Laser-deposited tin dioxide and tin acetylacetonate layers for gas sensors

Thin active layers were deposited by the pulsed laser deposition (PLD) method from tin dioxide and tin acetylacetonate targets. The deposition was carried out employing an excimer KrF laser. The structure and parameters of the deposited layers were studied in connection with gas sensor applications. The influence of Ni dopant and Pd catalyst was investigated, employing PLD technology in order to introduce dopants as a multilayered structure. The properties of these layers were studied by Fourier transform infrared (FTIR), and X-ray photoelectron (XPS) spectroscopies and by measurement of their d.c. resistance. Under reducing gases the resistance of Ni-doped tin dioxide with a Pd catalyst layer decreases by 3 orders and the resistance of tin acetylacetonate with a Pd catalyst by 2 orders (synthetic air versus 1000 ppm H₂. Due to this, such layers are suitable as the active layers of gas sensors.     

Physical properties of CuCrO2 films prepared by pulsed laser deposition

High-quality CuCrO₂ films were prepared by pulsed laser deposition (PLD). The film deposited with the pulse energy density (PED) of 2 mJ/cm² is highly c-axis oriented. The refractive index of the CuCrO₂ films is about 1.29 obtained by transmission spectra of the films, which implies that the CuCrO₂ film will be a potential antireflection coating in visible light. The films prepared with different PEDs show different conduction mechanism, which suggested the different band structure between these CuCrO₂ films.     

Calcium phosphate thin film processing by pulsed laser deposition and in situ assisted ultraviolet pulsed laser deposition

Calcium orthophosphates (CaP) and hydroxyapatite (HA) were intensively studied in order to design and develop a new generation of bioactive and osteoconductive bone prostheses. The main drawback now in the CaP and HA thin films processing persists in their poor mechanical characteristics, namely hardness, tensile and cohesive strength, and adherence to the metallic substrate. We report here a critical comparison between the microstructure and mechanical properties of HA and CaP thin films grown by two methods. The films were grown by KrF* pulsed laser deposition (PLD) or KrF* pulsed laser deposition assisted by in situ ultraviolet radiation emitted by a low pressure Hg lamp (UV-assisted PLD). The PLD films were deposited at room temperature, in vacuum on Ti–5Al–2.5Fe alloy substrate previously coated with a TiN buffer layer. After deposition the films were annealed in ambient air at 500–600 °C. The UV-assisted PLD films were grown in (10^–2–10^–1 Pa) oxygen directly on Ti–5Al–2.5Fe substrates heated at 500–600 °C. The films grown by classical PLD are crystalline and stoichiometric. The films grown by UV-assisted PLD were crystalline and exhibit the best mechanical characteristics with values of hardness and Young modulus of 6–7 and 150–170 GPa, respectively, which are unusually high for the calcium phosphate ceramics. To the difference of PLD films, in the case of UV-assisted PLD, the GIXRD spectra show the decomposition of HA in Ca₂P₂O₇, Ca₂P₂O₉ and CaO. The UV lamp radiation enhanced the gas reactivity and atoms mobility during processing, increasing the tensile strength of the film, while the HA structure was destroyed.     

Application of pulsed laser deposited zinc oxide films to thin film transistor device

Transparent zinc oxide (ZnO) thin films were deposited on various substrates using a pulsed laser deposition (PLD) technique. During the PLD, oxygen pressure and substrate temperature were varied in order to find an optimal preparation condition of ZnO for thin film transistor (TFT) application. Dependence of optical, electrical and crystalline properties on the deposition conditions was investigated. The ZnO thin films were then deposited on SiN/c-Si layer structures in order to fabricate a TFT device. The pulsed laser deposited ZnO films showed a remarkable TFT performance: field effect mobility (μ_FE) of 2.4-12.85 cm²/V s and ratio of on and off current (R_on/off) in 2-6 order range. Influence of ZnO preparation conditions on the resulting TFT performance was discussed.     

