ITO thin films deposited by advanced pulsed laser deposition

Indium tin oxide thin films were deposited by computer assisted advanced PLD method in order to obtain transparent, conductive and homogeneous films on a large area. The films were deposited on glass substrates. We studied the influence of the temperature (room temperature (RT)-180 °C), pressure (1-6 × 10^− 2 Torr), laser fluence (1-4 J/cm²) and wavelength (266-355 nm) on the film properties. The deposition rate, roughness, film structure, optical transmission, electrical conductivity measurements were done. We deposited uniform ITO thin films (thickness 100-600 nm, roughness 5-10 nm) between RT and 180 °C on a large area (5 × 5 cm²). The films have electrical resistivity of 8 × 10^− 4 Ω cm at RT, 5 × 10^− 4 Ω cm at 180 °C and an optical transmission in the visible range, around 89%.     

Studies on chemically deposited CuInSe2 thin films

Nanocrystalline thin films of CuInSe₂ have been prepared by chemical bath deposition technique at temperatures below 60 °C. X-ray diffraction of the films confirmed the identity of CuInSe₂ and with largely broadened peaks indicated the nanocrystalline nature of the films. Images from scanning electron microscope represented spherical nanoparticles.     

Preparation of Al-Cu-Fe thin films by vapor deposition technique from a single source

In this paper, we report the formation of stable icosahedral Al-Cu-Fe quasicrystalline thin films by thermal vapor deposition techniques (indirect heating and e-beam heating) from a single source. Deposition of these films by a single-source indirect heating method, in the stable icosahedral phase, is reported for the first time. A direct comparison between the two different heating methods has been made. The final compositions of the prepared films with desired properties were found to be Al_62.9Cu_24.6Fe_12.5 (indirect heating method) and Al_63.1Cu_24.5Fe_12.4 (e-beam method), respectively. The resistivities of the films prepared by both methods were ∼2000 μΩ cm at room temperature and ∼4000 μΩ cm at 10 K.     

Hot-wire chemical vapor deposition and characterization of polycrystalline silicon thin films using a two-step growth method

A two-step growth method was proposed to reduce the amorphous incubation layer in the initial growth of polycrystalline silicon (poly-Si) films prepared by hot-wire chemical vapor deposition (HWCVD). In the two-step growth process, a thin seed layer was first grown on the glass substrate under high hydrogen dilution ratios (φ ≥ 0.9), and then a thick overlayer was subsequently deposited upon the seed layer at a lower φ value. The effect of various deposition parameters on the structural properties of poly-Si films was investigated by Raman spectroscopy and transmission electron microscopy. Moreover, the electrical properties, such as dark and photo conductivities, of poly-Si films were also measured. It was found that the Si incubation layer could be suppressed greatly in the initial growth of poly-Si with the two-step growth method. In the subsequent poly-Si film thickening, a lower φ value of the reactant gases can be applied to enhance the deposition rate. Therefore, a high-quality poly-Si film can be fabricated via a two-step growth method with a sufficient growth rate using HWCVD.     

Nanocone SiGe antireflective thin films fabricated by ultrahigh-vacuum chemical vapor deposition with in situ annealing

In this study, we fabricated nanocone-presenting SiGe antireflection layers using only ultrahigh-vacuum chemical vapor deposition. In situ thermal annealing was adopted to cause SiGe clustering, yielding a characteristic nanocone array on the SiGe surface. Atomic force microscopy indicated that the SiGe nanocones had uniform height and distribution. Spectrophotometric measurements revealed that annealing at 900 °C yielded SiGe thin films possessing superior antireflective properties relative to those of the as-grown SiGe sample. We attribute this decrease in reflectance to the presence of the nanostructured cones. Prior to heat treatment, the mean reflectance of ultraviolet rays (wavelength < 400 nm) of the SiGe thin film was ca. 61.7%; it reduced significantly to less than 28.5% when the SiGe thin film was annealed at 900 °C. Thus, the drop in reflectance of the SiGe thin film after thermal treatment exceeded 33%.     

