Optical and waveguiding properties of Nd:KGW films grown by pulsed laser deposition

 Nd: KGd(WO₄)₂ thin films were deposited by KrF laser ablation on MgO, YAP, YAG and Si substrates at temperatures up to 800 °C. Film crystallinity, morphology, stoichiometry (WDX, RBS and PIXE), excitation spectra, fluorescence, refractive index and waveguiding properties were studied in connection with deposition conditions. The best films were crystalline and exhibited losses of approximately 5 dB cm^-1 at a wavelength of 633 nm. Received: 8 January 2001 / Accepted: 7 November 2001 / Published online: 11 February 2002     

Structure and morphology of chemical bath-deposited CdS films and clusters

Thin films of cadmium sulfide have been deposited on glass substrates and the structural properties of films have been investigated using scanning electron microscopy and X-ray diffraction techniques. The films consist of domains (groups of grains) and weakly bound grain clusters. The structural parameters of grains, domains and clusters and the effect of film thickness on these parameters are reported. From the measurement of lattice constants in CdS films and in free CdS clusters, it has become evident that the films on glass substrates have a tensile strain along their planes. The effect of thermal annealing on the partial relaxation of the strain is discussed. Received: 29 January 2001 / Accepted: 30 January 2001 / Published online: 3 May 2001     

Growth of completely (110)-oriented Pt film on Si (100) by using MgO as a buffer by pulsed laser deposition

(110)-textured MgO films were grown on Si (100) with etching and without etching by pulsed laser deposition. The deposited MgO films were shown to be droplets-free. The MgO film was used as a buffer layer to further grow Pt film on Si (100). A completely (110)-oriented Pt film was obtained on such a buffer layer and its surface is very smooth with a roughness of about 7.5 nm over 5×5 μm. This can be used as a new oriented Pt electrode on silicon for devices. Received: 23 January 2001 / Accepted: 27 April 2001 / Published online: 27 June 2001     

Flexible ceramic–polymer composite films with temperature-insensitive and tunable dielectric permittivity

BaTiO₃–polymer composite layers have been produced by the spin-on technique (thickness 3–10 μm). The dielectric permittivity of the layers at room temperature can be tuned from 2.8 to approximately 33 by varying the ceramic filling from 0 to 60% by volume. The dielectric properties of the films are almost insensitive to temperature variations in the range 20–180 °C. Free-standing composite layers with ceramic content ≤50% are flexible without noticeable change of permittivity after repeated mechanical bending. Received: 22 November 2001 / Accepted: 24 November 2001 / Published online: 23 January 2002     

Deposition and characterization of ITO films produced by laser ablation at 355 nm

Indium tin oxide (ITO) films have been deposited by pulsed laser deposition (PLD) at 355 nm. Even though the absorption of laser light at the wavelength 355 nm is much smaller than that of the standard excimer lasers for PLD at 248 nm and 193 nm, high-quality films can be produced. At high fluence and at high substrate temperatures, the specific resistivity of the films, 2–3×10^-4 Ω cm, is comparable to values obtained with excimer lasers, whereas the resistivities obtained at room temperature are somewhat higher than those of films produced by excimer lasers. The transmission coefficient of visible light, about 0.9, is also comparable to values for films deposited by excimer lasers. The crystalline structure of films produced at 355 nm is similar to that of samples produced by these lasers. Received: 16 January 2001 / Accepted: 24 July 2001 / Published online: 17 October 2001     

Polymer-based multi-layer conductive electrode film for plastic LCD applications

Thin films of polymer-based multi-layer conductive electrode to be used as a substrate for a plastic liquid crystal display (LCD) have been prepared by a DC magnetron roll-to-roll sputtering method. The conductive layer is composed of three layers, ITO/Ag/ITO or ITO/APC/ITO, where APC is Ag-Pd-Cu alloy, on the polymer substrate (Arton?), which has been treated with hard-coat and gas-barrier layers. The properties of the conductive electrode for the plastic LCD were the following: (1) sheet resistance is 6 Ω/square; (2) transparency is 88% at 550 nm; (3) H₂O gas permeation through the plastics is 0.35 g/m² in 24 h; (4) durability against solvents is good for 5% NaOH solution, IPA, methanol, NMP, acetone, etc.; (5) the irreversible shrinkage and the compaction rate are both less than 3 ppm/h after annealing for 100 h at 150 °C. Received: 22 January 2001 / Accepted: 30 January 2001 / Published online: 26 April 2001     

