wholly depends on adsorption of electrolyte on electrode. We present a novel method for the synthesis of nitrogen -doped porous carbons and address the drawback by precisely controlling composition and surface area. Nitrogen-doped porous carbon was synthesized using a self-sacrificial template technique without any additional nitrogen and carbon sources. They exhibited exceptionally high capacitance (239 Fg-1) due to additional pseudocapacitance originating from doped nitrogen. Cycling tests showed no obvious capacitance decay even after 10,000 cycles, which meets the requirementmore » of commercial supercapacitors. Our method is simple and highly efficient for the production of large quantities of nitrogen-doped porous carbons.« less

New Insights into Sensitization Mechanism of the Doped Ce (IV) into Strontium Titanate

PubMed Central

Wang, Yuan; Liu, Chenglun; Xu, Longjun

2018-01-01

SrTiO3 and Ce4+ doped SrTiO3 were synthesized by a modified sol–gel process. The optimization synthesis parameters were obtained by a series of single factor experiments. Interesting phenomena are observable in Ce4+ doped SrTiO3 systems. Sr2+ in SrTiO3 system was replaced by Ce4+, which reduced the surface segregation of Ti4+, ameliorated agglomeration, increased specific surface area more than four times compared with pure SrTiO3, and enhanced quantum efficiency for SrTiO3. Results showed that Ce4+ doping increased the physical adsorption of H2O and adsorbed oxygen on the surface of SrTiO3, which produced additional catalytic active centers. Electrons on the 4f energy level for Ce4+ produced new energy states in the band gap of SrTiO3, which not only realized the use of visible light but also led to an easier separation between the photogenerated electrons and holes. Ce4+ repeatedly captured photoelectrons to produce Ce3+, which inhibited the recombination between photogenerated electrons and holes as well as prolonged their lifetime; it also enhanced quantum efficiency for SrTiO3. The methylene blue (MB) degradation efficiency reached 98.7% using 3 mol % Ce4+ doped SrTiO3 as a photocatalyst, indicating highly photocatalytic activity. PMID:29690605

Synthesis and characterization of P-doped amorphous and nanocrystalline Si

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jialing; Ganguly, Shreyashi; Sen, Sabyasachi

Intentional impurity doping lies at the heart of the silicon technology. The dopants provide electrons or holes as necessary carriers of the electron current and can significantly modify the electric, optical and magnetic properties of the semiconductors. P-doped amorphous Si (a-Si) was prepared by a solid state and solution metathesis reaction of a P-doped Zintl phase precursor, NaSi 0.99P 0.01, with an excess of NH 4X (X = Br, I). After the salt byproduct was removed from the solid state reaction, the a-Si material was annealed at 600 °C under vacuum for 2 h, resulting in P-doped nanocrystalline Si (nc-Si)more » material embedded in a-Si matrix. The product from the solution reaction also shows a combination of nc-Si embedded in a-Si; however, it was fully converted to nc-Si after annealing under argon at 650 °C for 30 min. Powder X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) show the amorphous nature of the P-doped Si material before the annealing and the nanocrystallinity after the annealing. Fourier Transform Infrared (FTIR) spectroscopy shows that the P-doped Si material surface is partially capped by H and O or with solvent. Finally, electron microprobe wavelength dispersive spectroscopy (WDS) as well as energy dispersive spectroscopy (EDS) confirm the presence of P in the Si material. 29Si and 31P solid state magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopy data provide the evidence of P doping into the Si structure with the P concentration of approximately 0.07 at.%.« less

On the state of Mn in Mn{sub x}Zn{sub 1−x}O nanoparticles and their surface modification with isonipecotic acid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiménez-Hernández, L.; Estévez-Hernández, O.; Instituto de Ciencia y Tecnología de Materiales

Mn-doped ZnO (Mn{sub x}Zn{sub 1−x}O) nanoparticles were synthesized by the co-precipitation method and coated with isonipecotic acid as capping ligand. The structure, composition and morphology of the resulting nanomaterial were investigated by energy disperse X-ray analysis, X-ray diffraction, and transmission electron microscopy data. Such measurements showed that the solid obtained contains 6 at% of Mn and it is formed by a highly crystalline material with 3–5 nm range of crystallite size, and only a small elongation of its cell parameter with respect to undoped ZnO wurtzite unit cell. Information on the state of manganese atom in the Mn{sub x}Zn{sub 1−x}Omore » nanostructures formed was obtained from X-ray photoelectron (XPS) and electron energy loss (EELS) spectroscopies. XPS and EELS spectra are composed of four peaks, corresponding to two species of Mn(II) and signals from Mn(III) and Mn(IV). Such spectral data on the state of Mn in the material studied is consistent with the mapping of Mn distribution observed in recorded transmission electron microscopy images, which reveal presence of clusters of Mn atoms. Only a fraction of doping Mn atoms were found forming a solid solution with the host ZnO structure. The functionalization of the nanoparticles system with Isonipecotic acid shows that this molecule remains anchored to the nanoparticles surface mainly through its N basic site. The availability of free carboxylate groups in the capping molecule was tested by conjugation to type IV horseradish peroxidase. - Graphical abstract: State of Mn atoms in Mn-doped ZnO nanostructures prepared by the precipitation method, their capping with isonipecotic acid and subsequent conjugation to peroxidase. - Highlights: • State of manganese in manganese-doped zinc oxide nanoparticles. • Isonipecotic acid as surface modifier of ZnO nanoparticles. • Peroxidase conjugation to ZnO nanoparticles modified with isonipecotic acid.« less

Enhancing CO2 electrolysis through synergistic control of non-stoichiometry and doping to tune cathode surface structures

PubMed Central

Ye, Lingting; Zhang, Minyi; Huang, Ping; Guo, Guocong; Hong, Maochun; Li, Chunsen; Irvine, John T. S.; Xie, Kui

2017-01-01

Sustainable future energy scenarios require significant efficiency improvements in both electricity generation and storage. High-temperature solid oxide cells, and in particular carbon dioxide electrolysers, afford chemical storage of available electricity that can both stabilize and extend the utilization of renewables. Here we present a double doping strategy to facilitate CO2 reduction at perovskite titanate cathode surfaces, promoting adsorption/activation by making use of redox active dopants such as Mn linked to oxygen vacancies and dopants such as Ni that afford metal nanoparticle exsolution. Combined experimental characterization and first-principle calculations reveal that the adsorbed and activated CO2 adopts an intermediate chemical state between a carbon dioxide molecule and a carbonate ion. The dual doping strategy provides optimal performance with no degradation being observed after 100 h of high-temperature operation and 10 redox cycles, suggesting a reliable cathode material for CO2 electrolysis. PMID:28300066

Investigation of Hydrogen-Like Muonium States in Nb-Doped SnO2 Films

NASA Astrophysics Data System (ADS)

Rabis, Annett; Prokscha, Thomas; Fabbri, Emiliana; Salman, Zaher; Schmidt, Thomas; Suter, Andreas

Little is known about the characteristics of hydrogen states in thin films of SnO2 and Nb doped SnO2 (NTO) and its influence on the electrical properties in these materials, which are promising candidates for metal-oxide supports in polymer electrolyte fuel cells. Here, we used low-energy muon spin rotation/relaxation (LE-μSR) to study hydrogen-like muonium (Mu) states between 5 and 300 K in undoped and Nb doped SnO2 films with Nb doping levels of 0.1 and 2%, respectively. The films were prepared by reactive DC magnetron sputtering on undoped Si substrates. Film thicknesses varied between 75 and 200 nm, and muons were implanted close to the surface at a mean depth of 10 nm, in the center of the films, and in some cases close to the NTO/Si interface. Our results of transverse-field and longitudinal-field μSR show striking similarities to recent bulk μSR measurements on various zirconia systems [Vieira et al., Phys. Rev. B 94, 115207 (2016)]. This suggests that in the NTO systems the same Mu configurations exist which are the interstitial site with a deep, isotropic atomic Mu state, and, as the dominant fraction, the oxygen bound configuration with polaronic character.

Study on Resistive Switching Property of Ti Doped Novel NiO Thin Films

NASA Astrophysics Data System (ADS)

Li, Y.; Zhao, G. Y.; Kou, Z. B.; Liu, J. C.; Zhu, R.

2018-01-01

Ti doped nickel oxide thin films have been fabricated by sol-gel dip-coating process using nickel acetate and tetrabutyl titanate as source materials. The effect of the amount of Ti dopant on the surface roughness, optical, chemical state and electrical properties of NiO: Ti thin films was observed by atomic force microscopy (AFM), Uv-vis spectroscopy, X-ray photoelectron spectroscopy(XPS) and I-V measurement, respectively. Results show that the Ti doping is an effective ways to improve the resistive switching behaviors and it is a convenient way to understand the mechanism of the resistive switching behaviors.

Understanding the interactions of CO 2 with doped and undoped SrTiO 3

DOE PAGES

Wu, Qiyuan; Cen, Jiajie; Goodman, Kenneth R.; ...

2016-06-17

SrTiO 3 and doped SrTiO 3 have a wide range of applications in different fields. For example, Rh-doped SrTiO 3 has been shown to have photocatalytic activity for both hydrogen production and CO 2 conversion. In this study, both undoped and Rh-doped SrTiO 3 were synthesized by hydrothermal and polymerizable complex methods. Different characterizations techniques including X-ray photoelectron spectroscopy (XPS), XRD, Raman, and UV/Vis spectroscopy were utilized to establish correlations between the preparation methods and the electronic/structural properties of Rh-doped SrTiO 3. The presence of dopants and oxygen vacancies substantially influenced the CO 2 interactions with the surface, as revealedmore » by the in situ infrared spectroscopic study. As a result, the presence of distinctly different adsorption sites was correlated to oxygen vacancies and oxidation states of Ti and Rh.« less

Plasmonic Properties of Silicon Nanocrystals Doped with Boron and Phosphorus.

PubMed

Kramer, Nicolaas J; Schramke, Katelyn S; Kortshagen, Uwe R

2015-08-12

Degenerately doped silicon nanocrystals are appealing plasmonic materials due to silicon's low cost and low toxicity. While surface plasmonic resonances of boron-doped and phosphorus-doped silicon nanocrystals were recently observed, there currently is poor understanding of the effect of surface conditions on their plasmonic behavior. Here, we demonstrate that phosphorus-doped silicon nanocrystals exhibit a plasmon resonance immediately after their synthesis but may lose their plasmonic response with oxidation. In contrast, boron-doped nanocrystals initially do not exhibit plasmonic response but become plasmonically active through postsynthesis oxidation or annealing. We interpret these results in terms of substitutional doping being the dominant doping mechanism for phosphorus-doped silicon nanocrystals, with oxidation-induced defects trapping free electrons. The behavior of boron-doped silicon nanocrystals is more consistent with a strong contribution of surface doping. Importantly, boron-doped silicon nanocrystals exhibit air-stable plasmonic behavior over periods of more than a year.

Colour centres and nanostructures on the surface of laser crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kulagin, N A

2012-11-30

This paper presents a study of structural and radiationinduced colour centres in the bulk and ordered nanostructures on the surface of doped laser crystals: sapphire, yttrium aluminium garnet and strontium titanate. The influence of thermal annealing, ionising radiation and plasma exposure on the spectroscopic properties of high-purity materials and crystals containing Ti, V and Cr impurities is examined. Colour centres resulting from changes in the electronic state of impurities and plasma-induced surface modification of the crystals are studied by optical, EPR and X-ray spectroscopies, scanning electron microscopy and atomic force microscopy. X-ray line valence shift measurements are used to assessmore » changes in the electronic state of some impurity and host ions in the bulk and on the surface of oxide crystals. Conditions are examined for the formation of one- and two-level arrays of ordered crystallites 10{sup -10} to 10{sup -7} m in size on the surface of crystals doped with irongroup and lanthanoid ions. The spectroscopic properties of the crystals are analysed using ab initio self-consistent field calculations for Me{sup n+} : [O{sup 2-}]{sub k} clusters. (interaction of laser radiation with matter. laser plasma)« less

Boron doping effect on the interface interaction and mechanical properties of graphene reinforced copper matrix composite

NASA Astrophysics Data System (ADS)

Fang, Bingcheng; Li, Jiajun; Zhao, Naiqin; Shi, Chunsheng; Ma, Liying; He, Chunnian; He, Fang; Liu, Enzuo

2017-12-01

In order to explore an efficient way of modifying graphene to improve the Cu/graphene interfacial bonding and remain the excellent mechanical and physical properties of graphene, the interaction between Cu and the pristine, atomic oxygen functionalized and boron- or nitrogen-doped graphene with and without defects was systematically investigated by density functional theory calculation. The electronic structure analysis revealed that the chemically active oxygen can enhance the binding energy Eb of Cu with graphene by forming strong covalent bonds, supporting the experimental study suggesting an vital role of intermediate oxygen in the improvement of the mechanical properties of graphene/Cu composites. Due to the strong hybridization between Cu-3d electron states and the 2p states of both boron and carbon atoms, the boron-doping effect is comparable to or even better than the chemical bridging role of oxygen in the reduced graphene oxide reinforced Cu matrix composite. Furthermore, we evidenced an enhancement of mechanical properties including bulk modulus, shear modulus and Young modulus of graphene/Cu composite after boron doping, which closely relates to the increased interfacial binding energy between boron-doped graphene and Cu surfaces.

Effects of Pretreatment on the Electronic Properties of Plasma Enhanced Chemical Vapor Deposition Hetero-Epitaxial Graphene Devices

NASA Astrophysics Data System (ADS)

Zhang, Lian-Chang; Shi, Zhi-Wen; Yang, Rong; Huang, Jian

2014-09-01

Quasi-monolayer graphene is successfully grown by the plasma enhanced chemical vapor deposition heteroepitaxial method we reported previously. To measure its electrical properties, the prepared graphene is fabricated into Hall ball shaped devices by the routine micro-fabrication method. However, impurity molecules adsorbed onto the graphene surface will impose considerable doping effects on the one-atom-thick film material. Our experiment demonstrates that pretreatment of the device by heat radiation baking and electrical annealing can dramatically influence the doping state of the graphene and consequently modify the electrical properties. While graphene in the as-fabricated device is highly p-doped, as confirmed by the position of the Dirac point at far more than +60 V, baking treatment at temperatures around 180°C can significantly lower the doping level and reduce the conductivity. The following electrical annealing is much more efficient to desorb the extrinsic molecules, as confirmed by the in situ measurement, and as a result, further modify the doping state and electrical properties of the graphene, causing a considerable drop of the conductivity and a shifting of Dirac point from beyond +60 V to 0 V.

Influence of Fe doping on the structural, optical and acetone sensing properties of sprayed ZnO thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prajapati, C.S.; Kushwaha, Ajay; Sahay, P.P., E-mail: dr_ppsahay@rediffmail.com

2013-07-15

Graphical abstract: All the films are found to be polycrystalline ZnO possessing hexagonal wurtzite structure. The intensities of all the peaks are diminished strongly in the Fe-doped films, indicating their lower crystallinity as compared to the undoped ZnO film. The average crystallite size decreases from 35.21 nm (undoped sample) to 15.43 nm (1 at% Fe-doped sample). - Highlights: • Fe-doped ZnO films show smaller crystallinity with crystallite size: 15–26 nm. • Optical band gap in ZnO films decreases on Fe doping. • Fe-doped films exhibit the normal dispersion for the wavelength range 450–600 nm. • PL spectra of the Fe-dopedmore » films show quenching of the broad green-orange emission. • Acetone response of the Fe-doped films increases considerably at 300 °C. - Abstract: The ZnO thin films (undoped and Fe-doped) deposited by chemical spray pyrolysis technique have been analyzed by X-ray powder diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM). Results show that all the films possess hexagonal wurtzite structure of zinc oxide having crystallite sizes in the range 15–36 nm. On 1 at% Fe doping, the surface roughness of the film increases which favors the adsorption of atmospheric oxygen on the film surface and thereby increase in the gas response. Optical studies reveal that the band gap decreases due to creation of some defect energy states below the conduction band edge, arising out of the lattice disorder in the doped films. The refractive index of the films decreases on Fe doping and follows the Cauchy relation of normal dispersion. Among all the films examined, the 1 at% Fe-doped film exhibits the maximum response (∼72%) at 300 °C for 100 ppm concentration of acetone in air.« less

The effects of annealing temperature on the in-field Jc and surface pinning in silicone oil doped MgB2 bulks and wires

NASA Astrophysics Data System (ADS)

Hossain, M. S. A.; Motaman, A.; Çiçek, Ö.; Ağıl, H.; Ertekin, E.; Gencer, A.; Wang, X. L.; Dou, S. X.

2012-12-01

The effects of sintering temperature on the lattice parameters, full width at half maximum (FWHM), strain, critical temperature (Tc), critical current density (Jc), irreversibility field (Hirr), upper critical field (Hc2), and resistivity (ρ) of 10 wt.% silicone oil doped MgB2 bulk and wire samples are investigated in state of the art by this article. The a-lattice parameter of the silicone oil doped samples which were sintered at different temperatures was drastically reduced from 3.0864 Å to 3.0745 Å, compared to the un-doped samples, which indicates the substitution of the carbon (C) into the boron sites. It was found that sintered samples at the low temperature of 600 °C shows more lattice distortion by more C-substitution and higher strain, lower Tc, higher impurity scattering, and enhancement of both magnetic Jc and Hc2, compared to those sintered samples at high temperatures. The flux pinning mechanism has been analyzed based on the extended normalized pinning force density fp = Fp/Fp,max scaled with b = B/Bmax. Results show that surface pinning is the dominant pinning mechanism for the doped sample sintered at the low temperature of 600 °C, while point pinning is dominant for the un-doped sample. The powder in tube (PIT) MgB2 wire was also fabricated by using of this liquid doping and found that both transport Jc and n-factor increased which proves this cheap and abundant silicone oil doping can be a good candidate for industrial application.

Modelling of electronic and vibrational properties of carbon nanostructures

NASA Astrophysics Data System (ADS)

Margine, Elena Roxana

The main goals of this dissertation work are the analysis and prediction of the properties of nanoscale carbon materials which hold great potential for nanotechnological applications such as strong conductive composites, field-effect transistors, diodes, rechargeable batteries, etc. Some of these exciting applications are already being actively developed, however their design via trial-and-error experimentation is often difficult and expensive. State-of-the-art simulation methods can be used as a powerful tool to streamline the path to practical implementations. In this thesis I use ab initio quantum-mechanical calculations to explore the response of nanoscale carbon materials to doping. A brief overview of the theoretical methods and of some basic concepts on carbon nanotubes are given in the first two chapters. In Chapter 3 we study the effect of doping in double-walled carbon nanotubes. These systems can be considered as nanoscale capacitors since they have two conducting (or semi-conducting) shells. The experimental work of our collaborators demonstrated for the first time that such a capacitor can be realized by the adsorption of bromine anions at the surface of the outer tube. Our theoretical analysis of the experimental results revealed that this quantum system, surprisingly, behaves exactly as the classical Faraday cage: the electric charge always resides on the outside surface of the conductor, even when the pristine tubes are not metallic. In Chapter 4 I present our findings on the phonon frequencies' response to electron doping in single-walled carbon nanotubes. It is well established that when graphite is doped with electrons, carbon-carbon bonds lengthen and all vibrational frequencies soften. However, in semiconducting carbon nanotubes, the frequency of one mode increases at low levels of alkali doping. Having carefully modelled the process with ab initio methods we conclude that the unusual behavior of the vibrational mode depends on which electronic states are filled first in a given nanotube and therefore this is a direct manifestation of the quantum confinement of electronic states in quasi-one dimensional nanotubes. In Chapter 5 we analyze the behavior of the nearly free electron states in carbon nanotubes. We demonstrate that the rapid decrease in these states' energy under electron doping occurs not because of their hybridization with valence states of the alkali dopant as previously thought, but due to a universal electrostatic mechanism. We show that the nearly free state, being weakly bound to the tube wall, is extraordinarily labile and distorts dramatically to concentrate in the region of highest positive countercharge. Therefore, by taking advantage of the changes in the surrounding environment, the nearly free states may become occupied at unexpectedly low doping levels and play an important role in the transport properties of electron-doped carbon nanotubes. Experimental results have shown that elemental cesium induces graphitization of nanoporous carbon at very low temperatures. In Chapter 6 we propose a compact representative model of nanoporous carbon constructed fully from sp2- connected atoms. Next, we investigate possible mechanisms of its transformation towards graphitization in the presence of dopants. Our results suggest that in addition to the alkali atoms there must be another chemical agent involved in this intriguing low-temperature transformation.

Optical absorption and oxygen passivation of surface states in III-nitride photonic devices

NASA Astrophysics Data System (ADS)

Rousseau, Ian; Callsen, Gordon; Jacopin, Gwénolé; Carlin, Jean-François; Butté, Raphaël; Grandjean, Nicolas

2018-03-01

III-nitride surface states are expected to impact high surface-to-volume ratio devices, such as nano- and micro-wire light-emitting diodes, transistors, and photonic integrated circuits. In this work, reversible photoinduced oxygen desorption from III-nitride microdisk resonator surfaces is shown to increase optical attenuation of whispering gallery modes by 100 cm-1 at λ = 450 nm. Comparison of photoinduced oxygen desorption in unintentionally and n+-doped microdisks suggests that the spectral changes originate from the unpinning of the surface Fermi level, likely taking place at etched nonpolar III-nitride sidewalls. An oxygen-rich surface prepared by thermal annealing results in a broadband Q improvement to state-of-the-art values exceeding 1 × 104 at 2.6 eV. Such findings emphasize the importance of optically active surface states and their passivation for future nanoscale III-nitride optoelectronic and photonic devices.

Novel hydrothermal method for effective doping of N and F into nano Titania for both, energy and environmental applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jyothi, M.S.; D’Souza Laveena, P.; Shwetharani, R.

2016-02-15

Highlights: • Novel method to synthesize N, F doped TiO{sub 2} via hydrothermal method is discussed. • Change in bandgap of TiO{sub 2} upon doping makes a photocatalyst visible active. • 94% of degradation of EtBr was achieved within a less time of 90 min. • The doped titania also showed good efficiency as photo anodic material for solar cell. - Abstract: A novel and an efficient hydrothermal method for the preparation of an effective doped titania photocatalyst is reported. The crystal phase, binding energy, elemental composition, morphology, optical and electronic structure analyses were done by various techniques. The dopedmore » titania proved as an efficient electrode material and photocatalyst for solar cells and water treatment respectively. The photocatalyst is able to degrade the most potent mutagen ethidium bromide under sunlight with an enhancement of 1.6 times over its undoped analogue. As photo-anode material, showed an improved open circuit potential and fill factor. The created electron states in the doped sample act as charge carrier traps suppressing recombination which later detraps the same to the surface of the catalyst causing enhanced interfacial charge transfer. Surface acidity caused by F induction and lowered band gap energy that can respond to visible light facilitates improved energy harvesting and energy transfer leading to better photo activity.« less

Thermally Diffused Al:ZnO Thin Films for Broadband Transparent Conductor.

PubMed

Tong, Chong; Yun, Juhyung; Chen, Yen-Jen; Ji, Dengxin; Gan, Qiaoqiang; Anderson, Wayne A

2016-02-17

Here, we report an approach to realize highly transparent low resistance Al-doped ZnO (AZO) films for broadband transparent conductors. Thin Al films are deposited on ZnO surfaces, followed by thermal diffusion processes, introducing the Al doping into ZnO thin films. By utilizing the interdiffusion of Al, Zn, and O, the chemical state of Al on the surfaces can be converted to a fully oxidized state, resulting in a low sheet resistance of 6.2 Ω/sq and an excellent transparency (i.e., 96.5% at 550 nm and higher than 85% up to 2500 nm), which is superior compared with some previously reported values for indium tin oxide, solution processed AZO, and many transparent conducting materials using novel nanostructures. Such AZO films are also applied as transparent conducting layers for AZO/Si heterojunction solar cells, demonstrating their applications in optoelectronic devices.

Hydrogen adsorption on two catalysts for the ortho- to parahydrogen conversion: Cr-doped silica and ferric oxide gel.

PubMed

Hartl, Monika; Gillis, Robert Chad; Daemen, Luke; Olds, Daniel P; Page, Katherine; Carlson, Stefan; Cheng, Yongqiang; Hügle, Thomas; Iverson, Erik B; Ramirez-Cuesta, A J; Lee, Yongjoong; Muhrer, Günter

2016-06-29

Molecular hydrogen exists in two spin-rotation coupled states: parahydrogen and orthohydrogen. Due to the variation of energy with rotational level, the occupation of ortho- and parahydrogen states is temperature dependent, with parahydrogen being the dominant species at low temperatures. The equilibrium at 20 K (99.8% parahydrogen) can be reached by natural conversion only after a lengthy process. With the use of a suitable catalyst, this process can be shortened significantly. Two types of commercial catalysts currently being used for ortho- to parahydrogen conversion are: iron(iii) oxide (Fe2O3, IONEX®), and chromium(ii) oxide doped silica catalyst (CrO·SiO2, OXISORB®). We investigate the interaction of ortho- and parahydrogen with the surfaces of these ortho-para conversion catalysts using neutron vibrational spectroscopy. The catalytic surfaces have been characterized using X-ray absorption fine structure (XAFS) and X-ray/neutron pair distribution function measurements.

Realization of a Hole-Doped Mott Insulator on a Triangular Silicon Lattice

NASA Astrophysics Data System (ADS)

Ming, Fangfei; Johnston, Steve; Mulugeta, Daniel; Smith, Tyler S.; Vilmercati, Paolo; Lee, Geunseop; Maier, Thomas A.; Snijders, Paul C.; Weitering, Hanno H.

2017-12-01

The physics of doped Mott insulators is at the heart of some of the most exotic physical phenomena in materials research including insulator-metal transitions, colossal magnetoresistance, and high-temperature superconductivity in layered perovskite compounds. Advances in this field would greatly benefit from the availability of new material systems with a similar richness of physical phenomena but with fewer chemical and structural complications in comparison to oxides. Using scanning tunneling microscopy and spectroscopy, we show that such a system can be realized on a silicon platform. The adsorption of one-third monolayer of Sn atoms on a Si(111) surface produces a triangular surface lattice with half filled dangling bond orbitals. Modulation hole doping of these dangling bonds unveils clear hallmarks of Mott physics, such as spectral weight transfer and the formation of quasiparticle states at the Fermi level, well-defined Fermi contour segments, and a sharp singularity in the density of states. These observations are remarkably similar to those made in complex oxide materials, including high-temperature superconductors, but highly extraordinary within the realm of conventional s p -bonded semiconductor materials. It suggests that exotic quantum matter phases can be realized and engineered on silicon-based materials platforms.

The sensing mechanism of N-doped SWCNTs toward SF6 decomposition products: A first-principle study

NASA Astrophysics Data System (ADS)

Gui, Yingang; Tang, Chao; Zhou, Qu; Xu, Lingna; Zhao, Zhongyong; Zhang, Xiaoxing

2018-05-01

In order to monitor the insulation status of SF6-insulated equipment on-line, SOF2 and SO2F2, two typical decomposition products of SF6 under electric discharge condition, are chosen as the target gases to evaluate the type and severity of discharge. In this work, single N atom doping method is adopted to improve the gas sensitivity of single wall carbon nanotubes to SOF2 and SO2F2. Single and double gas molecules adsorptions are considered to completely analyze the adsorption properties of N-doped single wall carbon nanotubes. Calculation results show that N atom doping enhances the surface activity of carbon nanotubes. When gas molecules physically adsorbed on N-doped single wall carbon nanotubes, the weak interaction between gas molecules and N-doped single wall carbon nanotubes nearly not changes the electrical property according to analysis of the density of states and molecular orbitals. While the chemisorption between gas molecules and N-doped single wall carbon nanotubes distinctly decreases the conductivity of adsorption system.

Atomic-Scale Fingerprint of Mn Dopant at the Surface of Sr3(Ru1−xMnx)2O7

PubMed Central

Li, Guorong; Li, Qing; Pan, Minghu; Hu, Biao; Chen, Chen; Teng, Jing; Diao, Zhenyu; Zhang, Jiandi; Jin, Rongying; Plummer, E. W.

2013-01-01

Chemical doping in materials is known to give rise to emergent phenomena. These phenomena are extremely difficult to predict a priori, because electron-electron interactions are entangled with local environment of assembled atoms. Scanning tunneling microscopy and low energy electron diffraction are combined to investigate how the local electronic structure is correlated with lattice distortion on the surface of Sr3(Ru1−xMnx)2O7, which has double-layer building blocks formed by (Ru/Mn)O6 octahedra with rotational distortion. The presence of doping-dependent tilt distortion of (Ru/Mn)O6 octahedra at the surface results in a C2v broken symmetry in contrast with the bulk C4v counterpart. It also enables us to observe two Mn sites associated with the octahedral rotation in the bulk through the “chirality” of local electronic density of states surrounding Mn, which is randomly distributed. These results serve as fingerprint of chemical doping on the atomic scale. PMID:24108411

Orbital superconductivity, defects, and pinned nematic fluctuations in the doped iron chalcogenide FeSe 0.45 Te 0.55

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sarkar, Saheli; Van Dyke, John; Sprau, Peter O.

We demonstrate that the differential conductance, dI/dV, measured via spectroscopic imaging scanning tunneling microscopy in the doped iron chalcogenide FeSe0.45Te0.55, possesses a series of characteristic features that allow one to extract the orbital structure of the superconducting gaps. This yields nearly isotropic superconducting gaps on the two holelike Fermi surfaces, and a strongly anisotropic gap on the electronlike Fermi surface. Moreover, we show that the pinning of nematic fluctuations by defects can give rise to a dumbbell-like spatial structure of the induced impurity bound states, and explains the related C-2 symmetry in the Fourier transformed differential conductance.

dxz/yz subband structure and Chiral Orbital Angular Momentum of Nb doped SrTiO3 surface states

NASA Astrophysics Data System (ADS)

Soltani, Shoresh; Cho, Soohyun; Ryu, Hanyoung; Han, Garam; Kim, Timur; Hoesch, Moritz; Kim, Changyoung

Using angle resolved photoemission spectroscopy (ARPES), we investigate subband structure and chiral orbital angular momentum (OAM) texture on the surface of lightly electron doped SrTiO3 single crystals. Our linearly polarized light ARPES data taken with 51 eV photons, reveal additional subbands for out-of-plane dxz/yzorbitals in addition to the previously reported ones. Our CD-ARPES data reveal a chiral OAM structure which we use as a clue to explain the origin of linear Rashba-like surface band splitting of Ti 3d t2g orbitals. The observed CD signal is enhanced near crossing points, where different orbitals hybridize, compatible with a linear Rashba-like surface band splitting. The work was supported by IBS-R009-G2. S.S., S.C., H.Y. and G. H. acknowledge were supported by Yonsei university, BK21 program.

Isotropic in-plane quenched disorder and dilution induce a robust nematic state in electron-doped pnictides

DOE PAGES

Liang, Shuhua; Bishop, Christopher B.; Moreo, Adriana; ...

2015-09-21

The phase diagram of electron-doped pnictides is studied varying the temperature, electronic density, and isotropic in-plane quenched disorder strength and dilution by means of computational techniques applied to a three-orbital (xz,yz,xy) spin-fermion model with lattice degrees of freedom. In experiments, chemical doping introduces disorder but in theoretical studies the relationship between electronic doping and the randomly located dopants, with their associated quenched disorder, is difficult to address. Moreover, in this publication, the use of computational techniques allows us to study independently the effects of electronic doping, regulated by a global chemical potential, and impurity disorder at randomly selected sites. Surprisingly,more » our Monte Carlo simulations reveal that the fast reduction with doping of the N eel T N and the structural T S transition temperatures, and the concomitant stabilization of a robust nematic state, is primarily controlled in our model by the magnetic dilution associated with the in-plane isotropic disorder introduced by Fe substitution. In the doping range studied, changes in the Fermi surface produced by electron doping affect only slightly both critical temperatures. Our results also suggest that the specific material-dependent phase diagrams experimentally observed could be explained as a consequence of the variation in disorder profiles introduced by the different dopants. Finally, our findings are also compatible with neutron scattering and scanning tunneling microscopy, unveiling a patchy network of locally magnetically ordered clusters with anisotropic shapes, even though the quenched disorder is locally isotropic. Our study reveals a remarkable and unexpected degree of complexity in pnictides: the fragile tendency to nematicity intrinsic of translational invariant electronic systems needs to be supplemented by quenched disorder and dilution to stabilize the robust nematic phase experimentally found in electron-doped 122 compounds.« less

Isotropic in-plane quenched disorder and dilution induce a robust nematic state in electron-doped pnictides

NASA Astrophysics Data System (ADS)

Liang, Shuhua; Bishop, Christopher B.; Moreo, Adriana; Dagotto, Elbio

2015-09-01

The phase diagram of electron-doped pnictides is studied varying the temperature, electronic density, and isotropic in-plane quenched disorder strength and dilution by means of computational techniques applied to a three-orbital (x z ,y z ,x y ) spin-fermion model with lattice degrees of freedom. In experiments, chemical doping introduces disorder but in theoretical studies the relationship between electronic doping and the randomly located dopants, with their associated quenched disorder, is difficult to address. In this publication, the use of computational techniques allows us to study independently the effects of electronic doping, regulated by a global chemical potential, and impurity disorder at randomly selected sites. Surprisingly, our Monte Carlo simulations reveal that the fast reduction with doping of the Néel TN and the structural TS transition temperatures, and the concomitant stabilization of a robust nematic state, is primarily controlled in our model by the magnetic dilution associated with the in-plane isotropic disorder introduced by Fe substitution. In the doping range studied, changes in the Fermi surface produced by electron doping affect only slightly both critical temperatures. Our results also suggest that the specific material-dependent phase diagrams experimentally observed could be explained as a consequence of the variation in disorder profiles introduced by the different dopants. Our findings are also compatible with neutron scattering and scanning tunneling microscopy, unveiling a patchy network of locally magnetically ordered clusters with anisotropic shapes, even though the quenched disorder is locally isotropic. This study reveals a remarkable and unexpected degree of complexity in pnictides: the fragile tendency to nematicity intrinsic of translational invariant electronic systems needs to be supplemented by quenched disorder and dilution to stabilize the robust nematic phase experimentally found in electron-doped 122 compounds.

Optical properties of an indium doped CdSe nanocrystal: A density functional approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Salini, K.; Mathew, Vincent, E-mail: vincent@cukerala.ac.in; Mathew, Thomas

2016-05-06

We have studied the electronic and optical properties of a CdSe nanocrystal doped with n-type impurity atom. First principle calculations of the CdSe nanocrystal based on the density functional theory (DFT), as implemented in the Vienna Ab Initio Simulation Package (VASP) was used in the calculations. We have introduced a single Indium impurity atom into CdSe nanocrystal with 1.3 nm diameter. Nanocrystal surface dangling bonds are passivated with hydrogen atom. The band-structure, density of states and absorption spectra of the doped and undopted nanocrystals were discussed. Inclusion of the n-type impurity atom introduces an additional electron in conduction band, and significantlymore » alters the electronic and optical properties of undoped CdSe nanocrystal. Indium doped CdSe nannocrystal have potential applications in optoelectronic devices.« less

SiN sub x passivation of silicon surfaces

NASA Technical Reports Server (NTRS)

Olsen, L. C.

1986-01-01

The objectives were to perform surface characterization of high efficiency n+/p and p+/n silicon cells, to relate surface density to substrate dopant concentration, and to identify dominant current loss mechanisms in high efficiency cells. The approach was to measure density of states on homogeneously doped substrates with high frequency C-V and Al/SiN sub x/Si structures; to investigate density of states and photoresponse of high efficiency N+/P and P+/N cells; and to conduct I-V-T studies to identify current loss nechanisms in high efficiency cells. Results are given in tables and graphs.

Kelp-derived three-dimensional hierarchical porous N, O-doped carbon for flexible solid-state symmetrical supercapacitors with excellent performance

NASA Astrophysics Data System (ADS)

Zhang, Yifu; Jiang, Hanmei; Wang, Qiushi; Zheng, Jiqi; Meng, Changgong

2018-07-01

Three-dimensional (3D) porous N, O-doped carbon with hierarchical structures composed of micropores, mesopores and macropores were synthesized by the direct carbonization of kelp with a "self-activation" process. The as-obtained 3D N, O-doped carbon remained abundant N and O functional groups and the BET specific surface area measured 656 m2 g-1. 3D hierarchical porous structures with the pore size ranged from several nanometers to hundred nanometers and lots of pores were attributed to mesopores with the average pore size of about 5.4 nm. Electrochemical properties of the 3D hierarchical porous N, O-doped carbon as a supercapactior (SC) electrode were investigated and it delivered excellent capacitance of 669 mF cm-2 at 1 mA cm-2 due to its 3D hierarchical porous structures with high specific surface area which is beneficial for improving ionic storage and transportation in electrodes. This kelp-derived carbon exhibited excellent cyclic performance with the retention of 104% after 10,000 cycles. A flexible solid-state symmetric SC (SSC) device was fabricated using the 3D hierarchical porous N, O-doped carbon and delivered an excellent capacitance of 412 mF cm-2 at 2 mA cm-2 and satisfying cyclic stability with the retention of 85% after 10,000 cycles. The areal energy density of the SSC device reach up to 0.146 mWh cm-2 at the power density of 0.8 mW cm-2. This facile route for low-cost carbonaceous materials with novel architecture and functionality can be as a promising alternative to synthesize biomass carbon for practical SC application.

Rapid Synthesis and Formation Mechanism of Core-Shell-Structured La-Doped SrTiO3 with a Nb-Doped Shell

PubMed Central

Park, Nam-Hee; Akamatsu, Takafumi; Itoh, Toshio; Izu, Noriya; Shin, Woosuck

2015-01-01

To provide a convenient and practical synthesis process for metal ion doping on the surface of nanoparticles in an assembled nanostructure, core-shell-structured La-doped SrTiO3 nanocubes with a Nb-doped surface layer were synthesized via a rapid synthesis combining a rapid sol-precipitation and hydrothermal process. The La-doped SrTiO3 nanocubes were formed at room temperature by a rapid dissolution of NaOH pellets during the rapid sol-precipitation process, and the Nb-doped surface (shell) along with Nb-rich edges formed on the core nanocubes via the hydrothermal process. The formation mechanism of the core-shell-structured nanocubes and their shape evolution as a function of the Nb doping level were investigated. The synthesized core-shell-structured nanocubes could be arranged face-to-face on a SiO2/Si substrate by a slow evaporation process, and this nanostructured 10 μm thick thin film showed a smooth surface. PMID:28793420

Surface modification of titania powder P25 with phosphate and phosphonic acids--effect on thermal stability and photocatalytic activity.

PubMed

Djafer, Lahcène; Ayral, André; Boury, Bruno; Laine, Richard M

2013-03-01

Phosphorus is frequently reported as a doping element for TiO(2) as photocatalyst; however, the previously reported methods used to prepare P-doped TiO(2) do not allow control over the location of the phosphorus either in the bulk or at the surface or both. In this study, we report on the surface modification of Evonik P25 with phosphonic (H(3)PO(3)) and octylphosphonic acid [C(8)H(17)-PO(OH)(2)], done to limit the introduction of phosphorus only to the photocatalyst surface. The effect of this element on the thermal behavior and photocatalytic properties is reported through characterization using elemental analyses, solid state (31)P NMR, X-ray powder diffraction, N(2) porosimetry, dilatometry, etc. Thus, the objective of the work reported here is to focus on the role(s) that phosphorus plays only at TiO(2) crystallite surfaces. For comparison, other samples were treated with phosphoric acid. Copyright © 2012 Elsevier Inc. All rights reserved.

Discrete impurity band from surface danging bonds in nitrogen and phosphorus doped SiC nanowires

NASA Astrophysics Data System (ADS)

Li, Yan-Jing; Li, Shu-Long; Gong, Pei; Li, Ya-Lin; Cao, Mao-Sheng; Fang, Xiao-Yong

2018-04-01

The electronic structure and optical properties of the nitrogen and phosphorus doped silicon carbide nanowires (SiCNWs) are investigated using first-principle calculations based on density functional theory. The results show doping can change the type of the band gap and improve the conductivity. However, the doped SiCNWs form a discrete impurity levels at the Fermi energy, and the dispersion degree decreases with the diameter increasing. In order to reveal the root of this phenomenon, we hydrogenated the doped SiCNWs, found that the surface dangling bonds were saturated, and the discrete impurity levels are degeneracy, which indicates that the discrete impurity band of the doped SiCNWs is derived from the dangling bonds. The surface passivation can degenerate the impurity levels. Therefore, both doping and surface passivation can better improve the photoelectric properties of the SiCNWs. The result can provide additional candidates in producing nano-optoelectronic devices.

Energetics and magnetic properties of V-doped MgO bulk and (001) surface: A GGA, GGA+U , and hybrid density functional study

NASA Astrophysics Data System (ADS)

Århammar, C.; Moyses Araujo, C.; Rao, K. V.; Norgren, Susanne; Johansson, Börje; Ahuja, Rajeev

2010-10-01

In this work, a first-principles study of the energetic and magnetic properties of V-doped MgO is presented, where both the bulk and (001) surface were investigated. It is found that V assumes a high-spin state with a local moment of about 3μB . In the bulk, the interaction between these local moments is very short ranged and the antiferromagnetic (AFM) ordering is energetically more favorable. The formation of V-VMg-V defect clusters is found to weaken the antiferromagnetic coupling in bulk MgO, degenerating the AFM and ferromagnetic state. However, these clusters are high in energy and will not form at equilibrium conditions. By employing the GGA+U approach, with U=5eV , the V3d states on the (001) surface are shifted below the Fermi level, and a reasonable surface geometry was achieved. A calculation with the hybrid HSE03 functional, contradicts the GGA+U results, indicating that the V-MgO surface should be metallic at this concentration. From the energetics it is concluded that, at the modeled concentration, VxOy phases will limit the solubility of V in MgO at equilibrium conditions, which is in agreement with previous experimental findings. In order to achieve higher concentrations of V, an off-equilibrium synthesis method is needed. Finally, we find that the formation energy of V at the surface is considerably higher than in the bulk and V is thus expected to diffuse from the surface into the bulk of MgO.

One-step synthesis of nitrogen, boron co-doped fluorescent carbon nanoparticles for glucose detection.

PubMed

Liang, Meijuan; Ren, Yi; Zhang, Haijuan; Ma, Yunxia; Niu, Xiaoying; Chen, Xingguo

2017-09-01

Heteroatom-doped carbon nanoparticles (CNPs) have attracted considerable attention due to an effective improvement in their intrinsic properties. Here, a facile and simple synthesis of nitrogen, boron co-doped carbon nanoparticles (NB-CNPs) from a sole precursor, 3-aminophenylboronic acid, was performed via a one-step solid-phase approach. Because of the presence of boronic acid, NB-CNPs can be used directly as a fluorescent probe for glucose. Based on a boronic acid-triggered specific reaction, we developed a simple NB-CNP probe without surface modification for the detection of glucose. When glucose was introduced, the fluorescence of NB-CNPs was suppressed through a surface-quenching states mechanism. Obvious fluorescence quenching allowed the highly sensitive determination of glucose with a limit of detection of 1.8 μM. Moreover, the proposed method has been successfully used to detect glucose in urine from people with diabetes, suggesting potential application in sensing glucose. Copyright © 2017 John Wiley & Sons, Ltd.

Enhanced doping effect on tuning structural phases of monolayer antimony

NASA Astrophysics Data System (ADS)

Wang, Jizhang; Yang, Teng; Zhang, Zhidong; Yang, Li

2018-05-01

Doping is capable to control the atomistic structure, electronic structure, and even to dynamically realize a semiconductor-metal transition in two-dimensional (2D) transition metal dichalcogenides (TMDs). However, the high critical doping density (˜1014 electron/cm2), compound nature, and relatively low carrier mobility of TMDs limits broader applications. Using first-principles calculations, we predict that, via a small transition potential, a substantially lower hole doping density (˜6 × 1012 hole/cm2) can switch the ground-state structure of monolayer antimony from the hexagonal β-phase, a 2D semiconductor with excellent transport performance and air stability but an indirect bandgap, to the orthorhombic α phase with a direct bandgap and potentially better carrier mobility. We further show that this structural engineering can be achieved by the established electrostatic doping, surface functional adsorption, or directly using graphene substrate. This gives hope to dynamically tuning and large-scale production of 2D single-element semiconductors that simultaneously exhibit remarkable transport and optical performance.

Superconductivity and ferromagnetism in topological insulators

NASA Astrophysics Data System (ADS)

Zhang, Duming

Topological insulators, a new state of matter discovered recently, have attracted great interest due to their novel properties. They are insulating inside the bulk, but conducting at the surface or edges. This peculiar behavior is characterized by an insulating bulk energy gap and gapless surface or edge states, which originate from strong spin-orbit coupling and time-reversal symmetry. The spin and momentum locked surface states not only provide a model system to study fundamental physics, but can also lead to applications in spintronics and dissipationless electronics. While topological insulators are interesting by themselves, more exotic behaviors are predicted when an energy gap is induced at the surface. This dissertation explores two types of surface state gap in topological insulators, a superconducting gap induced by proximity effect and a magnetic gap induced by chemical doping. The first three chapters provide introductory theory and experimental details of my research. Chapter 1 provides a brief introduction to the theoretical background of topological insulators. Chapter 2 is dedicated to material synthesis principles and techniques. I will focus on two major synthesis methods: molecular beam epitaxy for the growth of Bi2Se3 thin films and chemical vapor deposition for the growth of Bi2Se3 nanoribbons and nanowires. Material characterization is discussed in Chapter 3. I will describe structural, morphological, magnetic, electrical, and electronic characterization techniques used to study topological insulators. Chapter 4 discusses the experiments on proximity-induced superconductivity in topological insulator (Bi2Se3) nanoribbons. This work is motivated by the search for the elusive Majorana fermions, which act as their own antiparticles. They were proposed by Ettore Majorara in 1937, but have remained undiscovered. Recently, Majorana's concept has been revived in condensed matter physics: a condensed matter analog of Majorana fermions is predicted to exist when topological insulators are interfaced with superconductors. The observation of Majorana fermions would not only be fundamentally important, but would also lead to applications in fault-tolerant topological quantum computation. By interfacing topological insulator nanoribbons with superconducting electrodes, we observe distinct signatures of proximity-induced superconductivity, which is found to be present in devices with channel lengths that are much longer than the normal transport characteristic lengths. This might suggest preferential coupling of the proximity effect to a ballistic surface channel of the topological insulator. In addition, when the electrodes are in the superconducting state, we observe periodic magnetoresistance oscillations which suggest the formation of vortices in the proximity-induced region of the nanoribbons. Our results demonstrate that proximity-induced superconductivity and vortices can be realized in our nanoribbon geometry, which accomplishes a first important step towards the search for Majorana fermions in condensed matter. In Chapter 5, I will discuss experiments on a magnetically-doped topological insulator (Mn-doped Bi2Se3) to induce a surface state gap. The metallic Dirac cone surface states of a topological insulator are expected to be protected against small perturbations by time-reversal symmetry. However, these surface states can be dramatically modified and a finite energy gap can be opened at the Dirac point by breaking the time-reversal symmetry via magnetic doping. The interplay between magnetism and topological surface states is predicted to yield novel phenomena of fundamental interest such as a topological magneto-electric effect, a quantized anomalous Hall effect, and the induction of magnetic monopoles. Our systematic measurements reveal a close correlation between the onset of ferromagnetism and quantum corrections to diffusive transport, which crosses over from the symplectic (weak anti-localization) to the unitary (weak localization) class. A comprehensive interpretation of data obtained from electrical transport, angle-resolved photoemission spectroscopy, superconducting quantum interference device magnetometry, and scanning tunneling microscopy indicates that the ferromagnetism responsible for modifications in the surface states occurs in nanoscale regions on the surface where magnetic atoms segregate during sample growth. This suggests that some aspects of the observed magnetoconductance may indeed originate from surface transport despite the non-ideal nature of the samples. These observations are consistent with the prediction of a time-reversal symmetry breaking gap, which is further supported by angle-resolved photoemission spectroscopy measurements.

Transport (electrical and thermal) properties and surface morphology of Y1-xCaxFeO3 (where x = 0.03 and 0.05) ceramics

NASA Astrophysics Data System (ADS)

Suthar, Lokesh; Bhadala, Falguni; Roy, M.; Jha, V. K.

2018-05-01

The electrical transport behaviour of polycrystalline Calcium doped Yttrium orthoferrite (Y1-xCaxFeO3, where x = 0.03 and 0.05) have been synthesized by high temperature Solid state reaction route. The I-V characteristics have been measured which revels that Y1-xCaxFeO3 (where x = 0.03 and 0.05), behaves like semiconductor and its conductivity increases with increase in doping concentration. The thermal analysis experiment shows no phase change with the minor weight loss which reflects the high temperature thermal stability of the materials. The surface morphology was analyzed using the AFM. The results are discussed in detail.

Orbital superconductivity, defects, and pinned nematic fluctuations in the doped iron chalcogenide FeSe 0.45 Te 0.55

DOE PAGES

Sarkar, Saheli; Van Dyke, John; Sprau, Peter O.; ...

2017-08-09

We demonstrate that the differential conductance, dI/dV , measured via spectroscopic imaging scanning tunneling microscopy in the doped iron chalcogenide FeSe0.45Te0.55, possesses a series of characteristic features that allow one to extract the orbital structure of the superconducting gaps. This yields nearly isotropic superconducting gaps on the two hole-like Fermi surfaces, and a strongly anisotropic gap on the electron-like Fermi surface. Moreover, we show that the pinning of nematic fluctuations by defects can give rise to a dumbbell-like spatial structure of the induced impurity bound states, and explains the related C 2-symmetry in the Fourier transformed differential conductance.

Orbital superconductivity, defects, and pinned nematic fluctuations in the doped iron chalcogenide FeSe 0.45 Te 0.55

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sarkar, Saheli; Van Dyke, John; Sprau, Peter O.

We demonstrate that the differential conductance, dI/dV , measured via spectroscopic imaging scanning tunneling microscopy in the doped iron chalcogenide FeSe0.45Te0.55, possesses a series of characteristic features that allow one to extract the orbital structure of the superconducting gaps. This yields nearly isotropic superconducting gaps on the two hole-like Fermi surfaces, and a strongly anisotropic gap on the electron-like Fermi surface. Moreover, we show that the pinning of nematic fluctuations by defects can give rise to a dumbbell-like spatial structure of the induced impurity bound states, and explains the related C 2-symmetry in the Fourier transformed differential conductance.

DOE Office of Scientific and Technical Information (OSTI.GOV)

S. K. Kushwaha; Pletikosic, I.; Liang, T.

A long-standing issue in topological insulator research has been to find a bulk single crystal material that provides a high quality platform for characterizing topological surface states without interference from bulk electronic states. This material would ideally be a bulk insulator, have a surface state Dirac point energy well isolated from the bulk valence and conduction bands, display quantum oscillations from the surface state electrons, and be growable as large, high quality bulk single crystals. Here we show that this materials obstacle is overcome by bulk crystals of lightly Sn-doped Bi 1.1Sb 0.9Te 2S grown by the Vertical Bridgeman method.more » We characterize Sn-BSTS via angle-resolved photoemission spectroscopy, scanning tunneling microscopy, transport studies, X-ray diffraction, and Raman scattering. We present this material as a high quality topological insulator that can be reliably grown as bulk single crystals and thus studied by many researchers interested in topological surface states.« less

Hydrogen treatment as a detergent of electronic trap states in lead chalcogenide nanoparticles

NASA Astrophysics Data System (ADS)

Voros, Marton; Brawand, Nicholas; Galli, Giulia

Lead chalcogenide (PbX) nanoparticles are promising materials for solar energy conversion. However, the presence of trap states in their electronic gap limits their usability, and developing a universal strategy to remove trap states is a persistent challenge. Using calculations based on density functional theory, we show that hydrogen acts as an amphoteric impurity on PbX nanoparticle surfaces; hydrogen atoms may passivate defects arising from ligand imbalance or off-stoichiometric surface terminations, irrespective of whether they originate from cation or anion excess. In addition, we show, using constrained density functional theory calculations, that hydrogen treatment of defective nanoparticles is also beneficial for charge transport in films. We also find that hydrogen adsorption on stoichiometric nanoparticles leads to electronic doping, preferentially n-type. Our findings suggest that post-synthesis hydrogen treatment of lead chalcogenide nanoparticle films is a viable approach to reduce electronic trap states or to dope well-passivated films. Work supported by the Center for Advanced Solar Photophysics, an Energy Frontier Research Center funded by the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (NB) and U.S. DOE under Contract No. DE-AC02-06CH11357 (MV).

Defect induced structural inhomogeneity, ultraviolet light emission and near-band-edge photoluminescence broadening in degenerate In2O3 nanowires

NASA Astrophysics Data System (ADS)

Mukherjee, Souvik; Sarkar, Ketaki; Wiederrecht, Gary P.; Schaller, Richard D.; Gosztola, David J.; Stroscio, Michael A.; Dutta, Mitra

2018-04-01

We demonstrate here defect induced changes on the morphology and surface properties of indium oxide (In2O3) nanowires and further study their effects on the near-band-edge (NBE) emission, thereby showing the significant influence of surface states on In2O3 nanostructure based device characteristics for potential optoelectronic applications. In2O3 nanowires with cubic crystal structure (c-In2O3) were synthesized via carbothermal reduction technique using a gold-catalyst-assisted vapor-liquid-solid method. Onset of strong optical absorption could be observed at energies greater than 3.5 eV consistent with highly n-type characteristics due to unintentional doping from oxygen vacancy ({V}{{O}}) defects as confirmed using Raman spectroscopy. A combination of high resolution transmission electron microscopy, x-ray photoelectron spectroscopy and valence band analysis on the nanowire morphology and stoichiometry reveals presence of high-density of {V}{{O}} defects on the surface of the nanowires. As a result, chemisorbed oxygen species can be observed leading to upward band bending at the surface which corresponds to a smaller valence band offset of 2.15 eV. Temperature dependent photoluminescence (PL) spectroscopy was used to study the nature of the defect states and the influence of the surface states on the electronic band structure and NBE emission has been discussed. Our data reveals significant broadening of the NBE PL peak consistent with impurity band broadening leading to band-tailing effect from heavy doping.

Triplet p + ip pairing correlations in the doped Kane-Mele-Hubbard model: A quantum Monte Carlo study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ma, Tianxing; Lin, Hai-Qing; Gubernatis, James E.

2015-09-01

By using the constrained-phase quantum Monte Carlo method, we performed a systematic study of the pairing correlations in the ground state of the doped Kane-Mele-Hubbard model on a honeycomb lattice. We find that pairing correlations with d + id symmetry dominate close to half filling, but pairing correlations with p+ip symmetry dominate as hole doping moves the system below three-quarters filling. We correlate these behaviors of the pairing correlations with the topology of the Fermi surfaces of the non-interacting problem. We also find that the effective pairing correlation is enhanced greatly as the interaction increases, and these superconducting correlations aremore » robust against varying the spin-orbit coupling strength. Finally, our numerical results suggest a possible way to realize spin triplet superconductivity in doped honeycomb-like materials or ultracold atoms in optical traps.« less

Large optical conductivity of Dirac semimetal Fermi arc surface states

NASA Astrophysics Data System (ADS)

Shi, Li-kun; Song, Justin C. W.

2017-08-01

Fermi arc surface states, a hallmark of topological Dirac semimetals, can host carriers that exhibit unusual dynamics distinct from that of their parent bulk. Here we find that Fermi arc carriers in intrinsic Dirac semimetals possess a strong and anisotropic light-matter interaction. This is characterized by a large Fermi arc optical conductivity when light is polarized transverse to the Fermi arc; when light is polarized along the Fermi arc, Fermi arc optical conductivity is significantly muted. The large surface spectral weight is locked to the wide separation between Dirac nodes and persists as a large Drude weight of Fermi arc carriers when the system is doped. As a result, large and anisotropic Fermi arc conductivity provides a novel means of optically interrogating the topological surfaces states of Dirac semimetals.

Fabrication and Doping Methods for Silicon Nano- and Micropillar Arrays for Solar-Cell Applications: A Review.

PubMed

Elbersen, Rick; Vijselaar, Wouter; Tiggelaar, Roald M; Gardeniers, Han; Huskens, Jurriaan

2015-11-18

Silicon is one of the main components of commercial solar cells and is used in many other solar-light-harvesting devices. The overall efficiency of these devices can be increased by the use of structured surfaces that contain nanometer- to micrometer-sized pillars with radial p/n junctions. High densities of such structures greatly enhance the light-absorbing properties of the device, whereas the 3D p/n junction geometry shortens the diffusion length of minority carriers and diminishes recombination. Due to the vast silicon nano- and microfabrication toolbox that exists nowadays, many versatile methods for the preparation of such highly structured samples are available. Furthermore, the formation of p/n junctions on structured surfaces is possible by a variety of doping techniques, in large part transferred from microelectronic circuit technology. The right choice of doping method, to achieve good control of junction depth and doping level, can contribute to an improvement of the overall efficiency that can be obtained in devices for energy applications. A review of the state-of-the-art of the fabrication and doping of silicon micro and nanopillars is presented here, as well as of the analysis of the properties and geometry of thus-formed 3D-structured p/n junctions. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis and Spectroscopy of Silver-Doped PbSe Quantum Dots

DOE PAGES

Kroupa, Daniel M.; Hughes, Barbara K.; Miller, Elisa M.; ...

2017-06-25

Electronic impurity doping of bulk semiconductors is an essential component of semiconductor science and technology. Yet there are only a handful of studies demonstrating control of electronic impurities in semiconductor nanocrystals. Here, we studied electronic impurity doping of colloidal PbSe quantum dots (QDs) using a postsynthetic cation exchange reaction in which Pb is exchanged for Ag. We found that varying the concentration of dopants exposed to the as-synthesized PbSe QDs controls the extent of exchange. The electronic impurity doped QDs exhibit the fundamental spectroscopic signatures associated with injecting a free charge carrier into a QD under equilibrium conditions, including amore » bleach of the first exciton transition and the appearance of a quantum-confined, low-energy intraband absorption feature. Photoelectron spectroscopy confirms that Ag acts as a p-type dopant for PbSe QDs and infrared spectroscopy is consistent with k • p calculations of the size-dependent intraband transition energy. We find that to bleach the first exciton transition by an average of 1 carrier per QD requires that approximately 10% of the Pb be replaced by Ag. Here, we hypothesize that the majority of incorporated Ag remains at the QD surface and does not interact with the core electronic states of the QD. Instead, the excess Ag at the surface promotes the incorporation of <1% Ag into the QD core where it causes p-type doping behavior.« less

Sol-flame synthesis of cobalt-doped TiO2 nanowires with enhanced electrocatalytic activity for oxygen evolution reaction.

PubMed

Cai, Lili; Cho, In Sun; Logar, Manca; Mehta, Apurva; He, Jiajun; Lee, Chi Hwan; Rao, Pratap M; Feng, Yunzhe; Wilcox, Jennifer; Prinz, Fritz B; Zheng, Xiaolin

2014-06-28

Doping nanowires (NWs) is of crucial importance for a range of applications due to the unique properties arising from both impurities' incorporation and nanoscale dimensions. However, existing doping methods face the challenge of simultaneous control over the morphology, crystallinity, dopant distribution and concentration at the nanometer scale. Here, we present a controllable and reliable method, which combines versatile solution phase chemistry and rapid flame annealing process (sol-flame), to dope TiO2 NWs with cobalt (Co). The sol-flame doping method not only preserves the morphology and crystallinity of the TiO2 NWs, but also allows fine control over the Co dopant profile by varying the concentration of Co precursor solution. Characterizations of the TiO2:Co NWs show that Co dopants exhibit 2+ oxidation state and substitutionally occupy Ti sites in the TiO2 lattice. The Co dopant concentration significantly affects the oxygen evolution reaction (OER) activity of TiO2:Co NWs, and the TiO2:Co NWs with 12 at% of Co on the surface show the highest OER activity with a 0.76 V reduction of the overpotential with respect to undoped TiO2 NWs. This enhancement of OER activity for TiO2:Co NWs is attributed to both improved surface charge transfer kinetics and increased bulk conductivity.

Temperature Dependence Discontinuity in the Stability of Manganese doped Ceria Nanocrystals

DOE PAGES

Wu, Longjia; Dholabhai, Pratik; Uberuaga, Blas P.; ...

