Excimer Laser-assisted Metal Organic Deposition Research Articles

Integration Effect of O<sub>2</sub>-Plasma to an Excimer-Laser assisted Metal Organic Deposition Process for Functionalization of Photoelectrodes

Integration Effect of O<sub>2</sub>-Plasma to an Excimer-Laser assisted Metal Organic Deposition Process for Functionalization of Photoelectrodes

Low temperature vanadium oxide thin film sintering by thermal and excimer-laser-assisted Metal-Organic Deposition (MOD)

Vanadium oxide thin films (VO2 Monoclinic (M) or V2O5) on silica glass substrates were prepared by Metal-Organic Deposition (MOD) using Infra-Red furnace (Thermal-MOD) and Excimer Laser Assisted Metal-Organic Deposition (ELAMOD). On one hand, using thermal process (i.e. Infra-Red furnace sintering) for 90 min at 300 °C in air and O2 atmosphere, V2O5 was formed and in N2 atmosphere at 500 °C for 90 min, VO2 (M) was formed. On the other hand, VO2 (M) was obtained with laser (ELAMOD) sintering at 300 °C, with no specific atmosphere control (ambient air), for only 1 min and without any resort to a buffer layer to achieve homogeneous coverage. Formation mechanism of the VO2 (M) with thermal MOD process and UV laser process is discussed.

A method to give chemically stabilities of photoelectrodes for water splitting: Compositing of a highly crystalized TiO2 layer on a chemically unstable Cu2O photocathode using laser-induced crystallization process

To prevent the self-reduction of the Cu2O photocathode for solar hydrogen production, we developed a compositing process of a highly crystalized TiO2 layer on the Cu2O photocathode using an excimer-laser-assisted metal-organic deposition (ELAMOD) process. The TiO2 layer was successfully crystalized without oxidation of Cu2O to CuO mainly owing to a photothermal effect with nanosecond duration time induced by laser absorption of the TiO2 precursor while the crystallization of the TiO2 layer by usual furnace heating process was accompanied by oxidation of Cu2O which degrade the water reduction ability. On the TiO2/Cu2O photocathode prepared by ELAMOD process, the self-reduction of Cu2O did not occur and then photocurrent due to water reduction was constant with reaction time while on the bare Cu2O photocathode, the photocurrent decreased owing to the occurrence of the self-reduction. This indicated that reaction stability of the photocathode was largely enhanced after compositing of the crystallineTiO2 layer. This ELAMOD process would be applicable for any kinds of chemically unstable photoelectrodes containing non-oxides such as sulfides and phosphides, and therefore any kinds of photoelectrodes would have potentials toward a practical use by improving their chemical stabilities.

Control of Metal-Insulator Transition of Vanadium Dioxide Thin Film Grown by Excimer Laser Assisted Metal Organic Deposition

In order to fabricate the new devices for the next generation, it is necessary to develop new materials, nanostructured thin films, low temperature processing. To achieve these aims, we have developed the photo-induced chemical solution deposition such as excimer laser-assisted metal organic deposition (ELAMOD) and photo reaction of nano-particle method (PRNP) for the preparation of the patterned metal oxide thin film on organic, glass and single crystalline substrates. In this presentation, we will talk about epitaxial VO2 thin film with nanostructure by using the photo-induced chemical solution deposition, and its excellent properties of the thin film for new uncooled IR sensor.

Electrical properties of Sb-doped epitaxial SnO2 thin films prepared using excimer-laser-assisted metal–organic deposition

Excimer-laser-assisted metal–organic deposition (ELAMOD) was used to prepare Sb-doped epitaxial (001) SnO2 thin films on (001) TiO2 substrates at room temperature. The effects of laser fluence, the number of shots with the laser, and Sb content on the electrical properties such as resistivity, carrier concentration, and carrier mobility of the films were investigated. The resistivity of the Sb-doped epitaxial (001) SnO2 thin film prepared using an ArF laser was lower than that of the film prepared using a KrF laser. The van der Pauw method was used to measure the resistivity, carrier concentration, and carrier mobility of the Sb-doped epitaxial (001) SnO2 thin films in order to determine the effect of Sb content on the electrical resistivity of the films. The lowest resistivity obtained for the Sb-doped epitaxial (001) SnO2 thin films prepared using ELAMOD with the ArF laser and 2 % Sb content was 2.5 × 10−3 Ω cm. The difference between the optimal Sb concentrations and resistivities of the films produced using either ELAMOD or conventional thermal MOD was discussed.

