The electrical, optical properties of AlSb polycrystalline thin films deposited by magnetron co-sputtering without annealing

In order to fabricate AlSb polycrystalline thin films without post annealing, this paper studies a technology of magnetron co-sputtering onto intentionally heated substrate. It compares the structural characteristics and electrical properties of AlSb films which are deposited at different substrate temperatures. It finds that the films prepared at a substrate temperature of 450 oC exhibit an enhanced grain growth with an average grain size of 21 nm and the lattice constant is 0.61562 nm that goes well with unstained lattice constant (0.61355 nm). The ln(σ_dark) ～1/T curves show that the conductivity activation energy is about 0.38 eV when the film is deposited at 450 oC without an annealing. The transmittance and reflectance spectra show that the film deposited at 450 oC has an optical band gap of 1.6 eV. These results indicate that we have prepared AlSb polycrystalline films which do not need a post annealing.     

Thermodynamic conditions for formation of single phase in Bi-superconductor thin films

High quality BSCCO thin films have been fabricated by means of an ion beam sputtering at various substrate temperatures, T_sub, and ozone gas pressures, pO₃. The correlation diagrams of the BSCCO phases appearing against T_sub and pO₃ have been established in the 2212 and 2223 compositional films. In spite of 2212 compositional sputtering, Bi2201 and Bi2223 phases as well as Bi2212 have emerged as stable phases depending on T_sub and pO₃. From these results, the thermodynamic evaluations of ΔH and ΔS, which are related with Gibbs’ free energy change for single Bi2212 or Bi2223 phase have been performed.     

Role of growth temperature on nanostructure and field emission properties of PLD thin carbon films

Thin carbon films have been deposited in vacuum (∼10⁻⁴ Pa) on Si substrates by pulsed laser ablation of a graphite target using a Nd:YAG laser operating in the near infrared region (λ=1064 nm). The samples have been deposited at different substrate temperatures (T _sub) ranging from room temperature (RT) to 800°C. X-ray diffraction analysis established the progressive formation of nanosized graphene structures as T _sub increased. In fact, film structure evolves from almost amorphous to nanostructured phase characterized by graphene layers oriented perpendicularly to the film plane. The film density, evaluated by X-ray reflectivity measurements, is strongly affected by T _sub. At RT the film density is similar to the graphite one, while it decreases at higher T _sub. The electrical properties of the samples have been characterized by field emission measurements. The parameters describing the emitter properties (threshold field E _th and field enhancement factor β) have been evaluated using variable anode-to-cathode distance method. Samples deposited at low T _sub have shown the best emission properties, presenting lower E _th and larger β values than those deposited at higher T _sub. This is mainly attributed to the sensible density variation, which is in competition with the slighter augment of mean nanoparticle size.     

Influence of preparation conditions on the dispersion parameters of sprayed iron oxide thin films

Iron oxide thin films were prepared by spray pyrolysis technique (SPT) at various substrate temperatures (T_sub) and different deposition time. X-ray diffraction (XRD) analysis showed that, at T_sub ≥ 350 °C, a single phase of α-Fe₂O₃ film is formed which has the rhombohedral structure. Moreover, the crystallinity was improved by increasing T_sub. The effect of T_sub as well as deposition time on the optical dispersion of these films has been investigated. The optical transmittance and reflectance measurements were performed by using spectrophotometer in the wavelength range from 300 to 2500 nm. The refractive index was determined by using Murmann's exact equation. It was observed that, the refractive index increased with increasing in both the T_sub and film thickness. The optical dispersion parameters have been evaluated and analyzed by using Wemple-Didomenico equation. The obtained results showed that, the dielectric properties have weak dependencies of growth temperature and film thickness. At T_sub ≥ 350 °C, the average values of oscillator energy, E_o and dispersion energy, E_d were found to be 5.96 and 34.08 eV. While at different thickness, the average values of dispersion energies were found to be 3.93 and 17.08 eV. Also, the average values of oscillator strength S_o and single resonant frequency ω_o were estimated 10.78 × 10¹³ m⁻² and 5.99 × 10¹⁵ Hz, while at different thickness were evaluating 4.81 × 10¹³ m⁻² and 6.11 × 10¹⁵ Hz. Furthermore, the optical parameters such as wavelength of single oscillator λ_o, plasma frequency ω_p, and dielectric constant ? have been evaluated. The carrier concentration N_opt by using Drud's theory was obtained the range of 5.07 × 10²⁵ m⁻³ to 1.04 × 10²⁶ m⁻³.     

