Facile solution-processed aqueous MoOx for feasible application in organic light-emitting diode

NASA Astrophysics Data System (ADS)

Zheng, Qinghong; Qu, Disui; Zhang, Yan; Li, Wanshu; Xiong, Jian; Cai, Ping; Xue, Xiaogang; Liu, Liming; Wang, Honghang; Zhang, Xiaowen

2018-05-01

Solution-processed techniques attract increasing attentions in organic electronics for their low-cost and scalable manufacturing. We demonstrate the favorite hole injection material of solution-processed aqueous MoOx (s-MoOx) with facile fabrication process and cast successful application to constructing efficient organic light-emitting diodes (OLEDs). Atomic force microscopy and X-ray photoelectron spectroscopy analysis show that s-MoOx behaves superior film morphology and non-stoichiometry with slight oxygen deficiency. With tris(8-hydroxy-quinolinato)aluminium as emitting layer, s-MoOx based OLED shows maximum luminous efficiency of 7.9 cd/A and power efficiency of 5.9 lm/W, which have been enhanced by 43.6% and 73.5%, respectively, in comparison with the counterpart using conventional vacuum thermal evaporation MoOx. Current-voltage, impedance-voltage, phase-voltage and capacitance-voltage characteristics of hole-only devices indicate that s-MoOx with two processes of "spin-coating/annealing" shows mostly enhanced hole injection capacity and thus promoting device performance. Our experiments provide an alternative approach for constructing efficient OLED with solution process.

Magnetron Sputtered Molybdenum Oxide for Application in Polymers Solar Cells

NASA Astrophysics Data System (ADS)

Sendova-Vassileva, M.; Dikov, Hr; Vitanov, P.; Popkirov, G.; Gergova, R.; Grancharov, G.; Gancheva, V.

2016-10-01

Thin films of molybdenum oxide were deposited by radio frequency (RF) magnetron sputtering in Ar from a MoO3 target at different deposition power on glass and silicon substrates. The thickness of the films was determined by profilometer measurements and by ellipsometry. The films were annealed in air at temperatures between 200 and 400°C in air. The optical transmission and reflection spectra were measured. The conductivity of the as deposited and annealed films was determined. The crystal structure was probed by Raman spectroscopy. The oxidation state of the surface was studied by X-ray photoelectron spectroscopy (XPS) spectroscopy. The deposition technique described above was used to experiment with MoOx as a hole transport layer (HTL) in polymer solar cells with bulk hetrojunction active layer, deposited by spin coating. The performance of these layers was compared with poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), which is the standard material used in this role. The measured current-voltage characteristics of solar cells with the structure glass/ITO/HTL/Poly(3-hexyl)thiophene (P3HT):[6,6]-phenyl-C61- butyric acid methyl ester (PCBM)/Al demonstrate that the studied MoOx layer is a good HTL and leads to comparable characteristics to those with PEDOT:PSS. On the other hand the deposition by magnetron sputtering guarantees reliable and repeatable HTLs.

Formation of BaSi2 heterojunction solar cells using transparent MoOx hole transport layers

NASA Astrophysics Data System (ADS)

Du, W.; Takabe, R.; Baba, M.; Takeuchi, H.; Hara, K. O.; Toko, K.; Usami, N.; Suemasu, T.

2015-03-01

Heterojunction solar cells that consist of 15 nm thick molybdenum trioxide (MoOx, x < 3) as a hole transport layer and 600 nm thick unpassivated or passivated n-BaSi2 layers were demonstrated. Rectifying current-voltage characteristics were observed when the surface of BaSi2 was exposed to air. When the exposure time was decreased to 1 min, an open circuit voltage of 200 mV and a short circuit current density of 0.5 mA/cm2 were obtained under AM1.5 illumination. The photocurrent density under a reverse bias voltage of -1 V reached 25 mA/cm2, which demonstrates the significant potential of BaSi2 for solar cell applications.

Metal-support interactions during the adsorption of CO on thin layers and islands of epitaxial palladium

NASA Technical Reports Server (NTRS)

Park, C.; Poppa, H.; Soria, F.

1984-01-01

Islands and continuous layers of palladium were grown in an ultrahigh vacuum on substrates of Mo(110)c(14 x 7)-O, designated MoO(x), and of clean Mo(110). It was found that as-deposited islands and layers exhibited bulk palladium adsorption properties for CO when deposited at room temperature and for palladium thicknesses in excess of about 3 monolayers. CO adsorption was drastically reduced, however, on annealing. For islands, annealing temperatures of as low as 400 K led to some reduction in CO adsorption whereas more severe reductions were found to occur at 600 K for islands and at 800 K for continuous multilayers. The deactivation depended on the palladium thickness, the substrate species and the extent of thermal treatments. Auger electron spectroscopy, temperature-programmed desorption and Delta-Phi measurements were combined to interpret the deactivation behavior in terms of substrate-support interactions involving the diffusion of substrate species towards the palladium surface.

Direct and Dry Deposited Single-Walled Carbon Nanotube Films Doped with MoO(x) as Electron-Blocking Transparent Electrodes for Flexible Organic Solar Cells.

PubMed

Jeon, Il; Cui, Kehang; Chiba, Takaaki; Anisimov, Anton; Nasibulin, Albert G; Kauppinen, Esko I; Maruyama, Shigeo; Matsuo, Yutaka

2015-07-01

Organic solar cells have been regarded as a promising electrical energy source. Transparent and conductive carbon nanotube film offers an alternative to commonly used ITO in photovoltaics with superior flexibility. This communication reports carbon nanotube-based indium-free organic solar cells and their flexible application. Direct and dry deposited carbon nanotube film doped with MoO(x) functions as an electron-blocking transparent electrode, and its performance is enhanced further by overcoating with PSS. The single-walled carbon nanotube organic solar cell in this work shows a power conversion efficiency of 6.04%. This value is 83% of the leading ITO-based device performance (7.48%). Flexible application shows 3.91% efficiency and is capable of withstanding a severe cyclic flex test.

Electronic structure calculations on multiply charged anions containing M bond S bonds (M = Cr, Mo, W) and their heterobimetallic cluster complexes

NASA Astrophysics Data System (ADS)

Gili, Pedro; Tsipis, Athanassios C.

Molecular and electronic structures of multiply charged mononuclear [CrS4]2-/3-, [MoOxS4-x]2-/3- (x = 0-4) and [WS4]2-/3- anionic species, and their heterobimetallic dinuclear and trinuclear clusters formulated as [MoOS3(CuCl)]2-, [WOS3(CuCl)]2-, [MoS4{Cu(CN)}]2-, [(CN)Cu(?-CrS4)Cu(CN)]2-, [(CN)Cu(?-MoS4)Cu(CN)]2-, [ClCu(?-MoS4)CuCl]2-, [Cl2Fe(?-MoS4)CuCl2]2-, and [(CN)Cu(?-WS4)Cu(CN)]2- have been investigated using electronic structure calculation (HF, MP4SDQ and DFT) methods. For the discrete mononuclear anions HF/lanl2dz(M)?6-31+G*(S,O) method provided the best description of their molecular structures, while for the heterobimetallic dinuclear and trinuclear clusters the B3LYP/lanl2dz(M)?6-31+G* method gave equilibrium geometries closely resembling the experimental ones. Electronic and spectroscopic (IR, UV-Vis) properties of the thiometalates are discussed in relation to their structures, while the bonding mechanism was analyzed in the framework of the natural bond orbital (NBO) approach. The nature of the highest occupied molecular orbitals (HOMOs) of all thiometalates indicated their ability to act as ligands coordinated with metal centers and forming clusters of higher nuclearity. The lowest-lying vertical one-electron detachment processes from the ground state of the [CrS4]2/3-, [MoOxS4-x]2/3- (x = 0-4) and [WS4]2/3- anions have been calculated using the outer valence Green's function (OVGF) method. Interestingly, in the heterobimetallic dinuclear and trinuclear clusters intemetallic M?M? interactions exist corresponding to d10 ? d0 dative bonding. Finally, the complete energetic and geometric profile of the successive acid-catalyzed formation reactions:and the reverse hydrolysis reactions have been delineated and details of the mechanism have been furnished.

Controlled synthesis of nanostructured molybdenum oxide electrodes for high performance supercapacitor devices

NASA Astrophysics Data System (ADS)

Maheswari, Nallappan; Muralidharan, Gopalan

2017-09-01

Well defined crystallographic and one dimensional morphological structure of molybdenum oxide were successfully synthesized by adjusting the duration of hydrothermal treatment. The prepared molybdenum oxide was examined through XRD, SEM, FTIR, TEM, BET and electrochemical studies. The XRD patterns illustrate that MoOx prepared by variying the hydrothermal reaction time are in different crystallographic structure of MoyOx (Mo8O23 and MoO3). SEM studies reveal the different morphological structures ranging from flake like morphology to nanorods. TEM images confirm the excellent nanorod structure. The nanorod structure ensures good cyclic behaviour with maximum capacitance of 1080 F g-1 at a current density of 2 A g-1. This large capacity of the MoO3 nanostructures enabled fabrication of symmetric and asymmertic supercapacitor devices. The asymmertic device exhibits a maximum specific capacitance of 145 F g-1 at 2 mV s-1 with highest energy density of 38.6 W h kg-1 at 374.7 W kg-1 power density.

Small molecule solution-processed bulk heterojunction solar cells with inverted structure using porphyrin donor

NASA Astrophysics Data System (ADS)

Yamamoto, Takaki; Hatano, Junichi; Nakagawa, Takafumi; Yamaguchi, Shigeru; Matsuo, Yutaka

2013-01-01

Utilizing tetraethynyl porphyrin derivative (TE-Por) as a small molecule donor material, we fabricated a small molecule solution-processed bulk heterojunction (BHJ) solar cell with inverted structure, which exhibited 1.6% power conversion efficiency (JSC (short-circuit current) = 4.6 mA/cm2, VOC (open-circuit voltage) = 0.90 V, and FF (fill factor) = 0.39) in the device configuration indium tin oxide/TiOx (titanium sub-oxide)/[6,6]-phenyl-C61-butyric acid methyl ester:TE-Por (5:1)/MoOx (molybdenum sub-oxide)/Au under AM1.5 G illumination at 100 mW/cm2. Without encapsulation, the small molecule solution-processed inverted BHJ solar cell also showed remarkable durability to air, where it kept over 73% of its initial power conversion efficiency after storage for 28 days under ambient atmosphere in the dark.

Capabilities of CdTe-Based Detectors With {mathrm {MoO}}_{x} Contacts for Detection of X- and gamma -Radiation

NASA Astrophysics Data System (ADS)

Maslyanchuk, O. L.; Solovan, M. M.; Brus, V. V.; Kulchynsky, V. V.; Maryanchuk, P. D.; Fodchuk, I. M.; Gnatyuk, V. A.; Aoki, T.; Potiriadis, C.; Kaissas, Y.

2017-05-01

The charge transport mechanism and spectrometric properties of the X-ray and γ-ray detectors, fabricated by the deposition of molybdenum oxide thin films onto semi-insulating p-CdTe crystals were studied. The current transport processes in the Mo-MoOx/p-CdTe/MoOx-Mo structure are well described in the scope of the carrier's generation in the space-charge region and the space-charge-limited current models. The lifetime of charge carriers, the energy of hole traps, and the density of discrete trapping centers were determined from the comparison of the experimental data and calculations. Spectrometric properties of Mo-MoOx/p-CdTe/MoOx-Mo structures were also investigated. It is shown that the investigated heterojunctions have demonstrated promising characteristics for practical application in X-ray and γ-ray detector fabrication.

The feasibility of using solution-processed aqueous La2O3 as effective hole injection layer in organic light-emitting diode

NASA Astrophysics Data System (ADS)

Zhang, Yan; Li, Wanshu; Zhang, Ting; Yang, Bo; Zheng, Qinghong; Xu, Jiwen; Wang, Hua; Wang, Lihui; Zhang, Xiaowen; Wei, Bin

2018-01-01

Low-cost and scalable manufacturing boosts organic electronic devices with all solution process. La2O3 powders and corresponding aqueous solutions are facilely synthesized. Atomic force microscopy and scanning electron microscopy measurements show that solution-processed La2O3 behaves superior film morphology. X-ray diffraction and X-ray photoelectron spectroscopy measurements verify crystal phase and typical La signals. In comparison with the most widely-used hole injection layers (HILs) of MoOx and poly(ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), enhanced luminous efficiency is observed in organic light-emitting diode (OLED) using solution-processed La2O3 HIL. Current-voltage, impedance-voltage and phase angle-voltage transition curves clarify that solution-processed La2O3 behaves nearly comparable hole injection capacity to MoOx and PEDOT:PSS, and favorably tailors carrier balance. Moreover, the hole injection mechanism of solution-processed La2O3 is proven to be predominantly controlled by Fowler-Nordheim tunneling process and the hole injection barrier height between ITO and NPB via La2O3 interlayer is estimated to be 0.098 eV. Our experiments provide a feasible application of La2O3 in organic electronic devices with solution process.

Synthesis of 2-Butanol by Selective Hydrogenolysis of 1,4-Anhydroerythritol over Molybdenum Oxide-Modified Rhodium-Supported Silica.

PubMed

Arai, Takahiro; Tamura, Masazumi; Nakagawa, Yoshinao; Tomishige, Keiichi

2016-07-07

Rh-MoOx /SiO2 (Mo/Rh=0.13) is an effective catalyst for the hydrogenolysis of 1,4-anhydroerythritol (1,4-AHERY) and provides 2-BuOH in high yield of 51 %. This is the first report of the production of 2-BuOH from 1,4-AHERY by hydrogenolysis. 1,4-AHERY was more suitable as a starting material than erythritol because the 2-BuOH yield from erythritol was low (34 %). Based on the kinetics and comparison of reactivities of the related compounds using Rh-MoOx /SiO2 and Rh/SiO2 catalysts, the modification of Rh/SiO2 with MoOx leads to the high activity and high selectivity to 2-BuOH because of the generation of reactive hydride species and the strong adsorption of 1,4-AHERY on MoOx species. The reaction proceeds by main two routes, (I) the combination of single C-O hydrogenolysis with the desorption of intermediates, a usual route in hydrogenolysis, and (II) multiple C-O hydrogenolysis without the desorption of intermediates from the active site, and the reaction mechanism for Route (II) is proposed. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Narrow Gap, High Mobility, and Stable Pi Conjugated Polymers

DTIC Science & Technology

2012-09-20

wide-angle X-ray scattering (2D-WAXS) of P5.1 (extruded at 210oC). This trend is reflected in conventional bulk- heterojunction OPV devices as shown...Additives in Molecular Bulk Heterojunction Solar Cells Using a bithiophene capped, isoindigo core, DAD molecule as the donor phase, and PCBM as the...PCE values of 3.7% as illustrated in Figure 11. Figure 11. Combining interface control using MoOx as an electron transport material and PDMS

Hole-transport limited S-shaped I-V curves in planar heterojunction organic photovoltaic cells

NASA Astrophysics Data System (ADS)

Zhang, Minlu; Wang, Hui; Tang, C. W.

2011-11-01

Current-voltage (I-V) characteristics of planar heterojunction organic photovoltaic cells based on N',N'-Di-[(1-naphthyl)-N',N'-diphenyl]-1,1'-biphenyl)-4,4'-diamine (NPB) and C60 are investigated. Through variation of the layer thickness and composition, specifically chemical doping NPB with MoOx, we show that the hole-transport limitation in the NPB layer is the determining factor in shaping the I-V characteristics of NPB/C60 cells.

Electronic properties of MoS2/MoOx interfaces: Implications in Tunnel Field Effect Transistors and Hole Contacts

PubMed Central

K. C., Santosh; Longo, Roberto C.; Addou, Rafik; Wallace, Robert M.; Cho, Kyeongjae

2016-01-01

In an electronic device based on two dimensional (2D) transitional metal dichalcogenides (TMDs), finding a low resistance metal contact is critical in order to achieve the desired performance. However, due to the unusual Fermi level pinning in metal/2D TMD interface, the performance is limited. Here, we investigate the electronic properties of TMDs and transition metal oxide (TMO) interfaces (MoS2/MoO3) using density functional theory (DFT). Our results demonstrate that, due to the large work function of MoO3 and the relative band alignment with MoS2, together with small energy gap, the MoS2/MoO3 interface is a good candidate for a tunnel field effect (TFET)-type device. Moreover, if the interface is not stoichiometric because of the presence of oxygen vacancies in MoO3, the heterostructure is more suitable for p-type (hole) contacts, exhibiting an Ohmic electrical behavior as experimentally demonstrated for different TMO/TMD interfaces. Our results reveal that the defect state induced by an oxygen vacancy in the MoO3 aligns with the valance band of MoS2, showing an insignificant impact on the band gap of the TMD. This result highlights the role of oxygen vacancies in oxides on facilitating appropriate contacts at the MoS2 and MoOx (x < 3) interface, which consistently explains the available experimental observations. PMID:27666523

Improved performances of organic light-emitting diodes with mixed layer and metal oxide as anode buffer

NASA Astrophysics Data System (ADS)

Xue, Qin; Liu, Shouyin; Zhang, Shiming; Chen, Ping; Zhao, Yi; Liu, Shiyong

2013-01-01

We fabricated organic light-emitting devices (OLEDs) employing 2-methyl-9,10-di(2-naphthyl)-anthracene (MADN) as hole-transport material (HTM) instead of commonly used N,N'-bis-(1-naphthyl)-N,N'-diphenyl,1,1'-biphenyl-4,4'-diamine (NPB). After inserting a 0.9 nm thick molybdenum oxide (MoOx) layer at the indium tin oxide (ITO)/MADN interface and a 5 nm thick mixed layer at the organic/organic heterojunction interface, the power conversion efficiency of the device can be increased by 4-fold.

Molecular Dynamic Simulation of Space and Earth-Grown Crystal Structures of Thermostable T1 Lipase Geobacillus zalihae Revealed a Better Structure.

PubMed

Ishak, Siti Nor Hasmah; Aris, Sayangku Nor Ariati Mohamad; Halim, Khairul Bariyyah Abd; Ali, Mohd Shukuri Mohamad; Leow, Thean Chor; Kamarudin, Nor Hafizah Ahmad; Masomian, Malihe; Rahman, Raja Noor Zaliha Raja Abd

2017-09-25

Less sedimentation and convection in a microgravity environment has become a well-suited condition for growing high quality protein crystals. Thermostable T1 lipase derived from bacterium Geobacillus zalihae has been crystallized using the counter diffusion method under space and earth conditions. Preliminary study using YASARA molecular modeling structure program for both structures showed differences in number of hydrogen bond, ionic interaction, and conformation. The space-grown crystal structure contains more hydrogen bonds as compared with the earth-grown crystal structure. A molecular dynamics simulation study was used to provide insight on the fluctuations and conformational changes of both T1 lipase structures. The analysis of root mean square deviation (RMSD), radius of gyration, and root mean square fluctuation (RMSF) showed that space-grown structure is more stable than the earth-grown structure. Space-structure also showed more hydrogen bonds and ion interactions compared to the earth-grown structure. Further analysis also revealed that the space-grown structure has long-lived interactions, hence it is considered as the more stable structure. This study provides the conformational dynamics of T1 lipase crystal structure grown in space and earth condition.

The role of the hole-extraction layer in determining the operational stability of a polycarbazole:fullerene bulk-heterojunction photovoltaic device

NASA Astrophysics Data System (ADS)

Bovill, E.; Scarratt, N.; Griffin, J.; Yi, H.; Iraqi, A.; Buckley, A. R.; Kingsley, J. W.; Lidzey, D. G.

2015-02-01

We have made a comparative study of the relative operational stability of bulk-heterojunction organic photovoltaic (OPV) devices utilising different hole transport layers (HTLs). OPV devices were fabricated based on a blend of the polymer PCDTBT with the fullerene PC70BM, and incorporated the different HTL materials PEDOT:PSS, MoOx and V2O5. Following 620 h of irradiation by light from a solar simulator, we find that devices using the PEDOT:PSS HTL retained the highest efficiency, having a projected T80 lifetime of 14 500 h.

Bilayered Oxide thin films for transparent electrode application

NASA Astrophysics Data System (ADS)

Dutta, Titas; Narayan, Jagdish

2008-10-01

Ga doped ZnO films with electrical and optical properties comparable to indium tin oxide (ITO) is a promising candidate for transparent conducting oxides (TCOs) because of its superior stability in hydrogen environment, benign nature and relatively inexpensive supply. However, ZnO based TCO films suffer from low work function, which is a critical parameter for device applications. We report here the growth of a novel bilayered structure consisting of very thin (few monolayers) ITO, MoOx layer on Zn0.95Ga0.05O film for transparent electrode applications by using pulsed laser deposition technique at different temperatures and oxygen partial pressure. The characteristics of the ITO film and the heterostructure have been investigated in detail using XRD, TEM, XPS, and electrical and optical property measurements. It is envisaged that the overall transmittance and the resistivity are dictated by the thicker layer of ZnGa0.05O beneath the ITO layer. Hence, this study is aimed to improve the surface characteristics without affecting the overall transmittance and sheet resistance. This will enhance the transport of the carriers across the heterojunction in the device, thus, resulting in the increase in device efficiency.

Temperature Dependences of the Product of the Differential Resistance by the Area in MIS-Structures Based on Cd x Hg1- x Te Grown by Molecularbeam Epitaxy on Alternative Si and GaAs Substrates

NASA Astrophysics Data System (ADS)

Voitsekhovskii, A. V.; Nesmelov, S. N.; Dzyadukh, S. M.; Varavin, V. S.; Vasil'ev, V. V.; Dvoretskii, S. A.; Mikhailov, N. N.; Yakushev, M. V.; Sidorov, G. Yu.

2017-06-01

In a temperature range of 9-200 K, temperature dependences of the differential resistance of space-charge region in the strong inversion mode are experimentally studied for MIS structures based on CdxHg1-xTe (x = 0.22-0.40) grown by molecular-beam epitaxy. The effect of various parameters of structures: the working layer composition, the type of a substrate, the type of insulator coating, and the presence of a near-surface graded-gap layer on the value of the product of differential resistance by the area is studied. It is shown that the values of the product RSCRA for MIS structures based on n-CdHgTe grown on a Si(013) substrate are smaller than those for structures based on the material grown on a GaAs(013) substrate. The values of the product RSCRA for MIS structures based on p-CdHgTe grown on a Si(013) substrate are comparable with the value of the analogous parameter for MIS structures based on p-CdHgTe grown on a GaAs(013) substrate.

The structure study of thin semiconductor and dielectric films by diffraction of synchrotron radiation

NASA Astrophysics Data System (ADS)

Yurjev, G. S.; Fainer, N. I.; Maximovskiy, E. A.; Kosinova, M. L.; Sheromov, M. A.; Rumyantsev, Yu. M.

1998-02-01

The structure of semiconductor and dielectric thin (100-300 nm) films was studied by diffraction of synchrotron radiation. The diffraction experiments were performed at both the station "Anomalous scattering" of the storage ring synchrotron facility VEPP-3 and DRON-4 diffractometer. The structure of CdS thin films grown on fused silica, single Si(100) and InP(100) substrates was investigated. The structure of Cu 2S thin films grown on fused silica, single Si(100) substrates and CdS/Si(100)-heterostructure was studied. The structure study was performed on Si 3N 4 films grown on GaAs(100) substrates. The structure of thin BN layers grown on single Si(100) substrates was studied. It was established that structural parameters of above-mentioned thin films coincide on the parameters of JCPDS International Centre for Diffraction Data.

Substrate dependence of TM-polarized light emission characteristics of BAlGaN/AlN quantum wells

NASA Astrophysics Data System (ADS)

Park, Seoung-Hwan; Ahn, Doyeol

2018-06-01

To study the substrate dependence of light emission characteristics of transverse-magnetic (TM)-polarized light emitted from BAlGaN/AlN quantum wells (QWs) grown on GaN and AlN substrates were investigated theoretically. It is found that the topmost valence subband for QW structures grown on AlN substrate, is heavy hole state (HH1) while that for QW structures grown on GaN substrate is crystal-field split off light hole state (CL1), irrespective of the boron content. Since TM-polarized light emission is associated with the light hole state, the TM-polarized emission peak of BAlGaN/AlN QW structures grown on GaN substrate is expected to be much larger than that of the QW structure grown on AlN substrate. Also, both QW structures show that the spontaneous emission peak of BAlGaN/AlN QW structures would be improved with the inclusion of the boron. However, it rapidly begins to decrease when the boron content exceeds a critical value.

Characterization of thin MoO3 films formed by RF and DC-magnetron reactive sputtering for gas sensor applications

NASA Astrophysics Data System (ADS)

Yordanov, R.; Boyadjiev, S.; Georgieva, V.; Vergov, L.

2014-05-01

The present work discusses a technology for deposition and characterization of thin molybdenum oxide (MoOx, MoO3) films studied for gas sensor applications. The samples were produced by reactive radio-frequency (RF) and direct current (DC) magnetron sputtering. The composition and microstructure of the films were studied by XPS, XRD and Raman spectroscopy, the morphology, using high resolution SEM. The research was focused on the sensing properties of the sputtered thin MoO3 films. Highly sensitive gas sensors were implemented by depositing films of various thicknesses on quartz resonators. Making use of the quartz crystal microbalance (QCM) method, these sensors were capable of detecting changes in the molecular range. Prototype QCM structures with thin MoO3 films were tested for sensitivity to NH3 and NO2. Even in as-deposited state and without heating the substrates, these films showed good sensitivity. Moreover, no additional thermal treatment is necessary, which makes the production of such QCM gas sensors simple and cost-effective, as it is fully compatible with the technology for producing the initial resonator. The films are sensitive at room temperature and can register concentrations as low as 50 ppm. The sorption is fully reversible, the films are stable and capable of long-term measurements.

Interface Engineering of Organic Schottky Barrier Solar Cells and Its Application in Enhancing Performances of Planar Heterojunction Solar Cells

NASA Astrophysics Data System (ADS)

Jin, Fangming; Su, Zisheng; Chu, Bei; Cheng, Pengfei; Wang, Junbo; Zhao, Haifeng; Gao, Yuan; Yan, Xingwu; Li, Wenlian

2016-05-01

In this work, we describe the performance of organic Schottky barrier solar cells with the structure of ITO/molybdenum oxide (MoOx)/boron subphthalocyanine chloride (SubPc)/bathophenanthroline (BPhen)/Al. The SubPc-based Schottky barrier solar cells exhibited a short-circuit current density (Jsc) of 2.59 mA/cm2, an open-circuit voltage (Voc) of 1.06 V, and a power conversion efficiency (PCE) of 0.82% under simulated AM1.5 G solar illumination at 100 mW/cm2. Device performance was substantially enhanced by simply inserting thin organic hole transport material into the interface of MoOx and SubPc. The optimized devices realized a 180% increase in PCE of 2.30% and a peak Voc as high as 1.45 V was observed. We found that the improvement is due to the exciton and electron blocking effect of the interlayer and its thickness plays a vital role in balancing charge separation and suppressing quenching effect. Moreover, applying such interface engineering into MoOx/SubPc/C60 based planar heterojunction cells substantially enhanced the PCE of the device by 44%, from 3.48% to 5.03%. Finally, we also investigated the requirements of the interface material for Schottky barrier modification.

Interface Engineering of Organic Schottky Barrier Solar Cells and Its Application in Enhancing Performances of Planar Heterojunction Solar Cells.

PubMed

Jin, Fangming; Su, Zisheng; Chu, Bei; Cheng, Pengfei; Wang, Junbo; Zhao, Haifeng; Gao, Yuan; Yan, Xingwu; Li, Wenlian

2016-05-17

In this work, we describe the performance of organic Schottky barrier solar cells with the structure of ITO/molybdenum oxide (MoOx)/boron subphthalocyanine chloride (SubPc)/bathophenanthroline (BPhen)/Al. The SubPc-based Schottky barrier solar cells exhibited a short-circuit current density (Jsc) of 2.59 mA/cm(2), an open-circuit voltage (Voc) of 1.06 V, and a power conversion efficiency (PCE) of 0.82% under simulated AM1.5 G solar illumination at 100 mW/cm(2). Device performance was substantially enhanced by simply inserting thin organic hole transport material into the interface of MoOx and SubPc. The optimized devices realized a 180% increase in PCE of 2.30% and a peak Voc as high as 1.45 V was observed. We found that the improvement is due to the exciton and electron blocking effect of the interlayer and its thickness plays a vital role in balancing charge separation and suppressing quenching effect. Moreover, applying such interface engineering into MoOx/SubPc/C60 based planar heterojunction cells substantially enhanced the PCE of the device by 44%, from 3.48% to 5.03%. Finally, we also investigated the requirements of the interface material for Schottky barrier modification.

Environmental stresses of field growth allow cinnamyl alcohol dehydrogenase-deficient Nicotiana attenuata plants to compensate for their structural deficiencies.

PubMed

Kaur, Harleen; Shaker, Kamel; Heinzel, Nicolas; Ralph, John; Gális, Ivan; Baldwin, Ian T

2012-08-01

The organized lignocellulosic assemblies of cell walls provide the structural integrity required for the large statures of terrestrial plants. Silencing two CINNAMYL ALCOHOL DEHYDROGENASE (CAD) genes in Nicotiana attenuata produced plants (ir-CAD) with thin, red-pigmented stems, low CAD and sinapyl alcohol dehydrogenase activity, low lignin contents, and rubbery, structurally unstable stems when grown in the glasshouse (GH). However, when planted into their native desert habitat, ir-CAD plants produced robust stems that survived wind storms as well as the wild-type plants. Despite efficient silencing of NaCAD transcripts and enzymatic activity, field-grown ir-CAD plants had delayed and restricted spread of red stem pigmentation, a color change reflecting blocked lignification by CAD silencing, and attained wild-type-comparable total lignin contents. The rubbery GH phenotype was largely restored when field-grown ir-CAD plants were protected from wind, herbivore attack, and ultraviolet B exposure and grown in restricted rooting volumes; conversely, it was lost when ir-CAD plants were experimentally exposed to wind, ultraviolet B, and grown in large pots in growth chambers. Transcript and liquid chromatography-electrospray ionization-time-of-flight analysis revealed that these environmental stresses enhanced the accumulation of various phenylpropanoids in stems of field-grown plants; gas chromatography-mass spectrometry and nuclear magnetic resonance analysis revealed that the lignin of field-grown ir-CAD plants had GH-grown comparable levels of sinapaldehyde and syringaldehyde cross-linked into their lignins. Additionally, field-grown ir-CAD plants had short, thick stems with normal xylem element traits, which collectively enabled field-grown ir-CAD plants to compensate for the structural deficiencies associated with CAD silencing. Environmental stresses play an essential role in regulating lignin biosynthesis in lignin-deficient plants.

Environmental Stresses of Field Growth Allow Cinnamyl Alcohol Dehydrogenase-Deficient Nicotiana attenuata Plants to Compensate for their Structural Deficiencies1[C][W][OA

PubMed Central

Kaur, Harleen; Shaker, Kamel; Heinzel, Nicolas; Ralph, John; Gális, Ivan; Baldwin, Ian T.

2012-01-01

The organized lignocellulosic assemblies of cell walls provide the structural integrity required for the large statures of terrestrial plants. Silencing two CINNAMYL ALCOHOL DEHYDROGENASE (CAD) genes in Nicotiana attenuata produced plants (ir-CAD) with thin, red-pigmented stems, low CAD and sinapyl alcohol dehydrogenase activity, low lignin contents, and rubbery, structurally unstable stems when grown in the glasshouse (GH). However, when planted into their native desert habitat, ir-CAD plants produced robust stems that survived wind storms as well as the wild-type plants. Despite efficient silencing of NaCAD transcripts and enzymatic activity, field-grown ir-CAD plants had delayed and restricted spread of red stem pigmentation, a color change reflecting blocked lignification by CAD silencing, and attained wild-type-comparable total lignin contents. The rubbery GH phenotype was largely restored when field-grown ir-CAD plants were protected from wind, herbivore attack, and ultraviolet B exposure and grown in restricted rooting volumes; conversely, it was lost when ir-CAD plants were experimentally exposed to wind, ultraviolet B, and grown in large pots in growth chambers. Transcript and liquid chromatography-electrospray ionization-time-of-flight analysis revealed that these environmental stresses enhanced the accumulation of various phenylpropanoids in stems of field-grown plants; gas chromatography-mass spectrometry and nuclear magnetic resonance analysis revealed that the lignin of field-grown ir-CAD plants had GH-grown comparable levels of sinapaldehyde and syringaldehyde cross-linked into their lignins. Additionally, field-grown ir-CAD plants had short, thick stems with normal xylem element traits, which collectively enabled field-grown ir-CAD plants to compensate for the structural deficiencies associated with CAD silencing. Environmental stresses play an essential role in regulating lignin biosynthesis in lignin-deficient plants. PMID:22645069

All MBE grown InAs/GaAs quantum dot lasers on on-axis Si (001).

PubMed

Kwoen, Jinkwan; Jang, Bongyong; Lee, Joohang; Kageyama, Takeo; Watanabe, Katsuyuki; Arakawa, Yasuhiko

2018-04-30

Directly grown III-V quantum dot (QD) laser on on-axis Si (001) is a good candidate for achieving monolithically integrated Si photonics light source. Nowadays, laser structures containing high quality InAs / GaAs QD are generally grown by molecular beam epitaxy (MBE). However, the buffer layer between the on-axis Si (001) substrate and the laser structure are usually grown by metal-organic chemical vapor deposition (MOCVD). In this paper, we demonstrate all MBE grown high-quality InAs/GaAs QD lasers on on-axis Si (001) substrates without using patterning and intermediate layers of foreign material.

Multilayer porous structures of HVPE and MOCVD grown GaN for photonic applications

NASA Astrophysics Data System (ADS)

Braniste, T.; Ciers, Joachim; Monaico, Ed.; Martin, D.; Carlin, J.-F.; Ursaki, V. V.; Sergentu, V. V.; Tiginyanu, I. M.; Grandjean, N.

2017-02-01

In this paper we report on a comparative study of electrochemical processes for the preparation of multilayer porous structures in hydride vapor phase epitaxy (HVPE) and metal organic chemical vapor phase deposition (MOCVD) grown GaN. It was found that in HVPE-grown GaN, multilayer porous structures are obtained due to self-organization processes leading to a fine modulation of doping during the crystal growth. However, these processes are not totally under control. Multilayer porous structures with a controlled design have been produced by optimizing the technological process of electrochemical etching in MOCVD-grown samples, consisting of five pairs of thin layers with alternating-doping profiles. The samples have been characterized by SEM imaging, photoluminescence spectroscopy, and micro-reflectivity measurements, accompanied by transfer matrix analysis and simulations by a method developed for the calculation of optical reflection spectra. We demonstrate the applicability of the produced structures for the design of Bragg reflectors.

Large-area, laterally-grown epitaxial semiconductor layers

DOEpatents

Han, Jung; Song, Jie; Chen, Danti

2017-07-18

Structures and methods for confined lateral-guided growth of a large-area semiconductor layer on an insulating layer are described. The semiconductor layer may be formed by heteroepitaxial growth from a selective growth area in a vertically-confined, lateral-growth guiding structure. Lateral-growth guiding structures may be formed in arrays over a region of a substrate, so as to cover a majority of the substrate region with laterally-grown epitaxial semiconductor tiles. Quality regions of low-defect, stress-free GaN may be grown on silicon.

Structural, mechanical, electrical and optical properties of a new lithium boro phthalate NLO crystal synthesized by a slow evaporation method

NASA Astrophysics Data System (ADS)

Mohanraj, K.; Balasubramanian, D.; Jhansi, N.

2017-11-01

A new non-linear optical (NLO) single crystal of lithium boro phthalate (LiBP) was grown by slow solvent evaporation technique. The powder sample was subjected to powder X-ray diffraction (PXRD) to find its crystalline nature and the crystal structure of the grown crystal was determined using single crystal X-ray (SXRD) diffraction analysis. The Fourier Transform Infrared (FTIR) spectrum was recorded for grown crystal to identify the various functional groups present in the compound. The mechanical property of the LiBP single crystal was studied using Vickers microhardness tester. The dielectric constant and dielectric loss measurements were carried out for the grown crystal at various temperatures. The grown crystal was subjected to UV-Visible Spectral Studies to analyze the linear optical behavior of the grown crystal. The Kurtz-Perry Powder technique was employed to measure the Second Harmonic Generation efficiency of the grown crystal.

Method of photocatalytic nanotagging

DOEpatents

Shelnutt, John A [Tijeras, NM; Medforth, Craig J [Winters, CA; Song, Yujiang [Albuquerque, NM

2010-04-27

A nanotagged chemical structure comprising a chemical structure with an associated photocatalyst and a tagging nanoparticle (a nanotag) grown in proximity to the photocatalyst, and a method for making the nanotagged chemical structure. The nanoparticle is grown in proximity to the photocatalyst by using a photocatalytic reduction reaction.

Structural, spectral and birefringence studies of semiorganic nonlinear optical single crystal: Calcium5-sulfosalicylate

NASA Astrophysics Data System (ADS)

Shalini, D.; Kalainathan, S.; Ambika, V. Revathi; Hema, N.; Jayalakshmi, D.

2017-11-01

Semi-organic nonlinear optical crystal Calcium5-Sulfosalicylate (CA5SS) was grown by slow evaporation solution growth technique. The cell parameters and molecular structure of the grown crystal were studied by single crystal x-ray diffraction analysis. The presence of various functional groups of the grown crystal was confirmed using Fourier transform infrared (FT-IR), Fourier transform Raman (FT-Raman) analysis. UV-Visible spectrum shows that CA5SS crystals have high transmittance in the range of 330-900 nm. The refractive index, birefringence and transient photoluminescence properties of the grown crystal were analyzed. The frequency doubling of the grown crystal (CA5SS) were studied and compared with that of KDP.

Conductivity and structure of ErAs nanoparticles embedded in GaAs pn junctions analyzed via conductive atomic force microscopy

NASA Astrophysics Data System (ADS)

Park, K. W.; Dasika, V. D.; Nair, H. P.; Crook, A. M.; Bank, S. R.; Yu, E. T.

2012-06-01

We have used conductive atomic force microscopy to investigate the influence of growth temperature on local current flow in GaAs pn junctions with embedded ErAs nanoparticles grown by molecular beam epitaxy. Three sets of samples, one with 1 ML ErAs deposited at different growth temperatures and two grown at 530 °C and 575 °C with varying ErAs depositions, were characterized. Statistical analysis of local current images suggests that the structures grown at 575 °C have about 3 times thicker ErAs nanoparticles than structures grown at 530 °C, resulting in degradation of conductivity due to reduced ErAs coverage. These findings explain previous studies of macroscopic tunnel junctions.

Structural defects in GaN revealed by Transmission Electron Microscopy

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

Liliental-Weber, Zuzanna

This paper reviews the various types of structural defects observed by Transmission Electron Microscopy in GaN heteroepitaxial layers grown on foreign substrates and homoepitaxial layers grown on bulk GaN substrates. The structural perfection of these layers is compared to the platelet self-standing crystals grown by High Nitrogen Pressure Solution. Defects in undoped and Mg doped GaN are discussed. Lastly, some models explaining the formation of inversion domains in heavily Mg doped layers that are possible defects responsible for the difficulties of p-doping in GaN are also reviewed.

Structural defects in GaN revealed by Transmission Electron Microscopy

DOE PAGES

Liliental-Weber, Zuzanna

2014-09-08

This paper reviews the various types of structural defects observed by Transmission Electron Microscopy in GaN heteroepitaxial layers grown on foreign substrates and homoepitaxial layers grown on bulk GaN substrates. The structural perfection of these layers is compared to the platelet self-standing crystals grown by High Nitrogen Pressure Solution. Defects in undoped and Mg doped GaN are discussed. Lastly, some models explaining the formation of inversion domains in heavily Mg doped layers that are possible defects responsible for the difficulties of p-doping in GaN are also reviewed.

Characterization of re-grown floc size and structure: effect of mixing conditions during floc growth, breakage and re-growth process.

PubMed

Nan, Jun; Wang, Zhenbei; Yao, Meng; Yang, Yueming; Zhang, Xiaofei

2016-12-01

The impact of mixing speed in three stages-before breakage, during breakage, and after breakage-on re-grown floc properties was investigated by using a non-intrusive optical sampling and digital image analysis technique, respectively. And then, on the basis of different influence extent of mixing speed during each stage on size and structure of re-grown flocs, coagulation performance with varying mixing speed was analyzed. The results indicated that the broken flocs could not re-grow to the size before breakage in all cases. Furthermore, increasing mixing intensity contributed to the re-formation of smaller flocs with higher degree of compactness. For slow mixing before breakage, an increase in mixing speed had less influence on re-grown floc properties due to the same breakage strength during breakage, resulting in inconspicuous variation of coagulation efficiency. For rapid mixing during breakage, larger mixing speed markedly decreased the coagulation efficiency. This could be attributed that mixing speed during breakage generated greater influence on re-grown floc size. However, as slow mixing after breakage was elevated, the coagulation efficiency presented significant rise, indicating that slow mixing after breakage had more influence on re-grown floc structure upon re-structuring and re-arrangement mechanism.

Structural and magnetic properties of hexagonal Cr1-δTe films grown on CdTe(001) by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Kanazawa, Ken; Yamawaki, Kazuma; Sekita, Naoya; Nishio, Yôtarô; Kuroda, Shinji; Mitome, Masanori; Bando, Yoshio

2015-04-01

We investigated the structural and magnetic properties of Cr1-δTe thin films grown on CdTe(001) layers by molecular beam epitaxy (MBE) with systematic variations of the ratio between Cr and Te fluxes and the substrate temperature Ts during the growth. Cr1-δTe of the hexagonal structure (hex-Cr1-δTe) was always formed irrespective of the growth conditions, but the growth orientation was different depending on the Cr/Te flux ratio and Ts. Hex-Cr1-δTe was grown in the [0001] axis in the range of small Cr/Te ratios and high Ts while it was also grown in the direction normal to the (1-102) plane at larger Cr/Te ratios or lower Ts. Hex-Cr1-δTe films grown in the both orientations show ferromagnetism, but they exhibit a clear contrast in the field dependence of perpendicular magnetization at 2 K; a square hysteretic loop in the film grown in the [0001] axis versus a round-shape loop in the film grown in the direction normal to the (1-102) plane. Moreover, the films grown in the [0001] axis at the smallest Cr/Te ratio show variations of ferromagnetic properties with Curie temperature (Tc) and the coercivity (Hc) varying according to the value of Ts.

Efficient organic photovoltaic cells on a single layer graphene transparent conductive electrode using MoOx as an interfacial layer.

PubMed

Du, J H; Jin, H; Zhang, Z K; Zhang, D D; Jia, S; Ma, L P; Ren, W C; Cheng, H M; Burn, P L

2017-01-07

The large surface roughness, low work function and high cost of transparent electrodes using multilayer graphene films can limit their application in organic photovoltaic (OPV) cells. Here, we develop single layer graphene (SLG) films as transparent anodes for OPV cells that contain light-absorbing layers comprised of the evaporable molecular organic semiconductor materials, zinc phthalocyanine (ZnPc)/fullerene (C60), as well as a molybdenum oxide (MoO x ) interfacial layer. In addition to an increase in the optical transmittance, the SLG anodes had a significant decrease in surface roughness compared to two and four layer graphene (TLG and FLG) anodes fabricated by multiple transfer and stacking of SLGs. Importantly, the introduction of a MoO x interfacial layer not only reduced the energy barrier between the graphene anode and the active layer, but also decreased the resistance of the SLG by nearly ten times. The OPV cells with the structure of polyethylene terephthalate/SLG/MoO x /CuI/ZnPc/C60/bathocuproine/Al were flexible, and had a power conversion efficiency of up to 0.84%, which was only 17.6% lower than the devices with an equivalent structure but prepared on commercial indium tin oxide anodes. Furthermore, the devices with the SLG anode were 50% and 86.7% higher in efficiency than the cells with the TLG and FLG anodes. These results show the potential of SLG electrodes for flexible and wearable OPV cells as well as other organic optoelectronic devices.

Crystal growth, structure analysis and characterisation of 2 - (1, 3 - dioxoisoindolin - 2 - yl) acetic acid single crystal

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

Sankari, R. Siva, E-mail: sivasankari.sh@act.edu.in; Perumal, Rajesh Narayana

2014-04-24

Single crystal of dielectric material 2 - (1, 3 - dioxoisoindolin - 2 - yl) acetic acid has been grown by slow evaporation solution growth method. The grown crystal was harvested in 25 days. The crystal structure was analyzed by Single crystal X - ray diffraction. UV-vis-NIR analysis was performed to examine the optical property of the grown crystal. The thermal property of the grown crystal was studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The dielectric measurements were carried out and the dielectric constant was calculated and plotted at all frequencies.

Comparative effectiveness of a clinostat and a slow-turning lateral vessel at mimicking the ultrastructural effects of microgravity in plant cells

NASA Technical Reports Server (NTRS)

Moore, R.

1990-01-01

The object of this research was to determine how effectively the actions of a clinostat and a fluid-filled, slow-turning lateral vessel (STLV) mimic the ultrastructural effects of microgravity in plant cells. We accomplished this by qualitatively and quantitatively comparing the ultrastructures of cells grown on clinostats and in an STLV with those of cells grown at 1 g and in microgravity aboard the Space Shuttle Columbia. Columella cells of Brassica perviridis seedlings grown in microgravity and in an STLV have similar structures. Both contain significantly more lipid bodies, less starch, and fewer dictyosomes than columella cells of seedlings grown at 1 g. Cells of seedlings grown on clinostats have significantly different ultrastructures from those grown in microgravity or in an STLV, indicating that clinostats do not mimic microgravity at the ultrastructural level. The similar structures of columella cells of seedlings grown in an STLV and in microgravity suggest that an STLV effectively mimics microgravity at the ultrastructural level.

Synthesis, crystal growth, structural, thermal, optical and mechanical properties of solution grown 4-methylpyridinium 4-hydroxybenzoate single crystal.

PubMed

Sudhahar, S; Krishna Kumar, M; Sornamurthy, B M; Mohan Kumar, R

2014-01-24

Organic nonlinear optical material, 4-methylpyridinium 4-hydroxybenzoate (4MPHB) was synthesized and single crystal was grown by slow evaporation solution growth method. Single crystal and powder X-ray diffraction analyses confirm the structure and crystalline perfection of 4MPHB crystal. Infrared, Raman and NMR spectroscopy techniques were used to elucidate the functional groups present in the compound. TG-DTA analysis was carried out in nitrogen atmosphere to study the decomposition stages, endothermic and exothermic reactions. UV-visible and Photoluminescence spectra were recorded for the grown crystal to estimate the transmittance and band gap energy respectively. Linear refractive index, birefringence, and SHG efficiency of the grown crystal were studied. Laser induced surface damage threshold and mechanical properties of grown crystal were studied to assess the suitability of the grown crystals for device applications. Copyright © 2013 Elsevier B.V. All rights reserved.

Self-Supported Ni(P, O)x·MoOx Nanowire Array on Nickel Foam as an Efficient and Durable Electrocatalyst for Alkaline Hydrogen Evolution

PubMed Central

Hua, Wei; Liu, Huanyan

2017-01-01

Earth-abundant and low-cost catalysts with excellent electrocatalytic hydrogen evolution reaction (HER) activity in alkaline solution play an important role in the sustainable production of hydrogen energy. In this work, a catalyst of Ni(P, O)x·MoOx nanowire array on nickel foam has been prepared via a facile route for efficient alkaline HER. Benefiting from the collaborative advantages of Ni(P, O)x and amorphous MoOx, as well as three-dimensional porous conductive nickel scaffold, the hybrid electrocatalyst shows high catalytic activity in 1 M KOH aqueous solution, including a small overpotential of 59 mV at 10 mA cm−2, a low Tafel slope of 54 mV dec-1, and excellent cycling stability. PMID:29210991

Stacking of ZnSe/ZnCdSe Multi-Quantum Wells on GaAs (100) by Epitaxial Lift-Off

NASA Astrophysics Data System (ADS)

Eldose, N. M.; Zhu, J.; Mavridi, N.; Prior, Kevin; Moug, R. T.

2018-05-01

Here we present stacking of GaAs/ZnSe/ZnCdSe single-quantum well (QW) structures using epitaxial lift-off (ELO). Molecular beam epitaxy (MBE)-grown II-VI QW structure was lifted using our standard ELO technique. The QW structures were transferred onto glass plates and then subsequent layers stacked on top of each other to form a triple-QW structure. This was compared to an MBE-grown multiple-QW (MQW) structure of similar design. Low-temperature (77 K) photoluminescence (PL) spectroscopy was used to compare the two structures and showed no obvious degradation of the ELO stacked layer. It was observed that by stacking the single QW layer on itself we could increase the PL emission intensity beyond that of the grown MQW structure while maintaining narrow line width.

Interfacial Coupling and Electronic Structure of Two-Dimensional Silicon Grown on the Ag(111) Surface at High Temperature.

PubMed

Feng, Jiagui; Wagner, Sean R; Zhang, Pengpeng

2015-06-18

Freestanding silicene, a monolayer of Si arranged in a honeycomb structure, has been predicted to give rise to massless Dirac fermions, akin to graphene. However, Si structures grown on a supporting substrate can show properties that strongly deviate from the freestanding case. Here, combining scanning tunneling microscopy/spectroscopy and differential conductance mapping, we show that the electrical properties of the (√3 x √3) phase of few-layer Si grown on Ag(111) strongly depend on film thickness, where the electron phase coherence length decreases and the free-electron-like surface state gradually diminishes when approaching the interface. These features are presumably attributable to the inelastic inter-band electron-electron scattering originating from the overlap between the surface state, interface state and the bulk state of the substrate. We further demonstrate that the intrinsic electronic structure of the as grown (√3 x √3) phase is identical to that of the (√3 x √3)R30° reconstructed Ag on Si(111), both of which exhibit the parabolic energy-momentum dispersion relation with comparable electron effective masses. These findings highlight the essential role of interfacial coupling on the properties of two-dimensional Si structures grown on supporting substrates, which should be thoroughly scrutinized in pursuit of silicene.

Structural, optical and photoelectric properties of sprayed CdS thin films

NASA Astrophysics Data System (ADS)

Chandel, Tarun; Dwivedi, Shailendra Kumar; Zaman, M. Burhanuz; Rajaram, P.

2018-05-01

In this study, CdS thin films were grown via a facile spray pyrolysis technique. The crystalline phase, morphological, compositional and optical properties of the CdS thin films have been studied using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and UV-vis absorption spectroscopy, respectively. XRD patterns show that the grown CdS films crystallized in the hexagonal structure. Scanning electron microscopy (SEM) study shows that the surfaces of the films are smooth and are uniformly covered with nanoparticles. EDAX results reveal that the grown films have good stochiometry. UV-vis spectroscopy shows that the grown films have transparency above 80% over the entire visible region. The photo-electric response of the CdS films grown on glass substrates has been observed.

Interface Engineering of Organic Schottky Barrier Solar Cells and Its Application in Enhancing Performances of Planar Heterojunction Solar Cells

PubMed Central

Jin, Fangming; Su, Zisheng; Chu, Bei; Cheng, Pengfei; Wang, Junbo; Zhao, Haifeng; Gao, Yuan; Yan, Xingwu; Li, Wenlian

2016-01-01

In this work, we describe the performance of organic Schottky barrier solar cells with the structure of ITO/molybdenum oxide (MoOx)/boron subphthalocyanine chloride (SubPc)/bathophenanthroline (BPhen)/Al. The SubPc-based Schottky barrier solar cells exhibited a short-circuit current density (Jsc) of 2.59 mA/cm2, an open-circuit voltage (Voc) of 1.06 V, and a power conversion efficiency (PCE) of 0.82% under simulated AM1.5 G solar illumination at 100 mW/cm2. Device performance was substantially enhanced by simply inserting thin organic hole transport material into the interface of MoOx and SubPc. The optimized devices realized a 180% increase in PCE of 2.30% and a peak Voc as high as 1.45 V was observed. We found that the improvement is due to the exciton and electron blocking effect of the interlayer and its thickness plays a vital role in balancing charge separation and suppressing quenching effect. Moreover, applying such interface engineering into MoOx/SubPc/C60 based planar heterojunction cells substantially enhanced the PCE of the device by 44%, from 3.48% to 5.03%. Finally, we also investigated the requirements of the interface material for Schottky barrier modification. PMID:27185635

Molybdenum speciation and burial pathway in weakly sulfidic environments: Insights from XAFS

NASA Astrophysics Data System (ADS)

Wagner, Meghan; Chappaz, Anthony; Lyons, Timothy W.

2017-06-01

Sedimentary molybdenum (Mo) accumulation is a robust proxy for sulfidic conditions in both modern and ancient aquatic systems and has been used to infer changing marine redox chemistry throughout Earth's history. Accurate interpretation of any proxy requires a comprehensive understanding of its biogeochemical cycling, but knowledge gaps remain concerning the geochemical mechanism(s) leading to Mo burial in anoxic sediments. Better characterization of Mo speciation should provide mechanistic insight into sedimentary Mo accumulation, and therefore in this study we investigate Mo speciation from both modern (Castle Lake, USA) and ancient (Doushantuo Formation, China) environments using X-ray Absorption Near Edge Structure (XANES) spectroscopy. By utilizing a series of laboratory-synthesized oxythiomolybdate complexes-many containing organic ligands-we expand the number of available standards to encompass a greater range of known Mo chemistry and test the linkage between Mo and total organic carbon (TOC). In weakly euxinic systems ([H2S(aq)] < 11 μM), or where sulfide is restricted to pore waters, natural samples are best represented by a linear combination of MoO3, MoOxS4-x2- (intermediate thiomolybdates), and [MoOx(cat)4-x]2- (cat = catechol, x = 2 or 3). These results suggest a revised model for how Mo accumulates in weakly sulfidic sediments, including a previously unrecognized role for organic matter in early sequestration of Mo and a de-emphasized importance for MoS42- (tetrathiomolybdate).

Microstructures and growth mechanisms of GaN films epitaxially grown on AlN/Si hetero-structures by pulsed laser deposition at different temperatures.

PubMed

Wang, Wenliang; Yang, Weijia; Lin, Yunhao; Zhou, Shizhong; Li, Guoqiang

2015-11-13

2 inch-diameter GaN films with homogeneous thickness distribution have been grown on AlN/Si(111) hetero-structures by pulsed laser deposition (PLD) with laser rastering technique. The surface morphology, crystalline quality, and interfacial property of as-grown GaN films are characterized in detail. By optimizing the laser rastering program, the ~300 nm-thick GaN films grown at 750 °C show a root-mean-square (RMS) thickness inhomogeneity of 3.0%, very smooth surface with a RMS surface roughness of 3.0 nm, full-width at half-maximums (FWHMs) for GaN(0002) and GaN(102) X-ray rocking curves of 0.7° and 0.8°, respectively, and sharp and abrupt AlN/GaN hetero-interfaces. With the increase in the growth temperature from 550 to 850 °C, the surface morphology, crystalline quality, and interfacial property of as-grown ~300 nm-thick GaN films are gradually improved at first and then decreased. Based on the characterizations, the corresponding growth mechanisms of GaN films grown on AlN/Si hetero-structures by PLD with various growth temperatures are hence proposed. This work would be beneficial to understanding the further insight of the GaN films grown on Si(111) substrates by PLD for the application of GaN-based devices.

Photoluminescence spectroscopy and the effective mass theory of strained (In,Ga)As/GaAs heterostructures grown on (112)B GaAs substrates

NASA Technical Reports Server (NTRS)

Henderson, R. H.; Sun, D.; Towe, E.

1995-01-01

The photoluminescence characteristics of pseudomorphic In(0.19)Ga(0.81)As/GaAs quantum well structures grown on both the conventional (001) and the unconventional (112)B GaAs substrate are investigated. It is found that the emission spectra of the structures grown on the (112)B surface exhibit some spectral characteristics not observed on similar structures grown on the (001) surface. A spectral blue shift of the e yields hh1 transition with increasing optical pump intensity is observed for the quantum wells on the (112) surface. This shift is interpreted to be evidence of a strain-induced piezoelectric field. A second spectral feature located within the band gap of the In(0.19)Ga(0.81)As layer is also observed for the (112) structure; this feature is thought to be an impurity-related emission. The expected transition energies of the quantum well structures are calculated using the effective mass theory based on the 4 x 4 Luttinger valence band Hamiltonian, and related strain Hamiltonian.

Crystal growth, spectral, structural and optical studies of π-conjugated stilbazolium crystal: 4-bromobenzaldehyde-4'-N'-methylstilbazolium tosylate.

PubMed

Krishna Kumar, M; Sudhahar, S; Bhagavannarayana, G; Mohan Kumar, R

2014-05-05

Nonlinear optical (NLO) organic compound, 4-bromobenzaldehyde-4'-N'-methylstilbazolium tosylate was synthesized by reflux method. The formation of molecular complex was confirmed from (1)H NMR, FT-IR and FT-Raman spectral analyses. The single crystals were grown by slow evaporation solution growth method and the crystal structure and atomic packing of grown crystal was identified. The morphology and growth axis of grown crystal were determined. The crystal perfection was analyzed using high resolution X-ray diffraction study on (001) plane. Thermal stability, decomposition stages and melting point of the grown crystal were analyzed. The optical absorption coefficient (α) and energy band gap (E(g)) of the crystal were determined using UV-visible absorption studies. Second harmonic generation efficiency of the grown crystal was examined by Kurtz powder method with different particle size using 1064 nm laser. Laser induced damage threshold study was carried out for the grown crystal using Nd:YAG laser. Copyright © 2014 Elsevier B.V. All rights reserved.

Interfacial Coupling and Electronic Structure of Two-Dimensional Silicon Grown on the Ag(111) Surface at High Temperature

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

Feng, Jiagui; Wagner, Sean R.; Zhang, Pengpeng

Freestanding silicene, a monolayer of Si arranged in a honeycomb structure, has been predicted to give rise to massless Dirac fermions, akin to graphene. However, Si structures grown on a supporting substrate can show properties that strongly deviate from the freestanding case. Here, combining scanning tunneling microscopy/spectroscopy and differential conductance mapping, we show that the electrical properties of the (√3 x √3) phase of few-layer Si grown on Ag(111) strongly depend on film thickness, where the electron phase coherence length decreases and the free-electron-like surface state gradually diminishes when approaching the interface. These features are presumably attributable to the inelasticmore » inter-band electron-electron scattering originating from the overlap between the surface state, interface state and the bulk state of the substrate. We further demonstrate that the intrinsic electronic structure of the as grown (√3 x √3) phase is identical to that of the (√3 x √3) R30° reconstructed Ag on Si(111), both of which exhibit the parabolic energy-momentum dispersion relation with comparable electron effective masses. Lastly, these findings highlight the essential role of interfacial coupling on the properties of two-dimensional Si structures grown on supporting substrates, which should be thoroughly scrutinized in pursuit of silicene.« less

Synthesis, growth, structural, spectroscopic and optical studies of a semiorganic NLO crystal: zinc guanidinium phosphate.

PubMed

Suvitha, A; Murugakoothan, P

2012-02-01

The semi-organic nonlinear optical (NLO) crystal, zinc guanidinium phosphate (ZGuP) has been grown through synthesis between zinc sulphate, guanidine carbonate and orthophosphoric acid from its aqueous solution by slow solvent evaporation technique. Solubility of the synthesized material has been determined for various temperatures using water as solvent. The grown crystal has been characterized by powder X-ray diffraction to confirm the crystal structure. Investigation has been carried out to assign the vibrational frequencies of the grown crystals by Fourier transform infrared spectroscopy technique. (1)H and (13)C FT-NMR have been recorded to elucidate the molecular structure. The optical absorption study confirms the suitability of the crystal for device applications. The second harmonic generation (SHG) efficiency of ZGuP is found to be 1.825 times that of potassium dihydrogen phosphate (KDP). Thermal behavior of the grown crystals has been studied by thermogravimetric and differential thermal analysis. The mechanical properties of the grown crystals have been studied using Vickers microhardness tester. Copyright © 2011 Elsevier B.V. All rights reserved.

Atomic structure and stoichiometry of In(Ga)As/GaAs quantum dots grown on an exact-oriented GaP/Si(001) substrate

NASA Astrophysics Data System (ADS)

Schulze, C. S.; Huang, X.; Prohl, C.; Füllert, V.; Rybank, S.; Maddox, S. J.; March, S. D.; Bank, S. R.; Lee, M. L.; Lenz, A.

2016-04-01

The atomic structure and stoichiometry of InAs/InGaAs quantum-dot-in-a-well structures grown on exactly oriented GaP/Si(001) are revealed by cross-sectional scanning tunneling microscopy. An averaged lateral size of 20 nm, heights up to 8 nm, and an In concentration of up to 100% are determined, being quite similar compared with the well-known quantum dots grown on GaAs substrates. Photoluminescence spectra taken from nanostructures of side-by-side grown samples on GaP/Si(001) and GaAs(001) show slightly blue shifted ground-state emission wavelength for growth on GaP/Si(001) with an even higher peak intensity compared with those on GaAs(001). This demonstrates the high potential of GaP/Si(001) templates for integration of III-V optoelectronic components into silicon-based technology.

Origins of Moiré Patterns in CVD-grown MoS2 Bilayer Structures at the Atomic Scales.

PubMed

Wang, Jin; Namburu, Raju; Dubey, Madan; Dongare, Avinash M

2018-06-21

The chemical vapor deposition (CVD)-grown two-dimensional molybdenum disulfide (MoS 2 ) structures comprise of flakes of few layers with different dimensions. The top layers are relatively smaller in size than the bottom layers, resulting in the formation of edges/steps across adjacent layers. The strain response of such few-layer terraced structures is therefore likely to be different from exfoliated few-layered structures with similar dimensions without any terraces. In this study, the strain response of CVD-grown few-layered MoS 2 terraced structures is investigated at the atomic scales using classic molecular dynamics (MD) simulations. MD simulations suggest that the strain relaxation of CVD-grown triangular terraced structures is observed in the vertical displacement of the atoms across the layers that results in the formation of Moiré patterns. The Moiré islands are observed to nucleate at the corners or edges of the few-layered structure and propagate inwards under both tensile and compressive strains. The nucleation of these islands is observed to happen at tensile strains of ~ 2% and at compressive strains of ~2.5%. The vertical displacements of the atoms and the dimensions of the Moiré islands predicted using the MD simulation are in excellent agreement with that observed experimentally.

Growth and characterization of n-AlGaN 1-D structures with varying Al composition using u-GaN seeds

NASA Astrophysics Data System (ADS)

Kang, San; Chatterjee, Uddipta; Um, Dae-Young; Seo, In Seok; Lee, Cheul-Ro

2017-12-01

Like all the ternary alloys in III-nitride materials family, aluminum gallium nitride (AlGaN) has unique band gap tuning property which enables the alloy to be suitable for many opto-electronic applications. The direct band gap of AlGaN can be tuned from 3.4 to 6.2 eV by changing the composition. In this article, the growth of ternary n-AlGaN micro and nano structures on Si (1 1 1) substrate is demonstrated via 2-step growth method employing metal organic chemical vapor deposition. During the growth flow of Trimethygallium is varied to modulate the final Al/Ga ratio. After the growth, various morphological, crystalline and optical characterizations are carried out to probe in the properties of the grown structures. Recorded X-ray diffraction patterns reveal that the realized structures are wurtzite single crystalline n-AlGaN having a near homogeneous Al distribution and validated by energy dispersive X-ray spectroscopy. Low temperature cathodoluminescence spectra show band edge emission in deep UV region which enables the grown n-AlGaN structures to efficiently find opto-electronic applications in the aforementioned region. Finally, planar photoconductive devices are fabricated using the grown 1-D structures and photocurrent evolution is measured. Structure bearing highest Al content shows a manifold enhancement in photo activity compared to other grown samples. Absolute photoresponsivities of the grown samples are calculated to be 301.47, 116 and 38.13 mA/W which is in accord with the findings of low temperature cathodoluminescence investigation. Therefore, it can be concluded that the successful realization of n-AlGaN 1-D structures varying Al content facilitates the further developments of the field concerning nano- and opto-electronic devices.

Considerably improved photovoltaic performance of carbon nanotube-based solar cells using metal oxide layers.

PubMed

Wang, Feijiu; Kozawa, Daichi; Miyauchi, Yuhei; Hiraoka, Kazushi; Mouri, Shinichiro; Ohno, Yutaka; Matsuda, Kazunari

2015-02-18

Carbon nanotube-based solar cells have been extensively studied from the perspective of potential application. Here we demonstrated a significant improvement of the carbon nanotube solar cells by the use of metal oxide layers for efficient carrier transport. The metal oxides also serve as an antireflection layer and an efficient carrier dopant, leading to a reduction in the loss of the incident solar light and an increase in the photocurrent, respectively. As a consequence, the photovoltaic performance of both p-single-walled carbon nanotube (SWNT)/n-Si and n-SWNT/p-Si heterojunction solar cells using MoOx and ZnO layers is improved, resulting in very high photovoltaic conversion efficiencies of 17.0 and 4.0%, respectively. These findings regarding the use of metal oxides as multifunctional layers suggest that metal oxide layers could improve the performance of various electronic devices based on carbon nanotubes.

Considerably improved photovoltaic performance of carbon nanotube-based solar cells using metal oxide layers

NASA Astrophysics Data System (ADS)

Wang, Feijiu; Kozawa, Daichi; Miyauchi, Yuhei; Hiraoka, Kazushi; Mouri, Shinichiro; Ohno, Yutaka; Matsuda, Kazunari

2015-02-01

Carbon nanotube-based solar cells have been extensively studied from the perspective of potential application. Here we demonstrated a significant improvement of the carbon nanotube solar cells by the use of metal oxide layers for efficient carrier transport. The metal oxides also serve as an antireflection layer and an efficient carrier dopant, leading to a reduction in the loss of the incident solar light and an increase in the photocurrent, respectively. As a consequence, the photovoltaic performance of both p-single-walled carbon nanotube (SWNT)/n-Si and n-SWNT/p-Si heterojunction solar cells using MoOx and ZnO layers is improved, resulting in very high photovoltaic conversion efficiencies of 17.0 and 4.0%, respectively. These findings regarding the use of metal oxides as multifunctional layers suggest that metal oxide layers could improve the performance of various electronic devices based on carbon nanotubes.

Evaluation of the optical characteristics of c-axis oriented zinc oxide thin films grown by sol gel spin coating technique

NASA Astrophysics Data System (ADS)

Baisakh, K.; Behera, S.; Pati, S.

2018-03-01

In this work we have systematically studied the optical characteristics of synthesized wurzite zinc oxide thin films exhibiting (002) orientation. Using sol gel spin coating technique zinc oxide thin films are grown on pre cleaned fused quartz substrates. Structural properties of the films are studied using X-ray diffraction analysis. Micro structural analysis and thickness of the grown samples are analyzed using field emission scanning electron microscopy. With an aim to investigate the optical characteristics of the grown zinc oxide thin films the transmission and reflection spectra are evaluated in the ultraviolet-visible (UV-VIS) range. Using envelope method, the refractive index, extinction coefficient, absorption coefficient, band gap energy and the thickness of the synthesized films are estimated from the recorded UV-VIS spectra. An attempt has also been made to study the influence of crystallographic orientation on the optical characteristics of the grown films.