GaN thin films deposited by pulsed laser ablation in nitrogen and ammonia reactive atmospheres

Well-oriented, crystalline GaN films were grown on (11

Full-size image

0) sapphire substrates in reactive atmospheres of N₂ and NH₃ by pulsed laser deposition. GaN targets were ablated at 2.8 J cm⁻² and the substrate temperature was varied from 500 to 700°C. The background gas pressure was varied from 0.04 to 0.3 mbar. All the films had a wurtzite structure. The crystal quality and preferential orientation depended on the substrate temperature, laser fluence and the presence of the nitriding atmosphere. For both N₂ and NH₃, the most resistive films were preferentially orientated in the [000l] direction. For 700°C the film resistivity was found to increase from 10⁻³ Ω cm when deposited in NH₃ to 10² Ω cm when deposited in N₂. The band-gap, obtained from optical transmission measurements shifted from 3.1 to 3.4 eV. Violet photoluminescence was found in all samples and was centered at 3.2 eV with a full width at half maximum of 0.2 eV. A broad peak in the yellow, centered at 2.1 eV, was detected for films grown in vacuum and ammonia.     

Roughness evolution in Ga doped ZnO films deposited by pulsed laser deposition

We analyze the morphology evolution of the Ga doped ZnO(GZO) films deposited on quartz substrates by a laser deposition system. The surface morphologies of the film samples grown with different times are measured by the atomic force microscope, and they are analyzed quantitatively by using the image data. In the initial stage of the growth time shorter than 8 min, our analysis shows that the GZO surface morphologies are influenced by such factors as the random fluctuations, the smoothening effects in the deposition, the lateral strain and the substrate. The interface width uw(t) and the lateral correlation length ξ(t) at first decrease with deposition time t. For the growth time larger than 8 min, w(t) and ξ(t) increase with time and it indicates the roughening of the surface and the surface morphology exhibits the fractal characteristics. By fitting data of the roughness w(t) versus deposition time t larger than 4 min to the power-law function, we obtain the growth exponent β is 0.3; and by the height-height correlation functions of the samples to that of the self-affine fractal model, we obtain the value of roughness exponent α about 0.84 for all samples with different growth time t.     

Grain growth and structural transformation in ZnS nanocrystalline thin films

Fabrication of ZnS thin films having similar stoichiometry at different substrate temperatures (T_S) e.g. 200 °C, 300 °C and 400 °C by means of RF magnetron sputtering method is presented. The films grown at T_S of 200 °C are in cubic zinc-blende phase and textured along (111) plane. The films deposited at T_S of 300 °C and 400 °C are in hexagonal wurtzite phase. The surface roughness and grain size of the films increase with increasing T_S. The ultra-violet and visible absorption studies show that the bandgap of films can be tailored by varying T_S, taking advantage of the structural transformation.     

Spectroscopic ellipsometry investigations of the optical properties of manganese doped bismuth vanadate thin films

The optical properties of Bi₂V_1−xMn_xO_5.5−x {x = 0.05, 0.1, 0.15 and 0.2 at.%} thin films fabricated by pulsed laser deposition on platinized silicon substrates were studied in UV-visible spectral region (1.51-4.17 eV) using spectroscopic ellipsometry. The optical constants and thicknesses of these films have been obtained by fitting the ellipsometric data (Ψ and Δ) using a multilayer four-phase model system and a relaxed Lorentz oscillator dispersion relation. The surface roughness and film thickness obtained by spectroscopic ellipsometry were found to be consistent with the results obtained by atomic force and scanning electron microscopy. The refractive index measured at 650 nm does not show any marginal increase with Mn content. Further, the extinction coefficient does not show much decrease with increasing Mn content. An increase in optical band gap energy from 2.52 to 2.77 eV with increasing Mn content from x = 0.05 to 0.15 was attributed to the increase in oxygen ion vacancy disorder.     

Electrodeposition of SmS optical thin films on ITO glass substrate

SmS optical thin films were deposited on the surface of ITO glass with an electrodeposition method using aqueous solution containing SmCl₃·6H₂O and Na₂S₂O₃·5H₂O. The phase composition was analyzed by X-ray diffraction (XRD) and microstructure of the film was characterized by atomic force microscope (AFM). It is showed that SmS thin film could be obtained in the solution with n(Sm)/n(S) = 1:4, pH = 4.0 and annealing in Ar atmosphere at 200 °C for 0.5 h. The as-prepared thin films on the ITO glass exhibit a dense microstructure. The band gap of the thin film has been found to be 3.6 eV.     

