Structure prediction of boron-doped graphene by machine learning

NASA Astrophysics Data System (ADS)

M. Dieb, Thaer; Hou, Zhufeng; Tsuda, Koji

2018-06-01

Heteroatom doping has endowed graphene with manifold aspects of material properties and boosted its applications. The atomic structure determination of doped graphene is vital to understand its material properties. Motivated by the recently synthesized boron-doped graphene with relatively high concentration, here we employ machine learning methods to search the most stable structures of doped boron atoms in graphene, in conjunction with the atomistic simulations. From the determined stable structures, we find that in the free-standing pristine graphene, the doped boron atoms energetically prefer to substitute for the carbon atoms at different sublattice sites and that the para configuration of boron-boron pair is dominant in the cases of high boron concentrations. The boron doping can increase the work function of graphene by 0.7 eV for a boron content higher than 3.1%.

Facile microwave-assisted synthesis of Te-doped hydroxyapatite nanorods and nanosheets and their characterizations for bone cement applications.

PubMed

Yahia, I S; Shkir, Mohd; AlFaify, S; Ganesh, V; Zahran, H Y; Kilany, Mona

2017-03-01

In this work, the authors have fabricated the nanorods and nanosheets of pure and Te-doped HAp with different Te concentrations (0.04, 0.08, 0.16, 0.24wt%) by microwave-assisted technique at low temperature. The crystallite size, degree of crystallinity and lattice parameters are calculated. FE-SEM study confirms that the fabricated nanostructures are nanorods of diameter about 10nm in undoped and at low concentration of Te doping. However, at and higher concentration, it becomes nanosheets of about 5nm thickness. X-ray diffraction, FT-IR and FT-Raman studies shows that the prepared products are of HAp and Te has been successfully incorporated. From EDX the Ca/P molar ratio of the pure HAp is about 1.740, while this ratio for 0.04, 0.08, 0.16, 0.24 wt% Te doped is about 1.53, 1.678, 1.724, 1.792, respectively. Crystallite size was found to be increased with Te doping from 15nm to 62nm. The value of dielectric constant is found to be enhanced at higher concentrations of Te. The values of linear absorption coefficient were also determined and show that the prepared material with Te doping is more absorbable than pure and will be highly applicable in radiation detection applications. Furthermore, the antimicrobial potential of pure and Te doped HAp was examined against some Gram- negative and positive bacteria and fungi by agar disk diffusion method. The results demonstrated that the antimicrobial activity of Te doped HAp is stronger than that of pure HAp where it exhibited the highest activity against Bacillus subtilis>Candida albicans>Shigella dysenteriae. Copyright © 2016 Elsevier B.V. All rights reserved.

Structural and electrical properties of trimethylboron-doped silicon nanowires

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

Lew, K.-K.; Pan Ling; Bogart, Timothy E.

2004-10-11

Trimethylboron (TMB) was investigated as a p-type dopant source for the vapor-liquid-solid growth of boron-doped silicon nanowires (SiNWs). The boron concentration in the nanowires was measured using secondary ion mass spectrometry and results were compared for boron-doping using TMB and diborane (B{sub 2}H{sub 6}) sources. Boron concentrations ranging from 1x10{sup 18} to 4x10{sup 19} cm{sup -3} were obtained by varying the inlet dopant/SiH{sub 4} gas ratio. TEM characterization revealed that the B{sub 2}H{sub 6}-doped SiNWs consisted of a crystalline core with a thick amorphous Si coating, while the TMB-doped SiNWs were predominantly single crystal even at high boron concentrations. Themore » difference in structural properties was attributed to the higher thermal stability and reduced reactivity of TMB compared to B{sub 2}H{sub 6}. Four-point resistivity and gate-dependent conductance measurements were used to confirm p-type conductivity in the TMB-doped nanowires and to investigate the effect of dopant concentration on nanowire resistivity.« less

An investigation on the In doping of ZnO thin films by spray pyrolysis

NASA Astrophysics Data System (ADS)

Mahesh, Devika; Kumar, M. C. Santhosh

2018-04-01

Indium doped zinc oxide (IGZO)thin films are gaining much interest owing to its commercial application as transparent conductive oxide thin films. In the current study thin films indium doped ZnO thin films have been deposited on glass substrates by chemical spray pyrolysis technique with an indium concentration of 1, 2.5 and 4% in Zinc source. The films show a peak shift in the X-Ray Diffraction patterns with varying indium doping concentration. The (101) peak was enhanced for the 2.5 % indium doped films and variation in grain size with the different doping levels was studied. The as-deposited films are uniform and shown high transparency (>90%) in the visible region. Average thicknesses of films are found to be 800nm, calculated using the envelope method. The film with 2.5 % of indium content was found to be highly conducting than the rest, since for the lower and higher concentrations the conductivity was possibly halted by the limit in carrier concentration and indium segregation in the grain boundaries respectively. The enhancement of mobility and carrier concentration was clearly seen in the optimum films.

Electrical properties of aluminum-doped zinc oxide (AZO) nanoparticles synthesized by chemical vapor synthesis.

PubMed

Hartner, Sonja; Ali, Moazzam; Schulz, Christof; Winterer, Markus; Wiggers, Hartmut

2009-11-04

Aluminum-doped zinc oxide nanoparticles have been prepared by chemical vapor synthesis, which facilitates the incorporation of a higher percentage of dopant atoms, far above the thermodynamic solubility limit of aluminum. The electrical properties of aluminum-doped and undoped zinc oxide nanoparticles were investigated by impedance spectroscopy. The impedance is measured under hydrogen and synthetic air between 323 and 673 K. The measurements under hydrogen as well as under synthetic air show transport properties depending on temperature and doping level. Under hydrogen atmosphere, a decreasing conductivity with increasing dopant content is observed, which can be explained by enhanced scattering processes due to an increasing disorder in the nanocrystalline material. The temperature coefficient for the doped samples switches from positive temperature coefficient behavior to negative temperature coefficient behavior with increasing dopant concentration. In the presence of synthetic air, the conductivity firstly increases with increasing dopant content by six orders of magnitude. The origin of the increasing conductivity is the generation of free charge carriers upon dopant incorporation. It reaches its maximum at a concentration of 7.7% of aluminum, and drops for higher doping levels. In all cases, the conductivity under hydrogen is higher than under synthetic air and can be changed reversibly by changing the atmosphere.

[Optical and morphological investigation on the interaction of dual dopants in poly (N-vinylcarzole)].

PubMed

Zhang, Ting; Xu, Zheng; Teng, Feng; Qian, Lei; Wang, Yong-Sheng; Xu, Xu-Rong

2006-05-01

The effect of optical and electrical properties of poly(N-vinylcarzole) (PVK) doped with two dyes, i. e. 8-tris-hydroxyquinoline (Alq3) and 4-(dicyanomethylene)-2-tert-butyl-6 (1, 1, 7, 7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB), on the energy transfer and charge trapping processes was investigated. The phase separation in blends film at different doping concentration was also studied. More homogeneous dispersion of dyes in PVK with increasing doping concentration was showed. The results indicate that there is a certain interaction of Alq3 and DCJTB in this dual-doped system. It is the incorporation of DCJTB that untangled the aggregation of Alq3 owing to the interaction of DCJTB and Alq3. But for higher doping concentration, DCJTB results in an isolated charge transport channel that decreases the electroluminescence (EL) operating voltage.

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.%.

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

Highly concentrated, stable nitrogen-doped graphene for supercapacitors: Simultaneous doping and reduction

NASA Astrophysics Data System (ADS)

Jiang, Baojiang; Tian, Chungui; Wang, Lei; Sun, Li; Chen, Chen; Nong, Xiaozhen; Qiao, Yingjie; Fu, Honggang

2012-02-01

In this work, we developed a concentrated ammonia-assisted hydrothermal method to obtain N-doped graphene sheets by simultaneous N-doping and reduction of graphene oxide (GO) sheets. The effects of hydrothermal temperature on the surface chemistry and the structure of N-doped graphene sheets were also investigated. X-ray photoelectron spectroscopy (XPS) study of N-doped graphene reveals that the highest doping level of 7.2% N is achieved at 180 °C for 12 h. N binding configurations of sample consist of pyridine N, quaternary N, and pyridine-N oxides. N doping is accompanied by the reduction of GO with decreases in oxygen levels from 34.8% in GO down to 8.5% in that of N-doped graphene. Meanwhile, the sample exhibits excellent N-doped thermal stability. Electrical measurements demonstrate that products have higher capacitive performance than that of pure graphene, the maximum specific capacitance of 144.6 F/g can be obtained which ascribe the pseudocapacitive effect from the N-doping. The samples also show excellent long-term cycle stability of capacitive performance.

Effect of heavy Ag doping on the physical properties of ZnO

NASA Astrophysics Data System (ADS)

Hou, Qingyu; Zhao, Chunwang; Jia, Xiaofang; Xu, Zhenchao

2018-04-01

The band structure, density of state and absorption spectrum of Zn1‑xAgxO (x = 0.02778, 0.04167) were calculated. Results indicated that a higher doping content of Ag led to a higher total energy, lower stability, higher formation energy, narrower bandgap, more significant red shift of the absorption spectrum, higher relative concentration of free hole, smaller hole effective mass, lower mobility and better conductivity. Furthermore, four types of model with the same doping content of double Ag-doped Zn1‑xAgxO (x = 0.125) but different manners of doping were established. Two types of models with different doping contents of double Ag-doped Zn1‑xAgxO (x = 0.0626, 0.0833) but the same manner of doping, were also established. Under the same doping content and different ordering occupations in Ag double doping, the doped system almost caused magnetic quenching upon the nearest neighbor -Ag-O-Ag- bonding at the direction partial to the a- or b-axis. Upon the next-nearest neighbor of -Ag-O-Zn-O-Ag- bonding at the direction partial to the c-axis, the total magnetic moment of the doped system increased, and the doped system reached a Curie temperature above the room-temperature. All these results indicated that the magnetic moments of Ag double-doped ZnO systems decreased with increased Ag doping content. Within the range of the mole number of the doping content of 0.02778-0.04167, a greater Ag doping content led to a narrower bandgap of the doped system and a more significant red shift in the absorption spectrum. The absorption spectrum of the doped ZnO system with interstitial Ag also shows a red shift.

Alteration of magnetic and optical properties of ultrafine dilute magnetic semiconductor ZnO:Co2+ nanoparticles.

PubMed

Sharma, Prashant K; Dutta, Ranu K; Pandey, Avinash C

2010-05-15

Single-phase ZnO:Co(2+) nanoparticles of mean size 2-8 nm were synthesized by a simple co-precipitation technique. X-ray diffraction analysis reveals that the Co-doped ZnO nanoparticles crystallize in wurtzite structure without any impurity phase. The wurtzite structure (lattice constants) of ZnO nanoparticles decrease slightly with increasing Co doping concentration. Optical absorption spectra show an increase in the band gap with increasing Co content and also give an evidence of the presence of Co(2+) ions at tetrahedral sites of ZnO and substituted for the Zn site with no evidence of metallic Co. Initially these nanoparticles showed strong ferromagnetic behavior at room temperature, however at higher doping percentage of Co(2+), the ferromagnetic behavior was suppressed, and antiferromagnetic nature was enhanced. The enhanced antiferromagnetic interaction between neighboring Co-Co ions suppressed the ferromagnetism at higher doping concentrations of Co(2+). Photoluminescence intensity owing to the vacancies varies with the Co concentration because of the increment of oxygen vacancies. Copyright © 2010 Elsevier Inc. All rights reserved.

Photoluminescence and positron annihilation studies on Mg-doped nitrogen-polarity semipolar (101xAF1xAF) GaN heteroepitaxial layers grown by metalorganic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Onuma, T.; Uedono, A.; Asamizu, H.; Sato, H.; Kaeding, J. F.; Iza, M.; DenBaars, S. P.; Nakamura, S.; Chichibu, S. F.

2010-03-01

The influences of enhanced stacking fault (SF) formation, which is peculiar to nitrogen-(N-) polarity growth and lattice-mismatched semipolar heteroepitaxy, on the electrical properties of (101¯1¯) Mg-doped GaN (GaN:Mg) epilayers were investigated. Although the residual donor concentration was higher than (0001) GaN because of N-polar growth, comparatively low Mg doping (3×1019 cm-3) gave a hole concentration approximately 1.5×1018 cm-3, which was an order of magnitude higher than (0001) GaN:Mg. As the acceptor ionization energy estimated from low temperature photoluminescence was quite similar for (101¯1¯) and (0001) GaN:Mg, the high Mg activation seems to result with the aid of high density SFs. Because the Doppler broadening S parameter for the positron annihilation measurement, which reflects the concentration or size of negatively charged cation vacancies, of (101¯1¯) GaN:Mg was smaller than (0001) case, (101¯1¯) orientation is well suited to Mg-doping.

n-type dopants in (001) β-Ga2O3 grown on (001) β-Ga2O3 substrates by plasma-assisted molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Han, Sang-Heon; Mauze, Akhil; Ahmadi, Elaheh; Mates, Tom; Oshima, Yuichi; Speck, James S.

2018-04-01

Ge and Sn as n-type dopants in (001) β-Ga2O3 films were investigated using plasma-assisted molecular beam epitaxy. The Ge concentration showed a strong dependence on the growth temperature, whereas the Sn concentration remains independent of the growth temperature. The maximum growth temperature at which a wide range of Ge concentrations (from 1017 to 1020 cm-3) could be achieved was 675 °C while the same range of Sn concentration could be achieved at growth temperature of 750 °C. Atomic force microscopy results revealed that higher growth temperature shows better surface morphology. Therefore, our study reveals a tradeoff between higher Ge doping concentration and high quality surface morphology on (001) β-Ga2O3 films grown by plasma-assisted molecular beam epitaxy. The Ge doped films had an electron mobility of 26.3 cm2 V-1 s-1 at the electron concentration of 6.7 × 1017 cm-3 whereas the Sn doped films had an electron mobility of 25.3 cm2 V-1 s-1 at the electron concentration of 1.1 × 1018 cm-3.

The shift of optical band gap in W-doped ZnO with oxygen pressure and doping level

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

Chu, J.; Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Science, Chongqing 400714; Peng, X.Y.

2014-06-01

Highlights: • CVD–PLD co-deposition technique was used. • Better crystalline of the ZnO samples causes the redshift of the optical band gap. • Higher W concentration induces blueshift of the optical band gap. - Abstract: Tungsten-doped (W-doped) zinc oxide (ZnO) nanostructures were synthesized on quartz substrates by pulsed laser and hot filament chemical vapor co-deposition technique under different oxygen pressures and doping levels. We studied in detail the morphological, structural and optical properties of W-doped ZnO by SEM, XPS, Raman scattering, and optical transmission spectra. A close correlation among the oxygen pressure, morphology, W concentrations and the variation of bandmore » gaps were investigated. XPS and Raman measurements show that the sample grown under the oxygen pressure of 2.7 Pa has the maximum tungsten concentration and best crystalline structure, which induces the redshift of the optical band gap. The effect of W concentration on the change of morphology and shift of optical band gap was also studied for the samples grown under the fixed oxygen pressure of 2.7 Pa.« less

Optical properties of rare earth doped transparent oxyfluoride glass ceramics

NASA Astrophysics Data System (ADS)

Mendez-Ramos, J.; Lavin, V.; Martin, I. R.; Rodriguez-Mendoza, U. R.; Rodriguez, V. D.; Lozano-Gorrin, A. D.; Nunez, P.

2003-01-01

Optical properties of Eu3+ ions in oxyfluoride glasses and glass ceramics doped with low concentration (0.1 mol%) have been analysed and compared with previous results for high concentrated samples (2.5 mol%). The Eu3+ ions in the low dopant concentration glass ceramics are diluted into like crystalline environments with higher symmetry and lower coupled phonons energy than in the precursor glasses. Fluorescence line narrowing measurements indicate the presence of two main fluoride site distributions for the Eu3+ ions in these low concentrated glass ceramics.

Corrosion and Wear Behaviors of Cr-Doped Diamond-Like Carbon Coatings

NASA Astrophysics Data System (ADS)

Viswanathan, S.; Mohan, L.; Bera, Parthasarathi; Kumar, V. Praveen; Barshilia, Harish C.; Anandan, C.

2017-08-01

A combination of plasma-enhanced chemical vapor deposition and magnetron sputtering techniques has been employed to deposit chromium-doped diamond-like carbon (DLC) coatings on stainless steel, silicon and glass substrates. The concentrations of Cr in the coatings are varied by changing the parameters of the bipolar pulsed power supply and the argon/acetylene gas composition. The coatings have been studied for composition, morphology, surface nature, nanohardness, corrosion resistance and wear resistance properties. The changes in I D / I G ratio with Cr concentrations have been obtained from Raman spectroscopy studies. Ratio decreases with an increase in Cr concentration, and it has been found to increase at higher Cr concentration, indicating the disorder in the coating. Carbide is formed in Cr-doped DLC coatings as observed from XPS studies. There is a decrease in sp 3/ sp 2 ratios with an increase in Cr concentration, and it increases again at higher Cr concentration. Nanohardness studies show no clear dependence of hardness on Cr concentration. DLC coatings with lower Cr contents have demonstrated better corrosion resistance with better passive behavior in 3.5% NaCl solution, and corrosion potential is observed to move toward nobler (more positive) values. A low coefficient of friction (0.15) at different loads is observed from reciprocating wear studies. Lower wear volume is found at all loads on the Cr-doped DLC coatings. Wear mechanism changes from abrasive wear on the substrate to adhesive wear on the coating.

Effect of ethylene glycol doping on performance of PEDOT:PSS/µT-n-Si heterojunction solar cell

NASA Astrophysics Data System (ADS)

Singh, Prashant; Nakra, Rohan; Sivaiah, B.; Sardana, Sanjay K.; Prathap, P.; Rauthan, C. M. S.; Srivastava, Sanjay K.

2018-05-01

This study reports effect of co-solvent doping in poly (3, 4-ethyelenedioxythiophene):poly(dimethyl sulfoxide) (PEDOT:PSS) over the performance of Ag/PEDOT:PSS/µT-n-Si/In:Ga architecture based solar cell. PEDOT:PSS polymer is doped with varying concentration of ethylene glycol (EG). At 10% (volume) concentration performance of the device is highest with 4.69% power conversion efficiency. At higher or lower concentrations of ethylene glycol device performance deteriorates with sharp decline in short-circuit current density. Improvement in conductivity of the PEDOT:PSS polymer due to addition of co-solvent is the reason behind improvement in the performance of the device efficiency.

Effects of ionizing radiations on the optical properties of ionic copper-activated sol-gel silica glasses

NASA Astrophysics Data System (ADS)

Al Helou, Nissrine; El Hamzaoui, Hicham; Capoen, Bruno; Ouerdane, Youcef; Boukenter, Aziz; Girard, Sylvain; Bouazaoui, Mohamed

2018-01-01

Studying the impact of radiations on doped silica glasses is essential for several technological applications. Herein, bulk silica glasses, activated with various concentrations of luminescent monovalent copper (Cu+), have been prepared using the sol-gel technique. Thereafter, these glasses were subjected to X- or γ-rays irradiation at 1 MGy(SiO2) accumulated dose. The effect of these ionizing radiations on the optical properties of these glasses, as a function of the Cu-doping content, were investigated using optical absorption and photoluminescence spectroscopies. Before any irradiation, the glass with the lowest copper concentration exhibits blue and green luminescence bands under UV excitation, suggesting that Cu+ ions occupy both cubic and tetragonal symmetry sites. However, at higher Cu-doping level, only the green emission band exists. Moreover, we showed that the hydroxyl content decreases with increasing copper doping concentration. Both X and γ radiation exposures induced visible absorption due to HC1 color centers in the highly Cu-doped glasses. In the case of the lower Cu-doped glass, the Cu+ sites with a cubic symmetry are transformed into sites with tetragonal symmetry.

Distribution of caffeine levels in urine in different sports in relation to doping control before and after the removal of caffeine from the WADA doping list.

PubMed

Van Thuyne, W; Delbeke, F T

2006-09-01

Caffeine concentrations were measured in the urine of 4633 athletes tested for doping control in the Ghent Doping Control Laboratory in 2004. Determination of these concentrations was done using an alkaline extraction with a mixture of dichloromethane and methanol (9 : 1; v/v) followed by high performance liquid chromatography and ultraviolet detection (HPLC-UV). The method was validated according to ISO 17 025 standards (International Organisation for Standardisation). Quantification was done by using a linear calibration curve in the range from 0 to 20 microg/ml. The limit of quantification (LOQ) was 0.10 microg/ml. Because the results were not normally distributed, transformation of the data was done to evaluate the difference in detected concentrations in several sports. This resulted in an overall average concentration of 1.12 +/- 2.68 microg/ml. Comparison of the most frequently tested sports in 2004 demonstrated that caffeine concentrations in samples originating from power lifters are significantly higher in comparison to urines taken in other sports. Also, a significant difference between caffeine concentrations found in cycling and concentrations found in other sports, including athletics and some ball sports, was observed. A comparison was made between results obtained in 2004 and results obtained before the removal of caffeine from the WADA (World Anti-Doping Agency) doping list indicating that average caffeine concentrations decreased after the withdrawal of caffeine from the list of prohibited substances. The overall percentage of positive samples between the two periods remained the same although the percentage of positive samples noticed in cycling increased after the removal of caffeine from the doping list.

Electrochemically synthesis and optoelectronic properties of Pb- and Zn-doped nanostructured SnSe films

NASA Astrophysics Data System (ADS)

Jamali-Sheini, Farid; Cheraghizade, Mohsen; Yousefi, Ramin

2018-06-01

In this study, electrodeposition technique was applied to deposit un-, lead (Pb), and zinc (Zn)-doped SnSe films. X-ray diffraction (XRD) patterns of the films showed a polycrystalline SnSe phase with orthorhombic crystalline lattice. SEM images revealed ball-shaped, rod-shaped, and wire-shaped morphologies for SnSe films. Moreover, optical measurements indicated incorporation of dopant in the crystalline lattice of films by varying the optical energy band gap. Electrical characterization of Pb- and Zn-doped SnSe films showed their p-type nature. Finally, the solar cell device fabricated using the Zn-doped SnSe films reveal a higher efficiency because of their higher carrier concentration.

Enhancement of the Ultraviolet Photoresponsivity of Al-doped ZnO Thin Films Prepared by using the Sol-gel Spin-coating Method

NASA Astrophysics Data System (ADS)

Lee, Wookbin; Leem, Jae-Young

2018-03-01

We report the structural, morphological, optical, and ultraviolet (UV) photoresponse properties of Al-doped ZnO (AZO) thin films prepared on silicon substrates with different Al doping concentrations by using the sol-gel spin-coating method. An analysis of the X-ray diffraction patterns of the AZO thin films revealed that the average grain size decreased and the c-axis lattice constant increased with Al content. The field-emission scanning electron microscopy images showed that with Al doping, the grain size decreased, but the film density increased with increasing Al doping concentration from 0% to 3%. These results indicate that the surface area of the film increased with increasing Al doping. The absorbance spectra revealed that the UV absorbance of the AZO thin films increased with increasing Al doping concentration and that the absorption onset shifted towards lower energies. The photoluminescence spectra revealed that with increasing Al doping, the intensity of the visible emission greatly decreased and the visible emission peak shifted forward lower energy (a red shift). The UV sensor based on the AZO thin films exhibited a higher responsivity than that based on the undoped ZnO thin film. Therefore, this study provides a facile method for improving the photoresponsivity of UV sensors.

The Effect of High N-DOPED Anatase TiO2 on the Band Gap Narrowing and Redshift by First-Principles

NASA Astrophysics Data System (ADS)

Hou, Qingyu; Jin, Yongjun; Ying, Chun; Zhao, Erjun; Zhang, Yue; Dong, Hongying

2012-10-01

Anatase TiO2 supercells were studied by first-principles, in which one was undoped and another three were high N-doping. Partial densities of states, band structure, population and absorption spectrum were calculated. The calculated results indicated that in the condition of TiO2-xNx (x = 0.0625, 0.125, 0.25), the higher the doping concentration is, the shorter will be the lattice parameters parallel to the direction of c-axis. The strength of covalent bond significantly varied. The formation energy increases at first, and then decreases. The doping models become less stable as N-doping concentration increases. Meanwhile, the narrower the band gap is, the more significant will be the redshift, which is in agreement with the experimental results.

An insight into the origin of room-temperature ferromagnetism in SnO2 and Mn-doped SnO2 quantum dots: an experimental and DFT approach.

PubMed

Manikandan, Dhamodaran; Boukhvalov, D W; Amirthapandian, S; Zhidkov, I S; Kukharenko, A I; Cholakh, S O; Kurmaev, E Z; Murugan, Ramaswamy

2018-02-28

SnO 2 and Mn-doped SnO 2 single-phase tetragonal crystal structure quantum dots (QDs) of uniform size with control over dopant composition and microstructure were synthesized using the high pressure microwave synthesis technique. On a broader vision, we systematically investigated the influence of dilute Mn ions in SnO 2 under the strong quantum confinement regime through various experimental techniques and density functional theoretical (DFT) calculations to disclose the physical mechanism governing the observed ferromagnetism. DFT calculations revealed that the formation of the stable (001) surface was much more energetically favorable than that of the (100) surface, and the formation energy of the oxygen vacancies in the stable (001) surface was comparatively higher in the undoped SnO 2 QDs. X-ray photoelectron spectroscopy (XPS) and first-principles modeling of doped QDs revealed that the lower doping concentration of Mn favored the formation of MnO-like (Mn 2+ ) structures in defect-rich areas and the higher doping concentration of Mn led to the formation of multiple configurations of Mn (Mn 2+ and Mn 3+ ) in the stable surfaces of SnO 2 QDs. Electronic absorption spectra indicated the characteristic spin allowed ligand field transitions of Mn 2+ and Mn 3+ and the red shift in the band gap. DFT calculations clearly indicated that only the substitutional dopant antiferromagnetic configurations were more energetically favorable. The gradual increase of magnetization at a low level of Mn-doping could be explained by the prevalence of antiferromagnetic manganese-vacancy pairs. Higher concentrations of Mn led to the appearance of ferromagnetic interactions between manganese and oxygen vacancies. The increase in the concentration of metallic dopants caused not just an increase in the total magnetic moment of the system but also changed the magnetic interactions between the magnetic moments on the metal ions and oxygen. The present study provides new insight into the fundamental understanding of the origin of ferromagnetism in transition metal-doped QDs.

Synthesis of n-type semiconductor diamond single crystal under high pressure and high temperature

NASA Astrophysics Data System (ADS)

Li, Yong; Li, Shangsheng; Song, Mousheng; She, Yanchao; Wang, Qiang; Guan, Xuemao

2017-12-01

In this paper, diamond single crystal co-doped with sulfur and boron was successfully synthesized at the fixed pressure of 6.0 GPa and temperature range of 1535 K. Sulfur was detected in the co-doped diamond by Fourier Transform Infrared Spectroscopy (FTIR) and the corresponding characteristic peak located at 848 cm-1. Interestingly, Hall effect measurements indicated that the diamond co-doped with sulfur and boron exhibited n-type semiconductor behaviour. Furthermore, the Hall mobility and carrier concentration of the co-doped diamond higher than those of the boron-doping diamond.

A computational study on the electronic and field emission properties of Mg and Si doped AlN nanocones

NASA Astrophysics Data System (ADS)

Saedi, Leila; Soleymanabadi, Hamed; Panahyab, Ataollah

2018-05-01

Following an experimental work, we explored the effect of replacing an Al atom of an AlN nanocone by Si or Mg atom on its electronic and field emission properties using density functional theory calculations. We found that both Si-doping and Mg-doping increase the electrical conductivity of AlN nanocone, but their influences on the filed emission properties are significantly different. The Si-doping increases the electron concentration of AlN nanocone and results in a large electron mobility and a low work function, whereas Mg-doping leads to a high hole concentration below the conduction level and increases the work function in agreement with the experimental results. It is predicted that Si-doped AlN nanocones show excellent filed emission performance with higher emitted electron current density compared to the pristine AlN nanocone. But the Mg-doping meaningfully decreases the emitted electron current density from the surface of AlN nanocone. The Mg-doping can increase the work function about 41.9% and the Si-doping can decrease it about 6.3%. The Mg-doping and Si-doping convert the AlN nanocone to a p-type and n-type semiconductors, respectively. Our results explain in a molecular level what observed in the experiment.

Ex situ n+ doping of GeSn alloys via non-equilibrium processing

NASA Astrophysics Data System (ADS)

Prucnal, S.; Berencén, Y.; Wang, M.; Rebohle, L.; Böttger, R.; Fischer, I. A.; Augel, L.; Oehme, M.; Schulze, J.; Voelskow, M.; Helm, M.; Skorupa, W.; Zhou, S.

2018-06-01

Full integration of Ge-based alloys like GeSn with complementary-metal-oxide-semiconductor technology would require the fabrication of p- and n-type doped regions for both planar and tri-dimensional device architectures which is challenging using in situ doping techniques. In this work, we report on the influence of ex situ doping on the structural, electrical and optical properties of GeSn alloys. n-type doping is realized by P implantation into GeSn alloy layers grown by molecular beam epitaxy (MBE) followed by flash lamp annealing. We show that effective carrier concentration of up to 1 × 1019 cm‑3 can be achieved without affecting the Sn distribution. Sn segregation at the surface accompanied with an Sn diffusion towards the crystalline/amorphous GeSn interface is found at P fluences higher than 3 × 1015 cm‑2 and electron concentration of about 4 × 1019 cm‑3. The optical and structural properties of ion-implanted GeSn layers are comparable with the in situ doped MBE grown layers.

Determination of n-Type Doping Level in Single GaAs Nanowires by Cathodoluminescence.

PubMed

Chen, Hung-Ling; Himwas, Chalermchai; Scaccabarozzi, Andrea; Rale, Pierre; Oehler, Fabrice; Lemaître, Aristide; Lombez, Laurent; Guillemoles, Jean-François; Tchernycheva, Maria; Harmand, Jean-Christophe; Cattoni, Andrea; Collin, Stéphane

2017-11-08

We present an effective method of determining the doping level in n-type III-V semiconductors at the nanoscale. Low-temperature and room-temperature cathodoluminescence (CL) measurements are carried out on single Si-doped GaAs nanowires. The spectral shift to higher energy (Burstein-Moss shift) and the broadening of luminescence spectra are signatures of increased electron densities. They are compared to the CL spectra of calibrated Si-doped GaAs layers, whose doping levels are determined by Hall measurements. We apply the generalized Planck's law to fit the whole spectra, taking into account the electron occupation in the conduction band, the bandgap narrowing, and band tails. The electron Fermi levels are used to determine the free electron concentrations, and we infer nanowire doping of 6 × 10 17 to 1 × 10 18  cm -3 . These results show that cathodoluminescence provides a robust way to probe carrier concentrations in semiconductors with the possibility of mapping spatial inhomogeneities at the nanoscale.

The origin of current blocking in interfacial conduction in Sr-doped lanthanum gallates

NASA Astrophysics Data System (ADS)

Park, Hee Jung

2018-02-01

The grain boundary transport of lanthanum gallate has been studied with various doping concentrations, and the origins of blocking on the grain boundary are compared. La1-xSrxGaO3 samples (x = 0.005, 0.01, 0.05 and 0.1) have been prepared and their bulk (grain) and grain boundary resistances been experimentally measured as a function of temperature (T: 200-550 °C) and oxygen partial pressure (Po2) using ac-impedance measurements. In addition, Hebb-Wagner polarization measurements have been conducted to investigate the electrical conductivity of minor charge carriers in the lanthanum gallates. The grain boundary resistance in the low-doped materials (x = 0.005 and 0.01) increases with increasing Po2 while in the highly-doped materials (x = 0.05, 0.1) it hardly depended on Po2. At lower concentrations conduction is mixed and at higher concentrations is found to be predominantly ionic conductivity. The space charge model successfully describes the mixed conduction at the grain boundary at low-doping, but does not explain the predominant ionic conductivity at high-doping. The origin of blocking at high-doping is explained by the crystallographic asymmetry of the grain boundary with respect to the bulk and/or Sr-segregation.

Enhanced photoelectrochemical and optical performance of ZnO films tuned by Cr doping

NASA Astrophysics Data System (ADS)

Salem, M.; Akir, S.; Massoudi, I.; Litaiem, Y.; Gaidi, M.; Khirouni, K.

2017-04-01

In this paper, pure and Cr-doped nanostructured Zinc oxide thin films were synthesized by simple and low cost co-precipitation and spin-coating method with Cr concentration varying between 0.5 and 5 at.%. Crystalline structure of the prepared films was investigated by X-ray diffraction (XRD) and Raman spectroscopy techniques. XRD analysis indicated that the films were indexed as the hexagonal phase of wurtzite-type structure and demonstrated a decrease in the crystallite size with increasing Cr doping content. Cr doping revealed a significant effect on the optical measurements such as transmission and photoluminescence properties. The optical measurements indicated that Cr doping decreases the optical band gap and it has been shifted from 3.41 eV for pure ZnO film to 3.31 eV for 5 at.% Cr-doped one. The photoelectrochemical (PEC) sensing characteristics of Cr-doped ZnO layers were investigated. Amongst all photo-anodes with different Cr dopant concentration, the 2 at.% Cr incorporated ZnO films exhibited fast response and higher photoconduction sensitivity.

Supercritical temperature synthesis of fluorine-doped VO2(M) nanoparticle with improved thermochromic property

NASA Astrophysics Data System (ADS)

Riapanitra, Anung; Asakura, Yusuke; Cao, Wenbin; Noda, Yasuto; Yin, Shu

2018-06-01

Fluorine-doped VO2(M) nanoparticles have been successfully synthesized using the hydrothermal method at a supercritical temperature of 490 °C. The pristine VO2(M) has the critical phase transformation temperature of 64 °C. The morphology and homogeneity of the monoclinic structure VO2(M) were adopted by the fluorine-doped system. The obtained particle size of the samples is smaller at the higher concentration of anion doping. The best reduction of critical temperature was achieved by fluorine doping of 0.13% up to 48 °C. The thin films of the fluorine-doped VO2(M) showed pronounced thermochromic property and therefore are suitable for smart window applications.

Facile hydrothermal synthesis and characterization of cesium-doped PbI2 nanostructures for optoelectronic, radiation detection and photocatalytic applications

NASA Astrophysics Data System (ADS)

Shkir, Mohd; AlFaify, S.; Yahia, I. S.; Hamdy, Mohamed S.; Ganesh, V.; Algarni, H.

2017-10-01

Low-temperature hydrothermal-assisted synthesis of pure and cesium (Cs) (1, 3, 5, 7 and 10 wt%) doped lead iodide (PbI2) nanorods and nanosheets have been achieved successfully for the first time. The structural and vibrational studies confirm the formation of a 2H-polytypic PbI2 predominantly. Scanning electron microscope analysis confirms the formation of well-aligned nanorods of average size 100 nm at low concentration and nanosheets of average thicknesses in the range of 20-40 nm at higher concentrations of Cs doping. The presence of Cs doping was confirmed by energy dispersive X-ray study. Ultra-violet-visible absorbance spectra were recorded, and energy gap was calculated in the range of 3.33 to 3.45 eV for pure and Cs-doped PbI2 nanostructures which is higher than the bulk value (i.e., 2.27 eV) due to quantum confinement effect. Dielectric constant, loss, and AC conductivity studies have been done. Enhancement in Gamma linear absorption coefficient due to Cs doping confirms the suitability of prepared nanostructures for radiation detection applications. Furthermore, the photocatalytic performance of the synthesized nanostructures was evaluated in the decolorization of methyl green (MG) and methyl orange (MO) under the illumination of visible light (λ > 420 nm). The observed photocatalytic activity for 5 and 7 wt% Cs-doped PbI2 was observed to be more than pure PbI2 and also > 10 times higher than the commercially available photocatalysts. The results suggest that the prepared nanostructures are highly applicable in optoelectronic, radiation detection and many other applications. [Figure not available: see fulltext.

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.

Tuning the morphology, stability and photocatalytic activity of TiO{sub 2} nanocrystal colloids by tungsten doping

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

Xu, Haiping; Liao, Jianhua; School of Pharmaceutical Sciences, Gannan Medical University, Ganzhou, Jiangxi 341000

2014-03-01

Graphical abstract: - Highlights: • W{sup 6+}-doped TiO{sub 2} nanocrystal colloids were prepared by hydrothermal methods. • The properties of TiO{sub 2} nanocrystal colloids can be tuned by tungsten doping. • W{sup 6+}-doped TiO{sub 2} nanocrystal colloids show higher stability and dispersity. • W{sup 6+}-doped TiO{sub 2} nanocrystal colloids show higher photocatalytic activity. - Abstract: The effects of tungsten doping on the morphology, stability and photocatalytic activity of TiO{sub 2} nanocrystal colloids were investigated. The nanostructure, chemical state of Ti, W, O, and the properties of tungsten doped TiO{sub 2} samples were investigated carefully by TEM, XRD, XPS, UV–vis, PLmore » and photocatalytic degradation experiments. And the structure–activity relationship was discussed according to the analysis and measurement results. The analysis results reveal that the morphology, zeta potential and photocatalytic activity of TiO{sub 2} nanocrystals can be easily tuned by changing the tungsten doping concentration. The tungsten doped TiO{sub 2} colloid combines the characters of high dispersity and high photocatalytic activity.« less

Fluorescence properties and white light generation from Dy3+-doped niobium phosphate glasses

NASA Astrophysics Data System (ADS)

Srihari, T.; Jayasankar, C. K.

2017-07-01

Niobium phosphate glasses (P2O5+Nb2O5+K2O + Al2O3+Dy2O3) doped with different concentrations of Dy3+ ions have been synthesized by melt quenching technique and characterized through structural and optical measurements to evaluate the fluorescence properties and find their suitability for white light emitting diodes (LEDs). Phonon energy and vibrational groups of the host matrix have been analyzed from Raman spectra. Judd-Ofelt analysis has been applied for 1.0 mol% Dy2O3-doped glass and inturn radiative properties have been evaluated for excited states of the Dy3+ ion. The higher value of stimulated emission cross-section (σe = 6.4 × 10-21 cm2) for the 4F9/2 → 6H13/2 level confirms its potentiality to be used as yellow laser. The decay curves exhibit non-exponential nature at higher concentrations (≥1 mol %) of Dy3+ ion. From the decay curve analysis, the quantum efficiency for the 4F9/2 level of 1.0 mol % Dy3+-doped glass is found to be 92%. The yellow to blue intensity ratios and chromaticity color co-ordinates are found to vary with Dy3+ ion concentrations/excitation wavelengths and are within the white light region.

Effects of Mg pre-flow, memory, and diffusion on the growth of p-GaN with MOCVD (Conference Presentation)

NASA Astrophysics Data System (ADS)

Tu, Charng-Gan; Chen, Hao-Tsung; Chen, Sheng-Hung; Chao, Chen-Yao; Kiang, Yean-Woei; Yang, Chih-Chung

2017-02-01

In MOCVD growth, two key factors for growing a p-type structure, when the modulation growth or delta-doping technique is used, include Mg memory and diffusion. With high-temperature growth (>900 degree C), doped Mg can diffuse into the under-layer. Also, due to the high-pressure growth and growth chamber coating in MOCVD, plenty Mg atoms exist in the growth chamber for a duration after Mg supply is ended. In this situation, Mg doping continues in the following designated un-doped layers. In this paper, we demonstrate the study results of Mg preflow, memory, and diffusion. The results show that pre-flow of Mg into the growth chamber can lead to a significantly higher Mg doping concentration in growing a p-GaN layer. In other words, a duration for Mg buildup is required for high Mg incorporation. Based on SIMS study, we find that with the pre-flow growth, a high- and a low-doping p-GaN layer are formed. The doping concentration difference between the two layers is about 10 times. The thickness of the high- (low-) doping layer is about 40 (65) nm. The growth of the high-doping layer starts 10-15 min after Mg supply starts (Mg buildup time). The diffusion length of Mg into the AlGaN layer beneath (Mg content reduced to <5%) is about 10 nm. The memory time of Mg in the growth chamber is about 60 min, after which the Mg doping concentration is reduced to <1%.

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.

UV-light-induced one-color and two-color photorefractive effects in congruent and near-stoichiometric LiNbO 3:Mg crystals

NASA Astrophysics Data System (ADS)

Qiao, Haijun; Xu, Jingjun; Tomita, Yasuo; Zhu, Dengsong; Fu, Bo; Zhang, Guoquan; Zhang, Guangyin

2007-03-01

We describe the ultraviolet-light one-color photorefraction (UV-OPR) at 351 nm in LiNbO3 crystals with different Mg-doping concentrations and [Li]/[Nb] ratios. It is shown that as the Mg-doping concentration and/or the [Li]/[Nb] ratio increase, the refractive index change and the two-beam coupling gain increase but the response time decreases. It is also shown that the recording sensitivity as large as ∼27 cm/J is obtainable at a recording intensity of ∼1 W/cm2 in near-stoichiometric LiNbO3 doped with 2 mol% Mg. This sensitivity is approximately one order of magnitude higher than those for other LiNbO3 crystals. We also describe the ultraviolet-light-gating two-color photorefraction (UV-TPR) using 365 nm gating and 633 nm recording beams in LiNbO3 crystals with different Mg-doping concentrations and [Li]/[Nb] ratios. It is shown that UV-TPR is only observed in near-stoichiometric crystals and the grating-formation dynamics strongly depend on the Mg concentration.

Estimation of free carrier concentrations in high-quality heavily doped GaN:Si micro-rods by photoluminescence and Raman spectroscopy

NASA Astrophysics Data System (ADS)

Mohajerani, M. S.; Khachadorian, S.; Nenstiel, C.; Schimpke, T.; Avramescu, A.; Strassburg, M.; Hoffmann, A.; Waag, A.

2016-03-01

The controlled growth of highly n-doped GaN micro rods is one of the major challenges in the fabrication of recently developed three-dimensional (3D) core-shell light emitting diodes (LEDs). In such structures with a large active area, higher electrical conductivity is needed to achieve higher current density. In this contribution, we introduce high quality heavily-doped GaN:Si micro-rods which are key elements of the newly developed 3D core-shell LEDs. These structures were grown by metal-organic vapor phase epitaxy (MOVPE) using selective area growth (SAG). We employed spatially resolved micro-Raman and micro-photoluminescence (PL) in order to directly determine a free-carrier concentration profile in individual GaN micro-rods. By Raman spectroscopy, we analyze the low-frequency branch of the longitudinal optical (LO)-phonon-plasmon coupled modes and estimate free carrier concentrations from ≍ 2.4 × 1019 cm-3 up to ≍ 1.5 × 1020 cm-3. Furthermore, free carrier concentrations are determined by estimating Fermi energy level from the near band edge emission measured by low-temperature PL. The results from both methods reveal a good consistency.

AC conductivity studies of La doped Ba0.5Sr0.5TiO3

NASA Astrophysics Data System (ADS)

D'Souza, Slavia Deeksha; Rohith, Kotla Surya; Bhatnagar, Anil K.; Kumar, A. Sendil

2017-05-01

Ferroelectric material with high dielectric constant of Ba0.5Sr0.5TiO3 is synthesized through Solid State Reaction and fraction of Lanthanum is substituted to introduce hole concentration. XRay Diffraction shows all the samples are stabilized in cubic crystal structure. With La doped samples the Cole-Cole plot is modified and AC conductivity increases at higher temperatures as well as higher frequencies compared to undoped sample.

Hole transport in pure and doped hematite

NASA Astrophysics Data System (ADS)

Liao, Peilin; Carter, Emily A.

2012-07-01

Hematite (α-Fe2O3) is a promising candidate for use in photovoltaic (PV) and photoelectrochemical devices. Its poor conductivity is one major drawback. Doping hematite either p-type or n-type greatly enhances its measured conductivity and is required for potential p-n junctions in PVs. Here, we study hole transport in pure and doped hematite using an electrostatically embedded cluster model with ab initio quantum mechanics (unrestricted Hartree-Fock theory). Consistent with previous work, the model suggests that hole hopping is via oxygen anions for pure hematite. The activation energy for hole mobility is predicted to be at least 0.1 eV higher than the activation energy for electron mobility, consistent with the trend observed in experiments. We examine four dopants—magnesium(II), nickel(II), copper(II), and manganese(II/III) in direct cation substitution sites—to gain insight into the mechanism by which conductivity is improved. The activation energies are used to assess qualitative effects of different dopants. The hole carriers are predicted to be attracted to O anions near the dopants. The magnitude of the trapping effect is similar among the four dopants in their +2 oxidation states. The multivalent character of Mn doping facilitates local hole transport around Mn centers via a low-barrier O-Mn-O pathway, which suggests that higher hole mobility can be achieved with increasing Mn doping concentration, especially when a network of these low-barrier pathways is produced. Our results suggest that the experimentally observed conductivity increase in Mg-, Ni-, and Cu-doped p-type hematite is mostly due to an increase in hole carriers rather than improved mobility, and that Mg-, Ni-, and Cu-doping perform similarly, while the conductivity of Mn-doped hematite might be significantly improved in the high doping concentration limit.

Poor fluorinated graphene sheets carboxymethylcellulose polymer composite mode locker for erbium doped fiber laser

NASA Astrophysics Data System (ADS)

Mou, Chengbo; Arif, Raz; Lobach, Anatoly S.; Khudyakov, Dmitry V.; Spitsina, Nataliya G.; Kazakov, Valery A.; Turitsyn, Sergei; Rozhin, Aleksey

2015-02-01

We report poor fluorinated graphene sheets produced by thermal exfoliation embedding in carboxymethylcellulose polymer composite (GCMC) as an efficient mode locker for erbium doped fiber laser. Two GCMC mode lockers with different concentration have been fabricated. The GCMC based mode locked fiber laser shows stable soliton output pulse shaping with repetition rate of 28.5 MHz and output power of 5.5 mW was achieved with the high concentration GCMC, while a slightly higher output power of 6.9 mW was obtained using the low concentration GCMC mode locker.

Poor fluorinated graphene sheets carboxymethylcellulose polymer composite mode locker for erbium doped fiber laser

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

Mou, Chengbo, E-mail: mouc1@aston.ac.uk, E-mail: a.rozhin@aston.ac.uk; Turitsyn, Sergei; Rozhin, Aleksey, E-mail: mouc1@aston.ac.uk, E-mail: a.rozhin@aston.ac.uk

We report poor fluorinated graphene sheets produced by thermal exfoliation embedding in carboxymethylcellulose polymer composite (GCMC) as an efficient mode locker for erbium doped fiber laser. Two GCMC mode lockers with different concentration have been fabricated. The GCMC based mode locked fiber laser shows stable soliton output pulse shaping with repetition rate of 28.5 MHz and output power of 5.5 mW was achieved with the high concentration GCMC, while a slightly higher output power of 6.9 mW was obtained using the low concentration GCMC mode locker.

Diffusion and Stability of Hydrogen in Mg-Doped GaN: A Density Functional Study

NASA Astrophysics Data System (ADS)

Park, Ji-Sang; Chang, Kee Joo

2012-06-01

Using hybrid functional calculations, we study the diffusion and thermal stability of hydrogen in Mg-doped GaN. Compared with the generalized gradient approximation, we obtain a higher activation barrier for dissociating a Mg-H complex, which is attributed to the increase in the binding energy of Mg-H. Kinetic Monte Carlo simulations yield the annealing temperature of around 800 °C for activating Mg acceptors, close to the measured values. The results provide an insight to understanding the annealing effect such that the annealing temperature generally increases with the Mg-H concentration, and the retrapping of H is partly responsible for the low doping efficiencies at high Mg concentrations.

Physicochemical Properties and Cellular Responses of Strontium-Doped Gypsum Biomaterials

PubMed Central

Pouria, Amir; Bandegani, Hadis; Pourbaghi-Masouleh, Milad; Hesaraki, Saeed; Alizadeh, Masoud

2012-01-01

This paper describes some physical, structural, and biological properties of gypsum bioceramics doped with various amounts of strontium ions (0.19–2.23 wt%) and compares these properties with those of a pure gypsum as control. Strontium-doped gypsum (gypsum:Sr) was obtained by mixing calcium sulfate hemihydrate powder and solutions of strontium nitrate followed by washing the specimens with distilled water to remove residual salts. Gypsum was the only phase found in the composition of both pure and gypsum:Sr, meanwhile a shift into lower diffraction angles was observed in the X-ray diffraction patterns of doped specimens. Microstructure of all gypsum specimens consisted of many rod-like small crystals entangled to each other with more elongation and higher thickness in the case of gypsum:Sr. The Sr-doped sample exhibited higher compressive strength and lower solubility than pure gypsum. A continuous release of strontium ions was observed from the gypsum:Sr during soaking it in simulated body fluid for 14 days. Compared to pure gypsum, the osteoblasts cultured on strontium-doped samples showed better proliferation rate and higher alkaline phosphatase activity, depending on Sr concentration. These observations can predict better in vivo behavior of strontium-doped gypsum compared to pure one. PMID:22719270

Thermoluminescence (TL) dosimeter of dysprosium doped strontium borate glass for different glass modifiers (Na, Li, Ca) subjected from 1 to 9 Gy doses

NASA Astrophysics Data System (ADS)

Hamzah, S. A.; Saeed, M. A.; Wagiran, H.; Hashim, I. H.

2017-10-01

This article reports TL response for different glass modifier and doping concentration. Alkali oxides (Na2O and Li2O) and alkali earth oxide (CaO) will be used as a glass modifier for strontium borate based glass. The samples were prepared by melt quenching technique. Dy2O3 concentrations ranging from 0.00 to 0.70 mol% and exposure doses of 1 to 9 Gy will be varied. All glass samples exhibit the prominent peak temperature positioned at 186 oC to 232 oC. From all the samples, one of the samples shows an excellent linearity dose response, higher TL and show good reproducibility after 5 cycles exposure which is sodium strontium borate doped with 0.1 mol% Dy2O3 (optimum concentration).

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

Dholabhai, Pratik P., E-mail: pratik.dholabhai@asu.ed; Anwar, Shahriar, E-mail: anwar@asu.ed; Adams, James B., E-mail: jim.adams@asu.ed

Kinetic lattice Monte Carlo (KLMC) model is developed for investigating oxygen vacancy diffusion in praseodymium-doped ceria. The current approach uses a database of activation energies for oxygen vacancy migration, calculated using first-principles, for various migration pathways in praseodymium-doped ceria. Since the first-principles calculations revealed significant vacancy-vacancy repulsion, we investigate the importance of that effect by conducting simulations with and without a repulsive interaction. Initially, as dopant concentrations increase, vacancy concentration and thus conductivity increases. However, at higher concentrations, vacancies interfere and repel one another, and dopants trap vacancies, creating a 'traffic jam' that decreases conductivity, which is consistent with themore » experimental findings. The modeled effective activation energy for vacancy migration slightly increased with increasing dopant concentration in qualitative agreement with the experiment. The current methodology comprising a blend of first-principle calculations and KLMC model provides a very powerful fundamental tool for predicting the optimal dopant concentration in ceria related materials. -- graphical abstract: Ionic conductivity in praseodymium doped ceria as a function of dopant concentration calculated using the kinetic lattice Monte Carlo vacancy-repelling model, which predicts the optimal composition for achieving maximum conductivity. Display Omitted Research highlights: {yields} KLMC method calculates the accurate time-dependent diffusion of oxygen vacancies. {yields} KLMC-VR model predicts a dopant concentration of {approx}15-20% to be optimal in PDC. {yields} At higher dopant concentration, vacancies interfere and repel one another, and dopants trap vacancies. {yields} Activation energy for vacancy migration increases as a function of dopant content« less

Magnetic properties of Fe-doped organic-inorganic nanohybrids

NASA Astrophysics Data System (ADS)

Silva, N. J. O.; Amaral, V. S.; Carlos, L. D.; de Zea Bermudez, V.

2003-05-01

We present a magnetic study of Fe-doped diureasils (siloxane-based networks to which poly(ethylene oxide)-based chains are grafted by urea cross linkages doped with Fe(II) or Fe(III) ions. Structural studies show that the Fe(II) ions interact mainly with the organic chain, whereas the incorporation of Fe(III) leads to the formation of iron-based nanoclusters, with radius increasing from 20 to 40 Å. Fe(II)-doped samples behave as simple paramagnets, with μeff=5.32μB. Fe(III)-doped hybrids present antiferromagnetic interactions, with TN increasing with Fe(III) concentration up to 13.6 K for 6% doping. Thermal irreversibility was observed below ˜40 K and is stronger for higher concentrations. The coercive fields (HC) are of the order of 1000 Oe at 5 K. Hysteresis cycles are shifted to negative fields, revealing the presence of exchange anisotropy interactions with exchange fields (HE) of the order of 100 Oe. Both fields decrease rapidly with increasing temperature. We analyze this behavior in terms of the contribution of surface spin disorder to exchange anisotropy.

Improving the selective cancer killing ability of ZnO nanoparticles using Fe doping.

PubMed

Thurber, Aaron; Wingett, Denise G; Rasmussen, John W; Layne, Janet; Johnson, Lydia; Tenne, Dmitri A; Zhang, Jianhui; Hanna, Charles B; Punnoose, Alex

2012-06-01

This work reports a new method to improve our recent demonstration of zinc oxide (ZnO) nanoparticles (NPs) selectively killing certain human cancer cells, achieved by incorporating Fe ions into the NPs. Thoroughly characterized cationic ZnO NPs (∼6 nm) doped with Fe ions (Zn(1-x )Fe (x) O, x = 0-0.15) were used in this work, applied at a concentration of 24 μg/ml. Cytotoxicity studies using flow cytometry on Jurkat leukemic cancer cells show cell viability drops from about 43% for undoped ZnO NPs to 15% for ZnO NPs doped with 7.5% Fe. However, the trend reverses and cell viability increases with higher Fe concentrations. The non-immortalized human T cells are markedly more resistant to Fe-doped ZnO NPs than cancerous T cells, confirming that Fe-doped samples still maintain selective toxicity to cancer cells. Pure iron oxide samples displayed no appreciable toxicity. Reactive oxygen species generated with NP introduction to cells increased with increasing Fe up to 7.5% and decreased for >7.5% doping.

Materials, properties, and applications of nitrogen-doped organic semiconductors

NASA Astrophysics Data System (ADS)

Chan, Calvin Kar-Fai

As organic semiconducting materials draw increasing attention for many promising applications, including efficient organic light-emitting diodes (OLEDs), large-area organic photovoltaic (OPV) cells, and flexible organic thin-film transistors (OTFTs), chemical doping of organic materials is emerging as an important technique for overcoming performance deficiencies and material limitations of intrinsic organic films. Although p-doping has been amply demonstrated, molecular n-type doping has been difficult to study because of the inherent instability of easily oxidized n-dopants. In this work, the facile use of two low ionization energy (IE) small molecules that are suitable for n-doping a wide range of organic electronic materials is demonstrated. Cobaltocene (CoCp2) and its derivative, decamethylcobaltocene ( CoCp*2 ), were found to have fairly low IEs for organic compounds. Co-deposition of the n-dopants with different host molecules results in pronounced shifts of the Fermi-level towards unoccupied molecular states, indicating a significant increase in electron concentration. The Fermi-level shifts, measured with ultra-violet photoemission spectroscopy (UPS), are correlated with excess carrier densities using a model based on Fermi-Dirac (F-D) statistics and a Gaussian distributed density of states. The calculated electron densities suggest full dopant ionization at low concentrations, and diminished efficiency at high donor concentrations. The concentration of incorporated dopants is examined by chemical composition analysis of doped films using X-ray photoemission spectroscopy (XPS). Atomic concentration depth profiling determined by Rutherford backscattering (RBS) suggests that the incorporation of CoCp2 and CoCp*2 is well-controlled and the dopants are minimally diffusive. Organic films n-doped using CoCp2 and CoCp*2 show several orders of magnitude increase in current density resulting from both enhanced electron injection and increased electron conductivity in the bulk. Increases in the bulk conductivity suggest both improved electron mobility and higher electron concentrations. These findings are applied with previous work on p-doping to fabricate organic p-i-n homojunction devices that exhibit strong rectification and large built-in potentials. Heterojunction OPVs using undoped CuPc and n-doped C60 display significant increases in open-circuit voltage (Voc), short-circuit current (Isc), fill-factor (FF), and efficiency.

HOMO-LUMO analysis of multi walled carbon nanotubes doped Tetrafluoro Phthalate crystals for nonlinear optical applications

NASA Astrophysics Data System (ADS)

Latha, B.; Kumaresan, P.; Nithiyanantham, S.; Sampathkumar, K.

2018-01-01

The MWCNTs doped Tetrafluoro Phthalate (C6H2F4O4) precious stones are constantly having higher transmission rate contrasted with immaculate Tetrafluoro Phthalate crystal. The dependability of Tetrafluoro Phthalate crystal was enhanced by doping MWCNTs.The basic, synthetic, optical, mechanical and non-direct optical properties of the doped precious crystals were dissected with the portrayal concentrates, for example, powder XRD, FT-IR, UV-Visible, Hardness and SHG estimations individually. The dopants are relied upon to substitute the carbon iotas in the Tetrafluoro Phthalate grid because of their change of valency and in addition vicinity of ionic sweep. The strength and charge delocalization of the particle were additionally concentrated on by characteristic security orbital (NBO) examination. The HOMO-LUMO energies depict the charge exchange happens inside the atom. Atomic electrostatic potential has been dissected. The SHG productivity of the immaculate and colors doped TFP crystals were additionally contemplated utilizing Nd:YAG Q-exchanged laser.

Shallow Acceptor State in Mg-Doped CuAlO2 and Its Effect on Electrical and Optical Properties: An Experimental and First-Principles Study.

PubMed

Liu, Ruijian; Li, Yongfeng; Yao, Bin; Ding, Zhanhui; Jiang, Yuhong; Meng, Lei; Deng, Rui; Zhang, Ligong; Zhang, Zhenzhong; Zhao, Haifeng; Liu, Lei

2017-04-12

Shallow acceptor states in Mg-doped CuAlO 2 and their effect on structural, electrical, and optical properties are investigated by combining first-principles calculations and experiments. First-principles calculations demonstrate that Mg substituting at the Al site in CuAlO 2 plays the role of shallow acceptor and has a low formation energy, suggesting that Mg doping can increase hole concentration and improve the conductivity of CuAlO 2 . Hall effect measurements indicate that the hole concentration of the Mg-doped CuAlO 2 thin film is 2 orders of magnitude higher than that of undoped CuAlO 2 . The best room temperature conductivity of 8.0 × 10 -2 S/cm is obtained. A band gap widening is observed in the optical absorption spectra of Mg-doped CuAlO 2 , which is well supported by the results from first-principles electronic structure calculations.

Investigation on the compensation effect of residual carbon impurities in low temperature grown Mg doped GaN films

NASA Astrophysics Data System (ADS)

Yang, J.; Zhao, D. G.; Jiang, D. S.; Chen, P.; Liu, Z. S.; Le, L. C.; Li, X. J.; He, X. G.; Liu, J. P.; Zhang, S. M.; Wang, H.; Zhu, J. J.; Yang, H.

2014-04-01

The influence of unintentionally doped carbon impurities on electrical resistivity and yellow luminescence (YL) of low-temperature (LT) grown Mg doped GaN films is investigated. It is found that the resistivity of Mg doped GaN films are closely related to the residual carbon impurity concentration, which may be attributed to the compensation effect of carbon impurities. The carbon impurity may preferentially form deep donor complex CN-ON resulting from its relatively low formation energy. This complex is an effective compensate center for MgGa acceptors as well as inducing YL in photoluminescence spectra. Thus, the low resistivity LT grown p-type GaN films can be obtained only when the residual carbon impurity concentration is sufficiently low, which can explain why LT P-GaN films with lower resistivity were obtained more easily when relatively higher pressure, temperature, or NH3/TMGa flow rate ratio were used in the LT grown Mg doped GaN films reported in earlier reports.

Solution epitaxy of gallium-doped ZnO on p-GaN for heterojunction light-emitting diodes

NASA Astrophysics Data System (ADS)

Le, H. Q.; Lim, S. K.; Goh, G. K. L.; Chua, S. J.; Ang, N. S. S.; Liu, W.

2010-09-01

We report white light emission from a Ga-doped ZnO/p-GaN heterojunction light-emitting diode which was fabricated by growing gallium-doped ZnO film on the p-GaN in water at 90°C. As determined from Ga-doped ZnO films grown on (111) oriented MgAl2O4 spinel single crystal substrates, thermal treatment at 600°C in nitrogen ambient leads to a carrier concentration of 3.1×1020 cm-3 (and carrier mobility of 28 cm2/Vs) which is two orders of magnitude higher than that of the undoped films. Electroluminescence emissions at wavelengths of 393 nm (3.155 eV) and 529.5 nm (2.4 eV) were observed under forward bias in the heterojunction diode and white light could be visibly observed. The high concentration of electrons supplied from the Ga-doped ZnO films helped to enhance the carrier recombination and increase the light-emitting efficiency of the heterojunction diode.

Photocatalytic degradation of humic substances in aqueous solution using Cu-doped ZnO nanoparticles under natural sunlight irradiation.

PubMed

Maleki, Afshin; Safari, Mahdi; Shahmoradi, Behzad; Zandsalimi, Yahya; Daraei, Hiua; Gharibi, Fardin

2015-11-01

In this study, Cu-doped ZnO nanoparticles were investigated as an efficient synthesized catalyst for photodegradation of humic substances in aqueous solution under natural sunlight irradiation. Cu-doped ZnO nanocatalyst was prepared through mild hydrothermal method and was characterized using FT-IR, powder XRD and SEM techniques. The effect of operating parameters such as doping ratio, initial pH, catalyst dosage, initial concentrations of humic substances and sunlight illuminance were studied on humic substances degradation efficiency. The results of characterization analyses of samples confirmed the proper synthesis of Cu-doped ZnO nanocatalyst. The experimental results indicated the highest degradation efficiency of HS (99.2%) observed using 1.5% Cu-doped ZnO nanoparticles at reaction time of 120 min. Photocatalytic degradation efficiency of HS in a neutral and acidic pH was much higher than that at alkaline pH. Photocatalytic degradation of HS was enhanced with increasing the catalyst dosage and sunlight illuminance, while increasing the initial HS concentration led to decrease in the degradation efficiency of HS. Conclusively, Cu-doped ZnO nanoparticles can be used as a promising and efficient catalyst for degradation of HS under natural sunlight irradiation.

Thermoelectric Performance of Na-Doped GeSe

PubMed Central

2017-01-01

Recently, hole-doped GeSe materials have been predicted to exhibit extraordinary thermoelectric performance owing largely to extremely low thermal conductivity. However, experimental research on the thermoelectric properties of GeSe has received less attention. Here, we have synthesized polycrystalline Na-doped GeSe compounds, characterized their crystal structure, and measured their thermoelectric properties. The Seebeck coefficient decreases with increasing Na content up to x = 0.01 due to an increase in the hole carrier concentration and remains roughly constant at higher concentrations of Na, consistent with the electrical resistivity variation. However, the electrical resistivity is large for all samples, leading to low power factors. Powder X-ray diffraction and scanning electron microscopy/energy-dispersive spectrometry results show the presence of a ternary impurity phase within the GeSe matrix for all doped samples, which suggests that the optimal carrier concentration cannot be reached by doping with Na. Nevertheless, the lattice thermal conductivity and carrier mobility of GeSe is similar to those of polycrystalline samples of the leading thermoelectric material SnSe, leading to quality factors of comparable magnitude. This implies that GeSe shows promise as a thermoelectric material if a more suitable dopant can be found. PMID:29302637

Theoretical study of the characteristics of a continuous wave iron-doped ZnSe laser

NASA Astrophysics Data System (ADS)

Pan, Qikun; Chen, Fei; Xie, Jijiang; Wang, Chunrui; He, Yang; Yu, Deyang; Zhang, Kuo

2018-03-01

A theoretical model describing the dynamic process of a continuous-wave Fe2+:ZnSe laser is presented. The influence of some of the operating parameters on the output characteristics of an Fe2+:ZnSe laser is studied in detail. The results indicate that the temperature rise of the Fe2+:ZnSe crystal is significant with the use of a high power pump laser, especially for a high doped concentration of crystal. The optimal crystal length increases with decreasing the doped concentration of crystal, so an Fe2+:ZnSe crystal with simultaneous doping during growth is an attractive choice, which usually has a low doped concentration and long length. The laser pumping threshold is almost stable at low temperatures, but increases exponentially with a working temperature in the range of 180 K to room temperature. The main reason for this phenomenon is the short upper level lifetime and serious thermal temperature rise when the working temperature is higher than 180 K. The calculated optimum output mirror transmittance is about 35% and the performance of a continuous-wave Fe2+:ZnSe laser is more efficient at a lower operating temperature.

Role of defects in one-step synthesis of Cu-doped ZnO nano-coatings by electrodeposition method with enhanced magnetic and electrical properties

NASA Astrophysics Data System (ADS)

Niranjan, K.; Dutta, Subhajit; Varghese, Soney; Ray, Ajoy Kumar; Barshilia, Harish C.

2017-04-01

We report the growth of flower-like ferromagnetic Cu-doped ZnO (CZO) nanostructures using electrochemical deposition on FTO-coated glass substrates. X-ray photoelectron spectroscopy studies affirmed the presence of Cu in ZnO with an oxidation state of 2+. In order to find the optimized dopant concentration, different Cu dopant concentrations of 0.28, 0.30, 0.32, 0.35, 0.38, and 0.40 mM are applied and their magnetic, optical, and electrical properties are studied. Magnetic moment increased with the increasing dopant concentration up to 0.35 mM and then decreased with further increase in the concentration. Diamagnetic pure ZnO showed ferromagnetic nature even with a low doping concentration of 0.28 mM. Band gap increased with the increasing Cu concentration until a value of 0.35 mM and then remained the same for the higher dopant concentrations. It is ascribed to the Burstein-Moss effect. Defect-related broad photoluminescence (PL) peak is observed for the pure ZnO in the visible range. In contrast, Cu-doped samples showed a sharp and intense PL peak at 426 nm due to increased Zn interstitials. Kelvin probe measurements revealed that the Fermi level shifts toward the conduction band for the Cu-doped samples with respect to pure material. Electron transport mechanism in the samples is observed to be dominated by space charge-limited current and Schottky behavior with improved ideality factor up to 0.38 mM Cu.

Effect of Doping Materials on the Low-Level NO Gas Sensing Properties of ZnO Thin Films

NASA Astrophysics Data System (ADS)

Çorlu, Tugba; Karaduman, Irmak; Yildirim, Memet Ali; Ateş, Aytunç; Acar, Selim

2017-07-01

In this study, undoped, Cu-doped, and Ni-doped ZnO thin films have been successfully prepared by successive ionic layer adsorption and reaction method. The structural, compositional, and morphological properties of the thin films are characterized by x-ray diffractometer, energy dispersive x-ray analysis (EDX), and scanning electron microscopy, respectively. Doping effects on the NO gas sensing properties of these thin films were investigated depending on gas concentration and operating temperature. Cu-doped ZnO thin film exhibited a higher gas response than undoped and Ni-doped ZnO thin film at the operating temperature range. The sensor with Cu-doped ZnO thin film gave faster responses and recovery speeds than other sensors, so that is significant for the convenient application of gas sensor. The response and recovery speeds could be associated with the effective electron transfer between the Cu-doped ZnO and the NO molecules.

Design Issues of GaAs and AlGaAs Delta-Doped p-i-n Quantum-Well APD's

NASA Technical Reports Server (NTRS)

Wang, Yang

1994-01-01

We examine the basic design issues in the optimization of GaAs delta-doped and AlGAs delta-doped quantum-well avalanche photodiode (APD) structures using a theoretical analysis based on an ensemble Monte Carlo simulation. The devices are variations of the p-i-n doped quantum-well structure previously described in the literature. They have the same low-noise, high-gain and high-bandwidth features as the p-i-n doped quantum-well device. However, the use of delta doping provides far greater control or the doping concentrations within each stage possibly enhancing the extent to which the device can be depleted. As a result, it is expected that the proposed devices will operate at higher gain levels (at very low noise) than devices previously developed.

The Preparation Conditions of Chromium Doped ZnSe and Their Effect on The Infrared Luminescence Properties

NASA Technical Reports Server (NTRS)

Burger, A.; Chattopadhyay, K.; Ndap, J.-O.; Ma, X.; Morgan, S. H.; Rablau, C. I.; Su, C.-H.; Feth, S.; Page, Ralph H.; Schaffers, Kathleen I.;

Doping and compensation in Al-rich AlGaN grown on single crystal AlN and sapphire by MOCVD

NASA Astrophysics Data System (ADS)

Bryan, Isaac; Bryan, Zachary; Washiyama, Shun; Reddy, Pramod; Gaddy, Benjamin; Sarkar, Biplab; Breckenridge, M. Hayden; Guo, Qiang; Bobea, Milena; Tweedie, James; Mita, Seiji; Irving, Douglas; Collazo, Ramon; Sitar, Zlatko

2018-02-01

In order to understand the influence of dislocations on doping and compensation in Al-rich AlGaN, thin films were grown by metal organic chemical vapor deposition (MOCVD) on different templates on sapphire and low dislocation density single crystalline AlN. AlGaN grown on AlN exhibited the highest conductivity, carrier concentration, and mobility for any doping concentration due to low threading dislocation related compensation and reduced self-compensation. The onset of self-compensation, i.e., the "knee behavior" in conductivity, was found to depend only on the chemical potential of silicon, strongly indicating the cation vacancy complex with Si as the source of self-compensation. However, the magnitude of self-compensation was found to increase with an increase in dislocation density, and consequently, AlGaN grown on AlN substrates demonstrated higher conductivity over the entire doping range.

Impurity effects on electrical conductivity of doped bilayer graphene in the presence of a bias voltage

NASA Astrophysics Data System (ADS)

E, Lotfi; H, Rezania; B, Arghavaninia; M, Yarmohammadi

2016-07-01

We address the electrical conductivity of bilayer graphene as a function of temperature, impurity concentration, and scattering strength in the presence of a finite bias voltage at finite doping, beginning with a description of the tight-binding model using the linear response theory and Green’s function approach. Our results show a linear behavior at high doping for the case of high bias voltage. The effects of electron doping on the electrical conductivity have been studied via changing the electronic chemical potential. We also discuss and analyze how the bias voltage affects the temperature behavior of the electrical conductivity. Finally, we study the behavior of the electrical conductivity as a function of the impurity concentration and scattering strength for different bias voltages and chemical potentials respectively. The electrical conductivity is found to be monotonically decreasing with impurity scattering strength due to the increased scattering among electrons at higher impurity scattering strength.

Method of fabricating optical waveguides by ion implantation doping

DOEpatents

Appleton, B.R.; Ashley, P.R.; Buchal, C.J.

1987-03-24

A method for fabricating high-quality optical waveguides in optical quality oxide crystals by ion implantation doping and controlled epitaxial recrystallization is provided. Masked LiNbO/sub 3/ crystals are implanted with high concentrations of Ti dopant at ion energies of about 360 keV while maintaining the crystal near liquid nitrogen temperature. Ion implantation doping produces an amorphous, Ti-rich nonequilibrium phase in the implanted region. Subsequent thermal annealing in a water-saturated oxygen atmosphere at up to 1000/degree/C produces solid-phase epitaxial regrowth onto the crystalline substrate. A high-quality crystalline layer results which incorporates the Ti into the crystal structure at much higher concentrations than is possible by standard diffusion techniques, and this implanted region has excellent optical waveguiding properties.

Electronic phase diagram of disordered Co doped BaFe2As2-δ

NASA Astrophysics Data System (ADS)

Kurth, F.; Iida, K.; Trommler, S.; Hänisch, J.; Nenkov, K.; Engelmann, J.; Oswald, S.; Werner, J.; Schultz, L.; Holzapfel, B.; Haindl, S.

2013-02-01

Superconducting and normal state transport properties in iron pnictides are sensitive to disorder and impurity scattering. By investigation of Ba(Fe1-xCox)2As2-δ thin films with varying Co concentrations we demonstrate that in the dirty limit the superconducting dome in the electronic phase diagram of Ba(Fe1-xCox)2As2-δ shifts towards lower doping concentrations, which differs significantly from observations in single crystals. We show that especially in the underdoped regime superconducting transition temperatures higher than 27 K are possible.

Donor-acceptor-pair emission in fluorescent 4H-SiC grown by PVT method

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

Liu, Xi, E-mail: liuxi@mail.sic.ac.cn; Zhuo, Shi-Yi; Gao, Pan

Fluorescent SiC, which contains donor and acceptor impurities with optimum concentrations, can work as a phosphor for visible light emission by donor-acceptor-pair (DAP) recombination. In this work, 3 inch N-B-Al co-doped fluorescent 4H-SiC crystals are prepared by PVT method. The p-type fluorescent 4H-SiC with low aluminum doping concentration can show intensive yellow-green fluorescence at room temperature. N-B DAP peak wavelength shifts from 578nm to 525nm and weak N-Al DAP emission occurred 403/420 nm quenches, when the temperature increases from 4K to 298K. The aluminum doping induces higher defect concentration in the fluorescent crystal and decreases optical transmissivity of the crystalmore » in the visible light range. It triggers more non-radiative recombination and light absorption losses in the crystal.« less

Effects of an in vacancy on local distortion of fast phase transition in Bi-doped In3SbTe2

NASA Astrophysics Data System (ADS)

Choi, Minho; Choi, Heechae; Kim, Seungchul; Ahn, Jinho; Kim, Yong Tae

2017-12-01

Indium vacancies in Bi-doped In3SbTe2 (BIST) cause local distortion or and faster phase transition of BIST with good stability. The formation energy of the In vacancy in the BIST is relatively lower compared to that in IST due to triple negative charge state of the In vacancy ( V 3- In) and higher concentration of the V 3- In in BIST. The band gap of BIST is substantially reduced with increasing concentrations of the V 3- In and the hole carriers, which results in a higher electrical conductivity. The phase-change memory (PRAM) device fabricated with the BIST shows very fast, stable switching characteristics at lower voltages.