2017-01-05

CeO 2 has strong potential for chemical-looping water splitting. It has been shown that manganese doping decreases interface energies of CeO 2, allowing increased stability of high surface areas in this oxygen carrier oxide. The phenomenon is related to the segregation of Mn3+ at interfaces, which causes a measurable decrease in excess energy. Here in the present work, it is shown that, despite the stability of nanocrystals of manganese-doped CeO 2 with relation to undoped CeO 2, the effect is strongly dependent on the oxidation state of manganese, i.e., on the temperature. At temperatures below 800 °C, Mn is inmore » the 3+ valence state, and coarsening is hindered by the reduced interface energetics, showing smaller crystal sizes with increasing Mn content. At temperatures above 800 °C, Mn is reduced to its 2+ valence state, and coarsening is enhanced with increasing Mn content. Atomistic simulations show the segregation of Mn to grain boundaries is relatively insensitive to the charge state of the dopant. However, point defect modeling finds that the reduced state causes a decrease in cation vacancy concentration and an increase in cation interstitials, reducing drag forces for grain boundary mobility and increasing growth rates.« less

Electronic Structure of Ytterbium-Doped Strontium Fluoroapatite: Photoemission and Photoabsorption Investigation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nelson, Art J.; Van Buuren, Tony W.; Bostedt, C

X-ray photoemission and x-ray photoabsorption were used to study the composition and the electronic structure of ytterbium-doped strontium fluoroapatite (Yb:S-FAP). High resolution photoemission measurements on the valence band electronic structure and Sr 3d, P 2p and 2s, Yb 4d and 4p, F 1s and O 1s core lines were used to evaluate the surface and near surface chemistry of this fluoroapatite. Element specific density of unoccupied electronic states in Yb:S-FAP were probed by x-ray absorption spectroscopy (XAS) at the Yb 4d (N4,5-edge), Sr 3d (M4,5-edge), P 2p (L2,3-edge), F 1s and O 1s (K-edges) absorption edges. These results provide themore » first measurements of the electronic structure and surface chemistry of this material.« less

Superior lithium adsorption and required magnetic separation behavior of iron-doped lithium ion-sieves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Shulei; Zheng, Shili; Wang, Zheming

The recent research on adsorption-based lithium recovery from lithium-containing solutions has been centred on adsorption capacity and separation of lithium ion-sieves powder from solutions. Herein, an effective iron-doped lithium titanium oxide (Fe-doped Li 2TiO 3) was synthesized by Fe-doping via solid state reactions followed by acid treatment to form iron-doped lithium ion-sieves (Fe/Ti-x(H)). The resulting solid powder displays both superior adsorption capacity of lithium and high separation efficiency of the adsorbent from the solutions. SEM imaging and BET surface area measurement results showed that at Fe doping levels x ≤ 0.15, Fe-doping led to grain shrinkage as compared to Limore » 2TiO 3 and at the same time the BET surface area increased. The Fe/Ti-0.15(H) exhibited saturated magnetization values of 13.76 emu g -1, allowing effective separation of the material from solid suspensions through the use of a magnet. Consecutive magnetic separation results suggested that the Fe/Ti-0.15(H) powders could be applied at large-scale and continuously removed from LiOH solutions with separation efficiency of 96% or better. Lithium adsorption studies indicated that the equilibrium adsorption capacity of Fe/Ti-0.15(H) in LiOH solutions (1.8 g L -1 Li, pH 12) reached 53.3 mg g -1 within 24 h, which was higher than that of pristine Li 2TiO 3 (50.5 mg g-1) without Fe doping. Competitive adsorption and regeneration results indicated that the Fe/Ti-0.15(H) possessed a high selectivity for Li with facile regeneration. Therefore, it could be expected that the iron-doped lithium ion-sieves have practical applicability potential for large scale lithium extraction and recovery from lithium-bearing solutions.« less

Superior lithium adsorption and required magnetic separation behavior of iron-doped lithium ion-sieves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Shulei; Zheng, Shili; Wang, Zheming

The recent research on adsorption-based lithium recovery from lithium-containing solutions has been centred on adsorption capacity and separation of lithium ion-sieves powder from solutions. Herein, an effective iron-doped lithium titanium oxide (Fe-doped Li2TiO3) was synthesized by Fe-doping via solid state reactions followed by acid treatment to form iron-doped lithium ion-sieves (Fe/Ti-x(H)). The resulting solid powder displays both superior adsorption capacity of lithium and high separation efficiency of the adsorbent from the solutions. SEM imaging and BET surface area measurement results showed that at Fe doping levels x0.15, Fe-doping led to grain shrinkage as compared to Li2TiO3 and at the samemore » time the BET surface area increased. The Fe/Ti-0.15(H) exhibited saturated magnetization values of 13.76 emu g-1, allowing effective separation of the material from solid suspensions through the use of a magnet. Consecutive magnetic separation results suggested that the Fe/Ti-0.15(H) powders could be applied at large-scale and continuously removed from LiOH solutions with separation efficiency of 96% or better. Lithium adsorption studies indicated that the equilibrium adsorption capacity of Fe/Ti-0.15(H) in LiOH 2 solutions (1.8 g L-1 Li, pH 12) reached 53.3 mg g-1 within 24 h, which was higher than that of pristine Li2TiO3 (50.5 mg g-1) without Fe doping. Competitive adsorption and regeneration results indicated that the Fe/Ti-0.15(H) possessed a high selectivity for Li with facile regeneration. Therefore, it could be expected that the iron-doped lithium ion-sieves have practical applicability potential for large scale lithium extraction and recovery from lithium-bearing solutions.« less

Superior lithium adsorption and required magnetic separation behavior of iron-doped lithium ion-sieves

DOE PAGES

Wang, Shulei; Zheng, Shili; Wang, Zheming; ...

2018-09-09

The recent research on adsorption-based lithium recovery from lithium-containing solutions has been centred on adsorption capacity and separation of lithium ion-sieves powder from solutions. Herein, an effective iron-doped lithium titanium oxide (Fe-doped Li 2TiO 3) was synthesized by Fe-doping via solid state reactions followed by acid treatment to form iron-doped lithium ion-sieves (Fe/Ti-x(H)). The resulting solid powder displays both superior adsorption capacity of lithium and high separation efficiency of the adsorbent from the solutions. SEM imaging and BET surface area measurement results showed that at Fe doping levels x ≤ 0.15, Fe-doping led to grain shrinkage as compared to Limore » 2TiO 3 and at the same time the BET surface area increased. The Fe/Ti-0.15(H) exhibited saturated magnetization values of 13.76 emu g -1, allowing effective separation of the material from solid suspensions through the use of a magnet. Consecutive magnetic separation results suggested that the Fe/Ti-0.15(H) powders could be applied at large-scale and continuously removed from LiOH solutions with separation efficiency of 96% or better. Lithium adsorption studies indicated that the equilibrium adsorption capacity of Fe/Ti-0.15(H) in LiOH solutions (1.8 g L -1 Li, pH 12) reached 53.3 mg g -1 within 24 h, which was higher than that of pristine Li 2TiO 3 (50.5 mg g-1) without Fe doping. Competitive adsorption and regeneration results indicated that the Fe/Ti-0.15(H) possessed a high selectivity for Li with facile regeneration. Therefore, it could be expected that the iron-doped lithium ion-sieves have practical applicability potential for large scale lithium extraction and recovery from lithium-bearing solutions.« less

Effects of impurity adsorption on topological surface states of Bi2Te3

NASA Astrophysics Data System (ADS)

Shati, Khaqan; Arshad Farhan, M.; Selva Chandrasekaran, S.; Shim, Ji Hoon; Lee, Geunsik

2017-08-01

Electronic structures of Bi2Te3 with adsorption of Rb, In, Ga and Au atoms are studied by using the first-principle method, focusing on the effect of non-magnetic impurities on the topologically protected surface states. Upon monolayer formation, the bulk conduction band is moved down to the Fermi level with a significant Rashba splitting due to n-doping behavior with band modification details depending on the adatom chemistry. Our study shows the robustness of the intrinsic spin-momentum coupled surface band and emergence of a new similar one, which could provide helpful insight for developing novel spintronic devices.

Photoemission and Photoabsorption Investigation of the Electronic Structure of Ytterbium Doped Strontium Fluoroapatite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nelson, A J; van Buuren, T; Bostedt, C

X-ray photoemission and x-ray photoabsorption were used to study the composition and the electronic structure of ytterbium doped strontium fluoroapatite (Yb:S-FAP). High resolution photoemission measurements on the valence band electronic structure was used to evaluate the density of occupied states of this fluoroapatite. Element specific density of unoccupied electronic states in Yb:S-FAP were probed by x-ray absorption spectroscopy (XAS) at the Yb 4d (N{sub 4,5}-edge), Sr 3d (M{sub 4,5}-edge), P 2p (L{sub 2,3}-edge), F 1s and O 1s (K-edges) absorption edges. These results provide the first measurements of the electronic structure and surface chemistry of this material.

Effect of Surface Morphology and Magnetic Impurities on the Electronic Structure in Cobalt-Doped BaFe 2 As 2 Superconductors

DOE PAGES

Zou, Qiang; Wu, Zhiming; Fu, Mingming; ...

2017-02-03

Combined scanning tunneling microscopy, spectroscopy, and local barrier height (LBH) studies show that low-temperature-cleaved optimally doped Ba(Fe 1–xCo x) 2As 2 crystals with x = 0.06, with T c = 22 K, have complicated morphologies. Although the cleavage surface and hence the morphologies are variable, the superconducting gap maps show the same gap widths and nanometer size inhomogeneities irrelevant to the morphology. Based on the spectroscopy and LBH maps, the bright patches and dark stripes in the morphologies are identified as Ba- and As-dominated surface terminations, respectively. Magnetic impurities, possibly due to Co or Fe atoms, are believed to createmore » local in-gap state and, in addition, suppress the superconducting coherence peaks. Lastly, this study will clarify the confusion on the cleavage surface terminations of the Fe-based superconductors and its relation with the electronic structures.« less

Method and closing pores in a thermally sprayed doped lanthanum chromite interconnection layer

DOEpatents

Singh, Prabhakar; Ruka, Roswell J.

1995-01-01

A dense, substantially gas-tight electrically conductive interconnection layer is formed on an air electrode structure of an electrochemical cell by (A) providing an air electrode surface; (B) forming on a selected portion of the electrode surface, a layer of doped LaCrO.sub.3 particles doped with an element or elements selected from Ca, Sr, Ba, Mg, Co, Ni, Al and mixtures thereof by thermal spraying doped LaCrO.sub.3 particles, either by plasma arc spraying or flame spraying; (C) depositing a mixture of CaO and Cr.sub.2 O.sub.3 on the surface of the thermally sprayed layer; and (D) heating the doped LaCrO.sub.3 layer coated with CaO and Cr.sub.2 O.sub.3 surface deposit at from about 1000.degree. C. to 1200.degree. C. to substantially close the pores, at least at a surface, of the thermally sprayed doped LaCrO.sub.3 layer. The result is a dense, substantially gas-tight, highly doped, electrically conductive interconnection material bonded to the electrode surface. A solid electrolyte layer can be applied to the nonselected portion of the air electrode. A fuel electrode can be applied to the solid electrolyte, to form an electrochemical cell, for example for generation of electrical power.

Method and closing pores in a thermally sprayed doped lanthanum chromite interconnection layer

DOEpatents

Singh, P.; Ruka, R.J.

1995-02-14

A dense, substantially gas-tight electrically conductive interconnection layer is formed on an air electrode structure of an electrochemical cell by (A) providing an air electrode surface; (B) forming on a selected portion of the electrode surface, a layer of doped LaCrO{sub 3} particles doped with an element or elements selected from Ca, Sr, Ba, Mg, Co, Ni, Al and mixtures thereof by thermal spraying doped LaCrO{sub 3} particles, either by plasma arc spraying or flame spraying; (C) depositing a mixture of CaO and Cr{sub 2}O{sub 3} on the surface of the thermally sprayed layer; and (D) heating the doped LaCrO{sub 3} layer coated with CaO and Cr{sub 2}O{sub 3} surface deposit at from about 1,000 C to 1,200 C to substantially close the pores, at least at a surface, of the thermally sprayed doped LaCrO{sub 3} layer. The result is a dense, substantially gas-tight, highly doped, electrically conductive interconnection material bonded to the electrode surface. A solid electrolyte layer can be applied to the nonselected portion of the air electrode. A fuel electrode can be applied to the solid electrolyte, to form an electrochemical cell, for example for generation of electrical power. 5 figs.

DENSITY FUNCTIONAL STUDY OF ELEMENTAL MERCURY ADSORPTION ON X (X=Mn, Si, Ti, Al, AND Zn)-DOPED CuO (110) SURFACE

NASA Astrophysics Data System (ADS)

He, Ping; Peng, Xiaolong; Zhang, Zhongzhi; Wu, Jiang; Chen, Naichao; Ren, Jianxing

Copper oxide (CuO) is proved to be a potential adsorbent for elemental mercury in the flue gas emitted from coal-fired power plant. However, the O-terminated CuO(110) surface has relatively week adsorption capacity for Hg. In this work, the doped method is applied to enhance the mercury adsorption capacity of O-terminated CuO(110). Mn, Si, Ti, Al and Zn are selected as the doped atom. It is found that only Zn-doped CuO (110) surfaces have the higher adsorption energy than the pure O-terminated CuO(110) surface. The mercury adsorption capacity is a complex issue, which depends on a combination of oxygen and doped element. The results suggest that the lower electropositive doped element is favorable for the improvement of mercury adsorption capacity. However, the lower electronegativity of oxygen atoms does not facilitate the mercury capture, which is different from the organic material. Cu and doped metal element, rather than oxygen atom, mainly determine mercury adsorption capacity of O-terminated CuO(110) surface, which leads to the lower adsorption capacity of the O-terminated CuO(110) surface than the Cu-terminated CuO(110) surface. The conclusions can also offer a valuable reference for the other metal oxide regarding mercury capture.

Combined Embedding of N/F-Doping and CaCO3 Surface Modification in the TiO2 Photoanode for Dye-Sensitized Solar Cells.

PubMed

Park, Su Kyung; Yun, Tae Kwan; Bae, Jae Young

2016-03-01

N/F-doping and CaCO3 surface modification was carried out in TiO2 photoelectrodes for dye-sensitized solar cells (DSSCs). The combined effect of the N/F doped TiO2 and the CaCO3 coating showed a great increase of the short-circuit current (J(sc)), and photoelectric conversion efficiency (η) of the prepared cells; the efficiency (η) was improved from 7.00% of a commercial TiO2 photoelectrode to 7.90% of an uncoated N/F-doped electrode, and to 9.09% of a N/F-doped and CaCO3 surface modified electrode. An enhanced photoresponse in N/F-doped TiO2 nanoparticles generate more photo-excited electrons, as supported by measured UV-Vis diffuse reflectance spectra. A successive CaCO3 surface modification then forms a barrier on the surface of the N/F-doped TiO2 particles; the higher basicity of the CaCO3 modified TiO2 facilitates the dye adsorption, as supported by the direct measurement of the amount of adsorbed dye.

Effects of pentacene-doped PEDOT:PSS as a hole-conducting layer on the performance characteristics of polymer photovoltaic cells.

PubMed

Kim, Hyunsoo; Lee, Jungrae; Ok, Sunseong; Choe, Youngson

2012-01-05

We have investigated the effect of pentacene-doped poly(3,4-ethylenedioxythiophene:poly(4-styrenesulfonate) [PEDOT:PSS] films as a hole-conducting layer on the performance of polymer photovoltaic cells. By increasing the amount of pentacene and the annealing temperature of pentacene-doped PEDOT:PSS layer, the changes of performance characteristics were evaluated. Pentacene-doped PEDOT:PSS thin films were prepared by dissolving pentacene in 1-methyl-2-pyrrolidinone solvent and mixing with PEDOT:PSS. As the amount of pentacene in the PEDOT:PSS solution was increased, UV-visible transmittance also increased dramatically. By increasing the amount of pentacene in PEDOT:PSS films, dramatic decreases in both the work function and surface resistance were observed. However, the work function and surface resistance began to sharply increase above the doping amount of pentacene at 7.7 and 9.9 mg, respectively. As the annealing temperature was increased, the surface roughness of pentacene-doped PEDOT:PSS films also increased, leading to the formation of PEDOT:PSS aggregates. The films of pentacene-doped PEDOT:PSS were characterized by AFM, SEM, UV-visible transmittance, surface analyzer, surface resistance, and photovoltaic response analysis.

Effects of pentacene-doped PEDOT:PSS as a hole-conducting layer on the performance characteristics of polymer photovoltaic cells

PubMed Central

2012-01-01

We have investigated the effect of pentacene-doped poly(3,4-ethylenedioxythiophene:poly(4-styrenesulfonate) [PEDOT:PSS] films as a hole-conducting layer on the performance of polymer photovoltaic cells. By increasing the amount of pentacene and the annealing temperature of pentacene-doped PEDOT:PSS layer, the changes of performance characteristics were evaluated. Pentacene-doped PEDOT:PSS thin films were prepared by dissolving pentacene in 1-methyl-2-pyrrolidinone solvent and mixing with PEDOT:PSS. As the amount of pentacene in the PEDOT:PSS solution was increased, UV-visible transmittance also increased dramatically. By increasing the amount of pentacene in PEDOT:PSS films, dramatic decreases in both the work function and surface resistance were observed. However, the work function and surface resistance began to sharply increase above the doping amount of pentacene at 7.7 and 9.9 mg, respectively. As the annealing temperature was increased, the surface roughness of pentacene-doped PEDOT:PSS films also increased, leading to the formation of PEDOT:PSS aggregates. The films of pentacene-doped PEDOT:PSS were characterized by AFM, SEM, UV-visible transmittance, surface analyzer, surface resistance, and photovoltaic response analysis. PMID:22221320

Effects of rare earth doping on multi-core iron oxide nanoparticles properties

NASA Astrophysics Data System (ADS)

Petran, Anca; Radu, Teodora; Borodi, Gheorghe; Nan, Alexandrina; Suciu, Maria; Turcu, Rodica

2018-01-01

New multi-core iron oxide magnetic nanoparticles doped with rare earth metals (Gd, Eu) were obtained by a one step synthesis procedure using a solvothermal method for potential biomedical applications. The obtained clusters were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray microanalysis (EDX), X-ray photoelectron spectroscopy (XPS) and magnetization measurements. They possess high colloidal stability, a saturation magnetization of up to 52 emu/g, and nearly spherical shape. The presence of rare earth ions in the obtained samples was confirmed by EDX and XPS. XRD analysis proved the homogeneous distribution of the trivalent rare earth ions in the inverse-spinel structure of magnetite and the increase of crystal strain upon doping the samples. XPS study reveals the valence state and the cation distribution on the octahedral and tetrahedral sites of the analysed samples. The observed shift of the XPS valence band spectra maximum in the direction of higher binding energies after rare earth doping, as well as theoretical valence band calculations prove the presence of Gd and Eu ions in octahedral sites. The blood protein adsorption ability of the obtained samples surface, the most important factor of the interaction between biomaterials and body fluids, was assessed by interaction with bovine serum albumin (BSA). The rare earth doped clusters surface show higher afinity for binding BSA. In vitro cytotoxicity test results for the studied samples showed no cytotoxicity in low and medium doses, establishing a potential perspective for rare earth doped MNC to facilitate multiple therapies in a single formulation for cancer theranostics.

Surface acceptor states in MBE-grown CdTe layers

NASA Astrophysics Data System (ADS)

Wichrowska, Karolina; Wosinski, Tadeusz; Tkaczyk, Zbigniew; Kolkovsky, Valery; Karczewski, Grzegorz

2018-04-01

A deep-level hole trap associated with surface defect states has been revealed with deep-level transient spectroscopy investigations of metal-semiconductor junctions fabricated on nitrogen doped p-type CdTe layers grown by the molecular-beam epitaxy technique. The trap displayed the hole-emission activation energy of 0.33 eV and the logarithmic capture kinetics indicating its relation to extended defect states at the metal-semiconductor interface. Strong electric-field-induced enhancement of the thermal emission rate of holes from the trap has been attributed to the phonon-assisted tunneling effect from defect states involving very large lattice relaxation around the defect and metastability of its occupied state. Passivation with ammonium sulfide of the CdTe surface, prior to metallization, results in a significant decrease in the trap density. It also results in a distinct reduction in the width of the surface-acceptor-state-induced hysteresis loops in the capacitance vs. voltage characteristics of the metal-semiconductor junctions.

Property Morphology Correlations of Organic Semiconductor Nanowires

NASA Astrophysics Data System (ADS)

McFarland, Frederick Marshall

Chemically doped and non-doped P3HT nanoaggregates are studied to establish a comprehensive understanding of the interplay between their morphology and various optoelectronic properties. One-dimensional nanoaggregates of P3HT are chosen as the model systems here due to their high surface/volume ratio and suitability for microscopic investigations. Atomic force microscopy (AFM) and kelvin probe force microscopy (KPFM) are used to correlate property/morphology characteristics of non-doped P3HT nanowhiskers. Topographical measurements indicate that individually folded P3HT motifs stack via interfacial interactions to form nanowhiskers in solution. Further aging leads to multi-layered nanowhiskers with greater stability and less instances of ?-? sliding of interfacial edge-on oriented motifs. KPFM measurements show higher surface potentials on portions of nanowhiskers containing local defects and stacking faults due to overlapping, and nanowhiskers that are at least triple-layered. Simultaneous UV-Vis and AFM characterizations compare the aggregation rates and morphologies of doped and non-doped P3HT nanowhiskers. Allowing fully solubilized P3HT to age without doping may produce high aspect ratio nanowhiskers containing disordered segments protruding out from the edges of the nanowhiskers. These protruding segments could also serve as "tie-molecules" between adjacent nanowhiskers. Doping fully solubilized P3HT will lead to substantially higher rates of P3HT aggregation. Doped nanowhiskers also display different morphologies. They pack tighter, are smoother, and are thicker and higher versus non-doped nanowhiskers, indicating a different aggregation mechanism. Stopped flow-kinetics was employed to investigate the reactivity of two distinctively different morphological forms of P3HT towards dopants. Fully solubilized P3HT undergoes a slow doping mechanism whereas pre-aggregated P3HT undergoes a fast doping mechanism. Pseudo-single reactant rate fittings indicate that both mechanisms appear to be 1st order in P3HT, whereby pre-aggregated P3HT mixtures will produce more doped products per P3HT monomer unit than fully solubilized P3HT. This study highlights the impact of conjugated polymer's morphology on their doping efficiency. Density functional theory was used to investigate the charge transfer (CT) states between oligothiophene and F4-TCNQ. CT of several unreported complexes that feature two oligomers stacked in a sandwich or layered configuration is investigated. Our preliminary results suggest that these new complexes can generate substantially more charge per F4-TCNQ than previously reported.

Understanding the role of Si doping on surface charge and optical properties: Photoluminescence study of intrinsic and Si-doped InN nanowires

NASA Astrophysics Data System (ADS)

Zhao, S.; Mi, Z.; Kibria, M. G.; Li, Q.; Wang, G. T.

2012-06-01

In the present work, the photoluminescence (PL) characteristics of intrinsic and Si-doped InN nanowires are studied in detail. For intrinsic InN nanowires, the emission is due to band-to-band carrier recombination with the peak energy at ˜0.64 eV (at 300 K) and may involve free-exciton emission at low temperatures. The PL spectra exhibit a strong dependence on optical excitation power and temperature, which can be well characterized by the presence of very low residual electron density and the absence or a negligible level of surface electron accumulation. In comparison, the emission of Si-doped InN nanowires is characterized by the presence of two distinct peaks located at ˜0.65 and ˜0.73-0.75 eV (at 300 K). Detailed studies further suggest that these low-energy and high-energy peaks can be ascribed to band-to-band carrier recombination in the relatively low-doped nanowire bulk region and Mahan exciton emission in the high-doped nanowire near-surface region, respectively; this is a natural consequence of dopant surface segregation. The resulting surface electron accumulation and Fermi-level pinning, due to the enhanced surface doping, are confirmed by angle-resolved x-ray photoelectron spectroscopy measurements on Si-doped InN nanowires, which is in direct contrast to the absence or a negligible level of surface electron accumulation in intrinsic InN nanowires. This work elucidates the role of charge-carrier concentration and distribution on the optical properties of InN nanowires.

Probing Electronic States of Magnetic Semiconductors Using Atomic Scale Microscopy & Spectroscopy

DTIC Science & Technology

2013-12-01

the metal- insulator transition, a feature that has long been predicted theoretically. We showed that a similar picture is at play in magnetic doping of... magnetic atoms on the surface of a superconductor can be used as a versatile platform for creating a topological superconductor . These initial...topological superconductivity and Majorana fermions in a chain of magnetic atoms on the surface of a superconductor Students and postdocs supported

Zero energy states at a normal-metal/cuprate-superconductor interface probed by shot noise

NASA Astrophysics Data System (ADS)

Negri, O.; Zaberchik, M.; Drachuck, G.; Keren, A.; Reznikov, M.

2018-06-01

We report measurements of the current noise generated in the optimally doped, x =0.15 , Au-La2-xSrxCuO4 junctions. For high transmission junctions on a (110) surface, we observed a split zero-bias conductance peak (ZBCP), accompanied by enhanced shot noise. We observed no enhanced noise neither in low-transmission junctions on a (110) surface nor in any junction on a (100) surface. We attribute the enhanced noise to Cooper pair transport through the junctions.

Crystal Orientation-Dependent Reactivity of Oxide Surfaces in Contact with Lithium Metal.

PubMed

Connell, Justin G; Zhu, Yisi; Zapol, Peter; Tepavcevic, Sanja; Sharafi, Asma; Sakamoto, Jeff; Curtiss, Larry A; Fong, Dillon D; Freeland, John W; Markovic, Nenad M

2018-05-23

Understanding ionic transport across interfaces between dissimilar materials and the intrinsic chemical stability of such interfaces is a fundamental challenge spanning many disciplines and is of particular importance for designing conductive and stable solid electrolytes for solid-state Li-ion batteries. In this work, we establish a surface science-based approach for assessing the intrinsic stability of oxide materials in contact with Li metal. Through a combination of experimental and computational insights, using Nb-doped SrTiO 3 (Nb/STO) single crystals as a model system, we were able to understand the impact of crystallographic orientation and surface morphology on the extent of the chemical reactions that take place between surface Nb, Ti, and Sr upon reaction with Li. By expanding our approach to investigate the intrinsic stability of the technologically relevant, polycrystalline Nb-doped lithium lanthanum zirconium oxide (Li 6.5 La 3 Zr 1.5 Nb 0.5 O 12 ) system, we found that this material reacts with Li metal through the reduction of Nb, similar to that observed for Nb/STO. These results clearly demonstrate the feasibility of our approach to assess the intrinsic (in)stability of oxide materials for solid-state batteries and point to new strategies for understanding the performance of such systems.

Crystal Orientation-Dependent Reactivity of Oxide Surfaces in Contact with Lithium Metal.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Connell, Justin G.; Zhu, Yisi; Zapol, Peter

Understanding ionic transport across interfaces between dissimilar materials and the intrinsic chemical stability of such interfaces is a fundamental challenge spanning many disciplines and is of particular importance for designing conductive and stable solid electrolytes for solid-state Li-ion batteries. In this work, we establish a surface science-based approach for assessing the intrinsic stability of oxide materials in contact with Li metal. Through a combination of experimental and computational insights, using Nb-doped SrTiO3 (Nb/STO) single crystals as a model system, we were able to understand the impact of crystallographic orientation and surface morphology on the extent of the chemical reactions thatmore » take place between surface Nb, Ti, and Sr upon reaction with Li. By expanding our approach to investigate the intrinsic stability of the technologically relevant, polycrystalline Nb-doped lithium lanthanum zirconium oxide (Li6.5La3Zr1.5Nb0.5O12) system, we found that this material reacts with Li metal through the reduction of Nb, similar to that observed for Nb/STO. These results clearly demonstrate the feasibility of our approach to assess the intrinsic (in)stability of oxide materials for solid-state batteries and point to new strategies for understanding the performance of such systems.« less

Estimation of electron–phonon coupling and Urbach energy in group-I elements doped ZnO nanoparticles and thin films by sol–gel method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vettumperumal, R.; Kalyanaraman, S., E-mail: mayura_priya2003@yahoo.co.in; Santoshkumar, B.

Highlights: • Comparison of group-I elements doped ZnO nanoparticles and thin films. • Calculation of electron–phonon coupling and phonon lifetime from Raman spectroscopy. • Estimation of interband states from Urbach energy. - Abstract: Group-I (Li, Na, K & Cs) elements doped ZnO nanoparticles (NPs) and thin films were prepared using sol–gel method. XRD data and TEM images confirm the absence of any other secondary phase different from wurtzite type ZnO. Spherical shapes of grains are observed from the surfaces of doped ZnO films by atomic force microscope images (AFM) and presences of dopants are confirmed from energy dispersive X-ray spectra.more » The Raman active E{sub 2} (high), E{sub 2} (low), E{sub 1} and A{sub 1} (LO) modes are observed from both ZnO NPs and thin films. First-order longitudinal optical (LO) phonon is found to have contributions from direct band transition and localized excitons. Electron–phonon coupling, phonon lifetime and deformation energy of ZnO are calculated based on the effect of dopants with respect to the multiple Raman LO phonon scattering. Presence of localized interbands states in doped ZnO NPs and thin films are found from the Urbach energy calculations.« less

NEUTRON SCATTERING STUDY OF THE HIGH-Tc SUPERCONDUCTING SYSTEM YBa2Cu3O6+x

NASA Astrophysics Data System (ADS)

Rossat-Mignod, J.; Regnault, L. P.; Bourges, P.; Burlet, P.; Vettier, C.; Henry, J. Y.

The following sections are included: * Introduction * The neutron scattering technique * Phase diagrams of high-Tc superconductors * The undoped AF-doped * The doped AF-state * The weakly-doped metallic state * The heavily-doped metallic state * The overdoped metallic state * Discussion and concluding remarks * Acknowledgements * References

Disentangling the surface and bulk electronic structures of LaOFeAs

DOE PAGES

Zhang, P.; Ma, J.; Qian, T.; ...

2016-09-20

We performed a comprehensive angle-resolved photoemission spectroscopy study of the electronic band structure of LaOFeAs single crystals. We found that samples cleaved at low temperature show an unstable and very complicated band structure, whereas samples cleaved at high temperature exhibit a stable and clearer electronic structure. Using in situ surface doping with K and supported by first-principles calculations, we identify both surface and bulk bands. Our assignments are confirmed by the difference in the temperature dependence of the bulk and surface states.

Exact Solution of a Two-Species Quantum Dimer Model for Pseudogap Metals

NASA Astrophysics Data System (ADS)

Feldmeier, Johannes; Huber, Sebastian; Punk, Matthias

2018-05-01

We present an exact ground state solution of a quantum dimer model introduced by Punk, Allais, and Sachdev [Quantum dimer model for the pseudogap metal, Proc. Natl. Acad. Sci. U.S.A. 112, 9552 (2015)., 10.1073/pnas.1512206112], which features ordinary bosonic spin-singlet dimers as well as fermionic dimers that can be viewed as bound states of spinons and holons in a hole-doped resonating valence bond liquid. Interestingly, this model captures several essential properties of the metallic pseudogap phase in high-Tc cuprate superconductors. We identify a line in parameter space where the exact ground state wave functions can be constructed at an arbitrary density of fermionic dimers. At this exactly solvable line the ground state has a huge degeneracy, which can be interpreted as a flat band of fermionic excitations. Perturbing around the exactly solvable line, this degeneracy is lifted and the ground state is a fractionalized Fermi liquid with a small pocket Fermi surface in the low doping limit.

Ultra High p-doping Material Research for GaN Based Light Emitters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vladimir Dmitriev

2007-06-30

The main goal of the Project is to investigate doping mechanisms in p-type GaN and AlGaN and controllably fabricate ultra high doped p-GaN materials and epitaxial structures. Highly doped p-type GaN-based materials with low electrical resistivity and abrupt doping profiles are of great importance for efficient light emitters for solid state lighting (SSL) applications. Cost-effective hydride vapor phase epitaxial (HVPE) technology was proposed to investigate and develop p-GaN materials for SSL. High p-type doping is required to improve (i) carrier injection efficiency in light emitting p-n junctions that will result in increasing of light emitting efficiency, (ii) current spreading inmore » light emitting structures that will improve external quantum efficiency, and (iii) parameters of Ohmic contacts to reduce operating voltage and tolerate higher forward currents needed for the high output power operation of light emitters. Highly doped p-type GaN layers and AlGaN/GaN heterostructures with low electrical resistivity will lead to novel device and contact metallization designs for high-power high efficiency GaN-based light emitters. Overall, highly doped p-GaN is a key element to develop light emitting devices for the DOE SSL program. The project was focused on material research for highly doped p-type GaN materials and device structures for applications in high performance light emitters for general illumination P-GaN and p-AlGaN layers and multi-layer structures were grown by HVPE and investigated in terms of surface morphology and structure, doping concentrations and profiles, optical, electrical, and structural properties. Tasks of the project were successfully accomplished. Highly doped GaN materials with p-type conductivity were fabricated. As-grown GaN layers had concentration N{sub a}-N{sub d} as high as 3 x 10{sup 19} cm{sup -3}. Mechanisms of doping were investigated and results of material studies were reported at several International conferences providing better understanding of p-type GaN formation for Solid State Lighting community. Grown p-type GaN layers were used as substrates for blue and green InGaN-based LEDs made by HVPE technology at TDI. These results proved proposed technical approach and facilitate fabrication of highly conductive p-GaN materials by low-cost HVPE technology for solid state lighting applications. TDI has started the commercialization of p-GaN epitaxial materials.« less

Tuning the pure monoclinic phase of WO3 and WO3-Ag nanostructures for non-enzymatic glucose sensing application with theoretical insight from electronic structure simulations

NASA Astrophysics Data System (ADS)

Ponnusamy, Rajeswari; Gangan, Abhijeet; Chakraborty, Brahmananda; Sekhar Rout, Chandra

2018-01-01

Here, we report the controlled hydrothermal synthesis and tuning of the pure monoclinic phase of WO3 and WO3-Ag nanostructures. Comparative electrochemical nonenzymatic glucose sensing properties of WO3 and WO3-Ag were investigated by cyclic voltammetry and chronoamperometric tests. We observed enhanced glucose sensing performance of WO3-Ag porous spheres as compared to bare WO3 nanoslabs. The sensitivity of the pure WO3 nanoslabs is 11.1 μA μM-1 cm-2 whereas WO3-Ag porous spheres exhibit sensitivity of 23.3 μA μM-1 cm-2. The WO3-Ag porous spheres exhibited a good linear range (5-375 μM) with excellent anti-interference property. Our experimental observations are qualitatively supported by density functional theory simulations through investigation of bonding and charge transfer mechanism of glucose on WO3 and Ag doped WO3. As the binding energy of glucose is more on the Ag doped WO3 (100) surface compared to the bare WO3 (100) surface and the Ag doped WO3 (100) surface becomes more conducting due to enhancement of density of states near the Fermi level, we can infer that Ag doped WO3 exhibits a better charge transfer media compared to bare WO3 resulting in enhanced glucose sensitivity in consistency with our experimental data.

Doping Level of Boron-Doped Diamond Electrodes Controls the Grafting Density of Functional Groups for DNA Assays.

PubMed

Švorc, Ĺubomír; Jambrec, Daliborka; Vojs, Marian; Barwe, Stefan; Clausmeyer, Jan; Michniak, Pavol; Marton, Marián; Schuhmann, Wolfgang

2015-09-02

The impact of different doping levels of boron-doped diamond on the surface functionalization was investigated by means of electrochemical reduction of aryldiazonium salts. The grafting efficiency of 4-nitrophenyl groups increased with the boron levels (B/C ratio from 0 to 20,000 ppm). Controlled grafting of nitrophenyldiazonium was used to adjust the amount of immobilized single-stranded DNA strands at the surface and further on the hybridization yield in dependence on the boron doping level. The grafted nitro functions were electrochemically reduced to the amine moieties. Subsequent functionalization with a succinic acid introduced carboxyl groups for subsequent binding of an amino-terminated DNA probe. DNA hybridization significantly depends on the probe density which is in turn dependent on the boron doping level. The proposed approach opens new insights for the design and control of doped diamond surface functionalization for the construction of DNA hybridization assays.

Probing the electronic structure and photoactivation process of nitrogen-doped TiO2 using DRS, PL, and EPR.

PubMed

Zhang, Zizhong; Long, Jinlin; Xie, Xiuqiang; Lin, Huan; Zhou, Yangen; Yuan, Rusheng; Dai, Wenxin; Ding, Zhengxin; Wang, Xuxu; Fu, Xianzhi

2012-04-23

The electronic structure and photoactivation process in N-doped TiO(2) is investigated. Diffuse reflectance spectroscopy (DRS), photoluminescence (PL), and electron paramagnetic resonance (EPR) are employed to monitor the change of optical absorption ability and the formation of N species and defects in the heat- and photoinduced N-doped TiO(2) catalyst. Under thermal treatment below 573 K in vacuum, no nitrogen dopant is removed from the doped samples but oxygen vacancies and Ti(3+) states are formed to enhance the optical absorption in the visible-light region, especially at wavelengths above 500 nm with increasing temperature. In the photoactivation processes of N-doped TiO(2), the DRS absorption and PL emission in the visible spectral region of 450-700 nm increase with prolonged irradiation time. The EPR results reveal that paramagnetic nitrogen species (N(s)·, oxygen vacancies with one electron (V(o)·), and Ti(3+) ions are produced with light irradiation and the intensity of N(s)· species is dependent on the excitation light wavelength and power. The combined characterization results confirm that the energy level of doped N species is localized above the valence band of TiO(2) corresponding to the main absorption band at 410 nm of N-doped TiO(2), but oxygen vacancies and Ti(3+) states as defects contribute to the visible-light absorption above 500 nm in the overall absorption of the doped samples. Thus, a detailed picture of the electronic structure of N-doped TiO(2) is proposed and discussed. On the other hand, the transfer of charge carriers between nitrogen species and defects is reversible on the catalyst surface. The presence of oxygen-vacancy-related defects leads to quenching of paramagnetic N(s)· species but they stabilize the active nitrogen species N(s)(-). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Spin textures on general surfaces of the correlated topological insulator SmB6

NASA Astrophysics Data System (ADS)

Baruselli, Pier Paolo; Vojta, Matthias

2016-05-01

Employing the k .p expansion for a family of tight-binding models for SmB6, we analytically compute topological surface states on a generic (l m n ) surface. We show how the Dirac-cone spin structure depends on model ingredients and on the angle θ between the surface normal and the main crystal axes. We apply the general theory to (001), (110), (111), and (210) surfaces, for which we provide concrete predictions for the spin pattern of surface states which we also compare with tight-binding results. As shown in previous work, the spin pattern on a (001 ) surface can be related to the value of mirror Chern numbers, and we explore the possibility of topological phase transitions between states with different mirror Chern numbers and the associated change of the spin structure of surface states. Such transitions may be accessed by varying either the hybridization between conduction and f electrons or the crystal-field splitting of the low-energy f multiplets, and we compute corresponding phase diagrams. Experimentally, chemical doping is a promising route to realize such transitions.

DFT Study of PH3 Physisorption and Chemisorptions on Boron Nitride Nanotubes

NASA Astrophysics Data System (ADS)

Rakhshi, Mahdi; Mohsennia, Mohsen; Rasa, Hossein

2018-03-01

The adsorption of PH3 molecules on the NiB,N-doped(4,4) and (5,5) BNNTS surfaces has been investigated using density functional theory (DFT). The adsorption energies, geometric and electronic structures of the adsorbed systems were studied to judge the possible application of NiB,N-doped BNNTS in PH3 monitoring systems. Our calculated results showed that NiB,N-doped BNNTS had much higher adsorption energy and shorter binding distances than pure BNNTS owning to chemisorptions of the PH3 molecule. The obtained density of states (DOS) and frontier orbitals demonstrated that the orbital hybridization was obvious between the PH3 molecule and NiB,N-doped BNNTS. However, due to weak physisorption according to the total electron density maps, there was no evidence for hybridization between PH3 molecule and pure BNNTS. It was shown that after doping of Ni atom, the primary symmetry of BNNTS decreased which enhanced the chemical activity of BNNTS towards PH3 molecules. According to the obtained results, we highlight the high potential application of NiB,N-doped BNNTS in the design and fabrication of PH3 sensing devices.

Andreev Reflection Spectroscopy of Nb-doped Bi2Se3 Topological Insulator

NASA Astrophysics Data System (ADS)

Kurter, C.; Finck, A. D. K.; Qiu, Y.; Huemiller, E.; Weis, A.; Atkinson, J.; Medvedeva, J.; Hor, Y. S.; van Harlingen, D. J.

2015-03-01

Doped topological insulators are speculated to realize p-wave superconductivity with unusual low energy quasiparticles, such as surface Andreev bound states. We present point contact spectroscopy of thin exfoliated flakes of Nb-doped Bi2Se3 where superconductivity persists up to ~ 1 K, compared to 3.2 K in bulk crystals. The critical magnetic field is strongly anisotropic, consistent with quasi-2D behavior. Andreev reflection measurements of devices with low resistance contacts result in prominent BTK-like behavior with an enhanced conductance plateau at low bias. For high resistance contacts, we observe a split zero bias conductance anomaly and additional features at the superconducting gap. Our results suggest that this material is a promising platform for studying topological superconductivity. We acknowledge support from Microsoft Project Q.

Surface Passivation of CdSe Quantum Dots in All Inorganic Amorphous Solid by Forming Cd1-xZnxSe Shell.

PubMed

Xia, Mengling; Liu, Chao; Zhao, Zhiyong; Wang, Jing; Lin, Changgui; Xu, Yinsheng; Heo, Jong; Dai, Shixun; Han, Jianjun; Zhao, Xiujian

2017-02-07

CdSe quantum dots (QDs) doped glasses have been widely investigated for optical filters, LED color converter and other optical emitters. Unlike CdSe QDs in solution, it is difficult to passivate the surface defects of CdSe QDs in glass matrix, which strongly suppress its intrinsic emission. In this study, surface passivation of CdSe quantum dots (QDs) by Cd 1-x Zn x Se shell in silicate glass was reported. An increase in the Se/Cd ratio can lead to the partial passivation of the surface states and appearance of the intrinsic emission of CdSe QDs. Optimizing the heat-treatment condition promotes the incorporation of Zn into CdSe QDs and results in the quenching of the defect emission. Formation of CdSe/Cd 1-x Zn x Se core/graded shell QDs is evidenced by the experimental results of TEM and Raman spectroscopy. Realization of the surface passivation and intrinsic emission of II-VI QDs may facilitate the wide applications of QDs doped all inorganic amorphous materials.

Doped colloidal artificial spin ice

DOE PAGES

Libál, A.; Reichhardt, C. J. Olson; Reichhardt, C.

2015-10-07

We examine square and kagome artificial spin ice for colloids confined in arrays of double-well traps. Conversely, magnetic artificial spin ices, unlike colloidal and vortex artificial spin ice realizations, allow creation of doping sites through double occupation of individual traps. We find that doping square and kagome ice geometries produces opposite effects. For square ice, doping creates local excitations in the ground state configuration that produce a local melting effect as the temperature is raised. In contrast, the kagome ice ground state can absorb the doping charge without generating non-ground-state excitations, while at elevated temperatures the hopping of individual colloidsmore » is suppressed near the doping sites. Our results indicate that in the square ice, doping adds degeneracy to the ordered ground state and creates local weak spots, while in the kagome ice, which has a highly degenerate ground state, doping locally decreases the degeneracy and creates local hard regions.« less

Doped colloidal artificial spin ice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Libál, A.; Reichhardt, C. J. Olson; Reichhardt, C.

We examine square and kagome artificial spin ice for colloids confined in arrays of double-well traps. Conversely, magnetic artificial spin ices, unlike colloidal and vortex artificial spin ice realizations, allow creation of doping sites through double occupation of individual traps. We find that doping square and kagome ice geometries produces opposite effects. For square ice, doping creates local excitations in the ground state configuration that produce a local melting effect as the temperature is raised. In contrast, the kagome ice ground state can absorb the doping charge without generating non-ground-state excitations, while at elevated temperatures the hopping of individual colloidsmore » is suppressed near the doping sites. Our results indicate that in the square ice, doping adds degeneracy to the ordered ground state and creates local weak spots, while in the kagome ice, which has a highly degenerate ground state, doping locally decreases the degeneracy and creates local hard regions.« less

Highly improved sensibility and selectivity ethanol sensor of mesoporous Fe-doped NiO nanowires

NASA Astrophysics Data System (ADS)

Li, X. Q.; Wei, J. Q.; Xu, J. C.; Jin, H. X.; Jin, D. F.; Peng, X. L.; Hong, B.; Li, J.; Yang, Y. T.; Ge, H. L.; Wang, Xinqing

2017-12-01

In this paper, nickel oxides (NiO) and iron (Fe)-doped NiO nanowires (NWs) with the various doping content (from 1 to 9 at%) were synthesized by using SBA-15 templates with the nanocasting method. All samples were synthesized in the same conditions and exhibited the same mesoporous-structures, uniform diameter, and defects. Mesoporous-structures with high surface area created more active sites for the adsorption of oxygen on the surface of all samples, resulting in the smaller surface resistance in air. The impurity energy levels from the donor Fe-doping provided electrons to neutralize the holes of p-type Fe-doped NiO NWs, which greatly enhanced the total resistance. The comparative gas-sensing study between NiO NWs and Fe-doped NiO NWs indicated that the high-valence donor Fe-doping obviously improved the ethanol sensitivity and selectivity for Fe-doped NiO NWs. And Ni0.94Fe0.06O1.03 NWs sensor presented the highest sensitivity of 14.30 toward ethanol gas at 320 °C for the high-valence metal-doping.

The role of Nb in intensity increase of Er ion upconversion luminescence in zirconia

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smits, K., E-mail: smits@cfi.lu.lv; Sarakovskis, A.; Grigorjeva, L.

2014-06-07

It is found that Nb co-doping increases the luminescence and upconversion luminescence intensity in rare earth doped zirconia. Er and Yb-doped nanocrystalline samples with or without Nb co-doping were prepared by sol-gel method and thermally annealed to check for the impact of phase transition on luminescence properties. Phase composition and grain sizes were examined by X-ray diffraction; the morphology was checked by scanning- and high-resolution transmission electron microscopes. Both steady-state and time-resolved luminescence were studied. Comparison of samples with different oxygen vacancy concentrations and different Nb concentrations confirmed the known assumption that oxygen vacancies are the main agents for tetragonalmore » or cubic phase stabilization. The oxygen vacancies quench the upconversion luminescence; however, they also prevent agglomeration of rare-earth ions and/or displacement of rare-earth ions to grain surfaces. It is found that co-doping with Nb ions significantly (>20 times) increases upconversion luminescence intensity. Hence, ZrO{sub 2}:Er:Yb:Nb nanocrystals may show promise for upconversion applications.« less

Study of energy transfer and spectral downshifting in Ce, RE (RE = Nd and Yb) co-doped lanthanum phosphate

NASA Astrophysics Data System (ADS)

Sawala, N. S.; Omanwar, S. K.

2017-03-01

The phosphors LaPO4 (Lanthanum phosphate) doped with Ce(III)/Ce3+ and co-doped with Ce3+-Nd3+ and Ce3+-Yb3+ were effectively synthesized by conventional solid state reaction method. The prepared samples were characterized by powder X-ray diffraction (XRD) and surface morphology was studied by scanning electronic microscope (SEM). The photoluminescence (PL) properties were studied by spectrophotometers in near infrared (NIR) and ultraviolet visible (UV-VIS) region. Additionally the luminescence time decay curves of samples were investigated to confirm energy transfer (ET) process. The Ce3+-Nd3+ ion co-doped LaPO4 phosphors can convert a photon of UV region (278 nm) into photons of NIR region (1058 nm). While Ce3+-Yb3+ ion doped LaPO4 phosphors convert photons of UV region (278 nm) into photons of NIR region (979 nm). The Ce3+ ion acts like sensitizer and Nd3+/Yb3+ ions act as activators. Both kinds of emissions are suitable for improving spectral response of solar cells.

Analytical recursive method to ascertain multisite entanglement in doped quantum spin ladders

NASA Astrophysics Data System (ADS)

Roy, Sudipto Singha; Dhar, Himadri Shekhar; Rakshit, Debraj; SenDe, Aditi; Sen, Ujjwal

2017-08-01

We formulate an analytical recursive method to generate the wave function of doped short-range resonating valence bond (RVB) states as a tool to efficiently estimate multisite entanglement as well as other physical quantities in doped quantum spin ladders. We prove that doped RVB ladder states are always genuine multipartite entangled. Importantly, our results show that within specific doping concentration and model parameter regimes, the doped RVB state essentially characterizes the trends of genuine multiparty entanglement in the exact ground states of the Hubbard model with large on-site interactions, in the limit that yields the t -J Hamiltonian.

Determination of bulk and surface superconducting properties of N 2-doped cold worked, heat treated and electro-polished SRF grade niobium

DOE PAGES

Chetri, Santosh; Larbalestier, David C.; Lee, Peter J.; ...

2015-12-01

In this study, nitrogen-doped cavities show significant performance improvement in the medium accelerating field regime due to a lowered RF surface resistivity. However, the mechanism of enhancement has not been clearly explained. Our experiments explore how N 2-doping influences Nb bulk and surface superconducting properties, and compare the N 2-doped properties with those obtained previously with conventionally treated samples. High purity Nb-rod was mechanically deformed and post treated based on a typical SRF cavity treatment recipe. The onset of flux penetration at H c1, and the upper and the surface critical fields, H c2 and H c3, were characterized bymore » magnetic hysteresis and AC susceptibility techniques. The surface depth profile responsible for superconductivity was examined by changing AC amplitude in AC susceptibility, and the microstructure was directly observed with EBSD-OIM. We are also investigating surface chemistry for detailed composition using XPS. We have found that N 2-doping at 800 °C significantly reduces the H c3/H c2 ratio towards the ideal value of ~1.7, and conclude that AC susceptibility is capable of following changes to the surface properties induced by N 2-doping.« less

Defect induced structural inhomogeneity, ultraviolet light emission and near-band-edge photoluminescence broadening in degenerate In 2 O 3 nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mukherjee, Souvik; Sarkar, Ketaki; Wiederrecht, Gary P.

We demonstrate here defect induced changes on the morphology and surface properties of indium oxide (In2O3) nanowires and further study their effects on the near-band-edge (NBE) emission, thereby showing the significant influence of surface states on In2O3 nanostructure based device characteristics for potential optoelectronic applications. In2O3 nanowires with cubic crystal structure (c-In2O3) were synthesized via carbothermal reduction technique using a gold-catalyst-assisted vapor–liquid–solid method. Onset of strong optical absorption could be observed at energies greater than 3.5 eV consistent with highly n-type characteristics due to unintentional doping from oxygen vacancy (VO) defects as confirmed using Raman spectroscopy. A combination of highmore » resolution transmission electron microscopy, x-ray photoelectron spectroscopy and valence band analysis on the nanowire morphology and stoichiometry reveals presence of high-density of VO defects on the surface of the nanowires. As a result, chemisorbed oxygen species can be observed leading to upward band bending at the surface which corresponds to a smaller valence band offset of 2.15 eV. Temperature dependent photoluminescence (PL) spectroscopy was used to study the nature of the defect states and the influence of the surface states on the electronic band structure and NBE emission has been discussed. Our data reveals significant broadening of the NBE PL peak consistent with impurity band broadening leading to band-tailing effect from heavy doping.« less

Defect induced structural inhomogeneity, ultraviolet light emission and near-band-edge photoluminescence broadening in degenerate In2O3 nanowires.

PubMed

Mukherjee, Souvik; Sarkar, Ketaki; Wiederrecht, Gary P; Schaller, Richard D; Gosztola, David J; Stroscio, Michael A; Dutta, Mitra

2018-04-27

We demonstrate here defect induced changes on the morphology and surface properties of indium oxide (In 2 O 3 ) nanowires and further study their effects on the near-band-edge (NBE) emission, thereby showing the significant influence of surface states on In 2 O 3 nanostructure based device characteristics for potential optoelectronic applications. In 2 O 3 nanowires with cubic crystal structure (c-In 2 O 3 ) were synthesized via carbothermal reduction technique using a gold-catalyst-assisted vapor-liquid-solid method. Onset of strong optical absorption could be observed at energies greater than 3.5 eV consistent with highly n-type characteristics due to unintentional doping from oxygen vacancy [Formula: see text] defects as confirmed using Raman spectroscopy. A combination of high resolution transmission electron microscopy, x-ray photoelectron spectroscopy and valence band analysis on the nanowire morphology and stoichiometry reveals presence of high-density of [Formula: see text] defects on the surface of the nanowires. As a result, chemisorbed oxygen species can be observed leading to upward band bending at the surface which corresponds to a smaller valence band offset of 2.15 eV. Temperature dependent photoluminescence (PL) spectroscopy was used to study the nature of the defect states and the influence of the surface states on the electronic band structure and NBE emission has been discussed. Our data reveals significant broadening of the NBE PL peak consistent with impurity band broadening leading to band-tailing effect from heavy doping.

Surface photovoltage in exciton absorption range in CdS

NASA Technical Reports Server (NTRS)

Morawski, A.; Banisch, R.; Lagowski, J.

1977-01-01

The high resolution, intrinsic spectra of surface photovoltage are reported for semiconducting n-type CdS single crystals. At reduced temperatures (120-160 K) the spectra exhibit three sharp maxima due to A, B and C free exciton transitions. Energy positions of these lines and valence band parameters (spin-orbit and crystal field splittings) estimated from surface photovoltage are in good agreement with values obtained by other methods. The excitonic transitions are very sensitive to surface treatment, i.e. polishing, etching, background illumination and surface doping. The mechanism of direct interaction of free excitons with surface states is proposed to explain exciton lines in surface photovoltage.

Direct observation of a surface resonance state and surface band inversion control in black phosphorus

NASA Astrophysics Data System (ADS)

Ehlen, N.; Sanna, A.; Senkovskiy, B. V.; Petaccia, L.; Fedorov, A. V.; Profeta, G.; Grüneis, A.

2018-01-01

We report a Cs-doping-induced band inversion and the direct observation of a surface resonance state with an elliptical Fermi surface in black phosphorus (BP) using angle-resolved photoemission spectroscopy. By selectively inducing a higher electron concentration (1.7 ×1014cm-2 ) in the topmost layer, the changes in the Coulomb potential are sufficiently large to cause surface band inversion between the parabolic valence band of BP and a parabolic surface state around the Γ point of the BP Brillouin zone. Tight-binding calculations reveal that band gap openings at the crossing points in the two high-symmetry directions of the Brillouin zone require out-of-plane hopping and breaking of the glide mirror symmetry. Ab initio calculations are in very good agreement with the experiment if a stacking fault on the BP surface is taken into account. The demonstrated level of control over the band structure suggests the potential application of few-layer phosphorene in topological field-effect transistors.

NiO nanoparticles anchored on P-doped α-Fe2O3 nanoarrays: an efficient hole extraction p-n heterojunction photoanode for water oxidation.

PubMed

Li, Feng; Li, Jing; Zhang, Jie; Gao, Lili; Long, Xuefeng; Hu, Yiping; Li, Shuwen; Jin, Jun; Ma, Jiantai

2018-05-16

The photoelectrochemical (PEC) water splitting efficiency of hematite-based photoanode is still far from the theoretical value due to its poor surface reaction kinetics and high density of surface trapping states. To solve these drawbacks, a photoanode consisting of NiO nanoparticles anchored on a gradient P-doped α-Fe2O3 nanorod (NR) array (NiO/P-α-Fe2O3) was fabricated to achieve optimal light absorption and charge separation, and rapid surface reaction kinetic. Specifically, the photoanode with the NR arrays structure allowed high mass transport rate to be achieved while the P-doping effectively decreased surface trapping sites and improved the electrical conductivity of α-Fe2O3. Furthermore, the p-n junction formed between the NiO and P-α-Fe2O3 can further improve the PEC performance due to the efficient hole extraction property and water oxidization catalytic activity of NiO. Consequently, the NiO/P-α-Fe2O3 NR photoanode produced a high photocurrent density of 2.08 mA cm-2 at 1.23V vs. RHE and a 110 mV cathodic shift of the onset potential. This rational design of structure offers a new perspective in exploring high performance PEC photoanodes. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nonlocal Coulomb correlations in pure and electron-doped Sr2IrO4 : Spectral functions, Fermi surface, and pseudo-gap-like spectral weight distributions from oriented cluster dynamical mean-field theory

NASA Astrophysics Data System (ADS)

Martins, Cyril; Lenz, Benjamin; Perfetti, Luca; Brouet, Veronique; Bertran, François; Biermann, Silke

2018-03-01

We address the role of nonlocal Coulomb correlations and short-range magnetic fluctuations in the high-temperature phase of Sr2IrO4 within state-of-the-art spectroscopic and first-principles theoretical methods. Introducing an "oriented-cluster dynamical mean-field scheme", we compute momentum-resolved spectral functions, which we find to be in excellent agreement with angle-resolved photoemission spectra. We show that while short-range antiferromagnetic fluctuations are crucial to accounting for the electronic properties of Sr2IrO4 even in the high-temperature paramagnetic phase, long-range magnetic order is not a necessary ingredient of the insulating state. Upon doping, an exotic metallic state is generated, exhibiting cuprate-like pseudo-gap spectral properties, for which we propose a surprisingly simple theoretical mechanism.

Visible light absorbance enhanced by nitrogen embedded in the surface layer of Mn-doped sodium niobate crystals, detected by ultra violet - visible spectroscopy, x-ray photoelectron spectroscopy, and electric conductivity tests

DOE Office of Scientific and Technical Information (OSTI.GOV)

Molak, A., E-mail: andrzej.molak@us.edu.pl; Pilch, M.

2016-05-28

Sodium niobate crystals doped with manganese ions, Na(NbMn)O{sub 3}, were annealed in a nitrogen N{sub 2} flow at 600, 670, and 930 K. It was verified that simultaneous doping with Mn ions and annealing in nitrogen enhanced the photocatalytic features of sodium niobate. The transmission in the ultraviolet-visible range was measured at room temperature. The absorbance edge is in the range from 3.4 to 2.3 eV. The optical band gap E{sub gap} = 1.2–1.3 eV was evaluated using the Tauc relation. Crystals annealed at 670 K and 930 K exhibited an additional shift of the absorption edge of ∼20–40 nm toward longer wavelengths. The optical energy gap narrowedmore » as a result of the superimposed effect of Mn and N co-doping. The x-ray photoelectron spectroscopy test showed that N ions incorporated into the surface layer. The valence band consisted of O 2p states hybridized with Nb 4d, Mn 3d, and N 2s states. The disorder detected in the surroundings of Nb and O ions decreased due to annealing. The binding energy of oxygen ions situated within the surface layer was E{sub B} ≈ 531 eV. The other contributions were assigned to molecular contamination. The contribution centered at 535.5 eV vanished after annealing at 600 K and 670 K. The contribution centered at 534 eV vanished after annealing at 930 K. The N{sub 2} annealing partly removed carbonates from the surfaces of the samples. In the 480–950 K range, the electric conductivity activation energy, E{sub a} = 0.7–1.2 eV, was comparable with the optical E{sub gap}. The electric permittivity showed dispersion in the 0.1–800 kHz range that corresponds to the occurrence of defects.« less

Functionalization of SiO2 Surfaces for Si Monolayer Doping with Minimal Carbon Contamination.

PubMed

van Druenen, Maart; Collins, Gillian; Glynn, Colm; O'Dwyer, Colm; Holmes, Justin D

2018-01-17

Monolayer doping (MLD) involves the functionalization of semiconductor surfaces followed by an annealing step to diffuse the dopant into the substrate. We report an alternative doping method, oxide-MLD, where ultrathin SiO 2 overlayers are functionalized with phosphonic acids for doping Si. Similar peak carrier concentrations were achieved when compared with hydrosilylated surfaces (∼2 × 10 20 atoms/cm 3 ). Oxide-MLD offers several advantages over conventional MLD, such as ease of sample processing, superior ambient stability, and minimal carbon contamination. The incorporation of an oxide layer minimizes carbon contamination by facilitating attachment of carbon-free precursors or by impeding carbon diffusion. The oxide-MLD strategy allows selection of many inexpensive precursors and therefore allows application to both p- and n-doping. The phosphonic acid-functionalized SiO 2 surfaces were investigated using X-ray photoelectron spectroscopy and attenuated total reflectance Fourier transform infrared spectroscopy, whereas doping was assessed using electrochemical capacitance voltage and Hall measurements.

Surface passivation of n-type doped black silicon by atomic-layer-deposited SiO2/Al2O3 stacks

NASA Astrophysics Data System (ADS)

van de Loo, B. W. H.; Ingenito, A.; Verheijen, M. A.; Isabella, O.; Zeman, M.; Kessels, W. M. M.

2017-06-01

Black silicon (b-Si) nanotextures can significantly enhance the light absorption of crystalline silicon solar cells. Nevertheless, for a successful application of b-Si textures in industrially relevant solar cell architectures, it is imperative that charge-carrier recombination at particularly highly n-type doped black Si surfaces is further suppressed. In this work, this issue is addressed through systematically studying lowly and highly doped b-Si surfaces, which are passivated by atomic-layer-deposited Al2O3 films or SiO2/Al2O3 stacks. In lowly doped b-Si textures, a very low surface recombination prefactor of 16 fA/cm2 was found after surface passivation by Al2O3. The excellent passivation was achieved after a dedicated wet-chemical treatment prior to surface passivation, which removed structural defects which resided below the b-Si surface. On highly n-type doped b-Si, the SiO2/Al2O3 stacks result in a considerable improvement in surface passivation compared to the Al2O3 single layers. The atomic-layer-deposited SiO2/Al2O3 stacks therefore provide a low-temperature, industrially viable passivation method, enabling the application of highly n- type doped b-Si nanotextures in industrial silicon solar cells.

Dark current reduction of Ge photodetector by GeO₂ surface passivation and gas-phase doping.

PubMed

Takenaka, Mitsuru; Morii, Kiyohito; Sugiyama, Masakazu; Nakano, Yoshiaki; Takagi, Shinichi

2012-04-09

We have investigated the dark current of a germanium (Ge) photodetector (PD) with a GeO₂ surface passivation layer and a gas-phase-doped n+/p junction. The gas-phase-doped PN diodes exhibited a dark current of approximately two orders of magnitude lower than that of the diodes formed by a conventional ion implantation process, indicating that gas-phase doping is suitable for low-damage PN junction formation. The bulk leakage (Jbulk) and surface leakage (Jsurf) components of the dark current were also investigated. We have found that GeO₂ surface passivation can effectively suppress the dark current of a Ge PD in conjunction with gas-phase doping, and we have obtained extremely low values of Jbulk of 0.032 mA/cm² and Jsurf of 0.27 μA/cm.

Fermiology of the strongly spin-orbit coupled superconductor Sn(1-x)In(x)Te: implications for topological superconductivity.

PubMed

Sato, T; Tanaka, Y; Nakayama, K; Souma, S; Takahashi, T; Sasaki, S; Ren, Z; Taskin, A A; Segawa, Kouji; Ando, Yoichi

2013-05-17

We have performed angle-resolved photoemission spectroscopy on the strongly spin-orbit coupled low-carrier density superconductor Sn(1-x)In(x)Te (x = 0.045) to elucidate the electronic states relevant to the possible occurrence of topological superconductivity, as recently reported for this compound based on point-contact spectroscopy. The obtained energy-band structure reveals a small holelike Fermi surface centered at the L point of the bulk Brillouin zone, together with a signature of a topological surface state, indicating that this material is a doped topological crystalline insulator characterized by band inversion and mirror symmetry. A comparison of the electronic states with a band-noninverted superconductor possessing a similar Fermi surface structure, Pb(1-x)Tl(x)Te, suggests that the anomalous behavior in the superconducting state of Sn(1-x)In(x)Te is related to the peculiar orbital characteristics of the bulk valence band and/or the presence of a topological surface state.

