A comparative study of the polyaniline thin films produced by the cluster beam deposition and laser ablation methods

Polyaniline (PANI) thin films have been prepared by applying the novel neutral and ionized cluster beam deposition (NCBD and ICBD) methods and the pulsed laser deposition (PLD) technique to the PANI samples of half-oxidized emeraldine base (EB-PANI) and protoemeraldine base forms in a high-vacuum condition. Characterization of the oxidation states and structural changes of pristine and doped thin films has been performed by Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, and x-ray photoelectron spectroscopy. Spectroscopic measurements demonstrate that the dominant structure of NCBD and ICBD thin films corresponds to the reduced leucoemeraldine base state, whereas the chemical composition of PLD thin films depends critically on the laser fluence and the molecular weight of PANI target. The congruent deposition is only obtained for the PLD films deposited by the laser-induced decomposition of the low-molecular-weight targets in the low to intermediate fluence regime (below 100 mJ/cm2 with a pulse duration of 7 ns). The surface morphology examined by atomic force microscopy measurements shows that the cluster and laser beams are effective in producing smooth, uniform polymeric thin films. After I2 and HCl doping, the electrical conductivities of the NCBD, ICBD, and particularly PLD thin films are increased significantly. The higher conductivity of PLD films is ascribed to higher amounts of quinoid di-imine doping sites in the EB-PANI state, and the overall structure-conductivity characteristics are consistent with the spectroscopic observations.     

Carrier gas UV laser ablation sensitizers for photopolymerized thin films

Designed carrier gas UV laser ablation sensitizers were synthesized and proved to greatly enhance the UV laser ablation of photopolymerized thin films. Polymers containing dense ester groups are reported to have better laser ablation performance because of the tendency of the ester groups to decompose into gaseous products (“carrier gases”) during the ablation process. In order to introduce this mechanism to cationic UV curable coatings for better laser ablation, a series of “carrier gas” sensitizers were synthesized by reacting hydroxyl containing reactive diluents such as oxetane and polyester polyols with monomethyl oxalyl chloride or dimethyl oxalate; the oxalyl group is considered a “carrier gas” generating moiety. Furthermore, a UV absorbing chromophore, naphthalene, is either chemically bound to the oxalyl containing molecules or blended with the synthesized oxalyl containing compounds to produce a synergistic effect. The “carrier gas” sensitizers were added into a typical cationic UV curable formulation to form sensitized coatings, which were then characterized by thermogravimetric analysis, real time FTIR and ablated by a 355 nm laser. The ablation vias were examined using optical profilometry and SEM. Compared to the control, the sensitized coatings were found to have similar thermal decomposition temperatures and higher functional group conversion during photopolymerization. All of the sensitized coatings containing the “carrier gas” sensitizers exhibited better UV laser ablation performance than the control. The combination of naphthalene derivatives and the oxalyl group gave a better ablation result, suggesting a synergistic effect. The chemical combination of the naphthalene and oxalyl group exhibited better ablation sensitization than their blends, suggesting a more efficient intramolecular laser energy utilization process.     

Epitaxial oxide thin films by pulsed laser deposition: Retrospect and prospect

Pulsed laser deposition (PLD) is a unique method to obtain epitaxial multi-component oxide films. Highly stoichiometric, nearly single crystal-like materials in the form of films can be made by PLD. Oxides which are synthesized at high oxygen pressure can be made into films at low oxygen partial pressure. Epitaxial thin films of highT _c cuprates, metallic, ferroelectric, ferromagnetic, dielectric oxides, superconductor-metal-superconductor Josephson junctions and oxide superlattices have been made by PLD. In this article, an overview of preparation, characterization and properties of epitaxial oxide films and their applications are presented. Future prospects of the method for fabricating epitaxial films of transition metal nitrides, chalcogenides, carbides and borides are discussed.     

First-principles calculations of Cd-doped ZnO thin films deposited by pulse laser deposition

Zn_1−xCd_xO thin films are deposited on quartz substrate by pulse laser deposition. Their band structure and optical properties are experimentally and theoretically investigated. By varying Cd concentration, the band gap of Zn_1−xCd_xO films can be adjusted in a wide range from 3.219 eV for ZnO to 2.197 eV for Zn_0.5Cd_0.5O, which produces different emissions from ultraviolet to Kelly light in their photoluminescence spectra. Simultaneity, the electronic structure and band gap of Zn_1−xCd_xO are investigated by the density functional theory (DFT) with a combined generalized gradient approximation (GGA) plus Hubbard U approach, which precisely predicts the band-gaps of ZnO and Zn_1−xCd_xO alloys. Both the experimental results and theoretical simulation reveal that with increasing Cd concentration in Zn_1−xCd_xO alloys, their absorption coefficients in visible light range are evidently enhanced. The adjustable photoluminescence emission and enhanced visible light absorption endow Zn_1−xCd_xO alloys potential applications in optoelectronic and photocatalytic fields.     