Nano Techniques for Enhancing Critical Current in?Superconducting YBCO Films

A range of nano techniques is explored in order to increase the critical current in pulsed laser deposited (PLD) superconducting YBa₂Cu₃O _x (YBCO) thin films. The structural measurements are linked with magnetic and transport measurements of the films. The effectiveness of PLD techniques is analyzed from the point of view of the dimensionality of nanostructures formed prior to and during the film growth. It is shown that a combination of two-dimensional substrate decoration with nanoparticles before the film deposition and one-dimensional growth of external phase nanorods during the deposition offers a high critical current in magnetic field both along the c-axis and in the ab-plane of YBCO.     

Root growth of multi-wall carbon nanotubes by MPCVD

This work examines the relationships among the growth and interlayer reactions of carbon nanotubes (CNTs) to develop an effective process for controlling the nanostructure, orientation and characteristics of CNTs. Vertically oriented CNTs were successfully synthesized by microwave plasma chemical vapor deposition (MPCVD) with CH₄/H₂ as source gases. Additionally, the Ti and SiO₂ barrier layers and the Co catalyst were used in an experiment on the growth of CNTs on the Si wafer. Then, the SiO₂ barrier layer was deposited by low-pressure chemical vapor deposition (LPCVD). The Ti barrier layer and Co catalyst films were deposited on the Si wafer by physical vapor deposition (PVD). The deposited nanostructures were characterized by scanning and transmission electron microscopy, the results of which reveal that the deposited MWCNTs were grown under the influence of a catalyst on Si substrates with or without a barrier layer, by MPCVD. Vertically grown, dense MWCNTs attached to a catalytic film demonstrate that various MWCNTs penetrated the root particles. The diameter of the root particles, of approximately in the order of 100 nm, is larger than those of the tube, 10–15 nm. The well-known model of the growth of CNTs includes base- and tip-root growth. The interaction between the catalytic film and the supporting barrier layer is suggested to determine whether the catalytic particles are driven up or pinned down on the substrate during the growth.     

Biomolecular papain thin films growth by laser techniques

Papain thin films were synthesised by matrix assisted and conventional pulsed laser deposition (PLD) techniques. The targets submitted to laser radiation consisted on a frozen composite obtained by dissolving the biomaterials in distilled water. For the deposition of the thin films by conventional PLD pressed biomaterial powder targets were submitted to laser irradiation. An UV KrF* excimer laser source was used in the experiments at 0.5 J/cm² incident fluence value, diminished one order of magnitude as compared to irradiation of inorganic materials. The surface morphology of the obtained thin films was studied by atomic force profilometry and atomic force microscopy. The investigations showed that the growth mode and surface quality of the deposited biomaterial thin films is strongly influenced by the target preparation procedure.     

Microstructure of Mg-Zn-Ca thin film derived by pulsed laser deposition

Mg₆₀Zn_40−хCa_х (х = 5, 3, 1) powders and thin films have been produced by high energy mechanical alloying (HEMA) and pulsed laser deposition (PLD), respectively and the influence of PLD processing parameters on the microstructures of the Mg-Zn-Ca amorphous thin film was investigated using XRD, TEM, HRTEM and XEDS. Amorphous powder and thin film corresponding to Mg₆₀Zn₃₅Ca₅ composition have been successfully generated. The substrate temperature appears to be the dominant PLD processing parameter among others contributing to the formation of amorphous thin film.     

