Polycrystalline Structure Of Films Research Articles

The effect of ethyl alcohol on accuracy of time since death estimation using laser poliarimetric methods of cerebrospinal liquid polyristallic films investigation

The article analyzes the possibility of using laser polarimetry methods to determine the possible influence of ethyl alcohol in the body of the deceased on the change in the structure of the polycrystalline films of the cerebrospinal fluid. The efficiency of usage laser polarimetry methods (determination of complex degree of mutual polarization and autofluorescence of polycrystalline films of cerebrospinal fluid) have been proved.
 Relationships between the distribution of the intensity of the fluorescence of polycrystalline films of the cerebrospinal fluid of the cadavers as a result of cardiovascular pathology in the presence and absence of ethyl alcohol in the organism and the values and ranges of the change of statistical moments of the 1st - 4th orders that characterize such autofluorescence images are investigated. A good level of balanced differentiation of the presence of ethyl alcohol in the human body in the «green-yellow» and «red» sections of the spectrum has been achieved. There is a statistically significant difference between cases of death from cardiovascular disease in the presence and absence of ethyl alcohol in an organism by determining the magnitude of the statistical moment of the 4th order, which characterizes the distributions of the azimuth magnitude of the polarization of microscopic images of laser-induced fluorescence.
 On this basis, an excellent balanced accuracy of the differentiation of the presence of ethyl alcohol in the human body (Ac (M4) = 94%) has been achieved. Consequently, ethyl alcohol affects the structure of polycrystalline films of cerebrospinal fluid, which should be taken into account when time since death estimated using methods of laser polarimetry.

Structure and thermal stability of Bi3NbO7 thin films grown by pulsed laser deposition

Abstract Bismuth oxide-based materials containing the cubic δ-phase exhibit the highest ionic conductivity of all known solid-state ion conductors. However, its thermal instability prevents its application at low and intermediate temperatures. To enhance the stability of the materials other oxides are added to the bismuth oxide. In this work the effect of the substrate temperature on the structure, morphology and phase composition of Bi 2 O 3 –Nb 2 O 5 thin films deposited onto single-crystal sapphire via pulsed laser deposition technique is studied. The thin films are characterized using X-ray diffraction, transmission electron microscopy, and atomic force microscopy techniques. Three types of microstructures of Bi 3 NbO 7 are achieved by growing the films at different substrate temperatures. At low temperatures the disoriented columnar structure of polycrystalline films is observed. When the substrate temperature increases the (111)-oriented columns appear in thin films. As a consequence, high temperatures lead to a heteroepitaxial growth with an intermittent presence of low-angle grain boundaries. Out-of-plane X-ray diffraction and selected area electron diffraction patterns clearly confirm an epitaxial relationship, which is found to be Bi 3 NbO 7 (111) || α-Al 2 O 3 (0001). An interface between the thin films and substrate is sharp and abrupt. Simultaneously, interdiffusion and a formation of new chemical compounds were not observed. The face-centred cubic Bi 3 NbO 7 phase was detected in thin films with the absent of the tetragonal polymorphic phase. Remarkably, the as-deposited samples were stable during an ex-situ annealing up to 900 °C. However, above a temperature of 1000 °C, volatilization was taking place due to an uncontrollable loss of bismuth.

Ferroelectric Thin Films of Deuterated Betaine Arsenate

Ferroelectric thin films of partially deuterated betaine arsenate have been grown by evaporation method on NdGaO3 and α-Al2O3 substrates. The films consist of small single-crystal blocks, in which ferroelastic domains have been visualized by polarizing microscope. X-ray diffraction shows that the blocks form a polycrystalline structure of film. Ferroelectric phase transition in DBA films is followed by dielectric anomaly and appearance of dielectric hysteresis loops. The magnitude of dielectric anomaly is small as compared with DBA single crystals. Small value of anomaly is associated with polycrystalline structure of DBA films. The deuteration degree of betaine arsenate films is smaller than that of crystals used for film preparation due to substitution of deuterium by hydrogen ions during the crystallization process.

