Science.gov

Sample records for nanocrystalline zns thin

  1. Characterization of ZnS thin films synthesized through a non-toxic precursors chemical bath

    SciTech Connect

    Rodríguez, C.A.; Sandoval-Paz, M.G.; Cabello, G.; Flores, M.; Fernández, H.; Carrasco, C.

    2014-12-15

    Highlights: • High quality ZnS thin films have been deposited by chemical bath deposition technique from a non-toxic precursor’s solution. • Nanocrystalline ZnS thin films with large band gap energy were synthesized without using ammonia. • Evidence that the growing of the thin films is carried out by means of hydroxide mechanism was found. • The properties of these ZnS thin films are similar and in some cases better than the corresponding ones produced using toxic precursors such as ammonia. - Abstract: In solar cells, ZnS window layer deposited by chemical bath technique can reach the highest conversion efficiency; however, precursors used in the process normally are materials highly volatile, toxic and harmful to the environment and health (typically ammonia and hydrazine). In this work the characterization of ZnS thin films deposited by chemical bath in a non-toxic alkaline solution is reported. The effect of deposition technique (growth in several times) on the properties of the ZnS thin film was studied. The films exhibited a high percentage of optical transmission (greater than 80%); as the deposition time increased a decreasing in the band gap values from 3.83 eV to 3.71 eV was observed. From chemical analysis, the presence of ZnS and Zn(OH){sub 2} was identified and X-ray diffraction patterns exhibited a clear peak corresponding to ZnS hexagonal phase (1 0 3) plane, which was confirmed by electron diffraction patterns. From morphological studies, compact samples with well-defined particles, low roughness, homogeneous and pinhole-free in the surface were observed. From obtained results, it is evident that deposits of ZnS–CBD using a non-toxic solution are suitable as window layer for TFSC.

  2. Synthesis and characterization of nanostructured Mn-doped ZnS thin films and nanoparticles

    NASA Astrophysics Data System (ADS)

    Singh, S. P.; Perales-Perez, O. J.; Tomar, M. S.; Mata, O. V.

    2004-03-01

    Nanocrystalline ZnS:Mn2+ thin films and powders were prepared by chemical bath deposition (CBD) at 85 ° C for different concentration of Mn ions in bath solutions (Mn molar fraction, x = 0.0, 0.01, 0.02, 0.05, 0.1, 0.2 and 0.5). Produced nanocrystalline films and powders were characterized using X-ray diffraction (XRD), differential thermal analysis (DTA), scanning electron microscopy (SEM) and photoluminescence measurements. XRD patterns for Mn2+ doped and undoped ZnS powders showed broad peaks corresponding to ZnS exhibiting a mixture of cubic and hexagonal structures. Size of nanocrystallites was estimated to be 4 nm using Scherrer's equation. The DTA analyses evidenced the development of the oxide phase from ZnS nanocrystals at lower temperature than for bulk micron size particles. SEM observations showed the presence of nanocrystallites forming spherical aggregates of around 500 nm in diameter. Photoluminescence measurements reveal a strong emission peak at 580 nm which is characteristic emission peak of Mn2+ d-d transition confirming the actual incorporation of Mn2+ into ZnS framework.

  3. Optical and Optoelectronic Properties of ZnS Nanostructured Thin Film

    NASA Astrophysics Data System (ADS)

    Borah, J. P.; Sarma, K. C.

    2008-10-01

    ZnS nanocrystalline thin films were grown into the polyvinyl alcohol matrix and were synthesized by chemical route. Films were prepared on glass substrate by varying the deposition parameters and pH of the solution. Nanocrystalline thin film prepared under optimum growth conditions shows band gap value 3.88 eV as observed from optical absorption data. The band gap is found to be higher (3.88 eV) indicating blue shift. The particle size, calculated from the shift of direct band gap, due to quantum confinement effect is 5.8 nm. Photoluminescence spectrum shows the blue luminescence peaks (centered at 425 nm), which can be attributed to the recombination of the defect states. ZnS nanocrystalline thin films are also found to be photosensitive in nature. However, the photosensitivity decreases due to ageing and exposure to oxygen. In case of nanostructured film, the I-V characteristics are observed in dark and under illumination showing photosensitive nature of these films, too. The dark current, however, is found to be greater when observed in vacuum compared to air. Both dark current and photocurrent are found to be ohmic in nature up to a certain applied bias. The observed data shows that nanostructured films are found to be suitable for device application. The surface morphology of the film is also characterized by scanning electron microscope.

  4. Phase transition in ZnS thin film phosphor

    NASA Astrophysics Data System (ADS)

    Kryshtab, T.; Khomchenko, V. S.; Andraca-Adame, J. A.; Khachatryan, V. B.; Mazin, M. O.; Rodionov, V. E.; Mukhlio, M. F.

    2005-02-01

    The effect of an original non-vacuum annealing of thin ZnS films according to the annealing conditions and type of substrate on the film's crystalline structure and surface morphology in relation with photoluminescent (PL) properties was investigated. ZnS thin films were deposited by electron-beam evaporation (EBE) on ceramic (BaTiO 3) and glass substrates heated to 150-200 °C. Three types of the targets such as ZnS, ZnS:Cu and ZnS:Cu, Al were used. The film thickness varied from 0.6 to 1 μm. As-deposited films were annealed at the atmospheric pressure in S 2-rich ambient atmosphere at 600-950 °C for 1 h. The ZnS:Cu films were Ga co-doped by annealing in the same atmosphere and temperature with additional Ga vapor. The ZnS films were doped with Cu, Cl using the thermal diffusion method by embedding the samples in ZnS:Cu, Cl powder. X-ray diffraction (XRD) technique, atomic force microscopy (AFM) and the measurements of PL parameters were used for investigation. The temperature of the ZnS phase transition from the sphalerite to wurtzite structure depends on the presence, type and ratio of additional impurities. It was revealed that Ga and Cl act not only as co-dopant to improve the luminescent properties, but also as activators of recrystallization processes. The transition of ZnS film's sphalerite lattice to wurtzite leads to the displacement of the blue emission band position towards the short-wavelength range by 10 nm.

  5. Nonlinear optical characterization of ZnS thin film synthesized by chemical spray pyrolysis method

    SciTech Connect

    G, Sreeja V; Anila, E. I. R, Reshmi John, Manu Punnan; V, Sabitha P; Radhakrishnan, P.

    2014-10-15

    ZnS thin film was prepared by Chemical Spray Pyrolysis (CSP) method. The sample was characterized by X-ray diffraction method and Z scan technique. XRD pattern showed that ZnS thin film has hexagonal structure with an average size of about 5.6nm. The nonlinear optical properties of ZnS thin film was studied by open aperture Z-Scan technique using Q-switched Nd-Yag Laser at 532nm. The Z-scan plot showed that the investigated ZnS thin film has saturable absorption behavior. The nonlinear absorption coefficient and saturation intensity were also estimated.

  6. Nonlinear optical characterization of ZnS thin film synthesized by chemical spray pyrolysis method

    NASA Astrophysics Data System (ADS)

    G, Sreeja V.; V, Sabitha P.; Anila, E. I.; R, Reshmi; John, Manu Punnan; Radhakrishnan, P.

    2014-10-01

    ZnS thin film was prepared by Chemical Spray Pyrolysis (CSP) method. The sample was characterized by X-ray diffraction method and Z scan technique. XRD pattern showed that ZnS thin film has hexagonal structure with an average size of about 5.6nm. The nonlinear optical properties of ZnS thin film was studied by open aperture Z-Scan technique using Q-switched Nd-Yag Laser at 532nm. The Z-scan plot showed that the investigated ZnS thin film has saturable absorption behavior. The nonlinear absorption coefficient and saturation intensity were also estimated.

  7. Nanocrystalline silicon based thin film solar cells

    NASA Astrophysics Data System (ADS)

    Ray, Swati

    2012-06-01

    Amorphous silicon solar cells and panels on glass and flexible substrate are commercially available. Since last few years nanocrystalline silicon thin film has attracted remarkable attention due to its stability under light and ability to absorb longer wavelength portion of solar spectrum. For amorphous silicon/ nanocrystalline silicon double junction solar cell 14.7% efficiency has been achieved in small area and 13.5% for large area modules internationally. The device quality nanocrystalline silicon films have been fabricated by RF and VHF PECVD methods at IACS. Detailed characterizations of the materials have been done. Nanocrystalline films with low defect density and high stability have been developed and used as absorber layer of solar cells.

  8. Microstructural characterization of textured ZnS thin films

    SciTech Connect

    Kryshtab, T. . E-mail: tkrysh@esfm.ipn.mx; Andraca-Adame, J.A.; Kryvko, A.

    2007-08-15

    During thin film growth texture formation is controlled by several kinetic parameters that determine the grain structural evolution. For highly textured thin films, i.e. only one strong peak can be obtained from X-ray diffraction pattern, it is impossible to separate the effect of grain size and residual strains based on peak broadening. We propose an original method for evaluating residual strains, eliminating their contribution in peak breadth and determining the domain size. A two-axes diffractometer with a Ge monochromator and a K {sub {alpha}}{sub 1,2} doublet was used for this study. The measurements of 2{theta} scans were carried out in the grazing geometry for the incident beam. ZnS thin films as-deposited and annealed were studied. Structural analysis was carried out using a one-axis diffractometer for a {theta}-2{theta} scan in the standard symmetric geometry. Surface morphology was explored by atomic force microscopy. The specification of the proposed method and its application in microstructural characterization are introduced.

  9. Hydrogenated nanocrystalline silicon germanium thin films

    NASA Astrophysics Data System (ADS)

    Yusoff, A. R. M.; Syahrul, M. N.; Henkel, K.

    2007-08-01

    Hydrogenated nanocrystalline silicon germanium thin films (nc-SiGe:H) is an interesting alternative material to replace hydrogenated nanocrystalline silicon (nc-Si:H) as the narrow bandgap absorber in an a-Si/a-SiGe/nc-SiGe(nc-Si) triple-junction solar cell due to its higher optical absorption in the wavelength range of interest. In this paper, we present results of optical, structural investigations and electrical characterization of nc-SiGe:H thin films made by hot-wire chemical vapor deposition (HWCVD) with a coil-shaped tungsten filament and with a disilane/germane/hydrogen gas mixture. The optical band gaps of a-SiGe:H and nc-SiGe:H thin-films, which are deposited with the same disilane/germane/hydrogen gas mixture ratio of 3.4:1.7:7, are about 1.58 eV and 2.1 eV, respectively. The nc-SiGe:H thin film exhibits a larger optical absorption coefficient of about 2-4 in the 600-900 nm range when compared to nc-Si:H thin film. Therefore, a thinner nc-SiGe:H layer of sim500 nm thickness may be sufficient for the narrow bandgap absorber in an a-Si based multiple-junction solar cell. We enhanced the transport properties as measured by the photoconductivity frequency mixing technique. These improved alloys do not necessarily show an improvement in the degree of structural heterogeneity on the nanometer scale as measured by small-angle X-ray scattering. Decreasing both the filament temperature and substrate temperature produced a film with relatively low structural heterogeneity while photoluminescence showed an order of magnitude increase in defect density for a similar change in the process.

  10. Microstructural characterization in nanocrystalline ceramic thin films

    NASA Astrophysics Data System (ADS)

    Kim, Hakkwan

    The primary objective of this research is to investigate the effects of process variables on microstructure in several fluoride and oxide thin films prepared by vapor deposition, in order to predict the properties and behaviors of nanocrystalline thin film materials. There are three distinct stages of this research. The first stage focuses on measuring of the porosity in polycrystalline thin films of a variety of fluorides as a function of the substrate temperature during deposition, and discussing the mechanism by which the porosity varies as a function of the process variables. We have measured the porosity in thin films of lithium fluoride (LiF), magnesium fluoride (MgF2), barium fluoride (BaF 2) and calcium fluoride (CaF2) using an atomic force microscope (AFM) and a quartz crystal thickness monitor. The porosity is very sensitive to the substrate temperature and decreases as the substrate temperature increases. Consistent behavior is observed among all of the materials in this study. The second stage is to understand the film microstructure including grain growth and texture development, because these factors are known to influence the behavior and stability of polycrystalline thin films. This study focuses on grain growth and texture development in polycrystalline lithium fluoride thin films using dark field (DF) transmission electron microscopy (TEM). It is demonstrated that we can isolate the size distribution of <111> surface normal grains from the overall size distribution, based on simple and plausible assumptions about the texture. The {111} texture formation and surface morphology were also observed by x-ray diffraction (XRD) and AFM, respectively. The grain size distributions become clearly bimodal as the annealing time increases, and we deduce that the short-time size distributions are also a sum of two overlapping peaks. The smaller grain-size peak in the distribution corresponds to the {111}-oriented grains which do not grow significantly, while

  11. Post-annealing effects on ZnS thin films grown by using the CBD method

    NASA Astrophysics Data System (ADS)

    Ahn, Heejin; Um, Youngho

    2015-09-01

    Herein, the structural, morphological, and optical properties of zinc sulfide (ZnS) thin films deposited via the chemical bath deposition method are reported. These films were deposited on soda-lime glass (SLG) substrates by using ZnSO4, thiourea, and 25% ammonia at 90 °C. The effect of changing the annealing temperature from 100 °C to 300 °C on the properties of the ZnS thin films was investigated. X-ray diffraction (XRD) patterns showed that the ZnS thin film annealed at 100 °C had an amorphous structure; however, as the annealing temperature was increased, the crystalline quality of the thin film was enhanced. Moreover, transmission measurements showed that the optical transmittance was about 80% for wavelengths above 500 nm. The band gap energy (E g ) value of the film annealed at 300 °C was decreased to about 3.82 eV.

  12. Nanocrystalline silicon thin films for thermoelectric applications

    NASA Astrophysics Data System (ADS)

    Queen, Daniel; Jugdersuren, Battogtokh; Culberston, Jim; Wang, Qi; Nemeth, William; Metcalf, Tom; Liu, Xiao

    2014-03-01

    Recent advances in thermoelectric materials have come from reductions in thermal conductivity by manipulating both chemical composition and nanostructure to limit the phonon mean free path. However, wide spread applications for some of these materials may be limited due to high raw material and integration costs. In this talk we will discuss our recent results on nanocrystalline silicon thin films deposited by both hot-wire and plasma enhanced chemical vapor deposition where the nanocrystal size and crystalline volume fraction are varied by dilution of the silane precursor gas with hydrogen. Nanocyrstalline silicon is an established material technology used in multijunction amorphous silicon solar cells and has the potential to be a low cost and scalable material for use in thermoelectric devices. This work supported by the Office of Naval Research and the National Research Council.

  13. Deuterium storage in nanocrystalline magnesium thin films

    NASA Astrophysics Data System (ADS)

    Checchetto, R.; Bazzanella, N.; Miotello, A.; Brusa, R. S.; Zecca, A.; Mengucci, A.

    2004-02-01

    Nanocrystalline magnesium deuteride thin films with the β-MgD2 structure were prepared by vacuum evaporation of hexagonal magnesium (h-Mg) samples and thermal annealing in 0.15 MPa D2 atmosphere at 373 K. Thermal desorption spectroscopy analysis indicated that the rate-limiting step in the deuterium desorption was given by the thermal decomposition of the deuteride phase. The activation energy Δg of the β-MgD2→h-Mg+D2 reaction scaled from 1.13±0.03 eV in 650-nm-thick films to 1.01±0.02 eV in 75-nm-thick films most likely as consequence of different stress and defect level. Positron annihilation spectroscopy analysis of the thin-film samples submitted to deuterium absorption and desorption cycles reveal the presence of a high concentration of void-like defects in the h-Mg layers after the very first decomposition of the β-MgD2 phase, the presence of these open volume defects reduces the D2 absorption capacity of the h-Mg thin film.

  14. Enhanced visible-light photoactivity of La-doped ZnS thin films

    NASA Astrophysics Data System (ADS)

    Chen, Yuan; Huang, Gui-Fang; Huang, Wei-Qing; Zou, B. S.; Pan, Anlian

    2012-09-01

    ZnS and La-doped ZnS thin films were successfully synthesized using chemical-bath deposition on conductive glass substrates. The effects of La-doping on the surface morphology, composition, structure and optical properties of the films were investigated. The photocatalytic performances of undoped and doped ZnS films were evaluated by photodegrading methyl orange aqueous solution under both ultraviolet-light and visible-light irradiation. The results show that the stoichiometry ratio and the properties of ZnS can be tailored by the La-doping concentration. An appropriate amount of La-doping effectively extends the absorption edge to visible-light region, which leads to the significant enhancement of the photocatalytic activity of ZnS thin films under visible-light irradiation. The mechanism of enhanced visible-light photoactivity by La-doping is briefly discussed. The present study provides a simple method for designing the highly efficient semiconductor photocatalysts that can effectively utilize sunlight.

  15. Influence of Deposition Time on ZnS Thin Films Performance with Chemical Bath Deposition

    NASA Astrophysics Data System (ADS)

    Zhou, Limei; Tang, Nan; Wu, Sumei; Hu, Xiaofei; Xue, Yuzhi

    ZnS thin films had been deposited by chemical bath deposition method onto glass substrates in alkaline liquor. The reaction solution is made of ZnSO4, NH4OH and SC(NH2)2. Different deposition times (1 h, 1.5 h, 2 h, 2.5 h and 3 h) were selected to study the performance of ZnS thin films. As the results, the ZnS films' thickness were about 50-207 nm. XRD results showed an amorphous structure. Through comparing the surface morphology before and after annealing, it could be seen that annealing made some particles grow up and the surface smooth and even. The transmittance decreased with the increase of deposition time in the range of 300-800 nm. The transmittance of annealed ZnS film was lower than that of deposited one in the range of 300-800 nm. The ZnS band gap values were calculated in the range of 3.72-3.9 eV.

  16. Detection of ZnS Phases in CZTS Thin-Films by EXAFS

    SciTech Connect

    Hartman, K.; Newman, B. K.; Johnson, J. L.; Du, H.; Fernandes, P. A.; Chawla, V.; Bolin, T.; Clemens, B. M.; Da Cunha, A. F.; Teeter, G.; Scarpulla, M. A.; Buonassisi, T.

    2011-01-01

    Copper zinc tin sulfide (CZTS) is a promising Earth-abundant thin-film solar cell material; it has an appropriate band gap of {approx}1.45 eV and a high absorption coefficient. The most efficient CZTS cells tend to be slightly Zn-rich and Cu-poor. However, growing Zn-rich CZTS films can sometimes result in phase decomposition of CZTS into ZnS and Cu{sub 2}SnS{sub 3}, which is generally deleterious to solar cell performance. Cubic ZnS is difficult to detect by XRD, due to a similar diffraction pattern. We hypothesize that synchrotron-based extended X-ray absorption fine structure (EXAFS), which is sensitive to local chemical environment, may be able to determine the quantity of ZnS phase in CZTS films by detecting differences in the second-nearest neighbor shell of the Zn atoms. Films of varying stoichiometries, from Zn-rich to Cu-rich (Zn-poor) were examined using the EXAFS technique. Differences in the spectra as a function of Cu/Zn ratio are detected. Linear combination analysis suggests increasing ZnS signal as the CZTS films become more Zn-rich. We demonstrate that the sensitive technique of EXAFS could be used to quantify the amount of ZnS present and provide a guide to crystal growth of highly phase pure films.

  17. Cathodic electrodeposition of nanocrystalline titanium dioxide thin films

    SciTech Connect

    Natarajan, C.; Nogami, G.

    1996-05-01

    A new technique for depositing nanocrystalline titanium dioxide thin films on electronically conducting glass was developed. This technique is a two-stage process: (i) cathodic electrodeposition of titanium oxyhydroxide gel film from aqueous solution containing a Ti precursor and (ii) subsequent heat-treatment of this gel film results in the formation of titanium dioxide film. The deposition potential may have a considerable effect on the formation of nanocrystalline film. The nanocrystalline titanium dioxide film shows reversible electrochromism in lithium-ion-containing organic electrolyte. The coloration and bleaching throughout the visible and near-IR range can be switched on and off within a few seconds.

  18. The influence of doping element on structural and luminescent characteristics of ZnS thin films

    NASA Astrophysics Data System (ADS)

    Kryshtab, T.; Khomchenko, V. S.; Andraca-Adame, J. A.; Rodionov, V. E.; Khachatryan, V. B.; Tzyrkunov, Yu. A.

    2006-10-01

    For the fabrication of green and blue emitting ZnS structures the elements of I, III, and VII groups (Cu, Al, Ga, Cl) are used as dopants. The influence of type of impurity, doping technique, and type of substrate on crystalline structure and surface morphology together with luminescent properties was investigated. The doping of thin films was realized during the growth process and/or post-deposition thermal treatment. ZnS thin films were deposited by physical (EBE) and chemical (MOCVD) methods onto glass or ceramic (BaTiO 3) substrates. Closed spaced evaporation and thermodiffusion methods were used for the post-deposition doping of ZnS films. X-ray diffraction (XRD) techniques, atomic force microscopy (AFM), and measurements of photoluminescent (PL) spectra were used for the investigations. It was shown that the doping by the elements of I (Cu) and III (Al, Ga) groups does not change the crystal structure during the thermal treatment up to 1000 ∘C, whereas simultaneous use of the elements of I (Cu) and VII (Cl) groups leads to decrease of the phase transition temperature to 800 ∘C. The presence of impurities in the growth process leads to a grain size increase. At post-deposition treatment Ga and Cl act as activators of recrystallization process. The transition of ZnS sphalerite lattice to wurtzite one leads to the displacement of the blue emission band position towards the short-wavelength range by 10 nm.

  19. Tuning the Properties of Nanocrystalline CdS Thin Films

    NASA Astrophysics Data System (ADS)

    Ikhmayies, Shadia J.

    2014-01-01

    Tuning the properties of nanocrystalline cadmium sulfide (CdS) thin films is very important in the technology of photonics, detectors, and computing devices. This can be achieved through the appropriate selection of the synthesis techniques, types and concentrations of the chemicals, deposition parameters, and postdeposition heat treatments. In addition, control of the properties can be achieved by controlling the size, structure type, and surface states of the nanocrystallites without altering the chemical composition of the films. A review of the experimental methods for tuning the properties of nanocrystalline CdS thin films is performed. Although control of these variables is a complicated process, high-quality nanocrystalline CdS thin films with optimum structural, morphological, and optical properties have been produced by different authors.

  20. Biomolecularly capped uniformly sized nanocrystalline materials: glutathione-capped ZnS nanocrystals

    NASA Astrophysics Data System (ADS)

    Torres-Martínez, Claudia L.; Nguyen, Liem; Kho, Richard; Bae, Weon; Bozhilov, Krassimir; Klimov, Victor; Mehra, Rajesh K.

    1999-09-01

    Micro-organisms such as bacteria and yeasts form CdS to detoxify toxic cadmium ions. Frequently, CdS particles formed in yeasts and bacteria were found to be associated with specific biomolecules. It was later determined that these biomolecules were present at the surface of CdS. This coating caused a restriction in the growth of CdS particles and resulted in the formation of nanometre-sized semiconductors (NCs) that exhibited typical quantum confinement properties. Glutathione and related phytochelatin peptides were shown to be the biomolecules that capped CdS nanocrystallites synthesized by yeasts Candida glabrata and Schizosaccharomyces pombe. Although early studies showed the existence of specific biochemical pathways for the synthesis of biomolecularly capped CdS NCs, these NCs could be formed in vitro under appropriate conditions. We have recently shown that cysteine and cysteine-containing peptides such as glutathione and phytochelatins can be used in vitro to dictate the formation of discrete sizes of CdS and ZnS nanocrystals. We have evolved protocols for the synthesis of ZnS or CdS nanocrystals within a narrow size distribution range. These procedures involve three steps: (1) formation of metallo-complexes of cysteine or cysteine-containing peptides, (2) introduction of stoichiometric amounts of inorganic sulfide into the metallo-complexes to initiate the formation of nanocrystallites and finally (3) size-selective precipitation of NCs with ethanol in the presence of Na+. The resulting NCs were characterized by optical spectroscopy, high-resolution transmission electron microscopy (HRTEM), x-ray diffraction and electron diffraction. HRTEM showed that the diameter of the ZnS-glutathione nanocrystals was 3.45+/-0.5 nm. X-ray diffraction and electron diffraction analyses indicated ZnS-glutathione to be hexagonal. Photocatalytic studies suggest that glutathione-capped ZnS nanocrystals prepared by our procedure are highly efficient in degrading a test model

  1. ZnS Thin Films Deposited by a Spin Successive Ionic Layer Adsorption and Reaction Process

    SciTech Connect

    Han, Seungyeol; Lee, D. H.; Ryu, S. O.; Chang, Chih-hung

    2010-05-20

    In this article, we reported a spin successive ionic layer adsorption and reaction (SILAR) method for the first time. ZnS thin films were deposited by spin SILAR using ZnCl2 and Na2S aqueous precursor solutions at room temperature and atmosphere pressure. The optical, structural, and morphological characterizations of the films were studied by scanning electron microscopy, atomic force microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and UV/visible spectroscopy. Smooth (average roughness <3 nm), uniform, and highly transparent ZnS (transmittance of over 90% in the visible band) thin films could be successfully deposited using this technique with shorter cycle time and much less solvent usage.

  2. Scalable production of microbially-mediated ZnS nanoparticles and application to functional thin films

    SciTech Connect

    Moon, Ji Won; Ivanov, Ilia N; Joshi, Pooran C; Armstrong, Beth L; Wang, Wei; Jung, Hyunsung; Rondinone, Adam Justin; Jellison Jr, Gerald Earle; Meyer III, Harry M; Jang, Gyoung Gug; Meisner, Roberta; Duty, Chad E; Phelps, Tommy Joe

    2014-01-01

    A series of semiconducting zinc sulfide (ZnS) nanoparticles were scalably, reproducibly, controllably, and economically synthesized with anaerobic metal-reducing Thermoanaerobacter species. They reduced partially oxidized sulfur sources to sulfides that extracellularly and thermodynamically incorporated with zinc ions to produce sparingly soluble ZnS nanoparticles with ~5 nm crystallites at yields of ~5 g l 1 month 1. A predominant sphalerite formation was facilitated by rapid precipitation kinetics, low cation/anion ratio, higher zinc concentration, water stabilization, or some combination of the four. The sphalerite ZnS nanoparticles exhibited narrow size distribution, high emission intensity, and few native defects. Scale-up and emission tunability using copper-doping were confirmed spectroscopically. Surface characterization was determined using Fourier transform infrared and X-ray photoelectron spectroscopies, which confirmed amine and carboxylic acid not only maintaining a nano-dimensional average crystallite size, but also increasing aggregation. Application of ZnS nanoparticle ink to a functional thin film was successfully tested for potential future applications.

  3. Microstructure and cathodoluminescence study of sprayed Al and Sn doped ZnS thin films

    NASA Astrophysics Data System (ADS)

    El Hichou, A.; Addou, M.; Bubendorff, J. L.; Ebothé, J.; El Idrissi, B.; Troyon, M.

    2004-02-01

    Here we report on the study of ZnS and X-doped ZnS (with 4 at% of X = Al, Sn) thin films, prepared by spray pyrolysis technique using chloride precursors. Cathodoluminescence imaging and spectroscopy, x-ray diffraction, x-ray energy dispersive spectrometry and spectrophotometry have been used for their characterization. Deposited at their optimal substrate temperature (Ts = 773 K), these films are polycrystalline and consist of mixed hexagonal (agr) and cubic (bgr) phases with a predominance of the cubic phase. Their growth is preferentially oriented along the (111)bgr direction and their optical bandgap always remains close to 3.56 eV regardless of the sample considered. The cathodoluminescence spectra of ZnS and Al-ZnS films are similar and are characterized by a blue emission peak at 407 nm (3.05 eV) and a broad blue-green one located at 524 nm (2.36 eV) due to the presence of chlorine. The insertion of Sn2+ ions in the ZnS material leads to the formation of the SnCl2 compound and to the disappearance of the blue-green emission associated with Cl ionized donors.

  4. ZnS nanostructured thin-films deposited by successive ionic layer adsorption and reaction

    NASA Astrophysics Data System (ADS)

    Deshmukh, S. G.; Jariwala, Akshay; Agarwal, Anubha; Patel, Chetna; Panchal, A. K.; Kheraj, Vipul

    2016-04-01

    ZnS thin films were grown on glass substrate using successive ionic layer adsorption and reaction (SILAR) technique at room temperature. Aqueous solutions of ZnCl2 and Na2S were used as precursors. The X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Raman spectroscopy and optical absorption measurements were applied to study the structural, surface morphology and optical properties of as-deposited ZnS thin films. The X-ray diffraction profiles revealed that ZnS thin films consist of crystalline grains with cubic phase. Spherical nano grains of random size and well covered on the glass substrate were observed from FESEM. The average grain size were found to be 77 nm, 100 nm and 124 nm for 20 cycles, 40 cycles and 60 cycles samples respectively. For 60 cycle sample, Raman spectra show two prominent peaks at 554 cm-1 and 1094 cm-1. The optical band gap values were found to be 3.76 eV, 3.72 eV and 3.67 eV for 20 cycle, 40 cycle and 60 cycle samples respectively.

  5. Effect of anionic concentration on the structural and optical properties of nanostructured ZnS thin films

    NASA Astrophysics Data System (ADS)

    Safeera, T. A.; Johns, N.; Anila, E. I.

    2016-08-01

    Nanostructured Zinc Sulfide (ZnS) thin films with wurtzite structure were prepared by chemical spray pyrolysis method at low temperature. The effect of sulfur concentration on the structural and optical properties of ZnS thin films was studied. The films were analysed by x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), UV-Vis spectroscopy and photoluminescence (PL). Nano grain formation of ZnS was observed from XRD and SEM. Variation in band gap of different films is in agreement with size effects. But there is a red shift in the band gap of these films compared to bulk ZnS. This is due to band tailing effect experienced by the films due to the presence of large number of defects which was verified by PL spectrum. The overall emission was blue in colour for all the films and it was confirmed by Commission International d'Eclairage (CIE) diagram.

  6. Effects of pH on the characteristics of ZnS thin films grown by using the CBD method

    NASA Astrophysics Data System (ADS)

    Ahn, Heejin; Lee, Dongchan; Park, Sujung; Um, Youngho

    In CIGS-based thin film solar cells, a chemically deposited ZnS buffer layer with high resistivity is generally used between the absorber layer and transparent conducting oxide layer. In this work, we report a chemical process to prepare ZnS films by the CBD technique based on the typical bath deposition. The influences of ammonia (NH4OH) and Na2EDTA (Na2C10H16N2O8) as complexing agents on structural, morphological, and optical properties of ZnS thin films are investigated ranging pH concentration from 5 to 10. To investigate effects of pH on the characteristics of ZnS thin films, by using UV-visible transmittance, atomic force microscopy, and optical absorption were investigated. With changing the pH range, the ZnS thin films demonstrate high transmittance of 75~80% in the visible region, indicating the films are potentially useful in photovoltaic applications. The results will be presented in detail. This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education (2011-0024709).

  7. Thermal Conductivity in Nanocrystalline Ceria Thin Films

    SciTech Connect

    Marat Khafizov; In-Wook Park; Aleksandr Chernatynskiy; Lingfeng He; Jianliang Lin; John J. Moore; David Swank; Thomas Lillo; Simon R. Phillpot; Anter El-Azab; David H. Hurley

    2014-02-01

    The thermal conductivity of nanocrystalline ceria films grown by unbalanced magnetron sputtering is determined as a function of temperature using laser-based modulated thermoreflectance. The films exhibit significantly reduced conductivity compared with stoichiometric bulk CeO2. A variety of microstructure imaging techniques including X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron analysis, and electron energy loss spectroscopy indicate that the thermal conductivity is influenced by grain boundaries, dislocations, and oxygen vacancies. The temperature dependence of the thermal conductivity is analyzed using an analytical solution of the Boltzmann transport equation. The conclusion of this study is that oxygen vacancies pose a smaller impediment to thermal transport when they segregate along grain boundaries.

  8. Nanocrystalline-graphene-tailored hexagonal boron nitride thin films.

    PubMed

    Lee, Kang Hyuck; Shin, Hyeon-Jin; Kumar, Brijesh; Kim, Han Sol; Lee, Jinyeong; Bhatia, Ravi; Kim, Sang-Hyeob; Lee, In-Yeal; Lee, Hyo Sug; Kim, Gil-Ho; Yoo, Ji-Beom; Choi, Jae-Young; Kim, Sang-Woo

    2014-10-20

    Unintentionally formed nanocrystalline graphene (nc-G) can act as a useful seed for the large-area synthesis of a hexagonal boron nitride (h-BN) thin film with an atomically flat surface that is comparable to that of exfoliated single-crystal h-BN. A wafer-scale dielectric h-BN thin film was successfully synthesized on a bare sapphire substrate by assistance of nc-G, which prevented structural deformations in a chemical vapor deposition process. The growth mechanism of this nc-G-tailored h-BN thin film was systematically analyzed. This approach provides a novel method for preparing high-quality two-dimensional materials on a large surface. PMID:25204810

  9. Optical switch based on nanocrystalline VOx thin film

    NASA Astrophysics Data System (ADS)

    Chen, Xiqu; Dai, Jun

    2009-11-01

    An optical switch is fabricated based on nanocrystalline vanadium oxide (VOx) thin film using micromachining technology. An "on" state with semiconducting phase to an "off" state with metallic phase is controlled by applying a DC power to Aurum electrodes of the optical switch. The optical switching performance for the fabricated device is investigated at optical communication wavelength of 1.55μm. The heater power requires to achieve switching action is about 15mW. The testing results show that the extinction ratio and switching response time are 14dB and 2ms, respectively.

  10. Study of the morphology of ZnS thin films deposited on different substrates via chemical bath deposition.

    PubMed

    Gómez-Gutiérrez, Claudia M; Luque, P A; Castro-Beltran, A; Vilchis-Nestor, A R; Lugo-Medina, Eder; Carrillo-Castillo, A; Quevedo-Lopez, M A; Olivas, A

    2015-01-01

    In this work, the influence of substrate on the morphology of ZnS thin films by chemical bath deposition is studied. The materials used were zinc acetate, tri-sodium citrate, thiourea, and ammonium hydroxide/ammonium chloride solution. The growth of ZnS thin films on different substrates showed a large variation on the surface, presenting a poor growth on SiO2 and HfO2 substrates. The thin films on ITO substrate presented a uniform and compact growth without pinholes. The optical properties showed a transmittance of about 85% in the visible range of 300-800 nm with band gap of 3.7 eV. PMID:26011683

  11. Morphological, luminescence and structural properties of nanocrystalline silicon thin films

    SciTech Connect

    Ali, Atif Mossad; Kobayashi, Hikaru; Inokuma, Takao; Al-Hajry, Ali

    2013-03-15

    Highlights: ► The PL spectra showed two stronger peaks and one weaker peak. ► The PL peak energies and optical band-gap values were found higher than 1.12 eV. ► The structural change from an amorphous to nanocrystalline with increasing [SiH{sub 4}]. - Abstract: Nanocrystalline silicon (nc-Si) thin films deposited by plasma-enhanced chemical vapor deposition at various silane flow rates ([SiH{sub 4}]) are studied. The characterization of these films by high-resolution transmission electron microscopy, Raman spectroscopy and X-ray diffraction reveals that no film and very thin film is deposited at [SiH{sub 4}] = 0.0 and 0.1 sccm, respectively. In addition, the structural change from an amorphous to a nanocrystalline phase occurs at around [SiH{sub 4}] = 0.2 sccm. In this study, the importance of arriving species at surfaces and precursors is clearly demonstrated by the effect of a small addition of SiH{sub 4} on the frequency and width of a Raman peak and the structure of the grown film. The infrared spectroscopic analysis shows no hydrogen incorporation in the nc-Si film deposited at the low value of [SiH{sub 4}]. However, the intensity of the peak around 2100 cm{sup −1} due to SiH decreases with increasing [SiH{sub 4}]. All fabricated films give photoluminescence in the range between 1.7 and 2.4 eV at room temperature, indicating enlargement of the band-gap energy. The presence of very small crystallites leads to the appearance of quantum confinement effects. The variations of the photoluminescence energy and spectral width are well correlated with the structural properties of the films such as crystallite size, crystalline volume fraction, and the density of Si-H bonds.

  12. Structural, Optical, and Magnetic Properties of Solution-Processed Co-Doped ZnS Thin Films

    NASA Astrophysics Data System (ADS)

    Goktas, A.; Mutlu, İ. H.

    2016-07-01

    Co-doped ZnS thin films have been grown on glass substrates using solution-processing and dip-coating techniques, and the impact of the Co doping level (0% to 5%) and film thickness on certain characteristics examined. X-ray diffraction study revealed that all the films possessed hexagonal crystal structure. Energy-dispersive x-ray analysis confirmed presence of Zn, Co, and S in the samples. Scanning electron microscopy showed that the film surface was homogeneous and dense with some cracks and spots. X-ray photoelectron spectroscopy confirmed introduction and integration of Co2+ ions into the ZnS thin films. Compared with undoped ZnS, optical studies indicated a reduction in optical bandgap energy (E g) while the refractive index (n), extinction coefficient (k), and dielectric constants (ɛ 1, ɛ 2) increased with film thickness (t) and Co doping level (except for 5%). Photoluminescence spectra showed enhanced luminescence intensity as the Co concentration was increased, while the dependence on t showed an initial increase followed by a decrease. The origin of the observed low-temperature (5 K and 100 K) ferromagnetic order may be related to point defects such as zinc vacancies, zinc interstitials, and sulfide vacancies or to the grain-boundary effect.

  13. Growth of MPS-capped ZnS quantum dots in self-assembled thin films: Influence of heat treatment

    NASA Astrophysics Data System (ADS)

    Koç, Kenan; Tepehan, Fatma Zehra; Tepehan, Galip Gültekin

    2015-12-01

    The colloidal ZnS quantum dots (QDs) were prepared using 3-mercaptopropyltrimethoxysilane (MPS) molecules. Sol-gel spin coating method was used to deposit the colloidal nanoparticles on a glass substrate. Several features of the MPS were made use to produce self assembled thin films of ZnS quantum dots in a SiO2 network. Produced films were heat treated in between 225 °C and 325 °C to investigate their growth kinetics. The result showed that their size changed approximately from 3 nm to 4 nm and the first excitation peak position changed from 4.6 eV to 4.1 eV in this temperature interval. The activation energy of the nanoparticles for the Ostwald ripening process was found to be 59 kJ/mol.

  14. Investigation of primary crystallite sizes in nanocrystalline ZnS powders: comparison of microwave assisted with conventional synthesis routes.

    PubMed

    Rath, Thomas; Kunert, Birgit; Resel, Roland; Fritz-Popovski, Gerhard; Saf, Robert; Trimmel, Gregor

    2008-04-21

    ZnS powders with primary crystallite sizes of only a few nanometers were prepared by three different synthesis routes at temperatures below 130 degrees C. The reaction of zinc acetate dihydrate with thioacetamide (TAA) in the presence of pyridine and triphenylphosphite (TPP) was carried out using either conventional heating or microwave heating. The obtained powders exhibit sphalerite structure as determined by X-ray diffraction (XRD). The primary crystallites have diameters between 1 and 7 nm obtained by XRD. Small angle X-ray scattering (SAXS) measurements were analyzed by the model-free inverse Fourier-transformation approach, as well as by a hard sphere-model from which particle size and polydispersity were extracted. The particle sizes by SAXS are in good agreement with the primary crystallite sizes obtained by XRD. It has been found that an increasing amount of sulfur and/or using microwave heating increases crystallite sizes. The presence of TPP decreases the particle sizes but no significant influence on the TPP concentration was observed. In the alternative third preparation route, hexamethyldisilathiane (HMDST) was used as precipitation reagent at ambient temperature, which leads to the smallest crystallite sizes of only 1 nm together with low polydispersities. Scanning electron microscopy, dynamic light scattering and UV-vis spectroscopy showed that all three synthesis routes lead to ZnS powders with aggregate sizes between 650 and 1200 nm. Both of the TAA-precipitation routes lead to spherical agglomerates which consist of spherical substructures, whereas the HMDST agglomerates are assembled from elongated objects. PMID:18351732

  15. Experimental evidence of tunable space-charge-layer-induced electrical properties of nanocrystalline ceria thin films.

