Crystallites In Films Research Articles

Field electron emission from bunchy flake-like nano-carbon films

This paper reports that bunchy flake-like nano-graphite crystallite films (BNGCFs) were deposited on Si substrates by using the microwave chemical vapour deposition technique. Furthermore the BNGCFs were characterized by x-ray diffraction spectra, scanning electron microscopy, Raman spectra and field emission (FE) I–V measurements, and a lowest turn-on field of 1.5 V/μm, and a high average emission current density of 30 mA/cm2 at a macroscopic electric field of 8.0 V/μm were obtained. The J–E data did not follow the original Fowler–Nordheim (F–N) relation since they were not well represented in the F–N plot by a straight line. A model considering the F–N mechanism, and the statistic effects of FE tip structures has been applied successfully to explain all the FE data observed for E < 8.8 V/μm.

Properties of ZnO thin films deposited by DC reactive magnetron sputtering under different plasma power

ZnO thin films were prepared by DC reactive magnetron sputtering under various values of the plasma power at room temperature. The samples were characterized with X-ray diffraction (XRD), optical transmittance, photoluminescence (PL), and atomic force microscopy (AFM), respectively. The results show that samples change from ZnO (110) dominant crystal orientation to ZnO (002) dominant crystal orientation with the increase of plasma power. The samples also exhibit compressive intrinsic stresses. The coherent domain size of the film crystallite along with the root mean square (RMS) of the surface roughness increases with the increase of the plasma power. Optical transmittance spectra reveal that all samples have excellent optical properties. With the increase of plasma power, slight optical transmittance decreasing and fundamental absorption edge red shifting were observed. Films prepared under higher plasma powers show weaker emission intensities, which may be related to substoichiometric composition.

Atomic-force microscopy of bismuth film defects decorated by oxidation

A method has been developed for revealing intercrystalline boundaries and mutual orientation of crystallites in bismuth films with the use of natural oxidation in combination with atomic-force microscopy. For bismuth films prepared through vacuum thermal evaporation on mica substrates, the block boundaries have been revealed, the sizes of blocks have been determined, and their mutual crystallographic orientation has been established. The results obtained have been used to determine thermal evaporation conditions that ensure a higher perfection of the film structure.

Preparation and characterization of poly-Si films on different topography substrates by AIC

Polycrystalline silicon (poly-Si) thin-films were made on planar and textured glass substrates by aluminum-induced crystallization (AIC) of in situ amorphous silicon (a-Si) deposited by DC-magnetron. The poly-Si films were characterized by Raman spectroscopy, X-ray diffraction (XRD) and atomic force microscopy (AFM). A narrow and symmetrical Ranman peak at the wave number of about 521 cm(-1) was observed for all samples, indicating that the films were fully crystallized. XRD results show that the crystallites in the authors' AIC poly-Si films were preferably (111) oriented. The measurement of full width at half maximum (FWHW) of (111) XRD peaks showed that the quality of the films was affected by the a-Si deposition temperature and the surface morphology of the glass substrates. It is likely that an a-Si deposition temperature of 200 degrees C seems to be ideal for the preparation of poly-Si films by AIC.

Characteristics of Sputter-deposited Gadolinia-doped Ceria Thin Films on Al2O3/SiO2/Si Systems

Metal oxide films prepared by thin film technology have been reported for the potential applications on thin solid electrolyte layers for solid oxide fuel cells(SOFCs). Gadolinia-doped ceria(GDC) thin films and Al2O3 layers on SiO2/Si substrates are successively deposited by RF reactive magnetron sputtering from a cerium-gadolinium (90:10 at.%) alloy target and Al target in O2/Ar gas mixture and then perform post-thermal treatments at 300–700 ℃ and 900 ℃ for 2 h, respectively. Materials characteristics and chemical compositions of GDC films and Al2O3 layers are investigated by X-ray photoelectron spectroscopy(XPS), cross-sectional scanning electron microscopy(SEM), X-ray diffraction(XRD), and atomic force microscopy(AFM). Stoichiometric Al2O3 layers with polycrystalline structures are firstly prepared onto SiO2/Si substrates. A cubic fluorite structure with columnar crystallites of GDC films is successfully deposited on Al2O3/SiO2/Si systems. The chemical composition of 700 ℃-annealed GDC films is (Ce0.91Gd0.09)O1.94 and possesses a higher film density of 7.257 g/cm3. As a result, GDC thin films prepared by RF reactive magnetron sputtering and post-thermal treatments can be used as thin solid electrolyte layers for intermediate temperature SOFCs system as compared to the well-known yttria-stabilized zirconia(YSZ).