The Properties of p-GaN with Different Cp2Mg/Ga Ratios and Their Influence on Conductivity

NASA Astrophysics Data System (ADS)

Shang, Lin; Ma, Shufang; Liang, Jian; Li, Tianbao; Yu, Chunyan; Liu, Xuguang; Xu, Bingshe

2016-06-01

The effect of Cp2Mg/Ga ratio on the properties of p-GaN was explored by scanning Hall probe, photoluminescence (PL), and atomic force microscopy measurement. It was found that p-GaN has an optimal doping concentration under 2% Cp2Mg/Ga ratio, and higher or lower doping concentration is not beneficial to the conductivity. Hole concentration under the optimum condition is 4.2 × 1017 cm-3 at room temperature. If the Cp2Mg/Ga ratio exceeds the optimum value of 2%, surface morphology and electrical conduction properties become poor, and blue emission at 440 nm, considered deep donor-to-acceptor pair transitions in the PL spectra, are dominant. The decrease in electrical properties indicates the existence of compensating donors because the hole concentration decreases at such high Cp2Mg/Ga ratio. The obtained results indicate that Mg is not incorporated in the exact acceptor site under a heavy doping condition, but acts as a deep donor, instead.

Explicit continuous charge-based compact model for long channel heavily doped surrounding-gate MOSFETs incorporating interface traps and quantum effects

NASA Astrophysics Data System (ADS)

Hamzah, Afiq; Hamid, Fatimah A.; Ismail, Razali

2016-12-01

An explicit solution for long-channel surrounding-gate (SRG) MOSFETs is presented from intrinsic to heavily doped body including the effects of interface traps and fixed oxide charges. The solution is based on the core SRGMOSFETs model of the Unified Charge Control Model (UCCM) for heavily doped conditions. The UCCM model of highly doped SRGMOSFETs is derived to obtain the exact equivalent expression as in the undoped case. Taking advantage of the undoped explicit charge-based expression, the asymptotic limits for below threshold and above threshold have been redefined to include the effect of trap states for heavily doped cases. After solving the asymptotic limits, an explicit mobile charge expression is obtained which includes the trap state effects. The explicit mobile charge model shows very good agreement with respect to numerical simulation over practical terminal voltages, doping concentration, geometry effects, and trap state effects due to the fixed oxide charges and interface traps. Then, the drain current is obtained using the Pao-Sah's dual integral, which is expressed as a function of inversion charge densities at the source/drain ends. The drain current agreed well with the implicit solution and numerical simulation for all regions of operation without employing any empirical parameters. A comparison with previous explicit models has been conducted to verify the competency of the proposed model with the doping concentration of 1× {10}19 {{cm}}-3, as the proposed model has better advantages in terms of its simplicity and accuracy at a higher doping concentration.

On compensation in Si-doped AlN

NASA Astrophysics Data System (ADS)

Harris, Joshua S.; Baker, Jonathon N.; Gaddy, Benjamin E.; Bryan, Isaac; Bryan, Zachary; Mirrielees, Kelsey J.; Reddy, Pramod; Collazo, Ramón; Sitar, Zlatko; Irving, Douglas L.

2018-04-01

Controllable n-type doping over wide ranges of carrier concentrations in AlN, or Al-rich AlGaN, is critical to realizing next-generation applications in high-power electronics and deep UV light sources. Silicon is not a hydrogenic donor in AlN as it is in GaN; despite this, the carrier concentration should be controllable, albeit less efficiently, by increasing the donor concentration during growth. At low doping levels, an increase in the Si content leads to a commensurate increase in free electrons. Problematically, this trend does not persist to higher doping levels. In fact, a further increase in the Si concentration leads to a decrease in free electron concentration; this is commonly referred to as the compensation knee. While the nature of this decrease has been attributed to a variety of compensating defects, the mechanism and identity of the predominant defects associated with the knee have not been conclusively determined. Density functional theory calculations using hybrid exchange-correlation functionals have identified VAl+n SiAl complexes as central to mechanistically understanding compensation in the high Si limit in AlN, while secondary impurities and vacancies tend to dominate compensation in the low Si limit. The formation energies and optical signatures of these defects in AlN are calculated and utilized in a grand canonical charge balance solver to identify carrier concentrations as a function of Si content. The results were found to qualitatively reproduce the experimentally observed compensation knee. Furthermore, these calculations predict a shift in the optical emissions present in the high and low doping limits, which is confirmed with detailed photoluminescence measurements.

Influence of Y doping concentration on the properties of nanostructured MxZn1-xO (M=Y) thin film deposited by nebulizer spray pyrolysis technique

NASA Astrophysics Data System (ADS)

Mariappan, R.; Ponnuswamy, V.; Chandra Bose, A.; Suresh, R.; Ragavendar, M.

2014-09-01

Yttrium doped Zinc Oxide (YxZn1-xO) thin films deposited at a substrate temperature 400 °C. The effect of substrate temperature on the structural, surface morphology, compositional, optical and electrical properties of YxZn1-xO thin films was studied. X-ray diffraction studies show that all films are polycrystalline in nature with hexagonal crystal structure having highly textured (002) plane parallel to the surface of the substrate. The structural parameters, such as lattice constants (a and c), crystallite size (D), dislocation density (δ), microstrain (σ) and texture coefficient were calculated for different yttrium doping concentrations (x). High resolution scanning electron microscopy measurements reveal that the surface morphology of the films change from platelet like grains to hexagonal structure with grain size increase due to the yttrium doping. Energy dispersive spectroscopy confirms the presence of Y, Zn and O elements in the films prepared. Optical studies showed that all samples have a strong optical transmittance higher than 70% in the visible range. A slight shift of the absorption edge towards the large wavelengths was observed as the Y doping concentration increased. This result shows that the band gap is slightly decreased from 3.10 to 2.05 eV with increase of the yttrium doping concentrations (up to 7.5%) and then slightly increased. Room temperature PL measurements were done and the band-to-band emission energies of films were determined and reported. The complex impedance of the 10%Y doped ZnO film shows two distinguished semicircles and the diameter of the arcs got decreased in diameter as the temperature increases from 70 to 175 °C.

Minority carrier lifetime in iodine-doped molecular beam epitaxy-grown HgCdTe

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

Madni, I.; Umana-Membreno, G. A.; Lei, W.

2015-11-02

The minority carrier lifetime in molecular beam epitaxy grown layers of iodine-doped Hg{sub 1−x}Cd{sub x}Te (x ∼ 0.3) on CdZnTe substrates has been studied. The samples demonstrated extrinsic donor behavior for carrier concentrations in the range from 2 × 10{sup 16} cm{sup −3} to 6 × 10{sup 17} cm{sup −3} without any post-growth annealing. At a temperature of 77 K, the electron mobility was found to vary from 10{sup 4} cm{sup 2}/V s to 7 × 10{sup 3} cm{sup 2}/V s and minority carrier lifetime from 1.6 μs to 790 ns, respectively, as the carrier concentration was increased from 2 × 10{sup 16} cm{supmore » −3} to 6 × 10{sup 17} cm{sup −3}. The diffusion of iodine is much lower than that of indium and hence a better alternative in heterostructures such as nBn devices. The influence of carrier concentration and temperature on the minority carrier lifetime was studied in order to characterize the carrier recombination mechanisms. Measured lifetimes were also analyzed and compared with the theoretical models of the various recombination processes occurring in these materials, indicating that Auger-1 recombination was predominant at higher doping levels. An increase in deep-level generation-recombination centers was observed with increasing doping level, which suggests that the increase in deep-level trap density is associated with the incorporation of higher concentrations of iodine into the HgCdTe.« less

Mg,Ce co-doped Lu2Gd1(Ga,Al)5O12 by micro-pulling down method and their luminescence properties

NASA Astrophysics Data System (ADS)

Kamada, Kei; Yamaguchi, Hiroaki; Yoshino, Masao; Kurosawa, Shunsuke; Shoji, Yasuhiro; Yokota, Yuui; Ohashi, Yuji; Pejchal, Jan; Nikl, Martin; Yoshikawa, Akira

2018-04-01

The effects of Mg co-doping on the scintillation properties of Ce:Lu2Gd1(Ga,Al)5O12 (LGGAG) single crystals with different Ga/Al ratios were investigated. Mg co-doped and non co-doped Ce:LGGAG single crystals were grown by the micro-pulling down (µ-PD) method and then cut, polished and annealed for each measurement. Absorption spectra, radioluminescence (RL) spectra, pulse height spectra, and scintillation decay were measured to reveal the effect of Mg co-doping. Ce4+ charge transfer (CT) absorption band peaking at ∼260 nm was observed in Mg co-doped samples, which is in good agreement with previous reports for the Ce4+ CT absorption band in other garnet-based crystals. The scintillation decay time tended to be accelerated and the light yield tended to be decreased by Mg co-doping at higher Ga concentrations.

Simulation based comparative analysis of photoresponse in front- and back-illuminated GaN P-I-N ultraviolet photodetectors

NASA Astrophysics Data System (ADS)

Wang, Jun; Guo, Jin; Xie, Feng; Wang, Guosheng; Wu, Haoran; Song, Man; Yi, Yuanyuan

2016-10-01

This paper presents the comparative analysis of influence of doping level and doping profile of the active region on zero bias photoresponse characteristics of GaN-based p-i-n ultraviolet (UV) photodetectors operating at front- and back-illuminated. A two dimensional physically-based computer simulation of GaN-based p-i-n UV photodetectors is presented. We implemented GaN material properties and physical models taken from the literature. It is shown that absorption layer doping profile has notable impacts on the photoresponse of the device. Especially, the effect of doping concentration and distribution of the absorption layer on photoresponse is discussed in detail. In the case of front illumination, comparative to uniform n-type doping, the device with n-type Gaussian doping profiles at absorption layer has higher responsivity. Comparative to front illumination, back illuminated detector with p-type doping profiles at absorption layer has higher maximum photoresponse, while the Gaussian doping profiles have a weaker ability to enhance the device responsivity. It is demonstrated that electric field distribution, mobility degradation, and recombinations are jointly responsible for the variance of photoresponse. Our work enriches the understanding and utilization of GaN based p-i-n UV photodetectors.

Comparative study of (0001) and (11\\bar{2}2) InGaN based light emitting diodes

NASA Astrophysics Data System (ADS)

Pristovsek, Markus; Humphreys, Colin J.; Bauer, Sebastian; Knab, Manuel; Thonke, Klaus; Kozlowski, Grzegorz; O'Mahony, Donagh; Maaskant, Pleun; Corbett, Brian

2016-05-01

We have systematically investigated the doping of (11\\bar{2}2) with Si and Mg by metal-organic vapour phase epitaxy for light emitting diodes (LEDs). By Si doping of GaN we reached electron concentrations close to 1020 cm-3, but the topography degrades above mid 1019 cm-3. By Mg doping we reached hole concentrations close to 5 × 1017 cm-3, using Mg partial pressures about 3× higher than those for (0001). Exceeding the maximum Mg partial pressure led to a quick degradation of the sample. Low resistivities as well as high hole concentrations required a growth temperature of 900 °C or higher. At optimised conditions the electrical properties as well as the photoluminescence of (11\\bar{2}2) p-GaN were similar to (0001) p-GaN. The best ohmic p-contacts were achieved by NiAg metallisation. A single quantum well LED emitting at 465 nm was realised on (0001) and (11\\bar{2}2). Droop (sub-linear increase of the light output power) occurred at much higher current densities on (11\\bar{2}2). However, the light output of the (0001) LED was higher than that of (11\\bar{2}2) until deep in the droop regime. Our LEDs as well as those in the literature indicate a reduction in efficiency from (0001) over semi-polar to non-polar orientations. We propose that reduced fields open a loss channel for carriers.

Energetics of Intermediate Temperature Solid Oxide Fuel Cell Electrolytes: Singly and Doubly doped Ceria Systems

NASA Astrophysics Data System (ADS)

Buyukkilic, Salih

Solid oxide fuel cells (SOFCs) have potential to convert chemical energy directly to electrical energy with high efficiency, with only water vapor as a by-product. However, the requirement of extremely high operating temperatures (~1000 °C) limits the use of SOFCs to only in large scale stationary applications. In order to make SOFCs a viable energy solution, enormous effort has been focused on lowering the operating temperatures below 700 °C. A low temperature operation would reduce manufacturing costs by slowing component degradation, lessening thermal mismatch problems, and sharply reducing costs of operation. In order to optimize SOFC applications, it is critical to understand the thermodynamic stabilities of electrolytes since they directly influence device stability, sustainability and performance. Rare-earth doped ceria electrolytes have emerged as promising materials for SOFC applications due to their high ionic conductivity at the intermediate temperatures (500--700 °C). However there is a fundamental lack of understanding regarding their structure, thermodynamic stability and properties. Therefore, the enthalpies of formation from constituent oxides and ionic conductivities were determined to investigate a relationship between the stability, composition, structural defects and ionic conductivity in rare earth doped ceria systems. For singly doped ceria electrolytes, we investigated the solid solution phase of bulk Ce1-xLnxO2-0.5x where Ln = Sm and Nd (0 ≤ x ≤ 0.30) and analyzed their enthalpies of formation, mixing and association, and bulk ionic conductivities while considering cation size mismatch and defect associations. It was shown that for ambient temperatures in the dilute dopant region, the positive heat of formation reaches a maximum as the system becomes increasingly less stable due to size mismatch. In concentrated region, stabilization to a certain solubility limit was observed probably due to the defect association of trivalent cations with charge-balancing oxygen vacancies. At higher temperatures near 700 °C, maximum enthalpy of formation shifts toward higher dopant concentrations, as a result of defect disordering. This concentration coincides with that of maximum ionic conductivity, extending the correlation seen previously near room temperature. It is also possible to co-dope these systems with Sm and Nd to further enhance ionic conductivity. For doubly doped ceria electrolytes, the solid solution phase of Ce1-xSm0.5xNd0.5xO2-0.5x (0 ≤ x ≤ 0.30) was investigated. It has been shown that for doubly doped ceria, the maximum enthalpy of formation occurs towards higher dopant concentration than that of singly doped counterparts, with less exothermic association enthalpies. These studies provide insight into the structure-composition-property-stability relations and aid in the rational design of the future SOFCs electrolytes.

Strain induced atomic structure at the Ir-doped LaAlO3/SrTiO3 interface.

PubMed

Lee, M; Arras, R; Warot-Fonrose, B; Hungria, T; Lippmaa, M; Daimon, H; Casanove, M J

2017-11-01

The structure of Ir-doped LaAlO 3 /SrTiO 3 (001) interfaces was investigated on the atomic scale using probe-corrected transmission electron microscopy in high-angle annular dark-field scanning mode (HAADF-STEM) and electron energy loss spectroscopy (EELS), combined with first-principles calculations. We report the evolution of the strain state experimentally measured in a 5 unit-cell thick LaAlO 3 film as a function of the Ir concentration in the topmost SrTiO 3 layer. It is shown that the LaAlO 3 layers remain fully elastically strained up to 3% of Ir doping, whereas a higher doping level seems to promote strain relaxation through enhanced cationic interdiffusion. The observed differences between the energy loss near edge structure (ELNES) of Ti-L 2,3 and O-K edges at non-doped and Ir-doped interfaces are consistent with the location of the Ir dopants at the interface, up to 3% of Ir doping. These findings, supported by the results of density functional theory (DFT) calculations, provide strong evidence that the effect of dopant concentrations on the properties of this kind of interface should not be analyzed without obtaining essential information from the fine structural and chemical analysis of the grown structures.

Transport properties of Sb-doped Si nanowires

NASA Astrophysics Data System (ADS)

Nukala, Prathyusha; Sapkota, Gopal; Gali, Pradeep; Philipose, U.

2012-08-01

We present a safe and cost-effective approach for synthesis of n-type Sb-doped Si nanowires. The nanowires were synthesized at ambient pressure using SiCl4 as Si source and pure Sb as the dopant source. Structural and compositional characterization using electron microscopy and X-ray spectroscopy show crystalline nanowires with lengths of 30-40 μm and diameters of 40-100 nm. A 3-4 nm thick amorphous oxide shell covers the surface of the nanowire, post-growth. The composition of this shell was confirmed by Raman spectroscopy. Growth of Si nanowires, followed by low temperature annealing in Sb vapor, was shown to be an effective technique for synthesizing Sb-doped Si nanowires. The doping concentration of Sb was found to be dependent on temperature, with Sb re-evaporating from the Si nanowire at higher doping temperatures. Field effect transistors (FETs) were fabricated to investigate the electrical transport properties of these nanowires. The as-grown Si nanowires were found to be p-type with a channel mobility of 40 cm2 V-1 s-1. After doping with Sb, these nanowires exhibited n-type behavior. The channel mobility and carrier concentration of the Sb-doped Si nanowires were estimated to be 288 cm2 V-1 s-1 and 5.3×1018 cm-3 respectively.

Method of fabricating optical waveguides by ion implantation doping

DOEpatents

Appleton, Bill R.; Ashley, Paul R.; Buchal, Christopher J.

1989-01-01

A method for fabricating high-quality optical waveguides in optical quality oxide crystals by ion implantation doping and controlled epitaxial recrystallization is provided. Masked LiNbO.sub.3 crystals are implanted with high concentrations of Ti dopant at ion energies of about 350 keV while maintaining the crystal near liquid nitrogen temperature. Ion implantation doping produces an amorphous, Ti-rich nonequilibrium phase in the implanted region. Subsequent thermal annealing in a water-saturated oxygen atmosphere at up to 1000.degree. C. produces solid-phase epitaxial regrowth onto the crystalline substrate. A high-quality single crystalline layer results which incorporates the Ti into the crystal structure at much higher concentrations than is possible by standard diffusion techniques, and this implanted region has excellent optical waveguides properties.

Analysis of source/drain engineered 22nm FDSOI using high-k spacers

NASA Astrophysics Data System (ADS)

Malviya, Abhishek Kumar; Chauhan, R. K.

2018-04-01

While looking at the current classical scaling of devices there are lots of short channel effects come into consideration. In this paper, a novel device structure is proposed that is an improved structure of Modified Source(MS) FDSOI in terms of better electrical performance, on current and reduced off state leakage current with a higher Ion/Ioff ratio that helps in fast switching of low power nano electronic devices. Proposed structure has Modified drain and source regions with two different type to doping profile at 22nm gate length. In the upper part of engineered region (MD and MS) the doping concentration is kept high and less in the lower region. The purpose was to achieve low parasitic capacitance in source and drain region by reducing doping concentration [1].

Impurity Resonant States p-type Doping in Wide-Band-Gap Nitrides

NASA Astrophysics Data System (ADS)

Liu, Zhiqiang; Yi, Xiaoyan; Yu, Zhiguo; Yuan, Gongdong; Liu, Yang; Wang, Junxi; Li, Jinmin; Lu, Na; Ferguson, Ian; Zhang, Yong

2016-01-01

In this work, a new strategy for achieving efficient p-type doping in high bandgap nitride semiconductors to overcome the fundamental issue of high activation energy has been proposed and investigated theoretically, and demonstrated experimentally. Specifically, in an AlxGa1-xN/GaN superlattice structure, by modulation doping of Mg in the AlxGa1-xN barriers, high concentration of holes are generated throughout the material. A hole concentration as high as 1.1 × 1018 cm-3 has been achieved, which is about one order of magnitude higher than that typically achievable by direct doping GaN. Results from first-principle calculations indicate that the coupling and hybridization between Mg 2p impurity and the host N 2p orbitals are main reasons for the generation of resonant states in the GaN wells, which further results in the high hole concentration. We expect this approach to be equally applicable for other high bandgap materials where efficient p-type doing is difficult. Furthermore, a two-carrier-species Hall-effect model is proposed to delineate and discriminate the characteristics of the bulk and 2D hole, which usually coexist in superlattice-like doping systems. The model reported here can also be used to explain the abnormal freeze-in effect observed in many previous reports.

Impurity Resonant States p-type Doping in Wide-Band-Gap Nitrides.

PubMed

Liu, Zhiqiang; Yi, Xiaoyan; Yu, Zhiguo; Yuan, Gongdong; Liu, Yang; Wang, Junxi; Li, Jinmin; Lu, Na; Ferguson, Ian; Zhang, Yong

2016-01-18

In this work, a new strategy for achieving efficient p-type doping in high bandgap nitride semiconductors to overcome the fundamental issue of high activation energy has been proposed and investigated theoretically, and demonstrated experimentally. Specifically, in an AlxGa(1-x)N/GaN superlattice structure, by modulation doping of Mg in the AlxGa(1-x)N barriers, high concentration of holes are generated throughout the material. A hole concentration as high as 1.1 × 10(18) cm(-3) has been achieved, which is about one order of magnitude higher than that typically achievable by direct doping GaN. Results from first-principle calculations indicate that the coupling and hybridization between Mg 2p impurity and the host N 2p orbitals are main reasons for the generation of resonant states in the GaN wells, which further results in the high hole concentration. We expect this approach to be equally applicable for other high bandgap materials where efficient p-type doing is difficult. Furthermore, a two-carrier-species Hall-effect model is proposed to delineate and discriminate the characteristics of the bulk and 2D hole, which usually coexist in superlattice-like doping systems. The model reported here can also be used to explain the abnormal freeze-in effect observed in many previous reports.

The Effect of Acceptor and Donor Doping on Oxygen Vacancy Concentrations in Lead Zirconate Titanate (PZT).

PubMed

Slouka, Christoph; Kainz, Theresa; Navickas, Edvinas; Walch, Gregor; Hutter, Herbert; Reichmann, Klaus; Fleig, Jürgen

2016-11-22

The different properties of acceptor-doped (hard) and donor-doped (soft) lead zirconate titanate (PZT) ceramics are often attributed to different amounts of oxygen vacancies introduced by the dopant. Acceptor doping is believed to cause high oxygen vacancy concentrations, while donors are expected to strongly suppress their amount. In this study, La 3+ donor-doped, Fe 3+ acceptor-doped and La 3+ /Fe 3+ -co-doped PZT samples were investigated by oxygen tracer exchange and electrochemical impedance spectroscopy in order to analyse the effect of doping on oxygen vacancy concentrations. Relative changes in the tracer diffusion coefficients for different doping and quantitative relations between defect concentrations allowed estimates of oxygen vacancy concentrations. Donor doping does not completely suppress the formation of oxygen vacancies; rather, it concentrates them in the grain boundary region. Acceptor doping enhances the amount of oxygen vacancies but estimates suggest that bulk concentrations are still in the ppm range, even for 1% acceptor doping. Trapped holes might thus considerably contribute to the charge balancing of the acceptor dopants. This could also be of relevance in understanding the properties of hard and soft PZT.

The Effect of Acceptor and Donor Doping on Oxygen Vacancy Concentrations in Lead Zirconate Titanate (PZT)

PubMed Central

Slouka, Christoph; Kainz, Theresa; Navickas, Edvinas; Walch, Gregor; Hutter, Herbert; Reichmann, Klaus; Fleig, Jürgen

2016-01-01

The different properties of acceptor-doped (hard) and donor-doped (soft) lead zirconate titanate (PZT) ceramics are often attributed to different amounts of oxygen vacancies introduced by the dopant. Acceptor doping is believed to cause high oxygen vacancy concentrations, while donors are expected to strongly suppress their amount. In this study, La3+ donor-doped, Fe3+ acceptor-doped and La3+/Fe3+-co-doped PZT samples were investigated by oxygen tracer exchange and electrochemical impedance spectroscopy in order to analyse the effect of doping on oxygen vacancy concentrations. Relative changes in the tracer diffusion coefficients for different doping and quantitative relations between defect concentrations allowed estimates of oxygen vacancy concentrations. Donor doping does not completely suppress the formation of oxygen vacancies; rather, it concentrates them in the grain boundary region. Acceptor doping enhances the amount of oxygen vacancies but estimates suggest that bulk concentrations are still in the ppm range, even for 1% acceptor doping. Trapped holes might thus considerably contribute to the charge balancing of the acceptor dopants. This could also be of relevance in understanding the properties of hard and soft PZT. PMID:28774067

Study on the effects of Ga-2N high co-doping and preferred orientation on the stability, bandgap and absorption spectrum of ZnO

NASA Astrophysics Data System (ADS)

Hou, Qing-Yu; Li, Wen-Cai; Qu, Ling-Feng; Zhao, Chun-Wang

2017-06-01

Currently, the stability and visible light properties of Ga-2N co-doped ZnO systems have been studied extensively by experimental analysis and theoretical calculations. However, previous theoretical calculations arbitrarily assigned Ga- and 2N-doped sites in ZnO. In addition, the most stable and possible doping orientations of doped systems have not been fully and systematically considered. Therefore, in this paper, the electron structure and absorption spectra of the unit cells of doped and pure systems were calculated by first-principles plane-wave ultrasoft pseudopotential with the GGA+U method. Calculations were performed for pure ZnO, Ga-2N supercells heavily co-doped with Zn1-xGaxO1-yNy (x = 0.03125 - 0.0625, y = 0.0625 - 0.125) under different co-doping orientations and conditions, and the Zn16GaN2O14 interstitial model. The results indicated that under different orientations and constant Ga-2N co-doping concentrations, the systems co-doped with Ga-N atoms vertically oriented to the c-axis and with another N atom located in the nearest-neighboring site exhibited higher stability over the others, thus lowering formation energy and facilitating doping. Moreover, Ga-interstitial- and 2N-co-doped ZnO systems easily formed chemical compounds. Increasing co-doping concentration while the co-doping method remained constant decreased doped system volume and lowered formation energies. Meantime, co-doped systems were more stable and doping was facilitated. The bandgap was also narrower and red shifting of the absorption spectrum was more significant. These results agreed with previously reported experimental results. In addition, the absorption spectra of Ga-interstitial- and 2N-co-doped ZnO both blue shifted in the UV region compared with that of the pure ZnO system.

Investigating the effect of V2O5 addition on sodium barium borosilicate glasses

NASA Astrophysics Data System (ADS)

Halder, Rumu; Sengupta, Pranesh; Sudarsan, V.; Kaushik, C. P.; Dey, G. K.

2016-05-01

V2O5 doped sodium barium borosilicate glasses were characterized by photoluminescence spectroscopy and electron probe microanalyzer (EPMA). The glass remains homogeneous for lower concentration of V2O5 but a phase separation is observed when V2O5 doping is increased beyond 5 mol%. Detailed microanalysis reveals that the phase separated glass consists of a phase containing V, Ba and Si and a separate Si rich phase within the glass matrix. The luminescence study demonstrated that at low concentration the vanadium mainly interacts with the structural units of B/Si while at higher concentrations, V-O-V/ V-O- Na+/Ba2+ linkages are formed.

The effects of layering in ferroelectric Si-doped HfO{sub 2} thin films

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

Lomenzo, Patrick D.; Nishida, Toshikazu, E-mail: nishida@ufl.edu; Takmeel, Qanit

2014-08-18

Atomic layer deposited Si-doped HfO{sub 2} thin films approximately 10 nm thick are deposited with various Si-dopant concentrations and distributions. The ferroelectric behavior of the HfO{sub 2} thin films are shown to be dependent on both the Si mol. % and the distribution of Si-dopants. Metal-ferroelectric-insulator-semiconductor capacitors are shown to exhibit a tunable remanent polarization through the adjustment of the Si-dopant distribution at a constant Si concentration. Inhomogeneous layering of Si-dopants within the thin films effectively lowers the remanent polarization. A pinched hysteresis loop is observed for higher Si-dopant concentrations and found to be dependent on the Si layering distribution.

Cobalt doped proangiogenic hydroxyapatite for bone tissue engineering application.

PubMed

Kulanthaivel, Senthilguru; Roy, Bibhas; Agarwal, Tarun; Giri, Supratim; Pramanik, Krishna; Pal, Kunal; Ray, Sirsendu S; Maiti, Tapas K; Banerjee, Indranil

2016-01-01

The present study delineates the synthesis and characterization of cobalt doped proangiogenic-osteogenic hydroxyapatite. Hydroxyapatite samples, doped with varying concentrations of bivalent cobalt (Co(2+)) were prepared by the ammoniacal precipitation method and the extent of doping was measured by ICP-OES. The crystalline structure of the doped hydroxyapatite samples was confirmed by XRD and FTIR studies. Analysis pertaining to the effect of doped hydroxyapatite on cell cycle progression and proliferation of MG-63 cells revealed that the doping of cobalt supported the cell viability and proliferation up to a threshold limit. Furthermore, such level of doping also induced differentiation of the bone cells, which was evident from the higher expression of differentiation markers (Runx2 and Osterix) and better nodule formation (SEM study). Western blot analysis in conjugation with ELISA study confirmed that the doped HAp samples significantly increased the expression of HIF-1α and VEGF in MG-63 cells. The analysis described here confirms the proangiogenic-osteogenic properties of the cobalt doped hydroxyapatite and indicates its potential application in bone tissue engineering. Copyright © 2015 Elsevier B.V. All rights reserved.

Tungsten Doped TiO2 with Enhanced Photocatalytic and Optoelectrical Properties via Aerosol Assisted Chemical Vapor Deposition

PubMed Central

Sathasivam, Sanjayan; Bhachu, Davinder S.; Lu, Yao; Chadwick, Nicholas; Althabaiti, Shaeel A.; Alyoubi, Abdulrahman O.; Basahel, Sulaiman N.; Carmalt, Claire J.; Parkin, Ivan P.

2015-01-01

Tungsten doped titanium dioxide films with both transparent conducting oxide (TCO) and photocatalytic properties were produced via aerosol-assisted chemical vapor deposition of titanium ethoxide and dopant concentrations of tungsten ethoxide at 500 °C from a toluene solution. The films were anatase TiO2, with good n-type electrical conductivities as determined via Hall effect measurements. The film doped with 2.25 at.% W showed the lowest resistivity at 0.034 Ω.cm and respectable charge carrier mobility (14.9 cm3/V.s) and concentration (×1019 cm−3). XPS indicated the presence of both W6+ and W4+ in the TiO2 matrix, with the substitutional doping of W4+ inducing an expansion of the anatase unit cell as determined by XRD. The films also showed good photocatalytic activity under UV-light illumination, with degradation of resazurin redox dye at a higher rate than with undoped TiO2. PMID:26042724

Enhanced thermoelectric property of oxygen deficient nickel doped SnO2 for high temperature application

NASA Astrophysics Data System (ADS)

Paulson, Anju; Sabeer, N. A. Muhammad; Pradyumnan, P. P.

2018-04-01

Motivated by the detailed investigation on the thermoelectric performance of oxide materials our work concentrated on the influence of acceptor dopants and defect density in the lattice plane for the enhancement of thermoelectric power. The series of Sn1‑x Nix O2 (0.01 ≤ x ≤ 0.05) compositions were prepared by solid state reaction mechanism and found that 3 atomic percentage Ni doped SnO2 can be considered as a good candidate due to its promising electrical and transport properties. Defect lattices were introduced in the sample and the deviation from oxygen stochiometry was ensured using photoluminescence measurement. High power factor was obtained for the 3 atomic percentage nickel doped SnO2 due to the effective number of charge carrier concentration and the depletion of oxygen rich layers. Defect centered and acceptor doped SnO2 lattice opens a new door for energy harvesting at higher temperatures.

Atomic-Layer-Confined Doping for Atomic-Level Insights into Visible-Light Water Splitting.

PubMed

Lei, Fengcai; Zhang, Lei; Sun, Yongfu; Liang, Liang; Liu, Katong; Xu, Jiaqi; Zhang, Qun; Pan, Bicai; Luo, Yi; Xie, Yi

2015-08-03

A model of doping confined in atomic layers is proposed for atomic-level insights into the effect of doping on photocatalysis. Co doping confined in three atomic layers of In2S3 was implemented with a lamellar hybrid intermediate strategy. Density functional calculations reveal that the introduction of Co ions brings about several new energy levels and increased density of states at the conduction band minimum, leading to sharply increased visible-light absorption and three times higher carrier concentration. Ultrafast transient absorption spectroscopy reveals that the electron transfer time of about 1.6 ps from the valence band to newly formed localized states is due to Co doping. The 25-fold increase in average recovery lifetime is believed to be responsible for the increased of electron-hole separation. The synthesized Co-doped In2S3 (three atomic layers) yield a photocurrent of 1.17 mA cm(-2) at 1.5 V vs. RHE, nearly 10 and 17 times higher than that of the perfect In2S3 (three atomic layers) and the bulk counterpart, respectively. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ab initio simulation of elastic and mechanical properties of Zn- and Mg-doped hydroxyapatite (HAP).

PubMed

Aryal, Sitaram; Matsunaga, Katsuyuki; Ching, Wai-Yim

2015-07-01

Hydroxyapatite (HAP) is an important bioceramic which constitutes the mineral components of bones and hard tissues in mammals. It is bioactive and used as bioceramic coatings for metallic implants and bone fillers. HAP readily absorbs a large amount of impurities. Knowledge on the elastic and mechanical properties of impurity-doped HAP is a subject of great importance to its potential for biomedical applications. Zn and Mg are the most common divalent cations HAP absorbs. Using density function theory based ab initio methods, we have carried out a large number of ab initio calculations to obtain the bulk elastic and mechanical properties of HAP with Zn or Mg doped in different concentration at the Ca1 and Ca2 sites using large 352-atom supercells. Detailed information on their dependece on the concetraion of the substitued impurity is obtained. Our results show that Mg enhances overall elastic and bulk mechanical properties whereas Zn tends to degrade except at low concentrations. At a higher concentration, the mechanical properties of Zn and Mg doped HAP also depend significantly on impurity distribution between the Ca1 and Ca2 sites. There is a strong evidence that Zn prefers Ca2 site for substituion whereas Mg has no such preference. These results imply that proper control of dopant concentration and their site preference must carefully considered in using doped HAP for specific biomedical applications. Copyright © 2015 Elsevier Ltd. All rights reserved.

Prevalence of caffeine use in elite athletes following its removal from the World Anti-Doping Agency list of banned substances.

PubMed

Del Coso, Juan; Muñoz, Gloria; Muñoz-Guerra, Jesús

2011-08-01

The aim of this investigation was to determine the use of caffeine by athletes after its removal from the World Anti-Doping Agency list. For this purpose, we measured the caffeine concentration in 20 686 urine samples obtained for doping control from 2004 to 2008. We utilized only urine samples obtained after official national and international competitions. Urine caffeine concentration was determined using alkaline extraction followed by gas chromatography-mass spectrometry. The limit of detection (LOD) was set at 0.1 µg·mL(-1). The percentage of urine samples below the LOD was 26.2%; the remaining 73.8% of the urine samples contained caffeine. Most urine samples (67.3%) had urinary caffeine concentrations below 5 µg·mL(-1). Only 0.6% of urine samples exceeded the former threshold for caffeine doping (12 µg·mL(-1)). Triathlon (3.3 ± 2.2 µg·mL(-1)), cycling (2.6 ± 2.0 µg·mL(-1)), and rowing (1.9 ± 1.4 µg·mL(-1)) were the sports with the highest levels of urine caffeine concentration; gymnastics was the sport with the lowest urine caffeine concentration (0.5 ± 0.4 µg·mL(-1)). Older competitors (>30 y) had higher levels of caffeine in their urine than younger competitors (<20 y; p < 0.05); there were no differences between males and females. In conclusion, 3 out of 4 athletes had consumed caffeine before or during sports competition. Nevertheless, only a small proportion of these competitors (0.6%) had a urine caffeine concentration higher than 12 µg·mL(-1). Endurance sports were the disciplines showing the highest urine caffeine excretion after competition.

1-D and 2-D morphology of metal cation co-doped (Zn, Mn) TiO2 and investigation of their photocatalytic activity

NASA Astrophysics Data System (ADS)

Benjwal, Poonam; De, Bibekananda; Kar, Kamal K.

2018-01-01

Morphology and electronic bandgap of titania (TiO2) are considered to be the primary factors for determining the photocatalytic efficiency, as they determine the number of active sites for the photocatalytic reactions. In the present study, two different morphologies of TiO2 (nanosphere and nanorod) with varying Zn and Mn co-doping were synthesized by solvothermal and hydrothermal methods to examine their photocatalytic efficiency by methylene blue degradation. The co-doped photocatalysts were characterized by XRD, XPS, SEM, TEM, Raman, FTIR and UV-vis DRS. Further, a comparison has been made with co-doped TiO2 nanospheres and TiO2 nanorods, where Zn, Mn co-doped TiO2 nanorods show higher photocatalytic activity compared to nanospheres. This higher photocatalytic activity of co-doped TiO2 is attributed to its polymorphic phases, as they act as heterojunctions for TiO2. Further, being 1-D nanostructure, the TiO2 nanorods exhibit the straight diffusion path for charge carriers, which reduces the recombination possibilities. The obtained results suggest that the photocatalysis efficiency of TiO2 can be significantly enhanced by tailoring the shape and co-doping concentration, which enforce a new concept for developing the new nanostructures of TiO2.

Enhancement in ferroelectric, pyroelectric and photoluminescence properties in dye doped TGS crystals

NASA Astrophysics Data System (ADS)

Sinha, Nidhi; Goel, Neeti; Singh, B. K.; Gupta, M. K.; Kumar, Binay

2012-06-01

Pure and dye doped (0.1 and 0.2 mol%) Triglycine Sulfate (TGS) single crystals were grown by slow evaporation technique. A pyramidal coloring pattern, along with XRD and FT-IR studies confirmed the dye doping. Decrease in dielectric constant and increase in Curie temperature (Tc) were observed with increasing doping concentration. Low absorption cut off (231 nm) and high optical transparency (>90%) resulting in large band gap was observed in UV-VIS studies. In addition, strong hyper-luminescent emission bands at 350 and 375 nm were observed in which the relative intensity were found to be reversed as a result of doping. In P-E hysteresis loop studies, a higher curie temperature and an improved and more uniform figure of merit over a large region of the ferroelectric phase were observed. The improved dielectric, optical and ferroelectric/pyroelectric properties make the dye doped TGS crystals better candidate for various opto- and piezo-electronics applications.

Design consideration of δ-doping channels for high-performance n + - GaAs / p + -InGaP/n-GaAs camel-gate field effect transistors

NASA Astrophysics Data System (ADS)

Tsai, Jung-Hui; Chen, Jeng-Shyan; Chu, Yu-Jui

2005-01-01

The influence of δ-doping channels on the performance of n +-GaAs/p +-InGaP/n-GaAs camel-gate field effect transistors is investigated by theoretical analysis and experimental results. The depleted pn junction of the camel gate and the existence of considerable conduction band discontinuity at the InGaP/GaAs heterojunction enhance the potential barrier height and the forward gate voltage. As the concentration-thickness products of the n-GaAs layer and δ-doping layer are fixed, the higher δ-doping device exhibits a higher potential barrier height, a larger drain current, and a broader gate voltage swing, whereas the transconductance is somewhat lower. For a n +=5.5×10 12 cm -2δ-doping device, the experimental result exhibits a maximum transconductance of 240 mS/mm and a gate voltage swing of 3.5 V. Consequently, the studied devices provide a good potential for large signal and linear circuit applications.

Characteristic optimization of 1.55-μm InGaAsP/InP high-power diode laser

NASA Astrophysics Data System (ADS)

Ke, Qing; Tan, Shaoyang; Zhai, Teng; Zhang, Ruikang; Lu, Dan; Ji, Chen

2014-11-01

A comprehensive design optimization of 1.55-μm high power InGaAsP/InP board area lasers is performed aiming at increasing the internal quantum efficiency (IQE) while maintaing a low internal loss of the device as well. The P-doping profile and separate confinement heterostructure (SCH) layer band gap are optimized respectively with commercial software Crosslight. Analysis of lasers with different p-doping profiles shows that, although heavy doping in P-cladding layer increases the internal loss of the device, it ensures a high IQE because higher energy barrier at the SCH/P-cladding interface as a result of heavy doping helps reduce the carrier leakage from the waveguide to the InP-cladding layer. The band gap of the SCH layer are also optimized for high slope efficiency. Smaller band gap helps reduce the vertical carrier leakage from the waveguide to the P-cladding layer, but the corresponding higher carrier concentration in SCH layer will cause some radiative recombination, thus influencing the IQE. And as the injection current increases, the carrier concentration increases faster with smaller band gap, therefore, the output power saturates sooner. An optimized band gap in SCH layer of approximately 1.127eV and heavy doping up to 1e18/cm3 at the SCH/P-cladding interface are identified for our high power laser design, and we achieved a high IQE of 94% and internal loss of 2.99/cm for our design.

Influence of defects on the thermoelectricity in SnSe: A comprehensive theoretical study

NASA Astrophysics Data System (ADS)

Zhou, Yecheng; Li, Wei; Wu, Minghui; Zhao, Li-Dong; He, Jiaqing; Wei, Su-Huai; Huang, Li

2018-06-01

SnSe has emerged as an efficient and fascinating thermoelectric material. A fundamental understanding of the effects and nature of intrinsic defects and dopants in SnSe is crucial to optimize its thermoelectric performance. In this paper, we perform first-principles calculations to examine the native and extrinsic point-defect properties in SnSe. We show that the easy formation of acceptorlike Sn vacancy (VSn) is responsible for the p -type conductivity in intrinsic SnSe. We also propose a mechanism and explain the anomalous temperature dependence of the carrier concentration in intrinsic SnSe crystals. Concerning the extrinsic defects, we focus on the dopants used in experiments. We find that Na (Ag) substitution on Sn site, NaSn (AgSn), acts as acceptor, whereas, substitutional BrSe, ISe, and BiSn dopants act as donor. It is shown that for Ag doping, its carrier concentration will be saturated with increasing doping concentration due to the coexistence of compensated defects (Agi and AgSn). Furthermore, we analyze how this doping introduced carrier impact on their thermoelectric characteristics. It is found that the more efficient doping of Na, Br, and I can realize higher Z T .

Effects of Mg/Ga and V/III source ratios on hole concentration of N-polar (000\\bar{1}) p-type GaN grown by metalorganic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Nonoda, Ryohei; Shojiki, Kanako; Tanikawa, Tomoyuki; Kuboya, Shigeyuki; Katayama, Ryuji; Matsuoka, Takashi

2016-05-01

The effects of growth conditions such as Mg/Ga and V/III ratios on the properties of N-polar (000\\bar{1}) p-type GaN grown by metalorganic vapor phase epitaxy were studied. Photoluminescence spectra from Mg-doped GaN depended on Mg/Ga and V/III ratios. For the lightly doped samples, the band-to-acceptor emission was observed at 3.3 eV and its relative intensity decreased with increasing V/III ratio. For the heavily doped samples, the donor-acceptor pair emission was observed at 2.8 eV and its peak intensity monotonically decreased with V/III ratio. The hole concentration was maximum for the Mg/Ga ratio. This is the same tendency as in group-III polar (0001) growth. The V/III ratio also reduced the hole concentration. The higher V/III ratio reduced the concentration of residual donors such as oxygen by substituting nitrogen atoms. The surface became rougher with increasing V/III ratio and the hillock density increased.

Channel doping concentration and cell program state dependence on random telegraph noise spatial and statistical distribution in 30 nm NAND flash memory

NASA Astrophysics Data System (ADS)

Tomita, Toshihiro; Miyaji, Kousuke

2015-04-01

The dependence of spatial and statistical distribution of random telegraph noise (RTN) in a 30 nm NAND flash memory on channel doping concentration NA and cell program state Vth is comprehensively investigated using three-dimensional Monte Carlo device simulation considering random dopant fluctuation (RDF). It is found that single trap RTN amplitude ΔVth is larger at the center of the channel region in the NAND flash memory, which is closer to the jellium (uniform) doping results since NA is relatively low to suppress junction leakage current. In addition, ΔVth peak at the center of the channel decreases in the higher Vth state due to the current concentration at the shallow trench isolation (STI) edges induced by the high vertical electrical field through the fringing capacitance between the channel and control gate. In such cases, ΔVth distribution slope λ cannot be determined by only considering RDF and single trap.

Effect of cadmium telluride quantum dots on the dielectric and electro-optical properties of ferroelectric liquid crystals.

PubMed

Kumar, A; Biradar, A M

2011-04-01

We present here the dielectric and electro-optical studies of cadmium telluride quantum dots (CdTe QDs) doped ferroelectric liquid crystals (FLCs). It has been observed that the doping of CdTe QDs not only induced a pronounced memory effect but also affected the physical parameters of FLC material (LAHS19). The modifications in the physical parameters and memory effect of LAHS19 are found to depend on the concentration ratio of CdTe QDs. The lower concentration of CdTe QDs (1-3 wt%) enhanced the values of spontaneous polarization and rotational viscosity of LAHS19 material but did not favor the memory effect, whereas a higher concentration of CdTe QDs (>5 wt%) degraded the alignment of LAHS19 material. The doping of ∼5 wt% of CdTe QDs is found to be the most suitable for achieving good memory effect without significantly affecting the material parameters. ©2011 American Physical Society

Development of Ceramic Solid-State Laser Host Material

NASA Technical Reports Server (NTRS)

Prasad, Narasimha S.; Trivedi, Sudhir; Kutcher, Susan; Wang, Chen-Chia; Kim, Joo-Soo; Hommerich, Uwe; Shukla, Vijay; Sadangi, Rajendra

2009-01-01

Polycrystalline ceramic laser materials are gaining importance in the development of novel diode-pumped solid-state lasers. Compared to single-crystals, ceramic laser materials offer advantages in terms of ease of fabrication, shape, size, and control of dopant concentrations. Recently, we have developed Neodymium doped Yttria (Nd:Y2O3) as a solid-state ceramic laser material. A scalable production method was utilized to make spherical non agglomerated and monodisperse metastable ceramic powders of compositions that were used to fabricate polycrystalline ceramic material components. This processing technique allowed for higher doping concentrations without the segregation problems that are normally encountered in single crystalline growth. We have successfully fabricated undoped and Neodymium doped Yttria material up to 2" in diameter, Ytterbium doped Yttria, and erbium doped Yttria. We are also in the process of developing other sesquioxides such as scandium Oxide (Sc2O3) and Lutesium Oxide (Lu2O3) doped with Ytterbium, erbium and thulium dopants. In this paper, we present our initial results on the material, optical, and spectroscopic properties of the doped and undoped sesquioxide materials. Polycrystalline ceramic lasers have enormous potential applications including remote sensing, chem.-bio detection, and space exploration research. It is also potentially much less expensive to produce ceramic laser materials compared to their single crystalline counterparts because of the shorter fabrication time and the potential for mass production in large sizes.

High Thermoelectric Power Factor of a Diketopyrrolopyrrole-Based Low Bandgap Polymer via Finely Tuned Doping Engineering

PubMed Central

Jung, In Hwan; Hong, Cheon Taek; Lee, Un-Hak; Kang, Young Hun; Jang, Kwang-Suk; Cho, Song Yun

2017-01-01

We studied the thermoelectric properties of a diketopyrrolopyrrole-based semiconductor (PDPP3T) via a precisely tuned doping process using Iron (III) chloride. In particular, the doping states of PDPP3T film were linearly controlled depending on the dopant concentration. The outstanding Seebeck coefficient of PDPP3T assisted the excellent power factors (PFs) over 200 μW m−1K−2 at the broad range of doping concentration (3–8 mM) and the maximum PF reached up to 276 μW m−1K−2, which is much higher than that of poly(3-hexylthiophene), 56 μW m−1K−2. The high-mobility of PDPP3T was beneficial to enhance the electrical conductivity and the low level of total dopant volume was important to maintain high Seebeck coefficients. In addition, the low bandgap PDPP3T polymer effiectively shifted its absorption into near infra-red area and became more colorless after doping, which is great advantage to realize transparent electronic devices. Our results give importance guidance to develop thermoelectric semiconducting polymers and we suggest that the use of low bandgap and high-mobility polymers, and the accurate control of the doping levels are key factors for obtaining the high thermoelectric PF. PMID:28317929

Direct Observation of Surface Potential Distribution in Insulation Resistance Degraded Acceptor-Doped BaTiO3 Multilayered Ceramic Capacitors

NASA Astrophysics Data System (ADS)

Hong, Kootak; Lee, Tae Hyung; Suh, Jun Min; Park, Jae-Sung; Kwon, Hyung-Soon; Choi, Jaeho; Jang, Ho Won

2018-05-01

Insulation resistance (IR) degradation in BaTiO3 is a key issue for developing miniaturized multilayer ceramic capacitors (MLCCs) with high capacity. Despite rapid progress in BaTiO3-based MLCCs, the mechanism of IR degradation is still controversial. In this study, we demonstrate the Al doping effect on IR degradation behavior of BaTiO3 MLCCs by electrical measurements and scanning Kelvin probe microscopy (SKPM). As the Al doping concentration in BaTiO3 increases, IR degradation of MLCCs seems to be suppressed from electrical characterization results. However, SKPM results reveal that the conductive regions near the cathode become lager with Al doping after IR degradation. The formation of conducting regions is attributed to the migration of oxygen vacancies, which is the origin of IR degradation in BaTiO3, in dielectric layers. These results imply that acceptor doping in BaTiO3 solely cannot suppress the IR degradation in MLCC even though less asymmetric IR characteristics and IR degradation in MLCCs with higher Al doping concentration are observed from electrical characterization. Our results strongly suggest that observing the surface potential distribution in IR degraded dielectric layers using SKPM is an effective method to unravel the mechanism of IR degradation in MLCCs.

Impurity Resonant States p-type Doping in Wide-Band-Gap Nitrides

PubMed Central

Liu, Zhiqiang; Yi, Xiaoyan; Yu, Zhiguo; Yuan, Gongdong; Liu, Yang; Wang, Junxi; Li, Jinmin; Lu, Na; Ferguson, Ian; Zhang, Yong

2016-01-01

In this work, a new strategy for achieving efficient p-type doping in high bandgap nitride semiconductors to overcome the fundamental issue of high activation energy has been proposed and investigated theoretically, and demonstrated experimentally. Specifically, in an AlxGa1−xN/GaN superlattice structure, by modulation doping of Mg in the AlxGa1−xN barriers, high concentration of holes are generated throughout the material. A hole concentration as high as 1.1 × 1018 cm−3 has been achieved, which is about one order of magnitude higher than that typically achievable by direct doping GaN. Results from first-principle calculations indicate that the coupling and hybridization between Mg 2p impurity and the host N 2p orbitals are main reasons for the generation of resonant states in the GaN wells, which further results in the high hole concentration. We expect this approach to be equally applicable for other high bandgap materials where efficient p-type doing is difficult. Furthermore, a two-carrier-species Hall-effect model is proposed to delineate and discriminate the characteristics of the bulk and 2D hole, which usually coexist in superlattice-like doping systems. The model reported here can also be used to explain the abnormal freeze-in effect observed in many previous reports. PMID:26777294

Improving the Optoelectronic Properties of Mesoporous TiO2 by Cobalt Doping for High-Performance Hysteresis-free Perovskite Solar Cells.

PubMed

Sidhik, Siraj; Cerdan Pasarán, Andrea; Esparza, Diego; López Luke, Tzarara; Carriles, Ramón; De la Rosa, Elder

2018-01-31

We for the first time report the incorporation of cobalt into a mesoporous TiO 2 electrode for application in perovskite solar cells (PSCs). The Co-doped PSC exhibits excellent optoelectronic properties; we explain the improvements by passivation of electronic trap or sub-band-gap states arising due to the oxygen vacancies in pristine TiO 2 , enabling faster electron transport and collection. A simple postannealing treatment is used to prepare the cobalt-doped mesoporous electrode; UV-visible spectroscopy, X-ray photoemission spectroscopy, space charge-limited current, photoluminescence, and electrochemical impedance measurements confirm the incorporation of cobalt, enhanced conductivity, and the passivation effect induced in the TiO 2 . An optimized doping concentration of 0.3 mol % results in the maximum power conversion efficiency of 18.16%, 21.7% higher than that of a similar cell with an undoped TiO 2 electrode. Also, the device shows negligible hysteresis and higher stability, retaining 80.54% of the initial efficiency after 200 h.

Effect of modulation p-doping level on multi-state lasing in InAs/InGaAs quantum dot lasers having different external loss

NASA Astrophysics Data System (ADS)

Korenev, V. V.; Savelyev, A. V.; Maximov, M. V.; Zubov, F. I.; Shernyakov, Yu. M.; Kulagina, M. M.; Zhukov, A. E.

2017-09-01

The influence of the modulation p-doping level on multi-state lasing in InAs/InGaAs quantum dot (QD) lasers is studied experimentally for devices having various external losses. It is shown that in the case of short cavities (high external loss), there is an increase in the lasing power component corresponding to the ground-state optical transitions of QDs as the p-doping level grows. However, in the case of long cavities (small external loss), higher dopant concentrations may have an opposite effect on the output power. Based on these observations, an optimal design of laser geometry and an optimal doping level are discussed.

Influence of defects and doping on phonon transport properties of monolayer MoSe2

NASA Astrophysics Data System (ADS)

Yan, Zhequan; Yoon, Mina; Kumar, Satish

2018-07-01

The doping of monolayer MoSe2 by tungsten (W) can suppress the Se vacancy concentration, but how doping and resulting change in defect concentration can tune its thermal properties is not understood yet. We use first-principles density functional theory (DFT) along with the phonon Boltzmann transport equation (BTE) to study the phonon transport properties of pristine MoSe2 and W doped MoSe2 with and without the presence of Se vacancies. We found that for samples without Se vacancy, the W doping could enhance the thermal transport of monolayer MoSe2 due to reduced three-phonon scattering phase space. For example, we observed that the 16.7% W doping increases the thermal conductivity of the monolayer MoSe2 with 2% Se vacancy by 80% if all vacancies can be suppressed by W-doping. However, the W doping in the defective MoSe2 amplifies the influence of the phonon scattering caused by the Se vacancies, which results in a further decrease in thermal conductivity of monolayer MoSe2 with defects. This is found to be related with higher phonon density of states of Mo0.83W0.17Se2 and larger mass difference between W and Se atoms compared to Mo and Se atoms. This study deciphers the effect of defects and doping on the thermal conductivity of monolayer MoSe2, which helps us understand the mechanism of defect-induced phonon transport, and provides insights into enhancing the heat dissipation in MoSe2-based electronic devices.

Vacancy defects and optoelectrical properties for fluorine tin oxide thin films with various SnF2 contents

NASA Astrophysics Data System (ADS)

Zhou, Yawei; Xu, Wenwu; Li, Jingjing; Yin, Chongshan; Liu, Yong; Zhao, Bin; Chen, Zhiquan; He, Chunqing; Mao, Wenfeng; Ito, Kenji

2018-01-01

Fluorine doped tin oxide (FTO) thin films were deposited on glass substrates by e-beam evaporation. Much higher carrier concentration, broader optical band gap, and average transmittance over 80% were obtained with SnF2 doped SnO2 thin films. Positron annihilation results showed that there are two kinds of vacancy clusters with different sizes existing in the annealed FTO thin films, and the concentration of the larger vacancy clusters of VSnO in the thin films increases with increasing SnF2 contents. Meanwhile, photoluminescence spectra results indicated that the better electrical and optical properties of the FTO thin films are attributed to FO substitutions and oxygen vacancies with higher concentration, which are supported by positron annihilation Doppler broadening results and confirmed by X-ray photoelectron spectroscopy. The results showed that widening of the optical band gap of the FTO thin films strongly depends on the carrier concentration, which is interpreted for the Burstein-Moss effect and is associated with the formation of FO and oxygen vacancies with increasing SnF2 content.

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

Effect of the concentration of magnetic grains on the linear-optical-absorption coefficient of ferrofluid-doped lyotropic mesophases: deviation from the Beer-Lambert law.

PubMed

Cuppo, F L S; Gómez, S L; Figueiredo Neto, A M

2004-04-01

In this paper is reported a systematic experimental study of the linear-optical-absorption coefficient of ferrofluid-doped isotropic lyotropic mixtures as a function of the magnetic-grains concentration. The linear optical absorption of ferrolyomesophases increases in a nonlinear manner with the concentration of magnetic grains, deviating from the usual Beer-Lambert law. This behavior is associated to the presence of correlated micelles in the mixture which favors the formation of small-scale aggregates of magnetic grains (dimers), which have a higher absorption coefficient with respect to that of isolated grains. We propose that the indirect heating of the micelles via the ferrofluid grains (hyperthermia) could account for this nonlinear increase of the linear-optical-absorption coefficient as a function of the grains concentration.

Chemical state analysis of heavily phosphorus-doped epitaxial silicon films grown on Si (1 0 0) by X-ray photoelectron spectroscopy

NASA Astrophysics Data System (ADS)

Lee, Minhyeong; Kim, Sungtae; Ko, Dae-Hong

2018-06-01

In this work, we investigated the chemical bonding states in highly P-doped Si thin films epitaxially grown on Si (0 0 1) substrates using high-resolution X-ray photoelectron spectroscopy (HR-XPS). HR-XPS P 2p core-level spectra clearly show spin-orbital splitting between P 2p1/2 and P 2p3/2 peaks in Si films doped with a high concentration of P. Moreover, the intensities of P 2p1/2 and P 2p3/2 peaks for P-doped Si films increase with P concentrations, while their binding energies remained almost identical. These results indicate that more P atoms are incorporated into the substitutional sites of the Si lattice with the increase of P concentrations. In order to identify the chemical states of P-doped Si films shown in XPS Si 2p spectra, the spectra of bulk Si were subtracted from those of Si:P samples, which enables us to clearly identify the new chemical state related to Sisbnd P bonds. We observed that the presence of the two well-resolved new peaks only for the Si:P samples at the binding energy higher than those of a Sisbnd Si bond, which is due to the strong electronegativity of P than that of Si. Experimental findings in this study using XPS open up new doors for evaluating the chemical states of P-doped Si materials in fundamental researches as well as in industrial applications.

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.

Search for and Study of Novel Superconductor with Higher Tc and Jc

DTIC Science & Technology

2015-12-22

system. The high onset-Tc is also found to be RE- independent and dopant concentration independent. - Carried out detailed chemical composition...pure and doped multiferroics and demonstrated that the nature of dopants , including Fe, Co, Ni, Cu, Zn, can change the characteristics of the phase...Lorenz, and C. W. Chu, Journal of Applied Physics 111, 07D903 (2012). "Magnetic order and spin-flop transitions in the cobalt -doped multiferroic Mn1

Morphology-modulation of SnO2 Hierarchical Architectures by Zn Doping for Glycol Gas Sensing and Photocatalytic Applications

NASA Astrophysics Data System (ADS)

Zhao, Qinqin; Ju, Dianxing; Deng, Xiaolong; Huang, Jinzhao; Cao, Bingqiang; Xu, Xijin

2015-01-01

The morphology of SnO2 nanospheres was transformed into ultrathin nanosheets assembled architectures after Zn doping by one-step hydrothermal route. The as-prepared samples were characterized in detail by various analytical techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and nitrogen adsorption-desorption technique. The Zn-doped SnO2 nanostructures proved to be the efficient gas sensing materials for a series of flammable and explosive gases detection, and photocatalysts for the degradation of methyl orange (MO) under UV irradiation. It was observed that both of the undoped and Zn-doped SnO2 after calcination exhibited tremendous gas sensing performance toward glycol. The response (S = Ra/Rg) of Zn-doped SnO2 can reach to 90 when the glycol concentration is 100 ppm, which is about 2 times and 3 times higher than that of undoped SnO2 sensor with and without calcinations, respectively. The result of photocatalytic activities demonstrated that MO dye was almost completely degraded (~92%) by Zn-doped SnO2 in 150 min, which is higher than that of others (MO without photocatalyst was 23%, undoped SnO2 without and with calcination were 55% and 75%, respectively).

Morphology-modulation of SnO2 Hierarchical Architectures by Zn Doping for Glycol Gas Sensing and Photocatalytic Applications

PubMed Central

Zhao, Qinqin; Ju, Dianxing; Deng, Xiaolong; Huang, Jinzhao; Cao, Bingqiang; Xu, Xijin

2015-01-01

The morphology of SnO2 nanospheres was transformed into ultrathin nanosheets assembled architectures after Zn doping by one-step hydrothermal route. The as-prepared samples were characterized in detail by various analytical techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and nitrogen adsorption-desorption technique. The Zn-doped SnO2 nanostructures proved to be the efficient gas sensing materials for a series of flammable and explosive gases detection, and photocatalysts for the degradation of methyl orange (MO) under UV irradiation. It was observed that both of the undoped and Zn-doped SnO2 after calcination exhibited tremendous gas sensing performance toward glycol. The response (S = Ra/Rg) of Zn-doped SnO2 can reach to 90 when the glycol concentration is 100 ppm, which is about 2 times and 3 times higher than that of undoped SnO2 sensor with and without calcinations, respectively. The result of photocatalytic activities demonstrated that MO dye was almost completely degraded (~92%) by Zn-doped SnO2 in 150 min, which is higher than that of others (MO without photocatalyst was 23%, undoped SnO2 without and with calcination were 55% and 75%, respectively). PMID:25597269

Structure and thermoelectric property of Te doped paracostibite CoSb1-xTexS compounds

NASA Astrophysics Data System (ADS)

You, Yonghui; Su, Xianli; Liu, Wei; Yan, Yonggao; Fu, Jiefei; Cheng, Xin; Zhang, Cheng; Tang, Xinfeng

2018-06-01

Paracostibite (CoSbS), a newly developed thermoelectric material, has aroused lots of interest due to its highly earth abundant and inexpensive constituent elements and potential application for thermoelectric power generation in the intermediate temperature range. Herein, a series of CoSb1-xTexS (x = 0-0.09) compounds were prepared by vacuum melting and annealing followed by SPS processing, and the effects of Te doping on the structure and thermoelectric properties were systematically investigated. Doping Te on the Sb site increases the carrier concentration up to 7.24 × 1020 cm-3 for CoSb0.93Te0.07S compound which is several orders of magnitude higher than that of un-doped CoSbS, and enhances the power factor. The maximum power factor of 14.07 μW cm-1 K-2 is attained at 900 K. Concomitantly, doping with Te on the Sb site leads to effective scattering of heat carrying phonon, accompanying with a strong suppression of the thermal conductivity with the increase of Te content, resulting in an increase of the ZT. A maximum ZT of 0.43 at 900 K is attained for CoSb0.93Te0.07S compound, which is 139% higher than that of un-doped CoSbS compound.

Improved ferroelectric and pyroelectric parameters in iminodiacetic acid doped TGS crystal

NASA Astrophysics Data System (ADS)

Rai, Chitharanjan; Sreenivas, K.; Dharmaprakash, S. M.

2010-01-01

Single crystals of Iminodiacetic acid (HN(CH 2COOH) 2) doped Triglycine sulphate (IDATGS) has been grown from aqueous solution at constant temperature by slow evaporation technique. The concentration of the dopant in the TGS solution was 2 mol%. The X-ray diffraction analysis indicates that there is significant change in the lattice parameters compared to pure TGS crystal. The IDATGS crystal has larger transition temperature and observed higher and uniform figure of merit over most part of the ferroelectric phase. These crystals also exhibit higher internal bias field and micro-hardness number compared to pure TGS. Therefore IDATGS may be a potential material for IR detectors.

Impedance spectroscopy of undoped and Cr-doped ZnO gas sensors under different oxygen concentrations

NASA Astrophysics Data System (ADS)

Al-Hardan, N.; Abdullah, M. J.; Aziz, A. Abdul

2011-08-01

Thin films of undoped and chromium (Cr)-doped zinc oxide (ZnO) were synthesized by RF reactive co-sputtering for oxygen gas sensing applications. The prepared films showed a highly c-axis oriented phase with a dominant (0 0 2) peak appeared at a Bragg angle of around 34.13 °, which was lower than that of the standard reference of ZnO powder (34.42 °). The peak shifted to a slightly higher angle with Cr doping. The operating temperature of the ZnO gas sensor was around 350 °C, which shifted to around 250 °C with Cr-doping. The response of the sensor to oxygen gas was enhanced by doping ZnO with 1 at.% Cr. Impedance spectroscopy analysis showed that the resistance due to grain boundaries significantly contributed to the characteristics of the gas sensor.

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.

Addition of oxygen to and distribution of oxides in tantalum alloy T-111 at low concentrations

NASA Technical Reports Server (NTRS)

Stecura, S.

1975-01-01

Oxygen was added at 820 and 990 C at an oxygen pressure of about .0003 torr. The technique permitted predetermined and reproducible oxygen doping of the tantalum alloy (T-111). Based on the temperature dependency of the doping reaction, it was concluded that the initial rates of oxygen pickup are probably controlled by solution of oxygen into the T-111 lattice. Although hafnium oxides are more stable than those of tantalum or tungsten, analyses of extracted residues indicate that the tantalum and tungsten oxides predominate in the as-doped specimens, presumably because of the higher concentrations of tantalum and tungsten in the alloy. However, high-temperature annealing promotes gettering of dissolved oxygen and oxygen from other oxides to form hafnium oxides. Small amounts of tantalum and tungsten oxides were still present after high temperature annealing. Tungsten oxide (WO3) volatilizes slightly from the surface of T-111 at 990 C but not at 820 C. The vaporization of WO3 has no apparent effect on the doping reaction.

Cobalt-doped nanohydroxyapatite: synthesis, characterization, antimicrobial and hemolytic studies

NASA Astrophysics Data System (ADS)

Tank, Kashmira P.; Chudasama, Kiran S.; Thaker, Vrinda S.; Joshi, Mihir J.

2013-05-01

Hydroxyapatite (Ca10(PO4)6(OH)2; HAP) is a major mineral component of the calcified tissues, and it has various applications in medicine and dentistry. In the present investigation, cobalt-doped hydroxyapatite (Co-HAP) nanoparticles were synthesized by surfactant-mediated approach and characterized by different techniques. The EDAX was carried out to estimate the amount of doping in Co-HAP. The transmission electron microscopy result suggested the transformation of morphology from needle shaped to spherical type on increasing the doping concentration. The powder XRD study indicated the formation of a new phase of brushite for higher concentration of cobalt. The average particle size and strain were calculated using Williamson-Hall analysis. The average particle size was found to be 30-60 nm. The FTIR study confirmed the presence of various functional groups in the samples. The antimicrobial activity was evaluated against four organisms Pseudomonas aeruginosa and Shigella flexneri as Gram negative as well as Micrococcus luteus and Staphylococcus aureus as Gram positive. The hemolytic test result suggested that all samples were non-hemolytic. The photoluminescence study was carried out to identify its possible applicability as a fluorescent probe.

Investigating the effect of V{sub 2}O{sub 5} addition on sodium barium borosilicate glasses

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

Halder, Rumu, E-mail: rumuhalder24feb@gmail.com; Sengupta, Pranesh; Dey, G. K.

2016-05-23

V{sub 2}O{sub 5} doped sodium barium borosilicate glasses were characterized by photoluminescence spectroscopy and electron probe microanalyzer (EPMA). The glass remains homogeneous for lower concentration of V{sub 2}O{sub 5} but a phase separation is observed when V{sub 2}O{sub 5} doping is increased beyond 5 mol%. Detailed microanalysis reveals that the phase separated glass consists of a phase containing V, Ba and Si and a separate Si rich phase within the glass matrix. The luminescence study demonstrated that at low concentration the vanadium mainly interacts with the structural units of B/Si while at higher concentrations, V-O-V/ V-O{sup −} Na{sup +}/Ba{sup 2+} linkagesmore » are formed.« less

Confined Doping for Control of Transport Properties in Nanowires and Nanofilms

NASA Astrophysics Data System (ADS)

Zhong, Jianxin; Stocks, G. Malcolm

2006-03-01

Doping, an essential element for manipulation of electronic transport in traditional semiconductor industry, is widely expected to play important role as well in control of transport properties in nanostructures. However, traditional theory of electronic disorder predicts that doping in one-dimensional and two-dimensional systems leads to carrier localization, limiting practical applications due to poor carrier mobility. Here, a novel concept is proposed that offers the possibility to significantly increase carrier mobility by confining the distribution of dopants within a particular region [1]. Thus, the doped nanostructure becomes a coupled system comprising a doped subsystem and a perfect crystalline subsystem. We showed that carrier mobility in such a dopped nanowire or a nanofilm exhibits counterintuitive behavior in the regime of heavy doping. In particular, the larger the dopant concentration the higher the carrier mobility; we trace this transition to the existence of quasi-mobility-edges in the nanowires and mobility edges in nanofilms. *J.X. Zhong and G.M. Stocks, Nano Lett., in press, (2005)

Thermoelectric Properties of Bi2Te3: CuI and the Effect of Its Doping with Pb Atoms

PubMed Central

Han, Mi-Kyung; Lee, Da-Hee; Kim, Sung-Jin

2017-01-01

In order to understand the effect of Pb-CuI co-doping on the thermoelectric performance of Bi2Te3, n-type Bi2Te3 co-doped with x at % CuI and 1/2x at % Pb (x = 0, 0.01, 0.03, 0.05, 0.07, and 0.10) were prepared via high temperature solid state reaction and consolidated using spark plasma sintering. Electron and thermal transport properties, i.e., electrical conductivity, carrier concentration, Hall mobility, Seebeck coefficient, and thermal conductivity, of CuI-Pb co-doped Bi2Te3 were measured in the temperature range from 300 K to 523 K, and compared to corresponding x% of CuI-doped Bi2Te3 and undoped Bi2Te3. The addition of a small amount of Pb significantly decreased the carrier concentration, which could be attributed to the holes from Pb atoms, thus the CuI-Pb co-doped samples show a lower electrical conductivity and a higher Seebeck coefficient when compared to CuI-doped samples with similar x values. The incorporation of Pb into CuI-doped Bi2Te3 rarely changed the power factor because of the trade-off relationship between the electrical conductivity and the Seebeck coefficient. The total thermal conductivity(κtot) of co-doped samples (κtot ~ 1.4 W/m∙K at 300 K) is slightly lower than that of 1% CuI-doped Bi2Te3 (κtot ~ 1.5 W/m∙K at 300 K) and undoped Bi2Te3 (κtot ~ 1.6 W/m∙K at 300 K) due to the alloy scattering. The 1% CuI-Pb co-doped Bi2Te3 sample shows the highest ZT value of 0.96 at 370 K. All data on electrical and thermal transport properties suggest that the thermoelectric properties of Bi2Te3 and its operating temperature can be controlled by co-doping. PMID:29072613

Thermoelectric Properties of Bi₂Te₃: CuI and the Effect of Its Doping with Pb Atoms.

PubMed

Han, Mi-Kyung; Jin, Yingshi; Lee, Da-Hee; Kim, Sung-Jin

2017-10-26

In order to understand the effect of Pb-CuI co-doping on the thermoelectric performance of Bi₂Te₃, n -type Bi₂Te₃ co-doped with x at % CuI and 1/2 x at % Pb ( x = 0, 0.01, 0.03, 0.05, 0.07, and 0.10) were prepared via high temperature solid state reaction and consolidated using spark plasma sintering. Electron and thermal transport properties, i.e., electrical conductivity, carrier concentration, Hall mobility, Seebeck coefficient, and thermal conductivity, of CuI-Pb co-doped Bi₂Te₃ were measured in the temperature range from 300 K to 523 K, and compared to corresponding x % of CuI-doped Bi₂Te₃ and undoped Bi₂Te₃. The addition of a small amount of Pb significantly decreased the carrier concentration, which could be attributed to the holes from Pb atoms, thus the CuI-Pb co-doped samples show a lower electrical conductivity and a higher Seebeck coefficient when compared to CuI-doped samples with similar x values. The incorporation of Pb into CuI-doped Bi₂Te₃ rarely changed the power factor because of the trade-off relationship between the electrical conductivity and the Seebeck coefficient. The total thermal conductivity(κ tot ) of co-doped samples (κ tot ~ 1.4 W/m∙K at 300 K) is slightly lower than that of 1% CuI-doped Bi₂Te₃ (κ tot ~ 1.5 W/m∙K at 300 K) and undoped Bi₂Te₃ (κ tot ~ 1.6 W/m∙K at 300 K) due to the alloy scattering. The 1% CuI-Pb co-doped Bi₂Te 3 sample shows the highest ZT value of 0.96 at 370 K. All data on electrical and thermal transport properties suggest that the thermoelectric properties of Bi₂Te 3 and its operating temperature can be controlled by co-doping.

Synthesis and characterization of barium hexaferrite with manganese (Mn) doping material as anti-radar

NASA Astrophysics Data System (ADS)

Susilawati, Doyan, Aris; Khalilurrahman

2017-01-01

Have been successfully synthesized barium powder doping Manganese hexaferrite with the expected potential as anti-radar material. Synthesis was done by using the co-precipitation method, the variation of the variable x concentrations used were 0; 0.2; 0.4; and 0.6 and calcined at temperatures of 400, 600 and 800°C. Characterization powders of hexaferrite have used XRD (X-Ray Diffraction), SEM (Scanning Electron Microscopy), TEM (Transmission Electron Microscopy), LCR (inductance, capacitance, and resistance) meter, and VSM (Vibrating Sample Magnetometer). The higher the concentration and temperature of calcinations given affect the color of the powder. The test results using XRD indicates that it has formed barium hexaferrite phase with a hexagonal crystal structure. Tests using SEM showed that all the constituent elements barium powder hexaferrite by doping Manganese powders have been spread evenly. XRD test results were confirmed by a test using a TEM showing the crystal structure and the powder was sized nano particles. The results from the LCR meter showed that the barium powder hexaferrite by doping Manganese that has been synthesized classified in semiconductor materials. The result from VSM showed that the value of coercivity magnetic powder doped barium hexaferrite Manganese is smaller when compared with barium hexaferrite without doping and belong to the soft magnetic. Based on the results of the synthesis and characterization, we can conclude that the barium powder heksaferrite by doping Manganese potential as a material anti-radar.

Color tunable emission through energy transfer from Yb3+ co-doped SrSnO3: Ho3+ perovskite nano-phosphor

NASA Astrophysics Data System (ADS)

Jain, Neha; Singh, Rajan Kr.; Sinha, Shriya; Singh, R. A.; Singh, Jai

2018-04-01

First time color tunable lighting observed from Ho3+ and Yb3+ co-doped SrSnO3 perovskite. Down-conversion and up-conversion (UC) photoluminescence emission spectra were recorded to understand the whole mechanism of energy migration between Ho3+ and Yb3+ ions. The intensity of green and red emission varies with Yb3+ doping which causes multicolour emissions from nano-phosphor. The intensity of UC red emission (654 nm) obtained from 1 at.% Ho3+ and 3 at.% Yb3+ co-doped nano-phosphor is nine times higher than from 1 at.% Ho3+ doped SrSnO3 nano-phosphor. Enhanced brightness of 654 nm in UC process belongs in biological transparency window so that it might be a promising phosphor in the bio-medical field. Moreover, for the other Yb3+ co-doped nano-phosphor, Commission Internationale de l'Éclairage chromaticity co-ordinates were found near the white region and their CCT values lie in the range 4900-5100 K indicating cool white. Decay time was measured for 545 nm emission of Ho3+ ion found in 7.652 and 8.734 µs at 355 nm excitation. The variation in lifetime was observed in ascending order with increasing Yb3+ concentration which supports PL emission spectra observation that with increasing Yb3+ concentration, rate of transition has changed. These studies reveal that Ho3+ and Yb3+ co-doped phosphor is useful for fabrication of white LEDs.