High resolution synchrotron X-radiation diffraction imaging of crystals grown in microgravity and closely related terrestrial crystals

NASA Technical Reports Server (NTRS)

Steiner, Bruce; Dobbyn, Ronald C.; Black, David; Burdette, Harold; Kuriyama, Masao; Fripp, Archibald; Simchik, Richard

1991-01-01

Irregularities in three crystals grown in space and in four terrestrial crystals grown under otherwise comparable conditions have been observed in high resolution diffraction imaging. The images provide important new clues to the nature and origins of irregularities in each crystal. For two of the materials, mercuric iodide and lead tin telluride, more than one phase (an array of non-diffracting inclusions) was observed in terrestrial samples; but the formation of these multiple phases appears to have been suppressed in directly comparable crystals grown in microgravity. The terrestrial seed crystal of triglycine sulfate displayed an unexpected layered structure, which propagated during directly comparable space growth. Terrestrial Bridgman regrowth of gallium arsenide revealed a mesoscopic structure substantially different from that of the original Czochralski material. A directly comparable crystal is to be grown shortly in space.

Microstructures and growth mechanisms of GaN films epitaxially grown on AlN/Si hetero-structures by pulsed laser deposition at different temperatures

PubMed Central

Wang, Wenliang; Yang, Weijia; Lin, Yunhao; Zhou, Shizhong; Li, Guoqiang

2015-01-01

2 inch-diameter GaN films with homogeneous thickness distribution have been grown on AlN/Si(111) hetero-structures by pulsed laser deposition (PLD) with laser rastering technique. The surface morphology, crystalline quality, and interfacial property of as-grown GaN films are characterized in detail. By optimizing the laser rastering program, the ~300 nm-thick GaN films grown at 750 °C show a root-mean-square (RMS) thickness inhomogeneity of 3.0%, very smooth surface with a RMS surface roughness of 3.0 nm, full-width at half-maximums (FWHMs) for GaN(0002) and GaN(102) X-ray rocking curves of 0.7° and 0.8°, respectively, and sharp and abrupt AlN/GaN hetero-interfaces. With the increase in the growth temperature from 550 to 850 °C, the surface morphology, crystalline quality, and interfacial property of as-grown ~300 nm-thick GaN films are gradually improved at first and then decreased. Based on the characterizations, the corresponding growth mechanisms of GaN films grown on AlN/Si hetero-structures by PLD with various growth temperatures are hence proposed. This work would be beneficial to understanding the further insight of the GaN films grown on Si(111) substrates by PLD for the application of GaN-based devices. PMID:26563573

Optical properties of InGaN grown by MOCVD on sapphire and on bulk GaN

NASA Astrophysics Data System (ADS)

Osinski, Marek; Eliseev, Petr G.; Lee, Jinhyun; Smagley, Vladimir A.; Sugahara, Tamoya; Sakai, Shiro

1999-11-01

Experimental data on photoluminescence of various bulk and quantum-well epitaxial InGaN/GaN structures grown by MOCVD are interpreted in terms of a band-tail model of inhomogeneously broadened radiative recombination. The anomalous temperature-induced blue spectral is shown to result from band-tail recombination under non-degenerate conditions. Significant differences are observed between epilayers grown on sapphire substrates and on GaN substrates prepared by the sublimination method, with no apparent evidence of band tails in homoepitaxial structures, indicating their higher crystalline quality.

Optical and structural studies of films grown thermally on zirconium surfaces

NASA Astrophysics Data System (ADS)

Morgan, J. M.; McNatt, J. S.; Shepard, M. J.; Farkas, N.; Ramsier, R. D.

2002-06-01

Variable angle IR reflection spectroscopy and atomic force microscopy are used to determine the thickness and morphology of films grown thermally on Zr surfaces in air. The density and homogeneity of these films increases with temperature in the range studied (773-873 K) and growth at the highest temperature follows cubic rate law kinetics. We demonstrate a structure-property relationship for these thermally grown films and suggest the application of IR reflectivity as an inspection method during the growth of environmentally passive films on industrial Zr components.

Photoluminescence Mapping and Angle-Resolved Photoluminescence of MBE-Grown InGaAs/GaAs RC LED and VCSEL Structures

DTIC Science & Technology

2002-06-03

resonant-cavity light-emitting diodes (RC LEDs) and vertical-cavity surface-emitting lasers ( VCSELs )] fabricated from molecular beam epitaxy (MBE)-grown...grown 8470-631. by molecular beam epitaxy (MBE) using a Riber 32P E-mail address: muszal@ite.waw.pl (0. Muszalski). reactor. Details of the growth can be... molecular beams hit the center of a rotating sion features of RC LED and VCSEL structures, as well sample. However, due to the transversal distribution of as

Growth, structural, spectral, optical, and thermal studies on amino acid based new NLO single crystal: L-phenylalanine-4-nitrophenol.

PubMed

Prakash, M; Lydia Caroline, M; Geetha, D

2013-05-01

A new organic nonlinear optical single crystal, L-phenylalanine-4-nitrophenol (LPAPN) belonging to the amino acid group has been successfully grown by slow evaporation technique. The lattice parameters of the grown crystal have been determined by X-ray diffraction studies. FT-IR spectrum was recorded to identify the presence of functional group and molecular structure was confirmed by NMR spectrum. Thermal strength of the grown crystal has been studied using TG-DTA analyses. The grown crystals were found to be transparent in the entire visible region. The existence of second harmonic generation signals was observed using Nd:YAG laser with fundamental wavelength of 1064 nm. Copyright © 2013 Elsevier B.V. All rights reserved.

Growth, structural, optical, mechanical and quantum chemical analysis of unidirectional grown bis(guanidinium) 5-sulfosalicylate (BGSSA) single crystal

NASA Astrophysics Data System (ADS)

Sreedevi, R.; Saravana Kumar, G.; Amarsingh Bhabu, K.; Balu, T.; Murugakoothan, P.; Rajasekaran, T. R.

2018-02-01

Bis(guanidinium) 5-sulfosalicylate single crystal was grown by using Sankaranarayanan-Ramasamy (SR) method from the solution of methanol and water in equimolar ratio. Good quality crystal with 50 mm length and 10 mm in diameter was grown. The grown crystal was subjected to single crystal X-ray diffraction analysis to confirm the crystal structure and it was found to be orthorhombic. UV-Vis-NIR spectroscopic study revealed that the SR method grown crystal had good optical transparency with wide optical band gap of 4.4 eV. The presence of the functional groups and modes of vibrations were identified by FTIR spectroscopy recorded in the range 4000-400 cm-1. The mechanical strength of the grown crystal was confirmed using Vickers microhardness tester by applying load from 25 g to 100 g. Density functional theory (DFT) method with B3LYP/6-31-G (d,p) level basis set was employed and hence the optimized molecular geometry, first order hyperpolarizability, dipole moment, thermodynamic functions, molecular electrostatic potential and frontier molecular orbital analysis of the grown BGSSA sample was computed and analysed.

Trimethylamine alane for low-pressure MOVPE growth of AlGaAs-based materials and device structures

NASA Astrophysics Data System (ADS)

Schneider, R. P.; Bryan, R. P.; Jones, E. D.; Biefield, R. M.; Olbright, G. R.

The use of trimethylamine alane (TMAA1) as an alternative to trimethylaluminum (TMA1) for low-pressure metalorganic vapor-phase epitaxy (MOVPE) of AlGaAs thin films as well as complex optoelectronic device structures has been studied in detail. AlGaAs layers were grown in a horizontal reaction chamber at 20 - 110 mbar with growth temperatures in the range 650 C less than or equal to T(sub G) less than or equal to 750 C. Wafer thickness uniformity is strongly dependent on growth pressure, and is acceptable only for the highest linear flow velocities. The 12 K photoluminescence (PL) spectra of AlGaAs layers grown using TMAA1 and TEGa exhibit uniformly intense and narrow bound-exciton emission throughout the growth temperature range investigated. To assess the viability of this new source for the low-pressure OMVPE growth of advanced optoelectronic devices, several optically-pumped vertical-cavity surface-emitting laser (VCSEL) structures were grown using TMAA1 extensively. Room temperature lasing at 850 nm was reproducibly obtained from the VCSEL structures, with a threshold pumping power comparable to similar structures grown by molecular beam epitaxy in our laboratories.

Development of Mid-infrared GeSn Light Emitting Diodes on a Silicon Substrate

DTIC Science & Technology

2015-04-22

Materials, Heterostrucuture Semiconductor, Light Emitting Devices, Molecular Beam Epitaxy 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT...LED) structure. Optimization of traditional and hetero- P-i-N structures designed and grown on Ge-buffer Si (001) wafers using molecular beam epitaxy ...designed structures were grown on Ge-buffer Si (001) wafers using molecular beam epitaxy (MBE) with the low-temperature growth technique. (The Ge-buffer

Increased Alignment in Carbon Nanotube Growth

NASA Technical Reports Server (NTRS)

Delzeit, Lance D. (Inventor)

2007-01-01

Method and system for fabricating an array of two or more carbon nanotube (CNT) structures on a coated substrate surface, the structures having substantially the same orientation with respect to a substrate surface. A single electrode, having an associated voltage source with a selected voltage, is connected to a substrate surface after the substrate is coated and before growth of the CNT structures, for a selected voltage application time interval. The CNT structures are then grown on a coated substrate surface with the desired orientation. Optionally, the electrode can be disconnected before the CNT structures are grown.

Growth and characterization of PbSe and Pb{sub 1{minus}x}Sn{sub x}Se layers on Si (100)

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

Sachar, H.K.; Chao, I.; Fang, X.M.

1998-12-31

Crack-free layers of PbSe were grown on Si (100) by a combination of liquid phase epitaxy (LPE) and molecular beam epitaxy (MBE) techniques. The PbSe layer was grown by LPE on Si(100) using a MBE-grown PbSe/BaF{sub 2}/CaF{sub 2} buffer layer structure. Pb{sub 1{minus}x}Sn{sub x}Se layers with tin contents in the liquid growth solution equal to 3%, 5%, 6%, 7%, and 10%, respectively, were also grown by LPE on Si(100) substrates using similar buffer layer structures. The LPE-grown PbSe and Pb{sub 1{minus}x}Sn{sub x}Se layers were characterized by optical Nomarski microscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electronmore » microscopy (SEM). Optical Nomarski characterization of the layers revealed their excellent surface morphologies and good growth solution wipe-offs. FTIR transmission experiments showed that the absorption edge of the Pb{sub 1{minus}x}Sn{sub x}Se layers shifted to lower energies with increasing tin contents. The PbSe epilayers were also lifted-off from the Si substrate by dissolving the MBE-grown BaF{sub 2} buffer layer. SEM micrographs of the cleaved edges revealed that the lifted-off layers formed structures suitable for laser fabrication.« less

Structural and optical properties of WTe2 single crystals synthesized by DVT technique

NASA Astrophysics Data System (ADS)

Dixit, Vijay; Vyas, Chirag; Pathak, V. M.; Soalanki, G. K.; Patel, K. D.

2018-05-01

Layered transition metal di-chalcogenide (LTMDCs) crystals have attracted much attention due to their potential in optoelectronic device applications recently due to realization of their monolayer based structures. In the present investigation we report growth of WTe2 single crystals by direct vapor transport (DVT) technique. These crystals are then characterized by energy dispersive analysis of x-rays (EDAX) to study stoichiometric composition after growth. The structural properties are studied by x-ray diffraction (XRD) and selected area electron diffraction (SAED) is used to confirm orthorhombic structure of grown WTe2 crystal. Surface morphological properties of the crystals are also studied by scanning electron microscope (SEM). The optical properties of the grown crystals are studied by UV-Visible spectroscopy which gives direct band gap of 1.44 eV for grown WTe2 single crystals.

Synthesis of zinc oxide nanostructures on graphene/glass substrate by electrochemical deposition: effects of current density and temperature.

PubMed

Hambali, Nur Ashikyn; Yahaya, Hafizal; Mahmood, Mohamad Rusop; Terasako, Tomoaki; Hashim, Abdul Manaf

2014-01-01

The electrochemical growth of zinc oxide (ZnO) nanostructures on graphene on glass using zinc nitrate hexahydrate was studied. The effects of current densities and temperatures on the morphological, structural, and optical properties of the ZnO structures were studied. Vertically aligned nanorods were obtained at a low temperature of 75°C, and the diameters increased with current density. Growth temperature seems to have a strong effect in generating well-defined hexagonal-shape nanorods with a smooth top edge surface. A film-like structure was observed for high current densities above -1.0 mA/cm(2) and temperatures above 80°C due to the coalescence between the neighboring nanorods with large diameter. The nanorods grown at a temperature of 75°C with a low current density of -0.1 mA/cm(2) exhibited the highest density of 1.45 × 10(9) cm(-2). X-ray diffraction measurements revealed that the grown ZnO crystallites were highly oriented along the c-axis. The intensity ratio of the ultraviolet (UV) region emission to the visible region emission, I UV/I VIS, showed a decrement with the current densities for all grown samples. The samples grown at the current density below -0.5 mA/cm(2) showed high I UV/I VIS values closer to or higher than 1.0, suggesting their fewer structural defects. For all the ZnO/graphene structures, the high transmittance up to 65% was obtained at the light wavelength of 550 nm. Structural and optical properties of the grown ZnO structures seem to be effectively controlled by the current density rather than the growth temperature. ZnO nanorod/graphene hybrid structure on glass is expected to be a promising structure for solar cell which is a conceivable candidate to address the global need for an inexpensive alternative energy source.

Structural and optical characterization of NiSe film grown by screen-printing method

NASA Astrophysics Data System (ADS)

Sharma, Kapil; Sharma, D. K.; Dwivedi, D. K.; Kumar, Vipin

2018-05-01

In present investigation NiSe films were grown by economical screen-printing method. Optimum conditions for growing good quality screen-printed films were found. The films were characterized for their structural and optical properties. The polycrystalline nature of films with hexagonal structure was confirmed through XRD analysis. Direct type of optical band gap of 1.75 eV for the NiSe film was confirmed by optical characterization.

Low-temperature growth of aligned ZnO nanorods: effect of annealing gases on the structural and optical properties.

PubMed

Umar, Ahmad; Hahn, Yoon-Bong; Al-Hajry, A; Abaker, M

2014-06-01

Aligned ZnO nanorods were grown on ZnO/Si substrate via simple aqueous solution process at low-temperature of - 65 degrees C by using zinc nitrate and hexamethylenetetramine (HMTA). The detailed morphological and structural properties measured by FESEM, XRD, EDS and TEM confirmed that the as-grown nanorods are vertically aligned, well-crystalline possessing wurtzite hexagonal phase and grown along the [0001] direction. The room-temperature photoluminescence spectrum of the grown nanorods exhibited a strong and broad green emission and small ultraviolet emission. The as-prepared ZnO nanorods were post-annealed in nitrogen (N2) and oxygen (O2) environments and further characterized in terms of their morphological, structural and optical properties. After annealing the nanorods exhibit well-crystallinity and wurtzite hexagonal phase. Moreover, by annealing the PL spectra show the enhancement in the UV emission and suppression in the green emission. The presented results demonstrate that simply by post-annealing process, the optical properties of ZnO nanostructures can be controlled.

Atomic structure and stoichiometry of In(Ga)As/GaAs quantum dots grown on an exact-oriented GaP/Si(001) substrate

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

Schulze, C. S.; Prohl, C.; Füllert, V.

2016-04-04

The atomic structure and stoichiometry of InAs/InGaAs quantum-dot-in-a-well structures grown on exactly oriented GaP/Si(001) are revealed by cross-sectional scanning tunneling microscopy. An averaged lateral size of 20 nm, heights up to 8 nm, and an In concentration of up to 100% are determined, being quite similar compared with the well-known quantum dots grown on GaAs substrates. Photoluminescence spectra taken from nanostructures of side-by-side grown samples on GaP/Si(001) and GaAs(001) show slightly blue shifted ground-state emission wavelength for growth on GaP/Si(001) with an even higher peak intensity compared with those on GaAs(001). This demonstrates the high potential of GaP/Si(001) templates for integration ofmore » III-V optoelectronic components into silicon-based technology.« less

Confocal Raman studies in determining crystalline nature of PECVD grown Si nanowires

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

Ahmed, Nafis; Bhargav, P. Balaji; Ramasamy, P.

2015-06-24

Silicon nanowires of diameter ∼200 nm and length of 2-4 µm are grown in the plasma enhanced chemical vapour deposition technique using nanoclustered Au catalyst assisted vapour-liquid-solid process. The crystallinity in the as-grown and annealed samples is studied using confocal Raman spectroscopic studies. Amorphous phase is formed in the as-grown samples. Structural studies using high resolution transmission electron microscopy confirm the polycrystalline nature in the annealed sample.

Seed/Catalyst-Free Growth of Gallium-Based Compound Materials on Graphene on Insulator by Electrochemical Deposition at Room Temperature.

PubMed

Rashiddy Wong, Freddawati; Ahmed Ali, Amgad; Yasui, Kanji; Hashim, Abdul Manaf

2015-12-01

We report the growth of gallium-based compounds, i.e., gallium oxynitride (GaON) and gallium oxide (Ga2O3) on multilayer graphene (MLG) on insulator using a mixture of ammonium nitrate (NH4NO3) and gallium nitrate (Ga(NO3)3) by electrochemical deposition (ECD) method at room temperature (RT) for the first time. The controlling parameters of current density and electrolyte molarity were found to greatly influence the properties of the grown structures. The thicknesses of the deposited structures increase with the current density since it increases the chemical reaction rates. The layers grown at low molarities of both solutions basically show grain-like layer with cracking structures and dominated by both Ga2O3 and GaON. Such cracking structures seem to diminish with the increases of molarities of one of the solutions. It is speculated that the increase of current density and ions in the solutions helps to promote the growth at the area with uneven thicknesses of graphene. When the molarity of Ga(NO3)3 is increased while keeping the molarity of NH4NO3 at the lowest value of 2.5 M, the grown structures are basically dominated by the Ga2O3 structure. On the other hand, when the molarity of NH4NO3 is increased while keeping the molarity of Ga(NO3)3 at the lowest value of 0.8 M, the GaON structure seems to dominate where their cubic and hexagonal arrangements are coexisting. It was found that when the molarities of Ga(NO3)3 are at the high level of 7.5 M, the grown structures tend to be dominated by Ga2O3 even though the molarity of NH4NO3 is made equal or higher than the molarity of Ga(NO3)3. When the grown structure is dominated by the Ga2O3 structure, the deposition process became slow or unstable, resulting to the formation of thin layer. When the molarity of Ga(NO3)3 is increased to 15 M, the nanocluster-like structures were formed instead of continuous thin film structure. This study seems to successfully provide the conditions in growing either GaON-dominated or Ga2O3-dominated structure by a simple and low-cost ECD. The next possible routes to convert the grown GaON-dominated structure to either single-crystalline GaN or Ga2O3 as well as Ga2O3-dominated structure to single-crystalline Ga2O3 structure have been discussed.

Molybdenum speciation and burial pathway in weakly sulfidic environments: Insights from XAFS

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

Wagner, Meghan; Chappaz, Anthony; Lyons, Timothy W.

Sedimentary molybdenum (Mo) accumulation is a robust proxy for sulfidic conditions in both modern and ancient aquatic systems and has been used to infer changing marine redox chemistry throughout Earth’s history. Accurate interpretation of any proxy requires a comprehensive understanding of its biogeochemical cycling, but knowledge gaps remain concerning the geochemical mechanism(s) leading to Mo burial in anoxic sediments. Better characterization of Mo speciation should provide mechanistic insight into sedimentary Mo accumulation, and therefore in this study we investigate Mo speciation from both modern (Castle Lake, USA) and ancient (Doushantuo Formation, China) environments using X-ray Absorption Near Edge Structure (XANES)more » spectroscopy. By utilizing a series of laboratory-synthesized oxythiomolybdate complexes—many containing organic ligands—we expand the number of available standards to encompass a greater range of known Mo chemistry and test the linkage between Mo and total organic carbon (TOC). In weakly euxinic systems ([H2S(aq)] < 11 µM), or where sulfide is restricted to pore waters, natural samples are best represented by a linear combination of MoO3, MoOxS4-x2- (intermediate thiomolybdates), and [MoOx(cat)4-x]2- (cat = catechol, x = 2 or 3). These results suggest a revised model for how Mo accumulates in weakly sulfidic sediments, including a previously unrecognized role for organic matter in early sequestration of Mo and a de-emphasized importance for MoS42- (tetrathiomolybdate).« less

Surface structure analysis of BaSi2(100) epitaxial film grown on Si(111) using CAICISS

NASA Astrophysics Data System (ADS)

Okasaka, Shouta; Kubo, Osamu; Tamba, Daiki; Ohashi, Tomohiro; Tabata, Hiroshi; Katayama, Mitsuhiro

2015-05-01

Geometry and surface structure of a BaSi2(100) film on Si(111) formed by reactive deposition epitaxy (RDE) have been investigated using coaxial impact-collision ion scattering spectroscopy and atomic force microscopy. BaSi2(100) film can be grown only when the Ba deposition rate is sufficiently fast. It is revealed that a BaSi2(100) film grown at 600 °C has better crystallinity than a film grown at 750 °C owing to the mixture of planes other than (100) in the RDE process at higher temperatures. The azimuth angle dependence of the scattering intensity from Ba shows sixfold symmetry, indicating that the minimum height of surface steps on BaSi2(100) is half of the length of unit cell. By comparing the simulated azimuth angle dependences for more than ten surface models with experimental one, it is strongly indicated that the surface of a BaSi2(100) film grown on Si(111) is terminated by Si tetrahedra.

Cell wall canals formed upon growth of Candida maltosa in the presence of hexadecane are associated with polyphosphates.

PubMed

Zvonarev, Anton N; Crowley, David E; Ryazanova, Lubov P; Lichko, Lydia P; Rusakova, Tatiana G; Kulakovskaya, Tatiana V; Dmitriev, Vladimir V

2017-05-01

Canals are supramolecular complexes observed in the cell wall of Candida maltosa grown in the presence of hexadecane as a sole carbon source. Such structures were not observed in glucose-grown cells. Microscopic observations of cells stained with diaminobenzidine revealed the presence of oxidative enzymes in the canals. 4΄,6΄-diamino-2-phenylindole staining revealed that a substantial part of cellular polyphosphate was present in the cell wall of cells grown on hexadecane in condition of phosphate limitation. The content and chain length of polyphosphates were higher in hexadecane-grown cells than in glucose grown ones. The treatment of cells with yeast polyphosphatase PPX1 resulted in the decrease of the canal size. These data clearly indicated that polyphosphates are constituents of canals; they might play an important role in the canal structure and functioning. © FEMS 2017. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Electrochemical deposition of silver crystals aboard Skylab 4

NASA Technical Reports Server (NTRS)

Grodzka, P. G.; Facemire, B. R.; Johnston, M. H.; Gates, D. W.

1976-01-01

Silver crystals were grown aboard Skylab 4 by an electro-chemical reaction and subsequently returned to earth for comparison with crystals grown at 1- and 5-g. Both the Skylab and earth-grown crystals show a variety of structures. Certain tendencies in structure dependency on gravity level, however, can be discerned. In addition, downward growing dendrite streamers; upward growing chunky crystal streamers; growth along an air/liquid interface; and ribbon, film, and fiber crystal habits were observed in experiments conducted on the ground with solutions of varying concentrations. It was also observed that the crystal structures of space and ground electro-deposited silver crystals were very similar to the structures of germanium selenide and germanium telluride crystals grown in space and on the ground by a vapor transport technique. Consideration of the data leads to the conclusions that: (1) the rate of electrochemical displacement of silver ions from a 5 percent aqueous solution by copper is predominantly diffussion controlled in space and kinetically controlled in 1- and higher-g because of augmentation of mass transport by convection; (2) downward and upward crystal streamers are the result of gravity-driven convection, the flow patterns of which can be delineated. Lateral growths along an air/liquid interface are the result of surface-tension-driven convection, the pattern of which also can be delineated; (3) electrolysis in space or low-g environments can produce either dendritic crystals with more perfect microcrystalline structures or massive, single crystals with fewer defects than those grown on ground or at higher g-levels. Ribbons or films of space-grown silicon crystals would find a ready market for electronic substrate and photocell applications. Space-grown dendritic, metal crystals present the possibility of unique catalysts. Large perfect crystals of various materials are desired for a number of electronic and optical applications; and (4) vapor transport growth of germanium selenide and germanium telluride is affected by convection mechanisms similar to the mechanisms hypothesized for the electrochemical deposition of silver crystals. Evidence and considerations leading to the preceding summaries and conclusions are presented. The implications of the findings and conclusions for technological applications are discussed, and recommendations for further experiments are presented.

SKYLAB (SL)-3 - EXPERIMENT HARDWARE

NASA Image and Video Library

1973-11-08

S74-19677 (April 1974) --- This crystal of Germanium Selenide (GeSe) was grown under weightless conditions in an electric furnace aboard the Skylab space station. Experiment M556, Vapor Growth of IV-VI Compounds, was conducted as a comparative test of GeSe crystals grown on Earth and those grown in a weightless environment. Skylab postflight results indicate that crystals grown in a zero-gravity situation demonstrate greater growth and better composite structure than those grown in ground-bases laboratories. The GeSe crystal shown here is 20 millimeters long, the largest crystal ever grown on Earth or in space. Principal Investigator for Experiment M556 is Dr. Harry Wiedemaier, Rensselaer Polytechnic Institute, Troy, New York. (See NASA photograph S74-19676 for an example of an Earth-grown Germanium Selenide crystal.) Photo credit: NASA

Effect of diurnal photosynthetic activity on the fine structure of amylopectin from normal and waxy barley starch.

PubMed

Goldstein, Avi; Annor, George; Blennow, Andreas; Bertoft, Eric

2017-09-01

The impact of diurnal photosynthetic activity on the fine structure of the amylopectin fraction of starch synthesized by normal barley (NBS) and waxy barley (WBS), the latter completely devoid of amylose biosynthesis, was determined following the cultivation under normal diurnal or constant light growing conditions. The amylopectin fine structures were analysed by characterizing its unit chain length profiles after enzymatic debranching as well as its φ,β-limit dextrins and its clusters and building blocks after their partial and complete hydrolysis with α-amylase from Bacillus amyloliquefaciens, respectively. Regardless of lighting conditions, no structural effects were found when comparing both the amylopectin side-chain distribution and the internal chain fragments of these amylopectins. However, the diurnally grown NBS and WBS both showed larger amylopectin clusters and these had lower branching density and longer average chain lengths than clusters derived from plants grown under constant light conditions. Amylopectin clusters from diurnally grown plants also consisted of a greater number of building blocks, and shorter inter-block chain lengths compared to clusters derived from plants grown under constant light. Our data demonstrate that the diurnal light regime influences the fine structure of the amylopectin component both in amylose and non-amylose starch granules. Copyright © 2017 Elsevier B.V. All rights reserved.

Structural characterization of niobium oxide thin films grown on SrTiO3 (111) and (La,Sr)(Al,Ta)O3 (111) substrates

NASA Astrophysics Data System (ADS)

Dhamdhere, Ajit R.; Hadamek, Tobias; Posadas, Agham B.; Demkov, Alexander A.; Smith, David J.

2016-12-01

Niobium oxide thin films have been grown by molecular beam epitaxy on SrTiO3 (STO) (111) and (La0.18Sr0.82)(Al0.59Ta0.41)O3 (LSAT) (111) substrates. Transmission electron microscopy (TEM) confirmed the formation of high quality films with coherent interfaces. Films grown with higher oxygen pressure on STO (111) resulted in a (110)-oriented NbO2 phase with a distorted rutile structure, which can be described as body-centered tetragonal. The a lattice parameter of NbO2 was determined to be ˜13.8 Å in good agreement with neutron diffraction results published in the literature. Films grown on LSAT (111) at lower oxygen pressure produced the NbO phase with a defective rock salt cubic structure. The NbO lattice parameter was determined to be a ≈ 4.26 Å. The film phase/structure identification from TEM was in good agreement with in situ x-ray photoelectron spectroscopy measurements that confirmed the dioxide and monoxide phases, respectively. The atomic structure of the NbO2/STO and NbO/LSAT interfaces was determined based on comparisons between high-resolution electron micrographs and image simulations.

Magnetoelectric Effect in Gallium Arsenide-Nickel-Tin-Nickel Multilayer Structures

NASA Astrophysics Data System (ADS)

Filippov, D. A.; Tikhonov, A. A.; Laletin, V. M.; Firsova, T. O.; Manicheva, I. N.

2018-02-01

Experimental data have been presented for the magnetoelectric effect in nickel-tin-nickel multilayer structures grown on a GaAs substrate by cathodic electrodeposition. The method of fabricating these structures has been described, and the frequency dependence of the effect has been demonstrated. It has been shown that tin used as an intermediate layer reduces mechanical stresses due to the phase mismatch at the Ni-GaAs interface and, thus, makes it possible to grow good structures with a 70-μm-thick Ni layer. The grown structures offer good adhesion between layers and a high Q factor.

Molecule diagram from space-grown crystals

NASA Technical Reports Server (NTRS)

2004-01-01

Researchers' at Hauptman-Woodward Medical Research Institute, in Buffalo, N.Y. have analyzed the molecular structures of insulin crystals grown during Space Shuttle experiments and are unlocking the mystery of how insulin works.

Reduction of structural defects in thick 4H-SiC epitaxial layers grown on 4° off-axis substrates

NASA Astrophysics Data System (ADS)

Yazdanfar, M.; Ivanov, I. G.; Pedersen, H.; Kordina, O.; Janzén, E.

2013-06-01

By carefully controlling the surface chemistry of the chemical vapor deposition process for silicon carbide (SiC), 100 μm thick epitaxial layers with excellent morphology were grown on 4° off-axis SiC substrates at growth rates exceeding 100 μm/h. In order to reduce the formation of step bunching and structural defects, mainly triangular defects, the effect of varying parameters such as growth temperature, C/Si ratio, Cl/Si ratio, Si/H2 ratio, and in situ pre-growth surface etching time are studied. It was found that an in-situ pre growth etch at growth temperature and pressure using 0.6% HCl in hydrogen for 12 min reduced the structural defects by etching preferentially on surface damages of the substrate surface. By then applying a slightly lower growth temperature of 1575 °C, a C/Si ratio of 0.8, and a Cl/Si ratio of 5, 100 μm thick, step-bunch free epitaxial layer with a minimum triangular defect density and excellent morphology could be grown, thus enabling SiC power device structures to be grown on 4° off axis SiC substrates.

Structural and physical properties of InAlAs quantum dots grown on GaAs

NASA Astrophysics Data System (ADS)

Vasile, B. S.; Daly, A. Ben; Craciun, D.; Alexandrou, I.; Lazar, S.; Lemaître, A.; Maaref, M. A.; Iacomi, F.; Craciun, V.

2018-04-01

Quantum dots (QDs), which have particular physical properties due to the three dimensions confinement effect, could be used in many advanced optoelectronic applications. We investigated the properties of InAlAs/AlGaAs QDs grown by molecular beam epitaxy on GaAs/Al0.5Ga0.5As layers. The optical properties of QDs were studied by low-temperature photoluminescence (PL). Two bandgap transitions corresponding to the X-Sh and X-Ph energy structure were observed. The QDs structure was investigated using high-resolution X-ray diffraction (HRXRD) and high-resolution transmission electron microscopy (HRTEM). HRXRD investigations showed that the layers grew epitaxially on the substrate, with no relaxation. HRTEM investigations confirmed the epitaxial nature of the grown structures. In addition, it was revealed that the In atoms aggregated in some prismatic regions, forming areas of high In concentration, that were still in perfect registry with the substrate.

Synthesis and structural study of 4-(2-chlorophenyl)-2-ethoxy-5,6,7,8,9,10-hexahydrocycloocta[B]pyridine-3-carbonitrile

NASA Astrophysics Data System (ADS)

Fathima, K. Saiadali; Vasumathi, M.; Anitha, K.

2016-05-01

The novel organic material C20H21ClN2O was synthesized by One-Pot synthesis method and the single crystals were grown by slow evaporation solution growth technique. The crystal structure was elucidated by subjecting the grown crystals to the single crystal x-ray diffraction analysis and was refined by full matrix least-squares method to R=0.039 for 2746 reflections. Crystal system of the grown crystal was found to be monoclinic with the space group P21/a and a=9.196(4) Å, b=13.449(4) Å, c=14.818(4) Å, β= 101.542(3)°, V=1795.6(11) Å3 and Z=4. In this crystal structure, cyclooctanone prefers to reside in a chair-boat conformation. The structure is stabilized by attractive molecular force such as CH/π interaction called hydrophobic interaction.

Si Nanoribbons on Ag(110) Studied by Grazing-Incidence X-Ray Diffraction, Scanning Tunneling Microscopy, and Density-Functional Theory: Evidence of a Pentamer Chain Structure.

PubMed

Prévot, Geoffroy; Hogan, Conor; Leoni, Thomas; Bernard, Romain; Moyen, Eric; Masson, Laurence

2016-12-30

We report a combined grazing incidence x-ray diffraction (GIXD), scanning tunneling microscopy (STM), and density-functional theory (DFT) study which clearly elucidates the atomic structure of the Si nanoribbons grown on the missing-row reconstructed Ag(110) surface. Our study allows us to discriminate between the theoretical models published in the literature, including the most stable atomic configurations and those based on a missing-row reconstructed Ag(110) surface. GIXD measurements unambiguously validate the pentamer model grown on the reconstructed surface, obtained from DFT. This pentamer atomistic model accurately matches the high-resolution STM images of the Si nanoribbons adsorbed on Ag(110). Our study closes the long-debated atomic structure of the Si nanoribbons grown on Ag(110) and definitively excludes a honeycomb structure similar to that of freestanding silicene.

Nanotransfer and nanoreplication using deterministically grown sacrificial nanotemplates

DOEpatents

Melechko, Anatoli V [Oak Ridge, TN; McKnight, Timothy E [Greenback, TN; Guillorn, Michael A [Ithaca, NY; Ilic, Bojan [Ithaca, NY; Merkulov, Vladimir I [Knoxville, TN; Doktycz, Mitchel J [Knoxville, TN; Lowndes, Douglas H [Knoxville, TN; Simpson, Michael L [Knoxville, TN

2011-08-23

Methods, manufactures, machines and compositions are described for nanotransfer and nanoreplication using deterministically grown sacrificial nanotemplates. An apparatus, includes a substrate and a nanoreplicant structure coupled to a surface of the substrate.

Influence of growth temperature on properties of zirconium dioxide films grown by atomic layer deposition

NASA Astrophysics Data System (ADS)

Kukli, Kaupo; Ritala, Mikko; Aarik, Jaan; Uustare, Teet; Leskela, Markku

2002-08-01

ZrO2 films were grown by atomic layer deposition from ZrCl4 and H2O or a mixture of H2O and H2O2 on Si(100) substrates in the temperature range of 180-600 degC. The films were evaluated in the as-deposited state, in order to follow the effect of deposition temperature on the film quality. The rate of crystal growth increased and the content of residual impurities decreased with increasing temperature. The zirconium-to-oxygen atomic ratio, determined by ion-beam analysis, corresponded to the stoichiometric dioxide regardless of the growth temperature. The effective permittivity of ZrO2 in Al/ZrO2/Si capacitor structures increased from 13-15 in the films grown at 180 degC to 19 in the films grown at 300-600 degC, measured at 100 kHz. The permittivity was relatively high in the crystallized films, compared to the amorphous ones, but rather insensitive to the crystal structure. The permittivity was higher in the films grown using water. The leakage current density tended to be lower and the breakdown field higher in the films grown using hydrogen peroxide.

Synthesis, growth, structural, optical, luminescence, surface and HOMO LUMO analysis of 2-[2-(4-cholro-phenyl)-vinyl]-1-methylquinolinium naphthalene-2-sulfonate organic single crystals grown by a slow evaporation technique

NASA Astrophysics Data System (ADS)

Karthigha, S.; Kalainathan, S.; Maheswara Rao, Kunda Uma; Hamada, Fumio; Yamada, Manabu; Kondo, Yoshihiko

2016-02-01

Single crystals of 2-[2-(4-cholro-phenyl)-vinyl]-1-methylquinolinium naphthalene-2-sulfonate (4CLNS) were grown by a slow evaporation technique. The formation of molecule was confirmed from 1H NMR and FTIR analysis. The confirmation of crystal structure was done by single crystal XRD and atomic packing of grown crystal was identified. The grown single crystal crystallized in triclinic structure with centrosymmetric space group P-1. The crystalline nature of the synthesised material was recorded by powder XRD. The optical absorption properties of the grown crystals were analyzed by UV-vis spectral studies. The thermal behaviour of the title material has been studied by TG/DTA analysis which revealed the stability of the compound till its melting point 276.7 °C. The third order nonlinear optical property of 4CLNS was investigated in detail by Z scan technique and it confirms that the title crystal is suitable for photonic devices and NLO optical applications. Emissions at 519 nm in green region of the EM spectrum were found by photoluminescence studies. The charge transfer occurring within the molecule is explained by the calculated HOMO and LUMO energies.

Structural and optical characteristics of GaAs films grown on Si/Ge substrates

NASA Astrophysics Data System (ADS)

Rykov, A. V.; Dorokhin, M. V.; Vergeles, P. S.; Baidus, N. V.; Kovalskiy, V. A.; Yakimov, E. B.; Soltanovich, O. A.

2018-03-01

A GaAs/AlAs heterostructure and a GaAs film grown on Si/Ge substrates have been fabricated and studied. A Ge buffer on a silicon substrate was fabricated using the MBE process. A3B5 films were grown by MOCVD at low pressures. Photoluminescence spectroscopy was used to define the optical quality of A3B5 films. Structural properties were investigated using the electron beam induced current method. It was established that despite a rather high density of dislocations on the epitaxial layers, the detected photoluminescence radiation of layers indicates the acceptable crystalline quality of the top GaAs layer.

Accumulation of Background Impurities in Hydride Vapor Phase Epitaxy Grown GaN Layers

NASA Astrophysics Data System (ADS)

Usikov, Alexander; Soukhoveev, Vitali; Kovalenkov, Oleg; Syrkin, Alexander; Shapovalov, Liza; Volkova, Anna; Ivantsov, Vladimir

2013-08-01

We report on accumulation of background Si and O impurities measured by secondary ion mass spectrometry (SIMS) at the sub-interfaces in undoped, Zn- and Mg-doped multi-layer GaN structures grown by hydride vapor phase epitaxy (HVPE) on sapphire substrates with growth interruptions. The impurities accumulation is attributed to reaction of ammonia with the rector quartz ware during the growth interruptions. Because of this effect, HVPE-grown GaN layers had excessive Si and O concentration on the surface that may hamper forming of ohmic contacts especially in the case of p-type layers and may complicate homo-epitaxial growth of a device structure.

Effect of RF power density on micro- and macro-structural properties of PECVD grown hydrogenated nanocrystalline silicon thin films

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

Gokdogan, Gozde Kahriman, E-mail: gozdekahriman@gmail.com; Anutgan, Tamila, E-mail: tamilaanutgan@karabuk.edu.tr

2016-03-25

This contribution provides the comparison between micro- and macro-structure of hydrogenated nanocrystalline silicon (nc-Si:H) thin films grown by plasma enhanced chemical vapor deposition (PECVD) technique under different RF power densities (P{sub RF}: 100−444 mW/cm{sup 2}). Micro-structure is assessed through grazing angle X-ray diffraction (GAXRD), while macro-structure is followed by surface and cross-sectional morphology via field emission scanning electron microscopy (FE-SEM). The nanocrystallite size (∼5 nm) and FE-SEM surface conglomerate size (∼40 nm) decreases with increasing P{sub RF}, crystalline volume fraction reaches maximum at 162 mW/cm{sup 2}, FE-SEM cross-sectional structure is columnar except for the film grown at 162 mW/cm{sup 2}. The dependence of previously determinedmore » ‘oxygen content–refractive index’ correlation on obtained macro-structure is investigated. Also, the effect of P{sub RF} is discussed in the light of plasma parameters during film deposition process and nc-Si:H film growth models.« less

Enhanced Structural and Luminescent Properties of Carbon-Assisted ZnO Nanorod Arrays on (100) Si Substrate

NASA Astrophysics Data System (ADS)

Yoon, Im Taek; Cho, Hak Dong; Lee, Sejoon; Roshchupkin, Dmitry V.

2018-02-01

We have fabricated as-grown ZnO nanorods (NRs) and carbon-assisted NR arrays on semi-insulating (100)-oriented Si substrates. We compared the structural and luminescent properties of them. High-resolution transmission microscopy, field emission scanning electron microscopy, x-ray diffraction and energy-dispersive x-ray revealed that the as-grown ZnO NRs and carbon-assisted ZnO NRs were single crystals with a hexagonal wurtzite structure, and grew with a c-axis orientation perpendicular to the Si substrate. These measurements show that the carbon-assisted ZnO NRs were better synthesized vertically on an Si substrate compared to the as-grown ZnO NRs. Photoluminescence measurements showed that luminescence intensity of the carbon-assisted ZnO NRs was enhanced compared to the as-grown ZnO NRs. The enhanced luminescence intensity of the carbon-assisted ZnO demonstrates the possible improvement in the performance of photovoltaic nanodevices based on ZnO-like materials. This method can be applied to the fabrication of well-aligned ZnO NRs used widely in optoelectronic devices.

Synthesis of cobalt doped BiFeO3 multiferroic thin films on p-Si substrate by sol-gel method

NASA Astrophysics Data System (ADS)

Prasannakumara, R.; Shrisha, B. V.; Naik, K. Gopalakrishna

2018-05-01

Bismuth ferrite (BiFeO3) and cobalt doped BiFeO3 (BiFe1-xCoxO3) nanostructure thin films were grown on p-silicon substrates by sol-gel spin coating method with a sequence of coating and annealing process. The post-annealing of the grown films was carried out under high pure argon atmosphere. The grown nanostructure thin films were characterized using XRD, FESEM, and AFM for the structural, morphological and topological studies, respectively. The elemental compositions of the samples were studied by EDX spectra. The PL spectra of the grown sample shows a narrow emission peak around 559 nm which corresponds to the energy band gap of BFO thin films. The XRD peaks of the BiFeO3 nanostructure thin film reveals the rhombohedral structure and transformed from rhombohedral to orthorhombic or tetragonal structure in Co doped BiFeO3 thin films. The Co substitution in BiFeO3 helped to obtain higher dense nanostructure thin films with smaller grain size than the BiFeO3 thin films.

Crystal growth, structural, low temperature thermoluminescence and mechanical properties of cubic fluoroperovskite single crystal (LiBaF3)

NASA Astrophysics Data System (ADS)

Daniel, D. Joseph; Ramasamy, P.; Ramaseshan, R.; Kim, H. J.; Kim, Sunghwan; Bhagavannarayana, G.; Cheon, Jong-Kyu

2017-10-01

Polycrystalline compounds of LiBaF3 were synthesized using conventional solid state reaction route and the phase purity was confirmed using powder X-ray diffraction technique. Using vertical Bridgman technique single crystal was grown from melt. Rocking curve measurements have been carried out to study the structural perfection of the grown crystal. The single peak of diffraction curve clearly reveals that the grown crystal was free from the structural grain boundaries. The low temperature thermoluminescence of the X-ray irradiated sample has been analyzed and found four distinguishable peaks having maximum temperatures at 18, 115, 133 and 216 K. Activation energy (E) and frequency factor (s) for the individual peaks have been studied using Peak shape method and the computerized curve fitting method combining with the Tmax- TStop procedure. Nanoindentation technique was employed to study the mechanical behaviour of the crystal. The indentation modulus and Vickers hardness of the grown crystal have values of 135.15 GPa and 680.81 respectively, under the maximum indentation load of 10 mN.

Growth and properties of wide bandgap (MgSe)n(ZnxCd1-xSe)m short-period superlattices

NASA Astrophysics Data System (ADS)

Garcia, Thor A.; Tamargo, Maria C.

2017-12-01

We report the molecular beam epitaxy (MBE) growth and properties of (MgSe)n(ZnxCd1-x Se)m short-period superlattices(SPSLs) for potential application in II-VI devices grown on InP substrates. SPSL structures up to 1 μm thick with effective bandgaps ranging from 2.6 eV to above 3.42 eV are grown and characterized, extending the typical range possible for the ZnxCdyMg1-x-ySe random alloy beyond 3.2 eV. Additionally, ZnxCd1-xSe single and multiple quantum well structures using the SPSL barriers are also grown and investigated. The structures are characterized utilizing reflection high-energy electron diffraction, X-ray reflectance, X-ray diffraction and photoluminescence. We observed layer-by-layer growth and smoother interfaces in the QWs grown with SPSL when compared to the ZnxCdyMg1-x-ySe random alloy. The results indicate that this materials platform is a good candidate to replace the random alloy in wide bandgap device applications.

Magnetic structure and phase stability of the van der Waals bonded ferromagnet Fe 3-xGeTe 2

DOE PAGES

May, Andrew F.; Calder, Stuart A.; Cantoni, Claudia; ...

2016-01-08

The magnetic structure and phase diagram of the layered ferromagnetic compound Fe 3GeTe 2 have been investigated by a combination of synthesis, x-ray and neutron diffraction, high-resolution microscopy, and magnetization measurements. Single crystals were synthesized by self-flux reactions, and single-crystal neutron diffraction finds ferromagnetic order with moments of 1.11(5)μ B/Fe aligned along the c axis at 4 K. These flux-grown crystals have a lower Curie temperature T c ≈ 150 K than crystals previously grown by vapor transport (T c = 220 K). The difference is a reduced Fe content in the flux-grown crystals, as illustrated by the behavior observedmore » in a series of polycrystalline samples. As Fe content decreases, so do the Curie temperature, magnetic anisotropy, and net magnetization. Furthermore, Hall-effect and thermoelectric measurements on flux-grown crystals suggest that multiple carrier types contribute to electrical transport in Fe 3–xGeTe 2 and structurally similar Ni 3–xGeTe 2.« less

Structural, magnetic and electronic properties of pulsed-laser-deposition grown SrFeO3-δ thin films and SrFeO3-δ /La2/3Ca1/3MnO3 multilayers

NASA Astrophysics Data System (ADS)

Perret, E.; Sen, K.; Khmaladze, J.; Mallett, B. P. P.; Yazdi-Rizi, M.; Marsik, P.; Das, S.; Marozau, I.; Uribe-Laverde, M. A.; de Andrés Prada, R.; Strempfer, J.; Döbeli, M.; Biškup, N.; Varela, M.; Mathis, Y.-L.; Bernhard, C.

2017-12-01

We studied the structural, magnetic and electronic properties of SrFeO3-δ (SFO) thin films and SrFeO3-δ /La2/3 Ca1/3 MnO3 (LCMO) superlattices that have been grown with pulsed laser deposition (PLD) on La0.3 Sr0.7 Al0.65 Ta0.35 O3 (LSAT) substrates. X-ray reflectometry and scanning transmission electron microscopy (STEM) confirm the high structural quality of the films and flat and atomically sharp interfaces of the superlattices. The STEM data also reveal a difference in the interfacial layer stacking with a SrO layer at the LCMO/SFO and a LaO layer at the SFO/LCMO interfaces along the PLD growth direction. The x-ray diffraction (XRD) data suggest that the as grown SFO films and SFO/LCMO superlattices have an oxygen-deficient SrFeO3-δ structure with I4/ mmm space group symmetry (δ≤slant 0.2 ). Subsequent ozone annealed SFO films are consistent with an almost oxygen stoichiometric structure (δ ≈ 0 ). The electronic and magnetic properties of these SFO films are similar to the ones of corresponding single crystals. In particular, the as grown SrFeO3-δ films are insulating whereas the ozone annealed films are metallic. The magneto-resistance effects of the as grown SFO films have a similar magnitude as in the single crystals, but extend over a much wider temperature range. Last but not least, for the SFO/LCMO superlattices we observe a rather large exchange bias effect that varies as a function of the cooling field.

Growth and microtopographic study of CuInSe{sub 2} single crystals

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

Chauhan, Sanjaysinh M.; Chaki, Sunil, E-mail: sunilchaki@yahoo.co.in; Deshpande, M. P.

2016-05-23

The CuInSe{sub 2} single crystals were grown by chemical vapour transport (CVT) technique using iodine as transporting agent. The elemental composition of the as-grown CuInSe{sub 2} single crystals was determined by energy dispersive analysis of X-ray (EDAX). The unit cell crystal structure and lattice parameters were determined by X-ray diffraction (XRD) technique. The surface microtopographic study of the as-grown CuInSe{sub 2} single crystals surfaces were done to study the defects, growth mechanism, etc. of the CVT grown crystals.

High nitrogen pressure solution growth of GaN

NASA Astrophysics Data System (ADS)

Bockowski, Michal

2014-10-01

Results of GaN growth from gallium solution under high nitrogen pressure are presented. Basic of the high nitrogen pressure solution (HNPS) growth method is described. A new approach of seeded growth, multi-feed seed (MFS) configuration, is demonstrated. The use of two kinds of seeds: free-standing hydride vapor phase epitaxy GaN (HVPE-GaN) obtained from metal organic chemical vapor deposition (MOCVD)-GaN/sapphire templates and free-standing HVPE-GaN obtained from the ammonothermally grown GaN crystals, is shown. Depending on the seeds’ structural quality, the differences in the structural properties of pressure grown material are demonstrated and analyzed. The role and influence of impurities, like oxygen and magnesium, on GaN crystals grown from gallium solution in the MFS configuration is presented. The properties of differently doped GaN crystals are discussed. An application of the pressure grown GaN crystals as substrates for electronic and optoelectronic devices is reported.

Crystal growth, thermal and optical studies of semiorganic nonlinear optical material: L-lysine hydrochloride dihydrate

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

Kalaiselvi, D.; Mohan Kumar, R.; Jayavel, R.

2008-07-01

Single crystals of L-lysine hydrochloride dihydrate (LLHCD), a nonlinear optical material, have been grown by slow cooling technique from its aqueous solution. LLHCD was found to be highly soluble in water. The grown crystals have been subjected to single crystal X-ray diffraction to confirm the structure and to estimate the lattice parameters. The vibrational structure of the molecule is elucidated from FTIR spectra. Thermal analysis revealed the thermal stability of the grown crystals. The optical transmittance spectrum shows that the material possesses good optical transparency in the entire visible region with a UV cut-off wavelength at 228 nm. The mechanicalmore » properties of the grown crystal have been studied using Vicker's microhardness test. The laser damage threshold of 52.25 MW/cm{sup 2} has been measured by irradiating Q-switched Nd:YAG laser (1064 nm)« less

Terahertz radiation in In{sub 0.38}Ga{sub 0.62}As grown on a GaAs wafer with a metamorphic buffer layer under femtosecond laser excitation

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

Ponomarev, D. S., E-mail: ponomarev-dmitr@mail.ru; Khabibullin, R. A.; Yachmenev, A. E.

The results of time-domain spectroscopy of the terahertz (THz) generation in a structure with an In{sub 0.38}Ga{sub 0.62}As photoconductive layer are presented. This structure grown by molecular-beam epitaxy on a GaAs substrate using a metamorphic buffer layer allows THz generation with a wide frequency spectrum (to 6 THz). This is due to the additional contribution of the photo-Dember effect to THz generation. The measured optical-to-terahertz conversion efficiency in this structure is 10{sup –5} at a rather low optical fluence of ~40 μJ/cm{sup 2}, which is higher than that in low-temperature grown GaAs by almost two orders of magnitude.

Zeolite Crystal Growth (ZCG) Flight on USML-2

NASA Technical Reports Server (NTRS)

Sacco, Albert, Jr.; Bac, Nurcan; Warzywoda, Juliusz; Guray, Ipek; Marceau, Michelle; Sacco, Teran L.; Whalen, Leah M.

1997-01-01

The extensive use of zeolites and their impact on the world's economy has resulted in many efforts to characterize their structure, and improve the knowledge base for nucleation and growth of these crystals. The zeolite crystal growth (ZCG) experiment on USML-2 aimed to enhance the understanding of nucleation and growth of zeolite crystals, while attempting to provide a means of controlling the defect concentration in microgravity. Zeolites A, X, Beta, and Silicalite were grown during the 16 day - USML-2 mission. The solutions where the nucleation event was controlled yielded larger and more uniform crystals of better morphology and purity than their terrestrial/control counterparts. The external surfaces of zeolite A, X, and Silicalite crystals grown in microgravity were smoother (lower surface roughness) than their terrestrial controls. Catalytic studies with zeolite Beta indicate that crystals grown in space exhibit a lower number of Lewis acid sites located in micropores. This suggests fewer structural defects for crystals grown in microgravity. Transmission electron micrographs (TEM) of zeolite Beta crystals also show that crystals grown in microgravity were free of line defects while terrestrial/controls had substantial defects.

Vertical growth of ZnO nanorods on ZnO seeded FTO substrate for dye sensitized solar cells

NASA Astrophysics Data System (ADS)

Marimuthu, T.; Anandhan, N.

2018-04-01

Zinc oxide (ZnO) nanorods (NRs) were electrochemically grown on fluorine doped tin oxide (FTO) and ZnO seeded FTO substrates. X-ray diffraction (XRD) patterns, Raman spectra and photoluminescence (PL) spectra reveal that the hexagonal wurtzite structured ZnO grown on a seeded FTO substrate has a high crystallinity, crystal quality and less atomic defects. Felid emission scanning electron microscope (FE-SEM) images display a high growth density of NRs grown on seeded FTO substrate compared to NRs grown on FTO substrate. The efficiency of the DSSCs based on NRs grown on FTO and seeded FTO substrates is 0.85 and 1.52 %, respectively. UV-Vis absorption spectra and electrochemical impedance spectra depict that the NRs grown on seeded FTO photoanode have higher dye absorption and charge recombination resistance than that of the NRs grown on FTO substrate.

Molecule diagram from earth-grown crystals

NASA Technical Reports Server (NTRS)

2004-01-01

Like many chemicals in the body, the three-dimensional structure of insulin is extremely complex. When grown on the ground, insulin crystals do not grow as large or as ordered as researchers desire--obscuring the blueprint of the insulin molecules.

Synthesis, crystal structure, thermal and nonlinear optical properties of new metal-organic single crystal: Tetrabromo (piperazinium) zincate (II) (TBPZ)

NASA Astrophysics Data System (ADS)

Boopathi, K.; Babu, S. Moorthy; Ramasamy, P.

2018-04-01

Tetrabromo (piperazinium) zincate, a new metal-organic crystal has been synthesized and its single crystal grown by slow evaporation method. The grown crystal has characterized by structural, spectral, thermal, linear and nonlinear optical properties. Single crystal X-ray diffractions study reveals that grown crystal belongs to orthorhombic crystal system with space group P212121. The presence of functional groups is identified by FT-IR spectral analysis. Thermal stability of the crystal was ascertained by TG-DTA measurement. The second order harmonic generation efficiency was measured using Kurtz and Perry technique and it was found to be 1.5 times that of KDP.

Structural, optical and Carrier dynamics of self-assembled InGaN nanocolumns on Si(111)

NASA Astrophysics Data System (ADS)

Kumar, Praveen; Devi, Pooja; Soto Rodriguez, P. E. D.; Jain, Rishabh; Jaggi, Neena; Sinha, R. K.; Kumar, Mahesh

2018-05-01

We investigated the morphological, structural, optical, electrical and carrier relaxation dynamic changes on the self-assembled grown InGaN nanocolumns (NCs) directly on p-Si(111) substrate at two different substrate temperature, namely 580 °C (A) and 500 °C (B). The emission wavelength of comparably low temperature (LT) grown NCs was red-shifted from 3.2eV to 2.4eV. First observations on the charge carrier dynamics of these directly grown NCs show comparable broad excited state absorption (ESA) for LT gown NCs, which manifest bi-exponential decay due to the radiative defects generated during the coalescence of these NCs.

Efficient hydrogen evolution in transition metal dichalcogenides via a simple one-step hydrazine reaction

PubMed Central

Cummins, Dustin R.; Martinez, Ulises; Sherehiy, Andriy; Kappera, Rajesh; Martinez-Garcia, Alejandro; Schulze, Roland K.; Jasinski, Jacek; Zhang, Jing; Gupta, Ram K.; Lou, Jun; Chhowalla, Manish; Sumanasekera, Gamini; Mohite, Aditya D.; Sunkara, Mahendra K.; Gupta, Gautam

2016-01-01

Hydrogen evolution reaction is catalysed efficiently with precious metals, such as platinum; however, transition metal dichalcogenides have recently emerged as a promising class of materials for electrocatalysis, but these materials still have low activity and durability when compared with precious metals. Here we report a simple one-step scalable approach, where MoOx/MoS2 core-shell nanowires and molybdenum disulfide sheets are exposed to dilute aqueous hydrazine at room temperature, which results in marked improvement in electrocatalytic performance. The nanowires exhibit ∼100 mV improvement in overpotential following exposure to dilute hydrazine, while also showing a 10-fold increase in current density and a significant change in Tafel slope. In situ electrical, gate-dependent measurements and spectroscopic investigations reveal that hydrazine acts as an electron dopant in molybdenum disulfide, increasing its conductivity, while also reducing the MoOx core in the core-shell nanowires, which leads to improved electrocatalytic performance. PMID:27282871

Efficient hydrogen evolution in transition metal dichalcogenides via a simple one-step hydrazine reaction.

PubMed

Cummins, Dustin R; Martinez, Ulises; Sherehiy, Andriy; Kappera, Rajesh; Martinez-Garcia, Alejandro; Schulze, Roland K; Jasinski, Jacek; Zhang, Jing; Gupta, Ram K; Lou, Jun; Chhowalla, Manish; Sumanasekera, Gamini; Mohite, Aditya D; Sunkara, Mahendra K; Gupta, Gautam

2016-06-10

Hydrogen evolution reaction is catalysed efficiently with precious metals, such as platinum; however, transition metal dichalcogenides have recently emerged as a promising class of materials for electrocatalysis, but these materials still have low activity and durability when compared with precious metals. Here we report a simple one-step scalable approach, where MoOx/MoS2 core-shell nanowires and molybdenum disulfide sheets are exposed to dilute aqueous hydrazine at room temperature, which results in marked improvement in electrocatalytic performance. The nanowires exhibit ∼100 mV improvement in overpotential following exposure to dilute hydrazine, while also showing a 10-fold increase in current density and a significant change in Tafel slope. In situ electrical, gate-dependent measurements and spectroscopic investigations reveal that hydrazine acts as an electron dopant in molybdenum disulfide, increasing its conductivity, while also reducing the MoOx core in the core-shell nanowires, which leads to improved electrocatalytic performance.

Degradable Molybdenum Oxide Nanosheets with Rapid Clearance and Efficient Tumor Homing Capabilities as a Therapeutic Nanoplatform.

PubMed

Song, Guosheng; Hao, Jiali; Liang, Chao; Liu, Teng; Gao, Min; Cheng, Liang; Hu, Junqing; Liu, Zhuang

2016-02-05

Molybdenum oxide (MoOx) nanosheets with high near-infrared (NIR) absorbance and pH-dependent oxidative degradation properties were synthesized, functionalized with polyethylene glycol (PEG), and then used as a degradable photothermal agent and drug carrier. The nanosheets, which are relatively stable under acidic pH, could be degraded at physiological pH. Therefore, MoOx-PEG distributed in organs upon intravenous injection would be rapidly degraded and excreted without apparent in vivo toxicity. MoOx-PEG shows efficient accumulation in tumors, the acidic pH of which then leads to longer tumor retention of those nanosheets. Along with the capability of acting as a photothermal agent for effective tumor ablation, MoOx-PEG can load therapeutic molecules with high efficiencies. This concept of inorganic theranostic nanoagent should be relatively stable in tumors to allow imaging and treatment, while being readily degradable in normal organs to enable rapid excretion and avoid long-term retention/toxicity. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

High-performance tandem organic light-emitting diodes based on a buffer-modified p/n-type planar organic heterojunction as charge generation layer

NASA Astrophysics Data System (ADS)

Wu, Yukun; Sun, Ying; Qin, Houyun; Hu, Shoucheng; Wu, Qingyang; Zhao, Yi

2017-04-01

High-performance tandem organic light-emitting diodes (TOLEDs) were realized using a buffer-modified p/n-type planar organic heterojunction (OHJ) as charge generation layer (CGL) consisting of common organic materials, and the configuration of this p/n-type CGL was "LiF/N,N'-diphenyl-N,N'-bis(1-napthyl)-1,1'-biphenyl-4,4'-diamine (NPB)/4,7-diphenyl-1,10-phenanthroline (Bphen)/molybdenum oxide (MoOx)". The optimized TOLED exhibited a maximum current efficiency of 77.6 cd/A without any out-coupling techniques, and the efficiency roll-off was greatly improved compared to the single-unit OLED. The working mechanism of the p/n-type CGL was discussed in detail. It is found that the NPB/Bphen heterojunction generated enough charges under a forward applied voltage and the carrier extraction was a tunneling process. These results could provide a new method to fabricate high-performance TOLEDs.

Green, yellow and bright red (In,Ga,Al)P-GaP diode lasers grown on high-index GaAs substrates

NASA Astrophysics Data System (ADS)

Ledentsov, N. N.; Shchukin, V. A.; Shernyakov, Yu. M.; Kulagina, M. M.; Payusov, A. S.; Gordeev, N. Yu.; Maximov, M. V.; Cherkashin, N. A.

2017-02-01

Low threshold current density (<400 A/cm2) injection lasing in (AlxGa1-x)0.5In0.5P-GaAs-based diodes down to the green spectral range (<570 nm) is obtained. The epitaxial structures are grown on high-index (611)A and (211)A GaAs substrates by metal-organic vapor phase epitaxy and contain tensile-strained GaP-enriched insertions aimed at preventing escape of the injected nonequilibrium electrons from the active region. Extended waveguide concept results in a vertical beam divergence with a full width at half maximum of 15o for (611)A substrates. The lasing at 569 nm is realized at 85 K. In the orange-red laser diode structure low threshold current density (200 A/cm2) in the orange spectral range (598 nm) is realized at 85 K. The latter devices demonstrate room temperature lasing at 628 nm at 2 kA/cm2 and a total power above 3W. The red laser diodes grown on (211)A substrates demonstrate vertically multimode lasing far field pattern indicating a lower optical confinement factor for the fundamental mode as compared to the devices grown on (611)A. However the temperature stability of the threshold current and the wavelength stability are significantly higher for (211)A-grown structures in agreement with the conduction band modeling data.

The influence of elevated CO2 on non-structural carbohydrate distribution and fructan accumulation in wheat canopies

NASA Technical Reports Server (NTRS)

Smart, D. R.; Chatterton, N. J.; Bugbee, B.

1994-01-01

We grew 2.4 m2 wheat canopies in a large growth chamber under high photosynthetic photon flux (1000 micromoles m-2 s-1) and using two CO2 concentrations, 360 and 1200 micromoles mol-1. Photosynthetically active radiation (400-700 nm) was attenuated slightly faster through canopies grown in 360 micromoles mol-1 than through canopies grown in 1200 micromoles mol-1, even though high-CO2 canopies attained larger leaf area indices. Tissue fractions were sampled from each 5-cm layer of the canopies. Leaf tissue sampled from the tops of canopies grown in 1200 micromoles mol-1 accumulated significantly more total non-structural carbohydrate, starch, fructan, sucrose, and glucose (p < 0.05) than for canopies grown in 360 micromoles mol-1. Non-structural carbohydrate did not significantly increase in the lower canopy layers of the elevated CO2 treatment. Elevated CO2 induced fructan synthesis in all leaf tissue fractions, but fructan formation was greatest in the uppermost leaf area. A moderate temperature reduction of 10 degrees C over 5 d increased starch, fructan and glucose levels in canopies grown in 1200 micromoles mol-1, but concentrations of sucrose and fructose decreased slightly or remained unchanged. Those results may correspond with the use of fructosyl-residues and release of glucose when sucrose is consumed in fructan synthesis.

Synthesis and structural study of 4-(2-chlorophenyl)-2-ethoxy-5,6,7,8,9,10-hexahydrocycloocta[B] pyridine-3-carbonitrile

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

Fathima, K. Saiadali; Vasumathi, M.; Anitha, K., E-mail: singlecrystalxrd@gmail.com

2016-05-23

The novel organic material C{sub 20}H{sub 21}ClN{sub 2}O was synthesized by One-Pot synthesis method and the single crystals were grown by slow evaporation solution growth technique. The crystal structure was elucidated by subjecting the grown crystals to the single crystal x-ray diffraction analysis and was refined by full matrix least-squares method to R=0.039 for 2746 reflections. Crystal system of the grown crystal was found to be monoclinic with the space group P2{sub 1}/a and a=9.196(4) Å, b=13.449(4) Å, c=14.818(4) Å, β= 101.542(3)°, V=1795.6(11) Å{sup 3} and Z=4. In this crystal structure, cyclooctanone prefers to reside in a chair-boat conformation. Themore » structure is stabilized by attractive molecular force such as CH/π interaction called hydrophobic interaction.« less

Ga/1-x/Al/x/As LED structures grown on GaP substrates.

NASA Technical Reports Server (NTRS)

Woodall, J. M.; Potemski, R. M.; Blum, S. E.; Lynch, R.

1972-01-01

Ga(1-x)Al(x)As light-emitting diode structures have been grown on GaP substrates by the liquid-phase-epitaxial method. In spite of the large differences in lattice constants and thermal-expansion coefficients, room-temperature efficiencies up to 5.5% in air have been observed for a peak emission of 8500 A. Using undoped GaP substrates, which are transparent to the infrared and red portions of the spectrum, thin structures of Ga(1-x)Al(x)As with large external efficiencies can now be made.

A novel structure of gel grown strontium cyanurate crystal and its structural, optical, electrical characterization

NASA Astrophysics Data System (ADS)

Divya, R.; Nair, Lekshmi P.; Bijini, B. R.; Nair, C. M. K.; Gopakumar, N.; Babu, K. Rajendra

2017-12-01

Strontium cyanurate crystals with novel structure and unique optical property like mechanoluminescence have been grown by conventional gel method. Transparent crystals were obtained. The single crystal X-ray diffraction analysis reveals the exquisite structure of the grown crystal. The crystal is centrosymmetric and has a three dimensional polymeric structure. The powder X ray diffraction analysis confirms its crystalline nature. The functional groups present in the crystal were identified by Fourier transform infrared spectroscopy. Elemental analysis confirmed the composition of the complex. A study of thermal properties was done by thermo gravimetric analysis and differential thermal analysis. The optical properties like band gap, refractive index and extinction coefficient were evaluated from the UV visible spectral analysis. The etching study was done to reveal the dislocations in the crystal which in turn explains mechanoluminescence emission. The mechanoluminescence property exhibited by the crystal makes it suitable for stress sensing applications. Besides being a centrosymmetric crystal, it also exhibits NLO behavior. Dielectric properties were studied and theoretical calculations of Fermi energy, valence electron plasma energy, penn gap and polarisability have been done.

