Screened remote plasma-enhanced atomic vapor deposition of Sb–Te thin film for the improvement of trench-covering ability

A new screened remote plasma-enhanced atomic vapor deposition (SPEAVD) technique was studied for depositing Sb–Te phase-change materials inside trench structures with high aspect ratios. The theoretical model of the screening mechanism included the concepts of a plasma sheath and a sticking coefficient. Plasma’s limitation of poor step coverage was overcome by filtering its high-energy ions and electrons. Cross-sectional observation was conducted using field emission scanning electron microscopy (SEM). The trench-covering ability of SPEAVD was much better than that of direct remote PEAVD under broad chamber conditions. Surface morphology was observed by SEM and atomic force microscopy. The surface chemical state of the deposited film was measured by X-ray photoelectron spectroscopy. The crystallinity in various deposition temperatures was analyzed by X-ray diffraction measurements. The electrical characteristics of the films were measured by a four-point probe. We expect this research to provide a new deposition method that will allow fine control of step coverage and other characteristics.     

Optimal deposition condition of chlorophyll a Langmuir–Blodgett film

The optimal deposition condition of chlorophyll a (Chl a) Langmuir–Blodgett (LB) film were investigated based on π–a isotherms, absorption spectrum and scanning tunneling microscopy (STM) observation. The π–a isotherms of Chl a LB film at various air temperatures and subphase pHs were obtained. Optimum temperature and pH for dense packing of Chl a LB layers are 25 °C and 7.0, respectively. The formation of J- and H-aggregations of the ordered chlorophyll a molecules was confirmed by absorption spectrum measurements. The well-ordered structure of Chl a LB layer was observed by STM. Thus, the densely packed Chl a LB layer could be fabricated by the proposed optimal deposition condition.     

Growth of germanium–carbide thin film on crystal substrate

The formation of germanium-carbide in crystalline germanium substrate is studied using the perturbed γ–γ angular correlation (PAC) method. The growth of Ge–C micro-crystalline system in the host matrix was observed after annealing the sample above 450°C in vacuum. The Ge–C complexes have been detected at high dose carbon implantation in germanium (≥1 × 10¹⁵cm ⁻²). Information about the lattice locations of the carbon atoms in the host lattice can be obtained via the interaction between carbon atoms with unstable probe nucleus (¹¹¹In). Several carbon related complexes have been detected in this investigations which can be characterized by unique quadrupole interaction frequencies. The parameters of the hyperfine interactions drawn from the time spectra provide additional information about the formation of Ge–C system in germanium.     

Electrochemical studies of n-Cd1−xMnxSe thin film photodetector

Studies on dilute semimagnetic semiconductor thin films are of immense importance. Coupled with their semiconducting properties, they have the characteristic magnetic properties, which make them an attractive alternative in a variety of electronic and optoelectronic devices including gas sensors and solar energy conversion devices. The basic materials are cheap and the actual material can easily be obtained from an aqueous alkaline medium (pH=10.5±0.2) by deposition of Cd²⁺, Mn²⁺ and Se^2– ions. The temperature and time for deposition were optimized as 50 °C and 120 min, respectively. The deposits were adherent to the substrate support, uniform and smooth with color changing from deep orange red to yellowish orange as Mn²⁺ concentration was varied from 0 to 0.5. The electrochemical detector cells were formed out of these series of films as the active photoelectrodes, an electrolyte and a counter electrode and were characterized through their electrical properties. A short circuit current (I _sc) of 147 A/cm² and open circuit voltage (V _oc) 468 mV were noticed at x=0.1 under a steady illumination intensity of 20 mW/cm². The calculated conversion efficiency (%) approached to 0.13% whereas the maximum cell fill factor is 38.45%. These electrochemical detectors exhibited a considerable amount of recombination and series resistance effects.     

