Laser-assisted Metal Organic Deposition Research Articles

Resonant and nonresonant vibrational excitation of ammonia molecules in the growth of gallium nitride using laser-assisted metal organic chemical vapour deposition

The influence of exciting ammonia (NH3) molecular vibration in the growth of gallium nitride (GaN) was investigated by using an infrared laser-assisted metal organic chemical vapor deposition method. A wavelength tunable CO2 laser was used to selectively excite the individual vibrational modes. Resonantly exciting the NH-wagging mode (v2) of NH3 molecules at 9.219 μm led to a GaN growth rate of 84 μm/h, which is much higher than the reported results. The difference between the resonantly excited and conventional thermally populated vibrational states was studied via resonant and nonresonant vibrational excitations of NH3 molecules. Resonant excitation of various vibrational modes was achieved at 9.219, 10.35, and 10.719 μm, respectively. Nonresonant excitation was conducted at 9.201 and 10.591 μm, similar to conventional thermal heating. Compared to nonresonant excitation, resonant excitation noticeably promotes the GaN growth rate and crystalline quality. The full width at half maximum value of the XRD rocking curves of the GaN (0002) and GaN (10–12) diffraction peaks decreased at resonant depositions and reached its minimum value of 45 and 53 arcmin, respectively, at the laser wavelength of 9.219 μm. According to the optical emission spectroscopic studies, resonantly exciting the NH3 v2 mode leads to NH3 decomposition at room temperature, reduces the formation of the TMGa:NH3 adduct, promotes the supply of active species in GaN formation, and, therefore, results in the increased GaN growth rate.

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.

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.

Pulsed Laser Assisted Polycrystalline Growth of Oxide Thin Films for Efficient Processing

ABSTRACTWe have investigated the polycrystalline growth by means of an excimer laser assisted metal organic deposition process and the strategy for the efficient growth. It was revealed that the pulsed photo thermal heating properties must be controlled by changing the laser fluence according to the substrate properties, such as thermal diffusivity. The threshold of the teff value for initial crystal nucleation is approximately 70 ns for oxide thin films. For the fabrication of good quality films with high crystallinity and without a laser ablation of the film surface, it is necessary that the irradiated laser fluence is adjusted to the conditions of teff (efficient annealing time) > 70 ns and Tmax (maximum temperature) < Tm (melting point). Obtained oxide films by using the pulsed UV laser has large crystallite size, and it well functioned to enhance physical properties of films. For further efficient growth for polycrystalline growth of the oxide films, the starting solution containing nanoparticles is very useful: it is named as photo-reaction of nanoparticles 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

Low temperature uniaxial growth of conducting LaNiO3 thin films on glass substrates with RbLaNb2O7 seed layer

Conducting LaNiO3 thin films have been fabricated on the borosilicate glass substrates with and without the uniaxial oriented RbLaNb2O7 seed layer by an excimer laser assisted metal organic deposition process with a KrF laser irradiation at 400°C in air. The LaNiO3 thin film prepared on the seed layer had a very high Lotgering factor at F(100)=0.971, indicating highly (100)-oriented growth. The obtained LaNiO3 thin films with and without the seed layer showed low resistivity values, 4.42 and 1.02 mΩ cm at room temperature, respectively. The ρ value of the (100)-oriented LaNiO3 film on the seed layer was comparably lowered to that of the films prepared at high process temperatures reported in the previous reports.

Facile on-demand oriented growth of perovskite oxide thin films: applications of Dion–Jacobson phase as seed layer