The Influence of Temperature Distribution on YBCO Coated Conductor Deposited by Reel-to-Reel PLD Method

It is known that the tape’s temperature controlled by a close substrate heater will still deviate after the deposition process. In this work, we deposited YBa₂Cu₃O_7−δ (YBCO) films on RABiTS substrates with multilayer CeO₂/YSZ/CeO₂ buffer layers by pulsed laser deposition (PLD) under a different distribution of temperature deviation in order to improve it. Thermocouples were applied to exactly measure the temperature. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to inspect c-axis oriented crystals and surface morphology of YBCO films. Through this work, we found that the even shape is best. Under the temperature deviation with the best shape, a transport J _c of 3.2×10⁶ A/cm² and I _c =240 A was obtained for a 0.75 μm thick YBCO film on CeO₂/YSZ/CeO₂-bufferd RABiTS Ni–W alloy.     

Large area Ba1 − xSrxTiO3 thin films for microwave applications deposited by pulsed laser ablation

Large area Ba_1 − xSr_xTiO₃ (BST) thin films with x = 0.4 or x = 0.5 were deposited on 75 mm diameter Si wafers in a pulsed laser deposition (PLD) chamber enabling full-wafer device fabrication using standard lithography. The deposition conditions were re-optimized for large PLD chambers to obtain uniform film thickness, grain size, crystal structure, orientation, and dielectric properties of BST films. X-ray diffraction and microstructural analyses on the BST films grown on Pt/Au/Ti electrodes deposited on SiO₂/Si wafers revealed films with (110) preferred orientation with a grain size < 100 nm. An area map of the thickness and crystal orientation of a BST film deposited on SiO₂/Si wafer also showed (110) preferred orientation with a film thickness variation < 6%. Large area BST films were found to have a high dielectric tunability of 76% at an electric field of 400 kV/cm and dielectric loss tangent below 0.03 at microwave frequencies up to 20 GHz and a commutation quality factor of ~ 4200.     

Imposed quasi-layer-by-layer homoepitaxial growth of SrTiO3 films by large area pulsed laser deposition

The homoepitaxial growth of SrTiO₃ (STO) films was investigated by a large-area pulsed laser deposition (PLD), which was in-situ monitored by a high pressure reflective high energy electron diffraction. By combining a conventionally continuous film deposition with a followed interval relaxation, a persistent layer-by-layer (LBL) film growth of more than 100 unit cells STO films was achieved. This interrupted PLD technique could realize persistent LBL film growth at any laser frequency between 1 and 10 Hz and provides an effective way to fabricate high quality complex oxide films on unit cell scale.     

Effect of ZnO film deposition methods on the photovoltaic properties of ZnO–Cu2O heterojunction devices

The effect of ZnO film depositions using various film deposition methods such as magnetron sputtering (MSP), pulsed laser deposition (PLD) and vacuum arc plasma evaporation (VAPE) on the photovoltaic properties of ZnO–Cu₂O heterojunction solar cells is described in this report. In addition, the relationship between the resulting photovoltaic properties and the film deposition conditions such as supply power and substrate arrangement was investigated in Al-doped ZnO (AZO)–Cu₂O heterojunction devices fabricated using AZO thin films prepared by d.c. magnetron sputtering (d.c.MSP) or r.f. magnetron sputtering (r.f.MSP). The results showed that the measured photovoltaic properties of devices fabricated with films deposited on substrates oriented perpendicular to the target were better than those of devices fabricated with films deposited on substrates oriented parallel to the target. It was also found that ZnO film depositions under conditions where a relatively weaker oxidizing atmosphere was used yield better properties than films derived from MSP, which utilizes a high-density and high-energy plasma. Using VAPE and PLD, for example, high efficiencies of 1.52 and 1.42%, respectively, were obtained under AM2 solar illumination in devices fabricated at a substrate temperature around 200 °C.     

The Effect of Laser Energy and Target–Substrate Distance on the Quality of CeO<Subscript>2</Subscript> Seed Layer Deposited by PLD

In this work, CeO₂ seed layers have been deposited on RABiTS substrates by pulsed laser deposition (PLD) in a reel-to-reel chamber. We have systematically investigated the effect of laser energy and target–substrate distance on the quality of CeO₂ seed layers. It was found that the orientation of CeO₂ thin films was very sensitive to laser energy and target–substrate distance. X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to investigate how to exactly control the (00l) orientation and get smooth surface morphology. Through this work, we achieved optimum condition of pure c-axis oriented of CeO₂ seed layer.     