Robust optical properties of sandwiched lateral composition modulation GaInP structure grown by molecular beam epitaxy

DOE PAGES

Park, Kwangwook; Kang, Seokjin; Ravindran, Sooraj; ...

2016-12-26

Double-hetero structure lateral composition modulated (LCM) GaInP and sandwiched LCM GaInP having the same active layer thickness were grown and their optical properties were compared. Sandwiched LCM GaInP showed robust optical properties due to periodic potential nature of the LCM structure, and the periodicity was undistorted even for thickness far beyond the critical layer thickness. A thick LCM GaInP structure with undistorted potential that could preserve the properties of native LCM structure was possible by stacking thin LCM GaInP structures interspaced with strain compensating GaInP layers. Furthermore, the sandwiched structure could be beneficial in realizing the LCM structure embedded highmore » efficiency solar cells.« less

Defects in High Speed Growth of EFG Silicon Ribbon

NASA Technical Reports Server (NTRS)

Rao, C. V. H. N.; Cretella, M. C.

1984-01-01

Silicon ribbons grown by the Edge-defined Film-fed Growth (EFG) technique exhibit a characteristic defect structure typified by twins, dislocations, grain boundaries and silicon carbide inclusions. As growth speed is increased from less than 2.5 cm per minute, the structural details change. The major difference between the ribbons grown at speeds below and above 2.5 cm per minute is in the generation of a cellular structure at the higher growth speeds, observable in the ribbon cross section. The presence of the cross sectional structure leads, in general, to a reduction in cell performance. Models to explain the formation of such a cross sectional structure are presented and discussed.

Growth of low temperature silicon nano-structures for electronic and electrical energy generation applications.

PubMed

Gabrielyan, Nare; Saranti, Konstantina; Manjunatha, Krishna Nama; Paul, Shashi

2013-02-15

This paper represents the lowest growth temperature for silicon nano-wires (SiNWs) via a vapour-liquid-solid method, which has ever been reported in the literature. The nano-wires were grown using plasma-enhanced chemical vapour deposition technique at temperatures as low as 150°C using gallium as the catalyst. This study investigates the structure and the size of the grown silicon nano-structure as functions of growth temperature and catalyst layer thickness. Moreover, the choice of the growth temperature determines the thickness of the catalyst layer to be used.The electrical and optical characteristics of the nano-wires were tested by incorporating them in photovoltaic solar cells, two terminal bistable memory devices and Schottky diode. With further optimisation of the growth parameters, SiNWs, grown by our method, have promising future for incorporation into high performance electronic and optical devices.

Growth of low temperature silicon nano-structures for electronic and electrical energy generation applications

PubMed Central

2013-01-01

This paper represents the lowest growth temperature for silicon nano-wires (SiNWs) via a vapour-liquid–solid method, which has ever been reported in the literature. The nano-wires were grown using plasma-enhanced chemical vapour deposition technique at temperatures as low as 150°C using gallium as the catalyst. This study investigates the structure and the size of the grown silicon nano-structure as functions of growth temperature and catalyst layer thickness. Moreover, the choice of the growth temperature determines the thickness of the catalyst layer to be used. The electrical and optical characteristics of the nano-wires were tested by incorporating them in photovoltaic solar cells, two terminal bistable memory devices and Schottky diode. With further optimisation of the growth parameters, SiNWs, grown by our method, have promising future for incorporation into high performance electronic and optical devices. PMID:23413969

Growth of epitaxial Pb(Zr,Ti)O3 films by pulsed laser deposition

NASA Astrophysics Data System (ADS)

Lee, J.; Safari, A.; Pfeffer, R. L.

1992-10-01

Lead zirconate titanate (PZT) thin films with a composition near the morphotropic phase boundary have been grown on MgO (100) and Y1Ba2Cu3Ox (YBCO) coated MgO substrates. Substrate temperature and oxygen pressure were varied to achieve ferroelectric films with a perovskite structure. Films grown on MgO had the perovskite structure with an epitaxial relationship with the MgO substrate. On the other hand, films grown on the YBCO/MgO substrate had an oriented structure to the surface normal with a misorientation in the plane parallel to the surface. The measured dielectric constant and loss tangent at 1 kHz were 670 and 0.05, respectively. The remnant polarization and coercive field were 42 μC/cm2 and 53 kV/cm. A large internal bias field (12 kV/cm) was observed in the as-deposited state of the undoped PZT films.

Growth, structural, optical, thermal and mechanical properties of ammonium pentaborate single crystal.

PubMed

Balakrishnan, T; Bhagavannarayana, G; Ramamurthi, K

2008-11-15

Nonlinear optical single crystals of ammonium pentaborate (APB) were grown by the slow cooling method from aqueous solution. Grown crystal was characterized by powder X-ray diffraction (PXRD) and FT-IR spectral analysis. Perfection of the grown crystal was evaluated by high-resolution X-ray diffractometry (HRXRD). The effect of nylon threading on the perfection of the grown bigger crystal was also studied by HRXRD. The range and percentage of optical transmission was ascertained by recording UV-vis-NIR spectrum. Thermal properties were investigated by TG-DTA and DSC analyses. Its mechanical hardness was estimated by Vickers microhardness tester.

Comparison of the structural properties of Zn-face and O-face single crystal homoepitaxial ZnO epilayers grown by RF-magnetron sputtering

NASA Astrophysics Data System (ADS)

Schifano, R.; Riise, H. N.; Domagala, J. Z.; Azarov, A. Yu.; Ratajczak, R.; Monakhov, E. V.; Venkatachalapathy, V.; Vines, L.; Chan, K. S.; Wong-Leung, J.; Svensson, B. G.

2017-01-01

Homoepitaxial ZnO growth is demonstrated from conventional RF-sputtering at 400 °C on both Zn and O polar faces of hydrothermally grown ZnO substrates. A minimum yield for the Rutherford backscattering and channeling spectrum, χmin, equal to ˜3% and ˜12% and a full width at half maximum of the 00.2 diffraction peak rocking curve of (70 ± 10) arc sec and (1400 ± 100) arc sec have been found for samples grown on the Zn and O face, respectively. The structural characteristics of the film deposited on the Zn face are comparable with those of epilayers grown by more complex techniques like molecular beam epitaxy. In contrast, the film simultaneously deposited on the O-face exhibits an inferior crystalline structure ˜0.7% strained in the c-direction and a higher atomic number contrast compared with the substrate, as revealed by high angle annular dark field imaging measurements. These differences between the Zn- and O-face films are discussed in detail and associated with the different growth mechanisms prevailing on the two surfaces.

Epitaxial Fe(1-x)Gax/GaAs structures via electrochemistry for spintronics applications

NASA Astrophysics Data System (ADS)

Reddy, K. Sai Madhukar; Maqableh, Mazin M.; Stadler, Bethanie J. H.

2012-04-01

In this study, thin films of Fe83Ga17 (a giant magnetostrictive alloy) were grown on single-crystalline n-GaAs (001) and polycrystalline brass substrates via electrochemical synthesis from ferrous and gallium sulfate electrolytes. Extensive structural characterization using microdiffraction, high-resolution ω - 2θ, and rocking-curve analysis revealed that the films grown on GaAs(001) are highly textured with ⟨001⟩ orientation along the substrate normal, and the texture improved further upon annealing at 300 °C for 2 h in N2 environment. On the contrary, films grown on brass substrates exhibited ⟨011⟩ preferred orientation. Rocking-curve analysis done on Fe83Ga17/GaAs structures further confirmed that the ⟨001⟩ texture in the Fe83Ga17 thin film is a result of epitaxial nucleation and growth. The non-linear current-voltage plot obtained for the Fe-Ga/GaAs Schottky contacts was characteristic of tunneling injection, and showed improved behavior with annealing. Thus, this study demonstrates the feasibility of fabricating spintronic devices that incorporate highly magnetostrictive Fe(1-x)Gax thin films grown epitaxially via electrochemistry.

Suppression of gate leakage current in in-situ grown AlN/InAlN/AlN/GaN heterostructures based on the control of internal polarization fields

NASA Astrophysics Data System (ADS)

Kotani, Junji; Yamada, Atsushi; Ishiguro, Tetsuro; Yamaguchi, Hideshi; Nakamura, Norikazu

2017-03-01

This paper investigates the gate leakage characteristics of in-situ AlN capped InAlN/AlN/GaN heterostructures grown by metal-organic vapor phase epitaxy. It was revealed that the leakage characteristics of AlN capped InAlN/AlN/GaN heterostructures are strongly dependent on the growth temperature of the AlN cap. For an AlN capped structure with an AlN growth temperature of 740 °C, the leakage current even increased although there exists a large bandgap material on InAlN/AlN/GaN heterostructures. On the other hand, a large reduction of the gate leakage current by 4-5 orders of magnitudes was achieved with a very low AlN growth temperature of 430 °C. X-ray diffraction analysis of the AlN cap grown at 740 °C indicated that the AlN layer is tensile-strained. In contrast to this result, the amorphous structure was confirmed for the AlN cap grown at 430 °C by transmission electron microscopy. Furthermore, theoretical analysis based on one-dimensional band simulation was carried out, and the large increase in two-dimensional electron gas (2DEG) observed in Hall measurements was well reproduced by taking into account the spontaneous and piezo-electric polarization in the AlN layer grown at 740 °C. For the AlN capped structure grown at 430 °C, it is believed that the reduced polarization field in the AlN cap suppressed the penetration of 2DEG into the InAlN barrier layer, resulting in a small impact on 2DEG mobility and density. We believe that an in-situ grown AlN cap with a very low growth temperature of 430 °C is a promising candidate for high-frequency/high-power GaN-based devices with low gate leakage current.

Effect of rapid thermal annealing on the electrical, optical and structural properties of ZnO-doped In2O3 films grown by linear facing target sputtering.

PubMed

Cho, Chung-Ki; Kim, Han-Ki

2012-04-01

We investigated the effect of rapid thermal annealing on the electrical, optical, and structural properties of ZnO-doped In2O3 (ZIO) films grown at different Ar/O2 flow ratios (15/0 and 15/1 sccm) by using linear facing target sputtering. It was found that the ZIO films grown at different Ar/O2, flow ratios showed different electrical and optical behavior with increasing rapid thermal annealing temperature. Synchrotron X-ray scattering examination showed that the different electrical and optical properties of the ZIO films could be attributed to the difference in preferred orientation with an increase in rapid thermal annealing temperature.

Growth of vertically aligned carbon nanofibers by low-pressure inductively coupled plasma-enhanced chemical vapor deposition

NASA Astrophysics Data System (ADS)

Caughman, J. B. O.; Baylor, L. R.; Guillorn, M. A.; Merkulov, V. I.; Lowndes, D. H.; Allard, L. F.

2003-08-01

Vertically aligned carbon nanofibers (VACNFs) have been grown using a low-pressure, plasma-enhanced, chemical vapor deposition process. The nanofibers are grown from a nickel catalyst that can be patterned to form arrays of individual, isolated VACNFs. The fibers are grown at pressures below 100 mTorr, using an inductively coupled plasma source with a radio-frequency bias on the sample substrate to allow for independent control of the ion energies. Plasma conditions are related to growth results by comparing optical emission from the plasma to the physical structure of the nanofibers. We find that the ratio of etching species in the plasma to depositing species is critical to the final shape of the carbon structures that are formed.

Highly resistive C-doped hydride vapor phase epitaxy-GaN grown on ammonothermally crystallized GaN seeds

NASA Astrophysics Data System (ADS)

Iwinska, Malgorzata; Piotrzkowski, Ryszard; Litwin-Staszewska, Elzbieta; Sochacki, Tomasz; Amilusik, Mikolaj; Fijalkowski, Michal; Lucznik, Boleslaw; Bockowski, Michal

2017-01-01

GaN crystals were grown by hydride vapor phase epitaxy (HVPE) and doped with C. The seeds were high-structural-quality ammonothermally crystallized GaN. The grown crystals were highly resistive at 296 K and of high structural quality. High-temperature Hall effect measurements revealed p-type conductivity and a deep acceptor level in the material with an activation energy of 1 eV. This is in good agreement with density functional theory calculations based on hybrid functionals as presented by the Van de Walle group. They obtained an ionization energy of 0.9 eV when C was substituted for N in GaN and acted as a deep acceptor.

Structure and sublimation of water ice films grown in vacuo at 120-190 K studied by positron and positronium annihilation.

PubMed

Townrow, S; Coleman, P G

2014-03-26

The crystalline structure of ∼ 5-20 μm water ice films grown at 165 and 172 K has been probed by measuring the fraction of positrons forming ortho-positronium (ortho-Ps) and decaying into three gamma photons. It has been established that films grown at slower rates (water vapour pressure ≥ 1 mPa) have lower concentrations of lattice defects and closed pores, which act as Ps traps, than those grown at higher rates (vapour pressure ∼ 100 mPa), evidenced by ortho-Ps diffusion lengths being approximately four times greater in the former. By varying the growth temperature between 162 and 182 K it was found that films become less disordered at temperatures above ∼ 172 K, with the ortho-Ps diffusion length rising by ∼ 60%, in this range. The sublimation energy for water ice films grown on copper has been measured to be 0.462(5) eV using the time dependence of positron annihilation parameters from 165 to 195 K, in agreement with earlier studies and with no measurable dependence on growth rate and thermal history.

Plasma impact on structural, morphological and optical properties of copper acetylacetonate thin films

NASA Astrophysics Data System (ADS)

Abdel-Khalek, H.; El-Samahi, M. I.; El-Mahalawy, Ahmed M.

2018-06-01

The influence of plasma exposure on structural, morphological and optical properties of copper (II) acetylacetonate thin films deposited by thermal evaporation technique was investigated. Copper (II) acetylacetonate as-grown thin films were exposed to the atmospheric plasma for different times. The exposure of as-grown cu(acac)2 thin film to atmospheric plasma for 5 min modified its structural, morphological and optical properties. The effect of plasma exposure on structure and roughness of cu(acac)2 thin films was evaluated by XRD and AFM techniques, respectively. The XRD results showed an increment in crystallinity due to exposure for 5 min, but, when the exposure time reaches 10 min, the film was transformed to an amorphous state. The AFM results revealed a strong modification of films roughness when the average roughness decreased from 63.35 nm to 1 nm as a result of interaction with plasma. The optical properties of as-grown and plasma exposured cu(acac)2 thin films were studied using spectrophotometric method. The exposure of cu(acac)2 thin films to plasma produced the indirect energy gap decrease from 3.20 eV to 2.67 eV for 10 min exposure time. The dispersion parameters were evaluated in terms of single oscillator model for as-grown and plasma exposured thin films. The influence of plasma exposure on third order optical susceptibility was studied.

Studies on the growth, structural, spectral and third-order nonlinear optical properties of ammonium 3-carboxy-4-hydroxy benzenesulfonate monohydrate single crystal.

PubMed

Silambarasan, A; Krishna Kumar, M; Thirunavukkarasu, A; Mohan Kumar, R; Umarani, P R

2015-01-25

An organic nonlinear optical bulk single crystal, Ammonium 3-carboxy-4-hydroxy benzenesulfonate monohydrate (ACHBS) was successfully grown by solution growth technique. Single crystal X-ray diffraction study confirms that, the grown crystal belongs to P21/c space group. Powder X-ray diffraction and high resolution X-ray diffraction analyses revealed the crystallinity of the grown crystal. Infrared spectral analysis showed the vibrational behavior of chemical bonds and its functional groups. The thermal stability and decomposition stages of the grown crystal were studied by TG-DTA analysis. UV-Visible transmittance studies showed the transparency region and cut-off wavelength of the grown crystal. The third-order nonlinear optical susceptibility of the grown crystal was estimated by Z-scan technique using He-Ne laser source. The mechanical property of the grown crystal was studied by using Vicker's microhardness test. Copyright © 2014 Elsevier B.V. All rights reserved.

Effects of surface morphology of ZnO seed layers on growth of ZnO nanostructures prepared by hydrothermal method and annealing.

PubMed

Yim, Kwang Gug; Kim, Min Su; Leem, Jae-Young

2013-05-01

ZnO nanostructures were grown on Si (111) substrates by a hydrothermal method. Prior to growing the ZnO nanostructures, ZnO seed layers with different post-heat temperatures were prepared by a spin-coating process. Then, the ZnO nanostructures were annealed at 500 degrees C for 20 min under an Ar atmosphere. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL) were carried out at room temperature (RT) to investigate the structural and optical properties of the as-grown and annealed ZnO nanostructures. The surface morphologies of the seed layers changed from a smooth surface to a mountain chain-like structure as the post-heating temperatures increased. The as-grown and annealed ZnO nanostructures exhibited a strong (002) diffraction peak. Compared to the as-grown ZnO nanostructures, the annealed ZnO nanostructures exhibited significantly strong enhancement in the PL intensity ratio by almost a factor of 2.

Studies on synthesis, growth, structural, thermal, linear and nonlinear optical properties of organic picolinium maleate single crystals.

PubMed

Pandi, P; Peramaiyan, G; Sudhahar, S; Chakkaravarthi, G; Mohan Kumar, R; Bhagavannarayana, G; Jayavel, R

2012-12-01

Picolinium maleate (PM), an organic material has been synthesised and single crystals were grown by slow evaporation technique. The structure of the grown crystal was elucidated by using single crystal X-ray diffraction analysis. PM crystal belongs to the monoclinic crystallographic system with space group P2(1)/c. The crystalline perfection of the grown crystals was analyzed by high-resolution X-ray diffraction rocking curve measurements. The presence of functional groups in PM was identified by FTIR and FT-NMR spectral analyses. Thermal behaviour and stability of picolinium maleate were studied by TGA/DTA analyses. UV-Vis spectral studies reveal that PM crystals are transparent in the wavelength region 327-1100 nm. The laser damage threshold value of PM crystal was found to be 4.3 GW/cm(2) using Nd:YAG laser. The Kurtz and Perry powder second harmonic generation technique confirms the nonlinear optical property of the grown crystal. Copyright © 2012 Elsevier B.V. All rights reserved.

Process for depositing epitaxial alkaline earth oxide onto a substrate and structures prepared with the process

DOEpatents

McKee, Rodney A.; Walker, Frederick J.

1996-01-01

A process and structure involving a silicon substrate utilize molecular beam epitaxy (MBE) and/or electron beam evaporation methods and an ultra-high vacuum facility to grow a layup of epitaxial alkaline earth oxide films upon the substrate surface. By selecting metal constituents for the oxides and in the appropriate proportions so that the lattice parameter of each oxide grown closely approximates that of the substrate or base layer upon which oxide is grown, lattice strain at the film/film or film/substrate interface of adjacent films is appreciably reduced or relieved. Moreover, by selecting constituents for the oxides so that the lattice parameters of the materials of adjacent oxide films either increase or decrease in size from one parameter to another parameter, a graded layup of films can be grown (with reduced strain levels therebetween) so that the outer film has a lattice parameter which closely approximates that of, and thus accomodates the epitaxial growth of, a pervoskite chosen to be grown upon the outer film.

Structural, optical, mechanical and dielectric studies of pure and doped L-Prolinium trichloroacetate single crystals.

PubMed

Renuka, N; Ramesh Babu, R; Vijayan, N; Vasanthakumar, Geetha; Krishna, Anuj; Ramamurthi, K

2015-02-25

In the present work, pure and metal substituted L-Prolinium trichloroacetate (LPTCA) single crystals were grown by slow evaporation method. The grown crystals were subjected to single crystal X-ray diffraction (XRD), powder X-ray diffraction, FTIR, UV-Visible-NIR, hardness, photoluminescence and dielectric studies. The dopant concentration in the crystals was measured by inductively coupled plasma (ICP) analysis. Single crystal X-ray diffraction studies of the pure and metal substituted LPTCA revealed that the grown crystals belong to the trigonal system. Ni(2+) and Co(2+) doping slightly altered the lattice parameters of LPTCA without affecting the basic structure of the crystal. FTIR spectral analysis confirms the presence of various functional groups in the grown crystals. The mechanical behavior of pure and doped crystals was analyzed by Vickers's microhardness test. The optical transmittance, dielectric and photoluminescence properties of the pure and doped crystals were analyzed. Copyright © 2014 Elsevier B.V. All rights reserved.

LPE growth of crack-free PbSe layers on Si(100) using MBE-Grown PbSe/BaF2CaF2 buffer layers

NASA Astrophysics Data System (ADS)

Strecker, B. N.; McCann, P. J.; Fang, X. M.; Hauenstein, R. J.; O'Steen, M.; Johnson, M. B.

1997-05-01

Crack-free PbSe on (100)-oriented Si has been obtained by a combination of liquid phase epitaxy (LPE) and molecular beam epitaxy (MBE) techniques. MBE is employed first to grow a PbSe/BaF2/CaF2 buffer structure on the (100)-oriented Si. A 2.5 μm thick PbSe layer is then grown by LPE. The LPE-grown PbSe displays excellent surface morphology and is continuous over the entire 8×8 mm2 area of growth. This result is surprising because of the large mismatch in thermal expansion coefficients between PbSe and Si. Previous attempts to grow crack-free PbSe by MBE alone using similar buffer structures on (100)-oriented Si have been unsuccessful. It is speculated that the large concentration of Se vacancies in the LPE-grown PbSe layer may allow dislocation climb along higher order slip planes, providing strain relaxation.

Investigation on nonlinear optical properties of MoS2 nanoflakes grown on silicon and quartz substrates

NASA Astrophysics Data System (ADS)

Bayesteh, Samaneh; Zahra Mortazavi, Seyedeh; Reyhani, Ali

2018-05-01

In this study, MoS2 nanoflakes were directly grown on different substrates—Si/SiO2 and quartz—by one-step thermal chemical vapor deposition using MoO3 and sulfide powders as precursors. Scanning electron microscopy and x-ray diffraction patterns demonstrated the formation of MoS2 structures on both substrates. Moreover, UV-visible and photoluminescence analysis confirmed the formation of MoS2 few-layer structures. According to Raman spectroscopy, by assessment of the line width and frequency shift differences between the and A 1g, it was inferred that the MoS2 grown on the silicon substrate was monolayer and that grown on the quartz substrate was multilayer. In addition, open-aperture and close-aperture Z-scan techniques were employed to study the nonlinear optical properties including nonlinear absorption and nonlinear refraction of the grown MoS2. All experiments were performed using a diode laser with a wavelength of 532 nm as the light source. It is noticeable that both samples demonstrate obvious self-defocusing behavior. The monolayer MoS2 grown on the silicon substrate displayed considerable two-photon absorption while, the multilayer MoS2 synthesized on the quartz exhibited saturable absorption. In general, few-layered MoS2 would be useful for the development of nanophotonic devices like optical limiters, optical switchers, etc.

Characterization of potassium bromide crystals grown in the aqueous solution of picric acid

NASA Astrophysics Data System (ADS)

Maheswari, J. Uma; Krishnan, C.; Kalyanaraman, S.; Selvarajan, P.

2016-12-01

Potassium bromide crystals were grown in the aqueous solution of picric acid by slow evaporation technique at room temperature. X-ray Diffraction (XRD) analysis ensures that the grown sample is in Fm3m space group and FCC structure. Energy Dispersive X-ray Spectroscopy (EDX) reveals the presence of elements in the title compound. UV-Vis-NIR spectrum reveals that the grown sample is a promising nonlinear optical (NLO) material. FTIR analysis confirms the functional groups present in the sample. The thermogravimetric (TG) and differential thermogravimetric (DTA) analyses ensure that the sample material is thermally stable up to 160 °C. The second harmonic efficiency of the sample is 1.3 times greater than that of standard KDP. The mechanical strength of the grown sample is estimated by Vickers microhardness tester. The electrical properties were investigated by impedance analysis and the results of various studies of the grown crystals are discussed.

(In,Ga,Al)P-GaP laser diodes grown on high-index GaAs surfaces emitting in the green, yellow and bright red spectral range

NASA Astrophysics Data System (ADS)

Ledentsov, N. N.; Shchukin, V. A.; Shernyakov, Yu M.; Kulagina, M. M.; Payusov, A. S.; Gordeev, N. Yu; Maximov, M. V.; Cherkashin, N. A.

2017-02-01

We report on low threshold current density (<400 A cm-2) injection lasing in (Al x Ga1-x )0.5In0.5P-GaAs-based diodes down to the green spectral range (<570 nm). The epitaxial structures are grown on high-index (611)A and (211)A GaAs substrates by metal-organic vapor phase epitaxy and contain tensile-strained GaP-enriched insertions aimed at reflection of the injected nonequilibrium electrons preventing their escape from the active region. Extended waveguide concept results in a vertical beam divergence with a full width at half maximum of 15° for (611)A substrates. The lasing at the wavelength of 569 nm is realized at 85 K. In an orange-red laser diode structure low threshold current density (190 A cm-2) in the orange spectral range (598 nm) is realized at 85 K. The latter devices demonstrated room temperature lasing at 628 nm at ˜2 kA cm-2 and a total power above 3 W. The red laser diodes grown on (211)A substrates demonstrated a far field characteristic for vertically multimode lasing indicating a lower optical confinement factor for the fundamental mode as compared to the devices grown on (611)A. However, as expected from previous research, the temperature stability of the threshold current and the wavelength stability were significantly higher for (211)A-grown structures.

Structural evolution of dilute magnetic (Sn,Mn)Se films grown by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Kanzyuba, Vasily; Dong, Sining; Liu, Xinyu; Li, Xiang; Rouvimov, Sergei; Okuno, Hanako; Mariette, Henri; Zhang, Xueqiang; Ptasinska, Sylwia; Tracy, Brian D.; Smith, David J.; Dobrowolska, Margaret; Furdyna, Jacek K.

2017-02-01

We describe the structural evolution of dilute magnetic (Sn,Mn)Se films grown by molecular beam epitaxy on GaAs (111) substrates, as revealed by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. When the Mn concentration is increased, the lattice of the ternary (Sn,Mn)Se films evolves quasi-coherently from a SnSe2 two-dimensional (2D) crystal structure into a more complex quasi-2D lattice rearrangement, ultimately transforming into the magnetically concentrated antiferromagnetic MnSe 3D rock-salt structure as Mn approaches 50 at. % of this material. These structural transformations are expected to underlie the evolution of magnetic properties of this ternary system reported earlier in the literature.

Simultaneous growth of pure hyperbranched Zn3As2 structures and long Ga2O3 nanowires.

PubMed

Li, Jianye; Wang, Lung-Shen; Buchholz, D Bruce; Chang, Robert P H

2009-05-01

Through a facile and highly repeatable chemical vapor method, pure three-dimensional hyperbranched Zn(3)As(2) structures and ultralong Ga(2)O(3) nanowires were simultaneously grown with controllable locations in the same experiment. The hyperbranched Zn(3)As(2) consists of cone-shaped submicro-/nanowires and has a single-crystalline tetragonal structure. This is the first report of nano Zn(3)As(2) and hyperbranched Zn(3)As(2) structures. The as-grown Ga(2)O(3) nanowires are monoclinic single crystals. A vapor-solid-solid mechanism is suggested for the growth of the Ga(2)O(3) nanowires, and a vapor-solid mechanism, for the Zn(3)As(2) structures.

Localized variations in electronic structure of AlGaN/GaN heterostructures grown by molecular-beam epitaxy

NASA Astrophysics Data System (ADS)

Smith, K. V.; Yu, E. T.; Elsass, C. R.; Heying, B.; Speck, J. S.

2001-10-01

Local electronic properties in a molecular-beam-epitaxy-grown AlxGa1-xN/GaN heterostructure field-effect transistor epitaxial layer structure are probed using depth-resolved scanning capacitance microscopy. Theoretical analysis of contrast observed in scanning capacitance images acquired over a range of bias voltages is used to assess the possible structural origins of local inhomogeneities in electronic structure, which are shown to be concentrated in areas where Ga droplets had formed on the surface during growth. Within these regions, there are significant variations in the local electronic structure that are attributed to variations in both AlxGa1-xN layer thickness and Al composition. Increased charge trapping is also observed in these regions.

Ultrastructure of potato tubers formed in microgravity under controlled environmental conditions

NASA Technical Reports Server (NTRS)

Cook, Martha E.; Croxdale, Judith G.; Tibbitts, T. W. (Principal Investigator)

2003-01-01

Previous spaceflight reports attribute changes in plant ultrastructure to microgravity, but it was thought that the changes might result from growth in uncontrolled environments during spaceflight. To test this possibility, potato explants were examined (a leaf, axillary bud, and small stem segment) grown in the ASTROCULTURETM plant growth unit, which provided a controlled environment. During the 16 d flight of space shuttle Columbia (STS-73), the axillary bud of each explant developed into a mature tuber. Upon return to Earth, tuber slices were examined by transmission electron microscopy. Results showed that the cell ultrastructure of flight-grown tubers could not be distinguished from that of tuber cells grown in the same growth unit on the ground. No differences were observed in cellular features such as protein crystals, plastids with starch grains, mitochondria, rough ER, or plasmodesmata. Cell wall structure, including underlying microtubules, was typical of ground-grown plants. Because cell walls of tubers formed in space were not required to provide support against the force due to gravity, it was hypothesized that these walls might exhibit differences in wall components as compared with walls formed in Earth-grown tubers. Wall components were immunolocalized at the TEM level using monoclonal antibodies JIM 5 and JIM 7, which recognize epitopes of pectins, molecules thought to contribute to wall rigidity and cell adhesion. No difference in presence, abundance or distribution of these pectin epitopes was seen between space- and Earth-grown tubers. This evidence indicates that for the parameters studied, microgravity does not affect the cellular structure of plants grown under controlled environmental conditions.

The influence of gravity on the formation of amyloplasts in columella cells of Zea mays L

NASA Technical Reports Server (NTRS)

Moore, R.; Fondren, W. M.; Koon, E. C.; Wang, C. L.

1986-01-01

Columella (i.e., putative graviperceptive) cells of Zea mays seedlings grown in the microgravity of outer space allocate significantly less volume to putative statoliths (amyloplasts) than do columella cells of Earth-grown seedlings. Amyloplasts of flight-grown seedlings are significantly smaller than those of ground controls, as is the average volume of individual starch grains. Similarly, the relative volume of starch in amyloplasts in columella cells of flight-grown seedlings is significantly less than that of Earth-grown seedlings. Microgravity does not significantly alter the volume of columella cells, the average number of amyloplasts per columella cell, or the number of starch grains per amyloplast. These results are discussed relative to the influence of gravity on cellular and organellar structure.

Two-dimensional Si nanosheets with local hexagonal structure on a MoS(2) surface.

PubMed

Chiappe, Daniele; Scalise, Emilio; Cinquanta, Eugenio; Grazianetti, Carlo; van den Broek, Bas; Fanciulli, Marco; Houssa, Michel; Molle, Alessandro

2014-04-02

The structural and electronic properties of a Si nanosheet (NS) grown onto a MoS2 substrate by means of molecular beam epitaxy are assessed. Epitaxially grown Si is shown to adapt to the trigonal prismatic surface lattice of MoS2 by forming two-dimensional nanodomains. The Si layer structure is distinguished from the underlying MoS2 surface structure. The local electronic properties of the Si nanosheet are dictated by the atomistic arrangement of the layer and unlike the MoS2 hosting substrate they are qualified by a gap-less density of states. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ternary AlGaN Alloys with High Al Content and Enhanced Compositional Homogeneity Grown by Plasma-Assisted Molecular Beam Epitaxy

NASA Astrophysics Data System (ADS)

Fellmann, Vincent; Jaffrennou, Périne; Sam-Giao, Diane; Gayral, Bruno; Lorenz, Katharina; Alves, Eduardo; Daudin, Bruno

2011-03-01

We have studied the influence of III/N flux ratio and growth temperature on structural and optical properties of high Al-content, around 50-60%, AlGaN alloy layers grown by plasma-assisted molecular beam epitaxy. In a first part, based on structural analysis by Rutherford Backscattering Spectroscopy, we establish that a III/N flux ratio slightly above 1 produces layers with low amount of structural defects. In a second part, we study the effect of growth temperature on structural and optical properties of layers grown with previously determined optimal III/N flux ratio. We find that optimal growth temperatures for Al0.50Ga0.50N layers with compositional homogeneity related with narrow UV photoluminescence properties are in the low temperature range for growing GaN layers, i.e., 650-680 °C. We propose that lowering Ga adatom diffusion on the surface favors random incorporation of both Ga and Al adatoms on wurtzite crystallographic sites leading to the formation of an homogeneous alloy.

High-performance ultraviolet photodetectors based on solution-grown ZnS nanobelts sandwiched between graphene layers

PubMed Central

Kim, Yeonho; Kim, Sang Jin; Cho, Sung-Pyo; Hong, Byung Hee; Jang, Du-Jeon

2015-01-01

Ultraviolet (UV) light photodetectors constructed from solely inorganic semiconductors still remain unsatisfactory because of their low electrical performances. To overcome this limitation, the hybridization is one of the key approaches that have been recently adopted to enhance the photocurrent. High-performance UV photodetectors showing stable on-off switching and excellent spectral selectivity have been fabricated based on the hybrid structure of solution-grown ZnS nanobelts and CVD-grown graphene. Sandwiched structures and multilayer stacking strategies have been applied to expand effective junction between graphene and photoactive ZnS nanobelts. A multiply sandwich-structured photodetector of graphene/ZnS has shown a photocurrent of 0.115 mA under illumination of 1.2 mWcm−2 in air at a bias of 1.0 V, which is higher 107 times than literature values. The multiple-sandwich structure of UV-light sensors with graphene having high conductivity, flexibility, and impermeability is suggested to be beneficial for the facile fabrication of UV photodetectors with extremely efficient performances. PMID:26197784

Luminescence studies of HgCdTe- and InAsSb-based quantum-well structures

NASA Astrophysics Data System (ADS)

Izhnin, I. I.; Izhnin, A. I.; Fitsych, O. I.; Voitsekhovskii, A. V.; Gorn, D. I.; Semakova, A. A.; Bazhenov, N. L.; Mynbaev, K. D.; Zegrya, G. G.

2018-04-01

Results of photoluminescence studies of single-quantum-well HgCdTe-based structures and electroluminescence studies of multiple-quantum-well InAsSb-based structures are reported. HgCdTe structures were grown with molecular beam epitaxy on GaAs substrates. InAsSb-based structures were grown with metal-organic chemical vapor deposition on InAs substrates. The common feature of luminescence spectra of all the structures was the presence of peaks with the energy much larger than that of calculated optical transitions between the first quantization levels for electrons and heavy holes. Possibility of observation of optical transitions between the quantization levels of electrons and first and/or second heavy and light hole levels is discussed in the paper in relation to the specifics of the electronic structure of the materials under consideration.

High resolution X-ray diffraction imaging of lead tin telluride

NASA Technical Reports Server (NTRS)

Steiner, Bruce; Dobbyn, Ronald C.; Black, David; Burdette, Harold; Kuriyama, Masao; Spal, Richard; Simchick, Richard; Fripp, Archibald

1991-01-01

High resolution X-ray diffraction images of two directly comparable crystals of lead tin telluride, one Bridgman-grown on Space Shuttle STS 61A and the other terrestrially Bridgman-grown under similar conditions from identical material, present different subgrain structure. In the terrestrial, sample 1 the appearance of an elaborate array of subgrains is closely associated with the intrusion of regions that are out of diffraction in all of the various images. The formation of this elaborate subgrain structure is inhibited by growth in microgravity.

Self-Catalyzed Growth of Axial GaAs/GaAsSb Nanowires by Molecular Beam Epitaxy for Photodetectors

DTIC Science & Technology

2015-06-01

blende structure with mixture of stacking faults and twins and the presence of these faults were significantly reduced in the NWs grown on chemically...a) TEM image of the core NW (b) HR-TEM image displaying the stacking faults and twinning defects. (c)SAED pattern showing the ZB crystal structure...of stacking faults and twins and the presence of these faults were significantly reduced in the NWs grown on chemically etched substrates. For

Investigation of layered structure SAW devices fabricated using low temperature grown AlN thin film on GaN/sapphire.

PubMed

Lin, Hui-Feng; Wu, Chun-Te; Chien, Wei-Cheng; Chen, Sheng-Wen; Kao, Hui-Ling; Chyi, Jen-Inn; Chen, Jyh-Shin

2005-05-01

Epitaxial AlN films have been grown on GaN/sapphire using helicon sputtering at 300 degrees C. The surface acoustic wave (SAW) filters fabricated on AlN/GaN/sapphire exhibit more superior characteristics than those made on GaN/sapphire. This composite structure of AlN on GaN may bring about the development of high-frequency components, which integrate and use their semiconducting, optoelectronic, and piezoelectric properties.

Growth, structural, optical and surface analysis of piperazinium tartrate: A NLO single crystal

NASA Astrophysics Data System (ADS)

Gupta, Apurva; Raseel Rahman M., K.; Nair, Lekha

2018-05-01

Single crystal of piperazinium tartrate (PPZT) was grown by the slow evaporation solution growth technique at room temperature. Crystallinity of grown crystal was examined by powder X-ray diffraction. High transparency and wide band gap were observed in the UV-Visible spectroscopic studies. Intense and broad emissions were observed in the blue region, as that is indicated by photoluminescence spectroscopy. The quality of the grown PPZT single crystals were analyzed by the etching studies using the water as the etchant.

Process for growing a film epitaxially upon a MGO surface and structures formed with the process

DOEpatents

McKee, Rodney Allen; Walker, Frederick Joseph

1998-01-01

A process and structure wherein optical quality perovskites, such as BaTiO.sub.3 or SrTiO.sub.3, are grown upon a single crystal MgO substrate involves the epitaxial build up of alternating planes of TiO.sub.2 and metal oxide wherein the first plane grown upon the MgO substrate is a plane of TiO.sub.2. The layering sequence involved in the film build up reduces problems which would otherwise result from the interfacial electrostatics at the first atomic layers, and these oxides can be stabilized as commensurate thin films at a unit cell thickness or grown with high crystal quality to thicknesses of 0.5-0.7 .mu.m for optical device applications.

Synchrotron studies of top-down grown silicon nanowires

NASA Astrophysics Data System (ADS)

Turishchev, S. Yu.; Parinova, E. V.; Nesterov, D. N.; Koyuda, D. A.; Sivakov, V.; Schleusener, A.; Terekhov, V. A.

2018-06-01

Morphology of the top-down grown silicon nanowires obtained by metal-assisted wet-chemical approach on silicon substrates with different resistance were studied by scanning electron microscopy. Obtained arrays of compact grown Si nanowires were a subject for the high resolution electronic structures studies by X-ray absorption near edge structure technique performed with the usage of high intensity synchrotron radiation of the SRC storage ring of the University of Wisconsin-Madison. The different oxidation rates were found by investigation of silicon atoms local surrounding specificity of the highly developed surface and near surface layer that is not exceeded 70 nm. Flexibility of the wires arrays surface morphology and its composition is demonstrated allowing smoothly form necessary surface oxidation rate and using Si nanowires as a useful matrixes for a wide range of further functionalization.

Effect of L-aspartic acid on the growth, structure and spectral studies of Zinc (tris) Thiourea Sulphate (ZTS) single crystals

NASA Astrophysics Data System (ADS)

Samuel, Bincy Susan; Krishnamurthy, R.; Rajasekaran, R.

2014-11-01

Single crystals of pure and L-aspartic acid doped Zinc (Tris) Thiourea Sulphate (ZTS) were grown from aqueous solution by solution growth method. The cell parameters and structure of the grown crystals were determined by X-ray diffraction studies. The presence of functional group in the compound has been confirmed by FTIR and FT-Raman analysis. The optical transparency range has been studied through UV-Vis spectroscopy. TGA/DTA studies show thermal stability of the grown crystals. Microhardness study reveals that the hardness number (Hv) increases with load for pure and doped ZTS crystals. Dielectric studies have been carried out and the results are discussed. The second harmonic generation was confirmed for L-aspartic acid doped ZTS which is greater than pure ZTS.

Dipicolinate salt of imidazole: Discovering its structure and properties using different experimental methodologies and quantum chemical investigations

NASA Astrophysics Data System (ADS)

Thirumurugan, R.; Anitha, K.

2018-03-01

A novel organic proton transfer complex of imidazolium dipicolinate (ID) has been synthesized and it was grown as single crystals using slow evaporation method. The molecular structure of synthesized compound and vibrational modes of its functional groups were confirmed by (1H and 13C) NMR, FTIR and FT-Raman spectroscopic studies, respectively. Single crystal X-ray diffraction (SCXRD) analysis confirmed the orthorhombic system with noncentrosymmetric (NCS), P212121, space group of grown ID crystal. UV-Vis-NIR spectral study confirmed its high optical transparency within the region of 285-1500 nm. Powder second harmonic generation (SHG) efficiency of ID crystal was confirmed and it was 6.8 times that of KDP crystal. TG-DTA and DSC analysis revealed the higher thermal stability of grown crystal as 249 °C. The dielectric response and mechanical behaviour of grown crystal were studied effectively. Density functional theory calculations were performed to probe the relationship between the structure and its properties including molecular optimization, Mulliken atomic charge distribution, frontier molecular orbital (FMOs) and molecular electrostatic potential map (MEP) analysis and first hyperpolarizability. All these experimental and computational results were discussed in this communication and it endorsed the ID compound as a potential NLO candidate could be employed in optoelectronics device applications in near future.

Electrical and structural properties of (Pd/Au) Schottky contact to as grown and rapid thermally annealed GaN grown by MBE

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

Nirwal, Varun Singh, E-mail: varun.nirwal30@gmail.com; Singh, Joginder; Gautam, Khyati

2016-05-06

We studied effect of thermally annealed GaN surface on the electrical and structural properties of (Pd/Au) Schottky contact to Ga-polar GaN grown by molecular beam epitaxy on Si substrate. Current voltage (I-V) measurement was used to study electrical properties while X-ray diffraction (XRD) measurement was used to study structural properties. The Schottky barrier height calculated using I-V characteristics was 0.59 eV for (Pd/Au) Schottky contact on as grown GaN, which increased to 0.73 eV for the Schottky contact fabricated on 700 °C annealed GaN film. The reverse bias leakage current at -1 V was also significantly reduced from 6.42×10{sup −5} Amore » to 7.31×10{sup −7} A after annealing. The value of series resistance (Rs) was extracted from Cheung method and the value of R{sub s} decreased from 373 Ω to 172 Ω after annealing. XRD results revealed the formation of gallide phases at the interface of (Pd/Au) and GaN for annealed sample, which could be the reason for improvement in the electrical properties of Schottky contact after annealing.« less

Synthesis and characterization of structural, morphological and photosensor properties of Cu0.1Zn0.9S thin film prepared by a facile chemical method

NASA Astrophysics Data System (ADS)

Gubari, Ghamdan M. M.; Ibrahim Mohammed S., M.; Huse, Nanasaheb P.; Dive, Avinash S.; Sharma, Ramphal

2018-05-01

The Cu0.1Zn0.9S thin film was grown by facile chemical bath deposition (CBD) method on glass substrates at 60°C. The structural, morphological, photosensor properties of the as-grown thin film has been investigated. The structural and phase confirmation of the as-grown thin film was carried out by X-ray diffraction (XRD) technique and Raman spectroscopy. The FE-SEM images showed that the thin films are well covered with material on an entire glass substrate. From the optical absorption spectrum, the direct band gap energy for the Cu0.1Zn0.9S thin film was found to be ˜3.16 eV at room temperature. The electrical properties were measured at room temperature in the voltage range ±2.5 V, showed a drastic enhancement in current under light illumination with the highest photosensitivity of ˜72 % for 260 W.

SPE-LEEM Studies on the Surface and Electronic Structure of 2-D Transition Metal Dichalcogenides

NASA Astrophysics Data System (ADS)

Yeh, Po-Chun; Jin, Wencan; Zaki, Nader; Zhang, Datong; Sadowski, Jerzy; Al-Mahboob, Abdullah; van de Zande, Arend; Chenet, Daniel; Dadap, Jerry; Herman, Irving; Sutter, Petter; Hone, James; Osgood, Richard

2014-03-01

In this work, we studied the surface and electronic structure of monolayer and few-layer exfoliated MoS2 and WSe2, as well as chemical-vapor-deposition (CVD) grown MoS2, using Spectroscopic Photoemission and Low Energy Electron Microscope (SPE-LEEM). LEEM measurements reveal that, unlike exfoliated MoS2, CVD-grown MoS2 exhibits grain-boundary alterations due to surface strain. However, LEEM and micro-probe low energy electron diffraction show that the quality of CVD-grown MoS2 is comparable to that of exfoliated MoS2. Micrometer-scale angle-resolved photoemission spectroscopy (ARPES) measurement on exfoliated MoS2 and WSe2 single-crystals provides direct evidence for the shifting of the valence band maximum from Γ to K, when the layer number is thinned down to one, as predicted by density functional theory. Our measurements of the k-space resolved electronic structure allow for further comparison with other theoretical predictions and with transport measurements. Session I and II

A bioengineered niche promotes in vivo engraftment and maturation of pluripotent stem cell derived human lung organoids.

PubMed

Dye, Briana R; Dedhia, Priya H; Miller, Alyssa J; Nagy, Melinda S; White, Eric S; Shea, Lonnie D; Spence, Jason R

2016-09-28

Human pluripotent stem cell (hPSC) derived tissues often remain developmentally immature in vitro, and become more adult-like in their structure, cellular diversity and function following transplantation into immunocompromised mice. Previously we have demonstrated that hPSC-derived human lung organoids (HLOs) resembled human fetal lung tissue in vitro (Dye et al., 2015). Here we show that HLOs required a bioartificial microporous poly(lactide-co-glycolide) (PLG) scaffold niche for successful engraftment, long-term survival, and maturation of lung epithelium in vivo. Analysis of scaffold-grown transplanted tissue showed airway-like tissue with enhanced epithelial structure and organization compared to HLOs grown in vitro. By further comparing in vitro and in vivo grown HLOs with fetal and adult human lung tissue, we found that in vivo transplanted HLOs had improved cellular differentiation of secretory lineages that is reflective of differences between fetal and adult tissue, resulting in airway-like structures that were remarkably similar to the native adult human lung.

Optical, structural, thermal and dielectric spectroscopy characterizations of seeded melt grown 2-hydroxy biphenyl single crystal.

PubMed

Sadhasivam, S; Rajesh, Narayana Perumal

2014-09-15

Organic single crystal of 2-hydroxy biphenyl (2-HB) was grown by top seeded melt growth method. Scanning electron microscopy studies has been carried out on the surface of the grown crystals to investigate the nature of growth and defects. The crystalline perfection and lattice parameters of 2-HB has been determined by single crystal XRD analysis and it belongs to orthorhombic crystal system with space group Fdd2. The functional groups and molecular associations were confirmed by FT-IR. The optical characteristics such as cut-off and transmittance were carried out using UV-Vis-NIR spectra. Absence of absorption in the region between 320 and 1100 nm makes the grown crystal desirable to optical applications. Thermal stability of grown crystals was characterized by thermogravimetric (TGA), differential thermal analysis (DTA) and differential scanning calorimetric (DSC) analyses. Broadband dielectric studies reveals that dielectric constant of grown crystal is low. The resistivity of grown crystal was studied by impedance analysis. The second harmonic generation intensity of 3.8 mJ was studied. The grown crystal belongs to soft material studied by hardness test. Copyright © 2014 Elsevier B.V. All rights reserved.

Atomic moments in Mn 2CoAl thin films analyzed by X-ray magnetic circular dichroism

DOE PAGES

Jamer, M. E.; Assaf, B. A.; Sterbinsky, G. E.; ...

2014-12-05

Spin gapless semiconductors are known to be strongly affected by structural disorder when grown epitaxially as thin films. The magnetic properties of Mn 2CoAl thin films grown on GaAs (001) substrates are investigated here as a function of annealing. This study investigates the atomic-specific magnetic moments of Mn and Co atoms measured through X-ray magnetic circular dichroism as a function of annealing and the consequent structural ordering. Results indicate that the structural distortion mainly affects the Mn atoms as seen by the reduction of the magnetic moment from its predicted value.

Ferromagnetism enhanced by structural relaxation of biaxially compressed LaCoO3 films

NASA Astrophysics Data System (ADS)

Mehta, Virat; Suzuki, Yuri

2011-04-01

Epitaxial LaCoO3 films were synthesized on LaAlO3 substrates to explore the role of epitaxial strain and structure on the ferromagnetism observed in these biaxially compressed films. Coherent strain and tetragonal structure were only achieved in thin film samples grown using higher energy densities. The strain relaxed with increasing thickness and was accompanied by increasing mosaic spread. Higher magnetization values were consistently seen in fully relaxed films grown using lower laser energy density. These results suggest that epitaxial strain is not the only factor determining the ferromagnetism and that the microstructure and defects may play a significant role.

Defects in mercury-cadmium telluride heteroepitaxial structures grown by molecular-beam epitaxy on silicon substrates

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

Mynbaev, K. D., E-mail: mynkad@mail.ioffe.ru; Zablotsky, S. V.; Shilyaev, A. V.

Defects in mercury-cadmium-telluride heteroepitaxial structures (with 0.3 to 0.4 molar fraction of cadmium telluride) grown by molecular-beam epitaxy on silicon substrates are studied. The low-temperature photoluminescence method reveals that there are comparatively deep levels with energies of 50 to 60 meV and shallower levels with energies of 20 to 30 meV in the band gap. Analysis of the temperature dependence of the minority carrier lifetime demonstrates that this lifetime is controlled by energy levels with an energy of ∼30 meV. The possible relationship between energy states and crystal-structure defects is discussed.

Structural and optical characterization of the propolis films

NASA Astrophysics Data System (ADS)

Drapak, S. I.; Bakhtinov, A. P.; Gavrylyuk, S. V.; Drapak, I. T.; Kovalyuk, Z. D.

2006-10-01

We have performed structural and optical characterizations of the propolis (an organic entity of biological nature) films grown on various non-organic substrates. The films were grown from a propolis melt or a propolis alcohol solution. The crystal structure has been observed in the films precipitated from the solution onto substrates such as an amorphous glass and sapphire or semiconductor indium monoselenide. For any growth method, the propolis film is a semiconductor with the bandgap of 3.07 eV at 300 K that is confirmed by a maximum in photoluminescence spectra at 2.86 eV. We argue that propolis films might be used in various optoelectronic device applications.

Electron-beam pumped laser structures based on MBE grown {ZnCdSe}/{ZnSe} superlattices

NASA Astrophysics Data System (ADS)

Kozlovsky, V. I.; Shcherbakov, E. A.; Dianov, E. M.; Krysa, A. B.; Nasibov, A. S.; Trubenko, P. A.

1996-02-01

Cathodoluminescence (CL), photoreflection (PR), phototransmission (PT) of single and multiquantum wells (MQWs) and strain layer {ZnCdSe}/{ZnSe} superlattices (SLs) grown by molecular beam epitaxy (MBE) were studied. An increase of the Stokes shift with the number of quantum wells (QWs) and the appearance of new lines in CL and PT spectra were observed. Room temperature (RT) vertical-cavity surface-emitting laser (VCSEL) operation was achieved by using the SL structures. Output power up to 2.2 W in single longitudinal mode with λ = 493 nm was obtained. Cut facet laser wavelength of the same SL structure was 502 nm.

Plasma impact on structural, morphological and optical properties of copper acetylacetonate thin films.

PubMed

Abdel-Khalek, H; El-Samahi, M I; El-Mahalawy, Ahmed M

2018-06-15

The influence of plasma exposure on structural, morphological and optical properties of copper (II) acetylacetonate thin films deposited by thermal evaporation technique was investigated. Copper (II) acetylacetonate as-grown thin films were exposed to the atmospheric plasma for different times. The exposure of as-grown cu(acac) 2 thin film to atmospheric plasma for 5min modified its structural, morphological and optical properties. The effect of plasma exposure on structure and roughness of cu(acac) 2 thin films was evaluated by XRD and AFM techniques, respectively. The XRD results showed an increment in crystallinity due to exposure for 5min, but, when the exposure time reaches 10min, the film was transformed to an amorphous state. The AFM results revealed a strong modification of films roughness when the average roughness decreased from 63.35nm to ~1nm as a result of interaction with plasma. The optical properties of as-grown and plasma exposured cu(acac) 2 thin films were studied using spectrophotometric method. The exposure of cu(acac) 2 thin films to plasma produced the indirect energy gap decrease from 3.20eV to 2.67eV for 10min exposure time. The dispersion parameters were evaluated in terms of single oscillator model for as-grown and plasma exposured thin films. The influence of plasma exposure on third order optical susceptibility was studied. Copyright © 2018 Elsevier B.V. All rights reserved.

Investigation of superlattice device structures

NASA Technical Reports Server (NTRS)

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

1985-01-01

This report describes the investigation of growth properties, and the structure of epitaxial multilayer Si(Si(1x)Ge(x)) films grown on bulk Silicon Substrates. It also describes the fabrication and characterization of MOSFET and MESFET devices made on these epitaxial films. Films were grown in a CVD reactor using hydrides of Si and Ge with H2 and He as carrier gases. Growth temperatures were between 900 C and 1050 C with most films grown at 1000 C. Layer thickness was between 300A and 2000A and total film thickness was between 0.25 micro m and 7 micro m. The Ge content (X) in the alloy layers was between .05 and 0.2. N-type multilayer films grown on (100) p-type Si showed Hall mobility in the range 1000 to 1500 sq cm/v for an average carrier concentration of approx. 10 to the 16th power/cu cm. This is up to 50% higher than the Hall mobility observed in epitaxial Si films grown under the same conditions and with the same average carrier concentration. The mobility enhancement occurred in films with average carrier concentration (n) from 0.7 x 10 to the 16th power to 2 x 10 to the 17th power/cu cm, and total film thickness greater than 1.0 micro m. No mobility enhancement was seen in n-type multilayer films grown on (111) Si or in p-type multilayer films. The structure of the films was investigated was using SEM, TEM, AES, SIMS, and X-ray double crystal diffraction techniques. The film composition profile (AES, SIMS) showed that the transition region between layers is of the order of about 100A. The TEM examination revealed a well defined layered structure with fairly sharp interfaces and good crystalline quality. It also showed that the first few layers of the film (closest to the substrate) are uneven, most probably due to the initial growth pattern of the epitaxial film where growth occurs first in isolated islands that eventually growth and coalesce. The X-ray diffraction measurement determined the elastic strain and strain relief in the alloy layers of the film and the elastic strain in the intervening Si layers.

Growth of NBT-BT single crystals by flux method and their structural, morphological and electrical characterizations

NASA Astrophysics Data System (ADS)

Kanuru, Sreenadha Rao; Baskar, K.; Dhanasekaran, R.; Kumar, Binay

2016-05-01

In this paper, one of the important, eco-friendly polycrystalline material, (1-x)(Na0.5Bi0.5)TiO3 (NBT) - xBaTiO3 (BT) of different compositions (x=0.07, 0.06 and 0.05 wt%) around the morphotropic phase boundary (MPB) were synthesized by solid state reaction technique. And the single crystals with 13×7×7 mm3, 12×12×7 mm3 and 10×7×4 mm3 dimensions were grown by self flux method. The morphology, crystal structure and unit-cell parameters have been studied and the monoclinic phase has been identified for 0.07 wt% of BT. Higher BT concentration changes the crystal habit and the mechanism has been studied clearly. Raman spectroscopy at room-temperature confirms the presence of functional groups. The quality of the as grown single crystals was examined by high resolution x-ray diffraction analysis. The dielectric properties of the as grown crystals were investigated in the frequency range of 20 Hz-2 MHz from room temperature to 450 °C. The broad dielectric peak and frequency dispersion demonstrates the relaxor behavior of grown crystals. The dielectric constant (εr), transition temperature (Tm), and depolarization temperature (Td) of the grown crystals are found to be comparatively good. The diffusive factor (γ) from Curie-Weiss law confirms the as grown NBT-BT single crystals are relaxor in nature.

Stress evolution of GaN/AlN heterostructure grown on 6H-SiC substrate by plasma assisted molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Agrawal, M.; Ravikiran, L.; Dharmarasu, N.; Radhakrishnan, K.; Karthikeyan, G. S.; Zheng, Y.

2017-01-01

The stress evolution of GaN/AlN heterostructure grown on 6H-SiC substrate by plasma assisted molecular beam epitaxy (PA-MBE) has been studied. AlN nucleation layer and GaN layer were grown as a function of III/V ratio. GaN/AlN structure is found to form buried cracks when AlN is grown in the intermediate growth regime(III/V˜1)and GaN is grown under N-rich growth regime (III/V<1). The III/V ratio determines the growth mode of the layers that influences the lattice mismatch at the GaN/AlN interface. The lattice mismatch induced interfacial stress at the GaN/AlN interface relaxes by the formation of buried cracks in the structure. Additionally, the stress also relaxes by misorienting the AlN resulting in two misorientations with different tilts. Crack-free layers were obtained when AlN and GaN were grown in the N-rich growth regime (III/V<1) and metal rich growth regime (III/V≥1), respectively. AlGaN/GaN high electron mobility transistor (HEMT) heterostructure was demonstrated on 2-inch SiC that showed good two dimensional electron gas (2DEG) properties with a sheet resistance of 480 Ω/sq, mobility of 1280 cm2/V.s and sheet carrier density of 1×1013 cm-2.

Controlling the defects and transition layer in SiO2 films grown on 4H-SiC via direct plasma-assisted oxidation

PubMed Central

Kim, Dae-Kyoung; Jeong, Kwang-Sik; Kang, Yu-Seon; Kang, Hang-Kyu; Cho, Sang W.; Kim, Sang-Ok; Suh, Dongchan; Kim, Sunjung; Cho, Mann-Ho

2016-01-01

The structural stability and electrical performance of SiO2 grown on SiC via direct plasma-assisted oxidation were investigated. To investigate the changes in the electronic structure and electrical characteristics caused by the interfacial reaction between the SiO2 film (thickness ~5 nm) and SiC, X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), density functional theory (DFT) calculations, and electrical measurements were performed. The SiO2 films grown via direct plasma-assisted oxidation at room temperature for 300s exhibited significantly decreased concentrations of silicon oxycarbides (SiOxCy) in the transition layer compared to that of conventionally grown (i.e., thermally grown) SiO2 films. Moreover, the plasma-assisted SiO2 films exhibited enhanced electrical characteristics, such as reduced frequency dispersion, hysteresis, and interface trap density (Dit ≈ 1011 cm−2 · eV−1). In particular, stress induced leakage current (SILC) characteristics showed that the generation of defect states can be dramatically suppressed in metal oxide semiconductor (MOS) structures with plasma-assisted oxide layer due to the formation of stable Si-O bonds and the reduced concentrations of SiOxCy species defect states in the transition layer. That is, energetically stable interfacial states of high quality SiO2 on SiC can be obtained by the controlling the formation of SiOxCy through the highly reactive direct plasma-assisted oxidation process. PMID:27721493

Structural and photoluminescence studies on europium-doped lithium tetraborate (Eu:Li2B4O7) single crystal grown by microtube Czochralski (μT-Cz) technique

NASA Astrophysics Data System (ADS)

A, Kumaresh; R, Arun Kumar; N, Ravikumar; U, Madhusoodanan; B, S. Panigrahi; K, Marimuthu; M, Anuradha

2016-05-01

Rare earth europium (Eu3+)-doped lithium tetraborate (Eu:Li2B4O7) crystal is grown from its stoichiometric melt by microtube Czochralski pulling technique (μT-Cz) for the first time. The grown crystals are subjected to powder x-ray diffraction (PXRD) analysis which reveals the tetragonal crystal structure of the crystals. UV-vis-NIR spectral analysis is carried out to study the optical characteristics of the grown crystals. The crystal is transparent in the entire visible region, and the lower cutoff is observed to be at 304 nm. The existence of BO3 and BO4 bonding structure and the molecular associations are analyzed by Fourier transform infrared (FTIR) spectroscopy. The results of excitation and emission-photoluminescence spectra of europium ion incorporated in lithium tetraborate (LTB) single crystal reveal that the observations of peaks at 258, 297, and 318 nm in the excitation spectra and peaks at 579, 591, 597, 613, and 651 nm are observed in the emission spectra. The chromaticity coordinates are calculated from the emission spectra, and the emission intensity of the grown crystal is characterized through a CIE 1931 (Commission International d’Eclairage) color chromaticity diagram. Project supported by the Department of Science and Technology-Science and Engineering Research Board (Grant No. SR/S2/LOP-0012/2011), the Government of India for Awarding Major Research Project, the University Grants Commission-Department of Atomic Research-Consortium for Scientific Research (Grant No. CSR-KN/CSR-63/2014-2015/503), and the Kalpakkam and Indore, India.

Single-crystalline BaTiO3 films grown by gas-source molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Matsubara, Yuya; Takahashi, Kei S.; Tokura, Yoshinori; Kawasaki, Masashi

2014-12-01

Thin BaTiO3 films were grown on GdScO3 (110) substrates by metalorganic gas-source molecular beam epitaxy. Titanium tetra-isopropoxide (TTIP) was used as a volatile precursor that provides a wide growth window of the supplied TTIP/Ba ratio for automatic adjustment of the film composition. Within the growth window, compressively strained films can be grown with excellent crystalline quality, whereas films grown outside of the growth window are relaxed with inferior crystallinity. This growth method will provide a way to study the intrinsic properties of ferroelectric BaTiO3 films and their heterostructures by precise control of the stoichiometry, structure, and purity.

Potassium-cobalt sulphate crystal growth assisted by low frequency vibrations

NASA Astrophysics Data System (ADS)

Sadovsky, A.; Ermochenkov, I.; Dubovenko, E.; Sukhanova, E.; Bebyakin, M.; Dubov, V.; Avetissov, I.

2018-02-01

Single crystals of K2Co(SO4)2·6H2O were grown from solution using the temperature reduction method enhanced by the axial low frequency vibration control technique (AVC-technique). Physical modeling of heat-mass transfer in solution under the AVC action was performed. The growth rate of the AVC grown crystal was found to be twice that of the crystal grown under natural convection conditions. Analysis of spectral characteristics (absorption and Raman spectra) as well as structural properties (dislocation density and microhardness) of the grown crystals showed the significant superiority of the AVC technique for the growth of K2Co(SO4)2·6H2O crystals.

Growth, structural, physical and computational perspectives of trans-4-hydroxy-l-proline: a promising organic nonlinear optical material with large laser-induced damage threshold

NASA Astrophysics Data System (ADS)

Thirumurugan, Ramaiah; Anitha, Kandasamy

2017-05-01

In this work, a systematic study of an organic nonlinear optical (NLO) material, trans-4-hydroxy-l-proline (THP), C5H9NO3 is reported. An optical quality single crystals of THP have been successfully grown by using slow evaporation solution growth technique (SEST). The single crystal x-ray diffraction (SXRD) analysis reveals that grown crystal belongs to the orthorhombic system with non-centrosymmetric space group (NCS), P212121. Powder x-ray diffraction (PXRD) analysis shows relatively a good crystalline nature. The molecular structure of THP was recognized by NMR (1H and 13C) studies and its vibrational modes were confirmed by FTIR and FT-Raman vibrational studies. UV-Vis-NIR spectrum of grown crystal shows high optical transparency in the visible and near-IR region with low near-UV cut-off wavelength at 218 nm. Photoluminescence study confirms ultraviolet wavelength emission of THP crystal. The second harmonic generation (SHG) efficiency of grown crystal is 1.6 times greater with respect to standard potassium dihydrogen phosphate (KDP). Nonlinear refractive index (n 2) and nonlinear absorption coefficient (β) were determined using the Z-scan technique. The title compound owns high thermal stability of 294 °C and specific heat capacity (C P) of 1.21 J g-1 K-1 at 300 K and 11.33 J g-1 K-1 at 539 K (melting point). The laser-induced damage threshold (LDT) value of grown crystal was measured as 7.25 GW cm-2. The crystal growth mechanism and defects of grown crystal were studied by chemical etching technique. Mechanical strength was extensively studied by Vickers microhardness test and crystal void percentage analysis. Moreover, density functional theory (DFT) studies were carried out to probe the Mulliken charge distribution, frontier molecular orbitals (FMOs) and first order hyperpolarizability (β) of the optimized molecular structure to get a better insight of the molecular properties. These characterization results endorse that grown THP crystal as a suitable candidate for NLO applications with large LDT.

Growth mechanism and optical properties of aligned hexagonal ZnO nanoprisms synthesized by noncatalytic thermal evaporation.

PubMed

Umar, Ahmad; Karunagaran, B; Kim, S H; Suh, E-K; Hahn, Y B

2008-05-19

Vertically aligned perfectly hexagonal-shaped ZnO nanoprisms have been grown on a Si(100) substrate via a noncatalytic thermal evaporation process by using metallic zinc powder in the presence of oxygen gas. The as-grown nanoprisms consist of ultra smooth Zn-terminated (0001) facets bounded with the {0110} surfaces. The as-synthesized products are single-crystalline with the wurtzite hexagonal phase and grown along the [0001] direction, as confirmed from the detailed structural investigations. The presence of a sharp and strong nonpolar optical phonon high-E2 mode at 437 cm(-1) in the Raman scattering spectrum further confirms good crystallinity and wurtzite hexagonal phase for the as-grown products. The as-grown nanoprisms exhibit a strong near-band-edge emission with a very weak deep-level emission in the room-temperature and low-temperature photoluminescence measurements, confirming good optical properties for the deposited products. Moreover, systematic time-dependent experiments were also performed to determine the growth process of the grown vertically aligned nanoprisms.

Optical, mechanical and thermal behaviors of Nitrilotriacetic acid single crystal

NASA Astrophysics Data System (ADS)

Deepa, B.; Philominathan, P.

2017-11-01

An organic nonlinear single crystal of Nitrilotriacetic acid (NTAA) was grown for the first time by employing a simple slow evaporation technique. Single crystal X-ray diffraction (XRD) analysis reveals that the grown crystal belongs to the monoclinic system with noncentrosymmetric space group CC. Fourier transform infrared (FTIR) spectral study ascertains the presence of functional groups in NTAA. The molecular structure of the grown crystal was confirmed by Nuclear Magnetic Resonance (NMR) spectral analysis. The optical parameters such as transmittance, absorption coefficient and band gap were calculated from UV-Visible and fluorescence studies. Dielectric measurements were carried out for different frequency and temperature. The mechanical strength of the grown crystal was measured using Vickers microhardness test. The high thermal stability and the melting point of the grown crystal were also estimated using thermogravimetric (TGA) and differential thermal analyses (DTA). The confirmation of the grown crystals belonging to nonlinear optical crystals was performed by Kurtz-Perry technique and found as suitable candidate for optoelectronics applications.