    PubMed

    Lee, Kyung-Ryul; Lee, Jong-Ho; Yoo, Han-Ill

    2013-10-01

    Fully dense nanocrystalline ceria films were successfully deposited on a MgO single crystal by pulsed laser deposition (PLD). The electrical conductivity of the nanocrystalline thin film was 20 times higher than that of the bulk sample. The activation energy of bulk ceria was 2.3 eV, whereas the activation energy of the nanocrystalline sample was only 1.2 eV. After post-annealing at 1273 K in which the grain size of the nanocrystalline thin film increased to ~400 nm, the electrical conductivity and activation energy of the film were changed similar to those of bulk. These unique electrical properties of the nano-crystalline thin-film can be attributed to the grain size effect, or more specifically, to the space charge layer (SCL) effect. Furthermore, the electrical conductivity of the nanocrystalline thin film became similar to that of the bulk in an extremely reducing atmosphere because of the unusual dependence of the SCL effect on the oxygen partial pressure. PMID:23942424

  16. Electrodeposited ZnS Precursor Layer with Improved Electrooptical Properties for Efficient Cu2ZnSnS4 Thin-Film Solar Cells

    NASA Astrophysics Data System (ADS)

    Mkawi, E. M.; Ibrahim, K.; Ali, M. K. M.; Farrukh, M. A.; Mohamed, A. S.

    2015-10-01

    Zinc sulfide (ZnS) thin films were prepared on indium tin oxide-coated glass by electrodeposition using aqueous zinc sulfate, thiourea, and ammonia solutions at 80°C. The effects of sulfurization at temperatures of 350°C, 400°C, 450°C, and 500°C on the morphological, structural, optical, and electrical properties of the ZnS thin films were investigated. X-ray diffraction analysis showed that the ZnS thin films exhibited cubic zincblende structure with preferred (111) orientation. The film crystallization improved with increasing annealing temperature. Field-emission scanning electron microscopy images showed that the film morphology became more compact and uniform with increasing annealing temperature. The percentage of sulfur in the ZnS thin films increased after sulfurization until a stoichiometric S/Zn ratio was achieved at 500°C. The annealed films showed good adhesion to the glass substrates, with moderate transmittance (85%) in the visible region. Based on absorption measurements, the direct bandgap increased from 3.71 eV to 3.79 eV with annealing temperature, which is attributed to the change of the buffer material composition and suitable crystal surface properties for effective p- n junction formation. The ZnS thin films were used as a buffer layer in thin-film solar cells with the structure of soda-lime glass/Mo/Cu2ZnSnS4/ZnS/ZnO/Al grid. The best solar cell efficiency was 1.86%.

  17. Ultrasensitive, Real-time and Discriminative Detection of Improvised Explosives by Chemiresistive Thin-film Sensory Array of Mn2+ Tailored Hierarchical ZnS

    NASA Astrophysics Data System (ADS)

    Zhou, Chaoyu; Wu, Zhaofeng; Guo, Yanan; Li, Yushu; Cao, Hongyu; Zheng, Xuefang; Dou, Xincun

    2016-05-01

    A simple method combing Mn2+ doping with a hierarchical structure was developed for the improvement of thin-film sensors and efficient detection of the explosives relevant to improvised explosive devices (IEDs). ZnS hierarchical nanospheres (HNs) were prepared via a solution-based route and their sensing performances were manipulated by Mn2+ doping. The responses of the sensors based on ZnS HNs towards 8 explosives generally increase firstly and then decrease with the increase of the doped Mn2+ concentration, reaching the climate at 5% Mn2+. Furthermore, the sensory array based on ZnS HNs with different doping levels achieved the sensitive and discriminative detection of 6 analytes relevant to IEDs and 2 military explosives in less than 5 s at room temperature. Importantly, the superior sensing performances make ZnS HNs material interesting in the field of chemiresistive sensors, and this simple method could be a very promising strategy to put the sensors based on thin-films of one-dimensional (1D) nanostructures into practical IEDs detection.

  18. Ultrasensitive, Real-time and Discriminative Detection of Improvised Explosives by Chemiresistive Thin-film Sensory Array of Mn2+ Tailored Hierarchical ZnS

    PubMed Central

    Zhou, Chaoyu; Wu, Zhaofeng; Guo, Yanan; Li, Yushu; Cao, Hongyu; Zheng, Xuefang; Dou, Xincun

    2016-01-01

    A simple method combing Mn2+ doping with a hierarchical structure was developed for the improvement of thin-film sensors and efficient detection of the explosives relevant to improvised explosive devices (IEDs). ZnS hierarchical nanospheres (HNs) were prepared via a solution-based route and their sensing performances were manipulated by Mn2+ doping. The responses of the sensors based on ZnS HNs towards 8 explosives generally increase firstly and then decrease with the increase of the doped Mn2+ concentration, reaching the climate at 5% Mn2+. Furthermore, the sensory array based on ZnS HNs with different doping levels achieved the sensitive and discriminative detection of 6 analytes relevant to IEDs and 2 military explosives in less than 5 s at room temperature. Importantly, the superior sensing performances make ZnS HNs material interesting in the field of chemiresistive sensors, and this simple method could be a very promising strategy to put the sensors based on thin-films of one-dimensional (1D) nanostructures into practical IEDs detection. PMID:27161193

  19. Ultrasensitive, Real-time and Discriminative Detection of Improvised Explosives by Chemiresistive Thin-film Sensory Array of Mn(2+) Tailored Hierarchical ZnS.

    PubMed

    Zhou, Chaoyu; Wu, Zhaofeng; Guo, Yanan; Li, Yushu; Cao, Hongyu; Zheng, Xuefang; Dou, Xincun

    2016-01-01

    A simple method combing Mn(2+) doping with a hierarchical structure was developed for the improvement of thin-film sensors and efficient detection of the explosives relevant to improvised explosive devices (IEDs). ZnS hierarchical nanospheres (HNs) were prepared via a solution-based route and their sensing performances were manipulated by Mn(2+) doping. The responses of the sensors based on ZnS HNs towards 8 explosives generally increase firstly and then decrease with the increase of the doped Mn(2+) concentration, reaching the climate at 5% Mn(2+). Furthermore, the sensory array based on ZnS HNs with different doping levels achieved the sensitive and discriminative detection of 6 analytes relevant to IEDs and 2 military explosives in less than 5 s at room temperature. Importantly, the superior sensing performances make ZnS HNs material interesting in the field of chemiresistive sensors, and this simple method could be a very promising strategy to put the sensors based on thin-films of one-dimensional (1D) nanostructures into practical IEDs detection. PMID:27161193

  20. Ferroelectric Polarization in Nanocrystalline Hydroxyapatite Thin Films on Silicon

    PubMed Central

    Lang, S. B.; Tofail, S. A. M.; Kholkin, A. L.; Wojtaś, M.; Gregor, M.; Gandhi, A. A.; Wang, Y.; Bauer, S.; Krause, M.; Plecenik, A.

    2013-01-01

    Hydroxyapatite nanocrystals in natural form are a major component of bone- a known piezoelectric material. Synthetic hydroxyapatite is widely used in bone grafts and prosthetic pyroelectric coatings as it binds strongly with natural bone. Nanocrystalline synthetic hydroxyapatite films have recently been found to exhibit strong piezoelectricity and pyroelectricity. While a spontaneous polarization in hydroxyapatite has been predicted since 2005, the reversibility of this polarization (i.e. ferroelectricity) requires experimental evidence. Here we use piezoresponse force microscopy to demonstrate that nanocrystalline hydroxyapatite indeed exhibits ferroelectricity: a reversal of polarization under an electrical field. This finding will strengthen investigations on the role of electrical polarization in biomineralization and bone-density related diseases. As hydroxyapatite is one of the most common biocompatible materials, our findings will also stimulate systematic exploration of lead and rare-metal free ferroelectric devices for potential applications in areas as diverse as in vivo and ex vivo energy harvesting, biosensing and electronics. PMID:23884324

  1. Ferroelectric polarization in nanocrystalline hydroxyapatite thin films on silicon.

    PubMed

    Lang, S B; Tofail, S A M; Kholkin, A L; Wojtaś, M; Gregor, M; Gandhi, A A; Wang, Y; Bauer, S; Krause, M; Plecenik, A

    2013-01-01

    Hydroxyapatite nanocrystals in natural form are a major component of bone--a known piezoelectric material. Synthetic hydroxyapatite is widely used in bone grafts and prosthetic pyroelectric coatings as it binds strongly with natural bone. Nanocrystalline synthetic hydroxyapatite films have recently been found to exhibit strong piezoelectricity and pyroelectricity. While a spontaneous polarization in hydroxyapatite has been predicted since 2005, the reversibility of this polarization (i.e. ferroelectricity) requires experimental evidence. Here we use piezoresponse force microscopy to demonstrate that nanocrystalline hydroxyapatite indeed exhibits ferroelectricity: a reversal of polarization under an electrical field. This finding will strengthen investigations on the role of electrical polarization in biomineralization and bone-density related diseases. As hydroxyapatite is one of the most common biocompatible materials, our findings will also stimulate systematic exploration of lead and rare-metal free ferroelectric devices for potential applications in areas as diverse as in vivo and ex vivo energy harvesting, biosensing and electronics. PMID:23884324

  2. Ferroelectric Polarization in Nanocrystalline Hydroxyapatite Thin Films on Silicon

    NASA Astrophysics Data System (ADS)

    Lang, S. B.; Tofail, S. A. M.; Kholkin, A. L.; Wojtaś, M.; Gregor, M.; Gandhi, A. A.; Wang, Y.; Bauer, S.; Krause, M.; Plecenik, A.

    2013-07-01

    Hydroxyapatite nanocrystals in natural form are a major component of bone- a known piezoelectric material. Synthetic hydroxyapatite is widely used in bone grafts and prosthetic pyroelectric coatings as it binds strongly with natural bone. Nanocrystalline synthetic hydroxyapatite films have recently been found to exhibit strong piezoelectricity and pyroelectricity. While a spontaneous polarization in hydroxyapatite has been predicted since 2005, the reversibility of this polarization (i.e. ferroelectricity) requires experimental evidence. Here we use piezoresponse force microscopy to demonstrate that nanocrystalline hydroxyapatite indeed exhibits ferroelectricity: a reversal of polarization under an electrical field. This finding will strengthen investigations on the role of electrical polarization in biomineralization and bone-density related diseases. As hydroxyapatite is one of the most common biocompatible materials, our findings will also stimulate systematic exploration of lead and rare-metal free ferroelectric devices for potential applications in areas as diverse as in vivo and ex vivo energy harvesting, biosensing and electronics.

  3. Method for the preparation of nanocrystalline diamond thin films

    DOEpatents

    Gruen, Dieter M.; Krauss, Alan R.

    1998-01-01

    A method and system for manufacturing nanocrystalline diamond film on a substrate such as field emission tips. The method involves forming a carbonaceous vapor, providing a gas stream of argon, hydrocarbon and possibly hydrogen, and combining the gas with the carbonaceous vapor, passing the combined carbonaceous vapor and gas carrier stream into a chamber, forming a plasma in the chamber causing fragmentation of the carbonaceous vapor and deposition of a diamond film on the field emission tip.

  4. Method for the preparation of nanocrystalline diamond thin films

    DOEpatents

    Gruen, D.M.; Krauss, A.R.

    1998-06-30

    A method and system are disclosed for manufacturing nanocrystalline diamond film on a substrate such as field emission tips. The method involves forming a carbonaceous vapor, providing a gas stream of argon, hydrocarbon and possibly hydrogen, and combining the gas with the carbonaceous vapor, passing the combined carbonaceous vapor and gas carrier stream into a chamber, forming a plasma in the chamber causing fragmentation of the carbonaceous vapor and deposition of a diamond film on the field emission tip. 40 figs.

  5. Effect of deposition variables on properties of CBD ZnS thin films prepared in chemical bath of ZnSO4/SC(NH2)2/Na3C3H5O7/NH4OH

    NASA Astrophysics Data System (ADS)

    Liu, Wei-Long; Yang, Chang-Siao; Hsieh, Shu-Huei; Chen, Wen-Jauh; Fern, Chi-Lon

    2013-01-01

    The CBD ZnS thin films were prepared on substrates of soda lime glass in chemical bath. The effect of deposition variables including zinc sulfate, thiourea, tri-sodium citrate, ammoina water, bath temperature, and deposition time on the properties of CBD ZnS thin films were comprehensively studied. The CBD ZnS thin films were characterized by a field emission scanning electron microscope (FESEM) for the surface and cross section morphologies and thicknesses, an energy dispersive spectrometer equipped in FESEM for the atomic% of Zn and S, an ultraviolet-visible spectrometer (300-800 nm) for the transmittance and energy gap, and an atomic force microscope for the surface roughness. The results showed that the CBD ZnS thin films have a transmittance for ultraviolet-visible rays (300-800 nm) from 70.8 to 87.8%. The CBD ZnS thin films prepared in bath 5 have an energy gap from 3.881 to 3.980 eV. The CBD ZnS thin films prepared in bath 6 have a growth rate from 1.8 to 3.2 nm/min and activation energy of 59.8 kJ/mol for their growth.

  6. Effect of dopent on the structural and optical properties of ZnS thin film as a buffer layer in solar cell application

    SciTech Connect

    Vashistha, Indu B. Sharma, S. K.; Sharma, Mahesh C.; Sharma, Ramphal

    2015-08-28

    In order to find the suitable alternative of toxic CdS buffer layer, deposition of pure ZnS and doped with Al by chemical bath deposition method have been reported. Further as grown pure and doped thin films have been annealed at 150°C. The structural and surface morphological properties have been characterized by X-Ray diffraction (XRD) and Atomic Force Microscope (AFM).The XRD analysis shows that annealed thin film has been polycrystalline in nature with sphalerite cubic crystal structure and AFM images indicate increment in grain size as well as growth of crystals after annealing. Optical measurement data give band gap of 3.5 eV which is ideal band gap for buffer layer for solar cell suggesting that the obtained ZnS buffer layer is suitable in a low-cost solar cell.

  7. Implantation induced hardening of nanocrystalline titanium thin films.

    PubMed

    Krishnan, R; Amirthapandian, S; Mangamma, G; Ramaseshan, R; Dash, S; Tyagi, A K; Jayaram, V; Raj, Baldev

    2009-09-01

    Formation of nanocrystalline TiN at low temperatures was demonstrated by combining Pulsed Laser Deposition (PLD) and ion implantation techniques. The Ti films of nominal thickness approximatly 250 nm were deposited at a substrate temperature of 200 degrees C by ablating a high pure titanium target in UHV conditions using a nanosecond pulsed Nd:YAG laser operating at 1064 nm. These films were implanted with 100 keV N+ ions with fluence ranging from 1.0 x 10(16) ions/cm2 to 1.0 x 10(17) ions/cm2 The structural, compositional and morphological evolutions were tracked using Transmission Electron Microscopy (TEM), Secondary Ion Mass Spectrometry (SIMS) and Atomic Force Microscopy (AFM), respectively. TEM analysis revealed that the as-deposited titanium film is an fcc phase. With increasing ion fluence, its structure becomes amorphous phase before precipitation of nanocrystalline fcc TIN phase. Compositional depth profiles obtained from SIMS have shown the extent of nitrogen concentration gradient in the implantation zone. Both as-deposited and ion implanted films showed much higher hardness as compared to the bulk titanium. AFM studies revealed a gradual increase in surface roughness leading to surface patterning with increase in ion fluence. PMID:19928244

  8. Coexistence of colossal stress and texture gradients in sputter deposited nanocrystalline ultra-thin metal films

    SciTech Connect

    Kuru, Yener; Welzel, Udo; Mittemeijer, Eric J.

    2014-12-01

    This paper demonstrates experimentally that ultra-thin, nanocrystalline films can exhibit coexisting colossal stress and texture depth gradients. Their quantitative determination is possible by X-ray diffraction experiments. Whereas a uniform texture by itself is known to generally cause curvature in so-called sin{sup 2}ψ plots, it is shown that the combined action of texture and stress gradients provides a separate source of curvature in sin{sup 2}ψ plots (i.e., even in cases where a uniform texture does not induce such curvature). On this basis, the texture and stress depth profiles of a nanocrystalline, ultra-thin (50 nm) tungsten film could be determined.

  9. YBa2Cu3O7 thin films on nanocrystalline diamond films for HTSC bolometer

    NASA Technical Reports Server (NTRS)

    Cui, G.; Beetz, C. P., Jr.; Boerstler, R.; Steinbeck, J.

    1993-01-01

    Superconducting YBa2Cu3O(7-x) films on nanocrystalline diamond thin films have been fabricated. A composite buffer layer system consisting of diamond/Si3N4/YSZ/YBCO was explored for this purpose. The as-deposited YBCO films were superconducting with Tc of about 84 K and a relatively narrow transition width of about 8 K. SEM cross sections of the films showed very sharp interfaces between diamond/Si3N4 and between Si3N4/YSZ. The deposited YBCO film had a surface roughness of about 1000 A, which is suitable for high-temperature superconductive (HTSC) bolometer fabrication. It was also found that preannealing of the nanocrystalline diamond thin films at high temperature was very important for obtaining high-quality YBCO films.

  10. Dye-Sensitization Of Nanocrystalline ZnO Thin Films

    NASA Astrophysics Data System (ADS)

    Ajimsha, R. S.; Tyagi, M.; Das, A. K.; Misra, P.; Kukreja, L. M.

    2010-12-01

    Nannocrystalline and nanoporus thin films of ZnO were synthesized on glass substrates by using wet chemical drop casting method. X-ray diffraction measurements on these samples confirmed the formation of ZnO nanocrystallites in hexagonal wurtzite phase with mean size of ˜20 nm. Photo sensitization of these nanostructured ZnO thin films was carried out using three types of dyes Rhodamine 6 G, Chlorophyll and cocktail of Rhodamine 6 G and Chlorophyll in 1:1 ratio. Dye sensitized ZnO thin films showed enhanced optical absorption in visible spectral region compared to the pristine ZnO thin films.

  11. Dye-Sensitization Of Nanocrystalline ZnO Thin Films

    SciTech Connect

    Ajimsha, R. S.; Tyagi, M.; Das, A. K.; Misra, P.; Kukreja, L. M.

    2010-12-01

    Nannocrystalline and nanoporus thin films of ZnO were synthesized on glass substrates by using wet chemical drop casting method. X-ray diffraction measurements on these samples confirmed the formation of ZnO nanocrystallites in hexagonal wurtzite phase with mean size of {approx}20 nm. Photo sensitization of these nanostructured ZnO thin films was carried out using three types of dyes Rhodamine 6 G, Chlorophyll and cocktail of Rhodamine 6 G and Chlorophyll in 1:1 ratio. Dye sensitized ZnO thin films showed enhanced optical absorption in visible spectral region compared to the pristine ZnO thin films.

  12. Fabrication and Characterization of Amorphous/Nanocrystalline Thin Film Composite

    NASA Astrophysics Data System (ADS)

    Newton, Benjamin S.

    Combining the absorption abilities of amorphous silicon and the electron transport capabilities of crystalline silicon would be a great advantage to not only solar cells but other semiconductor devices. In this work composite films were created using molecular beam epitaxy and electron beam deposition interchangeably as a method to create metallic precursors. Aluminum induced crystallization techniques were used to convert an amorphous silicon film with a capping layer of aluminum nanodots into a film composed of a mixture of amorphous silicon and nanocrystalline silicon. This layer was grown into the amorphous layer by cannibalizing a portion of the amorphous silicon material during the aluminum induced crystallization. Characterization was performed on films and metallic precursors utilizing SEM, TEM, ellipsometry and spectrophotometer.

  13. Enhanced optical constants of nanocrystalline yttrium oxide thin films

    SciTech Connect

    Ramana, C. V.; Mudavakkat, V. H.; Bharathi, K. Kamala; Atuchin, V. V.; Pokrovsky, L. D.; Kruchinin, V. N.

    2011-01-17

    Yttrium oxide (Y{sub 2}O{sub 3}) films with an average crystallite-size (L) ranging from 5 to 40 nm were grown by sputter-deposition onto Si(100) substrates. The optical properties of grown Y{sub 2}O{sub 3} films were evaluated using spectroscopic ellipsometry measurements. The size-effects were significant on the optical constants and their dispersion profiles of Y{sub 2}O{sub 3} films. A significant enhancement in the index of refraction (n) is observed in well-defined Y{sub 2}O{sub 3} nanocrystalline films compared to that of amorphous Y{sub 2}O{sub 3}. A direct, linear L-n relationship found for Y{sub 2}O{sub 3} films suggests that tuning optical properties for desired applications can be achieved by controlling the size at the nanoscale dimensions.

  14. Microstructural evolution of nanocrystalline nickel thin films due to high-energy heavy-ion irradiation

    SciTech Connect

    Rajasekhara, S.; Ferreira, P. J.; Hattar, K.

    2013-04-19

    This initial feasibility study demonstrates that recent advancements in precession electron diffraction microscopy can be applied to nanostructured metals exposed to high displacement damage from a Tandem accelerator. In this study, high purity, nanocrystalline, free-standing nickel thin films produced by pulsed laser deposition were irradiated with approximately 3 Multiplication-Sign 10{sup 14} ions/cm{sup 2} of 35 MeV Ni{sup 6+} ions resulting in an approximately uniform damage profile to approximately 16 dpa. Pristine and ionirradiated regions of the nanocrystalline Ni films were characterized by conventional transmission electron microscopy and precession electron diffraction microscopy. Precession electron diffraction microscopy provided additional insight into the texture, phase, and grain boundary distribution resulting from the displacement damage that could not be obtained from traditional electron microscopy techniques. For the nanocrystalline nickel film studied, this included the growth in number and percentage of a metastable hexagonal closed packed phase grains and the formation of large <001> textured face centered cubic grains. The application of precession electron diffraction microscopy to characterize other nanocrystalline metals, which are being considered for radiation tolerant applications, will permit a comparison of materials that goes beyond the dominant length scale to consider the effects of local phase, texture, and grain boundary or interface information.

  15. RF sputter deposited nanocrystalline (110) magnetite thin film from alpha-Fe2O3 target.

    PubMed

    Bohra, Murtaza; Venkataramani, N; Prasad, Shiva; Kumar, Naresh; Misra, D S; Sahoo, S C; Krishnan, R

    2007-06-01

    Nanocrystalline magnetite thin film was prepared on to fused quartz substrate by sputtering at an rf power of 50 W. X-ray diffraction study showed that the sputtered film was (110) oriented. The stoichiometry in the thin film has been confirmed through a variety of characterization techniques. The room temperature spontaneous magnetization value (4piMs) of the film was 5100 G. This is about 85% of the bulk value. The resistivity of the film showed a sharp change around 120 K, indicative of the Verwey transition. PMID:17654991

  16. The influence of substrate temperature on the structural and optical properties of ZnS thin films

    SciTech Connect

    Ashraf, M.; Akhtar, S. M. J.; Ali, Z.; Qayyum, A.

    2011-05-15

    Thin films of ZnS were deposited on soda lime glass substrates by a modified close-space sublimation technique. The change in optical and structural properties of the films deposited at various substrate temperatures (150-450 Degree-Sign C) was investigated. X-ray diffraction spectra showed that films were polycrystalline in nature having cubic structure oriented only along (111) plan. The crystallinity of films increased with the substrate temperature up to 250 Degree-Sign C. However, crystallinity decreased with further increase of substrate temperature and films became amorphous at 450 Degree-Sign C. The atomic force microscopy data revealed that the films become more uniform and dense with the increase of substrate temperature. Optical properties of the films were determined from the transmittance data using Swanepoel model. It was observed that the energy band gap is increased from 3.52 to 3.65 eV and refractive index of the films are decreased with the increase of substrate temperature. Moreover, considerable improvement in blue response of the films was noticed with increasing substrate temperature.

  17. Intrinsic Doping in Electrodeposited ZnS Thin Films for Application in Large-Area Optoelectronic Devices

    NASA Astrophysics Data System (ADS)

    Madugu, Mohammad Lamido; Olusola, Olajide Ibukun-Olu; Echendu, Obi Kingsley; Kadem, Burak; Dharmadasa, Imyhamy Mudiy

    2016-06-01

    Zinc sulphide (ZnS) thin films with both n- and p-type electrical conductivity were grown on glass/fluorine-doped tin oxide-conducting substrates from acidic and aqueous solution containing ZnSO4 and (NH4)2S2O3 by simply changing the deposition potential in a two-electrode cell configuration. After deposition, the films were characterised using various analytical techniques. X-ray diffraction analysis reveals that the materials are amorphous even after heat treatment. Optical properties (transmittance, absorbance and optical bandgap) of the films were studied. The bandgaps of the films were found to be in the range (3.68-3.86) eV depending on the growth voltage. Photoelectrochemical cell measurements show both n- and p-type electrical conductivity for the films depending on the growth voltage. Scanning electron microscopy shows material clusters on the surface with no significant change after heat treatment at different temperatures. Atomic force microscopy shows that the surface roughness of these materials remain fairly constant reducing only from 18 nm to 17 nm after heat treatment. Thickness estimation of the films was also carried out using theoretical and experimental methods. Direct current conductivity measurements on both as-deposited and annealed films show that resistivity increased after heat treatment.

  18. Hydrothermal synthesis of {beta}-nickel hydroxide nanocrystalline thin film and growth of oriented carbon nanofibers

    SciTech Connect

    Zhang Enlei; Tang Yuanhong; Zhang Yong; Guo Chi; Yang Lei

    2009-08-05

    Novel well-crystallized {beta}-nickel hydroxide nanocrystalline thin films were successfully synthesized at low temperature on the quartz substrates by hydrothermal method, and the oriented carbon nanofibers (CNFs) were prepared by acetylene cracking at 750 deg. C on thin film as the catalyst precursor. High resolution transmission electron microscopy (HR-TEM) measurement shows that thin films were constructed mainly with hexagonal {beta}-nickel hydroxide nanosheets. The average diameter of the nanosheets was about 80 nm and thickness about 15 nm. Hydrothermal temperature played an important role in the film growth process, influencing the morphologies and catalytic activity of the Ni catalysts. Ni thin films with high catalytic activity were obtained by reduction of these Ni(OH){sub 2} nanocrystalline thin films synthesized at 170 deg. C for 2 h in hydrothermal condition. The highest carbon yield was 1182%, and was significantly higher than the value of the catalyst precursor which was previously reported as the carbon yield (398%) for Ni catalysts. The morphology and growth mechanism of oriented CNFs were also studied finally.

  19. The role of confinement on stress-driven grain boundary motion in nanocrystalline aluminum thin films

    NASA Astrophysics Data System (ADS)

    Gianola, Daniel S.; Farkas, Diana; Gamarra, Martin; He, Mo-rigen

    2012-12-01

    3D molecular dynamics simulations are performed to investigate the role of microstructural confinement on room temperature stress-driven grain boundary (GB) motion for a general population of GBs in nanocrystalline Al thin films. Detailed analysis and comparison with experimental results reveal how coupled GB migration and GB sliding are manifested in realistic nanoscale networks of GBs. The proximity of free surfaces to GBs plays a significant role in their mobility and results in unique surface topography evolution. We highlight the effects of microstructural features, such as triple junctions, as constraints to otherwise uninhibited GB motion. We also study the pinning effects of impurities segregated to GBs that hinder their motion. Finally, the implications of GB motion as a deformation mechanism governing the mechanical behavior of nanocrystalline materials are discussed.

  20. Synthesis and characterization of nanocrystalline MoBi2Te5 thin films for photoelectrode applications

    NASA Astrophysics Data System (ADS)

    Salunkhe, M. M.; Kharade, R. R.; Mane, R. M.; Bhosale, P. N.

    2012-10-01

    Molybdenum bismuth telluride thin films have been prepared on clean glass substrate using arrested precipitation technique which is based on self-organized growth process. As deposited MoBi2Te5 thin films were dried in constant temperature oven at 110°C and further characterized for their optical, structural, morphological, compositional, and electrical analysis. Optical absorption spectra recorded in the wavelength range 300-800 nm showed band gap (E g) 1.44 eV. X-ray diffraction pattern and scanning electron microscopic images showed that MoBi2Te5 thin films are granular, nanocrystalline having rhombohedral structure. The compositional analysis showed close agreements in theoretical and experimental atomic percentages of Mo4+, Bi3+, and Te2- suggest that chemical formula MoBi2Te5 assigned to as deposited molybdenum bismuth telluride new material is confirmed. The electrical conductivity and thermoelectric power measurement showed that the films are semiconducting with n-type conduction. The fill factor and conversion efficiency was characterized by photoelectrochemical (PEC) technique. In this article, we report the optostructural, morphological, compositional, and electrical characteristics of nanocrystalline MoBi2Te5 thin films to check its suitability as photoelectrode in PEC cell.

  1. In-Situ Transmission Electron Microscope High Temperature Behavior in Nanocrystalline Platinum Thin Films

    NASA Astrophysics Data System (ADS)

    Garcia, Davil; Leon, Alexander; Kumar, Sandeep

    2016-01-01

    In this work, we present a micro electro-mechanical systems (MEMS)-based in situ transmission electron microscope (TEM) experimental setup for high-temperature uniaxial tensile behavior of nanocrystalline thin films. This setup utilizes self-heating (Ohmic) to raise the temperature of thin films while applying uniaxial tensile loading using electro-thermal actuators. Self-heating is achieved by passing a high-density direct current through the specimen. We carried out a qualitative uniaxial tensile experiment on a 75-nm platinum thin film at 360 K. Temperature is estimated using COMSOL modeling. In this qualitative experiment, we observed initial grain growth followed by formation of edge serrations. We propose that grain boundary sliding coupled with grain growth is the underlying mechanism responsible for the observed behavior.

  2. Correlation between surface chemistry, density, and band gap in nanocrystalline WO3 thin films.

    PubMed

    Vemuri, R S; Engelhard, M H; Ramana, C V

    2012-03-01

    Nanocrystalline WO(3) thin films were produced by sputter-deposition by varying the ratio of argon to oxygen in the reactive gas mixture during deposition. The surface chemistry, physical characteristics, and optical properties of nanocrystalline WO(3) films were evaluated using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray reflectivity (XRR), and spectrophotometric measurements. The effect of ultramicrostructure was significant on the optical properties of WO(3) films. The XPS analyses indicate the formation of stoichiometric WO(3) with tungsten existing in fully oxidized valence state (W(6+)). However, WO(3) films grown at high oxygen concentration (>60%) in the sputtering gas mixture were over stoichiometric with excess oxygen. XRR simulations based on isotropic WO(3) film-SiO(2) interface-Si substrate modeling indicate that the density of WO(3) films is sensitive to the oxygen content in the sputtering gas. The spectral transmission of the films increased with increasing oxygen. The band gap of these films increases from 2.78 to 3.25 eV with increasing oxygen. A direct correlation between the film density and band gap in nanocrystalline WO(3) films is established on the basis of the observed results. PMID:22332637

  3. Correlation between surface chemistry, density and band gap in nanocrystalline WO3 thin films

    SciTech Connect

    Vemuri, Venkata Rama Ses; Engelhard, Mark H.; Ramana, C.V.

    2012-03-01

    Nanocrystalline WO3 thin films were produced by sputter-deposition by varying the ratio of argon to oxygen in the reactive gas mixture during deposition. The surface chemistry, physical characteristics, and optical properties of nanocrystalline WO3 films were evaluated using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray reflectivity (XRR), and spectrophotometric measurements. The effect of ultra-microstructure was significant on the optical properties of WO3 films. The XPS analyses indicate the formation of stoichiometric WO3 with tungsten existing in fully oxidized valence state (W6+). However, WO3 films grown at high oxygen concentration (>60%) in the sputtering gas mixture were over stoichiometric with excess oxygen. XRR simulations, which are based on isotropic WO3 film - SiO2 interface - Si substrate model, indicate that the density of WO3 films is sensitive to the oxygen content in the sputtering gas. The spectral transmission of the films increased with the increasing oxygen. The band gap of these films increases from 2.78 eV to 3.25 eV with increasing oxygen. A direct correlation between the film-density and band gap in nanocrystalline WO3 films is established based on the observed results.

  4. Photoconductivity on nanocrystalline ZnO/TiO2 thin films obtained by sol-gel

    NASA Astrophysics Data System (ADS)

    Valverde-Aguilar, G.; García-Macedo, J. A.; Juárez-Arenas, R.

    2008-08-01

    In this paper we report results on the synthesis, characterization and photoconductivity behaviour of amorphous and nanocrystalline ZnO/TiO2 thin films. They were produced by the sol-gel process at room temperature by using the spin-coating method and deposited on glass substrates. The ZnO/TiO2 films were synthesized by using tetrabutyl orthotitanate and zinc nitrate hexahydrate as the inorganic precursors. The samples were sintered at 520°C for 1 hour. The obtained films were characterized by X-ray diffraction (XRD), optical absorption (OA), infrared spectroscopy (IR) and scanning electronic microscopy (SEM) studies. Photoconductivity studies were performed on amorphous and nanocrystalline (anatase phase) films to determine the charge transport parameters. The experimental data were fitted with straight lines at darkness and under illumination at 310 nm, 439 nm and 633 nm. This indicates an ohmic behavior. The Φμτ and Φl0 parameters were fitted by least-squares with straight lines (nanocrystalline films) and polynomial fits (amorphous films).

  5. Field-induced macroscopic barrier model for persistent photoconductivity in nanocrystalline oxide thin-film transistors

    NASA Astrophysics Data System (ADS)

    Choi, Hyun-Sik; Jeon, Sanghun

    2014-03-01

    Persistent photoconductivity (PPC) in nanocrystalline InZnO thin-film transistors (TFTs) was studied using carrier fluctuation measurements and transient analysis. Low-frequency noise measurements and decay kinetics indicate that the band bending by the external field together with the ionized oxygen vacancy (Vo++) generated during the light exposure is the main cause of the PPC phenomenon. Based on these observations, a field-induced macroscopic barrier model is proposed as the origin of PPC for InZnO TFTs. In particular, this model explains that the carrier separation between e and Vo++ is induced by the external field applied to the three electrodes inside the transistor.

  6. Thin nanocrystalline zirconia films prepared by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Dikovska, A. Og; Atanasova, G. B.; Avdeev, G. V.; Strijkova, V. Y.

    2016-03-01

    In the present work, thin zirconia films were prepared by pulsed laser deposition at different substrate temperatures and oxygen partial pressures. The substrate temperature was varied from 400 °C to 600 °C, and the oxygen pressure, from 0.01 to 0.05 mbar. The effect was investigated of the substrate temperature and oxygen pressure on the formation of m-zirconia and t-zirconia phases.The formation of a cubic phase of ZrO2 by using targets doped with 3 and 8 mol % content Y2O3 was also investigated. The variation in the optical properties was studied and discussed in relation with the zirconia films' microstructure.

  7. Chemical synthesis of p-type nanocrystalline copper selenide thin films for heterojunction solar cells

    NASA Astrophysics Data System (ADS)

    Ambade, Swapnil B.; Mane, R. S.; Kale, S. S.; Sonawane, S. H.; Shaikh, Arif V.; Han, Sung-Hwan

    2006-12-01

    Nanocrystalline thin films of copper selenide have been grown on glass and tin doped-indium oxide substrates using chemical method. At ambient temperature, golden films have been synthesized and annealed at 200 °C for 1 h and were examined for their structural, surface morphological and optical properties by means of X-ray diffraction (XRD), scanning electron microscopy and UV-vis spectrophotometry techniques, respectively. Cu 2- xSe phase was confirmed by XRD pattern and spherical grains of 30 ± 4 - 40 ± 4 nm in size aggregated over about 130 ± 10 nm islands were seen by SEM images. Effect of annealing on crystallinity improvement, band edge shift and photoelectrochemical performance (under 80 mW/cm 2 light intensity and in lithium iodide electrolyte) has been studied and reported. Observed p-type electrical conductivity in copper selenide thin films make it a suitable candidate for heterojunction solar cells.

  8. Room temperature ferromagnetism in Co defused CdTe nanocrystalline thin films

    SciTech Connect

    Rao, N. Madhusudhana; Kaleemulla, S.; Begam, M. Rigana

    2014-04-24

    Nanocrystalline Co defused CdTe thin films were prepared using electron beam evaporation technique by depositing CdTe/Co/CdTe stacked layers with different Co thickness onto glass substrate at 373 K followed by annealing at 573K for 2 hrs. Structural, morphological and magnetic properties of of all the Co defused CdTe thin films has been investigated. XRD pattern of all the films exhibited zinc blende structure with <111> preferential orientation without changing the crystal structure of the films. The grain size of the films increased from 31.5 nm to 48.1 nm with the increase of Co layer thickness from 25nm to 100nm. The morphological studies showed that uniform texture of the films and the presence of Co was confirmed by EDAX. Room temperature magnetization curves indicated an improved ferromagnetic behavior in the films with increase of the Co thickness.

  9. Sulfidation of electrodeposited microcrystalline/nanocrystalline cuprous oxide thin films for solar energy applications

    NASA Astrophysics Data System (ADS)

    Jayathilaka, K. M. D. C.; Kapaklis, V.; Siripala, W.; Jayanetti, J. K. D. S.

    2012-12-01

    Grain size of polycrystalline semiconductor thin films in solar cells is optimized to enhance the efficiency of solar cells. This paper reports results on an investigation carried out on electrodeposited n-type cuprous oxide (Cu2O) thin films on Ti substrates with small crystallites and sulfidation of them to produce a thin-film solar cell. During electrodeposition of Cu2O films, pH of an aqueous acetate bath was optimized to obtain films of grain size of about 100 nm, that were then used as templates to grow thicker n-type nanocrystalline Cu2O films. XRD and SEM analysis revealed that the films were of single phase and the substrates were well covered by the films. A junction of Cu2O/CuxS was formed by partially sulfiding the Cu2O films using an aqueous sodium sulfide solution. It was observed that the photovoltaic properties of nano Cu2O/CuxS heterojunction structures are better than micro Cu2O/CuxS heterojunction solar cells. Resulting Ti/nano Cu2O/CuxS/Au solar cell structure produced an energy conversion efficiency of 0.54%, Voc = 610 mV and Jsc = 3.4 mA cm-2, under AM 1.5 illumination. This is a significant improvement compared to the use of microcrystalline thin film Cu2O in the solar cell structure where the efficiency of the cell was limited to 0.11%. This improvement is attributed mainly to the increased film surface area associated with nanocrystalline Cu2O films.