Study on chemical vapor deposited copper films on cyano and carboxylic self-assembled monolayer diffusion barriers

Thin copper films were produced by chemical vapor deposition using the precursor Cu^IIbis-hexafluoroacetylacetonate on the SiO₂/Si substrate modified with cyano and carboxylic self-assembled monolayers (SAMs) as diffusion barriers. The characterizations of the deposited copper films were measured by various thin film analysis techniques, i.e., scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. The comparison between copper deposited on SiO₂ and on the SAM-modified SiO₂ substrates indicates that the copper films tend to be deposited onto the SAM-modified substrate, which is further proved by the calculation results of the interaction energies of copper and the SAMs with density functional theory method.     

Structural and textural characterization of LiFePO4 thin films prepared by pulsed laser deposition on Si substrates

LiFePO₄ thin films were grown on silicon (100) substrates by pulsed laser deposition using Traditional Geometry (TG) and Off-Axis Geometry (OAG) deposition chambers. We examined and compared the structure and composition of the so formed thin films. The nails observed on the OAG-film present an amorphous “body” and a crystallized “head”. The Fe/P ratio determined using energy dispersive spectrometry combined with high angle annular dark field images reveals a metallic iron heart surrounded by LiFePO₄ shell. On the other hand, the protuberances on TG-film are pure iron. The focused ion beam prepared cross-section of the film suggests the presence of iron particles and iron dendritic like filaments inside the LiFePO₄ layer.     

Plasma deposition of fluorocarbon thin films using pulsed /continuous and downstream radio frequency plasmas

Fluorocarbon (FC) films deposited in continuous wave (cw) and pulsed difluoromethane radio frequency (r.f.) plasmas were characterized using Fourier transform infrared spectroscopy and atomic force microscopy. The effects of varying r.f. power, cw/pulsed discharge mode, and the distance of the substrate from the coil on the deposition rate, film structure, and surface roughness were investigated. These cw and pulsed deposition systems were characterized in-situ by means of optical emission spectroscopy. Emission intensities of H_α, H_β, H₂ and carbon-containing species in the coil region and downstream plasmas as a function of plasma parameters were measured. The hydrogen excitation temperature obtained from the relative emission intensities of H_α and H_β lines shows a clear dependence on the r.f. power and the substrate position. Correlations between film properties, gas-phase plasma diagnostic data, and film growth processes were discussed. Experimental results indicate that the film growth within the coil region in cw plasmas is controlled by the synergistic effect between energetic ions and low-energy species. The film growth in pulsed and downstream plasmas is controlled by the growth of coalesced nuclei via surface diffusion of adsorbed species, which results in the deposition of FC films with relatively rough surfaces.     

Electrical resistivity of Ti-Zn mixed oxide thin films deposited by atomic layer deposition

Ti-Zn mixed oxide thin films, with thickness less than 50 nm, were grown with atomic layer deposition (ALD) technique at low temperature (90 °C) varying the composition. ALD is a powerful chemical technique to deposit thin films with thickness of few atomic layers. ALD oxide material growth is achieved by dosing sequentially the metal precursor and the oxidizing agent. Thanks to ALD nature of layer by layer growth it was possible to realize mixed metal, Ti and Zn, oxide thin films with controlled composition, simply by changing the number of cycles of each metal oxide layer. Structural and electrical properties of the prepared thin films were studied as a function of their composition. Synchrotron radiation X-ray diffraction technique was used to follow thin film crystallization during sample annealing, performed in situ. It was observed that the onset temperature of crystallization raises with Ti content, and sample structure was Zn₂TiO4 phase. Electrical resistivity measurements were performed on crystalline samples, annealed at 600 °C, revealing an increase in resistivity with Ti content.     

3D characterization of microstructured poly(methacrylic acid) thin films via Mach-Zehnder interference microscopy

We demonstrate the adaption of a further developed Mach-Zehnder interference (MZI) microscope for the rapid 3D characterization of transparent microstructured polymer thin films. In order to quantify the accuracy of the Mach-Zehnder interferometer, comparative film thickness measurements of photolithographically patterned poly(methacrylic acid) polymer brushes are performed employing two alternative techniques: white light profilometry (WIM) and atomic force microscopy (AFM). When the refractive index of the polymer brushes is calculated from MZI data, we obtain a good agreement with results received from an independent method (ellipsometry).In contrast to surface probing techniques such as AFM or WIM, Mach-Zehnder interferometry is a transmitted light method that measures both surface height profiles and refractive index distributions. MZI thus enables the quantification of film homogeneity with respect to height and density variations at the lateral resolution of a refraction limited microscope. We conclude that MZI is an adequate tool for the rapid and non-destructive characterization of structured polymer thin films. This method should be particularly useful for production quality control of microstructured polymer thin films which possess great potential in electronic device fabrication and biotechnology.     