Hot pressing sintered CuxMo6S8 targets for laser ablation thin films deposition

Sintering conditions of Cu₄Mo₆S₈ pellets, 20 mm in diameter and about 4 mm thick have been determined. The expulsion of copper out of the pellet for an annealing temperature of 1100 ° C has been observed, in agreement with the evolution of the phase diagram when the temperature increases. The appearance of Cu₂S cristallites on the surface of the films deposited from highly densified targets associated with a high excess of copper and sulfur can be correlated with the behavior observed on the pellets. In fact the increase of the temperature of the target under the laser beam impact is likely responsible for a copper migration on its surface, which leads to the observed composition of the film.     

Photoelectrochemical deposition of thin tellurium films

Effect of polychromatic light on the electrochemical deposition of tellurium(IV) ions on a glass carbon electrode from acid solutions of 0.45 M Na₂SO₄ + 0.05 M H₂SO₄ with pH 2.2 was studied. It is shown that electrochemical reduction of tellurium(IV) is possible in two stages in the potentiodynamic mode at potentials in the range from 0 to ?1000 mV. Elementary tellurium is formed in the first stage (E = ?320 ± 20 mV) and is reduced to telluride ions in the second (E = ?700 ± 50 mV). It is demonstrated that, under potentiodynamic deposition conditions, visible light affects the generation of Te^2? ions at potentials more positive than the electrochemical potential. The chronoamperometric method revealed differences in the behavior of transient currents in the dark and under illumination. The elemental composition and the film surface morphology were studied by electron-probe analysis.     

Excimer laser ablation of Langmuir-Blodgett films

Photoablation of several Langmuir-Blodgett (LB) films on Silicon substrates was performed at the excimer laser wavelength of 248 nm. This is a fast, solvent-free, one-step method for structuring thin organic films. Structures were produced both by projection of a mask and also using direct writing of the laser beam, yielding feature sizes on the order of microns. Spectral analysis of the remaining material showed no change compared to the unexposed material, suggesting that no degradation has occurred. This technique appears to be viable for use in the lithography of LB films.     

Electrochemical deposition and characterization of SnS thin films

Thin films of SnS were cathodically deposited onto stainless steel substrates from bath containing 0.025 M SnSO₄, 0.25 M KSCN and 0.25 M Na₂SO₄. The mechanism of electrochemical co-deposition of tin and sulphur was investigated by cyclic voltammetry. Analysis of the chronoamperometric current–time transients suggested that, in the potential range −560 to −590 mV vs saturated calomel electrode, the electrodeposition of SnS involved progressive nucleation model. However, at a potential −600 mV, the electrodeposition involved instantaneous nucleation model. The deposits have been characterized by scanning electron microscopy, X-ray diffraction and optical measurements. SnS films were found to be polycrystalline with an optical energy gap of 1.38 eV.     

Perovskite thin films deposited by pulsed laser ablation as model systems for electrochemical applications

Thin films of a bifunctional electrocatalyst with the compositions La_0.6Ca_0.4CoO_3−δ and La_0.7Ca_0.3CoO_3−δ have been deposited by a variation of pulsed laser deposition, i.e. pulsed reactive crossed-beam laser ablation. These perovskite phases have been used as catalysts for oxygen reduction and evolution in re-chargeable Zn/air batteries. The utilization of a synchronized reactive gas pulse with N₂O or O₂ allows the preparation of perovskite films with almost ideal oxygen content without additional annealing steps and to control the oxygen content of the films. The films with higher oxygen content reveal a lower resistivity. These compositions have been selected to study the influence of the texture on the electrocatalytical activity for oxygen reduction and evolution of the films. Amorphous films, or films with mixed or single orientation can be obtained by varying the target–substrate distance and substrate temperature without changing the composition of the films. A clear influence of the crystallinity on the catalytic activity, i.e. smaller overpotential for the two oxygen reactions, is observed. The amorphous films reveal the largest overpotential, followed by the polycrystalline films with one or more orientations, and the single crystalline films with (100) orientation.     