Effect of substrate temperature on structure and electrical resistivity of laser-ablated IrO2 thin films

IrO₂ thin films were prepared on Si(1 0 0) substrates by laser ablation. The effect of substrate temperature (T_sub) on the structure (crystal orientation and surface morphology) and property (electrical resistivity) of the laser-ablated IrO₂ thin films was investigated. Well crystallized and single-phase IrO₂ thin films were obtained at T_sub = 573-773 K in an oxygen partial pressure of 20 Pa. The preferred orientation of the laser-ablated IrO₂ thin films changed from (2 0 0) to (1 1 0) and (1 0 1) depending on T_sub. With the increasing of T_sub, both the surface roughness and crystallite size increased. The room-temperature electrical resistivity of IrO₂ thin films decreased with increasing T_sub, showing a low value of (42 ± 6) × 10⁻⁸ Ω m at T_sub = 773 K.     

Mechanical,Thermal, and Surface Properties of Ultrahigh Molecular Weight Polyethylene/Polypropylene Blends

Various compositions of ultrahigh molecular weight polyethylene/polypropylene (UHMWPE/PP) blends were prepared in decalin, with the rheological, mechanical, thermal, and surface properties of the blends being determined using the solution cast film. Viscosity and mechanical properties of the blends decreased below the additivity value with increasing PP content implying that PP molecules disturb the entanglement of UHMWPE. Contact angle of the blend films with a water drop increased with increasing content of PP. The atomic force microscope (AFM) images showed that the surface of cast UHMWPE was very smooth whereas that of cast PP was very uneven. For blends, the surface became rough and uneven with increasing content of PP. The melting temperature of PP (T _mP) decreased in the blends with increasing UHMWPE content while that of UHMWPE (T _mU) remained almost constant in blends.     

Kinetic Monte Carlo simulation of thin film growth

A three-dimensional kinetic Monte Carlo technique has been developed for simulating growth of thin Cu films. The model involves incident atom attachment, diffusion of the atoms on the growing surface, and detachment of the atoms from the growing surface. The related effect by surface atom diffusion was taken into account. A great improvement was made on calculation of the activation energy for atom diffusion based on a reasonable assumtion of interaction potential between atoms. The surface roughness and the relative density of the films were simulated as the functions of growth substrate temperature and film thickness. The results showed that there exists an optimum growth temperatureT _opt at a given deposition rate. When the substrate temperature approaches toT _opt, the growing surface becomes smoothing and the relative density of the films increases. The surface roughness minimizes and the relative density saturates atT _opt. The surface roughness increases with an increment of substrate, temperature when the temperature is higher thanT _opt.T _opt is a function of the deposition rate and the influence of the deposition rate on the surface roughness depends on the substrate temperatures. The simulation results also showed that the relative density decreases with the increasing of the deposition rate and the average thickness of the film.     

Growth of Ba2−x Sr x NaNb5O15 thin film on La0.05Sr0.95TiO3 substrate by pulsed laser deposition

Ba_2−x Sr _x NaNb₅O₁₅ thin films were prepared on La_0.05Sr_0.95TiO₃ substrates by pulsed laser deposition. The structural and ferroelectric properties of the thin films depended on substrate temperature (T _sub) and Sr concentration. When T _sub was fixed at 700 °C, the Ba_2−x Sr _x NaNb₅O₁₅ (x = 0, 0.6, 1.0, and 1.4) thin films exhibited a high c-axis orientation. The thin films consisted of well-developed grains and exhibited a smooth surface. The c-axis-oriented Ba_0.6Sr_1.4NaNb₅O₁₅ thin film with the lowest Curie temperature also exhibited a high c-axis orientation and a P-E hysteresis loop with a high ferroelectricity at T _sub 650 °C. Thus, its remanent polarization (P _r) and coercive field (E _c) were 2P _r 24.9 μC/cm² and 2E _c 107 kV/cm, respectively. These values indicate that Ba_2−x Sr _x NaNb₅O₁₅ has ferroelectricity in the thin film form.     