Influence of native defects on structural and electronic properties of magnesium silicide

NASA Astrophysics Data System (ADS)

Hirayama, Naomi; Iida, Tsutomu; Nishio, Keishi; Kogo, Yasuo; Takarabe, Kenji; Hamada, Noriaki

2017-05-01

The narrow-gap semiconductor magnesium silicide (Mg2Si) is a promising candidate for mid-temperature (500-800 K) thermoelectric applications. Mg2Si exhibits intrinsic n-type conductivity because of its interstitial Mg defects and is generally doped with n-type dopants; however, the synthesis of p-type Mg2Si has proven difficult. In the present study, we examined several types of defects, such as vacancies and the insertion of constituent atoms (Mg and Si) into crystals, to elucidate their stability in Mg2Si and their influence on its electronic states. A first-principles calculation has revealed that the insertion of Mg into a cell is the most stable and causes n-type conductivity in terms of formation energy. In contrast, the vacancy of Mg produces hole doping although its formation energy per conventional unit cell is approximately 0.07 eV higher than that of the insertion of Mg, at their concentration of 1.04 at. %. Furthermore, the insertion and vacancy of Si atoms generate electrons with higher formation energies compared to the Mg-related defects. As these defects alter the carrier concentration, they can compensate for intentional doping because of the added impurity atoms.

Buffer Layer Doping Concentration Measurement Using VT-VSUB Characteristics of GaN HEMT with p-GaN Substrate Layer

NASA Astrophysics Data System (ADS)

Hu, Cheng-Yu; Nakatani, Katsutoshi; Kawai, Hiroji; Ao, Jin-Ping; Ohno, Yasuo

To improve the high voltage performance of AlGaN/GaN heterojunction field effect transistors (HFETs), we have fabricated AlGaN/GaN HFETs with p-GaN epi-layer on sapphire substrate with an ohmic contact to the p-GaN (p-sub HFET). Substrate bias dependent threshold voltage variation (VT-VSUB) was used to directly determine the doping concentration profile in the buffer layer. This VT-VSUB method was developed from Si MOSFET. For HFETs, the insulator is formed by epitaxially grown and heterogeneous semiconductor layer while for Si MOSFETs the insulator is amorphous SiO2. Except that HFETs have higher channel mobility due to the epitaxial insulator/semiconductor interface, HFETs and Si MOSFETs are basically the same in the respect of device physics. Based on these considerations, the feasibility of this VT-VSUB method for AlGaN/GaN HFETs was discussed. In the end, the buffer layer doping concentration was measured to be 2 × 1017cm-3, p-type, which is well consistent with the Mg concentration obtained from secondary ion mass spectroscopy (SIMS) measurement.

Comparison of solution-mixed and sequentially processed P3HT: F4TCNQ films: effect of doping-induced aggregation on film morphology

DOE PAGES

Jacobs, Ian E.; Aasen, Erik W.; Oliveira, Julia L.; ...

2016-03-23

Doping polymeric semiconductors often drastically reduces the solubility of the polymer, leading to difficulties in processing doped films. Here, we compare optical, electrical, and morphological properties of P3HT films doped with F4TCNQ, both from mixed solutions and using sequential solution processing with orthogonal solvents. We demonstrate that sequential doping occurs rapidly (<1 s), and that the film doping level can be precisely controlled by varying the concentration of the doping solution. Furthermore, the choice of sequential doping solvent controls whether dopant anions are included or excluded from polymer crystallites. Atomic force microscopy (AFM) reveals that sequential doping produces significantly moremore » uniform films on the nanoscale than the mixed-solution method. In addition, we show that mixed-solution doping induces the formation of aggregates even at low doping levels, resulting in drastic changes to film morphology. Sequentially coated films show 3–15 times higher conductivities at a given doping level than solution-doped films, with sequentially doped films processed to exclude dopant anions from polymer crystallites showing the highest conductivities. In conclusion, we propose a mechanism for doping induced aggregation in which the shift of the polymer HOMO level upon aggregation couples ionization and solvation energies. To show that the methodology is widely applicable, we demonstrate that several different polymer:dopant systems can be prepared by sequential doping.« less

Comparison of solution-mixed and sequentially processed P3HT: F4TCNQ films: effect of doping-induced aggregation on film morphology

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

Jacobs, Ian E.; Aasen, Erik W.; Oliveira, Julia L.

Doping polymeric semiconductors often drastically reduces the solubility of the polymer, leading to difficulties in processing doped films. Here, we compare optical, electrical, and morphological properties of P3HT films doped with F4TCNQ, both from mixed solutions and using sequential solution processing with orthogonal solvents. We demonstrate that sequential doping occurs rapidly (<1 s), and that the film doping level can be precisely controlled by varying the concentration of the doping solution. Furthermore, the choice of sequential doping solvent controls whether dopant anions are included or excluded from polymer crystallites. Atomic force microscopy (AFM) reveals that sequential doping produces significantly moremore » uniform films on the nanoscale than the mixed-solution method. In addition, we show that mixed-solution doping induces the formation of aggregates even at low doping levels, resulting in drastic changes to film morphology. Sequentially coated films show 3–15 times higher conductivities at a given doping level than solution-doped films, with sequentially doped films processed to exclude dopant anions from polymer crystallites showing the highest conductivities. In conclusion, we propose a mechanism for doping induced aggregation in which the shift of the polymer HOMO level upon aggregation couples ionization and solvation energies. To show that the methodology is widely applicable, we demonstrate that several different polymer:dopant systems can be prepared by sequential doping.« less

Electrical characterisation of deep level defects in Be-doped AlGaAs grown on (100) and (311)A GaAs substrates by MBE

PubMed Central

2011-01-01

The growth of high mobility two-dimensional hole gases (2DHGs) using GaAs-GaAlAs heterostructures has been the subject of many investigations. However, despite many efforts hole mobilities in Be-doped structures grown on (100) GaAs substrate remained considerably lower than those obtained by growing on (311)A oriented surface using silicon as p-type dopant. In this study we will report on the properties of hole traps in a set of p-type Be-doped Al0.29Ga0.71As samples grown by molecular beam epitaxy on (100) and (311)A GaAs substrates using deep level transient spectroscopy (DLTS) technique. In addition, the effect of the level of Be-doping concentration on the hole deep traps is investigated. It was observed that with increasing the Be-doping concentration from 1 × 1016 to 1 × 1017 cm-3 the number of detected electrically active defects decreases for samples grown on (311)A substrate, whereas, it increases for (100) orientated samples. The DLTS measurements also reveal that the activation energies of traps detected in (311)A are lower than those in (100). From these findings it is expected that mobilities of 2DHGs in Be-doped GaAs-GaAlAs devices grown on (311)A should be higher than those on (100). PMID:21711687

Effects of doping concentration ratio on electrical characterization in pseudomorphic HEMT-based MMIC switches for ICT system

NASA Astrophysics Data System (ADS)

Mun, Jae-Kyoung; Oh, Jung-Hun; Sung, Ho-Kun; Wang, Cong

2015-12-01

The effects of the doping concentration ratios between upper and lower silicon planar-doping layers on the DC and RF characteristics of the double planar doped pseudomorphic high electron mobility transistors (pHEMTs) are investigated. From the device simulation, an increase of maximum extrinsic transconductance and a decrease of total on- and off-state capacitances are observed, as well as an increase of the upper to lower planar-doping concentration ratios (UTLPDR), which give rise to an enhancement of the switching speed and isolation characteristics. On the basis of simulation results, two types of pHEMTs are fabricated with two different UTLPDRs of 4:1 and 1:2. After applying these two types' pHEMTs, single-pole-double-throw (SPDT) transmitter/receiver monolithic microwave integrated circuit (MMIC) switches are also designed and fabricated. The SPDT MMIC switch with a 4:1 UTLPDR shows an insertion loss of 0.58 dB, isolation of 40.2 dB, and switching speed of 100 ns, respectively, which correspondingly indicate a 0.23 dB lower insertion loss, 2.90 dB higher isolation and 2.5 times faster switching speed than those of 1:2 UTLPDR at frequency range of 2-6 GHz. From the simulation results and comparative studies, we propose that the UTLPDR must be greater than 4:1 for the best switching performance. With the abovementioned excellent performances, the proposed switch would be quite promising in the application of information and communications technology system.

Boron doped ZnO embedded into reduced graphene oxide for electrochemical supercapacitors

NASA Astrophysics Data System (ADS)

Alver, Ü.; Tanrıverdi, A.

2016-08-01

In this work, reduced graphene oxide/boron doped zinc oxide (RGO/ZnO:B) composites were fabricated by a hydrothermal process and their electrochemical properties were investigated as a function of dopant concentration. First, boron doped ZnO (ZnO:B) particles was fabricated with different boron concentrations (5, 10, 15 and 20 wt%) and then ZnO:B particles were embedded into RGO sheets. The physical properties of sensitized composites were characterized by XRD and SEM. Characterization indicated that the ZnO:B particles with plate-like structure in the composite were dispersed on graphene sheets. The electrochemical properties of the RGO/ZnO:B composite were investigated through cyclic voltammetry, galvanostatic charge/discharge measurements in a 6 M KOH electrolyte. Electrochemical measurements show that the specific capacitance values of RGO/ZnO:B electrodes increase with increasing boron concentration. RGO/ZnO:B composite electrodes (20 wt% B) display the specific capacitance as high as 230.50 F/g at 5 mV/s, which is almost five times higher than that of RGO/ZnO (52.71 F/g).

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.

Pressure effects on magnetic ground states in cobalt doped multiferroic Mn 1-xCo xWO 4

DOE PAGES

Wang, Jinchen; Ye, Feng; Chi, Songxue; ...

2016-04-28

Using x-ray and high pressure neutron diffraction, we studied the pressure effect on structural and magnetic properties of multiferroic Mn 1-xCo xWO 4 single crystals (x = 0, 0.05, 0.135 and 0.17), and compared it with the effects of doping. Both Co doping and pressure stretch the Mn-Mn chain along the c direction. At high doping level (x = 0.135 and 0.17), pressure and Co doping drive the system in a very similar way and induce a spin-flop transition for the x = 0.135 compound. In contrast, magnetic ground states at lower doping level (x = 0 and 0.05) aremore » robust against pressure but experience a pronounced change upon Co substitution. As Co introduces both chemical pressure and magnetic anisotropy into the frustrated magnetic system, our results suggest the magnetic anisotropy is the main driving force for the Co induced phase transitions at low doping level, and chemical pressure plays a more significant role at higher Co concentrations.« less

Heavily Sn-doped GaAs with abrupt doping profiles grown by migration-enhanced epitaxy at low temperatures

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

Chavanapranee, Tosaporn; Horikoshi, Yoshiji

The characteristics of heavily Sn-doped GaAs samples grown at 300 deg. C by a migration-enhanced epitaxy (MEE) technique are investigated in comparison with those of the samples grown by a conventional molecular-beam epitaxy (MBE) at 580 deg. C. While no discernible difference is observed in the low doping regime, the difference in doping characteristics between the MBE- and MEE-grown samples becomes apparent when the doping concentration exceeds 1x10{sup 19} cm{sup -3}. Sn atoms as high as 4x10{sup 21} cm{sup -3} can be incorporated into MEE-grown GaAs films, unlike the MBE-grown samples that have a maximum doping level limited around 1x10{supmore » 19} cm{sup -3}. Due to an effective suppression of Sn segregation in the MEE growth case, high quality GaAs films with abrupt high-concentration Sn-doping profiles are achieved with the doping concentrations of up to 2x10{sup 21} cm{sup -3}. It has been shown that even though a high concentration of Sn atoms is incorporated into the GaAs film, the electron concentration saturates at 6x10{sup 19} cm{sup -3} and then gradually decreases with Sn concentration. The uniform doping limitation, as well as the electron concentration saturation, is discussed by means of Hall-effect measurement, x-ray diffraction, and Raman scattering spectroscopy.« less

Preparation, structural, photoluminescence and magnetic studies of Cu doped ZnO nanoparticles co-doped with Ni by sol-gel method

NASA Astrophysics Data System (ADS)

Theyvaraju, D.; Muthukumaran, S.

2015-11-01

Zn0.96-xNi0.04CuxO nanoparticles have been synthesized by varying different Cu concentrations between 0% and 4% using simple sol-gel method. X-ray diffraction studies confirmed the hexagonal structure of the prepared samples. The formation of secondary phases, CuO (111) and Zn (101) at higher Cu content is due un-reacted Cu2+ and Zn2+ ions present in the solution which reduces the interaction between precursor ions and surfaces of ZnO. Well agglomerated and rod-like structure noticed at Cu=4% greatly de-generate and enhanced the particle size. The nominal elemental composition of Zn, Cu, Ni and O was confirmed by energy dispersive X-ray analysis. Even though energy gap was increased (blue-shift) from Cu=0-2% by quantum size effect, the s-d and p-d exchange interactions between the band electrons of ZnO and localized d electrons of Cu and Ni led to decrease (red-shift) the energy gap at Cu=4%. Presence of Zn-Ni-Cu-O bond was confirmed by Fourier transform infrared analysis. Ultraviolet emission by band to band electronic transition and defect related blue emission were discussed by photoluminescence spectra. The observed optical properties concluded that the doping of Cu in the present system is useful to tune the emission wavelength and hence acting as the important candidates for the optoelectronic device applications. Ferromagnetic ordering of Cu=2% sample was enhanced by charge carrier concentration where as the antiferromagnetic interaction between neighboring Cu-Cu ions suppressed the ferromagnetism at higher doping concentrations of Cu.

Influence of high Mg doping on the microstructural and opto-electrical properties of AlGaN alloys

NASA Astrophysics Data System (ADS)

Xu, Qingjun; Zhang, Shiying; Liu, Bin; Tao, Tao; Xie, Zili; Xiu, Xiangqian; Chen, Dunjun; Chen, Peng; Han, Ping; Zheng, Youdou; Zhang, Rong

2018-07-01

Mg-doped AlxGa1-xN (x = 0.23 and 0.35) alloys have been grown on GaN templates with high temperature AlN (HT-AlN) interlayer by metalorganic chemical vapor deposition (MOCVD). A combination of secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM) indicates the formation of more inversion domains in the high Al mole fraction Mg-doped AlGaN alloys at Mg concentration ∼1020 cm-3. For Mg-doped Al0.23Ga0.77N epilayer, the analysis of cathodoluminescence (CL) spectra supports the existence of self-compensation effects due to the presence of intrinsic defects and Mg-related centers. The energy level of Mg is estimated to be around 193 meV from the temperature dependence of the resistivity measured by Hall effect experiments. And hole concentration and mobility are measured to be 1.2 × 1018 cm-3 and 0.56 cm2/V at room temperature, respectively. The reduction of acceptor activation energy and low hole mobility are attributed to inversion domains and self-compensation. Moreover, impurity band conduction is dominant in carrier transport up to a relatively higher temperature in high Al content Mg-doped AlGaN alloys.

Pure and Sn-doped ZnO films produced by pulsed laser deposition

NASA Astrophysics Data System (ADS)

Holmelund, E.; Schou, J.; Tougaard, S.; Larsen, N. B.

2002-09-01

A new technique, metronome doping, has been used for doping of films during pulsed laser deposition (PLD). This technique makes it possible to dope continuously during film growth with different concentrations of a dopant in one deposition sequence. Films of pure and doped ZnO have been produced with Sn concentrations up to 16%. The specific resistivity is found to increase and the transmission of visible light to decrease with increasing Sn concentration.

Effect of growth pressure on the morphology evolution and doping characteristics in nonpolar a-plane GaN

NASA Astrophysics Data System (ADS)

Song, Keun Man; Kim, Jong Min; Kang, Bong Kyun; Shin, Chan Soo; Ko, Chul Gi; Kong, Bo Hyun; Cho, Hyung Koun; Yoon, Dae Ho; Kim, Hogyoung; Hwang, Sung Min

2012-02-01

Nonpolar a-plane GaN layers grown on r-plane sapphire substrates were examined by using a two-step growth process. The higher initial growth pressure for the nucleation layer resulted in the improved crystalline quality with lower density of both threading dislocations and basal stacking faults. This was attributed to the higher degree of initial roughening and recovery time via a growth mode transition from three-dimensional (3D) to quasi two-dimensional (2D) lateral growth. Using Hall-effect measurements, the overgrown Si doped GaN layers grown with higher initial growth pressure were found to have higher mobility. The scattering mechanism due to the dislocations was dominant especially at low temperature (<200 K) for the lower initial growth pressure, which was insignificant for the higher initial growth pressure. The temperature-dependent Hall-effect measurements for the Mg doped GaN with a higher initial growth pressure yielded the activation energy and the acceptor concentration to be 128 meV and 1.2 × 1019 cm-3, respectively, corresponding to about 3.6% of activation at room temperature. Two-step growth scheme with a higher initial growth pressure is suggested as a potential method to improve the performance of nonpolar a-plane GaN based devices.

Microwave absorption properties of gold nanoparticle doped polymers

NASA Astrophysics Data System (ADS)

Jiang, C.; Ouattara, L.; Ingrosso, C.; Curri, M. L.; Krozer, V.; Boisen, A.; Jakobsen, M. H.; Johansen, T. K.

2011-03-01

This paper presents a method for characterizing microwave absorption properties of gold nanoparticle doped polymers. The method is based on on-wafer measurements at the frequencies from 0.5 GHz to 20 GHz. The on-wafer measurement method makes it possible to characterize electromagnetic (EM) property of small volume samples. The epoxy based SU8 polymer and SU8 doped with gold nanoparticles are chosen as the samples under test. Two types of microwave test devices are designed for exciting the samples through electrical coupling and magnetic coupling, respectively. Measurement results demonstrate that the nanocomposites absorb a certain amount of microwave energy due to gold nanoparticles. Higher nanoparticle concentration results in more significant absorption effect.

Effect of concentration variation on 2.0 µm emission of Ho3+-doped SiO2-Al2O3-Na2CO3-SrF2-CaF2 oxyfluorosilicate glasses

NASA Astrophysics Data System (ADS)

Gelija, Devarajulu; Borelli, Deva Prasad Raju

2018-02-01

The concentration variation of Ho3+ ion-doped SiO2-Al2O3-Na2CO3-SrF2-CaF2 glasses has been prepared by conventional melt quenching method. The thermal stability of 1 mol % of Ho3+-doped oxyfluorosilicate glass has been calculated using the differential thermal analysis (DTA) spectra. The phenomenological Judd-Ofelt intensity parameters Ωλ ( λ = 2, 4 and 6) were calculated for all concentrations of Ho3+ ions. The luminescence spectra in visible region of Ho3+ ion-doped glasses were recorded under the excitation wavelength of 452 nm. The spectra consists of several intense emission bands (5F4, 5S2) → 5I8 (547 nm), 5F3 → 5I8 (647 nm), 5F5 → 5I7 (660 nm) and (5F4, 5S2) → 5I7 (750 nm) in the range 500-780 nm. The fluorescence emission at ˜2.0 µm (5I7 → 5I8) was observed under the excitation of 488 nm Ar-ion laser. The stimulated emission cross section for 5I7 → 5I8 transition (˜2.0 µm) varies from 8.46 to 9.52 × 10-21 cm2, as calculated by the Fuchtbauer-Ladenburg (FL) theory. However, Mc-Cumber theory was used to calculate emission cross section values about 4.24-5.75 × 10-21 cm2 for the 5I7 → 5I8 transition in all concentrations of Ho3+-doped oxyfluorosilicate glasses. Therefore, these results reveal that the 0.5 mol % of Ho3+-doped oxyfluorosilicate glasses, exhibiting higher emission cross section, has potentially been used for laser applications at ˜ 2.0 µm.

Microscopic potential fluctuations in Si-doped AlGaN epitaxial layers with various AlN molar fractions and Si concentrations

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

Kurai, Satoshi, E-mail: kurai@yamaguchi-u.ac.jp; Yamada, Yoichi; Miyake, Hideto

2016-01-14

Nanoscopic potential fluctuations of Si-doped AlGaN epitaxial layers with the AlN molar fraction varying from 0.42 to 0.95 and Si-doped Al{sub 0.61}Ga{sub 0.39}N epitaxial layers with Si concentrations of 3.0–37 × 10{sup 17 }cm{sup −3} were investigated by cathodoluminescence (CL) imaging combined with scanning electron microscopy. The spot CL linewidths of AlGaN epitaxial layers broadened as the AlN molar fraction was increased to 0.7, and then narrowed at higher AlN molar fractions. The experimental linewidths were compared with the theoretical prediction from the alloy broadening model. The trends displayed by our spot CL linewidths were consistent with calculated results at AlN molar fractionsmore » of less than about 0.60, but the spot CL linewidths were markedly broader than the calculated linewidths at higher AlN molar fractions. The dependence of the difference between the spot CL linewidth and calculated line broadening on AlN molar fraction was found to be similar to the dependence of reported S values, indicating that the vacancy clusters acted as the origin of additional line broadening at high AlN molar fractions. The spot CL linewidths of Al{sub 0.61}Ga{sub 0.39}N epitaxial layers with the same Al concentration and different Si concentrations were nearly constant in the entire Si concentration range tested. From the comparison of reported S values, the increase of V{sub Al} did not contribute to the linewidth broadening, unlike the case of the V{sub Al} clusters.« less

Mg concentration profile and its control in the low temperature grown Mg-doped GaN epilayer

NASA Astrophysics Data System (ADS)

Liu, S. T.; Yang, J.; Zhao, D. G.; Jiang, D. S.; Liang, F.; Chen, P.; Zhu, J. J.; Liu, Z. S.; Liu, W.; Xing, Y.; Zhang, L. Q.; Wang, W. J.; Li, M.; Zhang, Y. T.; Du, G. T.

2018-01-01

In this work, the Cp2Mg flux and growth pressure influence to Mg doping concentration and depth profiles is studied. From the SIMS measurement we found that a transition layer exists at the bottom region of the layer in which the Mg doping concentration changes gradually. The thickness of transition layer decreases with the increases of Mg doping concentration. Through analysis, we found that this is caused by Ga memory effect which the Ga atoms stay residual in MOCVD system will react with Mg source, leading a transition layer formation and improve the growth rate. And the Ga memory effect can be well suppressed by increasing Mg doping concentration and growth pressure and thus get a steep Mg doping at the bottom region of p type layer.

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.

The Preparation Conditions of Chromium Doped ZnSe and Their Effect on the Infrared Luminescence Properties

NASA Technical Reports Server (NTRS)

Burger, A.; Chattopadhyay, K.; Ndap, J.-O.; Ma, X.; Morgan, S. H.; Rablau, C. I.; Su, C. H.; Feth, S.

2000-01-01

We report the investigation by photoluminescence lifetime measurements of the near-IR emissions from a series of chromium-doped ZnSe samples, correlated to their preparation conditions. The samples were polycrystalline or single crystals prepared by post growth diffusion doping or single crystals doped during growth by the physical vapor transport method. Room temperature lifetime values between 6 and 8 micro seconds were measured for samples with Cr2+ from low 10(exp 17) to high 10(exp 18) / cubic cm range. Lifetime data taken down to 78 K was found to be rather temperature independent, reconfirming previous reports indicating a quantum yield of the corresponding emission of close to 100% at room temperature. A strong decrease in the room temperature lifetime was found for chromium concentrations higher than 10(exp 19) / cubic CM.

Semiconductor superlattice photodetectors

NASA Technical Reports Server (NTRS)

Chuang, S. L.; Hess, K.; Coleman, J. J.; Leburton, J. P.

1986-01-01

Technical progress made in the study of superlattice photoconductors is summarized and papers submitted for publication are listed. Since the quantum-well regions may contain several subbands, each of which may be occupied by electrons depending on the doping concentrations, it is important to include the multi-subbands in calculating the impact ionization rate. The electrons occupying the higher subbands require a smaller amount of energy to get out of the quantum well; thus, those higher level subband electrons contribute significantly to the impact ionization rate. The results of the subbands have been calculated. Results concerning the nonparabolicity effect of the band structure, the effect of the quantum-well size, and the effect of the band-edge discontinuity and doping are also summarized.

Acid and alkali doped PBI electrolyte in electrochemical system

NASA Astrophysics Data System (ADS)

Xing, Baozhong

In this work the conductivity of blank PBI membrane, acid doped PBI and alkaline doped PBI was systematically studied. A new methodology for sorption kinetics study in electrolyte solution has been established by monitoring the conductivity change during the sorption process. The model of the doping process and mechanism of conductivity are proposed. The performance of PBI (doped under optimum conditions) in fuel cell as PEM was evaluated. The experimental results show that the blank PBI in acid solution is an ionic insulator. It clarified the long time confusion in this area. The acid doped PBI membrane is an ionic conductor. The conductivity increases with the concentration of the acid solution. In high concentration acid solution, the conductivity increases with the type of acid in the order: H2SO 4 > H3PO4 > HClO4 > HNO3 > HCl. The kinetics of the doping process was studied, by a continuous method. The ionic conductivity mechanism was established. The PBI membranes doped with H2SO4 and H3PO4 exhibit better performance than NafionRTM. The doped FBI has more resistance to CO poison. 3% CO in H2 has little effect on the H3PO 4 doped PBI membrane at 185°C. The conductivity of the alkali doped PBI membrane changes with the concentration of the alkaline solution and the type of the alkalis. The conductivity has a maximum in KOH and NaOH solution. The maximum conductivity in KOH is higher than in NaOH and LiOH. It is about 5 times of that of NafionRTM in alkaline solution. The two-step sorption process in alkaline solution was observed. The first step is the permeation process of the alkalis in the PBI membrane. The permeation is the results of diffusion and interaction. It is concluded that the permeation process is controlled by the rate of interaction between the alkali and PBI molecule. The second step is the relaxation process in the membrane. This step contributes more to the conductivity for the membrane than the first step. The ionic conductivity mechanism was established. In solution the cations and OH- all participate in the transport of current. It is the OH- that breaks the bonds between PBI molecules and enables the cations pass through the membrane. The performance of alkali doped PBI (doped under optimum conditions) in fuel cell as PEM is as good as NafionRTM.

The influence of different alkaline earth oxides on the structural and optical properties of undoped, Ce-doped, Sm-doped, and Sm/Ce co-doped lithium alumino-phosphate glasses

NASA Astrophysics Data System (ADS)

Othman, H. A.; Arzumanyan, G. M.; Möncke, D.

2016-12-01

Undoped, singly Sm doped, Ce doped, and Sm/Ce co-doped lithium alumino-phosphate glasses with different alkaline earth modifiers were prepared by melt quenching. The structure of the prepared glasses was investigated by FT-IR and Raman, as well as by optical spectroscopy. The effect of the optical basicity of the host glass matrix on the added active dopants was studied, as was the effect doping had on the phosphate structural units. The optical edge shifts toward higher wavelengths with an increase in the optical basicity due to the increased polarizability of the glass matrix, but also with increasing CeO2 concentration as a result of Ce3+/Ce4+ inter valence charge transfer (IV-CT) absorption. The optical band gap for direct and indirect allowed transitions was calculated for the undoped glasses. The glass sample containing Mg2+ modifier ions is found to have the highest value (4.16 eV) for the optical band gap while Ba2+ has the lowest value (3.61 eV). The change in the optical band gap arises from the structural changes and the overall polarizability (optical basicity). Refractive index, molar refractivity Rm and molar polarizability αm values increase with increasing optical basicity of the glasses. The characteristic absorption peaks of Sm3+ were also investigated. For Sm/Ce co-doped glasses, especially at high concentration of CeO2, the absorption of Ce3+ hinders the high energy absorption of Sm3+ and this effect becomes more obvious with increasing optical basicity.

High p-type doping, mobility, and photocarrier lifetime in arsenic-doped CdTe single crystals

NASA Astrophysics Data System (ADS)

Nagaoka, Akira; Kuciauskas, Darius; McCoy, Jedidiah; Scarpulla, Michael A.

2018-05-01

Group-V element doping is promising for simultaneously maximizing the hole concentration and minority carrier lifetime in CdTe for thin film solar cells, but there are roadblocks concerning point defects including the possibility of self-compensation by AX metastability. Herein, we report on doping, lifetime, and mobility of CdTe single crystals doped with As between 1016 and 1020 cm-3 grown from the Cd solvent by the travelling heater method. Evidence consistent with AX instability as a major contributor to compensation in samples doped below 1017 cm-3 is presented, while for higher-doped samples, precipitation of a second phase on planar structural defects is also observed and may explain spatial variation in properties such as lifetime. Rapid cooling after crystal growth increases doping efficiency and mobility for times up to 20-30 days at room temperature with the highest efficiencies observed close to 45% and a hole mobility of 70 cm2/Vs at room temperature. A doping limit in the low 1017/cm3 range is observed for samples quenched at 200-300 °C/h. Bulk minority carrier lifetimes exceeding 20 ns are observed for samples doped near 1016 cm-3 relaxed in the dark and for unintentionally doped samples, while a lifetime of nearly 5 ns is observed for 1018 cm-3 As doping. These results help us to establish limits on properties expected for group-V doped CdTe polycrystalline thin films for use in photovoltaics.

Highly active lanthanum doped ZnO nanorods for photodegradation of metasystox.

PubMed

Korake, P V; Dhabbe, R S; Kadam, A N; Gaikwad, Y B; Garadkar, K M

2014-01-05

La-doped ZnO nanorods with different La contents were synthesized by microwave assisted method and characterized by various sophisticated techniques such as XRD, UV-Vis., EDS, XPS, SEM and TEM. The XRD patterns of the La-doped ZnO indicate hexagonal crystal structure with an average crystallite size of 30nm. It was found that the crystallite size of La-doped ZnO is much smaller as compared to pure ZnO and decreases with increasing La content. The photocatalytic activity of 0.5mol% La-doped ZnO in the degradation of metasystox was studied. It was observed that degradation efficiency of metasystox over La-doped ZnO increases up to 0.5mol% doping then decreases for higher doping levels. Among the catalyst studied, the 0.5mol% La-doped ZnO was the most active, showing high photocatalytic activity for the degradation of metasystox. The maximum reduction of concentration of metasystox was observed under static condition at pH 8. Reduction in the Chemical Oxygen Demand (COD) of metasystox was observed after 150min. The cytotoxicological studies of meristematic root tip cells of Allium cepa were studied. The results obtained indicate that photocatalytically degraded products of metasystox were less toxic as compared to metasystox. Copyright © 2013 Elsevier B.V. All rights reserved.

Zn2+-Doped Polyaniline/Graphene Oxide as Electrode Material for Electrochemical Supercapacitors

NASA Astrophysics Data System (ADS)

Xu, Hui; Tang, Jing; Chen, Yong; Liu, Jian; Pu, Jinjuan; Li, Qi

2017-10-01

Electrodes based on Zn2+-doped polyaniline/graphene oxide (Zn2+/PANI/GO) were synthesized on stainless steel mesh substrates in H2SO4 solution via electrochemical codeposition. Different concentrations of graphene oxide (GO) were incorporated into the films to improve the electrochemical performance of the electrodes. Electrochemical properties of the films were tested by cyclic voltammetry, galvanostatic charge-discharge tests, and electrochemical impedance spectroscopy, in a three-electrode system. The maximum specific capacitance of the Zn2+/PANI/GO film with a GO concentration of 15 mg L-1 was found to be 1266 F g-1 at a scan rate of 3 mV s-1. This value was higher than that of a Zn2+ doped polyaniline (Zn2+/PANI) film (814 F g-1). The Zn2+/PANI/GO film also showed good cycling stability, retaining over 86% of its initial capacitance after 1000 cycles. These results indicate that the Zn2+/PANI/GO composites can be applied as high performance supercapacitor electrodes.

Growth of boron-doped few-layer graphene by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Soares, G. V.; Nakhaie, S.; Heilmann, M.; Riechert, H.; Lopes, J. M. J.

2018-04-01

We investigated the growth of boron-doped few-layer graphene on α-Al2O3 (0001) substrates by molecular beam epitaxy using two different growth approaches: one where boron was provided during the entire graphene synthesis and the second where boron was provided only during the second half of the graphene growth run. Electrical measurements show a higher p-type carrier concentration for samples fabricated utilizing the second approach, with a remarkable modulation in the carrier concentration of almost two orders of magnitude in comparison to the pristine graphene film. The results concerning the influence of the boron flux at different growth stages of graphene on the electrical and physicochemical properties of the films are presented.

Ab initio modeling of vacancies, antisites, and Si dopants in ordered InGaAs

NASA Astrophysics Data System (ADS)

Wang, Jingyang; Lukose, Binit; Thompson, Michael O.; Clancy, Paulette

2017-01-01

In0.53Ga0.47As, a III-V compound semiconductor with high electron mobility, is expected to bring better performance than silicon in next-generation n-type MOSFET devices. However, one major challenge to its wide scale adoption is the difficulty of obtaining high enough dopant activation. For Si-doped InGaAs, the best current experimental result, involving 10 min of furnace annealing at temperatures above 700 °C, yields a free electron concentration of 1.4 ×1019 cm-3, a value that still falls short of requirement for practical applications. In this paper, we investigate the origin of low dopant activation in InGaAs by calculating formation energies for a wide variety of single point defects (Si substutionals, Si tetrahedral interstitials, vacancies, and antisites) in Si-doped In0.5Ga0.5As in a CuAu-I type crystal structure. We find that (1) a high electron concentration can only be achieved under In/Ga-poor growth conditions, while As-poor conditions inhibit n-type doping; and (2) in heavily n-doped samples, cation vacancies VIn/Ga-3 contribute the most to the compensation of excess Si donors via the Si III - VIII mechanism (III = In/Ga), thus becoming the limiting factor to higher dopant activation. Under the most favorable growth conditions for n-doping, we find the maximum carrier concentration to be 5.2 ×1018 cm-3 under thermal equilibrium, within an order of magnitude of the best experimental value.

Novel materials as potential infrared laser hosts

NASA Astrophysics Data System (ADS)

Sarkies, Julian Richard

The work presented in this thesis has concentrated on an assessment and characterisation of potential laser host media which will only support low phonon or vibrational modes. This is a necessary criterion if systems in which the active ions are lanthanides are to be made to lase in the mid-infrared, as in conventional host media non- radiative processes dominate transitions in this region. Research has concentrated upon two main areas. Firstly a spectroscopic study of lanthanide doped PBr3/AlBr3/SbBr3 was undertaken. A detailed investigation and characterisation of the stable solution formation region was carried out. The doping levels achievable were seen to vary across the lanthanide series from a maximum 0.24mol% for praesodymium to a minimum 0.15mol% for ytterbium. Energies of the characteristic 4 f absorptions of the trivalent lanthanides were measured, along with their oscillator strengths. Judd-Ofelt parameters were found for several rare earths. Stimulated emission cross sections were found to be higher than in conventional glass hosts for certain transitions, such as 6.83 × 10 -20 cm2 for the 4F3/2 --> 4I11/2 transition in the Nd3+ doped liquid. This was verified both experimentally and by the Ladenburg-Fuchtbauer relation when compared to a standard silicate glass. The behaviour, both spectroscopic and physical, of the doped solutions was seen to change dramatically upon heating. Heating the solutions gave rise to higher crystallisation rates, but lower non-radiative relaxation rates. Waveguide and laser experiments were attempted in both bulk and capillary geometries, however material factors such as crystallisation and thermal lensing prevented laser action. Secondly, rare earth doped planar waveguides of zinc sulphide were prepared. A full characterisation of the way in which waveguide loss was affected by factors such as deposition rate, doping level and waveguide masking during evaporation was performed. Waveguide losses as low as 1.5dB/cm at 980nm were measured. The loss was seen to have a strong λ-4 dependence, indicating it was predominantly due to Rayleigh scattering. Deposition onto heated substrates and post deposition annealing increased the loss significantly. Shielding the substrate from the radiant heating of the evaporation boat by partial masking of the substrate reduced the loss significantly. Doping the films caused a large increase in the loss for dopant concentrations of above 0.8mol%. Emission was observed from both Er3+ and Nd 3+ doped waveguides, and fluorescent lifetimes measured. The emission cross sections were measured for the 4F3/2 --> 4I11/2 transition in the Nd3+ doped waveguide, and for the 4I13/2 --> 4I 15/2 transition in the Er3+ doped waveguide. Multilayer dielectric mirrors were deposited onto the ends of a Nd3+ doped waveguide, forming a fully integrated resonator. The low damage threshold of the multilayer coatings precluded laser action. These results are believed to be the first ever reported for thermally evaporated doped zinc sulphide waveguides. This system has shown considerable promise as an infrared laser host, the future implications of this work are discussed and possible directions for future research suggested.

A Fast Humidity Sensor Based on Li+-Doped SnO2 One-Dimensional Porous Nanofibers

PubMed Central

Yin, Min; Yang, Fang; Wang, Zhaojie; Zhu, Miao; Liu, Ming; Xu, Xiuru; Li, Zhenyu

2017-01-01

One-dimensional SnO2- and Li+-doped SnO2 porous nanofibers were easily fabricated via electrospinning and a subsequent calcination procedure for ultrafast humidity sensing. Different Li dopant concentrations were introduced to investigate the dopant’s role in sensing performance. The response properties were studied under different relative humidity levels by both statistic and dynamic tests. The best response was obtained with respect to the optimal doping of Li+ into SnO2 porous nanofibers with a maximum 15 times higher response than that of pristine SnO2 porous nanofibers, at a relative humidity level of 85%. Most importantly, the ultrafast response and recovery time within 1 s was also obtained with the 1.0 wt % doping of Li+ into SnO2 porous nanofibers at 5 V and at room temperature, benefiting from the co-contributions of Li-doping and the one-dimensional porous structure. This work provides an effective method of developing ultrafast sensors for practical applications—especially fast breathing sensors. PMID:28772895

Controlling the ambipolarity and improvement of RF performance using Gaussian Drain Doped TFET

NASA Astrophysics Data System (ADS)

Nigam, Kaushal; Gupta, Sarthak; Pandey, Sunil; Kondekar, P. N.; Sharma, Dheeraj

2018-05-01

Ambipolar conduction in tunnel field-effect transistors (TFETs) has been occurred as an inherent issue due to drain-channel tunneling. It makes TFET less efficient and restricts its application in complementary digital circuits. Therefore, this manuscript reports the application of Gaussian doping profile on nanometer regime silicon channel TFETs to completely eliminate the ambipolarity. For this, Gaussian doping is used in the drain region of conventional gate-drain overlap TFET to control the tunneling of electrons from the valence band of channel to the conduction band of drain. As a result, barrier width at the drain/channel junction increases significantly leading to the suppression of an ambipolar current even when higher doping concentration (1 ? 10 ? cm ?) is considered in the drain region. However, significant improvement in terms of RF figure-of-merits such as cut-off frequency (f ?), gain bandwidth product (GBW), and gate-to-drain capacitance (C ?) is achieved with Gaussian doped gate on drain overlap TFET as compared to its counterpart TFET.

Low doping concentration studies of doped PVA-Coumarin nanocomposite films

NASA Astrophysics Data System (ADS)

Tripathi, J.; Tripathi, S.; Bisen, R.; Sharma, A.; Choudhary, A.; Shripathi, T.

2016-05-01

The observations of combination of Poly (vinyl) alcohol and Coumarin properties in nanocmposite films are reported. The X-ray diffraction measurements reveal nanocrystalline nature of PVA film, which remains nanocrystalline after doping Coumarin but along with PVA peaks, additional peak due to dopant crystallinity is seen. The absorption edge shows a double edge feature, where distinct bandgaps for PVA host and dopant Coumarin are obtained. However at a higher doping wt % of 1 and 2, the absorption is mainly dominated by Coumarin and single absorption edge is observed giving a bandgap equal to that of bulk Coumarin (3.3 eV). The composite formation affects the bonding of host drastically and is seen through the bond modification in FTIR spectra. The results suggest that doping below 2 wt% is advantageous as combination of PVA and Coumarin properties are obtained but at 2 wt %, the properties are dominated by mainly Coumarin and the signature of PVA from optical properties is completely lost.

Low doping concentration studies of doped PVA-Coumarin nanocomposite films

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

Tripathi, J., E-mail: jtripathi00@rediffmail.com; Bisen, R.; Choudhary, A.

2016-05-23

The observations of combination of Poly (vinyl) alcohol and Coumarin properties in nanocmposite films are reported. The X-ray diffraction measurements reveal nanocrystalline nature of PVA film, which remains nanocrystalline after doping Coumarin but along with PVA peaks, additional peak due to dopant crystallinity is seen. The absorption edge shows a double edge feature, where distinct bandgaps for PVA host and dopant Coumarin are obtained. However at a higher doping wt % of 1 and 2, the absorption is mainly dominated by Coumarin and single absorption edge is observed giving a bandgap equal to that of bulk Coumarin (3.3 eV). Themore » composite formation affects the bonding of host drastically and is seen through the bond modification in FTIR spectra. The results suggest that doping below 2 wt% is advantageous as combination of PVA and Coumarin properties are obtained but at 2 wt %, the properties are dominated by mainly Coumarin and the signature of PVA from optical properties is completely lost.« less

Structure and functionality of bromine doped graphite.

PubMed

Hamdan, Rashid; Kemper, A F; Cao, Chao; Cheng, H P

2013-04-28

First-principles calculations are used to study the enhanced in-plane conductivity observed experimentally in Br-doped graphite, and to study the effect of external stress on the structure and functionality of such systems. The model used in the numerical calculations is that of stage two doped graphite. The band structure near the Fermi surface of the doped systems with different bromine concentrations is compared to that of pure graphite, and the charge transfer between carbon and bromine atoms is analyzed to understand the conductivity change along different high symmetry directions. Our calculations show that, for large interlayer separation between doped graphite layers, bromine is stable in the molecular form (Br2). However, with increased compression (decreased layer-layer separation) Br2 molecules tend to dissociate. While in both forms, bromine is an electron acceptor. The charge exchange between the graphite layers and Br atoms is higher than that with Br2 molecules. Electron transfer to the Br atoms increases the number of hole carriers in the graphite sheets, resulting in an increase of conductivity.

pn junctions based on a single transparent perovskite semiconductor BaSnO3

NASA Astrophysics Data System (ADS)

Kim, Hoon Min; Kim, Useong; Park, Chulkwon; Kwon, Hyukwoo; Lee, Woongjae; Kim, Tai Hoon; Kim, Kee Hoon; Char, Kookrin; Mdpl, Department Of Physics; Astronomy Team; Censcmr, Department Of Physics; Astronomy Team

2014-03-01

Successful p doping of transparent oxide semiconductor will further increase its potential, especially in the area of optoelectronic applications. We will report our efforts to dope the BaSnO3 (BSO) with K by pulsed laser deposition. Although the K doped BSO exhibits rather high resistivity at room temperature, its conductivity increases dramatically at higher temperatures. Furthermore, the conductivity decreases when a small amount of oxygen was removed from the film, consistent with the behavior of p type doped oxides. We have fabricated pn junctions by using K doped BSO as a p type and La doped BSO as an n type material. I_V characteristics of these devices show the typical rectifying behavior of pn junctions. We will present the analysis of the junction properties from the temperature dependent measurement of their electrical properties, which shows that the I_V characteristics are consistent with the material parameters such as the carrier concentration, the mobility, and the bandgap. Our demonstration of pn junctions based on a single transparent perovskite semiconductor further enhances the potential of BSO system with high mobility and stability.

Effects on the optical properties and conductivity of Ag-N co-doped ZnO

NASA Astrophysics Data System (ADS)

Xu, Zhenchao; Hou, Qingyu; Qu, Lingfeng

2017-01-01

Nowadays, the studies of the effects on the optical bandgap, absorption spectrum, and electrical properties of Ag-N co-doped ZnO have been extensively investigated. However, Ag and N atoms in doped systems are randomly doped, and the asymmetric structure of ZnO is yet to be explored. In this paper, the geometric structure, stability, density of states, absorption spectra and conductivity of pure and Ag-N co-doped Zn1-xAgxO1-xNx(x=0.03125, 0.0417 and 0.0625) in different orientations are calculated by using plane-wave ultrasoft pseudopotential on the basis of density functional theory with GGA+U method. Results show that the volume, equivalent total energy and formation energy of the doped system increase as the concentration of Ag-N co-doped Zn1-xAgxO1-xNx increases at the same doping mode. The doped systems also become unstable, and difficulty in doping. At the same concentration of Ag-N co-doped Zn1-xAgxO1-xNx, the systems with Ag-N along the c-axis orientation is unstable, and doping is difficult. The optical bandgap of Ag-N co-doped systems is narrower than that of the pure ZnO. At the same doping mode, the optical bandgap of the systems with Ag-N perpendicular to the c-axis orientation becomes narrow as the concentration of Ag-N co-doped Zn1-xAgxO1-xNx increases. The absorption spectra of the doped systems exhibit a red shift, and this red shift becomes increasingly significant as the concentration of Ag-N co-doped Zn1-xAgxO1-xNx increases. Under the same condition, the relative hole concentrations of the doped systems increases, the hole effective mass in valence band maximum decreases, the hole mobility decreases, the ionization energy decreases, Bohr radius increases, the conductance increases and the conductivity become better. Our results may be used as a basis for the designing and preparation of new optical and electrical materials for Ag-N co-doped ZnO applied in low temperature end of temperature difference battery.

Effect of Yb doping on the refractive index and thermo-optic coefficient of YVO₄ single crystals.

PubMed

Soharab, M; Bhaumik, Indranil; Bhatt, R; Saxena, A; Karnal, A K; Gupta, P K

2017-02-20

Single crystals of YVO₄ with different doping concentrations of Yb (1.5, 3.0, 8.0, and 15.0 at. %) and with good crystalline quality (FWHM ∼43-55 arc sec of rocking curve) were grown by the optical floating zone technique. Refractive index measurements were carried out at four wavelengths as a function of temperature. The measurements show that as the doping concentration of Yb is increased, the refractive index varies marginally for n_e whereas there is a significant change in the value of n_o. The thermo-optic coefficient (dn/dT) was found to be positive with a value ∼10^-5/°C, which is 1 order higher than that for the undoped YVO₄ crystal. The thermo-optic coefficient is higher for n_e compared to that of n_o. Also, a set of relations describing the wavelength dependence of the thermo-optic coefficient were established that are useful for calculating the thermo-optic coefficient at any temperature in the range 30°C-150°C and at any wavelength in the range 532-1551 nm.

Harmonically mode-locked erbium-doped waveguide laser

NASA Astrophysics Data System (ADS)

Fanto, Michael L.; Malowicki, John E.; Bussjager, Rebecca J.; Johns, Steven T.; Vettese, Elizabeth K.; Hayduk, Michael J.

2004-08-01

The generation of ultrastable picosecond pulses in the 1550 nm range is required for numerous applications that include photonic analog-to-digital converter systems and high-bit rate optical communication systems. Mode-locked erbium-doped fiber ring lasers (EDFLs) are typically used to generate pulses at this wavelength. In addition to timing stability and output power, the physical size of the laser cavity is of primary importance to the Air Force. The length of the erbium (Er)-doped fiber used as the gain medium may be on the order of meters or even tens of meters which adds complexity to packaging. However, with the recent advancements in the production of multi-component glasses, higher doping concentrations can be achieved as compared to silicate glasses. Even more recent is the introduction of Er-doped multi-component glass waveguides, thus allowing the overall footprint of the gain medium to be reduced. We have constructed a novel harmonically mode-locked fiber ring laser using the Er-doped multi-component glass waveguide as the gain medium. The performance characteristics of this Er-doped waveguide laser (EDWL) including pulse width, spectral width, harmonic suppression, optical output power, laser stability and single sideband residual phase noise will be discussed in this paper.

Nanoparticles doped film sensing based on terahertz metamaterials

NASA Astrophysics Data System (ADS)

Liu, Weimin; Fan, Fei; Chang, Shengjiang; Hou, Jiaqing; Chen, Meng; Wang, Xianghui; Bai, Jinjun

2017-12-01

A nanoparticles concentration sensor based on doped film and terahertz (THz) metamaterial has been proposed. By coating the nanoparticles doped polyvinyl alcohol (PVA) film on the surface of THz metamaterial, the effects of nanoparticle concentration on the metamaterial resonances are investigated through experiments and numerical simulations. Results show that resonant frequency of the metamaterial linearly decreases with the increment of doping concentration. Furthermore, numerical simulations illustrate that the redshift of resonance results from the changes of refractive index of the doped film. The concentration sensitivity of this sensor is 3.12 GHz/0.1%, and the refractive index sensitivity reaches 53.33 GHz/RIU. This work provides a non-contact, nondestructive and sensitive method for the detection of nanoparticles concentration and brings out a new application on THz film metamaterial sensing.

Structural and Magnetic Properties of {Eu}(3+) Eu 3 + -Doped {CdNb}_{2} {O}_{6} CdNb 2 O 6 Powders

NASA Astrophysics Data System (ADS)

Topkaya, Ramazan; Boyraz, Cihat; Ekmekçi, Mete Kaan

2018-03-01

Europium-doped CdNb2O6 powders with the molar concentration of Eu^{3+} (0.5, 3 and 6 mol%) were successfully prepared at 900°C by using molten salt synthesis method. The effect of europium (Eu) molar concentration on the structural and temperature-dependent magnetic properties of CdNb2O6 powders has been investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), vibrating sample magnetometer (VSM) and ferromagnetic resonance (FMR) techniques in the temperature range of 10-300 K. XRD results confirm that all the powders have orthorhombic crystal structure. It has been confirmed from VSM and FMR measurements that Eu^{3+}-doped CdNb2O6 powders have ferromagnetic behaviour for each Eu^{3+} molar concentration between 10 and 300 K. XRD and EDX analyses indicate that there is no magnetic impurity in Eu^{3+}-doped CdNb_2O_6 powders, supporting that the ferromagnetic behaviour of the powders arises from Eu^{3+} ions. The observed ferromagnetism was elucidated with the intrinsic exchange interactions between the magnetic moments associated with the unpaired 4 f electrons in Eu^{3+} ions. The saturation magnetization decreases with increasing Eu^{3+} molar concentration. The temperature-dependent magnetization behaviour was observed not to agree with Curie-Weiss law because europium obeys Van Vleck paramagnetism. Broad FMR spectra and a g-value higher than 2 were observed from FMR measurements, indicating the ferromagnetic behaviour of the powders. It was found that while the resonance field of FMR spectra decreases, the linewidth increases as a function of Eu^{3+} molar concentration.

The presence of Ti(II) centers in doped nanoscale TiO2 and TiO2-xNx

NASA Astrophysics Data System (ADS)

Mikulas, Tanya; Fang, Zongtang; Gole, James L.; White, Mark G.; Dixon, David A.

2012-06-01

Unusual trends are observed in the Ti (2s, 2p) XPS spectra of Fe(II) doped TiO2 and TiO2-xNx. The binding energy of Ti (2s, 2p) initially decreases with increasing Fe(II) concentration, as expected, but increases at higher Fe(II) doping levels. Density functional theory is used to analyze the results. The observed VB-XPS and core level XPS spectra are consistent with the facile charge transfer sequence Ti(IV) + Fe(II) → Ti(III) + Fe(III) followed by Ti(III) + Fe(II) → Ti(II) + Fe(III). The formed Ti(II) sites may be relevant to nanoparticle catalysis on TiO2 surfaces.

Analysis of Photoluminescence Thermal Quenching: Guidance for the Design of Highly Effective p-type Doping of Nitrides

PubMed Central

Liu, Zhiqiang; Huang, Yang; Yi, Xiaoyan; Fu, Binglei; Yuan, Guodong; Wang, Junxi; Li, Jinmin; Zhang, Yong

2016-01-01

A contact-free diagnostic technique for examining position of the impurity energy level of p-type dopants in nitride semiconductors was proposed based on photoluminescence thermal quenching. The Mg ionization energy was extracted by the phenomenological rate-equation model we developed. The diagnostic technique and analysis model reported here are priorities for the design of highly effective p-doping of nitrides and could also be used to explain the abnormal and seldom analyzed low characteristic temperature T0 (about 100 K) of thermal quenching in p-type nitrides systems. An In-Mg co-doped GaN system is given as an example to prove the validity of our methods. Furthermore, a hole concentration as high as 1.94 × 1018 cm−3 was achieved through In-Mg co-doping, which is nearly one order of magnitude higher than typically obtained in our lab. PMID:27550805

Analysis of Photoluminescence Thermal Quenching: Guidance for the Design of Highly Effective p-type Doping of Nitrides.

PubMed

Liu, Zhiqiang; Huang, Yang; Yi, Xiaoyan; Fu, Binglei; Yuan, Guodong; Wang, Junxi; Li, Jinmin; Zhang, Yong

2016-08-23

A contact-free diagnostic technique for examining position of the impurity energy level of p-type dopants in nitride semiconductors was proposed based on photoluminescence thermal quenching. The Mg ionization energy was extracted by the phenomenological rate-equation model we developed. The diagnostic technique and analysis model reported here are priorities for the design of highly effective p-doping of nitrides and could also be used to explain the abnormal and seldom analyzed low characteristic temperature T0 (about 100 K) of thermal quenching in p-type nitrides systems. An In-Mg co-doped GaN system is given as an example to prove the validity of our methods. Furthermore, a hole concentration as high as 1.94 × 10(18) cm(-3) was achieved through In-Mg co-doping, which is nearly one order of magnitude higher than typically obtained in our lab.

Analysis of Photoluminescence Thermal Quenching: Guidance for the Design of Highly Effective p-type Doping of Nitrides

NASA Astrophysics Data System (ADS)

Liu, Zhiqiang; Huang, Yang; Yi, Xiaoyan; Fu, Binglei; Yuan, Guodong; Wang, Junxi; Li, Jinmin; Zhang, Yong

2016-08-01

A contact-free diagnostic technique for examining position of the impurity energy level of p-type dopants in nitride semiconductors was proposed based on photoluminescence thermal quenching. The Mg ionization energy was extracted by the phenomenological rate-equation model we developed. The diagnostic technique and analysis model reported here are priorities for the design of highly effective p-doping of nitrides and could also be used to explain the abnormal and seldom analyzed low characteristic temperature T0 (about 100 K) of thermal quenching in p-type nitrides systems. An In-Mg co-doped GaN system is given as an example to prove the validity of our methods. Furthermore, a hole concentration as high as 1.94 × 1018 cm-3 was achieved through In-Mg co-doping, which is nearly one order of magnitude higher than typically obtained in our lab.

Effects of Nb doping level on the electronic transport, photoelectric effect and magnetoresistance across La0.5Ca0.5MnO3/Nb:SrTiO3 junctions

NASA Astrophysics Data System (ADS)

Wang, J. F.; Jiang, Y. C.; Chen, M. G.; Gao, J.

2013-12-01

Heterojunctions composed of La0.5Ca0.5MnO3 and Nb doped SrTiO3 were fabricated, and the effects of the Nb doping level on their electronic transport, photoelectric effect, and magnetoresistance were investigated. A lower doping concentration of Nb led to better rectifying properties and higher open circuit voltages. The I-V curves for La0.5Ca0.5MnO3/0.7 wt. % Nb-SrTiO3 showed a negligible response to magnetic fields for all temperatures, whereas La0.5Ca0.5MnO3/0.05 wt. % Nb-SrTiO3 exhibited distinct magnetoresistance, which depended on both the bias voltage and temperature. These results are discussed with the assistance of conventional semiconductor theories.

Sensitive measurement of nonlinear absorption and optical limiting in undoped and Fe-doped ZnO quantum dots using pulsed laser

NASA Astrophysics Data System (ADS)

Sharma, D.; Malik, B. P.; Gaur, A.

2016-11-01

Zinc oxide quantum dots (QDs) with Fe-doping at different concentrations were prepared by chemical co-precipitation method. The prepared QDs were characterized by UV-Vis spectroscopy, X-ray diffraction and Z-scan technique. The sizes of QDs were found to be within 4.6-6.6 nm range. The nonlinear parameters viz. two-photon absorption coefficient (βTPA) and two-photon absorption cross-section (σTPA) were extracted with the help of open aperture Z-scan technique using nanosecond Nd:YAG laser operating at wavelength 532 nm. Higher values of βTPA and σTPA for Fe doped ZnO implied that they were potential materials for development of photonics devices and sensor protection applications. Fe doped sample (3 % by wt) was found to be the best optical limiter with limiting threshold intensity of 0.64 TW/cm2.

Indium Substitution Effect on the Topological Crystalline Insulator Family (Pb 1$-$xSn x)1 $-$yInyTe: Topological and Superconducting Properties

DOE PAGES

Zhong, Ruidan; Schneeloch, John; Li, Qiang; ...

2017-02-16

Topological crystalline insulators (TCIs) have been of great interest in the area of condensed matter physics. We investigated the effect of indium substitution on the crystal structure and transport properties in the TCI system (Pb 1-xSn x) 1-yIn yTe. For samples with a tin concentration x ≤ 50% , the low-temperature resisitivities show a dramatic variation as a function of indium concentration: with up to ~2% indium doping, the samples show weak-metallic behavior similar to their parent compounds; with `6% indium doping, samples have true bulk-insulating resistivity and present evidence for nontrivial topological surface states; with higher indium doping levels,more » superconductivity was observed, with a transition temperature, T c , positively correlated to the indium concentration and reaching as high as 4.7 K. We address this issue from the view of bulk electronic structure modified by the indium-induced impurity level that pins the Fermi level. The current work summarizes the indium substitution effect on (Pb,Sn)Te, and discusses the topological and superconducting aspects, which can be provide guidance for future studies on this and related systems.« less

Low Dark-Current, High Current-Gain of PVK/ZnO Nanoparticles Composite-Based UV Photodetector by PN-Heterojunction Control.

PubMed

Lee, Sang-Won; Cha, Seung-Hwan; Choi, Kyung-Jae; Kang, Byoung-Ho; Lee, Jae-Sung; Kim, Sae-Wan; Kim, Ju-Seong; Jeong, Hyun-Min; Gopalan, Sai-Anand; Kwon, Dae-Hyuk; Kang, Shin-Won

2016-01-07

We propose a solution-processable ultraviolet (UV) photodetector with a pn-heterojunction hybrid photoactive layer (HPL) that is composed of poly-n-vinylcarbazole (PVK) as a p-type polymer and ZnO nanoparticles (NPs) as an n-type metal oxide. To observe the effective photo-inducing ability of the UV photodetector, we analyzed the optical and electrical properties of HPL which is controlled by the doping concentration of n-type ZnO NPs in PVK matrix. Additionally, we confirmed that the optical properties of HPL dominantly depend on the ZnO NPs from the UV-vis absorption and the photoluminescence (PL) spectral measurements. This HPL can induce efficient charge transfer in the localized narrow pn-heterojunction domain and increases the photocurrent gain. It is essential that proper doping concentration of n-type ZnO NPs in polymer matrix is obtained to improve the performance of the UV photodetector. When the ZnO NPs are doped with the optimized concentration of 3.4 wt.%, the electrical properties of the photocurrent are significantly increased. The ratio of the photocurrent was approximately 10³ higher than that of the dark current.

Low Dark-Current, High Current-Gain of PVK/ZnO Nanoparticles Composite-Based UV Photodetector by PN-Heterojunction Control

PubMed Central

Lee, Sang-Won; Cha, Seung-Hwan; Choi, Kyung-Jae; Kang, Byoung-Ho; Lee, Jae-Sung; Kim, Sae-Wan; Kim, Ju-Seong; Jeong, Hyun-Min; Gopalan, Sai-Anand; Kwon, Dae-Hyuk; Kang, Shin-Won

2016-01-01

We propose a solution-processable ultraviolet (UV) photodetector with a pn-heterojunction hybrid photoactive layer (HPL) that is composed of poly-n-vinylcarbazole (PVK) as a p-type polymer and ZnO nanoparticles (NPs) as an n-type metal oxide. To observe the effective photo-inducing ability of the UV photodetector, we analyzed the optical and electrical properties of HPL which is controlled by the doping concentration of n-type ZnO NPs in PVK matrix. Additionally, we confirmed that the optical properties of HPL dominantly depend on the ZnO NPs from the UV-vis absorption and the photoluminescence (PL) spectral measurements. This HPL can induce efficient charge transfer in the localized narrow pn-heterojunction domain and increases the photocurrent gain. It is essential that proper doping concentration of n-type ZnO NPs in polymer matrix is obtained to improve the performance of the UV photodetector. When the ZnO NPs are doped with the optimized concentration of 3.4 wt.%, the electrical properties of the photocurrent are significantly increased. The ratio of the photocurrent was approximately 103 higher than that of the dark current. PMID:26751453

Indium Substitution Effect on the Topological Crystalline Insulator Family (Pb 1$-$xSn x)1 $-$yInyTe: Topological and Superconducting Properties

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

Zhong, Ruidan; Schneeloch, John; Li, Qiang

Topological crystalline insulators (TCIs) have been of great interest in the area of condensed matter physics. We investigated the effect of indium substitution on the crystal structure and transport properties in the TCI system (Pb 1-xSn x) 1-yIn yTe. For samples with a tin concentration x ≤ 50% , the low-temperature resisitivities show a dramatic variation as a function of indium concentration: with up to ~2% indium doping, the samples show weak-metallic behavior similar to their parent compounds; with `6% indium doping, samples have true bulk-insulating resistivity and present evidence for nontrivial topological surface states; with higher indium doping levels,more » superconductivity was observed, with a transition temperature, T c , positively correlated to the indium concentration and reaching as high as 4.7 K. We address this issue from the view of bulk electronic structure modified by the indium-induced impurity level that pins the Fermi level. The current work summarizes the indium substitution effect on (Pb,Sn)Te, and discusses the topological and superconducting aspects, which can be provide guidance for future studies on this and related systems.« less

Enhancing multiphoton upconversion through energy clustering at sublattice level

NASA Astrophysics Data System (ADS)

Wang, Juan; Deng, Renren; MacDonald, Mark A.; Chen, Bolei; Yuan, Jikang; Wang, Feng; Chi, Dongzhi; Andy Hor, Tzi Sum; Zhang, Peng; Liu, Guokui; Han, Yu; Liu, Xiaogang

2014-02-01

The applications of lanthanide-doped upconversionnanocrystals in biological imaging, photonics, photovoltaics and therapeutics have fuelled a growing demand for rational control over the emission profiles of the nanocrystals. A common strategy for tuning upconversion luminescence is to control the doping concentration of lanthanide ions. However, the phenomenon of concentration quenching of the excited state at high doping levels poses a significant constraint. Thus, the lanthanide ions have to be stringently kept at relatively low concentrations to minimize luminescence quenching. Here we describe a new class of upconversion nanocrystals adopting an orthorhombic crystallographic structure in which the lanthanide ions are distributed in arrays of tetrad clusters. Importantly, this unique arrangement enables the preservation of excitation energy within the sublattice domain and effectively minimizes the migration of excitation energy to defects, even in stoichiometric compounds with a high Yb3+ content (calculated as 98 mol%). This allows us to generate an unusual four-photon-promoted violet upconversion emission from Er3+ with an intensity that is more than eight times higher than previously reported. Our results highlight that the approach to enhancing upconversion through energy clustering at the sublattice level may provide new opportunities for light-triggered biological reactions and photodynamic therapy.

Current-induced spin polarization in InGaAs and GaAs epilayers with varying doping densities

NASA Astrophysics Data System (ADS)

Luengo-Kovac, M.; Huang, S.; Del Gaudio, D.; Occena, J.; Goldman, R. S.; Raimondi, R.; Sih, V.

2017-11-01

The current-induced spin polarization and momentum-dependent spin-orbit field were measured in InxGa1 -xAs epilayers with varying indium concentrations and silicon doping densities. Samples with higher indium concentrations and carrier concentrations and lower mobilities were found to have larger electrical spin generation efficiencies. Furthermore, current-induced spin polarization was detected in GaAs epilayers despite the absence of measurable spin-orbit fields, indicating that the extrinsic contributions to the spin-polarization mechanism must be considered. Theoretical calculations based on a model that includes extrinsic contributions to the spin dephasing and the spin Hall effect, in addition to the intrinsic Rashba and Dresselhaus spin-orbit coupling, are found to reproduce the experimental finding that the crystal direction with the smaller net spin-orbit field has larger electrical spin generation efficiency and are used to predict how sample parameters affect the magnitude of the current-induced spin polarization.

High-voltage 4H-SiC trench MOS barrier Schottky rectifier with low forward voltage drop using enhanced sidewall layer

NASA Astrophysics Data System (ADS)

Cho, Doohyung; Sim, Seulgi; Park, Kunsik; Won, Jongil; Kim, Sanggi; Kim, Kwangsoo

2015-12-01

In this paper, a 4H-SiC trench MOS barrier Schottky (TMBS) rectifier with an enhanced sidewall layer (ESL) is proposed. The proposed structure has a high doping concentration at the trench sidewall. This high doping concentration improves both the reverse blocking and forward characteristics of the structure. The ESL-TMBS rectifier has a 7.4% lower forward voltage drop and a 24% higher breakdown voltage. However, this structure has a reverse leakage current that is approximately three times higher than that of a conventional TMBS rectifier owing to the reduction in energy barrier height. This problem is solved when ESL is used partially, since its use provides a reverse leakage current that is comparable to that of a conventional TMBS rectifier. Thus, the forward voltage drop and breakdown voltage improve without any loss in static and dynamic characteristics in the ESL-TMBS rectifier compared with the performance of a conventional TMBS rectifier.

Absolute instability of polaron mode in semiconductor magnetoplasma

NASA Astrophysics Data System (ADS)

Paliwal, Ayushi; Dubey, Swati; Ghosh, S.

2018-01-01

Using coupled mode theory under hydrodynamic regime, a compact dispersion relation is derived for polaron mode in semiconductor magnetoplasma. The propagation and amplification characteristics of the wave are explored in detail. The analysis deals with the behaviour of anomalous threshold and amplification derived from dispersion relation, as function of external parameters like doping concentration and applied magnetic field. The results of this investigation are hoped to be useful in understanding electron-longitudinal optical phonon interplay in polar n-type semiconductor plasmas under the influence of coupled collective cyclotron excitations. The best results in terms of smaller threshold and higher gain of polaron mode could be achieved by choosing moderate doping concentration in the medium at higher magnetic field. For numerical appreciation of the results, relevant data of III-V n-GaAs compound semiconductor at 77 K is used. Present study provides a qualitative picture of polaron mode in magnetized n-type polar semiconductor medium duly shined by a CO2 laser.

Enhanced characteristics of blue InGaN /GaN light-emitting diodes by using selective activation to modulate the lateral current spreading length

NASA Astrophysics Data System (ADS)

Lin, Ray-Ming; Lu, Yuan-Chieh; Chou, Yi-Lun; Chen, Guo-Hsing; Lin, Yung-Hsiang; Wu, Meng-Chyi

2008-06-01

We have studied the characteristics of blue InGaN /GaN multiquantum-well light-emitting diodes (LEDs) after reducing the length of the lateral current path through the transparent layer through formation of a peripheral high-resistance current-blocking region in the Mg-doped GaN layer. To study the mechanism of selective activation in the Mg-doped GaN layer, we deposited titanium (Ti), gold (Au), Ti /Au, silver, and copper individually onto the Mg-doped GaN layer and investigated their effects on the hole concentration in the p-GaN layer. The Mg-doped GaN layer capped with Ti effectively depressed the hole concentration in the p-GaN layer by over one order of magnitude relative to that of the as-grown layer. This may suggest that high resistive regions are formed by diffusion of Ti and depth of high resistive region from the p-GaN surface depends on the capped Ti film thickness. Selective activation of the Mg-doped GaN layer could be used to modulate the length of the lateral current path. Furthermore, the external quantum efficiency of the LEDs was improved significantly after reducing the lateral current spreading length. In our best result, the external quantum efficiency was 52.3% higher (at 100mA) than that of the as-grown blue LEDs.

Influence of niobium doping in hierarchically organized titania nanostructure on performance of dye-sensitized solar cells.

PubMed

Park, Jong Hoon; Noh, Jun Hong; Han, Byung Suh; Shin, Seong Sik; Park, Ik Jae; Kim, Dong Hoe; Hong, Kug Sun

2012-06-01

Niobium doped hierarchically organized TiO2 nanostructures composed of 20 nm size anatase nanocrystals were synthesized using pulsed laser deposition (PLD). The Nb doping concentration could be facilely controlled by adjusting the concentration of Nb in target materials. We could investigate the influence of Nb doping in the TiO2 photoelectrode on the cell performance of dye-sensitized solar cells (DSSCs) by the exclusion of morphological effects using the prepared Nb-doped TiO2 anostructures. We found no significant change in short circuit current density (Jsc) as a function of Nb doping concentration. However, open circuit voltage (Voc) and fill factor (FF) monotonously decrease with increasing Nb concentration. Dark current characteristics of the DSSCs reveal that the decrease in Voc and FF is attributed to the decrease in shunt resistance due to the increase in conductivity TiO2 by Nb doping. However, electrochemical impedance spectra (EIS) analysis at open circuit condition under illumination showed that the resistance at the TiO2/dye/electrolyte interface increases with Nb concentration, revealing that Nb doping suppress the charge recombination at the interface. In addition, electron life time obtained using characteristic frequency in Bode plot increases from 14 msec to 56 msec with increasing Nb concentration from 0 to 1.2 at%. This implies that the improved light harvesting can be achieved by increasing diffusion length through Nb-doping in the conventional TiO2 photoelectrode.

Effect of Boron Doping on High-Resolution X-Ray Diffraction Metrology

NASA Astrophysics Data System (ADS)

Faheem, M.; Zhang, Y.; Dai, X.

2018-03-01

The effect of boron (B) doping on high-resolution X-ray diffraction (HXRD) metrology has been investigated. Twelve samples of Si1-xGex films were epitaxially grown on Si (100) substrates with different thicknesses, germanium (Ge) concentrations and with/without B dopants. Secondary ion mass spectroscopy (SIMS) and HXRD were employed for measurements of B doping, Ge concentration, strain, and thickness of the layers. The SIMS results show the absence of B in two samples while the rest of the samples have B doping in the range of 8.40 × 1018-8.7 × 1020 atoms/cm3 with Ge concentration of 13.3-55.2 at.%. The HXRD measurements indicate the layers thickness of 7.07-108.13 nm along with Ge concentration of 12.82-49.09 at.%. The difference in the Ge concentration measured by SIMS and HXRD was found to deend on B doping. For the undoped samples, the difference is 0.5 at.% and increases with B doping but with no linear proportionality. The difference in the Ge concentration was 7.11 at.% for the highly B-doped (8.7 × 1020 atoms/cm3) sample. The B doping influences the Si1-xGex structure, causing a change in the lattice parameter and producing tensile strains shifting Si1-xGex peaks towards Si (100) substrate peaks in the HXRD diffraction patterns. As a result, Vegard's law is no longer effective and makes a high impact on the HXRD measurement. The comparison between symmetric (004) and asymmetric (+113, +224) reciprocal space mappings (RSM) showed a slight difference in Ge concentration between the undoped and lower B-doped samples. However, there is a change of 0.21 at.% observed for the highly doped Si1-xGex samples. RSM's (+113) demonstrate the small SiGe peak broadening as B doping increases, which indicates a minor crystal distortion.

Doping concentration dependence of microstructure and magnetic behaviours in Co-doped TiO2 nanorods

PubMed Central

2014-01-01

Co-doped titanium dioxide (TiO2) nanorods with different doping concentrations were fabricated by a molten salt method. It is found that the morphology of TiO2 changes from nanorods to nanoparticles with increasing doping concentration. The mechanism for the structure and phase evolution is investigated in detail. Undoped TiO2 nanorods show strong ferromagnetism at room temperature, whereas incorporating of Co deteriorates the ferromagnetic ordering. X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) results demonstrate that the ferromagnetism is associated with Ti vacancy. PMID:25593558

Electron mobility enhancement in epitaxial multilayer Si-Si/1-x/Ge/x/ alloy films on /100/Si

NASA Technical Reports Server (NTRS)

Manasevit, H. M.; Gergis, I. S.; Jones, A. B.

1982-01-01

Enhanced Hall-effect mobilities have been measured in epitaxial (100)-oriented multilayer n-type Si/Si(1-x)Ge(x) films grown on single-crystal Si substrates by chemical vapor deposition. Mobilities from 20 to 40% higher than that of epitaxial Si layers and about 100% higher than that of epitaxial SiGe layers on Si were measured for the doping range 8 x 10 to the 15th to 10 to the 17th/cu cm. No mobility enhancement was observed in multilayer p-type (100) films and n-type (111)-oriented films. Experimental studies included the effects upon film properties of layer composition, total film thickness, doping concentrations, layer thickness, and growth temperature.

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

High p-type doping, mobility, and photocarrier lifetime in arsenic-doped CdTe single crystals

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

Nagaoka, Akira; Kuciauskas, Darius; McCoy, Jedidiah

Here, Group-V element doping is promising for simultaneously maximizing the hole concentration and minority carrier lifetime in CdTe for thin film solar cells, but there are roadblocks concerning point defects including the possibility of self-compensation by AX metastability. Herein, we report on doping, lifetime, and mobility of CdTe single crystals doped with As between 10 16 and 10 20 cm –3 grown from the Cd solvent by the travelling heater method. Evidence consistent with AX instability as a major contributor to compensation in samples doped below 10 17 cm –3 is presented, while for higher-doped samples, precipitation of a secondmore » phase on planar structural defects is also observed and may explain spatial variation in properties such as lifetime. Rapid cooling after crystal growth increases doping efficiency and mobility for times up to 20–30 days at room temperature with the highest efficiencies observed close to 45% and a hole mobility of 70 cm 2/Vs at room temperature. A doping limit in the low 10 17/cm 3 range is observed for samples quenched at 200–300 °C/h. Bulk minority carrier lifetimes exceeding 20 ns are observed for samples doped near 10 16 cm –3 relaxed in the dark and for unintentionally doped samples, while a lifetime of nearly 5 ns is observed for 10 18 cm –3 As doping. These results help us to establish limits on properties expected for group-V doped CdTe polycrystalline thin films for use in photovoltaics.« less

High p-type doping, mobility, and photocarrier lifetime in arsenic-doped CdTe single crystals

DOE PAGES

Nagaoka, Akira; Kuciauskas, Darius; McCoy, Jedidiah; ...