In situ measurement of crystallization of oxide thin films during irradiation with pulsed UV laser in chemical solution deposition process

The epitaxial and polycrystalline growth of lanthanum strontium manganite films on single crystalline strontium titanate and lanthanum aluminate substrates, respectively, under the irradiation with XeCl lasers in the excimer laser-assisted metal organic deposition (ELAMOD) process have been previously reported. In order to investigate the growth phenomena, we monitored the thermal radiation from the sample surfaces irradiated with a pulsed ultraviolet laser in situ with near-infrared sensors. The cooling of the lanthanum strontium manganite films on strontium titanate substrates was significantly slower than that of films on lanthanum aluminate substrates. A similar behavior was also observed by the numerical simulation study. This difference in the cooling decay curves may play an important role in the mode by which crystal growth occurs in the ELAMOD process.

Nanomaterials for Light Management in Electro-Optical Devices

In the past decade, nanostructured materials and nanoparticles have emerged as the necessary ingredients for electrooptical applications and enhancement of device performance, in particular by making use of the light management aspects of the nanomaterials. The application areas that are being transformed profoundly include smart coating devices (e.g., electrochromic, photochromic, and thermochromic devices), solar energy, and sensing. Despite the large volume of work in the past on smart coating devices, and in particular on electrochromic devices and thermochromic fenestrations, for optical transmission or reflection control, applications remain limited because of slow response time and nonuniformity in the case of large surfaces. Recent works in the field indicate that nanostructured electrochromic coatings would be an integral part of the solution to the above problem. One aspect that can thus be focused on would be the fabrication and characterization of the nanostructured smart coating materials and their compatibility with other layers in the overall smart coating device. In the area of solar photovoltaics, nanomaterials have been used in designing light-trapping schemes for inorganic as well as organic solar cells. One particular category of solar cells that has attracted much interest is the plasmonic solar cells in which metallic nanoparticles are incorporated, helpingmore » in enhancing their energy conversion efficiency. Nanostructured solar cells would eventually develop into a 'game changing' technology for making solar cells that are affordable and highly efficient, providing a sizeable alternative energy source for our ever-increasing energy needs. Sensors based on the optical properties of constituting nanostructures and nanoparticles also form a most interesting class of bio- and electrochemical sensing devices. The possibility of synthetizing nanoparticles and structures of specifically desired sizes and shapes has indeed opened a whole new range of sensing applications. In parallel to the experimental development of nanomaterials for light management in devices, theoretical modeling and analysis have also accomplished much progress, and different methods for simulating the optical properties of nanoparticles and structures have been proposed. This special issue of the Journal of Nanomaterials is thus dedicated to articles dealing with nanostructured materials that can be used for light management purpose in different applications. Silicon-rich oxide (SRO) is a dielectric material that contains Si nanoparticles and exhibits interesting physical characteristics for applications in optoelectronic devices. The work by Aceves-Mijares et al. examine, in detail the electro-, cathode- and photoluminescence properties of SRO and discuss the origin of light emission in this type of materials. SRO films, of high and medium silicon excess density, obtained by low-pressure chemical vapor deposition and annealed at 1,100 C have been studied. Results obtained by the authors have led to conclude that SRO emission properties are due to oxidation state nanoagglomerates rather than to nanocrystals, and the emission mechanism is similar to that in the donor-acceptor decay in semiconductors with a specific wide emission spectrum. Two papers are devoted to nanostructured electrochromic thin films, a category of materials most suitable for controlling light transmission or absorption in electrooptical devices, including smart window coatings. Dinh et al. have shown that by mixing nanostructured Ti and W oxides films, one can obtain devices with considerable enhancement of electrochromic efficiency and electrochemical stability as compared to the conventional nonnanostructured films. As large-area mixed Ti and W oxides can be prepared by the simple doctor blade technique followed by an electrochemical process, this type of nanostructured electrochromic films can be considered a good candidate for smart window applications. Djaoued et al. have presented their studies on the synthesis, characterization, and electrochromic applications of porous WO{sub 3} thin films with different nanocrystalline phases. Asymmetric type electrochromic devices have been constructed using hexagonal, monoclinic, and orthorhombic porous WO{sub 3} thin porous films, and their enhanced electrochromic functionality has been well demonstrated. The paper on smart materials by Chen et al. presents the synthesis of thermochromic W-doped VO{sub 2} (monoclinic/rutile) nanopowders using a novel and simple solution-based process as opposed to other conventional techniques such as excimer laser-assisted metal organic deposition and magnetron sputtering. This simple process is based on the reaction of ammonium metavanadate (NH{sub 4}VO{sub 3}) and oxalic acid dihydrate (C{sub 2}H{sub 2}O{sub 4} {center_dot} 2H{sub 2}O) followed by addition of appropriate ammonium tungstate (N{sub 5}H{sub 37}W{sub 6}O{sub 24} {center_dot} H{sub 2}O).« less