Evaluation of carbon films electrodeposited on different substrates from different organic solvents

Diamond-like-carbon (DLC) films have been deposited on Si, aluminum and indium tin oxide-coated glass from several organic solvents with pulse-modulated power. The films are characterized by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. XPS spectra show that the main composition of the films is carbon and Raman spectra show that the films are typical DLC films and a high potential is preferable in the formation of sp ³-structure carbon. Comparing the results from different solvents and different substrates we deduce that the methyl group of the solvents has a critical function in forming the DLC films. However, the formation process and the characters of the films, such as appearance, resistivity and thickness, are mainly determined by the substrate. We may call this deposition a substrate-controlled reaction. Received: 31 May 2000 / Accepted: 9 January 2001 / Published online: 3 April 2001     

Etching of buried photoresist layers and its application to the formation of three-dimensional layered structures

The fabrication of three-dimensional layered structures with 180-nm-thick TaO_x top layers supported by 1.5-μm-thick Mo pillars formed on a glass substrate is presented. The photoresist used for planarization was successfully removed through the TaO_x layers using heat treatment at 270 °C with mixed vapors of ethyl alcohol and pure water at high pressure for 3 h. Vacancies underlying the TaO_x layers were consequently formed. The possibility of rapid and lateral crystallization of amorphous silicon films was demonstrated when the silicon films formed on the TaO_x overlaying the vacancy regions were irradiated using a frequency-doubled YAG laser at 250 mJ/cm². Energy sensors using Cr/Al metal wires, with a high sensitivity of 0.07 mW/cm², were also demonstrated using the present structure with vacancy regions for reduction of heat diffusion. Received: 22 January 2001 / Accepted: 24 January 2001 / Published online: 27 June 2001     

Texture control and its impact on the properties of SrBi2Ta2O9 thin films prepared by pulsed laser deposition

SrBi₂Ta₂O₉ (SBT) ferroelectric thin films with different preferred orientations were deposited by pulsed laser deposition (PLD). Several methods have been developed to control the preferred orientation of SBT thin films. For SBT films deposited directly on Pt/TiO₂/SiO₂/Si substrates and in situ crystallized at the deposition temperature, the substrate temperature has a significant impact on the orientation and the remnant polarization (Pr) of the films; a higher substrate temperature benefits the formation of (115) texture and larger grain size. The films deposited on Pt/TiO₂/SiO₂/Si substrates at 830 °C are (115)-oriented and exhibit 2Pr of 6 μC/cm². (115)- and (200)-predominant films can be formed by using a La_0.85Sr_0.15CoO₃ (LSCO) buffer layer or by annealing amorphous SBT films deposited on Pt/TiO₂/SiO₂/Si substrates at 450 °C using rapid thermal annealing (RTA). These films exhibit good electric properties; 2Pr of the films are up to 12 μC/cm² and 17 μC/cm², respectively. The much larger 2Pr of the films deposited on the LSCO buffer layer and of the films obtained by RTA than 2Pr of the films deposited on Pt/TiO₂/SiO₂/Si substrates at 830 °C is attributed to a stronger (200) texture. Received: 30 January 2001 / Accepted: 30 May 2001 / Published online: 25 July 2001     

Novel technique for hetero-epitaxial diamond film growth on cubic boron nitride from iron carbide at high temperature and high pressure

Cubic boron nitride (c-BN) crystals about 0.1–0.3 mmin dimension were treated with iron carbide powders (high purity 99%) with size of 80–100 mesh at a high temperature of 1620 K and a high pressure of 5.2 GPa. It was found that hetero-epitaxial diamond films have been grown on the c-BN from iron carbide. The formation of dia-mond films on the cubic boron nitride can be confirmed by laser Raman spectra, face scan of elements and reflective high-energy electron diffraction. It was suggested that diamond films could be epitaxially formed on the c-BN through decomposition of iron carbide. This approach provides a possible and very effective way to realize hetero-epitaxial growth of homogeneous and large-area diamond films on c-BN, which is different from the conventional technique using a chemical vapor deposition method. Received: 20 December 2000 / Accepted: 9 January 2001 / Published online: 28 February 2001     