Electron beam evaporated LaF3 thin films prepared by different temperatures and deposition rates

LaF₃ thin films were prepared by electron beam evaporation with different temperatures and deposition rates. Microstructure properties including crystalline structure and surface roughness were investigated by X-ray diffraction (XRD) and optical profilograph. X-ray photoelectron spectroscopy (XPS) was employed to study the chemical composition of the films. Optical properties (transmittance and refractive index) and laser induce damage threshold (LIDT) at 355 nm of the films were also characterized. The effects of deposition rate and substrate temperature on microstructure, optical properties and LIDT of LaF₃ thin films were discussed, respectively.     

Structural, optical and morphological studies on laser ablated nanostructured WO3 thin films

Thin films of tungsten trioxide (WO₃) are prepared by reactive pulsed laser deposition (PLD) technique on glass substrates at three different substrate temperatures (T_s). The structural, morphological and optical properties of the deposited films are systematically studied using X-ray diffraction (XRD), grazing incidence X-ray diffraction (GIXRD), micro-Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV-VIS spectrophotometry techniques. X-ray diffraction analysis reveals that crystalline WO₃ films can grow effectively even at 300 K at an oxygen pressure of 0.12 mbar. All the films deposited at various T_s exhibit mixed oxide phase consisting of orthorhombic and triclinic phase of tungsten oxide with a preferred orientation along (0 0 1) lattice plane reflection. Micro-Raman results are consistent with X-ray diffraction findings. The SEM analysis shows that deposited films are porous and crystalline grains are of nano-metric dimension. The effect of T_s on mean surface roughness studied by AFM analysis reveals that mean surface roughness decreases with increase in T_s. The optical response of WO₃ layers measured using UV-VIS spectrophotometry is used to extract the optical constants such as refractive index (n), extinction coefficient (k) and optical band gap (E_g), following the method of Swanepoel.     

Structural, optical properties and band gap alignments of ZrOxNy thin films on Si (1 0 0) by radio frequency sputtering at different deposition temperatures

ZrO_xN_y thin films have been prepared by radio frequency magnetron sputtering at various substrate temperatures. The effect of substrate temperature on structural, optical properties and energy-band alignments of as-deposited ZrO_xN_y thin films are investigated. Atomic force microscopy results indicate the decreased root-mean-square (rms) values with substrate temperature. Fourier transform infrared spectroscopy spectra indicate that an interfacial layer has been formed between Si substrate and ZrO_xN_y thin films during deposition. X-ray photoelectron spectroscopy and spectroscopy ellipsometry (SE) results indicate the increased nitrogen incorporation in ZrO_xN_y thin films and therefore, the decreased optical band gap (E_g) values as a result of the increased valence-band maximum and lowered conduction-band minimum.     

Effect of substrate temperature on structural, optical and electrical properties of pulsed laser ablated nanostructured indium oxide films

Nanocrystalline indium oxide (INO) films are deposited in a back ground oxygen pressure at 0.02 mbar on quartz substrates at different substrate temperatures (T_s) ranging from 300 to 573 K using pulsed laser deposition technique. The films are characterized using GIXRD, XPS, AFM and UV-visible spectroscopy to study the effect of substrate temperature on the structural and optical properties of films. The XRD patterns suggest that the films deposited at room temperature are amorphous in nature and the crystalline nature of the films increases with increase in substrate temperature. Films prepared at T_s ≥ 473 K are polycrystalline in nature (cubic phase). Crystalline grain size calculation based on Debye Scherrer formula indicates that the particle size enhances with the increase in substrate temperature. Lattice constant of the films are calculated from the XRD data. XPS studies suggest that all the INO films consist of both crystalline and amorphous phases. XPS results show an increase in oxygen content with increase in substrate temperature and reveals that the films deposited at higher substrate temperatures exhibit better stoichiometry. The thickness measurements using interferometric techniques show that the film thickness decreases with increase in substrate temperature. Analysis of the optical transmittance data of the films shows a blue shift in the values of optical band gap energy for the films compared to that of the bulk material owing to the quantum confinement effect due to the presence of quantum dots in the films. Refractive index and porosity of the films are also investigated. Room temperature DC electrical measurements shows that the INO films investigated are having relatively high electrical resistivity in the range of 0.80-1.90 Ωm. Low temperature electrical conductivity measurements in the temperature range of 50-300 K for the film deposited at 300 K give a linear Arrhenius plot suggesting thermally activated conduction. Surface morphology studies of the films using AFM reveal the formation of nanostructured indium oxide thin films.     

