Vacuum Thermal Evaporation Method Research Articles

Temperature Dependence of Bis(triisopropylsilylethynyl)-Pentacene Nanofilm Deposited on Octadecyltrichlorosilane Self Assembled Monolayer Surface as a Transistor Channel

Highly pure 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-PEN) nanofilms were deposited on a hydrophobic OTS-SAM surface at two different substrate temperatures (70 degrees C and 90 degrees C) via the vacuum thermal evaporation (VTE) method. X-ray reflectivity measurements over a wide temperature range (30 degrees C-284 degrees C) revealed that out-of-plane crystallinity of the film (approximately 10 nm) remains intact but in-plane crystallinity starts to become poor from approximately 100 degrees C, and to become much more worse from 260 degrees C. Atomic force microscope images showed that TIPS-PEN films (approximately 55 nm) prepared at the substrate temperature of 90 degrees C or above commonly have a number of huge cracks between enormous crystal domains (up to 3 microm) whereas the films didn't form such morphology below T(s) = 90 degrees C. These results clearly suggest that an optimum substrate temperature of TIPS-PEN nanofilms on OTS-SAM surface must be somewhere between 70 degrees C and 90 degrees C, and the process temperature must be kept below 90 degrees C in order to form and maintain a highly crystalline film for an organic thin film transistor device since in-plane crystallinity of a semiconductor channel deeply affects the performance of a transistor.

Thickness-Dependent Mechanical Behaviour of Aluminium-Coated Polyethylene Terephthalate (PET) Films

Mechanical behaviour of aluminium-coated PET films has been investigated through Dynamic Mechanical Analyser. Aluminium is coated on PET substrate by vacuum thermal evaporation method. As thickness of aluminium coating increases from 150 nm to 350 nm, tensile strength decreases from 108.88 MPa to 99.25 MPa. This mechanical behaviour is correlated with microstructure and its evolution with the thickness of aluminium coating. Al-PET film consists of fine globular grains and average grain size increases monotonically with the film thickness. The relative contribution of the grain size to the strength of aluminium thin films is in good agreement with Hall-Patch equation.

Mechanical study of metallized polyethylene terephthalate (PET) films

Mechanical properties such as Young's modulus ( Y), storage modulus ( E′), glass transition temperature ( T g), tensile strength ( σ), and yield strength ( σ y) of metallized polyethylene terephthalate (PET) films have been measured using Dynamic Mechanical Analyser (DMA). Commercially available PET film thickness of 20 μm has been used for metallization. Aluminium (Al) and lead (Pb) have been coated separately on PET films by vacuum thermal evaporation method to form metallized PET films. The T g of Al-PET and Pb-PET films has been found to be 112.3 °C and 111.2 °C respectively whereas T g of commercial PET film is 89.7 °C. The stress–strain curves of metallized PET films at room temperature and at different elevated temperatures have been taken which show significant temperature dependence. In particular, the yield strength shows a decrement with increasing temperature.

Role of hydrogen in electrical and structural characteristics of bilayer CdTe/Mn diluted magnetic semiconductor thin films

Abstract Bilayer thin films of diluted magnetic semiconductor CdTe/Mn have been prepared using vacuum thermal evaporation method at pressure of 10−5 torr. Annealing of bilayer thin films has been performed in atmospheric condition at constant temperature 400 °C for 1 hour. Hydrogenation of as-grown and annealed bilayer thin films has been performed by keeping these in hydrogenation cell. Structural characteristics of as-grown and heat treated thin films have been performed by X-ray diffractometer. Current–voltage characteristics of both as-grown hydrogenated and annealed hydrogenated bilayer thin films have been studied to find out the effect of hydrogenation. Surface topography of as-grown and annealed bilayer thin films has been confirmed by optical microscopy.

Synthesis and characterization of In2S3: Na thin films prepared by vacuum thermal evaporation technique for photovoltaic applications

In 2 S 3 thin films containing different quantities of sodium have been synthesized by co-evaporation of sodium and In 2 S 3 powder from separate sources using vacuum thermal evaporation method. Films were deposited on ordinary glass at 240 °C. The process of incorporation of sodium was studied as function of at.% Na. Films have been characterised by means of X-ray diffraction, SEM, EDAX and spectrophotometry. X-ray diffraction analysis confirmed the initial amorphous nature of deposited layers and revealed the formation of In 2 S 3 as function of annealing layers containing sodium in nitrogen at 300 °C for 2 h. Energy Dispersive X-ray Analysis (EDAX) revealed the composition of the films as a function of the sodium incorporation. Surface Electron Microscopy showed that these films were granular and homogenous. The films have an n-type electrical conductivity and their optical direct band gap can be managed between 2.20 and 2.45 eV by controlling their sodium content. The variation of parameters for as-deposited and annealed films has been studied within at.% solid solution composition. Thin layers with homogeneous surfaces, direct band gap energy of about 2.45 eV for 4 at.% Na and 0.9 μ m-thick have been achieved.