2018-05-07

Here, Group-V element doping is promising for simultaneously maximizing the hole concentration and minority carrier lifetime in CdTe for thin film solar cells, but there are roadblocks concerning point defects including the possibility of self-compensation by AX metastability. Herein, we report on doping, lifetime, and mobility of CdTe single crystals doped with As between 10 16 and 10 20 cm –3 grown from the Cd solvent by the travelling heater method. Evidence consistent with AX instability as a major contributor to compensation in samples doped below 10 17 cm –3 is presented, while for higher-doped samples, precipitation of a secondmore » phase on planar structural defects is also observed and may explain spatial variation in properties such as lifetime. Rapid cooling after crystal growth increases doping efficiency and mobility for times up to 20–30 days at room temperature with the highest efficiencies observed close to 45% and a hole mobility of 70 cm 2/Vs at room temperature. A doping limit in the low 10 17/cm 3 range is observed for samples quenched at 200–300 °C/h. Bulk minority carrier lifetimes exceeding 20 ns are observed for samples doped near 10 16 cm –3 relaxed in the dark and for unintentionally doped samples, while a lifetime of nearly 5 ns is observed for 10 18 cm –3 As doping. These results help us to establish limits on properties expected for group-V doped CdTe polycrystalline thin films for use in photovoltaics.« less

Density functional theory study of dopant effect on formation energy of intrinsic point defects in germanium crystals

NASA Astrophysics Data System (ADS)

Yamaoka, S.; Kobayashi, K.; Sueoka, K.; Vanhellemont, J.

2017-09-01

During the last decade the use of single crystal germanium (Ge) layers and structures in combination with silicon (Si) substrates has led to a revival of defect research on Ge. Ge is used because of the much higher carrier mobility compared to Si, allowing to design devices operating at much higher frequencies. A major issue for the use of Ge single crystal wafers is the fact that all Czochralski-grown Ge (CZ-Ge) crystals are vacancy-rich and contain vacancy clusters that are much larger than the ones in Si. In contrast to Si, control of intrinsic point defect concentrations has not yet been realized at the same level in Ge crystals due to the lack of experimental data especially on dopant effects. In this study, we have evaluated with density functional theory (DFT) calculations the dopant effect on the formation energy (Ef) of the uncharged vacancy (V) and self-interstitial (I) in Ge and compared the results with those for Si. The dependence of the total thermal equilibrium concentrations of point defects (sum of free V or I and V or I paired with dopant atoms) at melting temperature on the type and concentration of various dopants is obtained. It was found that (1) Ge crystals will be more V-rich by Tl, In, Sb, Sn, As and P doping, (2) Ge crystals will be more I-rich by Ga, C and B doping, (3) Si doping has negligible impact. The dopant impact on Ef of V and I in Ge has a narrower range and is smaller than that in Si. The obtained results are useful to control grown-in V and I concentrations, and will perhaps also allow to develop defect-free ;perfect; Ge crystals.

Role of nickel doping on structural, optical, magnetic properties and antibacterial activity of ZnO nanoparticles

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

Vijayaprasath, G.; Murugan, R.; Palanisamy, S.

Highlights: • The XRD analyses revealed that the synthesizes nickel doped ZnO (Zn{sub 1−x}Ni{sub x}O, x = 0.0, 0.03, 0.06 and 0.09) nanostructures have hexagonal wurtzite structure. • The photoluminescence measurements revealed that the broad emission was composed of different bands due to zinc and oxygen vacancies. • X-ray photoelectron spectroscopy (XPS) confirmed the Ni incorporation in ZnO lattice as Ni{sup 2+} ions. • Room temperature ferromagnetism was observed due to the oxygen vacancies and zinc interstitials are the main reasons for ferromagnetism in Ni doped ZnO NPs. - Abstract: Zn{sub 1−x}Ni{sub x}O nanoparticles were synthesized by co-precipitation method. Themore » crystallite sizes of the synthesized samples found to decrease from 38 to 26 nm with increase in nickel concentration. FTIR spectra confirmed the presence of Zn−O stretching bands at 577, 573, 569 and 565 cm{sup −1} in the respective ZnO NPs. Optical absorption spectra revealed the red shifted and estimated band gap is found to decrease with increase of Ni doping concentration. The PL spectra of all the samples exhibited a broad emission at 390 nm in the visible range. The carriers (donors) bounded on the Ni sites were observed from the micro Raman spectroscopic studies. Pure and Ni doped ZnO NPs showed significant changes in the M–H loop, especially the diamagnetic behavior changed into ferromagnetic nature for Ni doped samples. The antiferromagnetic super-exchange interactions between Ni{sup 2+} ions is increased in higher Ni doped ZnO NPs and also their antibacterial activity has been studied.« less

Optimization design on breakdown voltage of AlGaN/GaN high-electron mobility transistor

NASA Astrophysics Data System (ADS)

Yang, Liu; Changchun, Chai; Chunlei, Shi; Qingyang, Fan; Yuqian, Liu

2016-12-01

Simulations are carried out to explore the possibility of achieving high breakdown voltage of GaN HEMT (high-electron mobility transistor). GaN cap layers with gradual increase in the doping concentration from 2 × 1016 to 5 × 1019 cm-3 of N-type and P-type cap are investigated, respectively. Simulation results show that HEMT with P-doped GaN cap layer shows more potential to achieve higher breakdown voltage than N-doped GaN cap layer under the same doping concentration. This is because the ionized net negative space charges in P-GaN cap layer could modulate the surface electric field which makes more contribution to RESURF effect. Furthermore, a novel GaN/AlGaN/GaN HEMT with P-doped GaN buried layer in GaN buffer between gate and drain electrode is proposed. It shows enhanced performance. The breakdown voltage of the proposed structure is 640 V which is increased by 12% in comparison to UID (un-intentionally doped) GaN/AlGaN/GaN HEMT. We calculated and analyzed the distribution of electrons' density. It is found that the depleted region is wider and electric field maximum value is induced at the left edge of buried layer. So the novel structure with P-doped GaN buried layer embedded in GaN buffer has the better improving characteristics of the power devices. Project supported by the National Basic Research Program of China (No. 2014CB339900) and the Open Fund of Key Laboratory of Complex Electromagnetic Environment Science and Technology, China Academy of Engineering Physics (No. 2015-0214.XY.K).

Effect of laser irradiance and wavelength on the analysis of gold- and silver-bearing minerals with laser-induced breakdown spectroscopy

NASA Astrophysics Data System (ADS)

Díaz, Daniel; Molina, Alejandro; Hahn, David

2018-07-01

The influence of laser irradiance and wavelength on the analysis of gold and silver in ore and surrogate samples with laser-induced breakdown spectroscopy (LIBS) was evaluated. Gold-doped mineral samples (surrogates) and ore samples containing naturally-occurring gold and silver were analyzed with LIBS using 1064 and 355 nm laser wavelengths at irradiances from 0.36 × 109 to 19.9 × 109 W/cm2 and 0.97 × 109 to 4.3 × 109 W/cm2, respectively. The LIBS net, background and signal-to-background signals were analyzed. For all irradiances, wavelengths, samples and analytes the calibration curves behaved linearly for concentrations from 1 to 9 μg/g gold (surrogate samples) and 0.7 to 47.0 μg/g silver (ore samples). However, it was not possible to prepare calibration curves for gold-bearing ore samples (at any concentration) nor for gold-doped surrogate samples with gold concentrations below 1 μg/g. Calibration curve parameters for gold-doped surrogate samples were statistically invariant at 1064 and 355 nm. Contrary, the Ag-ore analyte showed higher emission intensity at 1064 nm, but the signal-to-background normalization reduced the effect of laser wavelength of silver calibration plots. The gold-doped calibration curve metrics improved at higher laser irradiance, but that did not translate into lower limits of detection. While coefficients of determination (R2) and limits of detection did not vary significantly with laser wavelength, the LIBS repeatability at 355 nm improved up to a 50% with respect to that at 1064 nm. Plasma diagnostics by the Boltzmann and Stark broadening methods showed that the plasma temperature and electron density did not follow a specific trend as the wavelength changed for the delay and gate times used. This research presents supporting evidence that the LIBS discrete sampling features combined with the discrete and random distribution of gold in minerals hinder gold analysis by LIBS in ore samples; however, the use of higher laser irradiances at 1064 nm increased the probability of sampling and detecting naturally-occurring gold.

Influence of Dopants in ZnO Films on Defects

NASA Astrophysics Data System (ADS)

Peng, Cheng-Xiao; Weng, Hui-Min; Zhang, Yang; Ma, Xing-Ping; Ye, Bang-Jiao

2008-12-01

The influence of dopants in ZnO films on defects is investigated by slow positron annihilation technique. The results show S that parameters meet SAl > Sun > SAg for Al-doped ZnO films, undoped and Ag-doped ZnO films. Zinc vacancies are found in all ZnO films with different dopants. According to S parameter and the same defect type, it can be induced that the zinc vacancy concentration is the highest in the Al-doped ZnO film, and it is the least in the Ag-doped ZnO film. When Al atoms are doped in the ZnO films grown on silicon substrates, Zn vacancies increase as compared to the undoped and Ag-doped ZnO films. The dopant concentration could determine the position of Fermi level in materials, while defect formation energy of zinc vacancy strongly depends on the position of Fermi level, so its concentration varies with dopant element and dopant concentration.

Doping process of p-type GaN nanowires: A first principle study

NASA Astrophysics Data System (ADS)

Xia, Sihao; Liu, Lei; Diao, Yu; Feng, Shu

2017-10-01

The process of p-type doping for GaN nanowires is investigated using calculations starting from first principles. The influence of different doping elements, sites, types, and concentrations is discussed. Results suggest that Mg is an optimal dopant when compared to Be and Zn due to its stronger stability, whereas Be atoms are more inclined to exist in the interspace of a nanowire. Interstitially-doped GaN nanowires show notable n-type conductivity, and thus, Be is not a suitable dopant, which is to be expected since systems with inner substitutional dopants are more favorable than those with surface substitutions. Both interstitial and substitutional doping affect the atomic structure near dopants and induce charge transfer between the dopants and adjacent atoms. By altering doping sites and concentrations, nanowire atomic structures remain nearly constant. Substitutional doping models show p-type conductivity, and Mg-doped nanowires with doping concentrations of 4% showing the strongest p-type conductivity. All doping configurations are direct bandgap semiconductors. This study is expected to direct the preparation of high-quality GaN nanowires.

Effect of Mo and Ti doping concentration on the structural and optical properties of ZnS nanoparticles

NASA Astrophysics Data System (ADS)

Naz, Hina; Ali, Rai Nauman; Zhu, Xingqun; Xiang, Bin

2018-06-01

In this paper, we report the effect of single phase Mo and Ti doping concentration on the structural and optical properties of the ZnS nanoparticles. The structural and optical properties of the as-synthesized samples have been examined by x-ray diffraction, transmission electron microscopy (TEM), UV-visible near infrared absorption spectroscopy and x-ray photoelectron spectroscopy. TEM characterizations reveal a variation in the doped ZnS nanoparticle size distribution by utilizing different dopants of Mo and Ti. In absorption spectra, a clear red shift of 14 nm is observed with increasing Mo concentration as compared to pure ZnS nanoparticles, while by increasing Ti doping concentration, blue shift of 14 nm is obtained. Moreover, it demonstrates that the value of energy band gap decreases from 4.03 eV to 3.89 eV in case of Mo doping. However, the value of energy band gap have shown a remarkable increase from 4.11 eV to 4.27 eV with increasing Ti doping concentration. Our results provide a new pathway to understand the effect of Mo and Ti doping concentrations on the structural and optical properties of ZnS nanoparticles as it could be the key to tune the properties for future optoelectronic devices.

Urine stability and steroid profile: towards a screening index of urine sample degradation for anti-doping purpose.

PubMed

Mazzarino, Monica; Abate, Maria Gabriella; Alocci, Roberto; Rossi, Francesca; Stinchelli, Raffaella; Molaioni, Francesco; de la Torre, Xavier; Botrè, Francesco

2011-01-10

The presence of microorganisms in urine samples, under favourable conditions of storage and transportation, may alter the concentration of steroid hormones, thus altering the correct evaluation of the urinary steroid profile in doping control analysis. According to the rules of the World Anti-Doping Agency (WADA technical document TD2004 EAAS), a testosterone deconjugation higher than 5% and the presence of 5α-androstane-3,17-dione and 5β-androstane-3,17-dione in the deconjugated fraction, are reliable indicators of urine degradation. The determination of these markers would require an additional quantitative analysis since the steroids screening analysis, in anti-doping laboratories, is performed in the total (free+conjugated) fraction. The aim of this work is therefore to establish reliable threshold values for some representative compounds (namely 5α-androstane-3,17-dione and 5β-androstane-3,17-dione) in the total fraction in order to predict directly at the screening stage the potential microbial degradation of the urine samples. Preliminary evidence on the most suitable degradation indexes has been obtained by measuring the urinary concentration of testosterone, epitestosterone, 5α-androstane-3,17-dione and 5β-androstane-3,17-dione by gas chromatography-mass spectrometric every day for 15 days in the deconjugated, glucuronide and total fraction of 10 pools of urines from 60 healthy subjects, stored under different pH and temperature conditions, and isolating the samples with one or more markers of degradation according to the WADA technical document TD2004EAAS. The threshold values for 5α-androstane-3,17-dione and 5β-androstane-3,17-dione were therefore obtained correlating the testosterone deconjugation rate with the urinary concentrations of 5α-androstane-3,17-dione and 5β-androstane-3,17-dione in the total fraction. The threshold values suggested as indexes of urine degradation in the total fraction were: 10 ng mL(-1) for 5α-androstane-3,17-dione and 20 ng mL(-1) for 5β-androstane-3,17-dione. The validity of this approach was confirmed by the analysis of routine samples for more than five months (i.e. on a total of more than 4000 urine samples): samples with a concentration of total 5α-androstane-3,17-dione and 5β-androstane-3,17-dione higher than the threshold values showed a percentage of free testosterone higher than 5 of its total amount; whereas free testosterone in a percentage higher than 5 of its total amount was not detected in urines with a concentration of total 5α-androstane-3,17-dione and 5β-androstane-3,17-dione lower than the threshold values. Copyright © 2010 Elsevier B.V. All rights reserved.

Concentration and wavelength dependent frequency downshifting photoluminescence from a Tb3+ doped yttria nano-phosphor: A photochromic phosphor

NASA Astrophysics Data System (ADS)

Yadav, Ram Sagar; Rai, Shyam Bahadur

2018-03-01

In this article, the Tb3+ doped Y2O3 nano-phosphor has been synthesized through solution combustion method. The structural measurements of the nano-phosphor have been carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques, which reveal nano-crystalline nature. The Fourier transform infrared (FTIR) measurements reveal the presence of different molecular species in the nano-phosphor. The UV-Vis-NIR absorption spectrum of the nano-phosphor shows large number of bands due to charge transfer band (CTB) and 4f-4f electronic transitions of Tb3+ ion. The Tb3+ doped Y2O3 nano-phosphor emits intense green downshifting photoluminescence centered at 543 nm due to 5D4 → 7F5 transition on excitation with 350 nm. The emission intensity of the nano-phosphor is optimized at 1.0 mol% concentration of Tb3+ ion. When the as-synthesized nano-phosphor is annealed at higher temperature the emission intensity of the nano-phosphor enhances upto 5 times. The enhancement in the emission intensity is due to an increase in crystallinity of the nano-phosphor, reduction in surface defects and optical quenching centers. The CIE diagram reveals that the Tb3+ doped nano-phosphor samples show the photochromic nature (color tunability) with a change in the concentration of Tb3+ ion and excitation wavelength. The lifetime measurement indicates an increase in the lifetime for the annealed sample. Thus, the Tb3+ doped Y2O3 nano-phosphor may be used in photochromic displays and photonic devices.

Mg doping of GaN by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Lieten, R. R.; Motsnyi, V.; Zhang, L.; Cheng, K.; Leys, M.; Degroote, S.; Buchowicz, G.; Dubon, O.; Borghs, G.

2011-04-01

We present a systematic study on the influence of growth conditions on the incorporation and activation of Mg in GaN layers grown by plasma-assisted molecular beam epitaxy. We show that high quality p-type GaN layers can be obtained on GaN-on-silicon templates. The Mg incorporation and the electrical properties have been investigated as a function of growth temperature, Ga : N flux ratio and Mg : Ga flux ratio. It was found that the incorporation of Mg and the electrical properties are highly sensitive to the Ga : N flux ratio. The highest hole mobility and lowest resistivity were achieved for slightly Ga-rich conditions. In addition to an optimal Ga : N ratio, an optimum Mg : Ga flux ratio was also observed at around 1%. We observed a clear Mg flux window for p-type doping of GaN : 0.31% < Mg : Ga < 5.0%. A lowest resistivity of 0.98 Ω cm was obtained for optimized growth conditions. The p-type GaN layer then showed a hole concentration of 4.3 × 1017 cm-3 and a mobility of 15 cm2 V-1 s-1. Temperature-dependent Hall effect measurements indicate an acceptor depth in these samples of 100 meV for a hole concentration of 5.5 × 1017 cm-3. The corresponding Mg concentration is 5 × 1019 cm-3, indicating approximately 1% activation at room temperature. In addition to continuous growth of Mg-doped GaN layers we also investigated different modulated growth procedures. We show that a modulated growth procedure has only limited influence on Mg doping at a growth temperature of 800 °C or higher. This result is thus in contrast to previously reported GaN : Mg doping at much lower growth temperatures of 500 °C.

Spin-state polarons as a precursor to ferromagnetism and metallicity in hole-doped LaCoO3

NASA Astrophysics Data System (ADS)

Podlesnyak, A.; Russina, M.; Pomjakushina, E.; Conder, K.; Khomskii, D.

2008-03-01

Lightly doped cobaltites La1-xSrxCoO3 exhibit magnetic properties at low temperatures, in strong contrast to the diamagnetic LaCoO3. We undertook an inelastic neutron scattering study with the goal to identify the energy spectrum and magnetic state of cobalt ions in the doped system with x=0.002. In distinguish to the parent compound, where no excitations have been found for T<30 K, an inelastic peak at δE ˜0.75 meV was observed in La0.998Sr0.002CoO3 at T=1.5 K. The intensity of this excitation is much higher than what is expected from an estimated concentration of doped holes. Furthermore, strong Zeeman splitting of the inelastic peak corresponds to an unusually high effective magnetic moment ˜15 μB. Neighboring low-spin (LS) Co^4+ and intermediate-spin Co^3+ ions can share an eg electron by swapping configuration. The t2g electrons, in their turn, couple ferromagnetically. Therefore, we propose that the holes introduced in the LS state of LaCoO3 are extended over the neighboring Co sites forming spin-state polarons and transforming the involved Co^3+ ions to the higher spin state. Grows of spin-state polarons with hole doping finally results in a metallic ferromagnetic state for x > 0.3.

In-situ sonosynthesis of nano N-doped ZnO on wool producing fabric with photo and bio activities, cell viability and enhanced mechanical properties.

PubMed

Behzadnia, Amir; Montazer, Majid; Rad, Mahnaz Mahmoudi

2015-08-01

Here, a simple processing route is introduced for preparation of N-doped nano structure ZnO at 75-80°C using in-situ sonosynthesis method through hydrolysis of zinc acetate at pH≈9-10 adjusting with ammonia. Synthesis and fabrication of nano N-doped ZnO were carried out on the wool fabric through impregnation of the fabric in ultrasound bath using different concentrations of zinc acetate followed by curing. The antibacterial and antifungal activities of the treated fabrics were assessed against two common pathogenic bacteria including Escherichia coli, Staphylococcus aureus and the diploid fungus namely Candida albicans. The photo-catalytic activity of nano N-doped ZnO particles on the wool fabric was determined by degradation of Methylene Blue under daylight irradiation. Increasing zinc acetate and prolonged sonication time led to higher photo-catalytic activity as more dye stain degraded from the stained treated fabric under daylight. Higher photo-catalytic activity was observed on the nano N-doped ZnO sonotreated wool fabric having more hydrophilicity. Finally, the treatment indicated no negative effect on the fabric safety while reduced alkaline solubility and yellowness even enhanced the fabric tensile strength. The response surface methodology was also utilized to optimize the wool fabric treatment conditions. Copyright © 2015 Elsevier B.V. All rights reserved.

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.

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

Kumar, Pragati, E-mail: pkumar.phy@gmail.com; Department of Physics and Astrophysics, University of Delhi, Delhi, 110 007; Saxena, Nupur

This work shows the influence of Ag concentration on structural properties of pulsed laser deposited nanocrystalline CdS thin film. X-ray photoelectron spectroscopy (XPS) studies confirm the dopant concentration in CdS films and atomic concentration of elements. XPS studies show that the samples are slightly sulfur deficient. GAXRD scan reveals the structural phase transformation from cubic to hexagonal phase of CdS without appearance of any phase of CdO, Ag{sub 2}O or Ag{sub 2}S suggesting the substitutional doping of Ag ions. Photoluminescence studies illustrate that emission intensity increases with increase in dopant concentration upto 5% and then decreases for higher dopant concentration.

Synergistic effect of non-covalent interaction in colloidal nematic liquid crystal doped with magnetic functionalized single-walled carbon nanotubes

NASA Astrophysics Data System (ADS)

Dalir, Nima; Javadian, Soheila

2018-03-01

Single-walled carbon nanotubes (SWCNTs), CNT@Fe3O4, and Fe3O4 nanocomposites were doped to eutectic uniaxial nematic liquid crystal (NLC's) (E5CN7) to improve physiochemical properties such as phase transition temperature, activation energy (Ea), dielectric anisotropy, and electro-optical properties. The thermal study of nematic phase shows a decrease in the nematic to isotropic phase transition temperature as CNT is doped. However, higher doping concentration of CNTs leads to the further increase in transition temperature. The anchoring effect or π-π interaction plays a key role in N-I phase transition. The functionalization of SWCNTs with Fe3O4 diminishes the CNT aggregation while the magnetic susceptibility is increased. The functionalized CNT doping to NLC's decrease significantly the phase transition temperature compared to doping of non-functionalized CNTs. Attractive interaction between guest and host molecules by magnetic and geometry effect increased the enthalpy and entropy of phase transition in the SWCNT@Fe3O4 sample compared to non-functionalized CNT doped system. Also, the Ea values are decreased as SWCNT@Fe3O4 is doped to pure E5CN7. The difference of N-I phase transition temperature was observed in Fe3O4 and CNT@Fe3O4 compared to SWCNT doped systems. Finally, dielectric anisotropy was increased in the doped system compared to pure NLC.

Seebeck and figure of merit enhancement in nanostructured antimony telluride by antisite defect suppression through sulfur doping.

PubMed

Mehta, Rutvik J; Zhang, Yanliang; Zhu, Hong; Parker, David S; Belley, Matthew; Singh, David J; Ramprasad, Ramamurthy; Borca-Tasciuc, Theodorian; Ramanath, Ganpati

2012-09-12

Antimony telluride has a low thermoelectric figure of merit (ZT < ∼0.3) because of a low Seebeck coefficient α arising from high degenerate hole concentrations generated by antimony antisite defects. Here, we mitigate this key problem by suppressing antisite defect formation using subatomic percent sulfur doping. The resultant 10-25% higher α in bulk nanocrystalline antimony telluride leads to ZT ∼ 0.95 at 423 K, which is superior to the best non-nanostructured antimony telluride alloys. Density functional theory calculations indicate that sulfur increases the antisite formation activation energy and presage further improvements leading to ZT ∼ 2 through optimized doping. Our findings are promising for designing novel thermoelectric materials for refrigeration, waste heat recovery, and solar thermal applications.

Fabrication of Smart Chemical Sensors Based on Transition-Doped-Semiconductor Nanostructure Materials with µ-Chips

PubMed Central

Rahman, Mohammed M.; Khan, Sher Bahadar; Asiri, Abdullah M.

2014-01-01

Transition metal doped semiconductor nanostructure materials (Sb2O3 doped ZnO microflowers, MFs) are deposited onto tiny µ-chip (surface area, ∼0.02217 cm2) to fabricate a smart chemical sensor for toxic ethanol in phosphate buffer solution (0.1 M PBS). The fabricated chemi-sensor is also exhibited higher sensitivity, large-dynamic concentration ranges, long-term stability, and improved electrochemical performances towards ethanol. The calibration plot is linear (r2 = 0.9989) over the large ethanol concentration ranges (0.17 mM to 0.85 M). The sensitivity and detection limit is ∼5.845 µAcm−2mM−1 and ∼0.11±0.02 mM (signal-to-noise ratio, at a SNR of 3) respectively. Here, doped MFs are prepared by a wet-chemical process using reducing agents in alkaline medium, which characterized by UV/vis., FT-IR, Raman, X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), and field-emission scanning electron microscopy (FE-SEM) etc. The fabricated ethanol chemical sensor using Sb2O3-ZnO MFs is simple, reliable, low-sample volume (<70.0 µL), easy of integration, high sensitivity, and excellent stability for the fabrication of efficient I–V sensors on μ-chips. PMID:24454785

Fabrication of smart chemical sensors based on transition-doped-semiconductor nanostructure materials with µ-chips.

PubMed

Rahman, Mohammed M; Khan, Sher Bahadar; Asiri, Abdullah M

2014-01-01

Transition metal doped semiconductor nanostructure materials (Sb2O3 doped ZnO microflowers, MFs) are deposited onto tiny µ-chip (surface area, ∼0.02217 cm(2)) to fabricate a smart chemical sensor for toxic ethanol in phosphate buffer solution (0.1 M PBS). The fabricated chemi-sensor is also exhibited higher sensitivity, large-dynamic concentration ranges, long-term stability, and improved electrochemical performances towards ethanol. The calibration plot is linear (r(2) = 0.9989) over the large ethanol concentration ranges (0.17 mM to 0.85 M). The sensitivity and detection limit is ∼5.845 µAcm(-2)mM(-1) and ∼0.11±0.02 mM (signal-to-noise ratio, at a SNR of 3) respectively. Here, doped MFs are prepared by a wet-chemical process using reducing agents in alkaline medium, which characterized by UV/vis., FT-IR, Raman, X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), and field-emission scanning electron microscopy (FE-SEM) etc. The fabricated ethanol chemical sensor using Sb2O3-ZnO MFs is simple, reliable, low-sample volume (<70.0 µL), easy of integration, high sensitivity, and excellent stability for the fabrication of efficient I-V sensors on μ-chips.

Combination of Carrier Concentration Regulation and High Band Degeneracy for Enhanced Thermoelectric Performance of Cu3SbSe4.

PubMed

Zhang, Dan; Yang, Junyou; Jiang, Qinghui; Zhou, Zhiwei; Li, Xin; Xin, Jiwu; Basit, Abdul; Ren, Yangyang; He, Xu; Chu, Weijing; Hou, Jingdi

2017-08-30

The effect of Al-, Ga-, and In-doping on the thermoelectric (TE) properties of Cu 3 SbSe 4 has been comparatively studied on the basis of theoretical prediction and experimental validation. It is found that tiny Al/Ga/In substitution leads to a great enhancement of electrical conductivity with high carrier concentration and also large Seebeck coefficient due to the preserved high band degeneracy and thereby a remarkably high power factor. Ultimately, coupled with the depressed lattice thermal conductivity, all three elements (Al/Ga/In) substituted samples have obtained a highly improved thermoelectric performance with respect to undoped Cu 3 SbSe 4 . Compared to the samples at the same Al/In doping level, the slightly Ga-doped sample presents better TE performance over the wide temperature range, and the Cu 3 Sb 0.995 Ga 0.005 Se 4 sample presents a record high ZT value of 0.9 among single-doped Cu 3 SbSe 4 at 623 K, which is about 80% higher than that of pristine Cu 3 SbSe 4 . This work offers an alternative approach to boost the TE properties of Cu 3 SbSe 4 by selecting efficient dopant to weaken the coupling between electrical conductivity and Seebeck coefficient.

First principles study of crystal Si-doped Ge2Sb2Te5

NASA Astrophysics Data System (ADS)

Yan, Beibei; Yang, Fei; Chen, Tian; Wang, Minglei; Chang, Hong; Ke, Daoming; Dai, Yuehua

2017-02-01

Ge2Sb2Te5 (GST) and Si-doped GST with hexagonal structure were investigated by means of First-principles calcucations. We performed many kinds of doping types and studied the electronic properties of Si-doped GST with various Si concentrations. The theoretical calculations show that the lowest formation energy appeared when Si atoms substitute the Sb atoms (SiSb). With the increasing of Si concentrations from 10% to 30%, the impurity states arise around the Fermi level and the band gap of the SiSb structure broadens. Meanwhile, the doping supercell has the most favorable structure when the doping concentration keeps in 20%. The Si-doped GST exhibits p-type metallic characteristics more distinctly owing to the Fermi level moves toward the valence band. The Te p, d-orbitals electrons have greater impact on electronic properties than that of Te s-orbitals.

Modulation of electronic transport properties in armchair phosphorene nanoribbons by doping and edge passivation.

PubMed

Guo, Caixia; Wang, Tianxing; Xia, Congxin; Liu, Yufang

2017-10-09

The electronic structures and transport properties of group IV atoms (C, Si, Ge)-doped armchair phosphorene nanoribbons (APNRs) are investigated using first-principles calculations, considering different edge passivation. The results show that the C, Si, Ge dopants can induce the transition occur from semiconductor to metal in the APNRs. The negative differential resistance (NDR) behavior in the doped APNR system is robust with respect to the doping concentration and edge passivation type. However, their current peak positions and peak-to-valley ratio (PVR) values are correlated with doping concentration and edge passivation type. In particular, for the C, Si-doped APNRs, the low bias NDR behavior with the PVR (10 5 -10 8 ) can be observed when doping concentration is low in the APNRs with the F and H edge passivation. These results may play an important role for the fabrication of future low power consumption nano-electronic devices.

The preparation of in situ doped hydrogenated amorphous silicon by homogeneous chemical vapor deposition

NASA Astrophysics Data System (ADS)

Meyerson, B. S.; Scott, B. A.; Wolford, D. J.

1983-03-01

Raman scattering, infrared absorption, conductivity measurements, electron microprobe, and secondary ion mass spectrometry (SIMS) were used to characterize boron and phosphorus doped hydrogenated amorphous silicon (a-Si:H) films prepared by Homogeneous Chemical Vapor Deposition (HOMOCVD). HOMOCVD is a thermal process which relies upon the gas phase pyrolysis of a source (silane containing up to 1.0% diborane or phosphine) to generate activated species for deposition upon a cooled substrate. Doped films prepared at 275 °C by this process were found to contain ˜12-at. % hydrogen as determined by infrared absorption. We examined dopant incorporation from the gas phase, obtaining values for a distribution coefficient CD (film dopant content/gas phase dopant concentration, atomic basis) of 0.33≤CD ≤0.63 for boron, while 0.4≤CD ≤10.75 in the limits 3.3×10-5≤PH3/SiH4≤0.004. We interpret the data as indicative of the formation of an unstable phosphorus/silicon intermediate in the gas phase, leading to the observed enhancements in CD at high gas phase phosphine content. HOMOCVD films doped at least as efficiently as their prepared counterparts, but tended to achieve higher conductivities [σ≥0.1 (Ω cm)-1 for 4.0% incorporated phosphorus] in the limit of heavy doping. Raman spectra showed no evidence of crystallinity in the doped films. Film properties (conductivity, activation energy of of conduction) have not saturated at the doping levels investigated here, making the attainment of higher ``active'' dopant levels a possibility. We attribute the observation that HOMOCVD appears more amenable to high ``active'' dopant levels than plasma techniques to the low (˜0.1 eV) thermal energy at which HOMOCVD proceeds, versus ˜10-100 eV for plasma techniques. Low substrate temperature (75 °C) doped films were prepared with initial results showing these films to dope as readily as those prepared at high temperature (T˜275 °C).

Layered Double Hydroxides: Potential Release-on-Demand Fertilizers for Plant Zinc Nutrition.

PubMed

López-Rayo, Sandra; Imran, Ahmad; Bruun Hansen, Hans Chr; Schjoerring, Jan K; Magid, Jakob

2017-10-11

A novel zinc (Zn) fertilizer concept based on Zn-doped layered double hydroxides (Zn-doped Mg-Fe-LDHs) has been investigated. Zn-doped Mg-Fe-LDHs were synthesized, their chemical composition was analyzed, and their nutrient release was studied in buffered solutions with different pH values. Uptake of Zn by barley (Hordeum vulgare cv. Antonia) was evaluated in short- (8 weeks), medium- (11 weeks), and long-term (28 weeks) experiments in quartz sand and in a calcareous soil enriched with Zn-doped Mg-Fe-LDHs. The Zn release rate of the Zn-doped Mg-Fe-LDHs was described by a first-order kinetics equation showing maximum release at pH 5.2, reaching approximately 45% of the total Zn content. The Zn concentrations in the plants receiving the LDHs were between 2- and 9.5-fold higher than those in plants without Zn addition. A positive effect of the LDHs was also found in soil. This work documents the long-term Zn release capacity of LDHs complying with a release-on-demand behavior and serves as proof-of-concept that Zn-doped Mg-Fe-LDHs can be used as Zn fertilizers.

Energy band gap and optical transition of metal ion modified double crossover DNA lattices.

PubMed

Dugasani, Sreekantha Reddy; Ha, Taewoo; Gnapareddy, Bramaramba; Choi, Kyujin; Lee, Junwye; Kim, Byeonghoon; Kim, Jae Hoon; Park, Sung Ha

2014-10-22

We report on the energy band gap and optical transition of a series of divalent metal ion (Cu(2+), Ni(2+), Zn(2+), and Co(2+)) modified DNA (M-DNA) double crossover (DX) lattices fabricated on fused silica by the substrate-assisted growth (SAG) method. We demonstrate how the degree of coverage of the DX lattices is influenced by the DX monomer concentration and also analyze the band gaps of the M-DNA lattices. The energy band gap of the M-DNA, between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO), ranges from 4.67 to 4.98 eV as judged by optical transitions. Relative to the band gap of a pristine DNA molecule (4.69 eV), the band gap of the M-DNA lattices increases with metal ion doping up to a critical concentration and then decreases with further doping. Interestingly, except for the case of Ni(2+), the onset of the second absorption band shifts to a lower energy until a critical concentration and then shifts to a higher energy with further increasing the metal ion concentration, which is consistent with the evolution of electrical transport characteristics. Our results show that controllable metal ion doping is an effective method to tune the band gap energy of DNA-based nanostructures.

Co-doping of CVD diamond with boron and sulfur

NASA Astrophysics Data System (ADS)

Eaton, Sally Catherine

Boron is well-established as a p-type dopant in diamond, but attempts to find a viable n-type dopant remain unsuccessful. In 1999, sulfur was reported to give n-type conductivity. However, later measurements indicated that the samples contained boron and were p-type. Recently, we showed that diamond co-doped with sulfur and small quantities of boron shows n-type conductivity, which was established by Mott-Schottky analyses, thermoelectric effect, Hall measurements, scanning tunneling spectroscopy (STS), and UV open-circuit photo-potential. At higher boron concentrations, a transition to p-type behavior is observed due to overcompensation. Experiments performed without boron in the feed gas or without residual boron in the reactor chamber showed no sulfur incorporation and no change in conductivity. There is evidence that the excess sulfur concentration in the near-surface region is not stable. At room temperature and below, the activation energies range from 0.06 to 0.12 eV. Above 400K there is an irreversible loss in conductivity and the activation energy increases to approximately 1.3 eV. Additionally, we observed by SIMS that there exists a concentration gradient in sulfur with film depth. This sulfur concentration gradient is also observed in our electrical measurements. STS shows a decrease in conductivity with film depth and Hall effect measurements show both p-type and n-type coefficients for samples which are n-type in the near-surface region. The flat-band potential obtained from the Mott-Schottky experiments is only 1 to 1.5 V more negative on the electrochemical scale than that for boron-doped diamond. This implies that the Fermi level is only 1 to 1.5 eV higher than the Fermi level in boron-doped diamond. This observation implies that the n-type conductivity is not by excitation of electrons to the conduction band, but by an alternate mechanism that occurs in the middle of the band gap. One such possibility is an acceptor impurity band. Electrons from individual donor states can be excited into this acceptor band where they are free to move. This mechanism would create n-type conductivity even if the Fermi level was low in the bandgap.

Defect-mediated magnetism of transition metal doped zinc oxide thin films

NASA Astrophysics Data System (ADS)

Roberts, Bradley Kirk

Magnetism in transition metal doped wide band-gap materials is of interest to further the fundamental science of materials and future spintronics applications. Large inter-dopant separations require mediation of ferromagnetism by some method; carrier-mediated mechanisms are typically applicable to dilute magnetic semiconductors with low Curie temperatures. Dilute magnetic oxides, commonly with poor conductivity and TC above room temperature, cannot be described within this theory. Recent experiment and theory developments suggest that ferromagnetic exchange in these materials can be mediated by defects. This research includes experimental results justifying and developing this approach. Thin films of Cr doped ZnO (band gap ˜3.3 eV) were deposited with several processing variations to enhance the effects of either 0-dimensional (vacancy, hydrogen-related defect) or two-dimensional defects (surface/interface) and thereby affect magnetism and conductivity. We observe surface magnetism in dielectric thin films of oxygen-saturated ZnO:Cr with spontaneous magnetic moment and conductance dropping approximately exponentially with increasing thickness. Uniform defect concentrations would not result in such magnetic ordering behavior indicating that magnetism is mediated either by surface defects or differing concentrations of point defects near the surface. Polarized neutron reflectivity profiling confirms a magnetically active region of ˜8 nm at the film surface. Hydrogen is notoriously present as a defect and carrier dopant in ZnO, and artificial introduction of hydrogen in dielectric ZnO:Cr films results in varying electronic and magnetic behavior. Free carriers introduced with hydrogen doping are not spin-polarized requiring an alternative explanation for ferromagnetism. We find from positron annihilation spectroscopy measurements that hydrogen doping increases the concentration of an altered VZn-related defect (a preliminary interpretation) throughout the film, which is may be magnetically active as mediator. Measurements suggest that this defect contribution is strongest (or concentration higher) near the surface too. This study concerns the wide-gap oxide ZnO when doped with the transition metal Cr, below the percolation threshold, and subject to defects that mediate ferromagnetism independent of polarized free carriers. Ultimately, by adjusting the volumetric concentration of certain defects, ferromagnetic ordering in ZnO:Cr can be controlled. The potential applicability of novel theories of defect-mediated magnetism to this system is discussed.

H sub 3 PMo sub 12 O sub 40 -doped polyacetylene as a catalyst for ethyl alcohol conversion

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

Pozniczek, J.; Bielanski, A.; Kulszewicz-Bajer, I.

1991-12-01

A new and highly efficient catalyst was obtained by exploiting the unique ability of polyacetylene to incorporate heteropolyanions (HPA) of the Keggin type via oxidative doping. 12-Molybdophosphoric acid, 20.8 wt%, was introduced into the polymer. A uniform distribution of HPA over the cross section of the polymer film was found. However, the concentration of HPA seemed to be higher at the surface of the polymer fibers than in their bulk. The conversion of ethyl alcohol was used as a catalytic test reaction. The catalyst exhibited both acid-base activity (formation of ethylene and diethyl ether) as well as redox activity (formationmore » of acetaldehyde). The acid-base activity was 10 times higher than that of unsupported H{sub 3}PMo{sub 12}O{sub 40}, and the redox activity was about 40 times higher.« less

Cu-Doped ZnO Thin Films Deposited by a Sol-Gel Process Using Two Copper Precursors: Gas-Sensing Performance in a Propane Atmosphere.

PubMed

Gómez-Pozos, Heberto; Arredondo, Emma Julia Luna; Maldonado Álvarez, Arturo; Biswal, Rajesh; Kudriavtsev, Yuriy; Pérez, Jaime Vega; Casallas-Moreno, Yenny Lucero; Olvera Amador, María de la Luz

2016-01-29

A study on the propane gas-sensing properties of Cu-doped ZnO thin films is presented in this work. The films were deposited on glass substrates by sol-gel and dip coating methods, using zinc acetate as a zinc precursor, copper acetate and copper chloride as precursors for doping. For higher sensitivity values, two film thickness values are controlled by the six and eight dippings, whereas for doping, three dippings were used, irrespective of the Cu precursor. The film structure was analyzed by X-ray diffractometry, and the analysis of the surface morphology and film composition was made through scanning electron microscopy (SEM) and secondary ion mass spectroscopy (SIMS), respectively. The sensing properties of Cu-doped ZnO thin films were then characterized in a propane atmosphere, C₃H₈, at different concentration levels and different operation temperatures of 100, 200 and 300 °C. Cu-doped ZnO films doped with copper chloride presented the highest sensitivity of approximately 6 × 10⁴, confirming a strong dependence on the dopant precursor type. The results obtained in this work show that the use of Cu as a dopant in ZnO films processed by sol-gel produces excellent catalysts for sensing C₃H₈ gas.

Synergistic effects of Mo and F doping on the quality factor of ZnO thin films prepared by a fully automated home-made nebulizer spray technique

NASA Astrophysics Data System (ADS)

Ravichandran, K.; Dineshbabu, N.; Arun, T.; Manivasaham, A.; Sindhuja, E.

2017-01-01

Transparent conducting oxide films of undoped, Mo doped, Mo + F co-doped ZnO were deposited using a facile homemade nebulizer spray pyrolysis technique. The effects of Mo and F doping on the structural, optical, electrical and surface morphological properties were investigated using XRD, UV-vis-NIR spectroscopy, I-V and Hall probe techniques, FESEM and AFM, and XPS, respectively. The XRD analysis confirms that all the films are well crystallized with hexagonal wurtzite structure. All the synthesized samples exhibit high transmittance (above 85%) in the visible region. The current-voltage (I-V) characteristics show the ohmic conduction nature of the films. The Hall probe measurements show that the synergistic effects of Mo and F doping cause desirable improvements in the quality factor of the ZnO films. A minimum resistivity of 5.12 × 10-3 Ω cm with remarkably higher values of mobility and carrier concentration is achieved for Mo (2 at.%) + F (15 at.%) co-doped ZnO films. A considerable variation in the intensity of deep level emission caused by Mo and F doping is observed in the photoluminescence (PL) studies. The presence of the constituent elements in the samples is confirmed by XPS analysis.

A biosensor based on Coriolopsis gallica laccase immobilized on nitrogen-doped multiwalled carbon nanotubes and graphene oxide for polyphenol detection

PubMed Central

Aguila, Sergio A; Shimomoto, David; Ipinza, Franscisco; Bedolla-Valdez, Zaira I; Romo-Herrera, José; Contreras, Oscar E; Farías, Mario H; Alonso-Núñez, Gabriel

2015-01-01

The use of nanomaterials allows the design of ultrasensitive biosensors with advantages in the detection of organic molecules. Catechol and catechin are molecules that occur naturally in fruits, and their presence in products like dyes and wines affects quality standards. In this study, catechol and catechin were measured at the nanoscale by means of cyclic voltammetry. The oxidation of Coriolopsis gallica laccase immobilized on nitrogen-doped multiwalled carbon nanotubes (Lac/CNx-MWCNT) and on graphene oxide (Lac/GO) was used to measure the concentrations of catechol and catechin. Nitrogen-doped multiwalled carbon nanotubes (CNx-MWCNT) were synthesized by spray pyrolysis and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS). Covalently bonded hybrids with laccase (Lac/CNx-MWCNT and Lac/GO) were generated. Catalytic activity of free enzymes determined with syringaldazine yielded 14 584 UmL−1. With Lac/CNx-MWCNT at concentrations of 6.4 mmol L−1 activity was 9326 U mL−1, while enzyme activity measured with Lac/GO at concentration of 6.4 mmol L−1 was 9 234 U mL−1. The Lac/CNx-MWCNT hybrid showed higher stability than Lac/GO at different ethyl alcohol concentrations. The Lac/CNx-MWCNT hybrid can measure concentrations, not previously reported, as low as 1 × 10−8 mol L−1 by measuring the electric current responses. PMID:27877839

A biosensor based on Coriolopsis gallica laccase immobilized on nitrogen-doped multiwalled carbon nanotubes and graphene oxide for polyphenol detection

NASA Astrophysics Data System (ADS)

Aguila, Sergio A.; Shimomoto, David; Ipinza, Franscisco; Bedolla-Valdez, Zaira I.; Romo-Herrera, José; Contreras, Oscar E.; Farías, Mario H.; Alonso-Núñez, Gabriel

2015-10-01

The use of nanomaterials allows the design of ultrasensitive biosensors with advantages in the detection of organic molecules. Catechol and catechin are molecules that occur naturally in fruits, and their presence in products like dyes and wines affects quality standards. In this study, catechol and catechin were measured at the nanoscale by means of cyclic voltammetry. The oxidation of Coriolopsis gallica laccase immobilized on nitrogen-doped multiwalled carbon nanotubes (Lac/CNx-MWCNT) and on graphene oxide (Lac/GO) was used to measure the concentrations of catechol and catechin. Nitrogen-doped multiwalled carbon nanotubes (CNx-MWCNT) were synthesized by spray pyrolysis and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS). Covalently bonded hybrids with laccase (Lac/CNx-MWCNT and Lac/GO) were generated. Catalytic activity of free enzymes determined with syringaldazine yielded 14 584 UmL-1. With Lac/CNx-MWCNT at concentrations of 6.4 mmol L-1 activity was 9326 U mL-1, while enzyme activity measured with Lac/GO at concentration of 6.4 mmol L-1 was 9 234 U mL-1. The Lac/CNx-MWCNT hybrid showed higher stability than Lac/GO at different ethyl alcohol concentrations. The Lac/CNx-MWCNT hybrid can measure concentrations, not previously reported, as low as 1 × 10-8 mol L-1 by measuring the electric current responses.

General control of transition-metal-doped GaN nanowire growth: toward understanding the mechanism of dopant incorporation.

PubMed

Stamplecoskie, Kevin G; Ju, Ling; Farvid, Shokouh S; Radovanovic, Pavle V

2008-09-01

We report the first synthesis and characterization of cobalt- and chromium-doped GaN nanowires (NWs), and compare them to manganese-doped GaN NWs. Samples were synthesized by chemical vapor deposition method, using cobalt(II) chloride and chromium(III) chloride as dopant precursors. For all three impurity dopants hexagonal, triangular, and rectangular NWs were observed. The fraction of NWs having a particular morphology depends on the initial concentration of the dopant precursors. While all three dopant ions have the identical effect on GaN NW growth and faceting, Co and Cr are incorporated at much lower concentrations than Mn. These findings suggest that the doping mechanism involves binding of the transition-metal intermediates to specific NW facets, inhibiting their growth and causing a change in the NW morphology. We discuss the doping concentrations of Mn, Co, and Cr in terms of differences in their crystal-field stabilization energies (DeltaCFSE) in their gas-phase intermediates and in substitutionally doped GaN NWs. Using iron(III) chloride and cobalt(II) acetate as dopant precursors we show that the doping concentration dependence on DeltaCFSE allows for the prediction of achievable doping concentrations for different dopant ions in GaN NWs, and for a rational choice of a suitable dopant-ion precursor. This work further demonstrates a general and rational control of GaN NW growth using transition-metal impurities.

Physical and optical properties of lithium borosilicate glasses doped with Dy3+ ions

NASA Astrophysics Data System (ADS)

Ramteke, D. D.; Gedam, R. S.; Swart, H. C.

2018-04-01

The borosilicate glasses with Dy3+ ions were prepared by the melt quench technique with varying concentration of Dy2O3. The glasses were characterized by the density calculation, absorbance and photoluminescence (PL) spectroscopy measurements. Density and molar volume of the glasses increases with increase in Dy3+ ions in the glass matrix. This behavior is correlated with the higher molecular weight and larger ionic radius of Dy3+ ion compared to the other constituents of glass matrix. Emission of Dy3+ doped glasses showed three bands at 482, 573 and at 665 nm which correspond to 6H15/2 (blue), 6H13/2 (yellow) and 6H11/2 (red) transitions. The emission spectra of glasses with different concentration of Dy3+ ions shows that, glasses with 0.5 mol% of Dy2O3 shows highest emission and decreases with further doping. CIE 1931 chromaticity diagram showed that the emission of these glasses was in the white region. Photographs of these glasses under 349 nm Light emitting diode excitation also confirmed the white light emission from these glasses.

An optical fiber glass containing PbSe quantum dots

NASA Astrophysics Data System (ADS)

Cheng, Cheng; Jiang, Huilü; Ma, Dewei; Cheng, Xiaoyu

2011-09-01

An optical fiber material, sodium-aluminum-borosilicate glass doped with PbSe quantum dots (QDs) is synthesized by a high-temperature melting method. Crystallization, size distribution and absorption-photoluminescence (PL) of this material are observed by XRD, TEM, and spectrometer respectively. The obtained results indicate that the glass contains QDs in diameter of 6-13 nm depending on the heat-treatment temperature and with a higher doped concentration than those available. It shows an enhanced PL, widened FWHM (275-808 nm), obvious Stokes shift (20-110 nm), with the PL peak wavelength located within 1676-2757 nm depending on the size of QD. The glass is fabricated into an optical fiber in diameter of 10-70 μm and length of 1 m, with pliability and ductility similar to usual SiO 2 fibers. It can be easily fused and spliced with SiO 2 fibers due to a small difference of melting point between them. Characterized by high doped concentration and broad FWHM, this study suggests that the glass can be applied to designing novel broadband fiber amplifiers working in C-L waveband.

Thermoelectric Properties of Cu-doped Bi2-xSbxTe3 Prepared by Encapsulated Melting and Hot Pressing

NASA Astrophysics Data System (ADS)

Jung, Woo-Jin; Kim, Il-Ho

2018-03-01

P-type Bi2-xSbxTe3:Cum (x = 1.5-1.7 and m = 0.002-0.003) solid solutions were synthesized using encapsulated melting and were consolidated using hot pressing. The effects of Sb substitution and Cu doping on the charge transport and thermoelectric properties were examined. The lattice constants decreased with increasing Sb and Cu contents. As the amount of Sb substitution and Cu doping was increased, the electrical conductivity increased, and the Seebeck coefficient decreased owing to the increase in the carrier concentration. All specimens exhibited degenerate semiconductor characteristics and positive Hall and Seebeck coefficients, indicating p-type conduction. The increased Sb substitution caused a shift in the onset temperature of the intrinsic transition and bipolar conduction to higher temperatures. The electronic thermal conductivity increased with increasing Sb and Cu contents owing to the increase in the carrier concentration, while the lattice thermal conductivity slightly decreased due to alloy scattering. A maximum figure of merit, ZTmax = 1.25, was achieved at 373 K for Bi0.4Sb1.6Te3:Cu0.003.

Visible light photocatalytic antibacterial activity of Ni-doped and N-doped TiO2 on Staphylococcus aureus and Escherichia coli bacteria.

PubMed

Ananpattarachai, Jirapat; Boonto, Yuphada; Kajitvichyanukul, Puangrat

2016-03-01

The Ni-doped and N-doped TiO2 nanoparticles were investigated for their antibacterial activities on Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) bacteria. Their morphological features and characteristics such as particle size, surface area, and visible light absorbing capacity were compared and discussed. Scanning electron microscopy, X-ray diffraction, and UV-visible spectrophotometry were used to characterize both materials. The inactivation of E. coli (as an example of Gram-negative bacteria) and S. aureus (as an example of Gram-positive bacteria) with Ni-doped and N-doped TiO2 was investigated in the absence and presence of visible light. Antibacterial activity tests were conducted using undoped, Ni-doped, and N-doped TiO2. The N-doped TiO2 nanoparticles show higher antibacterial activity than Ni-doped TiO2. The band gap narrowing of N-doped TiO2 can induce more visible light absorption and leads to the superb antibacterial properties of this material. The complete inactivation time for E. coli at an initial cell concentration of 2.7 × 10(4) CFU/mL was 420 min which is longer than the 360 min required for S. aureus inactivation. The rate of inactivation of S. aureus using the doped TiO2 nanoparticles in the presence of visible light is greater than that of E. coli. The median lethal dose (LD50) values of S. aureus and E. coli by antibacterial activity under an 18-W visible light intensity were 80 and 350 mg/ml for N-doped TiO2, respectively.

Kinetic analysis of Legionella inactivation using ozone in wastewater.

PubMed

Li, Jun; Li, Kunquan; Zhou, Yan; Li, Xuebin; Tao, Tao

2017-02-01

Legionella inactivation using ozone was studied in wastewater using kinetic analysis and modeling. The experimental results indicate that the relationship between the ozone concentration, germ concentration, and chemical oxygen demand (COD) can be used to predict variations in germ and COD concentrations. The ozone reaction with COD and inactivation of Legionella occurred simultaneously, but the reaction with COD likely occurred at a higher rate than the inactivation, as COD is more easily oxidized by ozone than Legionella. Higher initial COD concentrations resulted in a lower inactivation rate and higher lnN/N 0 . Higher temperature led to a higher inactivation efficiency. The relationship of the initial O 3 concentration and Legionella inactivation rate was not linear, and thus, the Ct value required for a 99.99% reduction was not constant. The initial O 3 concentration was more important than the contact time, and a reduction of the initial O 3 concentration could not be compensated by increasing the contact time. The Ct values were compared over a narrow range of initial concentrations; the Ct values could only be contrasted when the initial O 3 concentrations were very similar. A higher initial O 3 concentration led to a higher inflection point value for the lnN/N 0 vs C 0 t curve. Energy consumption using a plasma corona was lower than when using boron-doped diamond electrodes. Copyright © 2016 Elsevier Ltd. All rights reserved.

Enhancement of luminescence emission from GdVO{sub 4}:Er{sup 3+}/Yb{sup 3+} phosphor by Li{sup +} co-doping

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

Gavrilović, Tamara V.; Jovanović, Dragana J., E-mail: draganaj@vinca.rs; Lojpur, Vesna M.

2014-09-15

This paper demonstrates the effects of Li{sup +} co-doping on the structure, morphology, and luminescence properties of GdVO{sub 4}:Er{sup 3+}/Yb{sup 3+} phosphor prepared using a high-temperature solid-state chemistry method. The GdVO{sub 4}:Er{sup 3+}/Yb{sup 3+} powders synthesized with the Li{sup +} co-dopant (in concentrations of 0, 5, 10, and 15 mol%) are characterized by X-ray powder diffraction, scanning electron microscopy, and photoluminescence spectroscopy. Structural analysis showed that powders co-doped with Li{sup +} have larger crystallite sizes and slightly smaller crystal lattice parameters than powders prepared without Li{sup +} ions. Photoluminescence down-conversion (345-nm excitation) and up-conversion (980-nm excitation) spectra show characteristic Er{supmore » 3+} emissions, with the most intense bands peaking at 525 nm ({sup 2}H{sub 11/2}→{sup 4}I{sub 15/2} transition) and 552 nm ({sup 4}S{sub 3/2}→{sup 4}I{sub 15/2}). The intensity of up-conversion emission from GdVO{sub 4}:Er{sup 3+}/Yb{sup 3+} is enhanced (by a factor of four) by co-doping with 5 mol% of Li{sup +} ions. The mechanisms responsible for this emission enhancement are discussed. - Graphical abstract: UC emission spectra for GdVO{sub 4}:1.5-mol% Er{sup 3+}/20-mol% Yb{sup 3+} powders co-doped with different concentrations of Li{sup +} ions, recorded under 980-nm excitation. - Highlights: • 5-mol% Li{sup +} co-doped powders have 400% enhanced up-conversion emission intensity. • 15-mol% Li{sup +} co-doping produces 40% higher emission in down-conversion. • Li{sup +} co-doped powders have larger crystallite size and smaller lattice parameters.« less

Investigation of microstructure, electrical and photoluminescence behaviour of Ni-doped Zn0.96Mn0.04O nanoparticles: Effect of Ni concentration

NASA Astrophysics Data System (ADS)

Rajakarthikeyan, R. K.; Muthukumaran, S.

2017-07-01

ZnO, Zn0.96Mn0.04O and Ni-doped Zn0.96Mn0.04O nanoparticles with different Ni concentrations (0%, 2% and 4%) have been synthesized successfully by sol-gel method. The effects of Ni doping on the structural and optical properties were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy and photoluminescence (PL) spectroscopy. The XRD pattern confirmed the existence of single phase wurtzite-like hexagonal structure throughout the Ni concentrations without any additional phases. The substitution of Ni created the lattice distortion due to the disparity of ionic radius between Zn and Ni which reduced the crystallite size. The microscopic images showed that the size of ZnO nanoparticles reduced by Ni-doping while the shape remains almost spherical/hexagonal type. The electrical conductivity found to be maximum at Ni = 2% due to the availability of more charge carriers generated by Ni. The decrease of electrical conductivity at higher doping (Ni = 4%) is due to the fact that the generation of more defects. The enhanced band gap from 3.73 eV (Ni = 0%) to 3.79 eV (Ni = 4%) by the addition of Ni explained by Burstein-Moss effect. The change in infra-red (IR) intensity and full width at half maximum (FWHM) corresponding to the frequency around defect states were caused by the difference in the bond lengths that occurs when Ni ion replaces Zn ion. The observed blue band emission from 474 nm to 481 nm is due to a radiative transition of an electron from the deep donar level of Zni to an acceptor level of neutral VZn and the origin of green band may be due to oxygen vacancies and intrinsic defects. The tuning of the band gap and the visible emission bands by Ni doping concluded that Ni-doped Zn0.96Mn0.04O is suitable for various nano-photo-electronics applications.

Solution-processed organic thermoelectric materials exhibiting doping-concentration-dependent polarity.

PubMed

Hwang, Sunbin; Potscavage, William J; Yang, Yu Seok; Park, In Seob; Matsushima, Toshinori; Adachi, Chihaya

2016-10-26

Recent progress in conducting polymer-based organic thermoelectric generators (OTEGs) has resulted in high performance due to high Seebeck coefficient, high electrical conductivity (σ), and low thermal conductivity obtained by chemically controlling the materials's redox levels. In addition to improving the properties of individual OTEGs to obtain high performance, the development of solution processes for the fabrication of OTEG modules is necessary to realize large thermoelectric voltage and low-cost mass production. However, the scarcity of good candidates for soluble organic n-type materials limits the use of π-leg module structures consisting of complementary elements of p- and n-type materials because of unbalanced transport coefficients that lead to power losses. In particular, the extremely low σ of n-type materials compared with that of p-type materials is a serious challenge. In this study, poly(pyridinium phenylene) (P(PymPh)) was tested as an n-type semiconductor in solution-processed OTEGs, and the carrier density was controlled by a solution-based chemical doping process using the dopant sodium naphthalenide, a well-known reductant. The electronic structures and doping mechanism of P(PymPh) were explored based on the changes in UV-Vis-IR absorption, ultraviolet photoelectron, and X-ray photoelectron spectra. By controlling the dopant concentration, we demonstrate a maximum n-type power factor of 0.81 μW m -1 K -2 with high σ, and at higher doping concentrations, a switch from n-type to p-type TE operation. This is one of the first cases of a switch in polarity just by increasing the concentration of the reductant and may open a new route for simplified fabrication of complementary organic layers.

Gamma-ray shielding effect of Gd3+ doped lead barium borate glasses

NASA Astrophysics Data System (ADS)

Kummathi, Harshitha; Naveen Kumar, P.; Vedavathi T., C.; Abhiram, J.; Rajaramakrishna, R.

2018-05-01

The glasses of the batch xPbO: 10BaO: (90-x)B2O3: 0.2Gd2O3 (x = 40,45,50 mol %) were prepared by melt-quench technique. The work emphasizes on gamma ray shielding effect on doped lead glasses. The role of Boron is significant as it acts as better neutron attenuator as compared with any other materials, as the thermal neutron cross-sections are high for Gadolinium, 0.2 mol% is chosen as the optimum concentration for this matrix, as higher the concentration may lead to further increase as it produces secondary γ rays due to inelastic neutron scattering. Shielding effects were studied using Sodium Iodide (NaI) - Scintillation Gamma ray spectrometer. It was found that at higher concentration of lead oxide (PbO) in the matrix, higher the attenuation which can be co-related with density. Infra-red (I.R.) spectra reveals that the conversion of Lose triangles to tight tetrahedral structure results in enhancement of shielding properties. The Differential Scanning Calorimeter (D.S.C.) study also reveals that the increase in glass forming range increases the stability which in-turn results in inter-conversion of BO3 to BO4 units such that the density of glass increases with increase in PbO content, resulting in much stable and efficient gamma ray shielding glasses.

Plasmonic transparent conducting metal oxide nanoparticles and films for optical sensing applications

DOEpatents

Ohodnicki, Jr., Paul R; Wang, Congjun; Andio, Mark A

2014-01-28

The disclosure relates to a method of detecting a change in a chemical composition by contacting a doped oxide material with a monitored stream, illuminating the doped oxide material with incident light, collecting exiting light, monitoring an optical signal based on a comparison of the incident light and the exiting light, and detecting a shift in the optical signal. The doped metal oxide has a carrier concentration of at least 10.sup.18/cm.sup.3, a bandgap of at least 2 eV, and an electronic conductivity of at least 10.sup.1 S/cm, where parameters are specified at a temperature of 25.degree. C. The optical response of the doped oxide materials results from the high carrier concentration of the doped metal oxide, and the resulting impact of changing gas atmospheres on that relatively high carrier concentration. These changes in effective carrier densities of conducting metal oxide nanoparticles are postulated to be responsible for the change in measured optical absorption associated with free carriers. Exemplary doped metal oxides include but are not limited to Al-doped ZnO, Sn-doped In.sub.2O.sub.3, Nb-doped TiO.sub.2, and F-doped SnO.sub.2.

Nanocrystalline SnO2:F thin films for liquid petroleum gas sensors.

PubMed

Chaisitsak, Sutichai

2011-01-01

This paper reports the improvement in the sensing performance of nanocrystalline SnO(2)-based liquid petroleum gas (LPG) sensors by doping with fluorine (F). Un-doped and F-doped tin oxide films were prepared on glass substrates by the dip-coating technique using a layer-by-layer deposition cycle (alternating between dip-coating a thin layer followed by a drying in air after each new layer). The results showed that this technique is superior to the conventional technique for both improving the film thickness uniformity and film transparency. The effect of F concentration on the structural, surface morphological and LPG sensing properties of the SnO(2) films was investigated. Atomic Force Microscopy (AFM) and X-ray diffraction pattern measurements showed that the obtained thin films are nanocrystalline SnO(2) with nanoscale-textured surfaces. Gas sensing characteristics (sensor response and response/recovery time) of the SnO(2):F sensors based on a planar interdigital structure were investigated at different operating temperatures and at different LPG concentrations. The addition of fluorine to SnO(2) was found to be advantageous for efficient detection of LPG gases, e.g., F-doped sensors are more stable at a low operating temperature (300 °C) with higher sensor response and faster response/recovery time, compared to un-doped sensor materials. The sensors based on SnO(2):F films could detect LPG even at a low level of 25% LEL, showing the possibility of using this transparent material for LPG leak detection.

Bismuth doping effect on crystal structure and photodegradation activity of Bi-TiO2 nanoparticles

NASA Astrophysics Data System (ADS)

Wu, Ming-Chung; Chang, Yin-Hsuan; Lin, Ting-Han

2017-04-01

The bismuth precursor is adopted as dopant to synthesize bismuth doped titanium dioxide nanoparticles (Bi-TiO2 NPs) with sol-gel method following by the thermal annealing treatment. We systematically developed a series of Bi-TiO2 NPs at several calcination temperatures and discovered the corresponding crystal structure by varying the bismuth doping concentration. At a certain 650 °C calcination temperature, the crystal structure of bismuth titanate (Bi2Ti2O7) is formed when the bismuth doping concentration is as high as 10.0 mol %. The photocatalytic activity of Bi-TiO2 NPs is increased by varying the doping concentration at the particular calcination temperature. By the definition X-ray diffraction (XRD) structural identification, a phase diagram of Bi-TiO2 NPs in doping concentration versus calcination temperature is provided. It can be useful for further study in the crystal structure engineering and the development of photocatalyst.

Structural characteristics of Mg-doped (1-x)(K0.5Na0.5)NbO3-xLiSbO3 lead-free ceramics as revealed by Raman spectroscopy

NASA Astrophysics Data System (ADS)

Zhu, W. L.; Zhu, J. L.; Meng, Y.; Wang, M. S.; Zhu, B.; Zhu, X. H.; Zhu, J. G.; Xiao, D. Q.; Pezzotti, G.

2011-12-01

This paper presents a Raman spectroscopic study of compositional-change-induced structure variation and of the related mechanism of Mg doping in LiSbO3 (LS)-modified (K0.5Na0.5)NbO3 (KNN) ceramics. With increasing LS content from 0 to 0.06, a discontinuous shift towards higher wavenumbers was found for the band position of the A1g(v1) stretching mode of KNN, accompanied by a clearly nonlinear broadening of this band and a decrease in its intensity. Such morphological changes in the Raman spectrum result from two factors: (i) changes in polarizability/binding strength of the O-Nb-O vibration upon incorporation of Li ions in the KNN perovskitic structure and (ii) a polymorphic phase transition (PPT) from orthorhombic to tetragonal (O → T) phase at x > 0.04. Upon increasing the amount, w, of Mg dopant incorporated into the (1-x)KNN-xLS ceramic structure, the intensity of the Raman bands are enhanced, while the peak position and the full width at half maximum of the A1g(v1) mode was found to experience a clear dependence on both w and x. Raman characterization revealed that the mechanism of Mg doping is strongly correlated with the concentration of Li in the perovskite structure: Mg2+ ions will preferentially replace Li+ ions for low Mg doping while replace K/Na ions for higher doping of Mg. The PPT O → T was also found to be altered by the introduction of Mg and the critical value of LS concentration, xO-T, for incipient O → T transition in the KNN-xLS-wMT system was strongly dependent on Mg content, with xO → T being roughly equal to 0.04 + 2w, for the case of dilute Mg alloying.

Structural, morphological and gas sensing study of zinc doped tin oxide nanoparticles synthesized via hydrothermal technique

NASA Astrophysics Data System (ADS)

Singh, Davender; Kundu, Virender Singh; Maan, A. S.

2016-07-01

The pure and Zn-doped SnO2 nanoparticles were prepared successfully by hydrothermal route on large scale having different doping concentration of zinc from 0 to 0.20%. The calcined nanoparticles were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM) for structural and morphological studies. XRD analyses reveal that the nanoparticles of these doping concentrations are polycrystalline in nature and existed as tetragonal rutile structure, SEM study of images confirms the existence of very small, homogeneously distributed, and spherical nanoparticles. The particles size of the nanoparticles was calculated by Scherrer formula and was found in the range of 9-21 nm. The presence of dopant (i.e. zinc) and formation of Sn-O phase and hydrous nature of Zn-doped SnO2 nanoparticles are confirmed by EDX and FTIR study. The gas sensing properties of pure and Zn-doped SnO2 nanoparticles were investigated for various concentrations of methanol, ethanol and acetone at different operating temperatures and it has been found that with doping concentration of zinc (x = 0.20%) shows the maximum response 78% to methanol, 65% to ethanol and 62% to acetone respectively at different operating temperature within the measurement limit for a concentration of 100 ppm of each gases.

Study of the effects of focused high-energy boron ion implantation in diamond

NASA Astrophysics Data System (ADS)

Ynsa, M. D.; Agulló-Rueda, F.; Gordillo, N.; Maira, A.; Moreno-Cerrada, D.; Ramos, M. A.

2017-08-01

Boron-doped diamond is a material with a great technological and industrial interest because of its exceptional chemical, physical and structural properties. At modest boron concentrations, insulating diamond becomes a p-type semiconductor and at higher concentrations a superconducting metal at low temperature. The most conventional preparation method used so far, has been the homogeneous incorporation of boron doping during the diamond synthesis carried out either with high-pressure sintering of crystals or by chemical vapour deposition (CVD) of films. With these methods, high boron concentration can be included without distorting significantly the diamond crystalline lattice. However, it is complicated to manufacture boron-doped microstructures. A promising alternative to produce such microstructures could be the implantation of focused high-energy boron ions, although boron fluences are limited by the damage produced in diamond. In this work, the effect of focused high-energy boron ion implantation in single crystals of diamond is studied under different irradiation fluences and conditions. Micro-Raman spectra of the sample were measured before and after annealing at 1000 °C as a function of irradiation fluence, for both superficial and buried boron implantation, to assess the changes in the diamond lattice by the creation of vacancies and defects and their degree of recovery after annealing.

Bismuth doping strategies in GeTe nanowires to promote high-temperature phase transition from rhombohedral to face-centered cubic structure

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

Zhang, Jie; Huang, Rong; Wei, Fenfen

2014-11-17

The phase transition of Bi-doped (∼3 at. %) GeTe nanowires from a rhombohedral (R) to a face-centered cubic (C) structure was observed in in situ high-temperature X-ray diffraction. The promotion of high-temperature R-C phase transition by a doping approach was revealed. Ab initio energy calculations of doped GeTe at various Bi doping concentrations were performed to interpret the promoted temperature-induced phase transitions. Those results indicated that the total energy differences between R and C structures of doped GeTe decreased as Bi doping concentrations increased, which facilitated R-C phase transitions.

Synthesis and Characterization of Molybdenum Doped ZnO Thin Films by SILAR Deposition Method

NASA Astrophysics Data System (ADS)

Radha, R.; Sakthivelu, A.; Pradhabhan, D.

2016-08-01

Molybdenum (Mo) doped zinc oxide (ZnO) thin films were deposited on the glass substrate by Successive Ionic Layer Adsorption and Reaction (SILAR) deposition method. The effect of Mo dopant concentration of 5, 6.6 and 10 mol% on the structural, morphological, optical and electrical properties of n-type Mo doped ZnO films was studied. The X-ray diffraction (XRD) results confirmed that the Mo doped ZnO thin films were polycrystalline with wurtzite structure. The field emission scanning electron microscopy (FESEM) studies shows that the surface morphology of the films changes with Mo doping. A blue shift of the optical band gap was observed in the optical studies. Effect of Mo dopant concentration on electrical conductivity was studied and it shows comparatively high electrical conductivity at 10 mol% of Mo doping concentration.

Effect on Electron Structure and Magneto-Optic Property of Heavy W-Doped Anatase TiO2.

PubMed

Hou, Qingyu; Zhao, Chunwang; Guo, Shaoqiang; Mao, Fei; Zhang, Yue

2015-01-01

The spin or nonspin state of electrons in W-doped anatase TiO2 is very difficult to judge experimentally because of characterization method limitations. Hence, the effect on the microscopic mechanism underlying the visible-light effect of W-doped anatase TiO2 through the consideration of electronic spin or no-spin states is still unknown. To solve this problem, we establish supercell models of W-doped anatase TiO2 at different concentrations, followed by geometry optimization and energy calculation based on the first-principle planewave norm conserving pseudo-potential method of the density functional theory. Calculation results showed that under the condition of nonspin the doping concentration of W becomes heavier, the formation energy becomes greater, and doping becomes more difficult. Meanwhile, the total energy increases, the covalent weakens and ionic bonds strengthens, the stability of the W-doped anatase TiO2 decreases, the band gap increases, and the blue-shift becomes more significant with the increase of W doping concentration. However, under the condition of spin, after the band gap correction by the GGA+U method, it is found that the semimetal diluted magnetic semiconductors can be formed by heavy W-doped anatase TiO2. Especially, a conduction electron polarizability of as high as near 100% has been found for the first time in high concentration W-doped anatase TiO2. It will be able to be a promising new type of dilute magnetic semiconductor. And the heavy W-doped anatase TiO2 make the band gap becomes narrower and absorption spectrum red-shift.

Pseudocapacitance of Co doped NiO nanoparticles and its room temperature ferromagnetic behavior

NASA Astrophysics Data System (ADS)

Bharathy, G.; Raji, P.

2018-02-01

Co doped NiO nanoparticles CoxNi1-xO (x = 0.0, 0.1, 0.2, 0.3, 0.4) were synthesized by the Sol-gel technique. The impact of Co doping concentration on structural, functional and magnetic properties of NiO nanoparticles was analyzed by X-ray diffraction (XRD), FESEM with EDAX, FTIR and VSM. The average crystallite size was measured to be 34 nm and 11 nm for NiO and Co doped NiO nanoparticles respectively. FESEM reveals that particles are spherical in shape with average size around 30 nm. The elemental composition was analyzed by EDAX. FTIR spectra reveal the existence of NiO peaks in the prepared samples, room temperature ferromagnetism was observed for pure and Co doped NiO nanoparticles by VSM. Pure NiO particles shows ferromagnetic behavior with low coercivity and it increases gradually when doping ratio increases. Higher saturation magnetization was obtained for the sample 0.1 M of Co doped NiO nanoparticle as 22.09 emu/gm. An attempt has been made to study the pseudocapacitance behavior of pure and Co doped NiO nano particles in various scan rates. Electrochemical studies show that 0.4 M Co doped sample gives better charge storage capacity with maximum specific capacitance of 379 Fg-1 at a scan rate of 20 mVs-1. It reveals that it is a promising electrode material for super capacitor applications.

Room temperature synthesis of Mn2+ doped ZnS d-dots and observation of tunable dual emission: Effects of doping concentration, temperature, and ultraviolet light illumination

NASA Astrophysics Data System (ADS)

Kole, A. K.; Tiwary, C. S.; Kumbhakar, P.

2013-03-01

Mn2+ doped (0-50.0 molar %) ZnS d-dots have been synthesized in water medium by using an environment friendly low cost chemical technique. Tunable dual emission in UV and yellow-orange regions is achieved by tailoring the Mn2+ doping concentration in the host ZnS nanocrystal. The optimum doping concentration for achieving efficient photoluminescence (PL) emission is determined to be ˜1.10 (at. %) corresponding to 40.0 (molar %) of Mn2+ doping concentration used during synthesis. The mechanism of charge transfer from the host to the dopant leading to the intensity modulated tunable (594-610 nm) yellow-orange PL emission is straightforwardly understood as no capping agent is used. The temperature dependent PL emission measurements are carried out, viz., in 1.10 at. % Mn2+ doped sample and the experimental results are explained by using a theoretical PL emission model. It is found that the ratio of non-radiative to radiative recombination rates is temperature dependent and this phenomenon has not been reported, so far, in Mn2+ doped ZnS system. The colour tuning of the emitted light from the samples are evident from the calculated chromaticity coordinates. UV light irradiation for 150 min in 40.0 (molar %) Mn2+ doped sample shows an enhancement of 33% in PL emission intensity.

Study of the effects of neutron irradiation on silicon strip detectors

NASA Astrophysics Data System (ADS)

Guibellino, P.; Panizza, G.; Hall, G.; Sotthibandhu, S.; Ziock, H. J.; Ferguson, P.; Sommer, W. F.; Edwards, M.; Cartiglia, N.; Hubbard, B.; Lesloe, J.; Pitzl, D.; O'Shaughnessy, K.; Rowe, W.; Sadoziski, H. F.-W.; Seiden, A.; Spencer, E.