  10. Structural and nanomechanical properties of nanocrystalline carbon thin films for photodetection

    SciTech Connect

    Rawal, Ishpal; Panwar, Omvir Singh Tripathi, Ravi Kant; Chockalingam, Sreekumar; Srivastava, Avanish Kumar; Kumar, Mahesh

    2015-05-15

    This paper reports the effect of helium gas pressure upon the structural, nanomechanical, and photoconductive properties of nanocrystalline carbon thin (NCT) films deposited by the filtered cathodic jet carbon arc technique. High-resolution transmission electron microscopy images confirm the nanocrystalline nature of the deposited films with different crystallite sizes (3–7 nm). The chemical structure of the deposited films is further analyzed by x-ray photoelectron spectroscopy and Raman spectroscopy, which suggest that the deposited films change from graphitelike to diamondlike, increasing in sp{sup 3} content, with a minor change in the dilution of the inert gas (helium). The graphitic character is regained upon higher dilution of the helium gas, whereupon the films exhibit an increase in sp{sup 2} content. The nanomechanical measurements show that the film deposited at a helium partial pressure of 2.2 × 10{sup −4} has the highest value of hardness (37.39 GPa) and elastic modulus (320.50 GPa). At a light intensity of 100 mW/cm{sup 2}, the NCT films deposited at 2.2 × 10{sup −4} and 0.1 mbar partial pressures of helium gas exhibit good photoresponses of 2.2% and 3.6%, respectively.

  11. Photoconducting nanocrystalline lead sulphide thin films obtained by chemical bath deposition

    NASA Astrophysics Data System (ADS)

    Kotadiya, Naresh B.; Kothari, Anjana J.; Tiwari, Devendra; Chaudhuri, Tapas K.

    2012-09-01

    A chemical bath deposition method of preparing photoconducting nanocrystalline lead sulphide (PbS) thin films at room temperature (RT) is described. The aqueous bath of lead acetate, thiourea, and ammonium hydroxide produce films of about 100 nm thicknesses in 45 minutes. X-ray diffraction (XRD) studies show that these films are nanocrystalline cubic PbS with 10 nm crystallite size. Atomic Force Microscope (AFM) and Scanning Electron Microscope (SEM) revealed that the films consist of spherical grains of sizes 100 to 200 nm. The transmission spectra of the films show onset of absorption edge around 850 nm and the bandgap is around 1.65 eV. The films are p-type with dark conductivity of 2.5×10-3 S/cm and mobility of 0.07 cm2/Vṡs. The photosensitivity is 6-7 for an illumination of 80 mW/cm2 from a halogen lamp (50 W, 12 V). Transient photoconductivity measurements reveal short and long life times of minority carriers. Thermoelectric and photothermoelectric studies show that photoconductivity in these films is mainly due to photogenerated majority carriers.

  12. Room temperature atomic layerlike deposition of ZnS on organic thin films: Role of substrate functional groups and precursors

    SciTech Connect

    Shi, Zhiwei; Walker, Amy V.

    2015-09-15

    The room temperature atomic layerlike deposition (ALLD) of ZnS on functionalized self-assembled monolayers (SAMs) was investigated, using diethyl zinc (DEZ) and in situ generated H{sub 2}S as reactants. Depositions on SAMs with three different terminal groups, –CH{sub 3,} –OH, and –COOH, were studied. It was found that the reaction of DEZ with the SAM terminal group is critical in determining the film growth rate. Little or no deposition is observed on –CH{sub 3} terminated SAMs because DEZ does not react with the methyl terminal group. ZnS does deposit on both –OH and –COOH terminated SAMs, but the grow rate on –COOH terminated SAMs is ∼10% lower per cycle than on –OH terminated SAMs. DEZ reacts with the hydroxyl group on –OH terminated SAMs, while on –COOH terminated SAMs it reacts with both the hydroxyl and carbonyl bonds of the terminal groups. The carbonyl reaction is found to lead to the formation of ketones rather than deposition of ZnS, lowering the growth rate on –COOH terminated SAMs. SIMS spectra show that both –OH and –COOH terminated SAMs are covered by the deposited ZnS layer after five ALLD cycles. In contrast to ZnO ALLD where the composition of the film differs for the first few layers on –COOH and –OH terminated SAMs, the deposited film composition is the same for both –COOH and –OH terminated SAMs. The deposited film is found to be Zn-rich, suggesting that the reaction of H{sub 2}S with the Zn-surface adduct may be incomplete.

  13. Dip coated nanocrystalline CdZnS thin films for solar cell application

    NASA Astrophysics Data System (ADS)

    Dongre, J. K.; Chaturvedi, Mahim; Patil, Yuvraj; Sharma, Sandhya; Jain, U. K.

    2015-07-01

    Nanocrystalline cadmium sulfide (CdS) and zinc cadmium sulfide (ZnCdS) thin films have been grown via simple and low cost dip coating technique. The prepared films are characterized by X-ray diffraction (XRD), atomic force microscopic (AFM) and UV-VIS spectrophotometer techniques to reveal their structural, morphological and optical properties. XRD shows that both samples grown have zinc blende structure. The grain size is calculated as 6.2 and 8 nm using Scherrer's formula. The band gap value of CdS and CdZnS film is estimated to be 2.58 and 2.69 eV respectively by UV-vis spectroscopy. Photoelectrochemical (PEC) investigations are carried out using cell configuration as n-CdZnS/(1M NaOH + 1M Na2S + 1M S)/C. The photovoltaic output characteristic is used to calculate fill-factor (FF) and solar conversion efficiency (η).

  14. Mechanism of stress relaxation in nanocrystalline Fe-N thin films

    NASA Astrophysics Data System (ADS)

    Gupta, Ranjeeta; Gupta, Ajay; Leitenberger, W.; Rüffer, R.

    2012-02-01

    The mechanism of stress relaxation in nanocrystalline Fe-N thin film has been studied. The as-deposited film possesses a strong in-plane compressive stress which relaxes with thermal annealing. Precise diffusion measurements using nuclear resonance reflectivity show that stress relaxation does not involve any long-range diffusion of Fe atoms. Rather, a redistribution of nitrogen atoms at various interstitial sites, as evidenced by conversion electron Mössbauer spectroscopy, is responsible for the relaxation of internal stresses. On the other hand, formation of the γ'-Fe4N phase at temperatures above 523 K involves long-range rearrangement of Fe atoms. The activation energy for Fe self-diffusion is found to be 0.38±0.04 eV.

  15. Guided assembly of nanoparticles on electrostatically charged nanocrystalline diamond thin films

    PubMed Central

    2011-01-01

    We apply atomic force microscope for local electrostatic charging of oxygen-terminated nanocrystalline diamond (NCD) thin films deposited on silicon, to induce electrostatically driven self-assembly of colloidal alumina nanoparticles into micro-patterns. Considering possible capacitive, sp2 phase and spatial uniformity factors to charging, we employ films with sub-100 nm thickness and about 60% relative sp2 phase content, probe the spatial material uniformity by Raman and electron microscopy, and repeat experiments at various positions. We demonstrate that electrostatic potential contrast on the NCD films varies between 0.1 and 1.2 V and that the contrast of more than ±1 V (as detected by Kelvin force microscopy) is able to induce self-assembly of the nanoparticles via coulombic and polarization forces. This opens prospects for applications of diamond and its unique set of properties in self-assembly of nano-devices and nano-systems. PMID:21711679

  16. Temperature dependence of FMR and magnetization in nanocrystalline zinc ferrite thin films

    NASA Astrophysics Data System (ADS)

    Sahu, B. N.; Doshi, Akash S.; Prabhu, R.; Venkataramani, N.; Prasad, Shiva; Krishnan, R.

    2016-05-01

    Single phase nano-crystalline zinc ferrite thin films were deposited by RF-magnetron sputtering on quartz substrate at room temperature (RT) in pure Argon environment and annealed (in air) at different temperatures. Temperature dependence of magnetization was studied on these films using both VSM and by observing FMR (in X band). Value of exchange stiffness constant (D) was obtained by fitting Bloch's law to the low temperature magnetization data. The value of D decreased monotonously with the annealing temperature (TA) of the samples. A film annealed at TA = 523 K, exhibited the highest magnetization value. The FMR line width of the films decreased with increase in measurement temperature. At RT (˜293 K), the lowest value of line width (ΔH) was 15 kA/m and 13 kA/m in parallel and perpendicular configuration respectively for the sample annealed at TA = 623 K.

  17. Optical and mechanical properties of nanocrystalline ZrC thin films grown by pulsed laser deposition.

    SciTech Connect

    Craciun, D.; Socol, G.; Lambers, E.; McCumiskey, E. J.; Taylor, C. R.; Martin, C.; Argibay, Nicolas; Craciun, V.; Tanner, D. B.

    2015-01-17

    Thin ZrC films (<500 nm) were grown on (100) Si substrates at a substrate temperature of 500 °C by the pulsed laser deposition (PLD) technique using a KrF excimer laser under different CH4 pressures. Glancing incidence X-ray diffraction showed that films were nanocrystalline, while X-ray reflectivity studies found out films were very dense and exhibited a smooth surface morphology. Optical spectroscopy data shows that the films have high reflectivity (>90%) in the infrared region, characteristic of metallic behavior. Nanoindentation results indicated that films deposited under lower CH4 pressures exhibited slightly higher nanohardness and Young modulus values than films deposited under higher pressures. As a result, tribological characterization revealed that these films exhibited relatively high wear resistance and steady-state friction coefficients on the order of μ = 0.4.

  18. Optical and mechanical properties of nanocrystalline ZrC thin films grown by pulsed laser deposition.

    DOE PAGESBeta

    Craciun, D.; Socol, G.; Lambers, E.; McCumiskey, E. J.; Taylor, C. R.; Martin, C.; Argibay, Nicolas; Craciun, V.; Tanner, D. B.

    2015-01-17

    Thin ZrC films (<500 nm) were grown on (100) Si substrates at a substrate temperature of 500 °C by the pulsed laser deposition (PLD) technique using a KrF excimer laser under different CH4 pressures. Glancing incidence X-ray diffraction showed that films were nanocrystalline, while X-ray reflectivity studies found out films were very dense and exhibited a smooth surface morphology. Optical spectroscopy data shows that the films have high reflectivity (>90%) in the infrared region, characteristic of metallic behavior. Nanoindentation results indicated that films deposited under lower CH4 pressures exhibited slightly higher nanohardness and Young modulus values than films deposited undermore » higher pressures. As a result, tribological characterization revealed that these films exhibited relatively high wear resistance and steady-state friction coefficients on the order of μ = 0.4.« less

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

    PubMed

    Chaisitsak, Sutichai

    2011-01-01

    This paper reports the improvement in the sensing performance of nanocrystalline SnO(2)-based liquid petroleum gas (LPG) sensors by doping with fluorine (F). Un-doped and F-doped tin oxide films were prepared on glass substrates by the dip-coating technique using a layer-by-layer deposition cycle (alternating between dip-coating a thin layer followed by a drying in air after each new layer). The results showed that this technique is superior to the conventional technique for both improving the film thickness uniformity and film transparency. The effect of F concentration on the structural, surface morphological and LPG sensing properties of the SnO(2) films was investigated. Atomic Force Microscopy (AFM) and X-ray diffraction pattern measurements showed that the obtained thin films are nanocrystalline SnO(2) with nanoscale-textured surfaces. Gas sensing characteristics (sensor response and response/recovery time) of the SnO(2):F sensors based on a planar interdigital structure were investigated at different operating temperatures and at different LPG concentrations. The addition of fluorine to SnO(2) was found to be advantageous for efficient detection of LPG gases, e.g., F-doped sensors are more stable at a low operating temperature (300 °C) with higher sensor response and faster response/recovery time, compared to un-doped sensor materials. The sensors based on SnO(2):F films could detect LPG even at a low level of 25% LEL, showing the possibility of using this transparent material for LPG leak detection. PMID:22164007

  20. Nanocrystalline SnO2:F Thin Films for Liquid Petroleum Gas Sensors

    PubMed Central

    Chaisitsak, Sutichai

    2011-01-01

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

  1. Simultaneous optimization of nanocrystalline SnO2 thin film deposition using multiple linear regressions.

    PubMed

    Ebrahimiasl, Saeideh; Zakaria, Azmi

    2014-01-01

    A nanocrystalline SnO2 thin film was synthesized by a chemical bath method. The parameters affecting the energy band gap and surface morphology of the deposited SnO2 thin film were optimized using a semi-empirical method. Four parameters, including deposition time, pH, bath temperature and tin chloride (SnCl2·2H2O) concentration were optimized by a factorial method. The factorial used a Taguchi OA (TOA) design method to estimate certain interactions and obtain the actual responses. Statistical evidences in analysis of variance including high F-value (4,112.2 and 20.27), very low P-value (<0.012 and 0.0478), non-significant lack of fit, the determination coefficient (R2 equal to 0.978 and 0.977) and the adequate precision (170.96 and 12.57) validated the suggested model. The optima of the suggested model were verified in the laboratory and results were quite close to the predicted values, indicating that the model successfully simulated the optimum conditions of SnO2 thin film synthesis. PMID:24509767

  2. Photoluminescence from doped ZnS nanostructures

    NASA Astrophysics Data System (ADS)

    Karar, N.

    2007-05-01

    Photoluminescence (PL) properties of differently doped nanocrystalline ZnS encapsulated by ZnO (ZnS/ZnO) are reported. It is found that in all cases aluminium as an extra/additional dopant leads to PL enhancement. In comparison to reported blue emitting bulk ZnS:Ag, or green emitting bulk ZnS:Cu, our nanocrystalline samples show a different PL emission profile. This observation is attributed to nanogranule formation, different dopant levels and ZnO capping related energy level modifications.

  3. Defect engineered d{sup 0} ferromagnetism in tin-doped indium oxide nanostructures and nanocrystalline thin-films

    SciTech Connect

    Khan, Gobinda Gopal E-mail: sghoshphysics@gmail.com; Sarkar, Ayan; Ghosh, Shyamsundar E-mail: sghoshphysics@gmail.com; Mandal, Guruprasad; Mukherjee, Goutam Dev; Manju, Unnikrishnan; Banu, Nasrin; Dev, Bhupendra Nath

    2015-08-21

    Origin of unexpected defect engineered room-temperature ferromagnetism observed in tin-doped indium oxide (ITO) nanostructures (Nanowires, Nano-combs) and nanocrystalline thin films fabricated by pulsed laser deposition has been investigated. It is found that the ITO nanostructures prepared under argon environment exhibit strongest ferromagnetic signature as compared to that nanocrystalline thin films grown at oxygen. The evidence of singly ionized oxygen vacancy (V{sub 0}{sup +}) defects, obtained from various spectroscopic measurements, suggests that such V{sub 0}{sup +} defects are mainly responsible for the intrinsic ferromagnetic ordering. The exchange interaction of the defects provides extensive opportunity to tune the room-temperature d{sup 0} ferromagnetism and optical properties of ITOs.

  4. Synthesis and characterization of pure anatase phase nanocrystalline TiO2 thin film by magnetron sputtering method

    NASA Astrophysics Data System (ADS)

    Pawar, Nimisha; Bhargava, Ankita; Dayal, Saurabh; Kumar, C. Sasi

    2016-05-01

    In present work, our focus is to deposit anatase phase nanocrystalline TiO2 thin films. In order to prepare Titanium oxide films we first deposited Titanium thin films using DC magnetron sputtering and then the substrates were annealed in a muffle furnace at different temperatures. Further the samples were characterized for analysis of phase, morphology and optical properties using XRD, SEM, AFM and photoluminescence spectroscopy respectively. XRD shows the formation of tetragonal phase TiO2 with lattice parameters values a= 3.8 Å and c=9.6 Å. The surface roughness value of the films were found to vary from 1.6 nm to 15.9 nm. The grain size as estimated from AFM varies from 48 nm to 125 nm at different temperatures. Thus, the results revealed the formation of ultra-smooth anatase phase pure nanocrystalline TiO2 spherical particles.

  5. Synthesis and characterization of nanocrystalline CdS thin films for highly photosensitive self-powered photodetector

    NASA Astrophysics Data System (ADS)

    Husham, Mohammed; Hassan, Zainuriah; Selman, Abass M.

    2016-04-01

    A self-powered highly photosensitive photodetector based on a nanocrystalline CdS thin film was fabricated using a microwave-assisted chemical bath deposition. In this study, highly uniform nanocrystalline CdS thin films were grown on Si(1 0 0) substrates from aqueous solutions of cadmium chloride (CdCl2) and thiourea [SC(NH2)2], which served as cadmium Cd2+ and sulfur S2- ions sources, respectively. Structural, morphological and optical analysis revealed that good-quality nanocrystalline CdS thin films were synthesized. Current-voltage (I-V) measurements of the fabricated photodetector showed a significant sensitivity to visible light at zero applied voltage, indicating that the fabricated device is a self-powered photodetector. The device was highly photosensitive to low-power visible light; it showed a sensitivity of 97.2 × 103 to (1.20 mW/cm2) 500-nm light, without an external bias. Photoresponse measurements demonstrated the highly reproducible characteristics of the fabricated photodetector with rapid response and baseline recovery time. This work introduces a simple and low-cost method for fabricating a rapid-response, highly photosensitive photodetector with zero power consumption. The mechanism of self-powered photodetectors is discussed.

  6. Controlled growth of nanocrystalline silicon within amorphous silicon carbide thin films

    NASA Astrophysics Data System (ADS)

    Kole, Arindam; Chaudhuri, Partha

    2014-04-01

    Controlled formation of nanocrystalline silicon (nc-Si) within hydrogenated amorphous silicon carbide (a-SiC:H) thin films has been demonstrated by a rf (13.56 MHz) plasma chemical vapour deposition (PECVD) method at a low deposition temperature of 200°C by regulating the deposition pressure (Pr) between 26.7 Pa and 133.3 Pa. Evolution of the size and the crystalline silicon volume fraction within the a-SiC:H matrix has been studied by XRD, Raman and HRTEM. The study reveals that at Pr of 26.7 Pa there are mostly isolated grains of nc-Si within the a-SiC:H matrix with average size of 4.5 nm. With increase of Pr the isolated nc-Si grains coalesce more and more giving rise to larger size connected nc-Si islands which appear as microcrystalline silicon in the Raman spectra. As a result net isolated nc-Si volume fraction decreases while the total crystalline silicon volume fraction increases.

  7. Anodic vacuum arc developed nanocrystalline Cu-Ni and Fe-Ni thin film thermocouples

    SciTech Connect

    Mukherjee, S. K.; Sinha, M. K.; Pathak, B.; Rout, S. K.; Barhai, P. K.

    2009-12-01

    This paper deals with the development of nanocrystalline Cu-Ni and Fe-Ni thin film thermocouples (TFTCs) by using ion-assisted anodic vacuum arc deposition technique. The crystallographic structure and surface morphology of individual layer films have been studied by x-ray diffraction and scanning electron microscopy, respectively. The resistivity, temperature coefficient of resistance, and thermoelectric power of as deposited and annealed films have been measured. The observed departure of these transport parameters from their respective bulk values can be understood in terms of intrinsic scattering due to enhanced crystallite boundaries. From the measured values of thermoelectric power and the corresponding temperature coefficient of resistance of annealed Cu, Ni, and Fe films, the calculated values of log derivative of the mean free path of conduction electrons at the Fermi surface with respect to energy (U) are found to be -0.51, 3.22, and -8.39, respectively. The thermoelectric response of annealed Cu-Ni and Fe-Ni TFTCs has been studied up to a maximum temperature difference of 300 deg. C. Reproducibility of TFTCs has been examined in terms of the standard deviation in thermoelectric response of 16 test samples for each pair. Cu-Ni and Fe-Ni TFTCs agree well with their wire thermocouple equivalents. The thermoelectric power values of Cu-Ni and Fe-Ni TFTCs at 300 deg. C are found to be 0.0178 and 0.0279 mV/ deg. C, respectively.

  8. Selective Growth of Nanocrystalline 3C-SiC Thin Films on Si

    NASA Astrophysics Data System (ADS)

    Beke, D.; Pongrácz, A.; Battistig, G.; Josepovits, K.; Pécz, B.

    2010-11-01

    Epitaxial formation of SiC nanocrystals has been investigated on single crystal silicon surfaces. A simple and cheap method using reactive annealing in CO has been developed and patented by our group (BME AFT and MTA MFA). By this technique epitaxial 3C-SiC nanocrystals can be grown at the Si side of a SiO2/Si interface without void formation at the SiC/Si interface. CO diffusion and SiC nanocrystal formation on different silicon based systems (SiO2/Si, Si3N4/3Si and SiO2/LPCVD poly-Si) after CO treatment at 105 Pa at elevated temperatures (T>1000° C) will be presented. By optimizing the annealing time a thin continuous nanocrystalline SiC layer has been formed. Applying a patterned Si3N4 capping layer as a barrier layer against CO diffusion, SiC nanocrystal formation at the Si3N4/Si interface is inhibited. We will present the selective growth of SiC nanocrystals using the before mentioned technique.

  9. Oxidation-Based Continuous Laser Writing in Vertical Nano-Crystalline Graphite Thin Films

    NASA Astrophysics Data System (ADS)

    Loisel, Loïc; Florea, Ileana; Cojocaru, Costel-Sorin; Tay, Beng Kang; Lebental, Bérengère

    2016-05-01

    Nano and femtosecond laser writing are becoming very popular techniques for patterning carbon-based materials, as they are single-step processes enabling the drawing of complex shapes without photoresist. However, pulsed laser writing requires costly laser sources and is known to cause damages to the surrounding material. By comparison, continuous-wave lasers are cheap, stable and provide energy at a more moderate rate. Here, we show that a continuous-wave laser may be used to pattern vertical nano-crystalline graphite thin films with very few macroscale defects. Moreover, a spatially resolved study of the impact of the annealing to the crystalline structure and to the oxygen ingress in the film is provided: amorphization, matter removal and high oxygen content at the center of the beam; sp2 clustering and low oxygen content at its periphery. These data strongly suggest that amorphization and matter removal are controlled by carbon oxidation. The simultaneous occurrence of oxidation and amorphization results in a unique evolution of the Raman spectra as a function of annealing time, with a decrease of the I(D)/I(G) values but an upshift of the G peak frequency.

  10. Ultrananocrystalline and nanocrystalline diamond thin films for NEMS/MEMS applications.

    SciTech Connect

    Sumant, A. V.; Auciello, O.; Carpick, R. W.; Srinivasan, S.; Butler, J. E.

    2010-04-01

    There has been a tireless quest by the designers of micro- and nanoelectro mechanical systems (MEMS/NEMS) to find a suitable material alternative to conventional silicon. This is needed to develop robust, reliable, and long-endurance MEMS/NEMS with capabilities for working under demanding conditions, including harsh environments, high stresses, or with contacting and sliding surfaces. Diamond is one of the most promising candidates for this because of its superior physical, chemical, and tribomechanical properties. Ultrananocrystalline diamond (UNCD) and nanocrystalline diamond (NCD) thin films, the two most studied forms of diamond films in the last decade, have distinct growth processes and nanostructures but complementary properties. This article reviews the fundamental and applied science performed to understand key aspects of UNCD and NCD films, including the nucleation and growth, tribomechanical properties, electronic properties, and applied studies on integration with piezoelectric materials and CMOS technology. Several emerging diamond-based MEMS/NEMS applications, including high-frequency resonators, radio frequency MEMS and photonic switches, and the first commercial diamond MEMS product - monolithic diamond atomic force microscopy probes - are discussed.

  11. Room temperature growth of nanocrystalline anatase TiO 2 thin films by dc magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Singh, Preetam; Kaur, Davinder

    2010-03-01

    We report, the structural and optical properties of nanocrystalline anatase TiO 2 thin films grown on glass substrate by dc magnetron sputtering at room temperature. The influence of sputtering power and pressure over crystallinity and surface morphology of the films were investigated. It was observed that increase in sputtering power activates the TiO 2 film growth from relative lower surface free energy to higher surface free energy. XRD pattern revealed the change in preferred orientation from (1 0 1) to (0 0 4) with increase in sputtering power, which is accounted for different surface energy associated with different planes. Microstructure of the films also changes from cauliflower type to columnar type structures with increase in sputtering power. FESEM images of films grown at low pressure and low sputtering power showed typical cauliflower like structure. The optical measurement revealed the systematic variation of the optical constants with deposition parameters. The films are highly transparent with transmission higher than 90% with sharp ultraviolet cut off. The transmittance of these films was found to be influenced by the surface roughness and film thickness. The optical band gap was found to decrease with increase in the sputtering power and pressure. The refractive index of the films was found to vary in the range of 2.50-2.24 with increase in sputtering pressure or sputtering power, resulting in the possibility of producing TiO 2 films for device applications with different refractive index, by changing the deposition parameters.

  12. Investigations of Ar ion irradiation effects on nanocrystalline SiC thin films

    NASA Astrophysics Data System (ADS)

    Craciun, V.; Craciun, D.; Socol, G.; Behdad, S.; Boesl, B.; Himcinschi, C.; Makino, H.; Socol, M.; Simeone, D.

    2016-06-01

    The effects of 800 keV Ar ion irradiation on thin nanocrystalline SiC films grown on (100) Si substrates using the pulsed laser deposition (PLD) technique were investigated. On such PLD grown films, which were very dense, flat and smooth, X-ray reflectivity, glancing incidence X-ray diffraction and nanoindentation investigations were easily performed to evaluate changes induced by irradiation on the density, surface roughness, crystalline structure, and mechanical properties. Results indicated that the SiC films retained their crystalline nature, the cubic phase partially transforming into the hexagonal phase, which had a slightly higher lattice parameter then the as-deposited films. Simulations of X-ray reflectivity curves indicated a 3% decrease of the films density after irradiation. Nanoindentation results showed a significant decrease of the hardness and Young's modulus values with respect to those measured on as-deposited films. Raman and X-ray photoelectron spectroscopy investigations found an increase of the Csbnd C bonds and a corresponding decrease of the Sisbnd C bonds in the irradiated area, which could explain the degradation of mechanical properties.

  13. Direct-Coated Photoconducting Nanocrystalline PbS Thin Films with Tunable Band Gap

    NASA Astrophysics Data System (ADS)

    Vankhade, Dhaval; Kothari, Anjana; Chaudhuri, Tapas K.

    2016-06-01

    Nanocrystalline PbS thin films are deposited on glass by direct coating from a precursor solution of lead acetate and thiourea in methanol. A single coating has a thickness of 50 nm and greater thicknesses are obtained from layer by layer deposition. The films are smooth and shiny with roughness (rms) of about 1.5 nm. X-ray diffraction studies show that films are cubic PbS with crystallite size about 10 nm. The films are p-type with dark electrical conductivities in the range of 0.4-0.5 S/cm. These films are basically photoconducting. Photoconductivity monotonically increases with increase in thickness. The band gap of the films strongly depends on the thickness of the films. The band gap decreases from 2.4 eV to 1.6 eV as the thickness is increased from 50 nm to 450 nm. The tunability of the band gap is useful for technical applications, such as solar cells and photodetectors.

  14. 3D hexagonal (R-3m) mesostructured nanocrystalline titania thin films : synthesis and characterization.

    SciTech Connect

    Choi, S. Y.; Lee, B.; Carew, D. B.; Mamak, M; Peiris, F. C.; Speakman, S.; Chopra, N.; Ozin, G. A.; X-Ray Science Division; Univ. of Toronto; ORNL; Xerox Research Centre of Canada

    2006-01-01

    A straightforward and reproducible synthesis of crack-free large-area thin films of 3D hexagonal (R-3m) mesostructured nanocrystalline titania (meso-nc-TiO{sub 2}) using a Pluronic triblock copolymer (P123)/1-butanol templating system is described. The characterization of the films is achieved using a combination of electron microscopy (high-resolution scanning electron microscopy and scanning transmission electron microscopy), grazing-incidence small-angle X-ray scattering, in situ high-temperature X-ray diffraction, and variable-angle spectroscopic ellipsometry. The mesostructure of the obtained films is found to be based upon a 3D periodic array of large elliptically shaped cages with diameters around 20 nm interconnected by windows of about 5 nm in size. The mesopores of the film calcined at 300 C are very highly ordered, and the titania framework of the film has a crystallinity of 40 % being composed of 5.8 nm sized anatase crystallites. The film displays high thermal stability in that the collapse of the pore architecture is incomplete even at 600 C. The accessible surface area of 3D hexagonal meso-nc-TiO{sub 2} estimated by the absorption of methylene blue is nearly twice as large as that of 2D hexagonal meso-nc-TiO{sub 2} at the same annealing temperature.

  15. 3D HEXAGONAL (R-3M) MESOSTRUCTURED NANOCRYSTALLINE TITANIA THIN FILMS: SYNTHESIS AND CHARACTERIZATION

    SciTech Connect

    Choi, S Y; Lee, B; Carew, D B; Peiris, F C; Mamak, M; Speakman, Scott A; Chopra, N; Ozin, G A

    2006-01-01

    A straightforward and reproducible synthesis of crack-free large-area thin films of 3D hexagonal (R-3m) mesostructured nanocrystalline titania (meso-nc-TiO{sub 2}) using a Pluronic triblock copolymer (P123)/1-butanol templating system is described. The characterization of the films is achieved using a combination of electron microscopy (high-resolution scanning electron microscopy and scanning transmission electron microscopy), grazing-incidence small-angle X-ray scattering, in situ high-temperature X-ray diffraction, and variable-angle spectroscopic ellipsometry. The mesostructure of the obtained films is found to be based upon a 3D periodic array of large elliptically shaped cages with diameters around 20 nm interconnected by windows of about 5 nm in size. The mesopores of the film calcined at 300 C are very highly ordered, and the titania framework of the film has a crystallinity of 40 % being composed of 5.8 nm sized anatase crystallites. The film displays high thermal stability in that the collapse of the pore architecture is incomplete even at 600 C. The accessible surface area of 3D hexagonal meso-nc-TiO{sub 2} estimated by the absorption of methylene blue is nearly twice as large as that of 2D hexagonal meso-nc-TiO{sub 2} at the same annealing temperature.

  16. Oxidation-Based Continuous Laser Writing in Vertical Nano-Crystalline Graphite Thin Films.

    PubMed

    Loisel, Loïc; Florea, Ileana; Cojocaru, Costel-Sorin; Tay, Beng Kang; Lebental, Bérengère

    2016-01-01

    Nano and femtosecond laser writing are becoming very popular techniques for patterning carbon-based materials, as they are single-step processes enabling the drawing of complex shapes without photoresist. However, pulsed laser writing requires costly laser sources and is known to cause damages to the surrounding material. By comparison, continuous-wave lasers are cheap, stable and provide energy at a more moderate rate. Here, we show that a continuous-wave laser may be used to pattern vertical nano-crystalline graphite thin films with very few macroscale defects. Moreover, a spatially resolved study of the impact of the annealing to the crystalline structure and to the oxygen ingress in the film is provided: amorphization, matter removal and high oxygen content at the center of the beam; sp(2) clustering and low oxygen content at its periphery. These data strongly suggest that amorphization and matter removal are controlled by carbon oxidation. The simultaneous occurrence of oxidation and amorphization results in a unique evolution of the Raman spectra as a function of annealing time, with a decrease of the I(D)/I(G) values but an upshift of the G peak frequency. PMID:27194181

  17. Power-law photoconductivity time decay in nanocrystalline TiO2 thin films

    NASA Astrophysics Data System (ADS)

    Comedi, D.; Heluani, S. P.; Villafuerte, M.; Arce, R. D.; Koropecki, R. R.

    2007-12-01

    The sub-band-gap excited photoconductivity (PC) time decay and the film structure of rf-sputter deposited nanocrystalline TiO2 thin films have been studied. Atomic force microscopy and x-ray diffraction measurements were used to assess roughness, crystalline structure and mean grain size of the films. Samples fabricated under different deposition conditions exhibit different microstructures and absolute PC, but similar persistent PC behaviour after switching off the light source. The very slow PC decay can be well represented by a function that is nearly constant for short times and decreases as a power law for times longer than about 100 s. This function is shown to be consistent with a rate equation characterized by a relaxation time that increases linearly with time. This behaviour, in turn, agrees with predictions of a previously reported model that assumes electron-hole recombination limited by carrier-density-dependent potential barriers associated with inhomogeneities. These results may have important implications on attempts to determine distributions of trap energies from PC decay curves in TiO2.

  18. Oxidation-Based Continuous Laser Writing in Vertical Nano-Crystalline Graphite Thin Films

    PubMed Central

    Loisel, Loïc; Florea, Ileana; Cojocaru, Costel-Sorin; Tay, Beng Kang; Lebental, Bérengère

    2016-01-01

    Nano and femtosecond laser writing are becoming very popular techniques for patterning carbon-based materials, as they are single-step processes enabling the drawing of complex shapes without photoresist. However, pulsed laser writing requires costly laser sources and is known to cause damages to the surrounding material. By comparison, continuous-wave lasers are cheap, stable and provide energy at a more moderate rate. Here, we show that a continuous-wave laser may be used to pattern vertical nano-crystalline graphite thin films with very few macroscale defects. Moreover, a spatially resolved study of the impact of the annealing to the crystalline structure and to the oxygen ingress in the film is provided: amorphization, matter removal and high oxygen content at the center of the beam; sp2 clustering and low oxygen content at its periphery. These data strongly suggest that amorphization and matter removal are controlled by carbon oxidation. The simultaneous occurrence of oxidation and amorphization results in a unique evolution of the Raman spectra as a function of annealing time, with a decrease of the I(D)/I(G) values but an upshift of the G peak frequency. PMID:27194181

  19. Exchange Bias and Unusual Initial Magnetization in Nanocrystalline Spinel Ferrite Thin Films

    NASA Astrophysics Data System (ADS)

    Alaan, Urusa; Gollapudi, Sreenivasulu; Yu, Kin Man; Shafer, Padraic; Arenholz, Elke; Srinivasan, Gopalan; Suzuki, Yuri

    2015-03-01

    We report on unconventional magnetic behavior in nanocrystalline (Mn,Zn,Fe)3O4 (MZFO) thin films grown at room temperature. Structural studies show no secondary phases, yet these films are exchange biased, with magnetic hysteresis loops shifted by as much as ~ 200 Oe at 10 K after field-cooling. The samples can be ``trained'' so that successive magnetization loops exhibit reduced exchange bias. Shifts of the hysteresis loops exist even after cooling in zero field, indicating that the MZFO is not externally biased. We attribute the exchange bias to disordered, grain-boundary-like regions that bias more ordered MZFO. Annealing experiments that improved sample crystallinity decreased the exchange bias. Higher annealing temperatures resulted in reduced coercivities, higher magnetizations, and even the elimination of the exchange bias. Annealing also removed an unusual crossover of the initial magnetization curve outside of the saturated magnetization loop. This behavior has been seen in so-called ``mictomagnetic'' alloys. Using x-ray magnetic circular dichroism measurements, we have shown that cation disorder was reduced with annealing, and correlated the atypical initial magnetization with the degree of disorder. We gratefully acknowledge the National Science Foundation for funding this research.

  20. Dip coated nanocrystalline CdZnS thin films for solar cell application

    SciTech Connect

    Dongre, J. K. Chaturvedi, Mahim; Patil, Yuvraj; Sharma, Sandhya; Jain, U. K.

    2015-07-31

    Nanocrystalline cadmium sulfide (CdS) and zinc cadmium sulfide (ZnCdS) thin films have been grown via simple and low cost dip coating technique. The prepared films are characterized by X-ray diffraction (XRD), atomic force microscopic (AFM) and UV-VIS spectrophotometer techniques to reveal their structural, morphological and optical properties. XRD shows that both samples grown have zinc blende structure. The grain size is calculated as 6.2 and 8 nm using Scherrer’s formula. The band gap value of CdS and CdZnS film is estimated to be 2.58 and 2.69 eV respectively by UV-vis spectroscopy. Photoelectrochemical (PEC) investigations are carried out using cell configuration as n-CdZnS/(1M NaOH + 1M Na2S + 1M S)/C. The photovoltaic output characteristic is used to calculate fill-factor (FF) and solar conversion efficiency (η)

  1. Electrochemical Evaluation of Nanocrystalline Diamond Thin Films on Ti-6Al-4V Implant Alloy

    NASA Astrophysics Data System (ADS)

    Fries, Marc; Venugopalan, Ramakrishna; Vohra, Yogesh

    2002-03-01

    Some 186,000 hip replacement surgeries are peformed every year in the United States alone. About 10surgeries are revision operations to replace an implant that has most likely failed through mechanical-electrochemical interactions resulting in implant wear. The ability to enhance the resistance to such mechanical-electrochemical interaction and thereby reduce wear could result in significantly increased device lifespan. Nanocrystalline diamond (NCD) thin films were deposited on Ti-6Al-4V disk samples (processed per ASTM F86 standard for medical implant surface conditions) using microwave plasma chemical vapor deposition (MPCVD). As a first step, these samples (n=3/test per group) were subjected to electrochemical evaluation in inorganic neutral salt solution at 37 C. The electrochemical evaluation involved both impedence spectroscopy (per ASTM G106) and polarization testing (per ASTM G5). The impedence spectroscopy data indicated a significantly higher charge transfer resistance at the interface due to the protective NCD as compared to the bare or uncoated substrate. The polarization test data confirmed that this increased charge transfer resistance resulted in a decreased current density measurement. This decreased current density measurement resulted in an order of magnitude lower calculated static corrosion rate from the NCD coated samples as opposed to the uncoated controls. Future studies will focus on investigations that will facilitate transfer of these static electrochemical resistance results to a more relevant mechanical-electrochemical interaction milieu.

  2. Transient 2D IR spectroscopy of charge injection in dye-sensitized nanocrystalline thin films.

    PubMed

    Xiong, Wei; Laaser, Jennifer E; Paoprasert, Peerasak; Franking, Ryan A; Hamers, Robert J; Gopalan, Padma; Zanni, Martin T

    2009-12-23

    We use nonlinear 2D IR spectroscopy to study TiO(2) nanocrystalline thin films sensitized with a Re dye. We find that the free electron signal, which often obscures the vibrational features in the transient absorption spectrum, is not observed in the 2D IR spectra. Its absence allows the vibrational features of the dye to be much better resolved than with the typical IR absorption probe. We observe multiple absorption bands but no cross peaks in the 2D IR spectra, which indicates that the dyes have at least three conformations. Furthermore, by using a pulse sequence in which we initiate electron transfer in the middle of the infrared pulse train, we are able to assign the excited state features by correlating them to the ground state vibrational modes and determine that the three conformations have different time scales and cross sections for electron injection. 2D IR spectroscopy is proving to be very useful in disentangling overlapping structural distributions in biological and chemical physics processes. These experiments demonstrate that nonlinear infrared probes are also a powerful new tool for studying charge transfer at interfaces. PMID:19947603

  3. Investigation on structural, optical, morphological and electrical properties of thermally deposited lead selenide (PbSe) nanocrystalline thin films

    NASA Astrophysics Data System (ADS)

    Shyju, T. S.; Anandhi, S.; Sivakumar, R.; Garg, S. K.; Gopalakrishnan, R.

    2012-08-01

    In this paper, we report the substrate temperature induced changes in physical properties of thermal evaporated lead selenide (PbSe) thin films from the chemically synthesized nanocrystalline PbSe powders. As the first step, nanocrystalline lead selenide was synthesized by simple chemical method at 80 °C using lead nitrate [Pb(NO3)2] and sodium selenosulphate [Na2SeSO3] in the aqueous alkaline media. Ethylene Diamine Tetra acetic acid (0.1 M) was used as a complexing agent to form stable complexes with metal ions. Later on, the lead selenide thin films were deposited on the degreased glass substrates under a vacuum of 10-5 Torr at various substrate temperatures by thermal evaporation technique using the pre-synthesized nanocrystalline PbSe powders. X-ray diffraction results show the synthesized powders and the deposited PbSe films belong to cubic structure. A gradual reduction in optical bandgap of films was observed with increasing substrate temperatures, which revealed the crystallization of the films. These observations are corroborated by photoluminescence spectroscopy study. Changes in surface morphology of the films with respect to substrate temperature were studied by high resolution scanning electron microscopy and atomic force microscopy. Electrical study infers the deposited films are of p-type semiconducting nature.

