Reactive Pulsed Laser Deposition Research Articles

Synthesis of Cadmium Oxide/Si Heterostructure for Two-Band Sensor Application

Cadmium oxide on Si heterostructure device has been constructed using (111) oriented silicon substrate by reactive PLD technique. The deposition of CdO film was carried out by irradiating high-purity Cd target using Nd:YAG laser in the presence of reactive oxygen gas. The deposited tin films were characterized by the X-ray diffraction, scanning electron microscopy and AFM. The electrical properties of deposited films were investigated reaching to the optimum pressure of oxygen at which the device has been prepared. The films were polycrystalline in nature having high orientation along (111) (200) and (220) planes. The films are formed to give the lower value of the resistivity which was found to be 7.56 × 10−3 Ω cm at the ambient of oxygen pressure around 350 Torr and without using post-deposition heat treatment. The electrical properties such as current–voltage in dark and illumination and capacitance–voltage measurement were carried out and found to be directly related to the substrate temperature. Also, the detector parameters have been characterized by measuring responsivity and detectivity which are found to be 0.38 A/W and 3.9 × 1012 cm Hz1/2 W−1, respectively.

Investigation of electrochemical properties of bio-inspired SiOx/PI multilayered thin film anode for lithium ion batteries

The organic-inorganic multilayer thin film composed of SiOx (nonstoichiometric silicon suboxides) and PI (polyimide) has been synthesized by a hybrid sputtering system combining reactive RF sputtering and pulsed laser deposition. SiOx/PI thin films were deposited on a copper foil to investigate its electrochemical properties. The chemical composition of as-deposited SiOx/PI coatings was measured by a FE-EPMA. The overall multilayered structure was observed by a Scanning Electron Microscopy. The SiOx/PI multilayer thin film anode with proper architecture control exhibits higher columbic efficiency during 1st charge/discharge cycle and better capacity retention as compared to pure SiOx thin film anode. The fracture toughness of SiOx/PI multilayer thin film anode is measured via nanoindentation and be compared to the pure SiOx thin film anode. The results show that the multilayer structure reveals a higher fracture toughness, which leads to a better structure stability during the charge/discharge cycling.

Characterization of N, F Co-Doped Mixed-Anion TiO2 Thin Films Prepared By Reactive Pulsed Laser Deposition for Visible-Light Responsive Photocatalyst