Transparent SiON/Ag/SiON multilayer passivation grown on a flexible polyethersulfone substrate using a continuous roll-to-roll sputtering system

PubMed Central

2012-01-01

We have investigated the characteristics of a silicon oxynitride/silver/silicon oxynitride [SiON/Ag/SiON] multilayer passivation grown using a specially designed roll-to-roll [R2R] sputtering system on a flexible polyethersulfone substrate. Optical, structural, and surface properties of the R2R grown SiON/Ag/SiON multilayer were investigated as a function of the SiON thickness at a constant Ag thickness of 12 nm. The flexible SiON/Ag/SiON multilayer has a high optical transmittance of 87.7% at optimized conditions due to the antireflection and surface plasmon effects in the oxide-metal-oxide structure. The water vapor transmission rate of the SiON/Ag/SiON multilayer is 0.031 g/m2 day at an optimized SiON thickness of 110 nm. This indicates that R2R grown SiON/Ag/SiON is a promising thin-film passivation for flexible organic light-emitting diodes and flexible organic photovoltaics due to its simple and low-temperature process. PMID:22221400

Satellite Tobacco Mosaic Virus Structure

NASA Technical Reports Server (NTRS)

2000-01-01

The structure of the Satellite Tobacco Mosaic Viurus (STMV)--one of the smallest viruses known--has been successfully reduced using STMV crystals grown aboard the Space Shuttle in 1992 and 1994. The STMV crystals were up to 30 times the volume of any seen in the laboratory. At the time they gave the best resolution data ever obtained on any virus crystal. STMV is a small icosahedral plant virus, consisting of a protein shell made up of 60 identical protein subunits of molecular weight 17,500. Particularly noteworthy is the fact that, in contrast to the crystals grown on Earth, the crystals grown under microgravity conditions were visually perfect, with no striations or clumping of crystals. Furthermore, the x-ray diffraction data obtained from the space-grown crystals was of a much higher quality than the best data available at that time from ground-based crystals. This stylized ribbon model shows the protein coat in white and the nucleic acid in yellow. STMV is used because it is a simple protein to work with; studies are unrelated to tobacco. Credit: Dr. Alex McPherson, University of California at Irvin.

Structure and magnetism of Fe-doped BaSnO 3 thin films

DOE PAGES

Alaan, Urusa S.; N’Diaye, Alpha T.; Shafer, Padraic; ...

2017-02-28

BaSnO 3 is an excellent candidate system for developing a new class of perovskite-based dilute magnetic semiconductors. Here in this study, we show that BaSn 0.95Fe 0.05O 3 can be grown from a background pressure of ~2×10-3 mTorr to oxygen pressures of 300 mTorr with high crystallinity and excellent structural quality. When grown in vacuum, the films may be weakly ferromagnetic with a nonzero x-ray magnetic circular dichroism signal on the Fe L 3 edge. Growth with oxygen flow appears to suppress magnetic ordering. Even for very thick films grown in 100 mTorr O 2, the films are paramagnetic. Finally,more » the existence of ferromagnetism in vacuum-grown BaSnO 3 may be attributed to the F-center exchange mechanism, which relies on the presence of oxygen vacancies to facilitate the ferromagnetism. However, other possible extrinsic contributions to the magnetic ordering, such as clusters of Fe 3O 4 and FeO or contamination can also explain the observed behavior.« less

Crystal growth, structural, optical, spectral and thermal studies of tris( L-phenylalanine) L-phenylalaninium nitrate: A new organic nonlinear optical material

NASA Astrophysics Data System (ADS)

Prakash, M.; Geetha, D.; Lydia Caroline, M.

2011-10-01

Tris( L-phenylalanine) L-phenylalaninium nitrate, C 9H 12NO 2+·NO 3-·3C 9H 11NO 2 (TPLPN), a new organic nonlinear optical material was grown from aqueous solution by slow evaporation solution growth at room temperature. The grown crystals were subjected to powder X-ray diffraction and single crystal X-ray diffraction studies to confirm the crystalline nature and crystal structure. The modes of vibration of different molecular groups present in TPLPN have been identified by FTIR spectral analysis. The presence of hydrogen and carbon in the grown crystal were confirmed by using proton and carbon nuclear magnetic resonance (NMR) spectral analyses. The optical transmission spectral study establishes good transmitting ability of the crystal in the entire visible region. The thermogravimetric (TG) and differential thermal analyses (DTA) were carried out to understand the thermal stability of the sample. The nonlinear optical property of the compound observed using Kurtz powder second harmonic generation test assets the suitability of the grown material for the frequency conversion of laser radiation of Nd:YAG.

Effect of defects on reaction of NiO surface with Pb-contained solution

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

Kim, Jongjin; Hou, Binyang; Park, Changyong

In order to understand the role of defects in chemical reactions, we used two types of samples, which are molecular beam epitaxy (MBE) grown NiO(001) film on Mg(001) substrate as the defect free NiO prototype and NiO grown on Ni(110) single crystal as the one with defects. In-situ observations for oxide-liquid interfacial structure and surface morphology were performed for both samples in water and Pb-contained solution using high-resolution X-ray reflectivity and atomic force microscopy. For the MBE grown NiO, no significant changes were detected in the high-resolution X-ray reflectivity data with monotonic increase in roughness. Meanwhile, in the case ofmore » native grown NiO on Ni(110), significant changes in both the morphology and atomistic structure at the interface were observed when immersed in water and Pb-contained solution. Our results provide simple and direct experimental evidence of the role of the defects in chemical reaction of oxide surfaces with both water and Pb-contained solution.« less

Local electrical properties of thermally grown oxide films formed on duplex stainless steel surfaces

NASA Astrophysics Data System (ADS)

Guo, L. Q.; Yang, B. J.; He, J. Y.; Qiao, L. J.

2018-06-01

The local electrical properties of thermally grown oxide films formed on ferrite and austenite surfaces of duplex stainless steel at different temperatures were investigated by Current sensing atomic force microscopy, X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES). The current maps and XPS/AES analyses show that the oxide films covering austenite and ferrite surfaces formed at different temperatures exhibit different local electrical characteristics, thickness and composition. The dependence of electrical conductivity of oxide films covering austenite and ferrite surface on the formation temperature is attributed to the film thickness and semiconducting structures, which is intrinsically related to thermodynamics and kinetics process of film grown at different temperature. This is well elucidated by corresponding semiconductor band structures of oxide films formed on austenite and ferrite phases at different temperature.

Development of aluminum gallium nitride based optoelectronic devices operating in deep UV and terahertz spectrum ranges

NASA Astrophysics Data System (ADS)

Zhang, Wei

In this research project I have investigated AlGaN alloys and their quantum structures for applications in deep UV and terahertz optoelectronic devices. For the deep UV emitter applications the materials and devices were grown by rf plasma-assisted molecular beam epitaxy on 4H-SiC, 6H-SiC and c-plane sapphire substrates. In the growth of AlGaN/AlN multiple quantum wells on SiC substrates, the AlGaN wells were grown under excess Ga, far beyond than what is required for the growth of stoichiometric AlGaN films, which resulted in liquid phase epitaxy growth mode. Due to the statistical variations of the excess Ga on the growth front we found that this growth mode leads to films with lateral variations in the composition and thus, band structure potential fluctuations. Transmission electron microscopy shows that the wells in such structures are not homogeneous but have the appearance of quantum dots. We find by temperature dependent photoluminescence measurements that the multiple quantum wells with band structure potential fluctuations emit at 240 nm and have room temperature internal quantum efficiency as high as 68%. Furthermore, they were found to have a maximum net modal optical gain of 118 cm-1 at a transparency threshold corresponding to 1.4 x 1017 cm-3 excited carriers. We attribute this low transparency threshold to population inversion of only the regions of the potential fluctuations rather than of the entire matrix. Some prototype deep UV emitting LED structures were also grown by the same method on sapphire substrates. Optoelectronic devices for terahertz light emission and detection, based on intersubband transitions in III-nitride semiconductor quantum wells, were grown on single crystal c-plane GaN substrates. Growth conditions such the ratio of group III to active nitrogen fluxes, which determines the appropriate Ga-coverage for atomically smooth growth without requiring growth interruptions were employed. Emitters designed in the quantum cascade structure were fabricated into mesa-structure devices and the I-V characterization at 20 K indicates sequential tunneling with electroluminescence emission at about 10 THz. Similarly, Far-infrared photoconductive detectors were grown by the same method. Photocurrent spectra centered at 23 mum (13 THz) are resolved up to 50 K, with responsivity of approximately 7 mA/W.

Spine micromorphology of normal and hyperhydric Mammillaria gracilis Pfeiff. (Cactaceae) shoots.

PubMed

Peharec, P; Posilović, H; Balen, B; Krsnik-Rasol, M

2010-07-01

Artificial conditions of tissue culture affect growth and physiology of crassulacean acid metabolism plants which often results in formation of hyperhydric shoots. In in vitro conditions Mammillaria gracilis Pfeiff. (Cactaceae) growth switches from organized to unorganized way, producing a habituated organogenic callus which simultaneously regenerates morphologically normal as well as altered hyperhydric shoots. In this study, influence of tissue culture conditions on morphology of cactus spines of normal and hyperhydric shoots was investigated. Spines of pot-grown Mammillaria plants and of in vitro regenerated shoots were examined with stereo microscope and scanning electron microscope. The pot-grown plants had 16-17 spines per areole. In vitro grown normal shoots, even though they kept typical shoot morphology, had lower number of spines (11-12) and altered spine morphology. This difference was even more pronounced in spine number (six to seven) and morphology of the hyperhydric shoots. Scanning electron microscopy analysis revealed remarkable differences in micromorphology of spine surface between pot-grown and in vitro grown shoots. Spines of in vitro grown normal shoots showed numerous long trichomes, which were more elongated on spines of the hyperhydric shoots; the corresponding structures on spine surface of pot-grown plants were noticed only as small protrusions. Scanning electron microscopy morphometric studies showed that the spines of pot-grown plants were significantly longer compared to the spines of shoots grown in tissue culture. Moreover, transverse section shape varies from elliptical in pot-grown plants to circular in normal and hyperhydric shoots grown in vitro. Cluster and correspondence analyses performed on the scanning electron microscope obtained results suggest great variability among spines of pot-grown plants. Spines of in vitro grown normal and hyperhydric shoots showed low level of morphological variation among themselves despite the significant difference in shoot morphology.

Multiferroic GaN nanofilms grown within Na-4 mica channels

NASA Astrophysics Data System (ADS)

Bhattacharya, Santanu; Datta, A.; Chakravorty, D.

2010-03-01

Gallium nitride nanofilms grown within nanochannels of Na-4 mica structure, exhibit ferromagnetism even at room temperature due to the presence of gallium vacancies at the surfaces of the nanofilms. These nanofilms also show a ferroelectric behavior at room temperature ascribed to a small distortion in the crystal structure of GaN due to its growth within the Na-4 mica nanochannels. A colossal increase in 338% in dielectric constant was observed for an applied magnetic field of 26 kOe. The magnetoelectric effect is ascribed to magnetostriction of magnetic GaN phase.

The Growth of Expitaxial GaAs and GaAlAs on Silicon Substrates by OMVPE

DTIC Science & Technology

1988-08-01

structures have been grown on semi-insulating gallium arsenide substrates, and on high-resistivity silicon substrates using a two stage growth technique...fully in Quarter 9. 2. MATERIALS GROWTH 2.1 DOPING OF GALLIUM ARSENIDE FOR FETs As reported in quarter 7, doping levels for GaAs/SI 4ere found to be a...FET structures on both GaAs and Si substrates. A number of FET layers have been grown to the GAT4 specification on semi-insulating gallium arsenide

A multiple p-n junction structure obtained from as-grown Czochralski silicon crystals by heat treatment - Application to solar cells

NASA Technical Reports Server (NTRS)

Chi, J. Y.; Gatos, H. C.; Mao, B. Y.

1980-01-01

Multiple p-n junctions have been prepared in as-grown Czochralski p-type silicon through overcompensation near the oxygen periodic concentration maxima by oxygen thermal donors generated during heat treatment at 450 C. Application of the multiple p-n-junction configuration to photovoltaic energy conversion has been investigated. A new solar-cell structure based on multiple p-n-junctions was developed. Theoretical analysis showed that a significant increase in collection efficiency over the conventional solar cells can be achieved.

Anisotropy of electrical resistivity in PVT grown WSe2-x crystals

NASA Astrophysics Data System (ADS)

Solanki, G. K.; Patel, Y. A.; Agarwal, M. K.

2018-05-01

Single crystals of p-type WSe2 and WSe1.9 were grown by a physical vapour transport technique. The anisotropy in d.c. electrical resistivity was investigated in these grown crystals. The off-stoichiometric WSe1.9 exhibited a higher anisotropy ratio as compared to WSe2 crystals. The electron microscopic examination revealed the presence of a large number of stacking faults in these crystals. The resistivity enhancement along the c-axis and anisotropic effective mass ratio explained on the basis of structural disorder introduced due to off-stoichiometry.

High frequency capacitance-voltage characteristics of thermally grown SiO2 films on beta-SiC

NASA Technical Reports Server (NTRS)

Tang, S. M.; Berry, W. B.; Kwor, R.; Zeller, M. V.; Matus, L. G.

1990-01-01

Silicon dioxide films grown under dry and wet oxidation environment on beta-SiC films have been studied. The beta-SiC films had been heteroepitaxially grown on both on-axis and 2-deg off-axis (001) Si substrates. Capacitance-voltage and conductance-voltage characteristics of metal-oxide-semiconductor structures were measured in a frequency range of 10 kHz to 1 MHz. From these measurements, the interface trap density and the effective fixed oxide charge density were observed to be generally lower for off-axis samples.

Metamorphic InAsSb-based Barrier Photodetectors for the Long Wave Infrared Region

DTIC Science & Technology

2013-08-02

The character of the I–V for structures with AlInSb layer grown undoped reflects the complex nature of the potential profile in the valence band ...Al0.75In0.25Sb-based barrier photodetectors were grown metamorphically on compositionally graded Ga1?xInxSb buffer layers and GaSb substrates by...ABSTRACT InAs0.6Sb0.4/Al0.75In0.25Sb-based barrier photodetectors were grown metamorphically on compositionally graded Ga1?xInxSb buffer layers and GaSb

Electrochemically deposited gallium oxide nanostructures on silicon substrates

PubMed Central

2014-01-01

We report a synthesis of β-Ga2O3 nanostructures on Si substrate by electrochemical deposition using a mixture of Ga2O3, HCl, NH4OH, and H2O. The presence of Ga3+ ions contributed to the deposition of Ga2O3 nanostructures on the Si surface with the assistance of applied potentials. The morphologies of the grown structures strongly depended on the molarity of Ga2O3 and pH level of electrolyte. β-Ga2O3 nanodot-like structures were grown on Si substrate at a condition with low molarity of Ga2O3. However, Ga2O3 nanodot structures covered with nanorods on top of their surfaces were obtained at higher molarity, and the densities of nanorods seem to increase with the decrease of pH level. High concentration of Ga3+ and OH- ions may promote the reaction of each other to produce Ga2O3 nanorods in the electrolyte. Such similar nature of Ga2O3 nanorods was also obtained by using hydrothermal process. The grown structures seem to be interesting for application in electronic and optoelectronic devices as well as to be used as a seed structure for subsequent chemical synthesis of GaN by thermal transformation method. PMID:24629107

Oxide-mediated recovery of field-effect mobility in plasma-treated MoS2

PubMed Central

Jadwiszczak, Jakub; O’Callaghan, Colin; Zhou, Yangbo; Fox, Daniel S.; Weitz, Eamonn; Keane, Darragh; Cullen, Conor P.; O’Reilly, Ian; Downing, Clive; Shmeliov, Aleksey; Maguire, Pierce; Gough, John J.; McGuinness, Cormac; Ferreira, Mauro S.; Bradley, A. Louise; Boland, John J.; Duesberg, Georg S.; Nicolosi, Valeria; Zhang, Hongzhou

2018-01-01

Precise tunability of electronic properties of two-dimensional (2D) nanomaterials is a key goal of current research in this field of materials science. Chemical modification of layered transition metal dichalcogenides leads to the creation of heterostructures of low-dimensional variants of these materials. In particular, the effect of oxygen-containing plasma treatment on molybdenum disulfide (MoS2) has long been thought to be detrimental to the electrical performance of the material. We show that the mobility and conductivity of MoS2 can be precisely controlled and improved by systematic exposure to oxygen/argon plasma and characterize the material using advanced spectroscopy and microscopy. Through complementary theoretical modeling, which confirms conductivity enhancement, we infer the role of a transient 2D substoichiometric phase of molybdenum trioxide (2D-MoOx) in modulating the electronic behavior of the material. Deduction of the beneficial role of MoOx will serve to open the field to new approaches with regard to the tunability of 2D semiconductors by their low-dimensional oxides in nano-modified heterostructures. PMID:29511736

Room temperature direct band gap emission characteristics of surfactant mediated grown compressively strained Ge films

NASA Astrophysics Data System (ADS)

Katiyar, Ajit K.; Grimm, Andreas; Bar, R.; Schmidt, Jan; Wietler, Tobias; Joerg Osten, H.; Ray, Samit K.

2016-10-01

Compressively strained Ge films have been grown on relaxed Si0.45Ge0.55 virtual substrates using molecular beam epitaxy in the presence of Sb as a surfactant. Structural characterization has shown that films grown in the presence of surfactant exhibit very smooth surfaces with a relatively higher strain value in comparison to those grown without any surfactant. The variation of strain with increasing Ge layer thickness was analyzed using Raman spectroscopy. The strain is found to be reduced with increasing film thickness due to the onset of island nucleation following Stranski-Krastanov growth mechanism. No phonon assisted direct band gap photoluminescence from compressively strained Ge films grown on relaxed Si0.45Ge0.55 has been achieved up to room temperature. Excitation power and temperature dependent photoluminescence have been studied in details to investigate the origin of different emission sub-bands.

Bulk growth of <001> organic nonlinear optical (NLO) L-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) single crystals by SR method

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

Pandian, Muthu Senthil, E-mail: senthilpandianm@ssn.edu.in; Sivasubramani, V.; Ramasamy, P.

2015-06-24

A transparent uniaxial L-arginine 4-nitrophenolate 4-nitrophenol dehydrate (LAPP) single crystal having dimension of 20 mm diameter and 45 mm length was grown by Sankaranarayanan-Ramasamy (SR) method with a growth rate of 1 mm per day. Using an identical solution the conventional crystal grown to a dimension of 8×5×5 mm{sup 3} was obtained over a period of 30 days. The crystal structure has been confirmed by single crystal X-ray diffraction measurement. The crystalline perfection of LAPP crystals grown by slow evaporation solution technique (SEST) and SR method were characterized using Vickers microhardness, UV-Vis NIR, chemical etching, dark and photo current measurements. The above study indicatesmore » that the crystal quality of the Sankaranarayanan-Ramasamy (SR) method grown LAPP is good compared to the conventional method grown crystal.« less

Epitaxial Ge Solar Cells Directly Grown on Si (001) by MOCVD Using Isobutylgermane

NASA Astrophysics Data System (ADS)

Kim, Youngjo; Kim, Kangho; Lee, Jaejin; Kim, Chang Zoo; Kang, Ho Kwan; Park, Won-Kyu

2018-03-01

Epitaxial Ge layers have been grown on Si (001) substrates by metalorganic chemical vapor deposition (MOCVD) using an isobutylgermane (IBuGe) metalorganic source. Low and high temperature two-step growth and post annealing techniques are employed to overcome the lattice mismatch problem between Ge and Si. It is demonstrated that high quality Ge epitaxial layers can be grown on Si (001) by using IBuGe with surface RMS roughness of 2 nm and an estimated threading dislocation density of 4.9 × 107 cm -2. Furthermore, single-junction Ge solar cells have been directly grown on Si substrates with an in situ MOCVD growth. The epitaxial Ge p- n junction structures are investigated with transmission electron microscopy and electrochemical C- V measurements. As a result, a power conversion efficiency of 1.69% was achieved for the Ge solar cell directly grown on Si substrate under AM1.5G condition.

Solid-state reaction kinetics and optical studies of cadmium doped magnesium hydrogen phosphate crystals

NASA Astrophysics Data System (ADS)

Verma, Madhu; Gupta, Rashmi; Singh, Harjinder; Bamzai, K. K.

2018-04-01

The growth of cadmium doped magnesium hydrogen phosphate was successfully carried out by using room temperature solution technique i.e., gel encapsulation technique. Grown crystals were confirmed by single crystal X-ray diffraction (XRD). The structure of the grown crystal belongs to orthorhombic crystal system and crystallizes in centrosymmetric space group. Kinetics of the decomposition of the grown crystals were studied by non-isothermal analysis. Thermo gravimetric / differential thermo analytical (TG/DTA) studies revealed that the grown crystal is stable upto 119 °C. The various steps involved in the thermal decomposition of the material have been analysed using Horowitz-Metzger, Coats-Redfern and Piloyan-Novikova equations for evaluating various kinetic parameters. The optical studies shows that the grown crystals possess wide transmittance in the visible region and significant optical band gap of 5.5ev with cut off wavelength of 260 nm.

Structural, morphological and optical properties of pulsed laser deposited ZnSe/ZnSeO3 thin films

NASA Astrophysics Data System (ADS)

Hassan, Syed Ali; Bashir, Shazia; Zehra, Khushboo; Salman Ahmed, Qazi

2018-04-01

The effect of varying laser pulses on structural, morphological and optical behavior of Pulsed Laser Deposited (PLD) ZnSe/ZnSeO3 thin films has been investigated. The films were grown by employing Excimer laser (100 mJ, 248 nm, 18 ns, 30 Hz) at various number of laser pulses i.e. 3000, 4000, 5000 and 6000 with elevated substrate temperature of 300 °C. One film was grown at Room Temperature (RT) by employing 3000 number of laser pulses. In order to investigate the structural analysis of deposited films, XRD analysis was performed. It was observed that the room temperature is not favorable for the growth of crystalline film. However, elevated substrate temperature to 300°C, two phases with preferred orientation of ZnSeO3 (2 1 2) and ZnSe (3 3 1) were identified. AFM and SEM analysis were performed to explore the surface morphology of grown films. Morphological analysis also confirmed the non-uniform film growth at room temperature. At elevated substrate temperature (300 °C), the growth of dendritic rods and cubical crystalline structures are observed for lower number of laser pulses i.e. 3000 and 4000 respectively. With increased number of pulses i.e. 5000 and 6000, the films surface morphology becomes smooth which is confirmed by measurement of surface RMS roughness. Number of grains, skewness, kurtosis and other parameters have been evaluated by statistical analysis. In order to investigate the thickness, and optical properties of deposited films, ellipsometery and UV–Vis spectroscopy techniques were employed. The estimated band gap energy is 2.67 eV for the film grown at RT, whereas band gap values varies from 2.80 eV to 3.01 eV for the films grown at 300 °C with increasing number of laser pulses.

Contactless electroreflectance studies of surface potential barrier for N- and Ga-face epilayers grown by molecular beam epitaxy

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

Kudrawiec, R.; Janicki, L.; Gladysiewicz, M.

2013-07-29

Two series of N- and Ga-face GaN Van Hoof structures were grown by plasma-assisted molecular beam epitaxy to study the surface potential barrier by contactless electroreflectance (CER). A clear CER resonance followed by strong Franz-Keldysh oscillation of period varying with the thickness of undoped GaN layer was observed for these structures. This period was much shorter for N-polar structures that means smaller surface potential barrier in these structures than in Ga-polar structures. From the analysis of built-in electric field it was determined that the Fermi-level is located 0.27 ± 0.05 and 0.60 ± 0.05 eV below the conduction band formore » N- and Ga-face GaN surface, respectively.« less

Characterization of the scintillation anisotropy in crystalline stilbene scintillator detectors

DOE PAGES

Schuster, P.; Brubaker, E.

2016-11-23

This study reports a series of measurements that characterize the directional dependence of the scintillation response of crystalline melt-grown and solution-grown trans-stilbene to incident DT and DD neutrons. These measurements give the amplitude and pulse shape dependence on the proton recoil direction over one hemisphere of the crystal, confirming and extending previous results in the literature for melt-grown stilbene and providing the first measurements for solution-grown stilbene. In similar measurements of liquid and plastic detectors, no directional dependence was observed, confirming the hypothesis that the anisotropy in stilbene and other organic crystal scintillators is a result of internal effects duemore » to the molecular or crystal structure and not an external effect on the measurement system.« less

Crystalline perfection and optical studies of L-Histidinium dihydrogen phosphate orthophosphoric acid (LHDP) single crystals

NASA Astrophysics Data System (ADS)

Ittyachan, Reena; Arunkumar, A.; Bhagavannarayana, G.

2015-10-01

Single crystals of L-Histidinium dihydrogenphosphate orthophosphoric acid (LHDP) were grown by slow evaporation solution growth technique. The grown crystals were confirmed by single crystal X-ray diffraction techniques. The HRXRD rocking curve measurements revealed the crystalline perfection of grown crystal and the absence of structural grain boundaries. The lower optical cut-off wavelength for this crystal was observed at 240 nm. The third order nonlinear refractive index (n2), nonlinear absorption coefficient (β) and susceptibility (χ(3)) were calculated by Z-scan studies using Nd: YAG laser as a source. The single shot laser damage threshold of grown crystal was measured to be 6.286 GW/cm2 using Nd: YAG laser.

Roles of ionic strength and biofilm roughness on adhesion kinetics of Escherichia coli onto groundwater biofilm grown on PVC surfaces

PubMed Central

Janjaroen, Dao; Ling, Fangqiong; Monroy, Guillermo; Derlon, Nicolas; Mogenroth, Eberhard; Boppart, Stephen A.; Liu, Wen-Tso; Nguyen, Thanh H.

2013-01-01

Mechanisms of Escherichia coli attachment on biofilms grown on PVC coupons were investigated. Biofilms were grown in CDC reactors using groundwater as feed solution over a period up to 27 weeks. Biofilm physical structure was characterized at the micro- and meso-scales using Scanning Electron Microscopy (SEM) and Optical Coherence Tomography (OCT), respectively. Microbial community diversity was analyzed with Terminal Restricted Fragment Length Polymorphism (T-RFLP). Both physical structure and microbial community diversity of the biofilms were shown to be changing from 2 weeks to 14 weeks, and became relatively stable after 16 weeks. A parallel plate flow chamber coupled with an inverted fluorescent microscope was also used to monitor the attachment of fluorescent microspheres and E. coli on clean PVC surfaces and biofilms grown on PVC surfaces for different ages. Two mechanisms of E. coli attachment were identified. The adhesion rate coefficients (kd) of E. coli on nascent PVC surfaces and 2-week biofilms increased with ionic strength. However, after biofilms grew for 8 weeks, the adhesion was found to be independent of solution chemistry. Instead, a positive correlation between kd and biofilm roughness as determined by OCT was obtained, indicating that the physical structure of biofilms could play an important role in facilitating the adhesion of E. coli cells. PMID:23497979

Infiltration of CdTe nano crystals into a ZnO wire vertical matrix by using the isothermal closed space technique

NASA Astrophysics Data System (ADS)

Larramendi, S.; Vaillant Roca, Lidice; Saint-Gregoire, Pierre; Ferraz Dias, Johnny; Behar, Moni

2017-10-01

A ZnO nanorod structure was grown by the hydrothermal method and interpenetrated with CdTe using the isothermal closed space sublimation technique. The obtained structure was studied by using the Rutherford backscattering spectrometry (RBS), Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM). The X-ray Diffraction (XRD) technique confirmed the presence of CdTe nanocrystals (NCs) of very small size formed on the surface and in the interspaces between the ZnO nanorods. The RBS observations together with the SEM observations give information on the obtained structure. Finally the photoluminescence studies show a strong energy confinement effect on the grown CdTe NCs.

Process for depositing an oxide epitaxially onto a silicon substrate and structures prepared with the process

DOEpatents

McKee, Rodney A.; Walker, Frederick J.

1993-01-01

A process and structure involving a silicon substrate utilizes an ultra high vacuum and molecular beam epitaxy (MBE) methods to grow an epitaxial oxide film upon a surface of the substrate. As the film is grown, the lattice of the compound formed at the silicon interface becomes stabilized, and a base layer comprised of an oxide having a sodium chloride-type lattice structure grows epitaxially upon the compound so as to cover the substrate surface. A perovskite may then be grown epitaxially upon the base layer to render a product which incorporates silicon, with its electronic capabilities, with a perovskite having technologically-significant properties of its own.

Electronic and magnetic structure of ultra-thin Ni films grown on W(110)

NASA Astrophysics Data System (ADS)

Calloni, A.; Bussetti, G.; Berti, G.; Yivlialin, R.; Camera, A.; Finazzi, M.; Duò, L.; Ciccacci, F.

2016-12-01

We studied the electronic structure of thin Ni films grown on a W(110) single crystal, as a function of the Ni thickness, by means of angle-resolved photoemission and inverse photoemission spectroscopy, also with spin resolution. The results are discussed in the light of the different stages characterizing the transition from the pseudomorphic bcc to the fully relaxed fcc phase. A clear spin polarization is detected as soon as a bulk-like electronic structure is observed. In these conditions, we characterized the exchange splitting of the occupied bands at the Γbar and Mbar points of the surface Brillouin zone, providing further experimental support to previous interpretations of photoemission spectra from bulk Ni.

Monitoring of visually graded structural lumber

Treesearch

David E. Kretschmann; James W. Evans; Linda Brown

To satisfy the increased demand for forest products, much of the future timber supply is expected to be derived from improved trees grown on managed plantations. This fast-grown resource will tend to be harvested in short-age rotations and will contain higher proportions of juvenile wood compared with wood in current harvests. As a result, current allowable properties...

Estimating leaf area and leaf biomass of open-grown deciduous urban trees

Treesearch

David J. Nowak

1996-01-01

Logarithmic regression equations were developed to predict leaf area and leaf biomass for open-grown deciduous urban trees based on stem diameter and crown parameters. Equations based on crown parameters produced more reliable estimates. The equations can be used to help quantify forest structure and functions, particularly in urbanizing and urban/suburban areas.

Passivation of MBE grown InGaSb/InAs superlattice photodiodes

NASA Technical Reports Server (NTRS)

Hill, Cory J.; Keo, Sam S.; Mumolo, Jason M.; Gunapala, Sarath D.

2005-01-01

We have performed wet chemical passivation tests on InGaSb/InAs superlattice photodiode structures grown molecular beam epitaxy. The details of the devices growth and characterization as well as the results of chemical passivation involving RuCl3 and H2SO4 with SiO2 dielectric depositions are presented.

Crystal structure of Yersinia pestis virulence factor YfeA reveals two polyspecific metal-binding sites

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

Radka, Christopher D.; DeLucas, Lawrence J.; Wilson, Landon S.

2017-06-30

Gram-negative bacteria use siderophores, outer membrane receptors, inner membrane transporters and substrate-binding proteins (SBPs) to transport transition metals through the periplasm. The SBPs share a similar protein fold that has undergone significant structural evolution to communicate with a variety of differentially regulated transporters in the cell. InYersinia pestis, the causative agent of plague, YfeA (YPO2439, y1897), an SBP, is important for full virulence during mammalian infection. To better understand the role of YfeA in infection, crystal structures were determined under several environmental conditions with respect to transition-metal levels. Energy-dispersive X-ray spectroscopy and anomalous X-ray scattering data show that YfeA ismore » polyspecific and can alter its substrate specificity. In minimal-media experiments, YfeA crystals grown after iron supplementation showed a threefold increase in iron fluorescence emission over the iron fluorescence emission from YfeA crystals grown from nutrient-rich conditions, and YfeA crystals grown after manganese supplementation during overexpression showed a fivefold increase in manganese fluorescence emission over the manganese fluorescence emission from YfeA crystals grown from nutrient-rich conditions. In all experiments, the YfeA crystals produced the strongest fluorescence emission from zinc and could not be manipulated otherwise. Additionally, this report documents the discovery of a novel surface metal-binding site that prefers to chelate zinc but can also bind manganese. Flexibility across YfeA crystal forms in three loops and a helix near the buried metal-binding site suggest that a structural rearrangement is required for metal loading and unloading.« less

Quantum well infrared photodetectors (QWIP) with selectively regrown N-GaAs plugs

NASA Astrophysics Data System (ADS)

Matsukura, Yusuke; Nishino, Hironori; Tanaka, Hitoshi; Fujii, Toshio

2001-10-01

We fabricated the GaAs/AlGaAs Quantum Well Infrared Photo detector (QWIP) focal plane array with selectively re-grown N- GaAs interconnection plugs and demonstrated its device operation, in order to establish the technology to obtain both complex device functions and device manufacturability. MBE (Molecular Beam Epitaxy) grown QWIP MQW wafers were covered with SiON and SiNx mask films to obtain selectivity of the re-growth process. N-GaAs plugs were re-grown selectively with low-pressure MOCVD (Metal-Organic Chemical Vapor Deposition) with AsH3 and Dimethylgalliumchloride as precursors, only on the bottom surfaces of the holes for the interconnection to extract the electrodes from the underlying epilayer. Cross- sectional SEM observation revealed that the feature of the re- grown N-GaAs plugs was triangular, rather than rectangular as expected. The reason for this discrepancy is not yet clear. The electrical contact between the epilayer and re-grown N- GaAs plug was 'ohmic-like,' without any trace of interfacial barrier. The Current-Voltage characteristics of the fabricated QWIP device showed no tangible leakage current between the N- GaAs plug and device structure, indicating that electrical insulation between the N-GaAs plugs and device structure was sufficient. Fabricated devices were successfully operated as a hybrid focal plane array, indicating the selective re-growth was a promising technique to realize complex QWIP based devices.

Experimental and density functional theory (DFT): A dual approach to probe the key properties of creatininium L-tartrate monohydrate single crystal for nonlinear optical applications

NASA Astrophysics Data System (ADS)

Thirumurugan, R.; Babu, B.; Anitha, K.; Chandrasekaran, J.

2017-12-01

A novel organic nonlinear optical (NLO) material, creatininium L-tartrate monohydrate (CTM) was synthesized and it was grown as single crystals with optical quality. 1H and 13C NMR spectral studies were performed and molecular structure of synthesized CTM compound was confirmed. Single crystal X-ray diffraction (SXRD) analysis confirmed that CTM was crystallized in orthorhombic system with non-centrosymmetric (NCS), P212121, space group. The grown crystal exhibited admirable properties such as second harmonic generation efficiency (SHG) (1.9 times KDP), and high laser damage threshold (LDT) value of 3.7 GW cm-2. CTM crystal displayed high transparency (∼60%) in the visible and near-IR region with low cut-off wavelength at 249 nm. Photoluminescence study confirmed blue wavelength emission (∼463 nm) of grown crystal. Thermal and mechanical behaviours have been successfully analysed for grown crystals. The dielectric studies were carried out for grown crystal as a function of frequencies at different temperatures. Hirshfeld surface and fingerprint plots provided the percentage of individual interactions contributed by each atom. Moreover, density functional theory (DFT) calculations have been employed to probe the frontier molecular orbitals (FMOs) and first hyperpolarizability (β) analysis of the optimized CTM structure. These results validated CTM as a suitable NLO candidate and were discussed in this work.

Structural, thermal and optical properties of KTi(0.92)La(0.08)OPO4 and KTi(0.94)Nd(0.06)OPO4.

PubMed

Sadhasivam, S; Perumal, Rajesh Narayana; Ramasamy, P

2015-10-05

KTi0.92La0.08OPO4 (KTP:La) and KTi0.94Nd0.06OPO4 (KTP:Nd) single crystals are grown using high temperature top seeded flux growth technique. The strain derived from doping is calculated from Williamson-Hall relation. The packing structure and lattice parameter of the grown crystals are analyzed using single crystal X-ray diffraction. The bonding, distortion and change in inter-atomic distances by strain effects of doping are assessed by Raman spectroscopy. Thermal stabilities of grown crystals are evaluated by specific heat capacity measurement. Pronounced high specific heat capacity is recorded as 1.16 J/gK at 498 K for KTP:Nd. Second harmonic generation intensities are measured for KTP:Nd and KTP:La single crystal. Copyright © 2015 Elsevier B.V. All rights reserved.

Solid state parameters, structure elucidation, High Resolution X-Ray Diffraction (HRXRD), phase matching, thermal and impedance analysis on L-Proline trichloroacetate (L-PTCA) NLO single crystals.

PubMed

Kalaiselvi, P; Raj, S Alfred Cecil; Jagannathan, K; Vijayan, N; Bhagavannarayana, G; Kalainathan, S

2014-11-11

Nonlinear optical single crystal of L-Proline trichloroacetate (L-PTCA) was successfully grown by Slow Evaporation Solution Technique (SEST). The grown crystals were subjected to single crystal X-ray diffraction analysis to confirm the structure. From the single crystal XRD data, solid state parameters were determined for the grown crystal. The crystalline perfection has been evaluated using high resolution X-ray diffractometer. The frequencies of various functional groups were identified from FTIR spectral analysis. The percentage of transmittance was obtained from UV Visible spectral analysis. TGA-DSC measurements indicate the thermal stability of the crystal. The dielectric constant, dielectric loss and ac conductivity were measured by the impedance analyzer. The DC conductivity was calculated by the cole-cole plot method. Copyright © 2014 Elsevier B.V. All rights reserved.

Elimination of trench defects and V-pits from InGaN/GaN structures

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

Smalc-Koziorowska, Julita; Grzanka, Ewa; Czernecki, Robert

2015-03-09

The microstructural evolution of InGaN/GaN multiple quantum wells grown by metalorganic chemical vapor phase epitaxy was studied as a function of the growth temperature of the GaN quantum barriers (QBs). We observed the formation of basal stacking faults (BSFs) in GaN QBs grown at low temperature. The presence of BSFs terminated by stacking mismatch boundaries (SMBs) leads to the opening of the structure at the surface into a V-shaped trench loop. This trench may form above an SMB, thereby terminating the BSF, or above a junction between the SMB and a subsequent BSF. Fewer BSFs and thus fewer trench defectsmore » were observed in GaN QBs grown at temperatures higher than 830 °C. Further increase in the growth temperature of the GaN QBs led to the suppression of the threading dislocation opening into V-pits.« less

Properties of CsI, CsBr and GaAs thin films grown by pulsed laser deposition

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

Brendel, V M; Garnov, S V; Yagafarov, T F

2014-09-30

CsI, CsBr and GaAs thin films have been grown by pulsed laser deposition on glass substrates. The morphology and structure of the films have been studied using X-ray diffraction and scanning electron microscopy. The CsI and CsBr films were identical in stoichiometry to the respective targets and had a polycrystalline structure. Increasing the substrate temperature led to an increase in the density of the films. All the GaAs films differed in stoichiometry from the target. An explanation was proposed for this fact. The present results demonstrate that, when the congruent transport condition is not fulfilled, films identical in stoichiometry tomore » targets can be grown by pulsed laser deposition in the case of materials with a low melting point and thermal conductivity. (interaction of laser radiation with matter)« less

Structural and optical properties of ZnO nanorods on Mg0.2Zn0.8O seed layers grown by hydrothermal method.

PubMed

Kim, Min Su; Kim, Do Yeob; Kim, Sung-O; Leem, Jae-Young

2013-05-01

ZnO nanorods were grown on the Mg0.2Zn0.8O seed layers with different thickness by hydrothermal method. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL) were carried out to investigate the effects of the Mg0.2Zn0.8O seed layer thickness on the structural and the optical properties of the ZnO nanorods. The residual stress in the Mg0.2Zn0.8O seed layers was depended on the thickness while the texture coefficient of the Mg0.2Zn0.8O seed layers was not affected significantly. The smaller full width at half maximum (FWHM) of the ZnO (002) diffraction and near-band-edge emission (NBE) peak and the larger average grain size were observed from the ZnO nanorods grown on the Mg0.2Zn0.8O seed layers with 5 layers (thickness of 350 nm), which indicate the enhancement the structural and the optical properties of the ZnO nanorods.

Woody plant diversity and structure of shade-grown-coffee plantations in northern Chiapas, Mexico.

PubMed

Soto-Pinto, L; Romero-Alvarado, Y; Caballero-Nieto, J; Segura Warnholtz, G

2001-01-01

Shade-grown coffee is an agricultural system that contains some forest-like characteristics. However, structure and diversity are poorly known in shade coffee systems. In 61 coffee-growers' plots of Chiapas, Mexico, structural variables of shade vegetation and coffee yields were measured, recording species and their use. Coffee stands had five vegetation strata. Seventy seven woody species mostly used as wood were found (mean density 371.4 trees per hectare). Ninety percent were native species (40% of the local flora), the remaining were introduced species, mainly fruit trees/shrubs. Diametric distribution resembles that of a secondary forest. Principal Coordinates Analysis grouped plots in four classes by the presence of Inga, however the majority of plots are diverse. There was no difference in equitability among groups or coffee yields. Coffee yield was 835 g clean coffee per shrub, or ca. 1,668 kg ha-1. There is a significant role of shade-grown coffee as diversity refuge for woody plants and presumably associated fauna as well as an opportunity for shade-coffee growers to participate in the new biodiversity-friendly-coffee market.

Tunability of morphological properties of Nd-doped TiO2 thin films

NASA Astrophysics Data System (ADS)

Rehan, Imran; Sultana, Sabiha; Khan, Nauman; Qamar, Zahid; Rehan, Kamran

2016-11-01

In this work, an endeavor is made toward structural assessment and morphological variation of titanium dioxide (TiO2) thin films when doped with neodymium (Nd). The electron beam deposition technique was employed to fabricate Nd-based TiO2 thin films on n-Type Si substrates. Nd concentration was varied from 0.0 to 2.0 atomic percent (at.%) under identical growth environments. The films were deposited in an oxygen-deficient environment to cause the growth of rutile phases. Energy dispersive x-ray spectroscopy confirmed the presence and variation of Nd dopant in TiO2. X-ray diffraction analysis showed the transformation of amorphous structures of the as-grown samples to anatase polycrystalline after annealing at 500 °C, while atomic force microscopy exposed linearity in grain density in as-grown samples with doping until 1 at.%. Raman spectrums of as-grown and annealed samples revealed the growth of the anatase phase in the annealed samples. Based on these results it can be proposed that Nd doping has pronounced effects on the structural characteristics of TiO2 thin films.

Photoluminescence of Molecular Beam Epitaxy-Grown Mercury Cadmium Telluride: Comparison of HgCdTe/GaAs and HgCdTe/Si Technologies

NASA Astrophysics Data System (ADS)

Mynbaev, K. D.; Bazhenov, N. L.; Dvoretsky, S. A.; Mikhailov, N. N.; Varavin, V. S.; Marin, D. V.; Yakushev, M. V.

2018-05-01

Properties of HgCdTe films grown by molecular beam epitaxy on GaAs and Si substrates have been studied by performing variable-temperature photoluminescence (PL) measurements. A substantial difference in defect structure between films grown on GaAs (013) and Si (013) substrates was revealed. HgCdTe/GaAs films were mostly free of defect-related energy levels within the bandgap, which was confirmed by PL and carrier lifetime measurements. By contrast, the properties of HgCdTe/Si films are affected by uncontrolled point defects. These could not be always associated with typical "intrinsic" HgCdTe defects, such as mercury vacancies, so consideration of other defects, possibly inherent in HgCdTe/Si structures, was required. The post-growth annealing was found to have a positive effect on the defect structure by reducing the full-widths at half-maximum of excitonic PL lines for both types of films and lowering the concentration of defects specific to HgCdTe/Si.

Concentration and structure inhomogeneities in GaSb(Si) single crystals grown at different heat and mass transfer conditions

NASA Astrophysics Data System (ADS)

Serebryakov, Yu. A.; Prokhorov, I. A.; Vlasov, V. N.; Korobeynikova, E. N.; Zakharov, B. G.; Shul'pina, I. L.; Marchenko, M. P.; Fryazinov, I. V.

2007-06-01

Results of ground-based experiments on crystallization of gallium antimonide on the POLIZON facility carried out within the framework of space experiment preparation aboard FOTON satellite are submitted. Technical and technological opportunities of suppression of disturbing factors for improvement of quality of grown crystals in space are substantiated. Features of formation of concentration and structure inhomogeneities in GaSb:Si crystals grown under non-stationary and stationary convection conditions are investigated. Experimental data about structure and dopant distribution inhomogeneities are discussed taking into account results of numerical researches of GaSb:Si crystallization. Also earlier received results of modeling of GaSb:Te crystallization under close temperature conditions are used. Correlation between computational and experimental data is shown. The data on intensity of flows close to crystallization front are received at which non-stationary or stationary conditions of crystallization are realized. The forecast for space conditions is made. The influence of a rotating magnetic field on convection in melt for application in space experiment projected is investigated.

A bioengineered niche promotes in vivo engraftment and maturation of pluripotent stem cell derived human lung organoids

PubMed Central

Dye, Briana R; Dedhia, Priya H; Miller, Alyssa J; Nagy, Melinda S; White, Eric S; Shea, Lonnie D; Spence, Jason R

2016-01-01

Human pluripotent stem cell (hPSC) derived tissues often remain developmentally immature in vitro, and become more adult-like in their structure, cellular diversity and function following transplantation into immunocompromised mice. Previously we have demonstrated that hPSC-derived human lung organoids (HLOs) resembled human fetal lung tissue in vitro (Dye et al., 2015). Here we show that HLOs required a bioartificial microporous poly(lactide-co-glycolide) (PLG) scaffold niche for successful engraftment, long-term survival, and maturation of lung epithelium in vivo. Analysis of scaffold-grown transplanted tissue showed airway-like tissue with enhanced epithelial structure and organization compared to HLOs grown in vitro. By further comparing in vitro and in vivo grown HLOs with fetal and adult human lung tissue, we found that in vivo transplanted HLOs had improved cellular differentiation of secretory lineages that is reflective of differences between fetal and adult tissue, resulting in airway-like structures that were remarkably similar to the native adult human lung. DOI: http://dx.doi.org/10.7554/eLife.19732.001 PMID:27677847

Flexible metal-semiconductor-metal device prototype on wafer-scale thick boron nitride layers grown by MOVPE.

PubMed

Li, Xin; Jordan, Matthew B; Ayari, Taha; Sundaram, Suresh; El Gmili, Youssef; Alam, Saiful; Alam, Muhbub; Patriarche, Gilles; Voss, Paul L; Paul Salvestrini, Jean; Ougazzaden, Abdallah

2017-04-11

Practical boron nitride (BN) detector applications will require uniform materials over large surface area and thick BN layers. To report important progress toward these technological requirements, 1~2.5 µm-thick BN layers were grown on 2-inch sapphire substrates by metal-organic vapor phase epitaxy (MOVPE). The structural and optical properties were carefully characterized and discussed. The thick layers exhibited strong band-edge absorption near 215 nm. A highly oriented two-dimensional h-BN structure was formed at the film/sapphire interface, which permitted an effective exfoliation of the thick BN film onto other adhesive supports. And this structure resulted in a metal-semiconductor-metal (MSM) device prototype fabricated on BN membrane delaminating from the substrate. MSM photodiode prototype showed low dark current of 2 nA under 100 V, and 100 ± 20% photoconductivity yield for deep UV light illumination. These wafer-scale MOVPE-grown thick BN layers present great potential for the development of deep UV photodetection applications, and even for flexible (opto-) electronics in the future.

Magnetic anisotropy and transport properties of 70 nm SrRuO3 films grown on different substrates

NASA Astrophysics Data System (ADS)

Wang, X. W.; Zhang, Y. Q.; Meng, H.; Wang, Z. J.; Li, D.; Zhang, Z. D.

2011-04-01

Magnetic and transport properties of 70 nm SrRuO3 films grown on (001) SrTiO3, (001) LaAlO3 and (001) MgO have been investigated. A perpendicular magnetic anisotropy is observed in compressive strained films grown on SrTiO3. A weaker perpendicular magnetic anisotropy and a weak in-plane magnetic anisotropy are found in strain-free films grown on MgO and LAO, respectively, possibly due to different growth mechanisms. In addition, metallic behavior is observed in all the as-grown films and the resistivity of the film grown on MgO is lowest (230 μΩ cm at 300 K), which is close to that of bulk single crystal SrRuO3 (about 195 μΩ cm). The relation between structure and properties indicates that the magnetic anisotropy, as well as the magnitude of resistivity of SrRuO3 films, can be effectively tailored by taking advantage of different strains and growth mechanisms induced by growth on different substrates.

The deep levels in InGaAlP epilayers grown by metalorganic chemical vapor deposition using tertiarybutylphosphine

NASA Astrophysics Data System (ADS)

Izumiya, T.; Ishikawa, H.; Mashita, M.

1994-12-01

InGaAlP epilayers and double-hetero structure light emitting diodes (LEDs) were grown by metalorganic chemical vapor deposition (MOCVD) using tertiarybutylphosphine (TBP). The photoluminescence (PL) intensities were low compared with the epilayer grown using PH 3, and depended markedly on the TBP synthesis lots. Deep levels, were studied and two oxygen related levels were observed in the epilayers with small PL intensities. An intimate relation between the deep levels and the photoluminescence (PL) intensity has been found. A larger TBP flow rate reduced the deep level concentrations and improved the PL intensity.

Epitaxial heterojunctions of oxide semiconductors and metals on high temperature superconductors

NASA Technical Reports Server (NTRS)

Vasquez, Richard P. (Inventor); Hunt, Brian D. (Inventor); Foote, Marc C. (Inventor)

1994-01-01

Epitaxial heterojunctions formed between high temperature superconductors and metallic or semiconducting oxide barrier layers are provided. Metallic perovskites such as LaTiO3, CaVO3, and SrVO3 are grown on electron-type high temperature superconductors such as Nd(1.85)Ce(0.15)CuO(4-x). Alternatively, transition metal bronzes of the form A(x)MO(3) are epitaxially grown on electron-type high temperature superconductors. Also, semiconducting oxides of perovskite-related crystal structures such as WO3 are grown on either hole-type or electron-type high temperature superconductors.

A platform for large-scale graphene electronics--CVD growth of single-layer graphene on CVD-grown hexagonal boron nitride.

PubMed

Wang, Min; Jang, Sung Kyu; Jang, Won-Jun; Kim, Minwoo; Park, Seong-Yong; Kim, Sang-Woo; Kahng, Se-Jong; Choi, Jae-Young; Ruoff, Rodney S; Song, Young Jae; Lee, Sungjoo

2013-05-21

Direct chemical vapor deposition (CVD) growth of single-layer graphene on CVD-grown hexagonal boron nitride (h-BN) film can suggest a large-scale and high-quality graphene/h-BN film hybrid structure with a defect-free interface. This sequentially grown graphene/h-BN film shows better electronic properties than that of graphene/SiO2 or graphene transferred on h-BN film, and suggests a new promising template for graphene device fabrication. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Epitaxial Stabilization of a-PbO2 Structure in MnF2 Layers on Si and GaP

DTIC Science & Technology

2001-06-01

Before the epitaxy, the substrates were dipped in a HF solution and fixed on Si platelets with InGa eutectic . The crystalline quality of the substrates...15 keV. We used a recrystallization annealing (RA) in the 550-700’C range to improve the MnF2 film quality of some epitaxial structures grown at... recrystallization annealing. The inset in Fig. 1(a) shows the RHEED pattern of a 30 nm MnF2 film grown at 100°C and annealed at 550’C. Well-pronounced

Chemical lift-off and direct wafer bonding of GaN/InGaN P-I-N structures grown on ZnO

NASA Astrophysics Data System (ADS)

Pantzas, K.; Rogers, D. J.; Bove, P.; Sandana, V. E.; Teherani, F. H.; El Gmili, Y.; Molinari, M.; Patriarche, G.; Largeau, L.; Mauguin, O.; Suresh, S.; Voss, P. L.; Razeghi, M.; Ougazzaden, A.

2016-02-01

p-GaN/i-InGaN/n-GaN (PIN) structures were grown epitaxially on ZnO-buffered c-sapphire substrates by metal organic vapor phase epitaxy using the industry standard ammonia precursor for nitrogen. Scanning electron microscopy revealed continuous layers with a smooth interface between GaN and ZnO and no evidence of ZnO back-etching. Energy Dispersive X-ray Spectroscopy revealed a peak indium content of just under 5 at% in the active layers. The PIN structure was lifted off the sapphire by selectively etching away the ZnO buffer in an acid and then direct bonded onto a glass substrate. Detailed high resolution transmission electron microscoy and grazing incidence X-ray diffraction studies revealed that the structural quality of the PIN structures was preserved during the transfer process.

Internal structure of copper(II)-phthalocyanine thin films on SiO2/Si substrates investigated by grazing incidence x-ray reflectometry

NASA Astrophysics Data System (ADS)

Brieva, A. C.; Jenkins, T. E.; Jones, D. G.; Strössner, F.; Evans, D. A.; Clark, G. F.

2006-04-01

The internal structure of copper(II)-phthalocyanine (CuPc) thin films grown on SiO2/Si by organic molecular beam deposition has been studied by grazing incidence x-ray reflectometry (GIXR) and atomic force microscopy. The electronic density profile is consistent with a structure formed by successive monolayers of molecules in the α form with the b axis lying in the substrate surface plane. The authors present an electronic density profile model of CuPc films grown on SiO2/Si. The excellent agreement between the model and experimental data allows postdeposition monitoring of the internal structure of the CuPc films with the nondestructive GIXR technique, providing a tool for accurate control of CuPc growth on silicon-based substrates. In addition, since the experiments have been carried out ex situ, they show that these structures can endure ambient conditions.

Simulating phosphorus removal from a vertical-flow constructed wetland grown with C alternifolius species

Treesearch

Ying Ouyang; Lihua Cui; Gary Feng; John Read

2015-01-01

Vertical flow constructed wetland (VFCW) is a promising technique for removal of excess nutrients and certain pollutants from wastewaters. The aim of this study was to develop a STELLA (structural thinking, experiential learning laboratory with animation) model for estimating phosphorus (P) removal in an artificial VFCW (i.e., a substrate column with six zones) grown...

Identification of phanerosporic acid in birch degraded by Phanerochaete chrysosporium

Treesearch

Michael D. Mozuch; Philip J. Kersten

2003-01-01

Extracts of Phanerochaete chrysosporium cultures grown on birch or on a malt extract-peptone-glucose agar medium were analysed by HPLC. A major component from the two sources appears to be identical by HPLC and UV- visible spectrometry. The product isolated from agar-grown cultures was purified to apparent homogeneity and structure analysis by NMR indicates that the...

ZnO nanostructures directly grown on paper and bacterial cellulose substrates without any surface modification layer.

PubMed

Costa, Saionara V; Gonçalves, Agnaldo S; Zaguete, Maria A; Mazon, Talita; Nogueira, Ana F

2013-09-21

In this report, hierarchical ZnO nano- and microstructures were directly grown for the first time on a bacterial cellulose substrate and on two additional different papers by hydrothermal synthesis without any surface modification layer. Compactness and smoothness of the substrates are two important parameters that allow the growth of oriented structures.

Crystal growth, structural, optical, spectral and thermal studies of tris(L-phenylalanine)L-phenylalaninium nitrate: a new organic nonlinear optical material.

PubMed

Prakash, M; Geetha, D; Lydia Caroline, M

2011-10-15

Tris(L-phenylalanine)L-phenylalaninium nitrate, C(9)H(12)NO(2)(+)·NO(3)(-)·3C(9)H(11)NO(2) (TPLPN), a new organic nonlinear optical material was grown from aqueous solution by slow evaporation solution growth at room temperature. The grown crystals were subjected to powder X-ray diffraction and single crystal X-ray diffraction studies to confirm the crystalline nature and crystal structure. The modes of vibration of different molecular groups present in TPLPN have been identified by FTIR spectral analysis. The presence of hydrogen and carbon in the grown crystal were confirmed by using proton and carbon nuclear magnetic resonance (NMR) spectral analyses. The optical transmission spectral study establishes good transmitting ability of the crystal in the entire visible region. The thermogravimetric (TG) and differential thermal analyses (DTA) were carried out to understand the thermal stability of the sample. The nonlinear optical property of the compound observed using Kurtz powder second harmonic generation test assets the suitability of the grown material for the frequency conversion of laser radiation of Nd:YAG. Copyright © 2011 Elsevier B.V. All rights reserved.

Sn - Induced decomposition of SiGeSn alloys grown on Si by molecular-beam epitaxy

NASA Astrophysics Data System (ADS)

Talochkin, A. B.; Timofeev, V. A.; Gutakovskii, A. K.; Mashanov, V. I.

2017-11-01

Structural features of Si1-x-yGexSny alloy layers grown on Si by molecular-beam epitaxy are studied. These layers with the thickness of 2.0 nm, the nominal Ge composition of x0 ≈ 0.3, and the Sn-content of y ≈ 2-6 at.% have been grown at low temperatures (100-150 °C). We have used high-resolution transmission electron microscopy to analyze atomic structure of grown layers and Raman spectroscopy to evaluate the real Ge-content x from the observed optical phonon frequencies. It is found that the x value coincides with the nominal one at low Sn-content (2-3 at.%), and when it is increased (y ≥ 5 at.%), the decomposition of alloys into two fractions occurs. One of them is enriched by Ge with x up to 0.6 and the other fraction is Si-enriched. It is shown that the observed decomposition is Sn-induced and related to increase in Ge adatoms mobility in the growth process. This mechanism is similar to that theoretically predicted by Venezuela and Tersoff (Phys. Rev. 58, 10871 (1998)) for the case of high growth temperature.

Single crystal growth and characterization of kagomé-lattice shandites Co3Sn2-xInxS2

NASA Astrophysics Data System (ADS)

Kassem, Mohamed A.; Tabata, Yoshikazu; Waki, Takeshi; Nakamura, Hiroyuki

2015-09-01

Single crystals of the shandite-type half metallic ferromagnet Co3Sn2S2, and its In-substituted compounds, Co3Sn2-xInxS2 (0

Ultrathin type-II GaSb/GaAs quantum wells grown by OMVPE

NASA Astrophysics Data System (ADS)

Pitts, O. J.; Watkins, S. P.; Wang, C. X.; Stotz, J. A. H.; Meyer, T. A.; Thewalt, M. L. W.

2004-09-01

Heterostructures containing monolayer (ML) and submonolayer GaSb insertions in GaAs were grown using organometallic vapour phase epitaxy. At the GaAs-on-GaSb interface, strong intermixing occurs due to the surface segregation of Sb. To form structures with relatively abrupt interfaces, a flashoff growth sequence, in which growth interruptions are employed to desorb Sb from the surface, was introduced. Reflectance-difference spectroscopy and high-resolution X-ray diffraction data demonstrate that interfacial grading is strongly reduced by this procedure. For layer structures grown with the flashoff sequence, a GaSb coverage up to 1 ML can be obtained in the two-dimensional (2D) growth mode. For uncapped GaSb layers, on the other hand, atomic force microscope images show that the 2D-3D growth mode transition occurs at a submonolayer coverage between 0.3 and 0.5 ML. Low-temperature photoluminescence spectra of multiple quantum well samples grown using the flashoff sequence show a strong quantum well-related peak which shifts to lower energies as the amount of Sb incorporated increases. The PL peak energies are consistent with a type-II band lineup at the GaAs/GaSb interface.

Effect of annealing time and NH3 flow on GaN films deposited on amorphous SiO2 by MOCVD

NASA Astrophysics Data System (ADS)

Li, Tianbao; Liu, Chenyang; Zhang, Zhe; Yu, Bin; Dong, Hailiang; Jia, Wei; Jia, Zhigang; Yu, Chunyan; Xu, Bingshe

2018-05-01

GaN polycrystalline films were successfully grown on amorphous SiO2 by metal-organic chemical vapour deposition to fabricate transferable devices using inorganic films. Field-emission scanning electron microscopy images show that by prolonging the annealing time, re-evaporation is enhanced, which reduced the uniformity of the nucleation layer and GaN films. X-ray diffraction patterns indicate that the decomposition rate of the nucleation layer increases when the annealing flow rate of NH3 is 500 sccm, which makes the unstable plane and amorphous domains decompose rapidly, thereby improving the crystallinity of the GaN films. Photoluminescence spectra also indicate the presence of fewer defects when the annealing flow rate of NH3 is 500 sccm. The excellent crystal structure of the GaN films grown under optimized conditions was revealed by transmission electron microscopy analysis. More importantly, the crystal structure and orientation of GaN grown on SiO2 are the same as that of GaN grown on conventional sapphire substrate when a buffer layer is used. This work can aid in the development of transferable devices using GaN films.

Structural differences between native Hen egg white lysozyme and its fibrils under different environmental conditions

NASA Astrophysics Data System (ADS)

Bhattacharya, Susmita; Ghosh, Sudeshna; Dasgupta, Swagata; Roy, Anushree

2013-10-01

The difference in molecular structure of native HEWL and its fibrils, grown at a pH value near physiological pH 7.4 and at a pH value just above the pI, 10.7 in presence and absence of Cu(II) ions, is discussed. We focus on differences between the molecular structure of the native protein and fibrils using principal component analysis of their Raman spectra. The overlap areas of the scores of each species are used to quantify the difference in the structure of the native HEWL and fibrils in different environments. The overall molecular structures are significantly different for fibrils grown at two pH values. However, in presence of Cu(II) ions, the fibrils have similarities in their molecular structures at these pH environments. Spectral variation within each species, as obtained from the standard deviations of the scores in PCA plots, reveals the variability in the structure within a particular species.

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

Ying, Minju, E-mail: mjying@bnu.edu.cn, E-mail: g.gehring@sheffield.ac.uk; Key Laboratory of Beam Technology and Material Modification of Ministry of Education, College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875; Blythe, Harry J.

We investigate the magnetic properties of ZnCoO thin films grown by pulsed laser deposition (PLD) from targets made containing metallic Co or CoO precursors instead of the usual Co{sub 3}O{sub 4}. We find that the films grown from metallic Co precursors in an oxygen rich environment contain negligible amounts of Co metal and have a large magnetization at room temperature. Structural analysis by X-ray diffraction and magneto-optical measurements indicate that the enhanced magnetism is due, in part, from Zn vacancies that partially compensate the naturally occurring n-type defects. We conclude that strongly magnetic films of Zn{sub 0.95}Co{sub 0.05}O that domore » not contain metallic cobalt can be grown by PLD from Co-metal-precursor targets if the films are grown in an oxygen atmosphere.« less

Studies on the growth aspects, structural, thermal, dielectric and third order nonlinear optical properties of solution grown 4-methylpyridinium p-nitrophenolate single crystal

NASA Astrophysics Data System (ADS)

Devi, S. Reena; Kalaiyarasi, S.; Zahid, I. MD.; Kumar, R. Mohan

2016-11-01

An ionic organic optical crystal of 4-methylpyridinium p-nitrophenolate was grown from methanol by slow evaporation method at ambient temperature. Powder and single crystal X-ray diffraction studies revealed the crystal system and its crystalline perfection. The rocking curve recorded from HRXRD study confirmed the crystal quality. FTIR spectral analysis confirmed the functional groups present in the title compound. UV-visible spectral study revealed the optical window and band gap of grown crystal. The thermal, electrical and surface laser damage threshold properties of harvested crystal were examined by using TGA/DTA, LCR/Impedance Analyzer and Nd:YAG laser system respectively. The third order nonlinear optical property of grown crystal was elucidated by Z-scan technique.

Photoluminescence of ZnTe/ZnMgTe multiple quantum well structures grown on ZnTe substrates by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Tanaka, Tooru; Ohshita, Hiroshi; Saito, Katsuhiko; Guo, Qixin

2018-02-01

Photoluminescence (PL) properties of ZnTe/ZnMgTe quantum well (QW) structures grown by molecular beam epitaxy (MBE) were investigated systematically with respect to well widths and Mg contents. Observed PL peak energies were consistent well with the calculated emission energies of the QWs considering a lattice distortion in the ZnTe well. From the temperature dependence of PL intensity, it was found that a suppression of a carrier escape from QW is crucial to obtain a PL at higher temperature in the ZnTe/ZnMgTe QW. Based on the results, multiple quantum well structures were designed and fabricated, which exhibited a green PL at room temperature.

Structural, morphological and electronic properties of pulsed laser grown Eu2O3 thin films

NASA Astrophysics Data System (ADS)

Kumar, Sandeep; Prakash, Ram; Choudhary, R. J.; Phase, D. M.

2018-05-01

Herein, we report the growth, structural, morphological and electronic properties of Europium sesquioxide (Eu2O3) thin films on Si [1 0 0] substrate using pulsed laser deposition technique. The films were deposited at ˜750 °C substrate temperature while the oxygen partial pressure (OPP) was varied (vacuum,˜1 mTorr, ˜10 mTorr and ˜300 mTorr). X-ray diffraction results confirm the single phase cubic structure of the film grown at ˜300 mTorr. The XRD results are also supported by the Raman's spectroscopy results. Eu-3d XPS core level spectra confirms the dominant contributions from the "3+" states of Eu in the film.

The effect of induced strains on photoluminescence properties of ZnO nanostructures grown by thermal evaporation method

NASA Astrophysics Data System (ADS)

Arjmand, Yaser; Eshghi, Hosein

2016-03-01

In this paper, ZnO nanostructures have been synthesized by thermal evaporation process using metallic zinc powder in the presence of oxygen on p-Si (100) at different distances from the boat. The structural and optical characterizations have been carried out. The morphological study shows various shape nanostructures. XRD data indicate that all samples have a polycrystalline wurtzite hexagonal structure in such a way that the closer sample has a preferred orientation along (101) while the ones farther are grown along (002) direction. From the structural and optical data analysis, we found that the induced strains are the main parameter controlling the UV/green peaks ratios in the PL spectra of the studied samples.

Hybrid Organic/ZnO p-n Junctions with n-Type ZnO Grown by Atomic Layer Deposition

NASA Astrophysics Data System (ADS)

Łuka, G.; Krajewski, T.; Szczerbakow, A.; Łusakowska, E.; Kopalko, K.; Guziewicz, E.; Wachnicki, Ł.; Szczepanik, A.; Godlewski, M.; Fidelus, J. D.

2008-11-01

We report on fabrication of hybrid inorganic-on-organic thin film structures with polycrystalline zinc oxide films grown by atomic layer deposition technique. ZnO films were deposited on two kinds of thin organic films, i.e. pentacene and poly(dimethylosiloxane) elastomer with a carbon nanotube content (PDMS:CNT). Surface morphology as well as electrical measurements of the films and devices were analyzed. The current density versus voltage (I-V) characteristics of ITO/pentacene/ZnO/Au structure show a low-voltage switching phenomenon typical of organic memory elements. The I-V studies of ITO/PDMS:CNT/ZnO/Au structure indicate some charging effects in the system under applied voltages.

Morphology and Structural Characterization of Carbon Nanowalls Grown via VHF-PECVD

NASA Astrophysics Data System (ADS)

Akmal Hasanudin, M.; Wahab, Y.; Ismail, A. K.; Zahid Jamal, Z. A.