  4. XPS and electroluminescence studies on SrS 1- xSe x and ZnS 1- xSe x thin films deposited by atomic layer deposition technique

    NASA Astrophysics Data System (ADS)

    Ihanus, Jarkko; Lambers, Eric; Holloway, Paul H.; Ritala, Mikko; Leskelä, Markku

    2004-01-01

    SrS 1- xSe x and ZnS 1- xSe x thin films were deposited by the atomic layer deposition (ALD) technique using elemental selenium as the Se source, thus avoiding use of H 2Se or organometallic selenium compounds. X-ray diffraction (XRD) analysis showed that the films were solid solutions and X-ray photoelectron spectroscopy (XPS) data showed that the surface of both ZnS 1- xSe x and SrS 1- xSe x were covered with an oxide and carbon-containing contaminants from exposure to air. The oxidation of SrS 1- xSe x extended into the film and peak shifts from sulfate were found on the surface. Luminance measurements showed that emission intensity of the ZnS 1- xSe x:Mn alternating current thin film electroluminescent (ACTFEL) devices at fixed voltage was almost the same as that of the ZnS:Mn device, while emission intensity of the SrS 1- xSe x:Ce devices decreased markedly as compared to the SrS:Ce device. Emission colors of the devices were altered only slightly due to selenium addition.

  5. Microstructure factor and mechanical and electronic properties of hydrogenated amorphous and nanocrystalline silicon thin-films for microelectromechanical systems applications

    SciTech Connect

    Mouro, J.; Gualdino, A.; Chu, V.; Conde, J. P.

    2013-11-14

    Thin-film silicon allows the fabrication of MEMS devices at low processing temperatures, compatible with monolithic integration in advanced electronic circuits, on large-area, low-cost, and flexible substrates. The most relevant thin-film properties for applications as MEMS structural layers are the deposition rate, electrical conductivity, and mechanical stress. In this work, n{sup +}-type doped hydrogenated amorphous and nanocrystalline silicon thin-films were deposited by RF-PECVD, and the influence of the hydrogen dilution in the reactive mixture, the RF-power coupled to the plasma, the substrate temperature, and the deposition pressure on the structural, electrical, and mechanical properties of the films was studied. Three different types of silicon films were identified, corresponding to three internal structures: (i) porous amorphous silicon, deposited at high rates and presenting tensile mechanical stress and low electrical conductivity, (ii) dense amorphous silicon, deposited at intermediate rates and presenting compressive mechanical stress and higher values of electrical conductivity, and (iii) nanocrystalline silicon, deposited at very low rates and presenting the highest compressive mechanical stress and electrical conductivity. These results show the combinations of electromechanical material properties available in silicon thin-films and thus allow the optimized selection of a thin silicon film for a given MEMS application. Four representative silicon thin-films were chosen to be used as structural material of electrostatically actuated MEMS microresonators fabricated by surface micromachining. The effect of the mechanical stress of the structural layer was observed to have a great impact on the device resonance frequency, quality factor, and actuation force.

  6. Enhancement of photo sensor properties of nanocrystalline ZnO thin film by swift heavy ion irradiation

    SciTech Connect

    Mahajan, S. V.; Upadhye, D. S.; Bagul, S. B.; Shaikh, S. U.; Birajadar, R. B.; Siddiqui, F. Y.; Huse, N. P.; Sharma, R. B. E-mail: rps.phy@gmail.com

    2015-06-24

    Nanocrystalline Zinc Oxide (ZnO) thin film prepared by Low cost Successive Ionic Layer Adsorption and Reaction (SILAR) method. This film was irradiated by 120 MeV Ni{sup 7+} ions with the fluence of 5x10{sup 12}ions/cm{sup 2}. The X-ray diffraction study was shows polycrystalline nature with wurtzite structure. The optical properties as absorbance were determined using UV-Spectrophotometer and band gap was also calculated. The Photo Sensor nature was calculated by I-V characteristics with different sources of light 40W, 60W and 100W.

  7. Disorder induced semiconductor to metal transition and modifications of grain boundaries in nanocrystalline zinc oxide thin film

    SciTech Connect

    Singh, Fouran; Kumar, Vinod; Chaudhary, Babloo; Singh, R. G.; Kumar, Sanjeev; Kapoor, A.

    2012-10-01

    This paper report on the disorder induced semiconductor to metal transition (SMT) and modifications of grain boundaries in nanocrystalline zinc oxide thin film. Disorder is induced using energetic ion irradiation. It eliminates the possibility of impurities induced transition. However, it is revealed that some critical concentration of defects is needed for inducing such kind of SMT at certain critical temperature. Above room temperature, the current-voltage characteristics in reverse bias attributes some interesting phenomenon, such as electric field induced charge transfer, charge trapping, and diffusion of defects. The transition is explained by the defects induced disorder and strain in ZnO crystallites created by high density of electronic excitations.

  8. Magnetic domain structure in nanocrystalline Ni-Zn-Co spinel ferrite thin films using off-axis electron holography

    SciTech Connect

    Zhang, D.; Ray, N. M.; Petuskey, W. T.; Smith, D. J.; McCartney, M. R.

    2014-08-28

    We report a study of the magnetic domain structure of nanocrystalline thin films of nickel-zinc ferrite. The ferrite films were synthesized using aqueous spin-spray coating at low temperature (∼90 °C) and showed high complex permeability in the GHz range. Electron microscopy and microanalysis revealed that the films consisted of columnar grains with uniform chemical composition. Off-axis electron holography combined with magnetic force microscopy indicated a multi-grain domain structure with in-plane magnetization. The correlation between the magnetic domain morphology and crystal structure is briefly discussed.

  9. Direct synthesis and characterization of optically transparent conformal zinc oxide nanocrystalline thin films by rapid thermal plasma CVD

    PubMed Central

    2011-01-01

    We report a rapid, self-catalyzed, solid precursor-based thermal plasma chemical vapor deposition process for depositing a conformal, nonporous, and optically transparent nanocrystalline ZnO thin film at 130 Torr (0.17 atm). Pure solid zinc is inductively heated and melted, followed by ionization by thermal induction argon/oxygen plasma to produce conformal, nonporous nanocrystalline ZnO films at a growth rate of up to 50 nm/min on amorphous and crystalline substrates including Si (100), fused quartz, glass, muscovite, c- and a-plane sapphire (Al2O3), gold, titanium, and polyimide. X-ray diffraction indicates the grains of as-deposited ZnO to be highly textured, with the fastest growth occurring along the c-axis. The individual grains are observed to be faceted by (103) planes which are the slowest growth planes. ZnO nanocrystalline films of nominal thicknesses of 200 nm are deposited at substrate temperatures of 330°C and 160°C on metal/ceramic substrates and polymer substrates, respectively. In addition, 20-nm- and 200-nm-thick films are also deposited on quartz substrates for optical characterization. At optical spectra above 375 nm, the measured optical transmittance of a 200-nm-thick ZnO film is greater than 80%, while that of a 20-nm-thick film is close to 100%. For a 200-nm-thick ZnO film with an average grain size of 100 nm, a four-point probe measurement shows electrical conductivity of up to 910 S/m. Annealing of 200-nm-thick ZnO films in 300 sccm pure argon at temperatures ranging from 750°C to 950°C (at homologous temperatures between 0.46 and 0.54) alters the textures and morphologies of the thin film. Based on scanning electron microscope images, higher annealing temperatures appear to restructure the ZnO nanocrystalline films to form nanorods of ZnO due to a combination of grain boundary diffusion and bulk diffusion. PACS: films and coatings, 81.15.-z; nanocrystalline materials, 81.07.Bc; II-VI semiconductors, 81.05.Dz. PMID:22040295

  10. Photoluminescence of dense nanocrystalline titanium dioxide thin films: effect of doping and thickness and relation to gas sensing.

    PubMed

    Mercado, Candy; Seeley, Zachary; Bandyopadhyay, Amit; Bose, Susmita; McHale, Jeanne L

    2011-07-01

    The photoluminescence (PL) of dense nanocrystalline (anatase) TiO(2) thin films is reported as a function of calcination temperature, thickness, and tungsten and nickel doping. The dependence of the optical absorption, Raman spectra, and PL spectra on heat treatment and dopants reveals the role of oxygen vacancies, crystallinity, and phase transformation in the performance of TiO(2) films used as gas sensors. The broad visible PL from defect states of compact and undoped TiO(2) films is found to be much brighter and less sensitive to the presence of oxygen than that of mesoporous films. The dense nanocrystalline grains and the nanoparticles comprising the mesoporous film are comparable in size, demonstrating the importance of film morphology and carrier transport in determining the intensity of defect photoluminescence. At higher calcination temperatures, the transformation to rutile results in the appearance of a dominant near-infrared peak. This characteristic change in the shape of the PL spectra demonstrates efficient capture of conduction band electrons by the emerging rutile phase. The W-doped samples show diminished PL with quenching on the red side of the emission spectrum occurring at lower concentration and eventual disappearance of the PL at higher W concentration. The results are discussed within the context of the performance of the TiO(2) thin films as CO gas sensors and the chemical nature of luminescent defects. PMID:21702459

  11. Modeling and simulation of boron-doped nanocrystalline silicon carbide thin film by a field theory.

    PubMed

    Xiong, Liming; Chen, Youping; Lee, James D

    2009-02-01

    This paper presents the application of a multiscale field theory in modeling and simulation of boron-doped nanocrystalline silicon carbide (B-SiC). The multiscale field theory was briefly introduced. Based on the field theory, numerical simulations show that intergranular glassy amorphous films (IGFs) and nano-sized pores exist in triple junctions of the grains for nanocrystalline B-SiC. Residual tensile stress in the SiC grains and compressive stress on the grain boundaries (GBs) were observed. Under tensile loading, it has been found that mechanical response of 5 wt% boron-SiC exhibits five characteristic regimes. Deformation mechanism at atomic scale has been revealed. Tensile strength and Young's modulus of nanocrystalline SiC were accurately reproduced. PMID:19441448

  12. A study of structural transition in nanocrystalline titania thin films by X-ray diffraction Rietveld method

    SciTech Connect

    Murugesan, S.; Padhy, N.; Kuppusami, P.; Mudali, U. Kamachi; Mohandas, E.

    2010-12-15

    Structural and microstructural analyses of nanocrystalline titania thin films prepared by pulsed laser deposition have been carried out. At lower oxygen partial pressures ({<=}10{sup -4} mbar), rutile films were formed, whereas at 1.2 x 10{sup -3} mbar of oxygen partial pressure, the thin films contained both rutile and anatase phases. At 0.04 and 0.05 mbar of oxygen partial pressure, the film was purely anatase. Addition of oxygen has also shown a profound influence on the surface morphology of the as deposited titania films. Modified Rietveld method has been used to determine crystallite size, root mean square strain and fractional coordinates of oxygen of the anatase films. The influence of crystallite size and strain on the rutile to anatase phase transition is investigated.

  13. X-ray microstructural analysis of nanocrystalline TiZrN thin films by diffraction pattern modeling

    SciTech Connect

    Escobar, D.; Ospina, R.; Gómez, A.G.; Restrepo-Parra, E.; Arango, P.J.

    2014-02-15

    A detailed microstructural characterization of nanocrystalline TiZrN thin films grown at different substrate temperatures (T{sub S}) was carried out by X-ray diffraction (XRD). Total diffraction pattern modeling based on more meaningful microstructural parameters, such as crystallite size distribution and dislocation density, was performed to describe the microstructure of the thin films more precisely. This diffraction modeling has been implemented and used mostly to characterize powders, but the technique can be very useful to study hard thin films by taking certain considerations into account. Nanocrystalline films were grown by using the cathodic pulsed vacuum arc technique on stainless steel 316L substrates, varying the temperature from room temperature to 200 °C. Further surface morphology analysis was performed to study the dependence of grain size on substrate temperature using atomic force microscopy (AFM). The crystallite and surface grain sizes obtained and the high density of dislocations observed indicate that the films underwent nanostructured growth. Variations in these microstructural parameters as a function of T{sub S} during deposition revealed a competition between adatom mobility and desorption processes, resulting in a specific microstructure. These films also showed slight anisotropy in their microstructure, and this was incorporated into the diffraction pattern modeling. The resulting model allowed for the films' microstructure during synthesis to be better understood according to the experimental results obtained. - Highlights: • Mobility and desorption competition generates a critical temperature. • A microstructure anisotropy related to the local strain was observed in thin films. • Adatom mobility and desorption influence grain size and microstrain.

  14. Novel p-Type Conductive Semiconductor Nanocrystalline Film as the Back Electrode for High-Performance Thin Film Solar Cells.

    PubMed

    Zhang, Ming-Jian; Lin, Qinxian; Yang, Xiaoyang; Mei, Zongwei; Liang, Jun; Lin, Yuan; Pan, Feng

    2016-02-10

    Thin film solar cells, due to the low cost, high efficiency, long-term stability, and consumer applications, have been widely applied for harvesting green energy. All of these thin film solar cells generally adopt various metal thin films as the back electrode, like Mo, Au, Ni, Ag, Al, graphite, and so forth. When they contact with p-type layer, it always produces a Schottky contact with a high contact potential barrier, which greatly affects the cell performance. In this work, we report for the first time to find an appropriate p-type conductive semiconductor film, digenite Cu9S5 nanocrystalline film, as the back electrode for CdTe solar cells as the model device. Its low sheet resistance (16.6 Ω/sq) could compare to that of the commercial TCO films (6-30 Ω/sq), like FTO, ITO, and AZO. Different from the traditonal metal back electrode, it produces a successive gradient-doping region by the controllable Cu diffusion, which greatly reduces the contact potential barrier. Remarkably, it achieved a comparable power conversion efficiency (PCE, 11.3%) with the traditional metal back electrode (Cu/Au thin films, 11.4%) in CdTe cells and a higher PCE (13.8%) with the help of the Au assistant film. We believe it could also act as the back electrode for other thin film solar cells (α-Si, CuInS2, CIGSe, CZTS, etc.), for their performance improvement. PMID:26736028

  15. Development of Mathematical Model for Prediction and Optimization of Particle Size in Nanocrystalline CdS Thin Films Prepared by Sol-Gel Spin-Coating Method

    NASA Astrophysics Data System (ADS)

    Thambidurai, M.; Muthukumarasamy, N.; Murugan, N.; Agilan, S.; Vasantha, S.; Balasundaraprabhu, R.

    2010-12-01

    Nanocrystalline CdS thin films have been prepared by the sol-gel spin-coating method. The influence of spin-coating process parameters such as, thiourea concentration (U), annealing temperature (A), rotational speed (S), and annealing time (T), and so on, on the properties of the prepared films have been studied. The experiments have been carried out based on four factor-five-level central composite designs with the full replication technique, and mathematical models have been developed using regression technique. The central composite rotatable design has been used to minimize the number of experimental parameters. The analysis of variance technique is applied to check the validity of the developed models. The developed mathematical model can be used effectively to predict the particle size in CdS nanocrystalline thin films at 95 pct confidence level. The results have been verified by depositing the films using the same condition. An ultraviolet-visible optical spectroscopy study was carried out to determine the band gap of the CdS nanocrystalline thin films. The band gap has been observed to depend strongly on particle size, and it indicated a blue shift caused by quantum confinement effects. The high-resolution transmission electron microscopy analysis showed the grain size of the prepared CdS film to be 6 nm. The main and interaction effects of deposition parameters on the properties of CdS nanocrystalline thin films also have been studied.

  16. Correlation between surface phonon mode and luminescence in nanocrystalline CdS thin films: An effect of ion beam irradiation

    SciTech Connect

    Kumar, Pragati Agarwal, Avinash; Saxena, Nupur; Singh, Fouran; Gupta, Vinay

    2014-07-28

    The influence of swift heavy ion irradiation (SHII) on surface phonon mode (SPM) and green emission in nanocrystalline CdS thin films grown by chemical bath deposition is studied. The SHII of nanocrystalline CdS thin films is carried out using 70 MeV Ni ions. The micro Raman analysis shows that asymmetry and broadening in fundamental longitudinal optical (LO) phonon mode increases systematically with increasing ion fluence. To analyze the role of phonon confinement, spatial correlation model (SCM) is fitted to the experimental data. The observed deviation of SCM to the experimental data is further investigated by fitting the micro Raman spectra using two Lorentzian line shapes. It is found that two Lorentzian functions (LFs) provide better fitting than SCM fitting and facilitate to identify the contribution of SPM in the observed distortion of LO mode. The behavior of SPM as a function of ion fluence is studied to correlate the observed asymmetry (Γ{sub a}/Γ{sub b}) and full width at half maximum of LO phonon mode and to understand the SHII induced enhancement of SPM. The ion beam induced interstitial and surface state defects in thin films, as observed by photoluminescence (PL) spectroscopy studies, may be the underlying reason for enhancement in SPM. PL studies also show enhancement in green luminescence with increase in ion fluence. PL analysis reveals that the variation in population density of surface state defects after SHII is similar to that of SPM. The correlation between SPM and luminescence and their dependence on ion irradiation fluence is explained with the help of thermal spike model.

  17. Grain boundary character distribution and texture evolution during surface energy-driven grain growth in nanocrystalline gold thin films

    NASA Astrophysics Data System (ADS)

    Kobayashi, Shigeaki; Takagi, Hiroki; Watanabe, Tadao

    2013-04-01

    The evolution of grain boundary microstructure during annealing in sputtered gold thin films was investigated on the basis of FEG-SEM/EBSD/OIM analyses of nanocrystalline microstructure, in order to find a clue to the precise control of grain boundary microstructure for development of high performance polycrystalline thin films. Remarkably high fractions of coincidence site lattice (CSL) boundaries with specific Σ values such as Σ1, Σ3, Σ7, Σ13, Σ19 and Σ21 occurred in the gold thin film specimens on Pyrex glass substrate by annealing in air. The occurrence of higher fraction of these specific low-Σ boundaries is probably attributed to the evolution of a very sharp {111}-textures of different degrees which results from the preferential growth of {111}-oriented grains due to surface energy-driven grain growth. The fraction of low-Σ CSL boundaries increased with increasing area fraction of {111}-texture. The grain boundary character distribution in the gold thin film specimens was strongly affected by the annealing atmosphere and substrate materials. The sharpness of {111}-texture in the specimen annealed in low-vacuum was weaker than that in the specimen annealed in air, and an extraordinarily high fraction of Σ3 CSL boundaries occurred. The grain growth of gold thin film specimens on SiO2 glass substrate was much slower than that of specimens on Pyrex glass substrate. The fraction of low-Σ CSL boundaries observed for the gold thin film specimens on SiO2 glass substrate was lower than that in the specimens on Pyrex glass substrate. The inverse cubic root Σ dependence of low-Σ CSL boundaries in the gold thin film specimens was discussed in connection with the process of the evolution of grain boundary microstructure.

  18. Thickness-dependent photocatalytic performance of nanocrystalline TiO2 thin films prepared by sol-gel spin coating

    NASA Astrophysics Data System (ADS)

    Wu, Chung-Yi; Lee, Yuan-Ling; Lo, Yu-Shiu; Lin, Chen-Jui; Wu, Chien-Hou

    2013-09-01

    TiO2 nanocrystalline thin films on soda lime glass have been prepared by sol-gel spin coating. The thin films were characterized for surface morphology, crystal structure, chemical composition, thickness, and transparency by atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ellipsometry, and UV-vis spectrophotometry. The films prepared by titanium tetraisopropoxide (TTIP) as the precursor under pH of 3.5 ± 0.5 and with calcination temperature of 450 ̊C for 3 h exhibited superior homogeneous aggregation, good optical transparency, superhydrophilicity, and reliable thickness. The effect of film thickness on the photocatalytic degradation of acid yellow 17 was investigated under UV irradiation. The photocatalytic activity was strongly correlated with the number of coatings and followed Langmuir-type kinetics. Under the same film thickness, TiO2 thin films prepared by 0.1 M TTIP exhibited more efficient photocatalytic activity than those prepared by 0.3 M TTIP. For thin films prepared by 0.1 M TTIP, the maximum specific photocatalytic activity occurred at 5 coatings with thickness of 93 ± 1 nm. A model was proposed to rationalize the dependence of the film thickness on the photocatalytic activity, which predicts the existence of an optimum film thickness.

  19. Ellipsometric and Raman spectroscopic study of nanocrystalline silicon thin films prepared by a rf magnetron sputtering technique

    NASA Astrophysics Data System (ADS)

    Bouizem, Y.; Abbes, C.; Sib, J. D.; Benlakehal, D.; Baghdad, R.; Chahed, L.; Zellama, K.; Charvet, S.

    2008-11-01

    The structure of nanocrystalline silicon thin films (nc-Si:H) deposited by rf magnetron sputtering of a high-purity crystalline silicon target using argon (30%) and hydrogen (70%) gas mixture, under different pressures (P = 2, 3 and 4 Pa) and different substrate temperature (Ts = 100, 150 and 200 °C), has been studied with spectroscopic ellipsometry (SE; 1.5-5 eV) complemented with Raman spectroscopy measurements. The ellipsometry data were carefully analyzed using the Brüggeman effective medium approximation and the Tauc-Lorentz model. The results of this investigation clearly show that the samples deposited at 2 Pa present a completely amorphous structure whatever the substrate temperature, while those deposited at 3 and 4 Pa exhibit a nanocrystalline structure. These results suggest the existence of a threshold pressure around 3 Pa for which crystallization occurs. The samples are well crystallized with a crystalline volume fraction ranging from about 60 to 90%, and exhibit a mixture of small and large crystallite sizes. The deposition temperature has practically no effect on the size of the crystallites and on the average crystalline volume fractions. These results are in good agreement with the Raman spectroscopy data, and suggest the formation of Si crystallites in the gas phase. The analysis of the ellipsometric spectra also shows that the bulk layer is initiated from an amorphous interface (a-Si:H) present in the first steps of the growth, and is followed by a less crystallized subsurface layer.

  20. Enhanced performance of flexible nanocrystalline silicon thin-film solar cells using seed layers with high hydrogen dilution.

    PubMed

    Lee, Ji-Eun; Kim, Donghwan; Yoon, Kyung Hoon; Cho, Jun-Sik

    2013-12-01

    Flexible hydrogenated nanocrystalline (nc-Si:H) thin-film solar cells were prepared by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD), and the effect of highly crystalline intrinsic Si seed layers at the initial growth stage of i nc-Si:H absorbers on their structural and electrical properties and on the performance of solar cells was investigated. The crystallization of i nc-Si:H absorbers was significantly enforced by the introduction of highly crystalline seed layers, resulting in the reduction of defect-dense a-Si:H grain boundary and incubation layer thickness. The open circuit voltage of the nc-Si:H solar cells with the seed layers was improved by the decrease of charged defect density in the defect-rich amorphous region. PMID:24266159

  1. Synthesis of nanocrystalline Cu2ZnSnS4 thin films grown by the spray-pyrolysis technique

    NASA Astrophysics Data System (ADS)

    Chandel, Tarun; Singh, Joginder; Rajaram, P.

    2015-08-01

    Spray pyrolysis was used to deposit Cu2ZnSnS4 (CZTS) thin films on soda lime glass substrates at 300 °C. Aqueous solutions of copper chloride, zinc chloride, stannous chloride and thiourea were mixed together to form the spray liquid. The sprayed films were annealed under vacuum at 350 °C, 400 °C and 450 °C. Structural and optical characterization was performed on the CZTS films using X-ray diffraction (XRD) and UV-VIS spectrophotometry. XRD results indicate that the films are single phase nanocrystalline CZTS. Optical studies show that the optical gap values are 1.44 eV for the as-grown film and 1.46 eV, 1.48 eV and 1.49 eV for the films annealed at 350 °C, 400 °C and 450 °C, respectively.

  2. Nano-crystalline Ag-PbTe thermoelectric thin films by a multi-target PLD system

    NASA Astrophysics Data System (ADS)

    Cappelli, E.; Bellucci, A.; Medici, L.; Mezzi, A.; Kaciulis, S.; Fumagalli, F.; Di Fonzo, F.; Trucchi, D. M.

    2015-05-01

    It has been evaluated the ability of ArF pulsed laser ablation to grow nano-crystalline thin films of high temperature PbTe thermoelectric material, and to obtain a uniform and controlled Ag blending, through the entire thickness of the film, using a multi-target system in vacuum. The substrate used was a mirror polished technical alumina slab. The increasing atomic percentage of Ag effect on physical-chemical and electronic properties was evaluated in the range 300-575 K. The stoichiometry and the distribution of the Ag component, over the whole thickness of the samples deposited, have been studied by XPS (X-ray photoelectron spectroscopy) and corresponding depth profiles. The crystallographic structure of the film was analyzed by grazing incidence X-ray diffraction (GI-XRD) system. Scherrer analysis for crystallite size shows the presence of nano-structures, of the order of 30-35 nm. Electrical resistivity of the samples, studied by the four point probe method, as a function of increasing Ag content, shows a typical semi-conductor behavior. From conductivity values, carrier concentration and Seebeck parameter determination, the power factor of deposited films was calculated. Both XPS, Hall mobility and Seebeck analysis seem to indicate a limit value to the Ag solubility of the order of 5%, for thin films of ∼200 nm thickness, deposited at 350 °C. These data resulted to be comparable to theoretical evaluation for thin films but order of magnitude lower than the corresponding bulk materials.

  3. Boosting the mobility and bias stability of oxide-based thin-film transistors with ultra-thin nanocrystalline InSnO:Zr layer

    NASA Astrophysics Data System (ADS)

    Raja, Jayapal; Jang, Kyungsoo; Hussain, Shahzada Qamar; Balaji, Nagarajan; Chatterjee, Somenath; Velumani, S.; Yi, Junsin

    2015-01-01

    Extensive attention on high-definition flat panel displays is the driving force to fabricate high-performance thin-film transistors (TFTs). A hybrid oxide TFTs fabricated using an interfacial layer of nanocrystalline Zr-doped InSnO (nc-ITO:Zr) and an amorphous InSnZnO films as an active channel is reported here. Due to the presence of nc-ITO:Zr layer, an improvement of the field-effect mobility (86.4 cm2/V.s) and threshold voltage (0.43 V) values for TFTs are observed. Positive gate bias stress study indicates the role of nc-ITO:Zr layer in fabricated TFTs through the suppression of charge trapping capability between the channel and insulating layer.

  4. Intensity-dependent relaxation of photoconductivity in nanocrystalline titania thin films

    NASA Astrophysics Data System (ADS)

    Xie, Z.; Burlakov, V. M.; Henry, B. M.; Kirov, K. R.; Smith, H. E.; Grovenor, C. R. M.; Assender, H. E.; Briggs, G. A. D.; Kano, Mitsuru; Tsukahara, Yusuke

    2006-03-01

    We have discovered that the initial rate of the post-illumination decay of photoconductivity in nanocrystalline TiO2 depends on the intensity of the illumination. The phenomenon is described by hole detrapping processes affected by electrostatic interactions between the trapped holes, and screening of these interactions by free electrons. The analysis allows determination of both the electron concentration and the electron mobility. In our materials, the value of electron mobility μ≈10-6cm2V-1s-1 , in good agreement with results obtained by other methods.

  5. Microstructure and strain relaxation in thin nanocrystalline platinum films produced via different sputtering techniques

    NASA Astrophysics Data System (ADS)

    Gruber, Wolfgang; Baehtz, Carsten; Horisberger, Michael; Ratschinski, Ingmar; Schmidt, Harald

    2016-04-01

    In this study we investigated the correlation between microstructure and residual strain relaxation in nanocrystalline Pt films with a thickness of about 20 nm produced by different deposition techniques: magnetron sputtering and ion beam sputtering. X-ray diffractometry was carried out using synchrotron radiation. The out-of-plane interplanar distance was measured during isothermal in situ annealing at temperatures between 130 °C und 210 °C. The thermoelastic expansion coefficient is equal for both types of nanocrystalline Pt films and slightly lower than for coarse grained Pt. The relaxation of residual out-of-plain strain depends on temperature and is significantly stronger in the case of the magnetron sputtered films than for the ion beam sputtered films. Different relaxation of compressive stress is ascribed to the different microstructures which evolve during deposition via the corresponding deposition technique. Thickness fringes around the (1 1 1) Bragg peak deposited via magnetron sputtering reveal that these films are essentially composed of columnar (1 1 1) oriented grains which cover the whole film thickness. In contrast, no thickness fringes are observed around the (1 1 1) Bragg peak of films prepared by ion beam sputtering indicating a significantly different microstructure. This is confirmed by Electron Backscatter Diffraction which reveals a (1 1 1) texture for both types of films. The (1 1 1) texture, however, is significantly stronger in the case of the magnetron sputtered films. Grain growth at low homologous temperatures is considered to be an important contribution to relaxation of residual stress.

  6. Deformation-induced grain growth and twinning in nanocrystalline palladium thin films

    PubMed Central

    Lohmiller, Jochen; Schäfer, Jonathan; Kerber, Michael; Castrup, Anna; Kashiwar, Ankush; Gruber, Patric A; Albe, Karsten; Hahn, Horst

    2013-01-01

    Summary The microstructure and mechanical properties of nanocrystalline Pd films prepared by magnetron sputtering have been investigated as a function of strain. The films were deposited onto polyimide substrates and tested in tensile mode. In order to follow the deformation processes in the material, several samples were strained to defined straining states, up to a maximum engineering strain of 10%, and prepared for post-mortem analysis. The nanocrystalline structure was investigated by quantitative automated crystal orientation mapping (ACOM) in a transmission electron microscope (TEM), identifying grain growth and twinning/detwinning resulting from dislocation activity as two of the mechanisms contributing to the macroscopic deformation. Depending on the initial twin density, the samples behaved differently. For low initial twin densities, an increasing twin density was found during straining. On the other hand, starting from a higher twin density, the twins were depleted with increasing strain. The findings from ACOM-TEM were confirmed by results from molecular dynamics (MD) simulations and from conventional and in-situ synchrotron X-ray diffraction (CXRD, SXRD) experiments. PMID:24205451

  7. Increased upper critical field for nanocrystalline MoN thin films deposited on AlN buffered substrates at ambient temperature

    NASA Astrophysics Data System (ADS)

    Baskaran, R.; Thanikai Arasu, A. V.; Amaladass, E. P.; Vaidhyanathan, L. S.; Baisnab, D. K.

    2016-05-01

    Molybdenum nitride (MoN) thin films have been deposited using reactive DC magnetron sputtering on aluminum nitride buffered oxidized silicon substrates at ambient temperature. GIXRD of aluminum nitride (AlN) deposited under similar conditions has revealed the formation of wurtzite phase AlN. GIXRD characterization of molybdenum thin films deposited on AlN buffered oxidized silicon substrates has indicated the formation of nanocrystalline MoN thin films. The electrical resistivity measurements indicate MoN thin films have a superconducting transition temperature of ~8 K. The minimum transition width of the MoN thin film is 0.05 K at 0 T. The inferred upper critical field B c2(0) for these nanocrystalline MoN thin films obtained by fitting the temperature dependence of critical field with Werthamer, Helfand and Hohenberg theory lies in the range of 17–18 T which is the highest reported in literature for MoN thin films.

  8. A light-trapping strategy for nanocrystalline silicon thin-film solar cells using three-dimensionally assembled nanoparticle structures.

    PubMed

    Ha, Kyungyeon; Jang, Eunseok; Jang, Segeun; Lee, Jong-Kwon; Jang, Min Seok; Choi, Hoseop; Cho, Jun-Sik; Choi, Mansoo

    2016-02-01

    We report three-dimensionally assembled nanoparticle structures inducing multiple plasmon resonances for broadband light harvesting in nanocrystalline silicon (nc-Si:H) thin-film solar cells. A three-dimensional multiscale (3DM) assembly of nanoparticles generated using a multi-pin spark discharge method has been accomplished over a large area under atmospheric conditions via ion-assisted aerosol lithography. The multiscale features of the sophisticated 3DM structures exhibit surface plasmon resonances at multiple frequencies, which increase light scattering and absorption efficiency over a wide spectral range from 350-1100 nm. The multiple plasmon resonances, together with the antireflection functionality arising from the conformally deposited top surface of the 3D solar cell, lead to a 22% and an 11% improvement in power conversion efficiency of the nc-Si:H thin-film solar cells compared to flat cells and cells employing nanoparticle clusters, respectively. Finite-difference time-domain simulations were also carried out to confirm that the improved device performance mainly originates from the multiple plasmon resonances generated from three-dimensionally assembled nanoparticle structures. PMID:26751935

  9. A light-trapping strategy for nanocrystalline silicon thin-film solar cells using three-dimensionally assembled nanoparticle structures

    NASA Astrophysics Data System (ADS)

    Ha, Kyungyeon; Jang, Eunseok; Jang, Segeun; Lee, Jong-Kwon; Jang, Min Seok; Choi, Hoseop; Cho, Jun-Sik; Choi, Mansoo

    2016-02-01

    We report three-dimensionally assembled nanoparticle structures inducing multiple plasmon resonances for broadband light harvesting in nanocrystalline silicon (nc-Si:H) thin-film solar cells. A three-dimensional multiscale (3DM) assembly of nanoparticles generated using a multi-pin spark discharge method has been accomplished over a large area under atmospheric conditions via ion-assisted aerosol lithography. The multiscale features of the sophisticated 3DM structures exhibit surface plasmon resonances at multiple frequencies, which increase light scattering and absorption efficiency over a wide spectral range from 350-1100 nm. The multiple plasmon resonances, together with the antireflection functionality arising from the conformally deposited top surface of the 3D solar cell, lead to a 22% and an 11% improvement in power conversion efficiency of the nc-Si:H thin-film solar cells compared to flat cells and cells employing nanoparticle clusters, respectively. Finite-difference time-domain simulations were also carried out to confirm that the improved device performance mainly originates from the multiple plasmon resonances generated from three-dimensionally assembled nanoparticle structures.

  10. Microwave Plasma Source for Fabrication of Micro- and Nano-Crystalline Diamond Thin Films for Electronic Devices

    NASA Astrophysics Data System (ADS)

    Paosawatyanyong, Boonchoat; Rujisamphan, Nopporn; Bhanthumnavin, Worawan

    2013-01-01

    The design and utilization of an affordable compact-size high-density plasma reactor for micro- and nano-crystalline diamond (MCD/NCD) thin film deposition is presented. The system is based on a 2.45 GHz domestic microwave oven magnetron. A switching power supply module, which yields a low-voltage high-current AC filament feeding and a high-voltage low-current DC cathode bias, is constructed to serve as the magnetron power source. With a high stability of the power module combined with the usage of water cooling gaskets, over 100 h of plasma processing time was achieved without overheating or causing any damage to the magnetron. Depositions of well-faceted MCD/NCD thin films, with distinct diamond Raman characteristics, were obtained using H2-CH4 discharge with 1-5% CH4. Metal-semiconductor diode structures were fabricated using gold and aluminum as ohmic and rectifying contacts, respectively, and their responses to DC signals revealed a high rectification ratio of up to 106 in the intrinsic MCD/NCD devices.

  11. Preparation and bioactive properties of nanocrystalline hydroxyapatite thin films obtained by conversion of atomic layer deposited calcium carbonate.

    PubMed

    Holopainen, Jani; Kauppinen, Kyösti; Mizohata, Kenichiro; Santala, Eero; Mikkola, Esa; Heikkilä, Mikko; Kokkonen, Hanna; Leskelä, Markku; Lehenkari, Petri; Tuukkanen, Juha; Ritala, Mikko

    2014-09-01

    Nanocrystalline hydroxyapatite thin films were fabricated on silicon and titanium by atomic layer deposition (ALD) of CaCO3 and its subsequent conversion to hydroxyapatite by diammonium hydrogen phosphate (DAP) solution. The effects of conversion process parameters to crystallinity and morphology of the films were examined. DAP concentration was found to be critical in controlling the crystal size and homogeneity of the films. The hydroxyapatite phase was identified by XRD. ToF-elastic recoil detection analysis studies revealed that the films are calcium deficient in relation to hydroxyapatite with a Ca/P ratio of 1.39 for films converted with 0.2 M DAP at 95 °C. The coatings prepared on titanium conformally follow the rough surface topography of the substrate, verifying that the good step coverage of the ALD method was maintained in the conversion process. The dissolution tests revealed that the coating was nondissolvable in the cell culture medium. Annealing the coated sample at 700 °C for 1 h seemed to enhance its bonding properties to the substrate. Also, the biocompatibility of the coatings was confirmed by human bone marrow derived cells in vitro. The developed method provides a new possibility to produce thin film coatings on titanium implants with bone-type hydroxyapatite that is biocompatible with human osteoblasts and osteoclasts. PMID:25280849

  12. Multilayered nanocrystalline CrN/TiAlN/MoS2 tribological thin film coatings: preparation and characterization

    NASA Astrophysics Data System (ADS)

    Papp, S.; Kelemen, A.; Jakab-Farkas, L.; Vida-Simiti, I.; Biró, D.

    2013-12-01

    Nanocrystalline multilayer thin film coatings, composed of nanometer-scale thick CrN, TiAlN and MoS2 tri-layer systems, were prepared by reactive co-sputtering processes. The self-lubricated multilayer coating structures were deposited by one-fold oscillating movement of substrates in front of the sputter sources. Three independently operated direct current (dc) excited unbalanced magnetrons (UM) with rectangular cathodes of TiAl alloy (50/50%), pure chromium and MoS2 were used as sputter sources. The reactive sputtering process was performed in a mixture of Ar-N2 atmosphere. Hardened high-speed-steel (HSS) and thin oxide covered Si (100) wafers were used as substrates for tribological- and microstructure investigations, respectively. According to results of the chemical composition evaluated by Auger-electron spectroscopy (AES) and microstructure investigation by cross sectional transmission electron microscopy (XTEM), the CrN, TiAlN and the MoS2 phases form practically continuous layers with large gradient transition of composition. The as-deposited CrN/ (Al,Ti)N/MoS2 coatings have shown good friction behaviour, tested at room temperature in dry sliding condition with a ball-on-disk tribometer.