Ti-Doped VO2 Films Grown on Glass Substrates by Excimer-Laser-Assisted Metal Organic Deposition Process

V1-xTixO2 films were prepared on glass substrates by excimer-laser-assisted metal organic deposition (ELAMOD) and thermal MOD processes. The VO2 phase was successfully formed in the range of x = 0–0.35 at 300 °C in air using the ELAMOD process. This is a big advantage in terms of fabrication process for glass or organic substrates. It was also confirmed that dense films were obtained by preparing TiO2 buffer layers on glass substrates. Furthermore, the detailed effect of Ti content in VO2 films on metal–insulator (MI) transition properties was examined. As Ti content increased, the broadening of MI transition and the decreasing of the hysteresis width occurred. At x = 0.14, the hysteresis disappeared. The temperature coefficient of electrical resistance (TCR) value of the film (x = 0.14) remained at approximately -3%/K from 300 to 340 K and was more than -4%/K from 340 to 350 K.

Crystal quality and surface morphology of uniaxial oriented multilayer perovskite thin films grown by excimer laser assisted MOD

By means of an excimer laser-assisted metal organic deposition, a perfect uniaxial oriented Dion–Jacobson perovskite RbLaNb2O7 thin film and a multilayer film SrTiO3/RbLaNb2O7 on an amorphous borosilicate glass substrate has been successfully prepared. The films were crystallized only by an excimer laser irradiation in air at 400°C after a deposition of metal–organic solution and preheating at 400°C. The obtained SrTiO3 film on the (010)-oriented RbLaNb2O7 seed layer showed highly (100)-oriented growth: the Lotgering factor F(100) was evaluated to be 0.983. From the cross-sectional transmission electron microscopy analysis, the crystal quality of the RbLaNb2O7 film was confirmed to be good as a seed layer for the fabrication of oriented multilayer perovskite thin films, whereas the stacking faults were inevitably emerged in the structure. The surface morphology observations revealed that the surface of the seed layer thin film consisted of very smooth regions and roughened grains. On the smooth grains, the epitaxial growth of SrTiO3 film seems to be significantly enhanced. To reduce the roughened grains would be the most important issue for further improvement of orientation quality of multilayer perovskite thin films.

Non-hysteretic metal–insulator transition of VO2 films grown by excimer-laser-assisted metal organic deposition process

We examined the correlation between thickness of an epitaxial VO2 phase grown on a TiO2 (001) substrate by the excimer-laser-assisted metal organic deposition (ELAMOD) process and the metal–insulator transition (MIT) property of it. The abrupt and hysteretic MIT was observed for the epitaxial films (thickness: t≥6nm), and the epitaxial film (t≤4nm) showed semiconductor behavior. When an amorphous VOx layer was prepared on the ultrathin epitaxial phase (t≤4nm) by the ELAMOD, a non-hysteretic MIT was successfully observed. The non-hysteretic MIT was found to be owing to roughened interface between the epitaxial phase and the amorphous phase, where there would be a number of structural defects.

Perfect Uniaxial Growth of Dion−Jacobson Perovskite RbLaNb2O7 Thin Films under Pulsed Photothermal Gradient Heating

A new straightforward process for fabricating perfect uniaxial oriented Dion−Jacobson perovskite RbLaNb2O7 thin films by excimer-laser-assisted metal organic deposition (ELAMOD) has been investigated. The oriented crystal growth occurred only as a result of excimer laser irradiation in air at 400 °C, after deposition of metal organic solution and preheating at 400 °C. The obtained RbLaNb2O7 thin film exhibited perfect (010)-oriented growth on a silica glass substrate. We discuss the uniaxial growth mechanism in terms of spatial heating by comparing the gradient temperature distribution near the film surface under photothermal heating in the ELAMOD process and the temperature distribution under macroscopic homogeneous heating in the conventional MOD process. Under gradient heating by excimer laser irradiation, the first nucleation preferentially occurred at the film surface with (010)-layered structural ordering to reduce the crystal surface energy. Then, the film was epitaxially grown downward from the fi...