Effect of chain conformation on micro-mechanical behaviour of MEH–PPV thin film

The morphology, photoluminescent properties and micro-mechanical character of poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylene vinylene] (MEH–PPV) thin films prepared from toluene (T film) and chloroform (C film) were studied by transmission electron microscopy (TEM), absorption, photoluminescence spectrophotometry and nanoindentation test. The morphological feature of worm-like entities which appeared in T film was ~10–20 nm in length and 3–5 nm in width. The C film displayed the continuous cotton fibre-shaped morphology. In contrast with C film, the band-edge absorption and maximum emission for T film shifted to the longer wavelength. An analysis from TEM photograph, absorption and photoluminescence spectra indicated that different chain conformation presented in these two kinds of films. The nanoindentation test showed that the elastic modulus and indentation hardness of T film under the same experimental parameter (load: 50–200 μN, loading rate: 20 μN/s and holding time: 20 s) decreased by 33·3 ± 0·3 and 8·9 ± 0·5%, respectively comparing with C film. In addition, critical bending radius of these two films based on the flexible base was also evaluated from the obtained experimental results.     

Fabrication of nanocrystal ink based superstrate-type CuInS₂ thin film solar cells

A CuInS? (CIS) nanocrystal ink was applied to thin film solar cell devices with superstrate-type configuration. Monodispersed CIS nanocrystals were synthesized by a colloidal synthetic route and re-dispersed in toluene to form an ink. A spray method was used to coat CIS films onto conducting glass substrates. Prior to CIS film deposition, TiO? and CdS thin films were also prepared as a blocking layer and a buffer layer, respectively. We found that both a TiO? blocking layer and a CdS buffer layer are necessary to generate photoresponses in superstrate-type devices. The best power conversion efficiency (～1.45%) was achieved by the CIS superstrate-type thin film solar cell device with 200 and 100 nm thick TiO? and CdS films, respectively.     

Pulsed laser deposition of p-type α-AgGaO2 thin films

Polycrystalline α-AgGaO₂ powders were prepared by the hydrothermal conversion of β-AgGaO₂. The β-AgGaO₂ was synthesized by the ion exchange reaction between NaGaO₂ and molten AgNO₃ under nitrogen atmosphere. The α-AgGaO₂ thus synthesized was used as the target for pulsed laser ablation. The films grown on α-Al₂O₃ (0001) single crystal substrates are crystalline and are 50% transparent in the visible region. The temperature dependence of conductivity shows a semiconducting behaviour with room temperature conductivity 3 × 10^− 4 Scm^− 1. The positive sign of Seebeck coefficient (+ 70 μVK^− 1) demonstrated the p-type conduction in the films. Transparent p-n heterojunctions on a glass substrate were fabricated. The structure of the device was glass/ITO/n-ZnO/p-AgGaO₂. The ratio of forward to reverse current was more than 100 in the range of − 1.5 V to + 1.5 V.     

Study of optical characteristics of tin oxide thin film prepared by sol–gel method

In this paper, we present details of preparation of tin oxide (SnO $_{{2}})$ thin film by sol–gel process. The film was synthesized on a glass (Corning 7059) plate by dip coating method. Here, we used tin (II) chloride as precursor and methanol as solvent. Optical characteristics and physical properties like refractive index, absorption coefficient and thickness of thin film were calculated from the study of transmission spectrum (wavelength vs transmission curve) data given by UV/VIS Spectrophotometer. Effect of number of coatings on transmittance and refractive index was also examined. It was observed that refractive index decreases with the number of coating and transmission value was more than 80% at wavelength greater than 450 nm in all cases. Structural analysis was studied by XRD measurement by using diffractometer which confirms tetragonal rutile structure of SnO ₂ . Surface morphology was analysed from SEM micrograph and change in morphology on number of coat was discussed.     