2018-03-01

A 150 MHz very high frequency plasma enhanced chemical vapor deposition (150 MHz VHF-PECVD) system was utilized to fabricate two-dimensional carbon nanostructure from the mixture of methane and hydrogen. Morphology and structural properties of the grown nanostructure were investigated by FESEM imaging and Raman spectroscopy. Carbon nanowalls (CNW) with dense and wavy-like structure were successfully synthesized. The wavy-like morphology of CNW was found to be more distinct during growth at small electrode spacing and denser with increasing deposition time due to better flux of hydrocarbon radicals to the substrate and higher rate of reaction, respectively. Typical characteristics of CNW were observed from strong D band, narrow bandwidth of G band and single broad peak of 2D band of Raman spectra indicating the presence of disordered nanocrystalline graphite structure with high degree of graphitization.

Fe Oxides on Ag Surfaces: Structure and Reactivity

DOE PAGES

Shipilin, M.; Lundgren, E.; Gustafson, J.; ...

2016-09-09

One layer thick iron oxide films are attractive from both applied and fundamental science perspectives. The structural and chemical properties of these systems can be tuned by changing the substrate, making them promising materials for heterogeneous catalysis. In the present work, we investigate the structure of FeO(111) monolayer films grown on Ag(100) and Ag(111) substrates by means of microscopy and diffraction techniques and compare it with the structure of FeO(111) grown on other substrates reported in literature. We also study the NO adsorption properties of FeO(111)/Ag(100) and FeO(111)/Ag(111) systems utilizing different spectroscopic techniques. Finally, we discuss similarities and differences inmore » the data obtained from adsorption experiments and compare it with previous results for FeO(111)/Pt(111).« less

Fe Oxides on Ag Surfaces: Structure and Reactivity

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

Shipilin, M.; Lundgren, E.; Gustafson, J.

One layer thick iron oxide films are attractive from both applied and fundamental science perspectives. The structural and chemical properties of these systems can be tuned by changing the substrate, making them promising materials for heterogeneous catalysis. In the present work, we investigate the structure of FeO(111) monolayer films grown on Ag(100) and Ag(111) substrates by means of microscopy and diffraction techniques and compare it with the structure of FeO(111) grown on other substrates reported in literature. We also study the NO adsorption properties of FeO(111)/Ag(100) and FeO(111)/Ag(111) systems utilizing different spectroscopic techniques. Finally, we discuss similarities and differences inmore » the data obtained from adsorption experiments and compare it with previous results for FeO(111)/Pt(111).« less

Growth of ZnMgTe/ZnTe waveguide structures on ZnTe (0 0 1) substrates by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Kumagai, Y.; Imada, S.; Baba, T.; Kobayashi, M.

2011-05-01

ZnMgTe/ZnTe/ZnMgTe layered structures were grown on (0 0 1) ZnTe substrates by molecular beam epitaxy. This structure was designed to apply to waveguides in various optoelectronic devices to reduce light loss. Since the lattice mismatch between ZnTe and ZnMgTe was not negligible, the critical layer thickness (CLT) was theoretically derived. Structures with varying Mg composition and layer thickness of ZnMgTe cladding layer were grown and examined for crystal quality with respect to theoretical data. The crystal quality was investigated by means of cross sectional transmission electron microscopy (TEM) and reciprocal space mapping (RSM). Optical confinements were observed by irradiating a laser beam from one end of the sample and monitoring the transmitted light from the other end.

H2 gas sensing properties of a ZnO/CuO and ZnO/CuO/Cu2O Heterostructures

NASA Astrophysics Data System (ADS)

Ababii, N.; Postica, V.; Hoppe, M.; Adelung, R.; Lupan, O.; Railean, S.; Pauporté, T.; Viana, B.

2017-03-01

The most important parameters of gas sensors are sensitivity and especially high selectivity to specific chemical species. To improve these parameters we developed sensor structures based on layered semiconducting oxides, namely CuO/Cu2O, CuO:Zn/Cu2O:Zn, NiO/ZnO. In this work, the ZnO/CuxO (where x = 1, 2) bi-layer heterostructure were grown via a simple synthesis from chemical solution (SCS) at relatively low temperatures (< 95 °C), representing a combination of layered n-type and p-type semiconducting oxides which are widely used as sensing material for gas sensors. The main advantages of the developed device structures are given by simplicity of the synthesis and technological cost-efficiency. Structural investigations showed high crystallinity of synthesized layers confirming the presence of zinc oxide nanostructures on the surface of the copper oxide film deposited on glass substrate. Structural changes in morphology of grown nanostructures induced by post-grown thermal annealing were observed by scanning electron microscopy (SEM) investigations, and were studied in detail. The influence of thermal annealing type on the optical properties was also investigated. As an example of practical applications, the ZnO/CuxO bi-layer heterojunctions and ZnO/CuO/Cu2O three-layered structures were integrated into sensor structures and were tested to different types of reducing gases at different operating temperatures (OPT), showing promising results for fabrication of selective gas sensors.

Interface properties of MIS structures based on hetero-epitaxial graded-gap Hg1-xCdxTe with CdTe interlayer created in situ during MBE growth

NASA Astrophysics Data System (ADS)

Voitsekhovskii, Alexander V.; Nesmelov, Sergey N.; Dzyadukh, Stanislav M.; Varavin, Vasily S.; Dvoretsky, Sergey A.; Mikhailov, Nikolay N.; Yakushev, Maksim V.; Sidorov, Georgy Yu.

2017-11-01

Heterostructures based on n-Hg1-xCdxTe (x = 0.23-0.40) with near-surface graded-gap layers were grown by molecular beam epitaxy on Si (013) substrates. At 77 K, the admittance of the In/Al2O3/Hg1-xCdxTe metal-insulator-semiconductor (MIS) structures with grown in situ CdTe intermediate layer and without such a layer was investigated. It has been established that MIS structures of In/Al2O3/Hg1-xCdxTe with an interlayer of in situ grown CdTe are characterized by the electrical strength of the dielectric and the qualitative interface. The hysteresis of the capacitive characteristics is practically absent within a small range of variation in the bias voltage. The density of fast surface states at the minimum does not exceed 2.2 × 1010 eV-1 cm-2. MIS structures of In/Al2O3/Hg1-xCdxTe without an intermediate layer of CdTe have significantly higher densities of fast and slow surface states, as well as lower values of the differential resistance of the space-charge region in the regime of strong inversion.

Morphology-controlled synthesis of grass-like GO-CdSe nanocomposites with excellent optical properties and field emission properties

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

Xie, Pei, E-mail: peipeixie@163.com; Xue, Shaolin, E-mail: slxue@dhu.edu.cn; Wei, Jia, E-mail: Jojo.1125@hotmail.com

2016-02-15

Four different morphologies of the CdSe semiconductor nanograss have been successfully grown on graphene oxide (GO) sheets via hydrothermal method at 220 °C for 12 h. The morphologies, structures, chemical compositions and optical properties of the as-obtained GO-CdSe nanocomposites were characterized by XRD, SEM, TEM, EDS, XPS and Raman spectra. It was found that the EDTA/Cd{sup 2+} molar ratio is important for the formation of morphology of GO-CdSe nanocomposites. The results of XRD revealed that all the as-obtained GO-CdSe nanocomposites have zinc blend structure. Room temperature photoluminescence (PL) showed that the sample emits red light under different excitation wavelengths. Themore » results of Raman spectra, EDS and XPS showed that the CdSe nanograss is grown on GO sheets. The results showed that GO-CdSe nanocomposites composed of nanorods have best field emission (FE) properties with a low turn-on electric field of 4.14 V μm{sup −1} and a high field enhancement factor of 3315 among all the samples. - Graphical abstract: SEM images of as-synthesized CdSe nanograss grown on GO sheets. Room temperature PL emission spectra of the as-synthesized CdSe nanograss grown on GO sheets. Field emission J–E curve of the as-synthesized CdSe nanograss grown on GO sheets. - Highlights: • Novel CdSe nanograsses are grown on graphene oxide sheets by hydrothermal method. • The morphology of CdSe nanograsses is controlled by adjusting EDTA/Cd{sup 2+} molar ratio. • The FE performance of sample is investigated. • Optimum morphology for FE performance is CdSe nanograsses composed of nanorods on GO.« less

Synthesis and properties of ultra-long InP nanowires on glass.

PubMed

Dhaka, Veer; Pale, Ville; Khayrudinov, Vladislav; Kakko, Joona-Pekko; Haggren, Tuomas; Jiang, Hua; Kauppinen, Esko; Lipsanen, Harri

2016-12-16

We report on the synthesis of Au-catalyzed InP nanowires (NWs) on low-cost glass substrates. Ultra-dense and ultra-long (up to ∼250 μm) InP NWs, with an exceptionally high growth rate of ∼25 μm min -1 , were grown directly on glass using metal organic vapor phase epitaxy (MOVPE). Structural properties of InP NWs grown on glass were similar to the ones grown typically on Si substrates showing many structural twin faults but the NWs on glass always exhibited a stronger photoluminescence (PL) intensity at room temperature. The PL measurements of NWs grown on glass reveal two additional prominent impurity related emission peaks at low temperature (10 K). In particular, the strongest unusual emission peak with an activation energy of 23.8 ± 2 meV was observed at 928 nm. Different possibilities including the role of native defects (phosphorus and/or indium vacancies) are discussed but most likely the origin of this PL peak is related to the impurity incorporation from the glass substrate. Furthermore, despite the presence of suspected impurities, the NWs on glass show outstanding light absorption in a wide spectral range (60%-95% for λ = 300-1600 nm). The optical properties and the NW growth mechanism on glass is discussed qualitatively. We attribute the exceptionally high growth rate mostly to the atmospheric pressure growth conditions of our MOVPE reactor and stronger PL intensity on glass due to the impurity doping. Overall, the III-V NWs grown on glass are similar to the ones grown on semiconductor substrates but offer additional advantages such as low-cost and light transparency.

Epitaxial Gd2O3 on GaN and AlGaN: a potential candidate for metal oxide semiconductor based transistors on Si for high power application

NASA Astrophysics Data System (ADS)

Ghosh, Kankat; Das, S.; Khiangte, K. R.; Choudhury, N.; Laha, Apurba

2017-11-01

We report structural and electrical properties of hexagonal Gd2O3 grown epitaxially on GaN/Si (1 1 1) and AlGaN/GaN/Si(1 1 1) virtual substrates. GaN and AlGaN/GaN heterostructures were grown on Si(1 1 1) substrates by plasma assisted molecular beam epitaxy (PA-MBE), whereas the Gd2O3 layer was grown by the pulsed laser ablation (PLA) technique. Initial structural characterizations show that Gd2O3 grown on III-nitride layers by PLA, exhibit a hexagonal structure with an epitaxial relationship as {{≤ft[ 0 0 0 1 \\right]}G{{d2}{{O}3}}}||{{≤ft[ 0 0 0 1 \\right]}GaN} and {{≤ft[ 1 \\bar{1} 0 0 \\right]}G{{d2}{{O}3}}}||{{≤ft[ 1 \\bar{1} 0 0 \\right]}GaN} . X-ray photoelectron measurements of the valence bands revealed that Gd2O3 exhibits band offsets of 0.97 eV and 0.4 eV, for GaN and Al0.3Ga0.7N, respectively. Electrical measurements such as capacitance-voltage and leakage current characteristics further confirm that epi-Gd2O3 on III-nitrides could be a potential candidate for future metal-oxide-semiconductor (MOS)-based transistors also for high power applications in radio frequency range.

Effects of substrate on the structure and orientation of ZnO thin film grown by rf-magnetron sputtering

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

Liu, H. F.; Chua, S. J.; Hu, G. X.

2007-10-15

X-ray diffractions, Nomarski microscopy, scanning electron microscopy, and photoluminescence have been used to study the effects of substrate on the structure and orientation of ZnO thin films grown by rf-magnetron sputtering. GaAs(001), GaAs(111), Al{sub 2}O{sub 3}(0002) (c-plane), and Al{sub 2}O{sub 3}(1102) (r-plane) wafers have been selected as substrates in this study. X-ray diffractions reveal that the ZnO film grown on GaAs(001) substrate is purely textured with a high c-axis orientation while that grown on GaAs(111) substrate is a single ZnO(0002) crystal; a polycrystalline structure with a large-single-crystal area of ZnO(0002) is obtained on a c-plane Al{sub 2}O{sub 3} substrate whilemore » a ZnO(1120) single crystal is formed on an r-plane Al{sub 2}O{sub 3} substrate. There is absence of significant difference between the photoluminescence spectra collected from ZnO/GaAs(001), ZnO/GaAs(111), and ZnO/Al{sub 2}O{sub 3}(0002), while the photoluminescence from ZnO/Al{sub 2}O{sub 3}(1102) shows a reduced intensity together with an increased linewidth, which is, likely, due to the increased incorporation of native defects during the growth of ZnO(1120)« less

Spatial inhomogeneities in Al x Ga1-x N quantum wells induced by the surface morphology of AlN/sapphire templates

NASA Astrophysics Data System (ADS)

Zeimer, Ute; Jeschke, Joerg; Mogilatenko, Anna; Knauer, Arne; Kueller, Viola; Hoffmann, Veit; Kuhn, Christian; Simoneit, Tino; Martens, Martin; Wernicke, Tim; Kneissl, Michael; Weyers, Markus

2015-11-01

The effects of the template on the optical and structural properties of Al0.75Ga0.25N/Al0.8Ga0.2N multiple quantum well (MQWs) laser active regions have been investigated. The laser structures for optical pumping were grown on planar c-plane AlN/sapphire as well as on thick epitaxially laterally overgrown (ELO) AlN layers on patterned AlN/sapphire. Two ELO AlN/sapphire templates were investigated, one with a miscut of the sapphire surface to the m-direction with an angle of 0.25°, the other with a miscut angle of 0.25° to the sapphire a-direction. The MQWs are studied by atomic force microscopy, plan-view cathodoluminescence (CL) at room temperature and 83 K as well as transmission electron microscopy using high-angle annular dark-field imaging and energy-dispersive x-ray spectroscopy. The results are compared to optical pumping measurements. It was found that the surface morphology of the templates determines the lateral wavelength distribution in the MQWs observed by spectral CL mappings. The lateral wavelength spread is largest for the laser structures grown on ELO AlN with miscut to sapphire a-direction caused by the local variation of the MQW thicknesses and the Ga incorporation at macrosteps on the ELO-AlN. A CL peak wavelength spread of up to 7 nm has been found. The MQWs grown on planar AlN/sapphire templates show a homogeneous wavelength distribution. However, due to the high threading dislocation density and the resulting strong nonradiative recombination, laser operation could not be achieved. The laser structures grown on ELO AlN/sapphire show optically pumped lasing with a record short wavelength of 237 nm.

Study on structural, morphological, optical and thermal properties of guanidine carbonate doped nickel sulfate hexahydrate crystal.

PubMed

Silambarasan, A; Rajesh, P; Ramasamy, P

2015-01-05

The single crystal of guanidine carbonate doped nickel sulfate hexahydrate was grown from solution for ultraviolet filters. The single crystal XRD confirms that the grown single crystal belongs to the tetragonal system with the space group of P4₁2₁2. The crystallinity of the grown crystal was estimated by powder X-ray diffraction studies. The optical transmission and thermal stability of as-grown guanidine carbonate doped nickel sulfate single crystals have been studied. The optical transmission spectrum demonstrates the characteristics of ultraviolet filters. The TG/DTA studies confirm the thermal properties of grown crystals. Thermo-gravimetric analysis showed that the dehydration temperature of the guanidine carbonate doped nickel sulfate crystal is about 100 °C, which is much higher than that of pure nickel sulfate hexahydrate (NSH) crystals which is 72 °C. The growth behaviors and dislocation density were detected under the high resolution XRD and etching studies respectively. Copyright © 2014 Elsevier B.V. All rights reserved.

Habit modification of bis-thiourea zinc chloride (ZTC) semi organic crystals by impurities

NASA Astrophysics Data System (ADS)

Ruby Nirmala, L.; Thomas Joseph Prakash, J.

2013-06-01

Single crystals of bis-thiourea zinc chloride (ZTC) doped with metal ion (Li+) possess excellent nonlinear optical properties. These crystals were grown by slow evaporation solution growth technique. The effect of Li+ dopant on the growth and properties of ZTC single crystal were investigated and reported. The grown crystals were crystallized in orthorhombic structure with non-centro symmetric space group Pn21a through the parent compound. The amount of dopant incorporated in the parent crystal was revealed by the inductively coupled plasma (ICP-OES) studies. The FT-IR spectroscopy study was done for finding and confirming the functional groups present in the compound. The UV-Visible spectral study was carried out to find the optical behavior and transparency nature of the grown crystal. TG/DTA measurements and Vickers microhardness measurements were traced to find out the thermal and mechanical stability of the grown crystals respectively. Using Nd:YAG laser, the Second harmonic generation (SHG) for the grown crystals were confirmed.

Habit modification of bis-thiourea zinc chloride (ZTC) semi organic crystals by impurities.

PubMed

Ruby Nirmala, L; Thomas Joseph Prakash, J

2013-06-01

Single crystals of bis-thiourea zinc chloride (ZTC) doped with metal ion (Li(+)) possess excellent nonlinear optical properties. These crystals were grown by slow evaporation solution growth technique. The effect of Li(+) dopant on the growth and properties of ZTC single crystal were investigated and reported. The grown crystals were crystallized in orthorhombic structure with non-centro symmetric space group Pn21a through the parent compound. The amount of dopant incorporated in the parent crystal was revealed by the inductively coupled plasma (ICP-OES) studies. The FT-IR spectroscopy study was done for finding and confirming the functional groups present in the compound. The UV-Visible spectral study was carried out to find the optical behavior and transparency nature of the grown crystal. TG/DTA measurements and Vickers microhardness measurements were traced to find out the thermal and mechanical stability of the grown crystals respectively. Using Nd:YAG laser, the Second harmonic generation (SHG) for the grown crystals were confirmed. Copyright © 2013 Elsevier B.V. All rights reserved.

Growth, structural, spectral, mechanical, thermal and dielectric characterization of phosphoric acid admixtured L-alanine (PLA) single crystals.

PubMed

Rose, A S J Lucia; Selvarajan, P; Perumal, S

2011-10-15

Phosphoric acid admixtured L-alanine (PLA) single crystals were grown successfully by solution method with slow evaporation technique at room temperature. Crystals of size 18 mm×12 mm×8 mm have been obtained in 28 days. The grown crystals were colorless and transparent. The solubility of the grown samples has been found out at various temperatures. The lattice parameters of the grown crystals were determined by X-ray diffraction technique. The reflection planes of the sample were confirmed by the powder X-ray diffraction study and diffraction peaks were indexed. Fourier transform infrared (FTIR) studies were used to confirm the presence of various functional groups in the crystals. UV-visible transmittance spectrum was recorded to study the optical transparency of grown crystal. The nonlinear optical (NLO) property of the grown crystal was confirmed by Kurtz-Perry powder technique and a study of its second harmonic generation efficiency in comparison with potassium dihydrogen phosphate (KDP) has been made. The mechanical strength of the crystal was estimated by Vickers hardness test. The grown crystals were subjected to thermo gravimetric and differential thermal analysis (TG/DTA). The dielectric behavior of the sample was also studied. Copyright © 2011 Elsevier B.V. All rights reserved.

Longleaf Pine Root System Development and Seedling Quality in Response to Copper Root Pruning and Cavity Size

Treesearch

Mary Anne Sword Sayer; Shi-Jean Susana Sung; James D. Haywood

2011-01-01

Cultural practices that modify root system structure in the plug of container-grown seedlings have the potential to improve root system function after planting. Our objective was to assess how copper root pruning affects the quality and root system development of longleaf pine seedlings grown in three cavity sizes in a greenhouse. Copper root pruning increased seedling...

Crystal growth, physical properties and computational insights of semi-organic non-linear optical crystal diphenylguanidinium perchlorate grown by conventional solvent evaporation method

NASA Astrophysics Data System (ADS)

Kajamuhideen, M. S.; Sethuraman, K.; Ramamurthi, K.; Ramasamy, P.

2018-02-01

A splendid nonlinear optical single crystals diphenylguanidinium perchlorate (DPGP) was lucratively grown by low cost solvent evaporation method with the dimensions of 8 × 4 × 2 mm3. Structural and morphological studies of grown crystal were confirmed using X-ray diffraction studies. The presence of diverse functional groups was identified using FTIR and RAMAN studies. The molecular structure of a grown crystal was inveterate by NMR studies. The optical transmittance of DPGP crystal was analyzed using UV-vis-NIR studies. Photoluminescence spectrum shows sharp, well defined emission peak at 388 nm. Thermal studies assign that adduct is stable with the melting point of 164 °C. Microhardness studies declare that DPGP crystal belongs to the soft material class and their yield strength and elastic stiffness constant values were evaluated. Photoconductivity studies revealed the negative photoconductive nature of DPGP crystal. Second harmonic generation (SHG) efficiency of the DPGP crystal was 1.4 times that of potassium dihydrogen phosphate. Etching studies were carried out for different etching time. The dielectric studies were performed at different frequency. Laser damage threshold properties of DPGP crystal were examined using Nd:YAG laser system. The HOMO-LUMO energy gap evident the charge transfer interaction of the molecule. The calculated first order hyperpolarizability value is 5 times greater than that of urea. Thus, the grown DPGP single crystals are well suited for NLO device fabrications.

Development and photoelectric properties of In/p-Ag{sub 3}AsS{sub 3} surface-barrier structures

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

Rud', V. Yu., E-mail: rudvas@spbstu.ru; Rud', Yu. V.; Terukov, E. I.

2010-08-15

Homogeneous p-Ag{sub 3}AsS{sub 3} bulk single crystals with rhombic structure have been grown by planar crystallization from melts with atomic composition corresponding to this ternary compound. Photosensitive surface-barrier structures based on the interface between the surface of these crystals and thin films of pure indium are fabricated for the first time. The photosensitivity of fabricated structures is studied in natural and linearly polarized light. Photosensitivity spectra of In/p-Ag{sub 3}AsS{sub 3} structures are measured for the first time and used to determine the nature and energy of interband transitions in p-Ag{sub 3}AsS{sub 3} crystals. The phenomenon of natural photopleochroism is studiedmore » for surface-barrier structures grown on oriented p-Ag{sub 3}AsS{sub 3} single crystals. It is concluded that Ag{sub 3}AsS{sub 3} single crystals can be used in photoconverters of natural and linearly polarized light.« less

Fabrication of in-situ grown graphene reinforced Cu matrix composites

NASA Astrophysics Data System (ADS)

Chen, Yakun; Zhang, Xiang; Liu, Enzuo; He, Chunnian; Shi, Chunsheng; Li, Jiajun; Nash, Philip; Zhao, Naiqin

2016-01-01

Graphene/Cu composites were fabricated through a graphene in-situ grown approach, which involved ball-milling of Cu powders with PMMA as solid carbon source, in-situ growth of graphene on flaky Cu powders and vacuum hot-press sintering. SEM and TEM characterization results indicated that graphene in-situ grown on Cu powders guaranteed a homogeneous dispersion and a good combination between graphene and Cu matrix, as well as the intact structure of graphene, which was beneficial to its strengthening effect. The yield strength of 244 MPa and tensile strength of 274 MPa were achieved in the composite with 0.95 wt.% graphene, which were separately 177% and 27.4% enhancement over pure Cu. Strengthening effect of in-situ grown graphene in the matrix was contributed to load transfer and dislocation strengthening.

Bridgman growth of lead potassium niobate crystals

NASA Astrophysics Data System (ADS)

Fan, Shiji; Sun, Renying; Lin, Yafang; Wu, Jindi

1999-03-01

Lead potassium niobate Pb 2KNb 5O 15 (PKN) crystals with tetragonal tungsten bronze (TTB) structure have been grown by the modified Bridgman (BR) method. Nearly sealed Pt crucibles and small temperature gradients in the Bridgman furnace can limit volatilization of PbO and cracking of as-grown PKN crystals. Transparent PKN crystals of 1 inch diameter by ˜2 inch length with brownish color have been grown successfully at a crucible lowering rate <0.5 mm/h and a temperature gradient of 10-15°C/cm across the solid-liquid interface. Coupling between twins and growth directions of the crystal is also discussed.

Substrate nitridation induced modulations in transport properties of wurtzite GaN/p-Si (100) heterojunctions grown by molecular beam epitaxy

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

Bhat, Thirumaleshwara N.; Rajpalke, Mohana K.; Krupanidhi, S. B.

Phase pure wurtzite GaN films were grown on Si (100) substrates by introducing a silicon nitride layer followed by low temperature GaN growth as buffer layers. GaN films grown directly on Si (100) were found to be phase mixtured, containing both cubic ({beta}) and hexagonal ({alpha}) modifications. The x-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy studies reveal that the significant enhancement in the structural as well as in the optical properties of GaN films grown with silicon nitride buffer layer grown at 800 deg. C when compared to the samples grown in the absence of silicon nitridemore » buffer layer and with silicon nitride buffer layer grown at 600 deg. C. Core-level photoelectron spectroscopy of Si{sub x}N{sub y} layers reveals the sources for superior qualities of GaN epilayers grown with the high temperature substrate nitridation process. The discussion has been carried out on the typical inverted rectification behavior exhibited by n-GaN/p-Si heterojunctions. Considerable modulation in the transport mechanism was observed with the nitridation conditions. The heterojunction fabricated with the sample of substrate nitridation at high temperature exhibited superior rectifying nature with reduced trap concentrations. Lowest ideality factors ({approx}1.5) were observed in the heterojunctions grown with high temperature substrate nitridation which is attributed to the recombination tunneling at the space charge region transport mechanism at lower voltages and at higher voltages space charge limited current conduction is the dominating transport mechanism. Whereas, thermally generated carrier tunneling and recombination tunneling are the dominating transport mechanisms in the heterojunctions grown without substrate nitridation and low temperature substrate nitridation, respectively.« less

Correlation between oxygen stoichiometry, structure, and opto-electrical properties in amorphous In2O3:H films

NASA Astrophysics Data System (ADS)

Koida, Takashi; Shibata, Hajime; Kondo, Michio; Tsutsumi, Koichi; Sakaguchi, Akio; Suzuki, Michio; Fujiwara, Hiroyuki

2012-03-01

We have characterized amorphous In2O3:H (H : ˜4 at.%) transparent conducting films by Rutherford backscattering spectrometry (RBS), thermal desorption spectroscopy, spectroscopic ellipsometry, and Hall measurements. The amorphous In2O3:H films have been fabricated at room temperature by sputtering of an In2O3 ceramic target under Ar, O2, and H2O vapor with variation of a flow ratio r(O2) = O2/(O2+Ar). We observe (i) signals originating from Ar in RBS spectra for all the films and (ii) desorption of H2O and Ar gases during post thermal annealing of the films. Furthermore, O2 desorption together with H2O and Ar is observed for the films grown at r(O2) > 0.375%, whereas In desorption together with H2O and Ar is observed for the films grown at r(O2) < 0.375%. These results suggest that the films have void and/or multi-vacancy rich structures inside the amorphous network, and the variety of atoms, such as Ar, H2O, and weakly bonded O and In, is present in the void structures for the films grown at O2-rich and O2-poor conditions, respectively. Corresponding to the structural changes, optical and electrical properties also change at r(O2) = 0.375%. For the films grown at r(O2) < 0.375%, we observe a broad absorption in the visible wavelengths that cannot be explained by free carrier absorption. In this film, the carrier mobility reduces rapidly with increasing carrier density. Analysis of spectroscopic ellipsometry and Hall measurements reveals that a large decrease in mobility is due to a large increase in carrier effective mass, in addition to the effect of ionized impurity scattering. In this article, we discuss the optical and transport properties with the variation of oxygen stoichiometry and microscopic structures in the amorphous In2O3:H films.

A novel barium strontium titanate/nickel/titanium nitride/silicon structure for gigabit-scale DRAM capacitors

NASA Astrophysics Data System (ADS)

Ritums, Dwight Lenards

A materials system has been developed for advanced oxide high permittivity capacitors for use in Dynamic Random Access Memory (DRAM) applications. A capacitor test structure has been fabricated, demonstrating the integration of this materials system onto Si. It is a 3-D stacked electrode structure which uses the high-K dielectric material Ba1- xSrxTiO 3 (BST) and a novel Ni/TiN bottom electrode system. The structure was grown using pulsed laser deposition (PLD), photo-assisted metal-organic chemical vapor deposition (PhA-MOCVD), and electron beam deposition, and resulted in thin film capacitors with dielectric constants over 500. Other advanced oxides, principally SrVO3, were also investigated for use as electrode materials. The fabricated test structure is 3 μgm wide and 1 μm thick. RIE was used to generate the 3-D structure, and an etch gas recipe was developed to pattern the 3-D electrode structure onto the TiN. The Ni was deposited by electron beam deposition, and the BST was grown by PLD and PhA-MOCVD. Conformal coating of the electrode by the BST was achieved. The film structure was analyzed with XRD, SEM, EDS, XPS, AES, and AFM, and the electronic properties of the devices were characterized. Permittivites of up to 500 were seen in the PLD-grown films, and values up to 700 were seen in the MOCVD- deposited films. The proof of concept of a high permittivity material directly integrated onto Si has been demonstrated for this capacitor materials system. With further lithographic developments, this system can be applied toward gigabit device fabrication.

The nature of catalyst particles and growth mechanisms of GaN nanowires grown by Ni-assisted metal-organic chemical vapor deposition.

PubMed

Weng, Xiaojun; Burke, Robert A; Redwing, Joan M

2009-02-25

The structure and chemistry of the catalyst particles that terminate GaN nanowires grown by Ni-assisted metal-organic chemical vapor deposition were investigated using a combination of electron diffraction, high-resolution transmission electron microscopy, and x-ray energy dispersive spectrometry. The crystal symmetry, lattice parameter, and chemical composition obtained reveal that the catalyst particles are Ni(3)Ga with an ordered L 1(2) structure. The results suggest that the catalyst is a solid particle during growth and therefore favor a vapor-solid-solid mechanism for the growth of GaN nanowires under these conditions.

Nonlinear absorption in AlGaAs/GaAs multiple quantum well structures grown by metalorganic chemical vapor deposition

NASA Technical Reports Server (NTRS)

Lee, H. C.; Hariz, A.; Dapkus, P. D.; Kost, A.; Kawase, M.

1987-01-01

This paper reports the study of growth conditions for achieving the sharp exciton resonances and low-intensity saturation of these resonances in AlGaAs-GaAs multiple quantum well structures grown by metalorganic chemical vapor deposition. Low growth temperature is necessary to observe this sharp resonance feature at room temperature. The optimal growth conditions are a tradeoff between the high temperatures required for high quality AlGaAs and low temperatures required for high-purity GaAs. A strong optical saturation of the excitonic absorption has been observed. A saturation density as low as 250 W/sq cm is reported.

Rheed Investigation of Pd/Al Bimetallic System on KCl(001) Substrate

NASA Astrophysics Data System (ADS)

Masek, K.; Moroz, V.; Matolín, V.

Pd/Al alloys have very interesting properties from the point of view of their possible application in heterogeneous catalysis. Preparation of small heteroepitaxial Pd/Al alloy particles opens a new way in studies of the influence of Pd/Al crystallographic structure on the alloy catalytic properties. Pd/Al alloy particles were grown by the molecular beam epitaxy method. Their crystallographical structure was controlled by reflection high energy electron diffraction (RHEED). It was found that Pd deposited on epitaxial 3D Al particles grown on KCl is intermixing with Al. This process is accompanied by the variation of lattice parameter from the Al value to the Pd one.

Zinc oxide films chemically grown onto rigid and flexible substrates for TFT applications

NASA Astrophysics Data System (ADS)

Suchea, M.; Kornilios, N.; Koudoumas, E.

2010-10-01

This contribution presents some preliminary results regarding the use of a chemical route for the growth of good quality ZnO thin films that can be used for the fabrication of thin film transistors (TFTs). The films were grown at rather low temperature (60 °C) on glass and PET substrates using non-aqueous (zinc acetate dihydrate in methanol) precursor solution and their surface morphology, crystalline structure, optical transmittance and electrical characteristics were studied. The study indicated that good quality films with desirable ZnO structure onto rigid and flexible substrates can be obtained, using a simple, cheap, low temperature chemical growth method.

SPE-LEEM Studies on the Surface and Electronic Structure of 2-D Transition Metal Dichalcogenides (Part II)

NASA Astrophysics Data System (ADS)

Jin, Wencan; Yeh, Po-Chun; Zaki, Nader; Zhang, Datong; Sadowski, Jerzy; Al-Mahboob, Abdullah; van de Zande, Arend; Chenet, Daniel; Dadap, Jerry; Herman, Irving; Sutter, Peter; Hone, James; Osgood, Richard

2014-03-01

In this work, we studied the surface and electronic structure of monolayer and few-layer exfoliated MoS2 and WSe2, as well as chemical-vapor-deposition (CVD) grown MoS2, using Spectroscopic Photoemission and Low Energy Electron Microscope (SPE-LEEM). LEEM measurements reveal that, unlike exfoliated MoS2, CVD-grown MoS2 exhibits grain-boundary alterations due to surface strain. However, LEEM and micro-probe low energy electron diffraction show that the quality of CVD-grown MoS2 is comparable to that of exfoliated MoS2. Micrometer-scale angle-resolved photoemission spectroscopy (ARPES) measurement on exfoliated MoS2 and WSe2 single-crystals provides direct evidence for the shifting of the valence band maximum from Γ to K, when the layer number is thinned down to one, as predicted by density functional theory. Our measurements of the k-space resolved electronic structure allow for further comparison with other theoretical predictions and with transport measurements. This work is supported by DOE grant DE-FG 02-04-ER-46157, research carried out in part at the CFN and NSLS, Brookhaven National Laboratory.

Defect reduction in MBE-grown AlN by multicycle rapid thermal annealing

NASA Astrophysics Data System (ADS)

Greenlee, Jordan D.; Gunning, Brendan; Feigelson, Boris N.; Anderson, Travis J.; Koehler, Andrew D.; Hobart, Karl D.; Kub, Francis J.; Doolittle, W. Alan

2016-01-01

Multicycle rapid thermal annealing (MRTA) is shown to reduce the defect density of molecular beam epitaxially grown AlN films. No damage to the AlN surface occurred after performing the MRTA process at 1520°C. However, the individual grain structure was altered, with the emergence of step edges. This change in grain structure and diffusion of AlN resulted in an improvement in the crystalline structure. The Raman E2 linewidth decreased, confirming an improvement in crystal quality. The optical band edge of the AlN maintained the expected value of 6.2 eV throughout MRTA annealing, and the band edge sharpened after MRTA annealing at increased temperatures, providing further evidence of crystalline improvement. X-ray diffraction shows a substantial improvement in the (002) and (102) rocking curve FWHM for both the 1400 and 1520°C MRTA annealing conditions compared to the as-grown films, indicating that the screw and edge type dislocation densities decreased. Overall, the MRTA post-growth annealing of AlN lowers defect density, and thus will be a key step to improving optoelectronic and power electronic devices. [Figure not available: see fulltext.

High indium non-polar InGaN clusters with infrared sensitivity grown by PAMBE

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

Mukundan, Shruti; Mohan, Lokesh; Chandan, Greeshma

2015-03-15

Studies on the optical properties of InGaN alloy of relatively higher indium content are of potential interest to understand the effect of indium content on the optical band gap of epitaxial InGaN. We report the growth of self assembled non-polar high indium clusters of In{sub 0.55}Ga{sub 0.45}N over non-polar (11-20) a-plane In{sub 0.17}Ga{sub 0.83}N epilayer grown on a-plane (11-20)GaN/(1-102) r-plane sapphire substrate using plasma assisted molecular beam epitaxy (PAMBE). Such structures are potential candidates for high brightness LEDs emitting in longer wavelengths. The high resolution X-ray diffraction studies revealed the formation of two distinct compositions of In{sub x}Ga{sub 1−x}N alloys,more » which were further confirmed by photoluminescence studies. A possible mechanism for the formation of such structure was postulated which was supported with the results obtained by energy dispersive X-ray analysis. The structure hence grown when investigated for photo-detecting properties, showed sensitivity to both infrared and ultraviolet radiations due to the different composition of InGaN region.« less

Mechanisms of the micro-crack generation in an ultra-thin AlN/GaN superlattice structure grown on Si(110) substrates by metalorganic chemical vapor deposition

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

Shen, X. Q., E-mail: xq-shen@aist.go.jp; Takahashi, T.; Ide, T.

2015-09-28

We investigate the generation mechanisms of micro-cracks (MCs) in an ultra-thin AlN/GaN superlattice (SL) structure grown on Si(110) substrates by metalorganic chemical vapor deposition. The SL is intended to be used as an interlayer (IL) for relaxing tensile stress and obtaining high-quality crack-free GaN grown on Si substrates. It is found that the MCs can be generated by two different mechanisms, where large mismatches of the lattice constant (LC) and the coefficient of thermal expansion (CTE) play key roles in the issue. Different MC configurations (low-density and high-density MCs) are observed, which are considered to be formed during the differentmore » growth stages (SL growth and cooling down processes) due to the LC and the CTE effects. In-situ and ex-situ experimental results support the mechanism interpretations of the MCs generation. The mechanism understanding makes it possible to optimize the SL IL structure for growing high-quality crack-free GaN films on Si substrates for optical and electronic device applications.« less

Structural, quantum chemical, vibrational and thermal studies of a hydrogen bonded zwitterionic co-crystal (nicotinic acid: pyrogallol)

NASA Astrophysics Data System (ADS)

Prabha, E. Arockia Jeya Yasmi; Kumar, S. Suresh; Athimoolam, S.; Sridhar, B.

2017-02-01

In the present work, a new co-crystal of nicotinic acid with pyrogallol (NICPY) has been grown in the zwitterionic form and the corresponding structural, vibrational, thermal, solubility and anti-cancer characteristics have been reported. The single crystal X-ray diffraction analysis confirms that the structural molecular packing of the crystal stabilized through N-H⋯O and O-H⋯O hydrogen bond. The stabilization energy of the hydrogen bond motifs were calculated in the solid state. Vibrational spectral studies such as Fourier transform-infrared (FT-IR) and FT-Raman were adopted to understand the zwitterionic co-crystalline nature of the compound, which has been compared with theoretically calculated vibrational frequencies. The thermal stability of the grown co-crystal was analyzed by TG/DTA study. The solubility of the NICPY co-crystal was investigated in water at different temperature and compared with that of the nicotinic acid, which is the parent compound of NICPY co-crystal. The grown crystals were treated with human cervical cancer cell line (HeLa) to analyze the cytotoxicity of NICPY crystals and compared with the parent compound, which shows that NICPY has moderate activity against human cervical cancer cell line.

Development of GaAs/Si and GaAs/Si monolithic structures for future space solar cells

NASA Technical Reports Server (NTRS)

Spitzer, M. B.; Vernon, S. M.; Wolfson, R. G.; Tobin, S. P.

1984-01-01

The results of heteroepitaxial growth of GaAs and GaAlAs directly on Si are presented, and applications to new cell structures are suggested. The novel feature is the elimination of a Ge lattice transition region. This feature not only reduces the cost of substrate preparation, but also makes possible the fabrication of high efficiency monolithic cascade structures. All films to be discussed were grown by organometallic chemical vapor deposition at atmospheric pressure. This process yielded reproducible, large-area films of GaAs, grown directly on Si, that are tightly adherent and smooth, and are characterized by a defect density of 5 x 10(6) power/sq cm. Preliminary studies indicate that GaAlAs can also be grown in this way. A number of promising applications are suggested. Certainly these substrates are ideal for low-weight GaAs space solar ells. For very high efficiency, the absence of Ge makes the technology attractive for GaAlAs/Si monolithic cascades, in which the Si substrates would first be provided with a suitable p/n junction. An evaluation of a three bandgap cascade consisting of appropriately designed GaAlAs/GaAs/Si layers is also presented.

Transport Measurements and Synchrotron-Based X-Ray Absorption Spectroscopy of Iron Silicon Germanide Grown by Molecular Beam Epitaxy

NASA Astrophysics Data System (ADS)

Elmarhoumi, Nader; Cottier, Ryan; Merchan, Greg; Roy, Amitava; Lohn, Chris; Geisler, Heike; Ventrice, Carl, Jr.; Golding, Terry

2009-03-01

Some of the iron-based metal silicide and germanide phases have been predicted to be direct band gap semiconductors. Therefore, they show promise for use as optoelectronic materials. We have used synchrotron-based x-ray absorption spectroscopy to study the structure of iron silicon germanide films grown by molecular beam epitaxy. A series of Fe(Si1-xGex)2 thin films (2000 -- 8000å) with a nominal Ge concentration of up to x = 0.04 have been grown. X-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) measurements have been performed on the films. The nearest neighbor co-ordination corresponding to the β-FeSi2 phase of iron silicide provides the best fit with the EXAFS data. Temperature dependent (20 < T < 350 K) magneto transport measurements were done on the Fe(Si1-xGex)2 thin films via Van Der Paw (VDP) Hall configuration using a 0.5-1T magnetic field and a current of 10-200 μA through indium ohmic contacts, the Hall coefficient was calculated. Results suggest semiconducting behavior of the films which is consistent with the EXAFS results.

Polarization characteristics of semipolar (112̄2) InGaN/GaN quantum well structures grown on relaxed InGaN buffer layers and comparison with experiment.

PubMed

Park, Seoung-Hwan; Mishra, Dhaneshwar; Eugene Pak, Y; Kang, K; Park, Chang Yong; Yoo, Seung-Hyun; Cho, Yong-Hee; Shim, Mun-Bo; Kim, Sungjin

2014-06-16

Partial strain relaxation effects on polarization ratio of semipolar (112̄2) InxGa1−xN/GaN quantum well (QW) structures grown on relaxed InGaN buffers were investigated using the multiband effective-mass theory. The absolute value of the polarization ratio gradually decreases with increasing In composition in InGaN buffer layer when the strain relaxation ratio (ε0y′y′−εy′y′)/ε0y′y′ along y′-axis is assumed to be linearly proportional to the difference of lattice constants between the well and the buffer layer. Also, it changes its sign for the QW structure grown on InGaN buffer layer with a relatively larger In composition (x > 0.07). These results are in good agreement with the experiment. This can be explained by the fact that, with increasing In composition in the InGaN subsrate, the spontaneous emission rate for the y′-polarization gradually increases while that for x′-polarization decreases due to the decrease in a matrix element at the band-edge (k‖ = 0).

Effects of UV light intensity on electrochemical wet etching of SiC for the fabrication of suspended graphene

NASA Astrophysics Data System (ADS)

O, Ryong-Sok; Takamura, Makoto; Furukawa, Kazuaki; Nagase, Masao; Hibino, Hiroki

2015-03-01

We report on the effects of UV light intensity on the photo assisted electrochemical wet etching of SiC(0001) underneath an epitaxially grown graphene for the fabrication of suspended structures. The maximum etching rate of SiC(0001) was 2.5 µm/h under UV light irradiation in 1 wt % KOH at a constant current of 0.5 mA/cm2. The successful formation of suspended structures depended on the etching rate of SiC. In the Raman spectra of the suspended structures, we did not observe a significant increase in the intensity of the D peak, which originates from defects in graphene sheets. This is most likely explained by the high quality of the single-crystalline graphene epitaxially grown on SiC.

Growth, structural, optical, thermal and laser damage threshold studies of an organic single crystal: 1,3,5 – triphenylbenzene (TPB)

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

Raja, R. Subramaniyan; Babu, G. Anandha; Ramasamy, P., E-mail: E-mail-ramasamyp@ssn.edu.in

2016-05-23

Good quality single crystals of pure hydrocarbon 1,3,5-Triphenylbenzene (TPB) have been successfully grown using toluene as a solvent using controlled slow cooling solution growth technique. TPB crystallizes in orthorhombic structure with the space group Pna2{sub 1}. The structural perfection of the grown crystal has been analysed by high resolution X-ray diffraction measurements. The range and percentage of the optical transmission are ascertained by recording the UV-vis spectrum. Thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study its thermal properties. Powder second harmonic generation studies were carried out to explore its NLO properties. Laser damage threshold valuemore » has been determined using Nd:YAG laser operating at 1064 nm.« less

Characterization of graded interface In(x)Ga(1-x)As/In(0.52)Al(0.48)As (x between 0.53 and 0.70) structures grown by molecular-beam epitaxy

NASA Technical Reports Server (NTRS)

Peng, C. K.; Sinha, S.; Morkoc, H.

1987-01-01

Modulation-doped In(x)Ga(1-x)As/In(0.52)Al(0.48)As/InP structures were grown by molecular-beam epitaxy with x values between 53 and 70 percent. For pseudomorphic cases, graded instead of abrupt interfaces were used. Hall mobility and persistent photoconductivity measurements as a function of temperature were used to characterize samples with different structural parameters. Consistent trends in the variation of mobilities and two-dimensional carrier concentration, n(2D), under light and dark conditions have been observed and discussed in terms of applicable scattering mechanisms. The Hall mobilities are comparable to the best results obtained to date but with significantly higher n(2D) concentration.

Strained-layer superlattice focal plane array having a planar structure

DOEpatents

Kim, Jin K [Albuquerque, NM; Carroll, Malcolm S [Albuquerque, NM; Gin, Aaron [Albuquerque, NM; Marsh, Phillip F [Lowell, MA; Young, Erik W [Albuquerque, NM; Cich, Michael J [Albuquerque, NM

2010-07-13

An infrared focal plane array (FPA) is disclosed which utilizes a strained-layer superlattice (SLS) formed of alternating layers of InAs and In.sub.xGa.sub.1-xSb with 0.ltoreq.x.ltoreq.0.5 epitaxially grown on a GaSb substrate. The FPA avoids the use of a mesa structure to isolate each photodetector element and instead uses impurity-doped regions formed in or about each photodetector for electrical isolation. This results in a substantially-planar structure in which the SLS is unbroken across the entire width of a 2-D array of the photodetector elements which are capped with an epitaxially-grown passivation layer to reduce or eliminate surface recombination. The FPA has applications for use in the wavelength range of 3-25 .mu.m.

Strained layer superlattice focal plane array having a planar structure

DOEpatents

Kim, Jin K; Carroll, Malcolm S; Gin, Aaron; Marsh, Phillip F; Young, Erik W; Cich, Michael J

2012-10-23

An infrared focal plane array (FPA) is disclosed which utilizes a strained-layer superlattice (SLS) formed of alternating layers of InAs and In.sub.xGa.sub.1-xSb with 0.ltoreq.x.ltoreq.0.5 epitaxially grown on a GaSb substrate. The FPA avoids the use of a mesa structure to isolate each photodetector element and instead uses impurity-doped regions formed in or about each photodetector for electrical isolation. This results in a substantially-planar structure in which the SLS is unbroken across the entire width of a 2-D array of the photodetector elements which are capped with an epitaxially-grown passivation layer to reduce or eliminate surface recombination. The FPA has applications for use in the wavelength range of 3-25 .mu.m.

GaAs quantum dots in a GaP nanowire photodetector

NASA Astrophysics Data System (ADS)

Kuyanov, P.; McNamee, S. A.; LaPierre, R. R.

2018-03-01

We report the structural, optical and electrical properties of GaAs quantum dots (QDs) embedded along GaP nanowires. The GaP nanowires contained p-i-n junctions with 15 consecutively grown GaAs QDs within the intrinsic region. The nanowires were grown by molecular beam epitaxy using the self-assisted vapor-liquid-solid process. The crystal structure of the NWs alternated between twinned ZB and WZ as the composition along the NW alternated between the GaP barriers and the GaAs QDs, respectively, leading to a polytypic structure with a periodic modulation of the NW sidewall facets. Photodetector devices containing QDs showed absorption beyond the bandgap of GaP in comparison to nanowires without QDs. Voltage-dependent measurements suggested a field emission process of carriers from the QDs.

Effect of NiFeCr seed and capping layers on exchange bias and planar Hall voltage response of NiFe/Au/IrMn trilayer structures

NASA Astrophysics Data System (ADS)

Talantsev, Artem; Elzwawy, Amir; Kim, CheolGi

2018-05-01

Thin films and cross junctions, based on NiFe/Au/IrMn structures, were grown on Ta and NiFeCr seed layers by magnetron sputtering. The effects of substitution of Ta with NiFeCr in seed and capping layers on an exchange bias field are studied. A threefold improvement of the exchange bias value in the structures, grown with NiFeCr seed and capping layers, is demonstrated. The reasons for this effect are discussed. Formation of clusters in the NiFeCr capping layer is proved by atomic force microscopy technique. Ta replacement on NiFeCr in the capping layer results in the enhancement of magnetoresistive response and a reduction of noise.

Characterization of TEM Moiré Patterns Originating from Two Monolayer Graphenes Grown on the Front and Back Sides of a Copper Substrate by CVD Method

NASA Astrophysics Data System (ADS)

Yamazaki, Kenji; Maehara, Yosuke; Gohara, Kazutoshi

2018-06-01

The number of layers affects the electronic properties of graphene owing to its unique band structure, called the Dirac corn. Raman spectroscopy is a key diagnostic tool for identifying the number of graphene layers and for determining their physical properties. Here, we observed moiré structures in transmission electron microscopy (TEM) observations; these are signature patterns in multilayer, although Raman spectra showed the typical intensity of the 2D/G peak in the monolayer. We also performed a multi-slice TEM image simulation to compare the 3D atomic structures of the two graphene membranes with experimental TEM images. We found that the experimental moiré image was constructed with a 9-12 Å interlayer distance between graphene membranes. This structure was constructed by transferring CVD-grown graphene films that formed on both sides of the Cu substrate at once.

The Role of the Substrate on Photophysical Properties of Highly Ordered 15R-SiC Thin Films

NASA Astrophysics Data System (ADS)

Mourya, Satyendra; Jaiswal, Jyoti; Malik, Gaurav; Kumar, Brijesh; Chandra, Ramesh

2018-06-01

We report on the structural optimization and photophysical properties of in situ RF-sputtered single crystalline 15R-SiC thin films deposited on various substrates (ZrO2, MgO, SiC, and Si). The role of the substrates on the structural, electronic, and photodynamic behavior of the grown films have been demonstrated using x-ray diffraction, photoluminescence (PL) and time-resolved photoluminescence spectroscopy. The appropriate bonding order and the presence of native oxide on the surface of the grown samples are confirmed by x-ray photoelectron spectroscopy measurement. A deep-blue PL emission has been observed corresponding to the Si-centered defects occurring in the native oxide. Deconvolution of the PL spectra manifested two decay mechanisms corresponding to the radiative recombination. The PL intensity and carrier lifetime were found to be substrate- dependent which may be ascribed to the variation in the trap-density of the films grown on different substrates.

The Kinetics of the as Grown and Annealed Self-Assembled Monolayer Studied by Force Spectroscopy

NASA Astrophysics Data System (ADS)

Habib, Huma; Yasar, M.; Mehmood, S.; Rafique, Saima; Bhatti, A. S.; Naeem, Aisha

The growth of biological systems like DNA, peptides and proteins are accredited to the self-assembly processes from the molecular level to the nanoscale. The flawless immobilization of DNA on any surface is quite an important step to the development of DNA-based biosensors. The present paper reports the use of atomic force microscopy to determine the mechanical properties of the as grown and annealed self-assembled monolayer (SAM) as well as the mutated DNA immobilized on the SAM. The SAM of alkane thiol (16-mercapto-1-hexadecanol) was developed on Au surface, which was then annealed and analyzed for its structural and mechanical properties. The surface coverage, height and monolayer’s order was studied as a function of incubation time and annealing time. Excessive annealing led to the defragmentation and desorption of SAM structures due to breaking of hydrocarbon bonds. AFM was employed to determine the detach separation, pull-off and work of adhesion of the as grown and annealed SAM.

Chemical bath deposited (CBD) CuO thin films on n-silicon substrate for electronic and optical applications: Impact of growth time

NASA Astrophysics Data System (ADS)

Sultana, Jenifar; Paul, Somdatta; Karmakar, Anupam; Yi, Ren; Dalapati, Goutam Kumar; Chattopadhyay, Sanatan

2017-10-01

Thin film of p-type cupric oxide (p-CuO) is grown on silicon (n-Si) substrate by using chemical bath deposition (CBD) technique and a precise control of thickness from 60 nm to 178 nm has been achieved. The structural properties and stoichiometric composition of the grown films are observed to depend significantly on the growth time. The chemical composition, optical properties, and structural quality are investigated in detail by employing XRD, ellipsometric measurements and SEM images. Also, the elemental composition and the oxidation states of Cu and O in the grown samples have been studied in detail by XPS measurements. Thin film of 110 nm thicknesses exhibited the best performance in terms of crystal quality, refractive index, dielectric constant, band-gap, and optical properties. The study suggests synthesis route for developing high quality CuO thin film using CBD method for electronic and optical applications.

Structural, morphological and mechanical properties of niobium nitride thin films grown by ion and electron beams emanated from plasma

NASA Astrophysics Data System (ADS)

Siddiqui, Jamil; Hussain, Tousif; Ahmad, Riaz; Umar, Zeeshan A.; Abdus Samad, Ubair

2016-05-01

The influence of variation in plasma deposition parameters on the structural, morphological and mechanical characteristics of the niobium nitride films grown by plasma-emanated ion and electron beams are investigated. Crystallographic investigation made by X-ray diffractometer shows that the film synthesized at 10 cm axial distance with 15 plasma focus shots (PFS) exhibits better crystallinity when compared to the other deposition conditions. Morphological analysis made by scanning electron microscope reveals a definite granular pattern composed of homogeneously distributed nano-spheroids grown as clustered particles for the film synthesized at 10 cm axial distance for 15 PFS. Roughness analysis demonstrates higher rms roughness for the films synthesized at shorter axial distance and by greater number of PFS. Maximum niobium atomic percentage (35.8) and maximum average hardness (19.4 ± 0.4 GPa) characterized by energy-dispersive spectroscopy and nano-hardness analyzer respectively are observed for film synthesized at 10 cm axial distance with 15 PFS.

Carbon Nanotubes by CVD and Applications

NASA Technical Reports Server (NTRS)

Cassell, Alan; Delzeit, Lance; Nguyen, Cattien; Stevens, Ramsey; Han, Jie; Meyyappan, M.; Arnold, James O. (Technical Monitor)

2001-01-01

Carbon nanotube (CNT) exhibits extraordinary mechanical and unique electronic properties and offers significant potential for structural, sensor, and nanoelectronics applications. An overview of CNT, growth methods, properties and applications is provided. Single-wall, and multi-wall CNTs have been grown by chemical vapor deposition. Catalyst development and optimization has been accomplished using combinatorial optimization methods. CNT has also been grown from the tips of silicon cantilevers for use in atomic force microscopy.

Measuring mechanodynamics in an unsupported epithelial monolayer grown at an air–water interface

PubMed Central

Gullekson, Corinne; Walker, Matthew; Harden, James L.; Pelling, Andrew E.

2017-01-01

Actomyosin contraction and relaxation in a monolayer is a fundamental biophysical process in development and homeostasis. Current methods used to characterize the mechanodynamics of monolayers often involve cells grown on solid supports such as glass or gels. The results of these studies are fundamentally influenced by these supporting structures. Here we describe a new method for measuring the mechanodynamics of epithelial monolayers by culturing cells at an air–liquid interface. These model monolayers are grown in the absence of any supporting structures, removing cell–substrate effects. This method’s potential was evaluated by observing and quantifying the generation and release of internal stresses upon actomyosin contraction (800 ± 100 Pa) and relaxation (600 ± 100 Pa) in response to chemical treatments. Although unsupported monolayers exhibited clear major and minor strain axes, they were not correlated with nuclear alignment as observed when the monolayers were grown on soft deformable gels. It was also observed that both gels and glass substrates led to the promotion of long-range cell nuclei alignment not seen in the hanging-drop model. This new approach provides us with a picture of basal actomyosin mechanodynamics in a simplified system, allowing us to infer how the presence of a substrate affects contractility and long-range multicellular organization and dynamics. PMID:28035043

Broadband light-emitting diode

DOEpatents

Fritz, Ian J.; Klem, John F.; Hafich, Michael J.

1998-01-01

A broadband light-emitting diode. The broadband light-emitting diode (LED) comprises a plurality of III-V compound semiconductor layers grown on a semiconductor substrate, with the semiconductor layers including a pair of cladding layers sandwiched about a strained-quantum-well active region having a plurality of different energy bandgaps for generating light in a wavelength range of about 1.3-2 .mu.m. In one embodiment of the present invention, the active region may comprise a first-grown quantum-well layer and a last-grown quantum-well layer that are oppositely strained; whereas in another embodiment of the invention, the active region is formed from a short-period superlattice structure (i.e. a pseudo alloy) comprising alternating thin layers of InGaAs and InGaAlAs. The use a short-period superlattice structure for the active region allows different layers within the active region to be simply and accurately grown by repetitively opening and closing one or more shutters in an MBE growth apparatus to repetitively switch between different growth states therein. The broadband LED may be formed as either a surface-emitting LED or as an edge-emitting LED for use in applications such as chemical sensing, fiber optic gyroscopes, wavelength-division-multiplexed (WDM) fiber-optic data links, and WDM fiber-optic sensor networks for automobiles and aircraft.

Broadband light-emitting diode

DOEpatents

Fritz, I.J.; Klem, J.F.; Hafich, M.J.

1998-07-14

A broadband light-emitting diode is disclosed. The broadband light-emitting diode (LED) comprises a plurality of III-V compound semiconductor layers grown on a semiconductor substrate, with the semiconductor layers including a pair of cladding layers sandwiched about a strained-quantum-well active region having a plurality of different energy bandgaps for generating light in a wavelength range of about 1.3--2 {micro}m. In one embodiment of the present invention, the active region may comprise a first-grown quantum-well layer and a last-grown quantum-well layer that are oppositely strained; whereas in another embodiment of the invention, the active region is formed from a short-period superlattice structure (i.e. a pseudo alloy) comprising alternating thin layers of InGaAs and InGaAlAs. The use a short-period superlattice structure for the active region allows different layers within the active region to be simply and accurately grown by repetitively opening and closing one or more shutters in an MBE growth apparatus to repetitively switch between different growth states therein. The broadband LED may be formed as either a surface-emitting LED or as an edge-emitting LED for use in applications such as chemical sensing, fiber optic gyroscopes, wavelength-divisionmultiplexed (WDM) fiber-optic data links, and WDM fiber-optic sensor networks for automobiles and aircraft. 10 figs.

Cu-doped ZnO nanorod arrays: the effects of copper precursor and concentration

PubMed Central

2014-01-01

Cu-doped ZnO nanorods have been grown at 90°C for 90 min onto a quartz substrate pre-coated with a ZnO seed layer using a hydrothermal method. The influence of copper (Cu) precursor and concentration on the structural, morphological, and optical properties of ZnO nanorods was investigated. X-ray diffraction analysis revealed that the nanorods grown are highly crystalline with a hexagonal wurtzite crystal structure grown along the c-axis. The lattice strain is found to be compressive for all samples, where a minimum compressive strain of −0.114% was obtained when 1 at.% Cu was added from Cu(NO3)2. Scanning electron microscopy was used to investigate morphologies and the diameters of the grown nanorods. The morphological properties of the Cu-doped ZnO nanorods were influenced significantly by the presence of Cu impurities. Near-band edge (NBE) and a broad blue-green emission bands at around 378 and 545 nm, respectively, were observed in the photoluminescence spectra for all samples. The transmittance characteristics showed a slight increase in the visible range, where the total transmittance increased from approximately 80% for the nanorods doped with Cu(CH3COO)2 to approximately 90% for the nanorods that were doped with Cu(NO3)2. PMID:24855460

Control of Polarization of Vertical-Cavity Surface - Lasers

NASA Astrophysics Data System (ADS)

Sun, Decai

1995-01-01

To date, most vertical-cavity surface-emitting lasers (VCSELs) have been fabricated from structures grown on GaAs (InP) substrates oriented in the (001) crystallographic axis. For the most part, these devices have exhibited linear, but random polarization states with no definite relationship to the in-plane crystallographic axes. The control of the polarization states of these devices is important for polarization-sensitive applications. Such applications include magneto-optic disk recording and coherent detection in advanced communication systems. In this thesis, a novel approach for controlling the polarization eigen-states of VCSELs is investigated. The approach utilizes anisotropic optical properties found in quantum wells (QW) oriented in directions other than the (001) to stabilize their polarization states. Specifically, the (110) direction is chosen for this work. An analysis of the in-plane optical matrix element connected with the gain coefficient of (In,Ga)As/GaAs QW structures grown on (110) GaAs substrates is conducted. It is found that the in-plane gain distribution is elliptically anisotropic--with a maximum directed along the (110) - (110) crystallographic axis. The design and growth of (In,Ga)As/GaAs QW VCSEL structures is studied in this work. The transition wavelengths of the (001) - and (110) -oriented (In,Ga)As/GaAs QW structures are calculated using a finite QW model. Distributed Bragg reflector mirrors consisting of GaAs/AlAs quarter wave layers are modeled using a characteristic matrix method. Threshold gain, internal and differential quantum efficiencies are analyzed. The growth of III-V compounds on (110) GaAs substrates by molecular beam epitaxy is investigated. High quality materials are successfully grown on the misoriented (110) GaAs substrates tilted by 6^circ toward the (111)B surface. (In,Ga)As/GaAs QW VCSEL structures are grown on (001) and (110) GaAs substrates. (In,Ga)As/GaAs QW VCSELs are fabricated from structures grown on the (001) and (110) surfaces. Experimental characterization shows that the devices fabricated from the (110) surface exhibit stable, well-defined polarization states at room temperature; this is in contrast to the random polarization characteristics observed from the VCSELs fabricated from the (001) surface. This stability is believed to be a consequence of the predicted anisotropic gain distribution on the (110) surface. Of the two orthogonal eigen-polarizations observed, the one with the higher optical intensity is found to be aligned along the (110) - (110) crystallographic axis; this is in agreement with theoretical predictions.

The management of stress in MOCVD-grown InGaN/GaN LED multilayer structures on Si(1 1 1) substrates

NASA Astrophysics Data System (ADS)

Jiang, Quanzhong; Allsopp, Duncan W. E.; Bowen, Chris R.; Wang, Wang N.

2013-09-01

The tensile stress in light-emitting diode (LED)-on-Si(1 1 1) multilayer structures must be reduced so that it does not compromise the multiple quantum well emission wavelength uniformity and structural stability. In this paper it is shown for non-optimized LED structures grown on Si(1 1 1) substrates that both emission wavelength uniformity and structural stability can be achieved within the same growth process. In order to gain a deeper understanding of the stress distribution within such a structure, cross-sectional Raman and photo-luminescence spectroscopy techniques were developed. It is observed that for a Si:GaN layer grown on a low-temperature (LT) AlN intermediate layer there is a decrease in compressive stress with increasing Si:GaN layer thickness during MOCVD growth which leads to a high level of tensile stress in the upper part of the layer. This may lead to the development of cracks during cooling to room temperature. Such a phenomenon may be associated with annihilation of defects such as dislocations. Therefore, a reduction of dislocation intensity should take place at the early stage of GaN growth on an AlN or AlGaN layer in order to reduce a build up of tensile stress with thickness. Furthermore, it is also shown that a prolonged three dimensional GaN island growth on a LT AlN interlayer for the reduction of dislocations may result in a reduction in the compressive stress in the resulting GaN layer.

Surface structures of L10-MnGa (001) by scanning tunneling microscopy and first-principles theory

NASA Astrophysics Data System (ADS)

Corbett, J. P.; Guerrero-Sanchez, J.; Richard, A. L.; Ingram, D. C.; Takeuchi, N.; Smith, A. R.

2017-11-01

We report on the surface reconstructions of L10-ordered MnGa (001) thin films grown by molecular beam epitaxy on a 50 nm Mn3N2 (001) layer freshly grown on a magnesium oxide (001) substrate. Scanning tunneling microscopy, Auger electron spectroscopy, and reflection high energy electron diffraction are combined with first-principles density functional theory calculations to determine the reconstructions of the L10-ordered MnGa (001) surface. We find two lowest energy reconstructions of the MnGa (001) face: a 1 × 1 Ga-terminated structure and a 1 × 2 structure with a Mn replacing a Ga in the 1 × 1 Ga-terminated surface. The 1 × 2 reconstruction forms a row structure along [100]. The manganese:gallium stoichiometry within the surface based on theoretical modeling is in good agreement with experiment. Magnetic moment calculations for the two lowest energy structures reveal important surface and bulk effects leading to oscillatory total magnetization for ultra-thin MnGa (001) films.

Electron transport in gated InGaAs and InAsP quantum well wires in selectively grown InP ridge structures

NASA Astrophysics Data System (ADS)

Granger, G.; Kam, A.; Studenikin, S. A.; Sachrajda, A. S.; Aers, G. C.; Williams, R. L.; Poole, P. J.

2010-09-01

The purpose of this work is to fabricate ribbon-like InGaAs and InAsP wires embedded in InP ridge structures and investigate their transport properties. The InP ridge structures that contain the wires are selectively grown by chemical beam epitaxy (CBE) on pre-patterned InP substrates. To optimize the growth and micro-fabrication processes for electronic transport, we explore the Ohmic contact resistance, the electron density, and the mobility as a function of the wire width using standard transport and Shubnikov-de Haas measurements. At low temperatures the ridge structures reveal reproducible mesoscopic conductance fluctuations. We also fabricate ridge structures with submicron gate electrodes that exhibit non-leaky gating and good pinch-off characteristics acceptable for device operation. Using such wrap gate electrodes, we demonstrate that the wires can be split to form quantum dots evidenced by Coulomb blockade oscillations in transport measurements.

Genetic structure of traditional varieties of bitter manioc in three soils in Central Amazonia.

PubMed

Alves-Pereira, Alessandro; Peroni, Nivaldo; Abreu, Aluana Gonçalves; Gribel, Rogério; Clement, Charles R

2011-10-01

Manioc is the most important food crop that originated in Amazonia. Many studies have increased our understanding of its evolutionary dynamics under cultivation. However, most of them focused on manioc cultivation in environments with low soil fertility, generally Oxisols. Recent ethnobotanical observations showed that bitter manioc also performs well in high fertility soils, such as Amazonian dark earths (ADE) and the floodplain. We used 10 microsatellite loci to investigate the genetic diversity and structure of bitter manioc varieties grown in different soil types in communities of smallholder farmers along the middle Madeira River in Central Amazonia. The genetic diversity of some sweet varieties and seedlings was also evaluated. Adult individuals showed higher levels of genetic diversity and smaller inbreeding coefficients (A ( R ) = 5.52, H ( O ) = 0.576, f = 0.086) than seedlings (A ( R ) = 4.39, H ( O ) = 0.421, f = 0.242). Bitter manioc varieties from the floodplain showed higher levels of genetic diversity (A ( R ) = 5.19, H ( O ) = 0.606) than those from ADE (A ( R ) = 4.45, H ( O ) = 0.538) and from Oxisols (A ( R ) = 4.15, H ( O ) = 0.559). The varieties grown in the floodplain were strongly differentiated from the varieties grown in Oxisols (F ( ST ) = 0.093) and ADE (F ( ST ) = 0.108), suggesting important genetic structuring among varieties grown in the floodplain and upland soils (ADE and Oxisols). This is the first time that genetic divergence of bitter manioc varieties in cultivation in different Amazonian soils in a small geographic area is reported.