Deposition of NiFe(200) and NiFe(111) textured films onto Si/SiO<Subscript>2</Subscript> substrates by DC magnetron sputtering

The effect of substrate temperature T_sub and bias voltage U_bias on the texture of NiFe films with thickness d ～ 30–340 nm deposited by DC magnetron sputtering onto Si(111)/SiO₂ substrates under working gas pressure ～ 0.2 Pa has been investigated. It has been demonstrated that films grown at room substrate temperature have the (111) texture that is refined under a negative bias voltage. The deposition of films onto a grounded (U_bias ～ 0) substrate heated to T_sub ～ 440–640 K results in the formation of textured NiFe(200) films.     

Silicon substrate temperature effects on surface roughness induced by ultrafast laser processing

We report the effect of substrate temperature (T_sub) in the range 300-900 K on the surface roughness of silicon wafer resulted from femtosecond laser ablation. The surface roughness observed at the laser fluences less then 0.3 J/cm² increases with increasing T_sub. However, the surface roughness decreases with increasing T_sub for the laser fluences between 0.5 and 1.0 J/cm². If the laser fluence is higher than 2.0 J/cm², the surface roughness is independent of T_sub. The effect of T_sub on the surface roughness can be understood in terms of the temperature dependence of optical absorption coefficient of silicon substrate, which eventually alters a mechanism underlying the fs-laser-material ablation process between optical penetration and thermal diffusion processes.     

ZnO-Based transparent electrodes: Optimization of composition and synthesis conditions,study of properties

We present the results of comparative studies of the characteristics of ZnO-based transparent conductive layers doped with gallium (GZO) and aluminum (AZO), grown by dc magnetron sputtering of ceramic targets at various substrate temperatures (T _sub). Particular attention is paid to the study of stability of electrical characteristics of layers under temperature and humidity.     

Controlling the size and alignment of ZnO microrods using ZnO thin film templates deposited by pulsed laser ablation

The production of dense arrays of well aligned ZnO nano- and microrods with a controllable distribution of diameters is demonstrated. The rods were grown using a hydrothermal method, on pre-deposited ZnO thin films exhibiting a range of different grain sizes. These template ZnO thin films were deposited by pulsed laser ablation, at 193 nm, in a low background pressure of O₂; average grain sizes ranged from 10 nm (room temperature deposition) to 50 nm when deposited at a substrate temperature (T_sub) of 500 °C. The morphology of the ZnO microrod arrays grown onto these ZnO thin films was found to depend on the T_sub used during film deposition. Increasing T_sub resulted in a lower density of larger nanorods, with a more pronounced [0001] alignment. The diameters of the rods produced are typically an order of magnitude greater than the grain size of the template ZnO film. Thus the rods cannot be a direct continuation of the grain structure of the template films. Rather, we suggest that the rod diameter is controlled by the density of sites at which the initial nucleation occurs, which is expected to be higher on the smaller grain size films deposited at lower temperatures. The factor controlling the final size of the rods is thus the available free space into which they can grow, which is smaller at the higher nucleation densities. The increased extent of [0001] texturing of the thin film templates deposited at higher T_sub is proposed as the reason for the improved [0001] alignment of rods grown on these templates. PACS 81.07.De; 81.10.Dn; 52.38.Mf     

Low temperature plasma production of hydrogenated nanocrystalline silicon thin films