Introduction The study of water splitting by photocatalyst as the method of directly producing hydrogen from water has been reported in 1972, well-known as “Honda-Fuzishima effect”. Conventional TiO2 material can produce hydrogen under only ultraviolet light and the its production rate is still low. In order to use TiO2 under visible light, the anion doping is one of the effective solution. In this study, photocatalytic N, F-doped TiO2 thin film was synthesized by the responsible pulsed laser deposition(PLD) technique. Nitridation and fluoridation of TiO2 were simultaneously conducted with PLD under O2/N2/NF3 gas. Experimental TiO2 thin film was prepared by pulsed laser deposition (PLD). A Nd:YAG laser operating at a wavelength of 532 nm was focused on a sintered TiO2 target. We used a chamber which can be evacuated to a base pressure of 5.0 x 10-4 Pa by means of a turbo-molecular pump. When depositing TiO2 thin film, the total pressure of the mixed gas was fixed to 5 Pa. FTO (Fluorine doped tin oxide) was used as the glass substrate for film deposition. The substrate temperature was changed from room temperature to 400℃. The target (φ10) was produced by sintering the Rutile TiO2 powder at 1000℃ for 12h in air. Structural analysis of TiO2 is carried out by XRD (X-ray diffiraction) and XAFS (X-ray Absorption Spectroscopy). Especially, the product identification was observed by XRD with parallel beam method at SPring-8 BL02B2. An incident angle of X-ray is 0.1o and wavelength of X-ray is 0.7Å. Measurement of the absorption edge of Ti K was carried out by XAFS with electron yield method. In addition, for defining of the flatband level and bandgap carried out by UV-vis and AC impedance measurement. Photoelectrochemical measurements were conducted in an aqueous Na2SO4 solution (0.1 M, pH=9) using a potentiostat (Hokuto Denko HSV-110) connected to the photocatalyst-deposited FTO glass as a working electrode an Ag/AgCl reference electrode (in saturated KCl aqueous solution), and Pt wire as a counter electrode. The solution was purged with Ar gas for 30 min. To measure photocurrent responses, intermittent visible light (420 < λ < 800 nm) was applied to the working electrode with a Xe lamp (300 W, output current: 20 A). Result & Discussion Fig. 1 shows that XRD results under various gas atmosphere. In the case of under the O2 atmosphere, Anatase/Rutile TiO2 composition was observed. Under the N2 atmosphere, TiN was observed and under the NF3 atmosphere, Anatase TiO2 was observed. Under the N2 and N2/NF3 atmosphere, FTO substrate was decomposed. Under the O2/N2/NF3 atmosphere, the decomposition of the substrate was suppressed while the compounds derived from Ti couldn’t be observed. These results indicated that O2 gas was necessary for depositing TiO2 by suppressing of substrate as well as supplementation of the oxygen defects. Fig. 2 shows that the visible light response as a function of the photocurrent and voltage. By switching Xe lamp on/off per 3 second, the increase and decrease of current density was observed over 0.4 µA cm-2. The photocurrent response under visible light was observed for the atmosphere of O2/N2/NF3 and O2/N2 while that of O2/NF3 was not. In addition, the photocurrent was larger for the materials prepared under O2/N2/NF3 than O2/N2. UV-vis diffuse reflectance spectrum indicated that N, F-doped TiO2 showed a wide absorption band in visible region in contrast to a narrow one of N-doped TiO2. This extended absorption band of N, F-doped TiO2 in the visible region allowed the materials to improve the efficiency of the catalytic reactions such as water oxidation. Conclusion It is necessary that O2 gas to suppress substrate decomposition and compensate oxygen defect. PLD performed under O2/N2/NF3 mixed gas could successfully incorporated N3- and F- into TiO2 matrix. The visible light response of co-doping of N3- and F- was better than N3- single doping. It was subjected to the UV-vis measurement, the N3-, F- co-doped TiO2 thin film has wide absorption band of a visible light, which was considered to have led to a visible light absorption. Reference 1) A. Nakada et al., J.Mater. Chem. A, 2017, 5, 11710-11719. 2) K. Maeda et al., J. Phys. Chem. C, 2007, 111 (49), 18264–18270. Figure 1

Microstructure and electromagnetic performance of the FeCoAlON films tuned by N2 pressure during reactive pulsed laser deposition

FeCoAlON films were fabricated by reactive pulsed laser deposition. The microstructure and electromagnetic properties have been investigated as a function of N2 pressure, which was varied from 0 to 5 mtorr. All the FeCoAlON films contains ultrafine FeCo nanoparticles isolated by nonmagnetic insulating layers. Those insulating layers ensure high electrical resistivity of the films and will be transformed from Al2O3 into AlN with increasing N2 pressure. The oxidation of Fe and Co can be effectively suppressed by introducing N2. The Fe tends to form amorphous iron nitrides at higher N2 pressures, leading to different magnetic response. Optimized electromagnetic properties can be achieved under 3 mtorr of N2, showing great potential in noise suppression application at high frequencies. Further increased N2 pressure to 5 mtorr leads to shrunken FeCo nanoparticles and thickened insulating layers due to the formation of nonmagnetic iron nitrides, giving rise to superparamagnetic response of the FeCoAlON thin film. Consequently, appropriate N2 pressure plays an essential role in inducing favorable microstructure and phase composition for enhanced electromagnetic performance.