Structural and optical effects induced by gamma irradiation on NdPO{sub 4}: X-ray diffraction, spectroscopic and luminescence study

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

Sadhasivam, S.; Rajesh, N.P., E-mail: rajeshnp@hotmail.com

2016-02-15

Highlights: • Inorganic NdPO{sub 4} crystal was grown first time using potassium polyphosphate (K{sub 6}P{sub 4}O{sub 13}) flux. • NdPO{sub 4} crystal is insoluble in water, non-hygroscopic and high radiation resistance favoring for actinides host. • Actinide immobilization can be made at 1273 K. • High yield of 1061 nm photon emission. - Abstract: Rare earth orthophosphate (NdPO{sub 4}) monazite single crystals were grown using high temperature flux growth method employing K{sub 6}P{sub 4}O{sub 13} (K{sub 6}) as molten solvent. Their structural parameters were studied using single crystal X-ray diffraction (XRD) method. The grown crystals were examined by SEM andmore » EDX techniques for their homogeniousity and inclusion in the crystals. The influence of gamma irradiation in structural and optical absorption properties were studied by the powder XRD, FTIR and reflectance spectroscopy. The effect of gamma irradiation on luminescence properties was recorded. No significant structural change is observed up to 150 kGy gamma dose. The gamma ray induced charge trap in the crystal was saturated to 40 kGy dose. The luminescence intensity decreases with an increase in the irradiation. The emission of luminescence intensity stabilizes above 40 kGy gamma dose.« less

4H-SiC p i n diodes grown by sublimation epitaxy in vacuum (SEV) and their application as microwave diodes

NASA Astrophysics Data System (ADS)

Camara, N.; Zekentes, K.; Zelenin, V. V.; Abramov, P. L.; Kirillov, A. V.; Romanov, L. P.; Boltovets, N. S.; Krivutsa, V. A.; Thuaire, A.; Bano, E.; Tsoi, E.; Lebedev, A. A.

2008-02-01

Sublimation epitaxy under vacuum (SEV) was investigated as a method for growing 4H-SiC epitaxial structures for p-i-n diode fabrication. The SEV-grown 4H-SiC material was investigated with scanning electron microscopy (SEM), atomic force microscopy (AFM), x-ray diffraction, photo-luminescence spectroscopy (PL), cathodo-luminescence (CL) spectroscopy, photocurrent method for carrier diffusion length determination, electro-luminescence microscopy (EL), deep level transient spectroscopy (DLTS), C-V profiling and Hall-effect measurements. When possible, the same investigation techniques were used in parallel with similar layers grown by chemical vapour deposition (CVD) epitaxy and the physical properties of the two kind of epitaxied layers were compared. p-i-n diodes were fabricated in parallel on SEV and CVD-grown layers and showed close electrical performances in dc mode in term of capacitance, resistance and transient time switching, despite the lower mobility and the diffusion length of the SEV-grown layers. X-band microwave switches based on the SEV-grown p-i-n diodes have been demonstrated with insertion loss lower than 4 dB and an isolation higher than 17 dB. These single-pole single-throw (SPST) switches were able to handle a pulsed power up to 1800 W in isolation mode, similar to the value obtained with switches incorporating diodes with CVD-grown layers.

Wafer-scale controlled exfoliation of metal organic vapor phase epitaxy grown InGaN/GaN multi quantum well structures using low-tack two-dimensional layered h-BN

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

Ayari, Taha; Li, Xin; Voss, Paul L.

Recent advances in epitaxial growth have led to the growth of III-nitride devices on 2D layered h-BN. This advance has the potential for wafer-scale transfer to arbitrary substrates, which could improve the thermal management and would allow III-N devices to be used more flexibly in a broader range of applications. We report wafer scale exfoliation of a metal organic vapor phase epitaxy grown InGaN/GaN Multi Quantum Well (MQW) structure from a 5 nm thick h-BN layer that was grown on a 2-inch sapphire substrate. The weak van der Waals bonds between h-BN atomic layers break easily, allowing the MQW structure tomore » be mechanically lifted off from the sapphire substrate using a commercial adhesive tape. This results in the surface roughness of only 1.14 nm on the separated surface. Structural characterizations performed before and after the lift-off confirm the conservation of structural properties after lift-off. Cathodoluminescence at 454 nm was present before lift-off and 458 nm was present after. Electroluminescence near 450 nm from the lifted-off structure has also been observed. These results show that the high crystalline quality ultrathin h-BN serves as an effective sacrificial layer—it maintains performance, while also reducing the GaN buffer thickness and temperature ramps as compared to a conventional two-step growth method. These results support the use of h-BN as a low-tack sacrificial underlying layer for GaN-based device structures and demonstrate the feasibility of large area lift-off and transfer to any template, which is important for industrial scale production.« less

Studies on 2-amino-5-nitropyridinium nitrate (2A5NPN): A semi-organic third order nonlinear optical single crystal

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

Sivasubramani, V.; Pandian, Muthu Senthil, E-mail: senthilpandianm@ssn.edu.in; Ramasamy, P.

2016-05-23

2-amino-5-nitropyridinium nitrate (2A5NPN) is a semi-organic nonlinear optical crystal and optically good quality 2A5NPN single crystals were successfully grown by slow evaporation solution growth technique (SEST) at ambient temperature. The crystallographic structure of the grown crystal was determined by single crystal X-Ray diffraction analysis and it belongs to Monoclinic crystal system with centro symmetric crystalline nature. The crystallinity of the grown crystal was confirmed by powder X-ray diffraction analysis. The other physical properties of grown crystals are also characterized using TG-DTA, UV-Visible NIR, chemical etching, photoconductivity and Z-scan measurements. The Z-scan method reveals that the 2A5NPN crystal possesses multi photonmore » absorption behaviour and the significantly higher third order susceptibility and it is a promising potential NLO material.« less

Growth and characterization of unidirectional benzil single crystal for photonic applications

NASA Astrophysics Data System (ADS)

Saranraj, A.; Thirupathy, J.; Dhas, S. Sahaya Jude; Jose, M.; Vinitha, G.; Dhas, S. A. Martin Britto

2018-06-01

Organic nonlinear optical benzil single crystal of fine quality with the dimensions of 168 × 14 mm2 was successfully grown in (100) plane from saturated solution by unidirectional SR method. The structural identity of the grown crystal was confirmed by powder XRD. High-resolution X-ray diffraction analysis indicates the crystalline perfection of the grown benzil crystal. The optical analysis was carried out by UV-visible spectroscopy which shows that the benzil crystal's cut off wavelength is 437 nm. The dielectric constant and dielectric loss of benzil crystal are found to be very much depending upon temperature and frequency. Ferroelectric nature of grown crystal was identified by P- E hysteresis analysis and to find the values of spontaneous polarization and coercive field. The laser damage threshold energy was studied with the help of Nd:YAG laser. The presence of third harmonic generation was identified by z-scan techniques.

LEED and AES characterization of the GaAs(110)-ZnSe interface

NASA Technical Reports Server (NTRS)

Tu, D.-W.; Kahn, A.

1984-01-01

In this paper, a study is conducted of the composition and structure of epitaxial ZnSe films grown by congruent evaporation on GaAs(110) at a rate of 2 A/min. It is found that the films grown on 300 C GaAs are nearly stoichiometric and form an abrupt interface with the substrate. Films grown at higher temperature (T greater than 350-400 C) are Se rich. The crystallinity of films grown at 300 C is good and their surface atomic geometry is identical to that of a ZnSe crystal. The GaAs-ZnSe interface geometry seems to be dominated by the Se-substrate bonds. The adsorption of Se, during the formation of very thin ZnSe films (2-3 A), produces a (1 x 2) LEED pattern and modifications of the LEED I-V profiles, which probably indicate a change in the substrate atomic relaxation.

Cryptococcus neoformans responds to mannitol by increasing capsule size in vitro and in vivo

PubMed Central

Guimarães, Allan Jefferson; Frases, Susana; Cordero, Radamés J. B.; Nimrichter, Leonardo; Casadevall, Arturo; Nosanchuk, Joshua D.

2010-01-01

The polysaccharide capsule of the fungus Cryptococcus neoformans is its main virulence factor. In this study, we determined the effects of mannitol and glucose on the capsule and exopolysaccharide production. Growth in mannitol significantly increased capsular volume compared to cultivation in glucose. However, cells grown in glucose concentrations higher than 62.5mM produced more exopolysaccharide than cells grown in mannitol. The fiber lengths and glycosyl composition of capsular polysaccharide from yeast grown in mannitol was structurally different from that of yeast grown in glucose. Furthermore, mannitol treatment of mice infected intratracheally with C. neoformans resulted in fungal cells with significantly larger capsules and the mice had reduced fungal dissemination to the brain. Our results demonstrate the capacity of carbohydrate source and concentration to modify the expression of a major virulence factor of C. neoformans. These findings may impact the clinical management of cryptococcosis. PMID:20070311

Investigation of anodic and chemical oxides grown on p-type InP with applications to surface passivation for n(+)-p solar cell fabrication

NASA Technical Reports Server (NTRS)

Faur, Maria; Faur, Mircea; Goradia, Manju; Goradia, Chandra; Jenkins, Phillip; Jayne, Douglas; Weinberg, Irving

1991-01-01

Most of the previously reported InP anodic oxides were grown on a n-type InP with applications to fabrication of MISFET structures and were described as a mixture of In2O3 and P2O5 stoichiometric compounds or nonstoichiometric phases which have properties similar to crystalline compounds In(OH)3, InPO4, and In(PO3)3. Details of the compositional change of the anodic oxides grown under different anodization conditions were previously reported. The use of P-rich oxides grown either by anodic or chemical oxidation are investigated for surface passivation of p-type InP and as a protective cap during junction formation by closed-ampoule sulfur diffusion. The investigation is based on but not limited to correlations between PL intensity and X-ray photoelectron spectroscopy (XPS) chemical composition data.

Growth and characterizations of various GaN nanostructures on C-plane sapphire using laser MBE

NASA Astrophysics Data System (ADS)

Ch., Ramesh; Tyagi, P.; Maurya, K. K.; Kumar, M. Senthil; Kushvaha, S. S.

2017-05-01

We have grown various GaN nanostructures such as three-dimensional islands, nanowalls and nanocolumns on c-plane sapphire substrates using laser assisted molecular beam epitaxy (LMBE) system. The shape of the GaN nanostructures was controlled by using different nucleation surfaces such as bare and nitridated sapphire with GaN or AlN buffer layers. The structural and surface morphological properties of grown GaN nanostructures were characterized by ex-situ high resolution x-ray diffraction, Raman spectroscopy and field emission scanning electron microscopy. The symmetric x-ray rocking curve along GaN (0002) plane shows that the GaN grown on pre-nitridated sapphire with GaN or AlN buffer layer possesses good crystalline quality compared to sapphire without nitridation. The Raman spectroscopy measurements revealed the wurtzite phase for all the GaN nanostructures grown on c-sapphire.

Synthesis, growth, structural, spectral, thermal, chemical etching, linear and nonlinear optical and mechanical studies of an organic single crystal 4-chloro 4-nitrostilbene (CONS): a potential NLO material.

PubMed

Dinakaran, Paul M; Kalainathan, S

2013-07-01

4-Chloro 4-nitrostilbene (CONS) a new organic nonlinear optical material has been synthesized. Employing slow evaporation method, good optical quality single crystals (dimensions up to 6×2×3 mm(3)) have been grown using ethyl methyl ketone (EMK) as a solvent. The grown crystals have been subjected to various characterizations such as single crystal X-ray diffraction, powder XRD, Fourier Transform Infrared spectroscopy (FTIR), proton NMR, solid UV absorption, SHG studies. Single crystal X-ray diffraction reveals that the crystal system belongs to monoclinic with noncentrosymmetric space group P21. The UV-Vis absorption spectrum has been recorded and found that the cut off wavelength is 380 nm. Functional groups and the structure of the title compound have been confirmed by FTIR and (1)H NMR spectroscopic analyses respectively. Molecular mass of the CONS confirmed by the high resolution mass spectral analysis .The thermal behavior of the grown crystal has been studied by TG/DTA analysis and it shows the melting point is at 188.66 °C. Dislocations and growth pattern present in the grown crystal revealed by the etching study. The mechanical strength of the CONS crystal has been studied by Vicker's hardness measurement. The SHG efficiency of the grown crystal has been determined by Kurtz and Perry powder test which revealed that the CONS crystal (327 mV) has 15 times greater efficiency than that of KDP (21.7 mV). Copyright © 2013 Elsevier B.V. All rights reserved.

Crystal growth, structural, optical, mechanical and thermal properties of a new nonlinear optical single crystal: L-Ornithine monohydrochloride.

PubMed

Balakrishnan, T; Ramamurthi, K

2009-03-01

Amino acid family crystals exhibit excellent nonlinear optical and electro optical properties. l-Ornithine monohydrochloride single crystal, belongs to the amino acid group, was grown by the slow evaporation solution growth technique at room temperature. The grown crystals were characterized by single crystal and powder X-ray diffraction analysis, Fourier transform infrared (FTIR) spectroscopy, TGA, DTA and DSC analyses. UV-vis-NIR spectrum shows excellent transmission in the UV, visible and NIR region (300-1600nm). The mechanical properties of grown crystals were studied using Vickers microhardness tester. Its second harmonic generation efficiency was tested using Nd:YAG laser and is 1.25 times that of KDP.

Structural, thermal and optical properties of a semiorganic nonlinear optical single crystal: glycine zinc sulphate.

PubMed

Balakrishnan, T; Ramamurthi, K

2007-10-01

Glycine zinc sulphate salt was synthesized and the solubility and metastable zonewidth were estimated from the aqueous solution. Single crystals of glycine zinc sulphate were grown by solvent evaporation method from aqueous solution. Grown crystals were characterized by X-ray diffraction and FT-IR spectral analyses. The range and percentage of optical transmission was ascertained by recording UV-vis-NIR spectrum. Thermal properties of the crystal were investigated by thermogravimetric analysis. Microhardness study was carried out on (01-1) face of the grown crystal. Its powder second harmonic generation efficiency was measured using Nd:YAG laser and the value was observed to be 0.7 times that of potassium dihydrogen orthophosphate.

Electrical and optical properties of binary CNx nanocone arrays synthesized by plasma-assisted reaction deposition.

PubMed

Liu, Xujun; Guan, Leilei; Fu, Xiaoniu; Zhao, Yu; Wu, Jiada; Xu, Ning

2014-03-21

Light-absorbing and electrically conductive binary CNx nanocone (CNNC) arrays have been fabricated using a glow discharge plasma-assisted reaction deposition method. The intact CNNCs with amorphous structure and central nickel-filled pipelines could be vertically and neatly grown on nickel-covered substrates according to the catalyst-leading mode. The morphologies and composition of the as-grown CNNC arrays can be well controlled by regulating the methane/nitrogen mixture inlet ratio, and their optical absorption and resistivity strongly depend on their morphologies and composition. Beside large specific surface area, the as-grown CNNC arrays demonstrate high wideband absorption, good conduction, and nice wettability to polymer absorbers.

Characterization of 3C-SiC Films Grown on 4H- and 6H-SiC Substrate Mesas During Step-Free Surface Heteroepitaxy

NASA Technical Reports Server (NTRS)

Neudeck, Philip G.; Powel J. Anthony; Spry, David J.; Trunek, Andrew J.; Huang, Xianrong; Vetter, William M.; Dudley, Michael; Skowronski, Marek; Liu, Jinqiang

2002-01-01

This paper reports detailed structural characterization of 3C-SiC heteroepitaxial films grown on 4H- and 6H-SiC mesa surfaces. 3C-SiC heterofilms grown by the "step-free surface heteroepitaxy" process, free of double-positioning boundary (DPB) and stacking-fault (SF) defects, were compared to less-optimized 3C-SiC heterofilms using High Resolution X-ray Diffraction (HRXRD), High Resolution Cross-sectional Transmission Electron Microscopy (HRXTEM), molten potassium hydroxide (KOH) etching, and dry thermal oxidation. The results suggest that step free surface heteroepitaxy enables remarkably benign partial lattice mismatch strain relief during heterofilm growth.

Solid-state reaction kinetics of neodymium doped magnesium hydrogen phosphate system

NASA Astrophysics Data System (ADS)

Gupta, Rashmi; Slathia, Goldy; Bamzai, K. K.

2018-05-01

Neodymium doped magnesium hydrogen phosphate (NdMHP) crystals were grown by using gel encapsulation technique. Structural characterization of the grown crystals has been carried out by single crystal X-ray diffraction (XRD) and it revealed that NdMHP crystals crystallize in orthorhombic crystal system with space group Pbca. Kinetics of the decomposition of the grown crystals has been studied by non-isothermal analysis. The estimation of decomposition temperatures and weight loss has been made from the thermogravimetric/differential thermo analytical (TG/DTA) in conjuncture with DSC studies. The various steps involved in the thermal decomposition of the material have been analysed using Horowitz-Metzger, Coats-Redfern and Piloyan-Novikova equations for evaluating various kinetic parameters.

Optical parameters and dispersion behavior of potassium magnesium chloride sulfate single crystals doped with Co+2 ions

NASA Astrophysics Data System (ADS)

Abu El-Fadl, A.; Abd-Elsalam, A. M.

2018-05-01

Single crystals of potassium magnesium chloride sulfate (KMCS) doped with cobalt ions were grown by slow cooling method. Powder XRD study confirmed the monoclinic structure of the grown crystals. The functional group vibrations were checked through FTIR spectroscopy measurements. In optical studies, the absorbance behavior of the crystals and their optical energy gap were established by Tauc plot. The refractive index, the extinction coefficient and other optical constants were calculated for the grown crystals. The normal dispersion of the refractive index was analyzed according to single oscillator Sellmeier's model. The Urbach's rule was applied to analyze the localized states density in the forbidden gap.

Crystal growth, structural, thermal and mechanical behavior of l-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) single crystals.

PubMed

Mahadevan, M; Ramachandran, K; Anandan, P; Arivanandhan, M; Bhagavannarayana, G; Hayakawa, Y

2014-12-10

Single crystals of l-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) have been grown successfully from the solution of l-arginine and 4-nitrophenol. Slow evaporation of solvent technique was adopted to grow the bulk single crystals. Single crystal X-ray diffraction analysis confirms the grown crystal has monoclinic crystal system with space group of P21. Powder X-ray diffraction analysis shows the good crystalline nature. The crystalline perfection of the grown single crystals was analyzed by HRXRD by employing a multicrystal X-ray diffractometer. The functional groups were identified from proton NMR spectroscopic analysis. Linear and nonlinear optical properties were determined by UV-Vis spectrophotometer and Kurtz powder technique respectively. It is found that the grown crystal has no absorption in the green wavelength region and the SHG efficiency was found to be 2.66 times that of the standard KDP. The Thermal stability of the crystal was found by obtaining TG/DTA curve. The mechanical behavior of the grown crystal has been studied by Vicker's microhardness method. Copyright © 2014 Elsevier B.V. All rights reserved.

Atomic force microscopy studies of homoepitaxial GaN layers grown on GaN template by laser MBE

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

Choudhary, B. S.; Rajasthan Technical University, Rawatbhata Road, Kota 324010; Singh, A.

We have grown homoepitaxial GaN films on metal organic chemical vapor deposition (MOCVD) grown 3.5 µm thick GaN on sapphire (0001) substrate (GaN template) using an ultra-high vacuum (UHV) laser assisted molecular beam epitaxy (LMBE) system. The GaN films were grown by laser ablating a polycrystalline solid GaN target in the presence of active r.f. nitrogen plasma. The influence of laser repetition rates (10-30 Hz) on the surface morphology of homoepitaxial GaN layers have been studied using atomic force microscopy. It was found that GaN layer grown at 10 Hz shows a smooth surface with uniform grain size compared to the rough surfacemore » with irregular shape grains obtained at 30 Hz. The variation of surface roughness of the homoepitaxial GaN layer with and without wet chemical etching has been also studied and it was observed that the roughness of the film decreased after wet etching due to the curved structure/rough surface.« less

All-MOCVD-grown BH laser on P-InP substrates

NASA Astrophysics Data System (ADS)

Nishimura, Tadashi; Ishimura, E.; Nakajima, Yasuo; Tada, Hitoshi; Kimura, T.; Ohkura, Y.; Goto, Katsuhiko; Omura, Etsuji; Aiga, Masao

1993-07-01

A very low cw threshold current of 2.5 mA ( 25 degree(s)C) and 8.0 mA ( 80 degree(s)C) with high reliability has been realized in the all-MOCVD grown BH lasers on p-InP substrates. A strained MQW active layer of 1.3 micrometers wavelength and the precise carrier confinement buried structure by MOCVD is employed for the BH lasers. The excellent potential of long lifetime of the all-MOCVD grown laser has also been confirmed. After the high temperature and the high current (100 degree(s)C, 200 mA) aging test, no significant degradation is observed which is comparable with the well-established LPE grown lasers. The BH laser is also operating stably over 3700 hrs under the APC condition of 50 degree(s)C, 10 mW. Finally, an extremely uniform 10-element all-MOCVD grown LD array is demonstrated, which has the threshold current uniformity of 2.4 +/- 0.1 mA ( 25 degree(s)C) and 9.2 +/- 0.2 mA ( 80 degree(s)C). The growth mechanism in the MOCVD is also described.

Growth and characterization of AgGa0.5In0.5Se2 single crystals by modified vertical Bridgman method

NASA Astrophysics Data System (ADS)

Vijayakumar, P.; Ramasamy, P.

2016-05-01

AgGa0.5In0.5Se2 single crystal was grown using a double wall quartz ampoule with accelerated crucible rotation technique by modified vertical Bridgman method. The structural perfection was measured using HRXRD. The grown single crystal composition was measured using ICP-OES analysis and compositional uniformities were measured using Raman spectroscopy analysis. Photoconductivity measurements confirm the positive photoconducting nature.

Off-grid MEMS sensors configurations for transportation applications.

DOT National Transportation Integrated Search

2013-10-01

The worsening problem of aging and deficient infrastructure in this nation and across the world has demonstrated the need for an improved system to monitor and maintain these structures. The field of structural health monitoring has grown in recent y...

Synthesis, growth, structural and optical studies of a novel organic Piperazine (bis) p-toluenesulfonate single crystal.

PubMed

Rekha, P; Peramaiyan, G; NizamMohideen, M; Kumar, R Mohan; Kanagadurai, R

2015-03-15

A novel organic single crystal of Piperazinium (bis) p-toluenesulfonate (PPTS) was grown by a slow evaporation solution growth technique. The structure of the grown crystal was determined using single crystal X-ray diffraction analysis. The PPTS crystal belongs to the triclinic crystal system with space group of P1¯. The presence of functional groups was confirmed by FTIR spectral analysis. The optical transmittance range and cut-off wavelength were identified by UV-vis-NIR spectral studies. The luminescent properties of PPTS crystal were investigated. The thermal behavior of PPTS crystal was studied by TG-DT analyses. Copyright © 2014 Elsevier B.V. All rights reserved.

Synthesis, structural, thermal and optical studies of 1-ethyl-2,6-dimethyl-4-hydroxy pyridinium halides.

PubMed

Dhanuskodi, S; Manivannan, S; Kirschbaum, K

2006-05-15

1-Ethyl-2,6-dimethyl-4-hydroxy pyridinium chloride dihydrate and bromide dihydrate salts have been synthesized and their single crystals were grown by the slow evaporation of aqueous solution at 30 degrees C. The grown crystals were characterized by elemental analysis, FT-NMR and FT-IR techniques to confirm the formation of the expected compound. Optical transmittance window in aqueous solution was found to be 275-1100 nm by UV-vis-NIR technique. Thermogravimetric and differential thermal analyses reveal thermal stability and the presence of two water molecules in the crystal lattices. The crystal structure of chloride salt was also determined by X-ray diffraction method.

Structural and electrical characterization of ultra-thin SrTiO3 tunnel barriers grown over YBa2Cu3O7 electrodes for the development of high Tc Josephson junctions.

PubMed

Félix, L Avilés; Sirena, M; Guzmán, L A Agüero; Sutter, J González; Vargas, S Pons; Steren, L B; Bernard, R; Trastoy, J; Villegas, J E; Briático, J; Bergeal, N; Lesueur, J; Faini, G

2012-12-14

The transport properties of ultra-thin SrTiO(3) (STO) layers grown over YBa(2)Cu(3)O(7) electrodes were studied by conductive atomic force microscopy at the nano-scale. A very good control of the barrier thickness was achieved during the deposition process. A phenomenological approach was used to obtain critical parameters regarding the structural and electrical properties of the system. The STO layers present an energy barrier of 0.9 eV and an attenuation length of 0.23 nm, indicating very good insulating properties for the development of high-quality Josephson junctions.

Nanocylindrical confinement imparts highest structural order in molecular self-assembly of organophosphonates on aluminum oxide.

PubMed

Pathak, Anshuma; Bora, Achyut; Braunschweig, Björn; Meltzer, Christian; Yan, Hongdan; Lemmens, Peter; Daum, Winfried; Schwartz, Jeffrey; Tornow, Marc

2017-05-18

We report the impact of geometrical constraint on intramolecular interactions in self-assembled monolayers (SAMs) of alkylphosphonates grown on anodically oxidized aluminum (AAO). Molecular order in these films was determined by sum frequency generation (SFG) spectroscopy, a more sensitive measure of order than infrared absorption spectroscopy. Using SFG we show that films grown on AAO are, within detection limits, nearly perfectly ordered in an all-trans alkyl chain configuration. In marked contrast, films formed on planar, plasma-oxidized aluminum oxide or α-Al 2 O 3 (0001) are replete with gauche defects. We attribute these differences to the nanocylindrical structure of AAO, which enforces molecular confinement.

Synthesis of parallel and antiparallel core-shell triangular nanoparticles

NASA Astrophysics Data System (ADS)

Bhattacharjee, Gourab; Satpati, Biswarup

2018-04-01

Core-shell triangular nanoparticles were synthesized by seed mediated growth. Using triangular gold (Au) nanoparticle as template, we have grown silver (Ag) shellto get core-shell nanoparticle. Here by changing the chemistry we have grown two types of core-shell structures where core and shell is having same symmetry and also having opposite symmetry. Both core and core-shell nanoparticles were characterized using transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX) to know the crystal structure and composition of these synthesized core-shell nanoparticles. From diffraction pattern analysis and energy filtered TEM (EFTEM) we have confirmed the crystal facet in core is responsible for such two dimensional growth of core-shell nanostructures.

Conduction- and Valence-Band Energies in Bulk InAs(1-x)Sb(x) and Type II InAs(1-x) Sb(x)/InAs Strained-Layer Superlattices

DTIC Science & Technology

2013-03-08

tions in the studied SLS structures . The fit of the dependence of the valence- band energy of unstrained InAs1!xSbx on the composition x with a... band . STRUCTURES Bulk InAsSb epilayers on metamorphic buffers and InAsSb/InAs strained-layer superlattices (SLS) were grown on GaSb substrates by solid...meV in InAs and Ev = 0 meV in InSb. For InAsSb with 22.5% Sb grown on GaSb , an unstrained valence- band energy of Ev = !457 meV was obtained. For the

Ti-doped ZnO Thin Films Prepared at Different Ambient Conditions: Electronic Structures and Magnetic Properties

PubMed Central

Yong, Zhihua; Liu, Tao; Uruga, Tomoya; Tanida, Hajime; Qi, Dongchen; Rusydi, Andrivo; Wee, Andrew T. S.

2010-01-01

We present a comprehensive study on Ti-doped ZnO thin films using X-ray Absorption Fine Structure (XAFS) spectroscopy. Ti K edge XAFS spectra were measured to study the electronic and chemical properties of Ti ions in the thin films grown under different ambient atmospheres. A strong dependence of Ti speciation, composition, and local structures upon the ambient conditions was observed. The XAFS results suggest a major tetrahedral coordination and a 4+ valence state. The sample grown in a mixture of 80% Ar and 20% O2 shows a portion of precipitates with higher coordination. A large distortion was observed by the Ti substitution in the ZnO lattice. Interestingly, the film prepared in 80% Ar, 20% O2 shows the largest saturation magnetic moment of 0.827 ± 0.013 µB/Ti.

Center for Macromolecular Crystallography, University of Alabama in Birmingham

NASA Technical Reports Server (NTRS)

Navia, Manuel A.

1991-01-01

Porcine pancreatic elastase (PPE) crystals grown under microgravity conditions on mission STS-26 of the Space Shuttle Discovery were shown to diffract to considerably higher resolution than the best PPE crystals grown by us on the ground. We have now independently refined both the microgravity and ground-based data. Preliminary results of these refinements are summarized. These results show nearly a doubling of experimental diffraction data for this structure, exceeding 1.3 A resolution. Improved phase information derived from the refined structure of PPE based on this microgravity data has allowed us to interpret previously-uninterpretable electron density obtained from ground-based crystals of a complex of PPE with a chemically-reactive inhibitor. Intermediate stages in the enzyme-inhibitor reaction mechanism in the crystal can now be directly observed. Further refinement of PPE structures is in progress.

Sputtering growth of Y3Fe5O12/Pt bilayers and spin transfer at Y3Fe5O12/Pt interfaces

NASA Astrophysics Data System (ADS)

Chang, Houchen; Liu, Tao; Reifsnyder Hickey, Danielle; Janantha, P. A. Praveen; Mkhoyan, K. Andre; Wu, Mingzhong

2017-12-01

For the majority of previous work on Y3Fe5O12 (YIG)/normal metal (NM) bi-layered structures, the YIG layers were grown on Gd3Ga5O12 first and were then capped by an NM layer. This work demonstrates the sputtering growth of a Pt/YIG structure where the Pt layer was grown first and the YIG layer was then deposited on the top. The YIG layer shows well-oriented (111) texture, a surface roughness of 0.15 nm, and an effective Gilbert damping constant less than 4.7 × 10-4, and the YIG/Pt interface allows for efficient spin transfers. This demonstration indicates the feasibility of fabricating high-quality NM/YIG/NM tri-layered structures for new physics studies.

Epitaxially Grown Films of Standing and Lying Pentacene Molecules on Cu(110) Surfaces

PubMed Central

2011-01-01

Here, it is shown that pentacene thin films (30 nm) with distinctively different crystallographic structures and molecular orientations can be grown under essentially identical growth conditions in UHV on clean Cu(110) surfaces. By X-ray diffraction, we show that the epitaxially oriented pentacene films crystallize either in the “thin film” phase with standing molecules or in the “single crystal” structure with molecules lying with their long axes parallel to the substrate. The morphology of the samples observed by atomic force microscopy shows an epitaxial alignment of pentacene crystallites, which corroborates the molecular orientation observed by X-ray diffraction pole figures. Low energy electron diffraction measurements reveal that these dissimilar growth behaviors are induced by subtle differences in the monolayer structures formed by slightly different preparation procedures. PMID:21479111

Substrate impact on the low-temperature growth of GaN thin films by plasma-assisted atomic layer deposition

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

Kizir, Seda; Haider, Ali; Biyikli, Necmi, E-mail: biyikli@unam.bilkent.edu.tr

2016-07-15

Gallium nitride (GaN) thin films were grown on Si (100), Si (111), and c-plane sapphire substrates at 200 °C via hollow-cathode plasma-assisted atomic layer deposition (HCPA-ALD) using GaEt{sub 3} and N{sub 2}/H{sub 2} plasma as group-III and V precursors, respectively. The main aim of the study was to investigate the impact of substrate on the material properties of low-temperature ALD-grown GaN layers. Structural, chemical, and optical characterizations were carried out in order to evaluate and compare film quality of GaN on different substrates. X-ray reflectivity measurements showed film density values of 5.70, 5.74, and 5.54 g/cm{sup 3} for GaN grown on Simore » (100), Si (111), and sapphire, respectively. Grazing incidence x-ray diffraction measurements exhibited hexagonal wurtzite structure in all HCPA-ALD grown GaN samples. However, dominant diffraction peak for GaN films grown on Si and sapphire substrates were detected differently as (002) and (103), respectively. X-ray diffraction gonio scans measured from GaN grown on c-plane sapphire primarily showed (002) orientation. All samples exhibited similar refractive index values (∼2.17 at 632 nm) with 2–3 at. % of oxygen impurity existing within the bulk of the films. The grain size was calculated as ∼9–10 nm for GaN grown on Si (100) and Si (111) samples while it was ∼5 nm for GaN/sapphire sample. Root-mean-square surface roughness values found as 0.68, 0.76, and 1.83 nm for GaN deposited on Si (100), Si (111), and sapphire, respectively. Another significant difference observed between the samples was the film growth per cycle: GaN/sapphire sample showed a considerable higher thickness value when compared with GaN/Si samples, which might be attributed to a possibly more-efficient nitridation and faster nucleation of sapphire surface.« less

Nitrogen-mediated effects of elevated CO2 on intra-aggregate soil pore structure

USDA-ARS?s Scientific Manuscript database

While previous elevated atmospheric CO2 research has addressed changes in belowground processes, its effects on soil structure remain virtually undescribed. This study examined the long-term effects of elevated CO2 and N fertilization on soil structural changes in a bahiagrass pasture grown on a san...

Optimization of the defects and the nonradiative lifetime of GaAs/AlGaAs double heterostructures

NASA Astrophysics Data System (ADS)

Cevher, Z.; Folkes, P. A.; Hier, H. S.; VanMil, B. L.; Connelly, B. C.; Beck, W. A.; Ren, Y. H.

2018-04-01

We used Raman scattering and time-resolved photoluminescence spectroscopy to investigate the molecular-beam-epitaxy (MBE) growth parameters that optimize the structural defects and therefore the internal radiative quantum efficiency of MBE-grown GaAs/AlGaAs double heterostructures (DH). The DH structures were grown at two different temperatures and three different As/Ga flux ratios to determine the conditions for an optimized structure with the longest nonradiative minority carrier lifetime. Raman scattering measurements show an improvement in the lattice disorder in the AlGaAs and GaAs layers as the As/Ga flux ratio is reduced from 40 to 15 and as the growth temperature is increased from 550 to 595 °C. The optimized structure is obtained with the As/Ga flux ratio equal to 15 and the substrate temperature 595 °C. This is consistent with the fact that the optimized structure has the longest minority carrier lifetime. Moreover, our Raman studies reveal that incorporation of a distributed Bragg reflector layer between the substrate and DH structures significantly reduces the defect density in the subsequent epitaxial layers.

Study of the influence of strained superlattices introduced into a metamorphic buffer on the electrophysical properties and the atomic structure of InAlAs/InGaAs MHEMT heterostructures

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

Galiev, G. B.; Pushkarev, S. S., E-mail: s_s_e_r_p@mail.ru; Vasil'evskii, I. S.

The results of studying the influence of strained superlattices introduced into a metamorphic buffer on the electrophysical properties and atomic crystal structure of In{sub 0.70}Al{sub 0.30}As/In{sub 0.76}Ga{sub 0.24}As/In{sub 0.70}Al{sub 0.30}As metamorphic high-electron-mobility transistor (MHEMT) nanoheterostructures on GaAs substrates are presented. Two types of MHEMT structures are grown by molecular beam epitaxy, namely, one with a linear increase in x in the In{sub x}Al{sub 1-x}As metamorphic buffer, and the second with two mismatched superlattices introduced inside the metamorphic buffer. The electrophysical and structural parameters of the grown samples are studied by the van der Pauw method, transmission electron microscopy (including scanningmore » and high-resolution microscopy), atomic-force microscopy, and energy dispersive X-ray analysis. It is revealed that the introduction of superlattices into a metamorphic buffer substantially improves the electrophysical and structural characteristics of MHEMT structures.« less

van der Waals epitaxy of SnS film on single crystal graphene buffer layer on amorphous SiO2/Si

NASA Astrophysics Data System (ADS)

Xiang, Yu; Yang, Yunbo; Guo, Fawen; Sun, Xin; Lu, Zonghuan; Mohanty, Dibyajyoti; Bhat, Ishwara; Washington, Morris; Lu, Toh-Ming; Wang, Gwo-Ching

2018-03-01

Conventional hetero-epitaxial films are typically grown on lattice and symmetry matched single crystal substrates. We demonstrated the epitaxial growth of orthorhombic SnS film (∼500 nm thick) on single crystal, monolayer graphene that was transferred on the amorphous SiO2/Si substrate. Using X-ray pole figure analysis we examined the structure, quality and epitaxy relationship of the SnS film grown on the single crystal graphene and compared it with the SnS film grown on commercial polycrystalline graphene. We showed that the SnS films grown on both single crystal and polycrystalline graphene have two sets of orientation domains. However, the crystallinity and grain size of the SnS film improve when grown on the single crystal graphene. Reflection high-energy electron diffraction measurements show that the near surface texture has more phases as compared with that of the entire film. The surface texture of a film will influence the growth and quality of film grown on top of it as well as the interface formed. Our result offers an alternative approach to grow a hetero-epitaxial film on an amorphous substrate through a single crystal graphene buffer layer. This strategy of growing high quality epitaxial thin film has potential applications in optoelectronics.

Suppression of Hydroxycinnamate Network Formation in Cell Walls of Rice Shoots Grown under Microgravity Conditions in Space

PubMed Central

Wakabayashi, Kazuyuki; Soga, Kouichi; Hoson, Takayuki; Kotake, Toshihisa; Yamazaki, Takashi; Higashibata, Akira; Ishioka, Noriaki; Shimazu, Toru; Fukui, Keiji; Osada, Ikuko; Kasahara, Haruo; Kamada, Motoshi

2015-01-01

Network structures created by hydroxycinnamate cross-links within the cell wall architecture of gramineous plants make the cell wall resistant to the gravitational force of the earth. In this study, the effects of microgravity on the formation of cell wall-bound hydroxycinnamates were examined using etiolated rice shoots simultaneously grown under artificial 1 g and microgravity conditions in the Cell Biology Experiment Facility on the International Space Station. Measurement of the mechanical properties of cell walls showed that shoot cell walls became stiff during the growth period and that microgravity suppressed this stiffening. Amounts of cell wall polysaccharides, cell wall-bound phenolic acids, and lignin in rice shoots increased as the shoot grew. Microgravity did not influence changes in the amounts of cell wall polysaccharides or phenolic acid monomers such as ferulic acid (FA) and p-coumaric acid, but it suppressed increases in diferulic acid (DFA) isomers and lignin. Activities of the enzymes phenylalanine ammonia-lyase (PAL) and cell wall-bound peroxidase (CW-PRX) in shoots also increased as the shoot grew. PAL activity in microgravity-grown shoots was almost comparable to that in artificial 1 g-grown shoots, while CW-PRX activity increased less in microgravity-grown shoots than in artificial 1 g-grown shoots. Furthermore, the increases in expression levels of some class III peroxidase genes were reduced under microgravity conditions. These results suggest that a microgravity environment modifies the expression levels of certain class III peroxidase genes in rice shoots, that the resultant reduction of CW-PRX activity may be involved in suppressing DFA formation and lignin polymerization, and that this suppression may cause a decrease in cross-linkages within the cell wall architecture. The reduction in intra-network structures may contribute to keeping the cell wall loose under microgravity conditions. PMID:26378793

Anisotropic structural and optical properties of semi-polar (11-22) GaN grown on m-plane sapphire using double AlN buffer layers.

PubMed

Zhao, Guijuan; Wang, Lianshan; Yang, Shaoyan; Li, Huijie; Wei, Hongyuan; Han, Dongyue; Wang, Zhanguo

2016-02-10

We report the anisotropic structural and optical properties of semi-polar (11-22) GaN grown on m-plane sapphire using a three-step growth method which consisted of a low temperature AlN buffer layer, followed by a high temperature AlN buffer layer and GaN growth. By introducing double AlN buffer layers, we substantially improve the crystal and optical qualities of semi-polar (11-22) GaN, and significantly reduce the density of stacking faults and dislocations. The high resolution x-ray diffraction measurement revealed that the in-plane anisotropic structural characteristics of GaN layer are azimuthal dependent. Transmission electron microscopy analysis showed that the majority of dislocations in the GaN epitaxial layer grown on m-sapphire are the mixed-type and the orientation of GaN layer was rotated 58.4° against the substrate. The room temperature photoluminescence (PL) spectra showed the PL intensity and wavelength have polarization dependence along parallel and perpendicular to the [1-100] axis (polarization degrees ~ 0.63). The realization of a high polarization semi-polar GaN would be useful to achieve III-nitride based lighting emission device for displays and backlighting.

Interface and Electronic Characterization of Thin Epitaxial Co3O4 Films

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

Vaz, C.A.; Zhu, Y.; Wang, H.-Q.

2009-01-15

The interface and electronic structure of thin ({approx} 20-74 nm) Co{sub 3}O{sub 4}(1 1 0) epitaxial films grown by oxygen-assisted molecular beam epitaxy on MgAl{sub 2}O{sub 4}(1 1 0) single crystal substrates have been investigated by means of real and reciprocal space techniques. As-grown film surfaces are found to be relatively disordered and exhibit an oblique low energy electron diffraction (LEED) pattern associated with the O-rich CoO{sub 2} bulk termination of the (1 1 0) surface. Interface and bulk film structure are found to improve significantly with post-growth annealing at 820 K in air and display sharp rectangular LEED patterns,more » suggesting a surface stoichiometry of the alternative Co{sub 2}O{sub 2} bulk termination of the (1 1 0) surface. Non-contact atomic force microscopy demonstrates the presence of wide terraces separated by atomic steps in the annealed films that are not present in the as-grown structures; the step height of {approx}2.7 {angstrom} corresponds to two atomic layers and confirms a single termination for the annealed films, consistent with the LEED results. A model of the (1 x 1) surfaces that allows for compensation of the polar surfaces is presented.« less

Growth, structure, and magnetic properties of γ-Fe2O3 epitaxial films on MgO

NASA Astrophysics Data System (ADS)

Gao, Y.; Kim, Y. J.; Thevuthasan, S.; Chambers, S. A.; Lubitz, P.

1997-04-01

Single-crystal epitaxial thin films of γ-Fe2O3(001) have been grown on MgO(001) using oxygen-plasma-assisted molecular beam epitaxy. The structure and magnetic properties of these films have been characterized by a variety of techniques, including reflection high-energy electron diffraction (RHEED), low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy and x-ray photoelectron/Auger electron diffraction (XPD/AED), vibrating sample magnetometry, and ferromagnetic resonance. Real-time RHEED reveals that the film growth occurs in a layer-by-layer fashion. The γ-Fe2O3(001) film surface exhibits a (1×1) LEED pattern. The growth of γ-Fe2Ooverflow="scroll">3 films at 450 °C is accompanied by significant Mg outdiffusion. AED of Mg KLL Auger emission reveals that Mg substitutionally incorporates in the γ-Fe2O3 lattice, occupying the octahedral sites. Magnetic moments are ˜2300 G and ˜4500 G for γ-Fe2O3 films grown at 250 °C and 450 °C, respectively. The high magnetic moment for the films grown at 450 °C could be attributed to the high degree of structural order of the films and Mg substitution at octahedral sites.

The Development of Ultraviolet Light Emitting Diodes on p-SiC Substrates

NASA Astrophysics Data System (ADS)

Brummer, Gordon

Ultraviolet (UV) light emitting diodes (LEDs) are promising light sources for purification, phototherapy, and resin curing applications. Currently, commercial UV LEDs are composed of AlGaN-based n-i-p junctions grown on sapphire substrates. These devices suffer from defects in the active region, inefficient p-type doping, and poor light extraction efficiency. This dissertation addresses the development of a novel UV LED device structure, grown on p-SiC substrates. In this device structure, the AlGaN-based intrinsic (i) and n-layers are grown directly on the p-type substrate, forming a p-i-n junction. The intrinsic layer (active region) is composed of an AlN buffer layer followed by three AlN/Al0.30Ga0.70N quantum wells. After the intrinsic layer, the n-layer is formed from n-type AlGaN. This device architecture addresses the deficiencies of UV LEDs on sapphire substrates while providing a vertical device geometry, reduced fabrication complexity, and improved thermal management. The device layers were grown by molecular beam epitaxy (MBE). The material properties were optimized by considering varying growth conditions and by considering the role of the layer within the device. AlN grown at 825 C and with a Ga surfactant yielded material with screw dislocation density of 1x10 7 cm-2 based on X-ray diffraction (XRD) analysis. AlGaN alloys grown in this work contained compositional inhomogeneity, as verified by high-resolution XRD, photoluminescence, and absorption measurements. Based on Stokes shift measurements, the degree of compositional inhomogeneity was correlated with the amount of excess Ga employed during growth. Compositional inhomogeneity yields carrier localizing potential fluctuations, which are advantages in light emitting device layers. Therefore, excess Ga growth conditions were used to grow AlN/Al0.30Ga0.70N quantum wells (designed using a wurtzite k.p model) with 35% internal quantum efficiency. Potential fluctuations limit the mobility of carriers and introduce sub-bandgap absorption, making them undesirable in the n-AlGaN layers. n-Al0.60Ga 0.40N grown under stoichiometric Ga flux and an In surfactant reduced the Stokes shift (compared to n-AlGaN grown without In) by 150 meV. However, even under these growth modes, some compositional inhomogeneity persisted which is speculatively attributed to the vicinal substrate. Device epitaxial layer stacks utilizing the optimum growth conditions were fabricated into prototype vertical UV LEDs which emit from 295-320 nm. In order to increase light extraction efficiency, UV distributed Bragg reflectors (DBRs) based on compositionally graded AlGaN alloys were designed using the transfer matrix method (TMM) and grown by MBE. DBRs were formed from repeated compositionally graded AlGaN alloys. This structure utilized the polarization doping and index of refraction variation of graded composition AlGaN. DBRs with square wave, sinusoidal, triangular, and sawtooth compositional profiles were realized, with reflectivity peaks over 50%, centered at 280 nm.

Highly strained InxGa(1-x)As-InyAl(1-y)As (x>0.8,y<0.3) layers for short wavelength QWIP and QCL structures grown by MBE

NASA Astrophysics Data System (ADS)

Missous, M.; Mitchell, C.; Sly, J.; Lai, K. T.; Gupta, R.; Haywood, S. K.

2004-01-01

Highly strained quantum cascade laser (QCL) and quantum well infrared photodetector (QWIPs) structures based on InxGa(1-x)As-InyAl(1-y)As (x>0.8,y<0.3) layers have been grown by molecular beam epitaxy. Conditions of exact stoichiometric growth were used at a temperature of ∼420°C to produce structures that are suitable for both emission and detection in the 2- 5 μm mid-infrared regime. High structural integrity, as assessed by double crystal X-ray diffraction, room temperature photoluminescence and electrical characteristics were observed. Strong room temperature intersubband absorption in highly tensile strained and strain-compensated In 0.84Ga 0.16As/AlAs/In 0.52Al 0.48As double barrier quantum wells grown on InP substrates is demonstrated. Γ- Γ intersubband transitions have been observed across a wide range of the mid-infrared spectrum (2- 7 μm) in three structures of differing In 0.84Ga 0.16As well width (30, 45, and 80 Å). We demonstrate short-wavelength IR, intersubband operation in both detection and emission for application in QC and QWIP structures. By pushing the InGaAs-InAlAs system to its ultimate limit, we have obtained the highest band offsets that are theoretically possible in this system both for the Γ- Γ bands and the Γ-X bands, thereby opening up the way for both high power and high efficiency coupled with short-wavelength operation at room temperature. The versatility of this material system and technique in covering a wide range of the infrared spectrum is thus demonstrated.

Possibilities for LWIR detectors using MBE-grown Si(/Si(1-x)Ge(x) structures

NASA Technical Reports Server (NTRS)

Hauenstein, Robert J.; Miles, Richard H.; Young, Mary H.

1990-01-01

Traditionally, long wavelength infrared (LWIR) detection in Si-based structures has involved either extrinsic Si or Si/metal Schottky barrier devices. Molecular beam epitaxially (MBE) grown Si and Si/Si(1-x)Ge(x) heterostructures offer new possibilities for LWIR detection, including sensors based on intersubband transitions as well as improved conventional devices. The improvement in doping profile control of MBE in comparison with conventional chemical vapor deposited (CVD) Si films has resulted in the successful growth of extrinsic Si:Ga, blocked impurity-band conduction detectors. These structures exhibit a highly abrupt step change in dopant profile between detecting and blocking layers which is extremely difficult or impossible to achieve through conventional epitaxial growth techniques. Through alloying Si with Ge, Schottky barrier infrared detectors are possible, with barrier height values between those involving pure Si or Ge semiconducting materials alone. For both n-type and p-type structures, strain effects can split the band edges, thereby splitting the Schottky threshold and altering the spectral response. Measurements of photoresponse of n-type Au/Si(1-x)Ge(x) Schottky barriers demonstrate this effect. For intersubband multiquntum well (MQW) LWIR detection, Si(1-x)Ge(x)/Si detectors grown on Si substrates promise comparable absorption coefficients to that of the Ga(Al)As system while in addition offering the fundamental advantage of response to normally incident light as well as the practical advantage of Si-compatibility. Researchers grew Si(1-x)Ge(x)/Si MQW structures aimed at sensitivity to IR in the 8 to 12 micron region and longer, guided by recent theoretical work. Preliminary measurements of n- and p-type Si(1-x)Ge(x)/Si MQW structures are given.

Microgravity

NASA Image and Video Library

1997-07-01

Parvalbumins are found in the muscles, endocrine glands, skin cells, and some neurons of vertebrates, but the role they play for musculature is not yet understood. Researchers are exploring theories of a correlation between parvalbumin concentration levels and the relaxation speed of mammalian muscles after contraction. An ultra-high resolution structure was achieved from samples grown on STS-83 and in July 1997, during STS-94, PCAM produced the largest crystals of pike parvalbumin grown to date. Principal Investigator: Dan Carter of New Century Pharmaceuticals.

Pike Parvalbumin

NASA Technical Reports Server (NTRS)

1997-01-01

Parvalbumins are found in the muscles, endocrine glands, skin cells, and some neurons of vertebrates, but the role they play for musculature is not yet understood. Researchers are exploring theories of a correlation between parvalbumin concentration levels and the relaxation speed of mammalian muscles after contraction. An ultra-high resolution structure was achieved from samples grown on STS-83 and in July 1997, during STS-94, PCAM produced the largest crystals of pike parvalbumin grown to date. Principal Investigator: Dan Carter of New Century Pharmaceuticals.

Microstructure of thermally grown and deposited alumina films probed with positrons

NASA Astrophysics Data System (ADS)

Somieski, Bertram; Hulett, Lester D.; Xu, Jun; Pint, Bruce A.; Tortorelli, Peter F.; Nielsen, Bent; Asoka-Kumar, Palakkal; Suzuki, Ryoichi; Ohdaira, Toshiyuki

1999-03-01

Aluminum oxide films used for corrosion protection of iron and nickel aluminides were generated by substrate oxidation as well as plasma and physical vapor depositions. The films grown by oxidation were crystalline. The others were amorphous. Defect structures of the films were studied by positron spectroscopy techniques. Lifetimes of the positrons, and Doppler broadening of the γ photons generated by their annihilation, were measured as functions of the energies with which they were injected. In this manner, densities and sizes of the defects were determined as functions of depths from the outer surfaces of the films. Alumina films generated by oxidation had high densities of open volume defects, mainly consisting of a few aggregated vacancies. In the outer regions of the films the structures of the defects did not depend on substrate compositions. Positron lifetime measurements, and the S and W parameters extracted from Doppler broadening spectra, showed uniform distributions of defects in the crystalline Al2O3 films grown on nickel aluminide substrates, but these data indicated intermediate layers of higher defect contents at the film/substrate interfaces of oxides grown on iron aluminide substrates. Amorphous films generated by plasma and physical vapor deposition had much larger open volume defects, which caused the average lifetimes of the injected positrons to be significantly longer. The plasma deposited film exhibited a high density of large cavities.

Effect of in situ annealing on the structural and electrical properties and infrared photodetection of III-Sb on GaAs using interfacial misfit array

NASA Astrophysics Data System (ADS)

Jia, Bo Wen; Tan, Kian Hua; Loke, Wan Khai; Wicaksono, Satrio; Yoon, Soon Fatt

2018-01-01

This work presents the effects of in situ thermal annealing under antimony overpressure on the structural, electrical, and optical properties of III-Sb (GaSb and InSb) grown on (100) GaAs using an interfacial misfit array to accommodate the lattice mismatch. Both the sample growth and the in situ thermal annealing were carried out in the in the molecular beam epitaxy system, and the temperature of the as-grown sample was increased to exceed its growth temperature during the annealing. X-ray diffraction demonstrates nearly fully relaxed as-grown and annealed III-Sb layers. The optimal annealing temperatures and durations are for 590 °C, 5 min for GaSb and 420 °C, 15 min for InSb, respectively. In situ annealing decreased the surface roughness of the III-Sb layers. X-ray reciprocal space mapping and transmission electron microscopy observation showed stable interfacial misfit arrays, and no interfacial diffusion occurred in the annealed III-Sb layers. A Hall measurement of unintentionally doped III-Sb layers showed greater carrier mobility and a lower carrier concentration in the annealed samples at both 77 and 300 K. In situ annealing improved the photoresponsivity of GaSb and InSb photoconductors grown on GaAs in the near- and mid-infrared ranges, respectively.

Computational Analysis of the Optical and Charge Transport Properties of Ultrasonic Spray Pyrolysis-Grown Zinc Oxide/Graphene Hybrid Structures.

PubMed

Ali, Amgad Ahmed; Hashim, Abdul Manaf

2016-12-01

We demonstrate a systematic computational analysis of the measured optical and charge transport properties of the spray pyrolysis-grown ZnO nanostructures, i.e. nanosphere clusters (NSCs), nanorods (NRs) and nanowires (NWs) for the first time. The calculated absorbance spectra based on the time-dependent density functional theory (TD-DFT) shows very close similarity with the measured behaviours under UV light. The atomic models and energy level diagrams for the grown nanostructures were developed and discussed to explain the structural defects and band gap. The induced stresses in the lattices of ZnO NSCs that formed during the pyrolysis process seem to cause the narrowing of the gap between the energy levels. ZnO NWs and NRs show homogeneous distribution of the LUMO and HOMO orbitals all over the entire heterostructure. Such distribution contributes to the reduction of the band gap down to 2.8 eV, which has been confirmed to be in a good agreement with the experimental results. ZnO NWs and NRs exhibited better emission behaviours under the UV excitation as compared to ZnO NSCs and thin film as their visible range emissions are strongly quenched. Based on the electrochemical impedance measurement, the electrical models and electrostatic potential maps were developed to calculate the electron lifetime and to explain the mobility or diffusion behaviours in the grown nanostructure, respectively.

Computational Analysis of the Optical and Charge Transport Properties of Ultrasonic Spray Pyrolysis-Grown Zinc Oxide/Graphene Hybrid Structures

NASA Astrophysics Data System (ADS)

Ali, Amgad Ahmed; Hashim, Abdul Manaf

2016-05-01

We demonstrate a systematic computational analysis of the measured optical and charge transport properties of the spray pyrolysis-grown ZnO nanostructures, i.e. nanosphere clusters (NSCs), nanorods (NRs) and nanowires (NWs) for the first time. The calculated absorbance spectra based on the time-dependent density functional theory (TD-DFT) shows very close similarity with the measured behaviours under UV light. The atomic models and energy level diagrams for the grown nanostructures were developed and discussed to explain the structural defects and band gap. The induced stresses in the lattices of ZnO NSCs that formed during the pyrolysis process seem to cause the narrowing of the gap between the energy levels. ZnO NWs and NRs show homogeneous distribution of the LUMO and HOMO orbitals all over the entire heterostructure. Such distribution contributes to the reduction of the band gap down to 2.8 eV, which has been confirmed to be in a good agreement with the experimental results. ZnO NWs and NRs exhibited better emission behaviours under the UV excitation as compared to ZnO NSCs and thin film as their visible range emissions are strongly quenched. Based on the electrochemical impedance measurement, the electrical models and electrostatic potential maps were developed to calculate the electron lifetime and to explain the mobility or diffusion behaviours in the grown nanostructure, respectively.

Growth, microstructure and electrical properties of sputter-deposited hafnium oxide (HfO2) thin films grown using HfO2 ceramic target

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

Aguirre, B.; Vemuri, R. S.; Zubia, David

2011-01-01

Hafnium oxide (HfO₂) thin films have been made by radio-frequency (rf) magnetron-sputtering onto Si(100) substrates under varying growth temperature (Ts). HfO₂ ceramic target has been employed for sputtering while varying the Ts from room temperature to 500⁰C during deposition. The effect of Ts on the growth and microstructure of deposited HfO₂ films has been studied using grazing incidence x-ray diffraction (GIXRD), X-ray photoelectron spectroscopy (XPS), and high-resolution scanning electron microscopy (HR-SEM) coupled with energy dispersive x-ray spectrometry (EDS). The results indicate that the effect of Ts is significant on the growth, surface and interface structure, morphology and chemical composition ofmore » the HfO₂ films. Structural characterization indicates that the HfO₂ films grown at Ts<200 ⁰C are amorphous while films grown at Ts>200 ⁰C are nanocrystalline. An amorphous-to-crystalline transition occurs at Ts=200 ⁰C. Nanocrystalline HfO₂ films crystallized in a monoclinic structure with a (-111) orientation. XPS measurements indicated the high surface-chemical quality and stoichiometric nature of the grown HfO₂ films. An interface layer (IL) formation occurs due to reaction at the HfO₂-Si interface for HfO₂ films deposited at Ts>200 ⁰C. The thickness of IL increases with increasing Ts. XPS and EDS at the HfO₂-Si cross-section indicate the IL is a (Hf, Si)-O compound. The electrical characterization using capacitance-voltage measurements indicate that the dielectric constant decreases from 25 to 16 with increasing Ts.« less

Low dislocation density InAlN/AlN/GaN heterostructures grown on GaN substrates and the effects on gate leakage characteristics

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

Kotani, Junji, E-mail: kotani.junji-01@jp.fujitsu.com; Yamada, Atsushi; Ishiguro, Tetsuro

2016-04-11

This paper reports on the electrical characterization of Ni/Au Schottky diodes fabricated on InAlN high-electron-mobility transistor (HEMT) structures grown on low dislocation density free-standing GaN substrates. InAlN HEMT structures were grown on sapphire and GaN substrates by metal-organic vapor phase epitaxy, and the effects of threading dislocation density on the leakage characteristics of Ni/Au Schottky diodes were investigated. Threading dislocation densities were determined to be 1.8 × 10{sup 4 }cm{sup −2} and 1.2 × 10{sup 9 }cm{sup −2} by the cathodoluminescence measurement for the HEMT structures grown on GaN and sapphire substrates, respectively. Leakage characteristics of Ni/Au Schottky diodes were compared between the two samples, andmore » a reduction of the leakage current of about three to four orders of magnitude was observed in the forward bias region. For the high reverse bias region, however, no significant improvement was confirmed. We believe that the leakage current in the low bias region is governed by a dislocation-related Frenkel–Poole emission, and the leakage current in the high reverse bias region originates from field emission due to the large internal electric field in the InAlN barrier layer. Our results demonstrated that the reduction of dislocation density is effective in reducing leakage current in the low bias region. At the same time, it was also revealed that another approach will be needed, for instance, band modulation by impurity doping and insertion of insulating layers beneath the gate electrodes for a substantial reduction of the gate leakage current.« less

Crystal structure, optical and thermal studies of a new organic nonlinear optical material: L-Histidinium maleate 1.5-hydrate

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

Gonsago, C. Alosious; Albert, Helen Merina; Karthikeyan, J.

2012-07-15

Highlights: ► L-Histidinium maleate 1.5-hydrate, a new organic crystal has been grown for the first time. ► The crystal structure is reported for the first time (CCDC 845975). ► The crystal belongs to monoclinic system with space group P2{sub 1}, Z = 4, a = 11.4656(7) Å, b = 8.0530(5) Å, c = 14.9705(9) Å and β = 101.657(2)°. ► The optical absorption study substantiates the complete transparency of the crystal. ► Kurtz powder SHG test confirms the nonlinear property of the crystal. -- Abstract: A new organic nonlinear optical material L-histidinium maleate 1.5-hydrate (LHM) with the molecular formula C{submore » 10}H{sub 16}N{sub 3}O{sub 7.5} has been successfully synthesized from aqueous solution by slow solvent evaporation method. The structural characterization of the grown crystal was carried out by single crystal X-ray diffraction at 293(2) K. In the crystal, molecules are linked through inter and intramolecular N-H⋯O and O-H⋯O hydrogen bonds, generate edge fused ring motif. The hydrogen bonded motifs are linked to each other to form a three dimensional network. The FT-IR spectroscopy was used to identify the functional groups of the synthesized compound. The optical behavior of the grown crystal was examined by UV–visible spectral analysis, which shows that the optical absorption is almost negligible in the wavelength range 280–1300 nm. The nonlinear optical property was confirmed by the powder technique of Kurtz and Perry. The thermal behavior of the grown crystal was analyzed by thermogravimetric analysis.« less

Sensing Properties of Multiwalled Carbon Nanotubes Grown in MW Plasma Torch: Electronic and Electrochemical Behavior, Gas Sensing, Field Emission, IR Absorption

PubMed Central

Majzlíková, Petra; Sedláček, Jiří; Prášek, Jan; Pekárek, Jan; Svatoš, Vojtěch; Bannov, Alexander G.; Jašek, Ondřej; Synek, Petr; Eliáš, Marek; Zajíčková, Lenka; Hubálek, Jaromír

2015-01-01

Vertically aligned multi-walled carbon nanotubes (VA-MWCNTs) with an average diameter below 80 nm and a thickness of the uniform VA-MWCNT layer of about 16 μm were grown in microwave plasma torch and tested for selected functional properties. IR absorption important for a construction of bolometers was studied by Fourier transform infrared spectroscopy. Basic electrochemical characterization was performed by cyclic voltammetry. Comparing the obtained results with the standard or MWCNT‐modified screen-printed electrodes, the prepared VA-MWCNT electrodes indicated their high potential for the construction of electrochemical sensors. Resistive CNT gas sensor revealed a good sensitivity to ammonia taking into account room temperature operation. Field emission detected from CNTs was suitable for the pressure sensing application based on the measurement of emission current in the diode structure with bending diaphragm. The advantages of microwave plasma torch growth of CNTs, i.e., fast processing and versatility of the process, can be therefore fully exploited for the integration of surface-bound grown CNTs into various sensing structures. PMID:25629702

New Three-Dimensional Porous Electrode Concept: Vertically-Aligned Carbon Nanotubes Directly Grown on Embroidered Copper Structures.

PubMed

Aguiló-Aguayo, Noemí; Amade, Roger; Hussain, Shahzad; Bertran, Enric; Bechtold, Thomas

2017-12-11

New three-dimensional (3D) porous electrode concepts are required to overcome limitations in Li-ion batteries in terms of morphology (e.g., shapes, dimensions), mechanical stability (e.g., flexibility, high electroactive mass loadings), and electrochemical performance (e.g., low volumetric energy densities and rate capabilities). Here a new electrode concept is introduced based on the direct growth of vertically-aligned carbon nanotubes (VA-CNTs) on embroidered Cu current collectors. The direct growth of VA-CNTs was achieved by plasma-enhanced chemical vapor deposition (PECVD), and there was no application of any post-treatment or cleaning procedure. The electrochemical behavior of the as-grown VA-CNTs was analyzed by charge/discharge cycles at different specific currents and with electrochemical impedance spectroscopy (EIS) measurements. The results were compared with values found in the literature. The as-grown VA-CNTs exhibit higher specific capacities than graphite and pristine VA-CNTs found in the literature. This together with the possibilities that the Cu embroidered structures offer in terms of specific surface area, total surface area, and designs provide a breakthrough in new 3D electrode concepts.

Screening and structural elucidation of the zwitterionic cocrystal o-picolinic acid with p-nitro aniline

NASA Astrophysics Data System (ADS)

Mekala, R.; Jagdish, P.; Mathammal, R.; Sangeetha, K.

2017-04-01

The cocrystal was screened by solvent drop grinding method and the crystals were grown by slow evaporation method at ambient conditions. The cocrystal formation of o-picolinic acid with p-nitro aniline was initially analysed by powder X-ray diffraction. Further the structural properties of the grown crystal were confirmed by the single X-ray diffraction which indicates that the cocrystal were connected by the strong N+sbnd H-⋯O hydrogen bond interaction. The cell parameters of the grown crystal were a = 14.2144(5) Å, b = 5.7558(2) Å, c = 16.0539(6) Å. The functional groups were identified using Fourier transform infrared and Raman spectral analysis. The excitation and emission state of the sample was analysed by the UV-Visible and Fluorescence studies. The red emission was observed from the Fluorescence studies. NMR studies revealed the chemical shift of the cocrystal. Thermal stability and its melting behaviour were studied by TGA and DSC analytical techniques. Electrical behaviour was studied using the dielectric studies. The intermolecular charge transfer within the molecule were analysed using HOMO- LUMO plots.

Growth, structural, thermal, dielectric and nonlinear optical properties of potassium hexachloro cadmate (IV) a novel single crystal

NASA Astrophysics Data System (ADS)

Umarani, P.; Jagannathan, K.

2018-02-01

The Potassium hexachloro cadmate (IV) (PHC) single crystal was grown from the aqueous of the solution by a controlled evaporation method. Single crystal XRD solved the structure. FTIR is used to identify the functional groups of grown crystal. The UV-Vis-NIR spectrometer was used to find out the UV cut off region and to calculate the optical band gap of the Potassium hexachloro cadmate (IV) single crystal. The EDAX spectrum has been used to identify the compounds present in title compound. The TG-DTA profile shows the thermal stability of the grown crystal of Potassium hexachloro cadmate (IV). The Vicker's hardness measurement was used to calculate the material hardness of the title compound. The dielectric loss and constant varied with frequencies and activation energy is also calculated. The solid state parameters like plasma energy, Penn gap, Fermi energy, electronic polarizability using Penn analysis and Clausius-Mossotti equation were also calculated for the title compound. The Z-scan technique is used to calculate the third order nonlinear susceptibility of a real and imaginary part.

Pressure relaxation and diffusion of vacancies in rapidly grown helium crystals

NASA Astrophysics Data System (ADS)

Birchenko, A. P.; Mikhin, N. P.; Rudavskii, E. Ya.; Smirnov, S. N.; Fysun, Ya. Yu.

2018-04-01

An experimental study of the features of pressure relaxation in rapidly grown crystals of a diluted solid solution 3He-4He, at temperatures above 1.3 K, was performed. A cylindrical cell with capacitive pressure sensors at the ends was used for measurements. It was found that, when the helium crystals were grown at cooling rates ≳4 mK/s, the difference in pressure ΔP registered by the sensors at 1.3 K reached 2.4 bars. The ΔP value decreased with subsequent stepwise increase in temperature, but reached zero only after thorough annealing at the premelting temperatures. The kinetics of pressure changes at the sample ends at different temperatures was recorded. The results obtained were interpreted within the framework of the structural relaxation model based on the monovacancy diffusion mechanism. The proposed model made it possible to explain the dependence of ΔP on the time and temperature recorded in the experiment, as well as to determine the activation energy of the structural relaxation process and the diffusion coefficient of vacancies. The details of the vacancy model are described in the Appendix.