Structure and conditions for the formation of fullerite crystallites in Sn-C60 films

The structure of tin-fullerite films with different thicknesses of the Sn coating layer (50, 100, 200, 300, 450, and 700 nm) and the conditions for the formation and growth of fullerite crystallites on the tin surface during sample exposure in air have been investigated. The methods of X-ray diffraction; scanning electron, transmission electron, and atomic force microscopy; and X-ray microanalysis were used to reveal changes in the structure and phase composition of the tin-fullerite films. Fullerite crystallites in the form of plates and bolts grown under internal stress have been found on the surface of tin films with thicknesses of 50, 100, and 200 nm. The incubation period of crystallite formation is established to be 12–22 months, depending on the thickness of the tin layer.

Large effect of the deformation on magnetoresistance of stretched and compressed thin polycrystalline Bi films

Substantial influence of uniaxial stretch S and compression P on resistivity ρ and magnetoresistance (MR) of high-quality polycrystalline Bi films consisting of up to 200 μm length crystallites was observed. The investigated 1.5 μm thick films were deposited on non-crystalline substrate and annealed at critical temperature close to the film melting temperature. The experimental results are interpreted on the basis of improved polycrystalline Bi thin film model, including the electron intervalley repopulation in deformed film crystallites. It was found that S and P cause different dependence of ρ and MR on the magnetic field strength. The effect of P on ρ and MR is of opposite sign as compared to S and is larger than that for S. In a strong non-quantizing magnetic field region the transverse ρ appeared to be independent of the deformation. The calculations show that in n-Bi films the effect of P on ρ at 77 K can be many times larger because the T-holes in Bi films significantly reduce the effect of deformation. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Light-enhanced sensitivity of SnO2 − x gas sensors

The effect of emission of red, yellow, green, and blue LEDs on the sensitivity of SnO2-film gas sensors manufactured by a reactive magnetron sputtering with addition of Sb, In, and catalytic coatings of Pt and Pd to vapors of ethyl and isopropyl spirits, acetone, and benzene is investigated. For the first time, it is shown that all types of emission for all listed reactants increase the sensor sensitivity by 2 to 100 times in the case of small (1–10 ppm) doses of all reactants for the sensors, which are low-sensitive without illumination. It is found that the character of dependence of the sensor sensitivity on the illumination intensity is determined by the type of the catalytic coating, linearly growing in the case of Pd and sharply increasing at the highest intensity in the case of Pt. The nature of this phenomenon is discussed taking into account the vapor adsorption and the conductivity of crystallites in tin-dioxide films.

Properties of YSZ thin films deposited by e-beam technique

In the present study yttrium stabilized zirconia (YSZ) thin films were deposited on the Alloy-600, optical quartz and porous Ni–YSZ substrates using e-beam deposition technique controlling deposition parameters: substrate temperature and electron gun power. These parameters are influencing the thin film deposition mechanism. The dependence of substrate temperature and electron gun power on thin film ionic conductivity, structure and surface morphology was investigated by X-ray diffraction, scanning electron microscopy (SEM). It was found that electron gun power has influence on the crystallite size and growth of YSZ films. Dominating dispersion in the deposited YSZ thin films (substrate temperature T = 250 °C, e-beam gun power P = 0.9 kW) relates to ionic transport in the crystallites in the measured frequencies and temperature ranges. The measured values of conductivity (9.6 ÷ 41.2 × 10 − 4 Sm − 1 ) and activation energies of conductivity (0.87 ÷ 1.1 eV) at 387 °C temperatures are typical to the polycrystalic ZrO 2 — 8 mol% Y 2O 3 compound. The conductivity values of crystallites of YSZ thin films and ceramic are similar. To find out about the stability of formed YSZ thin films and to understand the influence of high temperature on crystallite size was done thermal annealing at 1100 °C temperature. It was found that crystallite sizes increases in size after annealing (3 ÷ 18 nm) and that depends on substrate temperature and e-beam gun power during the formation of YSZ thin films and crystallographic orientation of crystallite.

