Effects of post-deposition annealing on morphology and optical properties of electron beam evaporated Bromoaluminium phthalocyanine thin films

In this paper, effects of post-deposition annealing on morphology and optical properties of electron beam evaporated Bromoaluminium phthalocyanine thin films have been investigated. Surface morphology of the films have been characterized by field emission scanning electron microscopy (FESEM). The FESEM micrographs have shown densely packed nanoparticles and nanorod-like structures for the films annealed at different temperatures. Conditions leading to β-phase have been identified by monitoring post-deposition annealing using optical absorption spectroscopy (UV–Vis). The optical absorption measurements on the as-deposited and annealed films shows that the absorption mechanism is due to direct transition. Also, it is found that the optical band gap decreases with increase in annealing temperature.     

Structural and optical properties of thermally evaporated zinc phthalocyanine thin films

Thermally evaporated zinc phthalocyanine (ZnPc) films in the as deposited condition were identified to be as-amorphous. It undergoes structural transformation upon annealing up to 613 K. The optical properties and spectral behavior of as deposited and annealed thin films of ZnPc were studied using spectrophotometric measurements of the transmissivity and reflectivity at normal incidence of light in the wavelength range 200–2500 nm. The refractive index, n, and absorption index, k, were calculated and it was found that they are independent of film thickness in the thickness range 205–530 nm. Annealing at 613 K increases absorbance of films by 5–6 times in comparison with absorbance of as deposited ones and shifts peak positions of all bands towards low energy side of spectra except the peak position of N-band is shifted towards high energy side of spectra. The absorption spectra in the UV–VIS. region has been analyzed in terms of both molecular orbital and band theories. Indirect allowed transitions near the onset and fundamental absorption edges were observed. The energy at the onset was obtained and equals to 1.45 and 1.51 eV for as deposited and annealed films, respectively. The fundamental energy gap was obtained and equals to 2.94 and 2.88 eV for as deposited and annealed films, respectively. The absorption spectra shows four absorption bands. The oscillator strength, f, the electric dipole strength, q², the molar extinction coefficient, ζ_molar, were calculated for as deposited and annealed ZnPc thin films.     

Electrical and optical properties of phthalocyanine films

Thin films of various phthalocyanines (Pcs) were sublimed onto quartz glass in ultrahigh vacuum. The electrical and optical properties were studied without breaking the ultrahigh vacuum. The dyes were purified by repeated sublimation in vacuum.The conductivity varied with pretreatment (modification) and temperature. Exposure to oxygen, iodine and bromine increased the p-type conductivity by orders of magnitude and lithium doping caused n-type conductivity. Heavy exposure to halogens caused not only broadening of the optical absorption band but also bleaching. Annealing in vacuum removed the electrical and optical effects of doping nearly completely.Field effect studies were used to identify p- and n-type conductivity, to determine the drift mobility and to estimate the trap densities. The field effect and the photoconductivity of p- and n-type films increased by several orders of magnitude with the dark conductivity, i.e. with doping. This correlation is attributed either to traps with a continuous distribution in energy or to trapping by at least two discrete defect levels crossing the Fermi level within the surface-induced accumulation layer. Possible consequences for the sensitivity of semiconductor gas sensors are discussed.     

Mechanical properties of nanocomposite thin films

The mechanical properties of nanocomposite thin films are reviewed. Two types of films are considered: artificially multilayered thin films and granular metal thin films. Artificially multilayered thin films, which are composed of alternating layers of two different materials, can display variations (reductions or enhancements) of the order of 15 to 30% in their elastic behavior as the bilayer repeat length is reduced below about 5 nm. Significant enhancements in the hardness of these materials are also observed for this range of bilayer repeat length. Granular metal films, which are composed of a thin film ceramic matrix embedded with metal granules of diameters as small as a few nanometers, display novel behavior in their hardness and apparent elastic behavior as measured by low-load indentation methods. This appears to be correlated with the percolation threshold of the metal.     