Optical and non-linear optical properties of vanadium oxide phthalocyanine films

The optical and non-linear optical properties of peripheral-substituted vanadium oxide phthalocyanine (VOPc) film and substituted VOPc/polymer composite film were investigated using stationary and transient spectroscopy techniques. The absorption Q band of the VOPc/polymer composite film shows a red shift relative to that of the peripheral-substituted VOPc film, revealing the monomeric characteristics of VOPc molecules. Effective quenching of PL emission was observed for the VOPc/polymer composite film and could be assigned to the efficient VOPc–polymer interaction. From pump-probe and optical Kerr effect (OKE) measurements, two decay components were obtained by fitting the transients for both VOPc films. The fast component, in a femtosecond time domain, originates from the electron–phonon interaction, and the difference in their slow decay is an indication of an efficient ISC process in the VOPc/polymer composite film. The third-order non-linear optical susceptibilities of these films were determined to be in the order of 10^-11 esu. Received: 25 October 2001 / Revised version: 8 January 2002 / Published online: 7 February 2002     

Rapid joule heating of metal films used to crystallize silicon films

We analyzed the rapid heating properties of 50-nm-thick silicon films via 250-nm-thick SiO₂ intermediate layers by heat diffusion from joule heating induced by electrical current flow in chromium strips. Numerical heat-flow simulation resulted in that the silicon films were heated to the melting point by a joule-heating intensity above 1 MW/cm². A marked increase in electrical conductance associated with silicon melting was experimentally detected. Taper-shaped chromium strips detected the temperature gradient in the lateral direction caused by the spatial distribution of the joule-heating intensity. Crystallization occurred according to the temperature gradient. A 2–4-μm lateral crystalline grain growth was demonstrated for the silicon films. Received: 20 November 2001 / Accepted: 22 November 2001 / Published online: 20 March 2002     

Processing effects on the microstructure and ferroelectric properties of strontium bismuth tantalate thin films

Ferroelectric thin films of strontium bismuth tantalate compositions with Bi/Sr ratios of 2.75 and 2.50 have been produced by deposition of solutions derived from sol-gels followed by crystallization using rapid thermal processing (RTP) at 650 °C. Single-step and two-step processes have been used for the RTP crystallization of the films. Both the composition and the heating process used affect the grain size, grain shape and compositional heterogeneity of the films, acting on their ferroelectric switching behaviour and dielectric properties. Larger and more elongated grains are obtained by crystallization using a single-step process. These films exhibit less slanted hysteresis loops. The combination of the study of the pure-ferroelectric-switching loop and the lambda curves through the application of a Curie–Weiss-like model gives a deeper insight into the influence of film heterogeneity on its ferroelectric properties. The observation of net polarisation without poling in all the films is attributed to the effects of 180° ferroelectric domains. Received: 16 May 2001 / Accepted: 27 October 2001 / Published online: 20 March 2002     

Holographic recording mechanisms of gratings in indium oxide films using 325 nm helium–cadmium laser irradiation

UV (325 nm) holographic recording of gratings in indium oxide films fabricated by reactive pulsed laser deposition has been investigated as a function of growth temperature, oxygen pressure and angle of incidence of the plasma plume on the substrate. The influence of the ambient environment (air or vacuum) and the film temperature during recording has also been studied. Large steady state refractive index changes up to 6×10^-3 were observed in layers grown at an oblique angle of 75°. About 77% of the magnitude of these changes residues after thermal annealing and is attributed to UV-induced permanent structural rearrangements. In contrast, refractive index changes in films grown at normal incidence were smaller in magnitude and completely reversible. Received: 30 July 2001 / Accepted: 20 November 2001 / Published online: 23 January 2002     

Pulsed laser deposition of conductive metallo-dielectric optical filters

We describe the fabrication by room-temperature pulsed laser deposition of a transparent conductor comprising alternating layers of silver and aluminum oxide, forming a metallo-dielectric filter. Transmittances of 0.7 over specific wavelength bands were achieved with resistivities as low as 6.0×10^-6 Ω cm, almost two orders of magnitude lower than that of the best single-substrate thin films, such as indium tin oxide. The resistivity can be predicted without adjustable parameters and designed using a simple parallel-circuit model; the optical properties are well described by standard matrix transmission calculations. This demonstrates that pulsed laser deposition may be used to fabricate prototypes of high-quality transparent conductors with predictable properties for conducting windows where low-temperature deposition is critical, as in organic light-emitting diodes and for non-linear optical films. Received: 10 June 2001 / Accepted: 9 August 2001 / Published online: 20 December 2001     