1992-05-01

Silicon strip detectors and test structures were exposed to neutron fluences up to Φ = 6.1 × 10 14 n/cm 2, using the ISIS neutron source at the Rutherford Appleton Laboratory (UK). In this paper we report some of our results concerning the effects of displacement damage, with a comparison of devices made of silicon of different resistivity. The various samples exposed showed a very similar dependence of the leakage current on the fluence received. We studied the change of effective doping concentration, and observed a behaviour suggesting the onset of type inversion at a fluence of ˜ 2.0 × 10 13 n/cm 2, a value which depends on the initial doping concentration. The linear increase of the depletion voltage for fluences higher than the inversion point could eventually determine the maximum fluence tolerable by silicon detectors.

[Effect of Eu(Pr) substitution at Ba sites on microstructure and superconductivity in EuBa2Cu3O7-delta ceramics].

PubMed

Peng, Zhen-sheng; Wang, Zhi-he

2004-04-01

Ceramics of Eu1+xBa2-xCu3O7-delta with x = 0.0, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5 and EuBa2-xPrxCu3O7-delta with x=0.0, 0.05, 0.1, 0.2, 0.3, 0.4 have been synthesized and investigated by X-ray diffraction, resistivity, and Raman spectroscopy. The results show that the transition of crystal structure from orthorhombic to tetragonal occurs and the criticaltemperature decreases withthe increase in doping concentration x. The Raman spectra show that the frequency of the Cu(1)-O(4) stretching mode andthe Cu(2)-(2, 3) out-of-phase mode shifts to higher wave number with increasing doping concentration x.

Enhanced Thermoelectric Properties of Polycrystalline SnSe via LaCl₃ Doping.

PubMed

Li, Fu; Wang, Wenting; Ge, Zhen-Hua; Zheng, Zhuanghao; Luo, Jingting; Fan, Ping; Li, Bo

2018-01-28

LaCl₃ doped polycrystalline SnSe was synthesized by combining mechanical alloying (MA) process with spark plasma sintering (SPS). It is found that the electrical conductivity is enhanced after doping due to the increased carrier concentration and carrier mobility, resulting in optimization of the power factor at 750 K combing with a large Seebeck coefficient over 300 Μvk -1 . Meanwhile, all the samples exhibit lower thermal conductivity below 1.0 W/mK in the whole measured temperature. The lattice thermal conductivity for the doped samples was reduced, which effectively suppressed the increscent of the total thermal conductivity because of the improved electrical conductivity. As a result, a ZT value of 0.55 has been achieved for the composition of SnSe-1.0 wt % LaCl₃ at 750 K, which is nearly four times higher than the undoped one and reveals that rare earth element is an effective dopant for optimization of the thermoelectric properties of SnSe.

Effect of TiO2 nanoparticles doping on structural and electrical properties of PVA: NaBr polymer electrolyte

NASA Astrophysics Data System (ADS)

Sagar, Rohan N.; Ravindrachary, V.; Guruswamy, B.; Hegde, Shreedatta; Mahanthesh, B. K.; Kumari, R. Padma

2018-05-01

The effect of TiO2 nanoparticles on morphology and electrical properties of PVA: NaBr composite films were carried out using various techniques. The pure and TiO2 nanoparticle doped PVA: NaBr composite films were prepared using solvent casting method. The FTIR spectral studies shows that the Ti+ ions of TiO2 interacts with hydroxyl group (OH) of PVA via hydrogen bonding and forms the charge transfer complexes (CTC). These interactions are of inter/intra molecular type and affects the surface morphology as well as the electrical properties of composite films. XRD study shows that the crystallinity of the composite increases with doping level. SEM studies shows that the increase in roughness of the surface of the composite films and uniform dispersion of nanofillers in polymer matrix. Electrical properties are analyzed using impedance analyzer and higher conductivity (10-4Scm-1) is achieved for 5 wt % TiO2 doping concentration.

Electrochemical capacitance voltage measurements in highly doped silicon and silicon-germanium alloys

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

Sermage, B.; Essa, Z.; Taleb, N.

2016-04-21

The electrochemical capacitance voltage technique has been used on highly boron doped SiGe and Si layers. Although the boron concentration is constant over the space charge depth, the 1/C{sup 2} versus voltage curves are not linear. They indeed present a negative curvature. This can be explained by the existence of deep acceptors which ionise under a high electric field (large inverse voltage) and not at a low inverse voltage. The measured doping concentration in the electrochemical capacitance voltage increases strongly as the inverse voltage increases. Thanks to a comparison with the boron concentration measured by secondary ions mass spectrometry, wemore » show that the relevant doping concentrations in device layers are obtained for small inverse voltage in agreement with the existence of deep acceptors. At the large inverse voltage, the measured doping can be more than twice larger than the boron concentration measured with a secondary ion mass spectroscopy.« less

Splitting CO2 with a ceria‐based redox cycle in a solar‐driven thermogravimetric analyzer

PubMed Central

Takacs, M.; Ackermann, S.; Bonk, A.; Neises‐von Puttkamer, M.; Haueter, Ph.; Scheffe, J. R.; Vogt, U. F.

2016-01-01

Thermochemical splitting of CO2 via a ceria‐based redox cycle was performed in a solar‐driven thermogravimetric analyzer. Overall reaction rates, including heat and mass transport, were determined under concentrated irradiation mimicking realistic operation of solar reactors. Reticulated porous ceramic (RPC) structures and fibers made of undoped and Zr4+‐doped CeO2, were endothermally reduced under radiative fluxes of 1280 suns in the temperature range 1200–1950 K and subsequently re‐oxidized with CO2 at 950–1400 K. Rapid and uniform heating was observed for 8 ppi ceria RPC with mm‐sized porosity due to its low optical thickness and volumetric radiative absorption, while ceria fibers with μm‐sized porosity performed poorly due to its opacity to incident irradiation. The 10 ppi RPC exhibited higher fuel yield because of its higher sample density. Zr4+‐doped ceria showed increasing reduction extents with dopant concentration but decreasing specific CO yield due to unfavorable oxidation thermodynamics and slower kinetics. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1263–1271, 2017 PMID:28405030

Pr3+ doped biphasic TiO2 (rutile-brookite) nanorod arrays grown on activated carbon fibers: Hydrothermal synthesis and photocatalytic properties

NASA Astrophysics Data System (ADS)

Li, Min; Zhang, Xiaomei; Liu, Ying; Yang, Yi

2018-05-01

Praseodymium-doped biphasic TiO2 (rutile-brookite) nanorod arrays (Pr-TiO2 NRAs) were successfully prepared via a two-step hydrothermal reaction on activated carbon fibers (ACFs) which pre-coated with TiO2 nanoparticles at first step. The bicrystalline arrays grown on ACFs are primarily constructed by the well-aligned TiO2 nanorods growing along [0 0 1] direction, which were indicated by the results of SEM and XRD. The nanorods are uniform in diameter and length with about 250 nm and 2.5 μm. The composite photocatalyst with high specific surface area and well-aligned nanostructure are beneficial to enhance the adsorption capacity and even help to suppress electron-hole recombination effectively, which consequently revealed much better (2 times) catalytic performance than that of commercially available P25 TiO2 on methylene blue(MB) photodegradation. In addition, the existence of praseodymium in TiO2 gives rise to shift of absorption edge towards long wavelength, which was indicated by the results of UV-vis DRS. Photodegradation results reveal that Pr-doping significantly improves the activity of TiO2, which was 20% higher than that of undoped TiO2 NRAs for the photodegradation of MB in aqueous medium under visible light irradiation. Meanwhile, the doped amount of Pr had a tiny influence on the photocatalytic performance of the composites. In our experiment, 3% Pr-doped molar concentration was proven to be the relatively optimal dopant concentration for the doping of TiO2 NRAs. Moreover, the photocatalyst grown on ACFs substrates is favorable to reuse and photodegradation rate kept on 76% even after 4 times of reuse.

Current-induced spin polarization in InGaAs and GaAs epilayers with varying doping densities

DOE PAGES

Luengo-Kovac, Marta; Huang, Simon; Del Gaudio, Davide; ...

2017-11-16

Here, the current-induced spin polarization and momentum-dependent spin-orbit field were measured in In xGa 1-xAs epilayers with varying indium concentrations and silicon doping densities. Samples with higher indium concentrations and carrier concentrations and lower mobilities were found to have larger electrical spin generation efficiencies. Furthermore, current-induced spin polarization was detected in GaAs epilayers despite the absence of measurable spin-orbit fields, indicating that the extrinsic contributions to the spin-polarization mechanism must be considered. Theoretical calculations based on a model that includes extrinsic contributions to the spin dephasing and the spin Hall effect, in addition to the intrinsic Rashba and Dresselhaus spin-orbitmore » coupling, are found to reproduce the experimental finding that the crystal direction with the smaller net spin-orbit field has larger electrical spin generation efficiency and are used to predict how sample parameters affect the magnitude of the current-induced spin polarization.« less

Aspects of silicon bulk lifetimes

NASA Technical Reports Server (NTRS)

Landsberg, P. T.

1985-01-01

The best lifetimes attained for bulk crytalline silicon as a function of doping concentrations are analyzed. It is assumed that the dopants which set the Fermi level do not contribute to the recombination traffic which is due to the unknown defect. This defect is assumed to have two charge states: neutral and negative, the neutral defect concentration is frozen-in at some temperature T sub f. The higher doping concentrations should include the band-band Auger effect by using a generalization of the Shockley-Read-Hall (SRH) mechanism. The generalization of the SRH mechanism is discussed. This formulation gives a straightforward procedure for incorporating both band-band and band-trap Auger effects in the SRH procedure. Two related questions arise in this context: (1) it may sometimes be useful to write the steady-state occupation probability of the traps implied by SRH procedure in a form which approximates to the Fermi-Dirac distribution; and (2) the effect on the SRH mechanism of spreading N sub t levels at one energy uniformly over a range of energies is discussed.

Current-induced spin polarization in InGaAs and GaAs epilayers with varying doping densities

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

Luengo-Kovac, Marta; Huang, Simon; Del Gaudio, Davide

Here, the current-induced spin polarization and momentum-dependent spin-orbit field were measured in In xGa 1-xAs epilayers with varying indium concentrations and silicon doping densities. Samples with higher indium concentrations and carrier concentrations and lower mobilities were found to have larger electrical spin generation efficiencies. Furthermore, current-induced spin polarization was detected in GaAs epilayers despite the absence of measurable spin-orbit fields, indicating that the extrinsic contributions to the spin-polarization mechanism must be considered. Theoretical calculations based on a model that includes extrinsic contributions to the spin dephasing and the spin Hall effect, in addition to the intrinsic Rashba and Dresselhaus spin-orbitmore » coupling, are found to reproduce the experimental finding that the crystal direction with the smaller net spin-orbit field has larger electrical spin generation efficiency and are used to predict how sample parameters affect the magnitude of the current-induced spin polarization.« less

Effect of Er{sup 3+} ions on the phase formation and properties of In{sub 2}O{sub 3}nanostructures crystallized upon microwave heating

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

Lemos, Samantha C.S.; Romeiro, Fernanda C.; Paula, Leonardo F. de

Regular sized nanostructures of indium oxide (In{sub 2}O{sub 3}) were homogeneously grown using a facile route, i.e. a microwave-hydrothermal method combined with rapid thermal treatment in a microwave oven. The presence of Er{sup 3+} doping plays an important role in controlling the formation of cubic (bcc) and rhombohedral (rh) In{sub 2}O{sub 3} phases. The samples presented broad photoluminescent emission bands in the green-orange region, which were attributed to the recombination of electrons at oxygen vacancies. The photocatalytic activities of pure bcc-In{sub 2}O{sub 3} and a bcc-rh-In{sub 2}O{sub 3} mixture towards the UVA degradation of methylene blue (MB) were also evaluated.more » The results showed that Er{sup +3} doped In{sub 2}O{sub 3} exhibited the highest photocatalytic activity with a photonic efficiency three times higher than the pure oxide. The improved performance was attributed to the higher surface area, the greater concentration of electron traps due the presence of the dopant and the possible formation of heterojunctions between the cubic and rhombohedral phases. - Graphical abstract: Photodegradation curves as a function of irradiation time of the samples obtained upon rapid microwave heating. - Highlights: • Efficient and rapid microwave heating to obtain Er{sup 3+} doped In{sub 2}O{sub 3} nanostructures. • Er{sup 3+} ions doping is fundamental to stabilizing the crystalline rhombohedral phase. • Symmetry breaking induced by vacancies in the lattice leads to photoluminescence. • Surface area of doped sample was two times higher than the surface of pure oxide. • The presence of defects in the lattice structure favors photocatalytic activity.« less

Evolution of the mechanical and tribological properties of DLC thin films doped with low-concentration hafnium on 316L steel

NASA Astrophysics Data System (ADS)

Qi, Meng; Xiao, Jianrong; Gong, Chenyang; Jiang, Aihua; Chen, Yong

2018-01-01

Low concentrations (<1 at%) of hafnium doped into diamond-like thin films (Hf-DLC) were deposited on 316L stainless steel and silicon (1 0 0) substrates by magnetron sputtering to attain superior mechanical and tribological properties. Ar and CH4 were used as source gases. The microstructure, chemical composition, and morphology of the Hf-DLC thin films in various concentrations were analyzed using x-ray diffraction, Raman spectroscopy, x-ray photoelectron spectroscopy, scanning electron microscopy and atomic force microscopy. Results showed that Hf species transferred from the particulate microstructure to Hf carbide phases, and the surface roughness increased monotonically with increasing Hf concentration. Moreover, the hardness and elastic modulus exhibited high values when the doped Hf concentration was 0.42 at%. Similarly, the tribological behaviors and wear life of Hf-DLC thin films had a low friction coefficient and excellent wear resistance at 0.42 at% Hf concentration. Therefore, 0.42 at% Hf is an optimal doping concentration to improve the mechanical and tribological properties of DLC thin films. Generally, the use of low-concentration Hf doping into DLC thin films is novel, and the present results provide guidance for the selection of suitable and effective concentration to optimize Hf-DLC thin films with superior performance.

Hall-effect measurements of metalorganic vapor-phase epitaxy-grown p-type homoepitaxial GaN layers with various Mg concentrations

NASA Astrophysics Data System (ADS)

Horita, Masahiro; Takashima, Shinya; Tanaka, Ryo; Matsuyama, Hideaki; Ueno, Katsunori; Edo, Masaharu; Takahashi, Tokio; Shimizu, Mitsuaki; Suda, Jun

2017-03-01

Mg-doped p-type gallium nitride (GaN) layers with doping concentrations in the range from 6.5 × 1016 cm-3 (lightly doped) to 3.8 × 1019 cm-3 (heavily doped) were investigated by Hall-effect measurement for the analysis of hole concentration and mobility. p-GaN was homoepitaxially grown on a GaN free-standing substrate by metalorganic vapor-phase epitaxy. The threading dislocation density of p-GaN was 4 × 106 cm-2 measured by cathodoluminescence mapping. Hall-effect measurements of p-GaN were carried out at a temperature in the range from 130 to 450 K. For the lightly doped p-GaN, the acceptor concentration of 7.0 × 1016 cm-3 and the donor concentration of 3.2 × 1016 cm-3 were obtained, where the compensation ratio was 46%. We also obtained the depth of the Mg acceptor level to be 220 meV. The hole mobilities of 86, 31, 14 cm2 V-1 s-1 at 200, 300, 400 K, respectively, were observed in the lightly doped p-GaN.

Influence of Nb Doping Concentration on Bolometric Properties of RF Magnetron Sputtered Nb:TiO2- x Films

NASA Astrophysics Data System (ADS)

Reddy, Y. Ashok Kumar; Shin, Young Bong; Kang, In-Ku; Lee, Hee Chul

2018-03-01

The present study directly addresses the improved bolometric properties by means of different Nb doping concentrations into TiO2- x films. The x-ray diffraction patterns do not display any obvious diffraction peaks, suggesting that all the films deposited at room temperature had an amorphous structure. A small binding energy shift was observed in x-ray photo electron spectroscopy due to the change of chemical composition with Nb doping concentration. All the device samples exhibit linear I- V characteristics, which attests to the formation of good ohmic contact with low contact resistance between the Nb:TiO2- x (TNO) film and the electrode (Ti) material. The performance of the bolometric material can be evaluated through the temperature coefficient of resistance (TCR), and the absolute value of TCR was found to be increased from 2.54% to 2.78% with increasing the Nb doping concentration. The voltage spectral density of 1/ f noise was measured in the frequency range of 1-60 Hz and found to be decreased with increase of Nb doping concentration. As a result, for 1 at.% Nb-doped TNO sample exhibits improved bolometric properties towards the good infrared image sensor device.

Difference between resistance degradation of fixed valence acceptor (Mg) and variable valence acceptor (Mn)-doped BaTiO3 ceramics

NASA Astrophysics Data System (ADS)

Yoon, Seok-Hyun; Randall, Clive A.; Hur, Kang-Heon

2010-09-01

The difference in the resistance degradation behavior was investigated between fixed valence acceptor (Mg) and the variable valence acceptor (Mn)-doped BaTiO3 ceramics with an increase of each acceptor concentration. Coarse-grained specimens with uniform grain sizes and different acceptor concentrations were prepared. In the case of Mg-doped BaTiO3, the time to degradation systematically decreased with the increase in Mg concentration. In contrast, there is a systematically increased time to degradation with the increase in Mn concentration in Mn-doped BaTiO3. The fast degradation by the increase in Mg concentration directly corresponded to an increase in the Warburg impedance and ionic transference number (tion) associated with an increase in oxygen vacancy concentration ([VO••]). On the other hand, no distinct Warburg impedance or ionic conduction contribution could be observed with the increase in Mn concentration. It is supposed that the increase in [VO••] is negligible in spite of the increase in acceptor Mn concentration, when it is compared to Mg-doped BaTiO3. The much lower [VO••] and more dominant electron/hole trapping effect due to multivalence nature of Mn are supposed to cause such a contrary degradation behavior between Mg and Mn-doped BaTiO3. Reoxidation in a slightly reducing atmosphere (N2) showed better resistance to degradation behavior than in a oxidizing air atmosphere in both Mg and Mn-doped BaTiO3, which is anticipated to be an increase in the electron/hole trapping sites. All these behaviors could be explained by the low temperature defect chemical model that shows difference in the defect structure between Mg and Mn-doped BaTiO3, and its dependence on the oxygen partial pressure (pO2) during reoxidation and cooling. Not only the [VO••], but also the density of electron/hole trap sites, are believed to be crucial in controlling resistance degradation.

Porous nitrogen-doped carbon nanosheet on graphene as metal-free catalyst for oxygen reduction reaction in air-cathode microbial fuel cells.

PubMed

Wen, Qing; Wang, Shaoyun; Yan, Jun; Cong, Lijie; Chen, Ye; Xi, Hongyuan

2014-02-01

Porous nitrogen-doped carbon nanosheet on graphene (PNCN) was used as an alternative cathode catalyst for oxygen reduction reaction (ORR) in air-cathode microbial fuel cells (MFCs). Here we report a novel, low-cost, scalable, synthetic method for preparation of PNCN via the carbonization of graphite oxide-polyaniline hybrid (GO-PANI), subsequently followed by KOH activation treatment. Due to its high concentration of nitrogen and high specific surface area, PNCN exhibited an excellent catalytic activity for ORR. As a result, the maximum power density of 1159.34mWm(-2) obtained with PNCN catalyst was higher than that of Pt/C catalyst (858.49mWm(-2)) in a MFC. Therefore, porous nitrogen-doped carbon nanosheet could be a good alternative to Pt catalyst in MFCs. © 2013.

Low-Concentration Indium Doping in Solution-Processed Zinc Oxide Films for Thin-Film Transistors.

PubMed

Zhang, Xue; Lee, Hyeonju; Kwon, Jung-Hyok; Kim, Eui-Jik; Park, Jaehoon

2017-07-31

We investigated the influence of low-concentration indium (In) doping on the chemical and structural properties of solution-processed zinc oxide (ZnO) films and the electrical characteristics of bottom-gate/top-contact In-doped ZnO thin-film transistors (TFTs). The thermogravimetry and differential scanning calorimetry analysis results showed that thermal annealing at 400 °C for 40 min produces In-doped ZnO films. As the In content of ZnO films was increased from 1% to 9%, the metal-oxygen bonding increased from 5.56% to 71.33%, while the metal-hydroxyl bonding decreased from 72.03% to 9.63%. The X-ray diffraction peaks and field-emission scanning microscope images of the ZnO films with different In concentrations revealed a better crystalline quality and reduced grain size of the solution-processed ZnO thin films. The thickness of the In-doped ZnO films also increased when the In content was increased up to 5%; however, the thickness decreased on further increasing the In content. The field-effect mobility and on/off current ratio of In-doped ZnO TFTs were notably affected by any change in the In concentration. Considering the overall TFT performance, the optimal In doping concentration in the solution-processed ZnO semiconductor was determined to be 5% in this study. These results suggest that low-concentration In incorporation is crucial for modulating the morphological characteristics of solution-processed ZnO thin films and the TFT performance.

Low-Concentration Indium Doping in Solution-Processed Zinc Oxide Films for Thin-Film Transistors

PubMed Central

Zhang, Xue; Lee, Hyeonju; Kim, Eui-Jik; Park, Jaehoon

2017-01-01

We investigated the influence of low-concentration indium (In) doping on the chemical and structural properties of solution-processed zinc oxide (ZnO) films and the electrical characteristics of bottom-gate/top-contact In-doped ZnO thin-film transistors (TFTs). The thermogravimetry and differential scanning calorimetry analysis results showed that thermal annealing at 400 °C for 40 min produces In-doped ZnO films. As the In content of ZnO films was increased from 1% to 9%, the metal-oxygen bonding increased from 5.56% to 71.33%, while the metal-hydroxyl bonding decreased from 72.03% to 9.63%. The X-ray diffraction peaks and field-emission scanning microscope images of the ZnO films with different In concentrations revealed a better crystalline quality and reduced grain size of the solution-processed ZnO thin films. The thickness of the In-doped ZnO films also increased when the In content was increased up to 5%; however, the thickness decreased on further increasing the In content. The field-effect mobility and on/off current ratio of In-doped ZnO TFTs were notably affected by any change in the In concentration. Considering the overall TFT performance, the optimal In doping concentration in the solution-processed ZnO semiconductor was determined to be 5% in this study. These results suggest that low-concentration In incorporation is crucial for modulating the morphological characteristics of solution-processed ZnO thin films and the TFT performance. PMID:28773242

Highly improved hydration level sensing properties of copper oxide films with sodium and potassium doping

NASA Astrophysics Data System (ADS)

Sahin, Bünyamin; Kaya, Tolga

2016-01-01

In this study, un-doped, Na-doped, and K-doped nanostructured CuO films were successfully synthesized by the successive ionic layer adsorption and reaction (SILAR) technique and then characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and current-voltage (I-V) measurements. Structural properties of the CuO films were affected from doping. The XRD pattern indicates the formation of polycrystalline CuO films with no secondary phases. Furthermore, doping affected the crystal structure of the samples. The optimum conductivity values for both Na and K were obtained at 4 M% doping concentrations. The comparative hydration level sensing properties of the un-doped, Na-doped, and K-doped CuO nanoparticles were also investigated. A significant enhancement in hydration level sensing properties was observed for both 4 M% Na and K-doped CuO films for all concentration levels. Detailed discussions were reported in the study regarding atomic radii, crystalline structure, and conductivity.

Investigations of different doping concentration of phosphorus and boron into silicon substrate on the variable temperature Raman characteristics

NASA Astrophysics Data System (ADS)

Li, Xiaoli; Ding, Kai; Liu, Jian; Gao, Junxuan; Zhang, Weifeng

2018-01-01

Different doped silicon substrates have different device applications and have been used to fabricate solar panels and large scale integrated circuits. The thermal transport in silicon substrates are dominated by lattice vibrations, doping type, and doping concentration. In this paper, a variable-temperature Raman spectroscopic system is applied to record the frequency and linewidth changes of the silicon peak at 520 cm-1 in five chips of silicon substrate with different doping concentration of phosphorus and boron at the 83K to 1473K temperature range. The doping has better heat sensitive to temperature on the frequency shift over the low temperature range from 83K to 300K but on FWHM in high temperature range from 300K to 1473K. The results will be helpful for fundamental study and practical applications of silicon substrates.

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.

Effect on Electron Structure and Magneto-Optic Property of Heavy W-Doped Anatase TiO2

PubMed Central

Hou, Qingyu; Zhao, Chunwang; Guo, Shaoqiang; Mao, Fei; Zhang, Yue

2015-01-01

The spin or nonspin state of electrons in W-doped anatase TiO2 is very difficult to judge experimentally because of characterization method limitations. Hence, the effect on the microscopic mechanism underlying the visible-light effect of W-doped anatase TiO2 through the consideration of electronic spin or no-spin states is still unknown. To solve this problem, we establish supercell models of W-doped anatase TiO2 at different concentrations, followed by geometry optimization and energy calculation based on the first-principle planewave norm conserving pseudo-potential method of the density functional theory. Calculation results showed that under the condition of nonspin the doping concentration of W becomes heavier, the formation energy becomes greater, and doping becomes more difficult. Meanwhile, the total energy increases, the covalent weakens and ionic bonds strengthens, the stability of the W-doped anatase TiO2 decreases, the band gap increases, and the blue-shift becomes more significant with the increase of W doping concentration. However, under the condition of spin, after the band gap correction by the GGA+U method, it is found that the semimetal diluted magnetic semiconductors can be formed by heavy W-doped anatase TiO2. Especially, a conduction electron polarizability of as high as near 100% has been found for the first time in high concentration W-doped anatase TiO2. It will be able to be a promising new type of dilute magnetic semiconductor. And the heavy W-doped anatase TiO2 make the band gap becomes narrower and absorption spectrum red-shift. PMID:25955308

Influence of Co doping on combined photocatalytic and antibacterial activity of ZnO nanoparticles

NASA Astrophysics Data System (ADS)

Anandan, M.; Dinesh, S.; Krishnakumar, N.; Balamurugan, K.

2016-11-01

The present work aims to investigate the structural, optical, photocatalyst and antibacterial properties of bare and cobalt doped ZnO nanoparticles (NPs) with different concentrations Zn1-x Co x O (x = 0, 0.03, 0.06 and 0.09) synthesized by co-precipitation method. The XRD patterns confirmed that all samples of cobalt doped ZnO nanostructures revealed the formation of single phase having hexagonal wurtzite structure with crystallite size in the range of 31-41 nm. Further, the decreasing trend in lattice parameters and grain sizes were also seen with increasing doping concentrations which confirms the incorporation of Co ions into the ZnO lattice. This result was further supported by the FT-IR data. HR-TEM images demonstrated the distinct hexagonal like morphology with small agglomeration. The UV-visible absorption spectra exhibits red shift with increase in Co doping concentration in ZnO while corresponding bandgap energy of cobalt doped ZnO NPs decreased with increased Co doping concentration. PL spectra showed a weak UV and visible emission band which may be ascribed to the reduction in oxygen vacancy and defects by cobalt doping. XPS and EDX spectral results confirm the composition and the purity of Co doped ZnO NPs. Furthermore, the Co doped ZnO NPs were found to exhibit lesser photocatalytic activity for the degradation of methyl green dye under UV light illumination in comparison with the bare ZnO NPs. Moreover, anti-bacterial studies reveals that the Co doped ZnO NPs possess more antibacterial effect against gram positive Basillus subtills and gram negative Klebsiella pneumoniae bacterial strains than the bare ZnO NPs.

The Electronic Properties of O-Doped Pure and Sulfur Vacancy-Defect Monolayer WS₂: A First-Principles Study.

PubMed

Wang, Weidong; Bai, Liwen; Yang, Chenguang; Fan, Kangqi; Xie, Yong; Li, Minglin

2018-01-31

Based on the density functional theory (DFT), the electronic properties of O-doped pure and sulfur vacancy-defect monolayer WS₂ are investigated by using the first-principles method. For the O-doped pure monolayer WS₂, four sizes (2 × 2 × 1, 3 × 3 × 1, 4 × 4 × 1 and 5 × 5 × 1) of supercell are discussed to probe the effects of O doping concentration on the electronic structure. For the 2 × 2 × 1 supercell with 12.5% O doping concentration, the band gap of O-doped pure WS₂ is reduced by 8.9% displaying an indirect band gap. The band gaps in 3 × 3 × 1 and 4 × 4 × 1 supercells are both opened to some extent, respectively, for 5.55% and 3.13% O doping concentrations, while the band gap in 5 × 5 × 1 supercell with 2.0% O doping concentration is quite close to that of the pure monolayer WS₂. Then, two typical point defects, including sulfur single-vacancy (V S ) and sulfur divacancy (V 2S ), are introduced to probe the influences of O doping on the electronic properties of WS₂ monolayers. The observations from DFT calculations show that O doping can broaden the band gap of monolayer WS₂ with V S defect to a certain degree, but weaken the band gap of monolayer WS₂ with V 2S defect. Doping O element into either pure or sulfur vacancy-defect monolayer WS₂ cannot change their band gaps significantly, however, it still can be regarded as a potential method to slightly tune the electronic properties of monolayer WS₂.

Influence of the dopant concentration on structural, optical and photovoltaic properties of Cu-doped ZnS nanocrystals based bulk heterojunction hybrid solar cells

NASA Astrophysics Data System (ADS)

Jabeen, Uzma; Adhikari, Tham; Shah, Syed Mujtaba; Pathak, Dinesh; Wagner, Tomas; Nunzi, Jean-Michel

2017-06-01

Zinc sulphide (ZnS) and Cu-doped ZnS nanoparticles were synthesized by the wet chemical method. The nanoparticles were characterized by UV-visible, fluorescence, fourier transform infra-red (FTIR) spectrometry, X-ray diffraction (XRD), X-ray photoelectron spectrometry (XPS), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). Scanning electron microscopy supplemented with EDAX was employed to observe the morphology and chemical composition of the un-doped and doped samples. A significant blue shift of the absorption band with respect to the un-doped zinc sulphide was sighted by increasing the Cu concentration in the doped sample with decreasing the size of nanoparticles. Consequently, the band gap was tuned from 3.13 to 3.49 eV due to quantum confinement. The green emission arises from the recombination between the shallow donor level (sulfur vacancy) and the t2 level of Cu2+. However, the fluorescence emission spectrum of the undoped ZnS nanoparticles was deconvoluted into two bands, which are centered at 419 and 468 nm. XRD analysis showed that the nanomaterials were in cubic crystalline state. XRD peaks show that there were no massive crystalline distortions in the crystal lattice when the Cu concentration (0.05-0.1 M) was increased in the ZnS lattice. However, in the case of Cu-doped samples (0.15-0.2 M), the XRD pattern showed an additional peak at 37° due to incomplete substitution occurring during the experimental reaction step. A comparative study of surfaces of undoped and Cu-doped ZnS nanoparticles were investigated using X-ray photoelectron spectroscopy (XPS). The synthesized nanomaterial in combination with poly(3-hexylthiophene) (P3HT) was used in the fabrication of solar cells. The devices with ZnS nanoparticles showed an efficiency of 0.31%. The overall power conversion efficiency of the solar cells at 0.1 M Cu content in doped ZnS nanoparticles was found to be 1.6 times higher than the reference device (P3HT:ZnS). Furthermore, atomic force microscopy and X-ray diffraction techniques were employed to study morphology and packing behavior of blends of nanocrystals and polymer respectively. Contribution to the topical issue "Materials for Energy harvesting, conversion and storage II (ICOME 2016)", edited by Jean-Michel Nunzi, Rachid Bennacer and Mohammed El Ganaoui

Electrical Transport Ability of Nanostructured Potassium-Doped Titanium Oxide Film

NASA Astrophysics Data System (ADS)

Lee, So-Yoon; Matsuno, Ryosuke; Ishihara, Kazuhiko; Takai, Madoka

2011-02-01

Potassium-doped nanostructured titanium oxide films were fabricated using a wet corrosion process with various KOH solutions. The doped condition of potassium in TiO2 was confirmed by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Nanotubular were synthesized at a dopant concentration of <0.27% when the dopant concentration increased to >0.27%, these structures disappeared. To investigate the electrical properties of K-doped TiO2, pseudo metal-oxide-semiconductor field-effect transistor (MOSFET) samples were fabricated. The samples exhibited a distinct electrical behavior and p-type characteristics. The electrical behavior was governed by the volume of the dopant when the dopant concentration was <0.10% and the volume of the TiO2 phase when the dopant concentration was >0.18%.

High efficient white organic light-emitting diodes with single emissive layer using phosphorescent red, green, and blue dopants

NASA Astrophysics Data System (ADS)

Kim, You-Hyun; Wai Cheah, Kok; Young Kim, Woo

2013-07-01

Phosphorescent white organic light-emitting diodes (PHWOLEDs) with single emissive layer were fabricated by co-doping phosphorescent blue, green, and red emitters with different concentrations. WOLEDs using Ir(piq)3 and Ir(ppy)3 as red and green dopants along with 8% of Firpic as blue dopant with host materials of 4CzPBP in the emissive layer were compared under various doping ratio between Ir(piq)3 and Ir(ppy)3. Triplet-triplet Dexter energy transfer in single emissive PHWOLEDs including three primary colors was saturated from higher triplet energy levels to lower triplet energy levels directly.

Effects of Concentration of Nanoscale Tin-Doped Indium Oxide on Electrical Breakdown of High-Resistance Liquid Crystal

NASA Astrophysics Data System (ADS)

Liang, Bau-Jy; Liu, Don-Gey; Chang, Chih-Yuan; Shie, Wun-Yi

2011-05-01

According to our previous study, a high concentration of nanoscale tin-doped indium oxide (ITO) may be beneficial for protecting liquid crystal (LC) against attacks by electrostatic discharge (ESD). In this study, the influence of high-voltage stresses in an ESD test was investigated for cells doped with different concentrations of ITO. It was found that nano-ITO with a concentration of 0.4% in weight ratio deteriorated the physical properties of LC of transparency transition and charge retention. However, our experiment showed that the capability of ESD protection for the doped LC was still improved at the ITO concentration of 0.4 wt %. This finding supports the proposed model in our previous report. The role of ITO in the LC is not always beneficial, as discussed in this paper.

Structural and optical properties of Dy3+ doped Aluminofluoroborophosphate glasses for white light applications

NASA Astrophysics Data System (ADS)

Vijayakumar, M.; Mahesvaran, K.; Patel, Dinesh K.; Arunkumar, S.; Marimuthu, K.

2014-11-01

Dy3+ doped Aluminofluoroborophosphate glasses (BPAxD) have been prepared following conventional melt quenching technique and their structural and optical properties were explored through XRD, FTIR, optical absorption, excitation, emission and decay measurements. The coexistence of BO3 groups in borate rich domain and BO4 groups in phosphate rich domain have been confirmed through vibrational energy analysis. Negative bonding parameter (δ) values indicate that, the metal-ligand environment in the prepared glasses is of ionic in nature. The oscillator strength and the luminescent intensity Ωλ (λ = 2, 4 and 6) parameters are calculated using Judd-Ofelt theory. The radiative properties such as transition probability (A), stimulated emission cross-section (σpE) and branching ratios (β) have been calculated using JO intensity parameters and compared with the reported Dy3+ doped glasses. Concentration effect on Y/B intensity ratios and the CIE chromaticity coordinates were calculated for the generation of white light from the luminescence spectra. The color purity and the correlated color temperature were also calculated and the results are discussed in the present work. The decay of the 4F9/2 excited level is found to be single exponential for lower concentration and become non-exponential for higher concentration. The non-exponential behavior arises due to the efficient energy transfer between the Dy3+ ions through various non-radiative relaxation channels and the decay of the 4F9/2 excited level have been analyzed with IH model. Among the prepared glasses, BPA0.5D glass exhibits higher σpE, βR, σpE×σpE, σpE×Δλeff and η values for the 6H13/2 emission band which in turn specifies its suitability for white LEDs, laser applications and optical amplifiers.

Effect of doping on structural, optical and electrical properties of nanostructure ZnO films deposited onto a-Si:H/Si heterojunction

NASA Astrophysics Data System (ADS)

Sali, S.; Boumaour, M.; Kermadi, S.; Keffous, A.; Kechouane, M.

2012-09-01

We investigated the structural; optical and electrical properties of ZnO thin films as the n-type semiconductor for silicon a-Si:H/Si heterojunction photodiodes. The ZnO film forms the front contact of the super-strata solar cell and has to exhibit good electrical (high conductivity) and optical (high transmittance) properties. In this paper we focused our attention on the influence of doping on device performance. The results show that the X-ray diffraction (XRD) spectra revealed a preferred orientation of the crystallites along c-axis. SEM images show that all films display a granular, polycrystalline morphology and the ZnO:Al exhibits a better grain uniformity. The transmittance of the doped films was found to be higher when compared to undoped ZnO. A low resistivity of the order of 2.8 × 10-4 Ω cm is obtained for ZnO:Al using 0.4 M concentration of zinc acetate. The photoluminescence (PL) spectra exhibit a blue band with two peaks centered at 442 nm (2.80 eV) and 490 nm (2.53 eV). It is noted that after doping the ZnO films a shift of the band by 22 nm (0.15 eV) is recorded and a high luminescence occurs when using Al as a dopant. Dark I-V curves of ZnO/a-Si:H/Si structure showed large difference, which means there is a kind of barrier to current flow between ZnO and a-Si:H layer. Doping films was applied and the turn-on voltages are around 0.6 V. Under reverse bias, the current of the ZnO/a-Si:H/Si heterojunction is larger than that of ZnO:Al/a-Si:H/Si. The improvement with ZnO:Al is attributed to a higher number of generated carriers in the nanostructure (due to the higher transmittance and a higher luminescence) that increases the probability of collisions.

Cu-Doped ZnO Thin Films Deposited by a Sol-Gel Process Using Two Copper Precursors: Gas-Sensing Performance in a Propane Atmosphere

PubMed Central

Gómez-Pozos, Heberto; Arredondo, Emma Julia Luna; Maldonado Álvarez, Arturo; Biswal, Rajesh; Kudriavtsev, Yuriy; Pérez, Jaime Vega; Casallas-Moreno, Yenny Lucero; Olvera Amador, María de la Luz

2016-01-01

A study on the propane gas-sensing properties of Cu-doped ZnO thin films is presented in this work. The films were deposited on glass substrates by sol-gel and dip coating methods, using zinc acetate as a zinc precursor, copper acetate and copper chloride as precursors for doping. For higher sensitivity values, two film thickness values are controlled by the six and eight dippings, whereas for doping, three dippings were used, irrespective of the Cu precursor. The film structure was analyzed by X-ray diffractometry, and the analysis of the surface morphology and film composition was made through scanning electron microscopy (SEM) and secondary ion mass spectroscopy (SIMS), respectively. The sensing properties of Cu-doped ZnO thin films were then characterized in a propane atmosphere, C3H8, at different concentration levels and different operation temperatures of 100, 200 and 300 °C. Cu-doped ZnO films doped with copper chloride presented the highest sensitivity of approximately 6 × 104, confirming a strong dependence on the dopant precursor type. The results obtained in this work show that the use of Cu as a dopant in ZnO films processed by sol-gel produces excellent catalysts for sensing C3H8 gas. PMID:28787885

Highly Sensitive and Selective Ethanol Sensor Fabricated with In-Doped 3DOM ZnO.

PubMed

Wang, Zhihua; Tian, Ziwei; Han, Dongmei; Gu, Fubo

2016-03-02

ZnO is an important n-type semiconductor sensing material. Currently, much attention has been attracted to finding an effective method to prepare ZnO nanomaterials with high sensing sensitivity and excellent selectivity. A three-dimensionally ordered macroporous (3DOM) ZnO nanostructure with a large surface area is beneficial to gas and electron transfer, which can enhance the gas sensitivity of ZnO. Indium (In) doping is an effective way to improve the sensing properties of ZnO. In this paper, In-doped 3DOM ZnO with enhanced sensitivity and selectivity has been synthesized by using a colloidal crystal templating method. The 3DOM ZnO with 5 at. % of In-doping exhibits the highest sensitivity (∼88) to 100 ppm ethanol at 250 °C, which is approximately 3 times higher than that of pure 3DOM ZnO. The huge improvement to the sensitivity to ethanol was attributed to the increase in the surface area and the electron carrier concentration. The doping by In introduces more electrons into the matrix, which is helpful for increasing the amount of adsorbed oxygen, leading to high sensitivity. The In-doped 3DOM ZnO is a promising material for a new type of ethanol sensor.

Thermoelectric Properties of Poly(3-hexylthiophene) (P3HT) Doped with 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F 4TCNQ) by Vapor-Phase Infiltration

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

Lim, Eunhee; Peterson, Kelly A.; Su, Gregory M.

Doping of thin films of semiconducting polymers provides control of their electrical conductivity and thermopower. The electrical conductivity of semiconducting polymers rises nonlinearly with the carrier concentration, and there is a lack of understanding of the detailed factors that lead to this behavior. Here, we report a study of the morphological effects of doping on the electrical conductivity of poly(3-hexylthiophene) (P3HT) thin films doped with small molecule 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F 4TCNQ). Resonant soft X-ray scattering shows that the morphology of films of P3HT is not strongly changed by infiltration of F 4TCNQ from the vapor phase. We show that the localmore » ordering of P3HT, the texture and form factor of crystallites, and the long-range connectivity of crystalline domains contribute to the electrical conductivity in thin films. The thermopower of films of P3HT doped with F 4TCNQ from the vapor phase is not strongly enhanced relative to films doped from solution, but the electrical conductivity is significantly higher, improving the thermoelectric power factor.« less

Thermoelectric Properties of Poly(3-hexylthiophene) (P3HT) Doped with 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F 4TCNQ) by Vapor-Phase Infiltration

DOE PAGES

Lim, Eunhee; Peterson, Kelly A.; Su, Gregory M.; ...

2018-01-29

Doping of thin films of semiconducting polymers provides control of their electrical conductivity and thermopower. The electrical conductivity of semiconducting polymers rises nonlinearly with the carrier concentration, and there is a lack of understanding of the detailed factors that lead to this behavior. Here, we report a study of the morphological effects of doping on the electrical conductivity of poly(3-hexylthiophene) (P3HT) thin films doped with small molecule 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F 4TCNQ). Resonant soft X-ray scattering shows that the morphology of films of P3HT is not strongly changed by infiltration of F 4TCNQ from the vapor phase. We show that the localmore » ordering of P3HT, the texture and form factor of crystallites, and the long-range connectivity of crystalline domains contribute to the electrical conductivity in thin films. The thermopower of films of P3HT doped with F 4TCNQ from the vapor phase is not strongly enhanced relative to films doped from solution, but the electrical conductivity is significantly higher, improving the thermoelectric power factor.« less

Scintillation properties of rare-earth doped NaPO3-Al(PO3)3 glasses

NASA Astrophysics Data System (ADS)

Kuro, Tomoaki; Okada, Go; Kawaguchi, Noriaki; Fujimoto, Yutaka; Masai, Hirokazu; Yanagida, Takayuki

2016-12-01

We systematically investigated photoluminescence (PL), scintillation and dosimeter properties of rare-earth (RE) doped NaPO3-Al(PO3)3 (NAP) glasses. The NAP glasses doped with a series of RE ions (La-Yb, except Pm) with a consistent concentration (0.3 wt%) were prepared by the conventional melt-quenching method. The PL and scintillation decay time profiles showed fast (ns) and slow (μs or ms) components: the fast components from 15 to 100 ns were due to the host or 5d-4f transition emission, and the slow components from 15 μs to 5 ms were due to the 4f-4f transitions of RE. The thermally stimulated luminescence (TSL) was evaluated as a dosimeter property, and glow peaks appeared around 400 °C in all the samples. The TSL dose response function was examined in the dose range from 10 mGy to 10 Gy. Among the samples tested, Nd and Tb doped glasses showed higher signal by at least one order of magnitude than those of non-doped and other RE-doped samples. Over the dose range tested, the TSL signals are linearly related with the incident X-ray dose, showing a potential for practical applications.

Semiconducting behavior of substitutionally doped bilayer graphene

NASA Astrophysics Data System (ADS)

Mousavi, Hamze; Khodadadi, Jabbar; Grabowski, Marek

2018-02-01

In the framework of the Green's functions approach, random tight-binding model and using the coherent potential approximation, electronic characteristics of the bilayer graphene are investigated by exploring various forms of substitutional doping of a single or both layers of the system by either boron and (or) nitrogen atoms. The results for displacement of the Fermi level resemble the behavior of acceptor or donor doping in a conventional semiconductor, dependent on the impurity type and concentration. The particular pattern of doping of just one layer with one impurity type is most efficient for opening a gap within the energy bands which could be tuned directly by impurity concentration. Doping both layers at the same time, each with one impurity type, leads to an anomaly whereby the gap decreases with increasing impurity concentration.

Photocatalytic characteristics of single phase Fe-doped anatase TiO{sub 2} nanoparticles sensitized with vitamin B{sub 12}

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

Gharagozlou, Mehrnaz, E-mail: gharagozlou@icrc.ac.ir; Bayati, R.

Highlights: • Anatase TiO{sub 2}/B{sub 12} hybrid nanostructured catalyst was successfully synthesized by sol–gel technique. • The nanoparticle catalyst was doped with iron at several concentrations. • Nanoparticles were characterized in detail by XRD, Raman, TEM, EDS, and spectroscopy techniques. • The formation mechanism and role of point defects on photocatalytic properties were discussed. • A structure-property-processing correlation was established. - Abstract: We report a processing-structure-property correlation in B{sub 12}-anatase titania hybrid catalysts doped with several concentrations of iron. Our results clearly show that low-level iron doping alters structure, defect content, and photocatalytic characteristics of TiO{sub 2}. XRD and Ramanmore » studies revealed formation of a single-phase anatase TiO{sub 2} where no iron based segregation in particular iron oxide, was detected. FT-IR spectra clearly confirmed sensitization of TiO{sub 2} nanoparticles with vitamin B{sub 12}. TEM micrographs and diffraction patterns confirmed crystallization of anatase nanoparticles with a radius of 15–20 nm. Both XRD and Raman signals showed a peak shift and a peak broadening which are surmised to originate from creation of point defects, namely oxygen vacancy and titanium interstitial. The doped samples revealed a narrower band gap as compared to undoped samples. Photocatalytic activity of the samples was assessed through measuring the decomposition rate of rhodamine B. It was found that sensitization with vitamin B{sub 12} and Fe-doping significantly enhances the photocatalytic efficiency of the anatase nanoparticles. We also showed that there is an optimum Fe-doping level where the maximum photocatalytic activity is achieved. The boost of photocatalytic activity was qualitatively understood to originate from a more effective use of the light photons, formation of point defects, which enhance the charge separation, higher carrier mobility.« less

Alkali earth co-doping effects on luminescence and scintillation properties of Ce doped Gd3Al2Ga3O12 scintillator

NASA Astrophysics Data System (ADS)

Kamada, Kei; Nikl, Martin; Kurosawa, Shunsuke; Beitlerova, Alena; Nagura, Aya; Shoji, Yasuhiro; Pejchal, Jan; Ohashi, Yuji; Yokota, Yuui; Yoshikawa, Akira

2015-03-01

The Mg and Ca co-doped Ce:Gd3Al2Ga3O12 single crystals were prepared by micro pulling down method with a wide concentration range 0-1000 ppm of the codopants. Absorption and luminescence spectra were measured together with several other scintillation characteristics, namely the scintillation decay and light yield to reveal the effect of Mg and Ca co-doping. The scintillation decays were accelerated by both Mg and Ca codopants. Comparing to Ca co-doping, the Mg co-doped samples showed much faster decay and comparatively smaller light output decrease with increasing Mg dopant concentration.

Characterization and improved solar light activity of vanadium doped TiO2/diatomite hybrid catalysts.

PubMed

Wang, Bin; Zhang, Guangxin; Leng, Xue; Sun, Zhiming; Zheng, Shuilin

2015-03-21

V-doped TiO2/diatomite composite photocatalysts with different vanadium concentrations were synthesized by a modified sol-gel method. The diatomite was responsible for the well dispersion of TiO2 nanoparticles on the matrix and consequently inhibited the agglomeration. V-TiO2/diatomite hybrids showed red shift in TiO2 absorption edge with enhanced absorption intensity. Most importantly, the dopant energy levels were formed in the TiO2 bandgap due to V(4+) ions substituted to Ti(4+) sites. The 0.5% V-TiO2/diatomite photocatalyst displayed narrower bandgap (2.95 eV) compared to undoped sample (3.13 eV) and other doped samples (3.05 eV) with higher doping concentration. The photocatalytic activities of V doped TiO2/diatomite samples for the degradation of Rhodamine B under stimulated solar light illumination were significantly improved compared with the undoped sample. In our case, V(4+) ions incorporated in TiO2 lattice were responsible for increased visible-light absorption and electron transfer to oxygen molecules adsorbed on the surface of TiO2 to produce superoxide radicals ˙O2(-), while V(5+) species presented on the surface of TiO2 particles in the form of V2O5 contributed to e(-)-h(+) separation. In addition, due to the combination of diatomite as support, this hybrid photocatalyst could be separated from solution quickly by natural settlement and exhibited good reusability. Copyright © 2014 Elsevier B.V. All rights reserved.

Nanocrystalline SnO2:F Thin Films for Liquid Petroleum Gas Sensors

PubMed Central

Chaisitsak, Sutichai

2011-01-01

This paper reports the improvement in the sensing performance of nanocrystalline SnO2-based liquid petroleum gas (LPG) sensors by doping with fluorine (F). Un-doped and F-doped tin oxide films were prepared on glass substrates by the dip-coating technique using a layer-by-layer deposition cycle (alternating between dip-coating a thin layer followed by a drying in air after each new layer). The results showed that this technique is superior to the conventional technique for both improving the film thickness uniformity and film transparency. The effect of F concentration on the structural, surface morphological and LPG sensing properties of the SnO2 films was investigated. Atomic Force Microscopy (AFM) and X-ray diffraction pattern measurements showed that the obtained thin films are nanocrystalline SnO2 with nanoscale-textured surfaces. Gas sensing characteristics (sensor response and response/recovery time) of the SnO2:F sensors based on a planar interdigital structure were investigated at different operating temperatures and at different LPG concentrations. The addition of fluorine to SnO2 was found to be advantageous for efficient detection of LPG gases, e.g., F-doped sensors are more stable at a low operating temperature (300 °C) with higher sensor response and faster response/recovery time, compared to un-doped sensor materials. The sensors based on SnO2:F films could detect LPG even at a low level of 25% LEL, showing the possibility of using this transparent material for LPG leak detection. PMID:22164007

High temperature superconductivity in distinct phases of amorphous B-doped Q-carbon

NASA Astrophysics Data System (ADS)

Narayan, Jagdish; Bhaumik, Anagh; Sachan, Ritesh

2018-04-01

Distinct phases of B-doped Q-carbon are formed when B-doped and undoped diamond tetrahedra are packed randomly after nanosecond laser melting and quenching of carbon. By changing the ratio of doped to undoped tetrahedra, distinct phases of B-doped Q-carbon with concentration varying from 5.0% to 50.0% can be created. We have synthesized three distinct phases of amorphous B-doped Q-carbon, which exhibit high-temperature superconductivity following the Bardeen-Cooper-Schrieffer mechanism. The first phase (QB1) has a B-concentration ˜17 at. % (Tc = 37 K), the second phase (QB2) has a B-concentration ˜27 at. % (Tc = 55 K), and the third phase (QB3) has a B-concentration ˜45 at. % (Tc expected over 100 K). From geometrical modeling, we derive that QB1 consists of randomly packed tetrahedra, where one out of every three tetrahedra contains a B atom in the center which is sp3 bonded to four carbon atoms with a concentration of 16.6 at. %. QB2 consists of randomly packed tetrahedra, where one out of every two tetrahedra contains a B atom in the center which is sp3 bonded to four carbon atoms with a concentration of 25 at. %. QB3 consists of randomly packed tetrahedra, where every tetrahedron contains a B atom in the center which is sp3 bonded to four carbon atoms with a concentration of 50 at. %. We present detailed high-resolution TEM results on structural characterization, and EELS and Raman spectroscopy results on the bonding characteristics of B and C atoms. From these studies, we conclude that the high electronic density of states near the Fermi energy level coupled with moderate electron-phonon coupling result in high-temperature superconductivity in B-doped Q-carbon.

Photocatalytic performance of Cu-doped TiO2 nanofibers treated by the hydrothermal synthesis and air-thermal treatment

NASA Astrophysics Data System (ADS)

Wu, Ming-Chung; Wu, Po-Yeh; Lin, Ting-Han; Lin, Tz-Feng

2018-02-01

Series of transition metal-doped TiO2 (metal/TiO2) is prepared by combining the hydrothermal synthesis and air-thermal treatment without any reduction process. The selected transition metal precursors, including Ag, Au, Co, Cr, Cu, Fe, Ni, Pd, Pt, Y, and Zn, were individually doped into TiO2 nanofibers to evaluate the photocatalytic degradation activity and photocatalytic hydrogen generation. Consider the photocatalytic performance of these synthesized metal/TiO2 under UV-A irradiation, copper doped TiO2 nanofibers (Cu/TiO2 NFs) was chosen for further study due to its extraordinary reactivity. Systematical studies were spread to optimize the doping concentration and the calcination condition for much higher photocatalytic activity Cu/TiO2 NFs. In the photocatalytic degradation test, 0.5 mol%-Cu/TiO2 NFs calcined at 650 °C exhibits the highest activity, which is even higher than commercial TiO2-AEROXIDE® TiO2 P25 under UV-A irradiation. The synthesized 0.5 mol%-Cu/TiO2-650 NFs also have the capability in the photocatalytic hydrogen production. The hydrogen evolution rates are 200 μmol/g·h under UV-A irradiation and 280 μmol/g·h under UV-B irradiation. The density of state calculated by CASTEP for Cu/TiO2 indicates that Cu doping contributes to the states near valence band edge and narrows the band gap. The disclosed process in this study is industrial safe, convenient and cost-effective. We further produce a significant amount of TiO2-based catalysts without any hydrogen reduction treatment.

Defects and properties of cadmium oxide based transparent conductors

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

Yu, Kin Man, E-mail: kinmanyu@cityu.edu.hk; Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720; Detert, D. M.

Transparent conductors play an increasingly important role in a number of semiconductor technologies. This paper reports on the defects and properties of Cadmium Oxide, a transparent conducting oxide which can be potentially used for full spectrum photovoltaics. We carried out a systematic investigation on the effects of defects in CdO thin films undoped and intentionally doped with In and Ga under different deposition and annealing conditions. We found that at low growth temperatures (<200 °C), sputter deposition tends to trap both oxygen vacancies and compensating defects in the CdO film resulting in materials with high electron concentration of ∼2 × 10{sup 20}/cm{sup 3}more » and mobility in the range of 40–100 cm{sup 2}/V s. Thermal annealing experiments in different ambients revealed that the dominating defects in sputtered CdO films are oxygen vacancies. Oxygen rich CdO films grown by sputtering with increasing O{sub 2} partial pressure in the sputter gas mixture results in films with resistivity from ∼4 × 10{sup −4} to >1 Ω cm due to incorporation of excess O in the form of O-related acceptor defects, likely to be O interstitials. Intentional doping with In and Ga donors leads to an increase of both the electron concentration and the mobility. With proper doping CdO films with electron concentration of more than 10{sup 21 }cm{sup −3} and electron mobility higher than 120 cm{sup 2}/V s can be achieved. Thermal annealing of doped CdO films in N{sub 2} ambient can further improve the electrical properties by removing native acceptors and improving film crystallinity. Furthermore, the unique doping behavior and electrical properties of CdO were explored via simulations based on the amphoteric defect model. A comparison of the calculations and experimental results show that the formation energy of native donors and acceptors at the Fermi stabilization energy is ∼1 eV and that the mobility of sputtered deposited CdO is limited by a background acceptor concentration of ∼5–6 × 10{sup 20}/cm{sup 3}. The calculations offer an insight into understanding of the effects of defects on electrical properties of undoped and doped CdO and offer a potential to use similar methods to analyze doping and defect properties of other semiconductor materials.« less

Visible luminescence of Dy3+ doped PbF2-Li2O-SrO-ZnO-B2O3 glasses for yellow light applications

NASA Astrophysics Data System (ADS)

Anjaiah, G.; Sasikala, T.; Kistaiah, P.

2018-05-01

The present studies on various concentrations of Dy3+ ions doped PLSrZFB glasses were carried out through optical absorption, photoluminescence and decay time measurements. The Judd-Ofelt (JO) intensity parameters Ωλ (λ = 2,4,6) can be utilized to evaluate the emission properties. The decay curves for the 4F9/2 levels have been measured and these turns to non-exponential nature at higher concentrations (> 0.1 mol%) is due to energy transfer between the Dy3+-Dy3+ ions dipole -dipole type through cross relaxation channels. The CIE chromaticity color coordinates were calculated and they were all located within the vicinity of white region of the color coordination diagram. The Inokuti-Hirayama model is used to analyze the energy transfer process and also energy transfer parameters have been calculated and discussed.

Effect of fabrication parameters on morphological and optical properties of highly doped p-porous silicon

NASA Astrophysics Data System (ADS)

Zare, Maryam; Shokrollahi, Abbas; Seraji, Faramarz E.

2011-09-01

Porous silicon (PS) layers were fabricated by anodization of low resistive (highly doped) p-type silicon in HF/ethanol solution, by varying current density, etching time and HF concentration. Atomic force microscopy (AFM) and field emission scanning electron microscope (FESEM) analyses were used to investigate the physical properties and reflection spectrum was used to investigate the optical behavior of PS layers in different fabrication conditions. Vertically aligned mesoporous morphology is observed in fabricated films and with HF concentration higher than 20%. The dependence of porosity, layer thickness and rms roughness of the PS layer on current density, etching time and composition of electrolyte is also observed in obtained results. Correlation between reflectivity and fabrication parameters was also explored. Thermal oxidation was performed on some mesoporous layers that resulted in changes of surface roughness, mean height and reflectivity of the layers.

Effect of Pr 3+ concentration on thermoluminescence from K 2Y 1- xPr xF 5 crystals

NASA Astrophysics Data System (ADS)

Marcazzo, J.; Santiago, M.; Caselli, E.; Nariyama, N.; Khaidukov, N. M.

2004-06-01

Thermoluminescence dosimetric characteristics of K 2YF 5 crystals doped with Pr 3+ are reported for the first time. The efficiency of the 0.5 at.% Pr 3+ doped K 2YF 5 crystal has been found to be maximum for this concentration series and three times higher than that of the commercial dosimeter TLD-700. The thermoluminescence glow curve of this novel phosphor has no appreciable fading. Furthermore, it bears linear dose response and good stability after reutilization. According to these results, K 2YF 5:Pr 3+ appears to be a promising base for developing effective phosphors for TL solid state dosimetry. In this context, the spectral composition of the TL emission is also mentioned along with the values obtained by glow curve deconvolution for the trap parameters characterising electron trap centres involved in thermoluminescence.

Urinary concentrations of morphine and codeine after consumption of poppy seeds.

PubMed

Thevis, Mario; Opfermann, Georg; Schänzer, Wilhelm

2003-01-01

A quantitative analysis of morphine and codeine in human urine was performed after oral intake of cakes containing commercially available poppy seeds in order to estimate the possibility of positive doping results. Therefore, eight products from different manufacturers (poppy seeds or baking mixtures) and origin were obtained and analyzed by gas chromatography-mass spectrometry for the presence of the alkaloids. One selected batch of poppy seeds was used as an ingredient in a typical cake and was the object of an excretion study with nine volunteers. After application, several urine specimens contained morphine with concentrations higher than 1 microg/mL, and peak values of approximately 10.0 microg/mL were detected. Because the International Olympic Committee set a cutoff limit for morphine at 1 microg/mL, high-performance athletes could possibly test positive in doping control after consumption of products containing poppy seeds.

Improved electrical conductivity of poly(ethylene oxide) nanofibers using multi-walled carbon nanotubes

NASA Astrophysics Data System (ADS)

Lee, J. Y.; Kang, T.-H.; Choi, J. H.; Choi, I.-S.; Yu, W.-R.

2018-03-01

Highly conductive nanofibers with 1570 S/m were obtained from an electrospun solution of polymer containing multiwalled carbon nanotubes (MWCNTs). Homogeneous dispersion of high concentrations of MWCNTs was achieved by attaching poly(styrenesulfonic acid graft aniline) (PSS-g-ANI), an amphiphilic surfactant, to the MWCNT surface. The hydrophilic sulfonic acid group facilitated the dissolution of PSS-g-ANI-grafted MWCNTs in a polyethylene oxide (PEO) solution up to 6.7 wt% MWCNT. To our knowledge, this is the highest level of MWCNT doping attained in a solution designed for electrospinning. With the incorporation of PSS-g-ANI, the concentration of MWCNTs embedded in the electrospun nanofibers increased. More importantly, the alignment of MWCNTs along the nanofiber axis increased significantly, as confirmed by observed birefringence under crossed polarizers. The combination of higher doping levels and better alignment afforded highly conductive nanofibers suitable for electronic nanodevices.

Optical, compositional and structural properties of pulsed laser deposited nitrogen-doped Titanium-dioxide

NASA Astrophysics Data System (ADS)

Farkas, B.; Heszler, P.; Budai, J.; Oszkó, A.; Ottosson, M.; Geretovszky, Zs.

2018-03-01

N-doped TiO2 thin films were prepared using pulsed laser deposition by ablating metallic Ti target with pulses of 248 nm wavelength, at 330 °C substrate temperature in reactive atmospheres of N2/O2 gas mixtures. These films were characterized by spectroscopic ellipsometry, X-ray photoelectron spectroscopy and X-ray diffraction. Optical properties are presented as a function of the N2 content in the processing gas mixture and correlated to nitrogen incorporation into the deposited layers. The optical band gap values decreased with increasing N concentration in the films, while a monotonically increasing tendency and a maximum can be observed in case of extinction coefficient and refractive index, respectively. It is also shown that the amount of substitutional N can be increased up to 7.7 at.%, but the higher dopant concentration inhibits the crystallization of the samples.

Lithium-doped hydroxyapatite nano-composites: Synthesis, characterization, gamma attenuation coefficient and dielectric properties

NASA Astrophysics Data System (ADS)

Badran, H.; Yahia, I. S.; Hamdy, Mohamed S.; Awwad, N. S.

2017-01-01

Lithium-hydroxyapatite (0, 1, 5, 10, 20, 30 and 40 wt% Li-HAp) nano-composites were synthesized by sol-gel technique followed by microwave-hydrothermal treatment. The composites were characterized by X-ray diffraction (XRD), Field emission scanning electron microscope (FE-SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared (FTIR) and Raman techniques. Gamma attenuation coefficient and the dielectric properties for all composites were investigated. The crystallinity degree of Li-doped HAp was higher than that of un-doped HAp. Gamma attenuation coefficient values increased from 0.562 cm-1 for 0 wt% Li-HAp to 2.190 cm-1 for 40 wt% Li-HAp. The alternating current conductivity increased with increasing frequency. The concentration of Li affect the values of dielectric constant where Li doped HAp of low dielectric constant can have an advantage for healing in bone fractures. The calcium to phosphorus ratio decreased from 1.43 to 1.37 with the addition of lithium indicating the Ca deficiency in the studied composites. Our findings lead to the conclusion that Li-HAp is a new nano-composite useful for medical applications and could be doped with gamma shield materials.

Influence of the ``second gap'' on the optical absorption of transparent conducting oxides

NASA Astrophysics Data System (ADS)

Ha, Viet-Anh; Waroquiers, David; Rignanese, Gian-Marco; Hautier, Geoffroy

Transparent conducting oxides (TCOs) are critical to many technologies (e.g., thin-film solar cells, flat-panel displays or organic light-emitting diodes). TCOs are heavily doped (n or p-type) oxides that satisfy many design criteria such as high transparency to visible light (i.e., a band gap > 3 eV), high concentration and mobility of carriers (leading to high conductivity), ... In such (highly doped) systems, optical transitions from the conduction band minimum to higher energy bands in n-type or from lower energy bands to the valence band maximum in p-type are possible and can degrade transparency. In fact, it has been claimed that a high energy (> 3eV) for any of these transitions made possible by doping, commonly referred as a high ``second gap'', is a necessary design criterion for high performance TCOs. Here, we study the influence of this second gap on the transparency of doped TCOs by using ab initio calculations within the random phase approximation (RPA) for several well-known p-type and n-type TCOs. Our work highlights how the second gap affects the transparency of doped TCOs, shining light on more accurate design criteria for high performance TCOs.

Nitrogen-Doped Three Dimensional Graphene for Electrochemical Sensing.

PubMed

Yan, Jing; Chen, Ruwen; Liang, Qionglin; Li, Jinghong

2015-07-01

The rational assembly and doping of graphene play an crucial role in the improvement of electrochemical performance for analytical applications. Covalent assembly of graphene into ordered hierarchical structure provides an interconnected three dimensional conductive network and large specific area beneficial to electrolyte transfer on the electrode surface. Chemical doping with heteroatom is a powerful tool to intrinsically modify the electronic properties of graphene due to the increased free charge-carrier densities. By incorporating covalent assembly and nitrogen doping strategy, a novel nitrogen doped three dimensional reduced graphene oxide nanostructure (3D-N-RGO) was developed with synergetic enhancement in electrochemical behaviors. The as prepared 3D-N-RGO was further applied for catechol detection by differential pulse voltammetry. It exhibits much higher electrocatalytic activity towards catechol with increased peak current and decreased potential difference between the oxidation and reduction peaks. Owing to the improved electro-chemical properties, the response of the electrochemical sensor varies linearly with the catechol concentrations ranging from 5 µM to 100 µM with a detection limit of 2 µM (S/N = 3). This work is promising to open new possibilities in the study of novel graphene nanostructure and promote its potential electrochemical applications.

Doping Attitudes and Covariates of Potential Doping Behaviour in High-Level Team-Sport Athletes; Gender Specific Analysis.

PubMed

Sekulic, Damir; Tahiraj, Enver; Zvan, Milan; Zenic, Natasa; Uljevic, Ognjen; Lesnik, Blaz

2016-12-01

Team sports are rarely studied with regard to doping behaviour and doping-related factors regardless of their global popularity. This study aimed to investigate doping factors and covariates of potential doping behaviour in high-level team-sport athletes. The subjects were 457 high-performing, national- and international-level athletes (21.9 ± 3.4 years of age; 179 females) involved in volleyball (n = 77), soccer (n = 163), basketball (n = 114) and handball (n = 103). Previously validated self-administered questionnaires aimed at evidencing sport factors, doping-related factors, knowledge on sport nutrition and doping, and attitudes to performance enhancement were used. The results indicated a higher doping likelihood in male athletes, with a significant gender difference for basketball and handball. In males, a higher doping likelihood is found for athletes who had achieved better results at junior-age level, those who regularly consume dietary supplements, and who perceive their sport as being contaminated by doping. A higher sport achievement at senior-age level is protective against potential doping behaviour in males. In females, a higher likelihood of doping is evidenced in those athletes involved in binge drinking, while a lower tendency for doping is evidenced in female athletes who possess better knowledge on sport nutrition. Knowledge about doping is very low and thus education about doping is urgently needed. An improvement of knowledge on sport nutrition might be a potentially effective method for reducing the tendency for doping in females. Future studies should consider other approaches and theories, such as theory of planned behaviour and/or social-cognitive theory, in studying the problem of doping behaviour in team-sports.

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.

Sputter-Grown Sb-DOPED Silicon Nanocrystals Embedded in Silicon-Rich Carbide for si Heterojunction Solar Cells

NASA Astrophysics Data System (ADS)

Chen, Xiaobo; Tang, Yu; Hao, Jiabo

Sb-doped silicon nanocrystals (Si-NCs) films were fabricated by magnetron co-sputtering combined with rapid-thermal annealing. The effects of Sb content on the structural and electrical properties of the films were studied. The dot size increased with the increasing Sb content, and could be correlated to the effect of Sb-induced crystallization. The variation in the concentration of Sb shows a significant impact on the film properties, where as doped with 0.8at.% of Sb exhibited major property improvements when compared with other films. By employing Sb-doped Si-NCs films as emitter layers, Si-NCs/monocrystalline silicon heterojunction solar cells were fabricated and the effect of the Sb doping concentration on the photovoltaic properties was studied. It is found that the doping level in the Si-NCs layer is a key factor in determining the short-circuit current density and power conversion efficiency (PCE). With an optimized doping concentration of 0.8at.% of Sb, a maximal PCE of 7.10% was obtained. This study indicates that the Sb-doped Si-NCs can be good candidates for all-silicon tandem solar cells.

Metallic conduction induced by direct anion site doping in layered SnSe2

PubMed Central

Kim, Sang Il; Hwang, Sungwoo; Kim, Se Yun; Lee, Woo-Jin; Jung, Doh Won; Moon, Kyoung-Seok; Park, Hee Jung; Cho, Young-Jin; Cho, Yong-Hee; Kim, Jung-Hwa; Yun, Dong-Jin; Lee, Kyu Hyoung; Han, In-taek; Lee, Kimoon; Sohn, Yoonchul

2016-01-01

The emergence of metallic conduction in layered dichalcogenide semiconductor materials by chemical doping is one of key issues for two-dimensional (2D) materials engineering. At present, doping methods for layered dichalcogenide materials have been limited to an ion intercalation between layer units or electrostatic carrier doping by electrical bias owing to the absence of appropriate substitutional dopant for increasing the carrier concentration. Here, we report the occurrence of metallic conduction in the layered dichalcogenide of SnSe2 by the direct Se-site doping with Cl as a shallow electron donor. The total carrier concentration up to ~1020 cm−3 is achieved by Cl substitutional doping, resulting in the improved conductivity value of ~170 S·cm−1 from ~1.7 S·cm−1 for non-doped SnSe2. When the carrier concentration exceeds ~1019 cm−3, the conduction mechanism is changed from hopping to degenerate conduction, exhibiting metal-insulator transition behavior. Detailed band structure calculation reveals that the hybridized s-p orbital from Sn 5s and Se 4p states is responsible for the degenerate metallic conduction in electron-doped SnSe2. PMID:26792630

Metallic conduction induced by direct anion site doping in layered SnSe2.

PubMed

Kim, Sang Il; Hwang, Sungwoo; Kim, Se Yun; Lee, Woo-Jin; Jung, Doh Won; Moon, Kyoung-Seok; Park, Hee Jung; Cho, Young-Jin; Cho, Yong-Hee; Kim, Jung-Hwa; Yun, Dong-Jin; Lee, Kyu Hyoung; Han, In-taek; Lee, Kimoon; Sohn, Yoonchul

2016-01-21

The emergence of metallic conduction in layered dichalcogenide semiconductor materials by chemical doping is one of key issues for two-dimensional (2D) materials engineering. At present, doping methods for layered dichalcogenide materials have been limited to an ion intercalation between layer units or electrostatic carrier doping by electrical bias owing to the absence of appropriate substitutional dopant for increasing the carrier concentration. Here, we report the occurrence of metallic conduction in the layered dichalcogenide of SnSe2 by the direct Se-site doping with Cl as a shallow electron donor. The total carrier concentration up to ~10(20) cm(-3) is achieved by Cl substitutional doping, resulting in the improved conductivity value of ~170 S · cm(-1) from ~1.7 S · cm(-1) for non-doped SnSe2. When the carrier concentration exceeds ~10(19) cm(-3), the conduction mechanism is changed from hopping to degenerate conduction, exhibiting metal-insulator transition behavior. Detailed band structure calculation reveals that the hybridized s-p orbital from Sn 5s and Se 4p states is responsible for the degenerate metallic conduction in electron-doped SnSe2.

Effects of ultraviolet light on B-doped CdS thin films prepared by spray pyrolysis method using perfume atomizer

NASA Astrophysics Data System (ADS)

Novruzov, V. D.; Keskenler, E. F.; Tomakin, M.; Kahraman, S.; Gorur, O.

2013-09-01

Boron doped CdS thin films were deposited by spray pyrolysis method using perfume atomizer. The effects of ultraviolet light on the structural, optical and electrical properties of B-doped CdS thin films were investigated as a function of dopant concentration (B/Cd). X-ray diffraction studies showed that all samples were polycrystalline nature with hexagonal structure. It was determined that the preferred orientation of non-illuminated samples changes from (1 0 1) to (0 0 2) with B concentration. The c lattice constant of films decreases from 6.810 Å to 6.661 Å with boron doping. The XRD peak intensity increased with the illumination for almost all the samples. The lattice parameters of B-doped samples remained nearly constant after illumination. It was found that the optical transmittance, photoluminescence spectra, resistivity and carrier concentration of the B-doped samples are stable after the illumination with UV light. Also the effects of UV light on B-doped CdS/Cu2S solar cell were investigated and it was determined that photoelectrical parameters of B-doped solar cell were more durable against the UV light.

Dopant incorporation in Al0.9Ga0.1As0.06Sb0.94 grown by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Patra, Saroj Kumar; Tran, Thanh-Nam; Vines, Lasse; Kolevatov, Ilia; Monakhov, Edouard; Fimland, Bjørn-Ove

2017-04-01

Incorporation of beryllium (Be) and tellurium (Te) dopants in epitaxially grown Al0.9Ga0.1As0.06Sb0.94 layers was investigated. Carrier concentrations and mobilities of the doped layers were obtained from room temperature Hall effect measurements, and dopant densities from secondary ion mass spectrometry depth profiling. An undoped Al0.3Ga0.7As cap layer and side wall passivation were used to reduce oxidation and improve accuracy in Hall effect measurements. The measurements on Be-doped samples revealed high doping efficiency and the carrier concentration varied linearly with dopant density up to the highest Be dopant density of 2.9 × 1019 cm-3, whereas for Te doped samples the doping efficiency was in general low and the carrier concentration saturated for Te-dopant densities above 8.0 × 1018 cm-3. The low doping efficiency in Te-doped Al0.9Ga0.1As0.06Sb0.94 layer was studied by deep-level transient spectroscopy, revealing existence of deep trap levels and related DX-centers which explains the low doping efficiency.

Microstructure and spectroscopic investigations of calcium zinc bismuth phosphate glass ceramics doped with manganese ions

NASA Astrophysics Data System (ADS)

Suneel Kumar, A.; Sambasiva Rao, M. V.; Chinna Ram, G.; Krishna Rao, D.