Effect of tri-sodium citrate concentration on structural, optical and electrical properties of chemically deposited tin sulfide films

Tin sulfide thin films were deposited onto glass substrates by chemical bath deposition. The effects of molar concentration of the complexing agent, tri-sodium citrate, on the structural, morphological, optical and electrical properties of the films were investigated. The films are characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy, optical absorption spectroscopy and Hall effect measurements. Polycrystalline film structure in orthorhombic phase was determined. Flower-like spherical grains are observed on the surface. While their average size increased from 345nm to 750nm when the tri-sodium citrate concentration was increased from 6.4×10−3M to 8.0×10−3M, the surface roughness varied in an opposite manner from approximately 120.18nm to 29.36nm. For these concentrations, optical band gap of the films decreased from 1.40eV to 1.17eV, whereas the Hall conductivity, mobility and carrier concentration of the films increased slightly from 5.91×10−5 to 8.78×10−5(Ωcm)−1, from 148 to 228cm2V−1s−1 and from 1.73×1012 to 3.59×1012cm−1, respectively.

Evolution of morphology and structure of Pb thin films grown by pulsed laser deposition at different substrate temperatures

Pb thin films were prepared by pulsed laser deposition on a Si (100) substrate at different growth temperatures to investigate their morphology and structure. The morphological analysis of the thin metal films showed the formation of spherical submicrometer grains whose average size decreased with temperature. X-ray diffraction measurements confirmed that growth temperature influences the Pb polycrystalline film structure. A preferred orientation of Pb (111) normal to the substrate was achieved at 30 °C and became increasingly pronounced along the Pb (200) plane as the substrate temperature increased. These thin films could be used to synthesize innovative materials, such as metallic photocathodes, with improved photoemission performances.

Microstructure of Polycrystalline PBTTT Films: Domain Mapping and Structure Formation

We utilize near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and scanning transmission X-ray microscopy (STXM) to study the microstructure and domain structure of polycrystalline films of the semiconducting polymer poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT). Total electron yield NEXAFS spectroscopy is used to examine the surface structure of the first 1-2 molecular layers, while bulk-sensitive STXM is used to produce maps of domain orientation and order sampled through the entire film thickness. We study different phases of PBTTT including as-cast, terraced and nanoribbon morphologies produced via spin-coating as well as aligned films of as-cast and nanoribbon morphologies produced by zone-casting. For the terraced morphology, domains are observed that are larger than the size of the terraced surface features, and the calculated degree of order is reduced compared to the nanoribbon morphology. For zone-cast films, we find that, although little optical anisotropy is observed in the bulk of as-cast films, a high degree of surface structural anisotropy is observed with NEXAFS spectroscopy, similar to what is observed in annealed nanoribbon films. This observation indicates that the aligned surface structure in unannealed zone-cast films templates the bulk ordering of the aligned nanoribbon phase. STXM domain mapping of aligned nanoribbon films reveals elongated, micrometer-wide domains with each domain misoriented with respect to its neighbor by up to 45°, but with broad domain boundaries. Within each nanoribbon domain, a high degree of X-ray dichroism is observed, indicating correlated ordering throughout the bulk of the film.

Deposition and characteristics of chromium nitride thin film coatings on precision balls for tribological applications

Thin film hard coatings on rolling element surfaces can enhance the overall wear resistance of rolling element bearings, as demonstrated previously for coated tapered, cylindrical, and spherical roller bearings. Hard coatings in ball bearings are less common because of the difficulty in achieving uniform film thickness on a ball surface. This limitation is overcome by a new process for depositing chromium nitride coatings with uniform thickness on precision balls using ion beam assisted deposition (IBAD) e-beam evaporation. Scanning electron microscopy indicated that the deposited films were smooth and conformal on the ball surfaces with no areas of localized delamination. Auger electron spectroscopy confirmed that Cr2N and CrN bulk film stoichiometry was achievable by modulating the argon to nitrogen process gas ratio during deposition. Transmission electron microscopy revealed dense, polycrystalline film structure. Film hardness and elastic modulus as measured using nanoindentation on the coated balls met expectations for chromium nitride, and tribological testing of the coated balls in angular contact ball bearings under moderate contact stress levels demonstrated adequate film adhesion for practical use of these coatings in bearing applications.