We investigated a new fabrication process for high-quality, uniaxial-oriented grown Dion–Jacobson perovskite (DJP) RbLaNb2O7 thin films by means of excimer laser assisted metal organic deposition. Oriented crystal growth occurred only by excimer laser irradiation in air at 400 °C after a deposition of metal–organic solution and preheating at 400 °C. The obtained RbLaNb2O7 thin film showed perfect (010)-oriented growth on borosilicate glass substrates, and the film surface had atomically flat terraces. We confirmed that the obtained DJP RbLaNb2O7 thin films functioned very well as a seed layer for the fabrication of various perovskite oxide thin films with high orientation quality. An oriented grown LaNiO3 thin film fabricated on the DJP seed layer and prepared at 400 °C exhibited low electrical resistivity at room temperature. Moreover, we demonstrated the utility of our methodology for on-demand fabrication by combining our method with an inkjet printing technique to pattern LaNiO3 thin films with a line shape, which also were successfully grown with uniaxial orientation on the DJP seed layer. A ferroelectric Na0.5K0.5NbO3 perovskite film was heteroepitaxially grown on the uniaxial-oriented grains of the LaNiO3/RbLaNb2O7 thin film, and this oriented film exhibited a higher dielectric constant than that of a film fabricated without the DJP seed layer. Thus, we demonstrated facile, oriented crystal growth enabled by the uniaxial-oriented DJP seed layer.

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.

Preparation of polycrystalline VO2 films on glass and TiO2/glass substrates by means of excimer laser assisted metal organic deposition

An excimer laser assisted metal organic deposition process for the preparation of vanadium dioxide (VO2) films is described. When a precursor film grown on a silica glass substrate by preheating at 300°C was irradiated with a KrF laser at room temperature in air, the film was crystallized into polycrystalline VO2 phases. Generally, the preparation of VO2 films requires strict atmosphere control, but in this process, the polycrystalline VO2 films were successfully prepared without it. Moreover, it was revealed that crystallization into the VO2 phases was promoted by a TiO2 buffer layer placed on the glass substrate. This means that the photochemical reaction induced by the TiO2 absorbing the laser participates in the crystallization. The electrical resistivity of the film grown on the TiO2/glass substrate was lowered compared to that of the film grown on the glass substrate due to improvement of the film uniformity. The crystallinity of the obtained film was dependent on the irradiation time. With the improved crystallinity of the film, the resistivity drop through the metal-insulator transition became large.

Amorphous film thickness dependence for epitaxy of perovskite oxide films under excimer laser irradiation

We have studied the epitaxial growth of perovskite manganite LaMnO 3 (LMO) on SrTiO 3(1 0 0) in the excimer laser assisted metal organic deposition process. The LMO was preferentially grown from the substrate surface by the KrF laser irradiation. The study of amorphous LMO film thickness dependence on epitaxial growth under the excimer laser irradiation revealed that the photo-thermal heating effect strongly depended on the amorphous film thickness due to a low thermal conductivity of amorphous LMO: the ion-migration for chemical bond-forming at the reaction interface would be strongly enhanced in the amorphous LMO film with the large film thickness about 210 nm. On the other hand, the photo-chemical effect occurred efficiently for the amorphous film thickness in the range of 35–210 nm. These results indicate that the epitaxial growing rate was dominated by the photo-thermal heating after the photo-chemical activation at the growth interface.

Direct conversion of a metal organic compound to epitaxial Sb-doped SnO 2 film on a (0 0 1) TiO 2 substrate using a KrF laser, and its resulting electrical properties

Epitaxial Sb-doped SnO 2 (0 0 1) thin film on a TiO 2 (0 0 1) substrate was successfully prepared by laser-assisted metal organic deposition at room temperature. The effects of the precursor thin film and laser fluence on the resistivity, carrier concentration, and mobility of the Sb-doped SnO 2 film were investigated. The resistivity of the Sb-doped SnO 2 film prepared by direct irradiation to metal organic film is one order of magnitude lower than that of film prepared by irradiation to amorphous Sb-doped SnO 2 film. From an analysis of Hall measurements, the difference between the resistivity of the Sb-doped SnO 2 film prepared using the metal organic precursor film and that of amorphous precursor film appears to be caused by the mobility. Direct conversion of the metal organic compound by excimer laser irradiation was found to be effective for preparing epitaxial Sb-doped SnO 2 film with low resistivity.

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...