Rapid solid-state metathesis route to transition-metal doped titanias

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coleman, Nathaniel; Perera, Sujith; Gillan, Edward G., E-mail: edward-gillan@uiowa.edu

2015-12-15

Rapid solid-state metathesis (SSM) reactions are often short-lived highly exothermic reactions that yield a molten alkali halide salt that aids in product growth and crystallization. SSM reactions may also produce kinetically stabilized structures due to the short (seconds) reaction times. This report describes the investigation of rapid SSM reactions in the synthesis of transition-metal doped titanias (M–TiO{sub 2}). The dopant targeted compositions were ten mol percent and based on elemental analysis, many of the M–TiO{sub 2} samples were close to this targeted level. Based on surface analysis, some samples showed large enrichment in surface dopant content, particularly chromium and manganesemore » doped samples. Due to the highly exothermic nature of these reactions, rutile structured TiO{sub 2} was observed in all cases. The M–TiO{sub 2} samples are visible colored and show magnetic and optical properties consistent with the dopant in an oxide environment. UV and visible photocatalytic experiments with these visibly colored rutile M–TiO{sub 2} powders showed that many of them are strongly absorbent for methylene blue dye and degrade the dye under both UV and visible light illumination. This work may open up SSM reactions as an alternate non-thermodynamic reaction strategy for dopant incorporation into a wide range of oxide and non-oxides.« less

Doped luminescent materials and particle discrimination using same

DOEpatents

Doty, F. Patrick; Allendorf, Mark D; Feng, Patrick L

2014-10-07

Doped luminescent materials are provided for converting excited triplet states to radiative hybrid states. The doped materials may be used to conduct pulse shape discrimination (PSD) using luminescence generated by harvested excited triplet states. The doped materials may also be used to detect particles using spectral shape discrimination (SSD).

Charge Carriers Modulate the Bonding of Semiconductor Nanoparticle Dopants As Revealed by Time-Resolved X-ray Spectroscopy

DOE PAGES

Hassan, Asra; Zhang, Xiaoyi; Liu, Xiaohan; ...

2017-08-28

Understanding the electronic structure of doped semiconductors is essential to realize advancements in electronics and in the rational design of nanoscale devices. Here, we report the results of time-resolved X-ray absorption studies on copper-doped cadmium sulfide nanoparticles that provide an explicit description of the electronic dynamics of the dopants. The interaction of a dopant ion and an excess charge carrier is unambiguously observed via monitoring the oxidation state. The experimental data combined with DFT calculations demonstrate that dopant bonding to the host matrix is modulated by its interaction with charge carriers. Additionally, the transient photoluminescence and the kinetics of dopantmore » oxidation reveal the presence of two types of surface-bound ions that create mid-gap states.« less

Quantum corrections crossover and ferromagnetism in magnetic topological insulators.

PubMed

Bao, Lihong; Wang, Weiyi; Meyer, Nicholas; Liu, Yanwen; Zhang, Cheng; Wang, Kai; Ai, Ping; Xiu, Faxian

2013-01-01

Revelation of emerging exotic states of topological insulators (TIs) for future quantum computing applications relies on breaking time-reversal symmetry and opening a surface energy gap. Here, we report on the transport response of Bi2Te3 TI thin films in the presence of varying Cr dopants. By tracking the magnetoconductance (MC) in a low doping regime we observed a progressive crossover from weak antilocalization (WAL) to weak localization (WL) as the Cr concentration increases. In a high doping regime, however, increasing Cr concentration yields a monotonically enhanced anomalous Hall effect (AHE) accompanied by an increasing carrier density. Our results demonstrate a possibility of manipulating bulk ferromagnetism and quantum transport in magnetic TI, thus providing an alternative way for experimentally realizing exotic quantum states required by spintronic applications.

Electronic structure Fermi liquid theory of high Tc superconductors: Comparison of predictions with experiments

NASA Technical Reports Server (NTRS)

Yu, Jaejun; Freeman, A. J.

1991-01-01

Predictions of local density functional (LDF) calculations of the electronic structure and transport properties of high T(sub c) superconductors are presented. As evidenced by the excellent agreement with both photoemission and positron annihilation experiments, a Fermi liquid nature of the 'normal' state of the high T(sub c) superconductors become clear for the metallic phase of these oxides. In addition, LDF predictions on the normal state transport properties are qualitatively in agreement with experiments on single crystals. It is emphasized that the signs of the Hall coefficients for the high T(sub c) superconductors are not consistent with the types of dopants (e.g., electron-doped or hole-doped) but are determined by the topology of the Fermi surfaces obtained from the LDF calculations.

Charge Carriers Modulate the Bonding of Semiconductor Nanoparticle Dopants As Revealed by Time-Resolved X-ray Spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hassan, Asra; Zhang, Xiaoyi; Liu, Xiaohan

Understanding the electronic structure of doped semiconductors is essential to realize advancements in electronics and in the rational design of nanoscale devices. Here, we report the results of time-resolved X-ray absorption studies on copper-doped cadmium sulfide nanoparticles that provide an explicit description of the electronic dynamics of the dopants. The interaction of a dopant ion and an excess charge carrier is unambiguously observed via monitoring the oxidation state. The experimental data combined with DFT calculations demonstrate that dopant bonding to the host matrix is modulated by its interaction with charge carriers. Additionally, the transient photoluminescence and the kinetics of dopantmore » oxidation reveal the presence of two types of surface-bound ions that create mid-gap states.« less

Dynamic modulation of electronic properties of graphene by localized carbon doping using focused electron beam induced deposition

NASA Astrophysics Data System (ADS)

Kim, S.; Russell, M.; Henry, M.; Kim, S. S.; Naik, R. R.; Voevodin, A. A.; Jang, S. S.; Tsukruk, V. V.; Fedorov, A. G.

2015-09-01

We report on the first demonstration of controllable carbon doping of graphene to engineer local electronic properties of a graphene conduction channel using focused electron beam induced deposition (FEBID). Electrical measurements indicate that an ``n-p-n'' junction on graphene conduction channel is formed by partial carbon deposition near the source and drain metal contacts by low energy (<50 eV) secondary electrons due to inelastic collisions of long range backscattered primary electrons generated from a low dose of high energy (25 keV) electron beam (1 × 1018 e- per cm2). Detailed AFM imaging provides direct evidence of the new mechanism responsible for dynamic evolution of the locally varying graphene doping. The FEBID carbon atoms, which are physisorbed and weakly bound to graphene, diffuse towards the middle of graphene conduction channel due to their surface chemical potential gradient, resulting in negative shift of Dirac voltage. Increasing a primary electron dose to 1 × 1019 e- per cm2 results in a significant increase of carbon deposition, such that it covers the entire graphene conduction channel at high surface density, leading to n-doping of graphene channel. Collectively, these findings establish a unique capability of FEBID technique to dynamically modulate the doping state of graphene, thus enabling a new route to resist-free, ``direct-write'' functional patterning of graphene-based electronic devices with potential for on-demand re-configurability.We report on the first demonstration of controllable carbon doping of graphene to engineer local electronic properties of a graphene conduction channel using focused electron beam induced deposition (FEBID). Electrical measurements indicate that an ``n-p-n'' junction on graphene conduction channel is formed by partial carbon deposition near the source and drain metal contacts by low energy (<50 eV) secondary electrons due to inelastic collisions of long range backscattered primary electrons generated from a low dose of high energy (25 keV) electron beam (1 × 1018 e- per cm2). Detailed AFM imaging provides direct evidence of the new mechanism responsible for dynamic evolution of the locally varying graphene doping. The FEBID carbon atoms, which are physisorbed and weakly bound to graphene, diffuse towards the middle of graphene conduction channel due to their surface chemical potential gradient, resulting in negative shift of Dirac voltage. Increasing a primary electron dose to 1 × 1019 e- per cm2 results in a significant increase of carbon deposition, such that it covers the entire graphene conduction channel at high surface density, leading to n-doping of graphene channel. Collectively, these findings establish a unique capability of FEBID technique to dynamically modulate the doping state of graphene, thus enabling a new route to resist-free, ``direct-write'' functional patterning of graphene-based electronic devices with potential for on-demand re-configurability. Electronic supplementary information (ESI) available: Optimization of a PMMA-mediated wet transfer method of graphene, transfer characteristics of all the channels, raw data of drain-source current measured by sweeping a backgate voltage and an AFM topography image and cross-sectional profiles of Fig. 4 and the corresponding electrical measurement along with an estimation of carbon diffusion coefficient. See DOI: 10.1039/c5nr04063a

Evidence for topologically protected surface states and a superconducting phase in [Tl4](Tl(1-x)Sn(x))Te3 using photoemission, specific heat, and magnetization measurements, and density functional theory.

PubMed

Arpino, K E; Wallace, D C; Nie, Y F; Birol, T; King, P D C; Chatterjee, S; Uchida, M; Koohpayeh, S M; Wen, J-J; Page, K; Fennie, C J; Shen, K M; McQueen, T M

2014-01-10

We report the discovery of surface states in the perovskite superconductor [Tl4]TlTe3 (Tl5Te3) and its nonsuperconducting tin-doped derivative [Tl4](Tl0.4Sn0.6)Te3 as observed by angle-resolved photoemission spectroscopy. Density functional theory calculations predict that the surface states are protected by a Z2 topology of the bulk band structure. Specific heat and magnetization measurements show that Tl5Te3 has a superconducting volume fraction in excess of 95%. Thus Tl5Te3 is an ideal material in which to study the interplay of bulk band topology and superconductivity.

Reduction in the Band Gap of Manganese-Doped Zinc Oxide: Role of the Oxidation State

NASA Astrophysics Data System (ADS)

Sharma, Sonia; Ramesh, Pranith; Swaminathan, P.

2015-12-01

Manganese-doped zinc oxide powders were synthesized by solid state reaction of the respective oxides. The high-temperature conditions were chosen such that multiple valence states of manganese were doped in the host zinc oxide lattice. Structural characterization was carried out to confirm the doping and to find the maximum amount of manganese that can be incorporated. Diffuse reflectance spectroscopy was used to measure the optical band gap of the doped sample and the lowering with respect to pure ZnO was attributed to the presence of higher oxidation states of manganese. The presence of these oxidation states was confirmed using x-ray photoelectron spectroscopy. The study shows that a solid state reaction is a viable route for synthesizing doped metal oxides with desired optical properties.

Investigation of pentacene growth on SiO2 gate insulator after photolithography for nitrogen-doped LaB6 bottom-contact electrode formation

NASA Astrophysics Data System (ADS)

Maeda, Yasutaka; Hiroki, Mizuha; Ohmi, Shun-ichiro

2018-04-01

Nitrogen-doped (N-doped) LaB6 is a candidate material for the bottom-contact electrode of n-type organic field-effect transistors (OFETs). However, the formation of a N-doped LaB6 electrode affects the surface morphology of a pentacene film. In this study, the effects of surface treatments and a N-doped LaB6 interfacial layer (IL) were investigated to improve the pentacene film quality after N-doped LaB6 electrode patterning with diluted HNO3, followed by resist stripping with acetone and methanol. It was found that the sputtering damage during N-doped LaB6 deposition on a SiO2 gate insulator degraded the crystallinity of pentacene. The H2SO4 and H2O2 (SPM) and diluted HF treatments removed the damaged layer on the SiO2 gate insulator surface. Furthermore, the N-doped LaB6 IL improved the crystallinity of pentacene and realized dendritic grain growth. Owing to these surface treatments, the hole mobility improved from 2.8 × 10-3 to 0.11 cm2/(V·s), and a steep subthreshold swing of 78 mV/dec for the OFET with top-contact configuration was realized in air even after bottom-contact electrode patterning.

Nanostructured KTaTeO6 and Ag-doped KTaTeO6 Defect Pyrochlores: Promising Photocatalysts for Dye Degradation and Water Splitting

NASA Astrophysics Data System (ADS)

Venkataswamy, Perala; Sudhakar Reddy, CH.; Gundeboina, Ravi; Sadanandam, Gullapelli; Veldurthi, Naveen Kumar; Vithal, M.

2018-03-01

In this study, the nanostructured parent KTaTeO6 (KTTO) and Ag-doped KTaTeO6 (ATTO) catalysts with defect pyrochlore structure were prepared by solid-state and ion-exchange methods, respectively. The synthesized materials were characterized by various techniques to determine their chemical composition, morphology and microstructural features. The XRD studies show that both KTTO and ATTO have cubic structure (space group Fd3m) with high crystallinity. The doping of Ag altered the BET surface area of parent KTTO. The nano nature of the samples was studied by TEM images. A considerable red-shift in the absorption edge is observed for ATTO compared to KTTO. Incorporation of Ag+ in the KTTO lattice is clearly identified from EDX, elemental mapping and XPS results. Degradation of methyl violet and solar water splitting reactions were used to access the photocatalytic activity of KTTO and ATTO. The results obtained suggest that compared to KTTO, the ATTO showed higher photocatalytic activity in both cases. The favourable properties such as high surface area, more surface hydroxyl groups, stronger light absorption in visible region and narrower band gap energy were supposed to be the reasons for the high activity observed in ATTO.

Surface Morphology of Undoped and Doped ZnSe Films

NASA Technical Reports Server (NTRS)

George, T.; Hayes, M.; Chen, H.; Chattopadhyay, K.; Thomas E.; Morgan, S.; Burger, A.

1998-01-01

Rare-earth doped ions in polar II-VI semiconductors have recently played an important role in the optical properties of materials and devices. In this study, undoped ZnSe and erbium doped ZnSe films were grown by radio frequency (RF) magnetron sputtering method. Atomic Force Microscopy (AFM) was used together with optical microscopy and UV-Vis spectroscopy to characterize the films. Doped samples were found to have higher surface roughness and quite different surface morphology compared to that of undoped samples. The grown films generally show a relatively smooth and uniform surface indicating that they are of overall good quality. The impact of plasma etching on ZnSe:Er film examined under AFM is also discussed.

Stabilization of MgAl 2O 4 spinel surfaces via doping

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hasan, Md. M.; Dholabhai, Pratik P.; Castro, Ricardo H. R.

Here, the surface structure of complex oxides plays a vital role in processes such as sintering, thin film growth, and catalysis, as well as being a critical factor determining the stability of nanoparticles. We report atomistic calculations of the low-index stoichiometric magnesium aluminate spinel (MgAl 2O 4) surfaces, each with two different chemical terminations. High temperature annealing was used to explore the potential energy landscape and provide more stable surface structures. We find that the lowest energy surface is {100} while the highest energy surface is {111}. The surfaces were subsequently doped with three trivalent dopants (Y 3+, Gd 3+,more » La 3+) and one tetravalent dopant (Zr 4+) and both the surface segregation energies of the dopants and surface energies of the doped surface were determined. All of the dopants reduce the surface energy of spinel, though this reduction in energy depends on both the size and valence of the dopant. Dopants with larger ionic radius tend to segregate to the surface more strongly and reduce the surface energy to a greater extent. Furthermore, the ionic valence of the dopants seems to have a stronger influence on the segregation than does ionic size. For both undoped and doped spinel, the predicted crystal shape is dominated by {100} surfaces, but the relative fraction of the various surfaces changes with doping due to the unequal changes in energy, which has implications on equilibrium nanoparticle shapes and therefore on applications sensitive to surface properties.« less

Stabilization of MgAl2O4 spinel surfaces via doping

NASA Astrophysics Data System (ADS)

Hasan, Md. M.; Dholabhai, Pratik P.; Castro, Ricardo H. R.; Uberuaga, Blas P.

2016-07-01

Surface structure of complex oxides plays a vital role in processes such as sintering, thin film growth, and catalysis, as well as being a critical factor determining the stability of nanoparticles. Here, we report atomistic calculations of the low-index stoichiometric magnesium aluminate spinel (MgAl2O4) surfaces, each with two different chemical terminations. High temperature annealing was used to explore the potential energy landscape and provide more stable surface structures. We find that the lowest energy surface is {100} while the highest energy surface is {111}. The surfaces were subsequently doped with three trivalent dopants (Y3+, Gd3+, La3+) and one tetravalent dopant (Zr4+) and both the surface segregation energies of the dopants and surface energies of the doped surface were determined. All of the dopants reduce the surface energy of spinel, though this reduction in energy depends on both the size and valence of the dopant. Dopants with larger ionic radius tend to segregate to the surface more strongly and reduce the surface energy to a greater extent. Furthermore, the ionic valence of the dopants seems to have a stronger influence on the segregation than does ionic size. For both undoped and doped spinel, the predicted crystal shape is dominated by {100} surfaces, but the relative fraction of the various surfaces changes with doping due to the unequal changes in energy, which has implications on equilibrium nanoparticle shapes and therefore on applications sensitive to surface properties.

Stabilization of MgAl 2O 4 spinel surfaces via doping

DOE PAGES

Hasan, Md. M.; Dholabhai, Pratik P.; Castro, Ricardo H. R.; ...

2016-02-06

Here, the surface structure of complex oxides plays a vital role in processes such as sintering, thin film growth, and catalysis, as well as being a critical factor determining the stability of nanoparticles. We report atomistic calculations of the low-index stoichiometric magnesium aluminate spinel (MgAl 2O 4) surfaces, each with two different chemical terminations. High temperature annealing was used to explore the potential energy landscape and provide more stable surface structures. We find that the lowest energy surface is {100} while the highest energy surface is {111}. The surfaces were subsequently doped with three trivalent dopants (Y 3+, Gd 3+,more » La 3+) and one tetravalent dopant (Zr 4+) and both the surface segregation energies of the dopants and surface energies of the doped surface were determined. All of the dopants reduce the surface energy of spinel, though this reduction in energy depends on both the size and valence of the dopant. Dopants with larger ionic radius tend to segregate to the surface more strongly and reduce the surface energy to a greater extent. Furthermore, the ionic valence of the dopants seems to have a stronger influence on the segregation than does ionic size. For both undoped and doped spinel, the predicted crystal shape is dominated by {100} surfaces, but the relative fraction of the various surfaces changes with doping due to the unequal changes in energy, which has implications on equilibrium nanoparticle shapes and therefore on applications sensitive to surface properties.« less

Structures and stability of metal-doped Ge nM (n = 9, 10) clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qin, Wei; Lu, Wen-Cai; Xia, Lin-Hua

The lowest-energy structures of neutral and cationic Ge nM (n = 9, 10; M = Si, Li, Mg, Al, Fe, Mn, Pb, Au, Ag, Yb, Pm and Dy) clusters were studied by genetic algorithm (GA) and first-principles calculations. The calculation results show that doping of the metal atoms and Si into Ge 9 and Ge 10 clusters is energetically favorable. Most of the metal-doped Ge cluster structures can be viewed as adding or substituting metal atom on the surface of the corresponding ground-state Ge n clusters. However, the neutral and cationic FeGe 9,10,MnGe 9,10 and Ge 10Al are cage-like withmore » the metal atom encapsulated inside. Such cage-like transition metal doped Ge n clusters are shown to have higher adsorption energy and thermal stability. Our calculation results suggest that Ge 9,10Fe and Ge 9Si would be used as building blocks in cluster-assembled nanomaterials because of their high stabilities.« less

Carrier dynamics in silicon nanowires studied using optical-pump terahertz-probe spectroscopy

NASA Astrophysics Data System (ADS)

Beaudoin, Alexandre; Salem, Bassem; Baron, Thierry; Gentile, Pascal; Morris, Denis

2014-03-01

The advance of non-contact measurements involving pulsed terahertz radiation presents great interests for characterizing electrical properties of a large ensemble of nanowires. In this work, N-doped and undoped silicon nanowires (SiNWs) grown by chemical vapour deposition (CVD) on quartz substrate were characterized using optical-pump terahertz probe (OPTP) transmission experiments. Our results show that defects and ionized impurities introduced by N-doping the CVD-grown SiNWs tend to reduce the photoexcited carrier lifetime and degrade their conductivity properties. Capture mechanisms by the surface trap states play a key role on the photocarrier dynamics in theses small diameters' (~100 nm) SiNWs and the doping level is found to alter this dynamics. We propose convincing capture and recombination scenarios that explain our OPTP measurements. Fits of our photoconductivity data curves, from 0.5 to 2 THz, using a Drude-plasmon conductivity model allow determining photocarrier mobility values of 190 and 70 cm2/V .s, for the undoped and N-doped NWs samples, respectively.

Structures and stability of metal-doped Ge nM (n = 9, 10) clusters

DOE PAGES

Qin, Wei; Lu, Wen-Cai; Xia, Lin-Hua; ...

2015-06-26

The lowest-energy structures of neutral and cationic Ge nM (n = 9, 10; M = Si, Li, Mg, Al, Fe, Mn, Pb, Au, Ag, Yb, Pm and Dy) clusters were studied by genetic algorithm (GA) and first-principles calculations. The calculation results show that doping of the metal atoms and Si into Ge 9 and Ge 10 clusters is energetically favorable. Most of the metal-doped Ge cluster structures can be viewed as adding or substituting metal atom on the surface of the corresponding ground-state Ge n clusters. However, the neutral and cationic FeGe 9,10,MnGe 9,10 and Ge 10Al are cage-like withmore » the metal atom encapsulated inside. Such cage-like transition metal doped Ge n clusters are shown to have higher adsorption energy and thermal stability. Our calculation results suggest that Ge 9,10Fe and Ge 9Si would be used as building blocks in cluster-assembled nanomaterials because of their high stabilities.« less

Synthesis, characterization and tin/copper-nitrogen substitutional effect on photocatalytic activity of honeycomb ordered P2-Na2Ni2TeO6

NASA Astrophysics Data System (ADS)

Kadari, Ramaswamy; Velchuri, Radha; Sreenu, K.; Ravi, Gundeboina; Munirathnam, Nagegownivari R.; Vithal, Muga

2016-11-01

We have successfully prepared visible light active tin/copper-nitrogen co-doped honeycomb ordered P2-Na2Ni2TeO6 photocatalysts by solid state/ion exchange methods. Powder XRD, TG analysis, SEM, surface area, O-N-H analysis, ICP-OES, FT-IR and UV-DRS measurements are employed to characterize all the samples. All the doped compositions adopted hexagonal lattice with space group P63/mcm. The photocatalytic activity of all the samples was studied against the degradation of methyl violet (MV) and methylene blue (MB) under visible light irradiation. The variation of the photocatalytic activity due to the substitution of cation, anion and co-doping in Na2Ni2TeO6 is investigated. Co-doped samples have exhibited higher activity compared to rest of the materials. The role of reactive intermediate species in the photocatalytic degradation of dyes is also studied using appropriate scavengers.

Effect of potassium doping on electronic structure and thermoelectric properties of topological crystalline insulator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roychowdhury, Subhajit; Biswas, Kanishka, E-mail: kanishka@jncasr.ac.in; Sandhya Shenoy, U.

2016-05-09

Topological crystalline insulator (TCI), Pb{sub 0.6}Sn{sub 0.4}Te, exhibits metallic surface states protected by crystal mirror symmetry with negligibly small band gap. Enhancement of its thermoelectric performances needs tuning of its electronic structure particularly through engineering of its band gap. While physical perturbations tune the electronic structure of TCI by breaking of the crystal mirror symmetry, chemical means such as doping have been more attractive recently as they result in better thermoelectric performance in TCIs. Here, we demonstrate that K doping in TCI, Pb{sub 0.6}Sn{sub 0.4}Te, breaks the crystal mirror symmetry locally and widens electronic band gap, which is confirmed bymore » direct electronic absorption spectroscopy and electronic structure calculations. K doping in Pb{sub 0.6}Sn{sub 0.4}Te increases p-type carrier concentration and suppresses the bipolar conduction via widening a band gap, which collectively boosts the thermoelectric figure of merit (ZT) to 1 at 708 K.« less

Structures and stability of metal-doped GenM (n = 9, 10) clusters

NASA Astrophysics Data System (ADS)

Qin, Wei; Lu, Wen-Cai; Xia, Lin-Hua; Zhao, Li-Zhen; Zang, Qing-Jun; Wang, C. Z.; Ho, K. M.

2015-06-01

The lowest-energy structures of neutral and cationic GenM (n = 9, 10; M = Si, Li, Mg, Al, Fe, Mn, Pb, Au, Ag, Yb, Pm and Dy) clusters were studied by genetic algorithm (GA) and first-principles calculations. The calculation results show that doping of the metal atoms and Si into Ge9 and Ge10 clusters is energetically favorable. Most of the metal-doped Ge cluster structures can be viewed as adding or substituting metal atom on the surface of the corresponding ground-state Gen clusters. However, the neutral and cationic FeGe9,10,MnGe9,10 and Ge10Al are cage-like with the metal atom encapsulated inside. Such cage-like transition metal doped Gen clusters are shown to have higher adsorption energy and thermal stability. Our calculation results suggest that Ge9,10Fe and Ge9Si would be used as building blocks in cluster-assembled nanomaterials because of their high stabilities.

Angle-resolved photoemission spectroscopy studies of the Mott insulator to superconductor evolution in calcium-sodium-copper-chloride

NASA Astrophysics Data System (ADS)

Shen, Kyle Michael

The parent compounds of the high-temperature cuprate superconductors are antiferromagnetic Mott insulators. To explain the microscopic mechanism behind high-temperature superconductivity, it is first necessary to understand how the electronic states evolve from the parent Mott insulator into the superconducting compounds. This dissertation presents angle-resolved photoemission spectroscopy (ARPES) studies of one particular family of the cuprate superconductors, Ca 2-xNaxCuO 2Cl2, to investigate how the single-electron excitations develop throughout momentum space as the system is hole doped from the Mott insulator into a superconductor with a transition temperature of 22 K. These measurements indicate that, due to very strong electron-boson interactions, the quasiparticle residue, Z, approaches zero in the parent Mott insulator due to the formation of small lattice polarons. As a result, many fundamental quantities such as the chemical potential, quasiparticle excitations, and the Fermi surface evolve in manners wholly unexpected from conventional weakly-interacting theories. In addition, highly anisotropic interactions have been observed in momentum space where quasiparticle-like excitations persist to low doping levels along the nodal direction of the d-wave super-conducting gap, in contrast to the unusual excitations near the d-wave antinode. This anisotropy may reflect the propensity of the lightly doped cuprates towards forming a competing, charge-ordered state. These results provide a novel and logically consistent explanation of the hole doping evolution of the lineshape, spectral weight, chemical potential, quasiparticle dispersion, and Fermi surface as Ca2- xNaxCuO2Cl2 evolves from the parent Mott insulator into a high-temperature superconductor.

Strong compensation hinders the p-type doping of ZnO: a glance over surface defect levels

NASA Astrophysics Data System (ADS)

Huang, B.

2016-07-01

We propose a surface doping model of ZnO to elucidate the p-type doping and compensations in ZnO nanomaterials. With an N-dopant, the effects of N on the ZnO surface demonstrate a relatively shallow acceptor level in the band gap. As the dimension of the ZnO materials decreases, the quantum confinement effects will increase and render the charge transfer on surface to influence the shifting of Fermi level, by evidence of transition level changes of the N-dopant. We report that this can overwhelm the intrinsic p-type conductivity and transport of the ZnO bulk system. This may provide a possible route of using surface doping to modify the electronic transport and conductivity of ZnO nanomaterials.

Micelle-templated composite quantum dots for super-resolution imaging.

PubMed

Xu, Jianquan; Fan, Qirui; Mahajan, Kalpesh D; Ruan, Gang; Herrington, Andrew; Tehrani, Kayvan F; Kner, Peter; Winter, Jessica O

2014-05-16

Quantum dots (QDs) have tremendous potential for biomedical imaging, including super-resolution techniques that permit imaging below the diffraction limit. However, most QDs are produced via organic methods, and hence require surface treatment to render them water-soluble for biological applications. Previously, we reported a micelle-templating method that yields nanocomposites containing multiple core/shell ZnS-CdSe QDs within the same nanocarrier, increasing overall particle brightness and virtually eliminating QD blinking. Here, this technique is extended to the encapsulation of Mn-doped ZnSe QDs (Mn-ZnSe QDs), which have potential applications in super-resolution imaging as a result of the introduction of Mn(2+) dopant energy levels. The size, shape and fluorescence characteristics of these doped QD-micelles were compared to those of micelles created using core/shell ZnS-CdSe QDs (ZnS-CdSe QD-micelles). Additionally, the stability of both types of particles to photo-oxidation was investigated. Compared to commercial QDs, micelle-templated QDs demonstrated superior fluorescence intensity, higher signal-to-noise ratios, and greater stability against photo-oxidization,while reducing blinking. Additionally, the fluorescence of doped QD-micelles could be modulated from a bright 'on' state to a dark 'off' state, with a modulation depth of up to 76%, suggesting the potential of doped QD-micelles for applications in super-resolution imaging.

High Performance Photoluminescent Carbon Dots for In Vitro and In Vivo Bioimaging: Effect of Nitrogen Doping Ratios.

PubMed

Wang, Junqing; Zhang, Pengfei; Huang, Chao; Liu, Gang; Leung, Ken Cham-Fai; Wáng, Yì Xiáng J

2015-07-28

Photoluminescent carbon dots (CDs) have received ever-increasing attention in the application of optical bioimaging because of their low toxicity, tunable fluorescent properties, and ultracompact size. We report for the first time on enhanced photoluminescence (PL) performance influenced by structure effects among the various types of nitrogen doped (N-doped) PL CDs. These CDs were facilely synthesized from condensation carbonization of linear polyethylenic amine (PEA) analogues and citric acid (CA) of different ratios. Detailed structural and property studies demonstrated that either the structures or the molar ratio of PEAs altered the PL properties of the CDs. The content of conjugated π-domains with C═N in the carbon backbone was correlated with their PL Quantum Yield (QY) (up to 69%). The hybridization between the surface/molecule state and the carbon backbone synergistically affected the chemical/physical properties. Also, long-chain polyethylenic amine (PEA) molecule-doped CDs exhibit increasing photostability, but at the expense of PL efficiency, proving that the PL emission of high QY CDs arise not only from the sp(2)/sp(3) carbon core and surface passivation of CDs, but also from the molecular fluorophores integrated in the CDs. In vitro and in vivo bioimaging of these N-doped CDs showed strong photoluminescence signals. Good biocompatibility demonstrates their potential feasibility for bioimaging applications. In addition, the overall size profile of the as-prepared CDs is comparable to the average size of capillary pores in normal living tissues (∼5 nm). Our study provides valuable insights into the effects of the PEA doping ratios on photoluminescence efficiency, biocompatibility, cellular uptake, and optical bioimaging of CDs.

Specific heat and Nernst effect of electron-doped cuprate superconductors

NASA Astrophysics Data System (ADS)

Balci, Hamza

This thesis consists of two separate studies on Pr2- xCexCuO4 (PCCO), a member of the electron-doped high temperature cuprate superconductor family: specific heat and the Nernst effect. We measured the specific heat of PCCO single crystals in order to probe the symmetry of the superconducting order parameter, to study the effect of oxygen reduction (annealing) on bulk properties of the crystals, and to determine proper ties like the condensation energy and the thermodynamic critical field. The order parameter symmetry has been established to be d-wave in the hole-doped cuprates. Experiments performed on electron-doped cuprates show conflicting results. Different experiments suggest s-wave symmetry, d-wave symmetry, or a transition from d-wave to s-wave symmetry with increasing cerium doping. However, most of these experiments are surface sensitive experiments. Specific heat, as a bulk method of probing the gap symmetry is essential in order to convincingly determine the gap symmetry. Our data proposes a way to reconcile all these conflicting results regarding the gap symmetry. In addition, prior specific heat measurements attempting to determine thermodynamic properties like the condensation energy were not successful due to inefficient methods of data analysis or poor sample quality. With improvements on sample quality and data analysis, we reliably determined these properties. The second part of this thesis is a study of the Nernst effect in PCCO thin films with different cerium dopings. We probed the superconducting fluctuations, studied transport phenomena in the normal state, and accurately measured H c2 by using the Nernst effect. After the discovery of the anomalous Nernst effect in the normal state of the hole-doped cuprates, many alternative explanations have been proposed. Vortex-like excitations above Tc, superconducting fluctuations, AFM fluctuations, and preformed Cooper pairs are some of these proposals. The electron-doped cuprates, due to their significant differences from the hole-doped cuprates in terms of coherence length and the phase stiffness temperature (a measure of superfluid density) are the ideal materials to test these ideas. Our data on the electron-doped cuprates does not show any anomalous Nernst effect, and hence it supports the superconducting fluctuations picture among the various proposals.

High-resolution, hard x-ray photoemission investigation of BaFe2As2 : Moderate influence of the surface and evidence for a low degree of Fe3d-As4p hybridization of electronic states near the Fermi energy

NASA Astrophysics Data System (ADS)

de Jong, S.; Huang, Y.; Huisman, R.; Massee, F.; Thirupathaiah, S.; Gorgoi, M.; Schaefers, F.; Follath, R.; Goedkoop, J. B.; Golden, M. S.

2009-03-01

Photoemission data taken with hard x-ray radiation on cleaved single crystals of the barium parent compound of the MFe2As2 pnictide high-temperature superconductor family are presented. Making use of the increased bulk sensitivity upon hard x-ray excitation, and comparing the results to data taken at conventional vacuum ultraviolet photoemission excitation energies, it is shown that the BaFe2As2 cleavage surface provides an electrostatic environment that is slightly different to the bulk, most likely in the form of a modified Madelung potential. However, as the data argue against a different surface doping level, and the surface-related features in the spectra are by no means as dominating as seen in systems such as YBa2Cu3Ox , we can conclude that the itinerant, near- EF electronic states are almost unaffected by the existence of the cleavage surface. Furthermore, exploiting the strong changes in photoionization cross section between the Fe and As states across the wide photon energy range employed, it is shown that the degree of energetic overlap between the iron 3d and arsenic 4p valence bands is particularly small at the Fermi level, which can only mean a very low degree of hybridization between the Fe3d and As4p states near and at EF . Consequently, this means that the itinerancy of the charge carriers in this group of materials involves mainly the Fe3d-Fe3d overlap integrals with at best a minor role for the Fe3d-As4p hopping parameters and that the states which support superconductivity upon doping are essentially of Fe3d character.

The influence of p-doping on two-state lasing in InAs/InGaAs quantum dot lasers

NASA Astrophysics Data System (ADS)

Maximov, M. V.; Shernyakov, Yu M.; Zubov, F. I.; Zhukov, A. E.; Gordeev, N. Yu; Korenev, V. V.; Savelyev, A. V.; Livshits, D. A.

2013-10-01

Two-state lasing in devices based on undoped and p-type modulation-doped InAs/InGaAs quantum dots is studied for various cavity lengths and temperatures. Modulation doping of the active region strongly enhances the threshold current of two-state lasing, preserves ground-state lasing up to higher temperatures and increases ground-state output power. The impact of modulation doping is especially strong in short cavities.

Delta Doping High Purity CCDs and CMOS for LSST

NASA Technical Reports Server (NTRS)

Blacksberg, Jordana; Nikzad, Shouleh; Hoenk, Michael; Elliott, S. Tom; Bebek, Chris; Holland, Steve; Kolbe, Bill

2006-01-01

A viewgraph presentation describing delta doping high purity CCD's and CMOS for LSST is shown. The topics include: 1) Overview of JPL s versatile back-surface process for CCDs and CMOS; 2) Application to SNAP and ORION missions; 3) Delta doping as a back-surface electrode for fully depleted LBNL CCDs; 4) Delta doping high purity CCDs for SNAP and ORION; 5) JPL CMP thinning process development; and 6) Antireflection coating process development.

Anti-site defected MoS2 sheet-based single electron transistor as a gas sensor

NASA Astrophysics Data System (ADS)

Sharma, Archana; Husain, Mushahid; Srivastava, Anurag; Khan, Mohd. Shahid

2018-05-01

To prevent harmful and poisonous CO gas molecules, catalysts are needed for converting them into benign substances. Density functional theory (DFT) calculations have been used to study the adsorption of CO and CO2 gas molecules on the surface of MoS2 monolayer with Mo atom embedded at S-vacancy site (MoS). The strong interaction between Mo metal with pristine MoS2 sheet suggests its strong binding nature. Doping Mo into MoS2 sheet enhances CO and CO2 adsorption strength. The sensing response of MoS-doped MoS2 system to CO and CO2 gas molecules is obtained in the single electron transistor (SET) environment by varying bias voltage. Doping reduces charging energy of the device which results in fast switching of the device from OFF to ON state.

Near-infrared localized surface plasmon resonance of self-growing W-doped VO2 nanoparticles at room temperature

NASA Astrophysics Data System (ADS)

Nishikawa, Kazutaka; Kishida, Yoshihiro; Ito, Kota; Tamura, Shin-ichi; Takeda, Yasuhiko

2017-11-01

Nanoparticles (NPs) of vanadium dioxide (VO2) in the metal state exhibit localized surface plasmon resonance (LSPR) at 1200-1600 nm, which fills the gap between the absorption ranges of silicon and the LSPR of conventional transparent conductor NPs (ZnO:Al, In2O3:Sn, etc.). However, two issues of the lithographic process for NP formation and the metal-insulator transition temperature (69 °C) higher than room temperature have made it difficult to use VO2 NPs for applications such as energy conversion devices, near infrared (NIR) light detectors, and bio-therapy. In this study, we developed a self-growing process for tungsten (W)-doped VO2 NPs that are in the metal state at room temperature, using sputter deposition and post-lamp annealing. The changes in the LSPR peak wavelengths with the NP size were well controlled by changing the deposited film thickness and oxygen pressure during the post-annealing treatment. The presented results resolve the difficulties of using the metal-insulator transition material VO2 for practical NIR utilization.

STM studies of topological phase transition in (Bi,In)2Se3

NASA Astrophysics Data System (ADS)

Zhang, Wenhan; Wang, Xueyun; Cheong, Sang-Wook; Wu, Weida; Weida Wu Team; Sang-Wook Cheong Collaboration

Topological insulators (TI) are a class of materials with insulating bulk and metallic surface state, which is the result of band inversion induced by strong spin-orbit coupling (SOC). The transition from topological phase to non-topological phase is of great significance. In theory, topological phase transition is realized by tuning SOC strength. It is characterized by the process of gap closing and reopening. Experimentally it was observed in two systems: TlBi(S1-xSex)2 and (Bi1-xInx)2 Se3 where the transition is realized by varying isovalent elements doping concentration. However, none of the previous studies addressed the impact of disorder, which is inevitable in doped systems. Here, we present a systematic scanning tunneling microscopy/spectroscopy study on (Bi1-xInx)2 Se3 single crystals with different In concentrations across the transition. Our results reveal an electronic inhomogeneity due to the random distribution of In defects which locally suppress the topological surface states. Our study provides a new angle of understanding the topological transition in the presence of strong disorders. This work is supported by NSF DMR-1506618.

Structural and morphological study of Fe-doped Bi-based superconductor

NASA Astrophysics Data System (ADS)

Singh, Yadunath; Kumar, Rohitash

2018-05-01

In the present work, we report the study of iron-doped Bi-based superconductor sample with stoichiometric composition of Bi2Sr2Can-1(Cu1-x Fex)3O2n+4 where n=3 and x = 0.7. This sample was prepared by grinding the precursor oxides in the Ball mill for 6 hours continuous at the rate of 400 rpm for a proper mixing and to obtain the required grain size. Then the solid-state reaction method was used to prepare the sample. X-ray diffraction (XRD) and scanning electron microscopy (SEM) in combination with energy dispersive X-ray fluorescence analysis (EDX) were performed for determination of the crystal structure, surface morphology and trace the material elements of samples, respectively. The surface microscopy data were collected over a selected area of the surface of the material and a two-dimensional image generated that displays spatial variations in properties including chemical characterization and orientation of materials.

Nitrogen-doped Carbon Microfiber with Wrinkled Surface for High Performance Supercapacitors

NASA Astrophysics Data System (ADS)

Liu, Ruili; Pan, Lixia; Jiang, Jianzhong; Xi, Xin; Liu, Xiaoxue; Wu, Dongqing

2016-02-01

In this work, nitrogen-doped carbon microfiber (NCMF) is fabricated via a facile co-assembly of natural silk and graphene oxide (GO) and the following thermal treatment. The amphiphilic nature of GO endows NCMF a crumpled surface with a high surface area of 115 m2 g-1. As the binder-free electrode in electrical double-layer capacitors, NCMF shows an excellent capacitance of 196 F g-1 at scan rate of 5 mV s-1, which is almost four times higher than that of the pristine CMF from silk (55 F g-1). Additionally, the capacitance of NCMF can be kept around 92 F g-1 at a high scan rate of 300 mV s-1 even after 10000 cycles. More importantly, a high energy density (≈22.7 μW h cm-2) and power density (≈10.26 mW cm-2) are achieved by the all-solid-state supercapacitor based on NCMF.

Gold surface supported spherical liposome-gold nano-particle nano-composite for label free DNA sensing.

PubMed

Bhuvana, M; Narayanan, J Shankara; Dharuman, V; Teng, W; Hahn, J H; Jayakumar, K

2013-03-15

Immobilization of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) liposome-gold nano-particle (DOPE-AuNP) nano-composite covalently on 3-mercaptopropionic acid (MPA) on gold surface is demonstrated for the first time for electrochemical label free DNA sensing. Spherical nature of the DOPE on the MPA monolayer is confirmed by the appearance of sigmoidal voltammetric profile, characteristic behavior of linear diffusion, for the MPA-DOPE in presence of [Fe(CN)(6)](3-/4-) and [Ru(NH(3))(6)](3+) redox probes. The DOPE liposome vesicle fusion is prevented by electroless deposition of AuNP on the hydrophilic amine head groups of the DOPE. Immobilization of single stranded DNA (ssDNA) is made via simple gold-thiol linkage for DNA hybridization sensing in the presence of [Fe(CN)(6)](3-/4-). The sensor discriminates the hybridized (complementary target hybridized), un-hybridized (non-complementary target hybridized) and single base mismatch target hybridized surfaces sensitively and selectively without signal amplification. The lowest target DNA concentration detected is 0.1×10(-12)M. Cyclic voltammetry (CV), electrochemical impedance (EIS), differential pulse voltammetry (DPV) and quartz crystal microbalance (QCM) techniques are used for DNA sensing on DOPE-AuNP nano-composite. Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), Atomic Force Microscopy (AFM), Dynamic Light Scattering (DLS) and Ultraviolet-Visible (UV) spectroscopic techniques are used to understand the interactions between the DOPE, AuNP and ssDNA. The results indicate the presence of an intact and well defined spherical DOPE-AuNP nano-composite on the gold surface. The method could be applied for fabrication of the surface based liposome-AuNP-DNA composite for cell transfection studies at reduced reagents and costs. Copyright © 2012 Elsevier B.V. All rights reserved.

Disorder-driven metal-insulator-transition assisted by interband Coulomb repulsion in a surface transfer doped electron system

NASA Astrophysics Data System (ADS)

Francisco Sánchez-Royo, Juan

2012-12-01

The two-dimensional conducting properties of the Si(111) \\sqrt {3} \\times \\sqrt {3} surface doped by the charge surface transfer mechanism have been calculated in the frame of a semiclassical Drude-Boltzmann model considering donor scattering mechanisms. To perform these calculations, the required values of the carrier effective mass were extracted from reported angle-resolved photoemission results. The calculated doping dependence of the surface conductance reproduces experimental results reported and reveals an intricate metallization process driven by disorder and assisted by interband interactions. The system should behave as an insulator even at relatively low doping due to disorder. However, when doping increases, the system achieves to attenuate the inherent localization effects introduced by disorder and to conduct by percolation. The mechanism found by the system to conduct appears to be connected with the increasing of the carrier effective mass observed with doping, which seems to be caused by interband interactions involving the conducting band and deeper ones. This mass enhancement reduces the donor Bohr radius and, consequently, promotes the screening ability of the donor potential by the electron gas.

Fabrication of a nanometer thick nitrogen delta doped layer at the sub-surface region of (100) diamond

NASA Astrophysics Data System (ADS)

Chandran, Maneesh; Michaelson, Shaul; Saguy, Cecile; Hoffman, Alon

2016-11-01

In this letter, we report on the proof of a concept of an innovative delta doping technique to fabricate an ensemble of nitrogen vacancy centers at shallow depths in (100) diamond. A nitrogen delta doped layer with a concentration of ˜1.8 × 1020 cm-3 and a thickness of a few nanometers was produced using this method. Nitrogen delta doping was realized by producing a stable nitrogen terminated (N-terminated) diamond surface using the RF nitridation process and subsequently depositing a thin layer of diamond on the N-terminated diamond surface. The concentration of nitrogen on the N-terminated diamond surface and its stability upon exposure to chemical vapor deposition conditions are determined by x-ray photoelectron spectroscopy analysis. The SIMS profile exhibits a positive concentration gradient of 1.9 nm/decade and a negative gradient of 4.2 nm/decade. The proposed method offers a finer control on the thickness of the delta doped layer than the currently used ion implantation and delta doping techniques.

Surface photoelectric and visible light driven photocatalytic properties of zinc antimonate-based photocatalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Shaojun; Li, Guoqiang; Zhang, Yang

2013-03-15

Highlights: ► N-doped and pristine ZnSb{sub 2}O{sub 6} photocatalysts were synthesized by a facile method. ► N-doped ZnSb{sub 2}O{sub 6} shows a significant enhanced visible light photocatalytic activity. ► The N-doped ZnSb{sub 2}O{sub 6} shows the reduced surface photovoltage signals. - Abstract: The N-doped and pristine ZnSb{sub 2}O{sub 6} photocatalysts were synthesized by a facile method. The samples were characterized by X-ray diffraction (XRD), UV–vis spectroscopy, surface photovoltage spectroscopy and scanning electron microscopy. The photocatalytic activities of the prepared samples were evaluated from the degradation of rhodamine B (RhB) under full arc and visible light irradiation of Xe lamp. Themore » XRD and UV–vis results indicated that the N-doping did not change the crystal structure, but decrease the band gap in comparison with the pristine one. The N-doped ZnSb{sub 2}O{sub 6} shows the reduced surface photovoltage signals and the significantly enhanced photocatalytic activity under two irradiation conditions.« less

Superionic Conductivity of Sm3+, Pr3+, and Nd3+ Triple-Doped Ceria through Bulk and Surface Two-Step Doping Approach.

PubMed

Liu, Yanyan; Fan, Liangdong; Cai, Yixiao; Zhang, Wei; Wang, Baoyuan; Zhu, Bin

2017-07-19

Sufficiently high oxygen ion conductivity of electrolyte is critical for good performance of low-temperature solid oxide fuel cells (LT-SOFCs). Notably, material conductivity, reliability, and manufacturing cost are the major barriers hindering LT-SOFC commercialization. Generally, surface properties control the physical and chemical functionalities of materials. Hereby, we report a Sm 3+ , Pr 3+ , and Nd 3+ triple-doped ceria, exhibiting the highest ionic conductivity among reported doped-ceria oxides, 0.125 S cm -1 at 600 °C. It was designed using a two-step wet-chemical coprecipitation method to realize a desired doping for Sm 3+ at the bulk and Pr 3+ /Nd 3+ at surface domains (abbreviated as PNSDC). The redox couple Pr 3+ /Pr 4+ contributes to the extraordinary ionic conductivity. Moreover, the mechanism for ionic conductivity enhancement is demonstrated. The above findings reveal that a joint bulk and surface doping methodology for ceria is a feasible approach to develop new oxide-ion conductors with high impacts on advanced LT-SOFCs.

Methanol adsorption and dissociation on LaMnO 3 and Sr doped LaMnO 3 (001) surfaces

DOE PAGES

Beste, Ariana

2017-06-20

Using density functional theory, we investigate in this paper methanol adsorption and dissociation on the MnO 2- and LaO-terminated LaMnO 3 (001) surface as a function of Sr dopant enrichment in and near the surface. In response to bulk cleavage, we find electron depletion of the negatively charged MnO 2 surface layer that is enhanced by Sr doping in the subsurface. In contrast, we observe electron accumulation in the positively charged LaO surface layer that is reduced by Sr doping in the surface layer. Methanol adsorbs dissociatively on the LaO termination of the LaMnO 3 (001) surface. Methanol adsorption onmore » the LaO termination is strongly preferred over adsorption on the MnO 2 termination. While moderate doping has a small influence on methanol adsorption and dissociation, when 100% of La is replaced by Sr in the surface or subsurface, the adsorption preference of methanol is reversed. Finally, if the surface is highly dopant enriched, methanol favours dissociative adsorption on the MnO 2-terminated surface.« less

Methanol adsorption and dissociation on LaMnO 3 and Sr doped LaMnO 3 (001) surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beste, Ariana

Using density functional theory, we investigate in this paper methanol adsorption and dissociation on the MnO 2- and LaO-terminated LaMnO 3 (001) surface as a function of Sr dopant enrichment in and near the surface. In response to bulk cleavage, we find electron depletion of the negatively charged MnO 2 surface layer that is enhanced by Sr doping in the subsurface. In contrast, we observe electron accumulation in the positively charged LaO surface layer that is reduced by Sr doping in the surface layer. Methanol adsorbs dissociatively on the LaO termination of the LaMnO 3 (001) surface. Methanol adsorption onmore » the LaO termination is strongly preferred over adsorption on the MnO 2 termination. While moderate doping has a small influence on methanol adsorption and dissociation, when 100% of La is replaced by Sr in the surface or subsurface, the adsorption preference of methanol is reversed. Finally, if the surface is highly dopant enriched, methanol favours dissociative adsorption on the MnO 2-terminated surface.« less

Topological superconductivity in an ultrathin, magnetically-doped topological insulator proximity coupled to a conventional superconductor

NASA Astrophysics Data System (ADS)

Kim, Youngseok; Philip, Timothy M.; Park, Moon Jip; Gilbert, Matthew J.

2016-12-01

As a promising candidate system to realize topological superconductivity, the system of a 3D topological insulator (TI) grown on top of the s -wave superconductor has been extensively studied. To access the topological superconductivity experimentally, the 3D TI sample must be thin enough to allow for Cooper pair tunneling to the exposed surface of TI. The use of magnetically ordered dopants to break time-reversal symmetry may allow the surface of a TI to host Majorana fermion, which are believed to be a signature of topological superconductivity. In this work, we study a magnetically-doped thin film TI-superconductor hybrid system. Considering the proximity induced order parameter in thin film of TI, we analyze the gap closing points of the Hamiltonian and draw the phase diagram as a function of relevant parameters: the hybridization gap, Zeeman energy, and chemical potential of the TI system. Our findings provide a useful guide in choosing relevant parameters to facilitate the observation of topological superconductivity in thin film TI-superconductor hybrid systems. In addition, we further perform numerical analysis on a TI proximity coupled to an s -wave superconductor and find that, due to the spin-momentum locked nature of the surface states in TI, the induced s -wave order parameter of the surface states persists even at large magnitude of the Zeeman energy.

Valence band-edge engineering of nickel oxide nanoparticles via cobalt doping for application in p-type dye-sensitized solar cells.

PubMed

Natu, Gayatri; Hasin, Panitat; Huang, Zhongjie; Ji, Zhiqiang; He, Mingfu; Wu, Yiying

2012-11-01

We have systematically studied the effects of substitutional doping of p-type nanoparticulate NiO with cobalt ions. Thin films of pure and Co-doped NiO nanoparticles with nominal compositions Co(x)Ni(1-x)O(y) (0 ≤ x ≤ 0.1) were fabricated using sol-gel method. X-ray photoelectron spectroscopy revealed a surface enrichment of divalent cobalt ions in the Co(x)Ni(1-x)O(y) nanoparticles. Mott-Schottky analysis in aqueous solutions was used to determine the space charge capacitance values of the films against aqueous electrolytes, which yielded acceptor state densities (N(A)) and apparent flat-band potentials (E(fb)). Both N(A) and E(fb) values of the doped NiO were found to gradually increase with increasing amount of doping; thus the Fermi energy level of the charge carriers decreased with Co-doping. The photovoltage of p-DSCs constructed using the Co(x)Ni(1-x)O(y) films increased with increasing amount of cobalt, as expected from the trend in the E(fb). Co-doping increased both carrier lifetimes within the p-DSCs and the carrier transport times within the nanoparticulate semiconductor network. The nominal composition of Co₀.₀₆Ni₀.₉₄O(y) was found to be optimal for use in p-DSCs.

Effects on the magnetic and optical properties of Co-doped ZnO at different electronic states

NASA Astrophysics Data System (ADS)

Huo, Qingyu; Xu, Zhenchao; Qu, Linfeng

2017-12-01

Both blue and red shifts in the absorption spectrum of Co-doped ZnO have been reported at a similar concentration range of doped Co. Moreover, the sources of magnetism of Co-doped ZnO are controversial. To solve these problems, the geometry optimization and energy of different Co-doped ZnO systems were calculated at the states of electron spin polarization and nonspin polarization by adopting plane-wave ultra-soft pseudopotential technology based on density function theory. At the state of electron nonspin polarization, the total energies increased as the concentration of Co-doped increased. The doped systems also became unstable. The formation energies increased and doping became difficult. Furthermore, the band gaps widened and the absorption spectrum exhibited a blue shift. The band gaps were corrected by local-density approximation + U at the state of electron spin polarization. The magnetic moments of the doped systems weakened as the concentration of doped Co increased. The magnetic moments were derived from the coupling effects of sp-d. The band gaps narrowed and the absorption spectrum exhibited a red shift. The inconsistencies of the band gaps and absorption spectrum at the states of electron spin polarization and nonspin polarization were first discovered in this research, and the sources of Co-doped ZnO magnetism were also reinterpreted.

Growth and optical characteristics of Tm-doped AlGaN layer grown by organometallic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Takatsu, J.; Fuji, R.; Tatebayashi, J.; Timmerman, D.; Lesage, A.; Gregorkiewicz, T.; Fujiwara, Y.

2018-04-01

We report on the growth and optical properties of Tm-doped AlGaN layers by organometallic vapor phase epitaxy (OMVPE). The morphological and optical properties of Tm-doped GaN (GaN:Tm) and Tm-doped AlGaN (AlGaN:Tm) were investigated by Nomarski differential interference contrast microscopy and photoluminescence (PL) characterization. Nomarski images reveal an increase of surface roughness upon doping Tm into both GaN and AlGaN layers. The PL characterization of GaN:Tm shows emission in the near-infrared range originating from intra-4f shell transitions of Tm3+ ions. In contrast, AlGaN:Tm also exhibits blue light emission from Tm3+ ions. In that case, the wider band gap of the AlGaN host allows energy transfer to higher states of the Tm3+ ions. With time-resolved PL measurements, we could distinguish three types of luminescent sites of Tm3+ in the AlGaN:Tm layer, having different decay times. Our results confirm that Tm ions can be doped into GaN and AlGaN by OMVPE, and show potential for the fabrication of novel high-color-purity blue light emitting diodes.

A facile method to synthesize boron-doped Ni/Fe alloy nano-chains as electrocatalyst for water oxidation

NASA Astrophysics Data System (ADS)

Yang, Yisu; Zhuang, Linzhou; Lin, Rijia; Li, Mengran; Xu, Xiaoyong; Rufford, Thomas E.; Zhu, Zhonghua

2017-05-01

We report a novel magnetic field assisted chemical reduction method for the synthesis of boron-doped Ni/Fe nano-chains as promising catalysts for the oxygen evolution reaction (OER). The boron-doped Ni/Fe nano-chains were synthesised in a one step process at room temperature using NaBH4 as a reducing agent. The addition of boron reduced the magnetic moment of the intermediate synthesis products and produced nano-chains with a high specific surface area of 73.4 m2 g-1. The boron-doped Ni/Fe nano-chains exhibited catalytic performance superior to state-of-the-art Ba0.5Sr0.5Co0.8Fe0.2O3-δ perovskite and RuO2 noble metal oxide catalysts. The mass normalized activity of the boron-doped Ni/Fe nano-chains measured at an overpotential of 0.35 V was 64.0 A g-1, with a Tafel slope of only 40 mV dec-1. The excellent performance of the boron-doped Ni/Fe nano-chains can be attributed to the uniform elemental distribution and highly amorphous structure of the B-doped nano-chains. These results provide new insights into the effect of doping transition-metal based OER catalysts with non-metallic elements. The study demonstrates a facile approach to prepare transition metal nano-chains using magnetic field assisted chemical reduction method as cheap and highly active catalysts for electrochemical water oxidation.

Doping-dependent charge order correlations in electron-doped cuprates

PubMed Central

da Silva Neto, Eduardo H.; Yu, Biqiong; Minola, Matteo; Sutarto, Ronny; Schierle, Enrico; Boschini, Fabio; Zonno, Marta; Bluschke, Martin; Higgins, Joshua; Li, Yangmu; Yu, Guichuan; Weschke, Eugen; He, Feizhou; Le Tacon, Mathieu; Greene, Richard L.; Greven, Martin; Sawatzky, George A.; Keimer, Bernhard; Damascelli, Andrea

2016-01-01

Understanding the interplay between charge order (CO) and other phenomena (for example, pseudogap, antiferromagnetism, and superconductivity) is one of the central questions in the cuprate high-temperature superconductors. The discovery that similar forms of CO exist in both hole- and electron-doped cuprates opened a path to determine what subset of the CO phenomenology is universal to all the cuprates. We use resonant x-ray scattering to measure the CO correlations in electron-doped cuprates (La2−xCexCuO4 and Nd2−xCexCuO4) and their relationship to antiferromagnetism, pseudogap, and superconductivity. Detailed measurements of Nd2−xCexCuO4 show that CO is present in the x = 0.059 to 0.166 range and that its doping-dependent wave vector is consistent with the separation between straight segments of the Fermi surface. The CO onset temperature is highest between x = 0.106 and 0.166 but decreases at lower doping levels, indicating that it is not tied to the appearance of antiferromagnetic correlations or the pseudogap. Near optimal doping, where the CO wave vector is also consistent with a previously observed phonon anomaly, measurements of the CO below and above the superconducting transition temperature, or in a magnetic field, show that the CO is insensitive to superconductivity. Overall, these findings indicate that, although verified in the electron-doped cuprates, material-dependent details determine whether the CO correlations acquire sufficient strength to compete for the ground state of the cuprates. PMID:27536726

Doping-dependent charge order correlations in electron-doped cuprates.

PubMed

da Silva Neto, Eduardo H; Yu, Biqiong; Minola, Matteo; Sutarto, Ronny; Schierle, Enrico; Boschini, Fabio; Zonno, Marta; Bluschke, Martin; Higgins, Joshua; Li, Yangmu; Yu, Guichuan; Weschke, Eugen; He, Feizhou; Le Tacon, Mathieu; Greene, Richard L; Greven, Martin; Sawatzky, George A; Keimer, Bernhard; Damascelli, Andrea

2016-08-01

Understanding the interplay between charge order (CO) and other phenomena (for example, pseudogap, antiferromagnetism, and superconductivity) is one of the central questions in the cuprate high-temperature superconductors. The discovery that similar forms of CO exist in both hole- and electron-doped cuprates opened a path to determine what subset of the CO phenomenology is universal to all the cuprates. We use resonant x-ray scattering to measure the CO correlations in electron-doped cuprates (La2-x Ce x CuO4 and Nd2-x Ce x CuO4) and their relationship to antiferromagnetism, pseudogap, and superconductivity. Detailed measurements of Nd2-x Ce x CuO4 show that CO is present in the x = 0.059 to 0.166 range and that its doping-dependent wave vector is consistent with the separation between straight segments of the Fermi surface. The CO onset temperature is highest between x = 0.106 and 0.166 but decreases at lower doping levels, indicating that it is not tied to the appearance of antiferromagnetic correlations or the pseudogap. Near optimal doping, where the CO wave vector is also consistent with a previously observed phonon anomaly, measurements of the CO below and above the superconducting transition temperature, or in a magnetic field, show that the CO is insensitive to superconductivity. Overall, these findings indicate that, although verified in the electron-doped cuprates, material-dependent details determine whether the CO correlations acquire sufficient strength to compete for the ground state of the cuprates.

Exceptionally crystalline and conducting acid doped polyaniline films by level surface assisted solution casting approach

NASA Astrophysics Data System (ADS)

Puthirath, Anand B.; Methattel Raman, Shijeesh; Varma, Sreekanth J.; Jayalekshmi, S.

2016-04-01

Emeraldine salt form of polyaniline (PANI) was synthesized by chemical oxidative polymerisation method using ammonium persulfate as oxidant. Resultant emeraldine salt form of PANI was dedoped using ammonia solution and then re-doped with camphor sulphonic acid (CSA), naphthaline sulphonic acid (NSA), hydrochloric acid (HCl), and m-cresol. Thin films of these doped PANI samples were deposited on glass substrates using solution casting method with m-cresol as solvent. A level surface was employed to get homogeneous thin films of uniform thickness. Detailed X-ray diffraction studies have shown that the films are exceptionally crystalline. The crystalline peaks observed in the XRD spectra can be indexed to simple monoclinic structure. FTIR and Raman spectroscopy studies provide convincing explanation for the exceptional crystallinity observed in these polymer films. FESEM and AFM images give better details of surface morphology of doped PANI films. The DC electrical conductivity of the samples was measured using four point probe technique. It is seen that the samples also exhibit quite high DC electrical conductivity, about 287 S/cm for CSA doped PANI, 67 S/cm for NSA doped PANI 65 S/cm for HCl doped PANI, and just below 1 S/cm for m-cresol doped PANI. Effect of using the level surface for solution casting is studied and correlated with the observed crystallinity.

Exceptionally crystalline and conducting acid doped polyaniline films by level surface assisted solution casting approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Puthirath, Anand B.; Varma, Sreekanth J.; Jayalekshmi, S., E-mail: jayalekshmi@cusat.ac.in

2016-04-18

Emeraldine salt form of polyaniline (PANI) was synthesized by chemical oxidative polymerisation method using ammonium persulfate as oxidant. Resultant emeraldine salt form of PANI was dedoped using ammonia solution and then re-doped with camphor sulphonic acid (CSA), naphthaline sulphonic acid (NSA), hydrochloric acid (HCl), and m-cresol. Thin films of these doped PANI samples were deposited on glass substrates using solution casting method with m-cresol as solvent. A level surface was employed to get homogeneous thin films of uniform thickness. Detailed X-ray diffraction studies have shown that the films are exceptionally crystalline. The crystalline peaks observed in the XRD spectra canmore » be indexed to simple monoclinic structure. FTIR and Raman spectroscopy studies provide convincing explanation for the exceptional crystallinity observed in these polymer films. FESEM and AFM images give better details of surface morphology of doped PANI films. The DC electrical conductivity of the samples was measured using four point probe technique. It is seen that the samples also exhibit quite high DC electrical conductivity, about 287 S/cm for CSA doped PANI, 67 S/cm for NSA doped PANI 65 S/cm for HCl doped PANI, and just below 1 S/cm for m-cresol doped PANI. Effect of using the level surface for solution casting is studied and correlated with the observed crystallinity.« less

Multifold polar states in Zn-doped Sr0.9Ba0.1TiO3 ceramics

NASA Astrophysics Data System (ADS)

Guo, Yan-Yan; Guo, Yun-Jun; Wei, Tong; Liu, Jun-Ming

2015-12-01

We investigate the effect of Zn doping on the dielectricity and ferroelectricity of a series of polycrystalline Sr0.9-xZnxBa0.1TiO3 (0.0% ≤ x ≤ 5.0%) ceramics. It is surprisingly observed that the Zn doping will produce the multifold polar states, i.e., the Zn-doped ceramic will convert a reduced polar state into an enhanced polar state, and eventually into a stabilized polar state with increasing the doping level x. It is revealed that in the background of quantum fluctuations, the competition between the Zn-doping-induced lattice contraction and the Ba-doping-induced lattice expansion is responsible for both the reduced polar state and the enhanced polar state coming into being. Also, the addition of the antiferrodistortive effect, which is the antipolar interaction originating from the opposite tilted-TiO6 octahedra rotation, represents the core physics behind the stabilized polar state. Project supported by the National Natural Science Foundation of China (Grant Nos. 11304158, 51431006, 51102277, and 11104118), the Scientific Research Foundation of Nanjing University of Posts and Telecommunications, China (Grant No. NY213020), and the Qing Lan Project of Jiangsu Province, China.