Uniaxial magnetic anisotropy for thin Co films on glass studied by magnetooptic Kerr effect

Thin Co films of different thickness deposited on glass are investigated by magnetooptic Kerr effect to study the uniaxial magnetic anisotropy of these films. The direction of the uniaxial magnetic anisotropy is determined from the azimuthal dependence of the magnetic remanence and differs with increasing thickness of the Co film investigated by x-ray reflectivity. Our experiments reveal that preparation conditions like temperature, deposition rate, or obliqueness of deposition cannot be the reason for this rotation effect of the uniaxial magnetic anisotropy. Also, strain in the substrate and possible textures in the film structure can be excluded as the origin of the magnetic behavior as studied by grazing incidence wide angle x-ray scattering. Thus, probably only the substrate shape in connection with the amorphous or polycrystalline film structure can explain the rotation of the uniaxial magnetic anisotropy.

Mapping of Domain Orientation and Molecular Order in Polycrystalline Semiconducting Polymer Films with Soft X‐Ray Microscopy

AbstractWe utilize scanning transmission X‐ray microscopy (STXM) to study the domain structure of polycrystalline films of the semiconducting polymer poly(9,9’‐dioctylfluorene‐co‐benzothiadiazole) (F8BT). By taking several images at different orientations of the film with respect to the polarization of the X‐ray beam, we are able to compute quantitative maps of molecular alignment/order and molecular orientation, including both the backbone direction and phenyl ring plane orientation, as well as the in‐plane and out‐of‐plane components. We show that polycrystalline F8BT films consist of well‐ordered micron‐sized domains with the transition from one domain orientation to another characterized either by a smooth transition of orientation or by ∼ 200 nm wide disordered domain boundaries. The morphology of the disordered domain boundaries resemble the electroluminescence patterns observed previously in F8BT light‐emitting field‐effect transistors suggesting that charge trapping at these disordered domain boundaries facilitates charge recombination in ambipolar operation. A relatively narrow distribution of local average tilt angles is observed that correlates with film structure, with the ordered domains in general showing a higher tilt angle than the disordered domain boundaries. We also use secondary electron detection to image the surface domain structure of polycrystalline F8BT films and demonstrate that the polycrystalline structure extends to the film/air interface. Finally, we calculate ideal NEXAFS spectra corresponding to a perfect F8BT crystal oriented with the 1s – π* transition dipole moment parallel and perpendicular to the electric field vector of a perfectly linearly polarized X‐ray beam.

Structural and electronic implications for carrier injection into organic semiconductors

We report on the structural and electronic interface formation between ITO (indium-tin-oxide) and prototypical organic small molecular semiconductors, i.e., CuPc (copper phthalocyanine) and α-NPD (N,N′-di(naphtalen-1-yl)-N,N′-diphenyl-benzidine). In particular, the effects of in situ oxygen plasma pretreatment of the ITO surface on interface properties are examined in detail: Organic layer-thickness dependent Kelvin probe measurements revealed a good alignment of the ITO work function and the highest occupied electronic level of the organic material in all samples. In contrast, the electrical properties of hole-only and bipolar organic diodes depend strongly on the treatment of ITO prior to organic deposition. This dependence is more pronounced for diodes made of polycrystalline CuPc than for those of amorphous α-NPD layers. X-ray diffraction and atomic force microscopic (AFM) investigations of CuPc nucleation and growth evidenced a more pronounced texture of the polycrystalline film structure on the ITO substrate that was oxygen plasma treated prior to organic layer deposition. These findings suggest that the anisotropic electrical properties of CuPc crystallites, and their orientation with respect to the substrate, strongly affect the charge carrier injection and transport properties at the anode interface.