The hydrogenated nanocrystalline silicon (nc-Si:H) thin films were produced by capacitively-coupled plasma enhanced chemical vapor deposition (PECVD) technique at low substrate temperatures (T_s ≈ 40–200 °C). Firstly, for particular growth parameters, the lowest stable T_s was determined to avoid temperature fluctuations during the film deposition. The influence of the T_s on the structural and optical properties of the films was investigated by the Fourier transform infrared (FTIR), UV–visible transmittance/reflectance and X-ray diffraction (XRD) spectroscopies. Also, the films deposited at the center of the PECVD electrode and those around the edge of the PECVD electrode were compared within each deposition cycle. The XRD and UV–visible reflectance analyses reveal the nanocrystalline phase for the films grown at the edge at all T_s and for the center films only at 200 °C. The crystallinity fraction and lateral dark conductivity decrease with lowered T_s. FTIR analyses were used to track the hydrogen content, void fraction and amorphous matrix volume fraction within the films. The optical constants obtained from the UV–visible transmittance spectroscopy were correlated well with the FTIR results. Finally, the optimal T_s was concluded for the application of the produced nc-Si:H in silicon-based thin film devices on plastic substrates.     

Effects of oxygen partial pressure and substrate temperature on the structure and optical properties of MgxZn1−xO thin films prepared by magnetron sputtering

Deposited with different oxygen partial pressures and substrate temperatures, Mg_xZn_1−xO thin films were prepared using a Mg_0.6Zn_0.4O ceramic target by magnetron sputtering. The structural and optical properties of the prepared thin films were investigated. The X-ray diffraction spectra reveal that all the films on quartz substrate are grown along (2 0 0) orientation with cubic structure. The lattice constant decreases and the crystallite size increases with the increase of substrate temperature. Both energy dispersive X-ray spectroscopy and calculated results suggest the ratio of Mg/Zn increases with increasing substrate temperature. The thin film deposited with T_s = 500 °C has a minimal rms roughness of 7.37 nm. The transmittance of all the films is higher than 85% in the visual region. The optical band gap is not sensitive to the oxygen partial pressure, while it increases from 5.63 eV for T_s = 100 °C to 5.95 eV for T_s = 700 °C. In addition, the refractive indices calculated from transmission spectra are sensitive to the substrate temperature. The photoluminescence spectra of Mg_xZn_1−xO thin films excited by 330 nm ultraviolet light indicate that the peak intensity of the spectra is influenced by the oxygen partial pressure and substrate temperature.     

Formation,growth and ageing of clathrate hydrate crystals in a porous medium

An experimental study was performed to visually observe the driving force dependence of hydrate growth in a porous medium filled with either liquid water and dissolved CO₂ or liquid water and gaseous CO₂. The given system subcooling, ΔT _sub, i.e. the deficiency of the system temperature from the triple CO₂?hydrate?water equilibrium temperature under a given pressure, ranged from 1.7?K to 7.3?K. The fine dendrites initially formed at ΔT _sub?=?7.3?K changed quickly into particulate crystals. For ΔT _sub?=?1.7?K, faceted hydrate crystals grew and the subsequent morphological change was hardly identified for an eight-day observation period. These results indicate that the physical bonding between hydrate crystals and skeletal materials becomes stronger with decreasing driving force, suggesting that the fluid dynamic and mechanical properties of hydrate-bearing sediments vary depending on the hydrate crystal growth process.     

Correlation between microstructure and optical properties of nano-crystalline TiO2 thin films prepared by sol-gel dip coating

Titanium dioxide thin films have been prepared from tetrabutyl-orthotitanate solution and methanol as a solvent by sol-gel dip coating technique. TiO₂ thin films prepared using a sol-gel process have been analyzed for different annealing temperatures. Structural properties in terms of crystal structure were investigated by Raman spectroscopy. The surface morphology and composition of the films were investigated by atomic force microscopy (AFM). The optical transmittance and reflectance spectra of TiO₂ thin films deposited on silicon substrate were also determined. Spectroscopic ellipsometry study was used to determine the annealing temperature effect on the optical properties and the optical gap of the TiO₂ thin films. The results show that the TiO₂ thin films crystallize in anatase phase between 400 and 800 °C, and into the anatase-rutile phase at 1000 °C, and further into the rutile phase at 1200 °C. We have found that the films consist of titanium dioxide nano-crystals. The AFM surface morphology results indicate that the particle size increases from 5 to 41 nm by increasing the annealing temperature. The TiO₂ thin films have high transparency in the visible range. For annealing temperatures between 1000 and 1400 °C, the transmittance of the films was reduced significantly in the wavelength range of 300-800 nm due to the change of crystallite phase and composition in the films. We have demonstrated as well the decrease of the optical band gap with the increase of the annealing temperature.