  13. Structure and electronic properties of pure and nitrogen doped nanocrystalline tungsten oxide thin films

    NASA Astrophysics Data System (ADS)

    Vemuri, Venkata Rama Sesha Ravi Kumar

    Tungsten oxide (WO3) is a multifunctional material which has applications in electronics, sensors, optoelectronics, and energy-related technologies. Recently, electronic structure modification of WO3 to design novel photocatalysts has garnered significant attention. However, a fundamental understanding of nitrogen-induced changes in the structure, morphology, surface/ interface chemistry, and electronic properties of WO 3 is a prerequisite to producing materials with the desired functionality and performance. Also, understanding the effect of thermodynamic and processing variables is highly desirable in order to derive the structure-property relationships in the W-O/W-O-N material system. The present work was, therefore, focused on studying the effects of processing parameters on the microstructure, optical properties, electrical conductivity, and electronic structures of pure and nitrogen-doped (N-doped) WO3 films grown by sputter deposition. Efforts were made to understand the properties and phenomena of pure and N-doped WO3 at reduced dimensionality (i.e., nanoscale dimensions). The results and analyses indicate that the growth temperature (Ts) has a significant effect on the microstructure of WO3 films. The grain size increases from 9 to 50 nm coupled with a phase transformation in the following sequence: amorphous (a) to monoclinic (m) to tetragonal (t) with increasing Ts (25--500°C). The nanocrystalline t-WO 3 films exhibit a strong (001) texturing. The band gap narrowing from 3.25 to 2.92 eV with grain size occurs due to quantum confinement effects. Correlated with the structure and optical properties, electrical conductivity also increases. Physical properties such as thickness, grain size, and density are also sensitive to oxygen/ nitrogen partial pressure during W-O/W-O-N sample fabrications. A direct relationship between film density and band gap is evident in nanocrystalline t-WO3 films grown at various oxygen pressures. It is observed that nitrogen

  14. Cohesive strength of nanocrystalline ZnO:Ga thin films deposited at room temperature

    PubMed Central

    2011-01-01

    In this study, transparent conducting nanocrystalline ZnO:Ga (GZO) films were deposited by dc magnetron sputtering at room temperature on polymers (and glass for comparison). Electrical resistivities of 8.8 × 10-4 and 2.2 × 10-3 Ω cm were obtained for films deposited on glass and polymers, respectively. The crack onset strain (COS) and the cohesive strength of the coatings were investigated by means of tensile testing. The COS is similar for different GZO coatings and occurs for nominal strains approx. 1%. The cohesive strength of coatings, which was evaluated from the initial part of the crack density evolution, was found to be between 1.3 and 1.4 GPa. For these calculations, a Young's modulus of 112 GPa was used, evaluated by nanoindentation. PMID:21711818

  15. Growth and characterization of Li-doped ZnO thin films on nanocrystalline diamond substrates

    NASA Astrophysics Data System (ADS)

    Huang, Jian; Xia, Yiben; Wang, Linjun; Xu, Jinyong; Hu, Guang; Zhu, Xuefeng; Shi, Weimin

    2008-02-01

    Nanocrystalline diamond(NCD) films with a mean surface roughness of 23.8 nm were grown on silicon substrates in a hot filament chemical vapor deposition(HFCVD) system. Then, Zn 1-xLi xO (x=0, 0.05, 0.10, 0.15) films were deposited on these NCD films by radio-frequency(RF) reactive magnetron sputtering method. When x was 0.1, the Li-doped ZnO film had a larger resistivity more than 10 8Ω•cm obtained from Hall effect measurement. All the Zn 1-xLi xO films had a strong c-axis orientation structure determined by X-ray diffraction (XRD). The above results suggested that the Li-doped ZnO film/NCD structure prepared in this work was attractive for the application of high frequency surface acoustic wave (SAW) devices.

  16. Structural order effect in visible photoluminescence properties of nanocrystalline Si :H thin films

    NASA Astrophysics Data System (ADS)

    Chen, H.; Shen, W. Z.; Wei, W. S.

    2006-03-01

    We report room-temperature visible photoluminescence (PL) properties of highly ordered hydrogenated nanocrystalline Si(nc-Si :H) with good electrical performance. The PL profiles can be well reproduced by the model of Islam and Kumar [J. Appl. Phys. 93, 1753 (2003)], incorporating the effects of quantum confinement and localized surface states, as well as a log-normal crystallite size distribution. Raman, PL, and electrical results consistently reveal that improvement of structural order within nc-Si :H is beneficial to enhance the PL efficiency. Owing to adequate order, strong visible PL and high electron mobility can coexist in nc-Si :H, which may provide possibilities in Si-based optoelectronics.

  17. Boron Doped Nanocrystalline Film with Improved Work Function as a Buffer Layer in Thin Film Silicon Solar Cells.

    PubMed

    Park, Jinjoo; Shin, Chonghoon; Park, Hyeongsik; Jung, Junhee; Lee, Youn-Jung; Bong, Sungjae; Dao, Vinh Ai; Balaji, Nagarajan; Yi, Junsin

    2015-03-01

    We investigated thin film silicon solar cells with boron doped hydrogenated nanocrystalline silicon/ hydrogenated amorphous silicon oxide [p-type nc-Si:H/a-SiOx:H] layer. First, we researched the bandgap engineering of diborane (B2H6) doped wide bandgap hydrogenated nanocryslline silicon (p-type nc-Si:H) films, which have excellent electrical properties of high dark conductivity, and low activation energy. The films prepared with lower doping ratio and higher hydrogen dilution ratio had higher optical gap (Eg), with higher dark conductivity (σ(d)), and lower activation energy (Ea). We controlled Eg from 2.10 eV to 1.75 eV, with σ(d) from 1.1 S/cm to 7.59 x 10(-3) S/cm, and Ea from 0.040 eV to 0.128 eV. Next, we focused on the fabrication of thin film silicon solar cells. By inserting p-type nc-Si:H film into the thin film silicon solar cells, we achieved a remarkable increase in the built-in potential from 0.803 eV to 0.901 eV. By forming p-type nc-Si:H film between SnO2:F/ZnO:Al (30 nm) and p-type a-SiOx:H layer, the solar cell properties of open circuit voltage (Voc), short circuit current density (Jsc), and efficiency (η) were improved by 3.7%, 9.2%, and 9.8%, respectively. PMID:26413646

  18. Effect of annealing temperature on photoelectrochemical properties of nanocrystalline MoBi2(Se0.5Te0.5)5 thin films

    NASA Astrophysics Data System (ADS)

    Salunkhe, Manauti; Pawar, Nita; Patil, P. S.; Bhosale, P. N.

    2014-10-01

    Nanocrystalline MoBi2(Se0.5Te0.5)5 thermoelectric thin films have been deposited on ultrasonically cleaned glass and FTO-coated glass substrates by Arrested Precipitation Technique. The change in properties of MoBi2(Se0.5Te0.5)5 thin films were examined after annealing at the temperature 473 K for 3 h. The structural, morphological, compositional and electrical properties of thin films were characterized by X-ray Diffraction, Scanning Electron Microscopy, Energy Dispersive Spectroscopy, etc. Thermoelectric properties of the thin films have been evaluated by measurements of electrical conductivity and Seebeck coefficient in the temperature range 300-500 K. Our aim is to investigate the effect of annealing on behaviour of MoBi2(Se0.5Te0.5)5 thin films along with photoelectrochemical properties.

  19. Nonlinear optical parameters of nanocrystalline AZO thin film measured at different substrate temperatures

    NASA Astrophysics Data System (ADS)

    Jilani, Asim; Abdel-wahab, M. Sh; Al-ghamdi, Attieh A.; Dahlan, Ammar sadik; Yahia, I. S.

    2016-01-01

    The 2.2 wt% of aluminum (Al)-doped zinc oxide (AZO) transparent and preferential c-axis oriented thin films were prepared by using radio frequency (DC/RF) magnetron sputtering at different substrate temperature ranging from room temperature to 200 °C. For structural analysis, X-ray Diffraction (XRD) and Atomic Force Electron Microscope (AFM) was used for morphological studies. The optical parameters such as, optical energy gap, refractive index, extinction coefficient, dielectric loss, tangent loss, first and third order nonlinear optical properties of transparent films were investigated. High transmittance above 90% and highly homogeneous surface were observed in all samples. The substrate temperature plays an important role to get the best transparent conductive oxide thin films. The substrate temperature at 150 °C showed the growth of highly transparent AZO thin film. Energy gap increased with the increased in substrate temperature of Al doped thin films. Dielectric constant and loss were found to be photon energy dependent with substrate temperature. The change in substrate temperature of Al doped thin films also affect the non-liner optical properties of thin films. The value of χ(3) was found to be changed with the grain size of the thin films that directly affected by the substrate temperature of the pure and Al doped ZnO thin films.

  20. Nanocrystalline Pd:NiFe2O4 thin films: A selective ethanol gas sensor

    NASA Astrophysics Data System (ADS)

    Rao, Pratibha; Godbole, R. V.; Bhagwat, Sunita

    2016-10-01

    In this work, Pd:NiFe2O4 thin films were investigated for the detection of reducing gases. These films were fabricated using spray pyrolysis technique and characterized using X-ray diffraction (XRD) to confirm the crystal structure. The surface morphology was studied using scanning electron microscopy (SEM). Magnetization measurements were carried out using SQUID VSM, which shows ferrimagnetic behavior of the samples. These thin film sensors were tested against methanol, ethanol, hydrogen sulfide and liquid petroleum gas, where they were found to be more selective to ethanol. The fabricated thin film sensors exhibited linear response signal for all the gases with concentrations up to 5 w/o Pd. Reduction in optimum operating temperature and enhancement in response was also observed. Pd:NiFe2O4 thin films exhibited faster response and recovery characteristic. These sensors have potential for industrial applications because of their long-term stability, low power requirement and low production cost.

  1. RETRACTED: Ammonia-free method for synthesis of CdS nanocrystalline thin films through chemical bath deposition technique

    NASA Astrophysics Data System (ADS)

    Karimi, M.; Rabiee, M.; Moztarzadeh, F.; Bodaghi, M.; Tahriri, M.

    2009-11-01

    This article has been retracted: please see Elsevier Policy on Article Withdrawal ( http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief of Solid State Communications as the authors have plagiarized part of a paper that has also appeared in Current Applied Physics: Controlled synthesis, characterization and optical properties of CdS nanocrystalline thin films via chemical bath deposition (CBD) route Meysam Karimi, Mohammad Rabiee, Fathollah Moztarzadeh, Mohammadreza Tahriri and Masoud Bodaghi; Curr. Appl. Phys., 9 (2009) 1263-1268, doi: 10.1016/j.cap.2009.02.006. One of the conditions of submission of a paper for publication is that authors declare explicitly that their work is original and has not appeared in a publication elsewhere. Re-use of any data should be appropriately cited. As such this article represents a severe abuse of the scientific publishing system. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process.

  2. Investigations of the drift mobility of carriers and density of states in nanocrystalline CdS thin films

    NASA Astrophysics Data System (ADS)

    Singh, Baljinder; Singh, Janpreet; Kaur, Jagdish; Moudgil, R. K.; Tripathi, S. K.

    2016-06-01

    Nanocrystalline Cadmium Sulfide (nc-CdS) thin films have been prepared on well-cleaned glass substrate at room temperature (300 K) by thermal evaporation technique using inert gas condensation (IGC) method. X-ray diffraction (XRD) analysis reveals that the films crystallize in hexagonal structure with preferred orientation along [002] direction. Scanning electron microscope (SEM) and Transmission electron microscope (TEM) studies reveal that grains are spherical in shape and uniformly distributed over the glass substrates. The optical band gap of the film is estimated from the transmittance spectra. Electrical parameters such as Hall coefficient, carrier type, carrier concentration, resistivity and mobility are determined using Hall measurements at 300 K. Transit time and mobility are estimated from Time of Flight (TOF) transient photocurrent technique in gap cell configuration. The measured values of electron drift mobility from TOF and Hall measurements are of the same order. Constant Photocurrent Method in ac-mode (ac-CPM) is used to measure the absorption spectra in low absorption region. By applying derivative method, we have converted the measured absorption data into a density of states (DOS) distribution in the lower part of the energy gap. The value of Urbach energy, steepness parameter and density of defect states have been calculated from the absorption and DOS spectra.

  3. Electronic and optical properties of nanocrystalline WO₃ thin films studied by optical spectroscopy and density functional calculations.

    PubMed

    Johansson, Malin B; Baldissera, Gustavo; Valyukh, Iryna; Persson, Clas; Arwin, Hans; Niklasson, Gunnar A; Osterlund, Lars

    2013-05-22

    The optical and electronic properties of nanocrystalline WO3 thin films prepared by reactive dc magnetron sputtering at different total pressures (Ptot) were studied by optical spectroscopy and density functional theory (DFT) calculations. Monoclinic films prepared at low Ptot show absorption in the near infrared due to polarons, which is attributed to a strained film structure. Analysis of the optical data yields band-gap energies Eg ≈ 3.1 eV, which increase with increasing Ptot by 0.1 eV, and correlate with the structural modifications of the films. The electronic structures of triclinic δ-WO3, and monoclinic γ- and ε-WO3 were calculated using the Green function with screened Coulomb interaction (GW approach), and the local density approximation. The δ-WO3 and γ-WO3 phases are found to have very similar electronic properties, with weak dispersion of the valence and conduction bands, consistent with a direct band-gap. Analysis of the joint density of states shows that the optical absorption around the band edge is composed of contributions from forbidden transitions (>3 eV) and allowed transitions (>3.8 eV). The calculations show that Eg in ε-WO3 is higher than in the δ-WO3 and γ-WO3 phases, which provides an explanation for the Ptot dependence of the optical data. PMID:23614973

  4. The influence of interfacial defects on fast charge trapping in nanocrystalline oxide-semiconductor thin film transistors

    NASA Astrophysics Data System (ADS)

    Kim, Taeho; Hur, Jihyun; Jeon, Sanghun

    2016-05-01

    Defects in oxide semiconductors not only influence the initial device performance but also affect device reliability. The front channel is the major carrier transport region during the transistor turn-on stage, therefore an understanding of defects located in the vicinity of the interface is very important. In this study, we investigated the dynamics of charge transport in a nanocrystalline hafnium-indium-zinc-oxide thin-film transistor (TFT) by short pulse I-V, transient current and 1/f noise measurement methods. We found that the fast charging behavior of the tested device stems from defects located in both the front channel and the interface, following a multi-trapping mechanism. We found that a silicon-nitride stacked hafnium-indium-zinc-oxide TFT is vulnerable to interfacial charge trapping compared with silicon-oxide counterpart, causing significant mobility degradation and threshold voltage instability. The 1/f noise measurement data indicate that the carrier transport in a silicon-nitride stacked TFT device is governed by trapping/de-trapping processes via defects in the interface, while the silicon-oxide device follows the mobility fluctuation model.

  5. Effect of thickness on structural, optical, electrical and morphological properties of nanocrystalline CdSe thin films for optoelectronic applications

    NASA Astrophysics Data System (ADS)

    Purohit, Anuradha; Chander, S.; Nehra, S. P.; Lal, C.; Dhaka, M. S.

    2015-09-01

    This paper presents effect of thickness on the physical properties of thermally evaporated cadmium selenide thin films. The films of thickness 445 nm, 631 nm and 810 nm were deposited employing thermal evaporation technique on glass and ITO coated glass substrates followed by thermal annealing in air atmosphere at temperature 300 °C. The as-deposited and annealed films were subjected to the XRD, UV-Vis spectrophotometer, source meter, SEM and EDS to find the structural, optical, electrical, morphological and compositional analysis respectively. The structural analysis shows that the films have cubic phase with preferred orientation (1 1 1) and nanocrystalline nature. The structural parameters like inter-planner spacing, lattice constant, grain size, number of crystallites per unit area, internal strain, dislocation density and texture coefficient are calculated. The optical band gap is found in the range 1.69-1.84 eV and observed to decrease with thickness. The electrical resistivity is found to increase with thickness for as-deposited films and decrease for annealed films. The morphological studies show that the as-deposited and annealed films are homogeneous, smooth, fully covered and free from crystal defects like pin holes and voids. The grains in the as-deposited films are densely packed, well defined and found to be increased with thickness.

  6. Influence of texture coefficient on surface morphology and sensing properties of W-doped nanocrystalline tin oxide thin films.

    PubMed

    Kumar, Manjeet; Kumar, Akshay; Abhyankar, A C

    2015-02-18

    For the first time, a new facile approach based on simple and inexpensive chemical spray pyrolysis (CSP) technique is used to deposit Tungsten (W) doped nanocrystalline SnO2 thin films. The textural, optical, structural and sensing properties are investigated by GAXRD, UV spectroscopy, FESEM, AFM, and home-built sensing setup. The gas sensing results indicate that, as compared to pure SnO2, 1 wt % W-doping improves sensitivity along with better response (<2 s) and recovery time (<25 s) toward NO2 gas at operating temperatures of ∼225 °C. The optimal composition of 1 wt % W-doped films exhibit lowest crystallite size of the order of ∼8-10 nm with reduced energy band gap and large roughness values of 3.82 eV and 3.01 nm, respectively. Reduction in texture coefficient along highly dense (110) planes with concomitant increase along loosely packed (200) planes is found to have prominent effect on gas sensing properties of W-doped films. PMID:25603393

  7. Tailoring the index of refraction of nanocrystalline hafnium oxide thin films

    SciTech Connect

    Vargas, Mirella; Murphy, N. R.; Ramana, C. V.

    2014-03-10

    Hafnium oxide (HfO{sub 2}) films were grown by sputter-deposition by varying the growth temperature (T{sub s} = 25–700 °C). HfO{sub 2} films grown at T{sub s} < 200 °C were amorphous, while those grown at T{sub s} ≥ 200 °C were monoclinic, nanocrystalline with (1{sup ¯}11) texturing. X-ray reflectivity (XRR) analyses indicate that the film-density (ρ) increases with increasing T{sub s}. The index of refraction (n) profiles derived from spectroscopic ellipsometry analyses follow the Cauchy dispersion relation. Lorentz-Lorenz analysis (n{sub (λ)} = 550 nm) and optical-model adopted agree well with the XRR data/analyses. A direct T{sub s}-ρ-n relationship suggests that tailoring the optical quality is possible by tuning T{sub s} and the microstructure of HfO{sub 2} films.

  8. Microarray of neuroblastoma cells on the selectively functionalized nanocrystalline diamond thin film surface

    NASA Astrophysics Data System (ADS)

    Park, Young-Sang; Son, Hyeong-Guk; Kim, Dae-Hoon; Oh, Hong-Gi; Lee, Da-Som; Kim, Min-Hye; Lim, Ki-Moo; Song, Kwang-Soup

    2016-01-01

    Nanocrystalline diamond (NCD) film surfaces were modified with fluorine or oxygen by plasma treatment in an O2 or C3F8 gas environment in order to induce wettability. The oxygenated-NCD (O-NCD) film surface was hydrophilic and the fluorinated-NCD (F-NCD) surface was hydrophobic. The efficiency of early cell adhesion, which is dependent on the wettability of the cell culture plate and necessary for the growth and proliferation of cells, was 89.62 ± 3.92% on the O-NCD film and 7.78 ± 0.77% on the F-NCD film surface after 3 h of cell culture. The wettability of the NCD film surface was artificially modified using a metal mask and plasma treatment to fabricate a micro-pattern. Four types of micro-patterns were fabricated (line, circle, mesh, and word) on the NCD film surface. We precisely arrayed the neuroblastoma cells on the micro-patterned NCD film surfaces by controlling the surface wettability and cell seeding density. The neuroblastoma cells adhered and proliferated along the O-NCD film surface.

  9. The influence of Cd doping on the microstructure and optical properties of nanocrystalline copper ferrite thin films

    SciTech Connect

    El-Hagary, M.; Matar, A.; Shaaban, E.R.; Emam-Ismail, M.

    2013-06-01

    Highlights: ► The structural and optical properties of Cu{sub 1−x}Cd{sub x}Fe{sub 2}O{sub 4} thin films were studied. ► The micro structural parameters of the films have been determined. ► The room temperature reflectance and transmittance data are analyzed. ► The refractive index and energy gap are determined. ► The single oscillator parameters were calculated. - Abstract: Nanocrystalline thin films of mixed Cu–Cd ferrites, Cu{sub 1−x}Cd{sub x}Fe{sub 2}O{sub 4} (x = 0, 0.2, 0.3, 0.5, 0.7, 0.8, 0.9 and 1), were deposited by electron beam evaporation technique. The films were annealed at 450 °C for 1 h. The effect of Cd doping on the structural and optical properties of the deposited films has been investigated by using X-ray diffraction (XRD) and optical spectrophotometry. XRD patterns of the annealed films show spinal cubic structure. The lattice parameter was found to increase with the increase of cadmium concentration. The crystallite size of the films was found to vary from 8 nm to 30 nm. The optical transition was found to be direct and indirect transitions with energy gaps decrease from 2.466 (x = 0) to 2.00 (x = 1) eV and from 2.148 (x = 0) to 1.824 (x = 1) eV, respectively. The refractive index dispersion of the films was found to increase with Cd content and discussed in terms of the Wemple–DiDomenico single oscillator model.

  10. Ag Nanodots Emitters Embedded in a Nanocrystalline Thin Film Deposited on Crystalline Si Solar Cells.

    PubMed

    Park, Seungil; Ryu, Sel Gi; Ji, HyungYong; Kim, Myeong Jun; Peck, Jong Hyeon; Kim, Keunjoo

    2016-06-01

    We fabricated crystalline Si solar cells with the inclusion of various Ag nanodots into the additional emitters of nanocrystallite Si thin films. The fabricated process was carried out on the emitter surface of p-n junction for the textured p-type wafer. The Ag thin films were deposited on emitter surfaces and annealed at various temperatures. The amorphous Si layers were also deposited on the Ag annealed surfaces by hot-wire chemical vapor deposition and then the deposited layers were doped by the second n-type doping process to form an additional emitter. From the characterization, both the Ag nanodots and the deposited amorphous Si thin films strongly reduce photo-reflectances in a spectral region between 200-400 nm. After embedding Ag nanodots in nanocrystallite Si thin films, a conversion efficiency of the sample with added emitter was achieved to 15.1%, which is higher than the 14.1% of the reference sample and the 14.7% of the de-posited sample with a-Si:H thin film after the Ag annealing process. The additional nanocrystallite emitter on crystalline Si with Ag nanodots enhances cell properties. PMID:27427665

  11. Anomalous hopping conduction in nanocrystalline/amorphous composites and amorphous semiconductor thin films

    NASA Astrophysics Data System (ADS)

    Kakalios, James; Bodurtha, Kent

    Composite nanostructured materials consisting of nanocrystals (nc) embedded within a thin film amorphous matrix can exhibit novel opto-electronic properties. Composite films are synthesized in a dual-chamber co-deposition PECVD system capable of producing nanocrystals of material A and embedding then within a thin film matrix of material B. Electronic conduction in composite thin films of hydrogenated amorphous silicon (a-Si:H) containing nc-germanium or nc-silicon inclusions, as well as in undoped a-Si:H, does not follow an Arrhenius temperature dependence, but rather is better described by an anomalous hopping expression (exp[-(To/T)3/4) , as determined from the ``reduced activation energy'' proposed by Zabrodskii and Shlimak. This temperature dependence has been observed in other thin film resistive materials, such as ultra-thin disordered films of Ag, Bi, Pb and Pd; carbon-black polymer composites; and weakly coupled Au and ZnO quantum dot arrays. There is presently no accepted theoretical understanding of this expression. The concept of a mobility edge, accepted for over four decades, appears to not be necessary to account for charge transport in amorphous semiconductors. Supported by NSF-DMR and the Minnesota Nano Center.

  12. Effect of pH on the properties of nanocrystalline CuO thin films deposited by sol-gel process

    NASA Astrophysics Data System (ADS)

    Saadat Niavol, S.; Ghodsi, F. E.

    2013-01-01

    Nanocrystalline cupric oxide thin films were prepared using the sol-gel method. Three sols with different pH were performed in order to evaluate the pH effect on the morphology and optical properties of the films. XRD pattern confirmed the nanocrystalline monoclinic CuO phase formation. The influences of pH on surface morphology of films were investigated by scanning electron microscopy (SEM). It was observed that grains size increases by increasing the pH of the sol. UV-Vis spectrum measurement showed low transparency of the films in the visible region. Optical constants such as extinction coefficient, refractive index and optical band gap were evaluated from these spectra by using the Pointwise Unconstrained Minimization Approach (PUMA). The band gap of the films varies from 2.20 to 1.98 eV for various pH of sol.

  13. Gasochromic switching of Ta and Pd-doped nanocrystalline TiO2 thin films.

    PubMed

    Domaradzki, J; Wojcieszak, D; Prociow, E; Kaczmarek, D; Winiarski, A; Szade, J

    2011-10-01

    In this work TiO2:(Ta, Pd) thin films with gasochromic properties have been described. Thin films were prepared by reactive magnetron sputtering process using mosaic Ti-Ta-Pd target. The amounts of dopants were 2.54 at.% and 12.36 at.% of Ta and Pd, respectively. The results of optical measurements performed at presence of ethanol and additional heating of the sample up to 350 degrees C have shown an abrupt change of transmission level from 80% down to 10% in VIS and in IR range. The gasochromic change was very fast. Moreover, rapid cooling (down to room temperature) in an air ambient results in stable thin film coloration. The reverse effect (bleaching) was obtained after annealing at 500 degrees C in an ambient air. PMID:22400253

  14. Post-annealing-free, room temperature processed nanocrystalline indium tin oxide thin films for plastic electronics

    NASA Astrophysics Data System (ADS)

    Nyoung Jang, Jin; Jong Lee, You; Jang, YunSung; Yun, JangWon; Yi, Seungjun; Hong, MunPyo

    2016-06-01

    In this study, we confirm that bombardment by high energy negative oxygen ions (NOIs) is the key origin of electro-optical property degradations in indium tin oxide (ITO) thin films formed by conventional plasma sputtering processes. To minimize the bombardment effect of NOIs, which are generated on the surface of the ITO targets and accelerated by the cathode sheath potential on the magnetron sputter gun (MSG), we introduce a magnetic field shielded sputtering (MFSS) system composed of a permanent magnetic array between the MSG and the substrate holder to block the arrival of energetic NOIs. The MFSS processed ITO thin films reveal a novel nanocrystal imbedded polymorphous structure, and present not only superior electro-optical characteristics but also higher gas diffusion barrier properties. To the best of our knowledge, no gas diffusion barrier composed of a single inorganic thin film formed by conventional plasma sputtering processes achieves such a low moisture permeability.

  15. Study of Photo-Conductivity in Nano-Crystalline Cadmium Telluride Thin Films

    SciTech Connect

    Mahesha, M. G.; Bangera, Kasturi V.; Shivakumar, G. K.

    2011-07-15

    Nano crystallite thin films of Cadmium Telluride have been grown on glass substrates by thermal evaporation under vacuum. The growth conditions to get stoichiometric films of the compound have been optimized. The effect of substrate temperature and annealing on photosensitivity has been investigated. Also the effect of deposition parameters and post deposition annealing on rise time and decay time have been studied in detail.

  16. Liquid-Phase Epitaxial Growth of ZnS, ZnSe and Their Mixed Compounds Using Te as Solvent

    NASA Astrophysics Data System (ADS)

    Nakamura, Hiroshi; Aoki, Masaharu

    1981-01-01

    Epitaxial layers of ZnS, ZnSe and their mixed compounds were grown on ZnS substrates by the liquid-phase epitaxial growth (LPE) method using Te as the solvent. The open-tube slide-boat technique was used, and a suitable starting temperature for growth was found to be 850°C for ZnS and 700-800°C for ZnSe. The ZnS epitaxial layers grown on {111}A and {111}B oriented ZnS substrates were thin (˜1 μm) and smooth, had low, uniform Te concentrations (˜0.1 at.%) and were highly luminescent. The ZnSe epitaxial layers were relatively thick (10-30 μm) and had fairly high Te concentrations (a few at.%). Various mixed compound ZnS1-xSex were also grown on ZnS substrates.

  17. Mesoporous semiconducting oxide thin films with nanocrystalline walls: Synthesis, characterization, and applications

    NASA Astrophysics Data System (ADS)

    Frindell, Karen Lynne

    Mesoporous titania thin films were synthesized using a novel modified sol-gel method, which involves the inhibition of rapid condensative polymerization of hydrolyzed titanium alkoxide using concentrated acid solutions. Lamellar, 2D-hexagonal, and cubic mesostructures were created by varying the volume fraction of the structure-directing block copolymer in the precursor solution. A mesostructured cubic semiconducting framework made up of three-dimensionally arranged anatase nanocrystallites embedded in an amorphous titania matrix was obtained by heat treating the films. Interesting absorbance and photoluminescence properties were observed including a blue shifted band gap and well-defined photoluminescence peaks owing to the high surface area and unusual surface environment of the nanocrystallites present in the framework. Selected rare earth ions were included into the walls of the mesoporous titania thin films and excitation of the mesoporous titania in its band gap resulted in sensitized photoluminescence in the visible and near infrared regions of the spectrum. The energy transfer mechanism was determined in part by evaluating which rare earth ions exhibited photoluminescence via energy transfer. Mesoporous titania thin films were incorporated into several devices including a dye sensitized solar cell. The photocurrent, photovoltage and power conversion efficiency of several iterations of solar cell devices were tested. Electrochromic devices were also fabricated and tested using pure mesoporous titania films and those doped with cerium ions. Contrary to the behavior of non-porous Ce-TiO2 thin films, the addition of cerium to mesoporous titania films caused an increased electrochromic effect. The calcination temperature was varied to correlate the evolution of the structure of the titania thin films with optical and electrochemical properties. Electron microscopy, optical absorbance, photoluminescence, lithium insertion, chronoamperometry, and

  18. Nanocrystalline CuInSSe thin films by chemical bath deposition technique

    NASA Astrophysics Data System (ADS)

    Shrotriya, Vipin; Rajaram, P.

    2016-05-01

    Crystalline CuInSSe thin films have been deposited on glass substrate by chemical bath deposition technique. The CuCl2, InCl3, thiourea and SeO2 were used as source materials for the Cu2+, In3+, S2- and Se2- ions and the Cu/In ratio was kept at 1.0. EDC was used as a complexing agent. The XRD, Scanning Electron Microscope (SEM), Energy Dispersive Analysis of X-Ray (EDAX) and Optical transmission studies were used for structural analysis, surface morphology, elemental analysis and optical band gap, of the grown thin films respectively. The deposition parameters such as pH, deposition temperature and deposition time were optimized.

  19. Effect of different sol concentrations on the properties of nanocrystalline ZnO thin films grown on FTO substrates by sol-gel spin-coating

    NASA Astrophysics Data System (ADS)

    Kim, Ikhyun; Kim, Younggyu; Nam, Giwoong; Kim, Dongwan; Park, Minju; Kim, Haeun; Lee, Wookbin; Leem, Jae-Young; Kim, Jong Su; Kim, Jin Soo

    2014-08-01

    Nanocrystalline ZnO thin films grown on fluorine-doped tinoxide (FTO) substrates were fabricated using the spin-coating method. The structural and the optical properties of the ZnO thin films prepared using different sol concentrations were investigated by using field-emission scanning electron microscopy (FE-SEM), X-ray diffractometry (XRD), photoluminescence (PL) measurements, and ultraviolet-visible (UV-vis) spectrometry. The surface morphology of the ZnO thin films, as observed in the SEM images, exhibited a mountain-chain structure. XRD results indicated that the thin films were preferentially orientated along the direction of the c-axis and that the grain size of the ZnO thin films increased with increasing sol concentration. The PL spectra showed a strong ultraviolet emission peak at 3.22 eV and a broad orange emission peak at 2.0 eV. The intensities of deep-level emission (DLE) gradually increased with increasing sol concentration from 0.4 to 1.0 M. The transmittance spectra of the ZnO thin films showed that the ZnO thin films were transparent (~85%) in the visible region and exhibited sharp absorption edges at 375 nm. Thus, The Urbach energy of ZnO thin films decreased with increasing sol concentration.

  20. Investigations of the electron field emission properties and microstructure correlation in sulfur-incorporated nanocrystalline carbon thin films

    NASA Astrophysics Data System (ADS)

    Gupta, S.; Weiner, B. R.; Morell, G.

    2002-06-01

    Results are reported on the electron field emission properties of sulfur (S)-incorporated nanocrystalline carbon (n-C:S) thin films grown on molybdenum (Mo) substrates by hot-filament chemical vapor deposition (HFCVD) technique. In addition to the conventionally used methane (CH4) as carbon precursor with high hydrogen (H2) dilution, hydrogen sulfide-hydrogen (H2)S/H2 premix gas was used for sulfur incorporation. The field emission properties for the S-incorporated films were investigated systematically as a function of substrate temperature (TS) and sulfur concentration. Lowest turn-on field achieved was observed at around 4.0 V/mum for the n-C:S sample grown at TS of 900 degC with 500 ppm of H2S. These results are compared with those films grown without sulfur (n-C) at a particular TS. The turn-on field was found to be almost half for the S-assisted film thus demonstrating the effect of sulfur addition to the chemical vapor deposition process. An inverse relation between turn-on field (EC), growth temperature and sulfur concentration was found. The S incorporation also causes significant microstructural changes, as characterized with non-destructive complementary ex situ techniques: scanning electron microscopy (SEM), atomic force microscopy (AFM), and Raman spectroscopy (RS). S-assisted films show relatively smoother and finer-grained surfaces than those grown without it. These findings are discussed in terms of the dual role of sulfur in enhancing the field emission properties by controlling the sp2 C cluster size and introducing substantial structural defects through its incorporation. The in-plane correlation length (La) of sp2 C cluster was determined from the intensity ratio of the D- and G-bands I(D)/I(G) in the visible RS as a function of deposition temperature and sulfur concentration using a phenomenological model. The turn-on field was found to decrease with increasing sp2 C cluster size in general ranging from 0.8 to 1.4 nm. The films having sp2 C

  1. Mono-textured nanocrystalline thin films with pronounced stress-gradients: On the role of grain boundaries in the stress evolution

    SciTech Connect

    Daniel, R. Mitterer, C.; Jäger, E.; Sartory, B.; Todt, J.; Keckes, J.

    2014-05-28

    The origins of residual stress gradients in nanocrystalline thin films, especially the role of grain size and texture gradients, are still not fully understood. In this work, the stress evolution in exemplary nanocrystalline TiN thin films with one and two fiber texture components as well as in homogeneous amorphous SiO{sub x} films is analyzed using wafer curvature as well as laboratory and synchrotron cross-sectional nanobeam X-ray diffraction techniques. The stress evolution across the film thickness is attributed to the evolutionary nature of microstructural development at the individual growth stages. While the effect of the smooth crystallographic texture changes during growth is only of minor importance, as this does not significantly affect the dominant stress formation mechanisms, the change in the grain size accompanied by a change of the volume fraction of grain boundaries plays a decisive role in the stress development across the film thickness. This is demonstrated on the monotextured thin films, where the residual stresses scale with the apparent grain size. These findings are validated also by the investigations of stress profiles in homogeneous amorphous SiO{sub x} films exhibiting no grain boundaries.

  2. Photoinduced charge, ion & energy transfer processes at transition-metal coordination compounds anchored to mesoporous, nanocrystalline metal-oxide thin films

    NASA Astrophysics Data System (ADS)

    Ardo, Shane

    Photovoltaics provide a direct means of converting photons into useful, electric power; however traditional silicon-based technologies are too expensive for global commercialization. Dye-sensitized mesoporous semiconducting thin films, when utilized in regenerative photoelectrochemical cells, are one category of next generation photovoltaics that could eventually circumvent this issue. In fact, their architecture also affords a clear platform for implementation of a direct, solar fuel-forming system. The mechanisms involved in the myriad of molecular processes that occur in these molecular--solid-state hybrid materials are poorly understood. Thus, the overriding goal of this dissertation was to evaluate sensitized mesoporous, nanocrystalline metal-oxide thin films critically so as to elucidate mechanistic phenomena. Using transient and steady-state absorption and emission spectroscopies as well as (photo)electrochemistry, various previously unobserved processes have been identified. Chapter 2 demonstrates for the first time that the electric fields emanating from these charged thin films affect surface-anchored molecular sensitizers via a Stark effect. In most cases, further, but incomplete, ionic screening of the charged nanoparticles from the sensitizers, as non-Faradaic electrolyte redistribution, was spectroscopically inferred after rapid semiconductor charging. Chapter 3 highlights the reactivity of Co(I) coordination-compound catalysts anchored to anatase TiO2 thin-film electrodes. Visible-light excitation resulted in prompt excited-state electron injection into TiO2 while introduction of benzylbromide into the fluid solution surrounding the thin film led to a 2e--transfer, oxidative-addition reaction to Co1 forming a stable Co--benzyl product. Subsequent visible-light excitation initiated a photocatalytic cycle for C--C bond formation. Unique to the nanocrystalline thin films employed here, Chapter 4 demonstrates that traditional time-resolved polarization

  3. Interlayer coupling dependent magnetic properties in amorphous and nanocrystalline FeTaC based multilayer thin films

    NASA Astrophysics Data System (ADS)

    Singh, Akhilesh K.; Perumal, Alagarsamy

    2016-03-01

    We report systematic studies on the effects of heat treatment, the number of multilayers and temperature on interlayer coupling dependent magnetic properties in amorphous and nanocrystalline ([FeTaC(y nm)/ Ta(1 nm)] n=1-4/ FeTaC(y nm)/substrate) multilayer structured thin films fabricated directly on thermally oxidized Si substrate at ambient temperature and post annealed at different elevated temperatures (T A). As-deposited films and the films annealed at 200 °C exhibit an amorphous structure. With an increase in T A  ⩾  300 °C, the nucleation of fine nanocrystals in a residual amorphous matrix appears and a fraction of such nanocrystals increases with increasing T A. The changes in the microstructure modify the interlayer coupling between FeTaC ferromagnetic layers due to the release of stress accumulated during film deposition and enhanced interface roughness with increasing T A. As a result, a change in the shape of the magnetic hysteresis (M-H) loop and multistep magnetization reversal process, where the number of steps in the M-H loop, their nature and positions strongly depend on the number of multilayers, T A and temperature, were observed. As-deposited films and the films annealed at 200 °C exhibit multistep magnetization reversal behavior only at temperatures below 80 K, but the films annealed above 200 °C show such multistep reversal behavior even at 300 K. This causes an unusual variation of temperature-dependent coercivity in these multilayer films having different microstructures. Furthermore, the coercivity due to individual or collective switching between FeTaC layers in these films varies unusually and is substantially influenced by the bottom FeTaC layer grown directly on the substrate. The observed results were discussed on the basis of variation in interlayer coupling with the multilayer structure, post annealing conditions and temperature. This provided evidence of controlling the soft magnetic properties and

  4. Non-toxic novel route synthesis and characterization of nanocrystalline ZnS{sub x}Se{sub 1−x} thin films with tunable band gap characteristics

    SciTech Connect

    Agawane, G.L.; Shin, Seung Wook; Vanalakar, S.A.; Moholkar, A.V.; Gurav, K.V.; Suryawanshi, M.P.; Lee, Jeong Yong; Yun, Jae Ho; Kim, Jin Hyeok

    2014-07-01

    Highlights: • A simple, inexpensive, and non-toxic CBD route is used to deposit ZnS thin films. • The ZnS{sub x}Se{sub 1−x} thin films formation takes place via annealing of ZnS thin films in Se atmosphere. • S/(S + Se) ratio found to be temperature dependent and easy tuning of band gap has been done by Se atom deposition. - Abstract: An environmentally benign chemical bath deposition (CBD) route was employed to deposit zinc sulfide (ZnS) thin films. The CBD-ZnS thin films were further selenized in a furnace at various temperatures viz. 200, 300, 400, and 500 °C and the S/(S + Se) ratio was found to be dependent on the annealing temperature. The effects of S/(S + Se) ratio on the structural, compositional and optical properties of the ZnS{sub x}Se{sub 1−x} (ZnSSe) thin films were investigated. EDS analysis showed that the S/(S + Se) ratio decreased from 0.8 to 0.6 when the film annealing temperature increased from 200 to 500 °C. The field emission scanning electron microscopy and atomic force microscopy studies showed that all the films were uniform, pin hole free, smooth, and adhered well to the glass substrate. The X-ray diffraction study on the ZnSSe thin films showed the formation of the cubic phase, except for the unannealed ZnSSe thin film, which showed an amorphous phase. The X-ray photoelectron spectroscopy revealed Zn-S, Zn-Se, and insignificant Zn-OH bonds formation from the Zn 2p{sub 3/2}, S 2p, Se 3d{sub 5/2}, and O 1s atomic states, respectively. The ultraviolet–visible spectroscopy study showed ∼80% transmittance in the visible region for all the ZnSSe thin films having various absorption edges. The tuning of the band gap energy of the ZnSSe thin films was carried out by selenizing CBD-ZnS thin films, and as the S/(S + Se) ratio decreased from 0.8 to 0.6, the band gap energy decreased from 3.20 to 3.12 eV.