Sputter Deposition of CuInSe2 and CuGaSe2 from Composite Targets on (100) Si

AbstractThin films of CuInSe2 (CIS) and CuGaSe2 (CGS) were deposited on (100) Si substrates by RF magnetron sputtering using stoichiometric targets, at various substrate temperatures. Prior to film deposition, the Si substrates were cleaned using the RCA cleaning procedure and treated in a buffered oxide etch (BOE) solution. Deposited films were characterized using Rutherford backscattering spectroscopy (RBS), transmission electron microscopy (TEM) of cross-sectional samples and Hall measurements. Rutherford backscattering analysis indicated that the CIS films had a composition of Cu0.8In1.1Se1.9, whereas CGS films were Cu-poor and Ga-rich with a composition of Cu0.3Ga1.5Se1.5. Clean Cu-chalcopyrite/Si interfaces were obtained using BOE treated Si substrates. Transmission electron micrographs of cross-sectional samples indicated a polycrystalline film structure and that the native oxide on the Si substrate was eliminated. Energy dispersive X-ray spectroscopy (EDS) conducted in the TEM showed that contamination levels in the films were low. The Hall-mobility experiments performed the CIS film indicated that the material was of p-type conductivity with a carrier concentration of 9.6 x 1020/cm3 and a Hall mobility of 390 cm2V-1s-1.

Characterization of nickel Germanide thin films for use as contacts to p-channel Germanium MOSFETs

We have measured the physical properties and resistivity of nickel germanide thin films formed by the rapid thermal annealing of nickel metal on p-type germanium substrates. Rutherford back scattering and high-resolution electron diffraction confirm that the stoichiometry of the resulting nickel germanide film corresponds to NiGe and has an orthorhombic unit cell with dimensions comparable to that of bulk samples. Transmission electron microscopy shows a poly-crystalline film structure with grain size > 0.1 /spl mu/m. The resistivity values for films annealed in the range 350/spl deg/C-500/spl deg/C are comparable to those of metal silicides. Measurements of the specific contact resistance suggest that values approaching 2 /spl times/ 10/sup -7/ /spl Omega/.cm/sup 2/ can be realized using NiGe formed on heavily doped p-type germanium.

Structural Analysis of Anatase Polycrystalline Films Using Time-Dependent Deformation Behavior

We introduce an analytical technique for time-dependent deformation behavior of polycrystalline films using a nanoindenter. This technique permits evaluation of structural deformation of thin films in the nanometer scale. The void structure of polycrystalline films of anatase was evaluated using time-dependent deformation behavior. The void structure was examined using a power-law model in which a strain rate sensitivity exponent m of the sample was determined. The m value enabled us to detect the existence of the void structure. In this study, appropriate conditions were determined to measure deformation behavior of polycrystalline films. The analysis of time-dependent deformation behavior is useful for investigating the void structure of polycrystalline films.

Crystal structure of polycrystalline films of quaterthiophene grown by organic molecular beam deposition

The growth of thin films of oligothiophenes by organic molecular beam deposition (OMBD) can produce highly ordered polycrystalline samples. Recently, quaterthiophene (4T) thin films were grown on different substrates (silica, graphite, potassium acid phthalate, silicon). In some cases, their optical behavior was found to resemble that of 4T single crystals, with a macroscopic anisotropy close to that of the bulk crystal. A careful structural characterization of these films was undertaken. A morphological and optical characterization was performed by atomic force microscopy (AFM) and optical absorption. Electron microscopic examination in both bright field and diffraction was carried out on 4T thin films deposited on two selected substrates: silica and single crystals of potassium phthalate acid salt. The crystal polymorph, contact plane, and coherent orientation obtained on these 4T micro-crystalline films fully agree with the optical behavior of the samples.

Impurity spin magnetization of thin Fe doped Au films

In order to probe the influence of the surface-induced anisotropy on the impurity spin magnetization, we measure the anomalous Hall effect in thin AuFe films at magnetic fields up to 15 T. The observed suppression of the anomalous Hall resistivity at low fields as well as the appearance of a minimum in the differential Hall resistivity at higher fields can be explained by our theoretical model, which takes into account the influence of a polycrystalline film structure on the surface-induced anisotropy. Our results imply that the apparent discrepancy between different experimental results for the size effects in dilute magnetic alloys can be linked to a different microstructure of the samples.