Enhanced adhesion of films to semiconductors or metals by high energy bombardment

NASA Technical Reports Server (NTRS)

Tombrello, Thomas A. (Inventor); Qiu, Yuanxun (Inventor); Mendenhall, Marcus H. (Inventor)

1985-01-01

Films (12) of a metal such as gold or other non-insulator materials are firmly bonded to other non-insulators such as semiconductor substrates (10), suitably silicon or gallium arsenide by irradiating the interface with high energy ions. The process results in improved adhesion without excessive doping and provides a low resistance contact to the semiconductor. Thick layers can be bonded by depositing or doping the interfacial surfaces with fissionable elements or alpha emitters. The process can be utilized to apply very small, low resistance electrodes (78) to light-emitting solid state laser diodes (60) to form a laser device 70.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kroupa, Daniel M.; Hughes, Barbara K.; Miller, Elisa M.

Electronic impurity doping of bulk semiconductors is an essential component of semiconductor science and technology. Yet there are only a handful of studies demonstrating control of electronic impurities in semiconductor nanocrystals. Here, we studied electronic impurity doping of colloidal PbSe quantum dots (QDs) using a postsynthetic cation exchange reaction in which Pb is exchanged for Ag. We found that varying the concentration of dopants exposed to the as-synthesized PbSe QDs controls the extent of exchange. The electronic impurity doped QDs exhibit the fundamental spectroscopic signatures associated with injecting a free charge carrier into a QD under equilibrium conditions, including amore » bleach of the first exciton transition and the appearance of a quantum-confined, low-energy intraband absorption feature. Photoelectron spectroscopy confirms that Ag acts as a p-type dopant for PbSe QDs and infrared spectroscopy is consistent with k • p calculations of the size-dependent intraband transition energy. We find that to bleach the first exciton transition by an average of 1 carrier per QD requires that approximately 10% of the Pb be replaced by Ag. Here, we hypothesize that the majority of incorporated Ag remains at the QD surface and does not interact with the core electronic states of the QD. Instead, the excess Ag at the surface promotes the incorporation of <1% Ag into the QD core where it causes p-type doping behavior.« less

Electrical properties of fluorine-doped ZnO nanowires formed by biased plasma treatment

NASA Astrophysics Data System (ADS)

Wang, Ying; Chen, Yicong; Song, Xiaomeng; Zhang, Zhipeng; She, Juncong; Deng, Shaozhi; Xu, Ningsheng; Chen, Jun

2018-05-01

Doping is an effective method for tuning electrical properties of zinc oxide nanowires, which are used in nanoelectronic devices. Here, ZnO nanowires were prepared by a thermal oxidation method. Fluorine doping was achieved by a biased plasma treatment, with bias voltages of 100, 200, and 300 V. Transmission electron microscopy indicated that the nanowires treated at bias voltages of 100 and 200 V featured low crystallinity. When the bias voltage was 300 V, the nanowires showed single crystalline structures. Photoluminescence measurements revealed that concentrations of oxygen and surface defects decreased at high bias voltage. X-ray photoelectron spectroscopy suggested that the F content increased as the bias voltage was increased. The conductivity of the as-grown nanowires was less than 103 S/m; the conductivity of the treated nanowires ranged from 1 × 104-5 × 104, 1 × 104-1 × 105, and 1 × 103-2 × 104 S/m for bias voltage treatments at 100, 200, and 300 V, respectively. The conductivity improvements of nanowires formed at bias voltages of 100 and 200 V, were attributed to F-doping, defects and surface states. The conductivity of nanowires treated at 300 V was attributed to the presence of F ions. Thus, we provide a method of improving electrical properties of ZnO nanowires without altering their crystal structure.

Electron transport in high aspect ratio semiconductor nanowires and metal-semiconductor interfaces

NASA Astrophysics Data System (ADS)

Sun, Zhuting

We are facing variability problems for modern semiconductor transistors due to the fact that the performances of nominally identical devices in the scale of 10 100 nm could be dramatically different attributed to the small manufacturing variations. Different doping strategies give statistical variations in the number of dopant atom density ND in the channel. The material size gives variations in wire diameter dW. And the immediate environment of the material leads to an additional level of variability. E.g. vacuum-semiconductor interface causes variations in surface state density Ds, metal-semiconductor interface causes variations in Schottky barrier and dielectric semiconductor interface induces dielectric confinement at small scales. To approach these variability problems, I choose Si-doped GaAs nanowires as an example. I investigate transport in Si-doped GaAs nanowire (NW) samples contacted by lithographically patterned Gold-Titanium films as function of temperature T. I find a drastically different temperature dependence between the wire resistance RW, which is relatively weak, and the zero bias resistance RC, which is strong. I show that the data are consistent with a model based on a sharp donor energy level slightly above the bottom of the semiconductor conduction band and develop a simple method for using transport measurements for estimates of the doping density after nanowire growth. I discuss the predictions of effective free carrier density n eff as function of the surface state density Ds and wire size dW. I also describe a correction to the widely used model of Schottky contacts that improves thermodynamic consistency of the Schottky tunnel barrier profile and show that the original theory may underestimate the barrier conductance under certain conditions. I also provide analytical calculations for shallow silicon dopant energy in GaAs crystals, and find the presence of dielectrics (dielectric screening) and free carriers (Coulomb screening) cause a reduction of ionization energy and shift the donor energy level ED upward, accompanying conduction band EC shift downward due to band gap narrowing for doped semiconductor material. The theoretical results are in a reasonable agreement with previous experimental data. I also find that when the material reduces to nanoscale, dielectric confinement and surface depletion compete with both Coulomb screening and dielectric screening that shift the donor level ED down towards the band gap. The calculation should be appropriate for all types of semiconductors and dopant species.

Genesis of charge orders in high temperature superconductors

PubMed Central

Tu, Wei-Lin; Lee, Ting-Kuo

2016-01-01

One of the most puzzling facts about cuprate high-temperature superconductors in the lightly doped regime is the coexistence of uniform superconductivity and/or antiferromagnetism with many low-energy charge-ordered states in a unidirectional charge density wave or a bidirectional checkerboard structure. Recent experiments have discovered that these charge density waves exhibit different symmetries in their intra-unit-cell form factors for different cuprate families. Using a renormalized mean-field theory for a well-known, strongly correlated model of cuprates, we obtain a number of charge-ordered states with nearly degenerate energies without invoking special features of the Fermi surface. All of these self-consistent solutions have a pair density wave intertwined with a charge density wave and sometimes a spin density wave. Most of these states vanish in the underdoped regime, except for one with a large d-form factor that vanishes at approximately 19% doping of the holes, as reported by experiments. Furthermore, these states could be modified to have a global superconducting order, with a nodal-like density of states at low energy. PMID:26732076

Performance improvement of doped TFET by using plasma formation concept

NASA Astrophysics Data System (ADS)

Soni, Deepak; Sharma, Dheeraj; Yadav, Shivendra; Aslam, Mohd.; Sharma, Neeraj

2018-01-01

Formation of abrupt doping profile at tunneling junction for the nanoscale tunnel field effect transistor (TFET) is a critical issue for attaining improved electrical behaviour. The realization of abrupt doping profile is more difficult in the case of physically doped TFETs due to material solubility limit. In this concern, we propose a novel design of TFET. For this, P+ (source)-I (channel)-N (drain) type structure has been considered, wherein a metal electrode is deposited over the source region. In addition to this, a negative voltage is applied to the source electrode (SE). It induces the surface plasma layer of holes in the source region, which is responsible for steepness in the bands at source/channel junction and provides the advantage of higher doping in source region without any addition of the physical impurity. The proposed modification is helpful for achieving steeper band bending at the source/channel interface, which enables higher tunneling generation rate of charge carriers at this interface and overcomes the issue of low ON-state current. Thus, the proposed device shows the increment of 2 decades in drain current and 252 mV reduction in threshold voltage compared with conventional device. The optimization of spacer length (LSG) between source/gate (LSG) and applied negative voltage (Vpg) over source electrode have been performed to obtain optimum drain current and threshold voltage (Vth). Further, for the suppression of ambipolar current, drain region is kept lightly doped, which reduces the ambipolar current up to level of Off state current. Moreover, in the proposed device gate electrode is underlapped for improving RF performance. It also reduces gate to drain capacitances (Cgd) and increases cut-off-frequency (fT), fmax, GBP, TFP. In addition to these, linearity analysis has been performed to validate the applicability of the device.

Photocatalytic activity of undoped and Ag-doped TiO{sub 2}-supported zeolite for humic acid degradation and mineralization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lazau, C.; Ratiu, C.; National Institute for Research and Development in Microtechnologies, Erou Iancu Nicolae Street, 077190 Bucharest

2011-11-15

Highlights: {yields} Hybrid materials based on natural zeolite and TiO{sub 2} obtained by solid-state reaction. {yields} XRD proved the presence of anatase form of undoped and Ag-doped TiO{sub 2} onto zeolite. {yields} FT-IR spectra evidenced the presence on TiO{sub 2} bounded at the zeolite network. {yields} Ag-doped TiO{sub 2} onto zeolitic matrix exhibited an enhanced photocatalytic activity. -- Abstract: The hybrid materials based on natural zeolite and undoped and Ag-doped TiO{sub 2}, i.e., Z-Na-TiO{sub 2} and Z-Na-TiO{sub 2}-Ag, were successfully synthesized by solid-state reaction in microwave-assisted hydrothermal conditions. Undoped TiO{sub 2} and Ag-doped TiO{sub 2} nanocrystals were previously synthesized bymore » sol-gel method. The surface characterization of undoped TiO{sub 2}/Ag-doped TiO{sub 2} and natural zeolite hybrid materials has been investigated by X-ray diffraction, DRUV-VIS spectroscopy, FT-IR spectroscopy, BET analysis, SEM microscopy and EDX analysis. The results indicated that anatase TiO{sub 2} is the dominant crystalline type as spherical form onto zeolitic matrix. The presence of Ag into Z-Na-TiO{sub 2}-Ag was confirmed by EDX analysis. The DRUV-VIS spectra showed that Z-Na-TiO{sub 2}-Ag exhibited absorption within the range of 400-500 nm in comparison with Z-Na-TiO{sub 2} catalyst. The enhanced photocatalytic activity of Z-Na-TiO{sub 2}-Ag catalyst is proved through the degradation and mineralization of humic acid under ultraviolet and visible irradiation.« less

Advancement in the Understanding of the Field and Frequency Dependent Microwave Surface Resistance of Niobium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martinello, M.; Aderhold, S.; Chandrasekaran, S. K.

The radio-frequency surface resistance of niobium resonators is incredibly reduced when nitrogen impurities are dissolved as interstitial in the material, conferring ultra-high Q-factors at medium values of accelerating field. This effect has been observed in both high and low temperature nitrogen treatments. As a matter of fact, the peculiar anti Q-slope observed in nitrogen doped cavities, i.e. the decreasing of the Q-factor with the increasing of the radio-frequency field, come from the decreasing of the BCS surface resistance component as a function of the field. Such peculiar behavior has been considered consequence of the interstitial nitrogen present in the niobiummore » lattice after the doping treatment. The study here presented show the field dependence of the BCS surface resistance of cavities with different resonant frequencies, such as: 650 MHz, 1.3 GHz, 2.6 GHz and 3.9 GHz, and processed with different state-of-the-art surface treatments. These findings show for the first time that the anti Q-slope might be seen at high frequency even for clean Niobium cavities, revealing useful suggestion on the physics underneath the anti Q-slope effect.« less

Hydrogen Doping into MoO3 Supports toward Modulated Metal-Support Interactions and Efficient Furfural Hydrogenation on Iridium Nanocatalysts.

PubMed

Xie, Lifang; Chen, Ting; Chan, Hang Cheong; Shu, Yijin; Gao, Qingsheng

2018-03-16

As promising supports, reducible metal oxides afford strong metal-support interactions to achieve efficient catalysis, which relies on their band states and surface stoichiometry. In this study, in situ and controlled hydrogen doping (H doping) by means of H 2 spillover was employed to engineer the metal-support interactions in hydrogenated MoO x -supported Ir (Ir/H-MoO x ) catalysts and thus promote furfural hydrogenation to furfuryl alcohol. By easily varying the reduction temperature, the resulting H doping in a controlled manner tailors low-valence Mo species (Mo 5+ and Mo 4+ ) on H-MoO x supports, thereby promoting charge redistribution on Ir and H-MoO x interfaces. This further leads to clear differences in H 2 chemisorption on Ir, which illustrates its potential for catalytic hydrogenation. As expected, the optimal Ir/H-MoO x with controlled H doping afforded high activity (turnover frequency: 4.62 min -1 ) and selectivity (>99 %) in furfural hydrogenation under mild conditions (T=30 °C, PH2 =2 MPa), which means it performs among the best of current catalysts. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Spontaneous and strong multi-layer graphene n-doping on soda-lime glass and its application in graphene-semiconductor junctions

DOE PAGES

Dissanayake, D. M. N. M.; Ashraf, A.; Dwyer, D.; ...

2016-02-12

Scalable and low-cost doping of graphene could improve technologies in a wide range of fields such as microelectronics, optoelectronics, and energy storage. While achieving strong p-doping is relatively straightforward, non-electrostatic approaches to n-dope graphene, such as chemical doping, have yielded electron densities of 9.5 × 10 12 e/cm 2 or below. Furthermore, chemical doping is susceptible to degradation and can adversely affect intrinsic graphene’s properties. Here we demonstrate strong (1.33 × 10 13 e/cm 2), robust, and spontaneous graphene n-doping on a soda-lime-glass substrate via surface-transfer doping from Na without any external chemical, high-temperature, or vacuum processes. Remarkably, the n-dopingmore » reaches 2.11 × 10 13 e/cm 2 when graphene is transferred onto a p-type copper indium gallium diselenide (CIGS) semiconductor that itself has been deposited onto soda-lime-glass, via surface-transfer doping from Na atoms that diffuse to the CIGS surface. Using this effect, we demonstrate an n-graphene/p-semiconductor Schottky junction with ideality factor of 1.21 and strong photo-response. As a result, the ability to achieve strong and persistent graphene n-doping on low-cost, industry-standard materials paves the way toward an entirely new class of graphene-based devices such as photodetectors, photovoltaics, sensors, batteries, and supercapacitors.« less

Formation of hydroxyl radicals and kinetic study of 2-chlorophenol photocatalytic oxidation using C-doped TiO2, N-doped TiO2, and C,N Co-doped TiO2 under visible light.

PubMed

Ananpattarachai, Jirapat; Seraphin, Supapan; Kajitvichyanukul, Puangrat

2016-02-01

This work reports on synthesis, characterization, adsorption ability, formation rate of hydroxyl radicals (OH(•)), photocatalytic oxidation kinetics, and mineralization ability of C-doped titanium dioxide (TiO2), N-doped TiO2, and C,N co-doped TiO2 prepared by the sol-gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV-visible spectroscopy were used to analyze the titania. The rate of formation of OH(•) for each type of titania was determined, and the OH-index was calculated. The kinetics of as-synthesized TiO2 catalysts in photocatalytic oxidation of 2-chlorophenol (2-CP) under visible light irradiation were evaluated. Results revealed that nitrogen was incorporated into the lattice of titania with the structure of O-Ti-N linkages in N-doped TiO2 and C,N co-doped TiO2. Carbon was joined to the Ti-O-C bond in the C-doped TiO2 and C,N co-doped TiO2. The 2-CP adsorption ability of C,N co-doped TiO2 and C-doped TiO2 originated from a layer composed of a complex carbonaceous mixture at the surface of TiO2. C,N co-doped TiO2 had highest formation rate of OH(•) and photocatalytic activity due to a synergistic effect of carbon and nitrogen co-doping. The order of photocatalytic activity per unit surface area was the same as that of the formation rate of OH(•) unit surface area in the following order: C,N co-doped TiO2 > C-doped TiO2 > N-doped TiO2 > undoped TiO2.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farrokhzadeh, Abdolkarim; Modarresi-Alam, Ali Reza, E-mail: modaresi@chem.usb.ac.ir

Poly [(±)-2-(sec-butyl) aniline]/silica-supported perchloric acid composites were synthesized by combination of poly[(±)-2-sec-butylaniline] base (PSBA) and the silica-supported perchloric acid (SSPA) as dopant solid acid in solid-state. The X-ray photoelectron spectroscopy (XPS) and CHNS results confirm nigraniline oxidation state and complete doping for composites (about 75%) and non-complete for the PSBA·HCl salt (about 49%). The conductivity of samples was (≈0.07 S/cm) in agreement with the percent of doping obtained of the XPS analysis. Also, contact resistance was determined by circular-TLM measurement. The morphology of samples by the scanning electron microscopy (SEM) and their coating were investigated by XPS, SEM-map and energy-dispersivemore » X-ray spectroscopy (EDX). The key benefits of this work are the preparation of conductive chiral composite with the delocalized polaron structure under green chemistry and solid-state condition, the improvement of the processability by inclusion of the 2-sec-butyl group and the use of dopant solid acid (SSPA) as dopant. - Highlights: • The solid-state synthesis of the novel chiral composites of poly[(±)-2-(sec-butyl)aniline] (PSBA) and silica-supported perchloric acid (SSPA). • It takes 120 h for complete deprotonation of PSBA.HCl salt. • Use of SSPA as dopant solid acid for the first time to attain the complete doping of PSBA. • The coating of silica surface with PSBA.« less

Microstructure, ferromagnetic and photoluminescence properties of ITO and Cr doped ITO nanoparticles using solid state reaction

NASA Astrophysics Data System (ADS)

Babu, S. Harinath; Kaleemulla, S.; Rao, N. Madhusudhana; Rao, G. Venugopal; Krishnamoorthi, C.

2016-11-01

Indium-tin-oxide (ITO) (In0.95Sn0.05)2O3 and Cr doped indium-tin-oxide (In0.90Sn0.05Cr0.05)2O3 nanoparticles were prepared using simple low cost solid state reaction method and characterized by different techniques to study their structural, optical and magnetic properties. Microstructures, surface morphology, crystallite size of the nanoparticles were studied using X-ray diffractometer (XRD), field emission scanning electron microscope (FE-SEM). From these methods it was found that the particles were about 45 nm. Chemical composition and valence states of the nanoparticles were studied using energy dispersive analysis of X-rays (EDAX) and X-ray photoelectron spectroscopy (XPS). From these techniques it was observed that the elements of indium, tin, chromium and oxygen were present in the system in appropriate ratios and they were in +3, +4, +3 and -2 oxidation states. Raman studies confirmed that the nanoparticle were free from unintentional impurities. Two broad emission peaks were observed at 330 nm and 460 nm when excited wavelength of 300 nm. Magnetic studies were carried out at 300 K and 100 K using vibrating sample magnetometer (VSM) and found that the ITO nanoparticles were ferromagnetic at 100 K and 300 K. Where-as the room temperature ferromagnetism completely disappeared in Cr doped ITO nanoparticles at 100 K and 300 K.

Enhancement of surface migration by Mg doping in the metalorganic vapor phase epitaxy of N-polar (000\\bar{1}) GaN/sapphire

NASA Astrophysics Data System (ADS)

Tanikawa, Tomoyuki; Shojiki, Kanako; Aisaka, Takashi; Kimura, Takeshi; Kuboya, Shigeyuki; Hanada, Takashi; Katayama, Ryuji; Matsuoka, Takashi

2014-01-01

With respect to N-polar (000\\bar{1}) GaN grown on a sapphire substrate, the effects of Mg doping on the surface morphology, and the optical, and electrical properties are precisely investigated. By doping Mg, hillocks observed on the surface of (000\\bar{1}) GaN can be suppressed, while step bunching becomes severe. The atomic terrace width is extended with increasing Mg/Ga precursor ratio. Mg doping can promote the surface migration of Ga adatoms on a GaN surface during growth. In the case of heavily Mg-doped GaN, atomic steps become wavy. From photoluminescence spectra, the dominant transition was found to change from near-band-edge transition to donor-acceptor-pair transition. Hall-effect measurement shows p-type conduction at room temperature for a sample grown with the Mg/Ga precursor ratio of 4.5 × 10-3. The activation energy is 143 meV, which is comparable to that of Mg in the conventional Ga-polar (0001) GaN.

Heavily doped n-type PbSe and PbS nanocrystals using ground-state charge transfer from cobaltocene

DOE PAGES

Koh, Weon-kyu; Koposov, Alexey Y.; Stewart, John T.; ...

2013-06-18

Colloidal nanocrystals (NCs) of lead chalcogenides are a promising class of tunable infrared materials for applications in devices such as photodetectors and solar cells. Such devices typically employ electronic materials in which charge carrier concentrations are manipulated through “doping;” however, persistent electronic doping of these NCs remains a challenge. In this paper, we demonstrate that heavily doped n-type PbSe and PbS NCs can be realized utilizing ground-state electron transfer from cobaltocene. This allows injecting up to eight electrons per NC into the band-edge state and maintaining the doping level for at least a month at room temperature. Doping is confirmedmore » by inter- and intra-band optical absorption, as well as by carrier dynamics. In conclusion, FET measurements of doped NC films and the demonstration of a p-n diode provide additional evidence that the developed doping procedure allows for persistent incorporation of electrons into the quantum-confined NC states.« less

Effect of Doping on Surface Reactivity and Conduction Mechanism in Sm-doped CeO2 Thin Films

DOE PAGES

Yang, Nan; Belianinov, Alex; Strelcov, Evgheni; ...

2014-11-21

Scanning probe microscopy measurements show irreversible surface electrochemistry in Sm-doped CeO2 thin films, which depends on humidity, temperature and doping concentration. A systematic study by electrochemical strain microscopy (ESM) in samples with two different Sm content and in several working conditions allows disclosing the microscopic mechanism underlying the difference in water adsorption and splitting with subsequent proton liberation. We measure the behavior of the hysteresis loops by changing temperature and humidity, both in standard ESM configuration and using the first order reversal curve (FORC) method. Complementing our study with spectroscopic measurements by hard x-ray photoemission spectroscopy we find that watermore » incorporation is favored until the doping with Sm is too high to allow the presence of Ce3+. The influence of doping on the surface reactivity and conduction mechanism clearly emerges from all of our experimental results. We find that at lower Sm concentration proton conduction is prevalent, featured by lower activation energy and higher mobility. Defect concentrations determine the type of the prevalent charge carrier in a doping dependent manner.« less

Cat-doping: Novel method for phosphorus and boron shallow doping in crystalline silicon at 80 °C

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matsumura, Hideki; Hayakawa, Taro; Ohta, Tatsunori

Phosphorus (P) or boron (B) atoms can be doped at temperatures as low as 80 to 350 °C, when crystalline silicon (c-Si) is exposed only for a few minutes to species generated by catalytic cracking reaction of phosphine (PH₃) or diborane (B₂H₆) with heated tungsten (W) catalyzer. This paper is to investigate systematically this novel doping method, “Cat-doping”, in detail. The electrical properties of P or B doped layers are studied by the Van der Pauw method based on the Hall effects measurement. The profiles of P or B atoms in c-Si are observed by secondary ion mass spectrometry mainlymore » from back side of samples to eliminate knock-on effects. It is confirmed that the surface of p-type c-Si is converted to n-type by P Cat-doping at 80 °C, and similarly, that of n-type c-Si is to p-type by B Cat-doping. The doping depth is as shallow as 5 nm or less and the electrically activated doping concentration is 10¹⁸ to 10¹⁹cm⁻³ for both P and B doping. It is also found that the surface potential of c-Si is controlled by the shallow Cat-doping and that the surface recombination velocity of minority carriers in c-Si can be enormously lowered by this potential control.« less

Cooperative and non-cooperative sensitization upconversion in lanthanide-doped LiYbF4 nanoparticles.

PubMed

Zou, Qilin; Huang, Ping; Zheng, Wei; You, Wenwu; Li, Renfu; Tu, Datao; Xu, Jin; Chen, Xueyuan

2017-05-18

Lanthanide (Ln 3+ )-doped upconversion nanoparticles (UCNPs) have attracted tremendous interest owing to their potential bioapplications. However, the intrinsic photophysics responsible for upconversion (UC) especially the cooperative sensitization UC (CSU) in colloidal Ln 3+ -doped UCNPs has remained untouched so far. Herein, we report a unique strategy for the synthesis of high-quality LiYbF 4 :Ln 3+ core-only and core/shell UCNPs with tunable particle sizes and shell thicknesses. Energy transfer UC from Er 3+ , Ho 3+ and Tm 3+ and CSU from Tb 3+ were comprehensively surveyed under 980 nm excitation. Through surface passivation, we achieved efficient non-cooperative sensitization UC with absolute UC quantum yields (QYs) of 3.36%, 0.69% and 0.81% for Er 3+ , Ho 3+ and Tm 3+ , respectively. Particularly, we for the first time quantitatively determined the CSU efficiency for Tb 3+ with an absolute QY of 0.0085% under excitation at a power density of 70 W cm -2 . By means of temperature-dependent steady-state and transient UC spectroscopy, we unraveled the dominant mechanisms of phonon-assisted cooperative energy transfer (T > 100 K) and sequential dimer ground-state absorption/excited-state absorption (T < 100 K) for the CSU process in LiYbF 4 :Tb 3+ UCNPs.

A Thermal Diode Based on Nanoscale Thermal Radiation.

PubMed

Fiorino, Anthony; Thompson, Dakotah; Zhu, Linxiao; Mittapally, Rohith; Biehs, Svend-Age; Bezencenet, Odile; El-Bondry, Nadia; Bansropun, Shailendra; Ben-Abdallah, Philippe; Meyhofer, Edgar; Reddy, Pramod

2018-05-23

In this work we demonstrate thermal rectification at the nanoscale between doped Si and VO 2 surfaces. Specifically, we show that the metal-insulator transition of VO 2 makes it possible to achieve large differences in the heat flow between Si and VO 2 when the direction of the temperature gradient is reversed. We further show that this rectification increases at nanoscale separations, with a maximum rectification coefficient exceeding 50% at ∼140 nm gaps and a temperature difference of 70 K. Our modeling indicates that this high rectification coefficient arises due to broadband enhancement of heat transfer between metallic VO 2 and doped Si surfaces, as compared to narrower-band exchange that occurs when VO 2 is in its insulating state. This work demonstrates the feasibility of accomplishing near-field-based rectification of heat, which is a key component for creating nanoscale radiation-based information processing devices and thermal management approaches.

The role of nitrogen doping in ALD Ta2O5 and its influence on multilevel cell switching in RRAM

NASA Astrophysics Data System (ADS)

Sedghi, N.; Li, H.; Brunell, I. F.; Dawson, K.; Potter, R. J.; Guo, Y.; Gibbon, J. T.; Dhanak, V. R.; Zhang, W. D.; Zhang, J. F.; Robertson, J.; Hall, S.; Chalker, P. R.

2017-03-01

The role of nitrogen doping on the stability and memory window of resistive state switching in N-doped Ta2O5 deposited by atomic layer deposition is elucidated. Nitrogen incorporation increases the stability of resistive memory states which is attributed to neutralization of electronic defect levels associated with oxygen vacancies. The density functional simulations with the screened exchange hybrid functional approximation show that the incorporation of nitrogen dopant atoms in the oxide network removes the O vacancy midgap defect states, thus nullifying excess defects and eliminating alternative conductive paths. By effectively reducing the density of vacancy-induced defect states through N doping, 3-bit multilevel cell switching is demonstrated, consisting of eight distinctive resistive memory states achieved by either controlling the set current compliance or the maximum voltage during reset. Nitrogen doping has a threefold effect: widening the switching memory window to accommodate the more intermediate states, improving the stability of states, and providing a gradual reset for multi-level cell switching during reset. The N-doped Ta2O5 devices have relatively small set and reset voltages (< 1 V) with reduced variability due to doping.

Application of Degenerately Doped Metal Oxides in the Study of Photoinduced Interfacial Electron Transfer.

PubMed

Farnum, Byron H; Morseth, Zachary A; Brennaman, M Kyle; Papanikolas, John M; Meyer, Thomas J

2015-06-18

Degenerately doped In2O3:Sn semiconductor nanoparticles (nanoITO) have been used to study the photoinduced interfacial electron-transfer reactivity of surface-bound [Ru(II)(bpy)2(4,4'-(PO3H2)2-bpy)](2+) (RuP(2+)) molecules as a function of driving force over a range of 1.8 eV. The metallic properties of the ITO nanoparticles, present within an interconnected mesoporous film, allowed for the driving force to be tuned by controlling their Fermi level with an external bias while their optical transparency allowed for transient absorption spectroscopy to be used to monitor electron-transfer kinetics. Photoinduced electron transfer from excited-state -RuP(2+*) molecules to nanoITO was found to be dependent on applied bias and competitive with nonradiative energy transfer to nanoITO. Back electron transfer from nanoITO to oxidized -RuP(3+) was also dependent on the applied bias but without complication from inter- or intraparticle electron diffusion in the oxide nanoparticles. Analysis of the electron injection kinetics as a function of driving force using Marcus-Gerischer theory resulted in an experimental estimate of the reorganization energy for the excited-state -RuP(3+/2+*) redox couple of λ* = 0.83 eV and an electronic coupling matrix element, arising from electronic wave function overlap between the donor orbital in the molecule and the acceptor orbital(s) in the nanoITO electrode, of Hab = 20-45 cm(-1). Similar analysis of the back electron-transfer kinetics yielded λ = 0.56 eV for the ground-state -RuP(3+/2+) redox couple and Hab = 2-4 cm(-1). The use of these wide band gap, degenerately doped materials provides a unique experimental approach for investigating single-site electron transfer at the surface of oxide nanoparticles.

Combined effects Na and SO2 in flue gas on Mn-Ce/TiO2 catalyst for low temperature selective catalytic reduction of NO by NH3 simulated by Na2SO4 doping

NASA Astrophysics Data System (ADS)

Zhou, Aiyi; Yu, Danqing; Yang, Liu; Sheng, Zhongyi

2016-08-01

A series of Mn-Ce/TiO2 catalysts were synthesized through an impregnation method and used for low temperature selective catalytic reduction (SCR) of NOx with ammonia (NH3). Na2SO4 was added into the catalyst to simulate the combined effects of alkali metal and SO2 in the flue gas. Experimental results showed that Na2SO4 had strong and fluctuant influence on the activity of Mn-Ce/TiO2, because the effect of Na2SO4 included pore occlusion and sulfation effect simultaneously. When Na2SO4 loading content increased from 0 to 1 wt.%, the SCR activities of Na2SO4-doped catalysts decreased greatly. With further increasing amount of Na2SO4, however, the catalytic activity increased gradually. XRD results showed that Na2SO4 doping could induce the crystallization of MnOx phases, which were also confirmed by TEM and SEM results. BET results showed that the surface areas decreased and a new bimodal mesoporous structure formed gradually with the increasing amount of Na2SO4. XPS results indicated that part of Ce4+ and Mn3+ were transferred to Ce3+ and Mn4+ due to the sulfation after Na2SO4 deposition on the surface of the catalysts. When the doped amounts of Na2SO4 increased, NH3-TPD results showed that the Lewis acid sites decreased and the Brønsted acid sites of Mn-Ce/TiO2 increased quickly, which could be considered as another reason for the observed changes in the catalytic activity. The decreased Mn and Ce atomic concentration, the changes of their oxidative states, and the variation in acidic properties on the surface of Na2SO4-doped catalysts could be the reasons for the fluctuant changes of the catalytic activity.

Origin of the low critical observing temperature of the quantum anomalous Hall effect in V-doped (Bi, Sb) 2Te 3 film

DOE PAGES

Li, W.; Claassen, M.; Chang, Cui -Zu; ...

2016-09-07

The experimental realization of the quantum anomalous Hall (QAH) effect in magnetically-doped (Bi, Sb) 2Te 3 films stands out as a landmark of modern condensed matter physics. However, ultra-low temperatures down to few tens of mK are needed to reach the quantization of Hall resistance, which is two orders of magnitude lower than the ferromagnetic phase transition temperature of the films. Here, we systematically study the band structure of V-doped (Bi, Sb) 2Te 3 thin films by angle-resolved photoemission spectroscopy (ARPES) and show unambiguously that the bulk valence band (BVB) maximum lies higher in energy than the surface state Diracmore » point. Finally, our results demonstrate clear evidence that localization of BVB carriers plays an active role and can account for the temperature discrepancy.« less

Doped phosphorene for hydrogen capture: A DFT study

NASA Astrophysics Data System (ADS)

Zhang, Hong-ping; Hu, Wei; Du, Aijun; Lu, Xiong; Zhang, Ya-ping; Zhou, Jian; Lin, Xiaoyan; Tang, Youhong

2018-03-01

Hydrogen capture and storage is the core of hydrogen energy application. With its high specific surface area, direct bandgap, and variety of potential applications, phosphorene has attracted much research interest. In this study, density functional theory (DFT) is utilized to study the interactions between doped phosphorenes and hydrogen molecules. The effects of different dopants and metallic or nonmetallic atoms on phosphorene/hydrogen interactions is systematically studied by adsorption energy, electron density difference, partial density of states analysis, and Hirshfeld population. Our results indicate that the metallic dopants Pt, Co, and Ni can help to improve the hydrogen capture ability of phosphorene, whereas the nonmetallic dopants have no effect on it. Among the various metallic dopants, Pt performs very differently, such that it can help to dissociate H2 on phosphorene. Specified doped phosphorene could be a promising candidate for hydrogen storage, with behaviors superior to those of intrinsic graphene sheet.

Temperature effects in contacts between a metal and a semiconductor nanowire near the degenerate doping

NASA Astrophysics Data System (ADS)

Sun, Zhuting; Burgess, Tim; Tan, H. H.; Jagadish, Chennupati; Kogan, Andrei

2018-04-01

We have investigated the nonlinear conductance in diffusion-doped Si:GaAs nanowires contacted by patterned metal films in a wide range of temperatures T. The wire resistance R W and the zero bias resistance R C, dominated by the contacts, exhibit very different responses to temperature changes. While R W shows almost no dependence on T, R C varies by several orders of magnitude as the devices are cooled from room temperature to T = 5 K. We develop a model that employs a sharp donor level very low in the GaAs conduction band and show that our observations are consistent with the model predictions. We then demonstrate that such measurements can be used to estimate carrier properties in nanostructured semiconductors and obtain an estimate for N D, the doping density in our samples. We also discuss the effects of surface states and dielectric confinement on carrier density in semiconductor nanowires.

Optical enhancement of Au doped ZrO2 thin films by sol-gel dip coating method

NASA Astrophysics Data System (ADS)

John Berlin, I.; Joy, K.

2015-01-01

Homogeneous and transparent Au doped ZrO2 thin films were prepared by sol-gel dip coating method. The films have mixed phase of tetragonal, monoclinic and face centered cubic with crack free surface. Due to the increase in Au doping concentration many-body interaction occurs between free carriers and ionized impurities causing decrease in optical band gap from 5.72 to 5.40 eV. Localized surface plasmon resonance peak of the Au doped films appeared at 610 nm. Conversion of photons to surface plasmons allows the sub-wavelength manipulation of electromagnetic radiation. Hence the prepared Au doped ZrO2 thin films can be applied in nanoscale photonic devices such as lenses, switches, waveguides etc. Moreover the photoluminescence (PL) intensity of Au doped ZrO2 thin films decrease due to decrease in the radiative recombination, life time of the excitons and suppression of grain growth of ZrO2 with increasing Au dopant.

Luminescent Photoelectrochemical Cells. 2. Doped Cadmium Sulfide Photoelectrodes as Probes of Excited-State Processes Which Influence Optical to Electrical Energy Conversion.

DTIC Science & Technology

1980-08-12

evidence for electrolyte oxidation processes, and the temporalL ._4 7 variation of photocurrent and emission. 1. Stoichiometrlc Data The stoichiometric...every 48 h. The electrodes, electrolyte compositions, and light sources are given in Table I. The HP 6214A power supply was connected in series with the... series 10 or 100 S resistor. At the end of the experiment, the crystal was demounted and re-weighed. Surface Effects The surfaces of several samples

Crafting ferromagnetism in Mn-doped MgO surfaces with p-type defects

PubMed Central

Panigrahi, Puspamitra; Araujo, C Moyses; Hussen, Tanveer; Ahuja, Rajeev

2014-01-01

We have employed first-principles calculations based on density functional theory (DFT) to investigate the underlying physics of unusual magnetism in Mn-doped MgO surface. We have studied two distinct scenarios. In the first one, two Mn atoms are substitutionally added to the surface, occupying the Mg sites. Both are stabilized in the Mn valence state carrying a local moment of 4.3 having a high-spin configuration. The magnetic interaction between the local moments display a very short-ranged characteristic, decaying very quickly with distance, and having antiferromagnetic ordering lower in energy. The energetics analysis also indicates that the Mn ions prefer to stay close to each other with an oxygen atom bridging the local interaction. In the second scenario, we started exploring the effect of native defects on the magnetism by crafting both Mg and O vacancies, which are p- and n-type defects, respectively. It is found that the electrons and holes affect the magnetic interaction between Mn ions in a totally different manner. The n-type defect leads to very similar magnetism, with the AFM configuration being energetically preferred. However, in the presence of Mg vacancy, the situation is quite different. The Mn atoms are further oxidized, giving rise to mixed Mn(d) ionic states. As a consequence, the Mn atoms couple ferromagnetically, when placed in the close configuration, and the obtained electronic structure is coherent with the double-exchange type of magnetic interaction. To guarantee the robustness of our results, we have benchmarked our calculations with three distinct theory levels, namely DFT-GGA, DFT-GGA+U and DFT-hybrid functionals. On the surface, the Mg vacancy displays lower formation energy occurring at higher concentrations. Therefore, our model systems can be the basis to explain a number of controversial results regarding transition metal doped oxides. PMID:27877684

The surface sulfur doping induced enhanced performance of cobalt catalysts in oxygen evolution reactions.

PubMed

Al-Mamun, Mohammad; Zhu, Zhengju; Yin, Huajie; Su, Xintai; Zhang, Haimin; Liu, Porun; Yang, Huagui; Wang, Dan; Tang, Zhiyong; Wang, Yun; Zhao, Huijun

2016-08-04

A novel surface sulfur (S) doped cobalt (Co) catalyst for the oxygen evolution reaction (OER) is theoretically designed through the optimisation of the electronic structure of highly reactive surface atoms which is also validated by electrocatalytic OER experiments.

Study of magnetic behavior in hexagonal-YMn1-xFexO3 (x=0 and 0.2) nanoparticles using remanent magnetization curves

NASA Astrophysics Data System (ADS)

Chauhan, Samta; Singh, Amit Kumar; Srivastava, Saurabh Kumar; Chandra, Ramesh

2016-09-01

We have studied the magnetic behavior of YMn1-xFexO3 (x=0 and 0.2) nanoparticles synthesized by conventional solid state reaction method. The as-synthesized nanoparticles were found to have hexagonal phase with P63cm space group confirmed by X-Ray diffraction. The particle size was found to be ~70 nm as confirmed by both X-Ray diffraction and Transmission Electron Microscopy. DC magnetization and memory effect measurements imply that the h-YMnO3 nanoparticles bear a resemblance to super spin-glass state following de Almeida-Thouless like behavior which is being suppressed by Fe-doping. The Fe-doping in YMnO3 enhances the antiferromagnetic (AFM) transition temperature TN to ~79 K and induces a new magnetic state due to the surface spins which is realized as diluted antiferromagnet in a field (DAFF) as explored by the thermoremanent and isothermoremanent magnetization measured with different applied magnetic field.

Si and Mg pair-doped interlayers for improving performance of AlGaN/GaN heterostructure field effect transistors grown on Si substrate

NASA Astrophysics Data System (ADS)

Ni, Yi-Qiang; He, Zhi-Yuan; Yao, Yao; Yang, Fan; Zhou, De-Qiu; Zhou, Gui-Lin; Shen, Zhen; Zhong, Jian; Zheng, Yue; Zhang, Bai-Jun; Liu, Yang

2015-05-01

We report a novel structure of AlGaN/GaN heterostructure field effect transistors (HFETs) with a Si and Mg pair-doped interlayer grown on Si substrate. By optimizing the doping concentrations of the pair-doped interlayers, the mobility of 2DEG increases by twice for the conventional structure under 5 K due to the improved crystalline quality of the conduction channel. The proposed HFET shows a four orders lower off-state leakage current, resulting in a much higher on/off ratio (˜ 109). Further temperature-dependent performance of Schottky diodes revealed that the inhibition of shallow surface traps in proposed HFETs should be the main reason for the suppression of leakage current. Project supported by the National Natural Science Foundation of China (Grant Nos. 51177175 and 61274039), the National Basic Research Project of China (Grant Nos. 2010CB923200 and 2011CB301903), the Ph.D. Program Foundation of Ministry of Education of China (Grant No. 20110171110021), the International Sci. & Tech. Collaboration Program of China (Grant No. 2012DFG52260), the National High-tech R&D Program of China (Grant No. 2014AA032606), the Science and Technology Plan of Guangdong Province, China (Grant No. 2013B010401013), and the Opened Fund of the State Key Laboratory on Integrated Optoelectronics (Grant No. IOSKL2014KF17).

Electronic structure of scandium-doped MgB2

NASA Astrophysics Data System (ADS)

de La Peña, Omar; Agrestini, Stefano

2005-03-01

Recently has been reported the synthesis of a new superconducting alloy based on MgB2, where Mg is partially substituted with Sc. In order to analyze the effect of Sc doping on the structural and superconducting properties of Mg1-xScxB2, we have performed a detailed study of the electronic structure for this new diboride. The calculations have been done using the first-principles LAPW method, within the supercell approach for modeling the doping. In this work we report results for the electronic band structure, Fermi surface, and density of states. The effect of the Sc-d orbitals on the structural and electronic properties of Mg1-xScxB2 is analyzed. Increasing the Sc concentration (x) the σ-band is gradually filled, because Sc have one valence electron more than Mg. Interestingly, the analysis of the band structure shows that even for ScB2 the top of the σ-band remain above the Fermi level, nevertheless the σ-band presents high dispersion and has an important contribution of d states. In this way, in addition to the band filling effect, Sc doping gradually reduces the two-dimensional character of the σ- band in Mg1-xScxB2 as a result of increasing the sp(B)-d(Sc) hybridization. This research was partially supported by Consejo Nacional de Ciencia y Tecnolog'ia (CONACYT, M'exico) under Grant. No. 43830-F

Temperature and doping dependent changes in surface recombination during UV illumination of (Al)GaN bulk layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Netzel, Carsten; Jeschke, Jörg; Brunner, Frank

2016-09-07

We have studied the effect of continuous illumination with above band gap energy on the emission intensity of polar (Al)GaN bulk layers during the photoluminescence experiments. A temporal change in emission intensity on time scales from seconds to hours is based on the modification of the semiconductor surface states and the surface recombination by the incident light. The temporal behavior of the photoluminescence intensity varies with the parameters such as ambient atmosphere, pretreatment of the surface, doping density, threading dislocation density, excitation power density, and sample temperature. By means of temperature-dependent photoluminescence measurements, we observed that at least two differentmore » processes at the semiconductor surface affect the non-radiative surface recombination during illumination. The first process leads to an irreversible decrease in photoluminescence intensity and is dominant around room temperature, and the second process leads to a delayed increase in intensity and becomes dominant around T = 150–200 K. Both processes become slower when the sample temperature decreases from room temperature. They cease for T < 150 K. Stable photoluminescence intensity at arbitrary sample temperature was obtained by passivating the analyzed layer with an epitaxially grown AlN cap layer.« less

Imposing long-range ferromagnetic order in rare-earth-doped magnetic topological-insulator heterostructures

NASA Astrophysics Data System (ADS)

Duffy, L. B.; Frisk, A.; Burn, D. M.; Steinke, N.-J.; Herrero-Martin, J.; Ernst, A.; van der Laan, G.; Hesjedal, T.

2018-05-01

The combination of topological properties and magnetic order can lead to new quantum states and exotic physical phenomena, such as the quantum anomalous Hall (QAH) effect. The size of the magnetic gap in the topological surface states, key for the robust observation of the QAH state, scales with the magnetic moment of the doped three-dimensional topological insulator (TI). The pioneering transition-metal doped (Sb,Bi ) 2(Se,Te ) 3 thin films only allow for the observation of the QAH effect up to some 100 mK, despite the much higher magnetic ordering temperatures. On the other hand, high magnetic moment materials, such as rare-earth-doped (Sb,Bi ) 2(Se,Te ) 3 thin films, show large moments but no long-range magnetic order. Proximity coupling and interfacial effects, multiplied in artificial heterostructures, allow for the engineering of the electronic and magnetic properties. Here, we show the successful growth of high-quality Dy:Bi2Te3 /Cr:Sb2Te3 thin film heterostructures. Using x-ray magnetic spectroscopy we demonstrate that high transition temperature Cr:Sb2Te3 can introduce long-range magnetic order in high-moment Dy:Bi2Te3 —up to a temperature of 17 K—in excellent agreement with first-principles calculations, which reveal the origin of the long-range magnetic order in a strong antiferromagnetic coupling between Dy and Cr magnetic moments at the interface extending over several layers. Engineered magnetic TI heterostructures may be an ideal materials platform for observing the QAH effect at liquid He temperatures and above.

Structures and stability of metal-doped Ge{sub n}M (n = 9, 10) clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qin, Wei, E-mail: qinw@qdu.edu.cn; Xia, Lin-Hua; Zhao, Li-Zhen

The lowest-energy structures of neutral and cationic Ge{sub n}M (n = 9, 10; M = Si, Li, Mg, Al, Fe, Mn, Pb, Au, Ag, Yb, Pm and Dy) clusters were studied by genetic algorithm (GA) and first-principles calculations. The calculation results show that doping of the metal atoms and Si into Ge{sub 9} and Ge{sub 10} clusters is energetically favorable. Most of the metal-doped Ge cluster structures can be viewed as adding or substituting metal atom on the surface of the corresponding ground-state Ge{sub n} clusters. However, the neutral and cationic FeGe{sub 9,10},MnGe{sub 9,10} and Ge{sub 10}Al are cage-like withmore » the metal atom encapsulated inside. Such cage-like transition metal doped Ge{sub n} clusters are shown to have higher adsorption energy and thermal stability. Our calculation results suggest that Ge{sub 9,10}Fe and Ge{sub 9}Si would be used as building blocks in cluster-assembled nanomaterials because of their high stabilities.« less

Enrichment of Pyrrolic Nitrogen by Hole Defects in Nitrogen and Sulfur Co-Doped Graphene Hydrogel for Flexible Supercapacitors.

PubMed

Tran, Ngoc Quang; Kang, Bong Kyun; Woo, Moo Hyun; Yoon, Dae Ho

2016-08-23

The effect of the doping configuration and concentration of nitrogen (N) and sulfur (S) on the electrochemical performance of 3 D N and S co-doped hole defect graphene hydrogel (NS-HGH) electrodes is investigated. Surprisingly, by introducing a hole defect on the graphene surface, the difference in the doping concentrations of N and S can be used to effectively modulate the electrochemical behavior of the NS-HGH. The hole defects provide a rapid ion diffusion path. Finally, we showed that the intriguing specific capacitance (536 F g(-1) ) of the NS-HGH could enhance the overall performance of the pseudocapacitance and electric double layer capacitance. The rational design of the NS-HGH-based flexible solid state supercapacitor results in not only outstanding electrochemical performance with a maximum energy density of 14.8 Wh kg(-1) and power density of 5.2 KW kg(-1) but also in extraordinary mechanical flexibility and excellent cycle stability. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electrical properties of lightly Ga-doped ZnO nanowires

NASA Astrophysics Data System (ADS)

Alagha, S.; Heedt, S.; Vakulov, D.; Mohammadbeigi, F.; Senthil Kumar, E.; Schäpers, Th; Isheim, D.; Watkins, S. P.; Kavanagh, K. L.

2017-12-01

We investigated the growth, crystal structure, elemental composition and electrical transport characteristics of ZnO nanowires, a promising candidate for optoelectronic applications in the UV-range. Nominally-undoped and Ga-doped ZnO nanowires were grown by metal-organic chemical vapor deposition. Photoluminescence measurements confirmed the incorporation of Ga via donor-bound exciton emission. With atom-probe tomography we estimated an upper limit of the Ga impurity concentration ({10}18 {{cm}}-3). We studied the electrical transport characteristics of these nanowires with a W-nanoprobe technique inside a scanning electron microscope and with lithographically-defined contacts allowing back-gated measurements. An increase in apparent resistivity by two orders of magnitude with decreasing radius was measured with both techniques with a much larger distribution width for the nanoprobe method. A drop in the effective carrier concentration and mobility was found with decreasing radius which can be attributed to carrier depletion and enhanced scattering due to surface states. Little evidence of a change in resistivity was observed with Ga doping, which indicates that the concentration of native or background dopants is higher than the Ga doping concentration.

Thermal and electrical transport in metals and superconductors across antiferromagnetic and topological quantum transitions

NASA Astrophysics Data System (ADS)

Chatterjee, Shubhayu; Sachdev, Subir; Eberlein, Andreas

2017-08-01

We study thermal and electrical transport in metals and superconductors near a quantum phase transition where antiferromagnetic order disappears. The same theory can also be applied to quantum phase transitions involving the loss of certain classes of intrinsic topological order. For a clean superconductor, we recover and extend well-known universal results. The heat conductivity for commensurate and incommensurate antiferromagnetism coexisting with superconductivity shows a markedly different doping dependence near the quantum critical point, thus allowing us to distinguish between these states. In the dirty limit, the results for the conductivities are qualitatively similar for the metal and the superconductor. In this regime, the geometric properties of the Fermi surface allow for a very good phenomenological understanding of the numerical results on the conductivities. In the simplest model, we find that the conductivities do not track the doping evolution of the Hall coefficient, in contrast to recent experimental findings. We propose a doping dependent scattering rate, possibly due to quenched short-range charge fluctuations below optimal doping, to consistently describe both the Hall data and the longitudinal conductivities.

Adsorption and photocatalytic degradation of pharmaceuticals and pesticides by carbon doped-TiO2 coated on zeolites under solar light irradiation.

PubMed

An, Ye; de Ridder, David Johannes; Zhao, Chun; Schoutteten, Klaas; Bussche, Julie Vanden; Zheng, Huaili; Chen, Gang; Vanhaecke, Lynn

2016-01-01

To evaluate the performance of zeolite-supported carbon-doped TiO(2) composite catalysts toward target pollutants under solar light irradiation, the adsorption and photocatalytic degradation of 18 pharmaceuticals and pesticides with distinguishing features (molecular size and volume, and photolysis) were investigated using mordenite zeolites with SiO(2)/Al(2)O(3) ratios of 18 and 240. Different quantities of carbon-doped TiO(2) were coated on the zeolites, and then the finished composite catalysts were tested in demineralized, surface, and hospital wastewater samples, respectively. The composite photocatalysts were characterized by X-ray diffraction, field emission scanning electron microscopy, and surface area and porosity analyses. Results showed that a dispersed layer of carbon-doped TiO(2) is formed on the zeolite surface; this layer blocks the micropores of zeolites and reduces their surface area. However, these reductions did not significantly affect adsorption onto the zeolites. Our results demonstrated that zeolite-supported carbon-doped TiO(2) systems can effectively degrade 18 pharmaceuticals and pesticides in demineralized water under natural and simulated solar light irradiation. In surface and hospital wastewaters, zeolite-supported carbon-doped TiO(2) systems present excellent anti-interference capability against radical scavengers and competitive organics for pollutants removal, and higher pollutants adsorption on zeolites evidently enhances the removal rate of target pollutants in surface and hospital wastewater samples with a complicated matrix.

Insight into doping efficiency of organic semiconductors from the analysis of the density of states in n-doped C60 and ZnPc

NASA Astrophysics Data System (ADS)

Gaul, Christopher; Hutsch, Sebastian; Schwarze, Martin; Schellhammer, Karl Sebastian; Bussolotti, Fabio; Kera, Satoshi; Cuniberti, Gianaurelio; Leo, Karl; Ortmann, Frank

2018-05-01

Doping plays a crucial role in semiconductor physics, with n-doping being controlled by the ionization energy of the impurity relative to the conduction band edge. In organic semiconductors, efficient doping is dominated by various effects that are currently not well understood. Here, we simulate and experimentally measure, with direct and inverse photoemission spectroscopy, the density of states and the Fermi level position of the prototypical materials C60 and zinc phthalocyanine n-doped with highly efficient benzimidazoline radicals (2-Cyc-DMBI). We study the role of doping-induced gap states, and, in particular, of the difference Δ1 between the electron affinity of the undoped material and the ionization potential of its doped counterpart. We show that this parameter is critical for the generation of free carriers and influences the conductivity of the doped films. Tuning of Δ1 may provide alternative strategies to optimize the electronic properties of organic semiconductors.

Highly improved ethanol gas-sensing performance of mesoporous nickel oxides nanowires with the stannum donor doping.

PubMed

Wei, Junqi; Li, Xiaoqing; Han, Yanbing; Xu, Jingcai; Jin, Hongxiao; Jin, Dingfeng; Peng, Xiaoling; Hong, Bo; Li, Jing; Yang, Yanting; Ge, Hongliang; Wang, Xinqing

2018-06-15

Mesoporous nickel oxides (NiO) and stannum(Sn)-doped NiO nanowires (NWs) were synthesized by using SBA-15 templates with the nanocasting method. X-ray diffraction, transmission electron microscope, energy dispersive spectrometry, nitrogen adsorption/desorption isotherm and UV-vis spectrum were used to characterize the phase structure, components and microstructure of the as-prepared samples. The gas-sensing analysis indicated that the Sn-doping could greatly improve the ethanol sensitivity for mesoporous NiO NWs. With the increasing Sn content, the ethanol sensitivity increased from 2.16 for NiO NWs up to the maximum of 15.60 for Ni 0.962 Sn 0.038 O 1.038 , and then decreased to 12.24 for Ni 0.946 Sn 0.054 O 1.054 to 100 ppm ethanol gas at 340 °C. The high surface area from the Sn-doping improved the adsorption of oxygen on the surface of NiO NWs, resulting in the smaller surface resistance in air. Furthermore, owing to the recombination of the holes in hole-accumulation lay with the electrons from the donor impurity level and the increasing the body defects for Sn-doping, the total resistance in ethanol gas enhanced greatly. It was concluded that the sensitivity of Sn-doped NiO NWs based sensor could be greatly improved by the higher surface area and high-valence donor substitution from Sn-doping.

Highly improved ethanol gas-sensing performance of mesoporous nickel oxides nanowires with the stannum donor doping

NASA Astrophysics Data System (ADS)

Wei, Junqi; Li, Xiaoqing; Han, Yanbing; Xu, Jingcai; Jin, Hongxiao; Jin, Dingfeng; Peng, Xiaoling; Hong, Bo; Li, Jing; Yang, Yanting; Ge, Hongliang; Wang, Xinqing

2018-06-01

Mesoporous nickel oxides (NiO) and stannum(Sn)-doped NiO nanowires (NWs) were synthesized by using SBA-15 templates with the nanocasting method. X-ray diffraction, transmission electron microscope, energy dispersive spectrometry, nitrogen adsorption/desorption isotherm and UV–vis spectrum were used to characterize the phase structure, components and microstructure of the as-prepared samples. The gas-sensing analysis indicated that the Sn-doping could greatly improve the ethanol sensitivity for mesoporous NiO NWs. With the increasing Sn content, the ethanol sensitivity increased from 2.16 for NiO NWs up to the maximum of 15.60 for Ni0.962Sn0.038O1.038, and then decreased to 12.24 for Ni0.946Sn0.054O1.054 to 100 ppm ethanol gas at 340 °C. The high surface area from the Sn-doping improved the adsorption of oxygen on the surface of NiO NWs, resulting in the smaller surface resistance in air. Furthermore, owing to the recombination of the holes in hole-accumulation lay with the electrons from the donor impurity level and the increasing the body defects for Sn-doping, the total resistance in ethanol gas enhanced greatly. It was concluded that the sensitivity of Sn-doped NiO NWs based sensor could be greatly improved by the higher surface area and high-valence donor substitution from Sn-doping.

N-doping effectively enhances the adsorption capacity of biochar for heavy metal ions from aqueous solution.

PubMed

Yu, Wenchao; Lian, Fei; Cui, Guannan; Liu, Zhongqi

2018-02-01

N-doping was successfully employed to improve the adsorption capacity of biochar (BC) for Cu 2+ and Cd 2+ by direct annealing of crop straws in NH 3 . The surface N content of BC increased more than 20 times by N-doping; meanwhile the content of oxidized-N was gradually diminished but graphitic-N was formed and increased with increasing annealing temperature and duration time. After N-doping, a high graphitic-N percentage (46.4%) and S BET (418.7 m 2 /g) can be achieved for BC. As a result, the N-doped BC exhibited an excellent adsorption capacity for Cu 2+ (1.63 mmol g -1 ) and Cd 2+ (1.76 mmol g -1 ), which was up to 4.0 times higher than that of the original BC. Furthermore, the adsorption performance of the N-doped BC remained stable even at acidic conditions. A positive correlation can be found between adsorption capacity with the graphitic N content on BC surface. The surface chemistry of N-doped BC before and after the heavy metal ions adsorption was carefully examined by XPS and FTIR techniques, which indicated that the adsorption mechanisms mainly included cation-π bonding and complexation with graphitic-N and hydroxyl groups of carbon surfaces. Copyright © 2017 Elsevier Ltd. All rights reserved.

Highly tunable magnetism in silicene doped with Cr and Fe atoms under isotropic and uniaxial tensile strain

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, Rui; Ni, Jun, E-mail: junni@mail.tsinghua.edu.cn; Collaborative Innovative Center of Quantum Matter, Beijing 100084

2015-12-28

We have investigated the magnetic properties of silicene doped with Cr and Fe atoms under isotropic and uniaxial tensile strain by the first-principles calculations. We find that Cr and Fe doped silicenes show strain-tunable magnetism. (1) The magnetism of Cr and Fe doped silicenes exhibits sharp transitions from low spin states to high spin states by a small isotropic tensile strain. Specially for Fe doped silicene, a nearly nonmagnetic state changes to a high magnetic state by a small isotropic tensile strain. (2) The magnetic moments of Fe doped silicene also show a sharp jump to ∼2 μ{sub B} at amore » small threshold of the uniaxial strain, and the magnetic moments of Cr doped silicene increase gradually to ∼4 μ{sub B} with the increase of uniaxial strain. (3) The electronic and magnetic properties of Cr and Fe doped silicenes are sensitive to the magnitude and direction of the external strain. The highly tunable magnetism may be applied in the spintronic devices.« less

Plasmon-polaritonic bands in sequential doped graphene superlattices

NASA Astrophysics Data System (ADS)

Ramos-Mendieta, Felipe; Palomino-Ovando, Martha; Hernández-López, Alejandro; Fuentecilla-Cárcamo, Iván

Doped graphene has the extraordinary quality of supporting two types of surface excitations that involve electric charges (the transverse magnetic surface plasmons) or electric currents (the transverse electric modes). We have studied numerically the collective modes that result from the coupling of surface plasmons in doped graphene multilayers. By use of structured supercells with fixed dielectric background and inter layer separation, we found a series of plasmon-polaritonic bands of structure dependent on the doping sequence chosen for the graphene sheets. Periodic and quasiperiodic sequences for the graphene chemical potential have been studied. Our results show that transverse magnetic bands exist only in the low frequency regime but transverse electric bands arise within specific ranges of higher frequencies. Our calculations are valid for THz frequencies and graphene sheets with doping levels between 0.1 eV and 1.2 eV have been considered. AHL and IFC aknowledge fellowship support from CONACYT México.

XPS studies of nitrogen doping niobium used for accelerator applications

NASA Astrophysics Data System (ADS)

Yang, Ziqin; Lu, Xiangyang; Tan, Weiwei; Zhao, Jifei; Yang, Deyu; Yang, Yujia; He, Yuan; Zhou, Kui

2018-05-01

Nitrogen doping study on niobium (Nb) samples used for the fabrication of superconducting radio frequency (SRF) cavities was carried out. The samples' surface treatment was attempted to replicate that of the Nb SRF cavities, which includes heavy electropolishing (EP), nitrogen doping and the subsequent EP with different amounts of material removal. The surface chemical composition of Nb samples with different post treatments has been studied by XPS. The chemical composition of Nb, O, C and N was presented before and after Gas Cluster Ion Beam (GCIB) etching. No signals of poorly superconducting nitrides NbNx was found on the surface of any doped Nb sample with the 2/6 recipe before GCIB etching. However, in the depth range greater than 30 nm, the content of N element is below the XPS detection precision scope even for the Nb sample directly after nitrogen doping treatment with the 2/6 recipe.

Lifshitz topological transitions, induced by doping and deformation in single-crystal bismuth wires

NASA Astrophysics Data System (ADS)

Nikolaeva, A. A.; Konopko, L. A.; Huber, T. E.; Kobylianskaya, A. K.; Para, Gh. I.