Synthesis of nanocrystalline material by sputtering and laser ablation at low temperatures

Physical vapor deposition techniques such as sputtering and laser ablation – which are very commonly used in thin film technology – appear to hold much promise for the synthesis of nanocrystalline thin films as well as loosely aggregated nanoparticles. We present a systematic study of the process parameters that facilitate the growth of nanocrystalline metals and oxides. The systems studied include TiO₂, ZnO, γ-Al₂O₃, Cu₂O, Ag and Cu. The mean particle size and crystallographic orientation are influenced mainly by the sputtering power, the substrate temperature and the nature, pressure and flow rate of the sputtering gas. In general, nanocrystalline thin films were formed at or close to 300 K, while loosely adhering nanoparticles were deposited at lower temperatures. Received: 31 October 2000 / Accepted: 9 January 2001 / Published online: 26 April 2001     

Improvement of optical properties of silica colloidal crystals by sintering

The optical properties of silica colloidal crystals have been improved considerably by sintering. This can be explained by the decrease of defects and the improvement of crystalline quality due to the structure compacting under thermal treatment. A drastic blue shift of the optical attenuation band was also observed. Received: 25 January 2001 / Accepted: 26 January 2001 / Published online: 26 April 2001     

Optical characterisation of CuInSe2 thin films prepared by two-stage process

Optical absorption spectra of CuInSe₂ chalcopyrite semiconductor films prepared using a two-stage technique were investigated. In addition to absorption measurements, energy-dispersive analysis of X-rays (EDAX) and X-ray diffraction measurements (XRD) were also performed. Direct bandgap energy values for the CuInSe₂ films were derived from the variation of (αhν)² with energy. All the measurements were performed on samples with various Cu/In ratios. It was determined from the absorption measurements that the materials have strong absorption at the fundamental band edge. The E_g values showed an increasing trend with decreasing Cu/In ratios. Received: 26 May 2000 / Accepted: 31 October 2000 / Published online: 10 January 2001     

Raman spectroscopy and field-emission properties of CVD-grown carbon-nanotube films

Carbon-nanotube films are very efficient cathodes for field-emission devices. This study presents a comprehensive comparison between structural, spectroscopic and field-emission properties of films of aligned and non-aligned multi-wall nanotubes (MWNTs) which are grown by thermal chemical vapour deposition. Three types of films are investigated: vertically aligned MWNTs with clean and coated nanotube side walls as well as non-aligned MWNT films. Raman spectra taken on the aligned MWNT films consist of many lines of first-, second- and third-order signals. Several lines are reported here for the first time for MWNTs. The presence of the surface coating leads to a decrease and broadening of the higher-order signals as well as an increase in the disorder-induced contributions in the first-order regime. The aligned MWNT films have excellent field-emission properties with very high emission current densities and low turn-on and threshold fields. The presence of a surface coating has no impact on the efficiency of the field-emission process. Films of non-aligned MWNTs show considerably reduced electron-emission current densities and larger critical fields. Received: 25 April 2001 / Accepted: 30 May 2001 / Published online: 25 July 2001     

Vapor deposition of intact polyethylene glycol thin films

Thin films of polyethylene glycol (PEG) of average molecular weight, 1400 amu, were deposited by both matrix-assisted pulsed laser evaporation (MAPLE) and pulsed laser deposition (PLD). The deposition was carried out in vacuum (∼10^-6 Torr) with an ArF (λ=193 nm) laser at a fluence between 150 and 300 mJ/cm². Films were deposited on NaCl plates, Si(111) wafers, and glass slides. The physiochemical properties of the films are compared via Fourier transform infrared spectroscopy (FTIR), electrospray ionization (ESI) mass spectrometry, and matrix-assisted laser desorption and ionization (MALDI) time-of-flight mass spectrometry. The results show that the MAPLE films nearly identically resemble the starting material, whereas the PLD films do not. These results are discussed within the context of biomedical applications such as drug delivery coatings and in vivo applications where there is a need for transfer of polymeric coatings of PEG without significant chemical modification. Received: 2 March 2001 / Accepted: 5 March 2001 / Published online: 23 May 2001