Silicon metal-semiconductor–metal photodetector with zinc oxide transparent conducting electrodes

Transparent conducting oxides thin layers, due to their optical and electrical properties, can be used as transparent electrodes in various optoelectronic devices. We present a metal-semiconductor–metal photodiode (MSM-PD) on silicon as optically active layer with zinc oxide (ZnO) thin layer as interdigitated Schottky transparent electrodes. The advantage of using a ZnO thin layer as Schottky electrodes consists in the improvement of the photoresponse by eliminating the shadowing of the active area by opaque metallic electrodes. ZnO thin layers were deposited on 10 Ω cm resistivity silicon epitaxial wafers by the vacuum thermal evaporation method. High purity metallic powders were mixed with an (Al+Sn)/Zn ratio of 0.03. In order to obtain transparent layers the metallic depositions were thermally treated at 450 °C for 2 h. The Al, Sn co-doped ZnO layers of 0.5–0.8 μm were investigated regarding structural, optical and electrical properties and surface morphology. The obtained thin layers have a high transparency (T>85%) over a large spectral range and the resistivity is quite low, ρ~10−4 Ω cm. The interdigitated Schottky contacts of ZnO were configurated onto the optically active Si layer providing an MSM-PD structure of 0.143 mm2 active area and finger spacing and finger width of 6 μm. The optoelectronic characteristics were measured and the Schottky barrier height of 0.62 eV was determined from the current–voltage characteristic. A responsivity of 0.2 A/W at 475 nm and a capacitance of 1.4 pF at 10 V bias were obtained for the MSM-PD structure with transparent conducting ZnO Schottky electrodes.

Giant Magnetoresistance inLa0.67Ca0.33MnO3/Alq3/Co Sandwiched-StructureOrganic Spin Valves

La0.67Ca0.33MnO3/Alq3/Cosandwiched-structure organic spin valves are fabricated by vacuumthermal evaporation method. A giant magnetoresistance (GMR) of 14% isobserved at low temperature 100 K. At 30 K, the magnetoresistance canincrease to 50%. The large GMR of the device is attributed to the highspin polarization and low conductivity of theLa0.67Ca0.33MnO3 contact. The magnetoresistanceΔR/R and the coercive field of the Co electrode dependstrongly on temperature. The large high-field magnetoresistancereported on La0.67Sr0.33MnO3/Alq3/Coorganic spin valves [Nature 427 (2004) 821] is not observed inour La0.67Ca0.33MnO3/Alq3/Co organic spin valves.

Solid-state supercapacitors for electronic device applications

We report an all-solid-state supercapacitor with device fabrication by a simple vacuum thermal evaporation method, which allows not only a multilayer stacking structure to further enhance the capacitance, but also permits the supercapacitor to be easily incorporated with other electronic devices, showing interesting characteristics for both fundamental study and practical applications. Discussions about the mechanism of the supercapacitor is given.

Fabrication and characterization of In 2S 3 thin films deposited by thermal evaporation technique

Indium sulphide, In 2S 3, thin films present an alternative to conventional CdS films as buffer layer for CIS-based thin film solar cells. The objective is to eliminate toxic cadmium for environmental reasons. Indium sulphide is synthesized and deposited by single source vacuum thermal evaporation method on glass substrates. The films are analyzed by X-ray diffraction (XRD) and spectrophotometric measurements. They have a good crystallinity, homogeneity and adhesion. The X-ray diffraction analysis confirmed the initial amorphous nature of the deposited InS film and phase transition into crystalline In 2S 3 formed upon annealing at free air for 250 °C substrate temperature for 2 h. The optical constants of the deposited films were obtained from the analysis of the experimental recorded transmission and reflectance spectral data over the wavelength range of 300–1800 nm. We note that the films annealed at 250 °C for 2 h show a good homogeneity with 80% transmission. An analysis of the optical absorption data of the deposited films revealed an optical direct band gap energy in the range of 2.0–2.2 eV.