Effects of working pressure on morphology,structural, electrical and optical properties of a-InGaZnO thin films

Amorphous In–Ga–Zn–O (a-IGZO) thin films (～200 nm thickness) were deposited by radio-frequency (RF) magnetron sputtering on silicon and glass substrates at various working pressures (0.67–2.67 Pa) and a fixed oxygen-to-argon gas-flow ratio (O₂/Ar = 5%). The transparency of all of the films was more than 85% in the visible range. With increased working pressure, the surface morphology of the films, as observed under atomic force microscopy (AFM), became rough; the optical band gap, estimated by Tauc plot, increased, and the mobility and carrier concentrations, according to Hall measurement, decreased and increased, respectively. The resistivity of the films initially decreased (up to 2.00 Pa working pressure) and then increased (at 2.67 Pa). It is suggested that the electrical property changes were affected by the role of the oxygen vacancies, whether as effective donors or as scattering centers.     

Influence of thermal annealing on optical properties and surface morphology of NiOx thin films

NiO_x thin films were deposited by reactive DC-magnetron sputtering from a nickel metal target in Ar + O₂ with the relative O₂ content of 5%. Thermal annealing effects on optical properties and surface morphology of NiO_x films were investigated by X-ray photoelectron spectroscopy, thermogravimetric analysis, scanning electron microscope and optical measurement. The results showed that the changes in optical properties and surface morphology depended on the temperature. The surface morphology of the films changed obviously as the annealing temperature increased due to the reaction NiO_x → NiO + O₂ releasing O₂. The surface morphology change was responsible for the variation of the optical properties of the films. The optical contrast between the as-deposited films and 400 °C annealed films was about 52%. In addition, the relationship of the optical energy band gap with the variation of annealing temperature was studied.     

Electrical,structural and gas sensing properties of zinc phthalocyanine thin films

The dark conductivity of zinc phthalocyanine (ZnPc) has been studied as a function of material purity, crystal phase transformation and temperature with particular regard to gas sensitivity in air, O₂, N₂, argon, NH₃ and NH₃-air mixtures. α-ZnPc was found to grow in the form of randomly oriented micro- crystallites but the β form showed oriented needle-like and whisker growth. The electrical properties were found to be dependent on material purity. Entrainer- sublimed ZnPc showed higher conductivity than impure material and displayed reproducible linear characteristics with less drift and hysteresis.The conductivity of both α- and β-ZnPc is found to be critically dependent on the presence of O₂. The sensitivity to other gases differs for the α and β forms but in both cases NH₃ causes a large dark conductivity decrease, possibly owing to catalytic behaviour, effectively removing oxygen acceptors.Conductivity-temperature data indicate a transition from extrinsic to non-extrinsic conduction for most cases.The conductivity of β-ZnPc is found to be greater than that of α-ZnPc, in contrast with other phthalocyanines.The relative sensitivities to the various gases suggests that ZnPc may be a viable material for selective gas sensing devices.     

On the correlation between morphology and electronic properties of copper phthalocyanine (CuPc) thin films

The morphology of vacuum deposited copper phthalocyanine (CuPc) thin films surface deposited on Si(111) have been studied using the contact mode Atomic Force Microscope (AFM). The influence of substrate temperature during deposition and of the post-deposition UHV annealing on surface roughness as well as on the average and maximum grain height was determined. The observed changes of surface morphology were in a good correlation with the shift of surface Fermi level position in the band gap after O₂ exposure determined in our recent photoemission studies.     