Temperature studies of optical parameters of (Ag3AsS3)0.6(As2S3)0.4 thin films prepared by rapid thermal evaporation and pulse laser deposition

(Ag₃AsS₃)_0.6(As₂S₃)_0.4 thin films were deposited using rapid thermal evaporation (RTE) and pulse laser deposition (PLD) techniques. Ag-enriched micrometre-sized cones (RTE) and bubbles (PLD) were observed on the thin film surface. Optical transmission spectra of the thin films were studied in the temperature range 77–300 K. The Urbach behaviour of the optical absorption edge in the thin films due to strong electron–phonon interaction was observed, the main parameters of the Urbach absorption edge were determined. Temperature dependences of the energy position of the exponential absorption edge and the Urbach energy are well described in the Einstein model. Dispersion and temperature dependences of refractive indices were analysed; a non-linear increase of the refractive indices with temperature was revealed. Disordering processes in the thin films were studied and compared with bulk composites, the differences between the thin films prepared by RTE and PLD were analysed.     

Preparation of the hard CNx thin films using NO ambient gas by pulsed laser deposition

Pulsed laser deposition (PLD) technique has been widely used in thin film preparation because of its wonderful and excellent properties and amorphous carbon nitride (CN_x) thin films are recognized to have potential for applications like hard coating and electron field emission device. We have deposited CN_x thin films by KrF excimer laser – (λ= 248 nm) ablation of pure graphite target in pure NO gas ambient condition. In this paper, we have prepared the CN_x thin films at various ambient NO gas pressure of 1.3–26 Pa and laser fluence of 2– 5J cm^?2 on Si (100) substrate. We consider that the hardness of CN_x thin films improves due to the increase the nitrogen/carbon (N/C) ratio. The N/C ratio depended on the ambient NO gas pressure and laser fluence. We obtainedthe maximum N/C ratio of 1.0 at NO 3.3 Pa. The typical absorption of CN bonds such as sp² C–N, sp³ C–N, G band and D band were detected from the infrared absorption measurement by FTIR in the deposited CN_x thin films.     

Preparation and Characterization of TiN Seed Layer in All-Conductive Multilayer Structure for Coated Conductors

TiN films were successfully prepared on biaxially textured Ni-5 at.%W substrates by pulsed laser deposition (PLD), serving as a seed layer of an all-conductive architecture, i.e., SrRuO₃(SRO)/TiN, for coated conductors. The structure and surface morphology of the TiN films were noticeably affected by the substrate temperature and pulse repetition rate. The subsequent conductive SRO and superconducting YBCO layer were deposited on the best sample of TiN buffered Ni-5 at.%W substrates. X-ray diffraction analysis confirmed that the biaxial textures were transferred from the TiN seed layer to the SRO cap layer and YBCO film with excellent out-of-plane and in-plane textures. The superconducting transition curves and the temperature-dependent resistivity of YBCO films on all-conductive buffer and on the traditional insulated CeO₂/YSZ/Y₂O₃ were also investigated.     

YSZ thin films deposited by e-beam technique

YSZ thin films were grown evaporating cubic and tetragonal phase ZrO₂ stabilized by 8 wt.% of Y₂O₃ (8% of YSZ) ceramic powders by using e-beam deposition technique. Operating technical parameters that influence thin film properties were studied. The influence of substrate crystalline structure on growth of deposited YSZ thin film was analyzed there. The YSZ thin films (1.5-2 μm of thickness) were deposited on three different types of substrates: Al₂O₃, optical quartz (SiO₂), and Alloy 600 (Fe-Ni-Cr). The dependence of substrate temperature, electron gun power, and phase of ceramic powder on thin film structure and surface morphology was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The substrate temperature was changed in the range of 20-600° C (during the YSZ thin film deposition) and its influence on the crystallinity of deposited YSZ thin films was analyzed. It was found that electron gun power and substrate temperature has the influence on the crystallite size, and texture of YSZ thin films. Also, the substrate has no influence on the crystal orientation. The crystallite size varied between 20 and 40 nm and increased linearly changing the substrate temperature. The crystal phase of evaporated YSZ powder has the influence on the structure of the deposited YSZ thin films.     