Structure, morphology and electrocatalytic properties of WOx thin films prepared by reactive pulsed laser deposition

Nanostructured WOx<3 films were prepared by pulsed laser deposition in air from W target. The pressure of air was varied in a range of 10 – 100 Pa and the temperature of a glassy carbon substrate during the film deposition was 22 or 500°C. For the films deposited at 22°C, thermal post-treatment in air of laboratory humidity at 500°C was applied. The increase of air pressure during PLD at 22°C caused both a decrease in packing density of ball-like amorphous nanoclusters of WOx and decline of their size. Post-treatment in air at 500 °C has initiated crystallization of the nanoclusters but characteristic morphology of the films was preserved in a whole. The PLD of WOx on a heated substrate resulted in the formation of nanoneedles and nanosheets. Fairly good catalytic properties in hydrogen evolution reaction (HER) and in electrolytic Pt deposition were revealed for the WOx films that consisted of loosely packed ball-like nanocrystals possessing a size of ∼20 nm. The catalytic activity of the films consisted of nanoneedles and nanosheets was not good enough. Adjustable electrolytic deposition of Pt on the nanostructured WOx support film allowed to prepare effective hybrid HER catalyst containing only ∼7 μg/cm2 of Pt.

Regulated growth of quasi-amorphous MoSx thin-film hydrogen evolution catalysts by pulsed laser deposition of Mo in reactive H2S gas

We report the preparation of MoSx thin films with reactive pulsed laser deposition (RPLD), an original technique that allows us to investigate the correlation between key MoSx properties, such as the composition, morphology, and local structure, and the catalytic performance in the hydrogen evolution reaction (HER). The use of two geometries of normal angle (NA) and sliding angle (SA) for the deposition by laser plume from a Mo target on a glassy carbon substrate made it possible to regulate the characteristics of MoSx films (1.5≤x≤10) by varying the H2S pressure and thus to circumvent the limitations inherent in traditional pulsed laser deposition. Amorphous MoSx<2, quasi-crystalline layered MoS2, disordered as well as rather perfect Mo3–S clusters, and sulfur clusters were formed. The films containing locally ordered clusters with a higher content of bridging S22− and apical S2− ligands could be prepared by SA RPLD. This film was demonstrated to be the most efficient electrocatalyst, possessing a lower overpotential of −130mV at a current density of −1mA/cm2, a Tafel slope of 44mV/dec, and a quite high exchange current density of ~1.2μA/cm2. The preparation of a low-resistance MoSx underlayer by NA RPLD made it possible to increase the catalytic performance of a bilayer coating by 10%.

Growth of epitaxial TiN (111) thin films with low resistivity on Si (111) by crossed-beam pulsed laser deposition

Titanium nitride (TiN) thin films were grown epitaxially on Si (111) substrates by reactive pulsed laser deposition. Substrate temperatures ranged from 550 to 950 °C while plume kinetic energies ranged from 46 to 154 eV. Quality of the grown films depended strongly on kinetic energy of the films than the growth temperatures. High quality film was grown at 750 °C with a laser plume kinetic energy of ~ 92 eV. Full width at half maximum for a ω-scan around the TiN (111) peak and a φ-scan through the TiN (002) peak were 0.3° and 0.43 °, respectively. The resistivity of the films was increased with increased temperatures and a room temperature resistivity of 3.8 μΩ-cm was obtained.

Materials Study of NbN and TaxN Thin Films for SNS Josephson Junctions

Properties of NbN and TaxN thin films grown at ambient temperatures on SiO2/Si substrates by reactive-pulsed laser deposition and reactive magnetron sputtering (MS) as a function of N2 gas flow were investigated. Both techniques produced films with smooth surfaces, where the surface roughness did not depend on the N2 gas flow during growth. High crystalline quality, (111) oriented NbN films with Tc up to 11 K were produced by both techniques for N contents near 50%. The low temperature transport properties of the TaxN films depended upon both the N2 partial pressure used during growth and the film thickness. The root mean square surface roughness of TaxN films grown by MS increased as the film thickness decreased down to 10 nm.