2017-02-01

The features associated with the manifestation of Lifshitz electron topological transitions (ETT) in glass-insulated bismuth wires upon qualitative changes to the topology of the Fermi surface are investigated. The variation of the energy spectrum parameters was implemented by doping Bi with an acceptor impurity Sn and using elastic strain of up to 2%, relative to the elongation in the weakly-doped p-type Bi wires. Pure and doped glass-insulated single-crystal bismuth with different diameters and (1011) orientations along the axis were prepared by the Ulitovsky liquid phase casting method. For the first time, ETT-induced anomalies are observed along the temperature dependences of the thermoemf α(T) as triple-changes of the α sign (given heavy doping of Bi wires with an acceptor impurity Sn). The concentration and energy position of the Σ-band given a high degree of bismuth doping with Sn was assessed using the Shubnikov-de Haas effect oscillations, which were detected both from L-electrons and from T-holes in magnetic fields of up to 14 T. It is shown that the Lifshitz electron-topological transitions with elastic deformation of weakly-doped p-type Bi wires are accompanied by anomalies along the deformation dependences of the thermoemf at low temperatures. The effect is interpreted in terms of the formation of a selective scattering channel of L-carriers into the T-band with a high density of states, which is in good agreement with existing theoretical ETT models.

Formation of an incoherent metallic state in Rh-doped Sr2IrO4

NASA Astrophysics Data System (ADS)

Louat, A.; Bert, F.; Serrier-Garcia, L.; Bertran, F.; Le Fèvre, P.; Rault, J.; Brouet, V.

2018-04-01

Sr2IrO4 is the archetype of the spin-orbit Mott insulator, but the nature of the metallic states that may emerge from this type of insulator is still not very well known. We study with angle-resolved photoemission the insulator-to-metal transition observed in Sr2Ir1 -xRhxO4 when Ir is substituted by Rh (0.02 0.07 , is not a Fermi liquid. It is characterized by the absence of quasiparticles, unrenormalized band dispersion compared to calculations, and an ˜30 -meV pseudogap on the entire Fermi surface.

Electrical properties of zinc-oxide-based thin-film transistors using strontium-oxide-doped semiconductors

NASA Astrophysics Data System (ADS)

Wu, Shao-Hang; Zhang, Nan; Hu, Yong-Sheng; Chen, Hong; Jiang, Da-Peng; Liu, Xing-Yuan

2015-10-01

Strontium-zinc-oxide (SrZnO) films forming the semiconductor layers of thin-film transistors (TFTs) are deposited by using ion-assisted electron beam evaporation. Using strontium-oxide-doped semiconductors, the off-state current can be dramatically reduced by three orders of magnitude. This dramatic improvement is attributed to the incorporation of strontium, which suppresses carrier generation, thereby improving the TFT. Additionally, the presence of strontium inhibits the formation of zinc oxide (ZnO) with the hexagonal wurtzite phase and permits the formation of an unusual phase of ZnO, thus significantly changing the surface morphology of ZnO and effectively reducing the trap density of the channel. Project supported by the National Natural Science Foundation of China (Grant No. 6140031454) and the Innovation Program of Chinese Academy of Sciences and State Key Laboratory of Luminescence and Applications.

Periodic DFT study of acidic trace atmospheric gas molecule adsorption on Ca- and Fe-doped MgO(001) surface basic sites.

PubMed

Baltrusaitis, Jonas; Hatch, Courtney; Orlando, Roberto

2012-08-02

The electronic properties of undoped and Ca- or Fe-doped MgO(001) surfaces, as well as their propensity toward atmospheric acidic gas (CO2, SO2, and NO2) uptake was investigated with an emphasis on gas adsorption on the basic MgO oxygen surface sites, O(surf), using periodic density functional theory (DFT) calculations. Adsorption energy calculations show that MgO doping will provide stronger interactions of the adsorbate with the O(surf) sites than the undoped MgO for a given adsorbate molecule. Charge transfer from the iron atom in Fe-doped MgO(001) to NO2 was shown to increase the binding interaction between adsorbate by an order of magnitude, when compared to that of undoped and Ca-doped MgO(001) surfaces. Secondary binding interactions of adsorbate oxygen atoms were observed with surface magnesium sites at distances close to those of the Mg-O bond within the crystal. These interactions may serve as a preliminary step for adsorption and facilitate further adsorbate transformations into other binding configurations. Impacts on global atmospheric chemistry are discussed as these adsorption phenomena can affect atmospheric gas budgets via altered partitioning and retention on mineral aerosol surfaces.

Periodic DFT study of acidic trace atmospheric gas molecule adsorption on Ca and Fe doped MgO (001) surface basic sites

PubMed Central

Hatch, Courtney; Orlando, Roberto

2012-01-01

The electronic properties of undoped and Ca or Fe doped MgO (001) surfaces, as well as their propensity towards atmospheric acidic gas (CO2, SO2 and NO2) uptake was investigated with an emphasis on gas adsorption on the basic MgO oxygen surface sites, Osurf, using periodic Density Functional Theory (DFT) calculations. Adsorption energy calculations show that MgO doping will provide stronger interactions of the adsorbate with the Osurf sites than the undoped MgO for a given adsorbate molecule. Charge transfer from the iron atom in Fe doped MgO (001) to NO2 was shown to increase the binding interaction between adsorbate by an order of magnitude, when compared to that of undoped and Ca doped MgO (001) surfaces. Secondary binding interactions of adsorbate oxygen atoms were observed with surface magnesium sites at distances close to those of the Mg-O bond within the crystal. These interactions may serve as a preliminary step for adsorption and facilitate further adsorbate transformations into other binding configurations. Impacts on global atmospheric chemistry are discussed as these adsorption phenomena can affect atmospheric gas budgets via altered partitioning and retention on mineral aerosol surfaces. PMID:22775293

Electronic, optical and photocatalytic behavior of Mn, N doped and co-doped TiO{sub 2}: Experiment and simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Ya Fei; Li, Can, E-mail: canli1983@gmail.com; Lu, Song

2016-03-15

The crystal phase structure, surface morphology, chemical states and optical properties of Mn, N mono-doped and co-doped TiO{sub 2} nanoparticles were investigated by X-ray powder diffractometry, Raman spectra, scanning electron microscopy, X-ray photoelectron spectroscopy and UV–vis diffuse reflectance spectroscopy. Meanwhile, geometry structures, formation energies, electronic and optical properties of all systems have been also analyzed by density functional theory. The results showed that the band gap values and the carrier mobility in the valence band, conduction band and impurity levels have a synergetic influence on the visible-light absorption and photocatalytic activity of the doped TiO{sub 2}. The number and themore » carrier mobility of impurity level jointly influence the photocatalytic activity of catalyst under visible-light. Especially, the photocatalytic activity of Mn-2N co-doped TiO{sub 2} beyond three-fold than that of pure TiO{sub 2} under visible-light. - Graphical abstract: The ILs formed by N-2p orbital in N single doped specimen lie above the VB, while the ILs formed by Mn-3d orbital in Mn single doped specimen appear below the CB. However, a large amount of ILs formed by N-2p orbital and Mn-3d orbital in N and Mn codoped specimens. The band gap values and the carrier mobility in the valence band, conduction band and impurity levels have a synergetic influence on the visible-light absorption and photocatalytic activity of the doped TiO{sub 2}. The number and the carrier mobility of impurity level jointly influence the photocatalytic activity of catalyst under visible-light.« less

Holon Wigner Crystal in a Lightly Doped Kagome Quantum Spin Liquid

DOE PAGES

Jiang, Hong -Chen; Devereaux, T.; Kivelson, S. A.

2017-08-07

We address the problem of a lightly doped spin liquid through a large-scale density-matrix renormalization group study of the t–J model on a kagome lattice with a small but nonzero concentration δ of doped holes. It is now widely accepted that the undoped (δ = 0) spin-1/2 Heisenberg antiferromagnet has a spin-liquid ground state. Theoretical arguments have been presented that light doping of such a spin liquid could give rise to a high temperature superconductor or an exotic topological Fermi liquid metal. Instead, we infer that the doped holes form an insulating charge-density wave state with one doped hole permore » unit cell, i.e., a Wigner crystal. Spin correlations remain short ranged, as in the spin-liquid parent state, from which we infer that the state is a crystal of spinless holons, rather than of holes. In conclusion, our results may be relevant to kagome lattice herbertsmithite upon doping.« less

Polycrystalline ZnO and Mn-doped ZnO nanorod arrays with variable dopant content via a template based synthesis from Zn(II) and Mn(II) Schiff base type single source molecular precursors

NASA Astrophysics Data System (ADS)

Pashchanka, Mikhail; Hoffmann, Rudolf C.; Burghaus, Olaf; Corzilius, Björn; Cherkashinin, Gennady; Schneider, Jörg J.

2011-01-01

The synthesis and full characterisation of pure and Mn-doped polycrystalline zinc oxide nanorods with tailored dopant content are obtained via a single source molecular precursor approach using two Schiff base type coordination compounds is reported. The infiltration of precursor solutions into the cylindrical pores of a polycarbonate template and their thermal conversion into a ceramic green body followed by dissolution of the template gives the desired ZnO and Mn-doped ZnO nanomaterial as compact rods. The ZnO nanorods have a mean diameter between 170 and 180 nm or 60-70 nm, depending on the template pore size employed, comprising a length of 5-6 μm. These nanorods are composed of individual sub-5 nm ZnO nanocrystals. Exact doping of these hierarchically structured ZnO nanorods was achieved by introducing Mn(II) into the ZnO host lattice with the precursor complex Diaquo-bis[2-(meth-oxyimino)-propanoato]manganese, which allows to tailor the exact Mn(II) doping content of the ZnO rods. Investigation of the Mn-doped ZnO samples by XRD, TEM, XPS, PL and EPR, reveals that manganese occurs exclusively in its oxidation state + II and is distributed within the volume as well as on the surface of the ZnO host.

Doping of Ga in antiferromagnetic semiconductor α-Cr2O3 and its effects on magnetic and electronic properties

NASA Astrophysics Data System (ADS)

Bhowmik, R. N.; Venkata Siva, K.; Ranganathan, R.; Mazumdar, Chandan

2017-06-01

The samples of Ga-doped Cr2O3 have been prepared using chemical co-precipitation route. X-ray diffraction pattern and Raman spectra have indicated rhombohedral crystal structure with space group R 3 bar C. Magnetic measurements indicated diluted antiferromagnetic (AFM) spin order in Ga-doped α-Cr2O3 and ferrimagnetic ordering of spins at about 50-60 K is confirmed from the analysis of the temperature dependence of dc magnetization and ac susceptibility data. Apart from magnetic dilution effect, the samples have shown superparamagnetic behavior below 50 K due to frustrated surface spins of the nano-sized grains. The samples have shown non-linear electronic properties. The current-voltage (I-V) characteristics of the Ga-doped α-Cr2O3 samples are remarkably different from α-Cr2O3 sample. The bi-stable electronic states and negative differential resistance are some of the unique non-linear electronic properties that the I-V curves of Ga-doped samples have exhibited. Optical study revealed three electronic transitions in the samples associated with band gap energy at about 2.67-2.81 eV, 1.91-2.11 eV, 1.28-1.35 eV, respectively. The results indicated multi-level electronic structure in Ga-doped α-Cr2O3 system.

Green synthesis of boron doped graphene and its application as high performance anode material in Li ion battery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sahoo, Madhumita; Sreena, K.P.; Vinayan, B.P.

2015-01-15

Graphical abstract: Boron doped graphene (B-G), synthesized by simple hydrogen induced reduction technique using boric acid as boron precursor, have more uneven surface as a result of smaller bonding distance of boron compared to carbon, showed high capacity and high rate capability compared to pristine graphene as an anode material for Li ion battery application. - Abstract: The present work demonstrates a facile route for the large-scale, catalyst free, and green synthesis approach of boron doped graphene (B-G) and its use as high performance anode material for Li ion battery (LIB) application. Boron atoms were doped into graphene framework withmore » an atomic percentage of 5.93% via hydrogen induced thermal reduction technique using graphite oxide and boric acid as precursors. Various characterization techniques were used to confirm the boron doping in graphene sheets. B-G as anode material shows a discharge capacity of 548 mAh g{sup −1} at 100 mA g{sup −1} after 30th cycles. At high current density value of 1 A g{sup −1}, B-G as anode material enhances the specific capacity by about 1.7 times compared to pristine graphene. The present study shows a simplistic way of boron doping in graphene leading to an enhanced Li ion adsorption due to the change in electronic states.« less

Effect of silicon, tantalum, and tungsten doping and polarization on bioactivity of hydroxyapatite

NASA Astrophysics Data System (ADS)

Dhal, Jharana

Hydroxyapatite (HAp) ceramics has important applications as bone graft because of the structural and compositional similarities with bone tissue. However, inferior osteogenic capacity to bone and poor mechanical properties have been identified to be major disadvantages of synthetic HAp compared to the living bone tissue. The objective of the current study is to evaluate the effect of doping with higher valent cations (Tungsten, tantalum, and silicon) and polarization or combination of both on change in property of doped HAp and subsequent impact its bioactivity. In vitro study with human osteoblast cells was used to investigate the influences of doping and polarization on bone cell-materials interactions. The bioactivity of doped HAp was compared with pure HAp. Effect of doping and polarization on the change in HAp was investigated by monitoring change in mineral phases, stored charge, and activation energy of HAp. Activation energy of depolarization was used to explain the possible mechanism of polarization in doped samples. Bioactivity of HAp increased when doped with tantalum and tungsten. Polarization further increased the bioactivity of tungsten- and tantalum-doped samples. Increase in bioactivity on polarized and doped samples was attributed to increase in surface energy and increase in surface wettability. Whereas, an increase in bioactivity on doped unpolarized surface was attributed to change in microstructure. Polarized charge calculated from TSDC indicates that polarized charge decreases on tantalum- and tungsten-doped HAp. The decrease in polarized charge was attributed to the presence of significant amount of different phases that may hinder the ionic motion in doped samples. However, for silicon-doped HAp, TSDC study showed no difference in the mechanism of polarization between doped and undoped samples. Increase in silicon doping decreased the grain size though mechanism is not affected by grain size. Total stored charge decreased with increase in dopant concentration at a particular sintering temperature. Results of this study provide further evidence for use of higher valence cations to improve biological performance of HAp ceramics and to advance our understanding on mechanism of polarization in doped samples.

Structural, Morphological, Optical and Photocatalytic Properties of Y, N-Doped and Codoped TiO2 Thin Films

PubMed Central

Hamden, Zeineb; Conceição, David; Boufi, Sami; Vieira Ferreira, Luís Filipe; Bouattour, Soraa

2017-01-01

Pure TiO2, Y-N single-doped and codoped TiO2 powders and thin films deposited on glass beads were successfully prepared using dip-coating and sol-gel methods. The samples were analyzed using grazing angle X-ray diffraction (GXRD), Raman spectroscopy, time resolved luminescence, ground state diffuse reflectance absorption and scanning electron microscopy (SEM). According to the GXRD patterns and micro-Raman spectra, only the anatase form of TiO2 was made evident. Ground state diffuse reflectance absorption studies showed that doping with N or codoping with N and Y led to an increase of the band gap. Laser induced luminescence analysis revealed a decrease in the recombination rate of the photogenerated holes and electrons. The photocatalytic activity of supported catalysts, toward the degradation of toluidine, revealed a meaningful enhancement upon codoping samples at a level of 2% (atomic ratio). The photocatalytic activity of the material and its reactivity can be attributed to a reduced, but significant, direct photoexcitation of the semiconductor by the halogen lamp, together with a charge-transfer-complex mechanism, or with the formation of surface oxygen vacancies by the N dopant atoms. PMID:28772962

Structural, Morphological, Optical and Photocatalytic Properties of Y, N-Doped and Codoped TiO₂ Thin Films.

PubMed

Hamden, Zeineb; Conceição, David; Boufi, Sami; Vieira Ferreira, Luís Filipe; Bouattour, Soraa

2017-05-31

Pure TiO₂, Y-N single-doped and codoped TiO₂ powders and thin films deposited on glass beads were successfully prepared using dip-coating and sol-gel methods. The samples were analyzed using grazing angle X-ray diffraction (GXRD), Raman spectroscopy, time resolved luminescence, ground state diffuse reflectance absorption and scanning electron microscopy (SEM). According to the GXRD patterns and micro-Raman spectra, only the anatase form of TiO₂ was made evident. Ground state diffuse reflectance absorption studies showed that doping with N or codoping with N and Y led to an increase of the band gap. Laser induced luminescence analysis revealed a decrease in the recombination rate of the photogenerated holes and electrons. The photocatalytic activity of supported catalysts, toward the degradation of toluidine, revealed a meaningful enhancement upon codoping samples at a level of 2% (atomic ratio). The photocatalytic activity of the material and its reactivity can be attributed to a reduced, but significant, direct photoexcitation of the semiconductor by the halogen lamp, together with a charge-transfer-complex mechanism, or with the formation of surface oxygen vacancies by the N dopant atoms.

The Path to High Q-Factors in Superconducting Accelerating Cavities: Flux Expulsion and Surface Resistance Optimization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martinello, Martina

Accelerating cavities are devices resonating in the radio-frequency (RF) range used to accelerate charged particles in accelerators. Superconducting accelerating cavities are made out of niobium and operate at the liquid helium temperature. Even if superconducting, these resonating structures have some RF driven surface resistance that causes power dissipation. In order to decrease as much as possible the power losses, the cavity quality factor must be increased by decreasing the surface resistance. In this dissertation, the RF surface resistance is analyzed for a large variety of cavities made with different state-of-the-art surface treatments, with the goal of finding the surface treatmentmore » capable to return the highest Q-factor values in a cryomodule-like environment. This study analyzes not only the superconducting properties described by the BCS surface resistance, which is the contribution that takes into account dissipation due to quasi-particle excitations, but also the increasing of the surface resistance due to trapped flux. When cavities are cooled down below their critical temperature inside a cryomodule, there is always some remnant magnetic field that may be trapped increasing the global RF surface resistance. This thesis also analyzes how the fraction of external magnetic field, which is actually trapped in the cavity during the cooldown, can be minimized. This study is performed on an elliptical single-cell horizontally cooled cavity, resembling the geometry of cavities cooled in accelerator cryomodules. The horizontal cooldown study reveals that, as in case of the vertical cooldown, when the cooling is performed fast, large thermal gradients are created along the cavity helping magnetic flux expulsion. However, for this geometry the complete magnetic flux expulsion from the cavity equator is more difficult to achieve. This becomes even more challenging in presence of orthogonal magnetic field, that is easily trapped on top of the cavity equator causing temperature rising. The physics behind the magnetic flux expulsion is also analyzed, showing that during a fast cooldown the magnetic field structures, called vortices, tend to move in the same direction of the thermal gradient, from the Meissner state region to the mixed state region, minimizing the Gibbs free energy. On the other hand, during a slow cool down, not only the vortices movement is limited by the absence of thermal gradients, but, also, at the end of the superconducting transition, the magnetic field concentrates along randomly distributed normal-conducting region from which it cannot be expelled anymore. The systematic study of the surface resistance components performed for the different surface treatments, reveals that the BCS surface resistance and the trapped flux surface resistance have opposite trends as a function of the surface impurity content, defined by the mean free path. At medium field value, the BCS surface resistance is minimized for nitrogen-doped cavities and significantly larger for standard niobium cavities. On the other hand, Nitrogen-doped cavities show larger dissipation due to trapped flux. This is consequence of the bell-shaped trend of the trapped flux sensitivity as a function of the mean free path. Such experimental findings allow also a better understanding of the RF dissipation due to trapped flux. The best compromise between all the surface resistance components, taking into account the possibility of trapping some external magnetic field, is given by light nitrogen-doping treatments. However, the beneficial effects of the nitrogen-doping is completely lost when large amount of magnetic field is trapped during the cooldown, underlying the importance of both cooldown and magnetic field shielding optimization in high quality factors cryomodules.« less

Quantum oscillations from the reconstructed Fermi surface in electron-doped cuprate superconductors

NASA Astrophysics Data System (ADS)

Higgins, J. S.; Chan, M. K.; Sarkar, Tarapada; McDonald, R. D.; Greene, R. L.; Butch, N. P.

2018-04-01

We have studied the electronic structure of electron-doped cuprate superconductors via measurements of high-field Shubnikov–de Haas oscillations in thin films. In optimally doped Pr2‑x Ce x CuO4±δ and La2‑x Ce x CuO4±δ , quantum oscillations indicate the presence of a small Fermi surface, demonstrating that electronic reconstruction is a general feature of the electron-doped cuprates, despite the location of the superconducting dome at very different doping levels. Negative high-field magnetoresistance is correlated with an anomalous low-temperature change in scattering that modifies the amplitude of quantum oscillations. This behavior is consistent with effects attributed to spin fluctuations.

Suppression of surface segregation of the phosphorous δ-doping layer by insertion of an ultra-thin silicon layer for ultra-shallow Ohmic contacts on n-type germanium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamada, Michihiro; Uematsu, Masashi; Itoh, Kohei M., E-mail: kitoh@appi.keio.ac.jp

2015-09-28

We demonstrate the formation of abrupt phosphorus (P) δ-doping profiles in germanium (Ge) by the insertion of ultra-thin silicon (Si) layers. The Si layers at the δ-doping region significantly suppress the surface segregation of P during the molecular beam epitaxial growth of Ge and high-concentration active P donors are confined within a few nm of the initial doping position. The current-voltage characteristics of the P δ-doped layers with Si insertion show excellent Ohmic behaviors with low enough resistivity for ultra-shallow Ohmic contacts on n-type Ge.

Humidity sensing properties of Al-doped zinc oxide coating films

NASA Astrophysics Data System (ADS)

Saidi, S. A.; Mamat, M. H.; Ismail, A. S.; Malek, M. F.; Yusoff, M. M.; Sin, N. D. Md.; Zoolfakar, A. S.; Khusaimi, Z.; Rusop, M.

2018-05-01

Humidity sensor was fabricated using Al-doped zinc oxide (ZnO) coating films through spin-coating at room temperature. The sensing mechanism was discussed based on their nanostructures, such as surface area and porous nanostructures. Surface area and water adsorption are an important component in the low humidity, while at high humidity, porous nanostructures and capillary condensation become important. The results showed that the sensitivity of the Al-doped ZnO coating improved compared to that of the Al-doped ZnO nanorod arrays, with values of 7.38 at 40% to 90%RH (Relative humidity). All these results indicated that Al-doped ZnO coating had high potential for humidity-sensor applications.

Ab initio study of Ga-GaN system: Transition from adsorbed metal atoms to a metal–semiconductor junction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Witczak, Przemysław; Kempisty, Pawel; Strak, Pawel

2015-11-15

Ab initio studies of a GaN(0001)-Ga system with various thicknesses of a metallic Ga layer were undertaken. The studied systems extend from a GaN(0001) surface with a fractional coverage of gallium atoms to a Ga-GaN metal–semiconductor (m–s) contact. Electronic properties of the system are simulated using density functional theory calculations for different doping of the bulk semiconductor. It is shown that during transition from a bare GaN(0001) surface to a m–s heterostructure, the Fermi level stays pinned at a Ga-broken bond highly dispersive surface state to Ga–Ga states at the m–s interface. Adsorption of gallium leads to an energy gainmore » of about 4 eV for a clean GaN(0001) surface and the energy decreases to 3.2 eV for a thickly Ga-covered surface. The transition to the m–s interface is observed. For a thick Ga overlayer such interface corresponds to a Schottky contact with a barrier equal to 0.9 and 0.6 eV for n- and p-type, respectively. Bond polarization-related dipole layer occurring due to an electron transfer to the metal leads to a potential energy jump of 1.5 eV, independent on the semiconductor doping. Additionally high electron density in the Ga–Ga bond region leads to an energy barrier about 1.2 eV high and 4 Å wide. This feature may adversely affect the conductivity of the n-type m–s system.« less

Biocompatibility of Mg Ion Doped Hydroxyapatite Films on Ti-6Al-4V Surface by Electrochemical Deposition.

PubMed

Lee, Kang; Choe, Han-Cheol

2016-02-01

In this study, we prepared magnesium (Mg) doped nano-phase hydroxyapatite (HAp) films on the TiO2 nano-network surface using electrochemical deposition method. Ti-6Al-4V ELI surface was anodized in 5 M NaOH solution at 0.3 A for 10 min. Nano-network TiO2 surface were formed by these anodization steps which acted as templates and anchorage for growth of the Mg doped HAp during subsequent pulsed electrochemical deposition process at 85 degrees C. The phase and morphologies of HAp deposits were influenced by the Mg ion concentration.

Optical and magnetic properties of free-standing silicene, germanene and T-graphene system

NASA Astrophysics Data System (ADS)

Chowdhury, Suman; Bandyopadhyay, Arka; Dhar, Namrata; Jana, Debnarayan

2017-05-01

The physics of two-dimensional (2D) materials is always intriguing in their own right. For all of these elemental 2D materials, a generic characteristic feature is that all the atoms of the materials are exposed on the surface, and thus tuning the structure and physical properties by surface treatments becomes very easy and straightforward. The discovery of graphene have fostered intensive research interest in the field of graphene like 2D materials such as silicene and germanene (hexagonal network of silicon and germanium, respectively). In contrast to the planar graphene lattice, the silicene and germanene honeycomb lattice is slightly buckled and composed of two vertically displaced sublattices.The magnetic properties were studied by introducing mono- and di-vacancy (DV), as well as by doping phosphorus and aluminium into the pristine silicene. It is observed that there is no magnetism in the mono-vacancy system, while there is large significant magnetic moment present for the DV system. The optical anisotropy of four differently shaped silicene nanodisks has revealed that diamond-shaped (DS) silicene nanodisk possesses highest static dielectric constant having no zero-energy states. The study of optical properties in silicene nanosheet network doped by aluminium (Al), phosphorus (P) and aluminium-phosphorus (Al-P) atoms has revealed that unlike graphene, no new electron energy loss spectra (EELS) peak occurs irrespective of doping type for parallel polarization. Tetragonal graphene (T-graphene) having non-equivalent (two kinds) bonds and non-honeycomb structure shows Dirac-like fermions and high Fermi velocity. The higher stability, large dipole moment along with high-intensity Raman active modes are observed in N-doped T-graphene. All these theoretical results may shed light on device fabrication in nano-optoelectronic technology and material characterization techniques in T-graphene, doped silicene, and germanene.

Electron Doping a Kagome Spin Liquid

NASA Astrophysics Data System (ADS)

Kelly, Zachary; Gallagher, Miranda; McQueen, Tyrel

In 1987, Anderson proposed that charge doping a material with the resonating valance bond (RVB) state would yield a superconducting state. Ever since, there has been a search for these RVB containing spin liquid materials and their charge doped counterparts. Studies on the most promising spin liquid candidate, Herbertsmithite, ZnCu3(OH)6Cl2, a two dimensional kagomé lattice, show evidence of fractionalized excitations and a gapped ground state. In this work, we report the synthesis and characterization of a newly synthesized electron doped spin liquid, ZnLixCu3(OH)6Cl2 from x = 0 to x = 1.8 (3 / 5 th per Cu2+). Despite heavy doping, the series remains insulating and the magnetism is systematically suppressed. We have done extensive structural studies of the doped series to determine the effect of the intercalated atoms on the structure, and whether these structural differences induce strong localization effects that suppress the metallic and superconducting states. Other doped spin liquid candidates are also being explored to understand if this localization is system dependent or systemic to all doped spin liquid systems. NSF, Division of Materials Research (DMR), Solid State Chemistry (SSMC), CAREER Grant under Award No. DMR- 1253562, Institute for Quantum Matter under Grant No.DE-FG02- 08ER46544, and the David and Lucile Packard Foundation.

Visible-light sensitization of TiO2 photocatalysts via wet chemical N-doping for the degradation of dissolved organic compounds in wastewater treatment: a review

NASA Astrophysics Data System (ADS)

Zhang, Wei; Jia, Baoping; Wang, Qiuze; Dionysiou, Dionysois

2015-05-01

Increased pollution of ground and surface water and emerging new micropollutants from a wide variety of industrial, municipal, and agricultural sources has increased demand on the development of innovative new technologies and materials whereby challenges associated with the provision of safe potable water can be addressed. Heterogeneous photocatalysis using visible-light sensitized TiO2 photocatalysts has attracted a lot of attention as it can effectively remove dissolved organic compound in water without generating harmful by-products. On this note, recent progress on visible-light sensitive TiO2 synthesis via wet chemical N-doping method is reviewed. In a typical visible-light sensitive TiO2 preparation via wet chemical methods, the chemical (e.g., N-doping content and states) and morphological properties (e.g., particle size, surface area, and crystal phase) of TiO2 in as-prepared resultants are sensitively dependent on many experimental variables during the synthesis. This has also made it very difficult to provide a universal guidance at this stage with a certainty for each variable of N-doping preparation. Instead of one-factor-at-a-time style investigation, a statistically valid parameter optimization investigation for general optima of photocatalytic activity will be certainly useful. Optimization of the preparation technique is envisaged to be beneficial to many environmental applications, i.e., dissolved organic compounds removal in wastewater treatment.

Structure disorder degree of polysilicon thin films grown by different processing: Constant C from Raman spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Quan, E-mail: wangq@mail.ujs.edu.cn; State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000; Zhang, Yanmin

2013-11-14

Flat, low-stress, boron-doped polysilicon thin films were prepared on single crystalline silicon substrates by low pressure chemical vapor deposition. It was found that the polysilicon films with different deposition processing have different microstructure properties. The confinement effect, tensile stresses, defects, and the Fano effect all have a great influence on the line shape of Raman scattering peak. But the effect results are different. The microstructure and the surface layer are two important mechanisms dominating the internal stress in three types of polysilicon thin films. For low-stress polysilicon thin film, the tensile stresses are mainly due to the change of microstructuremore » after thermal annealing. But the tensile stresses in flat polysilicon thin film are induced by the silicon carbide layer at surface. After the thin film doped with boron atoms, the phenomenon of the tensile stresses increasing can be explained by the change of microstructure and the increase in the content of silicon carbide. We also investigated the disorder degree states for three polysilicon thin films by analyzing a constant C. It was found that the disorder degree of low-stress polysilicon thin film larger than that of flat and boron-doped polysilicon thin films due to the phase transformation after annealing. After the flat polysilicon thin film doped with boron atoms, there is no obvious change in the disorder degree and the disorder degree in some regions even decreases.« less

High-surface-area nitrogen-doped reduced graphene oxide for electric double-layer capacitors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Youn, Hee-Chang; Bak, Seong-Min; Kim, Myeong-Seong

A two-step method consisting of solid-state microwave irradiation and heat treatment under NH₃ gas was used to prepare nitrogen-doped reduced graphene oxide (N-RGO) with a high specific surface area (1007m²g⁻¹), high electrical conductivity (1532S m⁻¹), and low oxygen content (1.5 wt%) for electric double-layer capacitor applications. The specific capacitance of N-RGO was 291 Fg⁻¹ at a current density of 1 A g⁻¹, and a capacitance of 261 F g⁻¹ was retained at 50 A g⁻¹, indicating a very good rate capability. N-RGO also showed excellent cycling stability, preserving 96% of the initial specific capacitance after 100,000 cycles. Near-edge X-ray absorptionmore » fine-structure spectroscopy evidenced the recover of π-conjugation in the carbon networks with the removal of oxygenated groups and revealed the chemical bonding of the nitrogen atoms in N-RGO. The good electrochemical performance of N-RGO is attributed to its high surface area, high electrical conductivity, and low oxygen content.« less

High-surface-area nitrogen-doped reduced graphene oxide for electric double-layer capacitors

DOE PAGES

Youn, Hee-Chang; Bak, Seong-Min; Kim, Myeong-Seong; ...

2015-06-08

A two-step method consisting of solid-state microwave irradiation and heat treatment under NH₃ gas was used to prepare nitrogen-doped reduced graphene oxide (N-RGO) with a high specific surface area (1007m²g⁻¹), high electrical conductivity (1532S m⁻¹), and low oxygen content (1.5 wt%) for electric double-layer capacitor applications. The specific capacitance of N-RGO was 291 Fg⁻¹ at a current density of 1 A g⁻¹, and a capacitance of 261 F g⁻¹ was retained at 50 A g⁻¹, indicating a very good rate capability. N-RGO also showed excellent cycling stability, preserving 96% of the initial specific capacitance after 100,000 cycles. Near-edge X-ray absorptionmore » fine-structure spectroscopy evidenced the recover of π-conjugation in the carbon networks with the removal of oxygenated groups and revealed the chemical bonding of the nitrogen atoms in N-RGO. The good electrochemical performance of N-RGO is attributed to its high surface area, high electrical conductivity, and low oxygen content.« less

A theoretical analysis of the current-voltage characteristics of solar cells. [and their energy conversion efficiency

NASA Technical Reports Server (NTRS)

Dunbar, P. M.; Hauser, J. R.

1976-01-01

Various mechanisms which limit the conversion efficiency of silicon solar cells were studied. The effects of changes in solar cell geometry such as layer thickness on performance were examined. The effects of various antireflecting layers were also examined. It was found that any single film antireflecting layer results in a significant surface loss of photons. The use of surface texturing techniques or low loss antireflecting layers can enhance by several percentage points the conversion efficiency of silicon cells. The basic differences between n(+)-p-p(+) and p(+)-n-n(+) cells are treated. A significant part of the study was devoted to the importance of surface region lifetime and heavy doping effects on efficiency. Heavy doping bandgap reduction effects are enhanced by low surface layer lifetimes, and conversely, the reduction in solar cell efficiency due to low surface layer lifetime is further enhanced by heavy doping effects. A series of computer studies is reported which seeks to determine the best cell structure and doping levels for maximum efficiency.

Manipulating charge density waves in 1 T -TaS2 by charge-carrier doping: A first-principles investigation

NASA Astrophysics Data System (ADS)

Shao, D. F.; Xiao, R. C.; Lu, W. J.; Lv, H. Y.; Li, J. Y.; Zhu, X. B.; Sun, Y. P.

2016-09-01

The transition-metal dichalcogenide 1 T -TaS2 exhibits a rich set of charge-density-wave (CDW) orders. Recent investigations suggested that using light or an electric field can manipulate the commensurate CDW (CCDW) ground state. Such manipulations are considered to be determined by charge-carrier doping. Here we use first-principles calculations to simulate the carrier-doping effect on the CCDW in 1 T -TaS2 . We investigate the charge-doping effects on the electronic structures and phonon instabilities of the 1 T structure, and we analyze the doping-induced energy and distortion ratio variations in the CCDW structure. We found that both in bulk and monolayer 1 T -TaS2 , the CCDW is stable upon electron doping, while hole doping can significantly suppress the CCDW, implying different mechanisms of such reported manipulations. Light or positive perpendicular electric-field-induced hole doping increases the energy of the CCDW, so that the system transforms to a nearly commensurate CDW or a similar metastable state. On the other hand, even though the CCDW distortion is more stable upon in-plane electric-field-induced electron injection, some accompanied effects can drive the system to cross over the energy barrier from the CCDW to a nearly commensurate CDW or a similar metastable state. We also estimate that hole doping can introduce potential superconductivity with a Tc of 6-7 K. Controllable switching of different states such as a CCDW/Mott insulating state, a metallic state, and even a superconducting state can be realized in 1 T -TaS2 . As a result, this material may have very promising applications in future electronic devices.

Growth behavior and growth rate dependency in LEDs performance for Mg-doped a-plane GaN

NASA Astrophysics Data System (ADS)

Song, Keun-Man; Kim, Jong-Min; Lee, Dong-Hun; Shin, Chan-Soo; Ko, Chul-Gi; Kong, Bo-Hyun; Cho, Hyung-Koun; Yoon, Dae-Ho

2011-07-01

We investigated the influence of growth rate of Mg-doped a-plane GaN on the surface morphological and electrical properties, and the characteristics of InGaN-based nonpolar LEDs. Mg-doped a-plane GaN layers were grown on r-plane sapphire substrate by metalorganic chemical vapor deposition (MOCVD). Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and cathode luminescence (CL) analysis exhibited that the surface morphology changed from stripe features with large triangular pits to rough and rugged surface with small asymmetric V-shape pits, as the growth rate increased. The Mg incorporation into a-plane GaN layers increased with increasing growth rate of Mg-doped a-plane GaN, while the activation efficiency of Mg dopants decreased in a-plane GaN. Additionally, it was found that operation voltage at 20 mA decreased in characteristics of LEDs, as the growth rate of Mg-doped a-plane GaN decreased. Meanwhile, the EL intensity of LEDs with p-GaN layers grown at higher growth rate was improved compared to that of LEDs with p-GaN layers grown at lower growth rate. Such an increase of EL intensity is attributed to the rougher surface morphology with increasing growth rate of Mg-doped a-plane GaN.

Ambipolar surface state thermoelectric power of topological insulator Bi2Se3.

PubMed

Kim, Dohun; Syers, Paul; Butch, Nicholas P; Paglione, Johnpierre; Fuhrer, Michael S

2014-01-01

We measure gate-tuned thermoelectric power of mechanically exfoliated Bi2Se3 thin films in the topological insulator regime. The sign of the thermoelectric power changes across the charge neutrality point as the majority carrier type switches from electron to hole, consistent with the ambipolar electric field effect observed in conductivity and Hall effect measurements. Near the charge neutrality point and at low temperatures, the gate-dependent thermoelectric power follows the semiclassical Mott relation using the expected surface state density of states but is larger than expected at high electron doping, possibly reflecting a large density of states in the bulk gap. The thermoelectric power factor shows significant enhancement near the electron-hole puddle carrier density ∼0.5 × 10(12) cm(-2) per surface at all temperatures. Together with the expected reduction of lattice thermal conductivity in low-dimensional structures, the results demonstrate that nanostructuring and Fermi level tuning of three-dimensional topological insulators can be promising routes to realize efficient thermoelectric devices.

Synthetic Control of Exciton Behavior in Colloidal Quantum Dots.

PubMed

Pu, Chaodan; Qin, Haiyan; Gao, Yuan; Zhou, Jianhai; Wang, Peng; Peng, Xiaogang

2017-03-08

Colloidal quantum dots are promising optical and optoelectronic materials for various applications, whose performance is dominated by their excited-state properties. This article illustrates synthetic control of their excited states. Description of the excited states of quantum-dot emitters can be centered around exciton. We shall discuss that, different from conventional molecular emitters, ground-state structures of quantum dots are not necessarily correlated with their excited states. Synthetic control of exciton behavior heavily relies on convenient and affordable monitoring tools. For synthetic development of ideal optical and optoelectronic emitters, the key process is decay of band-edge excitons, which renders transient photoluminescence as important monitoring tool. On the basis of extensive synthetic developments in the past 20-30 years, synthetic control of exciton behavior implies surface engineering of quantum dots, including surface cation/anion stoichiometry, organic ligands, inorganic epitaxial shells, etc. For phosphors based on quantum dots doped with transition metal ions, concentration and location of the dopant ions within a nanocrystal lattice are found to be as important as control of the surface states in order to obtain bright dopant emission with monoexponential yet tunable photoluminescence decay dynamics.

Precise parameterization of the recombination velocity at passivated phosphorus doped surfaces

NASA Astrophysics Data System (ADS)

Kimmerle, Achim; Momtazur Rahman, Md.; Werner, Sabrina; Mack, Sebastian; Wolf, Andreas; Richter, Armin; Haug, Halvard

2016-01-01

We investigate the surface recombination velocity Sp at the silicon-dielectric interface of phosphorus-doped surfaces for two industrially relevant passivation schemes for crystalline silicon solar cells. A broad range of surface dopant concentrations together with a high accuracy of evaluating the latter is achieved by incremental back-etching of the surface. The analysis of lifetime measurements and the simulation of the surface recombination consistently apply a set of well accepted models, namely, the Auger recombination by Richter et al. [Phys. Rev. B 86, 1-14 (2012)], the carrier mobility by Klaassen [Solid-State Electron. 35, 953-959 (1992); 35, 961-967 (1992)], the intrinsic carrier concentration for undoped silicon by Altermatt et al. [J. Appl. Phys. 93, 1598-1604 (2003)], and the band-gap narrowing by Schenk [J. Appl. Phys. 84, 3684-3695 (1998)]. The results show an increased Sp at textured in respect to planar surfaces. The obtained parameterizations are applicable in modern simulation tools such as EDNA [K. R. McIntosh and P. P. Altermatt, in Proceedings of the 35th IEEE Photovoltaic Specialists Conference, Honolulu, Hawaii, USA (2010), pp. 1-6], PC1Dmod [Haug et al., Sol. Energy Mater. Sol. Cells 131, 30-36 (2014)], and Sentaurus Device [Synopsys, Sentaurus TCAD, Zürich, Switzerland] as well as in the analytical solution under the assumption of local charge neutrality by Cuevas et al. [IEEE Trans. Electron Devices 40, 1181-1183 (1993)].

Chemical disorder influence on magnetic state of optimally-doped La0.7Ca0.3MnO3

NASA Astrophysics Data System (ADS)

Rozenberg, E.; Auslender, M.; Shames, A. I.; Jung, G.; Felner, I.; Tsindlekht, M. I.; Mogilyansky, D.; Sominski, E.; Gedanken, A.; Mukovskii, Ya. M.; Gorodetsky, G.

2011-10-01

X-band electron magnetic resonance and dc/ac magnetic measurements have been employed to study the effects of chemical disorder on magnetic ordering in bulk and nanometer-sized single crystals and bulk ceramics of optimally-doped La0.7Ca0.3MnO3 manganite. The magnetic ground state of bulk samples appeared to be ferromagnetic with the lower Curie temperature and higher magnetic homogeneity in the vicinity of the ferromagnetic-paramagnetic phase transition in the crystal, as compared with those characteristics in the ceramics. The influence of technological driven "macroscopic" fluctuations of Ca-dopant level in crystal and "mesoscopic" disorder within grain boundary regions in ceramics was proposed to be responsible for these effects. Surface spin disorder together with pronounced inter-particle interactions within agglomerated nano-sample results in well defined core/shell spin configuration in La0.7Ca0.3MnO3 nano-crystals. The analysis of the electron paramagnetic resonance data enlightened the reasons for the observed difference in the magnetic order. Lattice effects dominate the first-order nature of magnetic phase transition in bulk samples. However, mesoscale chemical disorder seems to be responsible for the appearance of small ferromagnetic polarons in the paramagnetic state of bulk ceramics. The experimental results and their analysis indicate that a chemical/magnetic disorder has a strong impact on the magnetic state even in the case of mostly stable optimally hole-doped manganites.

Correlation Effects and Hidden Spin-Orbit Entangled Electronic Order in Parent and Electron-Doped Iridates Sr2 IrO4

NASA Astrophysics Data System (ADS)

Zhou, Sen; Jiang, Kun; Chen, Hua; Wang, Ziqiang

2017-10-01

Analogs of the high-Tc cuprates have been long sought after in transition metal oxides. Because of the strong spin-orbit coupling, the 5 d perovskite iridates Sr2 IrO4 exhibit a low-energy electronic structure remarkably similar to the cuprates. Whether a superconducting state exists as in the cuprates requires understanding the correlated spin-orbit entangled electronic states. Recent experiments discovered hidden order in the parent and electron-doped iridates, some with striking analogies to the cuprates, including Fermi surface pockets, Fermi arcs, and pseudogap. Here, we study the correlation and disorder effects in a five-orbital model derived from the band theory. We find that the experimental observations are consistent with a d -wave spin-orbit density wave order that breaks the symmetry of a joint twofold spin-orbital rotation followed by a lattice translation. There is a Berry phase and a plaquette spin flux due to spin procession as electrons hop between Ir atoms, akin to the intersite spin-orbit coupling in quantum spin Hall insulators. The associated staggered circulating Jeff=1 /2 spin current can be probed by advanced techniques of spin-current detection in spintronics. This electronic order can emerge spontaneously from the intersite Coulomb interactions between the spatially extended iridium 5 d orbitals, turning the metallic state into an electron-doped quasi-2D Dirac semimetal with important implications on the possible superconducting state suggested by recent experiments.

Structural, electrical and mechanical properties of selenium doped thallium based high-temperature superconductors

NASA Astrophysics Data System (ADS)

Cavdar, S.; Kol, N.; Koralay, H.; Ozturk, O.; Asikuzun, E.; Tasci, A. T.

2016-01-01

In this study, highly-refined chemical powders were synthesized by having them ready in appropriate stoichiometric proportions with conventional solid state reaction method so that they would produce the superconductor TlPb0.3Sr2Ca1-xSexCu2Oy (x = 0; 0.4; 0.6; 1.0). This study aims to understand effect of the selenium doping on the superconducting, structural and mechanical properties of the aforementioned superconducting material. The effect of the doping rates on the structural and electrical properties of the sample has been identified. Electrical characteristics of the TlPb0.3Sr2Ca1-xSexCu2Oy material were measured using standard four point probe method. Structural characteristics were examined with the powder X-ray diffractometer (XRD) and scanning electron microscope (SEM). Mechanical properties were analyzed with Vickers microhardness measurements on the sample surface. According to the results, it was observed that the reflection comes from the (00l) and parallel planes increased with Se doping. Particle size increases with increasing doping ratio. According to results of the mechanical measurements, all samples exhibit indentation size effect (ISE) behavior. Comparing the obtained results with theoretical studies, it was understood that Hays Kendall approach is the best method in determination of mechanical properties and analyzing microhardness of the materials.

Dye based photodiodes for solar energy applications

NASA Astrophysics Data System (ADS)

Mensah-Darkwa, K.; Ocaya, R.; Dere, A.; Al-Sehemi, Abdullah G.; Al-Ghamdi, Ahmed A.; Soylu, M.; Gupta, R. K.; Yakuphanoglu, F.

2017-10-01

Coumarin (CO) doped methylene blue (MB) organic photo-devices were fabricated. The CO-doped MB (0.00, 0.01, 0.03, 0.05, 0.1 wt% CO) were coated onto the surface of a p-type Si substrate by drop casting method. Some electrical parameters of the devices have been examined by current-voltage ( I- V), capacitance-voltage ( C- V), and conductance-voltage ( G- V) measurements. The fabricated devices had excellent rectifying properties. The diode exhibits a non-ideal diode behavior due to the series resistance and interface layer. The ideality factor, the barrier height, and the series resistance values of the diode as a function of doping and light illumination have been estimated using modified Cheung-Cheung and Norde's method. The highest I photo/ I dark photosensitivity of 5606 was observed for the diode having 0.01 CO doping at 100 mW/cm2 under -3 V. Furthermore, change of capacitance and conductance measurements with frequency is related to the existence of interface states. A maximum power conversion efficiency of 2.4% is estimated for the fabricated devices. The results reveal that coumarin-doped methylene blue/ p-Si heterojunction can be used as a photodiode in optoelectronic applications. It is also usable in low-power photovoltaic applications.

Cu-doped CdS and its application in CdTe thin film solar cell

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deng, Yi; College of Electronic and Information Engineering, Hankou University, Wuhan, Hubei 430212; Yang, Jun

2016-01-15

Cu is widely used in the back contact formation of CdTe thin film solar cells. However, Cu is easily to diffuse from the back contact into the CdTe absorber layer and even to the cell junction interface CdS/CdTe. This phenomenon is generally believed to be the main factor affecting the CdTe solar cell stability. In this study Cu was intentionally doped in CdS thin film to study its effect on the microstructural, optical and electrical properties of the CdS material. Upon Cu doping, the V{sub Cd{sup −}} and the surface-state-related photoluminescence emissions were dramatically decreased/quenched. The presence of Cu atommore » hindered the recrystallization/coalescence of the nano-sized grains in the as-deposited CdS film during the air and the CdCl{sub 2} annealing. CdTe thin film solar cell fabricated with Cu-doped CdS window layers demonstrated much decreased fill factor, which was induced by the increased space-charge recombination near the p-n junction and the worsened junction crystalline quality. Temperature dependent current-voltage curve measurement indicated that the doped Cu in the CdS window layer was not stable at both room and higher temperatures.« less

DFT study of the adsorption of 2,3,7,8-tetrachlorodibenzo-p-dioxin on pristine and Ni-doped boron nitride nanotubes.

PubMed

Wang, Ruoxi; Zhang, Dongju; Liu, Chengbu

2017-02-01

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are highly toxic to humans and the environment. Developing efficient methods to detect or remove these pollutants is particularly important and urgent. Boron nitride nanotubes (BNNTs) with low dimension and high surface-to-volume ratio might be one of promising materials for the adsorption of PCDD/Fs. Here we present a density functional theory (DFT) study on the interaction of the pristine and Ni doped (8,0) single-walled BNNTs with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most toxic congener among PCDD/F family. The calculated results show that the pristine BNNT intrinsically interacts with TCDD via physisorption with π-π stacking interaction, in contrast, the Ni-doped BNNT presents much higher reactivities toward TCDD. The impurity Ni atom plays a crucial role for capturing TCDD molecule. We also find that the Ni doping introduces the local electronic states within the band gap of the BNNT and induces magnetism in the doped systems. The present results are expected to provide useful guidance for the potential application of BNNTs as adsorption materials for detecting or removing dioxin pollutants. Copyright © 2016 Elsevier Ltd. All rights reserved.

Nano-Architecture of nitrogen-doped graphene films synthesized from a solid CN source.

PubMed

Maddi, Chiranjeevi; Bourquard, Florent; Barnier, Vincent; Avila, José; Asensio, Maria-Carmen; Tite, Teddy; Donnet, Christophe; Garrelie, Florence

2018-02-19

New synthesis routes to tailor graphene properties by controlling the concentration and chemical configuration of dopants show great promise. Herein we report the direct reproducible synthesis of 2-3% nitrogen-doped 'few-layer' graphene from a solid state nitrogen carbide a-C:N source synthesized by femtosecond pulsed laser ablation. Analytical investigations, including synchrotron facilities, made it possible to identify the configuration and chemistry of the nitrogen-doped graphene films. Auger mapping successfully quantified the 2D distribution of the number of graphene layers over the surface, and hence offers a new original way to probe the architecture of graphene sheets. The films mainly consist in a Bernal ABA stacking three-layer architecture, with a layer number distribution ranging from 2 to 6. Nitrogen doping affects the charge carrier distribution but has no significant effects on the number of lattice defects or disorders, compared to undoped graphene synthetized in similar conditions. Pyridinic, quaternary and pyrrolic nitrogen are the dominant chemical configurations, pyridinic N being preponderant at the scale of the film architecture. This work opens highly promising perspectives for the development of self-organized nitrogen-doped graphene materials, as synthetized from solid carbon nitride, with various functionalities, and for the characterization of 2D materials using a significant new methodology.

The effect of p-doping on multi-state lasing in InAs/InGaAs quantum dot lasers for different cavity lengths

NASA Astrophysics Data System (ADS)

Korenev, V. V.; Savelyev, A. V.; Maximov, M. V.; Zubov, F. I.; Shernyakov, Yu M.; Zhukov, A. E.

2017-11-01

The effect of modulation p-doping on multi-state lasing in InAs/InGaAs quantum dot (QD) lasers is studied for different levels of acceptor concentration. It is shown that in case of the short laser cavities, p-doping results in higher output power of the ground-state optical transitions of InAs/InGaAs QDs whereas in longer samples p-doping may result in the decrease of this power component. On the basis of this observation, the optimal design of laser active region and optimal doping level are discussed in details.

Effect of doping on room temperature carrier escape mechanisms in InAs/GaAs quantum dot p-i-n junction photovoltaic cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sellers, D. G.; Chen, E. Y.; Doty, M. F.

2016-05-21

We investigate the effect of doping on the mechanisms of carrier escape from intermediate states in delta-doped InAs/GaAs intermediate band solar cells. The intermediate states arise from InAs quantum dots embedded in a GaAs p-i-n junction cell. We find that doping the sample increases the number of excited-state carriers participating in a cycle of trapping and carrier escape via thermal, optical, and tunneling mechanisms. However, we find that the efficiency of the optically-driven carrier escape mechanism is independent of doping and remains small.

Pseudogap and electronic structure of electron-doped Sr2IrO4

NASA Astrophysics Data System (ADS)

Moutenet, Alice; Georges, Antoine; Ferrero, Michel

2018-04-01

We present a theoretical investigation of the effects of correlations on the electronic structure of the Mott insulator Sr2IrO4 upon electron doping. A rapid collapse of the Mott gap upon doping is found, and the electronic structure displays a strong momentum-space differentiation at low doping level: The Fermi surface consists of pockets centered around (π /2 ,π /2 ) , while a pseudogap opens near (π ,0 ) . Its physical origin is shown to be related to short-range spin correlations. The pseudogap closes upon increasing doping, but a differentiated regime characterized by a modulation of the spectral intensity along the Fermi surface persists to higher doping levels. These results, obtained within the cellular dynamical mean-field-theory framework, are discussed in comparison to recent photoemission experiments and an overall good agreement is found.

Nonequilibrium-Plasma-Synthesized ZnO Nanocrystals with Plasmon Resonance Tunable via Al Doping and Quantum Confinement.

PubMed

Greenberg, Benjamin L; Ganguly, Shreyashi; Held, Jacob T; Kramer, Nicolaas J; Mkhoyan, K Andre; Aydil, Eray S; Kortshagen, Uwe R

2015-12-09

Metal oxide semiconductor nanocrystals (NCs) exhibit localized surface plasmon resonances (LSPRs) tunable within the infrared (IR) region of the electromagnetic spectrum by vacancy or impurity doping. Although a variety of these NCs have been produced using colloidal synthesis methods, incorporation and activation of dopants in the liquid phase has often been challenging. Herein, using Al-doped ZnO (AZO) NCs as an example, we demonstrate the potential of nonthermal plasma synthesis as an alternative strategy for the production of doped metal oxide NCs. Exploiting unique, thoroughly nonequilibrium synthesis conditions, we obtain NCs in which dopants are not segregated to the NC surfaces and local doping levels are high near the NC centers. Thus, we achieve overall doping levels as high as 2 × 10(20) cm(-3) in NCs with diameters ranging from 12.6 to 3.6 nm, and for the first time experimentally demonstrate a clear quantum confinement blue shift of the LSPR energy in vacancy- and impurity-doped semiconductor NCs. We propose that doping of central cores and heavy doping of small NCs are achievable via nonthermal plasma synthesis, because chemical potential differences between dopant and host atoms-which hinder dopant incorporation in colloidal synthesis-are irrelevant when NC nucleation and growth proceed via irreversible interactions among highly reactive gas-phase ions and radicals and ligand-free NC surfaces. We explore how the distinctive nucleation and growth kinetics occurring in the plasma influences dopant distribution and activation, defect structure, and impurity phase formation.

Band gap modulation in magnetically doped low-defect thin films of (Bi1-xSbx)2 Te3 with minimized bulk carrier concentration

NASA Astrophysics Data System (ADS)

Maximenko, Yulia; Scipioni, Kane; Wang, Zhenyu; Katmis, Ferhat; Steiner, Charles; Weis, Adam; van Harlingen, Dale; Madhavan, Vidya

Topological insulators Bi2Te3 and Sb2Te3 are promising materials for electronics, but both are naturally prone to vacancies and anti-site defects that move the Fermi energy onto the bulk bands. Fabricating (Bi1-xSbx)2 Te3 (BST) with the tuned x minimizes point defects and unmasks topological surface states by reducing bulk carriers. BST thin films have shown topological surface states and quantum anomalous Hall effect. However, different studies reported variable Sb:Bi ratios used to grow an undoped BST film. Here, we develop a reliable way to grow defect-free subnanometer-flat BST thin films having the Fermi energy tuned to the Dirac point. High-resolution scanning tunneling microscopy (STM) and Landau level spectroscopy prove the importance of crystallinity and surface roughness-not only Sb:Bi ratio-for the final bulk carrier concentration. The BST thin films were doped with Cr and studied with STM with atomic resolution. Counterintuitively, Cr density is anticorrelated with the local band gap due to Cr's antiferromagnetic order. We analyze the correlations and report the relevant band gap values. Predictably, high external magnetic field compromises antiferromagnetic order, and the local band gap increases. US DOE DE-SC0014335; Moore Found. GBMF4860; F. Seitz MRL.

Self-Assembled Si(111) Surface States: 2D Dirac Material for THz Plasmonics.

PubMed

Wang, Z F; Liu, Feng

2015-07-10

Graphene, the first discovered 2D Dirac material, has had a profound impact on science and technology. In the last decade, we have witnessed huge advances in graphene related fundamental and applied research. Here, based on first-principles calculations, we propose a new 2D Dirac band on the Si(111) surface with 1/3 monolayer halogen coverage. The sp(3) dangling bonds form a honeycomb superstructure on the Si(111) surface that results in an anisotropic Dirac band with a group velocity (∼10(6)  m/s) comparable to that in graphene. Most remarkably, the Si-based surface Dirac band can be used to excite a tunable THz plasmon through electron-hole doping. Our results demonstrate a new way to design Dirac states on a traditional semiconductor surface, so as to make them directly compatible with Si technology. We envision this new type of Dirac material to be generalized to other semiconductor surfaces with broad applications.

Self-Assembled Si(111) Surface States: 2D Dirac Material for THz Plasmonics

NASA Astrophysics Data System (ADS)

Wang, Z. F.; Liu, Feng

2015-07-01

Graphene, the first discovered 2D Dirac material, has had a profound impact on science and technology. In the last decade, we have witnessed huge advances in graphene related fundamental and applied research. Here, based on first-principles calculations, we propose a new 2D Dirac band on the Si(111) surface with 1 /3 monolayer halogen coverage. The s p3 dangling bonds form a honeycomb superstructure on the Si(111) surface that results in an anisotropic Dirac band with a group velocity (˜106 m /s ) comparable to that in graphene. Most remarkably, the Si-based surface Dirac band can be used to excite a tunable THz plasmon through electron-hole doping. Our results demonstrate a new way to design Dirac states on a traditional semiconductor surface, so as to make them directly compatible with Si technology. We envision this new type of Dirac material to be generalized to other semiconductor surfaces with broad applications.

Observation of non-Fermi liquid behavior in hole-doped LiFe 1-x V xAs

DOE PAGES

Xing, L. Y.; Shi, X.; Richard, P.; ...

2016-09-28

Here we synthesized a series of V-doped LiFe 1₋xV xAs single crystals. The superconducting transition temperature T c of LiFeAs decreases rapidly at a rate of 7 K per 1% V. The Hall coefficient of LiFeAs switches from negative to positive with 4.2% V doping, showing that V doping introduces hole carriers. This observation is further confirmed by the evaluation of the Fermi surface volume measured by angle-resolved photoemission spectroscopy (ARPES), from which a 0.3 hole doping per V atom introduced is deduced. Interestingly, the introduction of holes does not follow a rigid band shift. We also show that themore » temperature evolution of the electrical resistivity as a function of doping is consistent with a crossover from a Fermi liquid to a non-Fermi liquid. Our ARPES data indicate that the non-Fermi liquid behavior is mostly enhanced when one of the hole d xz/dyz Fermi surfaces is well nested by the antiferromagnetic wave vector to the inner electron Fermi surface pocket with the d xy orbital character. In conclusion, the magnetic susceptibility of LiFe 1₋xV xAs suggests the presence of strong magnetic impurities following V doping, thus providing a natural explanation to the rapid suppression of superconductivity upon V doping.« less

A first principle simulation of competitive adsorption of SF6 decomposition components on nitrogen-doped anatase TiO2 (101) surface

NASA Astrophysics Data System (ADS)

Dong, Xingchen; Zhang, Xiaoxing; Cui, Hao; Zhang, Jun

2017-11-01

Gas insulated switchgear has been widely used in modern electric systems due to its significantly excellent performances such as compact structure and low land occupation as well as the security stability. However, inside defects caused during manufacture process can lead to partial discharge which might develop into serious insulation failure. Online monitoring method on basis of gas sensors is considered a promising way of detecting partial discharge for alarm ahead of time. Research has found that TiO2 nanotubes sensors show good response to SO2, SOF2, SO2F2, the decomposition components as a result of partial discharge. In order to investigate the gas-sensing mechanism of nitrogen-doped TiO2 prepared via plasma treatment methods to SO2, SOF2, and SO2F2, the adsorption structures of both three gas molecules and anatase TiO2 (101) surface were built, and DFT calculations were then carried out for calculation and analysis of adsorption parameters. Adsorption property comparison of anatase TiO2 (101) surface after nitrogen doping with Au doping and without doping shows that nitrogen doping can obviously enhance the adsorption energy for SO2 and SOF2 adsorption and no charge transfer for SO2F2 adsorption, further explaining the adsorption mechanism and doping influence of different doping elements.

Observation of non-Fermi liquid behavior in hole-doped LiFe 1-x V xAs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xing, L. Y.; Shi, X.; Richard, P.

Here we synthesized a series of V-doped LiFe 1₋xV xAs single crystals. The superconducting transition temperature T c of LiFeAs decreases rapidly at a rate of 7 K per 1% V. The Hall coefficient of LiFeAs switches from negative to positive with 4.2% V doping, showing that V doping introduces hole carriers. This observation is further confirmed by the evaluation of the Fermi surface volume measured by angle-resolved photoemission spectroscopy (ARPES), from which a 0.3 hole doping per V atom introduced is deduced. Interestingly, the introduction of holes does not follow a rigid band shift. We also show that themore » temperature evolution of the electrical resistivity as a function of doping is consistent with a crossover from a Fermi liquid to a non-Fermi liquid. Our ARPES data indicate that the non-Fermi liquid behavior is mostly enhanced when one of the hole d xz/dyz Fermi surfaces is well nested by the antiferromagnetic wave vector to the inner electron Fermi surface pocket with the d xy orbital character. In conclusion, the magnetic susceptibility of LiFe 1₋xV xAs suggests the presence of strong magnetic impurities following V doping, thus providing a natural explanation to the rapid suppression of superconductivity upon V doping.« less

Enhancement of tunneling current in phosphorene tunnel field effect transistors by surface defects.

PubMed

Lu, Juan; Fan, Zhi-Qiang; Gong, Jian; Chen, Jie-Zhi; ManduLa, Huhe; Zhang, Yan-Yang; Yang, Shen-Yuan; Jiang, Xiang-Wei

2018-02-21

The effects of the staggered double vacancies, hydrogen (H), 3d transition metals, for example cobalt, and semiconductor covalent atoms, for example, germanium, nitrogen, phosphorus (P) and silicon adsorption on the transport properties of monolayer phosphorene were studied using density functional theory and non-equilibrium Green's function formalism. It was observed that the performance of the phosphorene tunnel field effect transistors (TFETs) with an 8.8 nm scaling channel length could be improved most effectively, if the adatoms or vacancies were introduced at the source channel interface. For H and P doped devices, the upper limit of on-state currents of phosphorene TFETs were able to be quickly increased to 2465 μA μm -1 and 1652 μA μm -1 , respectively, which not only outperformed the pristine sample, but also met the requirements for high performance logic applications for the next decade in the International Technology Roadmap for Semiconductors (ITRS). It was proved that the defect-induced band gap states make the effective tunneling path between the conduction band (CB) and valence band (VB) much shorter, so that the carriers can be injected easily from the left electrode, then transfer to the channel. In this regard, the tunneling properties of phosphorene TFETs can be manipulated using surface defects. In addition, the effects of spin polarization on the transport properties of doped phosphorene TFETs were also rigorously considered, H and P doped TFETs could achieve a high ON current of 1795 μA μm -1 and 1368 μA μm -1 , respectively, which is closer to realistic nanodevices.