Ion conduction studies on LaF3 thin film by impedance spectroscopy

Abstract Lanthanum fluoride thin film has been prepared by vacuum thermal evaporation method. The hexagonal-phase LaF 3 film has been detected by using glancing angle XRD analysis. The XPS analysis confirms the composition of lanthanum fluoride. The F − ion conduction through the grain and grain boundary has been analyzed using impedance analysis. The modulus spectra reveal the non-Debye nature and the distribution of relaxation times of the film.

Structural and optical properties of sulfur-annealed CuInS 2 thin films

CuInS 2 thin films were deposited by single source vacuum thermal evaporation method on substrates submitted to longitudinal thermal gradient. Some of these films were annealed in sulfur atmosphere and converted into CuInS 2 homogenous layers. Both of the as-deposited and sulfurated films were characterized by X-ray diffraction, optical transmission and reflection measurements. The optical band gap of films after sulfurization was 1.50 eV which is near the optimum value for photovoltaic energy conversion.

Abnormality detection method, abnormality detection apparatus, and solar cell power generating system using the same

Centimeter level AgCuAu composite nanowires were prepared by a solid-state ionics method under a direct current electric field (DCEF) using fast ionic conductor RbAg4I5 films and vacuum thermal evaporation method. The surface morphology and chemical composition of the AuAgCu composite nanowires were characterized by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), respectively. Raman enhancement performance of the AgCuAu composite nanowires substrates was detected by Rhodamine 6G (R6G) aqueous solutions as probe molecules. Long-range order and short-range order AgCuAu composite nanowires with the length of 1 cm were prepared. The nanowires were bamboo-shaped with high surface roughness and the diameters of nanowires ranged from 60 to 100 nm. The molar ratio of Ag:Cu:Au in composite nanowires is 15:2:1. The intrinsic Raman peaks of 10−16 mol/L R6G at 612, 773, 1125, 1182, 1307, 1361, 1418, 1506, 1545, 1575, 1597, 1650 cm−1 are all present when AgCuAu composite nanowires were used as the SERS substrates.

Effect of substrate thermal gradient on as-grown CuInS 2 properties

Copper indium disulfide thin films were deposited by vacuum thermal evaporation method. The interest of this study is focused on the effects of substrate heating conditions on the layer growth and properties. It was found that a longitudinal thermal gradient (LTG), even small, induces drastical changes in optical properties of the layers which behave as a highly absorbing material. Crystallized resistive and highly absorbing as-made layers were studied in comparison with “standard” CuInS 2 samples (conductive heating at 250 °C). Electrical, structural, and optical analysis showed that the involved prominent property (i.e., opacity) seems to be a volume effect occurring during growth stage and is clearly correlated to LTG conditions. On the other hand, thermal cycling in vacuum in the 293–573 K range did not show any electrical disturbance as exhibited in the “standard” CuInS 2 Case.

Comparative spectroelectrochemical investigation of vacuum evaporated and electrochemically synthesized electrochromic polyaniline films ag

A spectroelectrochemical study of thin electrochromic polyaniline (PAN) films deposited on SnO 2 glass substrates by a vacuum thermal evaporation method has been carried out. The films obtained were studied by means of spectral, spectroelectrochemical and electrochemical methods, and the results were compared with those obtained for PAN films prepared by electrochemical polymerization. Spectroelectrochemical data (obtained under a potential step) and cyclic voltammetry data showed that the evaporated PAN films did not undergo a second oxidation stage resulting in formation of a quinoid structure. Current vs. time dependences processed according to the Cottrell equation showed that the diffusion coefficient for the evaporated PAN layers was almost a factor of 3 lower than that for the electrochemically deposited films. During cyclic tests in a real electrochromic optical filter the evaporated PAN layers exhibited a stability more than 2.5 times higher than that of the electrochemically deposited films.

Measurement of thermal expansion at low temperatures

It is difficult to fabricate magnetic films containing small nanoparticles with a narrow size distribution. The nanomagnetic structural evolutions inside the nanoparticles in these types of films play a key role in the development of the magnetic properties. Magnetic composite films with a cubic array distribution of the nanoparticles are obtained using the layered growth of FeNi–SiO and SiO by the vacuum thermal evaporation method. The films contain small nanoparticles with a narrow size distribution (4.59 ± 0.18 nm) and an ordered cubic array. In the films, the magnetic induction lines measured by the differential phase contrast microscopy of the transmission electron microscope confirm that the disordered domain becomes multi-domain with an ordered cubic array. Furthermore, the saturation magnetization of such a film is higher than that of a pure FeNi film, despite the presence of the nonmagnetic SiO dielectric. This type of new material can be used in magnetic shields with a weak magnetic field and highly sensitive magnetic sensors.