Controlled growth and investigations on the morphology and mechanical properties of hydroxyapatite/titania nanocomposite thin films

In this paper, the focus is on understanding the properties of nanocomposite hydroxyapatite (HAp)/titania (TiO₂) thin films with respect to TiO₂ concentration. HAp/TiO₂ nanostructured composite thin films with different TiO₂ concentrations were successfully fabricated by a simple sol–gel dip coating method. Highly stable HAp and TiO₂ sols were prepared prior to the formation of nanocomposite thin films. The coatings were performed under controlled dipping and heat treatment processes. Phase pure HAp and TiO₂ were well developed in the nanocomposite after the heat treatment and this was confirmed by XRD. The SEM and AFM analyses of HAp/TiO₂ nanocomposite coatings show the variation in the morphology as a consequence different TiO₂ concentration. This shows a reduction in the particle size to nanoscale due to the addition of TiO₂. The mechanical strength of the coating also increased upon the addition of TiO₂ as determined by nanoindentation. The composite thin films with 50 and 80 vol.% of TiO₂ show good mechanical strength when compared to other concentrations of TiO₂.     

The role of growth parameters on structural,morphology and optical properties of sprayed ZnS thin films

ZnS thin films were prepared by spray pyrolysis technique using aqueous of zinc chloride and thiourea at molar ratio of 1:1, 1:2, and 2:1. The depositions were carried out on substrates heated from 400 to 520 °C The films were then annealed under sulphur atmosphere for 90 min at 450 and 550 °C. The crystallites exhibit preferential orientation along the [002]_α or [111]_β directions. The films were characterized by XRD and SEM. The structure and morphology of sprayed films are controlled by both, the substrate temperature and the precursors molar ratio in the solution. The values of optical bandgap have been determined from the absorption spectra.     

Polyimide/sepiolite nanocomposite films: Preparation, morphology and properties

Polyimide/sepiolite nanocomposite films have been prepared via an in situ polymerization method. The process involves the dispersion of sepioite in N,N-dimethylacetamide, polycondensation of 2,2′-bis [4-(3,4-dicarboxyphenoxy) phenyl] propane dianhydride and 4,4′-oxydianiline in the presence of sepiolite suspension to form poly(amic acid), and the thermal imidization of poly(amic acid)/sepiolite nanocomposite. The morphology, thermal and mechanical performance, and water absorption of nanocomposite films were systematically studied with various sepiolite contents. The results indicated that sepiolite was dispersed homogeneously at a nanometer scale in polyimide matrix. Owing to such nanodispersion of sepiolite, the polyimide/sepiolite nanocomposite films exhibit dramatic improvements on the mechanical properties and the coefficient of thermal expansion while fine thermal stability and low water absorption capacity were also maintained. When the sepiolite content increased to 16% the polyimide/sepiolite nanocomposite film achieved as much as 41% and 94% increase on the tensile strength and modulus respectively, and 50% decreased in coefficient of thermal expansion.     

C-Ti nanocomposite thin films: Structure, mechanical and electrical properties

Carbon-titanium nanocomposite thin films were deposited by DC magnetron sputtering on oxidized silicon substrates in argon. The films were prepared at different deposition temperatures between 25 and 800 °C. Transmission electron microscopy was used to determine the structure of the films. All the C-Ti nanocomposites consisted of columnar TiC structure with average column width ∼10 and 20 nm and a thin carbon matrix. The thickness of the carbon matrix between adjacent TiC columns was ∼2-5 nm.Mechanical properties (hardness, reduced modulus) of C-Ti films showed a distinct variation depending on the deposition temperature. Films deposited at 200 °C had the highest hardness ∼18 GPa and the highest reduced modulus ∼205 GPa.Temperature dependence of the film resistance was measured between 80 and 330 K. C-Ti nanocomposites have a non-metallic conduction mechanism characterized by a negative temperature coefficient of resistivity (TCR). The most negative TCR was observed for films showing high hardness and reduced modulus of elasticity.     