The effect of electro-annealing on the electrical properties of ITO film on colorless polyimide substrate

The effect of different annealing methods on the sheet resistance of indium tin oxide (ITO) on polyimide (PI) substrate has been investigated. ITO thin films were prepared by RF magnetron sputtering in pure Ar gas and electro-annealing, this was carried out in the flow of an electric current at several temperatures between 100 and 180 °C in air. Electro- and thermal annealing were compared in order to confirm differences between the electrical, optical and microstructural properties of the ITO thin films. As electro-annealing induced the predominant growth of crystallites of ITO thin films along (4 0 0) plane, the sheet resistance of ITO films that were electro-annealed for 2 mA at 180 °C considerably decreased from 50 to 28 Ω/cm 2.

Gadolinium doped ceria thin films deposited by e-beam technique

E-beam deposition technique was used for formation of gadolinium doped ceria oxide (GDC) thin films. GDC thin films were grown by evaporating (Ce 0.9Gd 0.1)O 1.95 ceramic nanopowder. Operating technical parameters that influence thin film microstructure and crystallite size were studied. The GDC thin films were deposited on porous NiO–YSZ (nickel oxide–yttrium stabilized zirconium), optical quartz and Alloy 600 (Fe–Ni–Cr). The influence of substrate temperature on thin film (2–3 μm of thickness) structure and surface morphology was investigated by X-ray diffraction and scanning electron microscopy. It was found that substrate temperature (changed in the range of 20–500 °C) had the influence on the crystallite size and texture. Crystallite size grows up to 53–56 nm with increasing substrate temperature during the deposition. The GDC thin film growing texture is changing at higher than 300 °C substrate temperature when is chosen Alloy 600 substrate.

Structural, chemical and optical characterizations of nanocrystallized AlN:Er thin films prepared by r.f. magnetron sputtering

Nanocrystalline n-AlN:Er thin films were deposited on (0 0 1) Silicon substrates by r.f. magnetron sputtering at room temperature to study the correlation between 1.54 μm IR photoluminescence (PL) intensity, AlN crystalline structure and Er concentration rate. This study first presents how Energy-Dispersive Spectroscopy of X-rays (EDSX) Er Cliff Lorimer sensitivity factor α = 5 is obtained by combining EDSX and electron probe micro analysis (EPMA) results on reference samples. It secondly presents the relative PL intensities of nanocrystallized samples prepared with identical sputtering parameters as a function of the Er concentration. The structure of crystallites in AlN films is observed by transmission electron microscopy.

Structural characterization and optical properties of ZnSe thin films

Zinc selenide (ZnSe) thin films ( d = 0.11–0.93 μm) were deposited onto glass substrates by the quasi-closed volume technique under vacuum. Their structural characteristics were studied by X-ray diffraction (XRD) and atomic force microscopy (AFM). The experiments showed that the films are polycrystalline and have a zinc blende (cubic) structure. The film crystallites are preferentially oriented with the (1 1 1) planes parallel to the substrate surface. AFM images showed that the films have a grain like surface morphology. The average roughness, R a = 3.3–6.4 nm, and the root mean square roughness, R rms = 5.4–11.9 nm, were calculated and found to depend on the film thickness and post-deposition heat treatment. The spectral dependence of the absorption coefficient was determined from transmission spectra, in the range 300–1400 nm. The values of optical bandgap were calculated from the absorption spectra, E g = 2.6–2.7 eV. The effect of the deposition conditions and post-deposition heat treatment on the structural and optical characteristics was investigated.

Leakage currents at crystallites in ZrAlxOy thin films measured by conductive atomic-force microscopy

The spatial distribution of the leakage current through ZrAlxOy thin films with different degrees of crystallinity was investigated at the nanometer-scale. Conductive atomic-force microscopy shows leakage currents at low electric fields in the polycrystalline but not in the amorphous films. Leakage occurs at large crystallites that protrude from the surface. Ring-shaped current distributions around some of the crystallites suggest a conduction at the boundary of crystalline grain and amorphous matrix, and not through the grain. In contrast, the leakage spots that are observed in amorphous films at high electric fields are not correlated to the morphology.

Microstructure of gadolinium doped ceria oxide thin films formed by electron beam deposition

Electron beam deposition technique was used for formation of gadolinium doped ceria oxide (GDC) thin films. GDC thin films were grown by evaporating (Ce 0.9Gd 0.1)O 1.95 ceramic powder. Operating technical parameters that influence thin film microstructure and crystallite size were studied. The GDC thin films were deposited on two different types of substrates: porous nickel oxide–yttrium stabilized zirconium (NiO–YSZ) and Alloy 600 (Fe–Ni–Cr). The influence of electron gun power on thin film (2–5 μm of thickness) structure and surface morphology were investigated by X-ray diffraction and scanning electron microscopy. It was found that electron gun power (changed in the range of 0.66–1.05 kW) has the influence on the crystallite size (it varied between 9.8 and 20.9 nm) of GDC thin films and decreased linearly increasing e-beam gun power. Also, it was found that a bias voltage applied to the substrate during the deposition of thin films has an influence on the densification and crystallite size of GDC layers.