Accurate potential drop sheet resistance measurements of laser-doped areas in semiconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heinrich, Martin, E-mail: mh.seris@gmail.com; NUS Graduate School for Integrative Science and Engineering, National University of Singapore, Singapore 117456; Kluska, Sven

2014-10-07

It is investigated how potential drop sheet resistance measurements of areas formed by laser-assisted doping in crystalline Si wafers are affected by typically occurring experimental factors like sample size, inhomogeneities, surface roughness, or coatings. Measurements are obtained with a collinear four point probe setup and a modified transfer length measurement setup to measure sheet resistances of laser-doped lines. Inhomogeneities in doping depth are observed from scanning electron microscope images and electron beam induced current measurements. It is observed that influences from sample size, inhomogeneities, surface roughness, and coatings can be neglected if certain preconditions are met. Guidelines are given onmore » how to obtain accurate potential drop sheet resistance measurements on laser-doped regions.« less

Antibacterial properties of Ag-doped hydroxyapatite layers prepared by PLD method

NASA Astrophysics Data System (ADS)

Jelínek, Miroslav; Kocourek, Tomáš; Jurek, Karel; Remsa, Jan; Mikšovský, Jan; Weiserová, Marie; Strnad, Jakub; Luxbacher, Thomas

2010-12-01

Thin hydroxyapatite (HA), silver-doped HA and silver layers were prepared using a pulsed laser deposition method. Doped layers were ablated from silver/HA targets. Amorphous and crystalline films of silver concentrations of 0.06 at.%, 1.2 at.%, 4.4 at.%, 8.3 at.% and 13.7 at.% were synthesized. Topology was studied using scanning electron microscopy and atomic force microscopy. Contact angle and zeta potential measurements were conducted to determine the wettability, surface free energy and electric surface properties. In vivo measurement (using Escherichia coli cells) of antibacterial properties of the HA, silver-doped HA and silver layers was carried out. The best antibacterial results were achieved for silver-doped HA layers of silver concentration higher than 1.2 at.%.

Measurement of steady-state minority-carrier transport parameters in heavily doped n-type silicon

NASA Technical Reports Server (NTRS)

Del Alamo, Jesus A.; Swanson, Richard M.

1987-01-01

The relevant hole transport and recombination parameters in heavily doped n-type silicon under steady state are the hole diffusion length and the product of the hole diffusion coefficient times the hole equilibrium concentration. These parameters have measured in phosphorus-doped silicon grown by epitaxy throughout nearly two orders of magnitude of doping level. Both parameters are found to be strong functions of donor concentration. The equilibrium hole concentration can be deduced from the measurement. A rigid shrinkage of the forbidden gap appears as the dominant heavy doping mechanism in phosphorus-doped silicon.

Bottom-up and top-down fabrication of nanowire-based electronic devices: In situ doping of vapor liquid solid grown silicon nanowires and etch-dependent leakage current in InGaAs tunnel junctions

NASA Astrophysics Data System (ADS)

Kuo, Meng-Wei

Semiconductor nanowires are important components in future nanoelectronic and optoelectronic device applications. These nanowires can be fabricated using either bottom-up or top-down methods. While bottom-up techniques can achieve higher aspect ratio at reduced dimension without having surface and sub-surface damage, uniform doping distributions with abrupt junction profiles are less challenging for top-down methods. In this dissertation, nanowires fabricated by both methods were systematically investigated to understand: (1) the in situ incorporation of boron (B) dopants in Si nanowires grown by the bottom-up vapor-liquid-solid (VLS) technique, and (2) the impact of plasma-induced etch damage on InGaAs p +-i-n+ nanowire junctions for tunnel field-effect transistors (TFETs) applications. In Chapter 2 and 3, the in situ incorporation of B in Si nanowires grown using silane (SiH4) or silicon tetrachloride (SiCl4) as the Si precursor and trimethylboron (TMB) as the p-type dopant source is investigated by I-V measurements of individual nanowires. The results from measurements using a global-back-gated test structure reveal nonuniform B doping profiles on nanowires grown from SiH4, which is due to simultaneous incorporation of B from nanowire surface and the catalyst during VLS growth. In contrast, a uniform B doping profile in both the axial and radial directions is achieved for TMBdoped Si nanowires grown using SiCl4 at high substrate temperatures. In Chapter 4, the I-V characteristics of wet- and dry-etched InGaAs p+-i-n+ junctions with different mesa geometries, orientations, and perimeter-to-area ratios are compared to evaluate the impact of the dry etch process on the junction leakage current properties. Different post-dry etch treatments, including wet etching and thermal annealing, are performed and the effectiveness of each is assessed by temperaturedependent I-V measurements. As compared to wet-etched control devices, dry-etched junctions have a significantly higher leakage current and a current kink in the reverse bias regime, which is likely due to additional trap states created by plasma-induced damage during the Cl2/Ar/H2 mesa isolation step. These states extend more than 60 nm from the mesa surface and can only be partially passivated after a thermal anneal at 350°C for 20 minutes. The evolution of the electrical properties with post-dry etch treatments indicates that the shallow and deep-level trap states resulting from ion-induced point defects, arsenic vacancies and hydrogen-dopant complexes are the primary cause of degradation in the electrical properties of the dry-etched junctions.

The impact of chemical doping on the magnetic state of the Sr{sub 2}YRuO{sub 6} double perovskite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kayser, Paula; Ranjbar, Ben; Kennedy, Brendan J.

The impact of chemical doping of the type Sr{sub 2−x}A{sub x}YRuO{sub 6} (A=Ca, Ba) on the low temperature magnetic properties of Sr{sub 2}YRuO{sub 6}, probed using variable temperature magnetic susceptibility, neutron diffraction and heat capacity measurements, are described. Specific-heat measurements of un-doped Sr{sub 2}YRuO{sub 6} reveal two features at ∼26 and ∼30 K. Neutron scattering measurements at these temperatures are consistent with a change from a 2D ordered state to the 3D type 1 AFM state. Magnetic and structural studies of a number of doped oxides are described that highlight the unique low temperature behavior of Sr{sub 2}YRuO{sub 6} andmore » demonstrate that doping destabilizes the intermediate 2D ordered state. - Graphical abstract: Neutron diffraction measurements of the ordered double perovskite Sr{sub 2}YRuO{sub 6}reveal a with a change from a 2D ordered state to the 3D type 1 AFM state upon cooling. The impact of chemical doping Sr{sub 2−x}A{sub x}YRuO{sub 6} (A=Ca, Ba) on the low temperature magnetic properties have also been investigated and these highlight the unique low temperature behavior of Sr{sub 2}YRuO{sub 6} with doping destabilizing the intermediate 2D ordered state. - Highlights: • Crystal and Magnetic Structure of Sr{sub 2}YRuO{sub 3} was studied using Neutron Diffraction. • Effect of doping on the magnetic ground state established. • Origin of two low temperature transitions discussed.« less

Magnetic phase diagram and critical behavior of electron-doped LaxCa1-xMnO3(0⩽x⩽0.25) nanoparticles

NASA Astrophysics Data System (ADS)

Wang, Yang; Fan, Hong Jin

2011-06-01

A comparative study of electron-doped perovskite manganites LaxCa1-xMnO3 (0 ⩽ x ⩽ 0.25) in nanoparticle and bulk form is reported. The bulks and nanoparticles exhibit different magnetic evolutions. Overall with increasing x, the bulks have a phase-separated ground state with ferromagnetic (FM) clusters and antiferromagnetic (AFM) matrix coexisting. The FM clusters gradually grow, and the magnetization M peaks at x= 0.1. Subsequently, charge-ordering (CO) or local CO occurs, which suppresses the increase in FM clusters but favors the development of antiferromagnetism so M starts to decrease. Finally the system becomes a homogeneous AFM state at x > 0.18. For the nanoparticles in the range of 0 ⩽ x ⩽ 0.1, the ground state is similar to that of the bulks, but M is slightly increased because of a surface ferromagnetism. Nevertheless because of the structure distortion induced by surface pressure and the size effect, CO does not occur in the nanoparticles. Consequently, the ferromagnetism still gradually develops at x > 0.1 and thus M monotonously rises. M reaches a maximum at x= 0.18, after which the competition between ferromagnetism and antiferromagnetism induces a cluster-glass (CG) state. On the basis of these observations the phase diagrams for both bulks and nanoparticles are established. For the nanoparticles that display enhanced ferromagnetism the critical behavior analysis indicates that they fall into a three-dimensional (3D) Heisenberg ferromagnet class.

Sintering of BaCe(sub 0.85)Y(sub 0.15)O(sub 3-delta) with/without SrTiO3 Dopant

NASA Technical Reports Server (NTRS)

Dynys, F.; Sayir, A.; Heimann, P. J.

2004-01-01

The perovskite composition, BaCe(sub 0.85)Y(sub 0.15)O(sub 3-delta), displays excellent protonic conduction at high temperatures making it a desirable candidate for hydrogen separation membranes. This paper reports on the sintering behavior of BaCe(sub 0.85)Y(sub 0.15)O(sub 3-delta) powders doped with SrTiO3. Two methods were used to synthesize BaCe(sub 0.85)Y(sub 0.15)O(sub 3-delta) powders: (1) solid state reaction and (2) wet chemical co-precipitation. Co-precipitated powder crystallized into the perovskite phase at 1000 C for 4 hrs. Complete reaction and crystallization of the perovskite phase by solid state was achieved by calcining at 1200 C for 24 hrs. Solid state synthesis produced a coarser powder with an average particle size of 1.3 microns and surface area of 0.74 sq m/g. Co-precipitation produced a finer powder with a average particle size of 65 nm and surface area of 14.9 sq m/g. Powders were doped with 1, 2, 5, and 10 mole % SrTiO3. Samples were sintered at 1450 C, 1550 C and 1650 C. SrTiO3 enhances sintering, optimal dopant level is different for powders synthesized by solid state and co-precipitation. Both powders exhibit similar grain growth behavior. Dopant levels of 5 and 10 mole % SrTiO3 significantly enhances the grain size.

Electrical and optical properties of Si-doped Ga2O3

NASA Astrophysics Data System (ADS)

Li, Yin; Yang, Chuanghua; Wu, Liyuan; Zhang, Ru

2017-05-01

The charge densities, band structure, density of states, dielectric functions of Si-doped β-Ga2O3 have been investigated based on the density functional theory (DFT) within the hybrid functional HSE06. The heavy doping makes conduction band split out more bands and further influences the band structure. It decreases the band gap and changes from a direct gap to an indirect gap. After doping, the top of the valence bands is mainly composed by the O-2p states, Si-3p states and Ga-4p states and the bottom of the conduction bands is almost formed by the Si-3s, Si-3p and Ga-4s orbits. The anisotropic optical properties have been investigated by means of the complex dielectric function. After the heavy Si doping, the position of absorption band edges did not change much. The slope of the absorption curve descends and indicates that the absorption became more slow for Si-doped β-Ga2O3 than undoped one due to the indirect gap of Si-doped β-Ga2O3.

Effect of Dopants on the Adsorption of Carbon Dioxide on Ceria Surfaces

DOE PAGES

Li, Meijun; Tumuluri, Uma; Wu, Zili; ...

2015-09-25

Here, high-surface-area nanosized CeO 2 and M-doped CeO 2 (M=Cu, La, Zr, and Mg) prepared by a surfactant-templated method were tested for CO 2 adsorption. Cu, La, and Zr are doped into the lattice of CeO 2, whereas Mg is dispersed on the CeO 2 surface. The doping of Cu and La into CeO 2 leads to an increase of the CO 2 adsorption capacity, whereas the doping of Zr has little or no effect. The addition of Mg causes a decrease of the CO 2 adsorption capacity at a low Mg content and a gradual increase at a highermore » content. The CO 2 adsorption capacity follows the sequence Cu-CeO 2>La-CeO 2>Zr-CeO 2≈CeO 2>Mg-CeO 2 at low dopant contents, in line with the relative amount of defect sites in the samples. It is the defect sites on the surface, not in the bulk of CeO 2, modified by the dopants that play the vital role in CO 2 chemisorption. Lastly, the role of surface oxygen vacancies is further supported by an in situ IR spectroscopic study of the surface chemistry during CO 2 adsorption on the doped CeO 2.« less

Impacts of Co-doping on the superconductivity and the orbital ordering state in Fe1-xCoxSe single crystal studied by the electrical transport.

NASA Astrophysics Data System (ADS)

Urata, Takahiro; Tanabe, Yoichi; Heguri, Satoshi; Tanigaki, Katsumi

2015-03-01

In the FeSe with the simplest crystal structure in the Fe-based superconductor families, although both the superconductivity and the orbital ordering states are investigated, the relation between them is still unclear. Here, we report Co doping effects on the superconductivity and the orbital ordering state in Fe1-xCoxSe single crystals. The electrical transport measurements demonstrated that the superconductivity vanishes at 4 % Co doping while the orbital ordering state may be robust against Co doping. Present results suggest that the orbital ordering state is not related to the emergence of the superconductivity in FeSe.

Quantum dimer model for the pseudogap metal

PubMed Central

Punk, Matthias; Allais, Andrea; Sachdev, Subir

2015-01-01

We propose a quantum dimer model for the metallic state of the hole-doped cuprates at low hole density, p. The Hilbert space is spanned by spinless, neutral, bosonic dimers and spin S=1/2, charge +e fermionic dimers. The model realizes a “fractionalized Fermi liquid” with no symmetry breaking and small hole pocket Fermi surfaces enclosing a total area determined by p. Exact diagonalization, on lattices of sizes up to 8×8, shows anisotropic quasiparticle residue around the pocket Fermi surfaces. We discuss the relationship to experiments. PMID:26195771

Dielectric properties of BaMg1/3Nb2/3O3 doped Ba0.45Sr0.55Tio3 thin films for tunable microwave applications

NASA Astrophysics Data System (ADS)

Alema, Fikadu; Pokhodnya, Konstantin

2015-11-01

Ba(Mg1/3Nb2/3)O3 (BMN) doped and undoped Ba0.45Sr0.55TiO3 (BST) thin films were deposited via radio frequency magnetron sputtering on Pt/TiO2/SiO2/Al2O3 substrates. The surface morphology and chemical state analyses of the films have shown that the BMN doped BST film has a smoother surface with reduced oxygen vacancy, resulting in an improved insulating properties of the BST film. Dielectric tunability, loss, and leakage current (LC) of the undoped and BMN doped BST thin films were studied. The BMN dopant has remarkably reduced the dielectric loss (˜38%) with no significant effect on the tunability of the BST film, leading to an increase in figure of merit (FOM). This is attributed to the opposing behavior of large Mg2+ whose detrimental effect on tunability is partially compensated by small Nb5+ as the two substitute Ti4+ in the BST. The coupling between MgTi″ and VO•• charged defects suppresses the dielectric loss in the film by cutting electrons from hopping between Ti ions. The LC of the films was investigated in the temperature range of 300-450K. A reduced LC measured for the BMN doped BST film was correlated to the formation of defect dipoles from MgTi″, VO•• and NbTi• charged defects. The carrier transport properties of the films were analyzed in light of Schottky thermionic emission (SE) and Poole-Frenkel (PF) emission mechanisms. The result indicated that while the carrier transport mechanism in the undoped film is interface limited (SE), the conduction in the BMN doped film was dominated by bulk processes (PF). The change of the conduction mechanism from SE to PF as a result of BMN doping is attributed to the presence of uncoupled NbTi• sitting as a positive trap center at the shallow donor level of the BST.

Josephson junctions of candidate topological crystalline insulator Pb1-xSnxTe

NASA Astrophysics Data System (ADS)

Snyder, Rodney; Trimble, Christie; Taylor, Patrick; Williams, James

Incorporating superconducting ordering through proximity effects in topological states of matter offers potential routes to novel excitations with properties beyond that of simple electrons. Topological crystalline insulators TCI offer alternative routes to topological states of matter with surface states of distinct character to those in more common 3d topological insulators. We report on the fabrication Josephson junctions using MBE-grown candidate TCI material Pb-doped SnTe as weak links and characterize the departures from conventional junctions using combined DC and RF techniques. Opportunities to create junction weak links from materials possessing electronic interactions will be discussed.

Tailoring the Hydrothermal Synthesis of Stainless Steel Wire Sieve-Supported Ag-Doped ZnO Nanowires to Optimize Their Photo-catalytic Activity

NASA Astrophysics Data System (ADS)

Jing, W. X.; Shi, J. F.; Xu, Z. P.; Jiang, Z. D.; Wei, Z. Y.; Zhou, F.; Wu, Q.; Cui, Q. B.

2018-03-01

Batches of un-doped and Ag-doped ZnO nanowires (ZnONWs) were prepared hydrothermally on stainless steel wire sieves at varied Zn2+ concentrations of the growth solution and at different Ag+ concentrations of the silver nitrate solution. Methylene blue solution was degraded with these as-prepared ZnONWs in the presences of ultraviolet irradiation. It is found that both the processing parameters greatly affect the surface textures, wettability, and photo-activity of the ZnONWs. The latter synthesizing parameter is optimized only after the former one has been finely regulated. The un-doped and Ag-doped ZnONWs at Zn2+ concentration of 75 mM of the growth solution and at Ag+ concentration of3 mM of the silver nitrate solution both produce Gaussian rough surfaces and in each batch are most hydrophilic. Therefore, in the related batch the contacting surface area of the catalyst is the largest, the hydroxyl radicals attached on the top ends of corresponding ZnONWs the most, and the catalytic activity of these catalysts the optimal. Besides these, the latter synthesizing parameter affects the photo-activity of Ag-doped ZnONWs more significantly than the former one does that of un-doped ZnONWs.

Deposition of boron doped DLC films on TiNb and characterization of their mechanical properties and blood compatibility

PubMed Central

Liza, Shahira; Hieda, Junko; Akasaka, Hiroki; Ohtake, Naoto; Tsutsumi, Yusuke; Nagai, Akiko; Hanawa, Takao

2017-01-01

Abstract Diamond-like carbon (DLC) material is used in blood contacting devices as the surface coating material because of the antithrombogenicity behavior which helps to inhibit platelet adhesion and activation. In this study, DLC films were doped with boron during pulsed plasma chemical vapor deposition (CVD) to improve the blood compatibility. The ratio of boron to carbon (B/C) was varied from 0 to 0.4 in the film by adjusting the flow rate of trimethylboron and acetylene. Tribological tests indicated that boron doping with a low B/C ratio of 0.03 is beneficial for reducing friction (μ = 0.1), lowering hardness and slightly increasing wear rate compared to undoped DLC films. The B/C ratio in the film of 0.03 and 0.4 exhibited highly hydrophilic surface owing to their high wettability and high surface energy. An in vitro platelet adhesion experiment was conducted to compare the blood compatibility of TiNb substrates before and after coating with undoped and boron doped DLC. Films with highly hydrophilic surface enhanced the blood compatibility of TiNb, and the best results were obtained for DLC with the B/C ratio of 0.03. Boron doped DLC films are promising surface coatings for blood contacting devices. PMID:28179961

Boosting surface charge-transfer doping efficiency and robustness of diamond with WO3 and ReO3

NASA Astrophysics Data System (ADS)

Tordjman, Moshe; Weinfeld, Kamira; Kalish, Rafi

2017-09-01

An advanced charge-transfer yield is demonstrated by employing single monolayers of transition-metal oxides—tungsten trioxide (WO3) and rhenium trioxide (ReO3)—deposited on the hydrogenated diamond surface, resulting in improved p-type sheet conductivity and thermal stability. Surface conductivities, as determined by Hall effect measurements as a function of temperature for WO3, yield a record sheet hole carrier concentration value of up to 2.52 × 1014 cm-2 at room temperature for only a few monolayers of coverage. Transfer doping with ReO3 exhibits a consistent narrow sheet carrier concentration value of around 3 × 1013 cm-2, exhibiting a thermal stability of up to 450 °C. This enhanced conductivity and temperature robustness exceed those reported for previously exposed surface electron acceptor materials used so far on a diamond surface. X-ray photoelectron spectroscopy measurements of the C1s core level shift as a function of WO3 and ReO3 layer thicknesses are used to determine the respective increase in surface band bending of the accumulation layers, leading to a different sub-surface two-dimensional hole gas formation efficiency in both cases. This substantial difference in charge-exchange efficiency is unexpected since both surface acceptors have very close work functions. Consequently, these results lead us to consider additional factors influencing the transfer doping mechanism. Transfer doping with WO3 reveals the highest yet reported transfer doping efficiency per minimal surface acceptor coverage. This improved surface conductivity performance and thermal stability will promote the realization of 2D diamond-based electronic devices facing process fabrication challenges.

Reduction Mechanisms of Cu2+-Doped Na2O-Al2O3-SiO2 Glasses during Heating in H2 Gas.

PubMed

Nogami, Masayuki; Quang, Vu Xuan; Ohki, Shinobu; Deguchi, Kenzo; Shimizu, Tadashi

2018-01-25

Controlling valence state of metal ions that are doped in materials has been widely applied for turning optical properties. Even though hydrogen has been proven effective to reduce metal ions because of its strong reducing capability, few comprehensive studies focus on practical applications because of the low diffusion rate of hydrogen in solids and the limited reaction near sample surfaces. Here, we investigated the reactions of hydrogen with Cu 2+ -doped Na 2 O-Al 2 O 3 -SiO 2 glass and found that a completely different reduction from results reported so far occurs, which is dominated by the Al/Na concentration ratio. For Al/Na < 1, Cu 2+ ions were reduced via hydrogen to metallic Cu, distributing in glass body. For Al/Na > 1, on the other hand, the reduction of Cu 2+ ions occurred simultaneously with the formation of OH bonds, whereas the reduced Cu metal moved outward and formed a metallic film on glass surface. The NMR and Fourier transform infrared results indicated that the Cu 2+ ions were surrounded by Al 3+ ions that formed AlO 4 , distorted AlO 4 , and AlO 5 units. The diffused H 2 gas reacted with the Al-O - ···Cu + units, forming Al-OH and metallic Cu, the latter of which moved freely toward glass surface and in return enhanced H 2 diffusion.

Fermi level pinning characterisation on ammonium fluoride-treated surfaces of silicon by energy-filtered doping contrast in the scanning electron microscope

PubMed Central

Chee, Augustus K. W.

2016-01-01

Two-dimensional dopant profiling using the secondary electron (SE) signal in the scanning electron microscope (SEM) is a technique gaining impulse for its ability to enable rapid and contactless low-cost diagnostics for integrated device manufacturing. The basis is doping contrast from electrical p-n junctions, which can be influenced by wet-chemical processing methods typically adopted in ULSI technology. This paper describes the results of doping contrast studies by energy-filtering in the SEM from silicon p-n junction specimens that were etched in ammonium fluoride solution. Experimental SE micro-spectroscopy and numerical simulations indicate that Fermi level pinning occurred on the surface of the treated-specimen, and that the doping contrast can be explained in terms of the ionisation energy integral for SEs, which is a function of the dopant concentration, and surface band-bending effects that prevail in the mechanism for doping contrast as patch fields from the specimen are suppressed. PMID:27576347

Codoping of Sb2Te3 thin films with V and Cr

NASA Astrophysics Data System (ADS)

Duffy, L. B.; Figueroa, A. I.; van der Laan, G.; Hesjedal, T.

2017-11-01

Magnetically doped topological insulators (TIs) are key to realizing the quantum anomalous Hall (QAH) effect, with the prospect of enabling dissipationless electronic devices in the future. Doping of the well-established three-dimensional TIs of the (Bi,Sb) 2(Se,Te) 3 family with the transition metals Cr and V is now an established approach for observing the QAH state at very low temperatures. While the magnetic transition temperatures of these materials are on the order of tens of degrees Kelvin, full quantization of the QAH state is achieved below ˜100 mK, governed by the size of the magnetic gap and thus the out-of-plane magnetic moment. In an attempt to raise the size of the magnetic moment and transition temperature, we carried out a structural and magnetic investigation of codoped (V,Cr):Sb2Te3 thin films. Starting from singly doped Cr:Sb2Te3 films, free of secondary phases and with a transition temperature of ˜72 K, we introduced increasing fractions of V and found a doubling of the transition temperature, while the magnetic moment decreases. In order to separate the properties and contributions of the two transition metals in the complex doping scenario independently, we employed spectroscopic x-ray techniques. Surprisingly, already small amounts of V lead to the formation of the secondary phase Cr2Te3 . No V was detectable in the Sb2Te3 matrix. Instead, it acts as a surfactant and can be found in the near-surface layers at the end of the growth. Our paper highlights the importance of x-ray-based studies for the doping of van der Waals systems, for which the optimization of magnetic moment or transition temperature alone is not necessarily a good strategy.

Synthesis and characterization of silver doped hydroxyapatite nanocomposite coatings and evaluation of their antibacterial and corrosion resistance properties in simulated body fluid.

PubMed

Mirzaee, Majid; Vaezi, Mohammadreza; Palizdar, Yahya

2016-12-01

Silver-doped hydroxyapatite (Ca10-xAgx(PO4)6(OH)2-x) films were synthesized and deposited on anodized titanium (Ti) using electrophoretic. The influence of different silver-dopant contents (X=0, 0.02, 0.05, 0.08 and 0.1) on the phase formation and microstructure of the powders were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscope (XPS), and Fourier transform infrared spectrum analysis (FT-IR). XRD analysis confirmed the formation of Hexagonal structure of hydroxyapatite (HAp) annealed at 600°C with a small shift in the major peak position toward lower angles with adding silver. FT-IR spectroscopy disclosed the presence of the different vibrational modes matching to phosphates and hydroxyl groups and the absence of any band characteristics to silver. XPS analysis showed that 75% and 23% of silver was in the chemical states of Ag(2+) and Ag(+), respectively. However, only about 2% of silver was in the Ag(0) state, resulting in the high quality of nanocomposite films. The anodization treatment improves the bond strength between the Ag doped HAp deposited layers on TiO2. HAp and silver doped HAp (X=0.05) are regarded to be hydrophilic due to a large number of -OH groups on the surface. The sample with content of silver (x=0.05) also showed excellent antimicrobial efficacy (>99% reduction in viable cells). Electrochemical reveals the passive current densities of the HAp coated anodized Ti are lower than those of silver doped HAp coated anodized Ti, leading to a slightly lower corrosion resistance. Copyright © 2016 Elsevier B.V. All rights reserved.

Size-dependent abnormal thermo-enhanced luminescence of ytterbium-doped nanoparticles.

PubMed

Cui, Xiangshui; Cheng, Yao; Lin, Hang; Huang, Feng; Wu, Qingping; Wang, Yuansheng

2017-09-21

Thermal quenching above 300 K is widely expected in photoluminescence. Luminescence quenching is usually ascribed to the non-radiative relaxation of excited electrons to the ground state of the activators, during which a high temperature always plays a role in pushing the excited electrons towards the quenching channels, leading to thermal quenching. For the lanthanide-doped nanoparticles, however, there is a special luminescence quenching channel that does not exist in their bulk counterparts, i.e., energy migration-induced surface quenching. Herein, a size-dependent abnormal thermal enhancement of luminescence in the temperature range of 300 K to 423 K in the ytterbium-doped fluoride nanoparticles is presented for the first time. Importantly, in this work, we originally demonstrate that the energy migration-induced surface quenching can be suppressed by increasing temperature, which results in the abnormal thermal enhancement of luminescence. According to the temperature-dependent X-ray diffraction and lifetime analyses, an underlying mechanism based on the effect of thermal lattice expansion on ytterbium-mediated energy migration is proposed. This new finding adds new insights to the size effect on the luminescent characteristics of nanoparticles, which could be utilized to construct some unique nanostructures, especially for many important temperature-related purposes, such as thermal sensing technology.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liang, Shuhua; Bishop, Christopher B.; Moreo, Adriana

The phase diagram of electron-doped pnictides is studied varying the temperature, electronic density, and isotropic in-plane quenched disorder strength and dilution by means of computational techniques applied to a three-orbital (xz,yz,xy) spin-fermion model with lattice degrees of freedom. In experiments, chemical doping introduces disorder but in theoretical studies the relationship between electronic doping and the randomly located dopants, with their associated quenched disorder, is difficult to address. Moreover, in this publication, the use of computational techniques allows us to study independently the effects of electronic doping, regulated by a global chemical potential, and impurity disorder at randomly selected sites. Surprisingly,more » our Monte Carlo simulations reveal that the fast reduction with doping of the N eel T N and the structural T S transition temperatures, and the concomitant stabilization of a robust nematic state, is primarily controlled in our model by the magnetic dilution associated with the in-plane isotropic disorder introduced by Fe substitution. In the doping range studied, changes in the Fermi surface produced by electron doping affect only slightly both critical temperatures. Our results also suggest that the specific material-dependent phase diagrams experimentally observed could be explained as a consequence of the variation in disorder profiles introduced by the different dopants. Finally, our findings are also compatible with neutron scattering and scanning tunneling microscopy, unveiling a patchy network of locally magnetically ordered clusters with anisotropic shapes, even though the quenched disorder is locally isotropic. Our study reveals a remarkable and unexpected degree of complexity in pnictides: the fragile tendency to nematicity intrinsic of translational invariant electronic systems needs to be supplemented by quenched disorder and dilution to stabilize the robust nematic phase experimentally found in electron-doped 122 compounds.« less

Method for Improving Mg Doping During Group-III Nitride MOCVD

DOEpatents

Creighton, J. Randall; Wang, George T.

2008-11-11

A method for improving Mg doping of Group III-N materials grown by MOCVD preventing condensation in the gas phase or on reactor surfaces of adducts of magnesocene and ammonia by suitably heating reactor surfaces between the location of mixing of the magnesocene and ammonia reactants and the Group III-nitride surface whereon growth is to occur.

Doped silicon nanocrystals from organic dopant precursor by a SiCl4-based high frequency nonthermal plasma

NASA Astrophysics Data System (ADS)

Zhou, Shu; Ding, Yi; Pi, Xiaodong; Nozaki, Tomohiro

2014-11-01

Doped silicon nanocrystals (Si NCs) are of great interest in demanding low-cost nanodevices because of the abundance and nontoxicity of Si. Here, we demonstrate a cost-effective gas phase approach to synthesize phosphorous (P)-doped Si NCs in which the precursors used, i.e., SiCl4, trimethyl phosphite (TMP), are both safe and economical. It is found that the TMP-enabled P-doping does not change the crystalline structure of Si NCs. The surface of P-doped Si NCs is terminated by both Cl and H. The Si-H bond density at the surface of P-doped Si NCs is found to be much higher than that of undoped Si NCs. The X-ray photoelectron spectroscopy and electron spin resonance results indicate that P atoms are doped into the substitutional sites of the Si-NC core and electrically active in Si NCs. Unintentional impurities, such as carbon contained in TMP, are not introduced into Si NCs.

An Organic Vertical Field-Effect Transistor with Underside-Doped Graphene Electrodes.

PubMed

Kim, Jong Su; Kim, Beom Joon; Choi, Young Jin; Lee, Moo Hyung; Kang, Moon Sung; Cho, Jeong Ho

2016-06-01

High-performance vertical field-effect transistors are developed, which are based on graphene electrodes doped using the underside doping method. The underside doping method enables effective tuning of the graphene work function while maintaining the surface properties of the pristine graphene. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cobalt-Doped Nickel Phosphite for High Performance of Electrochemical Energy Storage.

PubMed

Li, Bing; Shi, Yuxin; Huang, Kesheng; Zhao, Mingming; Qiu, Jiaqing; Xue, Huaiguo; Pang, Huan

2018-03-01

Compared to single metallic Ni or Co phosphides, bimetallic Ni-Co phosphides own ameliorative properties, such as high electrical conductivity, remarkable rate capability, upper specific capacity, and excellent cycle performance. Here, a simple one-step solvothermal process is proposed for the synthesis of bouquet-like cobalt-doped nickel phosphite (Ni 11 (HPO 3 ) 8 (OH) 6 ), and the effect of the structure on the pseudocapacitive performance is investigated via a series of electrochemical measurements. It is found that when the cobalt content is low, the glycol/deionized water ratio is 1, and the reaction is under 200 °C for 20 h, the morphology of the sample is uniform and has the highest specific surface area. The cobalt-doped Ni 11 (HPO 3 ) 8 (OH) 6 electrode presents a maximum specific capacitance of 714.8 F g -1 . More significantly, aqueous and solid-state flexible electrochemical energy storage devices are successfully assembled. The aqueous device shows a high energy density of 15.48 mWh cm -2 at the power density of 0.6 KW cm -2 . The solid-state device shows a high energy density of 14.72 mWh cm -2 at the power density of 0.6 KW cm -2 . These excellent performances confirm that the cobalt-doped Ni 11 (HPO 3 ) 8 (OH) 6 are promising materials for applications in electrochemical energy storage devices. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Noncontact Measurement of Doping Profile for Bare Silicon

NASA Astrophysics Data System (ADS)

Kohno, Motohiro; Matsubara, Hideaki; Okada, Hiroshi; Hirae, Sadao; Sakai, Takamasa

1998-10-01

In this study, we evaluate the doping concentrations of bare silicon wafers by noncontact capacitance voltage (C V) measurements. The metal-air-insulator-semiconductor (MAIS) method enables the measurement of C V characteristics of silicon wafers without oxidation and electrode preparation. This method has the advantage that a doping profile close to the wafer surface can be obtained. In our experiment, epitaxial silicon wafers were used to compare the MAIS method with the conventional MIS method. The experimental results obtained from the two methods showed good agreement. Then, doping profiles of boron-doped Czochralski (CZ) wafers were measured by the MAIS method. The result indicated a significant reduction of the doping concentration near the wafer surface. This observation is attributed to the well-known deactivation of boron with atomic hydrogen which permeated the silicon bulk during the polishing process. This deactivation was recovered by annealing in air at 180°C for 120 min.

Toward deep blue nano hope diamonds: heavily boron-doped diamond nanoparticles.

PubMed

Heyer, Steffen; Janssen, Wiebke; Turner, Stuart; Lu, Ying-Gang; Yeap, Weng Siang; Verbeeck, Jo; Haenen, Ken; Krueger, Anke

2014-06-24

The production of boron-doped diamond nanoparticles enables the application of this material for a broad range of fields, such as electrochemistry, thermal management, and fundamental superconductivity research. Here we present the production of highly boron-doped diamond nanoparticles using boron-doped CVD diamond films as a starting material. In a multistep milling process followed by purification and surface oxidation we obtained diamond nanoparticles of 10-60 nm with a boron content of approximately 2.3 × 10(21) cm(-3). Aberration-corrected HRTEM reveals the presence of defects within individual diamond grains, as well as a very thin nondiamond carbon layer at the particle surface. The boron K-edge electron energy-loss near-edge fine structure demonstrates that the B atoms are tetrahedrally embedded into the diamond lattice. The boron-doped diamond nanoparticles have been used to nucleate growth of a boron-doped diamond film by CVD that does not contain an insulating seeding layer.

A study of scandia and rhenium doped tungsten matrix dispenser cathode

NASA Astrophysics Data System (ADS)

Wang, Jinshu; Li, Lili; Liu, Wei; Wang, Yanchun; Zhao, Lei; Zhou, Meiling

2007-10-01

Scandia and rhenium doped tungsten powders were prepared by solid-liquid doping combined with two-step reduction method. The experimental results show that scandia was distributed evenly on the surface of tungsten particles. The addition of scandia and rhenium could decrease the particle size of doped tungsten, for example, the tungsten powders doped with Sc 2O 3 and Re had the average size of about 50 nm in diameter. By using this kind of powder, scandia and rhenium doped tungsten matrix with the sub-micrometer sized tungsten grains was obtained. This kind of matrix exhibited good anti-bombardment insensitivity at high temperature. The emission property result showed that high space charge limited current densities of more than 60 A/cm 2 at 900 °C could be obtained for this cathode. A Ba-Sc-O multilayer about 100 nm in thickness formed at the surface of cathode after activation led to the high emission property.

Influence of electron doping on the ground state of (Sr 1-xLa x) 2IrO 4

DOE PAGES

Chen, Xiang; Hogan, Tom; Walkup, D.; ...

2015-08-17

The evolution of the electronic properties of electron-doped (Sr 1-xLa x) 2IrO 4 is experimentally explored as the doping limit of La is approached. As electrons are introduced, the electronic ground state transitions from a spin-orbit Mott phase into an electronically phase separated state, where long-range magnetic order vanishes beyond x = 0:02 and charge transport remains percolative up to the limit of La substitution (x =0:06). In particular, the electronic ground state remains inhomogeneous even beyond the collapse of the parent state's long-range antiferromagnetic order, while persistent short-range magnetism survives up to the highest La-substitution levels. Furthermore, as electronsmore » are doped into Sr 2IrO 4, we observe the appearance of a low temperature magnetic glass-like state intermediate to the complete suppression of antiferromagnetic order. Universalities and di erences in the electron-doped phase diagrams of single layer and bilayer Ruddlesden-Popper strontium iridates are discussed.« less

Electrodes Based on Carbon Aerogels Partially Graphitized by Doping with Transition Metals for Oxygen Reduction Reaction

PubMed Central

Abdelwahab, Abdalla; Castelo-Quibén, Jesica; Vivo-Vilches, José F.; Pérez-Cadenas, María; Maldonado-Hódar, Francisco J.

2018-01-01

A series of carbon aerogels doped with iron, cobalt and nickel have been prepared. Metal nanoparticles very well dispersed into the carbon matrix catalyze the formation of graphitic clusters around them. Samples with different Ni content are obtained to test the influence of the metal loading. All aerogels have been characterized to analyze their textural properties, surface chemistry and crystal structures. These metal-doped aerogels have a very well-developed porosity, making their mesoporosity remarkable. Ni-doped aerogels are the ones with the largest surface area and the smallest graphitization. They also present larger mesopore volumes than Co- and Fe-doped aerogels. These materials are tested as electro-catalysts for the oxygen reduction reaction. Results show a clear and strong influence of the carbonaceous structure on the whole electro-catalytic behavior of the aerogels. Regarding the type of metal doping, aerogel doped with Co is the most active one, followed by Ni- and Fe-doped aerogels, respectively. As the Ni content is larger, the kinetic current densities increase. Comparatively, among the different doping metals, the results obtained with Ni are especially remarkable. PMID:29690602

Surface Spin Glass Ordering and Exchange Bias in Nanometric Sm0.09Ca0.91MnO3 Manganites

NASA Astrophysics Data System (ADS)

Giri, S. K.; Nath, T. K.

2011-07-01

We have thoroughly investigated the entire magnetic state of under doped ferromagnetic insulating manganite Sm0.09Ca0.91MnO3 through temperature dependent linear and non-linear ac magnetic susceptibility and magnetization measurements. This ferromagnetic insulating manganite is found to have frequency dependent ferromagnetic to paramagnetic transition temperature at around 108 K. Exchange- bias effect are observed in field -cooled magnetic hysteresis loops for this nanoparticle. We have attributed our observation to the formation of ferromagnetic cluster which are formed as a consequence of intrinsic phase separation below certain temperature in this under doped manganites. We have carried out electronic- and magneto-transport measurements to support these observed results.

Enhanced photoluminescence intensity by modifying the surface nanostructure of Nd3+-doped (Pb, La)(Zr, Ti)O3 ceramics.

PubMed

Xu, Long; Zhang, Jingwen; Zhao, Hua; Sun, Haibin; Xu, Caixia

2017-09-01

Quasi-period cylindrical nanostructures with both diameters and intervals of about 100 nm are manufactured on the surfaces of Nd 3+ -doped lanthanum lead zirconate titanate ceramics by femtosecond laser irradiation under SF 6 atmosphere. A light-emission enhancement of more than 20 times is investigated, accompanied by an extremely long trailing-off time of light emission and lower threshold. A specific polarization state of the light emission is achieved and tuned by changing the incident regions of the pumping source. The increased absorption coefficient of the specimen is discussed based on multiple scattering and weak localization of light. In addition, both the scatterers provided by the laser-machined nanostructure and the recurrent photoinduced trapping and re-excitation process participated in the enhancement of the light emission. This Letter offers new insight to improve the luminescence property of laser materials, as well as to broaden the range of exploring the weak localization of light and random lasers.

Color-coded multilayer photopatterned microstructures using lanthanide (III) ion co-doped NaYF4 nanoparticles with upconversion luminescence for possible applications in security.

PubMed

Kim, Won Jin; Nyk, Marcin; Prasad, Paras N

2009-05-06

We report a method for fabricating predefined photopatterns of upconversion nanophosphors using a chemical amplification reaction for direct writing of films with multilayer color-coded patterning for security applications. To photopattern the nanocrystal film we have synthesized rare-earth ion (Er(3+)/Yb(3+) or Tm(3+)/Yb(3+)) co-doped sodium yttrium fluoride (alpha-NaYF(4)) nanophosphors and functionalized the nanocrystal surfaces by incorporation of a photopatternable ligand such as t-butoxycarbonyl (t-BOC). The surface modification allows photopatterning of the nanophosphor solid state film. Furthermore, upconversion nanophosphors show a nearly quadratic dependence of the upconversion photoluminescence (PL) intensity on the excitation light power, and tailoring of the PL wavelength is possible by changing the lanthanide ions. We have demonstrated the capability of anchoring nanophosphors at desirable locations by a photolithography technique. The photopatterned films exhibit fixed nanophosphor structures clearly identifiable by strong upconversion photoluminescence under IR illumination which is useful for a number of applications in security.

Activation of the surface dark-layer to enhance upconversion in a thermal field

NASA Astrophysics Data System (ADS)

Zhou, Jiajia; Wen, Shihui; Liao, Jiayan; Clarke, Christian; Tawfik, Sherif Abdulkader; Ren, Wei; Mi, Chao; Wang, Fan; Jin, Dayong

2018-03-01

Thermal quenching, in which light emission experiences a loss with increasing temperature, broadly limits luminescent efficiency at higher temperature in optical materials, such as lighting phosphors1-3 and fluorescent probes4-6. Thermal quenching is commonly caused by the increased activity of phonons that leverages the non-radiative relaxation pathways. Here, we report a kind of heat-favourable phonons existing at the surface of lanthanide-doped upconversion nanomaterials to combat thermal quenching. It favours energy transfer from sensitizers to activators to pump up the intermediate excited-state upconversion process. We identify that the oxygen moiety chelating Yb3+ ions, [Yb...O], is the key underpinning this enhancement. We demonstrate an approximately 2,000-fold enhancement in blue emission for 9.7 nm Yb3+-Tm3+ co-doped nanoparticles at 453 K. This strategy not only provides a powerful solution to illuminate the dark layer of ultra-small upconversion nanoparticles, but also suggests a new pathway to build high-efficiency upconversion systems.

Fluidic Grooves on Doped-Ice Surface as Size-Tunable Channels

PubMed Central

Inagawa, Arinori; Harada, Makoto; Okada, Tetsuo

2015-01-01

We propose a new principle for fabrication of size-tunable fluidic nano- and microchannels with a ubiquitous green material, water. Grooves filled with a solution are spontaneously formed on the surface of ice when an appropriate dopant is incorporated. Sucrose doping allows the development of grooves with lengths of 300 μm along the boundaries of ice crystal grains. This paper focuses on controlling the size of the liquid-filled groove and reveals its applicability to size-selective differentiation of nano- and micromaterials. The width of this groove can be varied in a range of 200 nm to 4 μm by adjusting the working temperature of the frozen platform. The channel dimension is reproducible as long as the same frozen condition is employed. We demonstrate the size-selective entrapment of particles as well as the state evaluation of DNA by controlling the physical interference of the ice wall with the electrophoretic migration of particles. PMID:26601703

Fluidic Grooves on Doped-Ice Surface as Size-Tunable Channels

NASA Astrophysics Data System (ADS)

Inagawa, Arinori; Harada, Makoto; Okada, Tetsuo

2015-11-01

We propose a new principle for fabrication of size-tunable fluidic nano- and microchannels with a ubiquitous green material, water. Grooves filled with a solution are spontaneously formed on the surface of ice when an appropriate dopant is incorporated. Sucrose doping allows the development of grooves with lengths of 300 μm along the boundaries of ice crystal grains. This paper focuses on controlling the size of the liquid-filled groove and reveals its applicability to size-selective differentiation of nano- and micromaterials. The width of this groove can be varied in a range of 200 nm to 4 μm by adjusting the working temperature of the frozen platform. The channel dimension is reproducible as long as the same frozen condition is employed. We demonstrate the size-selective entrapment of particles as well as the state evaluation of DNA by controlling the physical interference of the ice wall with the electrophoretic migration of particles.

Plasmon-enhanced energy transfer for improved upconversion of infrared radiation in doped-lanthanide nanocrystals

NASA Astrophysics Data System (ADS)

Sun, Qi; Mundoor, Haridas; Ribot, Josep; Singh, Vivek; Smalyukh, Ivan; Nagpal, Prashant

2014-03-01

Upconversion of infrared radiation into visible light has been investigated for applications in biological imaging and photovoltaics. However, low conversion efficiency due to small absorption cross-section for infrared light (Yb3+) , and slow rate of energy transfer (to Er3+ states) has prevented application of upconversion photoluminescence (UPL) for diffuse sunlight or imaging tissue samples. Here, we utilize resonant surface plasmon polaritons (SPP) waves to enhance UPL in doped-lanthanide nanocrystals. Our analysis indicates that SPP waves not only enhance the electromagnetic field, and hence weak Purcell effect, but also increases the rate of resonant energy transfer from Yb3+ to Er3+ ions by 6 fold. While we do observe strong metal mediated quenching (14 fold) of green fluorescence on flat metal surfaces, the nanostructured metal is resonant in the infrared, and hence enhances the nanocrystal UPL. This strong columbic effect on energy transfer can have important implications for other fluorescent and excitonic systems too.

Ab initio study of (Fe, Ni) doped GaAs: Magnetic, electronic properties and Faraday rotation

NASA Astrophysics Data System (ADS)

Sbai, Y.; Ait Raiss, A.; Bahmad, L.; Benyoussef, A.

2017-06-01

The interesting diluted magnetic semiconductor (DMS), Gallium Arsenide (GaAs), was doped with the transition metals magnetic impurities: iron (Fe) and Nickel (Ni), in one hand to study the magnetic and magneto-optical properties of the material Ga(Fe, Ni) As, in the other hand to investigate the effect of the doping on the properties of this material, the calculations were performed within the spin polarized density functional theory (DFT) and generalized gradient approximation (GGA) with AKAI KKR-CPA method, the density of states (DOS) for different doping concentrations were calculated, giving the electronical properties, as well as the magnetic state and magnetic states energy, also the effect of these magnetic impurities on the Faraday rotation as magneto-optical property. Furthermore, we found the stable magnetic state for our doped material GaAs.

Fluorescent chemosensor for pyridine based on N-doped carbon dots.

PubMed

Campos, B B; Abellán, C; Zougagh, M; Jimenez-Jimenez, J; Rodríguez-Castellón, E; Esteves da Silva, J C G; Ríos, A; Algarra, M

2015-11-15

Fluorescent carbon dots (CDs) and its nitrogen doped (N-CDs) nanoparticles have been synthesized from lactose as precursor using a bottom-up hydrothermal methodology. The synthesized nanoparticles have been characterized by elemental analysis, FTIR, Raman, TEM, DLS, XPS, and steady-state and life-time fluorescence. The synthesized carbon nanoparticles, CDs and N-CDs, have a size at about 7.7±2.4 and 50±15nm, respectively, and quantum yields of 8% (CDs) and 11% (N-CDs). These techniques demonstrated the effectiveness of the synthesis procedure and the functionalization of the CDs surface with amine and amide groups in the presence of NH3 in aqueous media. The effect of excitation wavelength and pH on the luminescent properties was studied. Under the optimal conditions, the nitrogen doped nanoparticles can be used as pyridine sensor in aqueous media because they show an enhancement of its fluorescence with a good linear relationship. The analytical method is simple, reproducible and very sensitive for pyridine determination. Copyright © 2015 Elsevier Inc. All rights reserved.

Prospective high thermoelectric performance of the heavily p -doped half-Heusler compound CoVSn

DOE PAGES

Shi, Hongliang; Ming, Wenmei; Parker, David S.; ...

2017-05-11

The electronic structure and transport properties of the half-Heusler compound CoVSn are studied in this paper systematically by combining first-principles electronic structure calculations and Boltzmann transport theory. The band structure at the valence-band edge is complex with multiple maxima derived from hybridized transition element d states. The result is a calculated thermopower larger than 200 μV /Κ within a wide range of doping concentrations and temperatures for heavily doped p-type CoVSn. The thermoelectric properties additionally benefit from the corrugated shapes of the hole pockets in our calculated isoenergy surfaces. Our calculated power factor S 2σ/τ (with respect to an averagemore » unknown scattering time) of CoVSn is comparable to that of FeNbSb. A smaller lattice thermal conductivity can be expected from the smaller group velocities of acoustical modes compared to FeNbSb. Finally, overall, good thermoelectric performance for CoVSn can be expected by considering the electronic transport and lattice thermal conductivity.« less

Polymeric phase change nanocomposite (PMMA/Fe:ZnO) for electronic packaging application

NASA Astrophysics Data System (ADS)

Maji, Pranabi; Choudhary, Ram Bilash; Majhi, Malati

2018-01-01

This paper reported the effect of Fe-doped ZnO (Fe:ZnO) nanoparticles on the structural, morphological, thermal, optical and dielectric properties of PMMA matrix. Fe-doped ZnO nanoparticle was synthesized by co-precipitation method, after its surface modification incorporated into the PMMA matrix by free radical polymerization method. The phase analysis and crystal structure were investigated by XRD and FTIR technique. These studies confirmed the chemical structure of the PMMA/Fe:ZnO nanocomposite. FESEM image showed the pyramidal shape and high porosity of PMMA/Fe:ZnO nanocomposite. Thermal analysis of the sample was carried out by thermo-gravimetric analyzer. PMMA/Fe:ZnO nanocomposite was found to have better thermal stability compared to pure one. Broadband dielectric spectroscopic technique was used to investigate the transition of electrical properties of Fe-doped ZnO nanoparticle reinforced PMMA matrix in temperature range 313-373 K. The results elucidated a phase transition from glassy to rubbery state at 344 K.

A new preparation of doped photocatalytic TiO2 anatase nanoparticles: a preliminary study for the removal of pollutants in confined museum areas

NASA Astrophysics Data System (ADS)

Greco, Enrico; Ciliberto, Enrico; Cirino, Antonio M. E.; Capitani, Donatella; Di Tullio, Valeria

2016-05-01

The use of nanotechnology in conservation is a relatively new concept. Usually, classical cleanup methods take into account the use of other chemicals: On the one hand they help the environment destroying pollutants, but on the other hand they often become new pollutants. Among the new oxidation methods called advanced oxidation processes, heterogeneous photocatalysis has appeared an emerging technology with several economic and environmental advantages. A new sol-gel method of synthesis of TiO2 anatase is reported in this work using lithium and cobalt (II) salts. The activation energy of the doped photocatalyst was analyzed by solid-state UV-Vis spectrophotometer. The mobility of Li ions on TiO2 NPs surface was studied by 7Li MAS NMR spectroscopy. Use of doped nanotitania is suggested from authors for the removal of pollutants in confined areas containing goods that must be preserved from decomposition and aging phenomena.

Prospective high thermoelectric performance of the heavily p -doped half-Heusler compound CoVSn

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shi, Hongliang; Ming, Wenmei; Parker, David S.

The electronic structure and transport properties of the half-Heusler compound CoVSn are studied in this paper systematically by combining first-principles electronic structure calculations and Boltzmann transport theory. The band structure at the valence-band edge is complex with multiple maxima derived from hybridized transition element d states. The result is a calculated thermopower larger than 200 μV /Κ within a wide range of doping concentrations and temperatures for heavily doped p-type CoVSn. The thermoelectric properties additionally benefit from the corrugated shapes of the hole pockets in our calculated isoenergy surfaces. Our calculated power factor S 2σ/τ (with respect to an averagemore » unknown scattering time) of CoVSn is comparable to that of FeNbSb. A smaller lattice thermal conductivity can be expected from the smaller group velocities of acoustical modes compared to FeNbSb. Finally, overall, good thermoelectric performance for CoVSn can be expected by considering the electronic transport and lattice thermal conductivity.« less

Hierarchically porous carbons with optimized nitrogen doping as highly active electrocatalysts for oxygen reduction

NASA Astrophysics Data System (ADS)

Liang, Hai-Wei; Zhuang, Xiaodong; Brüller, Sebastian; Feng, Xinliang; Müllen, Klaus

2014-09-01

Development of efficient, low-cost and stable electrocatalysts as the alternative to platinum for the oxygen reduction reaction is of significance for many important electrochemical devices, such as fuel cells, metal-air batteries and chlor-alkali electrolysers. Here we report a highly active nitrogen-doped, carbon-based, metal-free oxygen reduction reaction electrocatalyst, prepared by a hard-templating synthesis, for which nitrogen-enriched aromatic polymers and colloidal silica are used as precursor and template, respectively, followed by ammonia activation. Our protocol allows for the simultaneous optimization of both porous structures and surface functionalities of nitrogen-doped carbons. Accordingly, the prepared catalysts show the highest oxygen reduction reaction activity (half-wave potential of 0.85 V versus reversible hydrogen electrode with a low loading of 0.1 mg cm-2) in alkaline media among all reported metal-free catalysts. Significantly, when used for constructing the air electrode of zinc-air battery, our metal-free catalyst outperforms the state-of the-art platinum-based catalyst.

Rayleigh surface waves in ultraheavily doped n-Si

NASA Astrophysics Data System (ADS)

Sood, A. K.; Cardona, M.

1986-11-01

We report the effect of free carriers on the velocity of surface Rayleight waves (SRW) in n-type Si studied by Brillouin scattering. The samples prepared by ion implantation followed by laser annealing have carrier concentrations up to 3 x 10 21cm-3. The SRW velocity is observed to decrease significantly on doping (-18% for the heaviest doped sample). The large softening of the velocity can be quantitatively explained on the basis of the decrease of all the three independent elastic constants C 11, C 12, and C 44 in n-Si along with the changes in the density of the doped layer due to the dopant ions.

Synthesis and Characterization of Manganese Doped Silicon Nanoparticles

PubMed Central

Zhang, Xiaoming; Brynda, Marcin; Britt, R. David; Carroll, Elizabeth; Larsen, Delmar S.; Louie, Angelique Y.; Kauzlarich, Susan M.

2008-01-01

Mn doped Si nanoparticles have been synthesized via a low temperature solution route and characterize by X-ray powder diffraction, TEM, optical and emission spectroscopy and by EPR. The particle diameter was 4 nm and the surface was capped by octyl groups. 5% Mn doping resulted in a green emission with slightly lower quantum yield than undoped Si nanoparticles prepared by the same method. Mn2+ doped into the nanoparticle is confirmed by epr hyperfine and the charge carrier dynamics were probed by ultrafast transient absorption spectroscopy. Both techniques are consistent with Mn2+ on or close to the surface of the nanoparticle. PMID:17691792

Relation between film thickness and surface doping of MoS2 based field effect transistors

NASA Astrophysics Data System (ADS)

Lockhart de la Rosa, César J.; Arutchelvan, Goutham; Leonhardt, Alessandra; Huyghebaert, Cedric; Radu, Iuliana; Heyns, Marc; De Gendt, Stefan

2018-05-01

Ultra-thin MoS2 film doping through surface functionalization with physically adsorbed species is of great interest due to its ability to dope the film without reduction in the carrier mobility. However, there is a need for understanding how the thickness of the MoS2 film is related to the induced surface doping for improved electrical performance. In this work, we report on the relation of MoS2 film thickness with the doping effect induced by the n-dopant adsorbate poly(vinyl-alcohol). Field effect transistors built using MoS2 films of different thicknesses were electrically characterized, and it was observed that the ION/OFF ratio after doping in thin films is more than four orders of magnitudes greater when compared with thick films. Additionally, a semi-classical model tuned with the experimental devices was used to understand the spatial distribution of charge in the channel and explain the observed behavior. From the simulation results, it was revealed that the two-dimensional carrier density induced by the adsorbate is distributed rather uniformly along the complete channel for thin films (<5.2 nm) contrary to what happens for thicker films.

Electrospark doping of steel with tungsten

DOE Office of Scientific and Technical Information (OSTI.GOV)

Denisova, Yulia, E-mail: yukolubaeva@mail.ru; Shugurov, Vladimir, E-mail: shugurov@opee.hcei.tsc.ru; Petrikova, Elizaveta, E-mail: elizmarkova@yahoo.com

2016-01-15

The paper is devoted to the numerical modeling of thermal processes and the analysis of the structure and properties of the surface layer of carbon steel subjected to electrospark doping with tungsten. The problem of finding the temperature field in the system film (tungsten) / substrate (iron) is reduced to the solution of the heat conductivity equation. A one-dimensional case of heating and cooling of a plate with the thickness d has been considered. Calculations of temperature fields formed in the system film / substrate synthesized using methods of electrospark doping have been carried out as a part of one-dimensionalmore » approximation. Calculations have been performed to select the mode of the subsequent treatment of the system film / substrate with a high-intensity pulsed electron beam. Authors revealed the conditions of irradiation allowing implementing processes of steel doping with tungsten. A thermodynamic analysis of phase transformations taking place during doping of iron with tungsten in equilibrium conditions has been performed. The studies have been carried out on the surface layer of the substrate modified using the method of electrospark doping. The results showed the formation in the surface layer of a structure with a highly developed relief and increased strength properties.« less

Enhanced superconductivity in surface-electron-doped iron pnictide Ba(Fe 1.94Co 0.06) 2As 2

DOE PAGES

Kyung, W. S.; Huh, S. S.; Koh, Y. Y.; ...

2016-08-15

The transition critical temperature (TC ) in a FeSe monolayer on SrTiO 3 is enhanced up to 100 K. High TC is also found in bulk iron chalcogenides with similar electronic structure to that of monolayer FeSe, which suggests that higher TC may be achieved through electron doping, pushing the Fermi surface (FS) topology towards leaving only electron pockets. Such observation, however, has been limited to chalcogenides and is in contrast with the iron pnictides for which the maximum TC is achieved with both hole and electron pockets forming considerable FS nesting instability. Here, we report angle-resolved photoemission (ARPES) characterizationmore » revealing a monotonic increase of TC from 24 to 41.5 K upon surface doping on optimally doped Ba(Fe 1-xCo x) 2As 2 . The doping changes the overall FS topology towards that of chalcogenides through a rigid downward band shift. Our findings suggest that higher electron doping and concomitant changes in FS topology are favorable conditions for the superconductivity, not only for iron chalcogenides but also for iron pnictides.« less

Screening based approach and dehydrogenation kinetics for MgH2: Guide to find suitable dopant using first-principles approach.

PubMed

Kumar, E Mathan; Rajkamal, A; Thapa, Ranjit

2017-11-14

First-principles based calculations are performed to investigate the dehydrogenation kinetics considering doping at various layers of MgH 2 (110) surface. Doping at first and second layer of MgH 2 (110) has a significant role in lowering the H 2 desorption (from surface) barrier energy, whereas the doping at third layer has no impact on the barrier energy. Molecular dynamics calculations are also performed to check the bonding strength, clusterization, and system stability. We study in details about the influence of doping on dehydrogenation, considering the screening factors such as formation enthalpy, bulk modulus, and gravimetric density. Screening based approach assist in finding Al and Sc as the best possible dopant in lowering of desorption temperature, while preserving similar gravimetric density and Bulk modulus as of pure MgH 2 system. The electron localization function plot and population analysis illustrate that the bond between Dopant-Hydrogen is mainly covalent, which weaken the Mg-Hydrogen bonds. Overall we observed that Al as dopant is suitable and surface doping can help in lowering the desorption temperature. So layer dependent doping studies can help to find the best possible reversible hydride based hydrogen storage materials.

Self-Assembled Formation of Well-Aligned Cu-Te Nano-Rods on Heavily Cu-Doped ZnTe Thin Films

NASA Astrophysics Data System (ADS)

Liang, Jing; Cheng, Man Kit; Lai, Ying Hoi; Wei, Guanglu; Yang, Sean Derman; Wang, Gan; Ho, Sut Kam; Tam, Kam Weng; Sou, Iam Keong

2016-11-01

Cu doping of ZnTe, which is an important semiconductor for various optoelectronic applications, has been successfully achieved previously by several techniques. However, besides its electrical transport characteristics, other physical and chemical properties of heavily Cu-doped ZnTe have not been reported. We found an interesting self-assembled formation of crystalline well-aligned Cu-Te nano-rods near the surface of heavily Cu-doped ZnTe thin films grown via the molecular beam epitaxy technique. A phenomenological growth model is presented based on the observed crystallographic morphology and measured chemical composition of the nano-rods using various imaging and chemical analysis techniques. When substitutional doping reaches its limit, the extra Cu atoms favor an up-migration toward the surface, leading to a one-dimensional surface modulation and formation of Cu-Te nano-rods, which explain unusual observations on the reflection high energy electron diffraction patterns and apparent resistivity of these thin films. This study provides an insight into some unexpected chemical reactions involved in the heavily Cu-doped ZnTe thin films, which may be applied to other material systems that contain a dopant having strong reactivity with the host matrix.

Adsorption of sugars on Al- and Ga-doped boron nitride surfaces: A computational study

NASA Astrophysics Data System (ADS)

Darwish, Ahmed A.; Fadlallah, Mohamed M.; Badawi, Ashraf; Maarouf, Ahmed A.

2016-07-01

Molecular adsorption on surfaces is a key element for many applications, including sensing and catalysis. Non-invasive sugar sensing has been an active area of research due to its importance to diabetes care. The adsorption of sugars on a template surface study is at the heart of matter. Here, we study doped hexagonal boron nitride sheets (h-BNNs) as adsorbing and sensing template for glucose and glucosamine. Using first principles calculations, we find that the adsorption of glucose and glucosamine on h-BNNs is significantly enhanced by the substitutional doping of the sheet with Al and Ga. Including long range van der Waals corrections gives adsorption energies of about 2 eV. In addition to the charge transfer occurring between glucose and the Al/Ga-doped BN sheets, the adsorption alters the size of the band gap, allowing for optical detection of adsorption. We also find that Al-doped boron nitride sheet is better than Ga-doped boron nitride sheet to enhance the adsorption energy of glucose and glucosamine. The results of our work can be potentially utilized when designing support templates for glucose and glucosamine.