Photocatalytic and antibacterial properties of TaON-Ag nanocomposite thin films

TaON-Ag nanocomposite thin films with Ag nano-particles embedded in TaON were prepared by reactive co-sputtering of Ta and Ag in the plasma of (O₂ + N₂)/Ar. The deposition temperature was either at room temperature or 300 °C. These films were characterized mainly by UV-Vis photometry and scanning electron microscopy. It is found that Ag doping into the TaON films leads to several beneficial changes on film properties. It would reduce the optical band gap and, therefore, enhance the films' photocatalytic behavior. It is also found that Ag nano-particles may emerge on the surface of TaON with or without RTA. This could be much meaningful since Ag particles' appearance is closely related to the antibacterial property of TaON-Ag films. The results show that TaON-Ag films deposited at 300 °C have an outstanding antibacterial behavior with the illumination of visible light due to the synergistic effects of Ag and photocatalytic behavior of TaON.     

氧化锌薄膜的p型掺杂及光学和电学性质研究

为了实现氧化锌薄膜的p型掺杂,从而制备氧化锌同质p-n结,采用化学气相沉积法,以二水合醋酸锌为前驱,醋酸铵为氮源,在氧气氛下制备了氮掺杂的p型氧化锌薄膜.利用X射线光电子能谱和X射线衍射分析,表征了氧化锌薄膜的化学成分.通过霍尔效应测量证实了薄膜的p型导电特性.探讨了制备过程中温度、压强、源物质等条件对反应产物的影响,研究了薄膜的光学和电学特性,得到了p型氧化锌薄膜的吸收光谱和光致发光光谱,以及氧化锌p-n结的伏安特性曲线.     

Single layer polycrystalline ZnO-Al2O3 nanocomposite thin films: optical and electrical properties

Nanometric size dependent optical absorption coefficients, dispersive nature of the dielectric constants and ac conductivity are observed for the single layer ZnOx(Al2O3)1-x (x = 0.20 and 0.50) nanocomposites thin films. The sol-gel prepared thin films with thickness approximately 119 nm, contains randomly dispersed ZnO nanocrystallites in the A2O3, matrix. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) revealed homogeneous distributions of the nanoparticles in the matrix. The shifting and broadening of the optical absorption peaks to the lower wavelength region at higher annealing temperatures was analyzed in order to relate the particle-particle interactions and the sizes of the dispersed nanoparticles in the matrix. AC impedance spectroscopy in the frequency range of 500 Hz to 5 MHz was measured at room temperature (300 K), 325 K, 395 K, and 450 K. The dielectric relaxations in each case were found to be of Cole-Cole type. The semicircular pattern of the ac capacitance in the complex plane showed contributions from the grain and grain boundary subject to concentration of ZnO in the matrix. The appearance of the negative capacitance at higher frequency was also analyzed.     

Synthesis and optical properties of photosensitive polyimide/silica hybrid thin films

In this study, the photopatternable fluorinated polyimide/silica hybrid materials were synthesized by 4,4′-hexafluoroisopropylidenediphthalic anhydride (6FDA), oxydianiline (ODA), aminopropyltriethoxysilane (APrTEOS), and 12 nm colloidal silica with a coupling agent. The monodispersed colloidal silica was used to form a silica domain instead of alkoxysilanes in the conventional process. The coupling agents used were 3-methacryloxypropyl trimethoxysilane (MPTMS) or (4-vinylphenethyl)trimethoxysilane (VPTMS). The coupling agent and the silica domain were designed to reduce the volume shrinkage and enhance the thermal properties, respectively. The retention of 2-methyl acrylic acid 2-dimethylamino-ethyl ester (MDAE) in the prepared hybrid films was supported by X-ray photoelectron spectroscopy (XPS) and thickness variation during the curing process. The particle size of silica in the hybrid materials based on SEM analysis was in the range of 10–25 nm. The prepared hybrid materials also exhibited a reduced refractive index after increasing the silica content. The SEM diagram suggested the prepared photosensitive hybrid materials could obtain lithographical patterns with a good resolution. These results indicate that the newly prepared photosensitive polyimide/silica hybrid materials may have potential applications for optical devices.