Growth of high-quality AlN epitaxial film by optimizing the Si substrate surface

NASA Astrophysics Data System (ADS)

Huang, Liegen; Li, Yuan; Wang, Wenliang; Li, Xiaochan; zheng, Yulin; Wang, Haiyan; Zhang, Zichen; Li, Guoqiang

2018-03-01

High-quality AlN epitaxial films have been grown on Si substrates by optimizing the hydrofluoric acid (HF) solution for cleaning of Si substrates. Effect of the Si substrate surface on the surface morphology and structural property of AlN epitaxial films is investigated in detail. It is revealed that as the concentration of HF solution increases from 0 to 2.0%, the surface morphology and the crystalline quality are initially improved and then get worse, and show an optimized value at 1.5%. The as-grown ∼200 nm-thick AlN epitaxial films on Si substrates grown with HF solution of 1.5% reveal the root-mean-square (RMS) surface roughness of 0.49 nm and the full-width at half-maximum for AlN(0002) X-ray rocking curve of 0.35°, indicating the smooth surface morphology and the high crystalline quality. The corresponding mechanism is proposed to interpret the effect of Si substrate surface on surface morphology and structural property of AlN epitaxial films, and provides an effective approach for the perspective fabrication of AlN-based devices.

Sensitivity of heterointerfaces on emission wavelength of quantum cascade lasers

NASA Astrophysics Data System (ADS)

Wang, C. A.; Schwarz, B.; Siriani, D. F.; Connors, M. K.; Missaggia, L. J.; Calawa, D. R.; McNulty, D.; Akey, A.; Zheng, M. C.; Donnelly, J. P.; Mansuripur, T. S.; Capasso, F.

2017-04-01

The measured emission wavelengths of AlInAs/GaInAs/InP quantum cascade lasers (QCLs) grown by metal organic vapor phase epitaxy (MOVPE) have been reported to be 0.5-1 μm longer than the designed QCL wavelength. This work clarifies the origin of the red-shifted wavelength. It was found that AlInAs/GaInAs heterointerfaces are compositionally graded over 2.5-4.5 nm, and indium accumulates at the AlInAs-to-GaInAs interface. Thus, the as-grown QCLs are far from the ideal abrupt interfaces used in QCL modeling. When graded layers are incorporated in QCL band structure and wavefunction calculations, the emission wavelengths are red shifted. Furthermore, we demonstrate that QCLs with graded interfaces can be designed without compromising performance and show greatly improved correlation between designed and measured emission wavelength. QCLs were designed for emission between 7.5 and 8.5 μm. These structures were grown and wet-etched ridge devices were fabricated. The QCLs exhibit room temperature peak powers exceeding 900 mW and pulsed efficiencies of 8 to 10%.

Production of novel types of antibacterial liamocins by diverse strains of Aureobasidium pullulans grown on different culture media.

PubMed

Leathers, Timothy D; Price, Neil P J; Bischoff, Kenneth M; Manitchotpisit, Pennapa; Skory, Christopher D

2015-10-01

To compare production of antibacterial liamocins (polyol lipids) by diverse strains of Aureobasidium pullulans grown on different culture media. Liamocins produced by strains of A. pullulans have potential agricultural and pharmaceutical applications as antibacterials with specificity against Streptococcus spp. Six strains of A. pullulans were characterized for liamocin production on four different culture media. The choice of strain and culture medium affected growth, liamocin yields, and production of contaminating pigments. Best growth and highest liamocin yields were obtained using A. pullulans strain NRRL 50384 grown on a sucrose basal medium. Unexpectedly, the choice of strain and culture medium also affected the structure of liamocins produced, providing novel types of liamocins. Liamocins varied not only in the ratios of trimer and tetramer polyester tail groups, but also in the nature of the polyol headgroup, which could include mannitol, arabitol, or glycerol. The ability to conveniently produce novel types of liamocins in good yields will provide novel antibacterials for applied uses, and facilitate structure-function studies on the mechanism of antibacterial activity.

From open to closed canopy: A century of change in Douglas-fir forest, Orcas Island, Washington

USGS Publications Warehouse

Peterson, D.L.; Hammer, R.D.

2001-01-01

During the past century, forest structure on south-facing slopes of Mount Constitution, Orcas Island, Washington, has changed from open-grown Douglas-fir (Pseudotsuga menziesii) mixed with prairie to primarily closed canopy forest. Density of open-grown Douglas-fir was approximately 7 stems/ha in the 19th century, while current density of trees in closed-canopy mature forest is 426 stems/ha. Trees occur at intermediate densities in areas of transition from savanna-like stands to closed canopy. Analysis of fire scars indicates that at least seven fires have occurred on Mount Constitution since 1736, but only one fire has occurred since 1893, which suggests that the recent increase in stem density has been caused primarily by fire exclusion. The high stem densities currently found in this landscape put the relict (120-350+ years old) Douglas-fir at risk from contemporary fires, which would likely be high-intensity crown fires. Given the transition of forests on Orcas Island during the 20th century to closed canopy structure, undisturbed open-grown coniferous forest is now extremely rare in the San Juan Islands.

Optical and Structural Properties of Microcrystalline GaN on an Amorphous Substrate Prepared by a Combination of Molecular Beam Epitaxy and Metal-Organic Chemical Vapor Deposition

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

Min, Jung-Wook; Hwang, Hyeong-Yong; Kang, Eun-Kyu

2016-05-01

Microscale platelet-shaped GaN grains were grown on amorphous substrates by a combined epitaxial growth method of molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). First, MBE GaN was grown on an amorphous substrate as a pre-orienting layer and its structural properties were investigated. Second, MOCVD grown GaN samples using the different growth techniques of planar and selective area growth (SAG) were comparatively investigated by transmission electron microscopy (TEM), cathodoluminescence (CL), and photoluminescence (PL). In MOCVD planar GaN, strong bound exciton peaks dominated despite the high density of the threading dislocations (TDs). In MOCVD SAG GaN, on the othermore » hand, TDs were clearly reduced with bending, but basal stacking fault (BSF) PL peaks were observed at 3.42 eV. The combined epitaxial method not only provides a deep understanding of the growth behavior but also suggests an alternative approach for the growth of GaN on amorphous substances.« less

Highly doped InP as a low loss plasmonic material for mid-IR region.

PubMed

Panah, M E Aryaee; Takayama, O; Morozov, S V; Kudryavtsev, K E; Semenova, E S; Lavrinenko, A V

2016-12-12

We study plasmonic properties of highly doped InP in the mid-infrared (IR) range. InP was grown by metal-organic vapor phase epitaxy (MOVPE) with the growth conditions optimized to achieve high free electron concentrations by doping with silicon. The permittivity of the grown material was found by fitting the calculated infrared reflectance spectra to the measured ones. The retrieved permittivity was then used to simulate surface plasmon polaritons (SPPs) propagation on flat and structured surfaces, and the simulation results were verified in direct experiments. SPPs at the top and bottom interfaces of the grown epilayer were excited by the prism coupling. A high-index Ge hemispherical prism provides efficient coupling conditions of SPPs on flat surfaces and facilitates acquiring their dispersion diagrams. We observed diffraction into symmetry-prohibited diffraction orders stimulated by the excitation of surface plasmon-polaritons in a periodically structured epilayer. Characterization shows good agreement between the theory and experimental results and confirms that highly doped InP is an effective plasmonic material aiming it for applications in the mid-IR wavelength range.

Templating effect of the substrate on the structure of Cu-phthalocyanine thin film

NASA Astrophysics Data System (ADS)

Pierantozzi, Gian Marco; Sbroscia, Marco; Ruocco, Alessandro

2018-03-01

An experimental study of electronic properties, structure and morphology of Copper-phthalocyanine films deposited onto Al(100) and Au(110), as a function of thickness up to tens of nanometers, is presented. The monolayers grown on these two model substrates are already known to exhibit very different behavior for what concerns both the degree of interaction with the substrate and the formation of long range order; in this experiment, by means of low energy electron scattering and Electron Energy Loss Spectroscopy (EELS), remarkable differences are revealed also in the successive growth. Exploiting the link between the crystal structure and the lineshape of HOMO-LUMO transition in EELS spectrum, two different structural phases are identified, compatible with α and β phases, respectively in the case of the film grown on aluminum and on gold. Besides, the evolution of the specular reflection elastic peak indicates the formation of islands on the gold substrate and a more homogeneous growth on the aluminum one.

Electrical characterizations of MIS structures based on variable-gap n(p)-HgCdTe grown by MBE on Si(0 1 3) substrates

NASA Astrophysics Data System (ADS)

Voitsekhovskii, A. V.; Nesmelov, S. N.; Dzyadukh, S. M.; Varavin, V. S.; Dvoretskii, S. A.; Mikhailov, N. N.; Yakushev, M. V.; Sidorov, G. Yu.

2017-12-01

Metal-insulator-semiconductor (MIS) structures based on n(p)-Hg1-xCdxTe (x = 0.22-0.40) with near-surface variable-gap layers were grown by the molecular-beam epitaxy (MBE) technique on the Si (0 1 3) substrates. Electrical properties of MIS structures were investigated experimentally at various temperatures (9-77 K) and directions of voltage sweep. The ;narrow swing; technique was used to determine the spectra of fast surface states with the exception of hysteresis effects. It is established that the density of fast surface states at the MCT/Al2O3 interface at a minimum does not exceed 3 × 1010 eV-1 × cm-2. For MIS structures based on n-MCT/Si(0 1 3), the differential resistance of the space-charge region in strong inversion mode in the temperature range 50-90 K is limited by the Shockley-Read-Hall generation in the space-charge region.

Process for growing a film epitaxially upon a MgO surface

DOEpatents

McKee, Rodney Allen; Walker, Frederick Joseph

1997-01-01

A process and structure wherein optical quality perovskites, such as BaTiO.sub.3 or SrTiO.sub.3, are grown upon a single crystal MgO substrate involves the epitaxial build up of alternating planes of TiO.sub.2 and metal oxide wherein the first plane grown upon the MgO substrate is a plane of TiO.sub.2. The layering sequence involved in the film build up reduces problems which would otherwise result from the interfacial electrostatics at the first atomic layers, and these oxides can be stabilized as commensurate thin films at a unit cell thickness or grown with high crystal quality to thicknesses of 0.5-0.7 .mu.m for optical device applications.

Morphology- and orientation-controlled gallium arsenide nanowires on silicon substrates.

PubMed

Ihn, Soo-Ghang; Song, Jong-In; Kim, Tae-Wook; Leem, Dong-Seok; Lee, Takhee; Lee, Sang-Geul; Koh, Eui Kwan; Song, Kyung

2007-01-01

GaAs nanowires were epitaxially grown on Si(001) and Si(111) substrates by using Au-catalyzed vapor-liquid-solid (VLS) growth in a solid source molecular beam epitaxy system. Scanning electron microscopy analysis revealed that almost all the GaAs nanowires were grown along <111> directions on both Si substrates for growth conditions investigated. The GaAs nanowires had a very uniform diameter along the growth direction. X-ray diffraction data and transmission electron microscopy analysis revealed that the GaAs<111> nanowires had a mixed crystal structure of the hexagonal wurtzite and the cubic zinc-blende. Current-voltage characteristics of junctions formed by the epitaxially grown GaAs nanowires and the Si substrate were investigated by using a current-sensing atomic force microscopy.

Micro-light-emitting diodes with III-nitride tunnel junction contacts grown by metalorganic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Hwang, David; Mughal, Asad J.; Wong, Matthew S.; Alhassan, Abdullah I.; Nakamura, Shuji; DenBaars, Steven P.

2018-01-01

Micro-light-emitting diodes (µLEDs) with tunnel junction (TJ) contacts were grown entirely by metalorganic chemical vapor deposition. A LED structure was grown, treated with UV ozone and hydrofluoric acid, and reloaded into the reactor for TJ regrowth. The silicon doping level of the n++-GaN TJ was varied to examine its effect on voltage. µLEDs from 2.5 × 10-5 to 0.01 mm2 in area were processed, and the voltage penalty of the TJ for the smallest µLED at 20 A/cm2 was 0.60 V relative to that for a standard LED with indium tin oxide. The peak external quantum efficiency of the TJ LED was 34%.

Effect of growth parameters on crystallinity and properties of ZnO films grown by plasma assisted MOCVD

NASA Astrophysics Data System (ADS)

Losurdo, M.; Giangregorio, M. M.; Sacchetti, A.; Capezzuto, P.; Bruno, G.; Malandrino, G.; Fragalà, I. L.

2007-07-01

Thin films of ZnO have been grown by plasma assisted metal-organic chemical vapour deposition (PA-MOCVD) using a 13.56 MHz O 2 plasma and the Zn(TTA)•tmed (HTTA=2-thenoyltrifluoroacetone, TMED=N,N,N',N'-tetramethylethylendiamine) precursor. The effects of growth parameters such as the plasma activation, the substrate, the surface temperature, and the ratio of fluxes of precursors on the structure, morphology, and optical and electrical properties of ZnO thin films have been studied. Under a very low plasma power of 20 W, c-axis oriented hexagonal ZnO thin films are grown on hexagonal sapphire (0001), cubic Si(001) and amorphous quartz substrates. The substrate temperature mainly controls grain size.

Comparison of trimethylgallium and triethylgallium as “Ga” source materials for the growth of ultrathin GaN films on Si (100) substrates via hollow-cathode plasma-assisted atomic layer deposition

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

Alevli, Mustafa, E-mail: mustafaalevli@marmara.edu.tr; Haider, Ali; Kizir, Seda

2016-01-15

GaN films grown by hollow cathode plasma-assisted atomic layer deposition using trimethylgallium (TMG) and triethylgallium (TEG) as gallium precursors are compared. Optimized and saturated TMG/TEG pulse widths were used in order to study the effect of group-III precursors. The films were characterized by grazing incidence x-ray diffraction, atomic force microscopy, x-ray photoelectron spectroscopy, and spectroscopic ellipsometry. Refractive index follows the same trend of crystalline quality, mean grain, and crystallite sizes. GaN layers grown using TMG precursor exhibited improved structural and optical properties when compared to GaN films grown with TEG precursor.

Nanoporous structures on ZnO thin films

NASA Astrophysics Data System (ADS)

Gür, Emre; Kılıç, Bayram; Coşkun, C.; Tüzemen, S.; Bayrakçeken, Fatma

2010-01-01

Porous structures were formed on ZnO thin films which were grown by an electrochemical deposition (ECD) method. The growth processes were carried out in a solution of dimethylsulfoxide (DMSO) zinc perchlorate, Zn(ClO 4) 2, at 120 ∘C on indium tin oxide (ITO) substrates. Optical and structural characterizations of electrochemically grown ZnO thin films have shown that the films possess high (0002) c-axis orientation, high nucleation, high intensity and low FWHM of UV emission at the band edge region and a sharp UV absorption edge. Nanoporous structures were formed via self-assembled monolayers (SAMs) of hexanethiol (C 6SH) and dodecanethiol (C 12SH). Scanning electron microscope (SEM) measurements showed that while a nanoporous structure (pore radius 20 nm) is formed on the ZnO thin films by hexanathiol solution, a macroporous structure (pore radius 360 nm) is formed by dodecanethiol solution. No significant variation is observed in X-ray diffraction (XRD) measurements on the ZnO thin films after pore formation. However, photoluminescence (PL) measurements showed that green emission is observed as the dominant emission for the macroporous structures, while no variation is observed for the thin film nanoporous ZnO sample.

GaAsP/InGaP HBTs grown epitaxially on Si substrates: Effect of dislocation density on DC current gain

NASA Astrophysics Data System (ADS)

Heidelberger, Christopher; Fitzgerald, Eugene A.

2018-04-01

Heterojunction bipolar transistors (HBTs) with GaAs0.825P0.175 bases and collectors and In0.40Ga0.60P emitters were integrated monolithically onto Si substrates. The HBT structures were grown epitaxially on Si via metalorganic chemical vapor deposition, using SiGe compositionally graded buffers to accommodate the lattice mismatch while maintaining threading dislocation density at an acceptable level (˜3 × 106 cm-2). GaAs0.825P0.175 is used as an active material instead of GaAs because of its higher bandgap (increased breakdown voltage) and closer lattice constant to Si. Misfit dislocation density in the active device layers, measured by electron-beam-induced current, was reduced by making iterative changes to the epitaxial structure. This optimized process culminated in a GaAs0.825P0.175/In0.40Ga0.60P HBT grown on Si with a DC current gain of 156. By considering the various GaAsP/InGaP HBTs grown on Si substrates alongside several control devices grown on GaAs substrates, a wide range of threading dislocation densities and misfit dislocation densities in the active layers could be correlated with HBT current gain. The effect of threading dislocations on current gain was moderated by the reduction in minority carrier lifetime in the base region, in agreement with existing models for GaAs light-emitting diodes and photovoltaic cells. Current gain was shown to be extremely sensitive to misfit dislocations in the active layers of the HBT—much more sensitive than to threading dislocations. We develop a model for this relationship where increased base current is mediated by Fermi level pinning near misfit dislocations.

Structural and optical properties of indium-doped highly conductive ZnO bulk crystals grown by the hydrothermal technique

NASA Astrophysics Data System (ADS)

Wang, Buguo; Claflin, Bruce; Look, David; Jiménez, Juan

2018-02-01

Indium-doped ZnO bulk crystals grown by the hydrothermal method are highly-conductive, with resistivity at 0.01 Ωcm at room temperature as revealed by Hall-effect measurement. In this paper we report on structural and optical properties of these crystals. The grown In:ZnO crystals have been studied by high resolution X-ray diffraction, micro-Raman scattering and low-temperature photoluminescence and cathodoluminescence. It was found that the c lattice parameter of the grown In:ZnO crystal expanded 0.06% with respect to the lithium-doped ZnO crystal seed, and the In-doped ZnO overgrew the seed crystal pseudomorphically but with high quality crystallinity; the X-ray rocking curves show the FWHM of the Zn face and O faces are only 0.05° and 0.1° ; and the indium concentration in the crystal reaches the solubility limit. Raman spectra show strain relaxation gradually from the regrowth interface as well as a weak spectral feature at 723 cm-1. The peak at 312 cm-1 noticed in hydrothermally grown In:ZnO nanostructures does not appear in our In-doped crystals, indicating that this peak may be associated with specific defects (e.g. surface related) of the nanostructures. Photoluminescence measurements show that an indium donor bound exciton peak I9 (In0X) is the dominant peak in the PL spectrum, located at 3.3586 eV on the zinc face and 3.3577 eV on the oxygen face. Both of them deviated from the consensus literature value of 3.3567 eV, probably due to strain in the crystal induced by impurities.

Cell Wall Remodeling Enzymes Modulate Fungal Cell Wall Elasticity and Osmotic Stress Resistance

PubMed Central

Ene, Iuliana V.; Walker, Louise A.; Schiavone, Marion; Lee, Keunsook K.; Martin-Yken, Hélène; Dague, Etienne; Gow, Neil A. R.; Munro, Carol A.

2015-01-01

ABSTRACT The fungal cell wall confers cell morphology and protection against environmental insults. For fungal pathogens, the cell wall is a key immunological modulator and an ideal therapeutic target. Yeast cell walls possess an inner matrix of interlinked β-glucan and chitin that is thought to provide tensile strength and rigidity. Yeast cells remodel their walls over time in response to environmental change, a process controlled by evolutionarily conserved stress (Hog1) and cell integrity (Mkc1, Cek1) signaling pathways. These mitogen-activated protein kinase (MAPK) pathways modulate cell wall gene expression, leading to the construction of a new, modified cell wall. We show that the cell wall is not rigid but elastic, displaying rapid structural realignments that impact survival following osmotic shock. Lactate-grown Candida albicans cells are more resistant to hyperosmotic shock than glucose-grown cells. We show that this elevated resistance is not dependent on Hog1 or Mkc1 signaling and that most cell death occurs within 10 min of osmotic shock. Sudden decreases in cell volume drive rapid increases in cell wall thickness. The elevated stress resistance of lactate-grown cells correlates with reduced cell wall elasticity, reflected in slower changes in cell volume following hyperosmotic shock. The cell wall elasticity of lactate-grown cells is increased by a triple mutation that inactivates the Crh family of cell wall cross-linking enzymes, leading to increased sensitivity to hyperosmotic shock. Overexpressing Crh family members in glucose-grown cells reduces cell wall elasticity, providing partial protection against hyperosmotic shock. These changes correlate with structural realignment of the cell wall and with the ability of cells to withstand osmotic shock. PMID:26220968

Outcomes of Structured Teaching for Children on the Autism Spectrum: Does the Research Evidence Neglect the Bigger Picture?

ERIC Educational Resources Information Center

Howley, Marie

2015-01-01

The adoption of "structured teaching" is evident in educational settings worldwide and has fast become one of the key "tools" in autism education. As calls for evidence-based practice have increased, research evidence has grown to interrogate the effectiveness of structured teaching components. Previous systematic literature…

Structural properties and gas sensing behavior of sol-gel grown nanostructured zinc oxide

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

Rajyaguru, Bhargav; Gadani, Keval; Kansara, S. B.

2016-05-06

In this communication, we report the results of the studies on structural properties and gas sensing behavior of nanostructured ZnO grown using acetone precursor based modified sol-gel technique. Final product of ZnO was sintered at different temperatures to vary the crystallite size while their structural properties have been studied using X-ray diffraction (XRD) measurement performed at room temperature. XRD results suggest the single phasic nature of all the samples and crystallite size increases from 11.53 to 20.96 nm with increase in sintering temperature. Gas sensing behavior has been studied for acetone gas which indicates that lower sintered samples are moremore » capable to sense the acetone gas and related mechanism has been discussed in the light of crystallite size, crystal boundary density, defect mechanism and possible chemical reaction between gas traces and various oxygen species.« less

Enhancement of thermoelectric characteristics in AlGaN/GaN films deposited on inverted pyramidal Si surfaces

NASA Astrophysics Data System (ADS)

Yalamarthy, Ananth Saran; So, Hongyun; Senesky, Debbie G.

2017-07-01

In this letter, we demonstrate an engineering strategy to boost thermoelectric power factor via geometry-induced properties of the pyramid structure. Aluminum gallium nitride (AlGaN)/GaN heterostructured films grown on inverted pyramidal silicon (Si) demonstrate higher power factor as compared to those grown on conventional flat Si substrates. We found that the magnitude of the Seebeck coefficient at room temperature increased from approximately 297 μVK-1 for the flat film to approximately 849 μVK-1 for the film on inverted pyramidal Si. In addition, the "effective" electrical conductivity of the AlGaN/GaN on the inverted pyramidal structure increased compared to the flat structure, generating an enhancement of thermoelectric power factor. The results demonstrate how manipulation of geometry can be used to achieve better thermoelectric characteristics in a manner that could be scaled to a variety of different material platforms.

Structural and optical properties of PbS thin films grown by chemical bath deposition

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

Seghaier, S.; Kamoun, N.; Guasch, C.

2007-09-19

Lead sulphide thin films are grown on glass substrates at various deposition times tD, in the range of 40-60 min per step of 2 min, using the chemical bath deposition technique. X-ray diffraction and atomic force microscopy are used to characterize the film structure. The surface composition is analysed by Auger electron spectroscopy. It appears that the as-prepared thin films are polycrystalline with cubic structure. Nanometric scale crystallites are uniformly distributed on the surface. They exhibit almost a stoechiometric composition with a [Pb]/[S] ratio equal to 1.10. Optical properties are studied in the range of 300-3300 nm by spectrophotometric measurements.more » Analysis of the optical absorption data of lead sulphide thin layers reveals a narrow optical direct band gap equal to 0.46 eV for the layer corresponding to a deposition time equal to 60 min.« less

The structural and optical properties of GaSb/InGaAs type-II quantum dots grown on InP (100) substrate

PubMed Central

2012-01-01

We have investigated the structural and optical properties of type-II GaSb/InGaAs quantum dots [QDs] grown on InP (100) substrate by molecular beam epitaxy. Rectangular-shaped GaSb QDs were well developed and no nanodash-like structures which could be easily found in the InAs/InP QD system were formed. Low-temperature photoluminescence spectra show there are two peaks centered at 0.75eV and 0.76ev. The low-energy peak blueshifted with increasing excitation power is identified as the indirect transition from the InGaAs conduction band to the GaSb hole level (type-II), and the high-energy peak is identified as the direct transition (type-I) of GaSb QDs. This material system shows a promising application on quantum-dot infrared detectors and quantum-dot field-effect transistor. PMID:22277096

Large area planar stanene epitaxially grown on Ag(1 1 1)

NASA Astrophysics Data System (ADS)

Yuhara, Junji; Fujii, Yuya; Nishino, Kazuki; Isobe, Naoki; Nakatake, Masashi; Xian, Lede; Rubio, Angel; Le Lay, Guy

2018-04-01

Artificial post-graphene elemental 2D materials have received much attention recently. Especially, stanene, the tin analogue of graphene, is expected to be a robust 2D topological insulator, even above room temperature. We have grown epitaxial 2D stanene on a Ag(1 1 1) single crystal template and determined its crystalline structure synergetically by scanning tunneling microscopy, high-resolution synchrotron radiation photoemission spectroscopy, and advanced first principles calculations. From the STM images, we show that stanene forms a nearly planar structure in large domains. A detailed core-level spectroscopy analysis as well as DFT calculations reveal that the stanene sheet lays over an ordered 2D Ag2Sn surface alloy, but not directly on a bulk-terminated Ag(1 1 1) surface. The electronic structure exhibits a characteristic 2D band with parabolic dispersion due to the non-negligible interaction with the underlying surface alloy.

Room temperature electroluminescence from the n-ZnO/p-GaN heterojunction device grown by MOCVD

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

Yang, T.P.; Zhu, H.C.; Bian, J.M.

2008-12-01

The heterojunction light-emitting diode with n-ZnO/p-GaN structure was grown on (0 0 0 1) sapphire substrate by metalorganic chemical vapor deposition (MOCVD) technique. The heterojunction structure was consisted of an Mg-doped p-type GaN layer with a hole concentration of {approx}10{sup 17} cm{sup -3} and a unintentionally doped n-type ZnO layer with an electron concentration of {approx}10{sup 18} cm{sup -3}. A distinct blue-violet electroluminescence with a dominant emission peak centered at {approx}415 nm was observed at room temperature from the heterojunction structure under forward bias conditions. The origins of the electroluminescence (EL) emissions are discussed in comparison with the photoluminescence spectra,more » and it was supposed to be attributed to a radiative recombination in both n-ZnO and p-GaN sides.« less

Irradiation of 4H-SiC UV detectors with heavy ions

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

Kalinina, E. V., E-mail: evk@mail.ioffe.ru; Lebedev, A. A.; Bogdanova, E.

Ultraviolet (UV) photodetectors based on Schottky barriers to 4H-SiC are formed on lightly doped n-type epitaxial layers grown by the chemical vapor deposition method on commercial substrates. The diode structures are irradiated at 25°C by 167-MeV Xe ions with a mass of 131 amu at a fluence of 6 × 10{sup 9} cm{sup −2}. Comparative studies of the optical and electrical properties of as-grown and irradiated structures with Schottky barriers are carried out in the temperature range 23–180°C. The specific features of changes in the photosensitivity and electrical characteristics of the detector structures are accounted for by the capture ofmore » photogenerated carriers into traps formed due to fluctuations of the conduction-band bottom and valence-band top, with subsequent thermal dissociation.« less

Large-Area Direct Hetero-Epitaxial Growth of 1550-nm InGaAsP Multi-Quantum-Well Structures on Patterned Exact-Oriented (001) Silicon Substrates by Metal Organic Chemical Vapor Deposition

NASA Astrophysics Data System (ADS)

Megalini, Ludovico; Cabinian, Brian C.; Zhao, Hongwei; Oakley, Douglas C.; Bowers, John E.; Klamkin, Jonathan

2018-02-01

We employ a simple two-step growth technique to grow large-area 1550-nm laser structures by direct hetero-epitaxy of III-V compounds on patterned exact-oriented (001) silicon (Si) substrates by metal organic chemical vapor deposition. Densely-packed, highly uniform, flat and millimeter-long indium phosphide (InP) nanowires were grown from Si v-grooves separated by silicon dioxide (SiO2) stripes with various widths and pitches. Following removal of the SiO2 patterns, the InP nanowires were coalesced and, subsequently, 1550-nm laser structures were grown in a single overgrowth without performing any polishing for planarization. X-ray diffraction, photoluminescence, atomic force microscopy and transmission electron microscopy analyses were used to characterize the epitaxial material. PIN diodes were fabricated and diode-rectifying behavior was observed.

Quantitative scanning thermal microscopy of ErAs/GaAs superlattice structures grown by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Park, K. W.; Nair, H. P.; Crook, A. M.; Bank, S. R.; Yu, E. T.

2013-02-01

A proximal probe-based quantitative measurement of thermal conductivity with ˜100-150 nm lateral and vertical spatial resolution has been implemented. Measurements on an ErAs/GaAs superlattice structure grown by molecular beam epitaxy with 3% volumetric ErAs content yielded thermal conductivity at room temperature of 9 ± 2 W/m K, approximately five times lower than that for GaAs. Numerical modeling of phonon scattering by ErAs nanoparticles yielded thermal conductivities in reasonable agreement with those measured experimentally and provides insight into the potential influence of nanoparticle shape on phonon scattering. Measurements of wedge-shaped samples created by focused ion beam milling provide direct confirmation of depth resolution achieved.

Synthesis, growth, structural, thermal and optical studies of pyrrolidinium-2-carboxylate-4-nitrophenol single crystals.

PubMed

Swarna Sowmya, N; Sampathkrishnan, S; Vidyalakshmi, Y; Sudhahar, S; Mohan Kumar, R

2015-06-15

Organic nonlinear optical material, pyrrolidinium-2-carboxylate-4-nitrophenol (PCN) was synthesized and single crystals were grown by slow evaporation solution growth method. Single crystal X-ray diffraction analysis confirmed the structure and lattice parameters of PCN crystals. Infrared, Raman and NMR spectral analyses were used to elucidate the functional groups present in the compound. The thermal behavior of synthesized compound was studied by thermogravimetric and differential scanning calorimetry (TG-DSC) analyses. The photoluminescence property was studied by exciting the crystal at 360 nm. The relative second harmonic generation (SHG) efficiency of grown crystal was estimated by using Nd:YAG laser with fundamental wavelength of 1,064 nm. Copyright © 2015 Elsevier B.V. All rights reserved.

FAST TRACK COMMUNICATION: Electronic structure of a graphene/hexagonal-BN heterostructure grown on Ru(0001) by chemical vapor deposition and atomic layer deposition: extrinsically doped graphene

NASA Astrophysics Data System (ADS)

Bjelkevig, Cameron; Mi, Zhou; Xiao, Jie; Dowben, P. A.; Wang, Lu; Mei, Wai-Ning; Kelber, Jeffry A.

2010-08-01

A significant BN-to-graphene charge donation is evident in the electronic structure of a graphene/h-BN(0001) heterojunction grown by chemical vapor deposition and atomic layer deposition directly on Ru(0001), consistent with density functional theory. This filling of the lowest unoccupied state near the Brillouin zone center has been characterized by combined photoemission/k vector resolved inverse photoemission spectroscopies, and Raman and scanning tunneling microscopy/spectroscopy. The unoccupied σ*(Γ1 +) band dispersion yields an effective mass of 0.05 me for graphene in the graphene/h-BN(0001) heterostructure, in spite of strong perturbations to the graphene conduction band edge placement.

Size dependent bandgap of molecular beam epitaxy grown InN quantum dots measured by scanning tunneling spectroscopy

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

Kumar, Mahesh; Roul, Basanta; Central Research Laboratory, Bharat Electronics, Bangalore-560013

InN quantum dots (QDs) were grown on Si (111) by epitaxial Stranski-Krastanow growth mode using plasma-assisted molecular beam epitaxy. Single-crystalline wurtzite structure of InN QDs was verified by the x-ray diffraction and transmission electron microscopy. Scanning tunneling microscopy has been used to probe the structural aspects of QDs. A surface bandgap of InN QDs was estimated from scanning tunneling spectroscopy (STS) I-V curves and found that it is strongly dependent on the size of QDs. The observed size-dependent STS bandgap energy shifts with diameter and height were theoretical explained based on an effective mass approximation with finite-depth square-well potential model.

Charging effect at grain boundaries of MoS2

NASA Astrophysics Data System (ADS)

Yan, Chenhui; Dong, Xi; Li, Connie H.; Li, Lian

2018-05-01

Grain boundaries (GBs) are inherent extended defects in chemical vapor deposited (CVD) transition metal dichalcogenide (TMD) films. Characterization of the atomic structure and electronic properties of these GBs is crucial for understanding and controlling the properties of TMDs via defect engineering. Here, we report the atomic and electronic structure of GBs in CVD grown MoS2 on epitaxial graphene/SiC(0001). Using scanning tunneling microscopy/spectroscopy, we find that GBs mostly consist of arrays of dislocation cores, where the presence of mid-gap states shifts both conduction and valence band edges by up to 1 eV. Our findings demonstrate the first charging effect near GBs in CVD grown MoS2, providing insights into the significant impact GBs can have on materials properties.

SEMICONDUCTOR MATERIALS: Chemical etching of a GaSb crystal incorporated with Mn grown by the Bridgman method under microgravity conditions

NASA Astrophysics Data System (ADS)

Xiaofeng, Chen; Nuofu, Chen; Jinliang, Wu; Xiulan, Zhang; Chunlin, Chai; Yude, Yu

2009-08-01

A GaSb crystal incorporated with Mn has been grown by the Bridgman method on the Polizon facility onboard the FOTON-M3 spacecraft. Structural defects and growth striations have been successfully revealed by the chemical etching method. By calculating various parameters of the convection, the striation patterns can be explained, and the critical value of the Taylor number, which characterizes the convective condition of the rotating magnetic field induced azimuthal flow, was shown. The stresses generated during crystal growth can be reflected by the observations of etch pit distribution and other structural defects. Suggestions for improving the space experiment to improve the quality of the crystal are given.

Second harmonic generation and crystal growth of new chalcone derivatives

NASA Astrophysics Data System (ADS)

Patil, P. S.; Dharmaprakash, S. M.; Ramakrishna, K.; Fun, Hoong-Kun; Sai Santosh Kumar, R.; Narayana Rao, D.

2007-05-01

We report on the synthesis, crystal structure and optical characterization of chalcone derivatives developed for second-order nonlinear optics. The investigation of a series of five chalcone derivatives with the second harmonic generation powder test according to Kurtz and Perry revealed that these chalcones show efficient second-order nonlinear activity. Among them, high-quality single crystals of 3-Br-4'-methoxychalcone (3BMC) were grown by solvent evaporation solution growth technique. Grown crystals were characterized by X-ray powder diffraction (XRD), laser damage threshold, UV-vis-NIR and refractive index measurement studies. Infrared spectroscopy, thermogravimetric analysis and differential thermal analysis measurements were performed to study the molecular vibration and thermal behavior of 3BMC crystal. Thermal analysis does not show any structural phase transition.

Strain-relaxed structure in (001)/(100)-oriented epitaxial PbTiO3 films grown on (100) SrTiO3 substrates by metal organic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Nakaki, Hiroshi; Kim, Yong Kwan; Yokoyama, Shintaro; Ikariyama, Rikyu; Funakubo, Hiroshi; Nishida, Ken; Saito, Keisuke

2007-09-01

The authors grew (001)- and (001)/(100)-oriented epitaxial PbTiO3 films with various thicknesses on (100)SrTiO3 substrates. They used x-ray diffraction to measure the angles between surface normal [001] of (001)-oriented domains and [100] of (100)-oriented domains. The angles were found to be approximately 3.6° when the film thickness exceeded 1100nm. This value is consistent with the value obtained by a geometric calculation for strain-free PbTiO3. This result suggests that thick epitaxial PbTiO3 films grown on (100)SrTiO3 substrates have a fully strain-relaxed structure.

Growth of a New Ternary BON Crystal on Si(100) by Plasma-Assisted MOCVD and Study on the Effects of Fed Gas and Growth Temperature

NASA Astrophysics Data System (ADS)

Chen, G. C.; Lee, S.-B.; Boo, J.-H.

A new ternary BOxNy crystal was grown on Si(100) substrate at 500°C by low-frequency (100 kHz) radio-frequency (rf) derived plasma-assisted MOCVD with an organoborate precursor. The as-grown deposits were characterized by SEM, TED, XPS, XRD, AFM and FT-IR. The experimental results showed that BOxNy crystal was apt to be formed at N-rich atmosphere and high temperature. The decrease of hydrogen flux in fed gases was of benefit to form BON crystal structure. The crystal structure of BOxNy was as similar to that of H3BO3 in this study.

Solidification structures grown under induced flow and continuous casting of steel

NASA Technical Reports Server (NTRS)

Tsavaras, A. A.

1984-01-01

The use of induced flow as a means to control solidification structures in strand cast steel is investigated. The quality problems in strand cast steel stemming from columnar growth can be partially controlled, by Electro Magnetic Stirring (EMS). Induced flow changes the normal morphology of dendrites. Solids grown under intense stirring conditions show both negative and positive segregation which is considered unacceptable by some steel producers. The inclusion size and population is strongly affected by induced flow (EMS). Laboratory and industrial data show substantial reduction in inclusion size and content, but the overall effect of flow on inclusions is affected by the particular type of flow patterns utilized in each case. Productivity and quality are raised substantially in steel strand casting by utilizing EMS.

AlGaAs/InGaAs/AlGaAs double pulse doped pseudomorphic high electron mobility transistor structures on InGaAs substrates

NASA Astrophysics Data System (ADS)

Hoke, W. E.; Lyman, P. S.; Mosca, J. J.; McTaggart, R. A.; Lemonias, P. J.; Beaudoin, R. M.; Torabi, A.; Bonner, W. A.; Lent, B.; Chou, L.-J.; Hsieh, K. C.

1997-10-01

Double pulse doped AlGaAs/InGaAs/AlGaAs pseudomorphic high electron mobility transistor (PHEMT) structures have been grown on InxGa1-xAs (x=0.025-0.07) substrates using molecular beam epitaxy. A strain compensated, AlGaInAs/GaAs superlattice was used for improved resistivity and breakdown. Excellent electrical and optical properties were obtained for 110-Å-thick InGaAs channel layers with indium concentrations up to 31%. A room temperature mobility of 6860 cm2/V s with 77 K sheet density of 4.0×1012cm-2 was achieved. The InGaAs channel photoluminescence intensity was equivalent to an analogous structure on a GaAs substrate. To reduce strain PHEMT structures with a composite InGaP/AlGaAs Schottky layer were also grown. The structures also exhibited excellent electrical and optical properties. Transmission electron micrographs showed planar channel interfaces for highly strained In0.30Ga0.70As channel layers.

Growth, structural, thermal, linear and nonlinear optical and laser damage threshold studies of picolinium tartrate monohydrate single crystals.

PubMed

Peramaiyan, G; Pandi, P; Sornamurthy, B M; Bhagavannarayana, G; Mohan Kumar, R

2012-09-01

Picolinium tartrate monohydrate (PTM), a novel organic nonlinear optical material was synthesized and bulk crystals were grown from aqueous solution by slow cooling technique. The cell parameters of the grown crystal were found by single and powder X-ray diffraction analyses. The crystalline perfection of the grown crystals has been analyzed by high-resolution X-ray diffraction (HRXRD) rocking curve measurements. The presence of functional groups in the grown crystal was identified by FTIR and FT-Raman spectral analyses. UV-Vis spectral studies reveal PTM crystals are transparent in the wavelength region of 295-1100 nm. The thermal characteristics of PTM were analyzed by TGA/DTA studies. The dielectric and mechanical behaviours of PTM crystals were investigated. Dislocation density was estimated to be 2.89 × 10(3) cm(-2) on the flat-surface of PTM crystals from the etching studies. The laser induced surface damage threshold for the grown crystal was measured using Nd:YAG laser. Its second harmonic generation relative efficiency was measured by Kurtz and Perry powder technique and was observed to be comparable with KDP crystal. Copyright © 2012 Elsevier B.V. All rights reserved.

Growth and physicochemical properties of organometallic (DL)-trithioureatartrato-O1,O2,O3-cadmium(II) single crystals

NASA Astrophysics Data System (ADS)

Sathyamoorthy, K.; Vinothkumar, P.; Irshad Ahamed, J.; Murali Manohar, P.; Priya, M.; Liu, Jinghe

2018-04-01

Single crystals of organometallic (DL)-trithioureatartrato-O1,O2,O3-cadmium(II) (TUDLC) have been grown from methanol solution by using the slow evaporation of solvent growth technique. The lattice structure and crystalline perfection have been determined by carrying out single crystal X-ray diffraction and high resolution X-ray diffraction measurements. The grown crystal was characterized thermally and mechanically by carrying out thermo-gravimetric and micro hardness measurements. The linear and nonlinear optical characterizations were made by carrying out optical transmittance, surface laser damage threshold, particle size-dependent second harmonic generation (SHG) efficiency and photo conductivity measurements. The grown crystal was electrically characterized by carrying out frequency-dependent dielectric measurements. Chemical etching study was also carried out and the dislocation density was estimated. Results obtained in the present study indicate that the grown TUDLC crystal is optically transparent with lower cut-off wavelength 304 nm, mechanically soft, thermally stable up to 101 °C and NLO active with SHG efficiency 2.13 (in KDP unit). The grown crystal is found to have considerably large size, good crystalline perfection, large specific heat capacity, higher surface laser damage threshold and negative photoconductivity.

Effect of carbon tetrabromide on the morphology of GaAs nanowires.

PubMed

Salehzadeh, O; Watkins, S P

2011-04-22

Carbon is a commonly used p-type dopant in planar III-V semiconductors, however its use in nanowire (NW) growth has been much less reported. In this work we show that the morphology of gold assisted GaAs NWs can be strongly modified by the presence of CBr(4) vapor during growth by metalorganic vapor phase epitaxy. GaAs NWs were grown under conditions which result in strong tapering and lateral growth at low growth temperatures by the use of triethylgallium (TEGa) instead of the more usual precursor, trimethylgallium (TMGa). Under these conditions, NWs grown in the presence of CBr(4) exhibit higher axial and lower radial growth rates, and negligible tapering compared with NWs grown in the absence of CBr(4) under the same conditions. We attribute this primarily to the suppression of the 2d growth rate by CBr(4), which enhances the axial growth rate of the nanowires. NWs grown with CBr(4) show stacking-fault-free zincblende structure, while the NWs grown without CBr(4) show a high density of stacking faults. This work underlines the striking effects which precursor chemistry can have on nanowire morphology.

Microstructures of GaN1-xPx layers grown on (0001) GaN substrates by gas source molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Seong, Tae-Yeon; Bae, In-Tae; Choi, Chel-Jong; Noh, D. Y.; Zhao, Y.; Tu, C. W.

1999-03-01

Transmission electron microscope (TEM), transmission electron diffraction (TED), and synchrotron x-ray diffraction (XRD) studies have been performed to investigate microstructural behavior of gas source molecular beam epitaxial GaN1-xPx layers grown on (0001) GaN/sapphire at temperatures (Tg) in the range 500-760 °C. TEM, TED, and XRD results indicate that the samples grown at Tg⩽600 °C undergo phase separation resulting in a mixture of GaN-rich and GaP-rich GaNP with zinc-blende structure. However, the samples grown at Tg⩾730 °C are found to be binary zinc-blende GaN(P) single crystalline materials. As for the 500 °C layer, the two phases are randomly oriented and distributed, whereas the 600 °C layer consists of phases that are elongated and inclined by 60°-70° clockwise from the [0001]α-GaN direction. The samples grown at Tg⩾730 °C are found to consist of two types of microdomains, namely, GaN(P)I and GaN(P)II; the former having twin relation to the latter.

Synthesis, characterization and anti-microbial activity of pure, Cu2+ and Cd2+ doped organic NLO l-arginine trifluoroacetate single crystals

NASA Astrophysics Data System (ADS)

Prasanyaa, T.; Haris, M.; Jayaramakrishnan, V.; Amgalan, M.; Mathivanan, V.

2013-10-01

Optically transparent Cu2+ and Cd2+ doped l-arginine trifluoroacetate (LATF) single crystals were grown from its aqueous solution using the slow solvent evaporation technique. The grown crystals were characterized by powder x-ray diffraction to confirm the monoclinic crystal structure. The percentage of transmittance measured using the ultraviolet-visible-near infrared spectrophotometer was found to be more than 80% for doped crystals. The functional group analysis of the grown crystals has been made by Fourier transform infrared spectroscopy. Thermogravimetric/differential thermal analysis was performed for the grown crystals. An atomic absorption study was carried out to determine the presence of Cu2+ and Cd2+. The hardness of the grown crystals was assessed and the results show a significant variation in the hardness value between the pure and doped LATF crystals. The second harmonic generation measurements show that Cu2+ doped LATF is 2.8 times greater and Cd2+ doped is 2.6 times greater than KDP. The anti-bacterial and anti-fungal activities of the title compound were performed using the disc diffusion method against standard bacteria Escherichia coli, Xanthomonas oryzae and against the fungus Aspergillus niger and Aspergillus flavus.

Growth and characterization of metal halide perovskite crystals: Benzyltributyl ammonium tetrachloro manganate(II) monohydrate

NASA Astrophysics Data System (ADS)

Dhandapani, M.; Sugandhi, K.; Nithya, S.; Muthuraja, P.; Balachandar, S.; Aranganayagam, K. R.

2018-05-01

The perovskite type organic-inorganic hybrid benzyltributyl ammoniumtetrachloro manganate (II) monohydrates (BTBA-Mn) are synthesized and the single crystals are grown by slow evaporation solution growth technique. The structure of the grown crystals are confirmed by using X-ray diffraction (XRD), unit cell parameter analysis, Fourier transform Infrared (FTIR), elemental analysis and 13C-NMR spectral studies. Thermogravimetry (TG), differential thermal analysis (DTA) and differential scanning colorimetric (DSC) analysis were carried out to understand thermal stability and occurrence of phase transition.

Evidence for graphite-like hexagonal AlN nanosheets epitaxially grown on single crystal Ag(111)

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

Tsipas, P.; Kassavetis, S.; Tsoutsou, D.

Ultrathin (sub-monolayer to 12 monolayers) AlN nanosheets are grown epitaxially by plasma assisted molecular beam epitaxy on Ag(111) single crystals. Electron diffraction and scanning tunneling microscopy provide evidence that AlN on Ag adopts a graphite-like hexagonal structure with a larger lattice constant compared to bulk-like wurtzite AlN. This claim is further supported by ultraviolet photoelectron spectroscopy indicating a reduced energy bandgap as expected for hexagonal AlN.

Helix handedness of Leptospira interrogans as determined by scanning electron microscopy.

PubMed Central

Carleton, O; Charon, N W; Allender, P; O'Brien, S

1979-01-01

Representative serovars and strains of the seven genetic groups of Leptospira interrogans, and two previously studied serovars, were all found to form exclusively right-handed helices as determined by scanning electron microscopy. No change in handedness occurred in cells grown in a minimal medium (Tween-80 albumin) compared to cells grown in a rich medium (rabbit serum). The right-handedness of the organisms was related to the evolution, cell wall structure, and the mechanism of motility of L. interrogans. Images PMID:438122

Why Won't They Just Do It?

ERIC Educational Resources Information Center

Gilbride, Dennis; Stensrud, Robert

2008-01-01

The gap (structural hole) between the manner in which rehabilitation agencies and business are structured, organized and managed has grown exponentially over the past 10-20 years. Three key changes have radically transformed American business: the globalization of financial capital and competition, the information technology revolution, and the…

Synthesis, growth, structural, optical and thermal properties of an organic single crystal: 4-nitroaniline 4-aminobenzoic acid.

PubMed

Silambarasan, A; Rajesh, P; Ramasamy, P

2014-01-24

The organic single crystals of 4-nitroaniline 4-aminobenzoic acid (4NAABA) were grown from ethanol solvent. The lattice parameters of the grown crystal have been confirmed from single crystal XRD analysis. The powder XRD pattern shows the various planes of grown crystal. The FTIR and (1)H NMR spectral analysis confirm the presence of various functional groups and the placement of proton in 4NAABA compound respectively. The UV absorption was carried out which shows the cutoff wavelength around 459 nm. The optical band gap of the crystal has been evaluated from the transmission spectra and absorption coefficient by extrapolation technique. In addition, a fluorescence spectral analysis is carried out for 4NAABA crystals. The thermal properties of crystals were evaluated from thermogravimetrical analysis. It shows that the grown crystal is stable up to 160°C and the crystal has sharp melting point at 151°C. Copyright © 2013 Elsevier B.V. All rights reserved.

The performance studies of DKDP crystals grown by a rapid horizontal growth method

NASA Astrophysics Data System (ADS)

Xie, Xiaoyi; Qi, Hongji; Wang, Bin; Wang, Hu; Chen, Duanyang; Shao, Jianda

2018-04-01

A deuterated potassium dihydrogen phosphate (DKDP) crystal with about 70% deuterium level was grown by a rapid horizontal growth method with independent design equipment, which includes a continuous filtration system. The cooling program during crystal growth was designed according to a self-developed software to catch the size of growing crystal in real time. The crystal structure, optical performance and laser induced damage threshold (LIDT) of this DKDP crystal were investigated in this paper. The deuterium concentration of the crystal was confirmed by the neutron diffraction technique, which was effective and available in determining a complete range of deuteration level. The dielectric property was measured to evaluate the perfection of the lattice. The transmittance and LIDT were carried out further to evaluate the optical and functional properties of this DKDP crystal grown in the rapid horizontal growth technique. All of the detailed characterization for DKDP figured out that the 70% deuterated KDP crystal grown in this way had relatively good qualities.

Growth and dielectric, mechanical, thermal and etching studies of an organic nonlinear optical L-arginine trifluoroacetate (LATF) single crystal

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

Arjunan, S.; Department of Physics, Presidency College, Chennai 600005; Mohan Kumar, R.

2008-08-04

L-arginine trifluoroacetate, an organic nonlinear optical material, has been synthesized from aqueous solution. Bulk single crystal of dimension 57 mm x 5 mm x 3 mm has been grown by temperature lowering technique. Powder X-ray diffraction studies confirmed the monoclinic structure of the grown L-arginine trifluoroacetate crystal. Linear optical property of the grown crystal has been studied by UV-vis spectrum. Dielectric response of the L-arginine trifluoroacetate crystal was analysed for different frequencies and temperatures in detail. Microhardness study on the sample reveals that the crystal possesses relatively higher hardness compared to many organic crystals. Thermal analyses confirmed that the L-argininemore » trifluoroacetate material is thermally stable upto 212 deg. C. The etching studies have been performed to assess the perfection of the L-arginine trifluoroacetate crystal. Kurtz powder second harmonic generation test confirms the nonlinear optical properties of the as-grown L-arginine trifluoroacetate crystal.« less

Correlation of process parameters and properties of TiO2 films grown by ion beam sputter deposition from a ceramic target

NASA Astrophysics Data System (ADS)

Bundesmann, Carsten; Lautenschläge, Thomas; Spemann, Daniel; Finzel, Annemarie; Mensing, Michael; Frost, Frank

2017-10-01

The correlation between process parameters and properties of TiO2 films grown by ion beam sputter deposition from a ceramic target was investigated. TiO2 films were grown under systematic variation of ion beam parameters (ion species, ion energy) and geometrical parameters (ion incidence angle, polar emission angle) and characterized with respect to film thickness, growth rate, structural properties, surface topography, composition, optical properties, and mass density. Systematic variations of film properties with the scattering geometry, namely the scattering angle, have been revealed. There are also considerable differences in film properties when changing the process gas from Ar to Xe. Similar systematics were reported for TiO2 films grown by reactive ion beam sputter deposition from a metal target [C. Bundesmann et al., Appl. Surf. Sci. 421, 331 (2017)]. However, there are some deviations from the previously reported data, for instance, in growth rate, mass density and optical properties.

Investigation on the growth and characterization of 4-aminobenzophenone single crystal by the vertical dynamic gradient freeze technique

NASA Astrophysics Data System (ADS)

Prabhakaran, SP.; Ramesh Babu, R.; Sukumar, M.; Bhagavannarayana, G.; Ramamurthi, K.

2014-03-01

Growth of bulk single crystal of 4-Aminobenzophenone (4-ABP) from the vertical dynamic gradient freeze (VDGF) setup designed with eight zone furnace was investigated. The experimental parameters for the growth of 4-ABP single crystal with respect to the design of VDGF setup are discussed. The eight zones were used to generate multiple temperature gradients over the furnace, and video imaging system helped to capture the real time growth and solid-liquid interface. 4-ABP single crystal with the size of 18 mm diameter and 40 mm length was grown from this investigation. Structural and optical quality of grown crystal was examined by high resolution X-ray diffraction and UV-visible spectral analysis, respectively and the blue emission was also confirmed from the photoluminescence spectrum. Microhardness number of the crystal was estimated at different loads using Vicker's microhardness tester. The size and quality of single crystal grown from the present investigation are compared with the vertical Bridgman grown 4-ABP.

Effect of solvents on the bulk growth of 4-aminobenzophenone single crystals: A potential material for blue and green lasers

NASA Astrophysics Data System (ADS)

Natarajan, V.; Usharani, S.; Arivanandhan, M.; Anandan, P.; Hayakawa, Y.

2015-06-01

Although 4-aminobenzophenone (4-ABP) is the best derivative of benzophenone with 260 times higher second harmonic generation (SHG) efficiency than potassium dihydrogen phosphate (KDP), growth of high quality bulk crystal still remains a difficult task. In the present work, the effect of solvents on solubility and growth aspects of 4-ABP was investigated to grow inclusion free 4-ABP crystals. The growth processes were discussed based on solute-solvent interaction in two different growth media of ethyl acetate and ethanol. The growth rate and thereby solvent inclusions are relatively higher in ethyl acetate grown crystal than the crystal grown from ethanol. The structural, thermal and optical properties of 4-ABP crystals were studied. The enthalpy of 4-ABP melting process was estimated from differential thermal analysis. The optical transmission study shows that 4-ABP crystals grown from ethanol has high transparency compared to ethyl acetate grown sample due to solvent inclusion in the later crystal.

Cytochrome components of nitrate- and sulfate-respiring Desulfovibrio desulfuricans ATCC 27774.

PubMed Central

Liu, M C; Costa, C; Coutinho, I B; Moura, J J; Moura, I; Xavier, A V; LeGall, J

1988-01-01

Three multiheme c-type cytochromes--the tetraheme cytochrome c3 (molecular weight [MW] 13,500), a dodecaheme cytochrome c (MW 40,800), and a "split-Soret" cytochrome c (MW 51,540), which is a dimer with 2 hemes per subunit (MW 26,300)--were isolated from the soluble fraction of Desulfovibrio desulfuricans (ATCC 27774) grown under nitrate- or sulfate-respiring conditions. Two of them, the dodecaheme and the split-Soret cytochromes, showed no similarities to any of the c-type cytochromes isolated from other sulfate-reducing bacteria, while the tetraheme cytochrome c3 appeared to be analogous to the cytochrome c3 found in other sulfate-reducing bacteria. For all three multiheme c-type cytochromes isolated, the homologous proteins from nitrate- and sulfate-grown cells were indistinguishable in amino acid composition, physical properties, and spectroscopic characteristics. It therefore appears that the same c-type cytochrome components are present when D. desulfuricans ATCC 27774 cells are grown under either condition. This is in contrast to the considerable difference found in Pseudomonas perfectomarina (Liu et al., J. Bacteriol. 154:278-286, 1983), a marine denitrifier, when the cells are grown on nitrate or oxygen as the terminal electron acceptor. In addition, two spectroscopy methods capable of revealing minute structural variations in proteins provided identical information about the tetraheme cytochrome c3 from nitrate-grown and sulfate-grown cells. PMID:2848008

An observation of direct-gap electroluminescence in GaAs structures with Ge quantum wells

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

Aleshkin, V. Ya.; Dikareva, N. V.; Dubinov, A. A., E-mail: sanya@ipm.sci-nnov.ru

2015-02-15

A light-emitting diode structure based on GaAs with eight narrow Ge quantum wells is grown by laser sputtering. An electroluminescence line polarized predominately in the plane parallel to the constituent layers of the structure is revealed. The line corresponds to the direct optical transitions in momentum space in the Ge quantum wells.

Growth and structure of hydrogenated carbon films containing fullerene-like structure

NASA Astrophysics Data System (ADS)

Wang, Peng; Wang, Xia; Liu, Weimin; Zhang, Junyan

2008-04-01

Hydrogenated carbon films were prepared by magnetron sputtering of a titanium target in methane and argon atmosphere. The film grown at -800 V bias exhibits excellent mechanical properties with a hardness of 20.9 GPa and an elastic recovery as high as 85%. Its structure, characterized by high-resolution transmission electron microscopy, Raman spectrum, and x-ray photoelectron spectroscopy, can be described as fullerene-like structures uniformly dispersed in an amorphous carbon matrix. In order to reveal the evolution of fullerene-like structures in our films, different bias voltages were introduced. The results show that high bias voltage leads to the accumulation of high compressive internal stress in the film and promotes the evolution of fullerene-like structures. Although the film grown at -800 V bias presents high sp2 bonding content, it exhibits good mechanical properties with high hardness and high elasticity at the same time; we attribute it to the unique structure of the film, in which a fullerene-like structure, just like a molecule spring dispersed in the film, reserves the elastic energy during distortion through reversible bond rotation and bond angle deflection, while the amorphous carbon matrix restrains the relaxation of the rigid C-C network and compressive stress and restricts the slip of graphene sheets.

Determination of composition of non-homogeneous GaInNAs layers

NASA Astrophysics Data System (ADS)

Pucicki, D.; Bielak, K.; Ściana, B.; Radziewicz, D.; Latkowska-Baranowska, M.; Kováč, J.; Vincze, A.; Tłaczała, M.

2016-01-01

Dilute nitride GaInNAs alloys grown on GaAs have become perspective materials for so called low-cost GaAs-based devices working within the optical wavelength range up to 1.6 μm. The multilayer structures of GaInNAs/GaAs multi-quantum well (MQW) samples usually are analyzed by using high resolution X-ray diffraction (HRXRD) measurements. However, demands for precise structural characterization of the GaInNAs containing heterostructures requires taking into consideration all inhomogeneities of such structures. This paper describes some of the material challenges and progress in structural characterization of GaInNAs layers. A new algorithm for structural characterization of dilute nitrides which bounds contactless electro-reflectance (CER) or photo-reflectance (PR) measurements and HRXRD analysis results together with GaInNAs quantum well band diagram calculation is presented. The triple quantum well (3QW) GaInNAs/GaAs structures grown by atmospheric-pressure metalorganic vapor-phase epitaxy (AP-MOVPE) were investigated according to the proposed algorithm. Thanks to presented algorithm, more precise structural data including the nonuniformity in the growth direction of GaInNAs/GaAs QWs were achieved. Therefore, the proposed algorithm is mentioned as a nondestructive method for characterization of multicomponent inhomogeneous semiconductor structures with quantum wells.

Origin of a needle-like granular structure for ultrananocrystalline diamond films grown in a N2/CH4 plasma

NASA Astrophysics Data System (ADS)

Sankaran, K. J.; Kurian, J.; Chen, H. C.; Dong, C. L.; Y Lee, C.; Tai, N. H.; Lin, I. N.

2012-09-01

Microstructural evolution as a function of substrate temperature (TS) for conducting ultrananocrystalline diamond (UNCD) films is systematically studied. Variation of the sp2 graphitic and sp3 diamond content with TS in the films is analysed from the Raman and near-edge x-ray absorption fine structure spectra. Morphological and microstructural studies confirm that at TS = 700 °C well-defined acicular structures evolve. These nanowire structures comprise sp3 phased diamond, encased in a sheath of sp2 bonded graphitic phase. TS causes a change in morphology and thereby the various properties of the films. For TS = 800 °C the acicular grain growth ceases, while that for TS = 700 °C ceases only upon termination of the deposition process. The grain-growth process for the unique needle-like granular structure is proposed such that the CN species invariably occupy the tip of the nanowire, promoting an anisotropic grain-growth process and the formation of acicular structure of the grains. The electron field emission studies substantiate that the films grown at TS = 700 °C are the most conducting, with conduction mediated through the graphitic phase present in the films.

High resolution x-ray diffraction of high quality 2 micron quaternary indium gallium arsenide antimonide digital alloy heterostructures grown by modulated molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Mourad, Carole Issa

2000-10-01

Growth of high quality mixed anion alloys such as InGaAsSb and AlGaAsSb are critical to laser heterostructures designed for 2--4 micron emission. However, run-to-run reproducibility as well as the ability to reproducibly change alloy compositions within a heterostructure tend to be poor. This is because the competition for incorporation between the two anions (As and Sb) is extremely sensitive to a large number of growth parameters such as temperature, incident fluxes, and growth rate, which may drift during the course of deposition, or are difficult to reset during growth. With the intent of improving reproducibility, we have grown and characterized InGaAsSb and AlGaAsSb "digital alloys" deposited using modulated incident As2 and Sb2 incident fluxes. In0.1Ga 0.9AsySb1-y alloy layers were grown by alternately exposing the film surface to As2 and Sb2 fluxes with a periodicity ranging from ˜9 to ˜22 A. Average alloy composition is determined by the duty-cycle of the anion-oven shutters. Structural characterization using high-resolution x-ray diffraction (HRXRD) shows clear satellite peaks indicating that the digital alloys retain the compositional modulation. Optical characterization using photoluminescence indicate that the digital alloys can successfully replace the conventionally grown quaternary alloys with the same average composition. In addition we have characterized digitally grown InGaAsSb layers using HRXRD and measured the sensitivity of the resulting average composition to the growth temperature. We find that the composition of In0.1Ga0.9AsySb1-y alloy layers grown digitally on GaSb substrates is nearly three times less sensitive to the growth temperature as conventional growth. Digital growth of InGaAsSb and AlGaAsSb layers has enabled the growth of heterostructures containing multiple alloy compositions by toggling between shutter duty-cycles during growth, without necessitating changes to the oven temperatures throughout deposition. We have grown and characterized optically pumped ˜2mum laser structures with InGaAsSb quantum wells and AlGaAsSb barriers both grown using the digital alloy technique. Room temperature operation, a low threshold current density of 104 W/cm2 (at 80K with 808nm pump), and a characteristic temperature (To) of 104 K show the feasibility of applying digital alloying techniques to mid-infrared optical devices.

Increased occurrence of pesticide residues on crops grown in protected environments compared to crops grown in open field conditions.

PubMed

Allen, Gina; Halsall, Crispin J; Ukpebor, Justina; Paul, Nigel D; Ridall, Gareth; Wargent, Jason J

2015-01-01

Crops grown under plastic-clad structures or in greenhouses may be prone to an increased frequency of pesticide residue detections and higher concentrations of pesticides relative to equivalent crops grown in the open field. To test this we examined pesticide data for crops selected from the quarterly reports (2004-2009) of the UK's Pesticide Residue Committee. Five comparison crop pairs were identified whereby one crop of each pair was assumed to have been grown primarily under some form of physical protection ('protected') and the other grown primarily in open field conditions ('open'). For each pair, the number of detectable pesticide residues and the proportion of crop samples containing pesticides were statistically compared (n=100 s samples for each crop). The mean concentrations of selected photolabile pesticides were also compared. For the crop pairings of cabbage ('open') vs. lettuce ('protected') and 'berries' ('open') vs. strawberries ('protected') there was a significantly higher number of pesticides and proportion of samples with multiple residues for the protected crops. Statistically higher concentrations of pesticides, including cypermethrin, cyprodinil, fenhexamid, boscalid and iprodione were also found in the protected crops compared to the open crops. The evidence here demonstrates that, in general, the protected crops possess a higher number of detectable pesticides compared to analogous crops grown in the open. This may be due to different pesticide-use regimes, but also due to slower rates of pesticide removal in protected systems. The findings of this study raise implications for pesticide management in protected-crop systems. Copyright © 2014 Elsevier Ltd. All rights reserved.

Photoluminescence studies of a perceived white light emission from a monolithic InGaN/GaN quantum well structure

PubMed Central

Ben Sedrine, N.; Esteves, T. C.; Rodrigues, J.; Rino, L.; Correia, M. R.; Sequeira, M. C.; Neves, A. J.; Alves, E.; Bockowski, M.; Edwards, P. R.; O’Donnell, K. P.; Lorenz, K.; Monteiro, T.

2015-01-01

In this work we demonstrate by photoluminescence studies white light emission from a monolithic InGaN/GaN single quantum well structure grown by metal organic chemical vapour deposition. As-grown and thermally annealed samples at high temperature (1000 °C, 1100 °C and 1200 °C) and high pressure (1.1 GPa) were analysed by spectroscopic techniques, and the annealing effect on the photoluminescence is deeply explored. Under laser excitation of 3.8 eV at room temperature, the as-grown structure exhibits two main emission bands: a yellow band peaked at 2.14 eV and a blue band peaked at 2.8 eV resulting in white light perception. Interestingly, the stability of the white light is preserved after annealing at the lowest temperature (1000 °C), but suppressed for higher temperatures due to a deterioration of the blue quantum well emission. Moreover, the control of the yellow/blue bands intensity ratio, responsible for the white colour coordinate temperatures, could be achieved after annealing at 1000 °C. The room temperature white emission is studied as a function of incident power density, and the correlated colour temperature values are found to be in the warm white range: 3260–4000 K. PMID:26336921

Structural, thermal, laser damage, photoconductivity, NLO and mechanical properties of modified vertical Bridgman method grown AgGa0.5In0.5Se2 single crystal

NASA Astrophysics Data System (ADS)

Vijayakumar, P.; Ramasamy, P.

2016-08-01

AgGa0.5In0.5Se2 single crystal was grown using modified vertical Bridgman method. The structural perfection of the AgGa0.5In0.5Se2 single crystal has been analyzed by high-resolution X-ray diffraction rocking curve measurements. The structural and compositional uniformities of AgGa0.5In0.5Se2 were studied using Raman scattering spectroscopy at room temperature. The FWHM of the Γ1 (W1) and Γ5L (Γ15) measured at different regions of the crystal confirms that the composition throughout its length is fairly uniform. Thermal properties of the as-grown crystal, including specific heat, thermal diffusivity and thermal conductivity have been investigated. The multiple shot surface laser damage threshold value was measured using Nd:YAG laser. Photoconductivity measurements with different temperatures have confirmed the positive photoconducting behavior. Second harmonic generation (SHG) on powder samples has been measured using the Kurtz and Perry technique and the results display that AgGa0.5In0.5Se2 is a phase-matchable NLO material. The hardness behavior has been measured using Vickers micro hardness measurement and the indentation size effect has been observed. The classical Meyer's law, propositional resistance model and modified propositional resistance model have been used to analyse the micro hardness behavior.