  5. On the thermal stability of physical vapor deposited oxide-hardened nanocrystalline gold thin films

    SciTech Connect

    Argibay, N. Mogonye, J. E.; Michael, J. R.; Goeke, R. S.; Kotula, P. G.; Scharf, T. W.; Dugger, M. T.; Prasad, S. V.

    2015-04-14

    We describe a correlation between electrical resistivity and grain size for PVD synthesized polycrystalline oxide-hardened metal-matrix thin films in oxide-dilute (<5 vol. % oxide phase) compositions. The correlation is based on the Mayadas-Shatzkes (M-S) electron scattering model, predictive of grain size evolution as a function of composition in the oxide-dilute regime for 2 μm thick Au-ZnO films. We describe a technique to investigate grain boundary (GB) mobility and the thermal stability of GBs based on in situ electrical resistivity measurements during annealing experiments, interpreted using a combination of the M-S model and the Michels et al. model describing solute drag stabilized grain growth kinetics. Using this technique, activation energy and pre-exponential Arrhenius parameter values of E{sub a} = 21.6 kJ/mol and A{sub o} = 2.3 × 10{sup −17} m{sup 2}/s for Au-1 vol. % ZnO and E{sub a} = 12.7 kJ/mol and A{sub o} = 3.1 × 10{sup −18} m{sup 2}/s for Au-2 vol. % ZnO were determined. In the oxide-dilute regime, the grain size reduction of the Au matrix yielded a maximum hardness of 2.6 GPa for 5 vol. % ZnO. A combined model including percolation behavior and grain refinement is presented that accurately describes the composition dependent change in electrical resistivity throughout the entire composition range for Au-ZnO thin films. The proposed correlations are supported by microstructural characterization using transmission electron microscopy and electron diffraction mapping for grain size determination.

  6. On the thermal stability of physical vapor deposited oxide-hardened nanocrystalline gold thin films

    NASA Astrophysics Data System (ADS)

    Argibay, N.; Mogonye, J. E.; Michael, J. R.; Goeke, R. S.; Kotula, P. G.; Scharf, T. W.; Dugger, M. T.; Prasad, S. V.

    2015-04-01

    We describe a correlation between electrical resistivity and grain size for PVD synthesized polycrystalline oxide-hardened metal-matrix thin films in oxide-dilute (<5 vol. % oxide phase) compositions. The correlation is based on the Mayadas-Shatzkes (M-S) electron scattering model, predictive of grain size evolution as a function of composition in the oxide-dilute regime for 2 μm thick Au-ZnO films. We describe a technique to investigate grain boundary (GB) mobility and the thermal stability of GBs based on in situ electrical resistivity measurements during annealing experiments, interpreted using a combination of the M-S model and the Michels et al. model describing solute drag stabilized grain growth kinetics. Using this technique, activation energy and pre-exponential Arrhenius parameter values of Ea = 21.6 kJ/mol and Ao = 2.3 × 10-17 m2/s for Au-1 vol. % ZnO and Ea = 12.7 kJ/mol and Ao = 3.1 × 10-18 m2/s for Au-2 vol. % ZnO were determined. In the oxide-dilute regime, the grain size reduction of the Au matrix yielded a maximum hardness of 2.6 GPa for 5 vol. % ZnO. A combined model including percolation behavior and grain refinement is presented that accurately describes the composition dependent change in electrical resistivity throughout the entire composition range for Au-ZnO thin films. The proposed correlations are supported by microstructural characterization using transmission electron microscopy and electron diffraction mapping for grain size determination.

  7. On the thermal stability of physical vapor deposited oxide-hardened nanocrystalline gold thin films

    SciTech Connect

    Argibay, Nicolas; Mogonye, J. E.; Michael, Joseph R.; Goeke, Ronald S.; Kotula, Paul G.; Scharf, T. W.; Dugger, Michael Thomas; Prasad, Somuri V.

    2015-04-08

    We describe a correlation between electrical resistivity and grain size for PVD synthesized polycrystalline oxide-hardened metal-matrix thin films in oxide-dilute (<5 vol. % oxide phase) compositions. The correlation is based on the Mayadas-Shatzkes (M-S) electron scattering model, predictive of grain size evolution as a function of composition in the oxide-dilute regime for 2 μm thick Au-ZnO films. We describe a technique to investigate grain boundary (GB) mobility and the thermal stability of GBs based on in situelectrical resistivity measurements during annealing experiments, interpreted using a combination of the M-S model and the Michels et al. model describing solute drag stabilized grain growth kinetics. Using this technique, activation energy and pre-exponential Arrhenius parameter values of Ea = 21.6 kJ/mol and Ao = 2.3 × 10-17 m2/s for Au-1 vol. % ZnO and Ea =12.7 kJ/mol and Ao = 3.1 × 10-18 m2/s for Au-2 vol.% ZnO were determined. In the oxide-dilute regime, the grain size reduction of the Au matrix yielded a maximum hardness of 2.6 GPa for 5 vol. % ZnO. A combined model including percolation behavior and grain refinement is presented that accurately describes the composition dependent change in electrical resistivity throughout the entire composition range for Au-ZnO thin films. As a result, the proposed correlations are supported by microstructural characterization using transmission electron microscopy and electron diffraction mapping for grain size determination.

  8. On the thermal stability of physical vapor deposited oxide-hardened nanocrystalline gold thin films

    DOE PAGESBeta

    Argibay, Nicolas; Mogonye, J. E.; Michael, Joseph R.; Goeke, Ronald S.; Kotula, Paul G.; Scharf, T. W.; Dugger, Michael Thomas; Prasad, Somuri V.

    2015-04-08

    We describe a correlation between electrical resistivity and grain size for PVD synthesized polycrystalline oxide-hardened metal-matrix thin films in oxide-dilute (<5 vol. % oxide phase) compositions. The correlation is based on the Mayadas-Shatzkes (M-S) electron scattering model, predictive of grain size evolution as a function of composition in the oxide-dilute regime for 2 μm thick Au-ZnO films. We describe a technique to investigate grain boundary (GB) mobility and the thermal stability of GBs based on in situelectrical resistivity measurements during annealing experiments, interpreted using a combination of the M-S model and the Michels et al. model describing solute drag stabilizedmore » grain growth kinetics. Using this technique, activation energy and pre-exponential Arrhenius parameter values of Ea = 21.6 kJ/mol and Ao = 2.3 × 10-17 m2/s for Au-1 vol. % ZnO and Ea =12.7 kJ/mol and Ao = 3.1 × 10-18 m2/s for Au-2 vol.% ZnO were determined. In the oxide-dilute regime, the grain size reduction of the Au matrix yielded a maximum hardness of 2.6 GPa for 5 vol. % ZnO. A combined model including percolation behavior and grain refinement is presented that accurately describes the composition dependent change in electrical resistivity throughout the entire composition range for Au-ZnO thin films. As a result, the proposed correlations are supported by microstructural characterization using transmission electron microscopy and electron diffraction mapping for grain size determination.« less

  9. Electronic transport in nanocrystalline germanium/hydrogenated amorphous silicon composite thin films

    NASA Astrophysics Data System (ADS)

    Bodurtha, Kent Edward

    Recent interest in composite materials based on hydrogenated amorphous silicon (a-Si:H) stems in part from its potential for technical applications in thin film transistors and solar cells. Previous reports have shown promising results for films of a-Si:H with embedded silicon nanocrystals, with the goal of combining the low cost, large area benefits of hydrogenated amorphous silicon with the superior electronic characteristics of crystalline material. These materials are fabricated in a dual-chamber plasma-enhanced chemical vapor deposition system in which the nanocrystals are produced separately from the amorphous film, providing the flexibility to independently tune the growth parameters of each phase; however, electronic transport through these and other similar materials is not well understood. This thesis reports the synthesis and characterization of thin films composed of germanium nanocrystals embedded in a-Si:H. The results presented here describe detailed measurements of the conductivity, photoconductivity and thermopower which reveal a transition from conduction through the a-Si:H for samples with few germanium nanocrystals, to conduction through the nanocrystal phase as the germanium crystal fraction XGe is increased. These films display reduced photosensitivity as XGe is increased, but an unexpected increase in the dark conductivity is found in samples with X Ge > 5% after long light exposures. Detailed studies of the conductivity temperature dependence in these samples exposes a subtle but consistent deviation from the standard Arrhenius expression; the same departure is found in samples of pure a-Si:H; a theoretical model is presented which accurately describes the actual conductivity temperature dependence.

  10. Vertically self-ordered orientation of nanocrystalline hexagonal boron nitride thin films for enhanced thermal characteristics

    NASA Astrophysics Data System (ADS)

    Cometto, Olivier; Sun, Bo; Tsang, Siu Hon; Huang, Xi; Koh, Yee Kan; Teo, Edwin Hang Tong

    2015-11-01

    Vertically self-ordered hexagonal boron nitride (ordered h-BN) is a highly ordered turbostratic BN (t-BN) material similar to hexagonal BN, with its planar structure perpendicularly oriented to the substrate. The ordered h-BN thin films were grown using a High Power Impulse Magnetron Sputtering (HiPIMS) system with a lanthanum hexaboride (LaB6) target reactively sputtered in nitrogen gas. The best vertical alignment was obtained at room temperature, with a grounded bias and a HiPIMS peak power density of 60 W cm-2. Even though the film contains up to 7.5 at% lanthanum, it retains its highly insulative properties and it was observed that an increase in compressive stress is correlated to an increase in film ordering quality. Importantly, the thermal conductivity of vertically ordered h-BN is considerably high at 5.1 W m-1 K-1. The favourable thermal conductivity coupled with the dielectric properties of this novel material and the low temperature growth could outperform SiO2 in high power density electronic applications.Vertically self-ordered hexagonal boron nitride (ordered h-BN) is a highly ordered turbostratic BN (t-BN) material similar to hexagonal BN, with its planar structure perpendicularly oriented to the substrate. The ordered h-BN thin films were grown using a High Power Impulse Magnetron Sputtering (HiPIMS) system with a lanthanum hexaboride (LaB6) target reactively sputtered in nitrogen gas. The best vertical alignment was obtained at room temperature, with a grounded bias and a HiPIMS peak power density of 60 W cm-2. Even though the film contains up to 7.5 at% lanthanum, it retains its highly insulative properties and it was observed that an increase in compressive stress is correlated to an increase in film ordering quality. Importantly, the thermal conductivity of vertically ordered h-BN is considerably high at 5.1 W m-1 K-1. The favourable thermal conductivity coupled with the dielectric properties of this novel material and the low temperature

  11. Microstructure and optical properties of nanocrystalline Cu2O thin films prepared by electrodeposition

    PubMed Central

    2014-01-01

    Cuprous oxide (Cu2O) thin films were prepared by using electrodeposition technique at different applied potentials (−0.1, −0.3, −0.5, −0.7, and −0.9 V) and were annealed in vacuum at a temperature of 100°C for 1 h. Microstructure and optical properties of these films have been investigated by X-ray diffractometer (XRD), field-emission scanning electron microscope (SEM), UV-visible (vis) spectrophotometer, and fluorescence spectrophotometer. The morphology of these films varies obviously at different applied potentials. Analyses from these characterizations have confirmed that these films are composed of regular, well-faceted, polyhedral crystallites. UV–vis absorption spectra measurements have shown apparent shift in optical band gap from 1.69 to 2.03 eV as the applied potential becomes more cathodic. The emission of FL spectra at 603 nm may be assigned as the near band-edge emission. PMID:24872805

  12. Vertically self-ordered orientation of nanocrystalline hexagonal boron nitride thin films for enhanced thermal characteristics.

    PubMed

    Cometto, Olivier; Sun, Bo; Tsang, Siu Hon; Huang, Xi; Koh, Yee Kan; Teo, Edwin Hang Tong

    2015-12-01

    Vertically self-ordered hexagonal boron nitride (ordered h-BN) is a highly ordered turbostratic BN (t-BN) material similar to hexagonal BN, with its planar structure perpendicularly oriented to the substrate. The ordered h-BN thin films were grown using a High Power Impulse Magnetron Sputtering (HiPIMS) system with a lanthanum hexaboride (LaB6) target reactively sputtered in nitrogen gas. The best vertical alignment was obtained at room temperature, with a grounded bias and a HiPIMS peak power density of 60 W cm(-2). Even though the film contains up to 7.5 at% lanthanum, it retains its highly insulative properties and it was observed that an increase in compressive stress is correlated to an increase in film ordering quality. Importantly, the thermal conductivity of vertically ordered h-BN is considerably high at 5.1 W m(-1) K(-1). The favourable thermal conductivity coupled with the dielectric properties of this novel material and the low temperature growth could outperform SiO2 in high power density electronic applications. PMID:26510890

  13. Determination of the Origin of Crystal Orientation for Nanocrystalline Bismuth Telluride-Based Thin Films Prepared by Use of the Flash Evaporation Method

    NASA Astrophysics Data System (ADS)

    Takashiri, M.; Tanaka, S.; Miyazaki, K.

    2014-06-01

    We have investigated the origin of crystal orientation for nanocrystalline bismuth telluride-based thin films. Thin films of p-type bismuth telluride antimony (Bi-Te-Sb) and n-type bismuth telluride selenide (Bi-Te-Se) were fabricated by a flash evaporation method, with exactly the same deposition conditions except for the elemental composition of the starting powders. For p-type Bi-Te-Sb thin films the main x-ray diffraction (XRD) peaks were from the c-axis (Σ{00l}/Σ{ hkl} = 0.88) whereas n-type Bi-Te-Se thin films were randomly oriented (Σ{00l}/Σ{ hkl} = 0.40). Crystal orientation, crystallinity, and crystallite size were improved for both types of thin film by sintering. For p-type Bi-Te-Sb thin films, especially, high-quality structures were obtained compared with those of n-type Bi-Te-Se thin films. We also estimated the thermoelectric properties of the as-grown and sintered thin films. The power factor was enhanced by sintering; maximum values were 34.9 μW/cm K2 for p-type Bi-Te-Sb thin films at a sintering temperature of 300°C and 23.9 μW/cm K2 for n-type Bi-Te-Se thin films at a sintering temperature of 350°C. The exact mechanisms of film growth are not yet clear but we deduce the crystal orientation originates from the size of nano-clusters generated on the tungsten boat during flash evaporation.

  14. Thermal and photochemical reactions of methanol on nanocrystalline anatase TiO2 thin films.

    PubMed

    Bennett, David A; Cargnello, Matteo; Gordon, Thomas R; Murray, Christopher B; Vohs, John M

    2015-07-14

    The catalytic and photo-catalytic activity of well-defined anatase TiO2 nanocrystals for the partial oxidation of methanol was investigated using temperature-programmed desorption (TPD) in ultra-high vacuum in order to determine how crystallite size and shape affect reactivity. The TiO2 films used in this study were prepared from well-defined TiO2 nanocrystals synthesized by colloidal methods. These nanocrystals had a truncated bi-pyramidal shape which exposes primarily (101) and to a lesser extent (001) surfaces and ranged in size from 10 to 25 nm. Two distinct regimes of reactivity were investigated, namely in the dark and under UV light illumination. In the dark, methanol adsorbed dissociatively on the (001) planes and only molecularly on the (101) surfaces. Dissociated methoxy groups on the (001) surfaces coupled to produce dimethyl ether, suggesting the presence of fourfold coordinate Ti cations. Under UV light illumination, the nanocrystals were additionally found to be active for the photo-catalytic oxidation of methanol to methyl formate. On the (101) surfaces, this reaction proceeded in a stepwise photocatalytic pathway involving dehydrogenation of methanol to form methoxy groups and then formaldehyde, followed by coupling of these latter two species to form methyl formate. The (001) surfaces were also found to be photo-catalytically active but surface methoxy groups could be produced thermally and the reaction proceeds only to formaldehyde in the absence of molecularly adsorbed methanol. The overall photocatalytic activity of the nanocrystals was also was found to increase with increasing crystallite size. The results of this study show that thin films of well-defined nanocrystals are excellent model systems that can be used to help bridge the materials gap between studies of single crystal surfaces and high surface area polycrystalline catalysts. PMID:26073428

  15. A size-dependent structural evolution of ZnS nanoparticles

    PubMed Central

    Khalkhali, Mohammad; Liu, Qingxia; Zeng, Hongbo; Zhang, Hao

    2015-01-01

    Recently, ZnS quantum dots have attracted a lot of attention since they can be a suitable alternative for cadmium-based quantum dots, which are known to be highly carcinogenic for living systems. However, the structural stability of nanocrystalline ZnS seems to be a challenging issue since ZnS nanoparticles have the potential to undergo uncontrolled structural change at room temperature. Using the molecular dynamics technique, we have studied the structural evolution of 1 to 5 nm freestanding ZnS nanoparticles with zinc-blende and wurtzite crystal structures. Simulation results revealed that relaxed configurations of ZnS nanoparticles larger than 3 nm consist of three regions: a) a crystalline core, b) a distorted network of 4-coordinated atoms environing the crystalline core, and c) a surface structure made entirely of 3-coordinated atoms. Decreasing the size of ZnS nanoparticle to 2 nm will cause the crystalline core to disappear. Further reducing the size will cause all of the atoms to become 3-coordinated. Dipole moments of zinc-blende and wurtzite nanoparticles are in the same range when the nanoparticles are smaller than 3 nm. Increasing the size makes dipole moments converge to the bulk values. This makes zinc-blende and wurtzite nanoparticles less and more polar, respectively. PMID:26381583

  16. New co-spray way to synthesize high quality ZnS films

    NASA Astrophysics Data System (ADS)

    Bouznit, Y.; Beggah, Y.; Boukerika, A.; Lahreche, A.; Ynineb, F.

    2013-11-01

    In the present study, we report for the first time the synthesis of ZnS films using co-spray method, in which the reactants were mixed in the vapor state contrary to that seen in previous spray configurations. In order to obtain the optimum conditions for growing high quality ZnS thin films related to this approach, a series of samples with different Zn:S atomic ratios were investigated. X-ray diffraction (XRD) analysis indicated that both solid state and phase formation were strongly dependent on Zn:S atomic ratio. In the absence of sulfur element, pure ZnO phase showing hexagonal wurtzite structure with (0 0 2) preferential orientation was obtained. When one eighth of sulfur was implicated, the (0 0 2) diffraction peak of ZnO was broadened and displaced toward lower angles. Once one quarter of sulfur was involved, no discernible diffraction peaks could be seen. Films deposited using solutions with Zn:S ratio of 1:1/2, 1:1 and 1:2 have pure ZnS phase showing hexagonal wurtzite structure with a strong preferential orientation. Near stoichiometric ZnS films were achieved with Zn:S atomic ratio close to 1:1. All films have high transmittance of about 80% in the visible region.

  17. Influence of γ-irradiation on optical parameters of electron beam evaporated ZnSe1-xTex nanocrystalline thin films

    NASA Astrophysics Data System (ADS)

    Emam-Ismail, Mohamed; El-Hagary, Magdy; Ramadan, Essam; Matar, Ahmed; El-Taher, Atef

    2014-01-01

    In the present paper, we reported the effect of γ-irradiation with different doses (100-300 kGy) on the optical parameters of nanocrystalline ZnSe1-xTex (x=0.0, 0.2, 0.5, 0.7, 1.0) thin films. In the wavelength range 400-2500 nm, the optical parameters of the as-deposited and γ-irradiated were extracted from transmission spectra using the Swanepoel method. It was found that the refractive index of the investigated films increases with increasing the doses of γ-radiation. Such post-irradiation increase in the refractive index was attributed to the increase of the density of the investigated films with irradiation doses due to structure transformation induced by thermal effects during irradiation. In addition, the refractive index dispersions of both as-deposited and γ-irradiated of nanocrystalline ZnSe0.8Te0.2 films are found to follow the single oscillator model. The calculated single oscillator parameters; oscillator strength Ed, static refractive index no, increased after irradiation while the oscillator energy Eo, reduced after irradiation. The absorption coefficient was found to increase with the increase of the doses of γ-radiation. Furthermore, the obtained optical energy gap of nanocrystalline ZnSe1-xTex films was found to decrease with increasing the doses of the γ-radiation which is attributed to the increase of the telluride (Te) atoms or defects after irradiation. This is confirmed by the decrease in the Urbach energy Ee after radiation. The γ-irradiation stimulated increase in the absorption coefficient and change in the optical parameters, which can be utilized for industrial dosimetric and detector purposes.

  18. Photoacoustic and Photoluminescence Characterization of Passivated and Unpassivated Mn-Doped ZnS Nanoparticles

    NASA Astrophysics Data System (ADS)

    Cruz, Almira Briones; Shen, Qing; Toyoda, Taro

    2005-06-01

    In this study, passivated and unpassivated nanocrystalline ZnS with varying Mn2+ concentrations (ZnS:Mn) were synthesized and their photoacoustic (PA) and photoluminescence (PL) characteristics were studied. The PA intensity peak for the nanocrystalline ZnS was found to be blue-shifted compared with that for the bulk material due to quantum confinement effects. The difference of the PA signals of doped ZnS and undoped ZnS yielded the Mn2+ optical absorption spectra. The intensity of the PA peak increased linearly with Mn concentration. The PL spectra showed a peak position at 2.08 eV corresponding to the d-d transition of Mn2+. For the unpassivated sample, a decrease in the PL intensities for higher Mn concentrations was observed. This could be attributed to concentration quenching. Addition of acrylic acid as a passivator led to an increase in PL intensity for all Mn concentrations and prevented the decrease in the PL intensity for higher Mn concentrations. These could be attributed to the surface passivation, which reduces the nonradiative recombination probabilities, thus increasing PL intensities.

  19. Synthesis of nanocrystalline Cu{sub 2}ZnSnS{sub 4} thin films grown by the spray-pyrolysis technique

    SciTech Connect

    Chandel, Tarun Singh, Joginder; Rajaram, P.

    2015-08-28

    Spray pyrolysis was used to deposit Cu{sub 2}ZnSnS{sub 4} (CZTS) thin films on soda lime glass substrates at 300 °C. Aqueous solutions of copper chloride, zinc chloride, stannous chloride and thiourea were mixed together to form the spray liquid. The sprayed films were annealed under vacuum at 350 °C, 400 °C and 450 °C. Structural and optical characterization was performed on the CZTS films using X-ray diffraction (XRD) and UV-VIS spectrophotometry. XRD results indicate that the films are single phase nanocrystalline CZTS. Optical studies show that the optical gap values are 1.44 eV for the as-grown film and 1.46 eV, 1.48 eV and 1.49 eV for the films annealed at 350 °C, 400 °C and 450 °C, respectively.

  20. Growth, electrical, and optical properties of nanocrystalline VO{sub 2} (011) thin films prepared by thermal oxidation of magnetron sputtered vanadium films

    SciTech Connect

    Luo Zhenfei; Wu Zhiming; Xu Xiangdong; Wang Tao; Jiang Yadong

    2010-07-15

    Nanocrystalline vanadium dioxide (VO{sub 2}) thin films were prepared on glass substrates at different deposition temperatures by oxidizing sputtered vanadium films. Atomic force microscope, x-ray diffraction, and Raman scattering were employed to characterize the films. It was confirmed that low deposition temperature resulted in improving oxygen atom diffusion and VO{sub 2} nanograin growth in the thermal oxidation process. Investigation of the electrical properties revealed that the amplitude of semiconductor-metal transition and transition temperature decreased, whereas the Hall mobility and carrier concentration increased as the deposition temperature elevated. Optical investigations were carried out in the ultraviolet-visible-near-infrared region. Narrow optical band gaps were observed in these films.

  1. Deposition of nanocrystalline thin TiO2 films for MOS capacitors using Sol-Gel spin method with Pt and Al top electrodes

    NASA Astrophysics Data System (ADS)

    Rathee, Davinder; Kumar, Mukesh; Arya, Sandeep K.

    2012-10-01

    Nanocrystalline titanium dioxide (TiO2) films were deposited by Sol-Gel spin coating method on well clean P<1 0 0> Si substrate. Titanium isoproxide Ti(OC3H7O2)4 (TIP) was used as the Titania precursor. The thickness, composition, and surface morphology of the thin films were characterized using Stylus profilometer, X-ray diffraction (XRD), Field-Emission Scanning Electron Microscope (FESEM) and Atomic Force Microscope (AFM). The crystallite sizes of the TiO2 grains were measured from the typical diffraction peaks and were found to be approximately 23-54 nm. The XRD pattern and Raman spectrum analysis of the deposited film confirmed the polymorphism nature of TiO2 thin films. After annealing at high temperature; the phase transition, improvement in crystallinity, structure and property of the films were being observed. The six Raman peaks were analyzed at 145 cm-1, 199 cm-1, 397 cm-1, 516 cm-1 (doublet) and 637 cm-1 corresponding to active mode of anatase phase. Capacitance-Voltage (C-V) measurement analysis was performed to obtain various devices and process parameters. Metal Oxide Semiconductor (MOS) capacitors with Pt and Al as the top electrode were fabricated to explore electrical characteristics. The refractive index by ellipsometry was found 2.36 and dielectric constant was calculated as 58. In this study, the comparison of the leakage current for TiO2 thin films fabricated by various methods has also been reported.

  2. Some physical investigations on ZnS 1- xSe x films obtained by selenization of ZnS sprayed films using the Boubaker polynomials expansion scheme

    NASA Astrophysics Data System (ADS)

    Fridjine, S.; Touihri, S.; Boubaker, K.; Amlouk, M.

    2010-01-01

    ZnS 1- xSe x thin films have been grown by selenization process, applied to ZnS sprayed thin films deposited on Pyrex glass substrates at 550 °C. The crystal structure and surface morphology were investigated by the XRD technique and by the atomic force microscopy. This structural study shows that selenium-free ( x=0) ZnS thin films, prepared at substrate temperature TS=450 °C, were well crystallized in cubic structure and oriented preferentially along (1 1 1) direction. The thermal and mechanical properties were also investigated using a photothermal protocol along with Vickers hardness measurements. On the other hand, the analyze of the transmittance T( λ) and the reflectance R( λ), optical measurements of these films depicts a decrease in the band gap energy value Eg with an increase in Se content ( x). Indeed, Eg values vary from 3.6 to 3.1 eV.

  3. Phase transformation from cubic ZnS to hexagonal ZnO by thermal annealing

    NASA Astrophysics Data System (ADS)

    Mahmood, K.; Asghar, M.; Amin, N.; Ali, Adnan

    2015-03-01

    We have investigated the mechanism of phase transformation from ZnS to hexagonal ZnO by high-temperature thermal annealing. The ZnS thin films were grown on Si (001) substrate by thermal evaporation system using ZnS powder as source material. The grown films were annealed at different temperatures and characterized by X-ray diffraction (XRD), photoluminescence (PL), four-point probe, scanning electron microscope (SEM) and energy dispersive X-ray diffraction (EDX). The results demonstrated that as-deposited ZnS film has mixed phases but high-temperature annealing leads to transition from ZnS to ZnO. The observed result can be explained as a two-step process: (1) high-energy O atoms replaced S atoms in lattice during annealing process, and (2) S atoms diffused into substrate and/or diffused out of the sample. The dissociation energy of ZnS calculated from the Arrhenius plot of 1000/T versus log (resistivity) was found to be 3.1 eV. PL spectra of as-grown sample exhibits a characteristic green emission at 2.4 eV of ZnS but annealed samples consist of band-to-band and defect emission of ZnO at 3.29 eV and 2.5 eV respectively. SEM and EDX measurements were additionally performed to strengthen the argument.

  4. The effect of solution pH on the electrochemical performance of nanocrystalline metal ferrites MFe2O4 (M=Cu, Zn, and Ni) thin films

    NASA Astrophysics Data System (ADS)

    Elsayed, E. M.; Rashad, M. M.; Khalil, H. F. Y.; Ibrahim, I. A.; Hussein, M. R.; El-Sabbah, M. M. B.

    2016-04-01

    Nanocrystalline metal ferrite MFe2O4 (M=Cu, Zn, and Ni) thin films have been synthesized via electrodeposition-anodization process. Electrodeposited (M)Fe2 alloys were obtained from aqueous sulfate bath. The formed alloys were electrochemically oxidized (anodized) in aqueous (1 M KOH) solution, at room temperature, to the corresponding hydroxides. The parameters controlling the current efficiency of the electrodeposition of (M)Fe2 alloys such as the bath composition and the current density were studied and optimized. The anodized (M)Fe2 alloy films were annealed in air at 400 °C for 2 h. The results revealed the formation of three ferrite thin films were formed. The crystallite sizes of the produced films were in the range between 45 and 60 nm. The microstructure of the formed film was ferrite type dependent. The corrosion behavior of ferrite thin films in different pH solutions was investigated using open circuit potential (OCP) and potentiodynamic polarization measurements. The open circuit potential indicates that the initial potential E im of ZnFe2O4 thin films remained constant for a short time, then sharply increased in the less negative direction in acidic and alkaline medium compared with Ni and Cu ferrite films. The values of the corrosion current density I corr were higher for the ZnFe2O4 films at pH values of 1 and 12 compared with that of NiFe2O4 and CuFe2O4 which were higher only at pH value 1. The corrosion rate was very low for the three ferrite films when immersion in the neutral medium. The surface morphology recommended that Ni and Cu ferrite films were safely used in neutral and alkaline medium, whereas Zn ferrite film was only used in neutral atmospheres.

  5. A study on the structural and mechanical properties of nanocrystalline CuS thin films grown by chemical bath deposition technique

    SciTech Connect

    Mukherjee, Nillohit; Sinha, Arijit; Khan, Gobinda Gopal; Chandra, Debraj; Bhaumik, Asim; Mondal, Anup

    2011-01-15

    We report a chemical route for the deposition of nanocrystalline thin films of CuS, using aqueous solutions of Cu(CH{sub 3}COO){sub 2}, SC(NH{sub 2}){sub 2} and N(CH{sub 2}CH{sub 2}OH){sub 3} [triethanolamine, i.e. TEA] in proper concentrations and ratios. The films were structurally characterized using X-ray diffraction technique (XRD), field emission scanning electron microscopy (FESEM) and optical analysis [both photo luminescence (PL) and ultraviolet-visible (UV-vis)]. Optical studies showed a large blue shift in the band gap energy of the films due to quantum confinement effect exerted by the nanocrystals. From both XRD and FESEM analyses, formation of CuS nanocrystals with sizes within 10-15 nm was evident. A study on the mechanical properties was carried out using nanoindentation and nanoscratch techniques, which showed good mechanical stability and high adherence of the films with the bottom substrate. Such study on the mechanical properties of the CuS thin films is being reported here for the first time. Current-voltage (I-V) measurements were also carried out for the films, which showed p-type conductivity.

  6. Synthesis of Nanocrystalline SnOx (x = 1–2) Thin Film Using a Chemical Bath Deposition Method with Improved Deposition Time, Temperature and pH

    PubMed Central

    Ebrahimiasl, Saeideh; Yunus, Wan Md. Zin Wan; Kassim, Anuar; Zainal, Zulkarnain

    2011-01-01

    Nanocrystalline SnOx (x = 1–2) thin films were prepared on glass substrates by a simple chemical bath deposition method. Triethanolamine was used as complexing agent to decrease time and temperature of deposition and shift the pH of the solution to the noncorrosive region. The films were characterized for composition, surface morphology, structure and optical properties. X-ray diffraction analysis confirms that SnOx thin films consist of a polycrystalline structure with an average grain size of 36 nm. Atomic force microscopy studies show a uniform grain distribution without pinholes. The elemental composition was evaluated by energy dispersive X-ray spectroscopy. The average O/Sn atomic percentage ratio is 1.72. Band gap energy and optical transition were determined from optical absorbance data. The film was found to exhibit direct and indirect transitions in the visible spectrum with band gap values of about 3.9 and 3.7 eV, respectively. The optical transmittance in the visible region is 82%. The SnOx nanocrystals exhibit an ultraviolet emission band centered at 392 nm in the vicinity of the band edge, which is attributed to the well-known exciton transition in SnOx. Photosensitivity was detected in the positive region under illumination with white light. PMID:22163690

  7. Micro-textures for efficient light trapping and improved electrical performance in thin-film nanocrystalline silicon solar cells

    NASA Astrophysics Data System (ADS)

    Tan, Hairen; Psomadaki, Efthymia; Isabella, Olindo; Fischer, Marinus; Babal, Pavel; Vasudevan, Ravi; Zeman, Miro; Smets, Arno H. M.

    2013-10-01

    Micro-textures with large opening angles and smooth U-shape are applied to nanocrystalline silicon (nc-Si:H) solar cells. The micro-textured substrates result in higher open-circuit-voltage (Voc) and fill-factor (FF) than nano-textured substrates. For thick solar cells, high Voc and FF are maintained. Particularly, the Voc only drops from 564 to 541 mV as solar cell thickness increases from 1 to 5 μm. The improvement in electrical performance of solar cells is ascribed to the growth of dense nc-Si:H layers free from defective filaments on micro-textured substrates. Thereby, micromorph tandem solar cells with an initial efficiency of 13.3%, Voc = 1.464 V, and FF = 0.759 are obtained.

  8. Magnetism in undoped ZnS studied from density functional theory

    SciTech Connect

    Xiao, Wen-Zhi E-mail: llwang@hun.edu.cn; Rong, Qing-Yan; Xiao, Gang; Wang, Ling-ling E-mail: llwang@hun.edu.cn; Meng, Bo

    2014-06-07

    The magnetic property induced by the native defects in ZnS bulk, thin film, and quantum dots are investigated comprehensively based on density functional theory within the generalized gradient approximation + Hubbard U (GGA + U) approach. We find the origin of magnetism is closely related to the introduction of hole into ZnS systems. The relative localization of S-3p orbitals is another key to resulting in unpaired p-electron, due to Hund's rule. For almost all the ZnS systems under study, the magnetic moment arises from the S-dangling bonds generated by Zn vacancies. The charge-neutral Zn vacancy, Zn vacancy in 1− charge sate, and S vacancy in the 1+ charge sate produce a local magnetic moment of 2.0, 1.0, and 1.0 μ{sub B}, respectively. The Zn vacancy in the neutral and 1− charge sates are the important cause for the ferromagnetism in ZnS bulk, with a Curie temperature (T{sub C}) above room temperature. For ZnS thin film with clean (111) surfaces, the spins on each surface are ferromagnetically coupled but antiferromagnetically coupled between two surfaces, which is attributable to the internal electric field between the two polar (111) surfaces of the thin film. Only surface Zn vacancies can yield local magnetic moment for ZnS thin film and quantum dot, which is ascribed to the surface effect. Interactions between magnetic moments on S-3p states induced by hole-doping are responsible for the ferromagnetism observed experimentally in various ZnS samples.

  9. Effect of the nanocrystalline structure type on the optical properties of TiO2:Nd (1 at.%) thin films

    NASA Astrophysics Data System (ADS)

    Mazur, Michal; Wojcieszak, Damian; Kaczmarek, Danuta; Domaradzki, Jaroslaw; Zatryb, Grzegorz; Misiewicz, Jan; Morgiel, Jerzy

    2015-04-01

    Titanium dioxide thin films, each doped with the same amount of neodymium (1 at.%) were deposited by Low Pressure Hot Target Reactive Sputtering and High Energy Reactive Magnetron Sputtering processes in order to obtain anatase and rutile thin film structures respectively. The microstructure and phase composition were analyzed using the transmission electron microscopy method including high resolution electron microscopy imaging. The measurements of the optical properties showed, that both prepared thin films were transparent in the visible light range and had a low extinction coefficient of ca. 3 ṡ 10-3. The thin film with the anatase structure had a lower cut-off wavelength and refractive index and a higher value of optical energy band gap as-compared to the TiO2:Nd coating with the rutile structure. Simultaneously, more efficient photoluminescence emission was observed for the rutile thin films.

  10. Evidence of quantum correction to conductivity and variable range hopping conduction in nano-crystalline Cu{sub 3}N thin film

    SciTech Connect

    Sahoo, Guruprasad Jain, Mahaveer K.

    2015-10-15

    We have investigated the temperature dependent carrier transport properties of nano-crystalline copper nitride thin films synthesized by modified activated reactive evaporation. The films, prepared in a Cu-rich growth condition are found to be highly disordered and the carrier transport in these films is mainly attributed to the impurity band conduction. We have observed that no single conduction mechanism is appropriate to elucidate the carrier transport in the entire temperature range of 20 – 300 K. Therefore, we have employed different conduction mechanisms in different temperature regimes. The carrier transport of the films in the low temperature regime (20 – 150 K) has been interpreted by implementing quantum correction to the conductivity. In the high temperature regime (200 – 300 K), the conduction mechanism has been successfully analyzed on the basis of Mott’s variable range hopping mechanism. Furthermore, it can be predicted that copper ions present at the surface of the crystallites are responsible for the hopping conduction mechanism.

  11. Anomalous behavior of B1g mode in highly transparent anatase nano-crystalline Nb-doped Titanium Dioxide (NTO) thin films

    NASA Astrophysics Data System (ADS)

    Gautam, Subodh K.; Gautam, Naina; Singh, R. G.; Ojha, S.; Shukla, D. K.; Singh, Fouran

    2015-12-01

    The effect of Niobium doping and size of crystallites on highly transparent nano-crystalline Niobium doped Titanium Dioxide (NTO) thin films with stable anatase phase are reported. The Nb doping concentration is varied within the solubility limit in TiO2 lattice. Films were annealed in controlled environment for improving the crystallinity and size of crystallites. Elemental and thickness analysis were carried out using Rutherford backscattering spectrometry and cross sectional field emission scanning electron microscopy. Structural characteristics reveal a substitutional incorporation of Nb+5 in the TiO2 lattice which inhibits the anatase crystallites growth with increasing the doping percentage. The micro-Raman (MR) spectra of films with small size crystallites shows stiffening of about 4 cm-1 for the Eg(1) mode and is ascribed to phonon confinement and non-stoichiometry. In contrast, B1g mode exhibits a large anomalous softening of 20 cm-1 with asymmetrical broadening; which was not reported for the case of pure TiO2 crystallites. This anomalous behaviour is explained by contraction of the apical Ti-O bonds at the surface upon substitutional Nb5+ doping induced reduction of Ti4+ ions also known as hetero-coordination effect. The proposed hypotheses is manifested through studying the electronic structure and phonon dynamics by performing the near edge x-ray absorption fine structure (NEXAFS) and temperature dependent MR down to liquid nitrogen temperature on pure and 2.5 at.% doped NTO films, respectively.

  12. Microscopic model for exchange bias from grain-boundary disorder in a ferromagnet/antiferromagnet thin film with a nanocrystalline microstructure

    SciTech Connect

    Cortie, D. L.; Biternas, A. G.; Chantrell, R. W.; Wang, X. L.; Klose, F.

    2014-07-21

    Monte Carlo spin simulations were coupled to a Voronoi microstructure-generator to predict the magnitude and behavior of exchange bias in a ferromagnet/antiferromagnet (AF) thin film bilayer with a nanocrystalline microstructure. Our model accounts for the effects of irregular grain-shapes, finite-sized particles, and the possible presence of local random-fields originating from the antiferromagnet's grain-boundary regions. As the grain-boundary represents a crystal-structure distortion, we model the local effect on the exchange constants in the Gaussian approximation which can cause regions resembling a spin glass confined to an unusual 2D topology. Although an ensemble of completely disconnected AF grains isolated by non-magnetic barriers provides a small exchange bias, the introduction of a spin-glass network at the boundaries causes a four-fold enhancement in the magnitude of the loop-shift. This implies the importance of local grain-boundary behavior in defect-engineered antiferromagnets.