Hydrothermal synthesis of β-nickel hydroxide nanocrystalline thin film and growth of oriented carbon nanofibers

Novel well-crystallized β-nickel hydroxide nanocrystalline thin films were successfully synthesized at low temperature on the quartz substrates by hydrothermal method, and the oriented carbon nanofibers (CNFs) were prepared by acetylene cracking at 750 °C on thin film as the catalyst precursor. High resolution transmission electron microscopy (HR-TEM) measurement shows that thin films were constructed mainly with hexagonal β-nickel hydroxide nanosheets. The average diameter of the nanosheets was about 80 nm and thickness about 15 nm. Hydrothermal temperature played an important role in the film growth process, influencing the morphologies and catalytic activity of the Ni catalysts. Ni thin films with high catalytic activity were obtained by reduction of these Ni(OH)₂ nanocrystalline thin films synthesized at 170 °C for 2 h in hydrothermal condition. The highest carbon yield was 1182%, and was significantly higher than the value of the catalyst precursor which was previously reported as the carbon yield (398%) for Ni catalysts. The morphology and growth mechanism of oriented CNFs were also studied finally.     

Fabrication of PANI–ZnO nanocomposite thin film for room temperature methanol sensor

In the recent past, polymer–metal oxide nanocomposites have been identified as one of the key and new class of materials for fabricating gas sensors owing to their swift redox characteristics. In this line of thought, chemical oxidative process was employed to synthesize zinc oxide (ZnO) and polyaniline (PANI) nanocomposite thin films with different mass concentrations of ZnO to explore their gas sensing signatures. X-ray diffraction patterns and Fourier transform infrared spectra confirmed the formation of pure ZnO and PANI–ZnO composites. Field emission scanning electron micrographs revealed the leaf like structure of ZnO, porous nature of PANI and the uniformly distributed blend of these two structures for the composite films. Further, the room temperature gas/vapour sensing characteristics revealed the selective nature of nanocomposite films towards methanol vapour in the presence of other vapours with better response, swift response and recovery times of 7 and 20 s respectively.     

Cation off-stoichiometric SrMnO<Subscript>3−δ</Subscript> thin film grown by pulsed laser deposition

The laser energy density (laser fluence) dependency of the Sr/Mn ratio was investigated for SrMnO_3−δ (SMO) thin films grown by pulsed laser deposition (PLD). It was found that the Sr/Mn ratio showed a steep increase followed by a gradual increase as the laser fluence was increased. However, the Sr/Mn ratio always showed Mn-excess under the present laser fluence condition as long as stoichiometric SrMnO₃ targets were used. In order to obtain cation stoichiometric SMO films, it was necessary to use Sr-excess SrMnO₃ targets in addition with laser fluence tuning. The crystal quality of the SMO thin film was found to vary with the Sr/Mn ratio. In stoichiometric or Sr-excess SMO thin films, epitaxial thin films could be obtained, whereas Mn-excess thin films showed very low crystallinity. Sr-excess films were also found to have some extra SrO planes. In addition, they exhibited out-of-plane lattice expansion which electron energy loss spectroscopy analysis revealed was due to Mn vacancies. The variation of film growth was closely related to point defects due to excess cations included in growing thin films.     

Structural and optical properties of γ-alumina thin films prepared by pulsed laser deposition

Preparation of γ-alumina thin films by pulsed laser deposition from a sintered α-alumina target is investigated. The films were deposited on (100) silicon substrates at 973 K with varying oxygen partial pressures in the range 2.0 × 10⁻⁵-3.5 × 10^− 1 mbar. X-ray diffraction results indicated that the films were polycrystalline γ-Al₂O₃ with cubic structure. The films prepared in the oxygen partial pressure range 2.0 × 10^− 5-3.5 × 10^− 2 mbar contained nanocrystals of sizes in the range 10-16 nm, and became amorphous at pressures > 3.5 × 10^− 1 mbar. Topography of the films was examined by atomic force microscopy using contact mode and it showed the formation of nanostructures. The root-mean square surface roughness of the film prepared at 2.0 × 10^− 5 mbar and 3.5 × 10^− 1 mbar were 1.4 nm and 3.5 nm, respectively. The thickness and optical properties were studied using ellipsometry in the energy range 1.5-5.5 eV for three different angles of incidence. The refractive index was found to decrease from 1.81 to 1.73 with the increase of oxygen partial pressures from 2.0 × 10^− 5 to 3.5 × 10^− 2 mbar. The variation in the refractive index has been found to be influenced by the microstructure of the films obtained as a function of oxygen partial pressure.     