Thermal stability of oxidized noble metal Schottky contacts to ZnO

Thermally stable oxidized palladium (PdOx, x=1.4) and oxidized iridium (IrOx, x=1.9) Schottky contacts (SCs) that showed strong rectification at 180°C were fabricated on the Zn-polar (0001) face of hydrothermally-grown single crystal ZnO wafers, using reactive rf sputtering and reactive eclipse pulsed laser deposition, respectively. These PdOx and IrOx SCs were highly rectifying with effective barrier heights of 1.25eV and 1.02eV, respectively, more than 12 orders of magnitude of room-temperature current rectification (at biases of ±2.0V), and were almost ‘ideal’ with ideality factors of 1.03 and 1.02, respectively, that were very close to the image-force-controlled limit for laterally homogeneous contacts. The strong rectifying performance of these SCs was maintained at 180°C, with current rectification in excess of 7 and 6 orders of magnitude for the PdOx and IrOx SCs, respectively, indicating their suitability for high temperature applications. Current-voltage characteristics over the temperature range 20–180°C were used to extract Richardson constant values of 39±15 Acm−2K−2 and 9±1 Acm−2K−2 for the PdOx and IrOx SCs, respectively, close to the theoretical value of 32 Acm−2K−2.

Characterization of thin MnSi and MnGe layers prepared by reactive UV pulsed laser deposition

Reactive pulsed laser deposition is a technique suitable for producing homogenous thin layers of silicon or germanium with high concentration of embedded manganese atoms. Linear calibration of EDS (Energy Dispersive X-ray Spectroscopy) was utilized for an elemental analysis of thin layers. MnSi and MnGe (manganese-silicon and manganese-germanium) layers containing non-oxidized Mn were obtained for Mn molar concentration in the range from 15 to 50%. Electron diffraction showed an amorphous character of MnSi layers. MnGe layers contained two different types of nanoparticles incorporated inside an amorphous matrix. The layers were semiconducting with resistivities from 10−3 to 10−5Ωm.

Laser synthesis of 2D heterostructures of transitional metal oxides for photo sensors with high sensitivity

Photons of a KrF laser (248 nm) were used for the synthesis of Cr3−XO3−Y/Fe2O3−X two dimensional (2D) multilayer heterostructures by reactive pulsed laser deposition. Each nanometric multilayer heterostructure with a definite number of layers of iron and chromium oxides was deposited in 2D form on ⟨100⟩ Si substrate at its temperature 293 or 800 K resulted in changing of 2D multilayer heterostructure thickness in the range of 25–85 nm. X-ray diffractometer analysis confirmed polycrystalline structure of these deposits. Element analysis was carried out by an energy dispersive x-ray spectroscopy. All synthesized 2D multilayer heterostructures demonstrated semiconductor temperature trend with variable equivalent energy band gap (Eg) in the range of 0.36–0.87 eV. The more substrate temperature was the more Eg value, and the more 2D multilayer heterostructure photosensitivity. Optimum experimental parameters were found out to obtain the highest photosensitivity of 2D multilayer heterostructure. Highest obtained photosensitivity was high as 420 VC/W at white light power density ∼6 × 10−3 W/cm2. VC is “chemical” photo electromotive force induced in the deposited 2D multilayer heterostructure while it irradiating with a white light, W is white light power. High photosensitivity nature of the 2D multilayer heterostructure synthesized on a heated substrate was explained. Therefore, such 2D multilayer heterostructures of iron and chromium oxides exhibiting high photosensitivity are exceptionally a strong candidate for effective photo sensors of white light.