Preparation of Y2O3:Eu thin films by excimer-laser-assisted metal organic deposition

Europium-doped yttrium oxide (Y2O3:Eu) thin films were successfully deposited on quartz and ITO/glass substrates by excimer-laser-assisted metal organic deposition (ELAMOD) at low temperatures. The effects of laser wavelength and thermal temperature on the films’ crystallinity and photoluminescence properties were investigated. Films irradiated by an ArF laser at 80 mJ/cm2 and 400–500°C were highly crystallized compared with those prepared by thermal MOD. In contrast, when the film was irradiated by a KrF laser at 500°C, no crystalline Y2O3:Eu was formed. The Y2O3:Eu film irradiated by the ArF laser at 80 mJ/cm2 and 500°C showed typical PL spectra of Eu3+ ions with cubic symmetry and a 5D0→7F2 transition at ∼612 nm. The PL intensity at 612 nm was much higher for the film prepared with ELAMOD than for that prepared by the thermal-assisted process, and the photoemission intensity of the film prepared with ELAMOD strongly depended on the substrate material.

Photoassisted chemical solution deposition method for fabricating uniformly epitaxial VO2 films

Epitaxial VO2 films were prepared on the TiO2 (001) substrates by the excimer-laser-assisted metal–organic deposition (ELAMOD). The quality of the epitaxial films obtained by irradiation with a KrF laser was found to be affected by the film structure obtained after preheating at 500 or 300°C. When the films containing crystal domains, which were obtained by preheating at 500°C, were irradiated with the laser at room temperature under a base pressure of 250 Pa, epitaxial and polycrystalline VO2 phases were simultaneously formed. In contrast, when the amorphous films containing organic components, which were obtained by preheating at 300°C, were irradiated with the laser at room temperature in air, a single phase of epitaxial VO2 was formed. By using thermal simulations, we determined that the formation of the epitaxial phase was affected both by the temperature distribution within the film during the laser irradiation and by the laser intensity at the interface between the substrate and the film. The latter factor is considered to play a role in the nucleation of crystallization, causing the epitaxial phase to form preferentially compared to the polycrystalline phase in the amorphous matrix of the films. These results indicate that the ELAMOD process is effective for the fabrication of epitaxial VO2 films at low temperature.

Influence of the laser wavelength on the epitaxial growth and electrical properties of La 0.8Sr 0.2MnO 3 films grown by excimer laser-assisted MOD

Epitaxial La 1− x Sr x MnO 3 (LSMO) films were prepared by excimer laser-assisted metal organic deposition (ELAMOD) at a low temperature using ArF, KrF, and XeCl excimer lasers. Cross-section transmission electron microscopy (XTEM) observations confirmed the epitaxial growth and homogeneity of the LSMO film on a SrTiO 3 (STO) substrate, which was prepared using ArF, KrF, and XeCl excimer lasers. It was found that uniform epitaxial films could be grown at 500 °C by laser irradiation. When an XeCl laser was used, an epitaxial film was formed on the STO substrate at a fluence range from 80 to 140 mJ/cm 2 of the laser fluence for the epitaxial growth of LSMO film on STO substrate was changed. When the LaAlO 3 (LAO) substrate was used, an epitaxial film was only obtained by ArF laser irradiation, and no epitaxial film was obtained using the KrF and XeCl lasers. When the back of the amorphous LSMO film on an LAO substrate was irradiated using a KrF laser, no epitaxial film formed. Based on the effect of the wavelength and substrate material on the epitaxial growth, formation of the epitaxial film would be found to be photo thermal reaction and photochemical reaction. The maximum temperature coefficient of resistance (TCR) of the epitaxial La 0.8Sr 0.2MnO 3 film on an STO substrate grown using an XeCl laser is 4.0%/K at 275 K. XeCl lasers that deliver stabilized pulse energies can be used to prepare LSMO films with good a TCR.

Epitaxial Growth Mechanism for Perovskite Oxide Thin Films under Pulsed Laser Irradiation in Chemical Solution Deposition Process

We have studied the epitaxial growth of perovskite manganite LaMnO3 (LMO) on SrTiO3(100) and LaAlO3(100) substrates by means of chemical solution deposition assisted by pulsed UV laser irradiation, termed excimer laser-assisted metal organic deposition (ELAMOD). Cross-sectional transmission electron microscopy observations revealed that the LMO was crystallized from a coated amorphous LMO matrix by the pulsed laser irradiation, and was preferentially grown from the substrate surface. In this process, the optical absorbance of the substrate for the irradiated laser plays an essential role for starting the epitaxial growth. This indicates a photochemical effect due to the UV laser irradiation; the photochemically activated growth interface strongly enhanced chemical bond formation, leading to epitaxial growth of LMO. The film temperature under the excimer laser irradiation was estimated using theoretical simulations with a one-dimensional heat equation, and it was found to increase to about 1000−1800 °C for...