2018-01-01

Multi-component 10CaF2-20ZnO-(15 - x)Bi2O3-55P2O5:xMnO (0 ≤ x ≤ 2.5) glass ceramics were synthesised by melt quenching technique and heat treatment. The prepared glass ceramics were characterised by XRD, DTA, EDS and SEM. Spectroscopic studies such as optical absorption, EPR, FTIR and Raman were also carried out on these glass ceramics. The XRD and SEM studies have indicated that ceramic samples contain well defined and randomly distributed grains of different crystalline phases. The observed increase of enthalpy from DTA patterns up to 1 mol% of MnO indicates that the crystallisation starts initially from the surface of the material then gradually it is extended to the volume of the material and this influence is meagre at higher concentrations of MnO. The absorption spectra of manganese doped glass ceramics have exhibited two types of conventional bands; one due to Mn2+ ions and other due to Mn3+ ions. The EPR spectra of MnO doped glass ceramics showed a resonance signal around g2 = 2.023 with a six line hyperfine structure and another signal at about g1 = 4.314. The relative intensity and half-width of these two signals are observed to increase with the increase in the concentration of manganese ions up to 1 mol% beyond this concentration it is found to decrease. Such observation indicates the conversion of part of Mn2+ ions into Mn3+ ions in the glass ceramic matrix. The observed increase in the intensity of symmetrical structural units at the expense of asymmetrical structural units from the FTIR and Raman spectra at higher concentration of MnO indicating that Mn2+ ions occupy the network forming positions in the glass ceramic structure.

Non-metal single/dual doped carbon quantum dots: a general flame synthetic method and electro-catalytic properties

NASA Astrophysics Data System (ADS)

Han, Yuzhi; Tang, Di; Yang, Yanmei; Li, Chuanxi; Kong, Weiqian; Huang, Hui; Liu, Yang; Kang, Zhenhui

2015-03-01

A combustion flame method is developed for the convenient and scalable fabrication of single- and dual-doped carbon quantum dots (CQDs) (N-CQDs, B-CQDs, P-CQDs, and S-CQDs and dual-doped B,N-CQDs, P,N-CQDs, and S,N-CQDs), and the doping contents can be easily adjusted by simply changing the concentrations of precursors in ethanol. These single/dual-doped CQDs, especially B,N-CQDs, show high catalytic activities for the oxygen reduction reaction.A combustion flame method is developed for the convenient and scalable fabrication of single- and dual-doped carbon quantum dots (CQDs) (N-CQDs, B-CQDs, P-CQDs, and S-CQDs and dual-doped B,N-CQDs, P,N-CQDs, and S,N-CQDs), and the doping contents can be easily adjusted by simply changing the concentrations of precursors in ethanol. These single/dual-doped CQDs, especially B,N-CQDs, show high catalytic activities for the oxygen reduction reaction. Electronic supplementary information (ESI) available: TEM images, UV-Vis absorption, PL, Raman, FTIR, XPS, CV, and LSV data of single/dual doped CQDs, a table for the calculated mass concentrations of different atoms in various B, N, P or S containing CQDs and a table for summary of the ORR performance of various catalysts in an O2-saturated 0.1 M KOH solution. See DOI: 10.1039/c4nr07116f

Impedance measurement of Cobalt doped ZnO Quantum dots

NASA Astrophysics Data System (ADS)

Tiwari, Ram; Kaphle, Amrit; Hari, Parameswar

We investigated structural, thermal and electrical properties of ZnO Quantum dots grown by precipitation method. QDs were spin coated on ITO and annealed at various temperatures ranging from 1000C to 300 0C. ZnO QDs were doped with cobalt for concentration ranging from 0-15%. XRD measurement showed increase in bond length, strain, dislocation density and Cell volume as the doping level varied from 0% to 15%. Impedance Spectroscopy measurements represented by Cole-Cole plot showed reduction in resistance as the cobalt doping concentration increased from 0-15%. Thermal activation energy was obtained by plotting resistivity Vs temperature for doped samples at temperatures from 1000C to 3000C. The thermal activation energy decreased from 85.13meV to 58.21meV as doping increased from 0-15%. Relaxation time was extracted by fitting data to RC model. Relaxation time varied from 61.57 ns to 3.76 ns as the cobalt concentration increased from 0% to 15%. We will also discuss applications of cobalt doped ZnO QDs on improving conversion efficiency of solar cells.

Enhancing Graphene Capacitance by Nitrogen: Effects of Doping Configuration and Concentration

DOE PAGES

Zhan, Cheng; Cummings, Peter; Jiang, De-en

2016-01-08

Recent experiments have shown that nitrogen doping enhances capacitance in carbon electrode supercapacitors. However, a detailed study of the effect of N-doping on capacitance is still lacking. In this paper, we study the doping concentration and the configuration effect on the electric double-layer (EDL) capacitance, quantum capacitance, and total capacitance. It is found that pyridinic and graphitic nitrogens can increase the total capacitance by increasing quantum capacitance, but pyrrolic configuration limits the total capacitance due to its much lower quantum capacitance than the other two configurations. We also find that, unlike the graphitic and pyridinic nitrogens, the pyrrolic configuration's quantummore » capacitance does not depend on the nitrogen concentration, which may explain why some capacitance versus voltage measurements of N-doped graphene exhibit a V-shaped curve similar to that of undoped graphene. Our investigation provides a deeper understanding of the capacitance enhancement of the N-doping effect in carbon electrodes and suggests a potentially effective way to optimize the capacitance by controlling the type of N-doping.« less

Tb3+ and Eu3+ doped zinc phosphate glasses for solid state lighting applications

NASA Astrophysics Data System (ADS)

Jha, Kaushal; Vishwakarma, Amit K.; Jayasimhadri, M.; Haranath, D.; Jang, Kiwan

2018-04-01

Tb3+ and Eu3+ doped zinc phosphate (ZP) glasses were prepared by conventional melt-quenching technique and their photoluminescence properties were investigated in detail. For, Tb3+ doped glasses the intense emission was at 545 nm corresponding to 5D4→7F5 transition under 377 nm n-UV excitation. The optimized concentration for Tb3+ doped zinc phosphate glass was 3 mol% and above this concentration quenching takes place. The Eu3+ doped zinc phosphate glass revealed intense emission at 613 nm attributed to the 5D0→7F2 transition under intense 392 nm n-UV excitation. The concentration quenching phenomenon was not observed in the Eu3+ doped ZP glasses. The CIE chromaticity coordinates for 3 mol% Tb3+ and 5 mol% Eu3+ doped ZP glasses were found to (0.283, 0.615) and (0.652, 0.331) lying in the green and red regions, respectively. The above mentioned results indicate that the prepared glass are suitable for application in the field of lighting and display devices.

Synthesis and photocatalytic activity of ytterbium-doped titania/diatomite composite photocatalysts

NASA Astrophysics Data System (ADS)

Tang, Wenjian; Qiu, Kehui; Zhang, Peicong; Yuan, Xiqiang

2016-01-01

Ytterbium-doped titanium dioxide (Yb-TiO2)/diatomite composite materials with different Yb concentrations were prepared by sol-gel method. The phase structure, morphology, and chemical composition of the as-prepared composites were well characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), and ultraviolet-visible (UV-vis) diffuse reflection spectroscopy. The XRD and Raman spectroscopy analysis indicated that the TiO2 existed in the form of pure anatase in the composites. The SEM images exhibited the well deposition and dispersion of TiO2 nanoparticles with little agglomeration on the surfaces of diatoms. The UV-vis diffuse reflection spectra showed that the band gap of TiO2 could be narrowed by the introduction of Yb species, which was further affected by doping concentration of Yb. The photocatalytic activity of synthesized samples was investigated by the degradation of methylene blue (MB) under UV light irradiation. It was observed that the photocatalytic degradation followed a pseudo-first-order kinetics according to the Langmuir-Hinshelwood model. Compared to TiO2 and TiO2/diatomite, the Yb-TiO2/diatomite composites exhibited higher photocatalytic activity toward degradation of MB using UV light irradiation.

Inhomogeneous Phase Effect of Smart Meta-Superconducting MgB2

NASA Astrophysics Data System (ADS)

Li, Yongbo; Chen, Honggang; Qi, Weichang; Chen, Guowei; Zhao, Xiaopeng

2018-05-01

The inhomogeneous phase of a smart meta-superconductor has a great effect on its superconductivity. In this paper, the effect of concentration, dimensions, electroluminescence (EL) intensity, and distribution of the inhomogeneous phase on the superconducting critical temperature (TC) has been systematically investigated. An ex situ solid sintering was utilized to prepare smart meta-superconducting MgB2 doped with six kinds of electroluminescent materials, such as YVO4{:}Eu^{3+} and Y2O3{:}Eu^{3+} flakes. Elemental mappings through energy dispersive spectroscopy (EDS) show that the inhomogeneous phase is comparatively uniformly dispersed around the MgB2 particles; thus V, Y, and Eu were accumulated at a small area. The measurement results show that the optimum doping concentration of the meta-superconducting MgB2 is 2.0 wt%. The offset temperature (TC^{{ off}}) of the sample doped with 2.0 wt% dopant A is 1.6 K higher than that of pure MgB2. The improvement in TC^{{ off}} is likely related to the sizes, thickness, and EL intensity of the inhomogeneous phase of MgB2 smart meta-superconductor. This experiment provides a novel approach to enhance TC.

Thermally stimulated currents in molecularly doped polymers

NASA Astrophysics Data System (ADS)

Stasiak, James W.; Storch, Teresa J.

1997-10-01

Thermally stimulated currents (TSC) were measured in molecularly doped polymers consisting of the hole transport molecule p-diethylaminobenzaldehyde diphenyihydrazone (DEH) and the polymer binder bisphenol A polycarbonate (PC) at two different doping concentrations. The TSC spectrum, which consisted of a single, well resolved peak, was found to be dependent on the applied electric field, the heating rate and the dopant concentration. The peak maxima were located between 170K and 250K. The spectra were analyzed within the theoretical framework of Zielinski and Samoc which provided a procedure to extract the hopping activation energy for each concentration. The principle observations of this study are: (1) the TSC peak is unambiguously associated with charge transport, (2) the magnitude of the activation energies were found to be larger than values obtained from isothermal transient photocurrent measurements and (3) the activation energies obtained from analysis of the TSC spectra were found to be dependent on the doping concentration. This last observation is inconsistent with previous isothermal transient photocurrent measurements of doped polymer systems containing DEH.

Influence of gold nanoparticles of varying size in improving the lipase activity within cationic reverse micelles.

PubMed

Maiti, Subhabrata; Das, Dibyendu; Shome, Anshupriya; Das, Prasanta Kumar

2010-02-08

Herein, we report the effect of gold nanoparticles (GNPs) in enhancing lipase activity in reverse micelles of cetyltrimethylammonium bromide (CTAB)/water/isooctane/n-hexanol. The size and concentration of the nanoparticles were varied and their specific roles were assessed in detail. An overall enhancement of activity was observed in the GNP-doped CTAB reverse micelles. The improvement in activity becomes more prominent with increasing concentration and size of the GNPs (0-52 microM and ca. 3-30 nm, respectively). The observed highest lipase activity (k(2)=1070+/-12 cm(3) g(-1) s(-1)) in GNP-doped CTAB reverse micelles ([GNP]: 52 microm, ca. 20 nm) is 2.5-fold higher than in CTAB reverse micelles without GNPs. Improvement in the lipase activity is only specific to the GNP-doped reverse micellar media, whereas GNP deactivates and structurally deforms the enzyme in aqueous media. The reason for this activation is probably due to the formation of larger-sized reverse micelles in which the GNP acts as a polar core and the surfactants aggregate around the nanoparticle ('GNP pool') instead of only water. Lipase at the augmented interface of the GNP-doped reverse micelle showed improved activity because of enhancement in both the substrate and enzyme concentrations and increased flexibility in the lipase conformation. The extent of the activation is greater in the case of the larger-sized GNPs. A correlation has been established between the activity of lipase and its secondary structure by using circular dichroism and FTIR spectroscopic analysis. The generalized influence of GNP is verified in the reverse micelles of another surfactant, namely, cetyltripropylammonium bromide (CTPAB). TEM, dynamic light scattering (DLS), and UV/Vis spectroscopic analysis were utilized to characterize the GNPs and the organized aggregates. For the first time, CTAB-based reverse micelles have been found to be an excellent host for lipase simply by doping with appropriately sized GNPs.

Zero-reabsorption doped-nanocrystal luminescent solar concentrators.

PubMed

Erickson, Christian S; Bradshaw, Liam R; McDowall, Stephen; Gilbertson, John D; Gamelin, Daniel R; Patrick, David L

2014-04-22

Optical concentration can lower the cost of solar energy conversion by reducing photovoltaic cell area and increasing photovoltaic efficiency. Luminescent solar concentrators offer an attractive approach to combined spectral and spatial concentration of both specular and diffuse light without tracking, but they have been plagued by luminophore self-absorption losses when employed on practical size scales. Here, we introduce doped semiconductor nanocrystals as a new class of phosphors for use in luminescent solar concentrators. In proof-of-concept experiments, visibly transparent, ultraviolet-selective luminescent solar concentrators have been prepared using colloidal Mn(2+)-doped ZnSe nanocrystals that show no luminescence reabsorption. Optical quantum efficiencies of 37% are measured, yielding a maximum projected energy concentration of ∼6× and flux gain for a-Si photovoltaics of 15.6 in the large-area limit, for the first time bounded not by luminophore self-absorption but by the transparency of the waveguide itself. Future directions in the use of colloidal doped nanocrystals as robust, processable spectrum-shifting phosphors for luminescent solar concentration on the large scales required for practical application of this technology are discussed.

EXAFS and XANES investigation of (Li, Ni) codoped ZnO thin films grown by pulsed laser deposition.

PubMed

Mino, Lorenzo; Gianolio, Diego; Bardelli, Fabrizio; Prestipino, Carmelo; Senthil Kumar, E; Bellarmine, F; Ramanjaneyulu, M; Lamberti, Carlo; Ramachandra Rao, M S

2013-09-25

Ni doped, Li doped and (Li, Ni) codoped ZnO thin films were successfully grown using a pulsed laser deposition technique. Undoped and doped ZnO thin films were investigated using extended x-ray absorption fine structure (EXAFS) and x-ray absorption near edge spectroscopy (XANES). Preliminary investigations on the Zn K-edge of the undoped and doped ZnO thin films revealed that doping has not influenced the average Zn-Zn bond length and Debye-Waller factor. This shows that both Ni and Li doping do not appreciably affect the average local environment of Zn. All the doped ZnO thin films exhibited more than 50% of substitutional Ni, with a maximum of 77% for 2% Ni and 2% Li doped ZnO thin film. The contribution of Ni metal to the EXAFS signal clearly reveals the presence of Ni clusters. The Ni-Ni distance in the Ni(0) nanoclusters, which are formed in the film, is shorter with respect to the reference Ni metal foil and the Debye-Waller factor is higher. Both facts perfectly reflect what is expected for metal nanoparticles. At the highest doping concentration (5%), the presence of Li favors the growth of a secondary NiO phase. Indeed, 2% Ni and 5% Li doped ZnO thin film shows %Nisub = 75 ± 11, %Nimet = 10 ± 8, %NiO = 15 ± 8. XANES studies further confirm that the substitutional Ni is more than 50% in all the samples. These results explain the observed magnetic properties.

Room-Temperature Synthesis of Mn-Doped Cesium Lead Halide Quantum Dots with High Mn Substitution Ratio.

PubMed

Zhu, Jingrun; Yang, Xiaoling; Zhu, Yihua; Wang, Yuanwei; Cai, Jin; Shen, Jianhua; Sun, Luyi; Li, Chunzhong

2017-09-07

Here we report the room-temperature, atmospheric synthesis of Mn-doped cesium lead halide (CsPbX 3 ) perovskite quantum dots (QDs). The synthesis is performed without any sort of protection, and the dual-color emission mechanism is revealed by density functional theory. The Mn concentration reaches a maximum atomic percentage of 37.73 at%, which is significantly higher in comparison to those achieved in earlier reports via high temperature hot injection method. The optical properties of as-prepared nanocrystals (NCs) remain consistent even after several months. Therefore, red-orange LEDs were fabricated by coating the composite of PS and as-prepared QDs onto ultraviolet LED chips. Additionally, the present approach may open up new methods for doping other ions in CsPbX 3 QDs under room temperature, the capability of which is essential for applications such as memristors and other devices.

Elevated transition temperature in Ge doped VO2 thin films

NASA Astrophysics Data System (ADS)

Krammer, Anna; Magrez, Arnaud; Vitale, Wolfgang A.; Mocny, Piotr; Jeanneret, Patrick; Guibert, Edouard; Whitlow, Harry J.; Ionescu, Adrian M.; Schüler, Andreas

2017-07-01

Thermochromic GexV1-xO2+y thin films have been deposited on Si (100) substrates by means of reactive magnetron sputtering. The films were then characterized by Rutherford backscattering spectrometry (RBS), four-point probe electrical resistivity measurements, X-ray diffraction, and atomic force microscopy. From the temperature dependent resistivity measurements, the effect of Ge doping on the semiconductor-to-metal phase transition in vanadium oxide thin films was investigated. The transition temperature was shown to increase significantly upon Ge doping (˜95 °C), while the hysteresis width and resistivity contrast gradually decreased. The precise Ge concentration and the film thickness have been determined by RBS. The crystallinity of phase-pure VO2 monoclinic films was confirmed by XRD. These findings make the use of vanadium dioxide thin films in solar and electronic device applications—where higher critical temperatures than 68 °C of pristine VO2 are needed—a viable and promising solution.

Longitudinal optical phonon-plasmon coupled modes of degenerate Al-doped ZnO films

NASA Astrophysics Data System (ADS)

Ding, K.; Hu, Q. C.; Lin, W. W.; Huang, J. K.; Huang, F.

2012-07-01

We have investigated the interaction between carriers and polar phonons by using Raman scattering spectroscopy in highly conductive Al-doped ZnO films grown by metalorganic chemical vapor deposition. Different from the longitudinal optical phonon-plasmon coupled modes (LOPPCM) observed in nondegenerate ZnO, an A1(LO)-like mode appears at the low frequency side of the uncoupled A1(LO) mode, and it monotonically shifts to higher frequencies and approaches to the uncoupled A1(LO) mode as Al composition increases. Based on line shape calculations, the A1(LO)-like mode is assigned to the large wave-vector LOPPCM arising from nonconserving scattering dominated by the Al impurity-induced Fröhlich mechanism. Benefiting from the nonmonotonic Al composition dependence of the electron density, it is revealed that the LOPPCM depends mainly on the doping level but not the carrier concentration.

Transport properties of CNT/oligosilane/CNT heterojunctions

NASA Astrophysics Data System (ADS)

Yu, J.; Zhang, G. L.; Shang, Y.; Wang, K. D.; Zhang, H.; Sun, M.; Liu, B.; Zeng, T.

2013-02-01

Combining the non-equilibrium Green's function formalism with density functional theory, the transport properties of nine CNT/oligosilane/CNT heterojunctions were systematically studied. We have found that the incorporation of oligosilane linkage to the carbon nanotube mouth could significantly tune the transport properties compared with the pure oligosilane and pure CNT. The P- and B-dopings upon the oligosilane moiety could not only enhance the conductivity but also give rise to multiple negative differential resistance behavior for the CNT/oligosilane/CNT heterojunctions. The concentration of heteroatom plays an important role in the transport properties of the CNT/oligosilane/CNT heterojunctions, while the number of the oligosilane linkage exerts little effect on the conductivity. The B-doped CNT/oligosilane/CNT heterojunctions show higher conductivity than those of the P-doped ones. The p-n junction caused by B- and P-codopings exhibits a rectifying effect and the rectification ratio is up to 7.19.

Enhancement of multiple-phonon resonant Raman scattering in Co-doped ZnO nanorods

NASA Astrophysics Data System (ADS)

Phan, The-Long; Vincent, Roger; Cherns, David; Dan, Nguyen Huy; Yu, Seong-Cho

2008-08-01

We have studied Raman scattering in Co-doped ZnO nanorods prepared by thermal diffusion. Experimental results show that the features of their non-resonant spectra are similar to Raman spectra from Co-doped ZnO materials investigated previously. Under resonant conditions, however, there is a strong enhancement of multiple-phonon Raman scattering processes. Longitudinal optical (LO)-phonon overtones up to eleventh order are observed. The modes become more obvious when the Co concentration diffused into ZnO nanorods goes to an appropriate value. This phenomenon is explained due to the shift of the band-gap energy and also due to the decrease in the intensity of near-band-edge luminescence. Our observation is in agreement with the prediction [J. F. Scott, Phys. Rev. B 2, 1209 (1970)] that the number of LO-phonon lines in ZnO is higher than that observed for CdS.

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

Effects of anhydrous AlCl3 dopant on the structural, optical and electrical properties of PVA-PVP polymer composite films

NASA Astrophysics Data System (ADS)

Shanmugam, G.; Krishnakumar, V.

2018-05-01

Polymer composite films based on PVA-PVP with AlCl3 as the dopant at different concentrations were prepared using solution casting technique. XRD patterns reveal the increase in amorphousity of the films with AlCl3 doping. Optical absorption studies exhibit that the values of optical absorption coefficient, direct and indirect optical band gaps are found to decrease with increase in AlCl3 concentration. It confirms the charge transfer in complexes between the polymer and the dopant. The dielectric studies show the increase in dielectric constant at low frequency with increasing AlCl3 concentration and temperature. The ac conductivity and ionic conductivity increase with the AlCl3 content and the maximum value at room temperature is found to be 6.89 × 10-4 and 8.05 × 10-5 S/cm for higher AlCl3 doped PVA-PVP film. The estimated ionic conductivity value is three or four orders of magnitude greater than those obtained in the certain representative polymer-salt complexes as reported earlier. Electrical modulus plots confirm the removal of electrode polarization and the low conductivity relaxation time with Al doping. The activation energy estimated from the temperature dependent dc conductivity plot is agreed well with the migration energy calculated from the temperature dependent electric modulus plot.

Quasi four-level Tm:LuAG laser

NASA Technical Reports Server (NTRS)

Jani, Mahendra G. (Inventor); Barnes, Norman P. (Inventor); Hutcheson, Ralph L. (Inventor); Rodriguez, Waldo J. (Inventor)

1997-01-01

A quasi four-level solid-state laser is provided. A laser crystal is disposed in a laser cavity. The laser crystal has a LuAG-based host material doped to a final concentration between about 2% and about 7% thulium (Tm) ions. For the more heavily doped final concentrations, the LuAG-based host material is a LuAG seed crystal doped with a small concentration of Tm ions. Laser diode arrays are disposed transversely to the laser crystal for energizing the Tm ions.

Segregation of chlorine in n-type tin monosulfide ceramics: Actual chlorine concentration for carrier-type conversion

NASA Astrophysics Data System (ADS)

Iguchi, Yuki; Sugiyama, Taiki; Inoue, Kazutoshi; Yanagi, Hiroshi

2018-05-01

Tin monosulfide (SnS) is an attractive material for photovoltaic cells because of its suitable band-gap energy, high absorption coefficient, and non-toxic and abundant constituent elements. The primary drawback of this material is the lack of n-type SnS. We recently demonstrated n-type SnS by doping with Cl. However, the Cl-doped n-type SnS bulk ceramics exhibited an odd behavior in which carrier-type conversion but not electron carrier concentration depended on the Cl concentration. In this study, the electron probe microanalysis (EPMA) elemental mapping of Cl-doped SnS revealed continuous homogeneous regions with a relatively low Cl concentration along with the islands of high Cl concentration in which Sn/S is far from unity. The difference between the Cl concentration in the homogeneous region (determined by EPMA) and the bulk Cl concentration (determined by wavelength-dispersive X-ray fluorescence spectroscopy) increased with the increasing Cl doping amount. The carrier concentration and the Hall coefficient clearly depended on the Cl concentration in the homogeneous region. Carrier-type conversion was observed at the Cl concentration of 0.26 at. % (in the homogeneous region).

Carbon-doping-induced negative differential resistance in armchair phosphorene nanoribbons

NASA Astrophysics Data System (ADS)

Guo, Caixia; Xia, Congxin; Wang, Tianxing; Liu, Yufang

2017-03-01

By using a combined method of density functional theory and non-equilibrium Green’s function formalism, we investigate the electronic transport properties of carbon-doped armchair phosphorene nanoribbons (APNRs). The results show that C atom doping can strongly affect the electronic transport properties of the APNR and change it from semiconductor to metal. Meanwhile, obvious negative differential resistance (NDR) behaviors are obtained by tuning the doping position and concentration. In particular, with reducing doping concentration, NDR peak position can enter into mV bias range. These results provide a theoretical support to design the related nanodevice by tuning the doping position and concentration in the APNRs. Project supported by the National Natural Science Foundation of China (No. 11274096), the University Science and Technology Innovation Team Support Project of Henan Province (No. 13IRTSTHN016), the University key Science Research Project of Henan Province (No.16A140043). The calculation about this work was supported by the High Performance Computing Center of Henan Normal University.

Electrical properties of tin-doped zinc oxide nanostructures doped at different dopant concentrations

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

Nasir, M. F., E-mail: babaibaik2002@yahoo.com; Zainol, M. N., E-mail: nizarzainol@yahoo.com; Hannas, M., E-mail: mhannas@gmail.com

This project has been focused on the electrical and optical properties respectively on the effect of Tin doped zinc oxide (ZnO) thin films at different dopant concentrations. These thin films were doped with different Sn dopant concentrations at 1 at%, 2 at%, 3 at%, 4 at% and 5 at% was selected as the parameter to optimize the thin films quality while the annealing temperature is fixed 500 °C. Sn doped ZnO solutions were deposited onto the glass substrates using sol-gel spin coating method. This project was involved with three phases, which are thin films preparation, deposition and characterization. The thinmore » films were characterized using Current Voltage (I-V) measurement and ultraviolet-visible-near-infrared (UV-vis-NIR) spectrophotometer (Perkin Elmer Lambda 750) for electrical properties and optical properties. The electrical properties show that the resistivity is the lowest at 4 at% Sn doping concentration with the value 3.08 × 10{sup 3} Ωcm{sup −1}. The absorption coefficient spectrum obtained shows all films exhibit very low absorption in the visible (400-800 nm) and near infrared (NIR) (>800 nm) range but exhibit high absorption in the UV range.« less

Compensating vacancy defects in Sn- and Mg-doped In2O3

NASA Astrophysics Data System (ADS)

Korhonen, E.; Tuomisto, F.; Bierwagen, O.; Speck, J. S.; Galazka, Z.

2014-12-01

MBE-grown Sn- and Mg-doped epitaxial In2O3 thin-film samples with varying doping concentrations have been measured using positron Doppler spectroscopy and compared to a bulk crystal reference. Samples were subjected to oxygen or vacuum annealing and the effect on vacancy type defects was studied. Results indicate that after oxygen annealing the samples are dominated by cation vacancies, the concentration of which changes with the amount of doping. In highly Sn-doped In2O3 , however, these vacancies are not the main compensating acceptor. Vacuum annealing increases the size of vacancies in all samples, possibly by clustering them with oxygen vacancies.

Highly doped layer for tunnel junctions in solar cells

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

Fetzer, Christopher M.

A highly doped layer for interconnecting tunnel junctions in multijunction solar cells is presented. The highly doped layer is a delta doped layer in one or both layers of a tunnel diode junction used to connect two or more p-on-n or n-on-p solar cells in a multijunction solar cell. A delta doped layer is made by interrupting the epitaxial growth of one of the layers of the tunnel diode, depositing a delta dopant at a concentration substantially greater than the concentration used in growing the layer of the tunnel diode, and then continuing to epitaxially grow the remaining tunnel diode.

Structural, electronic transport and optical properties of Cr doped PbS thin film by chemical bath deposition

NASA Astrophysics Data System (ADS)

Preetha, K. C.

2017-06-01

Incorporation of Chromium ions into Lead Sulphide thin films have been achieved by CBD technique. Effects of doping were investigated as a function of Pb/Cr ratio from o to 2 at %. X-ray diffraction patterns showed that films were polycrystalline in nature with increase in crystallite size up to an optimum doping concentration. Scanning electron microscopic study revealed excellent morphology with doping concentration. The low transmittance in the UV-VIS region offered the suitability of the samples as solar control coatings. The thin films were found to be P type and electrical conductivity enhanced on doping.

Time-Resolved Photoluminescence Studies of Si-doped AlGaN alloys

NASA Astrophysics Data System (ADS)

Nam, K. B.; Li, J.; Nakarmi, M. L.; Lin, J. Y.; Jiang, H. X.

2002-03-01

Si-doped n-type Al x Ga_1-x N alloys with x between 0.3 and 0.5 were grown by metal-organic chemical vapor deposition (MOCVD) on sapphire substrates. Time-resolved photoluminescence (PL) emission spectroscopy and variable temperature Hall-effect measurements were employed to study the optical and electrical properties of these epilayers. Our electrical data revealed that the conductivity of Si-doped Al x Ga_1-x N alloys (x > 0.4) increases with an increase of the Si doping concentration (N_Si) for a fixed x value and exhibits a sharp increase around N_Si= 1x10 ^18cm-3, suggesting the existence of a critical Si doping concentration needed to convert insulating Al x Ga_1-x N alloys (x > 0.4) to n-type conductivity. Time-resolved PL studies also showed that PL decay lifetime and activation energy decrease sharply when Si-doping concentration increases from N_Si= 0 to 1x10 ^18cm-3and then followed by gradual decreases as N_Si further increases. Our results thus suggest that Si-doping reduces the effect of carrier localization in Al x Ga_1-x N alloys and a sharp drop in carrier localization energy occurs at N_Si= 1x10 ^18cm-3, which is the critical Si-doping concentration needed to fill up the localized states in Al x Ga_1-x N alloys (x > 0.4). The implications of these results to UV optoelectronic devices are also discussed.

Thermoelectric properties of Sn doped BiCuSeO

NASA Astrophysics Data System (ADS)

Das, Sayan; Chetty, Raju; Wojciechowski, Krzysztof; Suwas, Satyam; Mallik, Ramesh Chandra

2017-10-01

BiCuSeO and Bi1-xSnxCuSeO (x = 0.02, 0.04, 0.06, 0.08) were prepared by a two-step solid state synthesis. The phase purity and the crystal structure were investigated by the X-Ray Diffraction (XRD) and confirmed by Energy Dispersive Spectroscopy (EDS). The volatilization of Bi and Bi2O3 lead to off-stoichiometry of the main phase and the formation of CuSe2 secondary phase in the undoped sample. SnO2 secondary phases were found in the doped samples. Both the Seebeck coefficient and the electrical resistivity, measured from the room temperature to 773 K linearly increases with the temperature, which indicates that the sample have metallic like behavior. The origin of such a behavior is due to high hole concentration originating from the Bi and the O vacancies. The Sn +4 valence state was confirmed from the X-Ray Photoelectron Spectroscopy (XPS) and from the reduction of lattice parameter 'a' with doping. The substitution of Sn+4 in the place of Bi+3 leads to the higher Seebeck coefficient and electrical resistivity in the doped samples. Highest power-factor (∼1 mW/m-K2 at 773 K), was obtained for the undoped sample and the 4% Sn doped sample (Bi0.96Sn0.04CuSeO). The lowest thermal conductivity was obtained for the undoped sample, from the room temperature to 773 K. The presence of thermally-conducting SnO2 secondary phases in the doped samples increases the thermal conductivity in comparison with the undoped sample. The zTs of the doped samples were lower compared to the undoped sample, owing to their higher thermal conductivity. The oxygen vacancies as well as the all-length scale phonon scattering, lowers the thermal conductivity of the undoped sample and, as a result, a maximum zT of 1.09 was achieved at 773 K.

Combination of cathodic reduction with adsorption for accelerated removal of Cr(VI) through reticulated vitreous carbon electrodes modified with sulfuric acid-glycine co-doped polyaniline.

PubMed

Mo, Xi; Yang, Zhao-hui; Xu, Hai-yin; Zeng, Guang-ming; Huang, Jing; Yang, Xia; Song, Pei-pei; Wang, Li-ke

2015-04-09

Improving the reduction kinetics is crucial in the electroreduction process of Cr(VI). In this study, we developed a novel adsorption-electroreduction system for accelerated removal of Cr(VI) by employing reticulated vitreous carbon electrode modified with sulfuric acid-glycine co-doped polyaniline (RVC/PANI-SA-GLY). Firstly, response surface methodology confirmed the optimum polymerization condition of co-doped polyaniline for modifying electrodes (Aniline, sulfuric acid and glycine, respectively, of 0.2 mol/L, 0.85 mol/L, 0.93 mol/L) when untraditional dopant glycine was added. Subsequently, RVC/PANI-SA-GLY showed higher Cr(VI) removal percentages in electroreduction experiments over RVC electrode modified with sulfuric acid doped polyaniline (RVC/PANI-SA) and bare RVC electrode. In contrast to RVC/PANI-SA, the improvement by RVC/PANI-SA-GLY was more significant and especially obvious at more negative potential, lower initial Cr(VI) concentration, relatively less acidic solution and higher current densities, best achieving 7.84% higher removal efficiency with entire Cr(VI) eliminated after 900 s. Current efficiencies were likewise enhanced by RVC/PANI-SA-GLY under quite negative potentials. Fourier transform infrared (FTIR) and energy dispersive spectrometer (EDS) analysis revealed a possible adsorption-reduction mechanism of RVC/PANI-SA-GLY, which greatly contributed to the faster reduction kinetics and was probably relative to the absorption between protonated amine groups of glycine and HCrO4(-). Eventually, the stability of RVC/PANI-SA-GLY was proven relatively satisfactory. Copyright © 2015 Elsevier B.V. All rights reserved.

The Preparation and Optical Properties of Novel LiLa(MoO4)2:Sm3+,Eu3+ Red Phosphor

PubMed Central

Luo, Li; Huang, Baoyu; He, Jingqi; Zhang, Wei; Zhao, Weiren; Wang, Jianqing

2018-01-01

Novel LiLa1−x−y(MoO4)2:xSm3+,yEu3+ (in short: LL1−x−yM:xSm3+,yEu3+) double molybdate red phosphors were synthesized by a solid-state reaction at as low temperature as 610 °C. The optimal doping concentration of Sm3+ in LiLa1−x(MoO4)2:xSm3+ (LL1−xM:xSm3+) phosphor is x = 0.05 and higher concentrations lead to emission quenching by the electric dipole—electric dipole mechanism. In the samples co-doped with Eu3+ ions, the absorption spectrum in the near ultraviolet and blue regions became broader and stronger than these of the Sm3+ single-doped samples. The efficient energy transfer from Sm3+ to Eu3+ was found and the energy transfer efficiency was calculated. Under the excitation at 403 nm, the chromaticity coordinates of LL0.95−yM:0.05Sm3+,yEu3+ approach to the NTSC standard values (0.670, 0.330) continuously with increasing Eu3+ doping concentration. The phosphor exhibits high luminous efficiency under near UV or blue light excitation and remarkable thermal stability. At 150 °C, the integrated emission intensity of the Eu3+ remained 85% of the initial intensity at room temperature and the activation energy is calculated to be 0.254 eV. The addition of the LL0.83M:0.05Sm3+,0.12Eu3+ red phosphors can improve the color purity and reduce the correlated color temperature of WLED lamps. Hence, LL1−x−yM:xSm3+,yEu3+ is a promising WLED red phosphor. PMID:29443910

The Preparation and Optical Properties of Novel LiLa(MoO4)2:Sm3+,Eu3+ Red Phosphor.

PubMed

Wang, Jiaxi; Luo, Li; Huang, Baoyu; He, Jingqi; Zhang, Wei; Zhao, Weiren; Wang, Jianqing

2018-02-14

Novel LiLa1-x-y(MoO4)2:xSm3+,yEu3+ (in short: LL1-x-yM:xSm3+,yEu3+) double molybdate red phosphors were synthesized by a solid-state reaction at as low temperature as 610 °C. The optimal doping concentration of Sm3+ in LiLa1-x(MoO4)2:xSm3+ (LL1-xM:xSm3+) phosphor is x = 0.05 and higher concentrations lead to emission quenching by the electric dipole-electric dipole mechanism. In the samples co-doped with Eu3+ ions, the absorption spectrum in the near ultraviolet and blue regions became broader and stronger than these of the Sm3+ single-doped samples. The efficient energy transfer from Sm3+ to Eu3+ was found and the energy transfer efficiency was calculated. Under the excitation at 403 nm, the chromaticity coordinates of LL0.95-yM:0.05Sm3+,yEu3+ approach to the NTSC standard values (0.670, 0.330) continuously with increasing Eu3+ doping concentration. The phosphor exhibits high luminous efficiency under near UV or blue light excitation and remarkable thermal stability. At 150 °C, the integrated emission intensity of the Eu3+ remained 85% of the initial intensity at room temperature and the activation energy is calculated to be 0.254 eV. The addition of the LL0.83M:0.05Sm3+,0.12Eu3+ red phosphors can improve the color purity and reduce the correlated color temperature of WLED lamps. Hence, LL1-x-yM:xSm3+,yEu3+ is a promising WLED red phosphor.

Doping optimization of polypyrrole with toluenesulfonic acid using Box-Behnken design

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

Syed Draman, Sarifah Fauziah; Daik, Rusli; El-Sheikh, Said M.

A three-level Box-Behnken design was employed in doping optimization of polypyrrole with toluenesulfonic acid (TSA-doped PPy). The material was synthesized via chemical oxidative polymerization using pyrrole, toluenesulfonic acid (TSA) and ammonium persulfate (APS) as monomer, dopant and oxidant, respectively. The critical factors selected for this study were concentration of dopant, molar ratio between dopant to monomer (pyrrole) and concentration of oxidant. Obtaining adequate doping level of TSA-doped PPy is crucial because it affects the charge carriers for doped PPy and usually be responsible for electronic mobility along polymeric chain. Furthermore, the doping level also affects other properties such as electricalmore » and thermal conductivity. Doping level was calculated using elemental analysis. SEM images shows that the prepared TSA-doped PPy particles are spherical in shape with the diameters of about. The range of nanoparticles size is around 80-100 nm. The statistical analysis based on a Box–Behnken design showed that 0.01 mol of TSA, 1:1 mole ratio TSA to pyrrole and 0.25 M APS were the optimum conditions for sufficient doping level.« less

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

Kaur, Ramneek; Tripathi, S. K., E-mail: surya@pu.ac.in, E-mail: surya-tr@yahoo.com

This paper reports the synthesis and electrical characterization of CdSe-PMMA nanocomposite. CdSe-PMMA nanocomposite has been prepared by ex-situ technique through chemical route. The influence of three different Ag doping concentrations on the electrical properties has been studied in the temperature range ∼ 303-353 K. Transmission electron micrograph reveals the spherical morphology of the CdSe nanoparticles and their proper dispersion in the PMMA matrix. The electrical conduction of the polymer nanocomposites is through thermally activated process with single activation energy. With Ag doping, initially the activation energy increases upto 0.2 % Ag doping concentration but with further increase in Ag concentration, itmore » decreases. This behavior has been discussed on the basis of randomly oriented grain boundaries and defect states. Thus, the results indicate that the transport properties of the polymer nanocomposites can be tailored by controlled doping concentration.« less

Influence of Ga doping ratio on the saturable absorption mechanism in Ga doped ZnO thin solid films processed by sol-gel spin coating technique

NASA Astrophysics Data System (ADS)

Sandeep, K. M.; Bhat, Shreesha; Dharmaprakash, S. M.; Byrappa, K.

2017-03-01

In the present study, the nonlinear optical properties of sol-gel spin coated gallium doped zinc oxide (GZO) thin solid films are explored with nanosecond laser pulses using the z-scan technique. The higher doping ratios of Ga result in a large redshift of the energy gap (0.38 eV) due to the existence of enhanced grain boundary defects in GZO films. A positive nonlinear absorption coefficient is observed in undoped 1 at.wt.% GZO and 2 at.wt.% GZO films, and a negative nonlinear absorption coefficient in 3 at.wt.% GZO film. Fewer defects in undoped 1% GZO and 2% GZO films resulted in reverse saturable absorption (RSA), whereas a saturable absorption (SA) mechanism is observed in 3% GZO films and is attributed to the enhanced defect concentration in the band structure of GZO. However, all the films showed a self-defocusing mechanism, derived by a closed aperture z-scan technique. The present work sheds light on the defect mechanism involved in the observed nonlinear properties of GZO films.

Dissolution kinetics of small amounts of oxygen in tantalum alloy T-111 and internal oxide displacement reactions during annealing

NASA Technical Reports Server (NTRS)

Stecura, S.

1976-01-01

Oxygen was added to T-111 (Ta-8W-2Hf, wt. %) at 820 and 990 C at an oxygen pressure of about 0.0003 torr. The technique employed permitted predetermined and reproducible doping of T-111 up to 3.0 at. % oxygen. Based on the temperature dependence of the doping reaction, it is concluded that the initial rates of oxygen pickup are probably controlled by solution of oxygen into the T-111 lattice. Although hafnium oxides are more stable than those of tantalum or tungsten, analyses of extracted residues indicate that the latter oxides predominate in the as-doped specimens, presumably because of the higher concentrations of tantalum and tungsten in the alloy. However, high-temperature annealing promotes gettering of dissolved oxygen and of other oxides to form hafnium oxides. Small amounts of tantalum and tungsten oxides were still present after high-temperature annealing. Tungsten oxide (WO3) volatilizes slightly from the surface of T-111 at 990 C. The vaporization of WO3 has no apparent affect on the doping reaction.

Vacancy defects and defect clusters in alkali metal ion-doped MgO nanocrystallites studied by positron annihilation and photoluminescence spectroscopy

NASA Astrophysics Data System (ADS)

Sellaiyan, S.; Uedono, A.; Sivaji, K.; Janet Priscilla, S.; Sivasankari, J.; Selvalakshmi, T.

2016-10-01

Pure and alkali metal ion (Li, Na, and K)-doped MgO nanocrystallites synthesized by solution combustion technique have been studied by positron lifetime and Doppler broadening spectroscopy methods. Positron lifetime analysis exhibits four characteristic lifetime components for all the samples. Doping reduces the Mg vacancy after annealing to 800 °C. It was observed that Li ion migrates to the vacancy site to recover Mg vacancy-type defects, reducing cluster vacancies and micropores. For Na- and K-doped MgO, the aforementioned defects are reduced and immobile at 800 °C. Coincidence Doppler broadening studies show the positron trapping sites as vacancy clusters. The decrease in the S parameter is due to the particle growth and reduction in the defect concentration at 800 °C. Photoluminescence study shows an emission peak at 445 nm and 498 nm, associated with F2 2+ and recombination of higher-order vacancy complexes. Further, annealing process is likely to dissociate F2 2+ to F+ and this F+ is converted into F centers at 416 nm.

Single crystalline ZnO radial homojunction light-emitting diodes fabricated by metalorganic chemical vapour deposition

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

Yoo, Jinkyoung; Ahmed, Towfiq; Tang, Wei

ZnO radial p–n junction architecture has the potential for forward-leap of light-emitting diode (LED) technology in terms of higher efficacy and economical production. Here, we report on ZnO radial p–n junction-based light emitting diodes prepared by full metalorganic chemical vapour deposition (MOCVD) with hydrogen-assisted p-type doping approach. The p-type ZnO(P) thin films were prepared by MOCVD with the precursors of dimethylzinc, tert-butanol, and tertiarybutylphosphine. Controlling the precursor flow for dopant results in the systematic change of doping concentration, Hall mobility, and electrical conductivity. Moreover, the approach of hydrogen-assisted phosphorous doping in ZnO expands the understanding of doping behaviour in ZnO.more » Ultraviolet and visible electroluminescence of ZnO radial p–n junction was demonstrated through a combination of position-controlled nano/microwire and crystalline p-type ZnO(P) radial shell growth on the wires. Lastly, the reported research opens a pathway of realisation of production-compatible ZnO p–n junction LEDs.« less

The effect of shallow vs. deep level doping on the performance of thermoelectric materials

NASA Astrophysics Data System (ADS)

Song, Qichen; Zhou, Jiawei; Meroueh, Laureen; Broido, David; Ren, Zhifeng; Chen, Gang

2016-12-01

It is well known that the efficiency of a good thermoelectric material should be optimized with respect to doping concentration. However, much less attention has been paid to the optimization of the dopant's energy level. Thermoelectric materials doped with shallow levels may experience a dramatic reduction in their figures of merit at high temperatures due to the excitation of minority carriers that reduces the Seebeck coefficient and increases bipolar heat conduction. Doping with deep level impurities can delay the excitation of minority carriers as it requires a higher temperature to ionize all dopants. We find through modeling that, depending on the material type and temperature range of operation, different impurity levels (shallow or deep) will be desired to optimize the efficiency of a thermoelectric material. For different materials, we further clarify where the most preferable position of the impurity level within the bandgap falls. Our research provides insight on why different dopants often affect thermoelectric transport properties differently and directions in searching for the most appropriate dopants for a thermoelectric material in order to maximize the device efficiency.

Growth and characterization of pure and Ca2+ doped MnHg(SCN)4 single crystals

NASA Astrophysics Data System (ADS)

Latha, C.; Mahadevan, C. K.; Guo, Li; Liu, Jinghe

2018-05-01

Manganese-mercury thiocyanate, MnHg(SCN)4, crystal is considered to be an important organometallic nonlinear optical (NLO) material exhibiting higher thermal stability and second harmonic generation (SHG) efficiency. In order to understand the effect of Ca2+ as an impurity on the physicochemical properties, we have grown pure and Ca2+ doped (with a concentration of 1 mol%) MnHg(SCN)4 single crystals by the free evaporation of solvent method and characterized structurally, chemically, optically and electrically by adopting the available standard methods. Results obtained indicate that Ca2+ doping increases significantly the optical transmittance, SHG efficiency, and DC electrical conductivity and decreases the dielectric loss factor (improves the crystal quality), and AC electrical conductivity without distorting the crystal structure. Also, the low dielectric constant (εr) values observed for both the pure and doped crystals considered at near ambient temperatures indicate the possibility of using these crystals not only as potential NLO materials (useful in the photonics industry) but also as promising low εr value dielectric materials (useful in the microelectronics industry).

Single crystalline ZnO radial homojunction light-emitting diodes fabricated by metalorganic chemical vapour deposition

DOE PAGES

Yoo, Jinkyoung; Ahmed, Towfiq; Tang, Wei; ...

2017-09-05

ZnO radial p–n junction architecture has the potential for forward-leap of light-emitting diode (LED) technology in terms of higher efficacy and economical production. Here, we report on ZnO radial p–n junction-based light emitting diodes prepared by full metalorganic chemical vapour deposition (MOCVD) with hydrogen-assisted p-type doping approach. The p-type ZnO(P) thin films were prepared by MOCVD with the precursors of dimethylzinc, tert-butanol, and tertiarybutylphosphine. Controlling the precursor flow for dopant results in the systematic change of doping concentration, Hall mobility, and electrical conductivity. Moreover, the approach of hydrogen-assisted phosphorous doping in ZnO expands the understanding of doping behaviour in ZnO.more » Ultraviolet and visible electroluminescence of ZnO radial p–n junction was demonstrated through a combination of position-controlled nano/microwire and crystalline p-type ZnO(P) radial shell growth on the wires. Lastly, the reported research opens a pathway of realisation of production-compatible ZnO p–n junction LEDs.« less

Emergence of microstructure and oxygen diffusion in yttrium-stabilized cubic zirconia

NASA Astrophysics Data System (ADS)

Yang, C.; Trachenko, K.; Hull, S.; Todorov, I. T.; Dove, M. T.

2018-05-01

Large-scale molecular dynamics simulations have been used to study the microstructure in Y-doped ZrO2. From simulations performed as a function of composition the dependence of microstructure on composition is quantified, showing how it is formed from two coexisting phases, and the transformation to the stabilized cubic form is observed at higher concentrations of yttrium and higher temperatures. The effect of composition and temperature on oxygen diffusion is also studied, showing strong correlations between microstructure and diffusion.

Spectroscopic investigations of Nd3+ doped Lithium Lead Alumino Borate glasses for 1.06 μm laser applications

NASA Astrophysics Data System (ADS)

Deopa, Nisha; Rao, A. S.; Gupta, Mohini; Vijaya Prakash, G.

2018-01-01

Neodymium doped lithium lead alumino borate glasses were synthesized with the molar composition 10Li2Osbnd 10PbOsbnd (10-x) Al2O3sbnd 70B2O3sbnd x Nd2O3 (where, x = 0.1, 0.5, 1.0, 1.5, 2.0 and 2.5 mol %) via conventional melt quenching technique to understand their lasing potentialities using the absorption, emission and photoluminescence decay spectral measurements. The oscillator strengths measured from the absorption spectra were used to estimate the Judd-Ofelt intensity parameters using least square fitting procedure. The emission spectra recorded for the as-prepared glasses under investigation exhibit two emission transitions 4F3/2 → 4I11/2 (1063 nm) and 4F3/2 → 4I9/2 (1350 nm) for which radiative parameters have been evaluated. The emission intensity increases with increase in Nd3+ ion concentration up to 1 mol % and beyond concentration quenching took place. The decay profile shows single exponential nature for lower Nd3+ ion concentration and non-exponential for higher concentration. To elucidate the nature of energy transfer process, the non-exponential decay curves were well fitted to Inokuti-Hirayama model. The relatively higher values of emission cross-sections, branching ratios and quantum efficiency values obtained for 1.0 mol% of Nd3+ ions in LiPbAlB glass suggests it's aptness in generating lasing action at 1063 nm in NIR region.

Optical properties of cerium doped oxyfluoroborate glass.

PubMed

Bahadur, A; Dwivedi, Y; Rai, S B

2013-06-01

Cerium doped oxyfluoroborate glasses have been prepared and its spectroscopic properties have been discussed. It is found that the absorption edge shifts towards the lower energy side for the higher concentration of cerium dopant. Optical band gap for these glasses have been calculated and it is found that the number of non-bridging oxygen increases with cerium content. The emission spectra of these glasses have been recorded using UV laser radiations (266 and 355 nm) and it is observed that these glasses show bright blue emission. On the basis of excitation and emission spectra we have reported the existence of at least two different emission centers of Ce(3+)ions. Copyright © 2013 Elsevier B.V. All rights reserved.

Investigation by Monte Carlo simulation of substitution doping in the Double Perovskite Sr2CrRe1-xWxO6

NASA Astrophysics Data System (ADS)

El Rhazouani, O.; Benyoussef, A.

2018-01-01

Re-substitution doping by W has been investigated in the Double Perovskite (DP) Sr2CrRe1-xWxO6 for x ranging from 10 to 90% by using a Monte Carlo Simulation (MCS) in the framework of Ising model. Exchange couplings used in the simulation have been approximated in previous work for experimental Curie temperatures (TC). Doping effect on: partial and total magnetization, magnetic susceptibility, internal energy, specific heat, and Curie temperature has been studied. A sharp drop of partial magnetizations at 40% of W-concentration has been noticed at the magnetic transition. Apparition of a non-monotonic behavior of the total magnetization at 20% of W-concentration. Effect of doping on the stability of the compound has been emphasized. A quasilinear decrease of TC has been observed by increasing the concentration percentage of substitution doping by W.

Enhanced photoluminescence properties of Al doped ZnO films

NASA Astrophysics Data System (ADS)

Chen, H. X.; Ding, J. J.

2018-01-01

Al doped ZnO films are fabricated by radio frequency magnetron sputtering. In general, visible emission is related to various defects in ZnO films. However, too much defects will cause light emission quench. So it is still a controversial issue to control appropriate defect concentrations. In this paper, based on our previous results, appropriate Al doping concentration is chosen to introduce more both interstitial Zn and O vacancy defects, which is responsible for main visible emission of ZnO films. A strong emission band located at 405 nm and a long tail peak is observed in the samples. As Al is doped in ZnO films, the intensity of emission peaks increases. Zn interstitial might increase with the increasing Al3+ substitute because ZnO was a self-assembled oxide compound. So Zn interstitial defect concentration in Al doped ZnO films will increase greatly, which results in the intensity of emission peaks increases.

Nanoscale doping of compound semiconductors by solid phase dopant diffusion

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

Ahn, Jaehyun, E-mail: jaehyun.ahn@utexas.edu; Koh, Donghyi; Roy, Anupam

2016-03-21

Achieving damage-free, uniform, abrupt, ultra-shallow junctions while simultaneously controlling the doping concentration on the nanoscale is an ongoing challenge to the scaling down of electronic device dimensions. Here, we demonstrate a simple method of effectively doping ΙΙΙ-V compound semiconductors, specifically InGaAs, by a solid phase doping source. This method is based on the in-diffusion of oxygen and/or silicon from a deposited non-stoichiometric silicon dioxide (SiO{sub x}) film on InGaAs, which then acts as donors upon activation by annealing. The dopant profile and concentration can be controlled by the deposited film thickness and thermal annealing parameters, giving active carrier concentration ofmore » 1.4 × 10{sup 18 }cm{sup −3}. Our results also indicate that conventional silicon based processes must be carefully reviewed for compound semiconductor device fabrication to prevent unintended doping.« less

On the structural and impedance characteristics of Li- doped PEO, using n-butyl lithium in hexane as dopant

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

Anand, P. B., E-mail: anandputhirath@gmail.com, E-mail: jayalekshmi@cusat.ac.in; Jayalekshmi, S., E-mail: anandputhirath@gmail.com, E-mail: jayalekshmi@cusat.ac.in

2014-01-28

Nowadays polymer based solid state electrolytes for applications in rechargeable battery systems are highly sought after materials, pursued extensively by various research groups worldwide. Numerous methods are discussed in literature to improve the fundamental properties like electrical conductivity, mechanical stability and interfacial stability of polymer based electrolytes. The application of these electrolytes in Li-ion cells is still in the amateur state, due to low ionic conductivity, low lithium transport number and the processing difficulties. The present work is an attempt to study the effects of Li doping on the structural and transport properties of the polymer electrolyte, poly-ethelene oxide (PEO)more » (Molecular weight: 200,000). Li doped PEO was obtained by treating PEO with n-Butyllithium in hexane for different doping concentrations. Structural characterization of the samples was done by XRD and FTIR techniques. Impedance measurements were carried out to estimate the ionic conductivity of Li doped PEO samples. It is seen that, the crystallinity of the doped PEO decreases on increasing the doping concentration. XRD and FTIR studies support this observation. It is inferred that, ionic conductivity of the sample is increasing on increasing the doping concentration since less crystallinity permits more ionic transport. Impedance measurements confirm the results quantitatively.« less

Band gap and conductivity variations of ZnO thin films by doping with Aluminium

NASA Astrophysics Data System (ADS)

Vattappalam, Sunil C.; Thomas, Deepu; T, Raju Mathew; Augustine, Simon; Mathew, Sunny

2015-02-01

Zinc Oxide thin films were prepared by Successive Ionic layer adsorption and reaction technique(SILAR). Aluminium was doped for different doping concentrations from 3 at.% to 12 at.% in steps of 3 at.%. Conductivity of the samples were taken at different temperatures. UV Spectrograph of the samples were taken and the band gap of each sample was found from the data. It was observed that as the doping concentration of Aluminium increases, the band gap of the samples decreases and concequently conductivity of the samples increases.

Pharmacokinetics of Oral and Inhaled Terbutaline after Exercise in Trained Men

PubMed Central

Dyreborg, Anders; Krogh, Nanna; Backer, Vibeke; Rzeppa, Sebastian; Hemmersbach, Peter; Hostrup, Morten

2016-01-01

Aim: The aim of the study was to investigate pharmacokinetics of terbutaline after oral and inhaled administration in healthy trained male subjects in relation to doping control. Methods: Twelve healthy well-trained young men (27 ±2 years; mean ± SE) underwent two pharmacokinetic trials that compared 10 mg oral terbutaline with 4 mg inhaled dry powder terbutaline. During each trial, subjects performed 90 min of bike ergometer exercise at 65% of maximal oxygen consumption. Blood (0–4 h) and urine (0–24 h) samples were collected before and after administration of terbutaline. Samples were analyzed for concentrations of terbutaline by high performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS). Results: Pharmacokinetics differed between the two routes of administration. Serum Cmax and area under the serum concentration-time curve (AUC) were lower after oral administration compared to inhalation (Cmax: 4.2 ± 0.3 vs. 8.5 ± 0.7 ng/ml, P ≤ 0.001; AUC: 422 ± 22 vs. 1308 ± 119 ng/ml × min). Urine concentrations (sum of the free drug and the glucuronide) were lower after oral administration compared to inhalation 2 h (1100 ± 204 vs. 61 ± 10 ng/ml, P ≤ 0.05) and 4 h (734 ± 110 vs. 340 ± 48 ng/ml, P ≤ 0.001) following administration, whereas concentrations were higher for oral administration than inhalation 12 h following administration (190 ± 41 vs. 399 ± 108 ng/ml, P ≤ 0.05). Urine excretion rate was lower after oral administration than inhalation the first 2 h following administration (P ≤ 0.001). Systemic bioavailability ratio between the two routes of administration was 3.8:1 (inhaled: oral; P ≤ 0.001). Conclusion: Given the higher systemic bioavailability of inhaled terbutaline compared to oral, our results indicate that it is difficult to differentiate allowed inhaled use of terbutaline from prohibited oral ingestion based on urine concentrations in doping control analysis. However given the potential performance enhancing effect of high dose terbutaline, it is essential to establish a limit on the WADA doping list. PMID:27375484

First-principles study on doping and temperature dependence of thermoelectric property of Bi{sub 2}S{sub 3} thermoelectric material

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

Guo, Donglin; Hu, Chenguo, E-mail: hucg@cqu.edu.cn; Zhang, Cuiling

2013-05-15

Graphical abstract: The direction-induced ZT is found. At ZZ direction and n = 1.47 × 10{sup 19} cm{sup −3}, the ZT can reach maximal value, 0.36, which is three times as much as maximal laboratorial value. This result matches well the analysis of electron effective mass. Highlights: ► Electrical transportations of Bi{sub 2}S{sub 3} depend on the concentration and temperature. ► The direction-induced ZT is found. ► At ZZ direction and n = 1.47 × 10{sup 19} cm{sup −3}, the ZT can reach maximal value, 0.36. ► The maximal ZT value is three times as much as maximal laboratorial value.more » ► By doping and temperature tuning, Bi{sub 2}S{sub 3} is a promising thermoelectric material. - Abstract: The electronic structure and thermoelectric property of Bi{sub 2}S{sub 3} are investigated. The electron and hole effective mass of Bi{sub 2}S{sub 3} is analyzed in detail, from which we find that the thermoelectric transportation varies in different directions in Bi{sub 2}S{sub 3} crystal. Along ac plane the higher figure of merit (ZT) could be achieved. For n-type doped Bi{sub 2}S{sub 3}, the optimal doping concentration is found in the range of (1.0–5.0) × 10{sup 19} cm{sup −3}, in which the maximal ZT reaches 0.21 at 900 K, but along ZZ direction, the maximal ZT reaches 0.36. These findings provide a new understanding of thermoelectricity-dependent structure factors and improving ZT ways. The donor concentration N increases as T increases at one bar of pressure under a suitable chemical potential μ, but above this chemical potential μ, the donor concentration N keeps a constant.« less

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

Kaspar, Tiffany C.; Sushko, Peter V.; Bowden, Mark E.

Epitaxial thin films of Cr2-xTixO3 were deposited by oxygen-plasma-assisted molecular beam epitaxy (OPA-MBE) for 0.04 ≤ x ≤ 0.26. Ti speciation is verified by both x-ray photoelectron spectroscopy (XPS) and Ti K-edge x-ray absorption near-edge spectroscopy (XANES) to be Ti4+. Substitution of Ti for Cr in the corundum lattice is confirmed by modeling of the Ti K-edge extended x-ray absorption fine structure (EXAFS). Room temperature electrical transport measurements confirm the highly insulating nature of Ti-doped Cr2O3, despite the presence of aliovalent Ti4+. The resistivity of highly pure, undoped Cr2O3 was measured to be three orders of magnitude higher than formore » Ti-doped Cr2O3. Although the formation of Cr vacancies in Ti-doped Cr2O3 is found by density functional theory (DFT) calculations to be the energetically preferable defect compensation mechanism to maintain charge neutrality, an analysis of the XPS and EXAFS data reveal the presence of both Cr vacancies and oxygen interstitials at intermediate and high Ti concentrations, with a weak trend towards Cr vacancies as the Ti concentration increases. At low Ti concentrations, a strong dependence of the XPS Ti 2p core level peak width on concentration is observed. This dependence is attributed to the presence of widely spaced Ti dopants, which renders compensation of two or three Ti by a single oxygen interstitial or Cr vacancy, respectively, less probable. Instead, defect clusters of unknown type occur, although they may involve Cr vacancies. The defect compensation model developed here provides insight into previous, conflicting reports of n-type versus p-type conductivity in Ti-doped Cr2O3 at high temperature, and will inform future studies to exploit the wide variety of electronic and magnetic properties of corundum-structure oxides.« less

Iodine Doping of CdTe and CdMgTe for Photovoltaic Applications

DOE PAGES

Ogedengbe, O. S.; Swartz, C. H.; Jayathilaka, P. A. R. D.; ...

2017-06-06

Here, iodine-doped CdTe and Cd 1-xMg xTe layers were grown by molecular beam epitaxy. Secondary ion mass spectrometry characterization was used to measure dopant concentration, while Hall measurement was used for determining carrier concentration. Photoluminescence intensity and time-resolved photoluminescence techniques were used for optical characterization. Maximum n-type carrier concentrations of 7.4 x 10 18 cm -3 for CdTe and 3 x 10 17 cm -3 for Cd 0.65Mg 0.35Te were achieved. Studies suggest that electrically active doping with iodine is limited with dopant concentration much above these values. Dopant activation of about 80% was observed in most of the CdTemore » samples. The estimated activation energy is about 6 meV for CdTe and the value for Cd 0.65Mg 0.35Te is about 58 meV. Iodine-doped samples exhibit long lifetimes with no evidence of photoluminescence degradation with doping as high as 2 x 10 18 cm -3, while indium shows substantial non-radiative recombination at carrier concentrations above 5 x 10 16 cm -3. Iodine was shown to be thermally stable in CdTe at temperatures up to 600 °C. Results suggest iodine may be a preferred n-type dopant compared to indium in achieving heavily doped n-type CdTe.« less

Photo-catalytic decolourisation of toxic dye with N-doped titania: a case study with Acid Blue 25.

PubMed

Chakrabortty, Dhruba; Gupta, Susmita Sen

2013-05-01

Dyes are one of the hazardous water pollutants. Toxic Acid Blue 25, an anthraquinonic dye, has been decolourised by photo-catalysing it with nitrogen doped titania in aqueous medium. The photo catalyst was prepared from 15% TiCl3 and 25% aqueous NH3 solution as precursor. XRD and TEM revealed the formation of well crystalline anatase phase having particle size in the nano-range. BET surface area of the sample was higher than that of pure anatase TiO2. DRS showed higher absorption of radiation in visible range compared to pure anatase TiO2. XPS revealed the presence of nitrogen in N-Ti-O environment. The experimental parameters, namely, photocatalyst dose, initial dye concentration as well as solution pH influence the decolourisation process. At pH 3.0, the N-TiO2 could decolourise almost 100% Acid Blue 25 within one hour. The influence of N-TiO2 dose, initial concentration of Acid Blue 25 and solution pH on adsorption-desorption equilibrium is also studied. The adsorption process follows Lagergren first order kinetics while the modified Langmuir-Hinselwood model is suitably fitted for photocatalytic decolourisation of Acid Blue 25.

Influence of porous texture and surface chemistry on the CO₂ adsorption capacity of porous carbons: acidic and basic site interactions.

PubMed

Sánchez-Sánchez, Angela; Suárez-García, Fabián; Martínez-Alonso, Amelia; Tascón, Juan M D

2014-12-10

Doped porous carbons exhibiting highly developed porosity and rich surface chemistry have been prepared and subsequently applied to clarify the influence of both factors on carbon dioxide capture. Nanocasting was selected as synthetic route, in which a polyaramide precursor (3-aminobenzoic acid) was thermally polymerized inside the porosity of an SBA-15 template in the presence of different H3PO4 concentrations. The surface chemistry and the porous texture of the carbons could be easily modulated by varying the H3PO4 concentration and carbonization temperature. Porous texture was found to be the determinant factor on carbon dioxide adsorption at 0 °C, while surface chemistry played an important role at higher adsorption temperatures. We proved that nitrogen functionalities acted as basic sites and oxygen and phosphorus groups as acidic ones toward adsorption of CO2 molecules. Among the nitrogen functional groups, pyrrolic groups exhibited the highest influence, while the positive effect of pyridinic and quaternary functionalities was smaller. Finally, some of these N-doped carbons exhibit CO2 heats of adsorption higher than 42 kJ/mol, which make them excellent candidates for CO2 capture.

Compositions of doped, co-doped and tri-doped semiconductor materials

DOEpatents

Lynn, Kelvin [Pullman, WA; Jones, Kelly [Colfax, WA; Ciampi, Guido [Watertown, MA

2011-12-06

Semiconductor materials suitable for being used in radiation detectors are disclosed. A particular example of the semiconductor materials includes tellurium, cadmium, and zinc. Tellurium is in molar excess of cadmium and zinc. The example also includes aluminum having a concentration of about 10 to about 20,000 atomic parts per billion and erbium having a concentration of at least 10,000 atomic parts per billion.

An experimental study of the local electronic structure of B-site gallium doped bismuth ferrite powders

NASA Astrophysics Data System (ADS)

Gholam, Turghunjan; Ablat, Abduleziz; Mamat, Mamatrishat; Wu, Rong; Aimidula, Aimierding; Bake, Muhammad Ali; Zheng, Lirong; Wang, Jiaou; Qian, Haijie; Wu, Rui; Ibrahim, Kurash

2017-08-01

The un-doped and gallium (Ga) doped multiferroic bismuth ferrite (BiFeO3) compounds were successfully synthesized by the hydrothermal technique. This is then followed by a series of detailed investigations into the influence of Ga doping on the structural, morphological, optical and magnetic properties of BiFe1 - xGaxO3 (0 ≤ x ≤ 0.15). X-ray diffraction (XRD) analyses reveal that B-site doping of Ga may lead to the transformation of its crystal structure from a rhombohedral with a space group of R3c to an orthorhombic with a space group of Pbnm phase. The scanning electron microscope (SEM) images show that doping with Ga causes a significant reduction in particle size, when compared to un-doped BiFeO3. X-ray absorption near-edge structure (XANES) spectra have also shown that as the substitution of Ga increases, the Fe K and Bi LIII-edge absorption spectra shift towards higher energy site. It also implies that doping of Ga affects the local structures of both Bi and Fe atoms. Distinct transmission band fluctuations, as shown by Fourier transform infrared (FT-IR) spectra, can provide significant evidence for a transformation in crystal structure, following the increase of Ga concentration. The magnetization hysteresis measurements show that the magnetization decreases when Ga content is x ≥ 0.05. Such a phenomenon mainly stems from the substitution of Fe for an excessive amount of Ga, resulting in reduction of both valence fluctuations and the magnetization in the BiFe1 - xGaxO3 system.

Two Carrier Analysis of Persistent Photoconductivity in Modulation-Doped Structures

NASA Technical Reports Server (NTRS)

Schacham, S. E.; Mena, R. A.; Haugland, E. J.; Alterovitz, S. A.

1995-01-01

A simultaneous fit of Hall and conductivity data gives quantitative results on the carrier concentration and mobility in both the quantum well and the parallel conduction channel. In this study this method was applied to reveal several new findings on the effect of persistent photoconductivity (PPC) on free-carrier concentrations and mobilities. The increase in the two-dimensional electron-gas (2DEG) concentration is significantly smaller than the apparent one derived from single carrier analysis of the Hall coefficient. In the two types of structures investigated, delta doped and continuously doped barrier, the apparent concentration almost doubles following illumination, while analysis reveals an increase of about 20% in the 2DEG. The effect of PPC on mobility depends on the structure. For the sample with a continuously doped barrier the mobility in the quantum well more than doubles. This increase is attributed to the effective screening of the ionized donors by the large electron concentration in the barrier. In the delta doped barrier sample the mobility is reduced by almost a factor of 2. This decrease is probably caused by strong coupling between the two wells, as is demonstrated by self-consistent analysis.

Effect of Co doping concentration on structural properties and optical parameters of Co-doped ZnO thin films by sol-gel dip-coating method.

PubMed

Nam, Giwoong; Yoon, Hyunsik; Kim, Byunggu; Lee, Dong-Yul; Kim, Jong Su; Leem, Jae-Young

2014-11-01

The structural and optical properties of Co-doped ZnO thin films prepared by a sol-gel dip-coating method were investigated. X-ray diffraction analysis showed that the thin films were grown with a c-axis preferred orientation. The position of the (002) peak was almost the same in all samples, irrespective of the Co concentration. It is thus clear that Co doping had little effect on the position of the (002) peak. To confirm that Co2+ was substituted for Zn2+ in the wurtzite structure, optical measurements were conducted at room temperature by a UV-visible spectrometer. Three absorption peaks are apparent in the Co-doped ZnO thin films that do not appear for the undoped ZnO thin film. As the Co concentration was increased, absorption related to characteristic Co2+ transitions increased because three absorption band intensities and the area underneath the absorption wells between 500 and 700 nm increased with increasing Co concentration. The optical band gap and static dielectric constant decreased and the Urbach energy and extinction coefficient increased with increasing Co concentration.

New integration concept of PIN photodiodes in 0.35μm CMOS technologies

NASA Astrophysics Data System (ADS)

Jonak-Auer, I.; Teva, J.; Park, J. M.; Jessenig, S.; Rohrbacher, M.; Wachmann, E.

2012-06-01

We report on a new and very cost effective way to integrate PIN photo detectors into a standard CMOS process. Starting with lowly p-doped (intrinsic) EPI we need just one additional mask and ion implantation in order to provide doping concentrations very similar to standard CMOS substrates to areas outside the photoactive regions. Thus full functionality of the standard CMOS logic can be guaranteed while the photo detectors highly benefit from the low doping concentrations of the intrinsic EPI. The major advantage of this integration concept is that complete modularity of the CMOS process remains untouched by the implementation of PIN photodiodes. Functionality of the implanted region as host of logic components was confirmed by electrical measurements of relevant standard transistor as well as ESD protection devices. We also succeeded in establishing an EPI deposition process in austriamicrosystems 200mm wafer fabrication which guarantees the formation of very lowly p-doped intrinsic layers, which major semiconductor vendors could not provide. With our EPI deposition process we acquire doping levels as low as 1•1012/cm3. In order to maintain those doping levels during CMOS processing we employed special surface protection techniques. After complete CMOS processing doping concentrations were about 4•1013/cm3 at the EPI surface while the bulk EPI kept its original low doping concentrations. Photodiode parameters could further be improved by bottom antireflective coatings and a special implant to reduce dark currents. For 100×100μm2 photodiodes in 20μm thick intrinsic EPI on highly p-doped substrates we achieved responsivities of 0.57A/W at λ=675nm, capacitances of 0.066pF and dark currents of 0.8pA at 2V reverse voltage.

Evolution of High-Temperature Superconductivity from a Low-T_{c} Phase Tuned by Carrier Concentration in FeSe Thin Flakes.

PubMed

Lei, B; Cui, J H; Xiang, Z J; Shang, C; Wang, N Z; Ye, G J; Luo, X G; Wu, T; Sun, Z; Chen, X H

2016-02-19

We report the evolution of superconductivity in an FeSe thin flake with systematically regulated carrier concentrations by the liquid-gating technique. With electron doping tuned by the gate voltage, high-temperature superconductivity with an onset at 48 K can be achieved in an FeSe thin flake with T_{c} less than 10 K. This is the first time such high temperature superconductivity in FeSe is achieved without either an epitaxial interface or external pressure, and it definitely proves that the simple electron-doping process is able to induce high-temperature superconductivity with T_{c}^{onset} as high as 48 K in bulk FeSe. Intriguingly, our data also indicate that the superconductivity is suddenly changed from a low-T_{c} phase to a high-T_{c} phase with a Lifshitz transition at a certain carrier concentration. These results help to build a unified picture to understand the high-temperature superconductivity among all FeSe-derived superconductors and shed light on the further pursuit of a higher T_{c} in these materials.

Homogeneous molybdenum disulfide tunnel diode formed via chemical doping

NASA Astrophysics Data System (ADS)

Liu, Xiaochi; Qu, Deshun; Choi, Min Sup; Lee, Changmin; Kim, Hyoungsub; Yoo, Won Jong

2018-04-01

We report on a simple, controllable chemical doping method to fabricate a lateral homogeneous MoS2 tunnel diode. MoS2 was doped to degenerate n- (1.6 × 1013 cm-2) and p-type (1.1 × 1013 cm-2) by benzyl viologen and AuCl3, respectively. The n- and p-doping can be patterned on the same MoS2 flake, and the high doping concentration can be maintained by Al2O3 masking together with vacuum annealing. A forward rectifying p-n diode and a band-to-band tunneling induced backward rectifying diode were realized by modulating the doping concentration of both the n- and p-sides. Our approach is a universal stratagem to fabricate diverse 2D homogeneous diodes with various functions.

Optical properties of highly n-doped germanium obtained by in situ doping and laser annealing

NASA Astrophysics Data System (ADS)

Frigerio, J.; Ballabio, A.; Gallacher, K.; Giliberti, V.; Baldassarre, L.; Millar, R.; Milazzo, R.; Maiolo, L.; Minotti, A.; Bottegoni, F.; Biagioni, P.; Paul, D.; Ortolani, M.; Pecora, A.; Napolitani, E.; Isella, G.

2017-11-01

High n-type doping in germanium is essential for many electronic and optoelectronic applications especially for high performance Ohmic contacts, lasing and mid-infrared plasmonics. We report on the combination of in situ doping and excimer laser annealing to improve the activation of phosphorous in germanium. An activated n-doping concentration of 8.8  ×  1019 cm-3 has been achieved starting from an incorporated phosphorous concentration of 1.1  ×  1020 cm-3. Infrared reflectivity data fitted with a multi-layer Drude model indicate good uniformity over a 350 nm thick layer. Photoluminescence demonstrates clear bandgap narrowing and an increased ratio of direct to indirect bandgap emission confirming the high doping densities achieved.

Structural and optical characterization of Eu3+ doped beta-Ga2O3 nanoparticles using a liquid-phase precursor method.

PubMed

Kim, Moung-O; Kang, Bongkyun; Yoon, Daeho

2013-08-01

Eu3+ doped beta-Ga2O3 and non-doped beta-Ga2O3 nanoparticles were synthesized at 800 degrees C using a liquid-phase precursor (LPP) method, with different annealing times and Eu3+ ion concentrations. Eu3+ doped beta-Ga2O3 nanoparticles showed broad XRD peaks, revealing a second phase compared with the non-doped beta-Ga2O3 nanoparticles. The cathode luminescence (CL) spectra of beta-Ga2O3 and Eu3+ doped beta-Ga2O3 nanoparticles showed a broad band emission (300-500 nm) of imperfection and two component emissions. The luminescence quenching properties of Eu3+ dopant ion concentration appeared gradually beyond 5 mol% in our investigation.