  13. Determination of the compositions of the DIGM zone in nanocrystalline Ag/Au and Ag/Pd thin films by secondary neutral mass spectrometry

    PubMed Central

    Molnár, Gábor Y; Shenouda, Shenouda S; Katona, Gábor L; Langer, Gábor A

    2016-01-01

    Summary Alloying by grain boundary diffusion-induced grain boundary migration is investigated by secondary neutral mass spectrometry depth profiling in Ag/Au and Ag/Pd nanocrystalline thin film systems. It is shown that the compositions in zones left behind the moving boundaries can be determined by this technique if the process takes place at low temperatures where solely the grain boundary transport is the contributing mechanism and the gain size is less than the half of the grain boundary migration distance. The results in Ag/Au system are in good accordance with the predictions given by the step mechanism of grain boundary migration, i.e., the saturation compositions are higher in the slower component (i.e., in Au or Pd). It is shown that the homogenization process stops after reaching the saturation values and further intermixing can take place only if fresh samples with initial compositions, according to the saturation values, are produced and heat treated at the same temperature. The reversal of the film sequence resulted in the reversal of the inequality of the compositions in the alloyed zones, which is in contrast to the above theoretical model, and explained by possible effects of the stress gradients developed by the diffusion processes itself. PMID:27335738

  14. Determination of the compositions of the DIGM zone in nanocrystalline Ag/Au and Ag/Pd thin films by secondary neutral mass spectrometry.

    PubMed

    Molnár, Gábor Y; Shenouda, Shenouda S; Katona, Gábor L; Langer, Gábor A; Beke, Dezső L

    2016-01-01

    Alloying by grain boundary diffusion-induced grain boundary migration is investigated by secondary neutral mass spectrometry depth profiling in Ag/Au and Ag/Pd nanocrystalline thin film systems. It is shown that the compositions in zones left behind the moving boundaries can be determined by this technique if the process takes place at low temperatures where solely the grain boundary transport is the contributing mechanism and the gain size is less than the half of the grain boundary migration distance. The results in Ag/Au system are in good accordance with the predictions given by the step mechanism of grain boundary migration, i.e., the saturation compositions are higher in the slower component (i.e., in Au or Pd). It is shown that the homogenization process stops after reaching the saturation values and further intermixing can take place only if fresh samples with initial compositions, according to the saturation values, are produced and heat treated at the same temperature. The reversal of the film sequence resulted in the reversal of the inequality of the compositions in the alloyed zones, which is in contrast to the above theoretical model, and explained by possible effects of the stress gradients developed by the diffusion processes itself. PMID:27335738

  15. Catastrophic vs gradual collapse of thin-walled nanocrystalline Ni hollow cylinders as building blocks of microlattice structures.

    PubMed

    Lian, Jie; Jang, Dongchan; Valdevit, Lorenzo; Schaedler, Tobias A; Jacobsen, Alan J; B Carter, William; Greer, Julia R

    2011-10-12

    Lightweight yet stiff and strong lattice structures are attractive for various engineering applications, such as cores of sandwich shells and components designed for impact mitigation. Recent breakthroughs in manufacturing enable efficient fabrication of hierarchically architected microlattices, with dimensional control spanning seven orders of magnitude in length scale. These materials have the potential to exploit desirable nanoscale-size effects in a macroscopic structure, as long as their mechanical behavior at each appropriate scale - nano, micro, and macro levels - is properly understood. In this letter, we report the nanomechanical response of individual microlattice members. We show that hollow nanocrystalline Ni cylinders differing only in wall thicknesses, 500 and 150 nm, exhibit strikingly different collapse modes: the 500 nm sample collapses in a brittle manner, via a single strain burst, while the 150 nm sample shows a gradual collapse, via a series of small and discrete strain bursts. Further, compressive strength in 150 nm sample is 99.2% lower than predicted by shell buckling theory, likely due to localized buckling and fracture events observed during in situ compression experiments. We attribute this difference to the size-induced transition in deformation behavior, unique to nanoscale, and discuss it in the framework of "size effects" in crystalline strength. PMID:21851060

  16. An investigation on the effect of high partial pressure of hydrogen on the nanocrystalline structure of silicon carbide thin films prepared by radio-frequency magnetron sputtering.

    PubMed

    Daouahi, Mohsen; Omri, Mourad; Kerm, Abdul Ghani Yousseph; Al-Agel, Faisal Abdulaziz; Rekik, Najeh

    2014-10-22

    The aim of the study reported in this paper is to investigate the role of the high partial pressure of hydrogen introduced during the growth of nanocrystalline silicon carbide thin films (nc-SiC:H). For this purpose, we report the preparation as well as spectroscopic studies of four series of nc-SiC:H obtained by radio-frequency magnetron sputtering at high partial pressure of hydrogen by varying the percentage of H2 in the gas mixture from 70% to 100% at common substrate temperature (TS=500°C). The effects of the dilution on the structural changes and the chemical bonding of the different series have been studied using Fourier transform infrared and Raman spectroscopy. For this range of hydrogen dilution, two groups of films were obtained. The first group is characterized by the dominance of the crystalline phase and the second by a dominance of the amorphous phase. This result confirms the multiphase structure of the grown nc-SiC:H thin films by the coexistence of the SiC network, carbon-like and silicon-like clusters. Furthermore, infrared results show that the SiC bond is the dominant absorption peak and the carbon atom is preferentially bonded to silicon. The maximum value obtained of the crystalline fraction is about 77%, which is relatively important compared to other results obtained by other techniques. In addition, the concentration of CHn bonds was found to be lower than that of SiHn for all series. Raman measurements revealed that the crystallization occurs in all series even at 100% H2 dilution suggesting that high partial pressure of hydrogen favors the formation of silicon nanocrystallites (nc-Si). The absence of both the longitudinal acoustic band and the transverse optical band indicate that the crystalline phase is dominant. PMID:25459700

  17. An investigation on the effect of high partial pressure of hydrogen on the nanocrystalline structure of silicon carbide thin films prepared by radio-frequency magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Daouahi, Mohsen; Omri, Mourad; Kerm, Abdul Ghani Yousseph; Al-Agel, Faisal Abdulaziz; Rekik, Najeh

    2015-02-01

    The aim of the study reported in this paper is to investigate the role of the high partial pressure of hydrogen introduced during the growth of nanocrystalline silicon carbide thin films (nc-SiC:H). For this purpose, we report the preparation as well as spectroscopic studies of four series of nc-SiC:H obtained by radio-frequency magnetron sputtering at high partial pressure of hydrogen by varying the percentage of H2 in the gas mixture from 70% to 100% at common substrate temperature (TS = 500 °C). The effects of the dilution on the structural changes and the chemical bonding of the different series have been studied using Fourier transform infrared and Raman spectroscopy. For this range of hydrogen dilution, two groups of films were obtained. The first group is characterized by the dominance of the crystalline phase and the second by a dominance of the amorphous phase. This result confirms the multiphase structure of the grown nc-SiC:H thin films by the coexistence of the Sisbnd C network, carbon-like and silicon-like clusters. Furthermore, infrared results show that the Sisbnd C bond is the dominant absorption peak and the carbon atom is preferentially bonded to silicon. The maximum value obtained of the crystalline fraction is about 77%, which is relatively important compared to other results obtained by other techniques. In addition, the concentration of CHn bonds was found to be lower than that of SiHn for all series. Raman measurements revealed that the crystallization occurs in all series even at 100% H2 dilution suggesting that high partial pressure of hydrogen favors the formation of silicon nanocrystallites (nc-Si). The absence of both the longitudinal acoustic band and the transverse optical band indicate that the crystalline phase is dominant.

  18. The Effect of Mn Incorporation on the Structural, Morphological, Optical, and Electrical Features of Nanocrystalline ZnO Thin Films Prepared by Chemical Spray Pyrolysis Technique

    NASA Astrophysics Data System (ADS)

    Yilmaz, Mehmet; Aydoğan, Şakir

    2015-06-01

    Un-doped and Mn-doped ZnO nanocrystalline thin films and n-ZnO /n-Si heterojunction have been prepared by chemical spray pyrolysis technique. The microstructure, morphology, optical, and electrical properties have been studied. The X-ray analyses have revealed that all films are in single phase and have wurtzite structure. Besides, it has been indicated that there are not any secondary phases. The optical properties have been evaluated by UV-Vis measurement. It has shown that band gap decreases with Mn incorporation from 3.29 to 3.19 eV. Schottky diode applications of the films have been performed by evaporation of Au on pure and Mn-doped ZnO films. Current-voltage (I-V) and capacitance-voltage (C-V) measurements of the n-ZnO /n-Si heterojunction indicate good diode characteristic and the barrier heights have been calculated as 0.89 and 0.79 eV for un-doped and Mn 1 pct-doped ZnO films. Besides, schematic cross section of the Au/ n-ZnO/ n-Si/Al device and energy band diagram of n-ZnO/ n-Si heterojunction has been illustrated to clarify the transport mechanism. All results suggest that the characteristic properties of the ZnO thin films can be adjustable with the Mn doping and Al/ n-Si/ n-ZnO/Au diode can be used for UV detection application in photonic devices.

  19. Structural, optical, and transport properties of nanocrystalline bismuth telluride thin films treated with homogeneous electron beam irradiation and thermal annealing

    NASA Astrophysics Data System (ADS)

    Takashiri, Masayuki; Asai, Yuki; Yamauchi, Kazuki

    2016-08-01

    We investigated the effects of homogeneous electron beam (EB) irradiation and thermal annealing treatments on the structural, optical, and transport properties of bismuth telluride thin films. Bismuth telluride thin films were prepared by an RF magnetron sputtering method at room temperature. After deposition, the films were treated with homogeneous EB irradiation, thermal annealing, or a combination of both the treatments (two-step treatment). We employed Williamson–Hall analysis for separating the strain contribution from the crystallite domain contribution in the x-ray diffraction data of the films. We found that strain was induced in the thin films by EB irradiation and was relieved by thermal annealing. The crystal orientation along c-axis was significantly enhanced by the two-step treatment. Scanning electron microscopy indicated the melting and aggregation of nano-sized grains on the film surface by the two-step treatment. Optical analysis indicated that the interband transition of all the thin films was possibly of the indirect type, and that thermal annealing and two-step treatment methods increased the band gap of the films due to relaxation of the strain. Thermoelectric performance was significantly improved by the two-step treatment. The power factor reached a value of 17.2 μW (cm‑1 K‑2), approximately 10 times higher than that of the as-deposited thin films. We conclude that improving the crystal orientation and relaxing the strain resulted in enhanced thermoelectric performance.

  20. Structural, optical, and transport properties of nanocrystalline bismuth telluride thin films treated with homogeneous electron beam irradiation and thermal annealing.

    PubMed

    Takashiri, Masayuki; Asai, Yuki; Yamauchi, Kazuki

    2016-08-19

    We investigated the effects of homogeneous electron beam (EB) irradiation and thermal annealing treatments on the structural, optical, and transport properties of bismuth telluride thin films. Bismuth telluride thin films were prepared by an RF magnetron sputtering method at room temperature. After deposition, the films were treated with homogeneous EB irradiation, thermal annealing, or a combination of both the treatments (two-step treatment). We employed Williamson-Hall analysis for separating the strain contribution from the crystallite domain contribution in the x-ray diffraction data of the films. We found that strain was induced in the thin films by EB irradiation and was relieved by thermal annealing. The crystal orientation along c-axis was significantly enhanced by the two-step treatment. Scanning electron microscopy indicated the melting and aggregation of nano-sized grains on the film surface by the two-step treatment. Optical analysis indicated that the interband transition of all the thin films was possibly of the indirect type, and that thermal annealing and two-step treatment methods increased the band gap of the films due to relaxation of the strain. Thermoelectric performance was significantly improved by the two-step treatment. The power factor reached a value of 17.2 μW (cm(-1) K(-2)), approximately 10 times higher than that of the as-deposited thin films. We conclude that improving the crystal orientation and relaxing the strain resulted in enhanced thermoelectric performance. PMID:27389820

  1. Transition from a nanocrystalline phase to an amorphous phase in In-Si-O thin films: The correlation between the microstructure and the optical properties

    SciTech Connect

    Park, Jun-Woo; So, Hyeon Seob; Lee, Hosun; Lee, Hye-Min; Kim, Hyo-Joong; Kim, Han-Ki

    2015-04-21

    We investigated the structural and optical properties of In-Si-O thin films as the phase abruptly changes from nanocrystalline (nc) to amorphous (a) with increasing Si content. In-Si-O thin films were deposited on Si substrate using a co-sputtering deposition method. The RF power of the In{sub 2}O{sub 3} target was fixed at 100 W, while the power applied to the SiO{sub 2} target was varied between 0 W and 60 W. At the Si = 2.8 at. %, i.e., at the onset of amorphous phase, the optical properties, including the dielectric functions, optical gap energies, and phonon modes, changed abruptly which were triggered by changes in the crystallinity and surface morphology. X-ray diffraction (XRD) spectra showed crystalline (c-) In{sub 2}O{sub 3}-like peaks below Si = 2.2%. Additionally, a broad peak associated with an amorphous (a-) In{sub 2}O{sub 3} phase appeared above 2.8%. However, the Raman spectra of In-Si-O showed very weak peaks associated with c-In{sub 2}O{sub 3} below 2.2%, and then showed a strong Raman peak associated with a-In-Si-O above 2.8%. X-ray photoelectron spectroscopy measurements showed that oxygen vacancy-related peak intensities increased abruptly above Si = 2.8%. The contrasting results of XRD and Raman measurements can be explained as follows: first, the large enhancement in Drude tails in the a-In-Si-O phase was caused by Si-induced amorphization and a large increase in the density of oxygen vacancies in the In-Si-O thin films. Second, the apparently drastic increase of the Raman peak intensity near 364 cm{sup −1} (for amorphous phase, i.e., above Si = 2.8%) is attributed to a disorder-activated infrared mode caused by both the amorphization and the increase in the oxygen vacancy density in In-Si-O thin films.

  2. Nanocrystalline biphasic resorbable calcium phosphate (HAp/β-TCP) thin film prepared by electron beam evaporation technique

    NASA Astrophysics Data System (ADS)

    Elayaraja, K.; Chandra, V. Sarath; Joshy, M. I. Ahymah; Suganthi, R. V.; Asokan, K.; Kalkura, S. Narayana

    2013-06-01

    Biphasic calcium phosphate (BCP) thin film having resorbable β-tricalcium phosphate (β-TCP) and non-resorbable hydroxyapatite (HAp) phases having enhanced bioactivity was synthesized by electron beam evaporation technique. Nanosized BCP was deposited as a layer (500 nm) on (0 0 1) silicon substrate by electron beam evaporation and crystalline phase of samples were found to improve on annealing at 700 °C. Uniform deposition of calcium phosphate on silicon substrate was verified from elemental mapping using scanning electron microscope (SEM-EDX). Annealing of the samples led to a decrease in surface roughness, hydrophobicity and dissolution of the coating layer. Amoxicillin loaded thin films exhibited significant bacterial resistance. In addition, BCP thin films did not exhibit any cytotoxicity. Antibiotics incorporated BCP coated implants might prevent the post-surgical infections and could promote bone-bonding of orthopedic devices.

  3. Effect of lead ion concentration on the structural and optical properties of nano-crystalline PbS thin films

    NASA Astrophysics Data System (ADS)

    Zaman, S.; Mehmood, S. K.; Mansoor, M.; Asim, M. M.

    2014-06-01

    PbS thin films have received considerable attention because of their potential applications in opto-electronics applications. Spontaneous reaction of lead acetate and thiourea in aqueous hydrazine hydrate has been used for depositing PbS thin films on glass substrates. Structural and optical properties of PbS thin films are greatly influenced by the morality of the reactants and crystal defects in the lattice. Our work focuses on the variation in lead ion concentration and its effect on the structural and optical properties of PbS thin films. The deposited films were analyzed using XRD, SEM, spectrophotometer and dark resistance measurement. XRD patterns indicated the formation of major phase of nano crystalline PbS with minor presence of lead oxide phase. We also noticed that peak intensity ratio of I111/I200 varied by changing the Pb ion concentration. The film thickness and dark resistance increased whereas optical band gap decreased with the decreasing Pb ion concentration. SEM scans showed that the grain size is less than 100 nm and is not affected by varying Pb ion concentration.

  4. Influencing the structural, microstructural and optical properties of PbS nanocrystalline thin films by Mg2+ doping

    NASA Astrophysics Data System (ADS)

    Gassoumi, Abdelaziz; Alleg, Safia; Kamoun-Turki, Najoua

    2016-07-01

    The aim of the current work is study the effect of Mg2+ doping (0-4%) on lead sulfide (PbS) thin films prepared using a simplest and cost effective chemical bath deposition (CBD) technique on glass substrates at ambient temperature and pressure. The effect of Mg2+ content on structural, morphological and optical properties of PbS thin films was studied. Powder X-ray diffraction and Atomic Force Microscopic results showed that all the deposited thin films exhibits both nanostructured and polycrystalline nature with cubic structure. The remarkable effect on optical transmittance and band gap was observed due to Mg2+ doping for all the films. The optical energy band gap values were found to enhance with increasing the Mg2+ content in PbS thin films. Further, the refractive index was calculated and a relationship with energy band gap was investigated and also the high frequency dielectric constant (ε∞) was determined using the energy band gap values as a function of the Mg2+ content.

  5. Enhanced Growth and Osteogenic Differentiation of Human Osteoblast-Like Cells on Boron-Doped Nanocrystalline Diamond Thin Films

    PubMed Central

    Grausova, Lubica; Kromka, Alexander; Burdikova, Zuzana; Eckhardt, Adam; Rezek, Bohuslav; Vacik, Jiri; Haenen, Ken; Lisa, Vera; Bacakova, Lucie

    2011-01-01

    Intrinsic nanocrystalline diamond (NCD) films have been proven to be promising substrates for the adhesion, growth and osteogenic differentiation of bone-derived cells. To understand the role of various degrees of doping (semiconducting to metallic-like), the NCD films were deposited on silicon substrates by a microwave plasma-enhanced CVD process and their boron doping was achieved by adding trimethylboron to the CH4:H2 gas mixture, the B∶C ratio was 133, 1000 and 6700 ppm. The room temperature electrical resistivity of the films decreased from >10 MΩ (undoped films) to 55 kΩ, 0.6 kΩ, and 0.3 kΩ (doped films with 133, 1000 and 6700 ppm of B, respectively). The increase in the number of human osteoblast-like MG 63 cells in 7-day-old cultures on NCD films was most apparent on the NCD films doped with 133 and 1000 ppm of B (153,000±14,000 and 152,000±10,000 cells/cm2, respectively, compared to 113,000±10,000 cells/cm2 on undoped NCD films). As measured by ELISA per mg of total protein, the cells on NCD with 133 and 1000 ppm of B also contained the highest concentrations of collagen I and alkaline phosphatase, respectively. On the NCD films with 6700 ppm of B, the cells contained the highest concentration of focal adhesion protein vinculin, and the highest amount of collagen I was adsorbed. The concentration of osteocalcin also increased with increasing level of B doping. The cell viability on all tested NCD films was almost 100%. Measurements of the concentration of ICAM-1, i.e. an immunoglobuline adhesion molecule binding inflammatory cells, suggested that the cells on the NCD films did not undergo significant immune activation. Thus, the potential of NCD films for bone tissue regeneration can be further enhanced and tailored by B doping and that B doping up to metallic-like levels is not detrimental for cells. PMID:21695172

  6. Influence of metal precursor on the synthesis and magnetic properties of nanocrystalline SrFe12O19 thin films

    NASA Astrophysics Data System (ADS)

    Masoudpanah, S. M.; Seyyed Ebrahimi, S. A.

    2013-10-01

    The effects of metal precursor on the structure and magnetic properties of strontium hexaferrite (SrFe12O19) thin films synthesized by polymeric precursor method have been investigated. Fourier transform infrared, thermal analyses, X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer techniques were applied to evaluate the microstructure, composition, crystallite size and magnetic properties of the SrFe12O19 thin films. The films synthesized from metal nitrate precursor offered the single phase SrFe12O19 with the crystallite size of 42 nm and isotropically magnetic properties of Ms=267 emu/cm3, Mr=134 emu/cm3, and Hc=4790 Oe after calcination at 800 °C. The films obtained from metal hydroxide and metal chloride precursors exhibited higher coercivities, 6063 and 5047 Oe, respectively, due to the smaller particle size; however, they were not single phase strontium hexaferrite.

  7. Structure and magnetic properties of nanocrystalline SrFe12O19 thin films synthesized by the Pechini method

    NASA Astrophysics Data System (ADS)

    Masoudpanah, S. M.; Ebrahimi, S. A. Seyyed

    2013-09-01

    Strontium hexaferrite (SrFe12O19) thin films have been synthesized by the Pechini method. The precursor solutions were prepared with different basic agents such as ammonia, trimethylamine, ethanolamine, diethanolamine. Fourier transform infrared and thermal analyses were conducted to determine the chelated species and phase evolution, respectively. The composition, crystallite size, microstructure and magnetic properties of the SrFe12O19 thin films were evaluated by X-ray diffraction, scanning electron microscope and vibrating sample magnetometer. The film prepared by using ammonia agent offered the largest coercivity of Hc=4790 Oe, while the strontium hexaferrite film prepared with using trimethylamine basic agent exhibited the largest magnetization of Ms=276 emu/cm3, with isotropic magnetic behavior.

  8. Anomalous behavior of B{sub 1g} mode in highly transparent anatase nano-crystalline Nb-doped Titanium Dioxide (NTO) thin films

    SciTech Connect

    Gautam, Subodh K. E-mail: fouran@gmail.com; Ojha, S.; Singh, Fouran E-mail: fouran@gmail.com; Gautam, Naina; Singh, R. G.; Shukla, D. K.

    2015-12-15

    The effect of Niobium doping and size of crystallites on highly transparent nano-crystalline Niobium doped Titanium Dioxide (NTO) thin films with stable anatase phase are reported. The Nb doping concentration is varied within the solubility limit in TiO{sub 2} lattice. Films were annealed in controlled environment for improving the crystallinity and size of crystallites. Elemental and thickness analysis were carried out using Rutherford backscattering spectrometry and cross sectional field emission scanning electron microscopy. Structural characteristics reveal a substitutional incorporation of Nb{sup +5} in the TiO{sub 2} lattice which inhibits the anatase crystallites growth with increasing the doping percentage. The micro-Raman (MR) spectra of films with small size crystallites shows stiffening of about 4 cm{sup −1} for the E{sub g(1)} mode and is ascribed to phonon confinement and non-stoichiometry. In contrast, B{sub 1g} mode exhibits a large anomalous softening of 20 cm{sup −1} with asymmetrical broadening; which was not reported for the case of pure TiO{sub 2} crystallites. This anomalous behaviour is explained by contraction of the apical Ti-O bonds at the surface upon substitutional Nb{sup 5+} doping induced reduction of Ti{sup 4+} ions also known as hetero-coordination effect. The proposed hypotheses is manifested through studying the electronic structure and phonon dynamics by performing the near edge x-ray absorption fine structure (NEXAFS) and temperature dependent MR down to liquid nitrogen temperature on pure and 2.5 at.% doped NTO films, respectively.

  9. Study of the photocatalytic activity of nanocrystalline S, N-codoped TiO2 thin films and powders under visible and sun light irradiation

    NASA Astrophysics Data System (ADS)

    Behpour, Mohsen; Atouf, Vajiheh

    2012-06-01

    Homogeneous and transparent sulfur and nitrogen (S, N)-codoped TiO2 nanocrystalline thin films were deposited on glass substrates by sol gel dip coating method using thiourea (Tu) as a source of sulfur and nitrogen. The surface structure of the films was modified by addition of different concentrations of polyethylene glycol (PEG) into the TiO2 sol. The equal powders of pure and modified TiO2 were also prepared to compare of their photocatalytic activity with films. The films and powders were characterized by different techniques like diffuse reflectance UV-Vis spectroscopy (DRS), X-ray diffraction (XRD) and scanning electron microscopy equipped with energy dispersive X-ray microanalysis (SEM-EDX). DRS exhibited a shift in optical absorption wavelength to visible region and XRD analysis showed that only the anatase TiO2 formed in both of film and powder. The photocatalytic activity was evaluated by the degradation of methyl orange (MO) as a model. The modified TiO2 films and powders showed excellent visible-light photocatalytic ability for the degradation of MO under both irradiation of visible and sun light. So that, up to 96% MO can be decomposed in sun light only within 3 h in the presence of a modified TiO2 film consist of Tu/TiO2 molar ratio of 0.45 and 0.9 g PEG. On the other hand, MO solution was discolored completely under sun light in 75 min in the presence of the modified TiO2 powder.

  10. Highly transparent and reproducible nanocrystalline ZnO and AZO thin films grown by room temperature pulsed-laser deposition on flexible Zeonor plastic substrates

    NASA Astrophysics Data System (ADS)

    Inguva, Saikumar; Vijayaraghavan, Rajani K.; McGlynn, Enda; Mosnier, Jean-Paul

    2015-09-01

    Zeonor plastics are highly versatile due to exceptional optical and mechanical properties which make them the choice material in many novel applications. For potential use in flexible transparent optoelectronic applications, we have investigated Zeonor plastics as flexible substrates for the deposition of highly transparent ZnO and AZO thin films. Films were prepared by pulsed laser deposition at room temperature in oxygen ambient pressures of 75, 150 and 300 mTorr. The growth rate, surface morphology, hydrophobicity and the structural, optical and electrical properties of as-grown films with thicknesses ˜65-420 nm were recorded for the three oxygen pressures. The growth rates were found to be highly linear both as a function of film thickness and oxygen pressure, indicating high reproducibility. All the films were optically smooth, hydrophobic and nanostructured with lateral grain shapes of ˜150 nm wide. This was found compatible with the deposition of condensed nanoclusters, formed in the ablation plume, on a cold and amorphous substrate. Films were nanocrystalline (wurtzite structure), c-axis oriented, with average crystallite size ˜22 nm for ZnO and ˜16 nm for AZO. In-plane compressive stress values of 2-3 GPa for ZnO films and 0.5 GPa for AZO films were found. Films also displayed high transmission greater than 95% in some cases, in the 400-800 nm wavelength range. The low temperature photoluminescence spectra of all the ZnO and AZO films showed intense near band edge emission. A considerable spread from semi-insulating to n-type conductive was observed for the films, with resistivity ˜103 Ω cm and Hall mobility in 4-14 cm2 V-1 s-1 range, showing marked dependences on film thickness and oxygen pressure. Applications in the fields of microfluidic devices and flexible electronics for these ZnO and AZO films are suggested.

  11. The role of the domain size and titanium dopant in nanocrystalline hematite thin films for water photolysis

    NASA Astrophysics Data System (ADS)

    Yan, Danhua; Tao, Jing; Kisslinger, Kim; Cen, Jiajie; Wu, Qiyuan; Orlov, Alexander; Liu, Mingzhao

    2015-11-01

    Here we develop a novel technique for preparing high quality Ti-doped hematite thin films for photoelectrochemical (PEC) water splitting, through sputtering deposition of metallic iron films from an iron target embedded with titanium (dopants) pellets, followed by a thermal oxidation step that turns the metal films into doped hematite. It is found that the hematite domain size can be tuned from ~10 nm to over 100 nm by adjusting the sputtering atmosphere from more oxidative to mostly inert. The better crystallinity at a larger domain size ensures excellent PEC water splitting performance, leading to record high photocurrent from pure planar hematite thin films on FTO substrates. Titanium doping further enhances the PEC performance of hematite photoanodes. The photocurrent is improved by 50%, with a titanium dopant concentration as low as 0.5 atom%. It is also found that the role of the titanium dopant in improving the PEC performance is not apparently related to the films' electrical conductivity which had been widely believed, but is more likely due to the passivation of surface defects by the titanium dopants.Here we develop a novel technique for preparing high quality Ti-doped hematite thin films for photoelectrochemical (PEC) water splitting, through sputtering deposition of metallic iron films from an iron target embedded with titanium (dopants) pellets, followed by a thermal oxidation step that turns the metal films into doped hematite. It is found that the hematite domain size can be tuned from ~10 nm to over 100 nm by adjusting the sputtering atmosphere from more oxidative to mostly inert. The better crystallinity at a larger domain size ensures excellent PEC water splitting performance, leading to record high photocurrent from pure planar hematite thin films on FTO substrates. Titanium doping further enhances the PEC performance of hematite photoanodes. The photocurrent is improved by 50%, with a titanium dopant concentration as low as 0.5 atom%. It is

  12. Nanocrystalline Cu2ZnSnSe4 thin films for solar cells application: Microdiffraction and structural characterization

    NASA Astrophysics Data System (ADS)

    Quiroz, Heiddy P.; Dussan, A.

    2016-08-01

    This work presents a study of the structural characterization of Cu2ZnSnSe4 (CZTSe) thin films by X-ray diffraction (XRD) and microdiffraction measurements. Samples were deposited varying both mass (MX) and substrate temperature (TS) at which the Cu and ZnSe composites were evaporated. CZTSe samples were deposited by co-evaporation method in three stages. From XRD measurements, it was possible to establish, with increased Ts, the presence of binary phases associated with the quaternary composite during the material's growth process. A stannite-type structure in Cu2ZnSnSe4 thin films and sizes of the crystallites varying between 30 and 40 nm were obtained. X-ray microdiffraction was used to investigate interface orientations and strain distributions when deposition parameters were varied. It was found that around the main peak, 2ϴ = 27.1°, the Cu1.8Se and ZnSe binary phases predominate, which are formed during the subsequent material selenization stage. A Raman spectroscopy study revealed Raman shifts associated with the binary composites observed via XRD.

  13. The role of the domain size and titanium dopant in nanocrystalline hematite thin films for water photolysis

    DOE PAGESBeta

    Yan, Danhua; Tao, Jing; Kisslinger, Kim; Cen, Jiajie; Wu, Qiyuan; Orlov, Alexander; Liu, Mingzhao

    2015-10-13

    In this study, we develop a novel technique for preparing high quality Ti-doped hematite thin films for photoelectrochemical (PEC) water splitting, through sputtering deposition of metallic iron films from an iron target embedded with titanium (dopants) pellets, followed by a thermal oxidation step that turns the metal films into doped hematite. It is found that the hematite domain size can be tuned from ~10 nm to over 100 nm by adjusting the sputtering atmosphere from more oxidative to mostly inert. The better crystallinity at a larger domain size ensures excellent PEC water splitting performance, leading to record high photocurrent frommore » pure planar hematite thin films on FTO substrates. Titanium doping further enhances the PEC performance of hematite photoanodes. The photocurrent is improved by 50%, with a titanium dopant concentration as low as 0.5 atom%. It is also found that the role of the titanium dopant in improving the PEC performance is not apparently related to the films’ electrical conductivity which had been widely believed, but is more likely due to the passivation of surface defects by the titanium dopants.« less

  14. Effect of annealing on the properties of nanocrystalline CuInSSe thin films deposited by spray pyrolysis

    SciTech Connect

    Shrotriya, Vipin Rajaram, P.

    2015-08-28

    The effect of annealing CuInSSe thin films, which were grown on glass substrates using the spray pyrolysis technique from spray solutions having S/Se ionic ratio 0.6, were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical transmission measurements. The CuInSSe films were co-deposited from an aqueous solution containing CuCl{sub 2}, InCl{sub 3}, thiourea and SeO{sub 2}. EDC was used as a complexing agent and films were deposited at the constant temperature 300°C. Post annealing (at 350°C) was used to improve the structural, morphological and optical properties of CuInSSe thin films. From the results, it is found that the films are single phase, p-type in conductivity having the chalcopyrite structure. From the Scherrer formula the average size of the films was found to be in the range (15-28) nm. Optical studies show that the optical band gap value increases slightly from 1.35 eV to 1.37 eV with annealing for films grown from spray solutions having S/Se ionic ratio 0.6.

  15. The role of the domain size and titanium dopant in nanocrystalline hematite thin films for water photolysis

    SciTech Connect

    Yan, Danhua; Tao, Jing; Kisslinger, Kim; Cen, Jiajie; Wu, Qiyuan; Orlov, Alexander; Liu, Mingzhao

    2015-10-13

    In this study, we develop a novel technique for preparing high quality Ti-doped hematite thin films for photoelectrochemical (PEC) water splitting, through sputtering deposition of metallic iron films from an iron target embedded with titanium (dopants) pellets, followed by a thermal oxidation step that turns the metal films into doped hematite. It is found that the hematite domain size can be tuned from ~10 nm to over 100 nm by adjusting the sputtering atmosphere from more oxidative to mostly inert. The better crystallinity at a larger domain size ensures excellent PEC water splitting performance, leading to record high photocurrent from pure planar hematite thin films on FTO substrates. Titanium doping further enhances the PEC performance of hematite photoanodes. The photocurrent is improved by 50%, with a titanium dopant concentration as low as 0.5 atom%. It is also found that the role of the titanium dopant in improving the PEC performance is not apparently related to the films’ electrical conductivity which had been widely believed, but is more likely due to the passivation of surface defects by the titanium dopants.

  16. Nanocrystalline diamond thin films on titanium-6 aluminum-4 vanadium alloy temporomandibular joint prosthesis simulants by microwave plasma chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Fries, Marc Douglas

    A course of research has been performed to assess the suitability of nanocrystal-line diamond (NCD) films on Ti-6Al-4V alloy as wear-resistant coatings in biomedical implant use. A series of temporomandibular (TMJ) joint condyle simulants were polished and acid-passivated as per ASTM F86 standard for surface preparation of implants. A 3-mum-thick coating of NCD film was deposited by microwave plasma chemical vapor deposition (MPCVD) over the hemispherical articulation surfaces of the simulants. Plasma chemistry conditions were measured and monitored by optical emission spectroscopy (OES), using hydrogen as a relative standard. The films consist of diamond grains around 20 nm in diameter embedded in an amorphous carbon matrix, free of any detectable film stress gradient. Hardness averages 65 GPa and modulus measures 600 GPa at a depth of 250 nm into the film surface. A diffuse film/substrate boundary produces a minimal film adhesion toughness (GammaC) of 158 J/m2. The mean RMS roughness is 14.6 +/- 4.2 nm, with an average peak roughness of 82.6 +/- 65.9 nm. Examination of the surface morphology reveals a porous, dendritic surface. Wear testing resulted in two failed condylar coatings out of three tests. No macroscopic delamination was found on any sample, but micron-scale film pieces broke away, exposing the substrate. Electrochemical corrosion testing shows a seven-fold reduction in corrosion rate with the application of an NCD coating as opposed to polished, passivated Ti-6Al-4V, producing a corrosion rate comparable to wrought Co-Cr-Mo. In vivo biocompatibility testing indicates that implanted NCD films did not elicit an immune response in the rabbit model, and osteointegration was apparent for both compact and trabecular bone on both NCD film and bare Ti-6Al-4V. Overall, NCD thin film material is reasonably smooth, biocompatible, and very well adhered. Wear testing indicates that this material is unacceptable for use in demanding TMJ applications without

  17. Study of transparent conductive oxides and back reflectors for amorphous and nano-crystalline silicon based thin film solar cells

    NASA Astrophysics Data System (ADS)

    Yang, Xiesen

    2007-12-01

    In this dissertation, back reflectors (BR) for hydrogenated amorphous silicon (a-Si:H) and hydrogenated nanocrystalline silicon (nc-Si:H) based solar cells have been systematically studied. The main results achieved in the dissertation are as follows: (1) By using the optical scattering theory and PVOPTICS simulation program, it is found that to characterize the texture of the BR, not only the texture height, but also the texture angle (which is usually not mentioned in the literature) is needed. Moreover, the optical scattering of a rough surface is mainly determined by the texture angle. Experimentally the texture angle has been calculated from the raw AFM data for our BR samples using a FORTRAN program. (2) It has been deduced in this dissertation that the light trapping scheme with ideal rough BR should have an effective light path enhancement factor of n(n+1)2 in the absorption media (with refractive index n), rather than 4n2, the generally quoted value in references. In the case of Si as the absorption media this factor could be 25% larger than 4n2. (3) The optical and textural properties of Al and Ag have been studied. The results obtained show that Ag film has an improved reflectance in the long wavelength range and 5 times higher deposition rate than Al films deposited at the same conditions. It is found that Ag films have random orientation and are difficult to get a large texture angle and height profile; so in order to get enough texture for application in solar cells Ag needs a high deposition temperature (Ts) of 300 ˜ 400°C. In contrast, Al films have preferred (111) orientation and are easy to get large texture angle and height profiles. The impacts of deposition rate on the morphology of Ag and Al films have also been compared. (4) On the basis of understanding of the optical and textural properties of Al and Ag, a stacked configuration of ZnO/Ag/Al BR has been studied. It shows a high total reflectance comparable to ZnO/Ag structure and a high

  18. Structural and mechanical properties changes induced in nanocrystalline ZrC thin films by Ar ion irradiation

    NASA Astrophysics Data System (ADS)

    Craciun, D.; Socol, G.; Simeone, D.; Behdad, S.; Boesl, B.; Vasile, B. S.; Craciun, V.

    2016-01-01

    Thin ZrC films (<500 nm), grown on (100) Si substrates at a substrate temperature of 500 °C by the pulsed laser deposition (PLD) technique using a KrF excimer laser, were irradiated by 800 keV Ar ion at room temperature under a fixed flux of 1011 cm2 s-1 with fluences ranging from 1 × 1014 at/cm2 to 2 × 1015 at/cm2. Glancing incidence X-ray diffraction, X-ray reflectivity, transmission electron microscopy and nanoindentation investigations were used to study the structural modifications in the films' density, composition and mechanical properties induced by irradiation. After irradiation, the lattice parameter and crystallite size slightly increased, while the films' density decreased. Significant decreases in nanohardness and Young modulus values were also measured after irradiation at 1 × 1014 at/cm2 and 1 × 1015 at/cm2 fluences. No further major decreases were observed for a fluence of 2 × 1015 at/cm2. Scanning transmission electron microscopy and energy dispersive X-ray analysis showed a decrease in the Zr/C values in the irradiated film from surface towards the Si substrate.

  19. Influence of sputtering power on structural, mechanical and photoluminescence properties of nanocrystalline SiC thin films

    NASA Astrophysics Data System (ADS)

    Singh, Narendra; Kaur, Davinder

    2016-05-01

    In the present study, SiC thin films were deposited on Si (100) substrate by magnetron sputtering using a 4N purity commercial SiC target in argon atmosphere. The effect of sputtering RF power (140-170W) on structural, mechanical and photoluminescence properties were systematically studied by X-ray diffraction, field emission scanning electron microscopy, Nanoindentation and Spectrophotometer respectively. X-ray diffraction shows polycrystalline 4H-SiC phase with (105) preferred orientation and an enhancement in crystallite size with increasing power was also observed. The decrement in hardness and Young's modulus with increment in RF power was ascribed to Hall-Petch relation. The maximum hardness and Young's modulus were found to be 32 GPa and 232 GPa respectively. The photoluminescence spectra show peaks at 384 nm (3.22 eV) which corresponds to bandgap of 4H-SiC (phonon assisted band to band recombination) and 416 nm (2.99 eV) may be attributed to defect states and intensity of both peaks decreases as power increases.