Crystal growth of phosphor perovskite titanate thin films under excimer laser irradiation

Ca0.997Pr0.002TiO3 (CPTO) thin films that show strong red luminescence were successfully prepared by means of an excimer laser assisted metal organic deposition (ELAMOD) process with a KrF laser at a fluence of 100 mJ/cm2, a pulse duration of 26 ns, and a repetition rate of 20 Hz at 100°C in air. The CPTO films grew on the silica, borosilicate, and indium-tin-oxide (ITO) glasses. The crystallinity of the CPTO films depended on the substrates; the films were well grown on the borosilicate and ITO glasses compared to the silica glass. To elucidate the key factors for the crystallization of the CPTO films in this process, we carried out numerical simulations for the temperature variation at the laser irradiation, using a heat diffusion equation, and compared the experimental data with thermal simulations. According to the results, we have shown that a large optical absorbance of the film and a small thermal conductivity of the substrate provide effective annealing time and temperature for the crystallization of the CPTO films, and polycrystalline intermediate layer which has a large optical absorption such as the ITO also plays a key role for the nucleation of the CPTO crystals in the ELAMOD process.

New route for low-temperature fabrication of Sr1−xPrxTiO3:Al3+ polycrystalline thin film phosphors

The preparation of Al3+-added perovskite titanate Sr1−xPrxTiO3:Al3+ (SPTO:Al) thin films that show strong red emission by an excimer laser assisted metal-organic-deposition (ELAMOD) process using XeCl and KrF lasers at temperatures below 400°C in air was investigated, and SPTO:Al polycrystalline thin films were successfully grown by KrF laser irradiation with a fluence of 100mJ/cm2 at 250°C. The fabricated polycrystalline film has good crystallinity and clearly shows red emission. The PL emission peaks were observed at 493, 533 and 612nm, which are assigned to the transitions of 3P0→3H4, 3P0→3H5 and 1D2→3H4 of Pr3+, respectively. The emission at 493nm, corresponding to 3P0→3H4 transition, of the film prepared by ELAMOD is relatively strong compared to the film prepared by thermal process. This could be due to the local lattice distortion around Pr3+ generated by the laser irradiation.

Epitaxial A-Site Ordered Perovskite Manganite SmBaMn2O6 Film on SrTiO3(001): Fabrication, Structure, and Physical Property

An A-site ordered perovskite manganite SmBaMn2O6-δ film was fabricated by means of an excimer laser-assisted metal−organic deposition (ELAMOD) and epitaxially grown on a SrTiO3(001) substrate. The ...

Preparation of epitaxial La 0.7Ba 0.3MnO 3 thin films on SrTiO 3 substrates by excimer laser-assisted metal organic deposition

A KrF excimer laser irradiation was successfully used at 773 K to crystallize and epitaxially grow La 0.7Ba 0.3MnO 3 (LBMO) thin films on SrTiO 3 substrates. The starting amorphous LBMO films were prepared by metal–organic deposition at 773 K. The effects of the irradiation time, the laser fluence and the film thickness on the electrical properties and the microstructures of the films were investigated. Ten pulses of the KrF laser at a fluence of 80 mJ/cm 2 were found to be sufficient to crystallize the 25 nm thick LBMO film. Increasing the irradiation time was found to be useful for the densification of the films and efficient to improve their oxidation states. High qualities of LBM/STO interfaces were obtained by the excimer-laser irradiation in comparison with those films obtained by thermal annealing process. The temperature dependence of resistance R( T) of the LBMO thin films were investigated as function of the preparation conditions.

Electrical properties of the epitaxial La 1− x− ySr xMnO 3 films grown by excimer laser-assisted metal organic deposition

An epitaxial La 1− x− y Sr x MnO 3 film was prepared by excimer laser-assisted metal organic deposition (ELAMOD) at 500 °C. To improve the temperature dependence of the resistance (TCR) of the film around 298 K, we investigated the effects of oxygen annealing, metal composition and orientation on the temperature of peak resistance ( T p), temperature of maximum TCR ( T m) and temperature coefficient of resistance (TCR) of the film. In the case of annealing the as-deposited film in oxygen for 24 h, the TCR of the film decreased from 4.0 to 3.1%, whereas the T m shifted to 280 K. When the oxygen annealed film was irradiated by a KrF laser under the same conditions, TCR of the film increased 4.0% at 272 K. When preparing the epitaxial La 0.7Sr 0.3MnO 3 ( x = 0.3) film on an STO substrate by ELAMOD, the T m of the film shifted to 298 K. However, the TCR of the film was 2.1%. On the other hand, the epitaxial La 0.7Sr 0.2MnO 3 film on the STO substrate by ELAMOD showed a maximum TCR of 4.3% at 298 K.