Thermokinetic study of CODA azoic liquid crystal and thin films deposition by matrix-assisted pulsed laser evaporation

Azoic dyes are compounds of interest from the point of view of their potential applications, such as the use of liquid crystals in optoelectronic and organic electroluminescent devices, or may be employed as template matrices for producing high-aspect ratio inorganic nanomaterials. Herein, 4-[(4-chlorobenzyl)oxy]-3,4′-dichloroazobenzene azoic dye, known as CODA, is selected as a choice compound among such materials due to its liquid crystalline properties and may be further used as nanostructured material in various applications. Thermokinetic study of CODA azoic dye thermal decomposition in air flow atmosphere was performed by employing thermogravimetric data; the kinetic parameters of the two decomposition steps were obtained under non-isothermal linear regimes, by means of multi-heating rates methods. Differential and integral “model-free” kinetic methods like Friedmann, Kissinger–Akahira–Sunose and Ortega, the invariant kinetic parameters method and the Perez-Maqueda et al. criterion (by Coats–Redfern and differential equations) were used. The kinetic study reveals very different behaviour related to the two decomposition steps of CODA, with complex processes composed of more than one kinetic mechanism for each of those, as indicated also by the Gotor et al. master plot method. Modern devices incorporating such materials tend to use them as thin films due to their specific properties; the CODA thin films were deposited on silicon substrates by matrix-assisted pulsed laser evaporation technique, using a Nd:YAG laser working at the wavelength of 266 nm. The preservation of the CODA compound after the transfer on the substrates was confirmed by Fourier transform infrared spectroscopy, while the morphology and topography of the deposited materials and of the thin film surfaces were investigated by atomic force microscopy and optical microscopy.     

Plasma-induced deposition of thin films of aluminum oxide

Plasma-induced deposition of wear-protecting A1₂O₃ films has been investigated for two different gas mixtures, one of which is ususally used in thermal CVD. It is shown that, contrary to thermal CVO, the properties of thin films deposited from an AlCl₃/O₂/Ar mixture are superior to those prepared from AICl₃/CO₂/H₂. High Vickers hardness of 1800-2500 and a low chlorine content of 0.7 at. % have been obtained in films deposited from an AICl₃/O₂/Ar mixture at a substrate temperature of 500°C.     

Characterization and electrochemical deposition of natural melanin thin films

Melanin is an important class of biological pigments because of its distinct chemical and physical properties. The electrochemical deposition of natural melanin thin films was studied using two different techniques; constant potential and cyclic voltammetry along with a deposition time of five hours. The thin films deposited electrochemically on a fluorine-doped tin oxide conductive glass substrate using the constant potential method, exhibited faster growth rate and better adhesion to the fluorine-doped tin oxide working electrodes than those deposited using the cyclic voltammetry method. The thin films deposited on the fluorine-doped tin oxide conductor glass using the constant potential method were also more homogeneous than those deposited via the cyclic voltammetry technique. The increase of film thickness is related to the increase of electrochemical deposition time. Interestingly, the electrochemical deposition using the constant potential method had the advantage of consuming less electric charge. The physical and chemical structures of the melanin thin films were characterized using ultraviolet–visible absorption spectroscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction analysis. The ultraviolet–visible absorption spectra showed the correlation between the variation of deposition rates of melanin and the type of electrochemical technique employed as well as the thickness of the film. The average thickness of the film is 500 nm which absorb 40% of light in both type of films. The atomic force microscopy images illustrated the homogeneous deposition of the melanin molecules on the fluorine-doped tin oxide conductive glass substrate, indicating that the thickness of the thin films can be controlled. We estimated an average grain size of 14.093 Å. The ease of preparing such thin films of organic materials can open new avenues towards the use of soft conductors, in contrast to the complex preparation of industrial semiconductors.     

Electrochemically induced sol-gel deposition of zirconia thin films

A novel electrochemical method for deposition of ZrO(2) thin films is described. The films, 50-600 nm thick, were obtained by applying moderate positive or negative potentials (+2.5 V to -1.5 V versus SHE) on conducting surfaces immersed in a 2-propanol solution of zirconium tetra-n-propoxide [Zr(OPr)(4)] in the presence of minute quantities of water (water/monomer molar ratios in the range of 10(-5) to 10(-1)), which was the limiting reagent. Oxidative electrochemical formation of solvated H(+) and reductive formation of OH(-) catalyze the hydrolysis and condensation of the metal alkoxide precursor. The magnitude of the applied potential and its duration provide a convenient way of controlling the film thickness. The films consist of an amorphous phase, as revealed by XRD measurements. The effects of different parameters, such as the applied potential and its duration, the amount of added water and the current-time characteristics, were studied. A mechanism for the electrodeposition of the zirconia films which is in accordance with our findings is proposed.     

Characterization of vapor deposition polymerized polyimide thin films

Vapor deposition polymerized (VDP) polyimide (PI) thin films were prepared and characterized by using thermogravimetrical analysis (TGA), scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR), and bending-beam techniques. The film properties investigated were thermal stability, wet-etching characteristics, surface topology, imidization characteristics, internal stress upon curing and thermal cycling, and hygroscopic stress upon moisture diffusion. Markedly different characteristics are observed for the VDP-PI films when comparing with the conventional ones. They seem denser in film structure and have better mechanical properties, but are somewhat less stable in thermal resistance. © 1996 John Wiley & Sons, Inc.     