Structural and optical properties of vapor deposited multi-layer CdSe thin films

Structural and optical properties of multi-layer cadmium selenide thin films of various thicknesses were studied. CdSe thin fims were prepared by physical vapor deposition method with alternate layers of cadmium and selenium on unheated glass substrate. The structural investigation performed by X-ray diffraction (XRD) and scanning electron microscopy showed that most of the films were polycrystalline in nature. The stoichiometry of the films determined from EDX results revealed that most of the films did not have equal atomic contents of cadmium and selenium. Refractive indices and absorption coefficient of the film were calculated from the optical transmission spectra. It is found that the size of the crystallites in the polycrystalline films determined from XRD measurements and the optical energy band gap, E g, calculated from optical measurements depend on the thickness and the composition of the films.

Screen printed thick self-biased, low-loss, barium hexaferrite films by hot-press sintering

Ba Fe 12 O 19 hexaferrite thick films having high hysteresis loop squareness (Mr∕Ms) and low ferromagnetic resonance (FMR) linewidths were processed through the use of a screen printing technique coupled with hot-press sintering. Scanning electron microscopy and x-ray diffraction measurements exhibit strong crystallographic c-axis alignment of crystals perpendicular to the film plane. Static magnetic resonance and FMR measurements were performed to determine the effect of the preparation technique on magnetic hysteresis and microwave properties. Hot pressing during sintering produced dense thick films having high squareness (&amp;gt;0.95) and reduced coercivity (∼1900Oe). Of greater importance was the measurement of a minimum peak-to-peak FMR linewidth, 320Oe at the U band, for films ranging in thickness from 100to500μm. Theoretic estimates suggest that such narrow linewidths can be attributed to the reduction in porosity and the improvement in c-axis orientation of crystallites in polycrystalline barium ferrite films. As such, haxaferrite materials prepared using this technique offer opportunities in the next generation of self-biased planar microwave devices.

The electrocatalytic behaviour of electroless Ni–P alloys

Electroless nickel–phosphorous coated carbon steel electrodes, with P content ranging from 4.0 to 13.8 at.% P, were prepared and employed to investigate the effect of the structural and morphological features on the alloy electrocatalytic activity. Subsequent heat (400 °C, 1 h) or electrochemical (anodizing at 0.5 V followed by multi-cycle polarization) treatments were performed and the so imparted modifications established. The deposits characterization by glazing X-ray diffraction and by atomic force microscopy provided information on the conditions for the formation of crystallites in amorphous films and its influence on the surface topography; the comparative analysis of the cyclic voltammetry data gave information on the importance of the P content in nickel hydroxides/oxides formation. The possibility of using the as-deposited or the treated electroless Ni–P coatings as cathodes, in alkaline media, was evaluated with the study of the hydrogen evolution reaction.

Raman light scattering in hydrogenated metal-carbon composite films

We have used Raman scattering, elemental analysis, and structural analysis to study the effect of the concentration of incorporated metals (Cu, Ni) on the ratio of sp2/sp3 carbon bonds in composite hydrogen-containing films a-C:H/Cu and a-C:H/Ni, formed by combining plasma-enhanced vapor phase deposition of carbon and sputtering of the metal, using a mixture of argon and methane or acetylene gases. We have shown that formation of a nanosized structure of metallic crystallites (2–5 nm) in the composite films leads to a significant increase in the fraction of disordered sp3-bonded carbon clusters and a decrease in the linear dimensions of the graphite-like carbon clusters.

Non-linear dielectric properties of vacuum deposited nanocrystalline polyaniline thin films

Vacuum deposited polyaniline thin films have been found to exhibit a strong degree of non-linearity in the dielectric properties. As a function of change in the differential capacitance of metal–polymer–metal thin film capacitor upon application of d.c. bias. Dielectric capacitance and dielectric loss of the films were investigated in the frequency range from 10 Hz to 1 MHz, at different bias voltage. The above investigations lead to the estimation of charge carrier mobility, concentration, thin film crystallite size and diffusion constant in vacuum deposited polyaniline thin films.