  20. Nanocrystalline spin coated sol-gel hydroxyapatite thin films on Ti substrate: Towards potential applications for implants

    NASA Astrophysics Data System (ADS)

    Carradò, Adele; Viart, Nathalie

    2010-07-01

    Sol-gel spin coating is a promising process to obtain hydroxyapatite (HA) thin films. It is an alternative route to the hydroxyapatite deposition techniques usually employed to cover orthopaedic or dental titanium implant surfaces. The sol-gel (SG) parameters leading to a pure and crystalline HA coatings on Ti substrate were determined. They allow to reach a stoichiometric hydroxyapatite composition (ideal Ca/P atomic ratio 1.67) and a control of the growth of the crystalline phases. The samples, when observed by Scanning Electron Microscopy (SEM), exhibit grains of ca. 200 nm, well adapted for cell proliferation. The crystallisation of the HA films was thoroughly studied by X-Ray diffraction (XRD). The aim of this paper is to validate the sol-gel method as a processing method allowing the control of the mechanical state of the films and, in particular, of the residual stresses (RS) at metal-ceramic interfaces. These stresses were determined on titanium substrates. While the uncoated Ti substrates were in a compressive residual state, the coated ones were in a low tensile state. These results suggest that the sol-gel process is indeed a processing route to obtain HA coated Ti implants.

  1. Influence of annealing temperature on structural and optical properties of nanocrystalline Platinum octaethylporphyrin (PtOEP) thin films

    NASA Astrophysics Data System (ADS)

    Abuelwafa, A. A.; El-Denglawey, A.; Dongol, M.; El-Nahass, M. M.; Soga, T.

    2015-11-01

    Thermal evaporation technique was used to prepare the Platinum octaethylporphyrin (PtOEP) thin films at room temperature. The deposited films were studied before and after thermal annealing at 373 and 473 K for 3 h under vacuum (10-3 Pa). The film structure, surface morphologies and molecular structure were investigated as a function of annealing temperature by X-ray Diffraction (XRD), Field-Emission Scanning Electron Microscopy (FESEM) and Fourier-transform infrared techniques (FT-IR) respectively. The results confirmed that the as-deposited and annealed films have nanostructural features. Optical constants of the as-deposited and annealed films have been obtained in the wavelength range 200-1100 nm by using spectrophotometric measurements. Analysis of the spectra of absorption coefficient showed indirect allowed transition and optical energy gap found to decrease with increase in annealing temperature. The dispersion of refractive index at the normal dispersion (λ > 600 nm) was discussed in terms of single oscillator model of Wemple-Didomenico. Based on generalized Miller's rule the third order non-linear susceptibility, χ(3) and nonlinear refractive index, n2 were estimated and studied at lower photon energy and showing lower value for the annealed film.

  2. Formation of Cu x Au1- x phases by cold homogenization of Au/Cu nanocrystalline thin films.

    PubMed

    Tynkova, Alona; Katona, Gabor L; Langer, Gabor A; Sidorenko, Sergey I; Voloshko, Svetlana M; Beke, Dezso L

    2014-01-01

    It is shown, by using depth profiling with a secondary neutral mass spectrometer and structure investigations by XRD and TEM, that at low temperatures, at which the bulk diffusion is frozen, a complete homogenization can take place in the Cu/Au thin film system, which leads to formation of intermetallic phases. Different compounds can be formed depending on the initial thickness ratio. The process starts with grain boundary interdiffusion, which is followed by a formation of reaction layers at the grain boundaries that leads to the motion of the newly formed interfaces perpendicular to the grain boundary plane. Finally, the homogenization finishes when all the pure components have been consumed. The process is asymmetric: It is faster in the Au layer. In Au(25nm)/Cu(50nm) samples the final state is the ordered AuCu3 phase. Decrease of the film thicknesses, as expected, results in the acceleration of the process. It is also illustrated that changing the thickness ratio either a mixture of Cu-rich AuCu and AuCu3 phases (in Au(25nm)/Cu(25nm) sample), or a mixture of disordered Cu- as well as Au-rich solid solutions (in Au(25nm)/Cu(12nm) sample) can be produced. By using a simple model the interface velocity in both the Cu and Au layers were estimated from the linear increase of the average composition and its value is about two orders of magnitude larger in Au (ca. 10(-11) m/s) than in Cu (ca. 10(-13) m/s). PMID:25247132

  3. Formation of CuxAu1− x phases by cold homogenization of Au/Cu nanocrystalline thin films

    PubMed Central

    Tynkova, Alona; Katona, Gabor L; Langer, Gabor A; Sidorenko, Sergey I; Voloshko, Svetlana M

    2014-01-01

    Summary It is shown, by using depth profiling with a secondary neutral mass spectrometer and structure investigations by XRD and TEM, that at low temperatures, at which the bulk diffusion is frozen, a complete homogenization can take place in the Cu/Au thin film system, which leads to formation of intermetallic phases. Different compounds can be formed depending on the initial thickness ratio. The process starts with grain boundary interdiffusion, which is followed by a formation of reaction layers at the grain boundaries that leads to the motion of the newly formed interfaces perpendicular to the grain boundary plane. Finally, the homogenization finishes when all the pure components have been consumed. The process is asymmetric: It is faster in the Au layer. In Au(25nm)/Cu(50nm) samples the final state is the ordered AuCu3 phase. Decrease of the film thicknesses, as expected, results in the acceleration of the process. It is also illustrated that changing the thickness ratio either a mixture of Cu-rich AuCu and AuCu3 phases (in Au(25nm)/Cu(25nm) sample), or a mixture of disordered Cu- as well as Au-rich solid solutions (in Au(25nm)/Cu(12nm) sample) can be produced. By using a simple model the interface velocity in both the Cu and Au layers were estimated from the linear increase of the average composition and its value is about two orders of magnitude larger in Au (ca. 10−11 m/s) than in Cu (ca. 10−13 m/s). PMID:25247132

  4. Dye-sensitized solar cell using sprayed ZnO nanocrystalline thin films on ITO as photoanode.

    PubMed

    Dhamodharan, P; Manoharan, C; Dhanapandian, S; Venkatachalam, P

    2015-02-01

    ZnO thin films had been successfully prepared by spray pyrolysis (SP) technique on ITO/Glass substrates at different substrate temperature in the range 250-400°C using Zinc acetylacetonate as precursor. The X-ray diffraction studies confirmed the hexagonal wurtzite structure with preferred orientation along (002) plane at substrate temperature 350°C and the crystallite size was found to vary from 18 to 47nm. The morphology of the films revealed the porous nature with the roughness value of 8-13nm. The transmittance value was found to vary from 60% to 85% in the visible region depending upon the substrate temperature and the band gap value for the film deposited at 350°C was 3.2eV. The obtained results revealed that the structures and properties of the films were greatly affected by substrate temperature. The near band edge emission observed at 398nm in PL spectra showed better crystallinity. The measured electrical resistivity for ZnO film was ∼3.5×10(-4)Ωcm at the optimized temperature 350°C and was of n-type semiconductor. The obtained porous nature with increased surface roughness of the film and good light absorbing nature of the dye paved way for implementation of quality ZnO in DSSCs fabrication. DSSC were assembled using the prepared ZnO film on ITO coated glass substrate as photoanode and its photocurrent - voltage performance was investigated. PMID:25459731

  5. Dye-sensitized solar cell using sprayed ZnO nanocrystalline thin films on ITO as photoanode

    NASA Astrophysics Data System (ADS)

    Dhamodharan, P.; Manoharan, C.; Dhanapandian, S.; Venkatachalam, P.

    2015-02-01

    ZnO thin films had been successfully prepared by spray pyrolysis (SP) technique on ITO/Glass substrates at different substrate temperature in the range 250-400 °C using Zinc acetylacetonate as precursor. The X-ray diffraction studies confirmed the hexagonal wurtzite structure with preferred orientation along (0 0 2) plane at substrate temperature 350 °C and the crystallite size was found to vary from 18 to 47 nm. The morphology of the films revealed the porous nature with the roughness value of 8-13 nm. The transmittance value was found to vary from 60% to 85% in the visible region depending upon the substrate temperature and the band gap value for the film deposited at 350 °C was 3.2 eV. The obtained results revealed that the structures and properties of the films were greatly affected by substrate temperature. The near band edge emission observed at 398 nm in PL spectra showed better crystallinity. The measured electrical resistivity for ZnO film was ∼3.5 × 10-4 Ω cm at the optimized temperature 350 °C and was of n-type semiconductor. The obtained porous nature with increased surface roughness of the film and good light absorbing nature of the dye paved way for implementation of quality ZnO in DSSCs fabrication. DSSC were assembled using the prepared ZnO film on ITO coated glass substrate as photoanode and its photocurrent - voltage performance was investigated.

  6. Nanocrystalline ceramic materials

    DOEpatents

    Siegel, Richard W.; Nieman, G. William; Weertman, Julia R.

    1994-01-01

    A method for preparing a treated nanocrystalline metallic material. The method of preparation includes providing a starting nanocrystalline metallic material with a grain size less than about 35 nm, compacting the starting nanocrystalline metallic material in an inert atmosphere and annealing the compacted metallic material at a temperature less than about one-half the melting point of the metallic material.

  7. Photo-electrochemical studies of chemically deposited nanocrystalline meso-porous n-type TiO2 thin films for dye-sensitized solar cell (DSSC) using simple synthesized azo dye

    NASA Astrophysics Data System (ADS)

    Ezema, C. G.; Nwanya, A. C.; Ezema, B. E.; Patil, B. H.; Bulakhe, R. N.; Ukoha, P. O.; Lokhande, C. D.; Maaza, Malik; Ezema, Fabian I.

    2016-04-01

    Nanocrystalline titanium dioxide (TiO2) thin films were deposited by successive ionic layer adsorption and reaction method onto fluorine doped tin oxide coated glass substrate at room temperature (300 K). Titanium trichloride and sodium hydroxide were used as cationic and anionic sources, respectively. The as-deposited and annealed films were characterized for structural, morphological, optical, electrical and wettability properties. The photoelectrochemical study of TiO2 sensitized with a laboratory synthesized organic dye (azo) was evaluated in the polyiodide electrolyte at 40 mW cm-2 light illumination intensity. The photovoltaic characteristics show a fill factor of 0.24 and solar conversion efficiency value of 0.032 % for a TiO2 thickness of 0.96 µm as compared to efficiency of 0.014 % for rose Bengal of the same thickness.

  8. Biomolecule-mediated synthesis of nanocrystalline semiconductors

    NASA Astrophysics Data System (ADS)

    Bae, Weon

    CdS and ZnS nanocrystalline semiconductors (NCs) were prepared by titrating inorganic sulfide into preformed Cd(II)- or Zn(II)-complexes of phytochelatins, glutathione or cysteine. This strategy resulted in the formation NCs capped by the chosen biomolecule. The range of sizes and their distributions depended primarily on the quantity of sulfide titrated and the biomolecule chosen for the initial metallo-complex. The processes of NC formation were studied by absorption and fluorescence spectrophotometry. The size distribution was analyzed by gel permeation chromatography. Ethanol precipitation of NCs under aqueous conditions was used to isolate nanoparticles within a very narrow size-range. Reduction of selected dyes was also studied on the surfaces of NCs. Glutathione-capped CdS nanoparticles exhibited significant size heterogeneity even at a single sulfide titration. In contrast, phytochelatins showed much less dispersion in size at a given sulfide titration. Phytochelatins could replace glutathione without changing the size of glutathione-capped CdS nanoparticles. Cysteine appeared to be intermediate between glutathione and phytochelatins in the formation of CdS nanoparticles. The calculated radii, using an effective mass approximation method, were 10.8-17.3, 10.6-11.8, and 13.5-15.5A for glutathione-, phytochelatin-, and cysteine-capped CdS nanoparticles, respectively. Cysteine-capped ZnS showed narrower size distribution than glutathione-capped ZnS. However, elevated temperatures were necessary to accomplish optimal yields of cysteine-capped ZnS NCs. An additional control over the size distribution of NCs was achieved by size-selective precipitation with ethanol. These procedures led to the isolation of nanoparticles that were more uniform in size and chemical compositions as determined by spectroscopic and chemical analyses of size-fractionated samples. Precipitation also allowed preparation of large quantities of powdered nanoparticles that could be

  9. Formation of high electrical-resistivity thin surface layer on carbonyl-iron powder (CIP) and thermal stability of nanocrystalline structure and vortex magnetic structure of CIP

    NASA Astrophysics Data System (ADS)

    Sugimura, K.; Miyajima, Y.; Sonehara, M.; Sato, T.; Hayashi, F.; Zettsu, N.; Teshima, K.; Mizusaki, H.

    2016-05-01

    This study focuses on the carbonyl-iron powder (CIP) used in the metal composite bulk magnetic core for high-efficient/light-weight SiC/GaN power device MHz switching dc-dc converter, where the fine CIP with a mean diameter of 1.1 μm is used to suppress the MHz band eddy current inside the CIP body. When applying the CIP to composite core together with the resin matrix, high electrical resistivity layer must be formed on the CIP-surface in order to suppress the overlapped eddy current between adjacent CIPs. In this study, tens nm thick silica (SiO2) was successfully deposited on the CIP-surface by using hydrolysis of TEOS (Si(OC2H5)4). Also tens nm thick oxidized layer of the CIP-surface was successfully formed by using CIP annealing in dry air. The SiC/GaN power device can operate at ambient temperature over 200 degree-C, and the composite magnetic core is required to operate at such ambient temperature. The as-made CIP had small coercivity below 800 A/m (10 Oe) due to its nanocrystalline-structure and had a single vortex magnetic structure. From the experimental results, both nanocrystalline and single vortex magnetic structure were maintained after heat-exposure of 250 degree-C, and the powder coercivity after same heat-exposure was nearly same as that of the as-made CIP. Therefore, the CIP with thermally stable nanocrystalline-structure and vortex magnetic state was considered to be heat-resistant magnetic powder used in the iron-based composite core for SiC/GaN power electronics.

  10. Nanocrystalline ceramic materials

    DOEpatents

    Siegel, R.W.; Nieman, G.W.; Weertman, J.R.

    1994-06-14

    A method is disclosed for preparing a treated nanocrystalline metallic material. The method of preparation includes providing a starting nanocrystalline metallic material with a grain size less than about 35 nm, compacting the starting nanocrystalline metallic material in an inert atmosphere and annealing the compacted metallic material at a temperature less than about one-half the melting point of the metallic material. 19 figs.

  11. Optical Properties of ZnO-Alloyed Nanocrystalline Films

    DOE PAGESBeta

    Che, Hui; Huso, Jesse; Morrison, John L.; Thapa, Dinesh; Huso, Michelle; Yeh, Wei Jiang; Tarun, M. C.; McCluskey, M. D.; Bergman, Leah

    2012-01-01

    ZnO is emore » merging as one of the materials of choice for UV applications. It has a deep excitonic energy level and a direct bandgap of ~3.4 eV. Alloying ZnO with certain atomic constituents adds new optical and electronic functionalities to ZnO. This paper presents research on M g x Z n 1 − x O and Z n S 1 − x O x nanocrystalline flexible films, which enable tunable optical properties in the deep-UV and in the visible range. The ZnO and Mg 0 .3 Zn 0 .7 O films were found to have bandgaps at 3.35 and 4.02 eV, respectively. The photoluminescence of the Mg 0 .3 Zn 0 .7 O exhibited a bandedge emission at 3.95 eV, and at lower energy 3.38 eV due to the limited solubility inherent to these alloys. ZnS 0 .76 O 0 .24 and ZnS 0 .16 O 0 .84 were found to have bandgaps at 3.21 and 2.65 eV, respectively. The effect of nitrogen doping on ZnS 0 .16 O 0 .84 is discussed in terms of the highly lattice mismatched nature of these alloys and the resulting valence-band modification.« less

  12. Surface plasmon resonance in nanostructured Ag incorporated ZnS films

    SciTech Connect

    Chalana, S. R.; Mahadevan Pillai, V. P.; Ganesan, V.

    2015-10-15

    Silver incorporated zinc sulfide thin films are prepared by RF magnetron sputtering technique and the influence of silver incorporation on the structural, optical and luminescence properties is analyzed using techniques like grazing incidence X-Ray diffraction (GIXRD), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), micro-Raman spectroscopy, UV-Vis spectroscopy and laser photoluminescence spectroscopy. XRD analysis presents hexagonal wurtzite structure for the films. A reduction of crystallinity of the films is observed due to Ag incorporation. The Raman spectral analysis confirms the reduction of crystallinity and increase of strain due to the Ag incorporation. AFM analysis reveals a rough surface morphology for the undoped film and Ag incorporation makes the films uniform, dense and smooth. A blue shift of band gap energy with increase in Ag incorporation is observed due to quantum confinement effect. An absorption band (450-650 nm region) due to surface plasmon resonance of the Ag clusters present in the ZnS matrix is observed for the samples with higher Ag incorporation. The complex dielectric constant, loss factor and distribution of volume and surface energy loss of the ZnS thin films are calculated. Laser photoluminescence measurements gives an intense bluish green emission from the ZnS films and a quenching of the PL emission is observed which can be due to the metal plasmonic absorption and non-radiative energy transfer due to Ag incorporation.

  13. Nanocrystalline cobalt oxides for carbon nanotube growth

    NASA Astrophysics Data System (ADS)

    Guo, Kun; Jayatissa, Ahalapitiya H.; Jayasuriya, Ambalangodage C.

    2007-09-01

    Thin Films of nanocrystalline cobalt oxide were formed by sol-gel method. Structure, optical properties and surface properties of these films were investigated by numerous characterization techniques. These films were successfully fabricated on glass substrates below 500°C. . Micropatterns of cobalt oxide thin films were also fabricated on glass and silicon substrates by employing a lift-off method. Crystal size of these nanocrystalline cobalt films could be successfully controllable by varying the amount of cobalt precursors and number of layers. These films were used as the seeding layers for carbon nanotube growth in a CVD process By changing the concentration of monomer precursors in the solgel coating solutions, different size nanoclusters hence different size carbon nanotubes could be synthesized in CVD process. This method can be used for controlled growth of carbon nanotubes for many different applications. In this paper, detail of these experimental results will be presented.

  14. Nano-crystalline thin and nano-particulate thick TiO{sub 2} layer: Cost effective sequential deposition and study on dye sensitized solar cell characteristics

    SciTech Connect

    Das, P.; Sengupta, D.; Kasinadhuni, U.; Mondal, B.; Mukherjee, K.

    2015-06-15

    Highlights: • Thin TiO{sub 2} layer is deposited on conducting substrate using sol–gel based dip coating. • TiO{sub 2} nano-particles are synthesized using hydrothermal route. • Thick TiO{sub 2} particulate layer is deposited on prepared thin layer. • Dye sensitized solar cells are made using thin and thick layer based photo-anode. • Introduction of thin layer in particulate photo-anode improves the cell efficiency. - Abstract: A compact thin TiO{sub 2} passivation layer is introduced between the mesoporous TiO{sub 2} nano-particulate layer and the conducting glass substrate to prepare photo-anode for dye-sensitized solar cell (DSSC). In order to understand the effect of passivation layer, other two DSSCs are also developed separately using TiO{sub 2} nano-particulate and compact thin film based photo-anodes. Nano-particles are prepared using hydrothermal synthesis route and the compact passivation layer is prepared by simply dip coating the precursor sol prepared through wet chemical route. The TiO{sub 2} compact layer and the nano-particles are characterised in terms of their micro-structural features and phase formation behavior. It is found that introduction of a compact TiO{sub 2} layer in between the mesoporous TiO{sub 2} nano-particulate layer and the conducting substrate improves the solar to electric conversion efficiency of the fabricated cell. The dense thin passivation layer is supposed to enhance the photo-excited electron transfer and prevent the recombination of photo-excited electrons.

  15. Creating bulk nanocrystalline metal.

    SciTech Connect

    Fredenburg, D. Anthony; Saldana, Christopher J.; Gill, David D.; Hall, Aaron Christopher; Roemer, Timothy John; Vogler, Tracy John; Yang, Pin

    2008-10-01

    Nanocrystalline and nanostructured materials offer unique microstructure-dependent properties that are superior to coarse-grained materials. These materials have been shown to have very high hardness, strength, and wear resistance. However, most current methods of producing nanostructured materials in weapons-relevant materials create powdered metal that must be consolidated into bulk form to be useful. Conventional consolidation methods are not appropriate due to the need to maintain the nanocrystalline structure. This research investigated new ways of creating nanocrystalline material, new methods of consolidating nanocrystalline material, and an analysis of these different methods of creation and consolidation to evaluate their applicability to mesoscale weapons applications where part features are often under 100 {micro}m wide and the material's microstructure must be very small to give homogeneous properties across the feature.

  16. Optical constants, dispersion energy parameters and dielectric properties of ultra-smooth nanocrystalline BiVO4 thin films prepared by rf-magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Sarkar, S.; Das, N. S.; Chattopadhyay, K. K.

    2014-07-01

    BiVO4 thin films have been prepared through radio frequency (rf) magnetron sputtering of a pre-fabricated BiVO4 target on ITO coated glass (ITO-glass) substrate and bare glass substrates. BiVO4 target material was prepared through solid-state reaction method by heating Bi2O3 and V2O5 mixture at 800 °C for 8 h. The films were characterized by X-ray diffraction, UV-Vis spectroscopy, LCR meter, field emission scanning electron microscopy, transmission electron microscopy and atomic force microscopy. BiVO4 thin films deposited on the ITO-glass substrate are much smoother compared to the thin films prepared on bare glass substrate. The rms surface roughness calculated from the AFM images comes out to be 0.74 nm and 4.2 nm for the films deposited on the ITO-glass substrate and bare glass substrate for the deposition time 150 min respectively. Optical constants and energy dispersion parameters of these extra-smooth BiVO4 thin films have been investigated in detail. Dielectric properties of the BiVO4 thin films on ITO-glass substrate were also investigated. The frequency dependence of dielectric constant of the BiVO4 thin films has been measured in the frequency range from 20 Hz to 2 MHz. It was found that the dielectric constant increased from 145 to 343 at 20 Hz as the film thickness increased from 90 nm to 145 nm (deposition time increased from 60 min to 150 min). It shows higher dielectric constant compared to the literature value of BiVO4.

  17. Influence of helium dilution of silane on microstructure and opto-electrical properties of hydrogenated nanocrystalline silicon (nc-Si:H) thin films deposited by HW-CVD

    SciTech Connect

    Waman, V.S.; Kamble, M.M.; Ghosh, S.S.; Hawaldar, R.R.; Amalnerkar, D.P.; Sathe, V.G.; Gosavi, S.W.; Jadkar, S.R.

    2012-11-15

    Highlights: ► nc-Si:H films synthesized using HW-CVD method from silane and helium gas mixture without hydrogen. ► Volume fraction of crystallites and its size in the films decreases with increase in He dilution of SiH{sub 4}. ► Increase in Urbach energy and defect density with increase in He dilution of SiH{sub 4}. ► Increasing He dilution, hydrogen bonding in the films shifts from Si-H{sub 2} and (Si-H{sub 2}){sub n} complexes to Si-H. ► Hydrogen content films were found to be <2.2 at.% but the bandgap remains as high as 2.0 eV or even more. -- Abstract: We report influence of helium dilution of silane in hot wire chemical vapor deposition for hydrogenated nano-crystalline silicon films. Structural properties of these films have been investigated by using Raman spectroscopy, low angle x-ray diffraction, Fourier transform infra-red spectroscopy and non-contact atomic force microscopy. Optical characterization has been performed by UV–visible spectroscopy. It has been observed that in contrast to conventional plasma enhanced chemical vapor deposition, the addition of helium with silane in hot wire chemical vapor deposition has an adverse effect on the crystallinity and the material properties. Hydrogen content in the films was found <2.2 at.% whereas the bandgap remain as high as 2 eV or more. Increase in Urbach energy and defect density also suggests the deterioration effect of helium on material properties. The possible reasons for the deterioration of crystallinity and the material properties have been discussed.

  18. In situ spectroelectrochemical and theoretical study on the oxidation of a 4H-imidazole-ruthenium dye adsorbed on nanocrystalline TiO2 thin film electrodes.

    PubMed

    Zhang, Ying; Kupfer, Stephan; Zedler, Linda; Schindler, Julian; Bocklitz, Thomas; Guthmuller, Julien; Rau, Sven; Dietzek, Benjamin

    2015-11-28

    Terpyridine 4H-imidazole-ruthenium(II) complexes are considered promising candidates for use as sensitizers in dye sensitized solar cells (DSSCs) by displaying broad absorption in the visible range, where the dominant absorption features are due to metal-to-ligand charge transfer (MLCT) transitions. The ruthenium(III) intermediates resulting from photoinduced MLCT transitions are essential intermediates in the photoredox-cycle of the DSSC. However, their photophysics is much less studied compared to the ruthenium(II) parent systems. To this end, the structural alterations accompanying one-electron oxidation of the RuIm dye series (including a non-carboxylic RuIm precursor, and, carboxylic RuImCOO in solution and anchored to a nanocrystalline TiO2 film) are investigated via in situ experimental and theoretical UV-Vis absorption and resonance Raman (RR) spectroelectrochemistry. The excellent agreement between the experimental and the TDDFT spectra derived in this work allows for an in-depth assignment of UV-Vis and RR spectral features of the dyes. A concordant pronounced wavelength dependence with respect to the charge transfer character has been observed for the model system RuIm, and both RuImCOO in solution and attached on the TiO2 surface. Excitation at long wavelengths leads to the population of ligand-to-metal charge transfer states, i.e. photoreduction of the central ruthenium(III) ion, while high-energy excitation features an intra-ligand charge transfer state localized on the 4H-imidazole moiety. Therefore, these 4H-imidazole ruthenium complexes investigated here are potential multi-photoelectron donors. One electron is donated from MLCT states, and additionally, the 4H-imidazole ligand reveals electron-donating character with a significant contribution to the excited states of the ruthenium(III) complexes upon blue-light irradiation. PMID:26478575

  19. Luminescent Processes Elucidated by Simple Experiments on ZnS.

    ERIC Educational Resources Information Center

    Schwankner, R.; And Others

    1981-01-01

    Describes some impurity-related optical properties of semiconductors, with special emphasis on the luminescence of zinc sulfide (ZnS). Presents and interprets five experiments using a ZnS screen, ultraviolet lamp, transparent Dewar liquid nitrogen, and a helium/neon gas base. Includes application of luminescence measurements to archaeology. (SK)

  20. Efficient preparation of nanocrystalline anatase TiO{sub 2} and V/TiO{sub 2} thin layers using microwave drying and/or microwave calcination technique

    SciTech Connect

    Zabova, H.; Sobek, J.; Cirkva, V.; Solcova, O.; Kment, S.; Hajek, M.

    2009-12-15

    This study has demonstrated that the synthesis of TiO{sub 2} and V/TiO{sub 2} thin layers may be significantly improved and extended if microwave energy is employed during the drying and/or calcination step. Thin nanoparticulate titania layers were prepared via the sol-gel method using titanium n-butoxide as a precursor. As prepared films were then analyzed by means of various characterization techniques (Raman spectroscopy, UV/Vis, AFM, XPS) in order to determine their functional properties. The photocatalytic activities of prepared layers were quantified by the decoloring rate of Rhodamine B. All thermal treatments in microwave field were done in the same manner, by using an IR pyrometer in the microwave oven and monitoring the temperature of the heating. Nevertheless the microwave and thermally prepared materials were different. This in turn may lead to differences in their functional and also photocatalytic properties. - Graphical abstract: This study has demonstrated that the synthesis of thin layers may be improved and extended if microwave energy is employed during the preparation process. Microwave processing has the potential to reduce the time, cost and energy input for the production of thin layers.

  1. Optical properties of ZnS1-xSex alloys fabricated by plasma-induced isoelectronic substitution

    NASA Astrophysics Data System (ADS)

    Rujkorakarn, Rong; Nelson, Art J.

    2000-06-01

    Nonequilibrium growth of thin-film ternary ZnS1-xSex semiconductor alloys was accomplished using physical vapor deposition with simultaneous electron cyclotron resonance H2S plasma activation. Substrate temperature, gas flow, and plasma power determine the ZnS1-xSex alloy composition and structure. Integrated optical transmission spectra for the ZnS1-xSex semiconductor alloys as a function of H2S plasma power are presented. Using the α2 vs hν plots for the various ZnS1-xSex films, the optical band gap Eg is extrapolated from each curve. This methodology yields the values of the band gap as a function of stoichiometry. We observe that the plasma induced isoelectronic substitution of S into the ZnSe lattice increases the band gap. This study shows that plasma-induced isoelectronic substitution is technologically feasible and useful for fabricating ternary II-VI alloys under nonequilibrium conditions.

  2. Resputtering Effect on Nanocrystalline Ni-Ti Alloy Films

    NASA Astrophysics Data System (ADS)

    Priydarshini, B. Geetha; Esakkiraja, N.; Aich, Shampa; Chakraborty, M.

    2016-04-01

    We report on the effect of resputtering on the properties of nanocrystalline Ni-Ti alloy thin films deposited using co-sputtering of Ni and Ti targets. In order to facilitate the formation of nanocrystalline phases, films were deposited at room temperature and 573 K (300 °C) with substrate bias voltage of -100 V. The influence of substrate material on the composition, surface topography microstructure, and phase formations of nanocrystalline Ni-Ti thin films was also systematically investigated. The preferential resputtering of Ti adatoms was lesser for Ni-Ti films deposited on quartz substrate owing to high surface roughness of 4.87 nm compared to roughness value of 1.27 nm for Si(100) substrate.

  3. Coherency strain and its effect on ionic conductivity and diffusion in solid electrolytes--an improved model for nanocrystalline thin films and a review of experimental data.

    PubMed

    Korte, C; Keppner, J; Peters, A; Schichtel, N; Aydin, H; Janek, J

    2014-11-28

    A phenomenological and analytical model for the influence of strain effects on atomic transport in columnar thin films is presented. A model system consisting of two types of crystalline thin films with coherent interfaces is assumed. Biaxial mechanical strain ε0 is caused by lattice misfit of the two phases. The conjoined films consist of columnar crystallites with a small diameter l. Strain relaxation by local elastic deformation, parallel to the hetero-interface, is possible along the columnar grain boundaries. The spatial extent δ0 of the strained hetero-interface regions can be calculated, assuming an exponential decay of the deformation-forces. The effect of the strain field on the local ionic transport in a thin film is then calculated by using the thermodynamic relation between (isostatic) pressure and free activation enthalpy ΔG(#). An expression describing the total ionic transport relative to bulk transport of a thin film or a multilayer as a function of the layer thickness is obtained as an integral average over strained and unstrained regions. The expression depends only on known material constants such as Young modulus Y, Poisson ratio ν and activation volume ΔV(#), which can be combined as dimensionless parameters. The model is successfully used to describe own experimental data from conductivity and diffusion studies. In the second part of the paper a comprehensive literature overview of experimental studies on (fast) ion transport in thin films and multilayers along solid-solid hetero-interfaces is presented. By comparing and reviewing the data the observed interface effects can be classified into three groups: (i) transport along interfaces between extrinsic ionic conductors (and insulator), (ii) transport along an open surface of an extrinsic ionic conductor and (iii) transport along interfaces between intrinsic ionic conductors. The observed effects in these groups differ by about five orders of magnitude in a very consistent way. The

  4. Nanosecond magnetization reversal in nanocrystalline magnetic films

    NASA Astrophysics Data System (ADS)

    Rahman, I. Z.; Gandhi, A. A.; Khaddem-Mousavi, M. V.; Lynch, T. F.; Rahman, M. A.

    2007-03-01

    This paper reports on the investigation of dynamic magnetization reversal process in electrodeposited nanocrystalline Ni and Ni80Fe20 films by employing nanosecond magnetic pulse technique. The surface morphology has been investigated using SEM, EDAX, XRD and AFM analyses and static magnetic properties of the films are characterized by vibrating sample magnetometer (VSM). Two different techniques are designed and employed to study the nanosecond magnetization reversal process in nanocrystalline thin films: Magneto-Optical Kerr Effect (MOKE) and nanosecond pulsed field magnetometer. Results of dynamical behavior as a function of several variables such as magnitude of applied bias magnetic field, amplitude and width of the pulsed magnetic field are analyzed in detail using both techniques. A computer simulation package called Object Oriented Micro-Magnetic Framework (OOMMF) has been used to simulate the magnetic domain patterns of the samples.

  5. Optimization of the ZnS Buffer Layer by Chemical Bath Deposition for Cu(In,Ga)Se2 Solar Cells.

    PubMed

    Jeon, Dong-Hwan; Hwang, Dae-Kue; Kim, Dae-Hwan; Kang, Jin-Kyu; Lee, Chang-Seop

    2016-05-01

    We evaluated a ZnS buffer layer prepared using a chemical bath deposition (CBD) process for application in cadmium-free Cu(In,Ga)Se2 (CIGS) solar cells. The ZnS buffer layer showed good transmittance (above 90%) in the spectral range from 300 to 800 nm and was non-toxic compared with the CdS buffer layers normally used in CIGS solar cells. The CBD process was affected by several deposition conditions. The deposition rate was dependent on the ammonia concentration (complexing agent). When the ammonia concentration was either too high or low, a decrease in the deposition rate was observed. In addition, post heat treatments at high temperatures had detrimental influences on the ZnS buffer layers because portions of the ZnS thin films were transformed into ZnO. With optimized deposition conditions, a CIGS solar cell with a ZnS buffer layer showed an efficiency of 14.18% with a 0.23 cm2 active area under 100 mW/cm2 illumination. PMID:27483938

  6. New route to the fabrication of nanocrystalline diamond films

    SciTech Connect

    Varshney, Deepak Morell, Gerardo; Palomino, Javier; Resto, Oscar; Gil, Jennifer; Weiner, Brad R.

    2014-02-07

    Nanocrystalline diamond (NCD) thin films offer applications in various fields, but the existing synthetic approaches are cumbersome and destructive. A major breakthrough has been achieved by our group in the direction of a non-destructive, scalable, and economic process of NCD thin-film fabrication. Here, we report a cheap precursor for the growth of nanocrystalline diamond in the form of paraffin wax. We show that NCD thin films can be fabricated on a copper support by using simple, commonplace paraffin wax under reaction conditions of Hot Filament Chemical Vapor Deposition (HFCVD). Surprisingly, even the presence of any catalyst or seeding that has been conventionally used in the state-of-the-art is not required. The structure of the obtained films was analyzed by scanning electron microscopy and transmission electron microscopy. Raman spectroscopy and electron energy-loss spectroscopy recorded at the carbon K-edge region confirm the presence of nanocrystalline diamond. The process is a significant step towards cost-effective and non-cumbersome fabrication of nanocrystalline diamond thin films for commercial production.

  7. High durability antireflection coatings for silicon and multispectral ZnS

    NASA Astrophysics Data System (ADS)

    Joseph, Shay; Marcovitch, Orna; Yadin, Ygal; Klaiman, Dror; Koren, Nitzan; Zipin, Hedva

    2007-04-01

    In the current complex battle field, military platforms are required to operate on land, at sea and in the air in all weather conditions both day and night. In order to achieve such capabilities, advanced electro-optical systems are being constantly developed and improved. These systems such as missile seeker heads, reconnaissance and target acquisition pods and tracking, monitoring and alert systems have external optical components (window or dome) which must remain operational even at extreme environmental conditions. Depending on the intended use of the system, there are a few choices of window and dome materials. Amongst the more common materials one can point out sapphire, ZnS, germanium and silicon. Other materials such as spinel, ALON and yittria may also be considered. Most infrared materials have high indices of refraction and therefore they reflect a large part of radiation. To minimize the reflection and increase the transmission, antireflection (AR) coatings are the most common choice. Since these systems operate at different environments and weather conditions, the coatings must be made durable to withstand these extreme conditions. In cases where the window or dome is made of relatively soft materials such as multispectral ZnS, the coating may also serve as protection for the window or dome. In this work, several antireflection coatings have been designed and manufactured for silicon and multispectral ZnS. The coating materials were chosen to be either oxides or fluorides which are known to have high durability. Ellipsometry measurements were used to characterize the optical constants of the thin films. The effects of the deposition conditions on the optical constants of the deposited thin films and durability of the coatings will be discussed. The coatings were tested according to MIL-STD-810E and were also subjected to rain erosion tests at the University of Dayton Research Institute (UDRI) whirling arm apparatus in which one of the coatings showed

  8. Surface transmission enhancement of ZnS via continuous-wave laser microstructuring

    NASA Astrophysics Data System (ADS)

    Major, Kevin J.; Florea, Catalin M.; Poutous, Menelaos K.; Busse, Lynda E.; Sanghera, Jasbinder S.; Aggarwal, Ishwar D.

    2014-03-01

    Fresnel reflectivity at dielectric boundaries between optical components, lenses, and windows is a major issue for the optics community. The most common method to reduce the index mismatch and subsequent surface reflection is to apply a thin film or films of intermediate indices to the optical materials. More recently, surface texturing or roughening has been shown to approximate a stepwise refractive index thin-film structure, with a gradient index of refraction transition from the bulk material to the surrounding medium. Short-pulse laser ablation is a recently-utilized method to produce such random anti-reflective structured surfaces (rARSS). Typically, high-energy femtosecond pulsed lasers are focused on the surface of the desired optical material to produce periodic or quasi-periodic assemblies of nanostructures which provide reduced surface reflection. This technique is being explored to generate a variety of structures across multiple optical materials. However, femtosecond laser systems are relatively expensive and more difficult to maintain. We present here a low power and low-cost alternative to femtosecond laser ablation, demonstrating random antireflective structures on the surface of Cleartran ZnS windows produced with a continuous-wave laser. In particular, we find that irradiation with a low-powered (<10 mW), defocused, CW 325nm-wavelength laser produces a random surface with significant roughness on ZnS substrates. The transmission through the structured ZnS windows is shown to increase by up to 9% across a broad wavelength range from the visible to the near-infrared.

  9. Effect of solvent volume on the physical properties of aluminium doped nanocrystalline zinc oxide thin films deposited using a simplified spray pyrolysis technique

    NASA Astrophysics Data System (ADS)

    Jabena Begum, N.; Mohan, R.; Ravichandran, K.

    2013-01-01

    Aluminium doped zinc oxide (AZO) thin films were deposited by employing a low cost and simplified spray technique using a perfume atomizer from starting solutions having different volumes (10, 20, … , 50 mL) of solvent. The effect of solvent volume on the structural, electrical, optical, photoluminescence (PL) and surface morphological properties was studied. The electrical resistivity of the AZO films is remarkably influenced by the variation in the solvent volume. The X-ray diffraction profiles clearly showed that all the films have preferential orientation along the (0 0 2) plane irrespective of the solvent volume. The crystallite size was found to be in the nano range of 35-46 nm. The optical transmittance in the visible region is desirably high (>85%). The AFM images show columnar morphology with varying grain size. The PL studies revealed that the AZO film deposited from 50 mL of solvent volume has good quality with lesser defect density.

  10. Nanocrystalline Heterojunction Materials

    DOEpatents

    Elder, Scott H.; Su, Yali; Gao, Yufei; Heald, Steve M.

    2004-02-03

    Mesoporous nanocrystalline titanium dioxide heterojunction materials and methods of making the same are disclosed. In one disclosed embodiment, materials comprising a core of titanium dioxide and a shell of a molybdenum oxide exhibit a decrease in their photoadsorption energy as the size of the titanium dioxide core decreases.