KrF pulsed laser ablation of thin films made from fluorinated heterocyclic poly(naphthyl-imide)s

Among the many aspects of laser ablation, development of conical structures induced by excimer laser radiation on polyimide surfaces has been thoroughly investigated. Because the mechanisms that produce these surface textures are not fully understood, two theories, photochemical bond breaking and thermal reaction, have been introduced. Here we present the first study of ultraviolet laser ablation behavior of thin films made from fluorinated poly(naphthyl-imide)s containing oxadiazole rings and the investigation of the mechanism of cone-like structure formation at two laser fluences, 57 and 240 mJ/cm(2). The morphology of thin films before and after laser ablation was studied by using various spectroscopy techniques such as Fourier transform infrared spectroscopy, time-resolved emission and X-ray photoelectron spectroscopy, atomic force microscopy, and contact angle measurements. All of the data suggest impurities shielded at low fluence radiation (57 mJ/cm(2)) and a radiation hardening process at high value fluence (240 mJ/cm(2)), which are proposed as the main mechanisms for laser ablation of our polyimide films, and we bring evidence to support them.     

Unexpected formation by pulsed laser deposition of nanostructured Fe/olivine thin films on MgO substrates

Olivine-type LiFePO₄ thin films were grown on MgO (1 0 0) substrates by pulsed laser deposition (PLD). The formation of an original nanostructure is evidenced by transmission electron microscopy measurements. Indeed, on focused ion beam prepared cross sections of the thin film, we observe, the amazing formation of metallic iron/olivine nanostructures. The appearance of such a structure is explained owing to a topotactic relation between the two phases as well as a strong Mg diffusion from the substrate to the film surface. Magnesium migration is thus concomitant with the creation of metallic iron domains that grow from the core of the film to the surface leading to large protuberances. To the best of our knowledge, this is the first report on iron extrusion from the olivine-type LiFePO₄.     

Pulsed laser ablation in liquid for micro-/nanostructure generation

Pulsed laser ablation in liquid is an approach for micro-/nanostructure generation directly from bulk materials. It has grown rapidly as a research field of photochemistry and physical chemistry in the last decade, and represents a combinatorial library of constituents and interactions, but the understanding of this library is still insufficient. This review attempts to build up a comprehensive mechanistic scenario of pulsed laser ablation in liquid and illustrate the underlying principles to micro-/nanostructure generation. Various structures produced by this method have been summarized that provide prototypes for potential applications in sensing, optoelectronics, and biomedicine, etc.     

In situ spectroelectrochemical behaviour of nanocrystalline TiO_2 thin films electrode fabricated by pulsed laser deposition

Nanocrystalline titanium oxide thin films have been successfully deposited on ITO coated glass by pulsed laser ablation of metallic Ti target in O_3/O_2 ambient gases. The intercalation of Li ions in the anatase TiO_2 film electrode is examined by cyclic vohammetry. The electrochromic behaviour of TiO_2 electrode is investigated by in-situ visible transmittance measurement, and two absorption bands at 420 and 650 nm are observed. The absorption falling and rising in color changing with excellent revisibility is relative to the insertion and deintercalation processes of Li ion. These resuits suggest that nanocrystalline titanium oxide films fabricated by pulsed laser deposition exhibit excellent spectroelectrochemical property.     

In situ spectroelectrochemical behaviour of nanocrystalline TiO2 thin films electrode fabricated by pulsed laser deposition

Nanocrystalline titanium oxide thin films have been successfully deposited on IT0 coated glass by pulsed laser ablation of metallic Ti target in 0₃/0₂ ambient gases. The intercalation of Li ions in the anatase TiO₂ film electrode is examined by cyclic voltammetry. The electrochromic behaviour of TiO₂ electrode is investigated byin-situ visible transmittance measurement, and two absorption bands at 420 and 650 nm are observed. The absorption falling and rising in color changing with excellent revisibility is relative to the insertion and deintercalation processes of Li ion. These results suggest that nanocrystalline titanium oxide films fabricated by pulsed laser deposition exhibit excellent spectroelectrochemical property. Project supported by the National Natural Science Foundation of China (Grant No. 29783001) and State Key Laboratory for Physical Chemistry of Solid Surface of Xiamen University (1997).     

Titanate nanotube thin films via alternate layer deposition

Layer-by-layer growth of titanate nanotubes on glass substrates was achieved by alternate layer deposition using an aqueous solution of colloidal titanate nanotubes and that of a polycation. Even a single layer thin film of titanate nanotube shows high photoinduced hydrophilicity.