Effects of hydrogen pressure on hydrogenated amorphous silicon thin films prepared by low‐temperature reactive pulsed laser deposition

We deposit intrinsic hydrogenated amorphous silicon (a‐Si:H) thin films by reactive pulsed laser deposition, for various hydrogen pressures in the 0–20 Pa range, at a low deposition temperature of 120 °C, and investigate the hydrogen incorporation, structural, optical, and electrical properties of the films, as a function of the ambient hydrogen pressure. The film thickness decreases linearly as the hydrogen pressure increases. The hydrogen content of the films is determined by infrared spectroscopy and the optical bandgap from UV‐Vis‐NIR transmittance and reflectance measurements. Electric measurements yield the dark conductivity of the films. The hydrogen concentration of the films lies in the 1021–1022cm–3 range and increases with the hydrogen pressure until the latter reaches 15 Pa, beyond which the hydrogen concentration decreases. The optical bandgap and dark conductivity follow the hydrogen concentration variation of the films. The dark conductivity lies in the 10–9–10–10S/cm range. An unusually wide optical bandgap of 2.2–2.6 eV is observed.

Comparative studies of monoclinic and orthorhombic WO3 films used for hydrogen sensor fabrication on SiC crystal

Amorphous WOx films were prepared on the SiC crystal by using two different methods, namely, reactive pulsed laser deposition (RPLD) and reactive deposition by ion sputtering (RDIS). After deposition, the WOx films were annealed in an air. The RISD film possessed a m-WO3 structure and consisted of closely packed microcrystals. Localized swelling of the films and micro-hills growth did not destroy dense crystal packing. RPLD film had layered β-WO3 structure with relatively smooth surface. Smoothness of the films were destroyed by localized swelling and the micro-openings formation was observed. Comparative study of m-WO3/SiC, Pt/m-WO3/SiC, and P-WO3/SiC samples shows that structural characteristics of the WO3 films strongly influence on the voltage/current response as well as on the rate of current growth during H2 detection at elevated temperatures.

Large third-order optical nonlinearities in iron oxide thin films synthesized by reactive pulsed laser deposition

We report on a study of the third-order nonlinear optical properties of Fe2O3 thin films, grown by the method of laser deposition on silica (SiO2) substrates. The films were synthesized on substrates at different temperatures (293 K and 800 K) and under different oxygen pressures (0.1 Pa, 0.5 Pa, 1.0 Pa). The resulting films were amorphous, if grown on cold substrates (293 K), or polycrystalline otherwise. The third-order optical susceptibility χ(3) of the films was determined by the Z-scan method at the wavelengths of 1064 nm and 532 nm and the laser pulse width of 20 ns. Remarkably high χ(3) values on the order of 10−4 esu at 1064 nm are obtained. The results show that Fe2O3 thin films are promising nonlinear materials for contemporary optoelectronics.

Tungsten-oxide thin films for a high-temperature semiconductor hydrogen detector based on a 6H-SiC crystal

We demonstrate the possibility of fabricating high-efficiency semiconductor hydrogen detectors based on tangsten-oxide thin films deposited onto silicon-carbide crystals by reactive pulsed-laser deposition. The obtained WO3/SiC structures ensure a noticeable voltage shift ΔU on the reverse branch of the I−V characteristics without commonly used catalyst layers of platinum-group metals. The ΔU value reached 2.1 V at a detected hydrogen concentration of 0.2% in air at 350°C. The response times to hydrogen inlet and recovery of the WO3/SiC structure after hydrogen outlet are found to be much shorter than those for the Pt/WO3/SiC structure. The high performances of the fabricated WO3/SiC sensor are due to the layered structure of the orthorhombic phase of tungsten oxide, which consists of loosely packed microcrystalline plates containing nanocrystals smaller than 100 nm.

Optical and structural properties of Cu2ZnSnS4 thin films obtained by pulsed laser deposition in a H2S atmosphere with subsequent annealing in a N2 atmosphere

The structural and optical properties of Cu2ZnSnS4 thin-film layers formed by reactive pulsed laser deposition in a H2S atmosphere at room temperature with the use of a Cu metal target and a Zn–Sn alloy target are studied in relation to the parameters of annealing in a N2 atmosphere.