Facile sol–gel preparation of nanocrystal embedded thin film material for memory device

A promising charge trapping film with crystal embedded material is proposed for future electronic devices. Instead of conventional high-vacuum and expensive tool, this technique adopts very cheaper process of sol–gel spin-coating for fabrication of thin film material in the charge trapping flash memory (CTFM). The crystal from spinodal phase separation is observed for sol–gel thin film at 900 °C annealing, and is strongly related to the thickness of the spin-coated thin film. The morphology of the crystal from the ethanol solvent system is in the isolated form, while from 2-propanol solvent is in the interconnected structure. The sol–gel-derived CTFM from ethanol exhibits the better memory performance of retention times for <5 and <10 % charge loss at applied temperature of 25 and 85 °C, respectively. The ethanol system CTFM demonstrates a large memory window (~10 V) and good reliability than 2-propanol (~3 V) due to the existence of several isolated crystals in silicon dioxide film.     

Enhanced hydrophilicity of the Si substrate for deposition of VO2 film by sol–gel method

We have illustrated the role of hydrophilic nature of Si substrate played in the improvement of the contact performance between the vanadium dioxide (VO₂) film and Si substrate. The VO₂ films were fabricated by sol–gel method on single crystal Si substrate, which was pre-treated with hydrophilic solution and obtained a quite improved hydrophilicity. The bonding of Si substrate with precursor V₂O₅ gel was interpreted. The morphology and crystalline structure of the films were investigated by field-emission scanning electron microscopy, atomic force microscopy and X-ray diffraction. It is shown that the surface of the film on Si substrate with enhanced hydrophilicity is quite homogeneous and uniform. The film exhibits the formation of VO₂ phase with (011) preferred orientation. Moreover, the optical pump induced phase transition property of the film was studied by terahertz time-domain spectroscopy, which revealed around 70% reduction of transmission at 0.1–1.5?THz in the VO₂ film across the phase transition.     

Fabrication of semi-transparent superoleophobic thin film by nanoparticle-based nano–microstructures on see-through fabrics

Superoleophobic thin films have many potential applications including fluid transfer, fluid power systems, stain-resistant and antifouling materials, and microfluidics. Transparency is also desired with superhydrophobicity for numerous applications; however, transparency and oleophobicity are almost incompatible with each other from the point of view of surface structure. Oleophobicity requires a rougher structure on the nano–microscale than hydrophobicity, and this rough structure brings light scattering. So far, there are few reports of compatible transparency and superoleophobicity. In this report, we propose see-through-type fabrics having nanoparticle-based hierarchical structure thin films to improve both oleophobicity and transparency. The vacant space between the fibers of the fabric has two important roles: to allow light to pass through and to induce an air layer to produce a Cassie state of a liquid droplet on the resulting thin film. To realize a low surface energy and nanoscale rough structured surface on fabric fibers, we used a spray method with perfluoroalkyl methacrylic copolymer, silica nanoparticles, and volatile solvent. Scanning electron microscopy images revealed that hierarchical nanoparticle structures were uniformly formed on the fabrics. The transparency of the obtained thin film was approximately 61 %, and the change of transparency between the non-coated and coated fabrics was 11 %. The contact angles of oil (rapeseed oil and hexadecane) and water droplets on the fabricated film were observed to be over 150° during investigation of its surface wettability.     