Pulsed laser deposition of crystalline ZrC thin films

ZrC thin films were grown on Si substrates by the pulsed laser deposition (PLD) technique under various conditions. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), X-ray diffraction and reflectivity, spectroscopic ellipsometry, and four point probe measurements were used to characterize the properties of the deposited films. It has been found that crystalline films could be grown only by using laser fluences higher than 5 J/cm² and substrate temperatures in excess of 500 °C. For a fluence of 10 J/cm² and a substrate temperature of 700 °C, cubic ZrC films (a = 0.469 nm) exhibiting a (200)-texture were deposited under vacuum or low pressure C₂H₂ atmosphere. These films were smooth, with surface roughness values below 1.0 nm and mass densities around the tabulated value of 6.7 g/cm³. AES depth profiling investigations showed oxygen contamination around 7% in the bulk region. Despite the relatively high levels of oxygen contamination, the deposited ZrC films were very conductive. The use of a low C₂H₂ pressure atmosphere during deposition had a small beneficial effect on crystallinity and stoichiometry of the films.     

Structural characterization and photocatalytic activity of ultrathin TiO2 films fabricated by Langmuir-Blodgett technique with octadecylamine

TiO₂ thin films with nanometer-scale thicknesses were prepared by the hydrolysis of titanium potassium oxalate using octadecylamine (ODA) Langmuir-Blodgett (LB) films as templates. After optimizing conditions in immersion process, the amount of TiO₂ generated in the ODA LB film was found to be precisely controlled by the number of deposited ODA layers. Morphological measurements showed that uniform TiO₂ film with surface roughness of less than 1.3 nm could be prepared from the monolayer LB films through subsequent heat-treatment process, while generation of cracks became less noticeable on the 5-layer film after heat-treatment at lower holding temperature with slow heating rate. In addition, photocatalytic activities of the TiO₂ films were examined from the decomposition of cadmium stearate (CdSt) LB films and stearic acid (SA) cast films for different time intervals of irradiation with UV light. Atomic force microscopy measurements showed that an almost flat surface of the CdSt LB film changes to a moth-eaten appearance as a result of decomposition under UV light irradiation. Furthermore, the post-heat-treatment at higher temperatures resulted in decreased photocatalytic activity of the TiO₂ film for the decomposition of SA cast film.     

ITO deposited by pyrosol for photovoltaic applications

The goal of this work is to investigate morphology, electrical and optical properties of indium-tin-oxide (ITO) deposited by pyrosol on glass and Si substrates at different temperatures and to implement such layers for the processing of Si-based solar cells. The influence of the methanol/H₂O ratio on general properties of ITO was investigated. Atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission spectra, ellipsometry and resistivity measurements were used for the analysis. It is shown that properties of ITO layers depend dramatically on the substrate used. It is shown that the resistivity of ITO layers deposited on a glass substrate is higher up to 2.5 times, compared to that of ITO layers deposited on a Si substrate at the same conditions, but in both cases decreases if the deposition temperature increases. Moreover, ITO layers deposited on a glass substrate are more flat and their refractive indexes are always lower for all deposition temperatures. An increase of the H₂O concentration in a film-forming solution leads to a decrease of the ITO film resistivity and to a slight increase of the roughness. An application of pyrosol deposited ITO films as the top transparent electrodes for the (p⁺nn⁺)Si and heterojunction ITO/n-Si solar cells is demonstrated.