Structural and morphological characterization of Pr and Er-containing SiO2-P2O5 sol-gel thin films

Present work is focused on obtaining and characterization of sol-gel thin films belonging to SiO₂-P₂O₅-Er₂O₃ (I) and SiO₂-P₂O₅-Pr₂O₃ (II) systems. The films have been obtained by spin coating technique for three rotation speeds: 2000, 3500 and 5000 rpm. The deposition of the films was performed at different periods of time, i.e. 24 h, 96 h, 120 h, 144 h and 168 h after instant preparation of the precursor sols. FTIR (Fourier transform infrared spectroscopy) and Raman characterization aimed at investigating the structural changes that occurred in silicophosphate network in dependence on the spin rate of the substrate as well as on the time period elapsed since the sol preparation till the deposition day. FTIR spectra recorded in the 400-4000 cm⁻¹ range revealed Si-O-Si, P-O-P and Si-O-P vibration modes and optical phonons specific for OH units. Raman spectra collected in the 100-4000 cm⁻¹ range put in evidence stretching, bending and mixed vibration modes specific for silicophosphate network as well as rare-earth ion peaks specific to certain electronic transitions. Morphological investigation made by AFM (atomic force microscopy) on Er and Pr-doped silicophosphate sol-gel films evidenced specific features depending on the parameters mentioned above and SEM (scanning electron microscopy) analysis revealed micron sphere structural units, exfoliation of the films and micro cracks.     

The influence of the additives composition and concentration on the properties of SnOx thin films used in photocatalysis

The aim of this study is to investigate the influence of different organic additives on the surface properties of SnO_x thin films used for photocatalytic degradation of methylene blue. The films were obtained by anodic oxidation of tin substrate in electrolyte solutions containing green additives based on hydrophobic and hydrophilic maleic anhydride copolymers. The hydrophobic copolymer leads to the formation of thin films with increased specific area which generates a larger interfacial area between the layers and the dye solution. The consequence is an improvement in the photocatalytic efficiency: up to 16% compared to less than 5% for samples electrodeposited without polymer. The hydrophilic copolymer presence in the electrolyte solution leads to higher grain size and lower surface energy which significantly reduce the photocatalytic properties of the layers. The use of copolymers can be a tool for enhancing the surface roughness and film's wettability and thus the photodegradation efficiency.     

Effect of annealing atmosphere on phase formation and electrical characteristics of bismuth ferrite thin films

Bismuth ferrite thin films were deposited on Pt/Ti/SiO₂/Si substrates by a soft chemical method and spin-coating technique. The effect of annealing atmosphere (air, N₂ and O₂) on the structure and electrical properties of the films are reported. X-ray diffraction analysis reveals that the film annealed in air atmosphere is a single-phase perovskite structure. The films annealed in air showed better crystallinity and the presence of a single BFO phase leading to lower leakage current density and superior ferroelectric hysteresis loops at room temperature. In this way, we reveal that BFO film crystallized in air atmosphere by the soft chemical method can be useful for practical applications, including nonvolatile digital memories, spintronics and data-storage media.     

Superhydrophobic polymer films via aerosol assisted deposition — Taking a leaf out of nature's book

Aerosol assisted deposition of three sets of polymer films based on commercially available resins was achieved on various substrates. The films were characterised using a range of methods, including water contact and slip angle to determine water repellent properties. The aerosol assisted deposition inside the chemical vapour deposition reactor was unique in generating a highly rough superhydrophobic surface with water contact angles up to 170°. During the deposition process, two of the polymers were cured resulting in the development of high surface morphology. It was observed that the polymer that did not cure did not develop such a rough surface resulting in a lower water contact angle (∼ 99°). The superhydrophobic films had a Cassie-Baxter type wetting with water failing to penetrate the surface porosity, water spraying on the surface would bounce off. These films had exceptionally low slide angles of ca 1-2° from the horizontal.