Epitaxial Growth of LSMO Film Prepared by Excimer Laser-Assisted Metal Organic Deposition (ELAMOD)

The La1-xAxMnO3 (A=Sr, Ca, Ba) film was prepared by excimaer laser-assisted metal organic deposition (ELAMOD). To understand the important controlling factor of the epitaxial growth using ELAMOD, the effects of the substrate temperature, substrate type, wavelength, and film thickness on the epitaxial growth were investigated. When the film thickness was 200nm with heating at 250°C, a polycrystalline LSMO film was formed on the LAO substrate. On the other hand, at 80nm, an epitaxial LSMO film was formed on the LAO substrate at 500°C. The epitaxial growth of the LSMO film was found to be dependent on the substrate materials and the laser wavelength. The formation of the epitaxial and polycrystalline LSMO films was discussed

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.

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.

Structural and physical property of A-site ordered perovskite manganite LaBaMn 2O 6 thin film on SrTiO 3(0 0 1)

An A-site ordered perovskite manganite LaBaMn 2O 6− δ ( δ ≅ 0.5) film was fabricated by means of an excimer laser assisted metal organic deposition (ELAMOD) method and epitaxially grown on a SrTiO 3(0 0 1) substrate. The LaBaMn 2O 6− δ film was crystallized in [0 1 0]- and [0 0 1]-oriented domains that were confirmed by X-ray diffraction. The A-site ordered structure formed at 500 °C under KrF laser irradiation at a laser fluence of 140 mJ/cm 2 for 60 min in an Ar flow. A LaBaMn 2O 6 film was obtained by oxygen annealing of the as-prepared LaBaMn 2O 6− δ film at 500 °C for 3 h. The magnetization for the LaBaMn 2O 6− δ film showed a ferromagnetic transition at 330 K, and the electrical resistivity exhibited a semiconductor-metal transition at 330 K. The magnetoresistance (MR) effect was observed below 370 K, and the MR efficiency was up to 135% at 300 K under 9 T. The ELAMOD process is expected to serve as a new key technique for the fabrication of A-site ordered perovskite manganite thin films.

Substrate effect on excimer laser assisted crystal growth in phosphor Ca 0.997Pr 0.002TiO 3 polycrystalline thin films

Ca 0.997Pr 0.002TiO 3 thin films that show strong red luminescence were successfully prepared by means of an excimer laser assisted metal organic deposition process with a KrF laser at a fluence of 100 mJ/cm 2 at 100 °C. The CPTO films grew on the silica, borosilicate, and indium-tin-oxide coated glasses. The crystallinity of the Ca 0.997Pr 0.002TiO 3 films depended on the substrates; the borosilicate and indium-tin-oxide coated glasses with a large optical absorption of a KrF laser ( λ = 248 nm) were effective for the crystallization for the Ca 0.997Pr 0.002TiO 3. In addition, a high thermal conductivity of the indium-tin-oxide coated glass substrate could also improve the crystallinity due to an enhancement of thermal propagation to the film. Oxygen annealing at 500 °C for 6 h successfully eliminated the oxygen vacancy produced by the laser irradiation, and also remarkably improved the PL emission intensity. Thus, we have shown that substrate properties such as an optical absorbance and a thermal conductivity were quite important factors for the crystal growth and the PL emission for the Ca 0.997Pr 0.002TiO 3 in the excimer laser assisted metal organic deposition process.

Transmission electron microscopy (TEM) studies of the epitaxial and polycrystalline Tin oxide films prepared by the excimer laser-assisted metal organic deposition

Epitaxial and polycrystalline SnO2 thin films were prepared by the excimer laser annealing of amorphous SnO2 films on TiO2 (001) and MgO (001) substrates. The amorphous SnO2 film was prepared by a metal organic deposition (MOD) using di-n-butylbis (2, 4-pentanedionate) tin at 300°C. The crystallinity and orientation of the product films were investigated by the XRDΘ—2Θ, pole figure and transmission electron microscopy (TEM) analyses. At 200 mJ/cm2, the (002) oriented SnO2 films were obtained by KrF laser irradiation. Using the XRD φ scanning measurement and TEM, it was found that the oriented SnO2 films were epitaxially grown on the (001) TiO2 substrate. On the other hand, the polycrystalline SnO2 film was obtained on the MgO (001) substrate. It was found that the grain size of the SnO2 film on the MgO substrate near the surface is larger than that of the near substrate based on crosssectional bright field TEM micrographs.