Effect of annealing on structural and optical properties of Cu2ZnSnS4 thin films grown by pulsed laser deposition

In this work, we compare the effect of different types of thermal annealing on the morphological, structural and optical properties of Cu2ZnSnS4 (CZTS) thin films grown by reactive Pulsed Laser Deposition in H2S flow. Rutherford backscattering spectrometry, atomic force microscopy, X-ray diffraction, Raman spectroscopy and optical spectrophotometry data reveal dramatic increase of the band gap and the crystallite size without the formation of secondary phases upon annealing in N2 at the optimized conditions.

Luminescent Si Nanocrystals Synthesized by Si Ion Implantation and Reactive Pulsed Laser Deposition: The Effects of RTA, Excimer-UV and E-Beam Irradiation

Luminescent Si Nanocrystals Synthesized by Si Ion Implantation and Reactive Pulsed Laser Deposition: The Effects of RTA, Excimer-UV and E-Beam Irradiation

Hybrid nanostructured thin-films by PLD for enhanced field emission performance for radiation micro-nano dosimetry applications

We report the observation of hybrid nanostructured thin-films such as diamond-like carbon (DLC) signature on the ZnO epitaxial thin-films grown onto the device silicon/quartz substrate by reactive pulsed laser deposition (r-PLD) under the argon–oxygen (Ar|O2) ambient at 573 K. Undoped and Carbon (C) doped epitaxial ZnO thin-film layer formation is revealed by the accelerator based ion-beam analysis (IBA) technique of resonant Rutherford backscattering spectrometry (RRBS), glancing-incidence X-ray diffraction (GIXRD) pattern, micro-Raman spectroscopy (μ-RS) and field-emission (F-E) studies. The RRBS and GIXRD results show the deposition of epitaxial thin-films containing C into ZnO. The μ-RS technique is a standard nondestructive tool (NDT) for the characterization of crystalline, nano-crystalline, and amorphous carbons (a-C). As grown ZnO and C-doped ZnO thin-films μ-RS result reveal the doping effect of C-impurities that appear in the form of DLC evident from Raman peaks at 1357 and 1575 cm−1 along with a wurtzite structure peak at 438 cm−1 with E2(h) phonon of ZnO. The electron transport F-E result shows the hybrid thin-films has high conductivity than the un-doped film. Fabricated hybrid nanostructured thin-films materials could be very useful for the emerging applications of micro-nano dosimetry.

Reactive pulsed laser deposited N–C codoped TiO2 thin films

TiO2 is a large bandgap chemically stable oxide useful for several applications that involve photo-activated processes, including photocatalysis, photovoltaics, photoelectrolysis, etc. However, the large band gap renders this material not a very efficient absorber of the solar spectrum. Various schemes of cation and anion doping have been utilized that reduce this deficiency to a certain extent. In this paper we present the results of N–C codoping of TiO2 thin films deposited by a reactive pulsed laser deposition technique. These films were compared for their optical and structural properties with undoped, N doped and C doped TiO2 films prepared by the same technique. While all samples contained polycrystalline anatase phase, varying N2 and CH4 partial pressures resulted in change in TiO2 lattice parameters due to codoping. X-ray diffraction high-resolution scans show the evidence of C incorporation into TiO2 lattice by 2θ shift in (101) reflections due to large ionic radius of C. N doping was confirmed by XPS analyses. Direct relationship between oxygen vacancies and doping concentration was established by the deconvolution of XPS peaks. Considerable bandgap reduction occurred that was measured by using UV–vis diffuse reflectance spectroscopy. Results show that reactive pulsed laser deposition is indeed a useful method for the synthesis of codoped TiO2 thin films as bandgap reduction of ~1.00eV via N–C codoping was successfully achieved.