Adsorption of CH4 on nitrogen- and boron-containing carbon models of coal predicted by density-functional theory

NASA Astrophysics Data System (ADS)

Liu, Xiao-Qiang; Xue, Ying; Tian, Zhi-Yue; Mo, Jing-Jing; Qiu, Nian-Xiang; Chu, Wei; Xie, He-Ping

2013-11-01

Graphene doped by nitrogen (N) and/or boron (B) is used to represent the surface models of coal with the structural heterogeneity. Through the density functional theory (DFT) calculations, the interactions between coalbed methane (CBM) and coal surfaces have been investigated. Several adsorption sites and orientations of methane (CH4) on graphenes were systematically considered. Our calculations predicted adsorption energies of CH4 on graphenes of up to -0.179 eV, with the strongest binding mode in which three hydrogen atoms of CH4 direct to graphene surface, observed for N-doped graphene, compared to the perfect (-0.154 eV), B-doped (-0.150 eV), and NB-doped graphenes (-0.170 eV). Doping N in graphene increases the adsorption energies of CH4, but slightly reduced binding is found when graphene is doped by B. Our results indicate that all of graphenes act as the role of a weak electron acceptor with respect to CH4. The interactions between CH4 and graphenes are the physical adsorption and slightly depend upon the adsorption sites on graphenes and the orientations of methane as well as the electronegativity of dopant atoms in graphene.

Perspective. Extremely fine tuning of doping enabled by combinatorial molecular-beam epitaxy

DOE PAGES

Wu, J.; Bozovic, I.

2015-04-06

Chemical doping provides an effective method to control the electric properties of complex oxides. However, the state-of-art accuracy in controlling doping is limited to about 1%. This hampers elucidation of the precise doping dependences of physical properties and phenomena of interest, such as quantum phase transitions. Using the combinatorial molecular beam epitaxy, we improve the accuracy in tuning the doping level by two orders of magnitude. We illustrate this novel method by two examples: a systematic investigation of the doping dependence of interface superconductivity, and a study of the competing ground states in the vicinity of the insulator-to-superconductor transition.

Transfer doping of single isolated nanodiamonds, studied by scanning probe microscopy techniques.

PubMed

Bolker, Asaf; Saguy, Cecile; Kalish, Rafi

2014-09-26

The transfer doping of diamond surfaces has been applied in various novel two-dimensional electronic devices. Its extension to nanodiamonds (ND) is essential for ND-based applications in many fields. In particular, understanding the influence of the crystallite size on transfer doping is desirable. Here, we report the results of a detailed study of the electronic energetic band structure of single, isolated transfer-doped nanodiamonds with nanometric resolution using a combination of scanning tunneling spectroscopy and Kelvin force microscopy measurements. The results show how the band gap, the valence band maximum, the electron affinity and the work function all depend on the ND's size and nanoparticle surface properties. The present analysis, which combines information from both scanning tunneling spectroscopy and Kelvin force microscopy, should be applicable to any nanoparticle or surface that can be measured with scanning probe techniques.

Nitrogen-Doped Carbon Nanotube-Supported Pd Catalyst for Improved Electrocatalytic Performance toward Ethanol Electrooxidation

NASA Astrophysics Data System (ADS)

Wei, Ying; Zhang, Xinyuan; Luo, Zhiyong; Tang, Dian; Chen, Changxin; Zhang, Teng; Xie, Zailai

2017-07-01

In this study, hydrothermal carbonization (HTC) was applied for surface functionalization of carbon nanotubes (CNTs) in the presence of glucose and urea. The HTC process allowed the deposition of thin nitrogen-doped carbon layers on the surface of the CNTs. By controlling the ratio of glucose to urea, nitrogen contents of up to 1.7 wt% were achieved. The nitrogen-doped carbon nanotube-supported Pd catalysts exhibited superior electrochemical activity for ethanol oxidation relative to the pristine CNTs. Importantly, a 1.5-fold increase in the specific activity was observed for the Pd/HTC-N1.67%CNTs relative to the catalyst without nitrogen doping (Pd/HTC-CNTs). Further experiments indicated that the introduction of nitrogen species on the surface of the CNTs improved the Pd(0) loading and increased the binding energy.

Enhanced electrical transport and thermoelectric properties in Ni doped Cu3SbSe4

NASA Astrophysics Data System (ADS)

Kumar, Aparabal; Dhama, P.; Das, Anish; Sarkar, Kalyan Jyoti; Banerji, P.

2018-05-01

In this study, we report the enhanced thermoelectric performance of Cu3SbSe4 by Ni doping at Cu site. Cu3-xNixSbSe4 (x = 0, 0.01, 0.03, 0.05) were prepared by melt growth, ball milling followed by spark plasma sintering. Structural characterization, phase analysis and surface morphology were carried out using X-ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. Electrical and thermal properties of all the samples were investigated in the temperature range 300 - 650 K. Decrease in electrical resistivity with Ni doping due to increase in carrier concentration with enhanced Seebeck coefficient via increase in density of state near the Fermi level gives a remarkably high power factor. At the same time, thermal conductivity was found to decrease due to increased carrier-phonon scattering and acoustic phonon scattering. Consequently, a remarkable enhancement in the thermoelectric figure of merit (ZT˜ 0.65) of Cu3-xNixSbSe4 was achieved for x = 0.01 sample. Thus, Ni doping is an effective approach to improve the efficiency of Cu3SbSe4.

Heteroatom-doped highly porous carbon from human urine.

PubMed

Chaudhari, Nitin Kaduba; Song, Min Young; Yu, Jong-Sung

2014-06-09

Human urine, otherwise potentially polluting waste, is an universal unused resource in organic form disposed by the human body. We present for the first time "proof of concept" of a convenient, perhaps economically beneficial, and innovative template-free route to synthesize highly porous carbon containing heteroatoms such as N, S, Si, and P from human urine waste as a single precursor for carbon and multiple heteroatoms. High porosity is created through removal of inherently-present salt particles in as-prepared "Urine Carbon" (URC), and multiple heteroatoms are naturally doped into the carbon, making it unnecessary to employ troublesome expensive pore-generating templates as well as extra costly heteroatom-containing organic precursors. Additionally, isolation of rock salts is an extra bonus of present work. The technique is simple, but successful, offering naturally doped conductive hierarchical porous URC, which leads to superior electrocatalytic ORR activity comparable to state of the art Pt/C catalyst along with much improved durability and methanol tolerance, demonstrating that the URC can be a promising alternative to costly Pt-based electrocatalyst for ORR. The ORR activity can be addressed in terms of heteroatom doping, surface properties and electrical conductivity of the carbon framework.

Heteroatom-doped highly porous carbon from human urine

NASA Astrophysics Data System (ADS)

Chaudhari, Nitin Kaduba; Song, Min Young; Yu, Jong-Sung

2014-06-01

Human urine, otherwise potentially polluting waste, is an universal unused resource in organic form disposed by the human body. We present for the first time ``proof of concept'' of a convenient, perhaps economically beneficial, and innovative template-free route to synthesize highly porous carbon containing heteroatoms such as N, S, Si, and P from human urine waste as a single precursor for carbon and multiple heteroatoms. High porosity is created through removal of inherently-present salt particles in as-prepared ``Urine Carbon'' (URC), and multiple heteroatoms are naturally doped into the carbon, making it unnecessary to employ troublesome expensive pore-generating templates as well as extra costly heteroatom-containing organic precursors. Additionally, isolation of rock salts is an extra bonus of present work. The technique is simple, but successful, offering naturally doped conductive hierarchical porous URC, which leads to superior electrocatalytic ORR activity comparable to state of the art Pt/C catalyst along with much improved durability and methanol tolerance, demonstrating that the URC can be a promising alternative to costly Pt-based electrocatalyst for ORR. The ORR activity can be addressed in terms of heteroatom doping, surface properties and electrical conductivity of the carbon framework.

Heteroatom-doped highly porous carbon from human urine

PubMed Central

Chaudhari, Nitin Kaduba; Song, Min Young; Yu, Jong-Sung

2014-01-01

Human urine, otherwise potentially polluting waste, is an universal unused resource in organic form disposed by the human body. We present for the first time “proof of concept” of a convenient, perhaps economically beneficial, and innovative template-free route to synthesize highly porous carbon containing heteroatoms such as N, S, Si, and P from human urine waste as a single precursor for carbon and multiple heteroatoms. High porosity is created through removal of inherently-present salt particles in as-prepared “Urine Carbon” (URC), and multiple heteroatoms are naturally doped into the carbon, making it unnecessary to employ troublesome expensive pore-generating templates as well as extra costly heteroatom-containing organic precursors. Additionally, isolation of rock salts is an extra bonus of present work. The technique is simple, but successful, offering naturally doped conductive hierarchical porous URC, which leads to superior electrocatalytic ORR activity comparable to state of the art Pt/C catalyst along with much improved durability and methanol tolerance, demonstrating that the URC can be a promising alternative to costly Pt-based electrocatalyst for ORR. The ORR activity can be addressed in terms of heteroatom doping, surface properties and electrical conductivity of the carbon framework. PMID:24909133

Improving the Thermodynamic Stability of Aluminate Spinel Nanoparticles with Rare Earths

DOE PAGES

Hasan, M. M.; Dey, Sanchita; Nafsin, Nazia; ...

2016-06-29

Surface energy is a key parameter to understand and predict the stability of catalysts. In this work, the surface energy of MgAl 2O 4, an important base material for catalyst support, was reduced by using dopants prone to form surface excess (surface segregation): Y 3+, Gd 3+, and La 3+. The energy reduction was predicted by atomistic simulations of spinel surfaces and experimentally demonstrated by using microcalorimetry. The surface energy of undoped MgAl 2O 4 was directly measured as 1.65 ± 0.04 J/m 2 and was reduced by adding 2 mol % of the dopants to 1.55 ± 0.04 J/mmore » 2 for Y-doping, 1.45 ± 0.05 J/m 2 for Gd-doping, and 1.26 ± 0.06 J/m 2 for La-doping. Atomistic simulations are qualitatively consistent with the experiments, reinforcing the link between the role of dopants in stabilizing the surface and the energy of segregation. Surface segregation was experimentally assessed using electron energy loss spectroscopy mapping in a scanning transmission electron microscopy image. Finally, the reduced energy resulted in coarsening inhibition for the doped samples and, hence, systematically smaller particle sizes (larger surface areas), meaning increased stability for catalytic applications. Moreover, both experiment and modeling reveal preferential dopant segregation to specific surfaces, which leads to the preponderance of {111} surface planes and suggests a strategy to enhance the area of desired surfaces in nanoparticles for better catalyst support activity.« less

AB INITIO Investigations of the Magnetism in Diluted Magnetic Semiconductor Fe-DOPED GaN

NASA Astrophysics Data System (ADS)

Cheng, Jie; Zhou, Jing; Xu, Wei; Dong, Peng

2014-01-01

In this paper, we present a first principle investigation on Fe-doped GaN with wurtzite and zinc-blend structure using full potential density functional calculations. Data point out that the magnetic behavior of Fe-doped GaN system is strongly dependent on Fe doping configurations. In agreement with the experimental reports, and independently by doping, antiferromagnetism occurs in the zinc-blend structure, while in the wurtzite structure ferromagnetism depends on the Fe doping configurations. Detailed analyses combined with density of state calculations support the assignment that the ferromagnetism is closely related to the impurity band at the origin of the hybridization of Fe 3d and N 2p states in the Fe-doped GaN of wurtzite phase.

Study on surface roughness evolvement of Nd-doped phosphate glass after IBF

NASA Astrophysics Data System (ADS)

Li, Furen; Xie, Xuhui; Zhou, Lin; Tie, Guipeng; Hu, Hao

2016-10-01

Nd doped phosphate glass is widely used as gain media in high power laser system. It is traditionally polished with the annular polishing technology. The edge effect is inevitable in annular polishing process and it results in the low manufacturing efficiency. Ion Beam Figuring (IBF) is a highly deterministic, non-contact method for the ultra-precision optics fabrication. So the edge effect is avoided. Nanometer and sub-nanometer precision is realizable in IBF. In this paper, Nd doped phosphate glass was polished with IBF, and the evolvement of surface roughness was emphasized. The roughness of surface polished with ion beam at normal and oblique incidence was researched. The oblique incident angle was 45°. The surface roughness was measured with the white light interferometer. No evident change was observed. This means that the pre-finish roughness can be preserved in IBF. The results denote that IBF is a feasible method to correct the contour errors of Nd doped phosphate glass, and the roughness will not be coarsened.

Enhanced surface transfer doping of diamond by V{sub 2}O{sub 5} with improved thermal stability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crawford, Kevin G., E-mail: k.crawford.2@research.gla.ac.uk; Moran, David A. J.; Cao, Liang

2016-01-25

Surface transfer doping of hydrogen-terminated diamond has been achieved utilising V{sub 2}O{sub 5} as a surface electron accepting material. Contact between the oxide and diamond surface promotes the transfer of electrons from the diamond into the V{sub 2}O{sub 5} as revealed by the synchrotron-based high resolution photoemission spectroscopy. Electrical characterization by Hall measurement performed before and after V{sub 2}O{sub 5} deposition shows an increase in hole carrier concentration in the diamond from 3.0 × 10{sup 12} to 1.8 × 10{sup 13 }cm{sup −2} at room temperature. High temperature Hall measurements performed up to 300 °C in atmosphere reveal greatly enhanced thermal stability of the hole channelmore » produced using V{sub 2}O{sub 5} in comparison with an air-induced surface conduction channel. Transfer doping of hydrogen-terminated diamond using high electron affinity oxides such as V{sub 2}O{sub 5} is a promising approach for achieving thermally stable, high performance diamond based devices in comparison with air-induced surface transfer doping.« less

Enhanced radial growth of Mg doped GaN nanorods: A combined experimental and first-principles study

NASA Astrophysics Data System (ADS)

Nayak, Sanjay; Kumar, Rajendra; Pandey, Nidhi; Nagaraja, K. K.; Gupta, Mukul; Shivaprasad, S. M.

2018-04-01

We discuss the microstructural origin of enhanced radial growth in magnesium (Mg) doped single crystalline wurtzite gallium nitride (w-GaN) nanorods (NRs) grown by MBE, using electron microscopy and first-principles Density Functional Theory calculations. Experimentally, we observe that Mg incorporation increases the surface coverage of the grown samples as a consequence of an increase in the radial growth rate of the NRs. We also observe that the coalescence of NRs becomes prominent and the height at which coalescence between proximal rods occurs decreases with increase in Mg concentration. From first-principles calculations, we find that the surface free energy of the Mg doped surface reduces with increasing Mg concentration in the samples. The calculations further suggest a reduction in the adsorption energy and the diffusion barrier of Ga adatoms along [ 11 2 ¯ 0 ] on the side wall surface of the NRs as the underlying mechanism for the observed enhancement in the radial growth rate of GaN NRs. The physics and chemistry behind reduction of the adsorption energy of Ga ad-atoms on the doped surface are explained in the light of electronic structure of the relevant surfaces.

Effect of impurity resonant states on optical and thermoelectric properties on the surface of a topological insulator.

PubMed

Zhong, Min; Li, Shuai; Duan, Hou-Jian; Hu, Liang-Bin; Yang, Mou; Wang, Rui-Qiang

2017-06-21

We investigate the thermoelectric effect on a topological insulator surface with particular interest in impurity-induced resonant states. To clarify the role of the resonant states, we calculate the dc and ac conductivities and the thermoelectric coefficients along the longitudinal direction within the full Born approximation. It is found that at low temperatures, the impurity resonant state with strong energy de-pendence can lead to a zero-energy peak in the dc conductivity, whose height is sensitively dependent on the strength of scattering potential, and even can reverse the sign of the thermopower, implying the switching from n- to p-type carriers. Also, we exhibit the thermoelectric signatures for the filling process of a magnetic band gap by the resonant state. We further study the impurity effect on the dynamic optical conductivity, and find that the resonant state also generates an optical conductivity peak at the absorption edge for the interband transition. These results provide new perspectives for understanding the doping effect on topological insulator materials.

Surface Charge Transfer Doping via Transition Metal Oxides for Efficient p-Type Doping of II-VI Nanostructures.

PubMed

Xia, Feifei; Shao, Zhibin; He, Yuanyuan; Wang, Rongbin; Wu, Xiaofeng; Jiang, Tianhao; Duhm, Steffen; Zhao, Jianwei; Lee, Shuit-Tong; Jie, Jiansheng

2016-11-22

Wide band gap II-VI nanostructures are important building blocks for new-generation electronic and optoelectronic devices. However, the difficulty of realizing p-type conductivity in these materials via conventional doping methods has severely handicapped the fabrication of p-n homojunctions and complementary circuits, which are the fundamental components for high-performance devices. Herein, by using first-principles density functional theory calculations, we demonstrated a simple yet efficient way to achieve controlled p-type doping on II-VI nanostructures via surface charge transfer doping (SCTD) using high work function transition metal oxides such as MoO 3 , WO 3 , CrO 3 , and V 2 O 5 as dopants. Our calculations revealed that these oxides were capable of drawing electrons from II-VI nanostructures, leading to accumulation of positive charges (holes injection) in the II-VI nanostructures. As a result, Fermi levels of the II-VI nanostructures were shifted toward the valence band regions after surface modifications, along with the large enhancement of work functions. In situ ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy characterizations verified the significant interfacial charge transfer between II-VI nanostructures and surface dopants. Both theoretical calculations and electrical transfer measurements on the II-VI nanostructure-based field-effect transistors clearly showed the p-type conductivity of the nanostructures after surface modifications. Strikingly, II-VI nanowires could undergo semiconductor-to-metal transition by further increasing the SCTD level. SCTD offers the possibility to create a variety of electronic and optoelectronic devices from the II-VI nanostructures via realization of complementary doping.

Sub-nanometer surface chemistry and orbital hybridization in lanthanum-doped ceria nano-catalysts revealed by 3D electron microscopy.

PubMed

Collins, Sean M; Fernandez-Garcia, Susana; Calvino, José J; Midgley, Paul A

2017-07-14

Surface chemical composition, electronic structure, and bonding characteristics determine catalytic activity but are not resolved for individual catalyst particles by conventional spectroscopy. In particular, the nano-scale three-dimensional distribution of aliovalent lanthanide dopants in ceria catalysts and their effect on the surface electronic structure remains unclear. Here, we reveal the surface segregation of dopant cations and oxygen vacancies and observe bonding changes in lanthanum-doped ceria catalyst particle aggregates with sub-nanometer precision using a new model-based spectroscopic tomography approach. These findings refine our understanding of the spatially varying electronic structure and bonding in ceria-based nanoparticle aggregates with aliovalent cation concentrations and identify new strategies for advancing high efficiency doped ceria nano-catalysts.

Electrical properties of surface and interface layers of the N- and In-polar undoped and Mg-doped InN layers grown by PA MBE

NASA Astrophysics Data System (ADS)

Komissarova, T. A.; Kampert, E.; Law, J.; Jmerik, V. N.; Paturi, P.; Wang, X.; Yoshikawa, A.; Ivanov, S. V.

2018-01-01

Electrical properties of N-polar undoped and Mg-doped InN layers and In-polar undoped InN layers grown by plasma-assisted molecular beam epitaxy (PA MBE) were studied. Transport parameters of the surface and interface layers were determined from the measurements of the Hall coefficient and resistivity as well as the Shubnikov-de Haas oscillations at magnetic fields up to 60 T. Contributions of the 2D surface, 3D near-interface, and 2D interface layers to the total conductivity of the InN films were defined and discussed to be dependent on InN surface polarity, Mg doping, and PA MBE growth conditions.

Synthesis and characterization of Ni doped ZnO nanoparticles

NASA Astrophysics Data System (ADS)

Tamgadge, Y. S.; Gedam, P. P.; Ganorkar, R. P.; Mahure, M. A.; Pahurkar, V. G.; Muley, G. G.

2018-05-01

In this paper, we present synthesis of L-valine assisted surface modification of Ni doped ZnO nanoparticles (NPs) using chemical precipitation method. Samples were calcined at 500oC for 2h. Uncalcined and calcined samples were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and ultraviolet-visible (UV-vis) spectroscopy. Ni doped ZnO NPs with average particle size of 8 nm have been successfully obtained using L-valine as surface modifying agent. Increase in the particle size was observed after the calcination. XRD and TEM studies confirmed the purity, surface morphology and hexagonal wurtzite crystal structure of ZnO NPs. UV-vis spectroscopy indicated the blue shift of excitons absorption wavelength and surface modification by L-valine.

Optimizing non-radiative energy transfer in hybrid colloidal-nanocrystal/silicon structures by controlled nanopillar architectures for future photovoltaic cells

NASA Astrophysics Data System (ADS)

Seitz, O.; Caillard, L.; Nguyen, H. M.; Chiles, C.; Chabal, Y. J.; Malko, A. V.

2012-01-01

To optimize colloidal nanocrystals/Si hybrid structures, nanopillars are prepared and organized via microparticle patterning and Si etching. A monolayer of CdSe nanocrystals is then grafted on the passivated oxide-free nanopillar surfaces, functionalized with carboxy-alkyl chain linkers. This process results to a negligible number of non-radiative surface state defects with a tightly controlled separation between the nanocrystals and Si. Steady-state and time-resolved photoluminescence measurements confirm the close-packing nanocrystal arrangement and the dominance of non-radiative energy transfer from nanocrystals to Si. We suggest that radially doped p-n junction devices based on energy transfer offer a viable approach for thin film photovoltaic devices.

Influence of nitrogen-doping concentration on the electronic structure of CuAlO2 by first-principles studies

NASA Astrophysics Data System (ADS)

Liu, Wei-wei; Chen, Hong-xia; Liu, Cheng-lin; Wang, Rong

2017-02-01

Effect of N doping concentration on the electronic structure of N-doped CuAlO2 was investigated by density functional theory based on generalized-gradient approximation plus orbital potential. Lattice parameters a and c both increase with increasing N-doping concentration. Formation energies increase with increasing N doping concentration and all N-doped CuAlO2 were structurally stable. The calculated band gaps for N-doped CuAlO2 narrowed compared to pure CuAlO2, which was attributed to the stronger hybridization between Cu-3d and N-2p states and the downward shift of Cu-3p states in conduction bands. The higher the N-doping concentration is, the narrower the band gap. N-doped CuAlO2 shows a typical p-type semiconductor. The band structure changed from indirect to direct after N doping which will benefit the application of the CuAlO2 materials in optoelectronic and electronic devices.

Enhancement of Catalytic Activity of Reduced Graphene Oxide Via Transition Metal Doping Strategy

NASA Astrophysics Data System (ADS)

Lee, Hangil; Hong, Jung A.

2017-06-01

To compare the catalytic oxidation activities of reduced graphene oxide (rGO) and rGO samples doped with five different transition metals (TM-rGO), we determine their effects on the oxidation of L-cysteine (Cys) in aqueous solution by performing electrochemistry (EC) measurements and on the photocatalytic oxidation of Cys by using high-resolution photoemission spectroscopy (HRPES) under UV illumination. Our results show that Cr-, Fe-, and Co-doped rGO with 3+ charge states (stable oxide forms: Cr3+, Fe3+, and Co3+) exhibit enhanced catalytic activities that are due to the charge states of the doped metal ions as we compare them with Cr-, Fe-, and Co-doped rGO with 2+ charge states.

Fabrication of superhydrophobic polyaniline films with rapidly switchable wettability

NASA Astrophysics Data System (ADS)

Zhou, Xiaoyan; Zhang, Zhaozhu; Men, Xuehu; Yang, Jin; Xu, Xianghui; Zhu, Xiaotao; Xue, Qunji

2011-10-01

A superhydrophobic polyaniline (PANI) film has been fabricated by using a facile one-step spraying method. The PANI was synthesized via in situ doping polymerization in the presence of perfluorooctanoic acid (PFOA) as the dopant. The water contact angle of this superhydrophobic surface reaches to 156°. Both the surface chemical compositions and morphological structures were analyzed. A granular morphology of PANI with a moderate amount of nanofibers was obtained. Moreover, a rapid surface wettability transition between superhydrophobicity and superhydrophilicity can be observed when it is doped with PFOA and de-doped with base. The mechanism for this tunable wettability has been discussed in detail.

Ni-Doping Effects on Oxygen Removal from an Orthorhombic Mo 2 C (001) Surface: A Density Functional Theory Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Mingxia; Cheng, Lei; Choi, Jae-Soon

Density functional theory (DFT) calculations were used to investigate the effect of Ni dopants on the removal of chemisorbed oxygen (O*) from the Mo-terminated (T-Mo) and C-terminated (Tc) Mo2C(001) surfaces. The removal of adsorbed oxygen from the catalytic site is essential to maintain the long-term activity and selectivity of the carbide catalysts in the deoxygenation process related to bio-oil stabilization and upgrading. In this contribution, the computed reaction energetics and reaction barriers of O* removal were compared among undoped and Ni-doped Mo2C(001) surfaces. The DFT calculations indicate that selected Ni-doped surfaces such as Ni adsorbed on T-Mo and Tc Mo2C(001)more » surfaces enable weaker binding of important reactive intermediates (O*, OH*) compared to the undoped counterparts, which is beneficial for the O* removal from the catalyst surface. This study thus confirms the promoting effect of the Ni dopant on O* removal reaction on the T-Mo Mo2C(001) and Tc Mo2C(001) surfaces. This computational prediction has been confirmed by the temperature-programmed reduction profiles of Mo2C and Ni-doped Mo2C catalysts, which had been passivated and stored in an oxygen environment.« less

Passive optical limiting studies of nanostructured Cu doped ZnO-PVA composite thin films

NASA Astrophysics Data System (ADS)

Tamgadge, Y. S.; Sunatkari, A. L.; Talwatkar, S. S.; Pahurkar, V. G.; Muley, G. G.

2016-01-01

We prepared undoped and Cu doped ZnO semiconducting nanoparticles (NPs) by chemical co-precipitation method and obtained Cu doped ZnO-polyvinyl alcohol (PVA) nanocomposite thin films by spin coating to investigate third order nonlinear optical and optical limiting properties under cw laser excitation. Powder samples of NPs were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy, transmission electron microscopy, ultraviolet-visible (UV-vis) and Fourier transform infrared spectroscopy. XRD pattern and FE-SEM micrograph revealed the presence of hexagonal wurtzite phase ZnO NPs having uniform morphology with average particle size of 20 nm. The presence of excitons and absorption peaks in the range 343-360 nm, revealed by UV-vis study, were attributed to excitons in n = 1 quantum state. Third order NLO properties of all composite thin films were investigated by He-Ne continuous wave (cw) laser of wavelength 632.8 nm using Z-scan technique. Thermally stimulated enhanced values of nonlinear refraction and absorption coefficients were obtained which may be attributed to self-defocusing effect, reverse saturable absorption, weak free carrier absorption and surface states properties originated from thermo optic effect. Optical limiting properties have been studied using cw diode laser of wavelength 808 nm and results are presented.

Precise parameterization of the recombination velocity at passivated phosphorus doped surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kimmerle, Achim, E-mail: achim-kimmerle@gmx.de; Momtazur Rahman, Md.; Werner, Sabrina

We investigate the surface recombination velocity S{sub p} at the silicon-dielectric interface of phosphorus-doped surfaces for two industrially relevant passivation schemes for crystalline silicon solar cells. A broad range of surface dopant concentrations together with a high accuracy of evaluating the latter is achieved by incremental back-etching of the surface. The analysis of lifetime measurements and the simulation of the surface recombination consistently apply a set of well accepted models, namely, the Auger recombination by Richter et al. [Phys. Rev. B 86, 1–14 (2012)], the carrier mobility by Klaassen [Solid-State Electron. 35, 953–959 (1992); 35, 961–967 (1992)], the intrinsic carriermore » concentration for undoped silicon by Altermatt et al. [J. Appl. Phys. 93, 1598–1604 (2003)], and the band-gap narrowing by Schenk [J. Appl. Phys. 84, 3684–3695 (1998)]. The results show an increased S{sub p} at textured in respect to planar surfaces. The obtained parameterizations are applicable in modern simulation tools such as EDNA [K. R. McIntosh and P. P. Altermatt, in Proceedings of the 35th IEEE Photovoltaic Specialists Conference, Honolulu, Hawaii, USA (2010), pp. 1–6], PC1Dmod [Haug et al., Sol. Energy Mater. Sol. Cells 131, 30–36 (2014)], and Sentaurus Device [Synopsys, Sentaurus TCAD, Zürich, Switzerland] as well as in the analytical solution under the assumption of local charge neutrality by Cuevas et al. [IEEE Trans. Electron Devices 40, 1181–1183 (1993)].« less

Electronic properties of B and Al doped graphane: A hybrid density functional study

NASA Astrophysics Data System (ADS)

Mapasha, R. E.; Igumbor, E.; Andriambelaza, N. F.; Chetty, N.

2018-04-01

Using a hybrid density functional theory approach parametrized by Heyd, Scuseria and Ernzerhof (HSE06 hybrid functional), we study the energetics, structural and electronic properties of a graphane monolayer substitutionally doped with the B (BCH) and Al (AlCH) atoms. The BCH defect can be integrated within a graphane monolayer at a relative low formation energy, without major structural distortions and symmetry breaking. The AlCH defect relaxes outward of the monolayer and breaks the symmetry. The density of states plots indicate that BCH doped graphane monolayer is a wide band gap semiconductor, whereas the AlCH defect introduces the spin dependent mid gap states at the vicinity of the Fermi level, revealing a metallic character with the pronounced magnetic features. We further examine the response of the Al dependent spin states on the multiple charge states doping. We find that the defect formation energy, structural and electronic properties can be altered via charge state modulation. The +1 charge doping opens an energy band gap of 1.75 eV. This value corresponds to the wavelength in the visible spectrum, suggesting an ideal material for solar cell absorbers. Our study fine tunes the graphane band gap through the foreign atom doping as well as via defect charge state modulation.

Synthesis of cerium and nickel doped titanium nanofibers for hydrolysis of sodium borohydride.

PubMed

Tamboli, Ashif H; Gosavi, S W; Terashima, Chiaki; Fujishima, Akira; Pawar, Atul A; Kim, Hern

2018-07-01

A recyclable titanium nanofibers, doped with cerium and nickel doped was successfully synthesized by using sol-gel and electrospinning method for hydrogen generation from alkali free hydrolysis of NaBH 4 . The resultant nanocomposite was characterized to find out the structural and physical-chemical properties by a series of analytical techniques such as FT-IR (Fourier transform infrared spectroscopy), XRD (X-ray diffraction), SEM (scanning electron microscope), EDX (energy-dispersive X-ray spectroscopy),N 2 adsorption-desorption and BET (Brunauer-Emmett-Teller), etc. The results revealed that cerium and nickel nanoparticles were homogeneously distributed on the surface of the TiO 2 nanofibers due to having similar oxidation state and atomic radium of TiO 2 nanofibers with CeO 2 and NiO for the effective immobilization of metal ions. The NiO doped catalyst showed superior catalytic performance towards the hydrolysis reaction of NaBH 4 at room temperature. These catalysts have ability to produce 305 mL of H 2 within the time of 160 min at room temperature. Additionally, reusability test revealed that the catalyst is active even after five runs of hydrolytic reaction, implying the as-prepared NiO doped TiO 2 nanofibers could be considered as a potential candidate catalyst for portable hydrogen fuel system such as PEMFC (proton exchange membrane fuel cells). Copyright © 2018 Elsevier Ltd. All rights reserved.

Persistent magnetism in silver-doped BaF e 2 A s 2 crystals

DOE PAGES

Li, Li; Cao, Huibo; Parker, David S.; ...

2016-10-12

Here, we investigate the thermodynamic and transport properties of silver-substituted BaF e 2 A s 2 (122) crystals up to ~ 4.5 % . Similar to other transition-metal substitutions in 122, Ag diminishes the antiferromagnetic ( T N ) and structural ( T S ) transition temperatures, but unlike other electron-doped 122s, T N and T S coincide without splitting. Though magnetism drops precipitously to T N = 84 K at doping x = 0.029 , it only weakly changes above this x , settling at T N = 80 K at x = 0.045 . Compared to this persistentmore » magnetism in Ag-122, doping other group 11 elements of either Cu or Au in 122 diminished T N and induced superconductivity near T c = 2 K at x = 0.044 or 0.031, respectively. Ag-122 crystals show reflective surfaces with surprising thicker cross sections for x ≥ 0.019 , the appearance that is in contrast to the typical thin stacked layered feature seen in all other flux-grown x-122 and lower Ag-122. We found that this physical trait may be a manifest of intrinsic weak changes in c lattice and T N . Our theoretical calculations suggest that Ag doping produces strong electronic scattering and yet a relatively small disruption of the magnetic state, both of which preclude superconductivity in this system.« less

A new strategy on utilizing nitrogen doped TiO{sub 2} in nanostructured solar cells: Embedded multifunctional N-TiO{sub 2} scattering particles in mesoporous photoanode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shogh, Shiva; Mohammadpour, Raheleh; Iraji zad, Azam, E-mail: Iraji@sharif.edu

2015-12-15

Highlights: • N-doped TiO{sub 2} scattering particles were synthesized for embedding into commercial photoanode of dye sensitized solar cells. • Embedded scatterers improved optical and electrical features of the cells. • These multifunctional scatterers increased cell performance up to 17%. - Abstract: Aggregated sub-micron size nitrogen doped TiO{sub 2} (N-TiO{sub 2}) particles with superior optical and electrical features were successfully synthesized for embedding into commercial mesoporous TiO{sub 2} photoelectrode of dye sensitized solar cells (DSSCs) as the light scattering particles compared to undoped one. X-ray photoelectron spectroscopy and absorption spectra confirmed that the titanium dioxide is sufficiently doped by nitrogenmore » in N-TiO{sub 2} sample. Employing these high-surface N-TiO{sub 2} in mesoporous photoelectrode of solar cells, the power conversion efficiency of 8% has been achieved which shows 17% improvement for the optimum embedded level of doping (30 wt%) compared to commercial photoelectrode without additive; while enhanced efficiency is only 3% embedding undoped sub-micron size TiO{sub 2} particles. These results can introduce the novel multifunctional photoelectrode for nanostructured solar cells with enhanced values of scattering efficiency and improved electrical features including trap states density reduction in comparison to commercial mesoporous photoelectrodes.« less

Iron pages of HTSC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gasparov, V. A., E-mail: vgasparo@issp.ac.r

Experimental data are presented on the superconducting and electronic properties of iron-based high-temperature superconductors in the normal and superconducting states. The following topics are discussed: lattice structure; structure of magnetic vortices; magnetic penetration depth; Fermi surface; isotope effect; and critical magnetic fields both in oxide compounds of 1111 type and oxide-free compounds of 122, 111, and 011 types as a function of the doping level, temperature, and external pressure.

Topological superconductivity in an ultrathin, magnetically-doped topological insulator proximity coupled to a conventional superconductor

NASA Astrophysics Data System (ADS)

Kim, Youngseok; Philip, Timothy M.; Park, Moon Jip; Gilbert, Matthew J.; University of Illinois at Urbana; Champaign Team

As a promising candidate system to realize topological superconductivity (SC), 3D time-reversal invariant topological insulators (TI) proximity-coupled to s-wave superconductors have been intensively studied. Recent experiments on proximity-coupled TI have shown that superconductivity may be induced in ultrathin TI. One proposal to observe the topological SC in proximity-coupled ultrathin TI system is to add magnetic dopants to the TI. However, detailed study on the impact of the experimental parameters on possible topological phase is sparse. In this work, we investigate ultrathin, magnetically-doped, proximity-coupled TI in order to determine the experimentally relevant parameters needed to observe topological SC. We find that, due to the spin-momentum locked nature of the surface states in TI, the induced s-wave order parameter within the surface states persists even at large magnitudes of the Zeeman energy, allowing us to explore the system in parameter space. We elucidate the phase diagram as a function of: the hybridization gap, Zeeman energy, and chemical potential of the TI system. Our findings provide a useful guide in choosing relevant parameters to facilitate the observation of topological SC in thin film TI-superconductor hybrid systems. National Science Foundation (NSF) under Grant CAREER ECCS-1351871.

Influence of Oxygen Stoichiometry Variations on the Properties of CaMnO3 thin films

NASA Astrophysics Data System (ADS)

Goehringer, Tyler; Yong, Grace; Otouloumougoye, Brenda; Keshavarz, Camron; Sharma, Prahash; Tanyi, E. Kevin; Schaefer, David; Kolagani, Rajeswari

2013-03-01

The family of alkaline-earth doped rare earth manganese oxides RE1-xAExMnO3 exhibit a rich variety of electronic phases depending on the cation stoichiometry. In thin films of these materials, the oxygen stoichiometry is also a variable, and together with cation stoichiometry is known to play a key role in determining the equilibrium phase. The cation and oxygen stoichiometry variations influence electrical and magnetic properties through changes in the mixed valence state of Mn, i.e. the ratio of Mn3+ to Mn4+ ions. CaMnO3 is one of the end members of this family with x =1. Stoichiometric CaMnO3 is a canted antiferromagnetic insulator with the Mn ion in the Mn4+ valence state. We will present our results on the effects of oxygen content variation on the structural, electrical, and magnetoresistive properties CaMnO3 thin films grown by Pulsed Laser Deposition. These results will be compared to the effects of oxygen stoichiometry variation in thin films of its doped counter-part La1-xCaxMnO3. We will also discuss surface morphology changes associated with variation in oxygen stoichiometry which may be associated with different surface terminations. We acknowledge support from the NSF grant ECCS 1128586 at Towson University.

Metal-insulator transition properties of sputtered silicon-doped and un-doped vanadium dioxide films at terahertz range

NASA Astrophysics Data System (ADS)

Zhang, Huafu; Wu, Zhiming; Niu, Ruihua; Wu, Xuefei; he, Qiong; Jiang, Yadong

2015-03-01

Silicon-doped and un-doped vanadium dioxide (VO2) films were synthesized on high-purity single-crystal silicon substrates by means of reactive direct current magnetron sputtering followed by thermal annealing. The structure, morphology and metal-insulator transition properties of silicon-doped VO2 films at terahertz range were measured and compared to those of un-doped VO2 films. X-ray diffraction and scanning electron microscopy indicated that doping the films with silicon significantly affects the preferred crystallographic orientation and surface morphologies (grain size, pores and characteristics of grain boundaries). The temperature dependence of terahertz transmission shows that the transition temperature, hysteresis width and transition sharpness greatly depend on the silicon contents while the transition amplitude was relatively insensitive to the silicon contents. Interestingly, the VO2 film doped with a silicon content of 4.6 at.% shows excellent terahertz switching characteristics, namely a small hysteresis width of 4.5 °C, a giant transmission modulation ratio of about 82% and a relatively low transition temperature of 56.1 °C upon heating. This work experimentally indicates that silicon doping can effectively control not only the surface morphology but also the metal-insulator transition characteristics of VO2 films at terahertz range.

Morphology, Composition, and Bioactivity of Strontium-Doped Brushite Coatings Deposited on Titanium Implants via Electrochemical Deposition

PubMed Central

Liang, Yongqiang; Li, Haoyan; Xu, Jiang; Li, Xin; Qi, Mengchun; Hu, Min

2014-01-01

Surface modification techniques have been applied to generate titanium implant surfaces that promote osseointegration for use in dental applications. In this study, strontium-doped brushite coatings were deposited on titanium by electrochemical deposition. The phase composition of the coating was investigated by energy dispersive X-ray spectroscopy and X-ray diffraction. The surface morphologies of the coatings were studied through scanning electron microscopy, and the cytocompatibility and bioactivity of the strontium-doped brushite coatings were evaluated using cultured osteoblasts. Osteoblast proliferation was enhanced by the addition of strontium, suggesting a possible mechanism by which strontium incorporation in brushite coatings increased bone formation surrounding the implants. Cell growth was also strongly influenced by the composition of the deposited coatings, with a 10% Sr-doped brushite coating inducing the greatest amount of bone formation among the tested materials. PMID:24901526

Transfer doping of single isolated nanodiamonds, studied by scanning probe microscopy techniques

NASA Astrophysics Data System (ADS)

Bolker, Asaf; Saguy, Cecile; Kalish, Rafi

2014-09-01

The transfer doping of diamond surfaces has been applied in various novel two-dimensional electronic devices. Its extension to nanodiamonds (ND) is essential for ND-based applications in many fields. In particular, understanding the influence of the crystallite size on transfer doping is desirable. Here, we report the results of a detailed study of the electronic energetic band structure of single, isolated transfer-doped nanodiamonds with nanometric resolution using a combination of scanning tunneling spectroscopy and Kelvin force microscopy measurements. The results show how the band gap, the valence band maximum, the electron affinity and the work function all depend on the ND’s size and nanoparticle surface properties. The present analysis, which combines information from both scanning tunneling spectroscopy and Kelvin force microscopy, should be applicable to any nanoparticle or surface that can be measured with scanning probe techniques.

Preparation and characterization of mesoporous ZnO-ZrO2 doped by Cr, Nd and Dy as a catalyst for conversion of coumarin using ultrasensitive fluorometric method

NASA Astrophysics Data System (ADS)

Ibrahim, M. M.

2017-04-01

Doping of mesoporous ZnO-ZrO2 nanoparticles with transition metal and lanthanides (Cr, Nd, Dy) were used as a catalyst to develop an ultrasensitive fluorometric method for the conversion of non fluorescent coumarin to highly fluorescent 7-hydroxycoumarin using H2O2 or light. It was found that doped- ZnO-ZrO2 mixed oxide can catalyze the decomposition of H2O2 to produce •OH radicals, which in turn convert coumarin to 7-hydroxycoumarin. At contrast, the doping has deleterious effect on conversion of coumarin by light due to high band gap and high concentrations of doping increase the recombination rate of electron and holes. Doped mixed oxides prepared by impregnation method and characterized by studying their structural, surface and optical properties. Chromium doped ZnO-ZrO2 had the highest rate of formation of hydroxyl radical due to decomposition of H2O2 and therefore 7-hydroxycoumarin due to surface area, small crystal size and high redox potential.

Compositionally modulated multilayer diamond-like carbon coatings with AlTiSi multi-doping by reactive high power impulse magnetron sputtering

NASA Astrophysics Data System (ADS)

Dai, Wei; Gao, Xiang; Liu, Jingmao; Kwon, Se-Hun; Wang, Qimin

2017-12-01

Diamond-like carbon (DLC) coatings with AlTiSi multi-doping were prepared by a reactive high power impulse magnetron sputtering with using a gas mixture of Ar and C2H2 as precursor. The composition, microstructure, compressive stress, and mechanical property of the as-deposited DLC coatings were studied systemically by using SEM, XPS, TEM, Raman spectrum, stress-tester, and nanoindentation as a function of the Ar fraction. The results show that the doping concentrations of the Al, Ti and Si atoms increased as the Ar fraction increased. The doped Ti and Si preferred to bond with C while the doped Al mainly existed in oxidation state without bonding with C. As the doping concentrations increased, TiC carbide nanocrystals were formed in the DLC matrix. The microstructure of coatings changed from an amorphous feature dominant AlTiSi-DLC to a carbide nanocomposite AlTiSi-DLC with TiC nanoparticles embedding. In addition, the coatings exhibited the compositionally modulated multilayer consisting of alternate Al-rich layer and Al-poor layer due to the rotation of the substrate holder and the diffusion behavior of the doped Al which tended to separate from C and diffuse towards the DLC matrix surface owing to its weak interactions with C. The periodic Al-rich layer can effectively release the compressive stress of the coatings. On the other hand, the hard TiC nanoparticles were conducive to the hardness of the coatings. Consequently, the DLC coatings with relatively low residual stress and high hardness could be acquired successfully through AlTiSi multi-doping. It is believed that the AlCrSi multi-doping may be a good way for improving the comprehensive properties of the DLC coatings. In addition, we believe that the DLC coatings with Al-rich multilayered structure have a high oxidation resistance, which allows the DLC coatings application in high temperature environment.

Microscopic effects of Dy doping in the topological insulator Bi2Te3

NASA Astrophysics Data System (ADS)

Duffy, L. B.; Steinke, N.-J.; Krieger, J. A.; Figueroa, A. I.; Kummer, K.; Lancaster, T.; Giblin, S. R.; Pratt, F. L.; Blundell, S. J.; Prokscha, T.; Suter, A.; Langridge, S.; Strocov, V. N.; Salman, Z.; van der Laan, G.; Hesjedal, T.

2018-05-01

Magnetic doping with transition metal ions is the most widely used approach to break time-reversal symmetry in a topological insulator (TI)—a prerequisite for unlocking the TI's exotic potential. Recently, we reported the doping of Bi2Te3 thin films with rare-earth ions, which, owing to their large magnetic moments, promise commensurately large magnetic gap openings in the topological surface states. However, only when doping with Dy has a sizable gap been observed in angle-resolved photoemission spectroscopy, which persists up to room temperature. Although disorder alone could be ruled out as a cause of the topological phase transition, a fundamental understanding of the magnetic and electronic properties of Dy-doped Bi2Te3 remained elusive. Here, we present an x-ray magnetic circular dichroism, polarized neutron reflectometry, muon-spin rotation, and resonant photoemission study of the microscopic magnetic and electronic properties. We find that the films are not simply paramagnetic but that instead the observed behavior can be well explained by the assumption of slowly fluctuating, inhomogeneous, magnetic patches with increasing volume fraction as the temperature decreases. At liquid helium temperatures, a large effective magnetization can be easily introduced by the application of moderate magnetic fields, implying that this material is very suitable for proximity coupling to an underlying ferromagnetic insulator or in a heterostructure with transition-metal-doped layers. However, the introduction of some charge carriers by the Dy dopants cannot be excluded at least in these highly doped samples. Nevertheless, we find that the magnetic order is not mediated via the conduction channel in these samples and therefore magnetic order and carrier concentration are expected to be independently controllable. This is not generally the case for transition-metal-doped topological insulators, and Dy doping should thus allow for improved TI quantum devices.

Sn-doped Bi1.1Sb0.9Te2S: An ideal bulk topological insulator

NASA Astrophysics Data System (ADS)

Kushwaha, Sk; Pletikosic, I.; Liang, T.; Gyenis, A.; Lapidus, Sh; Tian, Y.; Zhao, H.; Burch, Ks; Lin, J.; Wang, W.; Ji, H.; Fedorov, Av; Yazdani, A.; Ong, Np; Valla, T.; Cava, Rj

In the recent decade the topological insulators have been of significant importance for the condensed matter community. However, so far no real materials could fulfill all the requirements. Here, we present the Bridgman growth of slightly Sn-doped Bi1.1Sb0.9Te2S (with bulk band gap of 350) single crystals and characterization by electronic transport, STM and ARPES. The results on the crystals exhibit an intrinsic semiconducting behavior with the Fermi level and Dirac energies lie in bulk gap and high quality 2D surface states are detangled from the bulk states, and it fulfils all the requirements to be an ideal topological insulator. ARO MURI W911NF-12-1-0461; ARO W911NF-12-1-0461; MRSEC NSF-DMR-1420541; LBNL & BNL DE-AC02-05CH11231 & DE-SC0012704; DOE Office of Science DE-AC02-06CH11357; NSF DMR-1410846.

Three-Dimensional Hierarchical MoS2 Nanosheets/Ultralong N-Doped Carbon Nanotubes as High-Performance Electromagnetic Wave Absorbing Material.

PubMed

Liu, Lianlian; Zhang, Shen; Yan, Feng; Li, Chunyan; Zhu, Chunling; Zhang, Xitian; Chen, Yujin

2018-04-25

Here, we report a simple method to grow thin MoS 2 nanosheets (NSs) on the ultralong nitrogen-doped carbon nanotubes through anion-exchange reaction. The MoS 2 NSs are grown on ultralong nitrogen-doped carbon nanotube surfaces, leading to an interesting three-dimensional hierarchical structure. The fabricated hybrid nanotubes have a length of approximately 100 μm, where the MoS 2 nanosheets have a thickness of less than 7.5 nm. The hybrid nanotubes show excellent electromagnetic wave attenuation performance, with the effective absorption bandwidth of 5.4 GHz at the thicknesses of 2.5 mm, superior to the pure MoS 2 nanosheets and the MoS 2 nanosheets grown on the short N-doped carbon nanotube surfaces. The experimental results indicate that the direct growth of MoS 2 on the ultralong nitrogen-doped carbon nanotube surfaces is a key factor for the enhanced electromagnetic wave attenuation property. The results open the avenue for the development of ultralong transition metal dichalcogenides for electromagnetic wave absorbers.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thi, Trinh Cham, E-mail: s1240009@jaist.ac.jp; Koyama, Koichi; Ohdaira, Keisuke

We improve the passivation property of n-type crystalline silicon (c-Si) surface passivated with a catalytic chemical vapor deposited (Cat-CVD) Si nitride (SiN{sub x}) film by inserting a phosphorous (P)-doped layer formed by exposing c-Si surface to P radicals generated by the catalytic cracking of PH{sub 3} molecules (Cat-doping). An extremely low surface recombination velocity (SRV) of 2 cm/s can be achieved for 2.5 Ω cm n-type (100) floating-zone Si wafers passivated with SiN{sub x}/P Cat-doped layers, both prepared in Cat-CVD systems. Compared with the case of only SiN{sub x} passivated layers, SRV decreases from 5 cm/s to 2 cm/s. The decrease in SRVmore » is the result of field effect created by activated P atoms (donors) in a shallow P Cat-doped layer. Annealing process plays an important role in improving the passivation quality of SiN{sub x} films. The outstanding results obtained imply that SiN{sub x}/P Cat-doped layers can be used as promising passivation layers in high-efficiency n-type c-Si solar cells.« less

First-principle study of single TM atoms X (X=Fe, Ru or Os) doped monolayer WS2 systems

NASA Astrophysics Data System (ADS)

Zhu, Yuan-Yan; Zhang, Jian-Min

2018-05-01

We report the structural, magnetic and electronic properties of the pristine and single TM atoms X (X = Fe, Ru or Os) doped monolayer WS2 systems based on first-principle calculations. The results show that the W-S bond shows a stronger covalent bond, but the covalency is obviously weakened after the substitution of W atom with single X atoms, especially for Ru (4d75s1) with the easily lost electronic configuration. The smaller total energies of the doped systems reveal that the spin-polarized states are energetically favorable than the non-spin-polarized states, and the smallest total energy of -373.918 eV shows the spin-polarized state of the Os doped monolayer WS2 system is most stable among three doped systems. In addition, although the pristine monolayer WS2 system is a nonmagnetic-semiconductor with a direct band gap of 1.813 eV, single TM atoms Fe and Ru doped monolayer WS2 systems transfer to magnetic-HM with the total moments Mtot of 1.993 and 1.962 μB , while single TM atom Os doped monolayer WS2 systems changes to magnetic-metal with the total moments Mtot of 1.569 μB . Moreover, the impurity states with a positive spin splitting energies of 0.543, 0.276 and 0.1999 eV near the Fermi level EF are mainly contributed by X-dxy and X-dx2-y2 states hybridized with its nearest-neighbor atom W-dz2 states for Fe, Ru and Os doped monolayer WS2 system, respectively. Finally, we hope that the present study on monolayer WS2 will provide a useful theoretical guideline for exploring low-dimensional spintronic materials in future experiments.

High-Surface-Area Nitrogen-Doped Reduced Graphene Oxide for Electric Double-Layer Capacitors.

PubMed

Youn, Hee-Chang; Bak, Seong-Min; Kim, Myeong-Seong; Jaye, Cherno; Fischer, Daniel A; Lee, Chang-Wook; Yang, Xiao-Qing; Roh, Kwang Chul; Kim, Kwang-Bum

2015-06-08

A two-step method consisting of solid-state microwave irradiation and heat treatment under NH3 gas was used to prepare nitrogen-doped reduced graphene oxide (N-RGO) with a high specific surface area (1007 m(2)  g(-1) ), high electrical conductivity (1532 S m(-1) ), and low oxygen content (1.5 wt %) for electrical double-layer capacitor applications. The specific capacitance of N-RGO was 291 F g(-1) at a current density of 1 A g(-1) , and a capacitance of 261 F g(-1) was retained at 50 A g(-1) , which indicated a very good rate capability. N-RGO also showed excellent cycling stability and preserved 96 % of the initial specific capacitance after 100 000 cycles. Near-edge X-ray absorption fine-structure spectroscopy results provided evidenced for the recovery of π conjugation in the carbon networks with the removal of oxygenated groups and revealed chemical bonding of the nitrogen atoms in N-RGO. The good electrochemical performance of N-RGO is attributed to its high surface area, high electrical conductivity, and low oxygen content. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cu doped diamond: Effect of charge state and defect aggregation on spin interactions in a 3d transition metal doped wide band-gap semiconductor

NASA Astrophysics Data System (ADS)

Benecha, E. M.; Lombardi, E. B.

2018-05-01

We present a first principles study of Cu in diamond using DFT+U electronic structure methods, by carefully considering the impact of co-doping, charge state, and Fermi level position on its stability, lattice location, spin states, and electronic properties. We show that the energetic stability and spin states of Cu are strongly dependent on the Fermi level position and the type of diamond co-doping, with Cu being energetically more favorable in n-type or p-type co-doped diamond compared to intrinsic diamond. Since Cu has been predicted to order magnetically in a number of other wide band-gap semiconductors, we have also evaluated this possibility for Cu doped diamond. We show that while Cu exhibits strong spin interactions at specific interatomic separations in diamond, a detailed consideration of the impact of Fermi level position and Cu aggregation precludes magnetic ordering, with Cu forming non-magnetic, antiferromagnetic, or paramagnetic clusters. These results have important implications in the understanding of the properties of transition metal dopants in diamond for device applications.

Photovoltaic cell and production thereof

DOEpatents

Narayanan, Srinivasamohan [Gaithersburg, MD; Kumar, Bikash [Bangalore, IN

2008-07-22

An efficient photovoltaic cell, and its process of manufacture, is disclosed wherein the back surface p-n junction is removed from a doped substrate having an oppositely doped emitter layer. A front surface and edges and optionally the back surface periphery are masked and a back surface etch is performed. The mask is not removed and acts as an anti-reflective coating, a passivating agent, or both. The photovoltaic cell retains an untextured back surface whether or not the front is textured and the dopant layer on the back surface is removed to enhance the cell efficiency. Optionally, a back surface field is formed.

N-Type delta Doping of High-Purity Silicon Imaging Arrays

NASA Technical Reports Server (NTRS)

Blacksberg, Jordana; Hoenk, Michael; Nikzad, Shouleh

2005-01-01

A process for n-type (electron-donor) delta doping has shown promise as a means of modifying back-illuminated image detectors made from n-doped high-purity silicon to enable them to detect high-energy photons (ultraviolet and x-rays) and low-energy charged particles (electrons and ions). This process is applicable to imaging detectors of several types, including charge-coupled devices, hybrid devices, and complementary metal oxide/semiconductor detector arrays. Delta doping is so named because its density-vs.-depth characteristic is reminiscent of the Dirac delta function (impulse function): the dopant is highly concentrated in a very thin layer. Preferably, the dopant is concentrated in one or at most two atomic layers in a crystal plane and, therefore, delta doping is also known as atomic-plane doping. The use of doping to enable detection of high-energy photons and low-energy particles was reported in several prior NASA Tech Briefs articles. As described in more detail in those articles, the main benefit afforded by delta doping of a back-illuminated silicon detector is to eliminate a "dead" layer at the back surface of the silicon wherein high-energy photons and low-energy particles are absorbed without detection. An additional benefit is that the delta-doped layer can serve as a back-side electrical contact. Delta doping of p-type silicon detectors is well established. The development of the present process addresses concerns specific to the delta doping of high-purity silicon detectors, which are typically n-type. The present process involves relatively low temperatures, is fully compatible with other processes used to fabricate the detectors, and does not entail interruption of those processes. Indeed, this process can be the last stage in the fabrication of an imaging detector that has, in all other respects, already been fully processed, including metallized. This process includes molecular-beam epitaxy (MBE) for deposition of three layers, including metallization. The success of the process depends on accurate temperature control, surface treatment, growth of high-quality crystalline silicon, and precise control of thicknesses of layers. MBE affords the necessary nanometer- scale control of the placement of atoms for delta doping. More specifically, the process consists of MBE deposition of a thin silicon buffer layer, the n-type delta doping layer, and a thin silicon cap layer. The n dopant selected for initial experiments was antimony, but other n dopants as (phosphorus or arsenic) could be used. All n-type dopants in silicon tend to surface-segregate during growth, leading to a broadened dopant-concentration- versus-depth profile. In order to keep the profile as narrow as possible, the substrate temperature is held below 300 C during deposition of the silicon cap layer onto the antimony delta layer. The deposition of silicon includes a silicon- surface-preparation step, involving H-termination, that enables the growth of high-quality crystalline silicon at the relatively low temperature with close to full electrical activation of donors in the surface layer.

Effect of Porosity Parameters and Surface Chemistry on Carbon Dioxide Adsorption in Sulfur-Doped Porous Carbons.

PubMed

Wang, En-Jie; Sui, Zhu-Yin; Sun, Ya-Nan; Ma, Zhuang; Han, Bao-Hang

2018-05-22

In this work, a series of highly porous sulfur-doped carbons are prepared through physical activation methods by using polythiophene as a precursor. The morphology, structure, and physicochemical properties are revealed by a variety of characterization methods, such as scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and nitrogen sorption measurement. Their porosity parameters and chemical compositions can be well-tuned by changing the activating agents (steam and carbon dioxide) and reaction temperature. These sulfur-doped porous carbons possess specific surface area of 670-2210 m 2 g -1 , total pore volume of 0.31-1.26 cm 3 g -1 , and sulfur content of 0.6-4.9 atom %. The effect of porosity parameters and surface chemistry on carbon dioxide adsorption in sulfur-doped porous carbons is studied in detail. After a careful analysis of carbon dioxide uptake at different temperatures (273 and 293 K), pore volumes from small pore size (less than 1 nm) play an important role in carbon dioxide adsorption at 273 K, whereas surface chemistry is the key factor at a higher adsorption temperature or lower relative pressure. Furthermore, sulfur-doped porous carbons also possess good gas adsorption selectivity and excellent recyclability for regeneration.

The Effect of Eu Doping on Microstructure, Morphology and Methanal-Sensing Performance of Highly Ordered SnO2 Nanorods Array

PubMed Central

Zhao, Yanping; Li, Yuehua; Ren, Xingping; Gao, Fan; Zhao, Heyun

2017-01-01

Layered Eu-doped SnO2 ordered nanoarrays constructed by nanorods with 10 nm diameters and several hundred nanometers length were synthesized by a substrate-free hydrothermal route using alcohol and water mixed solvent of sodium stannate and sodium hydroxide at 200 °C. The Eu dopant acted as a crystal growth inhibitor to prevent the SnO2 nanorods growth up, resulting in tenuous SnO2 nanorods ordered arrays. The X-ray diffraction (XRD) revealed the tetragonal rutile-type structure with a systematic average size reduction and unit cell volume tumescence, while enhancing the residual strain as the Eu-doped content increases. The surface defects that were caused by the incorporation of Eu ions within the surface oxide matrix were observed by high-resolution transmission electron microscope (HRTEM). The results of the response properties of sensors based on the different levels of Eu-doped SnO2 layered nanoarrays demonstrated that the 0.5 at % Eu-doped SnO2 layered nanorods arrays exhibited an excellent sensing response to methanal at 278 °C. The reasons of the enhanced sensing performance were discussed from the complicated defect surface structure, the large specific surface area, and the excellent catalytic properties of Eu dopant. PMID:29168796

Cd doping at PVD-CdS/CuInGaSe 2 heterojunctions

DOE PAGES

He, Xiaoqing; Paulauskas, Tadas; Ercius, Peter; ...

2017-02-20

In this paper, we report on direct evidence of Cd doping of the CuInGaSe 2 (CIGS) surface in physical vapor deposited (PVD) CdS/CIGS heterojunctions by scanning transmission electron microscopy (STEM) and related techniques. We find Cd doping of the CIGS near-surface region regardless of the presence or absence of Cu rich domains in the CdS for both zinc-blende (zb) and wurtzite (wz) CdS. However, we find that the Cd penetrates much farther into the CIGS when Cu-rich domains are present in the CdS. This suggests that Cu exchanges with Cd, increasing the concentration gradient for Cd in the CIGS andmore » thus driving Cd into the CIGS surface. The Cd doping is clearly resolved at atomic resolution in aberration-corrected STEM-high angle annular dark field images. In zb-CdS/CIGS heterojunctions, Cd is shown to substitute for both Cu and Ga atoms, while in wz-CdS/CIGS heterojunctions Cd seems to predominantly occupy Cu sites. Finally, Cd doping in the CIGS surface layer suggests the formation of a p-n homojunction in the CIGS, which may account for the high device efficiencies, comparable to CBD-CdS/CIGS processed structures.« less

Nitrogen-doped graphene network supported copper nanoparticles encapsulated with graphene shells for surface-enhanced Raman scattering.

PubMed

Zhang, Xiang; Shi, Chunsheng; Liu, Enzuo; Li, Jiajun; Zhao, Naiqin; He, Chunnian

2015-10-28

In this study, we demonstrated nitrogen-doped graphene network supported few-layered graphene shell encapsulated Cu nanoparticles (NPs) (Cu@G-NGNs) as a sensing platform, which were constructed by a simple and scalable in situ chemical vapor deposition (CVD) technique with the assistance of a self-assembled three-dimensional (3D) NaCl template. Compared with pure Cu NPs and graphene decorated Cu NPs, the graphene shells can strengthen the plasmonic coupling between graphene and Cu, thereby contributing to an obvious improvement in the local electromagnetic field that was validated by finite element numerical simulations, while the 3D nitrogen-doped graphene walls with a large surface area facilitated molecule adsorption and the doped nitrogen atoms embedded in the graphene lattice can reduce the surface energy of the system. With these merits, a good surface enhanced Raman spectroscopy (SERS) activity of the 3D Cu@G-NGN painting film on glass was demonstrated using rhodamine 6G and crystal violet as model analytes, exhibiting a satisfactory sensitivity, reproducibility and stability. As far as we know, this is the first report on the in situ synthesis of nitrogen-doped graphene/copper nanocomposites and this facile and low-cost Cu-based strategy tends to be a good supplement to Ag and Au based substrates for SERS applications.