Impact of Substrate Types on Structure and Emission of ZnO Nanocrystalline Films

NASA Astrophysics Data System (ADS)

Ballardo Rodriguez, I. Ch.; El Filali, B.; Díaz Cano, A. I.; Torchynska, T. V.

2018-02-01

Zinc oxide (ZnO) films were simultaneously synthesized by an ultrasonic spray pyrolysis (USP) method on p-type Si (100), silicon carbide polytype [6H-SiC (0001)], porous 6H-SiC and amorphous glass substrates with the aim of studying the impact of substrate types on the structure and emission of ZnO nanocrystalline films. Porous silicon carbide (P-SiC) was prepared by the electrochemical anodization method at a constant potential of 20 V and etching time of 12 min. ZnO films grown on the SiC and P-SiC substrates are characterized by a wurtzite crystal structure with preferential growth along the (002) direction and with grain sizes of 90-180 and 70-160 nm, respectively. ZnO films grown on the Si substrate have just some small irregular hexagonal islands. The amorphous glass substrate did not promote the formation of any regular crystal forms. The obtained x-ray diffraction and photoluminescence (PL) results have shown that the better ZnO film crystallinity and high PL intensity of near-band edge emissions were achieved in the films grown on the porous SiC and SiC substrates. The preferential growth and crystalline nature of ZnO films on the SiC substrate have been discussed from the point of view of the lattice parameter compatibility between ZnO and SiC crystals.

Growth, structure, and magnetic properties of {gamma}-Fe{sub 2}O{sub 3} epitaxial films on MgO

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

Gao, Y.; Kim, Y.J.; Thevuthasan, S.

1997-04-01

Single-crystal epitaxial thin films of {gamma}-Fe{sub 2}O{sub 3}(001) have been grown on MgO(001) using oxygen-plasma-assisted molecular beam epitaxy. The structure and magnetic properties of these films have been characterized by a variety of techniques, including reflection high-energy electron diffraction (RHEED), low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy and x-ray photoelectron/Auger electron diffraction (XPD/AED), vibrating sample magnetometry, and ferromagnetic resonance. Real-time RHEED reveals that the film growth occurs in a layer-by-layer fashion. The {gamma}-Fe{sub 2}O{sub 3}(001) film surface exhibits a (1{times}1) LEED pattern. The growth of {gamma}-Fe{sub 2}O{sub 3} films at 450 {degree}C is accompanied by significant Mg outdiffusion. AED ofmore » Mg KLL Auger emission reveals that Mg substitutionally incorporates in the {gamma}-Fe{sub 2}O{sub 3} lattice, occupying the octahedral sites. Magnetic moments are {approximately}2300 G and {approximately}4500 G for {gamma}-Fe{sub 2}O{sub 3} films grown at 250{degree}C and 450{degree}C, respectively. The high magnetic moment for the films grown at 450{degree}C could be attributed to the high degree of structural order of the films and Mg substitution at octahedral sites. {copyright} {ital 1997 American Institute of Physics.}« less

Enhancement of optical and structural quality of semipolar (11-22) GaN by introducing nanoporous SiNx interlayers

NASA Astrophysics Data System (ADS)

Monavarian, Morteza; Metzner, Sebastian; Izyumskaya, Natalia; Müller, Marcus; Okur, Serdal; Zhang, Fan; Can, Nuri; Das, Saikat; Avrutin, Vitaliy; Özgür, Ümit; Bertram, Frank; Christen, Juergen; Morkoç, Hadis

2015-03-01

Enhancement of optical and structural quality of semipolar (11‾22) GaN grown by metal-organic chemical vapor deposition on planar m-sapphire substrates was achieved by using an in-situ epitaxial lateral overgrowth (ELO) technique with nanoporous SiNx layers employed as masks. In order to optimize the procedure, the effect of SiNx deposition time was studied by steady-state photoluminescence (PL), and X-ray diffraction. The intensity of room temperature PL for the (11‾22) GaN layers grown under optimized conditions was about three times higher compared to those for the reference samples having the same thickness but no SiNx interlayers. This finding is attributed to the blockage of extended defect propagation toward the surface by the SiNx interlayers as evidenced from the suppression of emissions associated with basal-plane and prismatic stacking faults with regard to the intensity of donor bound excitons (D0X) in lowtemperature PL spectra. In agreement with the optical data, full width at half maximum values of (11‾22) X-ray rocking curves measured for two different in-plane rotational orientations of [1‾100] and [11‾23] reduced from 0.33º and 0.26º for the reference samples to 0.2º and 0.16º for the nano-ELO structures grown under optimized conditions, respectively.

Effect of Arbuscular Mycorrhizal Fungi on Plant Biomass and the Rhizosphere Microbial Community Structure of Mesquite Grown in Acidic Lead/Zinc Mine Tailings

PubMed Central

Solís-Domínguez, Fernando A.; Valentín-Vargas, Alexis; Chorover, Jon; Maier, Raina M.

2011-01-01

Mine tailings in arid and semi-arid environments are barren of vegetation and subject to eolian dispersion and water erosion. Revegetation is a cost-effective strategy to reduce erosion processes and has wide public acceptance. A major cost of revegetation is the addition of amendments, such as compost, to allow plant establishment. In this paper we explore whether arbuscular mycorrhizal fungi (AMF) can help support plant growth in tailings at a reduced compost concentration. A greenhouse experiment was performed to determine the effects of three AMF inocula on biomass, shoot accumulation of heavy metals, and changes in the rhizosphere microbial community structure of the native plant Prosopis juliflora (mesquite). Plants were grown in an acidic lead/zinc mine tailings amended with 10% (w/w) compost amendment, which is slightly sub-optimal for plant growth in these tailings. After two months, AMF-inoculated plants showed increased dry biomass and root length (p < 0.05) and effective AMF colonization compared to controls grown in uninoculated compost-amended tailings. Mesquite shoot tissue lead and zinc concentrations did not exceed domestic animal toxicity limits regardless of whether AMF inoculation was used. The rhizosphere microbial community structure was assessed using denaturing gradient gel electrophoresis (DGGE) profiles of the small subunit RNA gene for bacteria and fungi. Canonical correspondence analysis (CCA) of DGGE profiles showed that the rhizosphere fungal community structure at the end of the experiment was significantly different from the community structure in the tailings, compost, and AMF inocula prior to planting. Further, CCA showed that AMF inoculation significantly influenced the development of both the fungal and bacterial rhizosphere community structures after two months. The changes observed in the rhizosphere microbial community structure may be either a direct effect of the AMF inocula, caused by changes in plant physiology induced by AMF, or a combination of both mechanisms. PMID:21211826

Role of low O 2 pressure and growth temperature on electrical transport of PLD grown ZnO thin films on Si substrates

NASA Astrophysics Data System (ADS)

Pandis, Ch.; Brilis, N.; Tsamakis, D.; Ali, H. A.; Krishnamoorthy, S.; Iliadis, A. A.

2006-06-01

Undoped ZnO thin films have been grown on (100) Si substrates by pulsed laser deposition. The effect of growth parameters such as temperature, O 2 partial pressure and laser fluence on the structural and electrical properties of the films has been investigated. It is shown that the well-known native n-type conductivity, attributed to the activation of hydrogenic donor states, exhibits a conversion from n-type to p-type when the O 2 partial pressure is reduced from 10 -4 to 10 -7 Torr at growth temperatures lower than 400 °C. The p-type conductivity could be attributed to the dominant role of the acceptor Zn vacancies for ZnO films grown at very low O 2 pressures.

Surface potential driven dissolution phenomena of [0 0 0 1]-oriented ZnO nanorods grown from ZnO and Pt seed layers

NASA Astrophysics Data System (ADS)

Seo, Youngmi; Kim, Jung Hyeun

2011-06-01

Highly oriented ZnO nanorods are synthesized hydrothermally on ZnO and Pt seed layers, and they are dissolved in KOH solution. The rods grown on ZnO seed layer show uniform dissolution, but those grown on Pt seed layer are rod-selectively dissolved. The ZnO nanorods from both seed layers show the same crystalline structure through XRD and Raman spectrometer data. However, the surface potential analysis reveals big difference for ZnO and Pt seed cases. The surface potential distribution is very uniform for the ZnO seed case, but it is much fluctuated on the Pt seed case. It suggests that the rod-selective dissolution phenomena on Pt seed case are likely due to the surface energy difference.

White emission from non-planar InGaN/GaN MQW LEDs grown on GaN template with truncated hexagonal pyramids.

PubMed

Lee, Ming-Lun; Yeh, Yu-Hsiang; Tu, Shang-Ju; Chen, P C; Lai, Wei-Chih; Sheu, Jinn-Kong

2015-04-06

Non-planar InGaN/GaN multiple quantum well (MQW) structures are grown on a GaN template with truncated hexagonal pyramids (THPs) featuring c-plane and r-plane surfaces. The THP array is formed by the regrowth of the GaN layer on a selective-area Si-implanted GaN template. Transmission electron microscopy shows that the InGaN/GaN epitaxial layers regrown on the THPs exhibit different growth rates and indium compositions of the InGaN layer between the c-plane and r-plane surfaces. Consequently, InGaN/GaN MQW light-emitting diodes grown on the GaN THP array emit multiple wavelengths approaching near white light.

A metal-semiconductor-metal detector based on ZnO nanowires grown on a graphene layer.

PubMed

Xu, Qiang; Cheng, Qijin; Zhong, Jinxiang; Cai, Weiwei; Zhang, Zifeng; Wu, Zhengyun; Zhang, Fengyan

2014-02-07

High quality ZnO nanowires (NWs) were grown on a graphene layer by a hydrothermal method. The ZnO NWs revealed higher uniform surface morphology and better structural properties than ZnO NWs grown on SiO2/Si substrate. A low dark current metal-semiconductor-metal photodetector based on ZnO NWs with Au Schottky contact has also been fabricated. The photodetector displays a low dark current of 1.53 nA at 1 V bias and a large UV-to-visible rejection ratio (up to four orders), which are significantly improved compared to conventional ZnO NW photodetectors. The improvement in UV detection performance is attributed to the existence of a surface plasmon at the interface of the ZnO and the graphene.

Inversion by metalorganic chemical vapor deposition from N- to Ga-polar gallium nitride and its application to multiple quantum well light-emitting diodes

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

Hosalli, A. M.; Van Den Broeck, D. M.; Bedair, S. M.

2013-12-02

We demonstrate a metalorganic chemical vapor deposition growth approach for inverting N-polar to Ga-polar GaN by using a thin inversion layer grown with high Mg flux. The introduction of this inversion layer allowed us to grow p-GaN films on N-polar GaN thin film. We have studied the dependence of hole concentration, surface morphology, and degree of polarity inversion for the inverted Ga-polar surface on the thickness of the inversion layer. We then use this approach to grow a light emitting diode structure which has the MQW active region grown on the advantageous N-polar surface and the p-layer grown on themore » inverted Ga-polar surface.« less

Changes in Escherichia coli cells starved in seawater or grown in seawater-wastewater mixtures.

PubMed Central

Munro, P M; Gauthier, M J; Laumond, F M

1987-01-01

Some metabolic modifications of Escherichia coli cells during starvation in seawater were studied in laboratory microcosms. The apparent die-off of this bacterium under such conditions, as observed by comparing the enumeration of CFU in conventional freshwater media and direct epifluorescence counts, was partially prevented when cells were previously grown in salted organic medium or on seawater-wastewater agar. beta-Galactosidase activity of starved cells disappeared gradually with time, even though some other enzymatic activities, such as that of alkaline phosphatase, increased. Moreover, some modifications of sensitivity to antibiotics, heavy metals, and bacteriophages in seawater- and wastewater-grown cells suggested that the cells undergo structural changes under natural marine conditions. These results provide additional experimental data indicating the possible active adaptation of E. coli cells to seawater. PMID:3116927

Growth and characterization of hexamethylenetetramine crystals grown from solution

NASA Astrophysics Data System (ADS)

Babu, B.; Chandrasekaran, J.; Balaprabhakaran, S.

2014-06-01

Organic nonlinear optical single crystals of hexamethylenetetramine (HMT; 10 × 10 × 5 mm3) were prepared by crystallization from methanol solution. The grown crystals were subjected to various characterization techniques such as single crystal XRD, powder XRD, UV-Vis and electrical studies. Single crystal XRD analysis confirmed the crystalline structure of the grown crystals. Their crystalline nature was also confirmed by powder XRD technique. The optical transmittance property was identified from UV-Vis spectrum. Dielectric measurements were performed as a function of frequency at different temperatures. DC conductivity and photoconductivity studies were also carried out for the crystal. The powder second harmonic generation efficiency (SHG) of the crystal was measured using Nd:YAG laser and the efficiency was found to be two times greater than that of potassium dihydrogen phosphate (KDP).

Room-temperature continuous-wave operation in the telecom wavelength range of GaSb-based lasers monolithically grown on Si

NASA Astrophysics Data System (ADS)

Castellano, A.; Cerutti, L.; Rodriguez, J. B.; Narcy, G.; Garreau, A.; Lelarge, F.; Tournié, E.

2017-06-01

We report on electrically pumped GaSb-based laser diodes monolithically grown on Si and operating in a continuous wave (cw) in the telecom wavelength range. The laser structures were grown by molecular-beam epitaxy on 6°-off (001) substrates. The devices were processed in coplanar contact geometry. 100 μm × 1 mm laser diodes exhibited a threshold current density of 1 kA/cm-2 measured under pulsed operation at 20 °C. CW operation was achieved up to 35 °C with 10 μm × 1 mm diodes. The output power at 20 °C was around 3 mW/uncoated facet, and the cw emission wavelength 1.59 μm, in the C/L-band of telecom systems.

Synthesis, growth, structural and optical studies of organic nonlinear optical material--piperazine-1,4-diium bis 2,4,6-trinitrophenolate.

PubMed

Suguna, S; Anbuselvi, D; Jayaraman, D; Nagaraja, K S; Jeyaraj, B

2014-11-11

Piperazine-1,4-diium bis 2,4,6-trinitrophenolate is one of the useful organic materials with nonlinear optical (NLO) and pharmaceutical applications. The material was grown by slow evaporation solution growth method at room temperature. The crystal system and lattice parameters were identified by single crystal XRD analysis. The grown material crystallizes in monoclinic system with P21/n space group. The main functional groups NH2, NO2, CN, CC, and phenolic 'O' atom were identified using FTIR analysis. The protons and carbons of grown crystal with various chemical environments were studied by 1H and 13C NMR spectroscopy to confirm the molecular structure. The optical properties of the crystal were studied by UV-vis-NIR spectroscopy and the transmission 100% range starts from 532 nm onwards. The optical band gap was measured as 2.63 eV from the plot of (αhν)2 versus hν. The thermal stability was detected at 304.1°C using TG-DTA analysis. The dielectric studies of the sample were carried out at different temperatures in the frequency range from 50 Hz to 5 MHz to establish the dielectric nature of the crystal. Photoconductivity measurements were carried out on the grown crystal. The Second Harmonic Generation (SHG) of the crystal was tested to confirm the nonlinear optical property. Copyright © 2014 Elsevier B.V. All rights reserved.

Crystal growth and dislocation etch pits observation of chalcopyrite CdSiP2

NASA Astrophysics Data System (ADS)

He, Zhiyu; Zhao, Beijun; Zhu, Shifu; Chen, Baojun; Huang, Wei; Lin, Li; Feng, Bo

2018-01-01

CdSiP2 is the only crystal that can offer Non-critical Phase Matching (NCPM) for a 1064 nm pumped optical parametric oscillation (OPO) with idler output in the 6 μm range. In this paper, a large, crack-free CdSiP2 single crystal measuring 18 mm in diameter and 65 mm in length was successfully grown by the Vertical Bridgman method (MVB) with an explosion-proof quartz ampoule. The results of lattice parameters, element composition and IR transmittance of the as-grown crystal characterized by X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDS) and Fourier transformation infrared spectrometer (FTIR) showed the as grown crystal crystallized well and the absorption coefficients at 4878 cm-1 and 2500 cm-1 were 0.14 cm-1 and 0.06 cm-1. Moreover, a new etchant composed of Br2, HCl, HNO3, CH3OH and H2O (1:800:800:400:400 in volume ratio) was prepared and the dislocation etch pits on oriented faces of as-grown CdSiP2 crystal were observed for the first time. It is found the etch pits are in rectangular structure on the (1 0 1) face, but in trigonal pyramid structure on (3 1 2) face. According to the quantities of the etch pits, the average densities of dislocation were evaluated to be 2.28 × 105/cm2 and 1.4 × 105/cm2, respectively.

Film growth and structure design in the barium oxide-strontium oxide-titanium dioxide system

NASA Astrophysics Data System (ADS)

Fisher, Patrick J.

This thesis describes the growth and characterization of thin films in the SrO-BaO-TiO2 system. The films are grown by molecular beam cpitaxy (MBE) and pulsed laser deposition (PLD) on ceramic substrates, and characterized using X-ray diffraction (XRD), atomic force microscopy (AFM), reflection-high energy electron diffraction (RHEED), and transmission electron microscopy (TEM). Films are grown with varied global and initial local stoichiometries, with the goal of determining the stability of specific cation organizations. Simple oxides, TiO2 (anatase) and SrO (rock salt) were grown on oxide substrates using MBE. Growth conditions, including substrate material, substrate temperature, O3 flux, and metal flux, are varied in each case. It is observed that the growth morphology of anatase is highly dependent on the ozone flux, with fluxes of 1.00 sccm and greater resulting in flat anatase surfaces. Increased roughness at higher substrate was determined to be a result of rutile inclusions. Growth oscillations are observed in the RHEED intensity for both TiO2 and SrO in overlapping regions of growth space, indicating 2D growth modes. Varied shuttering sequences were used during MBE growth of perovskites: globally non-stoichiometric films, as well as locally non-stoichiometric but globally stoichiometric perovskite. Films were grown within a (SrO) m(TiO2)n framework, where growth cycles involved m monolayers of SrO followed by n monolayers of TiO2. XRD results indicate that Ruddlesden-Popper defects, that is, rock salt double layers, enable incorporation of all levels of Sr excess, whereas excess Ti is observed to incorporate into the perovskite structure only at extreme excesses. A series of films with m equal to n were grown; that is, multiple monolayers of SrO deposited followed by multiple monolayers of TiO2. These initially locally non-stoichiometric arrangements interreact to form highly crystalline perovskite, even with layer thicknesses of up to 33 monolayers. The Ba0.6Sr0.4TiO3 films were characterized for their microwave dielectric properties, and were found to have high dielectric constants (epsilonr ˜1300 in each case, implying high tunabilities) but high tan delta values as well. The mechanisms by which the perovskite structure incorporates cation excesses is discussed, and it is argued that two probable mechanisms, one involving plane-sharing of Ti and Sr cations and the other involving rock salt multilayers, also enable the observed transport necessary for multilayer reaction. Working under the argument that these mechanisms involve low-energy architectures, a novel homologous series of phases based on rock salt multilayers is grown using monotayer control: the SrmTiO2+ m series, with each TiO2 monolayer followed by m SrO monolayers (m = 1-5). The phases in this series were characterized structurally, and an in-plane contraction was observed between the m = 2 and m = 3 phases, which is argued to be a relaxation of the SrO monolayers. Considering Ti-excess organizations, the BaTi2O5 structure is grown and observed to nucleate over a narrow window of growth conditions and substrates. LaAlO 3(100) promotes the nucleation of anatasc and ejection of perovskite; SrTiO3(100) promotes the nucleation of perovskite and ejection of TiO2; importantly, MgO(100) promotes the nucleation (010)-oriented BaTi2O5 growing with multiple domains. A BaTi2 O5 buffer layer was then used to promote the inclusion of Sr into (Ba,SOTi205 epilayers. Sr incorporation into a perovskite-related structure was observed to occur over the full range of (Ba,Sr)Ti2O 5 compositions.

Growth of semimetallic ErAs films epitaxially embedded in GaAs

NASA Astrophysics Data System (ADS)

Crook, Adam M.; Nair, Hari P.; Lee, Jong H.; Ferrer, Domingo A.; Akinwande, Deji; Bank, Seth R.

2011-10-01

We present models for the growth and electrical conductivity of ErAs films grown with the nanoparticle-seeded film growth technique. This growth mode overcomes the mismatch in rotational symmetry between the rocksalt ErAs crystal structure and the zincblende GaAs crystal structure. This results in films of ErAs grown through a thin film of GaAs that preserves the symmetry of the substrate. The conductivity of the films, as a function of film thickness, are investigated and a surface roughness model is used to explain observed trends. Transmission electron micrographs confirm the suppression of anti-phase domains. A simple diffusion model is developed to describe the diffusion and incorporation of surface erbium into subsurface ErAs layers and predict potential failure mechanisms of the growth method.

A novel organic nonlinear optical crystal: Creatininium succinate

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

Thirumurugan, R.; Anitha, K., E-mail: singlecerystalxrd@gmail.ciom

2015-06-24

A novel organic material complex of creatininium succinate (CS) has been synthesized and single crystals were grown by the reaction of creatinine and succinic acid from aqueous solution by employing the technique of slow evaporation at room temperature. The structure of the grown crystal has been elucidated using single crystal X-ray diffraction analysis and the structure was refined by least-squares method to R = 0.027 for 1840 reflections. FT-IR spectral investigation has been carried out to identify the various functional groups in the title compound. UV–Vis transmission was carried out which shows the crystal has a good optical transmittance inmore » the visible region with lower cutoff wavelength around 220 nm. Nonlinear optical property of the crystal was confirmed by Kurtz-Perry powder technique.« less

In situ study of the growth and degradation processes in tetragonal lysozyme crystals on a silicon substrate by high-resolution X-ray diffractometry

NASA Astrophysics Data System (ADS)

Kovalchuk, M. V.; Prosekov, P. A.; Marchenkova, M. A.; Blagov, A. E.; D'yakova, Yu. A.; Tereshchenko, E. Yu.; Pisarevskii, Yu. V.; Kondratev, O. A.

2014-09-01

The results of an in situ study of the growth of tetragonal lysozyme crystals by high-resolution X-ray diffractometry are considered. The crystals are grown by the sitting-drop method on crystalline silicon substrates of different types: both on smooth substrates and substrates with artificial surface-relief structures using graphoepitaxy. The crystals are grown in a special hermetically closed crystallization cell, which enables one to obtain images with an optical microscope and perform in situ X-ray diffraction studies in the course of crystal growth. Measurements for lysozyme crystals were carried out in different stages of the crystallization process, including crystal nucleation and growth, developed crystals, the degradation of the crystal structure, and complete destruction.

Interwell coupling effect in Si/SiGe quantum wells grown by ultra high vacuum chemical vapor deposition

PubMed Central

Wang, Rui; Lu, Fen; Fan, Wei Jun; Liu, Chong Yang; Loh, Ter-Hoe; Nguyen, Hoai Son; Narayanan, Balasubramanian

2007-01-01

Si/Si0.66Ge0.34coupled quantum well (CQW) structures with different barrier thickness of 40, 4 and 2 nm were grown on Si substrates using an ultra high vacuum chemical vapor deposition (UHV-CVD) system. The samples were characterized using high resolution x-ray diffraction (HRXRD), cross-sectional transmission electron microscopy (XTEM) and photoluminescence (PL) spectroscopy. Blue shift in PL peak energy due to interwell coupling was observed in the CQWs following increase in the Si barrier thickness. The Si/SiGe heterostructure growth process and theoretical band structure model was validated by comparing the energy of the no-phonon peak calculated by the 6 + 2-bandk·pmethod with experimental PL data. Close agreement between theoretical calculations and experimental data was obtained.

Indium hexagonal island as seed-layer to boost a-axis orientation of AlN thin films

NASA Astrophysics Data System (ADS)

Redjdal, N.; Salah, H.; Azzaz, M.; Menari, H.; Manseri, A.; Guedouar, B.; Garcia-Sanchez, A.; Chérif, S. M.

2018-06-01

Highly a-axis oriented aluminum nitride films have been grown on Indium coated (100) Si substrate by DC reactive magnetron sputtering. It is shown that In incorporated layer improve the extent of preferential growth along (100) axis and form dense AlN films with uniform surface and large grains, devoid of micro-cracks. As revealed by SEM cross section images, AlN structure consists of oriented columnar grains perpendicular to the Si surface, while AlN/In structure results in uniformely tilted column. SEM images also revealed the presence of In hexagonal islands persistent throughout the entire growth. Micro -Raman spectroscopy of the surface and the cross section of the AlN/In grown films evidenced their high degree of homogeneity and cristallinity.

Onset of runaway nucleation in aerosol reactors

NASA Technical Reports Server (NTRS)

Wu, Jin Jwang; Flagan, Richard C.

1987-01-01

The onset of homogeneous nucleation of new particles from the products of gas phase chemical reactions was explored using an aerosol reactor in which seed particles of silicon were grown by silane pyrolysis. The transition from seed growth by cluster deposition to catastrophic nucleation was extremely abrupt, with as little as a 17 percent change in the reactant concentration leading to an increase in the concentration of measurable particles of four orders of magnitude. From the structure of the particles grown near this transition, it is apparent that much of the growth occurs by the accumulation of clusters on the growing seed particles. The time scale for cluster diffusion indicates, however, that the clusters responsible for growth must be much smaller than the apparent fine structure of the product particles.

Structure and morphology of CdS thin films electrodeposited in fused salts

NASA Astrophysics Data System (ADS)

Markov, I.; Valova, E.; Ilieva, M.; Kristev, I.

1983-12-01

Thin films of CdS are catholically electrodeposited on copper and silver electrodes in solution of CdCl 2 and Na 2SO 3 in fused LiCl-KCl eutectic. The films consist only of the hexagonal wurtzite phase of CdS. The films grown on Cu substrates are polycrystalline without pronounced fibre texture. The films grown on Ag substrates show practically perfect (000-) texture exposing the Cd face at the film surface. Films deposited at high bath temperatures (450-500°C), low current densities (0.2-0.5 mA/cm 2) or doped with In during the growth are very smooth. From the morphological investigations it is concluded that the CdS films electrodeposited onto Ag substrates have well pronounced laminar structure.

Synthesis, structural, thermal and Hirshfeld surface analysis of novel [1,2,4]triazolo[3,4-b][1,3,4] thiadiazine carrying 1,4-benzothiazine-3-one moiety

NASA Astrophysics Data System (ADS)

Shruthi, C.; Ravindrachary, V.; Guruswamy, B.; Lokanath, N. K.; Kumara, Karthik; Goveas, Janet

2018-05-01

Needle shaped single crystal of the title compound was grown by slow evaporation solution growth technique using ethanol as solvent. The grown single crystal was characterized using FT-IR, Single crystal XRD and Thermal analysis. The FT-IR spectrum confirms the molecular structure and identifies the different functional groups present in the compound. Single crystal XRD study reveals that the crystallized compound belongs to the monoclinic crystal system with P21/c space group and the corresponding cell parameters were identified. The thermal stability of the material was determined using both TGA and DTA analysis. The intermolecular interaction of each individual atom in the crystal lattice was estimated using Hirshfeld surface and finger print analysis.

Optical and structural characterisation of epitaxial nanoporous GaN grown by CVD.

PubMed

Mena, Josué; Carvajal, Joan J; Martínez, Oscar; Jiménez, Juan; Zubialevich, Vitaly Z; Parbrook, Peter J; Diaz, Francesc; Aguiló, Magdalena

2017-09-15

In this paper we study the optical properties of nanoporous gallium nitride (GaN) epitaxial layers grown by chemical vapour deposition on non-porous GaN substrates, using photoluminescence, cathodoluminescence, and resonant Raman scattering, and correlate them with the structural characteristic of these films. We pay special attention to the analysis of the residual strain of the layers and the influence of the porosity in the light extraction. The nanoporous GaN epitaxial layers are under tensile strain, although the strain is progressively reduced as the deposition time and the thickness of the porous layer increases, becoming nearly strain free for a thickness of 1.7 μm. The analysis of the experimental data point to the existence of vacancy complexes as the main source of the tensile strain.

Multienergy gold ion implantation for enhancing the field electron emission characteristics of heterogranular structured diamond films grown on Au-coated Si substrates

NASA Astrophysics Data System (ADS)

Sankaran, K. J.; Manoharan, D.; Sundaravel, B.; Lin, I. N.

2016-09-01

Multienergy Au-ion implantation enhanced the electrical conductivity of heterogranular structured diamond films grown on Au-coated Si substrates to a high level of 5076.0 (Ω cm)-1 and improved the field electron emission (FEE) characteristics of the films to low turn-on field of 1.6 V/μm, high current density of 5.4 mA/cm2 (@ 2.65 V/μm), and high lifetime stability of 1825 min. The catalytic induction of nanographitic phases in the films due to Au-ion implantation and the formation of diamond-to-Si eutectic interface layer due to Au-coating on Si together encouraged the efficient conducting channels for electron transport, thereby improved the FEE characteristics of the films.

Structural variability and niche differentiation in the rhizosphere and endosphere bacterial microbiome of field-grown poplar trees.

PubMed

Beckers, Bram; Op De Beeck, Michiel; Weyens, Nele; Boerjan, Wout; Vangronsveld, Jaco

2017-02-23

The plant microbiome represents one of the key determinants of plant health and productivity by providing a plethora of functional capacities such as access to low-abundance nutrients, suppression of phytopathogens, and resistance to biotic and/or abiotic stressors. However, a robust understanding of the structural composition of the bacterial microbiome present in different plant microenvironments and especially the relationship between below-ground and above-ground communities has remained elusive. In this work, we addressed hypotheses regarding microbiome niche differentiation and structural stability of the bacterial communities within different ecological plant niches. We sampled the rhizosphere soil, root, stem, and leaf endosphere of field-grown poplar trees (Populus tremula × Populus alba) and applied 16S rRNA amplicon pyrosequencing to unravel the bacterial communities associated with the different plant habitats. We found that the structural variability of rhizosphere microbiomes in field-grown poplar trees (P. tremula × P. alba) is much lower than that of the endosphere microbiomes. Furthermore, our data not only confirm microbiome niche differentiation reports at the rhizosphere soil-root interface but also clearly show additional fine-tuning and adaptation of the endosphere microbiome in the stem and leaf compartment. Each plant compartment represents an unique ecological niche for the bacterial communities. Finally, we identified the core bacterial microbiome associated with the different ecological niches of Populus. Understanding the complex host-microbe interactions of Populus could provide the basis for the exploitation of the eukaryote-prokaryote associations in phytoremediation applications, sustainable crop production (bio-energy efficiency), and/or the production of secondary metabolites.

Tuning the structure of CsCaI3:Eu via substitution of bromine for iodine

NASA Astrophysics Data System (ADS)

Loyd, M.; Lindsey, A.; Stand, L.; Zhuravleva, M.; Melcher, C. L.; Koschan, M.

2017-06-01

CsCaI3:Eu is a promising scintillator material that can be grown from the melt, but undergoes a tetragonal to orthorhombic phase transition upon cooling at 255 °C, causing twinning and cloudiness. The purpose of this work is to suppress this solid to solid phase transition in the CsCaI3:Eu scintillator, which has a light yield of ∼40000 ph/MeV and energy resolution at 662 keV of ∼4%, by halide replacement to form the compound CsCaBrxI3-x. Crystals 8 cm3 in volume were grown using the vertical Bridgman method with varying bromine content from x = 0.2 to x = 1, resulting in improved transparency for crystals with bromine content x > 0.6. Powder X-ray diffraction data coupled with differential scanning calorimetry and radioluminescence measurements were used to investigate structural modifications, melting point dependence and spectral emission dependence on the bromine/iodine ratio. Partial replacement of iodine by bromine improves optical quality and scintillation properties by stabilizing the structure, rendering it useful for isotope identification for national security applications. The composition CsCaBr0.8I2.2:Eu was determined to be the best combination of improved structure and performance, and larger 22 and 38 mm Ø crystals were grown for further evaluation. Large size slabs of these crystals showed good crystal quality and improved performance over CsCaI3Eu with 8.4% and 9.5% energy resolution at 662 keV, respectively.

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.

Effect of annealing on the structural and optical properties of heavily carbon-doped ZnO

NASA Astrophysics Data System (ADS)

Huang, He; Deng, Z. W.; Li, D. C.; Barbir, E.; Y Jiang, W.; Chen, M. X.; Kavanagh, K. L.; Mooney, P. M.; Watkins, S. P.

2010-04-01

ZnO films grown by metalorganic vapor phase epitaxy (MOVPE) at low temperatures (~500 °C) exhibit very high levels of carbon incorporation in the range of up to several percent. Such large levels of carbon incorporation significantly affect the structural properties of the thin films resulting in broadening of symmetric (0 0 2) rocking curves as well as broadened (1 0 1) pole figures compared with films grown at high temperature. Annealing of the films under air ambient at temperatures between 800 and 1100 °C results in dramatic sharpening of symmetric (0 0 2) rocking curves, indicating improved crystal alignment along the c-axes. (1 0 1) pole figure scans also show significant sharpening in the azimuthal axis, indicating similar improvements in the in-plane crystal alignment perpendicular to the c-axis. Raman spectra for as-grown ZnO at 500 °C show strong D and G peaks at 1381 and 1578 cm-1 due to sp2 carbon clusters. Annealing at 1000 °C results in the elimination of these bands, indicating that post-growth annealing treatment is a useful method to reduce the concentration of sp2 carbon clusters.

Growth and characterization of GaAs/Al/GaAs heterostructures

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

Bhattacharya, P.; Oh, J.E.; Singh, J.

Theoretical and experimental aspects of the growth of GaAs/Al/GaAs heterostructures have been investigated. In these heterostructures the GaAs on top of the buried metal layer is grown by migration-enhanced epitaxy (MEE) at low temperatures (200 and 400 {degree}C) to provide a kinetic barrier to the outdiffusion of Al during superlayer growth. The crystallinity and orientation of the Al film itself deposited on (100) GaAs at {approx}0 {degree}C was studied by transmission electron diffraction, dark-field imaging, and x-ray diffraction measurements. It is found that the Al growth is polycrystalline with a grain size {approx}60 A and the preferred growth orientation ismore » (111), which may be textured in plane but oriented out of plane. The quality of the GaAs superlayer grown on top of Al by MEE is very sensitive to the growth temperature. The layer grown at 400 {degree}C has good structural and optical quality, but is accompanied by considerable outdiffusion of Al at the Al-GaAs heterointerface. At 200 {degree}C, where the interface has good structural integrity, the superlayer exhibits twinning and no luminescence is observed.« less

New Three-Dimensional Porous Electrode Concept: Vertically-Aligned Carbon Nanotubes Directly Grown on Embroidered Copper Structures

PubMed Central

Amade, Roger; Hussain, Shahzad; Bertran, Enric; Bechtold, Thomas

2017-01-01

New three-dimensional (3D) porous electrode concepts are required to overcome limitations in Li-ion batteries in terms of morphology (e.g., shapes, dimensions), mechanical stability (e.g., flexibility, high electroactive mass loadings), and electrochemical performance (e.g., low volumetric energy densities and rate capabilities). Here a new electrode concept is introduced based on the direct growth of vertically-aligned carbon nanotubes (VA-CNTs) on embroidered Cu current collectors. The direct growth of VA-CNTs was achieved by plasma-enhanced chemical vapor deposition (PECVD), and there was no application of any post-treatment or cleaning procedure. The electrochemical behavior of the as-grown VA-CNTs was analyzed by charge/discharge cycles at different specific currents and with electrochemical impedance spectroscopy (EIS) measurements. The results were compared with values found in the literature. The as-grown VA-CNTs exhibit higher specific capacities than graphite and pristine VA-CNTs found in the literature. This together with the possibilities that the Cu embroidered structures offer in terms of specific surface area, total surface area, and designs provide a breakthrough in new 3D electrode concepts. PMID:29232892

Enhanced performance of microbial fuel cell with a bacteria/multi-walled carbon nanotube hybrid biofilm

NASA Astrophysics Data System (ADS)

Zhang, Peng; Liu, Jia; Qu, Youpeng; Zhang, Jian; Zhong, Yingjuan; Feng, Yujie

2017-09-01

The biofilm on the anode of a microbial fuel cell (MFC) is a vital component in system, and its formation and characteristic determines the performance of the system. In this study, a bacteria/Multi-Walled Carbon Nanotube (MWCNT) hybrid biofilm is fabricated by effectively inserting the MWCNTs into the anode biofilm via an adsorption-filtration method. This hybrid biofilm has been demonstrated to be an efficient structure for improving an anode biofilm performance. Electrochemical impedance spectroscopy (EIS) results show that the hybrid biofilm takes advantage of the conductivity and structure of MWCNT to enhance the electron transfer and substrate diffusion of the biofilm. With this hybrid biofilm, the current density, power density and coulombic efficiency are increased by 46.2%, 58.8% and 84.6%, respectively, relative to naturally grown biofilm. Furthermore, the start-up time is reduced by 53.8% compared with naturally grown biofilm. The perturbation test demonstrates that this type of hybrid biofilm exhibits strong adsorption ability and enhances the biofilm's resistance to a sudden change of substrate concentration. The superior performance of the hybrid biofilm with MWCNT ;nanowire; matrix compared with naturally grown biofilm demonstrates its great potential for boosting the performance of MFCs.

Evaluation of Graphene/WO3 and Graphene/CeO x Structures as Electrodes for Supercapacitor Applications

NASA Astrophysics Data System (ADS)

Chaitoglou, Stefanos; Amade, Roger; Bertran, Enric

2017-12-01

The combination of graphene with transition metal oxides can result in very promising hybrid materials for use in energy storage applications thanks to its intriguing properties, i.e., highly tunable surface area, outstanding electrical conductivity, good chemical stability, and excellent mechanical behavior. In the present work, we evaluate the performance of graphene/metal oxide (WO3 and CeO x ) layered structures as potential electrodes in supercapacitor applications. Graphene layers were grown by chemical vapor deposition (CVD) on copper substrates. Single and layer-by-layer graphene stacks were fabricated combining graphene transfer techniques and metal oxides grown by magnetron sputtering. The electrochemical properties of the samples were analyzed and the results suggest an improvement in the performance of the device with the increase in the number of graphene layers. Furthermore, deposition of transition metal oxides within the stack of graphene layers further improves the areal capacitance of the device up to 4.55 mF/cm2, for the case of a three-layer stack. Such high values are interpreted as a result of the copper oxide grown between the copper substrate and the graphene layer. The electrodes present good stability for the first 850 cycles before degradation.

Ultrafast Carrier dynamics of InxGa1-xN nanostructures grown directly on Si(111)

NASA Astrophysics Data System (ADS)

Kumar, Praveen; Devi, Pooja; Rodriguez⁠, P. E. D. S.; Kumar, Manish; Shivling, V. D.; Noetzel, Richard; Sharma, Chhavi; Sinha, R. K.; Kumar, Mahesh

2018-05-01

We show a flux dependence changes in structural, optical and electronic properties of InxGa1-xN nanostructures (NSs) namely nanocolumns (NCs), nanoflakes (NFs) and nanowall network (NWN) grown directly on Si(111) surface. Field emission scanning electron microscopy (FESEM) images were recorded to see morphological changes from NFs to NCs and NWNc etc, while high-resolution X-ray diffraction (HRXRD) ω-2θ scans were used to determine In incorporation. The maximum In incorporation was observed to be 20, 33 and 38% for the sharp transition from NFs to NCs and NWNs, respectively. The charge carrier dynamics of these grown NSs were probed using Ultrafast Femtosecond Transient Absorption Spectroscopy (UFTAS) with excitation at 350 nm pump wavelength. The UFTAS studies show the comparative charge carriers dynamics of the NWS, NCs and NFs. The charge carrier studies show a higher lifetime in NWNs as compare to NCs and NFs. Further, to examine electronic structure and level of degeneracy of these NSs, core-level and valence band spectra were analyzed by X-ray photoelectron spectroscopy (XPS), which manifest the upward band bending ranging from 0.2 eV to 0.4 eV.

An International Look at the Single-Parent: Family Structure Matters More for U.S. Students

ERIC Educational Resources Information Center

Woessmann, Ludger

2015-01-01

When Daniel Patrick Moynihan raised the issue of family structure half a century ago, his concern was the increase in black families headed by women. Since then, the share of children raised in single-parent families in the United States has grown across racial and ethnic groups and with it evidence regarding the impact of family structure on…

Hydrogen passivation of n+p and p+n heteroepitaxial InP solar cell structures

NASA Technical Reports Server (NTRS)

Chatterjee, B.; Ringel, S. A.; Hoffman, R., Jr.

1995-01-01

High-efficiency, heteroepitaxial (HE) InP solar cells, grown on GaAs, Si or Ge substrates, are desirable for their mechanically strong, light-weight and radiation-hard properties. However, dislocations, caused by lattice mismatch, currently limit the performance of the HE cells. This occurs through shunting paths across the active photovoltaic junction and by the formation of deep levels. In previous work we have demonstrated that plasma hydrogenation is an effective and stable means to passivate the electrical activity of dislocations in specially designed HE InP test structures. In this work, we present the first report of successful hydrogen passivation in actual InP cell structures grown on GaAs substrates by metalorganic chemical vapor deposition (MOCVD). We have found that a 2 hour exposure to a 13.56 MHz hydrogen plasma at 275 C reduces the deep level concentration in HE n+n InP cell structures from as-grown values of approximately 10(exp 15)/cm(exp -3), down to 1-2 x 10(exp 13)/cm(exp -3). The deep levels in the p-type base region of the cell structure match those of our earlier p-type test structures, which were attributed to dislocations or related point defect complexes. All dopants were successfully reactivated by a 400 C, 5 minute anneal with no detectable activation of deep levels. I-V analysis indicated a subsequent approximately 10 fold decrease in reverse leakage current at -1 volt reverse bias, and no change in the forward biased series resistance of the cell structure which indicates complete reactivation of the n+ emitter. Furthermore, electrochemical C-V profiling indicates greatly enhanced passivation depth, and hence hydrogen diffusion, for heteroepitaxial structures when compared with identically processed homoepitaxial n+p InP structures. An analysis of hydrogen diffusion in dislocated InP will be discussed, along with comparisons of passivation effectiveness for n+p versus p+n heteroepitaxial cell configurations. Preliminary hydrogen-passivated HE InP cell results will also be presented.

Metal-electrode-free Window-like Organic Solar Cells with p-Doped Carbon Nanotube Thin-film Electrodes

PubMed Central

Jeon, Il; Delacou, Clement; Kaskela, Antti; Kauppinen, Esko I.; Maruyama, Shigeo; Matsuo, Yutaka

2016-01-01

Organic solar cells are flexible and inexpensive, and expected to have a wide range of applications. Many transparent organic solar cells have been reported and their success hinges on full transparency and high power conversion efficiency. Recently, carbon nanotubes and graphene, which meet these criteria, have been used in transparent conductive electrodes. However, their use in top electrodes has been limited by mechanical difficulties in fabrication and doping. Here, expensive metal top electrodes were replaced with high-performance, easy-to-transfer, aerosol-synthesized carbon nanotubes to produce transparent organic solar cells. The carbon nanotubes were p-doped by two new methods: HNO3 doping via ‘sandwich transfer’, and MoOx thermal doping via ‘bridge transfer’. Although both of the doping methods improved the performance of the carbon nanotubes and the photovoltaic performance of devices, sandwich transfer, which gave a 4.1% power conversion efficiency, was slightly more effective than bridge transfer, which produced a power conversion efficiency of 3.4%. Applying a thinner carbon nanotube film with 90% transparency decreased the efficiency to 3.7%, which was still high. Overall, the transparent solar cells had an efficiency of around 50% that of non-transparent metal-based solar cells (7.8%). PMID:27527565

Metal-electrode-free Window-like Organic Solar Cells with p-Doped Carbon Nanotube Thin-film Electrodes.

PubMed

Jeon, Il; Delacou, Clement; Kaskela, Antti; Kauppinen, Esko I; Maruyama, Shigeo; Matsuo, Yutaka

2016-08-16

Organic solar cells are flexible and inexpensive, and expected to have a wide range of applications. Many transparent organic solar cells have been reported and their success hinges on full transparency and high power conversion efficiency. Recently, carbon nanotubes and graphene, which meet these criteria, have been used in transparent conductive electrodes. However, their use in top electrodes has been limited by mechanical difficulties in fabrication and doping. Here, expensive metal top electrodes were replaced with high-performance, easy-to-transfer, aerosol-synthesized carbon nanotubes to produce transparent organic solar cells. The carbon nanotubes were p-doped by two new methods: HNO3 doping via 'sandwich transfer', and MoOx thermal doping via 'bridge transfer'. Although both of the doping methods improved the performance of the carbon nanotubes and the photovoltaic performance of devices, sandwich transfer, which gave a 4.1% power conversion efficiency, was slightly more effective than bridge transfer, which produced a power conversion efficiency of 3.4%. Applying a thinner carbon nanotube film with 90% transparency decreased the efficiency to 3.7%, which was still high. Overall, the transparent solar cells had an efficiency of around 50% that of non-transparent metal-based solar cells (7.8%).

Fast determination of the current loss mechanisms in textured crystalline Si-based solar cells

NASA Astrophysics Data System (ADS)

Nakane, Akihiro; Fujimoto, Shohei; Fujiwara, Hiroyuki

2017-11-01

A quite general device analysis method that allows the direct evaluation of optical and recombination losses in crystalline silicon (c-Si)-based solar cells has been developed. By applying this technique, the current loss mechanisms of the state-of-the-art solar cells with ˜20% efficiencies have been revealed. In the established method, the optical and electrical losses are characterized from the analysis of an experimental external quantum efficiency (EQE) spectrum with very low computational cost. In particular, we have performed the EQE analyses of textured c-Si solar cells by employing the experimental reflectance spectra obtained directly from the actual devices while using flat optical models without any fitting parameters. We find that the developed method provides almost perfect fitting to EQE spectra reported for various textured c-Si solar cells, including c-Si heterojunction solar cells, a dopant-free c-Si solar cell with a MoOx layer, and an n-type passivated emitter with rear locally diffused solar cell. The modeling of the recombination loss further allows the extraction of the minority carrier diffusion length and surface recombination velocity from the EQE analysis. Based on the EQE analysis results, the current loss mechanisms in different types of c-Si solar cells are discussed.

The Protein Data Bank: a historical perspective.

PubMed

Berman, Helen M

2008-01-01

The Protein Data Bank began as a grassroots effort in 1971. It has grown from a small archive containing a dozen structures to a major international resource for structural biology containing more than 40000 entries. The interplay of science, technology and attitudes about data sharing have all played a role in the growth of this resource.

Study on the structural, optical, and electrical properties of the yellow light-emitting diode grown on free-standing (0001) GaN substrate

NASA Astrophysics Data System (ADS)

Deng, Gaoqiang; Zhang, Yuantao; Yu, Ye; Yan, Long; Li, Pengchong; Han, Xu; Chen, Liang; Zhao, Degang; Du, Guotong

2018-04-01

In this paper, GaN-based yellow light-emitting diodes (LEDs) were homoepitaxially grown on free-standing (0001) GaN substrates by metal-organic chemical vapor deposition. X-ray diffraction (XRD), photoluminescence (PL), and electroluminescence (EL) measurements were conducted to investigate the structural, optical, and electrical properties of the yellow LED. The XRD measurement results showed that the InGaN/GaN multiple quantum wells (MQWs) in the LED structure have good periodicity because the distinct MQWs related higher order satellite peaks can be clearly observed from the profile of 2θ-ω XRD scan. The low temperature (10 K) and room temperature PL measurement results yield an internal quantum efficiency of 16% for the yellow LED. The EL spectra of the yellow LED present well Gaussian distribution with relatively low linewidth (47-55 nm), indicating the homogeneous In-content in the InGaN quantum well layers in the yellow LED structure. It is believed that this work will aid in the future development of GaN on GaN LEDs with long emission wavelength.

Fluorescence X-ray absorption spectroscopy using a Ge pixel array detector: application to high-temperature superconducting thin-film single crystals.

PubMed

Oyanagi, H; Tsukada, A; Naito, M; Saini, N L; Lampert, M O; Gutknecht, D; Dressler, P; Ogawa, S; Kasai, K; Mohamed, S; Fukano, A

2006-07-01

A Ge pixel array detector with 100 segments was applied to fluorescence X-ray absorption spectroscopy, probing the local structure of high-temperature superconducting thin-film single crystals (100 nm in thickness). Independent monitoring of pixel signals allows real-time inspection of artifacts owing to substrate diffractions. By optimizing the grazing-incidence angle theta and adjusting the azimuthal angle phi, smooth extended X-ray absorption fine structure (EXAFS) oscillations were obtained for strained (La,Sr)2CuO4 thin-film single crystals grown by molecular beam epitaxy. The results of EXAFS data analysis show that the local structure (CuO6 octahedron) in (La,Sr)2CuO4 thin films grown on LaSrAlO4 and SrTiO3 substrates is uniaxially distorted changing the tetragonality by approximately 5 x 10(-3) in accordance with the crystallographic lattice mismatch. It is demonstrated that the local structure of thin-film single crystals can be probed with high accuracy at low temperature without interference from substrates.

Epitaxial corundum-VTiO 3 thin films grown on c-cut sapphire

DOE PAGES

Kramer, Alan; Sutter, Eli; Su, Dong; ...

2017-04-12

Corundum structured VTiO 3 has been grown as epitaxial films on c-cut sapphire by laser molecular beam epitaxy. The properties of the film were characterized by reflection high energy electron diffraction, x-ray diffraction, transmission electron microscopy, and photoemission spectroscopy. All the structural probes clearly indicate the corundum structure of the film. X-ray photoemission spectroscopy (XPS) indicates that V is in a 3+ charge state implying that Ti also needs to adopt a 3+ charge state in order for the corundum structure to form. However, the Ti-2p XPS, while clearly broadened to the lower binding energy side compared to TiO 2,more » also exhibits a pronounced Ti 4+ component. This is tentatively assigned to a final state effect in XPS measurements and not as the true cation state. In conclusion, the valence band spectra show occupation of 3d metal states that resemble more closely those of Ti 2O 3 than for V 2O 3, suggesting that only the a1g molecular states are occupied.« less

Substrate morphology induced self-organization into carbon nanotube arrays, ropes, and agglomerates.

PubMed

Huang, Jia-Qi; Zhang, Qiang; Xu, Guang-Hui; Qian, Wei-Zhong; Wei, Fei

2008-10-29

In this paper, hydrophobic carbon nanotube (CNT) arrays, ropes, and agglomerates were synthesized through self-organization on quartz substrates with different micro-structures under the same growth condition. On a flat substrate, a uniform woven structure was formed which resulted in a synchronous growth into an array. When the substrate with 10 µm round concaves distributed on the surface was adopted, the woven structure was sporadic and a CNT cluster was grown in the concave. With further growth, CNT ropes were self-organized. Subsequently, when the substrate consisting of irregular ∼100 nm gaps was used, the initial woven structure was high density, thus resulting in the formation of CNT agglomerates. Study results showed that CNT arrays grown on the flat substrate were of the highest purity and had a contact angle of 153.8 ± 0.9°. Thus, the self-organization behavior among CNTs was in situ modulated by different substrate morphology without further treatments. This provides us with an additional understanding of the self-organization of CNTs during growth, as well as strategies for the controllable synthesis of CNTs with fixed properties.

Crystal growth, electronic structure and optical properties of Sr2Mg(BO3)2

NASA Astrophysics Data System (ADS)

Lv, Xianshun; Wei, Lei; Wang, Xuping; Xu, Jianhua; Yu, Huajian; Hu, Yanyan; Zhang, Huadi; Zhang, Cong; Wang, Jiyang; Li, Qinggang

2018-02-01

Single crystals of Sr2Mg(BO3)2 (SMBO) were grown by Kyropoulos method. X-ray powder diffraction (XRD) analysis, transmission spectrum, thermal properties, band structure, density of states and charge distribution as well as Raman spectra of SMBO were described. The as-grown SMBO crystals show wide transparency range with UV cut-off below 180 nm. A direct band gap of 4.66 eV was obtained from the calculated electronic structure results. The calculated band structure and density of states results indicated the top valence band is determined by O 2p states whereas the low conduction band mainly consists of Sr 5s states. Twelve Raman peaks were observed in the experimental spectrum, fewer than the number predicted by the site group analysis. Raman peaks of SMBO were assigned combining first-principle calculation and site group analysis results. The strongest peak at 917 cm-1 in the experimental spectrum is assigned to symmetric stretching mode A1‧(ν1) of free BO3 units. SMBO is a potential Raman crystal which can be used in deep UV laser frequency conversion.

Spatially modulated magnetic structure of EuS due to the tetragonal domain structure of SrTiO3

NASA Astrophysics Data System (ADS)

Rosenberg, Aaron J.; Katmis, Ferhat; Kirtley, John R.; Gedik, Nuh; Moodera, Jagadeesh S.; Moler, Kathryn A.

2017-12-01

The combination of ferromagnets with topological superconductors or insulators allows for new phases of matter that support excitations such as chiral edge modes and Majorana fermions. EuS, a wide-bandgap ferromagnetic insulator with a Curie temperature around 16 K, and SrTiO3 (STO), an important substrate for engineering heterostructures, may support these phases. We present scanning superconducting quantum interference device measurements of EuS grown epitaxially on STO that reveal micron-scale variations in ferromagnetism and paramagnetism. These variations are oriented along the STO crystal axes and only change their configuration upon thermal cycling above the STO cubic-to-tetragonal structural transition temperature at 105 K, indicating that the observed magnetic features are due to coupling between EuS and the STO tetragonal structure. We speculate that the STO tetragonal distortions may strain the EuS, altering the magnetic anisotropy on a micron scale. This result demonstrates that local variation in the induced magnetic order from EuS grown on STO needs to be considered when engineering new phases of matter that require spatially homogeneous exchange.

Group-III nitride VCSEL structures grown by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Ng, HockMin; Moustakas, Theodore D.

2000-07-01

III-nitride VCSEL structures designed for electron-beam pumping have been grown by molecular beam epitaxy (MBE). The structures consist of a sapphire substrate on which an AlN/GaN distributed Bragg reflector (DBR) with peak reflectance >99% at 402 nm is deposited. The active region consists of a 2-(lambda) cavity with 25 In0.1Ga0.9N/GaN multiquantum wells (MQWs) whose emission coincides with the high reflectance region of the DBR. The thicknesses of the InGaN wells and the GaN barriers are 35 angstrom and 75 angstrom respectively. The top reflector consists of a silver metallic mirror which prevents charging effects during electron-beam pumping. The structure was pumped from the top- side with a cw electron-beam using a modified cathodoluminescence (CL) system mounted on a scanning electron microscope chamber. Light output was collected from the polished sapphire substrate side. Measurements performed at 100 K showed intense emission at 407 nm with narrowing of the linewidth with increasing beam current. A narrow emission linewidth of 0.7 nm was observed indicating the onset of stimulated emission.

Hierarchical microstructures in CZT

NASA Astrophysics Data System (ADS)

Sundaram, S. K.; Henager, C. H.; Edwards, D. J.; Schemer-Kohrn, A. L.; Bliss, M.; Riley, B. R.; Toloczko, M. B.; Lynn, K. G.

2011-10-01

Advanced characterization tools, such as electron backscatter diffraction and transmitted IR microscopy, are being applied to study critical microstructural features and orientation relations in as-grown CZT crystals to aid in understanding the relation between structure and properties in radiation detectors. Even carefully prepared single crystals of CZT contain regions of slight misorientation, Te-particles, and dislocation networks that must be understood for more accurate models of detector response. This paper describes initial research at PNNL into the hierarchy of microstructures observed in CZT grown via the vertical gradient freeze or vertical Bridgman method at PNNL and WSU.

Solvothermally Synthesized Sb2Te3 Platelets Show Unexpected Optical Contrasts in Mid-Infrared Near-Field Scanning Microscopy.

PubMed

Hauer, Benedikt; Saltzmann, Tobias; Simon, Ulrich; Taubner, Thomas

2015-05-13

We report nanoscale-resolved optical investigations on the local material properties of Sb2Te3 hexagonal platelets grown by solvothermal synthesis. Using mid-infrared near-field microscopy, we find a highly symmetric pattern, which is correlated to a growth spiral and which extends over the entire platelet. As the origin of the optical contrast, we identify domains with different densities of charge carriers. On Sb2Te3 samples grown by other means, we did not find a comparable domain structure.

Ballistic Transport Exceeding 28 μm in CVD Grown Graphene.

PubMed

Banszerus, Luca; Schmitz, Michael; Engels, Stephan; Goldsche, Matthias; Watanabe, Kenji; Taniguchi, Takashi; Beschoten, Bernd; Stampfer, Christoph

2016-02-10

We report on ballistic transport over more than 28 μm in graphene grown by chemical vapor deposition (CVD) that is fully encapsulated in hexagonal boron nitride. The structures are fabricated by an advanced dry van-der-Waals transfer method and exhibit carrier mobilities of up to three million cm(2)/(Vs). The ballistic nature of charge transport is probed by measuring the bend resistance in cross- and square-shaped devices. Temperature-dependent measurements furthermore prove that ballistic transport is maintained exceeding 1 μm up to 200 K.

Optical properties of Mg doped p-type GaN nanowires

NASA Astrophysics Data System (ADS)

Patsha, Avinash; Pandian, Ramanathaswamy; Dhara, S.; Tyagi, A. K.

2015-06-01

Mg doped p-type GaN nanowires are grown using chemical vapor deposition technique in vapor-liquid-solid (VLS) process. Morphological and structural studies confirm the VLS growth process of nanowires and wurtzite phase of GaN. We report the optical properties of Mg doped p-type GaN nanowires. Low temperature photoluminescence studies on as-grown and post-growth annealed samples reveal the successful incorporation of Mg dopants. The as-grwon and annealed samples show passivation and activation of Mg dopants, respectively, in GaN nanowires.

Cathodoluminescence Studies of the Inhomogeneities in Sn-doped Ga2O3 Nanowires

DTIC Science & Technology

2009-01-01

Cathodoluminescence Studies of the Inhomogeneities in Sn-doped Ga2O3 Nanowires S. I. Maximenko, L. Mazeina, Y. N. Picard, J. A. Freitas, Jr., V. M...color imaging and spectroscopy were employed to study the properties of Ga2O3 nanowires grown with different Sn/Ga ratios. The structures grown under...green to red emission correlates with a phase transition of β- Ga2O3 to polycrystalline SnO2. The origin of the green emission band is discussed based

On Controlling the Hydrophobicity of Nanostructured Zinc-Oxide Layers Grown by Pulsed Electrodeposition

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

Klochko, N. P., E-mail: klochko-np@mail.ru; Klepikova, K. S.; Kopach, V. R.

The possibility of fabricating highly hydrophobic nanostructured zinc-oxide layers by the inexpensive method of pulsed electrodeposition from aqueous solutions without water-repellent coatings, adapted for large-scale production, is shown. The conditions of the deposition of highly hydrophobic nanostructured zinc-oxide layers exhibiting the “rose-petal” effect with specific morphology, optical properties, crystal structure and texture are determined. The grown ZnO nanostructures are promising for micro- and nanoelectronics as an adaptive material able to reversibly transform to the hydrophilic state upon exposure to ultraviolet radiation.

Synthesis of high crystallinity ZnO nanowire array on polymer substrate and flexible fiber-based sensor.

PubMed

Liu, Jinmei; Wu, Weiwei; Bai, Suo; Qin, Yong

2011-11-01

Well aligned ZnO nanowire (NW) arrays are grown on Kevlar fiber and Kapton film via the chemical vapor deposition (CVD) method. These NWs have better crystallinity than those synthesized through the low-temperature hydrothermal method. The average length and diameter of ZnO NWs grown on Kevlar fiber can be controlled from 0.5 to 2.76 μm and 30 to 300 nm, respectively. A flexible ultraviolet (UV) sensor based on Kevlar fiber/ZnO NWs hybrid structure is made to detect UV illumination quantificationally.

Growth, optical, luminescence, thermal and mechanical behavior of an organic single crystal: 3-Acetyl-2-methyl-4-phenylquinolin-1-ium chloride.

PubMed

Nirosha, M; Kalainathan, S; Sarveswari, S; Vijayakumar, V

2014-04-05

A single crystal of 3-acetyl-2-methyl-4-phenylquinolin-1-ium chloride has grown by slow evaporation solution growth technique using ethanol as solvent. The structural, thermal, optical and mechanical property has studied for the grown crystal. Single crystal XRD revealed that the crystal belongs to monoclinic system with space group P21/c. The presences of Functional groups in the crystallized material have confirmed using the FTIR vibrational spectrum. The optical absorbance spectrum recorded from 190 to 1100nm shows the cut-off wavelength occurs at 371nm. The material shows its transparency in the entire region of the visible spectrum. The photoluminescence spectrum shows the ultraviolet and blue emission in the crystal. Thermogravimetric and differential thermal analysis reveal the thermal stability of the grown crystal. Etching study shows the grown mechanism and surface features of the crystal. Vickers microhardness studies have carried out on the (01-1) plane to understand the mechanical properties of the grown crystal. The hardness of the title compound increases on increasing the load. The Meyer's index number (n), and the stiffness constants for different loads has calculated and reported. Copyright © 2013 Elsevier B.V. All rights reserved.

Nanomaterials' Influences on the Emergence of Life and Their Toxic Effects on Bacteria and Protozoa

NASA Astrophysics Data System (ADS)

Mielke, Randall Edward

This research investigates the unique properties of nanomaterials (NMs) with highly catalytic surfaces that make them ideal for the production of organic molecules but also confer toxic properties of some NMs. Iron-sulphide NMs were used in a hydrothermal reactor that released hydrogen sulphide and other metal ions in the effluent, as analyzed by inductively-coupled plasma (ICP) spectrometry. Using an environmental scanning electron microscope (ESEM), iron sulphide NM surfaces indicate severe weathering as a result of environmental conditions including high pressure (100 bar H2) and moderate temperatures (130°C). The effluent's chemical properties from the reactor experiment generated chimney structures from newly formed iron-sulphide NMs in a ferrous rich 'Hadean Ocean' solution. Using ESEM, we show that structural changes occur under different pHs, temperatures, and silicate concentrations. The presence of 5-mer peptides also shows distinct structural differences during the formation of iron-sulphide NM chimneys. Nano-titanium dioxide NMs (nTiO2) were used to show the toxicity of nTiO2 encrusted Pseudomonas aeruginosa (PA) fed to Tetrahymena thermophila (TT) protozoa under aerobic conditions. The control TT showed limited toxicity when grown in the presence of nTiO2, and scanning transmission electron microscopy (STEM) revealed the initial accumulation of nTiO2 in food vacuoles (FVs) of control TT cells that were not observed in the TT grown with nTiO2-encrusted PA. After 22 h, very little nTiO2 is observed in the control TT FVs as compared with the TT grown with nTiO2-encrusted PA FVs which had about 30% of the FV filled with nTiO2. Toxicity to nTiO2 was observed as reduced growth yields for both the control and the PA fed TT, but also as a reduction in growth rate for TT grown with nTiO2-encrusted PA. To understand biological weathering of NMs, the use of STEM energy dispersive spectroscopy (EDS) was enhanced to analyze single nano-sized particles. Contamination studies using cadmium selenide (CdSe) and cadmium telluride (CdTe) NMs with PA showed that CdSe weathering occurred in the cytoplasm while CdTe weathering predominantly occurred when associated with the PA cell wall. PA was shown to produce CdSe NMs in the cytoplasm when grown with cadmium and selenite salts as revealed by STEM-EDS. The use of STEM-EDS on embedded samples makes it possible to analyze NM structures while in their experimental location.

Seedborne fungal contamination: consequences in space-grown wheat

NASA Technical Reports Server (NTRS)

Bishop, D. L.; Levine, H. G.; Kropp, B. R.; Anderson, A. J.; Hood, E. E. (Principal Investigator)

1997-01-01

Plants grown in microgravity are subject to many environmental stresses that may promote microbial growth and result in disease symptoms. Wheat (cv. Super Dwarf) recovered from an 8-day mission aboard a NASA (National Aeronautics and Space Administration) space shuttle showed disease symptoms, including girdling of leaf sheaths and chlorosis and necrosis of leaf and root tissues. A Neotyphodium species was isolated from the seed and leaf sheaths of symptomatic wheat used in the spaceflight mission. Certain isozymes of a peroxidase unique to extracts from the microgravity-grown plants were observed in extracts from earth-grown Neotyphodium-infected plants but were not present in noninfected wheat. The endophytic fungus was eliminated from the wheat seed by prolonged heat treatment at 50 degrees C followed by washes with water at 50 degrees C. Plants from wheat seed infected with the Neotyphodium endophyte were symptomless when grown under greenhouse conditions, whereas symptoms appeared after only 4 days of growth in closed containers. Disease spread from an infected plant to noninfected plants in closed containers. Dispersion via spores was found on asymptomatic plants at distances of 7 to 18 cm from infected plants. The size and shape of the conidia, mycelia, and phialide-bearing structures and the ability to grow rapidly on carbohydrates, especially xylose, resembled the characteristics of N. chilense, which is pathogenic on orchard grass, Doctylis glomerati. The Neotyphodium wheat isolate caused disease symptoms on other cereals (wheat cv. Malcolm, orchard grass, barley, and maize) grown in closed containers.

Characterization of the absorbance bleaching in AllnAs/AlGaInAs multiple-quantum wells for semiconductor saturable absorbers.

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

Wanke, Michael Clement; Cederberg, Jeffrey George; Alliman, Darrell L.

2010-05-01

Semiconductor saturable absorbers (SESAs) introduce loss into a solid-state laser cavity until the cavity field bleaches the absorber producing a high-energy pulse. Multiple quantum wells (MQWs) of AlGaInAs grown lattice-matched to InP have characteristics that make them attractive for SESAs. The band gap can be tuned around the target wavelength, 1064 nm, and the large conduction band offset relative to the AlInAs barrier material helps reduces the saturation fluence, and transparent substrate reduces nonsaturable losses. We have characterized the lifetime of the bleaching process, the modulation depth, the nonsaturable losses, and the saturation fluence associated with SESAs. We compare differentmore » growth conditions and structure designs. These parameters give insight into the quality of the epitaxy and effect structure design has on SESA performance in a laser cavity. AlGaInAs MQWs were grown by MOVPE using a Veeco D125 machine using methyl-substituted metal-organics and hydride sources at a growth temperature of 660 C at a pressure of 60 Torr. A single period of the basic SESA design consists of approximately 130 to 140 nm of AlInAs barrier followed by two AlGaInAs quantum wells separated by 10 nm AlInAs. This design places the QWs near the nodes of the 1064-nm laser cavity standing wave. Structures consisting of 10-, 20-, and 30-periods were grown and evaluated. The SESAs were measured at 1064 nm using an optical pump-probe technique. The absorbance bleaching lifetime varies from 160 to 300 nsec. The nonsaturable loss was as much as 50% for structures grown on n-type, sulfur-doped InP substrates, but was reduced to 16% when compensated, Fe-doped InP substrates were used. The modulation depth of the SESAs increased linearly from 9% to 30% with the number of periods. We are currently investigating how detuning the QW transition energy impacts the bleaching characteristics. We will discuss how each of these parameters impacts the laser performance.« less