Linear and nonlinear optical discussions of nanostructured Zn-doped CdO thin films

NASA Astrophysics Data System (ADS)

Yahia, I. S.; Salem, G. F.; Iqbal, Javed; Yakuphanoglu, F.

2017-04-01

Here, we report the doping effect of zinc (Zn) on the physical properties of cadmium oxide (CdO) at various concentrations (1, 2, 3 and 4 wt% of Zn). The studied samples were prepared using sol-gel in addition with sol gel spin coating technique. The structural, optical and dispersive properties were compared with the already reported work in the literature. The structural properties were observed by using atomic force microscopy (AFM). The AFM images show that the grain size decreases with increasing the concentration of Zn. The highest value of average cluster size (78. 71 nm) was found at 1% and the lowest (60.23 nm) when the doping concentration of Zn was 4%. Similar trend was observed in the roughness of the doped thin film when the Zn concentration was increased. The optical properties were examined using Shimadzu UV-Vis-NIR spectrophotometer and we found that the optical band gap of the un-doped CdO and the Zn-doped CdO thin films increases from 2.54 to 2.62 eV as the Zn concentration is increased from 1% to 4%. Also, the optical dispersion parameters (Eo, Ed, n2∞, λ0 and So) were calculated and discussed. We observed that the refractive index dispersion of undoped CdO and the Zn-doped CdO thin films follow the single oscillator model. Finally, spectroscopic method has been exploited to analyze the 3rd order non-linear optical susceptibility χ (3) and nonlinear refractive index n (2).

Characterization of doped hydrogenated nanocrystalline silicon films prepared by plasma enhanced chemical vapour deposition

NASA Astrophysics Data System (ADS)

Wang, Jin-Liang; Wu, Er-Xing

2007-03-01

The B- and P-doped hydrogenated nanocrystalline silicon films (nc-Si:H) are prepared by plasma-enhanced chemical vapour deposition (PECVD). The microstructures of doped nc-Si:H films are carefully and systematically characterized by using high resolution electron microscopy (HREM), Raman scattering, x-ray diffraction (XRD), Auger electron spectroscopy (AES), and resonant nucleus reaction (RNR). The results show that as the doping concentration of PH3 increases, the average grain size (d) tends to decrease and the crystalline volume percentage (Xc) increases simultaneously. For the B-doped samples, as the doping concentration of B2H6 increases, no obvious change in the value of d is observed, but the value of Xc is found to decrease. This is especially apparent in the case of heavy B2H6 doped samples, where the films change from nanocrystalline to amorphous.

High carrier concentration ZnO nanowire arrays for binder-free conductive support of supercapacitors electrodes by Al doping.

PubMed

Zheng, Xin; Sun, Yihui; Yan, Xiaoqin; Sun, Xu; Zhang, Guangjie; Zhang, Qian; Jiang, Yaru; Gao, Wenchao; Zhang, Yue

2016-12-15

Doping semiconductor nanowires (NWs) for altering their electrical and optical properties is a critical strategy for tailoring the performance of nanodevices. Here, we prepared in situ Al-doped ZnO nanowire arrays by using continuous flow injection (CFI) hydrothermal method to promote the conductivity. This reasonable method offers highly stable precursor concentration for doping that effectively avoid the appearance of the low conductivity ZnO nanosheets. Benefit from this, three orders of magnitude rise of the carrier concentration from 10 16 cm -3 to 10 19 cm -3 can be achieved compared with the common hydrothermal (CH) mothed in Mott-Schottky measurement. Possible effect of Al-doping was discussed by first-principle theory. On this basis, Al-doped ZnO nanowire arrays was developed as a binder-free conductive support for supercapacitor electrodes and high capacitance was triggered. It is owing to the dramatically decreased transfer resistance induced by the growing free-moving electrons and holes. Our results have a profound significance not merely in the controlled synthesis of other doping nanomaterials by co-precipitation method but also in the application of binder-free energy materials or other materials. Copyright © 2016 Elsevier Inc. All rights reserved.

On Defect Cluster Aggregation and Non-Reducibilty in Tin-Doped Indium Oxide

NASA Astrophysics Data System (ADS)

Warschkow, Oliver; Ellis, Donald E.; Gonzalez, Gabriela; Mason, Thomas O.

2003-03-01

The conductivity of tin-doped indium oxide (ITO), a transparent conductor, is critically dependent on the amount of tin-doping and oxygen partial pressure during preparation and annealing. Frank and Kostlin (Appl. Phys. A 27 (1982) 197-206) rationalized the carrier concentration dependence by postulating the formation of two types of neutral defect clusters at medium tin-doping levels: "Reducible" and "non-reducible" defect clusters; so named to indicate their ability to create carriers under reduction. According to Frank and Kostlin, both are composed of a single oxygen interstitial and two tin atoms substituting for indium, positioned in non-nearest and nearest coordination, respectively. This present work, seeking to distinguish reducible and non-reducible clusters by use of an atomistic model, finds only a weak correlation of oxygen interstitial binding energies with the relative positioning of dopants. Instead, the number of tin-dopants in the vicinity of the interstitial has a much larger effect on how strongly it is bound, a simple consequence of Coulomb interactions. We postulate that oxygen interstitials become non-reducible when clustered with three or more Sn_In. This occurs at higher doping levels as reducible clusters aggregate and share tin atoms. A simple probabilistic model, estimating the average number of clusters so aggregated, provides a qualitatively correct description of the carrier density in reduced ITO as a function of Sn doping level.

Metal modulation epitaxy growth for extremely high hole concentrations above 1019 cm-3 in GaN

NASA Astrophysics Data System (ADS)

Namkoong, Gon; Trybus, Elaissa; Lee, Kyung Keun; Moseley, Michael; Doolittle, W. Alan; Look, David C.

2008-10-01

The free hole carriers in GaN have been limited to concentrations in the low 1018cm-3 range due to the deep activation energy, lower solubility, and compensation from defects, therefore, limiting doping efficiency to about 1%. Herein, we report an enhanced doping efficiency up to ˜10% in GaN by a periodic doping, metal modulation epitaxy growth technique. The hole concentrations grown by periodically modulating Ga atoms and Mg dopants were over ˜1.5×1019cm-3.

Structural and dielectric properties of Zn1-xAlxO nanoparticles

NASA Astrophysics Data System (ADS)

Giri, N.; Mondal, A.; Sarkar, S.; Ray, R.

2018-05-01

Aluminium doped ZnO (AZO) nano-crystalline sample has been synthesized using chemical precipitation method with different doping concentrations. Detailed structural and morphological investigations of Zn1-xAlxO have been carried out using X-ray diffraction (XRD) and FE-SEM, respectively. Dependence of grain size of AZO with dopant concentration has been studied. Ac conductivity, dielectric constant and dielectric loss of Zn1-xAlxO (0 ≤ x ≤ 0.1) are investigated as a function of frequency (ω) and doping concentration (x) at room temperature.

Effect of Fe doping concentration on photocatalytic activity of ZnO nanosheets under natural sunlight

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

Khokhra, Richa; Kumar, Rajesh, E-mail: rajesh.kumar@juit.ac.in

2015-05-15

A facile room temperature, aqueous solution-based chemical method has been adopted for large-scale synthesis of Fe doped ZnO nanosheets. The XRD and SEM results reveal the as-synthesized products well crystalline and accumulated by large amount of interweave nanosheets, respectively. Energy dispersive spectroscopy data confirmed Fe doping of the ZnO nanosheets with a varying Fe concentration. The photoluminescence spectrum reveals a continuous suppression of defect related emissions intensity by increasing the concentration of the Fe ion. A photocatalytic activity using these samples under sunlight irradiation in the mineralization of methylene blue dye was investigated. The photocatalytic activity of Fe doped ZnOmore » nanosheets depends upon the presence of surface oxygen vacancies.« less

Density functional theory and experimental study of the electronic structure and transport properties of La, V, Nb, and Ta doped SrTiO3

NASA Astrophysics Data System (ADS)

Baniecki, J. D.; Ishii, M.; Aso, H.; Kurihara, K.; Ricinschi, Dan

2013-01-01

The electronic structure and transport properties of donor doped SrTiO3 are studied using density functional theory with spin-orbit coupling and conductivity, Hall, and Seebeck effect measurements over a wide temperature range (100 K to 600 K). Split-off energies ΔSO are tunable through the dopant SO interaction strength and concentration varying from 28.1 meV for pure STO to 70.93 meV for SrTi0.5Nb0.5O3. At lower carrier concentrations and temperatures, SO coupling has a marked effect on both the filling dependence of the density-of-states mass as well as the temperature dependence of the Seebeck coefficient, with quantitative theoretical predictions based on DFT calculations that include the SO interaction in closer agreement to the experimental data. Moreover, the results suggest that the predictive power of the current theory is not unlimited, with less accuracy for the calculated S predicting the magnitude of the experimental S data at lower dopant concentrations than for degenerately doped systems. A concentration dependent mass enhancement of ˜2-5, relative to the density-of-states mass in the local density approximation, possibly due to the influence of electronic screening of the electron-phonon interaction, would bring the theoretical S in accord with the experimental S data. This additional carrier-dependent enhancement mechanism for S may give an additional degree of freedom in terms of designing new higher efficiency thermoelectric energy materials.

Cation vacancies and electrical compensation in Sb-doped thin-film SnO2 and ZnO

NASA Astrophysics Data System (ADS)

Korhonen, E.; Prozheeva, V.; Tuomisto, F.; Bierwagen, O.; Speck, J. S.; White, M. E.; Galazka, Z.; Liu, H.; Izyumskaya, N.; Avrutin, V.; Özgür, Ü.; Morkoç, H.

2015-02-01

We present positron annihilation results on Sb-doped SnO2 and ZnO thin films. The vacancy types and the effect of vacancies on the electrical properties of these intrinsically n-type transparent semiconducting oxides are studied. We find that in both materials low and moderate Sb-doping leads to formation of vacancy clusters of variable sizes. However, at high doping levels cation vacancy defects dominate the positron annihilation signal. These defects, when at sufficient concentrations, can efficiently compensate the n-type doping produced by Sb. This is the case in ZnO, but in SnO2 the concentrations appear too low to cause significant compensation.

Photoluminescence Studies of P-type Modulation Doped GaAs/AlGaAs Quantum Wells in the High Doping Regime

NASA Astrophysics Data System (ADS)

Wongmanerod, S.; Holtz, P. O.; Reginski, K.; Bugaiski, M.; Monemar, B.

The influence of high Be-acceptor doping on the modulation-doped GaAs/Al0.3Ga0.7As quantum wells structures has been optically studied by using the low-temperature photoluminescence (PL) and photoluminescence excitation (PLE) techniques.The modulation doped samples were grown by the molecular-beam epitaxy technique with a varying Be acceptor concentration ranging from 1×1018 to 8×1018cm-3. Several novels physical effects were observed. The main effect is a significant shift of the main emission towards lower energies as the doping concentrations increase. There are two contradictory mechanisms, which determine the peak energy of the main emission; the shrinkage of the effective bandgap due to many body effects and the reduction of the exciton binding energy due to the carrier screening effect. We conclude that the first one is the dominating effect. At a sufficiently high doping concentration (roughly 2×1018cm-3), the lineshape of the main PL emission is modified, and a new feature, the so called Fermi-edge singularity (FES), appears on the high energy side of the PL emission and exhibits a blue-shift as a function of doping concentration. This feature has been found to be very sensitive to a temperature change, already in the range of 4.4-50K. In addition, PLE spectra with a suitable detection energy show that the absorption edge is blue-shifted with respect to the PL main emission. The resulting Stoke shift is due to phase-space-filling of the carriers, in agreement with the FES interpretation. Finally, we have found from the PLE spectra that the exciton quenching is initiated in the same doping regime. Compared to the exciton quenching in other p-type structures, the critical acceptor concentration required to quench the excitons is significantly lower than in the case of 2D structures with acceptor doping within the well, but larger than in the case of 3D bulk.

Structural, optical, and electrical properties of NiO-In composite films deposited by radio frequency cosputtering

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

Chen, Sheng-Chi, E-mail: chensc@mail.mcut.edu.tw; Wen, Chao-Kuang; Lin, Yu-Chin

2014-03-15

In-doped NiO films with indium concentrations ranging from 0 to 30.3 at. % were deposited on glass substrates to investigate corresponding structural, optical, and electrical property variations. The x-ray diffraction patterns show that all films display only NiO peaks. When In atoms were added to NiO films, the NiO peaks shifted to lower angles, indicating that the lattice parameters of the films increased due to the larger In ions substituting for the smaller Ni ions. An electrical resistivity (ρ) too high to be measured occurred when the indium concentration in the NiO film was less than 15.6 at. %. Themore » ρ value dropped significantly to 0.06 Ω·cm as the indium concentration increased to 26.9 at. %. Upon further raising the In to 30.3 at. %, the ρ value decreased further to 0.01 Ω·cm. All the In-doped NiO films showed n-type conduction. The transmittance of undoped NiO film is as high as 96%. On raising the indium concentration to 15.6, 19.9, 26.9, and 30.3 at. %, the transmittances decreased further to 68%, 62%, 57%, and 47%, respectively. Introducing higher In concentrations improved the films’ thermal stability of electrical resistivity.« less

Doping Attitudes and Covariates of Potential Doping Behaviour in High-Level Team-Sport Athletes; Gender Specific Analysis

PubMed Central

Sekulic, Damir; Tahiraj, Enver; Zvan, Milan; Zenic, Natasa; Uljevic, Ognjen; Lesnik, Blaz

2016-01-01

Team sports are rarely studied with regard to doping behaviour and doping-related factors regardless of their global popularity. This study aimed to investigate doping factors and covariates of potential doping behaviour in high-level team-sport athletes. The subjects were 457 high-performing, national- and international-level athletes (21.9 ± 3.4 years of age; 179 females) involved in volleyball (n = 77), soccer (n = 163), basketball (n = 114) and handball (n = 103). Previously validated self-administered questionnaires aimed at evidencing sport factors, doping-related factors, knowledge on sport nutrition and doping, and attitudes to performance enhancement were used. The results indicated a higher doping likelihood in male athletes, with a significant gender difference for basketball and handball. In males, a higher doping likelihood is found for athletes who had achieved better results at junior-age level, those who regularly consume dietary supplements, and who perceive their sport as being contaminated by doping. A higher sport achievement at senior-age level is protective against potential doping behaviour in males. In females, a higher likelihood of doping is evidenced in those athletes involved in binge drinking, while a lower tendency for doping is evidenced in female athletes who possess better knowledge on sport nutrition. Knowledge about doping is very low and thus education about doping is urgently needed. An improvement of knowledge on sport nutrition might be a potentially effective method for reducing the tendency for doping in females. Future studies should consider other approaches and theories, such as theory of planned behaviour and/or social-cognitive theory, in studying the problem of doping behaviour in team-sports. Key points The doping knowledge among Kosovar team-sport athletes is very low and systematic anti-doping education is urgently needed. The highest risk of doping behaviour in males is found for those athletes who had been successful in their junior age and those who consume dietary supplements. An improvement of knowledge on sport nutrition might be a potentially effective method for reducing the tendency for doping in female team-sport athletes. While the associations between the studied factors and doping behaviour are different between males and females, the gender-specific approach to exploring the covariates of doping behaviour is warranted. PMID:27928206

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.

Genetic algorithm based approach to investigate doped metal oxide materials: Application to lanthanide-doped ceria

NASA Astrophysics Data System (ADS)

Hooper, James; Ismail, Arif; Giorgi, Javier B.; Woo, Tom K.

2010-06-01

A genetic algorithm (GA)-inspired method to effectively map out low-energy configurations of doped metal oxide materials is presented. Specialized mating and mutation operations that do not alter the identity of the parent metal oxide have been incorporated to efficiently sample the metal dopant and oxygen vacancy sites. The search algorithms have been tested on lanthanide-doped ceria (L=Sm,Gd,Lu) with various dopant concentrations. Using both classical and first-principles density-functional-theory (DFT) potentials, we have shown the methodology reproduces the results of recent systematic searches of doped ceria at low concentrations (3.2% L2O3 ) and identifies low-energy structures of concentrated samarium-doped ceria (3.8% and 6.6% L2O3 ) which relate to the experimental and theoretical findings published thus far. We introduce a tandem classical/DFT GA algorithm in which an inexpensive classical potential is first used to generate a fit gene pool of structures to enhance the overall efficiency of the computationally demanding DFT-based GA search.

Efficient Incorporation of Mg in Solution Grown GaN Crystals

NASA Astrophysics Data System (ADS)

Freitas, Jaime A., Jr.; Feigelson, Boris N.; Anderson, Travis J.

2013-11-01

Detailed spectrometry and optical spectroscopy studies carried out on GaN crystals grown in solution detect and identify Mg as the dominant shallow acceptor. Selective etching of crystals with higher Mg levels than that of the donor concentration background indicates that Mg acceptors incorporate preferentially in the N-polar face. Electrical transport measurements verified an efficient incorporation and activation of the Mg acceptors. These results suggest that this growth method has the potential to produce p-type doped epitaxial layers or p-type substrates characterized by high hole concentration and low defect density.

Effect of Er3+ doping on structural, morphological and photocatalytical properties of ZnO thin films

NASA Astrophysics Data System (ADS)

Bouhouche, S.; Bensouici, F.; Toubane, M.; Azizi, A.; Otmani, A.; Chebout, K.; Kezzoula, F.; Tala-Ighil, R.; Bououdina, M.

2018-05-01

In this research work, structure, microstructure, optical and photocatalytic properties of undoped and Erbium doped nanostructured ZnO thin films prepared by sol-gel dip-coating are investigated. X-ray diffraction (XRD) analysis indicates that the deposited films crystallize within the hexagonal wurtzite-type structure with a preferential growth orientation along (002) plane. Morphological observations using scanning electron microscopy (SEM) reveal important influence of Er concentration; displaying homogeneous and dense aspect for undoped to 0.3% then grid-like morphology for 0.4 and 0.5%. UV/vis/NIR transmittance spectroscopy spectra display a transmittance over 70%, and small variation in the energy gap energy 3.263–3.278 eV. Wettability test of ZnO thin films surface ranges from hydrophilic aspect for pure ZnO to hydrophobic one for Er doped ZnO, and the contact angle is found to increase from 58.7° for pure ZnO up to 98.4° for 0.4% Er doped ZnO. The photocatalytic activity measurements evaluated using the degradation of methylene blue (MB) under UV light irradiation demonstrate that undoped ZnO film shows higher photocatalytic activity compared to Er doped ZnO films, which may be attributed to the deterioration of films’crystallinity resulting in lower transmittance.

Processable dodecylbenzene sulfonic acid (DBSA) doped poly(N-vinyl carbazole)-poly(pyrrole) for optoelectronic applications

PubMed Central

Hammed, W. A.; Rahman, M. S.; Mahmud, H. N. M. E.; Yahya, R.; Sulaiman, K.

2017-01-01

Abstract A soluble poly (n-vinyl carbazole)–polypyrrole (PNVC–Ppy) copolymer was prepared through oxidative chemical polymerization wherein dodecyl benzene sulfonic acid (DBSA) was used as a dopant to facilitate polymer-organic solvent interaction and ammonium persulfate (APS) was used as an oxidant. Compared with undoped PNVC–Ppy, the DBSA-doped PNVC–Ppy copolymer showed higher solubility in some selected organic solvents. The composition and structural characteristics of the DBSA-doped PNVC–Ppy were determined by Fourier transform infrared, ultraviolet–visible, and X-ray diffraction spectroscopic methods. Field emission scanning electron microscopic method was employed to observe the morphology of the DBSA-doped PNVC–Ppy copolymer. The electrical conductivity of the DBSA-doped PNVC–Ppy copolymer was measured at room temperature. The conductivity increased with increasing concentration of APS oxidant, and the highest conductivity was recorded at 0.004 mol/dm3 APS at a polymerization temperature of −5 °C. The increased conductivity can be explained by the extended half-life of pyrrole free radical at a lower temperature and a gradual increase in chain length over a prolonged time due to the slow addition of APS. Furthermore, the obtained soluble copolymer exhibits unique optical and thermal properties different from those of PNVC and Ppy. PMID:29491808

Cubic to tetragonal phase transition of Tm{sup 3+} doped nanocrystals in oxyfluoride glass ceramics

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

Li, Yiming; Fu, Yuting; Shi, Yahui

2016-02-15

Tm{sup 3+} ions doped β-PbF{sub 2} nanocrystals in oxyfluoride glass ceramics with different doping concentrations and thermal temperatures are prepared by a traditional melt-quenching and thermal treatment method to investigate the structure and the phase transition of Tm{sup 3+} doped nanocrystals. The structures are characterized by X-ray diffraction Rietveld analysis and confirmed with numerical simulation. The phase transitions are proved further by the emission spectra. Both of the doping concentration and thermal temperature can induce an O{sub h} to D{sub 4h} site symmetry distortion and a cubic to tetragonal phase transition. The luminescence of Tm{sup 3+} doped nanocrystals at 800more » nm was modulated by the phase transition of the surrounding crystal field.« less

Structural and luminescence properties of self-yellow emitting undoped and (Ca, Ba, Sr)-doped Zn2V2O7 phosphors synthesized by combustion method

NASA Astrophysics Data System (ADS)

Foka, Kewele E.; Dejene, Birhanu F.; Koao, Lehlohonolo F.; Swart, Hendrik C.

2018-04-01

A self-activated yellow emitting Zn2V2O7 was synthesized by combustion method. The influence of the processing parameters such as synthesis temperature and dopants concentration on the structure, morphology and luminescence properties was investigated. The X-ray diffraction (XRD) analysis confirmed that the samples have a tetragonal structure and no significant structural change was observed in varying both the synthesis temperature and the dopants concentration. The estimated average crystallite size was 78 nm for the undoped samples synthesized at different temperatures and 77 nm for the doped samples. Scanning electron microscope (SEM) images showed agglomerated hexagonal-shaped particles with straight edges at low temperatures and the shape of the particles changed to cylindrical structures at moderate temperatures. At higher temperatures, the morphology changed completely. However, the morphologies of the doped samples looked alike. The photoluminescence (PL) of the product exhibited broad emission bands ranging from 400 to 800 nm. The best luminescence intensity was observed for the undoped Zn2V2O7 samples and those synthesized at 600 ℃ . Any further increase in synthesis temperature, type and concentration of dopants led to a decrease in the luminescence intensity. The broad band emission peak of Zn2V2O7 consisted of two broad bands corresponding to emissions from the Em1 (3T2→1A1) and Em2 (3T1→1A1) transitions.

Defect engineering of complex semiconductor alloys: Cu2-2xMxO1-yXy

NASA Astrophysics Data System (ADS)

Lany, Stephan; Stevanovic, Vladan

2013-03-01

The electrical properties of semiconductors are generally controlled via doping, i.e., the incorporation of dilute concentrations of aliovalent impurity atoms, whereas the band structure properties (gap, effective masses, optical properties) are manipulated by alloying, i.e., the incorporation of much larger amounts of isovalent elements. Theoretical approaches usually address either doping or alloying, but rarely both problems at the same time. By combining defect supercell calculations, GW quasi-particle energy calculation, and thermodynamic modeling, we study the range of electrical and band structure properties accessible by alloying aliovalent cations (M = Mg, Zn, Cd) and isovalent anions (X = S, Se) in Cu2O. In order to extend dilute defect models to higher concentrations, we take into account the association/dissociation of defect pairs and complexes, as well as the composition dependence of the band gap and the band edge energies. Considering a composition window for the Cu2-2xMxO1-yXy alloys of 0 <= (x,y) <= 0.2, we predict a wide range of possible band gaps from 1.7 to 2.6 eV, and net doping concentrations between p = 1019 cm-3 and n = 1017cm-3, notably achieving type conversion from p- to n-type at Zn or Cd compositions around x = 0.1. This work is supported as part of the SunShot initiative by the U. S. Department of Energy, Office of Energy Efficiency and Renewable Energy under Contract No. DE-AC36-08GO28308 to NREL.

A clear effect of charge compensation through Na+ co-doping on the luminescence spectra and decay kinetics of Nd3+-doped CaAl4O7

NASA Astrophysics Data System (ADS)

Puchalska, M.; Watras, A.

2016-06-01

We present a detailed analysis of luminescence behavior of singly Nd3+ doped and Nd3+, Na+ co-doped calcium aluminates powders: Ca1-xNdxAl4O7 and Ca1-2xNdxNaxAl4O7 (x=0.001-0.1). Relatively intense Nd3+ luminescence in IR region corresponding to typical 4F3/2→4IJ (J=9/2-13/2) transitions with maximum located at about 1079 nm was obtained in all samples on direct excitation into f-f levels. The effect of dopant concentration and charge compensation by co-doping with Na+ ions on morphology and optical properties were studied. The results show that both, the Nd3+ concentration and the alkali metal co-doping affected the optical properties but had no influence on the powders morphology. The studies of luminescence spectra (298 and 77 K) in a function of dopant concentration showed an increasing distortion of the local symmetry of Nd3+with raising activator content due to certain defects created in the crystal lattice. On the other hand Na+ addition led to significant narrowing of absorption and luminescence bands and also a reduction of the number of their components, showing smaller disturbance of Nd3+ ions local symmetries. Consequently, charge compensated by Na+ co-doping materials showed significantly enhanced Nd3+ luminescence. The decrease of emission intensity and luminescence lifetimes with increase of activator concentration was attributed mainly to phonon-assisted cross-relaxation processes between Nd3+ ions. Analysis with Inokuti-Hirayama model indicated dipole-dipole mechanism of ion-ion interaction. Na+ addition led to much smaller concentration quenching due to smaller clustering of dopant ions in CaAl4O7 lattice.

Characterization of n-Type and p-Type Long-Wave InAs/InAsSb Superlattices

NASA Astrophysics Data System (ADS)

Brown, A. E.; Baril, N.; Zuo, D.; Almeida, L. A.; Arias, J.; Bandara, S.

2017-09-01

The influence of dopant concentration on both in-plane mobility and minority carrier lifetime in long-wave infrared InAs/InAsSb superlattices (SLs) was investigated. Unintentially doped ( n-type) and various concentrations of Be-doped ( p-type) SLs were characterized using variable-field Hall and photoconductive decay techniques. Minority carrier lifetimes in p-type InAs/InAsSb SLs are observed to decrease with increasing carrier concentration, with the longest lifetime at 77 K determined to be 437 ns, corresponding to a measured carrier concentration of p 0 = 4.1 × 1015 cm-3. Variable-field Hall technique enabled the extraction of in-plane hole, electron, and surface electron transport properties as a function of temperature. In-plane hole mobility is not observed to change with doping level and increases with reducing temperature, reaching a maximum at the lowest temperature measured of 30 K. An activation energy of the Be-dopant is determined to be 3.5 meV from Arrhenius analysis of hole concentration. Minority carrier electrons populations are suppressed at the highest Be-doping levels, but mobility and concentration values are resolved in lower-doped samples. An average surface electron conductivity of 3.54 × 10-4 S at 30 K is determined from the analysis of p-type samples. Effects of passivation treatments on surface conductivity will be presented.

The Radar Effects of Perchlorate-Doped Ice in the Martian Polar Layered Deposits

NASA Astrophysics Data System (ADS)

Stillman, D.; Winebrenner, D. P.; Grimm, R. E.; Pathare, A.

2010-12-01

The presence of perchlorate in soil at near-polar latitudes on Mars suggests that dust in the ice of the North Polar Layered Deposits (NPLD) may introduce perchlorate impurities to that ice. Because eutectic temperatures of perchlorate salts range as low as 206 K (for magnesium perchlorate), perchlorate doping of NPLD ice may result in grain-scale liquid veins and softening of ice rheology at temperatures comparable to those computed for the base of the NPLD in the present climate. Any such softening would be important for understanding how processes including ice flow have shaped the NPLD. Observable consequences of such softening, or of the combination of perchlorate doping and temperatures that could cause softening, are thus similarly important. In particular, the dielectric properties of perchlorate-laden ice in a temperature gradient will change relatively rapidly at the point in the gradient near the eutectic temperature. Here we investigate the radar reflectivity of such a eutectic transition in ice with a model in which perchlorate concentration is constant and temperature varies linearly with depth in the ice. We have conducted measurements of the complex permittivity of Mg and Na perchlorate-doped ice over a range of temperatures (183 - 273 K) and concentrations. Below the eutectic temperature, the perchlorate-doped ice has electrical properties similar to that of choride-doped ice. However, above the eutectic temperature, some of the ice melts forming liquid at triple junctions. At concentrations above 3 mM, the liquid at triple junctions become connected forming brine channels, which greatly increase the dc conductivity and radar attenuation. At concentrations below 3 mM, the liquid at triple junctions are not connected and do not affect the dc conductivity. However, the liquid H2O molecules are able to rotate their permanent dipole at radar frequencies, thus causing an increase in radar attenuation. The MARSIS and SHARAD attenuation rates increase with temperature as the strength of the loss increases with a greater amount of liquid water even though the relaxation frequency (maximum loss) shifts to higher frequencies. We combine our electrical property measurements with a model for radar reflection from a continuously-varying dielectric profile. Because the change in permittivity occurs over a range of depths depending on the value of the temperature gradient, radar detectability of the eutectic transition depends on the radar frequency as well as gradient and concentration values. We compute expected radar echo strengths for MARSIS and SHARAD and depths relative to the bed at which transitions may be expected, to address whether information of direct rheological relevance may be available from those instruments.

A Brown Mesoporous TiO2-x /MCF Composite with an Extremely High Quantum Yield of Solar Energy Photocatalysis for H2 Evolution.

PubMed

Xing, Mingyang; Zhang, Jinlong; Qiu, Bocheng; Tian, Baozhu; Anpo, Masakazu; Che, Michel

2015-04-24

A brown mesoporous TiO2-x /MCF composite with a high fluorine dopant concentration (8.01 at%) is synthesized by a vacuum activation method. It exhibits an excellent solar absorption and a record-breaking quantum yield (Φ = 46%) and a high photon-hydrogen energy conversion efficiency (η = 34%,) for solar photocatalytic H2 production, which are all higher than that of the black hydrogen-doped TiO2 (Φ = 35%, η = 24%). The MCFs serve to improve the adsorption of F atoms onto the TiO2 /MCF composite surface, which after the formation of oxygen vacancies by vacuum activation, facilitate the abundant substitution of these vacancies with F atoms. The decrease of recombination sites induced by high-concentration F doping and the synergistic effect between lattice Ti(3+)-F and surface Ti(3+)-F are responsible for the enhanced lifetime of electrons, the observed excellent absorption of solar light, and the photocatalytic production of H2 for these catalysts. The as-prepared F-doped composite is an ideal solar light-driven photocatalyst with great potential for applications ranging from the remediation of environmental pollution to the harnessing of solar energy for H2 production. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Temperature independent quantum well FET with delta channel doping

NASA Technical Reports Server (NTRS)

Young, P. G.; Mena, R. A.; Alterovitz, S. A.; Schacham, S. E.; Haugland, E. J.

1992-01-01

A temperature independent device is presented which uses a quantum well structure and delta doping within the channel. The device requires a high delta doping concentration within the channel to achieve a constant Hall mobility and carrier concentration across the temperature range 300-1.4 K. Transistors were RF tested using on-wafer probing and a constant G sub max and F sub max were measured over the temperature range 300-70 K.

Altering properties of cerium oxide thin films by Rh doping

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

Ševčíková, Klára, E-mail: klarak.sevcikova@seznam.cz; NIMS Beamline Station at SPring-8, National Institute for Materials Science, Sayo, Hyogo 679-5148; Nehasil, Václav, E-mail: nehasil@mbox.troja.mff.cuni.cz

2015-07-15

Highlights: • Thin films of ceria doped by rhodium deposited by RF magnetron sputtering. • Concentration of rhodium has great impact on properties of Rh–CeO{sub x} thin films. • Intensive oxygen migration in films with low concentration of rhodium. • Oxygen migration suppressed in films with high amount of Rh dopants. - Abstract: Ceria containing highly dispersed ions of rhodium is a promising material for catalytic applications. The Rh–CeO{sub x} thin films with different concentrations of rhodium were deposited by RF magnetron sputtering and were studied by soft and hard X-ray photoelectron spectroscopies, Temperature programmed reaction and X-ray powder diffractionmore » techniques. The sputtered films consist of rhodium–cerium mixed oxide where cerium exhibits a mixed valency of Ce{sup 4+} and Ce{sup 3+} and rhodium occurs in two oxidation states, Rh{sup 3+} and Rh{sup n+}. We show that the concentration of rhodium has a great influence on the chemical composition, structure and reducibility of the Rh–CeO{sub x} thin films. The films with low concentrations of rhodium are polycrystalline, while the films with higher amount of Rh dopants are amorphous. The morphology of the films strongly influences the mobility of oxygen in the material. Therefore, varying the concentration of rhodium in Rh–CeO{sub x} thin films leads to preparing materials with different properties.« less

The steady-state and transient electron transport within bulk zinc-blende indium nitride: The impact of crystal temperature and doping concentration variations

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

Siddiqua, Poppy; O'Leary, Stephen K., E-mail: stephen.oleary@ubc.ca

2016-03-07

Within the framework of a semi-classical three-valley Monte Carlo electron transport simulation approach, we analyze the steady-state and transient aspects of the electron transport within bulk zinc-blende indium nitride, with a focus on the response to variations in the crystal temperature and the doping concentration. We find that while the electron transport associated with zinc-blende InN is highly sensitive to the crystal temperature, it is not very sensitive to the doping concentration selection. The device consequences of these results are then explored.

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

Ogedengbe, O. S.; Swartz, C. H.; Jayathilaka, P. A. R. D.

Here, iodine-doped CdTe and Cd 1-xMg xTe layers were grown by molecular beam epitaxy. Secondary ion mass spectrometry characterization was used to measure dopant concentration, while Hall measurement was used for determining carrier concentration. Photoluminescence intensity and time-resolved photoluminescence techniques were used for optical characterization. Maximum n-type carrier concentrations of 7.4 x 10 18 cm -3 for CdTe and 3 x 10 17 cm -3 for Cd 0.65Mg 0.35Te were achieved. Studies suggest that electrically active doping with iodine is limited with dopant concentration much above these values. Dopant activation of about 80% was observed in most of the CdTemore » samples. The estimated activation energy is about 6 meV for CdTe and the value for Cd 0.65Mg 0.35Te is about 58 meV. Iodine-doped samples exhibit long lifetimes with no evidence of photoluminescence degradation with doping as high as 2 x 10 18 cm -3, while indium shows substantial non-radiative recombination at carrier concentrations above 5 x 10 16 cm -3. Iodine was shown to be thermally stable in CdTe at temperatures up to 600 °C. Results suggest iodine may be a preferred n-type dopant compared to indium in achieving heavily doped n-type CdTe.« less

The optoelectronic properties and role of Cu concentration on the structural and electrical properties of Cu doped ZnO nanoparticles

NASA Astrophysics Data System (ADS)

Omri, K.; Bettaibi, A.; Khirouni, K.; El Mir, L.

2018-05-01

In the current study, we synthesized a Cu-doped ZnO (CZO) nanoparticles material using a sol-gel method with different doping concentrations of Cu (0, 2, 3 and 4 at.%). The control of the Cu concentration on structural, electrical and optical properties of CZO nanoparticles was investigated in detail. The XRD analysis of the CZO nanoparticles reveals the formation of ZnO hexagonal wurtzite structure for all samples which confirm the incorporation of Cu2+ ions into the ZnO lattice by substitution. Furthermore, CZO nanoparticles showed a small red shift of absorption band with the incorporation of Cu from 0 to 4 at.%; i.e. a decreased band gap value from 3.34 eV to 3.27 eV with increasing of Cu doping content. The frequency dispersion of the electric conductivity were studied using the Jonscher universal power law, according to relation σ(ω) = σDC + A ωs(T). Alternative current conductivity increases with increasing Cu content in spite of the decrease the activation energy with copper loading. It was found that the conductivity reached its maximum value for critical Cu concentration of 3 at.%. The frequency relaxation phenomenon was also investigated and all results were discussed in term of the copper doping concentration.

Correlating optical infrared and electronic properties of low tellurium doped GaSb bulk crystals

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

Roodenko, K., E-mail: kroodenko@intelliepi.com; Liao, P.-K.; Lan, D.

2016-04-07

Control over the Te doping concentration is especially challenging in the mass-production of optically transparent, high-resistivity Te-doped GaSb crystals. Driven by the necessity to perform fast, robust, and non-destructive quality control of the Te doping homogeneity of the optically transparent large-diameter GaSb wafers, we correlated electronic and optical infrared properties of Te-doped GaSb crystals. The study was based on the experimental Hall and Fourier-Transform Infrared (FTIR) data collected from over 50 samples of the low-doped n-type material (carrier concentration of 6 × 10{sup 16} cm{sup −3} to 7 × 10{sup 17} cm{sup −3}) and the Te-doped p-type GaSb (4.6 ×more » 10{sup 15} cm{sup −3} to 1 × 10{sup 16} cm{sup −3}). For the n-type GaSb, the analysis of the FTIR data was performed using free carrier absorption model, while for the p-type material, the absorption was modeled using inter-valence band absorption mechanism. Using the correlation between the Hall and the IR data, FTIR maps across the wafers allow a fast and reliable way to estimate carrier concentration profile within the wafer.« less

Zn doped CdO thin films with enhanced linear and third order nonlinear optical properties for optoelectronic applications

NASA Astrophysics Data System (ADS)

Bairy, Raghavendra; Jayarama, A.; Shivakumar, G. K.; Patil, P. S.; Bhat, K. Udaya

2018-04-01

Thin films of undoped and zinc doped CdO have been deposited on glass substrate using spray pyrolysis technique with various dopant concentrations of Zn such as 1, 5 and 10%. Influence of Zn doping on CdO thin films for the structural, morphological, optical and nonlinear optical properties are reported. XRD analysis reveals that as prepared pure and Zn doped CdO films show polycrystalline nature with face centered cubic structure. Also, Zn doping does not significantly modify the crystallinity and not much increase in the crystallite size of the film. SEM images shows grains which are uniform and grain size with increase in dopant concentration. The transmittance of the prepared CdO films recorded in the UV visible spectra and it shows 50 to 60% in the visible region. The estimated optical band gap increases from 2.60 to 2.70 eV for various dopant concentrations. The nonlinear optical absorption of Zn-doped CdO films have been measured used the Z-scan technique at a wavelength 532 nm. The nonlinear optical absorption coefficient (β), nonlinear refractive index (n2) and the third order nonlinear optical susceptibility (χ(3)) of the pure and Zn doped films were determined.

Structural and electrical properties of Ge-on-Si(0 0 1) layers with ultra heavy n-type doping grown by MBE

NASA Astrophysics Data System (ADS)

Yurasov, D. V.; Antonov, A. V.; Drozdov, M. N.; Yunin, P. A.; Andreev, B. A.; Bushuykin, P. A.; Baydakova, N. A.; Novikov, A. V.

2018-06-01

In this paper we report about the formation of ultra heavy doped n-Ge layers on Si(0 0 1) substrates by molecular beam epitaxy and their characterization by different independent techniques. Combined study of structural and electrical properties of fabricated layers using secondary ion mass spectroscopy, X-ray diffraction, Hall effect and reflection measurements was carried out and it has revealed the achievable charge carrier densities exceeding 1020 cm-3 without deterioration of crystalline quality of such doped layers. It was also shown that X-ray analysis can be used as a fast, reliable and non-destructive method for evaluation of the electrically active Sb concentration in heavy doped Ge layers. The appropriate set of doping density allowed to adjust the plasmonic resonance position in Ge:Sb layers in a rather wide range reaching the wavelength of 3.6 μm for the highest doping concentration. Room temperature photoluminescence confirmed the high crystalline quality of such doped layers. Our results indicated the attainability of high electron concentration in Ge:Sb layers grown on Si substrates without crystalline quality deterioration which may find potential applications in the fields of Si-based photonics and mid-IR plasmonics.

A novel approach for the improvement of electrostatic behaviour of physically doped TFET using plasma formation and shortening of gate electrode with hetero-gate dielectric

NASA Astrophysics Data System (ADS)

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

2018-04-01

This article presents a new device configuration to enhance current drivability and suppress negative conduction (ambipolar conduction) with improved RF characteristics of physically doped TFET. Here, we used a new approach to get excellent electrical characteristics of hetero-dielectric short gate source electrode TFET (HD-SG SE-TFET) by depositing a metal electrode of 5.93 eV work function over the heavily doped source (P+) region. Deposition of metal electrode induces the plasma (thin layer) of holes under the Si/HfO2 interface due to work function difference of metal and semiconductor. Plasma layer of holes is advantageous to increase abruptness as well as decrease the tunneling barrier at source/channel junction for attaining higher tunneling rate of charge carriers (i.e., electrons), which turns into 86.66 times higher ON-state current compared with the conventional physically doped TFET (C-TFET). Along with metal electrode deposition, gate electrode is under-lapped for inducing asymmetrical concentration of charge carriers in the channel region, which is helpful for widening the tunneling barrier width at the drain/channel interface. Consequently, HD-SG SE-TFET shows suppression of ambipolar behavior with reduction in gate-to-drain capacitance which is beneficial for improvement in RF performance. Furthermore, the effectiveness of hetero-gate dielectric concept has been used for improving the RF performance. Furthermore, reliability of C-TFET and proposed structures has been confirmed in term of linearity.

Improved efficiency in blue phosphorescent organic light-emitting diodes by the stepwise doping structure

NASA Astrophysics Data System (ADS)

Yang, Liping; Wang, Xiaoping; Kou, Zhiqi; Ji, Changyan

2017-04-01

The electro-optical properties of the blue phosphorescent organic light-emitting diodes (PHOLEDs) can be affected by the stepwise doping structure in the emitting layer (EML). A series of multi-EML devices with different doping concentration of blue dopant (FIrpic) are fabricated. The effect of the stepwise doping structure close to the electron transport layer is more obvious than that close to the hole transport layer. When the doping concentration increases gradually from the hole injection side to the electron injection side, the maximum values of the luminance, current and power efficiency can reach to 9745 cd/m2 (at 9 V), 32.0 cd/A and 25.1 lm/W in the device with the asymmetric tri-EML structure, which is improved by about 10% compared with that in the bi-EML device. When the number of the EML is four, the performance of the device becomes worse because of the interface effect resulting from different concentration of dopant.

N-type molecular electrical doping in organic semiconductors: formation and dissociation efficiencies of charge transfer complex

NASA Astrophysics Data System (ADS)

Kim, Jae-Min; Yoo, Seung-Jun; Moon, Chang-Ki; Sim, Bomi; Lee, Jae-Hyun; Lim, Heeseon; Kim, Jeong Won; Kim, Jang-Joo

2016-09-01

Electrical doping is an important method in organic electronics to enhance device efficiency by controlling Fermi level, increasing conductivity, and reducing injection barrier from electrode. To understand the charge generation process of dopant in doped organic semiconductors, it is important to analyze the charge transfer complex (CTC) formation and dissociation into free charge carrier. In this paper, we correlate charge generation efficiency with the CTC formation and dissociation efficiency of n-dopant in organic semiconductors (OSs). The CTC formation efficiency of Rb2CO3 linearly decreases from 82.8% to 47.0% as the doping concentration increases from 2.5 mol% to 20 mol%. The CTC formation efficiency and its linear decrease with doping concentration are analytically correlated with the concentration-dependent size and number of dopant agglomerates by introducing the degree of reduced CTC formation. Lastly, the behavior of dissociation efficiency is discussed based on the picture of the statistical semiconductor theory and the frontier orbital hybridization model.

Increased p-type conductivity through use of an indium surfactant in the growth of Mg-doped GaN

NASA Astrophysics Data System (ADS)

Kyle, Erin C. H.; Kaun, Stephen W.; Young, Erin C.; Speck, James S.

2015-06-01

We have examined the effect of an indium surfactant on the growth of p-type GaN by ammonia-based molecular beam epitaxy. p-type GaN was grown at temperatures ranging from 700 to 780 °C with and without an indium surfactant. The Mg concentration in all films in this study was 4.5-6 × 1019 cm-3 as measured by secondary ion mass spectroscopy. All p-type GaN films grown with an indium surfactant had higher p-type conductivities and higher hole concentrations than similar films grown without an indium surfactant. The lowest p-type GaN room temperature resistivity was 0.59 Ω-cm, and the highest room temperature carrier concentration was 1.6 × 1018 cm-3. Fits of the temperature-dependent carrier concentration data showed a one to two order of magnitude lower unintentional compensating defect concentration in samples grown with the indium surfactant. Samples grown at higher temperature had a lower active acceptor concentration. Improvements in band-edge luminescence were seen by cathodoluminescence for samples grown with the indium surfactant, confirming the trends seen in the Hall data.

Growth and properties of oxygen- and ion-doped Bi2Sr2CaCu2O8+δ single crystals

NASA Astrophysics Data System (ADS)

Mitzi, D. B.; Lombardo, L. W.; Kapitulnik, A.; Laderman, S. S.; Jacowitz, R. D.

1990-04-01

A directional solidification method for growing large single crystals in the Bi2Sr2CaCu2O8+δ system is reported. Ion doping, with replacement of La for Sr and Y for Ca, as well as oxygen doping in these crystals has been explored. Doped and undoped crystals have been characterized using microprobe analysis, x-ray diffraction, thermogravimetric analysis, and magnetic and Hall measurements. Ion doping results in little change of the superconducting transition for substitution levels below 20-25%, while beyond this level the Meissner signal broadens and the low-temperature Meissner signal decreases. Microprobe analysis and x-ray diffraction performed on these more highly substituted single crystals provide evidence for inhomogeneity and phase segregation into regions of distinct composition. Annealing unsubstituted crystals in increasing partial pressures of oxygen reversibly depresses the superconducting transition temperature from 90 (as made) to 77 K (oxygen pressure annealed), while the carrier concentrations, as determined from Hall effect measurements, increase from n=3.1(3)×1021 cm-3 (0.34 holes per Cu site) to 4.6(3)×1021 cm-3 (0.50 holes per Cu site). No degradation of the Meissner transition or other indications of inhomogeneity or phase segregation with doping are noted, suggesting that oxygen-doped Bi2Sr2CaCu2O8+δ is a suitable system for pursuing doping studies. The decrease in Tc with concentration for 0.34<=n<=0.50 indicates that a high-carrier-concentration regime exists in which Tc decreases with n and suggests that this decrease does not arise from material inhomogeneity or other materials problems. An examination of the variation of Tc with the density of states and lattice constants for all of the doped and undoped superconducting samples considered here indicates that changes in Tc with doping are primarily affected by changes in the density of states (or carrier concentration) rather than by structural variation induced by the doping.

Study on luminescence characteristics of blue OLED with phosphor-doped host-guest structure

NASA Astrophysics Data System (ADS)

Wang, Zhen; Liu, Fei; Zheng, Xin; Chen, Ai; Xie, Jia-feng; Zhang, Wen-xia

2018-05-01

In this study, we design and fabricate phosphor-doped host-guest structure organic light-emitting diodes (OLEDs), where the blue-ray iridium complex electrophosphorescent material FIrpic acts as object material. Properties of the device can be accommodated by changing the host materials, dopant concentration and thickness of the light-emitting layer. The study shows that the host material N,N'-dicarbazolyl-3,5-benzene (mCP) has a higher triplet excited state energy level, which can effectively prevent FIrpic triplet excited state energy backtracking to host material, thus the luminous efficiency is improved. When mCP is selected as the host material, the thickness of the light-emitting layer is 30 nm and the dopant concentration is 8 wt%, the excitons can be effectively confined in the light-emitting region. As a result, the maximum current efficiency and the maximum brightness of the blue device can reach 15.5 cd/A and 7 196.3 cd/m2, respectively.

Ultra-Thin Monocrystalline Silicon Solar Cell with 12.2% Efficiency Using Silicon-On-Insulator Substrate.

PubMed

Bian, Jian-Tao; Yu, Jian; Duan, Wei-Yuan; Qiu, Yu

2015-04-01

Single side heterojunction silicon solar cells were designed and fabricated using Silicon-On-Insulator (SOI) substrate. The TCAD software was used to simulate the effect of silicon layer thickness, doping concentration and the series resistance. A 10.5 µm thick monocrystalline silicon layer was epitaxially grown on the SOI with boron doping concentration of 2 x 10(16) cm(-3) by thermal CVD. Very high Voc of 678 mV was achieved by applying amorphous silicon heterojunction emitter on the front surface. The single cell efficiency of 12.2% was achieved without any light trapping structures. The rear surface recombination and the series resistance are the main limiting factors for the cell efficiency in addition to the c-Si thickness. By integrating an efficient light trapping scheme and further optimizing fabrication process, higher efficiency of 14.0% is expected for this type of cells. It can be applied to integrated circuits on a monolithic chip to meet the requirements of energy autonomous systems.

Optical absorption and thermally stimulated depolarization current studies of nickel chloride-doped poly(vinyl alcohol) irradiated with low-level fast neutron doses

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

Abd El-Kader, F.H.; Ibrahim, S.S.; Attia, G.

1993-11-15

The influence of neutron irradiation on ultraviolet/visible absorption and thermally stimulated depolarization current in nickel chloride-poly(vinyl alcohol) (PVA) cast films has been investigated. The spectral measurements indicate the responsibility of the Ni[sup 2][sup +] ion in its octahedral symmetry. Dopant concentrations higher than 10 wt % NiCl[sub 2] are found to make the samples more resistant to a degradation effect caused by neutron irradiation. The thermally stimulated depolarization currents (TSDC) of pure PVA revealed the existence of the glass transition T[sub g] and space charge relaxation peaks, whereas doped-PVA samples show a new sub-T[sub g] relaxation peak. A proposed mechanismmore » is introduced to account for the neutron effects on both glass transition and space charge relaxation peaks. The peak positions, peak currents, and stored charges of the sub-T[sub g] relaxation peak are strongly affected by both the concentration of the dopant and neutron exposure doses.« less

Influence of TiO2 Nanoparticles on Growth and Phenolic Compounds Production in Photosynthetic Microorganisms

PubMed Central

Comotto, Mattia; Casazza, Alessandro Alberto; Aliakbarian, Bahar; Caratto, Valentina; Ferretti, Maurizio; Perego, Patrizia

2014-01-01

The influence of titanium dioxide nanoparticles (pure anatase and 15% N doped anatase) on the growth of Chlorella vulgaris, Haematococcus pluvialis, and Arthrospira platensis was investigated. Results showed that pure anatase can lead to a significant growth inhibition of C. vulgaris and A. platensis (17.0 and 74.1%, resp.), while for H. pluvialis the nanoparticles do not cause a significant inhibition. Since in these stress conditions photosynthetic microorganisms can produce antioxidant compounds in order to prevent cell damages, we evaluated the polyphenols content either inside the cells or released in the medium. Although results did not show a significant difference in C. vulgaris, the phenolic concentrations of two other microorganisms were statistically affected by the presence of titanium dioxide. In particular, 15% N doped anatase resulted in a higher production of extracellular antioxidant compounds, reaching the concentration of 65.2 and 68.0 mg gDB −1 for H. pluvialis and A. platensis, respectively. PMID:25610914

Chemometric study on the electrochemical incineration of diethylenetriaminepentaacetic acid using boron-doped diamond anode.

PubMed

Xian, Jiahui; Liu, Min; Chen, Wei; Zhang, Chunyong; Fu, Degang

2018-05-01

The electrochemical incineration of diethylenetriaminepentaacetic acid (DTPA) with boron-doped diamond (BDD) anode had been initially performed under galvanostatic conditions. The main and interaction effects of four operating parameters (flow rate, applied current density, sulfate concentration and initial DTPA concentration) on mineralization performance were investigated. Under similar experimental conditions, Doehlert matrix (DM) and central composite rotatable design (CCRD) were used as statistical multivariate methods in the optimization of the anodic oxidation processes. A comparison between DM model and CCRD model revealed that the former was more accurate, possibly due to its higher operating level numbers employed (7 levels for two variables). Despite this, these two models resulted in quite similar optimum operating conditions. The maximum TOC removal percentages at 180 min were 76.2% and 73.8% for case of DM and CCRD, respectively. In addition, with the aid of quantum chemistry calculation and LC/MS analysis, a plausible degradation sequence of DTPA on BDD anode was also proposed. Copyright © 2018 Elsevier Ltd. All rights reserved.

Effect of oxygen vacancy distribution on the thermoelectric properties of La-doped SrTiO3 epitaxial thin films

NASA Astrophysics Data System (ADS)

Sarath Kumar, S. R.; Abutaha, A. I.; Hedhili, M. N.; Alshareef, H. N.

2012-12-01

A detailed study of the role of oxygen vacancies in determining the effective mass and high temperature (300-1000 K) thermoelectric properties of La-doped epitaxial SrTiO3 thin films is presented. It is observed that at intermediate temperatures, a transition from degenerate to non-degenerate behavior is observed in the Seebeck coefficient, but not electrical conductivity, which is attributed to heterogeneous oxygen non-stoichiometry. Heikes formula is found to be invalid for the films with oxygen vacancies. By fitting the spectroscopic ellipsometry (SE) data, obtained in the range 300-2100 nm, using a Drude-Lorentz dispersion relation with two Lorentz oscillators, the electrical and optical properties of the films are extracted. Using the excellent agreement between the transport properties extracted from SE modeling and direct electrical measurements, we demonstrate that an increase in concentration of oxygen vacancies results in a simultaneous increase of both carrier concentration and electron effective mass, resulting in a higher power factor.

Studying Structural, Optical, Electrical, and Sensing Properties of Nanocrystalline SnO2:Cu Films Prepared by Sol-Gel Method for CO Gas Sensor Application at Low Temperature

NASA Astrophysics Data System (ADS)

Al-Jawad, Selma M. H.; Elttayf, Abdulhussain K.; Saber, Amel S.

Nanocrystalline SnO2 and SnO2:Cu thin films derived from SnCl2ṡ2H2O precursors have been prepared on glass substrates using sol-gel dip-coating technique. The deposited film was 300±20nm thick and the films were annealed in air at 500∘C for 1h. Structural, optical and sensing properties of the films were studied under different preparation conditions, such as Cu-doping concentration of 2%, 4% and 6wt.%. X-ray diffraction studies show the polycrystalline nature with tetragonal rutile structure of SnO2 and Cu:SnO2 thin films. The films have highly preferred orientation along (110). The crystallite size of the prepared samples reduced with increasing Cu-doping concentrations and the addition of Cu as dopants changed the structural properties of the thin films. Surface morphology was determined through scanning electron microscopy and atomic force microscopy. Results show that the particle size decreased as doping concentration increased. The films have moderate optical transmission (up to 82.4% at 800nm), and the transmittance, absorption coefficient and energy gap at different Cu-doping concentration were measured and calculated. Results show that Cu-doping decreased the transmittance and energy gap whereas it increased the absorption coefficient. Two peaks were noted with Cu-doping concentration of 0-6wt.%; the first peak was positioned exactly at 320nm ultraviolet emission and the second was positioned at 430-480nm. Moreover, emission bands were noticed in the photoluminescence spectra of Cu:SnO2. The electrical properties of SnO2 films include DC electrical conductivity, showing that the films have two activation energies, namely, Ea1 and Ea2, which increase as Cu-doping concentration increases. Cudoped nanocrystalline SnO2 gas-sensing material has better sensitivity to CO gas compared with pure SnO2.

Strong far-infrared intersubband absorption under normal incidence in heavily n-type doped nonalloy GaSb-AlSb superlattices

NASA Technical Reports Server (NTRS)

Samoska, L. A.; Brar, Berinder; Kroemer, H.

1993-01-01

We report on long-wavelength intersubband absorption under normal incidence in heavily doped binary-binary GaSb-AlSb superlattices. Due to a small energy difference between the ellipsoidal L valleys in GaSb and the low-density-of-states Gamma minimum, electrons spill over from the first Gamma subband into the higher-energy L subband in GaSb wells, where they are allowed to make an intersubband transition under normally incident radiation. A peak fractional absorption per quantum well of 6.8 x 10 exp 3 (absorption coefficient alpha of about 8500/cm) is observed at about 15 microns wavelength for a sheet concentration of 1.6 x 10 exp 12 sq cm/well.

Structural and optical properties of chromium doped zinc oxide nanoparticles synthesized by sol-gel method

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

Naqvi, Syed Mohd. Adnan, E-mail: adiaks2004@yahoo.co.in; Irshad, Kashif, E-mail: alig.kashif@gmail.com; Soleimani, Hassan, E-mail: hassan.soleimani@petronas.com.my, E-mail: noorhana-yahya@petronas.com.my

2014-10-24

Nanosized Cr-doped ZnO nano particles were synthesized by facile sol-gel auto combustion method. The structural and optical properties of Cr-doped ZnO nanoparticles have been investigated by XRD and UV-Vis spectroscopy at room temperature for 0% to 8% concentration. X-ray diffraction analysis reveals that the Cr-doped ZnO crystallizes in a single phase polycrystalline nature with wurtzite lattice. With every % of doping, the peaks are shifting scarcely and doping of Cr is possible up to 7%. After that, the last peak vanishes, that signifies its structure is transmuted from 8% doping. The average crystallite size decreases with increase in Cr concentrationmore » (i.e. 28.9 nm for 0% to 25.8 nm for 8%). The UV-Vis spectra of the nanoparticles betoken an incrementation in the band gap energy from 3.401, 3.415, 3.431, 3.437,3.453, 3.514,3.521, 3.530 and 3.538 eV respectively, for 0,1, 2, 3, 4, 5, 6, 7 and 8 % doping concentration.« less

Tuning Superconductivity in FeSe Thin Films via Magnesium Doping.

PubMed

Qiu, Wenbin; Ma, Zongqing; Liu, Yongchang; Shahriar Al Hossain, Mohammed; Wang, Xiaolin; Cai, Chuanbing; Dou, Shi Xue

2016-03-01

In contrast to its bulk crystal, the FeSe thin film or layer exhibits better superconductivity performance, which recently attracted much interest in its fundamental research as well as in potential applications around the world. In the present work, tuning superconductivity in FeSe thin films was achieved by magnesium-doping technique. Tc is significantly enhanced from 10.7 K in pure FeSe films to 13.4 K in optimized Mg-doped ones, which is approximately 1.5 times higher than that of bulk crystals. This is the first time achieving the enhancement of superconducting transition temperature in FeSe thin films with practical thickness (120 nm) via a simple Mg-doping process. Moreover, these Mg-doped FeSe films are quite stable in atmosphere with Hc2 up to 32.7 T and Tc(zero) up to 12 K, respectively, implying their outstanding potential for practical applications in high magnetic fields. It was found that Mg enters the matrix of FeSe lattice, and does not react with FeSe forming any other secondary phase. Actually, Mg first occupies Fe-vacancies, and then substitutes for some Fe in the FeSe crystal lattices when Fe-vacancies are fully filled. Simultaneously, external Mg-doping introduces sufficient electron doping and induces the variation of electron carrier concentration according to Hall coefficient measurements. This is responsible for the evolution of superconducting performance in FeSe thin films. Our results provide a new strategy to improve the superconductivity of 11 type Fe-based superconductors and will help us to understand the intrinsic mechanism of this unconventional superconducting system.

Synthesis, characterization and photocatalytic activity of porous manganese oxide doped titania for toluene decomposition.

PubMed

Jothiramalingam, R; Wang, M K

2007-08-17

The present study describes the photocatalytic degradation of toluene in gas phase on different porous manganese oxide doped titanium dioxide. As synthesized birnessite and cryptomelane type porous manganese oxide were doped with titania and tested for photocatalytic decomposition of toluene in gas phase. The effects of the inlet concentration of toluene, flow rate (retention time) were examined and the relative humidity was maintained constantly. Thermal and textural characterization of manganese oxide doped titania materials were characterized by X-ray diffraction (XRD), thermogravemetry (TG), BET and TEM-EDAX studies. The aim of the present study is to synthesize the porous manganese oxide doped titania and to study its photocatalytic activity for toluene degradation in gas phase. Cryptomelane doped titania catalyst prepared in water medium [K-OMS-2 (W)] is shown the good toluene degradation with lower catalysts loading compared to commercial bulk titania in annular type photo reactor. The higher photocatalytic activity due to various factors such as catalyst preparation method, experimental conditions, catalyst loading, surface area, etc. In the present study manganese oxide OMS doped titania materials prepared by both aqueous and non-aqueous medium, aqueous medium prepared catalyst shows the good efficiency due to the presence of OH bonded groups on the surface of catalyst. The linear forms of different kinetic equations were applied to the adsorption data and their goodness of fit was evaluated based on the R2 and standard error. The goodness to the linear fit was observed for Elovich model with high R2 (>or=0.9477) value.

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.

Temperature Sensing Above 1000 C Using Cr-Doped GdAlO3 Spin-Allowed Broadband Luminescence

NASA Technical Reports Server (NTRS)

Eldridge, Jeffrey I.; Chambers, Matthew D.

2012-01-01

Cr-doped GdAlO3 (Cr:GdAlO3) is shown to produce remarkably high-intensity spin-allowed broadband luminescence with sufficiently long decay times to make effective luminescence-decay-time based temperature measurements above 1000 C. This phosphor is therefore an attractive alternative to the much lower luminescence intensity rare-earth-doped thermographic phosphors that are typically utilized at these elevated temperatures. In particular, Cr:GdAlO3 will be preferred over rare-earth-doped phosphors, such as Dy:YAG, at temperatures up to 1200 C for intensity-starved situations when the much lower emission intensity from rare-earth-doped phosphors is insufficient for accurate temperature measurements in the presence of significant radiation background. While transition-metal-doped phosphors such as Cr:Al2O3 (ruby) are known to exhibit high luminescence intensity at low dopant concentrations, quenching due to nonradiative decay pathways competing with the (sup 2)E to (sup 4)A(sub 2) radiative transition (R line) has typically restricted their use for temperature sensing to below 600 C. Thermal quenching of the broadband (sup 4)T(sub 2) to (sup 4)A(sub 2) radiative transition from Cr:GdAlO3, however, is delayed until much higher temperatures (above 1000 C). This spin-allowed broadband emission persists to high temperatures because the lower-lying (sup 2)E energy level acts as a reservoir to thermally populate the higher shorter-lived (sup 4)T(sub 2) energy level and because the activation energy for nonradiative crossover relaxation from the (sup 4)T(sub 2) level to the (sup 4)A(sub 2) ground state is high. The strong crystal field associated with the tight bonding of the AlO6 octahedra in the GdAlO3 perovskite structure is responsible for this behavior.

Hall and Seebeck measurements estimate the thickness of a (buried) carrier system: Identifying interface electrons in In-doped SnO{sub 2} films

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

Papadogianni, Alexandra; Bierwagen, Oliver; White, Mark E.

2015-12-21

We propose a simple method based on the combination of Hall and Seebeck measurements to estimate the thickness of a carrier system within a semiconductor film. As an example, this method can distinguish “bulk” carriers, with homogeneous depth distribution, from “sheet” carriers, that are accumulated within a thin layer. The thickness of the carrier system is calculated as the ratio of the integral sheet carrier concentration, extracted from Hall measurements, to the volume carrier concentration, derived from the measured Seebeck coefficient of the same sample. For rutile SnO{sub 2}, the necessary relation of Seebeck coefficient to volume electron concentration inmore » the range of 3 × 10{sup 17} to 3 × 10{sup 20 }cm{sup −3} has been experimentally obtained from a set of single crystalline thin films doped with varying Sb-doping concentrations and unintentionally doped bulk samples, and is given as a “calibration curve.” Using this calibration curve, our method demonstrates the presence of interface electrons in homogeneously deep-acceptor (In) doped SnO{sub 2} films on sapphire substrates.« less

Optical nonlinearity of CdSe-PMMA hybrid nanocomposite investigated via Z-scan technique and semi-empirical relations

NASA Astrophysics Data System (ADS)

Kaur, Ramneek; Tripathi, S. K.

2016-04-01

CdSe-PMMA nanocomposite has been synthesized by ex-situ technique. The effect of different Ag doping concentrations on its structural and optical properties has been studied. X-ray diffraction reveals the hexagonal wurtzite structure of the polymer nanocomposites with preferential growth of the nanocrystals along (1 0 0) direction. Transmission electron micrograph shows the spherical CdSe nanoparticles embedded in polymer matrix. The nonlinear refractive index of the nanocomposites has been calculated using Tichy & Ticha semi-empirical relations and Z-scan technique. Z-scan results disclose the two photon absorption process in the hybrid nanocomposites with self focussing behaviour. With Ag doping, the nonlinearity is found to be increased up to 0.2% Ag doping concentration due to the confined effect of Surface Plasmon, Quantum confinement and thermal lensing. Above 0.2% Ag concentration, its value decreases due to the declined linear refractive index of the nanocomposites. Maximum two photon figure of merit is 76 for 0.2% Ag doped CdSe-PMMA hybrid nanocomposite. The present results accentuate the possibility of tuning the optical non-linearity of CdSe-PMMA hybrid nanocomposite by adjusting the doping concentration.

Effect of Pr3+doping on key properties of CdO thin films deposited by spray pyrolysis using perfume atomizer

NASA Astrophysics Data System (ADS)

Ravikumar, M.; Chandramohan, R.; Kumar, K. Deva Arun; Valanarasu, S.; Kathalingam, A.; Ganesh, V.; Shkir, Mohd.; AlFaify, S.; Algarni, H.

2018-07-01

High quality Cadmium oxide thin films doped with Praseodymium (Pr) were prepared using perfume atomizer based spray pyrolysis technique at substrate temperature near 350 °C. Structural analysis of films was examined by XRD and confirmed that the films are cubic in structure. All un-doped and doped films were good crystalline in nature with smooth and flat surface without significant modifications owed to doping. Optical transmittances of doped films was decrease in the visible and IR range with increasing Pr doping concentration. Band gap widened from 2.42 to 2.20 eV when doped with Pr from 0 to 5 at. %. In addition, the photoluminescence property of the films was also observed. Further, the electrical studies were performed on pure and doped samples Viz., the electrical resistivity, carrier concentration (ρ) and Hall mobility (μ). It confirmed that the deposited films has good structural environments in terms of grain size, absolute stress correspond and low resistivity. Current-voltage measurements on the nanostructured Al/Pr-nCdO/p-Si/Al device showed a non-linear electric characteristics indicating diode like behavior.

Enhancement of p-type conductivity by modifying the internal electric field in Mg- and Si-δ-codoped AlxGa1-xN/AlyGa1-yN superlattices

NASA Astrophysics Data System (ADS)

Li, Jinchai; Yang, Weihuang; Li, Shuping; Chen, Hangyang; Liu, Dayi; Kang, Junyong

2009-10-01

The internal electric field is modified by using Mg- and Si-δ-codoped AlxGa1-xN/AlyGa1-yN superlattices (SLs). The first-principles simulation results show that the internal electric field in SL has been significantly intensified due to the charge transferring from Si-doped interface to Mg-doped interface. Accordingly, the Mg- and Si-δ-codoped p-type Al0.2Ga0.8N/GaN SLs are grown by metalorganic vapor phase epitaxy and higher hole concentration as much as twice of that in modulation-doped SL has been achieved, as determined by Hall effect measurements. Furthermore, by applying Mg- and Si-δ-codoped AlxGa1-xN/AlyGa1-yN SLs with high Al content as the p-type layers, we have fabricated deep ultraviolet light emitting diodes with superior current-voltage characteristics by lowering Mg-acceptor activation energy.

The composition dependence of magnetic, electronic and optical properties of Mn-doped SixGe1-x nanowires

NASA Astrophysics Data System (ADS)

Wei, Jianglin; Lan, Mu; Zhang, Xi; Xiang, Gang

2017-07-01

Mn-doped SixGe1-x nanowires (NWs) with different Ge concentrations have been studied by first-principles calculations. It is found that the spin dependent energy bands of the NWs show rich variations both in bandgap width and type (from indirect to direct) as the Ge concentration changes. The Mn-doped SixGe1-x NWs exhibit half-metallic characteristics for all Ge concentrations, and the ground states of the NWs are found to be ferromagnetic (FM). The net magnetization mapping and spin density of states calculations reveal that Mn 3d electrons have a strong hybridization effect with nearest Ge 4p electrons, which results in the Ge’s nontrivial contribution to the magnetic moment of the NWs. Further magnon dispersion studies show that the magnetic order stability of the NWs is influenced by Ge concentrations. Finally, the dependence of the optical properties of the magnetic NWs on the Ge concentration is demonstrated. Our results suggest that Mn-doped SixGe1-x NWs may be useful in spintronic and optoelectronic devices.

Heavily doped n-type a-IGZO by F plasma treatment and its thermal stability up to 600 °C

NASA Astrophysics Data System (ADS)

Um, Jae Gwang; Jang, Jin

2018-04-01

We report the electrical properties and thermal stability of heavily doped, amorphous indium-gallium-zinc-oxide (a-IGZO) treated with fluorine (F) plasma. When the F doping concentration in a-IGZO is 17.51 × 1021/cm-3, the a-IGZO exhibits a carrier concentration of 6 × 1019 cm-3, a resistivity of 3 × 10-3 Ω cm, and a Hall mobility of 20 cm2/V s. This indicates that F is a suitable n-type dopant in a-IGZO. The similarity of the ionic radius of F to that of oxygen (O) allows substitutional doping by replacing O with F or the occupation of the oxygen vacancy (VO) site by F and consequent reduction in defect density. The semiconducting property of a-IGZO can change into metallic behavior by F doping. The defect passivation by F incorporation is confirmed by the XPS depth profile, which reveals the significant reduction in the VO concentration due to the formation of In-F bonds. The heavily doped a-IGZO exhibits thermally stable conductivity up to 600 °C annealing and thus can be widely used for the ohmic contact of a-IGZO devices.

High Resolution X-ray Scattering Studies of Structural Phase Transitions in BaFe2-x Cr x As 2

NASA Astrophysics Data System (ADS)

Gaulin, B. D.; Clancy, J. P.; Wagman, J. J.; Sefat, A. S.

2011-03-01

While the effects of electron-doping on the parent compounds of the 122 family of Fe-based superconductors have been extremely well-studied in recent years, far less is known about the influence of hole-doping in compounds such as BaFe 2-x Cr x As 2 . In contrast to the electron-doped 122 systems, the hole-doped compounds do not become superconducting. Furthermore, while the hole-doped compounds exhibit similar structural and magnetic phase transitions, they appear to be much less sensitive to dopant concentration. We have performed high resolution x-ray scattering and magnetic susceptibility measurements on single crystal samples of BaFe 2-x Cr x As 2 for Cr concentrations ranging from 0 <= x <= 0.67 . These measurements allow us to determine the magnetic and structural phase transitions for this series and map out the low temperature phase diagram as a function of doping. In particular, we have carried out detailed measurements of the tetragonal (I4/mmm) to orthorhombic (Fmmm) structural phase transition which reveal how the orthorhombicity of the system evolves with increasing Cr concentration and how this correlates with the values of Ts and Tm .

Mixed Carrier Conduction in Modulation-doped Field Effect Transistors

NASA Technical Reports Server (NTRS)

Schacham, S. E.; Haugland, E. J.; Mena, R. A.; Alterovitz, S. A.

1995-01-01

The contribution of more than one carrier to the conductivity in modulation-doped field effect transistors (MODFET) affects the resultant mobility and complicates the characterization of these devices. Mixed conduction arises from the population of several subbands in the two-dimensional electron gas (2DEG), as well as the presence of a parallel path outside the 2DEG. We characterized GaAs/AlGaAs MODFET structures with both delta and continuous doping in the barrier. Based on simultaneous Hall and conductivity analysis we conclude that the parallel conduction is taking place in the AlGaAs barrier, as indicated by the carrier freezeout and activation energy. Thus, simple Hall analysis of these structures may lead to erroneous conclusions, particularly for real-life device structures. The distribution of the 2D electrons between the various confined subbands depends on the doping profile. While for a continuously doped barrier the Shubnikov-de Haas analysis shows superposition of two frequencies for concentrations below 10(exp 12) cm(exp -2), for a delta doped structure the superposition is absent even at 50% larger concentrations. This result is confirmed by self-consistent analysis, which indicates that the concentration of the second subband hardly increases.

Thermal, dielectric studies on pure and amino acid ( L-glutamic acid, L-histidine, L-valine) doped KDP single crystals

NASA Astrophysics Data System (ADS)

Kumaresan, P.; Moorthy Babu, S.; Anbarasan, P. M.

2008-05-01

Amino acids ( L-glutamic acid, L-histidine, L-valine) doped potassium dihydrogen phospate crystals are grown by solution growth technique. Slow cooling as well as slow evaporation methods were employed to grow these crystals. The concentration of dopants in the mother solution was varied from 0.1 mol% to 10 mol%. The solubility data for all dopants concentration were determined. There is variation in pH value and hence, there is habit modification of the grown crystals were characterized with UV-VIS, FT-IR studies, SHG trace elements and dielectric studies reveal slight distortion of lattice parameter for the heavily doped KDP crystals. UV-Visible spectra confirm the improvement in the transparency of these crystals on doping metal ions. FT-IR spectra reveal strong absorption band between 1400 and 1600 cm -1 for metal ion doped crystals. TGA-DTA studies reveal good thermal stability. The dopants increase the hardness value of the material and it also depends on the concentration of the dopants. Amino acids doping improved the NLO properties. The detailed results on the spectral parameters, habit modifications and constant values will be presented.

Deposition of Cu-doped PbS thin films with low resistivity using DC sputtering

NASA Astrophysics Data System (ADS)

Soetedjo, Hariyadi; Siswanto, Bambang; Aziz, Ihwanul; Sudjatmoko

2018-03-01

Investigation of the electrical resistivity of Cu-doped PbS thin films has been carried out. The films were prepared using a DC sputtering technique. The doping was achieved by introducing the Cu dopant plate material directly on the surface of the PbS sputtering target plate. SEM-EDX data shows the Cu concentration in the PbS film to be proportional to the Cu plate diameter. The XRD pattern indicates the film is in crystalline cubic form. The Hall effect measurement shows that Cu doping yields an increase in the carrier concentration to 3.55 × 1019 cm-3 and a significant decrease in electrical resistivity. The lowest resistivity obtained was 0.13 Ωcm for a Cu concentration of 18.5%. Preferential orientation of (1 1 1) and (2 0 0) occurs during deposition.