Adsorption of formamide over pristine and Al-doped boron nitride nanosheets: A dispersion-corrected DFT study.

PubMed

Esrafili, Mehdi D; Mousavian, Parisasadat; Arjomandi Rad, Farzad

2018-06-01

Using the dispersion-corrected DFT calculations, different adsorption modes of formamide molecule are studied over the pristine and Al-doped boron nitride nanosheets (BNNS). It is found that the interaction between the Al atom and its neighboring N atoms in the Al-doped BNNS is very strong, which would hinder the dispersion and clustering of the Al atoms over the BNNS surface. Unlike the pristine nanosheet, the electronic properties of Al-doped BNNS are very sensitive to the formamide adsorption. The adsorption energies of formamide over the Al-doped sheet are in the range of -0.93 to -1.85 eV, which indicates the quite strong interaction of this molecule with the surface. Moreover, the dehydrogenation of formamide over the Al-doped BNNS is examined. According to our results, the N-H bond scission of formamide is more energetically favorable than the C-H one. Copyright © 2018 Elsevier Inc. All rights reserved.

Dopant controlled photoinduced hydrophilicity and photocatalytic activity of SnO2 thin films

NASA Astrophysics Data System (ADS)

Talinungsang; Dhar Purkayastha, Debarun; Krishna, M. Ghanashyam

2018-07-01

The influence of Fe and Ni (1 wt.%) doping on the wettability and photocatalytic activity of sol-gel derived SnO2 films is reported. X-ray diffraction studies revealed the presence of tetragonal phase for both pure and doped SnO2 thin films. The crystallite size was of the order of 8 nm indicating the nanocrystalline nature of the films. The pure SnO2 films which were hydrophilic with a contact angle of 11.8° showed increase in contact angle with doping (38.7° for Fe and 48.6° for Ni). This is accompanied by decrease in surface energy and root mean square roughness, with doping of SnO2 film. In order to further increase the water contact angle, the film surfaces were modified using a layer of stearic acid. As a consequence, the water contact angles increased to 108°, 110° and 111° for the pure, Fe and Ni doped SnO2 films respectively, rendering them hydrophobic. Significantly, the unmodified surfaces that did not exhibit any change under UV irradiation showed photoinduced hydrophilicity on modification with stearic acid. There was a red-shift in the optical band gap of SnO2 films from 3.8 to 3.5 eV with doping, indicating the possibility of dopant controlled photocatalytic activity. This was confirmed by observing the photocatalytic degradation of an aqueous solution of methylene blue under UV irradiation. There was, indeed, significant improvement in the photocatalytic efficiency of the metal doped SnO2 thin film in comparison to undoped film. The current work, thus, demonstrates a simple method to chemically engineer the wettability and photocatalytic activity of SnO2 thin film surfaces.

Effect of Polishing on the Friction Behaviors and Cutting Performance of Boron-Doped Diamond Films on WC-Co Inserts

NASA Astrophysics Data System (ADS)

Wang, Liang; Shen, Bin; Sun, Fanghong; Zhang, Zhiming

2014-04-01

Boron doped (B-doped) diamond films are deposited onto WC-Co inserts by HFCVD with the mixture of acetone, trimethyl borate (C3H9BO3) and H2. The as-deposited B-doped diamond films are characterized with scanning electron microscope (SEM), X-ray diffraction (XRD) spectroscopy, Raman spectroscopy, 3D surface topography based on white-light interferometry and Rockwell hardness tester. The effects of mechanical polishing on the friction behavior and cutting performance of B-doped diamond are evaluated by ball-on-plate type reciprocating tribometer and turning of aluminum alloy 7075 materials, respectively. For comparison, the same tests are also conducted for the bare WC-Co inserts with smooth surface. Friction tests suggest that the unpolished and polished B-doped diamond films possess relatively low fluctuation of friction coefficient than as-received bare WC-Co samples. The average stable friction coefficient for B-doped diamond films decreases apparently after mechanical polishing. The values for WC-Co sample, unpolished and polished B-doped diamond films are approximately 0.38, 0.25 and 0.11, respectively. The cutting results demonstrate that the low friction coefficient and high adhesive strength of B-doped diamond films play an essential role in the cutting performance enhancement of the WC-Co inserts. However, the mechanical polishing process may lower the adhesive strength of B-doped diamond films. Consequently, the polished B-doped diamond coated inserts show premature wear in the machining of adhesive aluminum alloy materials.

Topological surface state of α -Sn on InSb(001) as studied by photoemission

NASA Astrophysics Data System (ADS)

Scholz, M. R.; Rogalev, V. A.; Dudy, L.; Reis, F.; Adler, F.; Aulbach, J.; Collins-McIntyre, L. J.; Duffy, L. B.; Yang, H. F.; Chen, Y. L.; Hesjedal, T.; Liu, Z. K.; Hoesch, M.; Muff, S.; Dil, J. H.; Schäfer, J.; Claessen, R.

2018-02-01

We report on the electronic structure of the elemental topological semimetal α -Sn on InSb(001). High-resolution angle-resolved photoemission data allow us to observe the topological surface state (TSS) that is degenerate with the bulk band structure and show that the former is unaffected by different surface reconstructions. An unintentional p -type doping of the as-grown films was compensated by deposition of potassium or tellurium after the growth, thereby shifting the Dirac point of the surface state below the Fermi level. We show that, while having the potential to break time-reversal symmetry, iron impurities with a coverage of up to 0.25 monolayers do not have any further impact on the surface state beyond that of K or Te. Furthermore, we have measured the spin-momentum locking of electrons from the TSS by means of spin-resolved photoemission. Our results show that the spin vector lies fully in-plane, but it also has a finite radial component. Finally, we analyze the decay of photoholes introduced in the photoemission process, and by this gain insight into the many-body interactions in the system. Surprisingly, we extract quasiparticle lifetimes comparable to other topological materials where the TSS is located within a bulk band gap. We argue that the main decay of photoholes is caused by intraband scattering, while scattering into bulk states is suppressed due to different orbital symmetries of bulk and surface states.

Controlling Short-Range Interactions by Tuning Surface Chemistry in HDPE/Graphene Nanoribbon Nanocomposites.

PubMed

Sadeghi, Soheil; Zehtab Yazdi, Alireza; Sundararaj, Uttandaraman

2015-09-03

Unique dispersion states of nanoparticles in polymeric matrices have the potential to create composites with enhanced mechanical, thermal, and electrical properties. The present work aims to determine the state of dispersion from the melt-state rheological behavior of nanocomposites based on carbon nanotube and graphene nanoribbon (GNR) nanomaterials. GNRs were synthesized from nitrogen-doped carbon nanotubes via a chemical route using potassium permanganate and some second acids. High-density polyethylene (HDPE)/GNR nanocomposite samples were then prepared through a solution mixing procedure. Different nanocomposite dispersion states were achieved using different GNR synthesis methods providing different surface chemistry, interparticle interactions, and internal compartments. Prolonged relaxation of flow induced molecular orientation was observed due to the presence of both carbon nanotubes and GNRs. Based on the results of this work, due to relatively weak interactions between the polymer and the nanofillers, it is expected that short-range interactions between nanofillers play the key role in the final dispersion state.

Few-mode vertical-cavity surface-emitting laser: Optional emission of transverse modes with different polarizations

NASA Astrophysics Data System (ADS)

Zhong, Chuyu; Zhang, Xing; Hofmann, Werner; Yu, Lijuan; Liu, Jianguo; Ning, Yongqiang; Wang, Lijun

2018-05-01

Few-mode vertical-cavity surface-emitting lasers that can be controlled to emit certain modes and polarization states simply by changing the biased contacts are proposed and fabricated. By directly etching trenches in the p-doped distributed Bragg reflector, the upper mesa is separated into several submesas above the oxide layer. Individual contacts are then deposited. Each contact is used to control certain transverse modes with different polarization directions emitted from the corresponding submesa. These new devices can be seen as a prototype of compact laser sources in mode division multiplexing communications systems.

Fermi Level Manipulation through Native Doping in the Topological Insulator Bi2Se3.

PubMed

Walsh, Lee A; Green, Avery J; Addou, Rafik; Nolting, Westly; Cormier, Christopher R; Barton, Adam T; Mowll, Tyler R; Yue, Ruoyu; Lu, Ning; Kim, Jiyoung; Kim, Moon J; LaBella, Vincent P; Ventrice, Carl A; McDonnell, Stephen; Vandenberghe, William G; Wallace, Robert M; Diebold, Alain; Hinkle, Christopher L

2018-06-08

The topologically protected surface states of three-dimensional (3D) topological insulators have the potential to be transformative for high-performance logic and memory devices by exploiting their specific properties such as spin-polarized current transport and defect tolerance due to suppressed backscattering. However, topological insulator based devices have been underwhelming to date primarily due to the presence of parasitic issues. An important example is the challenge of suppressing bulk conduction in Bi 2 Se 3 and achieving Fermi levels ( E F ) that reside in between the bulk valence and conduction bands so that the topologically protected surface states dominate the transport. The overwhelming majority of the Bi 2 Se 3 studies in the literature report strongly n-type materials with E F in the bulk conduction band due to the presence of a high concentration of selenium vacancies. In contrast, here we report the growth of near-intrinsic Bi 2 Se 3 with a minimal Se vacancy concentration providing a Fermi level near midgap with no extrinsic counter-doping required. We also demonstrate the crucial ability to tune E F from below midgap into the upper half of the gap near the conduction band edge by controlling the Se vacancy concentration using post-growth anneals. Additionally, we demonstrate the ability to maintain this Fermi level control following the careful, low-temperature removal of a protective Se cap, which allows samples to be transported in air for device fabrication. Thus, we provide detailed guidance for E F control that will finally enable researchers to fabricate high-performance devices that take advantage of transport through the topologically protected surface states of Bi 2 Se 3 .

Ni-doped (CeO2- δ )-YSZ mesoarchitectured with nanocrystalline framework: the effect of thermal treatment on structure, surface chemistry and catalytic properties in the partial oxidation of methane (CPOM)

NASA Astrophysics Data System (ADS)

Somacescu, Simona; Florea, Mihaela; Osiceanu, Petre; Calderon-Moreno, Jose Maria; Ghica, Corneliu; Serra, Jose Manuel

2015-11-01

Ni-doped (CeO2- δ )-YSZ (5 mol% Ni oxide, 10 mol% ceria) mesoarchitectures (MA) with nanocrystalline framework have been synthesized by an original, facile and cheap approach based on Triton X100 nonionic surfactant as template and water as solvent at a strong basic pH value. Following the hydrothermal treatment under autogenous pressure ( 18 bars), Ni, Ce, Y, and Zr were well ordered as MA with nanocrystalline framework, assuring thermal stability. A comprehensive investigation of structure, texture, morphology, and surface chemistry was performed by means of a variety of complementary techniques (X-Ray Diffraction, XRD; Raman Spectroscopy, RS; Brunauer—Emmett—Teller, BET; Temperature—Programmed Reduction, TPR; Transmission Electron Microscopy, TEM and DF-STEM; X-ray Photoelectron Spectroscopy, XPS; Catalytic activity and selectivity). N2 sorption measurements highlighted that the mesoporous structure is formed at 600 °C and remains stable at 800 °C. At 900 °C, the MA collapses, favoring the formation of macropores. The XRD and Raman Spectroscopy of all samples showed the presence of a pure, single phase with fluorite-type structure. At 900 °C, an increased tetragonal distortion of the cubic lattice was observed. The surface chemistry probed by XPS exhibits a mixture of oxidation states (Ce3+ + Ce4+) with high percentage of Ce3+ valence state 35 % and (Ni3+ and Ni2+) oxidation states induced by the thermal treatment. These nanoparticles assembled into MA show high stability and selectivity over time in catalytic partial oxidation of methane (CPOM). These promising performances suggest an interesting prospect for introduction as anode within IT-SOFC assemblies.

Monolayer Contact Doping of Silicon Surfaces and Nanowires Using Organophosphorus Compounds

PubMed Central

Hazut, Ori; Agarwala, Arunava; Subramani, Thangavel; Waichman, Sharon; Yerushalmi, Roie

2013-01-01

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra shallow and sharp doping profiles at the nanometer scale. In MLCD process the dopant source is a monolayer containing dopant atoms. In this article a detailed procedure for surface doping of silicon substrate as well as silicon nanowires is demonstrated. Phosphorus dopant source was formed using tetraethyl methylenediphosphonate monolayer on a silicon substrate. This monolayer containing substrate was brought to contact with a pristine intrinsic silicon target substrate and annealed while in contact. Sheet resistance of the target substrate was measured using 4 point probe. Intrinsic silicon nanowires were synthesized by chemical vapor deposition (CVD) process using a vapor-liquid-solid (VLS) mechanism; gold nanoparticles were used as catalyst for nanowire growth. The nanowires were suspended in ethanol by mild sonication. This suspension was used to dropcast the nanowires on silicon substrate with a silicon nitride dielectric top layer. These nanowires were doped with phosphorus in similar manner as used for the intrinsic silicon wafer. Standard photolithography process was used to fabricate metal electrodes for the formation of nanowire based field effect transistor (NW-FET). The electrical properties of a representative nanowire device were measured by a semiconductor device analyzer and a probe station. PMID:24326774

Gd{sup 3+} incorporated ZnO nanoparticles: A versatile material

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Surender, E-mail: surender40@gmail.com; Sahare, P.D.

Graphical abstract: - Highlights: • Chemically synthesized Gd{sup 3+} doped ZnO nanoparticles. • The broad visible emission of the ZnO is dependent on the surface defects and can be tailored by Gd{sup 3+} doing. • PL and magnetic properties are modified by Gd{sup 3+} doping. • Photocatalysis experiment reveals that the ZnO: Gd{sup 3+} degrades the Rh B dye faster than the undoped ZnO. - Abstract: Gd{sup 3+} doped ZnO nanoparticles are synthesized by wet chemical route method and investigated through structural, optical, magnetic and photocatalytic properties. Transmission Electron Microscopy technique has been performed on undoped and Gd{sup 3+} dopedmore » ZnO nanoparticles. X-ray diffraction, X-ray photoelectron spectroscopy and Raman analyses are carried out in order to examine the desired phase formation and substitution of Gd{sup 3+} in the ZnO matrix. Gd{sup 3+} doped ZnO nanoparticles show enhanced photoluminescent and ferromagnetic properties as compared to undoped ZnO. The broad visible emission of ZnO is found to be largely dependent on the surface defects and these surface defects can be tailored by Gd{sup 3+} doping concentration. Furthermore, Gd{sup 3+} doped ZnO nanoparticles also show improved photocatalytic properties as compared with undoped ZnO nanoparticles under ultraviolet irradiation.« less

Nitrogen-doped graphene network supported copper nanoparticles encapsulated with graphene shells for surface-enhanced Raman scattering

NASA Astrophysics Data System (ADS)

Zhang, Xiang; Shi, Chunsheng; Liu, Enzuo; Li, Jiajun; Zhao, Naiqin; He, Chunnian

2015-10-01

In this study, we demonstrated nitrogen-doped graphene network supported few-layered graphene shell encapsulated Cu nanoparticles (NPs) (Cu@G-NGNs) as a sensing platform, which were constructed by a simple and scalable in situ chemical vapor deposition (CVD) technique with the assistance of a self-assembled three-dimensional (3D) NaCl template. Compared with pure Cu NPs and graphene decorated Cu NPs, the graphene shells can strengthen the plasmonic coupling between graphene and Cu, thereby contributing to an obvious improvement in the local electromagnetic field that was validated by finite element numerical simulations, while the 3D nitrogen-doped graphene walls with a large surface area facilitated molecule adsorption and the doped nitrogen atoms embedded in the graphene lattice can reduce the surface energy of the system. With these merits, a good surface enhanced Raman spectroscopy (SERS) activity of the 3D Cu@G-NGN painting film on glass was demonstrated using rhodamine 6G and crystal violet as model analytes, exhibiting a satisfactory sensitivity, reproducibility and stability. As far as we know, this is the first report on the in situ synthesis of nitrogen-doped graphene/copper nanocomposites and this facile and low-cost Cu-based strategy tends to be a good supplement to Ag and Au based substrates for SERS applications.In this study, we demonstrated nitrogen-doped graphene network supported few-layered graphene shell encapsulated Cu nanoparticles (NPs) (Cu@G-NGNs) as a sensing platform, which were constructed by a simple and scalable in situ chemical vapor deposition (CVD) technique with the assistance of a self-assembled three-dimensional (3D) NaCl template. Compared with pure Cu NPs and graphene decorated Cu NPs, the graphene shells can strengthen the plasmonic coupling between graphene and Cu, thereby contributing to an obvious improvement in the local electromagnetic field that was validated by finite element numerical simulations, while the 3D nitrogen-doped graphene walls with a large surface area facilitated molecule adsorption and the doped nitrogen atoms embedded in the graphene lattice can reduce the surface energy of the system. With these merits, a good surface enhanced Raman spectroscopy (SERS) activity of the 3D Cu@G-NGN painting film on glass was demonstrated using rhodamine 6G and crystal violet as model analytes, exhibiting a satisfactory sensitivity, reproducibility and stability. As far as we know, this is the first report on the in situ synthesis of nitrogen-doped graphene/copper nanocomposites and this facile and low-cost Cu-based strategy tends to be a good supplement to Ag and Au based substrates for SERS applications. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr04259c

Site-selective substitutional doping with atomic precision on stepped Al (111) surface by single-atom manipulation

PubMed Central

2014-01-01

In fabrication of nano- and quantum devices, it is sometimes critical to position individual dopants at certain sites precisely to obtain the specific or enhanced functionalities. With first-principles simulations, we propose a method for substitutional doping of individual atom at a certain position on a stepped metal surface by single-atom manipulation. A selected atom at the step of Al (111) surface could be extracted vertically with an Al trimer-apex tip, and then the dopant atom will be positioned to this site. The details of the entire process including potential energy curves are given, which suggests the reliability of the proposed single-atom doping method. PMID:24899871

Site-selective substitutional doping with atomic precision on stepped Al (111) surface by single-atom manipulation.

PubMed

Chen, Chang; Zhang, Jinhu; Dong, Guofeng; Shao, Hezhu; Ning, Bo-Yuan; Zhao, Li; Ning, Xi-Jing; Zhuang, Jun

2014-01-01

In fabrication of nano- and quantum devices, it is sometimes critical to position individual dopants at certain sites precisely to obtain the specific or enhanced functionalities. With first-principles simulations, we propose a method for substitutional doping of individual atom at a certain position on a stepped metal surface by single-atom manipulation. A selected atom at the step of Al (111) surface could be extracted vertically with an Al trimer-apex tip, and then the dopant atom will be positioned to this site. The details of the entire process including potential energy curves are given, which suggests the reliability of the proposed single-atom doping method.

Magnetic and resonance properties of ferrihydrite nanoparticles doped with cobalt

NASA Astrophysics Data System (ADS)

Stolyar, S. V.; Yaroslavtsev, R. N.; Iskhakov, R. S.; Bayukov, O. A.; Balaev, D. A.; Dubrovskii, A. A.; Krasikov, A. A.; Ladygina, V. P.; Vorotynov, A. M.; Volochaev, M. N.

2017-03-01

Powders of undoped ferrihydrite nanoparticles and ferrihydrite nanoparticles doped with cobalt in the ratio of 5: 1 have been prepared by hydrolysis of 3 d-metal salts. It has been shown using Mössbauer spectroscopy that cobalt is uniformly distributed over characteristic crystal-chemical positions of iron ions. The blocking temperatures of ferrihydrite nanoparticles have been determined. The nanoparticle sizes, magnetizations, surface anisotropy constants, and bulk anisotropy constants have been estimated. The doping of ferrihydrite nanoparticles with cobalt leads to a significant increase in the anisotropy constant of a nanoparticle and to the formation of surface rotational anisotropy with the surface anisotropy constant K u = 1.6 × 10-3 erg/cm2.

Nanocrystals in compression: unexpected structural phase transition and amorphization due to surface impurities.

PubMed

Liu, Gang; Kong, Lingping; Yan, Jinyuan; Liu, Zhenxian; Zhang, Hengzhong; Lei, Pei; Xu, Tao; Mao, Ho-Kwang; Chen, Bin

2016-06-09

We report an unprecedented surface doping-driven anomaly in the compression behaviors of nanocrystals demonstrating that the change of surface chemistry can lead to an interior bulk structure change in nanoparticles. In the synchrotron-based X-ray diffraction experiments, titania nanocrystals with low concentration yttrium dopants at the surface are found to be less compressible than undoped titania nanocrystals. More surprisingly, an unexpected TiO2(ii) phase (α-PbO2 type) is induced and obvious anisotropy is observed in the compression of yttrium-doped TiO2, in sharp contrast to the compression behavior of undoped TiO2. In addition, the undoped brookite nanocrystals remain with the same structure up to 30 GPa, whereas the yttrium-doped brookite amorphizes above 20 GPa. The abnormal structural evolution observed in yttrium-doped TiO2 does not agree with the reported phase stability of nano titania polymorphs, thus suggesting that the physical properties of the interior of nanocrystals can be controlled by the surface, providing an unconventional and new degree of freedom in search for nanocrystals with novel tunable properties that can trigger applications in multiple areas of industry and provoke more related basic science research.

Atomically precise lateral modulation of a two-dimensional electron liquid in anatase TiO 2 thin films

DOE PAGES

Wang, Zhiming; Zhong, Z.; Walker, S. McKeown; ...

2017-03-10

Engineering the electronic band structure of two-dimensional electron liquids (2DELs) confined at the surface or interface of transition metal oxides is key to unlocking their full potential. Here we describe a new approach to tailoring the electronic structure of an oxide surface 2DEL demonstrating the lateral modulation of electronic states with atomic scale precision on an unprecedented length scale comparable to the Fermi wavelength. To this end, we use pulsed laser deposition to grow anatase TiO 2 films terminated by a (1 x 4) in-plane surface reconstruction. Employing photo-stimulated chemical surface doping we induce 2DELs with tunable carrier densities thatmore » are confined within a few TiO 2 layers below the surface. Subsequent in situ angle resolved photoemission experiments demonstrate that the (1 x 4) surface reconstruction provides a periodic lateral perturbation of the electron liquid. Furthermore, this causes strong backfolding of the electronic bands, opening of unidirectional gaps and a saddle point singularity in the density of states near the chemical potential.« less

Role of stable and metastable Mg-H complexes in p-type GaN for cw blue laser diodes

NASA Astrophysics Data System (ADS)

Castiglia, A.; Carlin, J.-F.; Grandjean, N.

2011-05-01

Secondary ion mass spectroscopy (SIMS) and capacitance-voltage measurements were combined to thoroughly study Mg doping in GaN layers grown by metal organic vapor phase epitaxy. First we found that the Mg steady-state incorporation regime occurs for a surface coverage of 0.3 monolayer. Additionally SIMS indicates that H incorporates proportionally with Mg until a certain [Mg] where [H] saturates. After thermal activation, [H] while being much lower still scales with [Mg]. These results suggest that H combines with Mg to form two different types of Mg-H complexes: a metastable one leading to the Mg acceptor after annealing, the other one (dominating at high [Mg]) being stable and electrically inactive. The obtained results allowed us optimizing doping conditions for blue laser diodes.

Growth of delta-doped layers on silicon CCD/S for enhanced ultraviolet response

NASA Technical Reports Server (NTRS)

Hoenk, Michael E. (Inventor); Grunthaner, Paula J. (Inventor); Grunthaner, Frank J. (Inventor); Terhune, Robert W. (Inventor); Hecht, Michael H. (Inventor)

1994-01-01

The backside surface potential well of a backside-illuminated CCD is confined to within about half a nanometer of the surface by using molecular beam epitaxy (MBE) to grow a delta-doped silicon layer on the back surface. Delta-doping in an MBE process is achieved by temporarily interrupting the evaporated silicon source during MBE growth without interrupting the evaporated p+ dopant source (e.g., boron). This produces an extremely sharp dopant profile in which the dopant is confined to only a few atomic layers, creating an electric field high enough to confine the backside surface potential well to within half a nanometer of the surface. Because the probability of UV-generated electrons being trapped by such a narrow potential well is low, the internal quantum efficiency of the CCD is nearly 100% throughout the UV wavelength range. Furthermore, the quantum efficiency is quite stable.

Concentration transient analysis of antimony surface segregation during Si(100) molecular beam epitaxy

NASA Technical Reports Server (NTRS)

Markert, L. C.; Greene, J. E.; Ni, W.-X.; Hansson, G. V.; Sundgren, J.-E.

1991-01-01

Antimony surface segregation during Si(100) molecular beam epitaxy (MBE) was investigated at temperatures T(sub s) = 515 - 800 C using concentration transient analysis (CTA). The dopant surface coverage Theta, bulk fraction gamma, and incorporation probability sigma during MBE were determined from secondary-ion mass spectrometry depth profiles of modulation-doped films. Programmed T(sub s) changes during growth were used to trap the surface-segregated dopant overlayer, producing concentration spikes whose integrated area corresponds to Theta. Thermal antimony doping by coevaporation was found to result in segregation strongly dependent on T(sub s) with Theta(sub Sb) values up to 0.9 monolayers (ML): in films doped with Sb(+) ions accelerated by 100 V, Theta(sub Sb) was less than or equal to 4 x 10(exp -3) ML. Surface segregation of coevaporated antimony was kinematically limited for the film growth conditions in these experiments.

Exploring the surface reactivity of 3d metal endofullerenes: a density-functional theory study.

PubMed

Estrada-Salas, Rubén E; Valladares, Ariel A

2009-09-24

Changes in the preferential sites of electrophilic, nucleophilic, and radical attacks on the pristine C60 surface with endohedral doping using 3d transition metal atoms were studied via two useful reactivity indices, namely the Fukui functions and the molecular electrostatic potential. Both of these were calculated at the density functional BPW91 level of theory with the DNP basis set. Our results clearly show changes in the preferential reactivity sites on the fullerene surface when it is doped with Mn, Fe, Co, or Ni atoms, whereas there are no significant changes in the preferential reactivity sites on the C60 surface upon endohedral doping with Cu and Zn atoms. Electron affinities (EA), ionization potentials (IP), and HOMO-LUMO gaps (Eg) were also calculated to complete the study of the endofullerene's surface reactivity. These findings provide insight into endofullerene functionalization, an important issue in their application.

Temperature dependence of nonlinear optical properties in Li doped nano-carbon bowl material

NASA Astrophysics Data System (ADS)

Li, Wei-qi; Zhou, Xin; Chang, Ying; Quan Tian, Wei; Sun, Xiu-Dong

2013-04-01

The mechanism for change of nonlinear optical (NLO) properties with temperature is proposed for a nonlinear optical material, Li doped curved nano-carbon bowl. Four stable conformations of Li doped corannulene were located and their electronic properties were investigated in detail. The NLO response of those Li doped conformations varies with relative position of doping agent on the curved carbon surface of corannulene. Conversion among those Li doped conformations, which could be controlled by temperature, changes the NLO response of bulk material. Thus, conformation change of alkali metal doped carbon nano-material with temperature rationalizes the variation of NLO properties of those materials.

Photocatalytic hydrogen generation enhanced by band gap narrowing and improved charge carrier mobility in AgTaO3 by compensated co-doping.

PubMed

Li, Min; Zhang, Junying; Dang, Wenqiang; Cushing, Scott K; Guo, Dong; Wu, Nianqiang; Yin, Penggang

2013-10-14

The correlation of the electronic band structure with the photocatalytic activity of AgTaO3 has been studied by simulation and experiments. Doping wide band gap oxide semiconductors usually introduces discrete mid-gap states, which extends the light absorption but has limited benefit for photocatalytic activity. Density functional theory (DFT) calculations show that compensated co-doping in AgTaO3 can overcome this problem by increasing the light absorption and simultaneously improving the charge carrier mobility. N/H and N/F co-doping can delocalize the discrete mid-gap states created by sole N doping in AgTaO3, which increases the band curvature and the electron-to-hole effective mass ratio. In particular, N/F co-doping creates a continuum of states that extend the valence band of AgTaO3. N/F co-doping thus improves the light absorption without creating the mid-gap states, maintaining the necessary redox potentials for water splitting and preventing from charge carrier trapping. The experimental results have confirmed that the N/F-codoped AgTaO3 exhibits a red-shift of the absorption edge in comparison with the undoped AgTaO3, leading to remarkable enhancement of photocatalytic activity toward hydrogen generation from water.

Rare-Earth Doping and Co-Doping of GaN for Magnetic and Luminescent Applications

DTIC Science & Technology

2010-08-16

The main focus of this project is the study of Gadolinium doped Gallium Nitride. Calculations were carried out to elucidate the origin of the reported...Ga vacancies in the triple negative charge state, which is the most likely charge state in semi-insulating samples, 1. REPORT DATE (DD-MM-YYYY) 4...applications Report Title ABSTRACT The main focus of this project is the study of Gadolinium doped Gallium Nitride. Calculations were carried out to

Electronic and magnetic properties of SnS2 monolayer doped with non-magnetic elements

NASA Astrophysics Data System (ADS)

Xiao, Wen-Zhi; Xiao, Gang; Rong, Qing-Yan; Wang, Ling-Ling

2018-05-01

We performed a systematic study of the electronic structures and magnetic properties of SnS2 monolayer doped with non-magnetic elements in groups IA, IIA and IIIA based on the first-principles methods. The doped systems exhibit half-metallic and metallic natures depending on the doping elements. The formation of magnetic moment is attributable to the cooperative effect of the Hund's rule coupling and hole concentration. The spin polarization can be stabilized and enhanced through confining the delocalized impurity states by biaxial tensile strain in hole-doped SnS2 monolayer. Both the double-exchange and p-p exchange mechanisms are simultaneously responsible for the ferromagnetic ground state in those hole-doped materials. Our results demonstrate that spin polarization can be induced and controlled in SnS2 monolayers by non-magnetic doping and tensile strain.

Habit modification of potassium acid phthalate (KAP) single crystals by impurities

NASA Astrophysics Data System (ADS)

Murugakoothan, P.; Mohan Kumar, R.; Ushasree, P. M.; Jayavel, R.; Dhanasekaran, R.; Ramasamy, P.

1999-12-01

Nonlinear optical materials potassium dihydrogen phosphate (KDP), urea and L-arginine phosphate (LAP)-doped KAP crystals were grown by the slow cooling method. The LAP-doped crystals show pronounced habit modification compared to KDP and urea doping. The effect of these impurities on growth kinetics, surface morphology, habit modification, structure, optical and mechanical properties have been studied. Among the three impurities, urea doping yields high mechanical stability and optical transmission and for KDP and LAP doping there is a decrease in optical transmission.

p-Type dopant incorporation and surface charge properties of catalyst-free GaN nanowires revealed by micro-Raman scattering and X-ray photoelectron spectroscopy.

PubMed

Wang, Q; Liu, X; Kibria, M G; Zhao, S; Nguyen, H P T; Li, K H; Mi, Z; Gonzalez, T; Andrews, M P

2014-09-07

Micro-Raman scattering and X-ray photoelectron spectroscopy were employed to investigate Mg-doped GaN nanowires. With the increase of Mg doping level, pronounced Mg-induced local vibrational modes were observed. The evolution of longitudinal optical phonon-plasmon coupled mode, together with detailed X-ray photoelectron spectroscopy studies, show that the near-surface region of nanowires can be transformed from weakly n-type to p-type with the increase of Mg doping.

Mechanical, dielectric and surface analysis of hydroxyapatite doped anions for implantations

NASA Astrophysics Data System (ADS)

Helen, S.; Kumar, A. Ruban

2018-04-01

Calcium Phosphate has broad applications in field of medicine and in tissue engineering. In that hydroxyapatite is one of the calcium phosphate similar to bone and teeth mineral phase. The aim of this paper is to improve mechanical property of hydroxyapatite which has less mechanical strength by doping of ions. The ions increase its strength which can be used in various medical applications. Surface property of hydroxyapatite and electrical property of ion doped hydroxyapatite analyzed and shown that it can be used in implantations, coatings.

Fe doped TiO2 nanofibers on the surface of graphene sheets for photovoltaics applications

NASA Astrophysics Data System (ADS)

Farhangi, Nasrin; Medina-Gonzalez, Yaocihuatl; Charpentier, Paul A.

2011-08-01

Highly ordered, visible light driven TiO2 nanowire arrays doped with Fe photocatalysts were grown on the surface of functionalized graphene sheets (FGSs) using a sol-gel method with titanium isopropoxide (TIP) monomer, acetic acid (HAc) as the polycondensation agent and iron chloride in the green solvent, supercritical carbon dioxide (scCO2). The morphology of the synthesized materials was studied by SEM and TEM, which showed uniform formation of Fe doped TiO2 nanofibers on the surface of graphene sheets, which acted as a template for nanowire growth through surface -COOH functionalities. Increasing Fe content in the nanowires did not change the morphology significantly. Optical properties of the synthesized composites were examined by UV spectroscopy which showed a significant reduction in band gap with increasing Fe content, i.e. 2.25 eV at 0.6% Fe. The enhancement of the optical properties of synthesized materials was confirmed by photocurrent measurement. The optimum sample containing 0.6% Fe doped TiO2 on the graphene sheets increased the power conversation efficiency by 6-fold in comparison to TiO2 alone.

Highly doped InP as a low loss plasmonic material for mid-IR region.

PubMed

Panah, M E Aryaee; Takayama, O; Morozov, S V; Kudryavtsev, K E; Semenova, E S; Lavrinenko, A V

2016-12-12

We study plasmonic properties of highly doped InP in the mid-infrared (IR) range. InP was grown by metal-organic vapor phase epitaxy (MOVPE) with the growth conditions optimized to achieve high free electron concentrations by doping with silicon. The permittivity of the grown material was found by fitting the calculated infrared reflectance spectra to the measured ones. The retrieved permittivity was then used to simulate surface plasmon polaritons (SPPs) propagation on flat and structured surfaces, and the simulation results were verified in direct experiments. SPPs at the top and bottom interfaces of the grown epilayer were excited by the prism coupling. A high-index Ge hemispherical prism provides efficient coupling conditions of SPPs on flat surfaces and facilitates acquiring their dispersion diagrams. We observed diffraction into symmetry-prohibited diffraction orders stimulated by the excitation of surface plasmon-polaritons in a periodically structured epilayer. Characterization shows good agreement between the theory and experimental results and confirms that highly doped InP is an effective plasmonic material aiming it for applications in the mid-IR wavelength range.

High-Temperature Isothermal Capacitance Transient Spectroscopy Study on Inductively Coupled Plasma Etching Damage for p-GaN Surfaces

NASA Astrophysics Data System (ADS)

Aoki, Toshichika; Wakayama, Hisashi; Kaneda, Naoki; Mishima, Tomoyoshi; Nomoto, Kazuki; Shiojima, Kenji

2013-11-01

The effects of the inductively coupled plasma (ICP) etching damage on the electrical characteristics of low-Mg-doped p-GaN Schottky contacts were evaluated by high-temperature isothermal capacitance transient spectroscopy. A large single peak for an acceptor-type surface state was dominantly detected for as-grown samples. The energy level and state density were obtained to be 1.18 eV above the valence band, which is close to a Ga vacancy (VGa), and 1.5×1013 cm-2, respectively. It was speculated that a small portion of Ga atoms were missing from the surface, and a high VGa density was observed in a few surface layers. The peak intensity decreased by 60% upon annealing at 800 °C, and further decrease was found by ICP etching. This decrease is consistent with the suppression of the memory effect in current-voltage characteristics. Upon annealing and ICP etching, since the VGa structure might be disordered, the peak intensity decreased.

Nitrogen-Doped Carbon Nanotube/Graphite Felts as Advanced Electrode Materials for Vanadium Redox Flow Batteries.

PubMed

Wang, Shuangyin; Zhao, Xinsheng; Cochell, Thomas; Manthiram, Arumugam

2012-08-16

Nitrogen-doped carbon nanotubes have been grown, for the first time, on graphite felt (N-CNT/GF) by a chemical vapor deposition approach and examined as an advanced electrode for vanadium redox flow batteries (VRFBs). The unique porous structure and nitrogen doping of N-CNT/GF with increased surface area enhances the battery performance significantly. The enriched porous structure of N-CNTs on graphite felt could potentially facilitate the diffusion of electrolyte, while the N-doping could significantly contribute to the enhanced electrode performance. Specifically, the N-doping (i) modifies the electronic properties of CNT and thereby alters the chemisorption characteristics of the vanadium ions, (ii) generates defect sites that are electrochemically more active, (iii) increases the oxygen species on CNT surface, which is a key factor influencing the VRFB performance, and (iv) makes the N-CNT electrochemically more accessible than the CNT.

Classification and characterization of topological insulators and superconductors

NASA Astrophysics Data System (ADS)

Mong, Roger

Topological insulators (TIs) are a new class of materials which, until recently, have been overlooked despite decades of study in band insulators. Like semiconductors and ordinary insulators, TIs have a bulk gap, but feature robust surfaces excitations which are protected from disorder and interactions which do not close the bulk gap. TIs are distinguished from ordinary insulators not by the symmetries they possess (or break), but by topological invariants characterizing their bulk band structures. These two pictures, the existence of gapless surface modes, and the nontrivial topology of the bulk states, yield two contrasting approaches to the study of TIs. At the heart of the subject, they are connected by the bulk-boundary correspondence, relating bulk and surface degrees of freedom. In this work, we study both aspects of topological insulators, at the same time providing an illumination to their mysterious connection. First, we present a systematic approach to the classification of bulk states of systems with inversion-like symmetries, deriving a complete set of topological invariants for such ensembles. We find that the topological invariants in all dimensions may be computed algebraically via exact sequences. In particular, systems with spatial inversion symmetries in one-, two-, and three-dimensions can be classified by, respectively, 2, 5, and 11 integer invariants. The values of these integers are related to physical observables such as polarization, Hall conductivity, and magnetoelectric coupling. We also find that, for systems with “antiferromagnetic symmetry,” there is a Z2 classification in three-dimensions, and hence a class of “antiferromagnetic topological insulators” (AFTIs) which are distinguished from ordinary antiferromagnets. From the perspective of the bulk, AFTI exhibits the quantized magnetoelectric effect, whereas on the surface, gapless one-dimensional chiral modes emerge at step-defects. Next, we study how the surface spectrum can be computed from bulk quantities. Specifically, we present an analytic prescription for computing the edge dispersion E(k) of a tight-binding Dirac Hamiltonian terminated at an abrupt crystalline edge, based on the bulk Hamiltonian. The result is presented as a geometric formula, relating the existence of surface states as well as their energy dispersion to properties of the bulk Hamiltonian. We further prove the bulk-boundary correspondence for this specific class of systems, connecting the Chern number and the chiral edge modes for quantum Hall systems given in terms of Dirac Hamiltonians. In similar spirit, we examine the existence of Majorana zero modes in superconducting doped-TIs. We find that Majorana zero modes indeed appear but only if the doped Fermi energy is below a critical chemical potential. The critical doping is associated with a topological phase transition of vortex lines, which supports gapless excitations spanning their length. For weak pairing, the critical point is dependent on the non-abelian Berry phase of the bulk Fermi surface. Finally, we investigate the transport properties on the surfaces of TIs. While the surfaces of “strong topological insulators” - TIs with an odd number of Dirac cones in their surface spectrum - have been well studied in literature, studies of their counterpart “weak topological insulators” (WTIs) are meager, with conflicting claims. Because WTIs have an even number of Dirac cones in their surface spectrum, they are thought to be unstable to disorder, which leads to an insulating surface. Here we argue that the presence of disorder alone will not localize the surface states, rather, presence of a time-reversal symmetric mass term is required for localization. Through numerical simulations, we show that in the absence of the mass term the surface always flow to a stable metallic phase and the conductivity obeys a one-parameter scaling relation, just as in the case of a strong topological insulator surface. With the inclusion of the mass, the transport properties of the surface of a weak topological insulator follow a two-parameter scaling form, reminiscent of the quantum Hall phase transition.

Ni-Doping Effects on Oxygen Removal from an Orthorhombic Mo 2C (001) Surface: A Density Functional Theory Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Mingxia; Cheng, Lei; Choi, Jae-Soon

Density functional theory (DFT) calculations were used in this paper to investigate the effect of Ni dopants on the removal of chemisorbed oxygen (O*) from the Mo-terminated (T Mo) and C-terminated (T C) Mo 2C(001) surfaces. The removal of adsorbed oxygen from the catalytic site is essential to maintain the long-term activity and selectivity of the carbide catalysts in the deoxygenation process related to bio-oil stabilization and upgrading. In this contribution, the computed reaction energetics and reaction barriers of O* removal were compared among undoped and Ni-doped Mo 2C(001) surfaces. The DFT calculations indicate that selected Ni-doped surfaces such asmore » Ni adsorbed on T Mo and T C Mo 2C(001) surfaces enable weaker binding of important reactive intermediates (O*, OH*) compared to the undoped counterparts, which is beneficial for the O* removal from the catalyst surface. This study thus confirms the promoting effect of the Ni dopant on O* removal reaction on the T Mo Mo 2C(001) and T C Mo 2C(001) surfaces. Finally, this computational prediction has been confirmed by the temperature-programmed reduction profiles of Mo 2C and Ni-doped Mo 2C catalysts, which had been passivated and stored in an oxygen environment.« less

Ni-Doping Effects on Oxygen Removal from an Orthorhombic Mo 2C (001) Surface: A Density Functional Theory Study

DOE PAGES

Zhou, Mingxia; Cheng, Lei; Choi, Jae-Soon; ...

2017-12-22

Density functional theory (DFT) calculations were used in this paper to investigate the effect of Ni dopants on the removal of chemisorbed oxygen (O*) from the Mo-terminated (T Mo) and C-terminated (T C) Mo 2C(001) surfaces. The removal of adsorbed oxygen from the catalytic site is essential to maintain the long-term activity and selectivity of the carbide catalysts in the deoxygenation process related to bio-oil stabilization and upgrading. In this contribution, the computed reaction energetics and reaction barriers of O* removal were compared among undoped and Ni-doped Mo 2C(001) surfaces. The DFT calculations indicate that selected Ni-doped surfaces such asmore » Ni adsorbed on T Mo and T C Mo 2C(001) surfaces enable weaker binding of important reactive intermediates (O*, OH*) compared to the undoped counterparts, which is beneficial for the O* removal from the catalyst surface. This study thus confirms the promoting effect of the Ni dopant on O* removal reaction on the T Mo Mo 2C(001) and T C Mo 2C(001) surfaces. Finally, this computational prediction has been confirmed by the temperature-programmed reduction profiles of Mo 2C and Ni-doped Mo 2C catalysts, which had been passivated and stored in an oxygen environment.« less

Modulation Doping of Silicon using Aluminium-induced Acceptor States in Silicon Dioxide

PubMed Central

König, Dirk; Hiller, Daniel; Gutsch, Sebastian; Zacharias, Margit; Smith, Sean

2017-01-01

All electronic, optoelectronic or photovoltaic applications of silicon depend on controlling majority charge carriers via doping with impurity atoms. Nanoscale silicon is omnipresent in fundamental research (quantum dots, nanowires) but also approached in future technology nodes of the microelectronics industry. In general, silicon nanovolumes, irrespective of their intended purpose, suffer from effects that impede conventional doping due to fundamental physical principles such as out-diffusion, statistics of small numbers, quantum- or dielectric confinement. In analogy to the concept of modulation doping, originally invented for III-V semiconductors, we demonstrate a heterostructure modulation doping method for silicon. Our approach utilizes a specific acceptor state of aluminium atoms in silicon dioxide to generate holes as majority carriers in adjacent silicon. By relocating the dopants from silicon to silicon dioxide, Si nanoscale doping problems are circumvented. In addition, the concept of aluminium-induced acceptor states for passivating hole selective tunnelling contacts as required for high-efficiency photovoltaics is presented and corroborated by first carrier lifetime and tunnelling current measurements. PMID:28425460

Surface Passivation by Quantum Exclusion Using Multiple Layers

NASA Technical Reports Server (NTRS)

Hoenk, Michael E. (Inventor)

2013-01-01

A semiconductor device has a multilayer doping to provide improved passivation by quantum exclusion. The multilayer doping includes a plurality M of doped layers, where M is an integer greater than 1. The dopant sheet densities in the M doped layers need not be the same, but in principle can be selected to be the same sheet densities or to be different sheet densities. M-1 interleaved layers provided between the M doped layers are not deliberately doped (also referred to as "undoped layers"). Structures with M=2, M=3 and M=4 have been demonstrated and exhibit improved passivation.

Aero dopes and varnishes

NASA Technical Reports Server (NTRS)

Britton, H T S

1927-01-01

Before proceeding to discuss the preparation of dope solutions, it will be necessary to consider some of the essential properties which should be possessed of a dope film, deposited in and on the surface of an aero fabric. The first is that it should tighten the material and second it should withstand weathering.

Evolution of microstructural defects of TiO2 nanocrystals by Zr4+ or/and Ge4+ doping lead to high disinfection efficiency for CWAs

NASA Astrophysics Data System (ADS)

Shen, Zhong; Zhong, Jin-Yi; Chai, Na-Na; He, Xin; Zang, Jian-Zheng; Xu, Hui; Han, Xiao-Yuan; Zhang, Peng

2017-06-01

Zr4+, Ge4+ doped and co-doped TiO2 nanoparticles were prepared by a 'one-pot' homogeneous precipitation method. The photocatalytic reaction kinetics of DMMP and the disinfection efficiency of HD, GD and VX on the samples were investigated. By means of a variety of characterization methods, especially the positron annihilation lifetime spectroscopy, the changes in structure and property of TiO2 across doping were studied. The results show that the reasonable engineering design of novel photocatalysts in the field of CWAs decontamination can be realized by adjusting the bulk-to-surface defects ratio, except for crystal structure, specific surface area, pore size distribution and light utilization.

Surface recombination velocity and diffusion length of minority carriers in heavily doped silicon layers

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Watanabe, M.; Actor, G.

1977-01-01

Quantitative analysis of the electron beam-induced current and the dependence of the effective diffusion length of the minority carriers on the penetration depth of the electron beam were employed for the analysis of the carrier recombination characteristics in heavily doped silicon layers. The analysis is based on the concept of the effective excitation strength of the carriers which takes into consideration all possible recombination sources. Two dimensional mapping of the surface recombination velocity of P-diffused Si layers will be presented together with a three dimensional mapping of minority carrier lifetime in ion implanted Si. Layers heavily doped with As exhibit improved recombination characteristics as compared to those of the layers doped with P.

Lateral Charge Transport in Silicon Nanomembranes

NASA Astrophysics Data System (ADS)

Hu, Weiwei

Silicon nanomembranes, also called SiNMs, Si thin sheets or films, are a great platform to study surface sciences, since the bulk is diminished and the surface-to-volume ratio is large. In a single crystalline material, atoms on the surface experience different forces, electric fields, thermodynamic surroundings, etc., than those within the bulk. Therefore, unique structural, mechanical, electronic, optical, and many other properties associated with surfaces overweigh bulk effects; novel phenomena emerge. In particular, electronic features of Si are of significance due to the extensive use of Si in integrated circuit devices and biochemical sensor technologies. As a result, especially with the size of transistors quickly decreasing nowadays, the exploration of electronic characteristics of Si surfaces become much more significant. This is also interesting as a topic within the area of fundamental surface science. Silicon-on-insulator (SOI) provides a new structure for studying charge transport in the SiNM, which is monocrystalline and sits on top of the SOI wafer. I use SOI based SiNMs with two surface orientations: Si (001) and Si (111). The former is pervasive in industrial applications while the latter has interesting metallic surface states when 7x7 reconstruction occurs on a clean surface. My goal is to measure/infer the sheet conductance in the true surface layer with different surface situations, and to further investigate the surface band structure and how carriers distribute and move accordingly. The biggest challenge is to eliminate interferences, e.g., bulk effects. The following are two solutions. 1) The thickness of the used SiNMs spans 40 nm to 500 nm, with a nominal doping level of 1015 cm -3 in our experiment. A straightforward calculation of areal dopant density indicates that charge carriers from the extrinsic doping are 1˜2 orders of magnitude fewer than the trap states at the interface between the buried oxide in SOI and the top SiNM, meaning that moderate doping is irrelevant and the SiNM acts like an intrinsic one. 2) The back gate that is applied to the measured sample is an innovative design among myriad analogous studies. It enables the tuning of the Fermi level (EF) throughout the SiNMs and makes it possible for a membrane to reach its most depleted status, thus efficiently removing the bulk conduction path. The four-probe van der Pauw measurements of film conductance are taken inside an ultrahigh vacuum chamber, where the surface condition remains stable and controllable. On Si (111) 7x7 surfaces, we find from the independence of conductance on membrane thickness that we are measuring the surface transport only. The sheet conductance is high, as it is on the microS/□scale, which supports the 7x7 surface having metallicity in lateral charge transport, a point which has been debated extensively. Nevertheless, weak semiconductor behavior is still present. For hydrogenated Si (001), which is obtained after hydrogen fluoric acid (HF) treatment, surface Fermi level is found around mid-bandgap based on temperature dependent measurements. No surface Fermi level pinning to closely below the conduction band minimum exists in my HF treated Si (001) NMs.

Photochemical Hydrogen Doping Induced Embedded Two-Dimensional Metallic Channel Formation in InGaZnO at Room Temperature.

PubMed

Kim, Myeong-Ho; Lee, Young-Ahn; Kim, Jinseo; Park, Jucheol; Ahn, Seungbae; Jeon, Ki-Joon; Kim, Jeong Won; Choi, Duck-Kyun; Seo, Hyungtak

2015-10-27

The photochemical tunability of the charge-transport mechanism in metal-oxide semiconductors is of great interest since it may offer a facile but effective semiconductor-to-metal transition, which results from photochemically modified electronic structures for various oxide-based device applications. This might provide a feasible hydrogen (H)-radical doping to realize the effectively H-doped metal oxides, which has not been achieved by thermal and ion-implantation technique in a reliable and controllable way. In this study, we report a photochemical conversion of InGaZnO (IGZO) semiconductor to a transparent conductor via hydrogen doping to the local nanocrystallites formed at the IGZO/glass interface at room temperature. In contrast to thermal or ionic hydrogen doping, ultraviolet exposure of the IGZO surface promotes a photochemical reaction with H radical incorporation to surface metal-OH layer formation and bulk H-doping which acts as a tunable and stable highly doped n-type doping channel and turns IGZO to a transparent conductor. This results in the total conversion of carrier conduction property to the level of metallic conduction with sheet resistance of ∼16 Ω/□, room temperature Hall mobility of 11.8 cm(2) V(-1) sec(-1), the carrier concentration at ∼10(20) cm(-3) without any loss of optical transparency. We demonstrated successful applications of photochemically highly n-doped metal oxide via optical dose control to transparent conductor with excellent chemical and optical doping stability.

Effect of Si, Mg, and Mg Zn doping on structural properties of a GaN layer grown by metalorganic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Cho, H. K.; Lee, J. Y.; Kim, K. S.; Yang, G. M.

2001-12-01

We have studied the structural properties of undoped, Si-doped, Mg-doped, and Mg-Zn codoped GaN using high-resolution X-ray diffraction (HRXRD) and transmission electron microscopy. When compared with undoped GaN, the dislocation density at the surface of the GaN layer decreases with Si doping and increases with Mg doping. In addition, we observed a reduction of dislocation density by codoping with Zn atoms in the Mg-doped GaN layer. The full width at half maximum of HRXRD shows that Si doping and Mg-Zn codoping improve the structural quality of the GaN layer as compared with undoped and Mg-doped GaN, respectively.

The effects of temperature on the surface resistivity of polyvinyl alcohol (PVA) thin films doped with silver nanoparticles and multi-walled carbon-nanotubes for optoelectronic and sensor applications

NASA Astrophysics Data System (ADS)

Polius, Jemilia R.

This thesis reports measurements of the temperature-dependent surface resistivity of multi-wall carbon nanotube doped polyvinyl alcohol (PVA) thin films. In the temperature range from 22°C to 40°C in a humidity controlled environment, it was found that the surface resistivity decreased initially but raised as the temperature continued to increase. I report surface resistivity measurements as a function of temperature of both multiwall and single-wall carbon nanotube doped PVA thin films, with comparison of the similarities and differences between the two types of film types. This research was conducted using the combined instrumentation of the KEITHLEY Model 6517 Electrometer and the KEITHLEY Model 8009 resistivity test fixture using both commercial and in-house produced organic thin films.

One-step surface doping of organic nanofibers to achieve high dark conductivity and chemiresistor sensing of amines.

PubMed

Huang, Helin; Gross, Dustin E; Yang, Xiaomei; Moore, Jeffrey S; Zang, Ling

2013-08-28

High dark electrical conductivity was obtained for a p-type organic nanofibril material simply through a one-step surface doping. The nanofibril composite thus fabricated has been proven robust under ambient conditions. The high conductivity, combined with the intrinsic large surface area of the nanofibers, enables development of chemiresistor sensors for trace vapor detection of amines, with detection limit down to sub-parts per billion range.

Effect of doping on the forward current-transport mechanisms in a metal-insulator-semiconductor contact to INP:ZN grown by metal organic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Cova, P.; Singh, A.; Medina, A.; Masut, R. A.

1998-04-01

A detailed study of the effect of doping density on current transport was undertaken in Au metal-insulator-semiconductor (MIS) contacts fabricated on Zn-doped InP layers grown by metal organic vapor phase epitaxy. A recently developed method was used for the simultaneous analysis of the current-voltage ( I- V) and capacitance-voltage ( C- V) characteristics in an epitaxial MIS diode which brings out the contributions of different current-transport mechanisms to the total current. I- V and high-frequency C- V measurements were performed on two MIS diodes at different temperatures in the range 220-395 K. The barrier height at zero bias of Au/InP:Zn MIS diodes, φ0 (1.06 V±10%), was independent both of the Zn-doping density and of the surface preparation. The interface state density distribution Nss as well as the thickness of the oxide layer (2.2±15% nm) unintentionally grown before Au deposition were independent of the Zn-doping concentration in the range 10 16< NA<10 17 cm -3; not so the effective potential barrier χ of the insulator layer and the density of the mid-gap traps. χ was much lower for the highly-doped sample. Our results indicate that at high temperatures, independent of the Zn-doping concentration, the interfacial layer-thermionic (ITE) and interfacial layer-diffusion (ID) mechanisms compete with each other to control the current transport. At intermediate temperatures, however, ITE and ID will no longer be the only dominant mechanisms in the MIS diode fabricated on the highly-doped sample. In this case, the assumption of a generation-recombination current permits a better fit to the experimental data. Analysis of the data suggests that the generation-recombination current, observed only in the highly-doped sample, is associated with an increase in the Zn-doping density. From the forward I- V data for this diode we obtained the energy level (0.60 eV from the conduction band) for the most effective recombination centers.

Moderate temperature-dependent surface and volume resistivity and low-frequency dielectric constant measurements of pure and multi-walled carbon nanotube (MWCNT) doped polyvinyl alcohol thin films

NASA Astrophysics Data System (ADS)

Edwards, Matthew; Guggilla, Padmaja; Reedy, Angela; Ijaz, Quratulann; Janen, Afef; Uba, Samuel; Curley, Michael

2017-08-01

Previously, we have reported measurements of temperature-dependent surface resistivity of pure and multi-walled carbon nanotube (MWNCT) doped amorphous Polyvinyl Alcohol (PVA) thin films. In the temperature range from 22 °C to 40 °C with humidity-controlled environment, we found the surface resistivity to decrease initially, but to rise steadily as the temperature continued to increase. Moreover, electric surface current density (Js) was measured on the surface of pure and MWCNT doped PVA thin films. In this regard, the surface current density and electric field relationship follow Ohm's law at low electric fields. Unlike Ohmic conduction in metals where free electrons exist, selected captive electrons are freed or provided from impurities and dopants to become conduction electrons from increased thermal vibration of constituent atoms in amorphous thin films. Additionally, a mechanism exists that seemingly decreases the surface resistivity at higher temperatures, suggesting a blocking effect for conducting electrons. Volume resistivity measurements also follow Ohm's law at low voltages (low electric fields), and they continue to decrease as temperatures increase in this temperature range, differing from surface resistivity behavior. Moreover, we report measurements of dielectric constant and dielectric loss as a function of temperature and frequency. Both the dielectric constant and dielectric loss were observed to be highest for MWCNT doped PVA compared to pure PVA and commercial paper, and with frequency and temperature for all samples.

A highly sensitive chemical gas detecting device based on N-doped ZnO as a modified nanostructure media: A DFT+NBO analysis

NASA Astrophysics Data System (ADS)

Abbasi, Amirali; Sardroodi, Jaber Jahanbin

2018-02-01

We presented a density functional theory study of the adsorption of O3 and NO2 molecules on ZnO nanoparticles. Various adsorption geometries of O3 and NO2 over the nanoparticles were considered. For both O3 and NO2 adsorption systems, it was found that the adsorption on the N-doped nanoparticle is more favorable in energy than that on the pristine one. Therefore, the N-doped ZnO has a better efficiency to be utilized as O3 and NO2 detection device. For all cases, the binding sites were located on the zinc atoms of the nanoparticle. The charge analysis based on natural bond orbital (NBO) analysis indicates that charge was transferred from the surface to the adsorbed molecule. The projected density of states of the interacting atoms represent the formation of chemical bonds at the interface region. Molecular orbitals of the adsorption systems indicate that the HOMOs were mainly localized on the adsorbed O3 and NO2 molecules, whereas the electronic densities in the LUMOs were dominant at the ZnO nanocrystal surface. By examining the distribution of spin densities, we found that the magnetization was mainly located over the adsorbed molecules. For NO2 adsorbate, we found that the symmetric and asymmetric stretches were shifted to a lower frequency. The bending stretch mode was shifted to the higher frequency. Our DFT results thus provide a theoretical basis for why the adsorption of O3 and NO2 molecules on the N-doped ZnO nanoparticles may increase, giving rise to design and development of innovative and highly efficient sensor devices for O3 and NO2 recognition.

Atomic and electronic structure of doped Si (111 ) (2 √{3 }×2 √{3 }) R 30∘ -Sn interfaces

NASA Astrophysics Data System (ADS)

Yi, Seho; Ming, Fangfei; Huang, Ying-Tzu; Smith, Tyler S.; Peng, Xiyou; Tu, Weisong; Mulugeta, Daniel; Diehl, Renee D.; Snijders, Paul C.; Cho, Jun-Hyung; Weitering, Hanno H.

2018-05-01

The hole-doped Si (111 ) (2 √ 3 ×2 √ 3 ) R 30∘ -Sn interface exhibits a symmetry-breaking insulator-insulator transition below 100 K that appears to be triggered by electron tunneling into the empty surface-state bands. No such transition is seen in electron-doped systems. To elucidate the nature and driving force of this phenomenon, the structure of the interface must be resolved. Here we report on an extensive experimental and theoretical study, including scanning tunneling microscopy and spectroscopy (STM/STS), dynamical low-energy electron diffraction (LEED) analysis, and density functional theory (DFT) calculations, to elucidate the structure of this interface. We consider six different structure models, three of which have been proposed before, and conclude that only two of them can account for the majority of experimental data. One of them is the model according to Törnevik et al. [C. Törnevik et al., Phys. Rev. B 44, 13144 (1991), 10.1103/PhysRevB.44.13144] with a total Sn coverage of 14/12 monolayers (ML). The other is the "revised trimer model" with a total Sn coverage of 13/12 ML, introduced in this work. These two models are very difficult to discriminate on the basis of DFT or LEED alone, but STS data clearly point toward the Törnevik model as the most viable candidate among the models considered here. The STS data also provide additional insights regarding the electron-injection-driven phase transformation. Similar processes may occur at other metal/semiconductor interfaces, provided they are nonmetallic and can be doped. This could open up a new pathway toward the creation of novel surface phases with potentially very interesting and desirable electronic properties.

Magnesiothermic synthesis of sulfur-doped graphene as an efficient metal-free electrocatalyst for oxygen reduction

PubMed Central

Wang, Jiacheng; Ma, Ruguang; Zhou, Zhenzhen; Liu, Guanghui; Liu, Qian

2015-01-01

Efficient metal-free electrocatalysts for oxygen reduction reaction (ORR) are highly expected in future low-cost energy systems. We have successfully prepared crumpled, sheet-like, sulfur-doped graphene by magnesiothermic reduction of easily available, low-cost, nontoxic CO2 (in the form of Na2CO3) and Na2SO4 as the carbon and sulfur sources, respectively. At high temperature, Mg can reduce not only carbon in the oxidation state of +4 in CO32− to form graphene, but also sulfur in SO42− from its highest (+6) to lowest valence which was hybridized into the carbon sp2 framework. Various characterization results show that sulfur-doped graphene with only few layers has an appropriate sulfur content, hierarchically robust porous structure, large surface area/pore volume, and highly graphitized textures. The S-doped graphene samples exhibit not only a high activity for ORR with a four-electron pathway, but also superior durability and tolerance to MeOH crossover to 40% Pt/C. This is mainly ascribed to the combination of sulfur-related active sites and hierarchical porous textures, facilitating fast diffusion of oxygen molecules and electrolyte to catalytic sites and release of products from the sites. PMID:25790856

Electric double-layer transistor using layered iron selenide Mott insulator TlFe1.6Se2

PubMed Central

Katase, Takayoshi; Hiramatsu, Hidenori; Kamiya, Toshio; Hosono, Hideo

2014-01-01

A1–xFe2–ySe2 (A = K, Cs, Rb, Tl) are recently discovered iron-based superconductors with critical temperatures (Tc) ranging up to 32 K. Their parent phases have unique properties compared with other iron-based superconductors; e.g., their crystal structures include ordered Fe vacancies, their normal states are antiferromagnetic (AFM) insulating phases, and they have extremely high Néel transition temperatures. However, control of carrier doping into the parent AFM insulators has been difficult due to their intrinsic phase separation. Here, we fabricated an Fe-vacancy-ordered TlFe1.6Se2 insulating epitaxial film with an atomically flat surface and examined its electrostatic carrier doping using an electric double-layer transistor (EDLT) structure with an ionic liquid gate. The positive gate voltage gave a conductance modulation of three orders of magnitude at 25 K, and further induced and manipulated a phase transition; i.e., delocalized carrier generation by electrostatic doping is the origin of the phase transition. This is the first demonstration, to the authors' knowledge, of an EDLT using a Mott insulator iron selenide channel and opens a way to explore high Tc superconductivity in iron-based layered materials, where carrier doping by conventional chemical means is difficult. PMID:24591598