Photoelectric properties of polycrystalline films grown on alternative substrates

The photoelectric and electrical properties and structure of polycrystalline films grown on and GaAs substrates are studied. The films obtained, having a high photosensitivity in particular at room temperature, show promise for infrared optoelectronics. A comprehensive investigation of the photoconductivity spectra, lux-ampere characteristics and temperature dependences of the photoelectric and electrical characteristics have established the significant influence of electrically active grain boundaries on the photoelectric parameters. It has been found that lux-ampere characteristics of films have a nonconventional pattern which is manifested in an increase of slope at high rates of laser excitation. The role of potential barriers in the generation-recombination processes in polycrystalline films is discussed in the context of a model of an inhomogeneous semiconductor whose energy bands are modulated by a random potential.

Growth of PbS and CdS thin films by low-pressure chemical vapour deposition using dithiocarbamates

Thin films of cadmium and lead sulphides grown by chemical vapour deposition (CVD) and remote plasma enhanced chemical vapour deposition (RPECVD) using dithiocarbamates as precursors were prepared on fused silica, sapphire, (111)Si and (111)InP substrates. These films were deposited in the temperature range 473–873 K. It was established that the activation energy of the CVD process is 191.5±1.5 kJ mol −1. The structure of polycrystalline films was halenide for PbS and wurtzite for CdS. It was also found that r.f.-plasma activation of the gas phase decreases remarkably the growth temperature and orders the film structure. RPECVD sulphide films had a high degree of preferred orientation.

Texture in Bi-Sr-Ca-Cu-O Films Prepared by a Paint-on Method

The texture and structure of polycrystalline films of Bi-Sr-Ca-Cu-O prepared by the paint-on method on alumina substrate has been investigated. A large variety of texture strength has been obtained as a result of various processing of 2:2:1:2, 1:1:1:2, 1:1:2:2 and 2:2:2:3 compounds. The X-ray diffraction analysis and measurements of conductivity have shown the presence of a low Tc phase. Imaging of the magnetic field distribution using the Faraday effect and the critical current measurements demonstrated that the critical current is very low. SEM observation of the microstructure indicate that the possible reason of low critical current density is a weak link between high Tc grains.

The simultaneous growth of monocrystalline and polycrystalline silicon films with controlled parameters

The influence of the temperature of deposition of nucleation layers on the structure of polycrystalline silicon films which grow locally during the epitaxial growth of monocrystalline films was investigated. The structure of polycrystalline films grown in the high temperature chloride process has been found to depend on the deposition mode of the nucleation layer. For temperature changes in the range 800–860°C, the grain sizes in polycrystalline silicon increase by more than one order of magnitude. It was shown that heat treatment of films of small grain size in an atmosphere of oxygen leads to a decrease in their resistance owing to recrystallization of the grains, whereas during the annealing of films of large grain size the oxidation of intergrain boundaries is the dominant process resulting in an increase in the resistance. The possibility of using polycrystalline films fabricated under specific technological conditions for the isolation of integrated circuit elements was demonstrated.

Growth of Polycrystalline Silicon Films: Grain Size

Transmission electron microscopy has been used to study the structure of polycrystalline films grown on silicon nitride and silicon dioxide substrates by chemical vapor deposition from silane gas. The effects of substrate temperature, type of carrier gas (nitrogen or hydrogen), and gas flow rate were examined. For substrate temperatures of 720°(993°and above, the films were polycrystalline, and under certain conditions a uniform grain size of ca. 30 nm was obtained. At the highest temperatures (ca. 1040°–1100°K), the films were discontinuous and showed also a type of secondary structure. Results obtained by field emission microscopy have been used to show how incident flux and surface diffusion coefficient may affect grain size in polycrystalline films: it is likely that the observed noncrystalline/polycrystalline transition is affected by recrystallization, decrease in density of preferred sites for nucleation, and change in critical nucleus size.