Effect of hydrogen and temperature on the resistivity of an aluminum-2 wt % copper thin film

Thin metallic films are required to provide interconnection between contacts on devices and between devices. As device dimensions decrease, the low electrical resistivity becomes the most important issue in microelectronics industry. Recently in thin metallic films, hydrogen has been shown to lower the electrical resistivity of thin metallic films, reduce the rate of electromigration in interconnect lines, and lower the stress generated in thin metallic films during annealing. These effects are referred to as hydrogen effects. Low temperature resistivity measurements were performed to determine the effect of hydrogen and temperature on the resistivity of an aluminum-2 wt% copper film. Low temperature control experiments were performed in helium since it has a similar thermal conductivity as hydrogen but is chemically inert. The electrical resistivity of an aluminum-2 wt% copper alloy is lowered by hydrogen even at low temperature. The temperature coefficient of resistivity (TCR) values are identical within the experimental error (±0.005 cm/K). This means that phonon scattering is identical. So the decrease of the electrical resistivity is due to the decrease in the residual resistivity. Hydrogen effects are reversible for an aluminum-2 wt% copper alloy at room temperature because the adsorption and desorption of hydrogen occur. Hydrogen effects are slowly reversible for an aluminum-2 wt% copper alloy at low temperature because the adsorption of hydrogen occurs, but the desorption of hydrogen does not occur readily.     

Investigation of superhydrophilic mechanism of titania nano layer thin film—Silica and indium oxide dopant effect

In this paper, TiO₂?CSiO₂?CIn₂O₃ nano layer thin films were deposited on glass substrate using sol?Cgel dip coating method. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and water contact angle measurements were used to evaluate chemical structure, surface composition, hydroxyl group contents and superhydrophilicity of titania films. FTIR result indicated that Si?CO?CSi, Si?CO?CTi and Ti?CO?CTi bands formed in TiO₂?CSiO₂?CIn₂O₃ sample. According to XPS, the hydroxyl content for TiO₂, TiO₂?CSiO₂ and TiO₂?CSiO₂?CIn₂O₃ films was calculated as 11·6, 17·1 and 20·7%, respectively. The water contact angle measurements indicated that silica and indium oxide dopant improved the superhydrophilicity of titania nano film surface especially in a dark place. The enhanced superhydrophilicity can be related to the generation of surface acidity on the titania nano film surfaces. In the present state, superhydrophilicity is induced by the simultaneous presence of both Lewis and Bronsted sites.     

Surface impedance of epitaxial YBCO thin films — Comparison of experimental data with a d-wave theory of superconductivity

The surface impedance of two 350nm thick YBCO films was measured for temperatures between 4.2K and 150K in a copper cavity at 87 GHz. Both films, one grown by electron beam evaporation on MgO, the other one by high oxygen-pressure dc sputtering from a stoichiometric target on LaAlO₃, provide critical temperatures of about 91K, low residual surface resistances of R_s(4.2K) < 1m and low specific resistivities in the normal state of (100K) < 85cm. The experimental data obtained on these two films are compared to a d-wave model of superconductivity which incorporates elastic and inelastic scattering. Good agreement between theory and the experimental results for both the surface resistance and the penetration depth in the whole temperature range is achieved for scattering phase shifts near 0.4 and order parameter amplitudes in the range of 2₀(0)/k_BT_c = 6.0 – 7.5 without subtracting an extrinsic residual surface resistance.     

Transport properties of thin SnO2〈Sb〉 films grown by pulsed laser deposition

Thin SnO₂<Sb> films grown by pulsed laser deposition have been characterized by X-ray diffraction, optical spectroscopy, and scanning electron microscopy. The carrier mobility and concentration in the films have been determined as functions of target composition (0–8 at % Sb) using Hall effect measurements, and the resistivity of the films has been measured by a four-probe technique. The lowest resistivity (ρ = 2 × 10^?3 Ω cm) and the highest transmission (? 85%) of the films in the spectral range 400-800 nm have been obtained at a target composition Sb/(Sn + Sb) = 2 at %. The observed variation in the resistivity of the films is determined by changes in carrier concentration to a greater extent than by changes in carrier mobility. X-ray photoelectron spectroscopy results demonstrate that the predominant charge state of the antimony in the films is Sb⁵⁺.