Structural and optical properties of cobalt doped multiferroics BiFeO3 nanostructure thin films

NASA Astrophysics Data System (ADS)

Prasannakumara, R.; Naik, K. Gopalakrishna

2018-05-01

Bismuth ferrite (BiFeO3) and Cobalt doped BiFeO3 (BiFe1-XCoXO3) nanostructure thin films were deposited on glass substrates by the sol-gel spin coating method. The X-ray diffraction patterns (XRD) of the grown BiFeO3 and BiFe1-XCoXO3 nanostructure thin films showed distorted rhombohedral structure. The shifting of peaks to higher angles was observed in cobalt doped BiFeO3. The surface morphology of the BiFeO3 and BiFe1-XCoXO3 nanostructure thin films were studied using FESEM, an increase in grain size was observed as Co concentration increases. The thickness of the nanostructure thin films was examined using FESEM cross-section. The EDX studies confirmed the elemental composition of the grown BiFeO3 and BiFe1-XCoXO3 nanostructure thin films. The optical characterizations of the grown nanostructure thin films were carried out using FTIR, it confirms the existence of Fe-O and Bi-O bands and UV-Visible spectroscopy shows the increase in optical band gap of the BiFeO3 nanostructure thin films with Co doping by ploting Tauc plot.

Tunable multicolor and enhanced red emission of monodisperse CaF2:Yb3+/Ho3+ microspheres via Mn2+ doping

NASA Astrophysics Data System (ADS)

Wang, Rui; Yuan, Maohui; Zhang, Chaofan; Wang, Hongyan; Xu, Xiaojun

2018-05-01

Transition metal ions (e.g. Mn2+) and lanthanide co-doped upconversion (UC) materials have attracted wide attention in recent years due to their promising application in multicolor display. Here, we report the hydrothermal synthesis and characterization of Mn2+ doped monodisperse CaF2:Yb3+/Ho3+ microspheres. The results of X-ray diffraction (XRD) revealed that Mn2+ doping does not change the cubic phase of CaF2 material but will lead to diffraction peaks shifting slightly towards higher angle due to the substitution of larger Ca2+ by the relatively smaller Mn2+. Under the excitation of 980 nm continuous wave (CW) laser, these microspheres exhibit green-yellow-red tuning colors and remarkable enhancement of both red to green ratio (R/G) and red to blue ratio (R/B) when increasing Mn2+ concentration from 0 to 30 mol%. The energy migration process between Ho3+ and Mn2+ was proposed and supported by time-decay and power dependence measurements of Ho3+ UC emission. These upconversion materials may have potential applications in optical devices, color display, nanoscale lasers and biomedical imaging.

Structural, electrical and optical properties of indium tin oxide thin film grown by metal organic chemical vapor deposition with tetramethyltin-precursor

NASA Astrophysics Data System (ADS)

Zhuo, Yi; Chen, Zimin; Tu, Wenbin; Ma, Xuejin; Wang, Gang

2018-01-01

Tin-doped indium oxide (ITO) is grown by metal organic chemical vapor deposition (MOCVD) using tetramethyltin (TDMASn) as tin precursor. The as-grown ITO films are polycrystalline with (111) and (100) textures. A gradual transition of crystallographic orientation from (111) preferred to (100) preferred is observed as the composition of tin changes. By precisely controlling the Sn doping, the ITO thin films present promising optical and electrical performances at either near-infrared-visible or visible-near-ultraviolet ranges. At low Sn doping level, the as-grown ITO possesses high electron mobility of 48.8 cm2 V-1 s-1, which results in high near-infrared transmittance and low resistivity. At higher Sn doping level, high carrier concentration (8.9 × 1020 cm-3) and low resistivity (3 × 10-4 Ω cm) are achieved. The transmittance is 97.8, 99.1, and 82.3% at the wavelength of 550, 365, and 320 nm, respectively. The results strongly suggest that MOCVD with TDMASn as tin precursor is an effective method to fabricate high quality ITO thin film for near-infrared, visible light, and near-ultraviolet application.

Poly-beta-pinene, a Novel Nonconjugated Conductive Polymer

NASA Astrophysics Data System (ADS)

Thakur, Mrinal; Vippa, Prakash; Rajagopalan, Harish

2004-03-01

Electrical conductivity in a novel nonconjugated conductive polymer, poly-beta-pinene, has been measured as a function of iodine doping. The conductivity increases about ten orders of magnitude to a maximum value ˜ 0.01 S/cm. The molar concentration of iodine corresponding to saturation is ˜ 0.8. The optical absorption measurements after light doping have shown two peaks: one at 4.1 eV and the other at 3.1 eV. The first peak is due to the radical cation and the second due the charge-transfer between the double bond and the dopant. As observed in other nonconjugated conductive polymers, the second peak becomes broader and undergoes a red-shift upon higher doping [1,2]. The FTIR spectroscopic studies have shown that the C=C stretching vibration at 1610 cm-1 and the =C-H bending vibration band at 728 cm-1 decrease upon doping as observed in other nonconjugated conductive polymers. Preliminary measurements have shown large quadratic electro-optic effects in this material. 1. M. Thakur, J. Macromol. Sci.-PAC,2001,A38(12),1337. 2. M. Thakur, S. Khatavkar and E.J. Parish, J. Macromol. Sci.-PAC,2003,A40(12),1397.

The investigation of photo-induced chemiluminescence on Co2+-doped TiO2 nanoparticles and its analytical application.

PubMed

Li, Guixin; Nan, Hongyan; Zheng, Xingwang

2009-07-01

A novel space- and time-resolved photo-induced chemiluminescence (PICL) analytical method was developed based on the photocatalysis of the Co2+-doped TiO2 nanoparticles. The PICL reaction procedure under the photocatalysis of Co2+-doped TiO2 nanoparticles was investigated using cyclic voltammetry and potentiometry. Meanwhile, the effect of the electrical double layer outside the Co2+-doped TiO2 nanoparticles on the PICL was investigated by contrasting with the Co2+-doped TiO2-SiO2 core-shell nanoparticles. Significantly, the CL intensity increased apparently and the time of the CL was prolonged in the presence of procaterol hydrochloride because the mechanism of the enhanced PICL reaction may be modified. The route of the PICL was changed due to the participation of the procaterol hydrochloride enriched at the surface of the Co2+-doped TiO2-SiO2 in the PICL reaction, which prolonged the time of the CL reaction and resulted in the long-term PICL. The analytical characteristics of the proposed in-situ PICL method were investigated using the procaterol hydrochloride as the model analyte. The investigation results showed that this new PICL analytical method offered higher sensitivity to the analysis of the procaterol hydrochloride and the PICL intensity was linear with the concentration of the procaterol hydrochloride in the range from ca. 2.0 x 10(-10) to 1.0 x 10(-8) g mL(-1).

High-concentration boron doping of graphene nanoplatelets by simple thermal annealing and their supercapacitive properties.

PubMed

Yeom, Da-Young; Jeon, Woojin; Tu, Nguyen Dien Kha; Yeo, So Young; Lee, Sang-Soo; Sung, Bong June; Chang, Hyejung; Lim, Jung Ah; Kim, Heesuk

2015-05-05

For the utilization of graphene in various energy storage and conversion applications, it must be synthesized in bulk with reliable and controllable electrical properties. Although nitrogen-doped graphene shows a high doping efficiency, its electrical properties can be easily affected by oxygen and water impurities from the environment. We here report that boron-doped graphene nanoplatelets with desirable electrical properties can be prepared by the simultaneous reduction and boron-doping of graphene oxide (GO) at a high annealing temperature. B-doped graphene nanoplatelets prepared at 1000 °C show a maximum boron concentration of 6.04 ± 1.44 at %, which is the highest value among B-doped graphenes prepared using various methods. With well-mixed GO and g-B2O3 as the dopant, highly uniform doping is achieved for potentially gram-scale production. In addition, as a proof-of-concept, highly B-doped graphene nanoplatelets were used as an electrode of an electrochemical double-layer capacitor (EDLC) and showed an excellent specific capacitance value of 448 F/g in an aqueous electrolyte without additional conductive additives. We believe that B-doped graphene nanoplatelets can also be used in other applications such as electrocatalyst and nano-electronics because of their reliable and controllable electrical properties regardless of the outer environment.

High-concentration boron doping of graphene nanoplatelets by simple thermal annealing and their supercapacitive properties

NASA Astrophysics Data System (ADS)

Yeom, Da-Young; Jeon, Woojin; Tu, Nguyen Dien Kha; Yeo, So Young; Lee, Sang-Soo; Sung, Bong June; Chang, Hyejung; Lim, Jung Ah; Kim, Heesuk

2015-05-01

For the utilization of graphene in various energy storage and conversion applications, it must be synthesized in bulk with reliable and controllable electrical properties. Although nitrogen-doped graphene shows a high doping efficiency, its electrical properties can be easily affected by oxygen and water impurities from the environment. We here report that boron-doped graphene nanoplatelets with desirable electrical properties can be prepared by the simultaneous reduction and boron-doping of graphene oxide (GO) at a high annealing temperature. B-doped graphene nanoplatelets prepared at 1000 °C show a maximum boron concentration of 6.04 ± 1.44 at %, which is the highest value among B-doped graphenes prepared using various methods. With well-mixed GO and g-B2O3 as the dopant, highly uniform doping is achieved for potentially gram-scale production. In addition, as a proof-of-concept, highly B-doped graphene nanoplatelets were used as an electrode of an electrochemical double-layer capacitor (EDLC) and showed an excellent specific capacitance value of 448 F/g in an aqueous electrolyte without additional conductive additives. We believe that B-doped graphene nanoplatelets can also be used in other applications such as electrocatalyst and nano-electronics because of their reliable and controllable electrical properties regardless of the outer environment.

Study of the thermoelectric properties of lead selenide doped with boron, gallium, indium, or thallium.

PubMed

Zhang, Qian; Cao, Feng; Lukas, Kevin; Liu, Weishu; Esfarjani, Keivan; Opeil, Cyril; Broido, David; Parker, David; Singh, David J; Chen, Gang; Ren, Zhifeng

2012-10-24

Group IIIA elements (B, Ga, In, and Tl) have been doped into PbSe for enhancement of thermoelectric properties. The electrical conductivity, Seebeck coefficient, and thermal conductivity were systematically studied. Room-temperature Hall measurements showed an effective increase in the electron concentration upon both Ga and In doping and the hole concentration upon Tl doping to ~7 × 10(19) cm(-3). No resonant doping phenomenon was observed when PbSe was doped with B, Ga, or In. The highest room-temperature power factor ~2.5 × 10(-3) W m(-1) K(-2) was obtained for PbSe doped with 2 atom % B. However, the power factor in B-doped samples decreased with increasing temperature, opposite to the trend for the other dopants. A figure of merit (ZT) of ~1.2 at ~873 K was achieved in PbSe doped with 0.5 atom % Ga or In. With Tl doping, modification of the band structure around the Fermi level helped to increase the Seebeck coefficient, and the lattice thermal conductivity decreased, probably as a result of effective phonon scattering by both the heavy Tl(3+) ions and the increased grain boundary density after ball milling. The highest p-type ZT value was ~1.0 at ~723 K.

High quality nitrogen-doped zinc oxide thin films grown on ITO by sol-gel method

NASA Astrophysics Data System (ADS)

Pathak, Trilok Kumar; Kumar, Vinod; Purohit, L. P.

2015-11-01

Highly transparent N-doped ZnO thin films were deposited on ITO coated corning glass substrate by sol-gel method. Ammonium nitrate was used as a dopant source of N with varying the doping concentration 0, 0.5, 1.0, 2.0 and 3.0 at%. The DSC analysis of prepared NZO sols is observed a phase transition at 150 °C. X-ray diffraction pattern showed the preferred (002) peak of ZnO, which was deteriorated with increased N concentrations. The transmittance of NZO thin films was observed to be ~88%. The bandgap of NZO thin films increased from 3.28 to 3.70 eV with increased N concentration from 0 to 3 at%. The maximum carrier concentration 8.36×1017 cm-3 and minimum resistivity 1.64 Ω cm was observed for 3 at% N doped ZnO thin films deposited on glass substrate. These highly transparent ZnO thin films can be used as a window layer in solar cells and optoelectronic devices.

Proton Relaxivity and Magnetic Hyperthermia Evaluation of Gadolinium Doped Nickel Ferrite Nanoparticles as Potential Theranostic Agents.

PubMed

Yadavalli, Tejabhiram; Raja, Paradeep; Ramaswamy, Shivaraman; Chandrasekharan, Gopalakrishnan; Chennakesavulu, Ramasamy

2017-02-01

This paper outlines the preparation of gadolinium doped nickel ferrite nanoparticles as potential magnetic carriers and longitudinal magnetic resonance imaging contrast agents using hydrothermal method with gadolinium concentration varying from 10% to 40%. A concise effect on the crystal structure was observed at 10% and 20% gadolinium doping, while gadolinium oxide was observed to leach at concentrations exceeding 20%. Further, gadolinium doped nickel ferrites were analyzed for their morphological, magnetic, proton relaxation and magnetic hyperthermia heating properties to understand their potential role as magnetic carrier agents. Low temperature and room temperature magnetic studies conducted on the samples showed comparatively high magnetic saturation with low remanent magnetization. Further, relaxometry studies revealed a high relaxation rate of 6.63 s−1 at a concentration of 0.1 mg/mL. Magnetic hyperthermia studies of the samples at a concentration of 1 mg/mL, assessed that the samples attained a temperature of 68 °C in 240 seconds.

Different annealing temperature suitable for different Mg doped P-GaN

NASA Astrophysics Data System (ADS)

Liu, S. T.; Yang, J.; Zhao, D. G.; Jiang, D. S.; Liang, F.; Chen, P.; Zhu, J. J.; Liu, Z. S.; Li, X.; Liu, W.; Zhang, L. Q.; Long, H.; Li, M.

2017-04-01

In this work, epitaxial GaN with different Mg doping concentration annealed at different temperature is investigated. Through Hall and PL spectra measurement we found that when Mg doping concentration is different, different annealing temperature is needed for obtaining the best p-type conduction of GaN, and this difference comes from the different influence of annealing on compensated donors. For ultra-heavily Mg doped sample, the process of Mg related donors transferring to non-radiative recombination centers is dominated, so the performance of P-GaN deteriorates with temperature increase. But for low Mg doped sample, the process of Mg related donors transfer to non-raditive recombination is weak compare to the Mg acceptor activation, so along the annealing temperature increase the performance GaN gets better.

Effect of La and W dopants on dielectric and ferroelectric properties of PZT thin films prepared by sol-gel process

NASA Astrophysics Data System (ADS)

Xiao, Mi; Zhang, Zebin; Zhang, Weikang; Zhang, Ping

2018-01-01

La or W-doped lead zirconate titanate thin films (PLZT or PZTW) were prepared on platinized silicon substrates by sol-gel process. The effects of La or W dopant on the phase development, microstructure, dielectric and ferroelectric characteristics of films were studied. For PLZT films, the optimum doping concentration was found to be 2 mol%. While for PZTW films, the dielectric and ferroelectric properties were found to be improved as the doping concentration increased. The fatigue properties of PLZT and PZTW thin films were also investigated, the results showed that A- or B-site donor doping could improve the fatigue properties of PZT thin films. The theory of oxygen vacancy was used to explain the performance improvement caused by donor doping.

In-Situ Grown P-N Junctions in MERCURY(1-X) Cadmium(x) Telluride for IR Detectors.

NASA Astrophysics Data System (ADS)

Rao, Vithal Rajaram

In-situ grown p-n junctions in mercury cadmium telluride (Hg_{1-x}Cd _{x}Te with x between 0.2-0.3) were fabricated and characterized in this study. Fabrication of these junctions involved the growth of p-n structures at 370^circC on CdTe substrates by Organometallic Vapor Phase Epitaxy. P-type doping with arsenic was achieved by using tertiarybutylarsine as the precursor. N-type doping was obtained either with indium, using trimethylindium as the precursor or by leaving the layer undoped. These p-n structures were processed to fabricate photodiodes. Their electrical performance was evaluated and conclusions regarding current mechanisms which determine their behavior were drawn. By varying the Hg pressure between 0.07-0.13 atm, p-type doping level in the 10^{16 }/cm^3-rm2times10 ^{17}/cm^3 range was achieved. At higher values of Hg pressure, the arsenic doping level in the layer increased significantly. This is possibly due to an increase in Te vacancies, allowing arsenic to occupy more group VI sites where they behave as acceptors. The activation efficiency of arsenic in the layers was measured to be equal to 50%. A high temperature anneal at 415 ^circC for 15 minutes did not result in any increase in the activation efficiency, possibly indicating the presence of stable As-complexes in the layer. Growth of p^+n structures was carried out in a single run. The acceptor concentration in the p-type cap layer was 5-rm10times10 ^{16}/cm^3. Indium doped n-type base layers had a carrier concentration of 1- rm2times10^{16}/cm^3 , while undoped layers had a n-type background carrier concentration of 4-rm6times10^ {14}/cm^3. The cap layer was 3 μm thick with x = 0.30, while the base layer was 8mum thick with x = 0.26. Under the growth conditions, arsenic showed a diffusion coefficient of rm2times10 ^{13}cm^2/s, which was higher than the interdiffusion coefficient of the alloy junction. This resulted in placement of the p-n junction in the lower bandgap base layer, which is necessary for high quantum efficiency devices. Photodiodes showed a cutoff wavelength of 7.5 mum, which correlates with the alloy composition of the base layer. Measured R_0 A of these diodes varied between 1-100 ohm-cm ^2. In the lower R_0A diodes, reverse bias was dominated by surface currents, possibly due to degradation of the passivating layer. Diodes with higher R_0A showed under reverse bias that trap assisted tunneling current dominated their performance. The origin of these traps is process related and could correspond to the presence of inactivated arsenic close to the p-n junction. Forward bias was dominated by diffusion and recombination currents, while the presence of additional leakage currents was evident.

A Pervaporation Study of Ammonia Solutions Using Molecular Sieve Silica Membranes

PubMed Central

Yang, Xing; Fraser, Thomas; Myat, Darli; Smart, Simon; Zhang, Jianhua; Diniz da Costa, João C.; Liubinas, Audra; Duke, Mikel

2014-01-01

An innovative concept is proposed to recover ammonia from industrial wastewater using a molecular sieve silica membrane in pervaporation (PV), benchmarked against vacuum membrane distillation (VMD). Cobalt and iron doped molecular sieve silica-based ceramic membranes were evaluated based on the ammonia concentration factor downstream and long-term performance. A modified low-temperature membrane evaluation system was utilized, featuring the ability to capture and measure ammonia in the permeate. It was found that the silica membrane with confirmed molecular sieving features had higher water selectivity over ammonia. This was due to a size selectivity mechanism that favoured water, but blocked ammonia. However, a cobalt doped silica membrane previously treated with high temperature water solutions demonstrated extraordinary preference towards ammonia by achieving up to a 50,000 mg/L ammonia concentration (a reusable concentration level) measured in the permeate when fed with 800 mg/L of ammonia solution. This exceeded the concentration factor expected by the benchmark VMD process by four-fold, suspected to be due to the competitive adsorption of ammonia over water into the silica structure with pores now large enough to accommodate ammonia. However, this membrane showed a gradual decline in selectivity, suspected to be due to the degradation of the silica material/pore structure after several hours of operation. PMID:24957120

Methanol-Tolerant Platinum-Palladium Catalyst Supported on Nitrogen-Doped Carbon Nanofiber for High Concentration Direct Methanol Fuel Cells

PubMed Central

Kim, Jiyoung; Jang, Jin-Sung; Peck, Dong-Hyun; Lee, Byungrok; Yoon, Seong-Ho; Jung, Doo-Hwan

2016-01-01

Pt-Pd catalyst supported on nitrogen-doped carbon nanofiber (N-CNF) was prepared and evaluated as a cathode electrode of the direct methanol fuel cell (DMFC). The N-CNF, which was directly synthesized by the catalytic chemical vapor deposition from acetonitrile at 640 °C, was verified as having a change of electrochemical surface properties such as oxygen reduction reaction (ORR) activities and the electrochemical double layer compared with common carbon black (CB). To attain the competitive oxygen reduction reaction activity with methanol tolerance, the Pt and Pd metals were supported on the CB or the N-CNF. The physical and electrochemical characteristics of the N-CNF–supported Pt-Pd catalyst were examined and compared with catalyst supported on the CB. In addition, DMFC single cells using these catalysts as the cathode electrode were applied to obtain I-V polarization curves and constant current operating performances with high-concentration methanol as the fuel. Pt-Pd catalysts had obvious ORR activity even in the presence of methanol. The higher power density was obtained at all the methanol concentrations when it applied to the membrane electrode assembly (MEA) of the DMFC. When the N-CNF is used as the catalyst support material, a better performance with high-concentration methanol is expected. PMID:28335275

Methanol-Tolerant Platinum-Palladium Catalyst Supported on Nitrogen-Doped Carbon Nanofiber for High Concentration Direct Methanol Fuel Cells.

PubMed

Kim, Jiyoung; Jang, Jin-Sung; Peck, Dong-Hyun; Lee, Byungrok; Yoon, Seong-Ho; Jung, Doo-Hwan

2016-08-15

Pt-Pd catalyst supported on nitrogen-doped carbon nanofiber (N-CNF) was prepared and evaluated as a cathode electrode of the direct methanol fuel cell (DMFC). The N-CNF, which was directly synthesized by the catalytic chemical vapor deposition from acetonitrile at 640 °C, was verified as having a change of electrochemical surface properties such as oxygen reduction reaction (ORR) activities and the electrochemical double layer compared with common carbon black (CB). To attain the competitive oxygen reduction reaction activity with methanol tolerance, the Pt and Pd metals were supported on the CB or the N-CNF. The physical and electrochemical characteristics of the N-CNF-supported Pt-Pd catalyst were examined and compared with catalyst supported on the CB. In addition, DMFC single cells using these catalysts as the cathode electrode were applied to obtain I-V polarization curves and constant current operating performances with high-concentration methanol as the fuel. Pt-Pd catalysts had obvious ORR activity even in the presence of methanol. The higher power density was obtained at all the methanol concentrations when it applied to the membrane electrode assembly (MEA) of the DMFC. When the N-CNF is used as the catalyst support material, a better performance with high-concentration methanol is expected.

Effects of impurity doping on ionic conductivity and polarization phenomenon in TlBr

NASA Astrophysics Data System (ADS)

Du, Mao-Hua

2013-02-01

Ionic conductivity due to vacancy diffusion and the resulting polarization phenomenon are major challenges to the development of TlBr radiation detector. It had been proposed that impurity doping of TlBr can suppress the ionic conductivity because the impurities can getter vacancies to form neutral complexes. This paper shows that the isolated vacancies can maintain their equilibrium concentrations even at room temperature, rendering any gettering methods ineffective. The main effect of doping is to change the Fermi level and consequently the vacancy concentration. The minimal ionic conductivity is reached at the donor concentration of [D+] = 4 × 1016 cm-3.

Electrical characterization of 6H crystalline silicon carbide. M.S. Thesis Final Report

NASA Technical Reports Server (NTRS)

Lempner, Stephen E.

1994-01-01

Crystalline silicon carbide (SiC) substrates and epilayers, undoped as well as n- and p-doped, have been electrically characterized by performing Hall effect and resistivity measurements (van der Pauw) over the temperature range of approximately 85 K to 650 K (200 K to 500 K for p-type sample). By fitting the measured temperature dependent carrier concentration data to the single activation energy theoretical model: (1) the activation energy for the nitrogen donor ranged from 0.078 eV to 0.101 eV for a doping concentration range of 10(exp 17) cm(exp -3) to 10(exp 18) cm(exp -3) and (2) the activation energy for the aluminum acceptor was 0.252 eV for a doping concentration of 4.6 x 10(exp 18) cm(exp -3). By fitting the measured temperature dependent carrier concentration data to the double activation energy level theoretical model for the nitrogen donor: (1) the activation energy for the hexagonal site was 0.056 eV and 0.093 eV corresponding to doping concentrations of 3.33 x 10 (exp 17) cm(exp -3) and 1.6 x 10(exp 18) cm(exp -3) and (2) the activation energy for the cubic site was 0.113 and 0.126 eV corresponding to doping concentrations of 4.2 x 10(exp 17) cm(exp -3) and 5.4 x 10(exp 18) cm(exp -3).

Calibration on wide-ranging aluminum doping concentrations by photoluminescence in high-quality uncompensated p-type 4H-SiC

NASA Astrophysics Data System (ADS)

Asada, Satoshi; Kimoto, Tsunenobu; Ivanov, Ivan G.

2017-08-01

Previous work has shown that the concentration of shallow dopants in a semiconductor can be estimated from the photoluminescence (PL) spectrum by comparing the intensity of the bound-to-the-dopant exciton emission to that of the free exciton. In this work, we study the low-temperature PL of high-quality uncompensated Al-doped p-type 4H-SiC and propose algorithms for determining the Al-doping concentration using the ratio of the Al-bound to free-exciton emission. We use three different cryogenic temperatures (2, 41, and 79 K) in order to cover the Al-doping range from mid 1014 cm-3 up to 1018 cm-3. The Al-bound exciton no-phonon lines and the strongest free-exciton replica are used as a measure of the bound- and free-exciton emissions at a given temperature, and clear linear relationships are obtained between their ratio and the Al-concentration at 2, 41, and 79 K. Since nitrogen is a common unintentional donor dopant in SiC, we also discuss the criteria allowing one to determine from the PL spectra whether a sample can be considered as uncompensated or not. Thus, the low-temperature PL provides a convenient non-destructive tool for the evaluation of the Al concentration in 4H-SiC, which probes the concentration locally and, therefore, can also be used for mapping the doping homogeneity.

Structural stability of bismuth-based superconductors under heterovalent substitution

NASA Astrophysics Data System (ADS)

Bonoldi, L.; Calestani, G. L.; Francesconi, M. G.; Salsi, G.; Sparpaglione, M.; Zini, L.

1995-02-01

The stability of the three CuO 2 layers phase of BiPbSrCaCuO superconducting system (BSCCO) with the addition of several rare-earth (RE) oxides is considered. It is shown that if a trivalent (Y, Nd, Gd, Dy, Ho, Er) or tetravalent (Ce) cation is nominally substituted “ab initio” on the Ca site, the higher- Tc phase of this system (the 2223 phase) does not form, at least for dopant molar concentration larger than or equal to 0.032 in the nominal formula of the 2223 phase. If RE oxides are added to a preformed 2223, a solid-state reaction at a temperature of about 840°C takes place giving rise to a substituted (Bi 2- yPb y)Sr 2Ca 1- xRE xCu 2O 8 compound plus other oxides. The synthesis of RE doped 2223 phase was attempted in different ways without success. We argue that this is due to thermodynamic rather than kinetic factors. A possible explanation of 2223 instability under doping in the calcium site with a higher-valence ion is proposed. It highlights the difference with the Bi 2Sr 2CaCu 2O 8 structural stability under the same doping conditions.

Chemo-sensors development based on low-dimensional codoped Mn2O3-ZnO nanoparticles using flat-silver electrodes.

PubMed

Rahman, Mohammed M; Gruner, George; Al-Ghamdi, Mohammed Saad; Daous, Muhammed A; Khan, Sher Bahadar; Asiri, Abdullah M

2013-03-28

Semiconductor doped nanostructure materials have attained considerable attention owing to their electronic, opto-electronic, para-magnetic, photo-catalysis, electro-chemical, mechanical behaviors and their potential applications in different research areas. Doped nanomaterials might be a promising owing to their high-specific surface-area, low-resistances, high-catalytic activity, attractive electro-chemical and optical properties. Nanomaterials are also scientifically significant transition metal-doped nanostructure materials owing to their extraordinary mechanical, optical, electrical, electronic, thermal, and magnetic characteristics. Recently, it has gained significant interest in manganese oxide doped-semiconductor materials in order to develop their physico-chemical behaviors and extend their efficient applications. It has not only investigated the basic of magnetism, but also has huge potential in scientific features such as magnetic materials, bio- & chemi-sensors, photo-catalysts, and absorbent nanomaterials. The chemical sensor also displays the higher-sensitivity, reproducibility, long-term stability, and enhanced electrochemical responses. The calibration plot is linear (r2 = 0.977) over the 0.1 nM to 50.0 μM 4-nitrophenol concentration ranges. The sensitivity and detection limit is ~4.6667 μA cm-2 μM-1 and ~0.83 ± 0.2 nM (at a Signal-to-Noise-Ratio, SNR of 3) respectively. To best of our knowledge, this is the first report for detection of 4-nitrophenol chemical with doped Mn2O3-ZnO NPs using easy and reliable I-V technique in short response time. As for the doped nanostructures, NPs are introduced a route to a new generation of toxic chemo-sensors, but a premeditate effort has to be applied for doped Mn2O3-ZnO NPs to be taken comprehensively for large-scale applications, and to achieve higher-potential density with accessible to individual chemo-sensors. In this report, it is also discussed the prospective utilization of Mn2O3-ZnO NPs on the basis of carcinogenic chemical sensing, which could also be applied for the detection of hazardous chemicals in ecological, environmental, and health care fields.

Chemo-sensors development based on low-dimensional codoped Mn2O3-ZnO nanoparticles using flat-silver electrodes

PubMed Central

2013-01-01

Background Semiconductor doped nanostructure materials have attained considerable attention owing to their electronic, opto-electronic, para-magnetic, photo-catalysis, electro-chemical, mechanical behaviors and their potential applications in different research areas. Doped nanomaterials might be a promising owing to their high-specific surface-area, low-resistances, high-catalytic activity, attractive electro-chemical and optical properties. Nanomaterials are also scientifically significant transition metal-doped nanostructure materials owing to their extraordinary mechanical, optical, electrical, electronic, thermal, and magnetic characteristics. Recently, it has gained significant interest in manganese oxide doped-semiconductor materials in order to develop their physico-chemical behaviors and extend their efficient applications. It has not only investigated the basic of magnetism, but also has huge potential in scientific features such as magnetic materials, bio- & chemi-sensors, photo-catalysts, and absorbent nanomaterials. Results The chemical sensor also displays the higher-sensitivity, reproducibility, long-term stability, and enhanced electrochemical responses. The calibration plot is linear (r2 = 0.977) over the 0.1 nM to 50.0 μM 4-nitrophenol concentration ranges. The sensitivity and detection limit is ~4.6667 μA cm-2 μM-1 and ~0.83 ± 0.2 nM (at a Signal-to-Noise-Ratio, SNR of 3) respectively. To best of our knowledge, this is the first report for detection of 4-nitrophenol chemical with doped Mn2O3-ZnO NPs using easy and reliable I-V technique in short response time. Conclusions As for the doped nanostructures, NPs are introduced a route to a new generation of toxic chemo-sensors, but a premeditate effort has to be applied for doped Mn2O3-ZnO NPs to be taken comprehensively for large-scale applications, and to achieve higher-potential density with accessible to individual chemo-sensors. In this report, it is also discussed the prospective utilization of Mn2O3-ZnO NPs on the basis of carcinogenic chemical sensing, which could also be applied for the detection of hazardous chemicals in ecological, environmental, and health care fields. PMID:23537000

Abbe's number and Cauchy's constant of iodine and selenium doped poly (methylmethacrylate) and polystyrene composites

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

Mehta, Sheetal, E-mail: smehta-29@yahoo.com; Das, Kallol, E-mail: smehta-29@yahoo.com; Keller, Jag Mohan, E-mail: smehta-29@yahoo.com

2014-04-24

Poly (methyl methacrylate) / Polystyrene and iodine / selenium hybrid matrixes have been prepared and characterized. Refractive index measurements were done at 390, 535, 590, 635 nm wavelengths. Abbe's number and Cauchy's constants of the iodine / selenium doped poly (methylmethacrylate) and polystyrene samples are being reported. The results also showed that the refractive index of the composite varies non-monotonically with the doping concentration at low iodine concentration or in the region of nanoparticles formation and is also dependent on thermal annealing.

Influence of Co2+ on electrical and optical behavior of Mn2+-doped ZnS quantum dots

NASA Astrophysics Data System (ADS)

Sakthivel, P.; Muthukumaran, S.

2018-07-01

Co2+-doped Zn0.98Mn0.02S quantum dots with various concentrations of Co2+ from 0% to 4% have been successfully synthesized by a simple co-precipitation method. X-ray diffraction (XRD) pattern confirmed the acquirement of cubic structure and phase purity in all the samples. The average crystallite size of the particles was ∼3 nm observed from XRD result. Surface morphology of the samples was studied using scanning electron microscope (SEM). TEM study was also taken to know the structural parameters of the samples. Fourier transform infrared (FTIR) spectra proved the presence of Co2+ and Mn2+ in ZnS host lattice. Energy dispersive X-ray (EDX) analysis confirmed the elemental composition with their normal stoichiometric ratio. In the dielectric study, dielectric dispersion and dielectric loss were increased with Co2+ composition due to the increase of carrier concentration. From the AC conductivity measurement, the maximum conductivity was observed for Co2+ = 2% due to their higher charge carrier density and it was decreased for Co2+ = 4% due to the scattering of charge carriers. Because of the low dielectric constant at higher frequency, these materials can be used for high-frequency applications. The variation of peak intensity and wavelength shifting in UV-vis absorption and transmittance were discussed on the basis of formation of secondary phase and variation of charge carrier density. The continuous red shift of energy gap by Co2+-doping is attributed to the direct energy transfer between excited states and 3d levels of Co2+ ions. Photoluminescence spectra showed the strong and broad blue emission bands between 468 nm and 483 nm. Since higher transmittance was observed for Co2+ = 2% addition, this material can be selected for optimum applications of optoelectronic devices.

Solder doped polycaprolactone scaffold enables reproducible laser tissue soldering.

PubMed

Bregy, Amadé; Bogni, Serge; Bernau, Vianney J P; Vajtai, Istvan; Vollbach, Felix; Petri-Fink, Alke; Constantinescu, Mihai; Hofmann, Heinrich; Frenz, Martin; Reinert, Michael

2008-12-01

In this in vitro feasibility study we analyzed tissue fusion using bovine serum albumin (BSA) and Indocyanine green (ICG) doped polycaprolactone (PCL) scaffolds in combination with a diode laser as energy source while focusing on the influence of irradiation power and albumin concentration on the resulting tensile strength and induced tissue damage. A porous PCL scaffold doped with either 25% or 40% (w/w) of BSA in combination with 0.1% (w/w) ICG was used to fuse rabbit aortas. Soldering energy was delivered through the vessel from the endoluminal side using a continuous wave diode laser at 808 nm via a 400 microm core fiber. Scaffold surface temperatures were analyzed with an infrared camera. Optimum parameters such as irradiation time, radiation power and temperature were determined in view of maximum tensile strength but simultaneously minimum thermally induced tissue damage. Differential scanning calorimetry (DSC) was performed to measure the influence of PCL on the denaturation temperature of BSA. Optimum parameter settings were found to be 60 seconds irradiation time and 1.5 W irradiation power resulting in tensile strengths of around 2,000 mN. Corresponding scaffold surface temperature was 117.4+/- 12 degrees C. Comparison of the two BSA concentration revealed that 40% BSA scaffold resulted in significant higher tensile strength compared to the 25%. At optimum parameter settings, thermal damage was restricted to the adventitia and its interface with the outermost layer of the tunica media. The DSC showed two endothermic peaks in BSA containing samples, both strongly depending on the water content and the presence of PCL and/or ICG. Diode laser soldering of vascular tissue using BSA-ICG-PCL-scaffolds leads to strong and reproducible tissue bonds, with vessel damage limited to the adventitia. Higher BSA content results in higher tensile strengths. The DSC-measurements showed that BSA denaturation temperature is lowered by addition of water and/or ICG-PCL. (c) 2008 Wiley-Liss, Inc.

Electrochemical treatment of anti-cancer drug carboplatin on mixed-metal oxides and boron doped diamond electrodes: Density functional theory modelling and toxicity evaluation.

PubMed

Barışçı, Sibel; Turkay, Ozge; Ulusoy, Ebru; Soydemir, Gülfem; Seker, Mine Gul; Dimoglo, Anatoli

2018-02-15

This study represents the electrooxidation of anti-cancer drug carboplatin (CrbPt) with different mixed metal oxide (MMO) and boron doped diamond (BDD) electrodes. The most effective anode was found as Ti/RuO 2 with the complete degradation of CrbPt in just 5min. The effect of applied current density, pH and electrolyte concentration on CrbPt degradation has been studied. The degradation of CrbPt significantly increased at the initial stages of the process with increasing current density. However, further increase in current density did not affect the degradation rate. While complete degradation of CrbPt was provided at pH 7, the degradation rates were 49% and 75% at pH 9 and 4, respectively. Besides, increasing supporting electrolyte (Na 2 SO 4 ) concentration provided higher degradation rate but further increase in Na 2 SO 4 concentration did not provide higher degradation rate due to excess amount of SO 4 -2 . According to the DFT calculations, the formation of [Pt(NH 3 ) 2 (H 2 O) 2 ] 2+ and [Pt(NH 3 ) 2 (OH) 2 ] takes place with molecular weights of 265 and 263gmol -1 , respectively. Toxicity of treated samples at BDD and Ti/RuO 2 electrodes has been also evaluated in this study. The results showed that Ti/RuO 2 anode provided zero toxicity at the end of the process. Copyright © 2017 Elsevier B.V. All rights reserved.

Photocatalytic degradation of furfural in aqueous solution by N-doped titanium dioxide nanoparticles.

PubMed

Veisi, Farzaneh; Zazouli, Mohammad Ali; Ebrahimzadeh, Mohammad Ali; Charati, Jamshid Yazdani; Dezfoli, Amin Shiralizadeh

2016-11-01

The photocatalytic degradation of furfural in aqueous solution was investigated using N-doped titanium dioxide nanoparticles under sunlight and ultraviolet radiation (N-TiO 2 /Sun and N-TiO 2 /UV) in a lab-scale batch photoreactor. The N-TiO 2 nanoparticles prepared using a sol-gel method were characterized using XRD, X-ray photoelectron spectroscopy (XPS), and SEM analyses. Using HPLC to monitor the furfural concentration, the effect of catalyst dosage, contact time, initial solution pH, initial furfural concentration, and sunlight or ultraviolet radiation on the degradation efficiency was studied. The efficiency of furfural removal was found to increase with increased reaction time, nanoparticle loading, and pH for both processes, whereas the efficiency decreased with increased furfural concentration. The maximum removal efficiencies for the N-TiO 2 /UV and N-TiO 2 /Sun processes were 97 and 78 %, respectively, whereas the mean removal efficiencies were 80.71 ± 2.08 % and 62.85 ± 2.41 %, respectively. In general, the degradation and elimination rate of furfural using the N-TiO 2 /UV process was higher than that using the N-TiO 2 /Sun process.

Effect of Al doping on performance of ZnO thin film transistors

NASA Astrophysics Data System (ADS)

Dong, Junchen; Han, Dedong; Li, Huijin; Yu, Wen; Zhang, Shendong; Zhang, Xing; Wang, Yi

2018-03-01

In this work, we investigate the Aluminum-doped Zinc Oxide (AZO) thin films and their feasibility as the active layer for thin film transistors (TFTs). A comparison on performance is made between the AZO TFTs and ZnO TFTs. The electrical properties such as saturation mobility, subthreshold swing, and on-to-off current ratio are improved when AZO is utilized as the active layer. Oxygen component of the thin film materials indicates that Al is the suppressor for oxygen defect in active layer, which improves the subthreshold swing. Moreover, based on band structure analyzation, we observe that the carrier concentration of AZO is higher than ZnO, leading to the enhancement of saturation mobility. The microstructure of the thin films convey that the AZO films exhibit much smaller grain boundaries than ZnO films, which results in the lower off-state current and higher on-to-off current ratio of AZO TFTs. The AZO thin films show huge potential to be the active layer of TFTs.

Characterization of Strain Due to Nitrogen Doping Concentration Variations in Heavy Doped 4H-SiC

NASA Astrophysics Data System (ADS)

Yang, Yu; Guo, Jianqiu; Raghothamachar, Balaji; Chan, Xiaojun; Kim, Taejin; Dudley, Michael

2018-02-01

Highly doped 4H-SiC will show a significant lattice parameter difference with respect to the undoped material. We have applied the recently developed monochromatic contour mapping technique for 4H-SiC crystals to a 4H-SiC wafer crystal characterized by nitrogen doping concentration variation across the whole sample surface using a synchrotron monochromatic x-ray beam. Strain maps of 0008 and - 2203 planes were derived by deconvoluting the lattice parameter variations from the lattice tilt. Analysis reveals markedly different strain values within and out of the basal plane indicating the strain induced by nitrogen doping is anisotropic in the 4H-SiC hexagonal crystal structure. The highest strain calculated along growth direction [0001] and along [1-100] on the closed packed basal plane is up to - 4 × 10-4 and - 2.7 × 10-3, respectively. Using an anisotropic elasticity model by separating the whole bulk crystal into numerous identical rectangular prism units, the measured strain was related to the doping concentration and the calculated highest nitrogen level inside wafer crystal was determined to be 1.5 × 1020 cm-3. This is in agreement with observation of double Shockley stacking faults in the highly doped region that are predicted to nucleate at nitrogen levels above 2 × 1019 cm-3.

The physical properties of Li-doped g-C{sub 3}N{sub 4} monolayer sheet investigated by the first-principles

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

Ruan, Linwei; Xu, Gengsheng; Gu, Lina

2015-06-15

Highlights: • Systematically research on Li-doped g-C{sub 3}N{sub 4} monolayer sheets by first-principles calculation. • Optimal dopant concentration for optical absorption is 7.12%. • Thermodynamics stability of the doped substrate g-C{sub 3}N{sub 4} decreased with Li dopant concentration increasing. • The values of work function Φ decreased monotonously with the increasing of Li dopant concentration. - Abstract: The geometric, electronic, optical properties, thermodynamic stability, and work function of Li-doped g-C{sub 3}N{sub 4} monolayer were investigated by the first-principles calculation. It was found that the Li atoms were preferentially substituted the open-hollow sites of g-C{sub 3}N{sub 4}. Interestingly, the “odd” numbermore » of Li doped g-C{sub 3}N{sub 4} showed metallic properties, while the “even” number of Li atoms widened the band gap of g-C{sub 3}N{sub 4}. The HOMO and LUMO distributions reveal that the active sites located at edge N and C atoms for both pristine and the Li-doped g-C{sub 3}N{sub 4}. In addition, thermodynamic analysis showed that the doped Li atoms reduced the thermodynamic stability of g-C{sub 3}N{sub 4} monolayer sheets.« less

Fabrication and characterization of a magnetic micro-actuator based on deformable Fe-doped PDMS artificial cilium using 3D printing

NASA Astrophysics Data System (ADS)

Liu, Fengli; Alici, Gursel; Zhang, Binbin; Beirne, Stephen; Li, Weihua

2015-03-01

This paper proposes the use of a 3D extrusion printer to fabricate artificial magnetic cilium. The cilia are fabricated using polydimethylsiloxane (PDMS) doped with iron particles so that they remain slender and flexible. They can be driven by a magnetic field to closely mimic the behaviour of biological cilia. Doping iron particles to the polymers has already been done; however, to the best of our knowledge, printing such active and soft magnetic structures has not. The existing methods for manufacturing magnetic polymeric structures are complex and difficult to use for the fabrication of micro-sized high-aspect-ratio cilia. The 3D printing technique we propose here is simple and inexpensive compared to previously suggested fabrication methods. In this study, free-standing magnetic PDMS cilia were fabricated in different sizes up to 5 mm in length and 1 mm in width. The stress-strain curves of the PDMS cilia were experimentally obtained to quantify the effect of the concentration of the iron particles on the modulus of elasticity of the cilia. The higher the iron concentration, the higher the modulus of elasticity. We have quantified the characteristics of the cilia made of 40% w/w iron particles in PDMS. A single cilium (5 × 1 × 0.0035 mm) can output up to 27 μN blocking force under a magnetic field of 160 mT. These cilia can be used as a mixer in lap-on-chip applications and as the anchoring and propulsion legs of endoscopic capsule robots operating within the gastrointestinal tract of humans. Analytical expressions estimating the blocking force are established and compared with the experimental results.

Light-induced degradation in gallium-doped silicon

NASA Astrophysics Data System (ADS)

Lindroos, Jeanette; Yli-Koski, Marko; Haarahiltunen, Antti; Schubert, Martin C.; Savin, Hele

2012-02-01

Light-induced degradation (LID) is a lifetime-decreasing effect in silicon solar cells attributed to the formation of B-O defect complexes during illumination [1-2]. However, Savin et al. [3] have recently observed degradation similar to LID in B- and P-doped Si contaminated with Cu, suggesting that Cu might be the cause of LID. Since Ga-doped Si is considered a degradation-free option to conventional B-doped Si [2], lifetime stability should also be studied in Cu-contaminated Ga-Si. Hence, in this paper, we intentionally contaminated high-oxygen 0.41 and 10.1 φcm Ga-doped Cz-Si with Cu and subjected the material to illumination. No lifetime degradation was measured with μ-PCD in clean Ga-Si or at low Cu levels, which is in agreement with the previously reported LID-free behavior of Ga-Si [2]. However, at higher Cu levels (20 ppb), a clear lifetime degradation was observed in Ga-Si. This lifetime degradation increased with increasing Cu concentration or with increasing wafer resistivity. [1] J. Schmidt, A.G. Aberle and R. Hezel, 26th IEEE PVSC, Anaheim, CA, USA, p.13-18 (1997). [2] S.W. Glunz, S. Rein, W. Warta, J. Knobloch and W. Wettling. Sol. Energ. Mat. Sol. C. 65, 219-229 (2001). [3] H. Savin, M. Yli-Koski and A. Haarahiltunen. Appl. Phys. Lett. 95, 152111 (2009).

High carrier concentration p-type transparent conducting oxide films

DOEpatents

Yan, Yanfa; Zhang, Shengbai

2005-06-21

A p-type transparent conducting oxide film is provided which is consisting essentially of, the transparent conducting oxide and a molecular doping source, the oxide and doping source grown under conditions sufficient to deliver the doping source intact onto the oxide.

Effect of Sn doping on structural, mechanical, optical and electrical properties of ZnO nanoarrays prepared by sol-gel and hydrothermal process

NASA Astrophysics Data System (ADS)

Agarwal, Manish Baboo; Sharma, Akash; Malaidurai, M.; Thangavel, R.

2018-05-01

Undoped and Sn doped Zinc oxide nanorods were prepared by two step process: initially growth of seed layers by sol-gel spin coating technique and then zinc oxide nanorods by hydrothermal process using the precursors zinc nitrate hexahydrate, hexamine and tin chloride. The effects on the electrical, optical, mechanical and structural properties for various Sn concentrations were studied. The crystalline phase determination from X-ray diffraction (XRD) confirms that Sn doped ZnO nanorods have hexagonal wurtzite structure. The variations of stress and strain with different doping concentration of Sn in ZnO nanorods were studied. The doping effect on electrical properties and optical bandgap is estimated by current voltage characteristics and absorbance spectra respectively. The surface morphology was studied with field emission scanning electron microscope (FESEM), which shows that the formation of hexagonal nanorods arrays with increasing Sn concentration. The calculated value of Young's modulus of elasticity (Y) for all the samples remains same. These results can be used in optoelectronic devices.

Hall-effect measurements of metalorganic vapor-phase epitaxy-grown p-type homoepitaxial GaN layers with various Mg concentrations

NASA Astrophysics Data System (ADS)

Horita, Masahiro; Takashima, Shinya; Tanaka, Ryo; Matsuyama, Hideaki; Ueno, Katsunori; Edo, Masaharu; Suda, Jun

2016-05-01

Mg-doped p-type gallium nitride (GaN) layers with doping concentrations in the range from 6.5 × 1016 cm-3 (lightly doped) to 3.8 × 1019 cm-3 (heavily doped) were investigated by Hall-effect measurement for the analysis of hole concentration and mobility. p-GaN was homoepitaxially grown on a GaN free-standing substrate by metalorganic vapor-phase epitaxy. The threading dislocation density of the p-GaN was 4 × 106 cm-2 measured by cathodoluminescence mapping. Hall-effect measurements of p-GaN were carried out at a temperature in the range from 160 to 450 K. A low compensation ratio of less than 1% was revealed. We also obtained the depth of the Mg acceptor level of 235 meV considering the lowering effect by the Coulomb potential of ionized acceptors. The hole mobilities of 33 cm2 V-1 s-1 at 300 K and 72 cm2 V-1 s-1 at 200 K were observed in lightly doped p-GaN.

Fluorine-doped NiO nanostructures: Structural, morphological and spectroscopic studies

NASA Astrophysics Data System (ADS)

Singh, Kulwinder; Kumar, Manjeet; Singh, Dilpreet; Singh, Manjinder; Singh, Paviter; Singh, Bikramjeet; Kaur, Gurpreet; Bala, Rajni; Thakur, Anup; Kumar, Akshay

2018-05-01

Nanostructured NiO has been prepared by co-precipitation method. In this study, the effect of fluorine doping (1, 3 and 5 wt. %) on the structural, morphological as well as optical properties of NiO nanostructures has been studied. X-ray diffraction (XRD) has employed for studying the structural properties. Cubic crystal structure of NiO was confirmed by the XRD analysis. Crystallite size increased with increase in doping concentration. Nelson-Riley factor (NRF) analysis indicated the presence of defect states in the synthesized samples. Field emission scanning electron microscopy showed the spherical morphology of the synthesized samples and also revealed that the particle size varied with dopant content. The optical properties were studied using UV-Visible Spectroscopy. The results indicated that the band gap energy of the synthesized nanostructures decreased with increase in doping concentration upto 3% but increased as the doping concentration was further raised to 5%. This can be ascribed to the defect states variations in the synthesized samples. The results suggested that the synthesized nanostructures are promising candidate for optoelectronic as well as gas sensing applications.

Electrically conductive nanostructured silver doped zinc oxide (Ag:ZnO) prepared by solution-immersion technique

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

Afaah, A. N., E-mail: afaahabdullah@yahoo.com; Asib, N. A. M., E-mail: amierahasib@yahoo.com; Aadila, A., E-mail: aadilaazizali@gmail.com

2016-07-06

p-type ZnO films have been fabricated on ZnO-seeded glass substrate, using AgNO{sub 3} as a source of silver dopant by facile solution-immersion. Cleaned glass substrate were seeded with ZnO by mist-atomisation, and next the seeded substrates were immersed in Ag:ZnO solution. The effects of Ag doping concentration on the Ag-doped ZnO have been investigated. The substrates were immersed in different concentrations of Ag dopant with variation of 0, 1, 3, 5 and 7 at. %. The surface morphology of the films was characterized by field emission scanning electron microscope (FESEM). In order to investigate the electrical properties, the films weremore » characterized by Current-Voltage (I-V) measurement. FESEM micrographs showed uniform distribution of nanostructured ZnO and Ag:ZnO. Besides, the electrical properties of Ag-doped ZnO were also dependent on the doping concentration. The I-V measurement result indicated the electrical properties of 1 at. % Ag:ZnO thin film owned highest electrical conductivity.« less

Effect of aging on ZnO and nitrogen doped P-Type ZnO

NASA Astrophysics Data System (ADS)

Majumdar, Sayanee; Bhunia, S.

2012-06-01

The withholding of p-type conductivity in as-prepared and 3% nitrogen (N) doped zinc oxide (ZnO) even after 2 months of preparation was systematically studied. The films were grown on glass substrates by pulsed laser deposition (PLD) at 350 °C under different conditions, viz. under vacuum and at oxygen (O) ambience using 2000 laser pulses. In O ambience for as-prepared ZnO the carrier concentration reduces and mobility increases with increasing number of laser shots. The resistivity of as-prepared and 3% N-doped ZnO is found to increase with reduction in hole concentration after 60 days of aging while maintaining its p-type conductivity irrespective of growth condition. AFM and electrical properties showed aging effect on the doped and undoped samples. For as-prepared ZnO, with time, O migration makes the film high resistive by reducing free electron concentrations. But for N-doped p-type ZnO, O-migration, metastable N and hydrogen atom present in the source induced instability in structure makes it less conducting p-type.

Tunable magnetism of 3d transition metal doped BiFeO3

NASA Astrophysics Data System (ADS)

Lu, S.; Li, C.; Zhao, Y. F.; Gong, Y. Y.; Niu, L. Y.; Liu, X. J.; Wang, T.

2017-10-01

Electronic polarization or bond relaxation can effectively alter the electronic and magnetic behavior of materials by doping impurity atom. For this aim, the thermodynamic, electronic and magnetic performances of cubic BiFeO3 have been modulated by the 3d transition metal (TM) dopants (Sc, Ti, V, Cr, Mn, Co, Ni, Cu and Zn) based on the density functional theory. Results show that the doped specimen with low impurity concentration is more stable than that with high impurity concentration. The Mulliken charge values and spin magnetic moments of TM element are making major changes, while those of all host atoms are making any major changes. Especially, it is the linear relation between the spin magnetic moments of TM dopants and the total magnetic moment of doped specimens; thus, the variations of total magnetic moment of doped specimens are decided by the spin magnetic moments of TM dopants, thought the total magnetic moments of doped specimens mainly come from Fe atom and TM dopants. Besides, as double TM atoms substitution the Fe atoms, the Sc-, Ti-, Mn-, Co- and Zn-doped specimens show AFM state, while the V-, Cr-, Ni- and Cu-doped specimens show FM state.

Ferromagnetic properties of Mn-doped HfS2 monolayer under strain

NASA Astrophysics Data System (ADS)

Ma, Xu; Zhao, Xu; Wu, Ninghua; Xin, Qianqian; Liu, Xiaomeng; Wang, Tianxing; Wei, Shuyi

2017-12-01

Using the first-principles calculations, we investigated electronic and magnetic properties of Mn-doped HfS2 monolayer for 4% and 8% Mn concentration. We study the strain tuning of electronic and magnetic properties of 4% Mn-doped HfS2 monolayer firstly. Our results show that the Mn-doped HfS2 monolayer is magnetic nanomaterial without strain. It keeps this character until the compressive strain comes to -8%, and the magnetism disappear with lager compressive strain. With the increasing tensile strain, the doped system transforms from semiconductor to half-metallic when the tensile strain is equivalent to or greater than 5%. The largest half-metallic gap is 1.307 eV at 5% tensile strain and the magnetic moment always keeps about 3μB, which indicates that Mn-doped HfS2 monolayer can be a candidate for superior half-metallic namomaterial. Furthermore, we find two Mn dopants couple ferromagnetically via antiferromagnetic (AFM) p-d exchange interaction at the environment of 8% concentration. It keeps the properties of magnetic semiconductor under two Mn-doped configurations with different Mn-Mn separations. Our studies predict Mn-doped HfS2 monolayer under strain to be candidates for dilute magnetic semiconductors.

Doping properties of cadmium-rich arsenic-doped CdTe single crystals: Evidence of metastable AX behavior

NASA Astrophysics Data System (ADS)

Nagaoka, Akira; Kuciauskas, Darius; Scarpulla, Michael A.

2017-12-01

Cd-rich composition and group-V element doping are of interest for simultaneously maximizing the hole concentration and minority carrier lifetime in CdTe, but the critical details concerning point defects are not yet fully established. Herein, we report on the properties of arsenic doped CdTe single crystals grown from Cd solvent by the travelling heater method. The photoluminescence spectra and activation energy of 74 ± 2 meV derived from the temperature-dependent Hall effect are consistent with AsTe as the dominant acceptor. Doping in the 1016 to 1017/cm3 range is achieved for measured As concentrations between 1016 and 1020/cm3 with the highest doping efficiency of 40% occurring near 1017 As/cm3. We observe persistent photoconductivity, a hallmark of light-induced metastable configuration changes consistent with AX behavior. Additionally, quenching experiments reveal at least two mechanisms of increased p-type doping in the dark, one decaying over 2-3 weeks and the other persisting for at least 2 months. These results provide essential insights for the application of As-doped CdTe in thin film solar cells.

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

Structural, Optical, and Electrical Properties of Cobalt-Doped CdS Quantum Dots

NASA Astrophysics Data System (ADS)

Thambidurai, M.; Muthukumarasamy, N.; Velauthapillai, Dhayalan; Agilan, S.; Balasundaraprabhu, R.

2012-04-01

In the present work, a systematic study has been carried out to understand the influence of cobalt (Co) doping on various properties of CdS nanoparticles. CdS and Co-doped CdS quantum dots have been prepared at room temperature using a chemical precipitation method without using catalysts, capping agents, or surfactants. X-ray diffraction reveals that both undoped and Co-doped CdS nanoparticles exhibit hexagonal structure without any impurity phase, and the lattice constants of CdS nanoparticles are observed to decrease slightly with increasing cobalt concentration. High-resolution transmission electron microscopy (HRTEM) shows that the particle size of CdS and 5.02% Co-doped CdS nanoparticles is in the range of 2 nm to 4 nm. The Raman spectra of Co-doped CdS nanoparticles exhibit a red-shift compared with that of bulk CdS, which may be attributed to optical phonon confinement. The optical absorption spectra of Co-doped CdS nanoparticles also exhibit a red-shift with respect to that of CdS nanoparticles. The electrical conductivity of CdS and Co-doped CdS nanoparticles is found to increase with increasing temperature and cobalt concentration.

Electrical and structural properties of Nb-doped TiO2 at different Nb concentrations deposited by spin coating technique

NASA Astrophysics Data System (ADS)

Saurdi, I.; Shafura, A. K.; Mamat, M. H.; Ishak, A.; Rusop, M.

2018-05-01

In this paper, the Nb-doped TiO2 films were deposited on glass substrate and their electrical and structural properties were investigated. The results revealed that the resistivity of Nb-doped TiO2 films of 0 at.%, 1 at.%, 3 at.%, 5 at.% and 7 at.% were 2.78 × 105, 1.35 × 105 Ω.cm, 5.89 × 104 Ω.cm, 9.20 × 102 Ω.cm and 9.56 × 103 Ω.cm, respectively. Where, the lowest resistivity of 9.20 × 102 Ω.cm was obtained at 5at.% Nb-doped TiO2 films. The resistivity of Nb-doped TiO2 films decreases as the Nb concentration increased from 0 at.% to 5 at.%. However, the resistivity decrease at 7 at.% Nb-doped TiO2 films. Meanwhile, from the FESEM images the Nb-doped TiO2 films with 0 at.%, 1 at.%, 3 at.% and 5 at.% Nb had a rough and porous structures were observed. However, the Nb-doped TiO2 at 7 at.% has a agglomerated and denser structures.

Effect of K-doping on structural and optical properties of ZnO thin films

NASA Astrophysics Data System (ADS)

Xu, Linhua; Li, Xiangyin; Yuan, Jun

2008-09-01

In this work, K-doped ZnO thin films were prepared by a sol-gel method on Si(111) and glass substrates. The effect of different K-doping concentrations on structural and optical properties of the ZnO thin films was studied. The results showed that the 1 at.% K-doped ZnO thin film had the best crystallization quality and the strongest ultraviolet emission ability. When the concentration of K was above 1 at.%, the crystallization quality and ultraviolet emission ability dropped. For the K-doped ZnO thin films, there was not only ultraviolet emission, but also a blue emission signal in their photoluminescent spectra. The blue emission might be connected with K impurity or/and the intrinsic defects (Zn interstitial and Zn vacancy) of the ZnO thin films.

Hole mobility in various transition-metal-oxides doped organic semiconductor films

NASA Astrophysics Data System (ADS)

Yoo, Seung-Jun; Lee, Jeong-Hwan; Kim, Jae-Min; Kim, Jang-Joo

2017-01-01

Hole mobility in various p-doped organic semiconductors possessing different energetic disorder parameters in low-to-moderate doping range is reported. The hole mobility is reduced by orders of magnitude and converged to 10-7-10-6 cm2/Vs at a doping concentration of 5 mol. % for all the materials, even though the pristine organic films possess orders of magnitude of different mobilities from 10-5 to 10-3 cm2/Vs. These results indicate that the ionized dopants behave as traps for generated carriers to reduce the mobility. Further increase in the doping concentration either increases or decreases the mobility depending on the energetic disorder parameters of the organic films. These phenomena are interpreted based on the Coulomb trap depth of the ionized dopants and energetic disorder of the host layers.

The mechanism of the UV band edge photorefractivity suppression in highly doped LiNbO3:Zr crystals

NASA Astrophysics Data System (ADS)

Xin, Fei-fei

2017-11-01

The ultraviolet (UV) band edge photorefractivity of LiNbO3:Zr at 325 nm has been investigated. The experimental results show that the resistance against photorefraction at 325 nm is quite obvious but not as strong as that at 351 nm, when the doping concentration of Zr reaches 2.0 mol%. It is reported that the photorefractivity in other tetravalently doped LiNbO3 crystals, such as LiNbO3:Hf and LiNbO3:Sn, is enhanced dramatically with doping concentration over threshold. Here we give an explicit explanation on such seemly conflicting behaviors of tetravalently doped LiNbO3, which is ascribed to the combined effect of increased photoconductivity and the absorption strength of the band edge photorefractive centers.

Synthesis of Antimony Doped Amorphous Carbon Films

NASA Astrophysics Data System (ADS)

Okuyama, H.; Takashima, M.; Akasaka, H.; Ohtake, N.

2013-06-01

We report the effects of antimony (Sb) doping on the electrical and optical properties of amorphous carbon (a-C:H) films grown on silicon and copper substrates by magnetron sputtering deposition. For film deposition, the mixture targets fabricated from carbon and antimony powders was used. The atomic concentration of carbon, hydrogen, and antimony, in the film deposited from the 1.0 mol% Sb containing target were 81, 17, 2 at.%, respectively. These elements were homogeneously distributed in the film. On the structural effect, the average continuous sp2 carbon bonding networks decreased with Sb concentration increasing, and defects in the films were increased with the Sb incorporation because atomic radius of Sb atoms is twice larger size than that of carbon. The optical gap and the electrical resistivity were carried out before and after the Sb doping. The results show that optical gap dropped from 3.15 to 3.04 eV corresponding to non-doping to Sb-doping conditions, respectively. The electrical resistivity reduced from 10.5 to 1.0 MΩm by the Sb doping. These results suggest the doping level was newly formed in the forbidden band.

Effect of Gd3+ Ions on the Thermal Behavior, Optical, Electrical and Magnetic Properties of PbS Thin Films

NASA Astrophysics Data System (ADS)

Ravishankar, S.; Balu, A. R.; Nagarethinam, V. S.

2018-02-01

This paper reports the effect of Gd doping concentration on the thermal behavior, structural, morphological, optical, electrical and magnetic properties of PbS thin films. Gd doping concentration in PbS was varied as 0 wt.%, 1 wt.%, 2 wt.%, 3 wt.% and 4 wt.%, respectively. Thermogravimetric-Differential Thermal Analysis curves confirm that both the undoped and doped films become well crystallized above 354°C and 342°C, respectively. X-ray diffraction studies confirm that all the films exhibit face-centered cubic crystal structure with a strong (2 0 0) preferential growth. Undoped films exhibit triangular-shaped grains which modify to small cuboids with Gd doping. Energy dispersive x-ray spectra confirm the presence of Gd in the doped films. Transmission electron microscopy images confirm the presence of nanosized grains for both the undoped and doped films. The doped films showed increased transparency and improved magnetic behaviour. The results obtained confirm that Gd3+, a rare earth ion, strongly influences the physical properties of PbS thin films to a large extent.

Synthesis, Optical and Photoluminescence Properties of Cu-Doped Zno Nano-Fibers Thin Films: Nonlinear Optics

NASA Astrophysics Data System (ADS)

Ganesh, V.; Salem, G. F.; Yahia, I. S.; Yakuphanoglu, F.

2018-03-01

Different concentrations of copper-doped zinc oxide thin films were coated on a glass substrate by sol-gel/spin-coating technique. The structural properties of pure and Cu-doped ZnO films were characterized by different techniques, i.e., atomic force microscopy (AFM), photoluminescence and UV-Vis-NIR spectroscopy. The AFM study revealed that pure and doped ZnO films are formed as nano-fibers with a granular structure. The photoluminescence spectra of these films showed a strong ultraviolet emission peak centered at 392 nm and a strong blue emission peak cantered at 450 nm. The optical band gap of the pure and copper-doped ZnO thin films calculated from optical transmission spectra (3.29-3.23 eV) were found to be increasing with increasing copper doping concentration. The refractive index dispersion curve of pure and Cu-doped ZnO film obeyed the single-oscillator model. The optical dispersion parameters such as E o , E d , and n_{∞}2 were calculated. Further, the nonlinear refractive index and nonlinear optical susceptibility were also calculated and interpreted.

Systematic approach on the fabrication of Co doped ZnO semiconducting nanoparticles by mixture of fuel approach for Antibacterial applications

NASA Astrophysics Data System (ADS)

Rajendar, V.; Dayakar, T.; Shobhan, K.; Srikanth, I.; Venkateswara Rao, K.

2014-11-01

Zinc oxide (ZnO) is a wide band gap semiconductor (3.2 eV) with a high exciton binding energy (60 meV), where it has wide applications in advanced spintronic devices. The theoretical prediction of room temperature ferromagnetism and also antibacterial activity will be possible through the investigation of diluted magnetic semiconductors (DMS), such as transition metal doped ZnO, especially Cobalt doped ZnO. The aim of the work is the synthesis of Cobalt (Co) doped ZnO nanopowders were prepared Zn1-xCoxO (0 ⩽ x ⩾ 0.09) nanopowders from Sol-Gel auto combustion method have been synthesized with precursors such as Zinc and Cobalt nitrates with the assistance Ammonium acetate & Urea as fuel by increasing the cobalt concentration in zinc oxide and their structural, morphological, optical, Thermal, magnetic and antibacterial properties were studied by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), Transmission Electron microscope (TEM), UV-visible spectroscopy, thermo gravimetric/differential thermal analysis (TG/DTA) and vibrating sample magneto meter (VSM). From the antibacterial studies, against gram positive Bacillus subtilis bacteria is most abundant bacteria in soil and indoor atmosphere, which affects the stored spintronic devices so that the devices should be made with antibacterial activity of DMS like Co doped ZnO. In this article is found that ZnO:Co nanopowders with higher Co doping level (0.07 and 0.09 wt%) exhibit good antibacterial efficiency. The magnetization curves obtained using vibrating sample magnetometer (VSM) show a sign of strong room temperature ferromagnetic behavior when the Co doping level is 0.05 wt% and a weak room temperature ferromagnetic behavior Co doping level is below 0.07 wt%, and also they found to exhibit antiferromagnetic and paramagnetic properties, when the Co doping levels are 0.07 and 0.09 wt%, respectively, to enhance and increase the special magnetic and antibacterial property for sophisticated devices for the sustainable technologies.

Performance enhancement of GaN ultraviolet avalanche photodiodes with p-type δ-doping

NASA Astrophysics Data System (ADS)

Bayram, C.; Pau, J. L.; McClintock, R.; Razeghi, M.

2008-06-01

High quality δ-doped p-GaN is used as a means of improving the performance of back-illuminated GaN avalanche photodiodes (APDs). Devices with δ-doped p-GaN show consistently lower leakage current and lower breakdown voltage than those with bulk p-GaN. APDs with δ-doped p-GaN also achieve a maximum multiplication gain of 5.1×104, more than 50 times higher than that obtained in devices with bulk p-GaN. The better device performance of APDs with δ-doped p-GaN is attributed to the higher structural quality of the p-GaN layer achieved via δ-doping.

Spectral hole lifetimes and spin population relaxation dynamics in neodymium-doped yttrium orthosilicate

NASA Astrophysics Data System (ADS)

Cruzeiro, E. Zambrini; Tiranov, A.; Usmani, I.; Laplane, C.; Lavoie, J.; Ferrier, A.; Goldner, P.; Gisin, N.; Afzelius, M.

2017-05-01

We present a detailed study of the lifetime of optical spectral holes due to population storage in Zeeman sublevels of Nd3 +:Y2SiO5 . The lifetime is measured as a function of magnetic field strength and orientation, temperature, and Nd3 + doping concentration. At the lowest temperature of 3 K we find a general trend where the lifetime is short at low field strengths, then increases to a maximum lifetime at a few hundred mT, and then finally decays rapidly for high field strengths. This behavior can be modeled with a relaxation rate dominated by Nd3 +-Nd3 + cross relaxation at low fields and spin lattice relaxation at high magnetic fields. The maximum lifetime depends strongly on both the field strength and orientation, due to the competition between these processes and their different angular dependencies. The cross relaxation limits the maximum lifetime for concentrations as low as 30 ppm of Nd3 + ions. By decreasing the concentration to less than 1 ppm we could completely eliminate the cross relaxation, reaching a lifetime of 3.8 s at 3 K. At higher temperatures the spectral hole lifetime is limited by the magnetic-field-independent Raman and Orbach processes. In addition we show that the cross relaxation rate can be strongly reduced by creating spectrally large holes of the order of the optical inhomogeneous broadening. Our results are important for the development and design of new rare-earth-ion doped crystals for quantum information processing and narrow-band spectral filtering for biological tissue imaging.

High-energy electron-induced damage production at room temperature in aluminum-doped silicon

NASA Technical Reports Server (NTRS)

Corbett, J. W.; Cheng, L. J.; Jaworowski, A.; Karins, J. P.; Lee, Y. H.; Lindstroem, L.; Mooney, P. M.; Oehrlen, G.; Wang, K. L.

1979-01-01

DLTS and EPR measurements are reported on aluminum-doped silicon that was irradiated at room temperature with high-energy electrons. Comparisons are made to comparable experiments on boron-doped silicon. Many of the same defects observed in boron-doped silicon are also observed in aluminum-doped silicon, but several others were not observed, including the aluminum interstitial and aluminum-associated defects. Damage production modeling, including the dependence on aluminum concentration, is presented.

Near-Unity Emitting Copper-Doped Colloidal Semiconductor Quantum Wells for Luminescent Solar Concentrators.

PubMed

Sharma, Manoj; Gungor, Kivanc; Yeltik, Aydan; Olutas, Murat; Guzelturk, Burak; Kelestemur, Yusuf; Erdem, Talha; Delikanli, Savas; McBride, James R; Demir, Hilmi Volkan

2017-08-01

Doping of bulk semiconductors has revealed widespread success in optoelectronic applications. In the past few decades, substantial effort has been engaged for doping at the nanoscale. Recently, doped colloidal quantum dots (CQDs) have been demonstrated to be promising materials for luminescent solar concentrators (LSCs) as they can be engineered for providing highly tunable and Stokes-shifted emission in the solar spectrum. However, existing doped CQDs that are aimed for full solar spectrum LSCs suffer from moderately low quantum efficiency, intrinsically small absorption cross-section, and gradually increasing absorption profiles coinciding with the emission spectrum, which together fundamentally limit their effective usage. Here, the authors show the first account of copper doping into atomically flat colloidal quantum wells (CQWs). In addition to Stokes-shifted and tunable dopant-induced photoluminescence emission, the copper doping into CQWs enables near-unity quantum efficiencies (up to ≈97%), accompanied by substantially high absorption cross-section and inherently step-like absorption profile, compared to those of the doped CQDs. Based on these exceptional properties, the authors have demonstrated by both experimental analysis and numerical modeling that these newly synthesized doped CQWs are excellent candidates for LSCs. These findings may open new directions for deployment of doped CQWs in LSCs for advanced solar light harvesting technologies. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Scintillation properties of YAlO3 doped with Lu and Nd perovskite single crystals

NASA Astrophysics Data System (ADS)

Akatsuka, Masaki; Usui, Yuki; Nakauchi, Daisuke; Kato, Takumi; Kawano, Naoki; Okada, Go; Kawaguchi, Noriaki; Yanagida, Takayuki

2018-05-01

YAlO3 (YAP) single crystals doped with Lu and Nd were grown by the Floating Zone (FZ) method to evaluate their scintillation properties particularly emissions in the near-infrared (NIR) range. The Nd concentration was fixed to 0 or 1 mol% while the Lu concentration was varied from 0 to 30%. When X-ray was irradiated, the scintillation of Nd-doped samples was observed predominantly at 1064 nm due to 4F3/2 → 4I11/2 transition of Nd3+. In contrast, a weak emission around 700 nm appeared in the samples doped with only Lu, and the emission origin was attributed to defect centers. In the Nd3+-doped samples, the decay time was 94-157 μs due to the 4f-4f transitions of Nd3+ whereas the Lu-doped samples showed signal with the decay time of 1.45-1.54 ms. The emission origin of the latter signal was attributed to the perovskite lattice defect.

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

Singh, Janpreet; Tripathi, S. K., E-mail: surya@pu.ac.in, E-mail: surya-tr@yahoo.com; Singh, Gurinder

To improve the phase change characteristics of Ge{sub 2}Sb{sub 2}Te{sub 5} (GST), doping is used as one of the effective methods. 4.4 atomic % of Pb doped GST has been studied using first principle calculations. No effect of doping on Te-Ge and Te-Sb bond length has been observed, but the Te-Te bond gets shrink with Pb doping. Due to which the Sb{sub 2}Te{sub 3} segregates as a second phase, with increased doping concentration of Pb in GST alloy. Using such type of calculation, we can calculate the desirable concentration of dopant atoms to prepare the desired material. We can controlmore » any segregation in required material with pre-theoretical calculations. The metallic nature of Pd doped GST has been discussed with band structure plots. The metallic character of alloys calculated as in this paper will be helpful to understand the tuning of conductivity of phase change materials, which helps to enhance the phase change properties.« less

Photogeneration of refractive-index patterns in doped polyimide films.

PubMed

Chakravorty, K K

1993-05-01

A photosensitive benzophenone tetracarboxylic dianhyride-alkylated diamine polyimide formulation has been evaluated for application in an optical interconnection area. The refractive-index patterns in this material were optically recorded by UV-assisted photodoping of sensitizers. The polyimide films were selectively doped with benzoin-type photosensitizers such as benzildimethylketal and benzoin ethyl ether, which cause a decrease in the refractive index. High-dose UV irradiation that causes cross linking of the polyimide chains was also employed for augmenting the refractive-index difference to 0.017 between the doped and undoped regions. Refractive-index variations and lightguiding properties were investigated as a function of doping concentrations and other processing conditions. The author utilized this technique for the fabrication of embedded polyimide channel waveguides. The two photosensitizers have different effects on the waveguiding characteristics of the polyimide films. Losses for benzoin ethyl ether remained low whereas doping with benzildimethylketal caused significant increase in the waveguiding loss at high doping concentrations. Near-field imaging of the output from such waveguides shows good confinement of 815-nm light.