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Defect mediated transport in self-powered, broadband and ultrafast photoresponse of MoS <sub/>2</sub> /AlN/Si based photodetector
摘要： By combining unique properties of ultrathin 2D materials with conventional 3D semiconductors, devices with enhanced functionalities can be realized. Here we report a self-powered and ultrafast photodetector based on hybrid MoS2/AlN/Si heterostructure. The heterojunction is formed by depositing MoS2 thin film by pulsed laser deposition on AlN/Si(111) template. The vertical transport properties of the device under dark and light illumination conditions, exhibit an excellent photoresponse in a broad range of wavelengths (300–1100 nm) at 0 V. The maximum responsivity of this photodetector is found to be 9.93 A/W at wavelength of 900 nm. The device shows an ultrafast temporal response with response/recovery times of 12.5/14.9 μs. X-ray photoelectron spectroscopy and cross-sectional transmission electron microscopy reveal presence of native oxygen impurities in AlN, throughout the bulk of the film. These oxygen defects form a deep donor level in AlN and play a crucial role in the transport of the photogenerated carriers, resulting in enhanced device performance.
关键词： broadband and ultrafast photoresponse,deep defects,MoS2,AlN,pulsed laser deposition
更新于2025-09-23 15:19:57
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Pulsed Laser Deposition of Bismuth Vanadate Thin Filmsa??The Effect of Oxygen Pressure on the Morphology, Composition, and Photoelectrochemical Performance
摘要： Thin layers of bismuth vanadate were deposited using the pulsed laser deposition technique on commercially available FTO (fluorine-doped tin oxide) substrates. Films were sputtered from a sintered, monoclinic BiVO4 pellet, acting as the target, under various oxygen pressures (from 0.1 to 2 mbar), while the laser beam was perpendicular to the target surface and parallel to the FTO substrate. The oxygen pressure strongly affects the morphology and the composition of films observed as a Bi:V ratio gradient along the layer deposited on the substrate. Despite BiVO4, two other phases were detected using XRD (X-ray diffraction) and Raman spectroscopy—V2O5 and Bi4V2O11. The V-rich region of the samples deposited under low and intermediate oxygen pressures was covered by V2O5 longitudinal structures protruding from BiVO4 film. Higher oxygen pressure leads to the formation of Bi4V2O11@BiVO4 bulk heterojunction. The presented results suggest that the ablation of the target leads to the plasma formation, where Bi and V containing ions can be spatially separated due to the interactions with oxygen molecules. In order to study the phenomenon more thoroughly, laser-induced breakdown spectroscopy measurements were performed. Then, obtained electrodes were used as photoanodes for photoelectrochemical water splitting. The highest photocurrent was achieved for films deposited under 1 mbar O2 pressure and reached 1 mA cm?2 at about 0.8 V vs Ag/AgCl (3 M KCl). It was shown that V2O5 on the top of BiVO4 decreases its photoactivity, while the presence of a bulk Bi4V2O11@BiVO4 heterojunction is beneficial in water photooxidation.
关键词： photoelectrochemistry,pulsed laser deposition,bismuth vanadate
更新于2025-09-23 15:19:57
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Reactive Pulsed Laser Deposition of Clustered-Type MoSx (x ~ 2, 3, and 4) Films and Their Solid Lubricant Properties at Low Temperature
摘要： We studied the tribological properties of amorphous molybdenum sulfide (MoSx) thin-film coatings during sliding friction in an oxidizing environment at a low temperature (?100 °C). To obtain films with different sulfur contents (x ~ 2, 3, and 4), we used reactive pulsed laser deposition, where laser ablation of the Mo target was performed in H2S at various pressures. The lowest coefficient of friction (0.08) was observed during tribo-testing of the MoS3 coating. This coating had good ductility and low wear; the wear of a steel counterbody was minimal. The MoS2 coating had the best wear resistance, due to the tribo-film adhering well to the coating in the wear track. Tribo-modification of the MoS2 coating, however, caused a higher coefficient of friction (0.16) and the most intensive wear of the counterbody. The MoS4 coating had inferior tribological properties. This study explored the mechanisms of possible tribo-chemical changes and structural rearrangements in MoSx coatings upon contact with a counterbody when exposed to oxygen and water. The properties of the tribo-film and the efficiency of its transfer onto the coating and/or the counterbody largely depended on local atomic packing of the nanoclusters that formed the structure of the amorphous MoSx films.
关键词： wear,molybdenum sulfides,solid lubricants,nanoclusters,reactive pulsed laser deposition,low temperature,coefficient of friction
更新于2025-09-23 15:19:57
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Space charge limited conduction in pulsed laser deposited BaTiO3/LaNiO3 hetero-junctions
摘要： We report the charge transport mechanism in BaTiO3 (BTO) thin film deposited on LaNiO3 (LNO) buffer layer using pulsed laser deposition technique thus, forming the metal – insulator – metal junction (Au/BTO/LNO). The temperature dependent Current density- Voltage (J-V) characteristics were measured, analyzed and compared with the La0.67Ca0.33MnO3 (LCMO) buffered BTO film (Au/BTO/LCMO). Although the mechanism was found to be space charge limited conduction (SCLC) as in case of BTO/LCMO but the absence of Ohmic region in Log J-Log V plot indicates higher injection rate. Various parameters such as trap density, activation energy, and ratio of free to trapped carriers (h) were extracted out from the fitted J-V plot and subsequently their temperature dependence was studied and compared with BTO/LCMO. Higher current density, lower activation energy, lower trap density and higher ratio of free to trapped carriers (h) were observed in BTO/LNO in contrast to BTO/LCMO. Furthermore, the lower activation energy indicates the presence of shallow trap level.
关键词： Non-volatile memories,Barium titanate,Metal-Insulator-Metal junction,Space charge limited conduction,Pulsed laser deposition
更新于2025-09-23 15:19:57
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Boron-doped graphene synthesis by pulsed laser co-deposition of carbon and boron
摘要： Incorporating dopants, such as boron, in graphene, is crucial for many applications in electrochemistry, sensors, photovoltaics, and catalysis. Many routes have been investigated for the preparation of B-doped graphene (BG) films, including chemical processes. A different way to obtain boron-doped layers to better control the concentration of boron in the doped graphene film, is pulsed laser co-ablation of C and B solid sources followed by rapid thermal heating of the B-doped carbon film deposited on a metal catalyst. Amorphous a-C:B films, containing 2%at. boron, are synthetized by pulse laser deposition onto a nickel film catalyst. Rapid thermal annealing at 1100°C leads to the formation of boron-doped graphene films, characterized by Raman, XPS, FEG-SEM, HRTEM and AFM. The results confirm the production of 1-4 layer boron doped graphene films, with a similar 2 at.% boron concentration to that of the a-C:B used as the graphene solid precursor. Boron doping does not modify the nano-architecture of graphene, but increases the concentration of defects in the films. Our results pave a new way for boron doped graphene synthesis using laser processing in a controlled and reproducible way, in particular to achieve designed electrical and chemical properties in various electronic and electrochemical applications.
关键词： Raman spectroscopy,Boron-doped graphene,Pulsed laser deposition,Rapid thermal annealing,HRTEM,XPS,AFM
更新于2025-09-23 15:19:57
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Development of Pd/TiO2 Porous Layers by Pulsed Laser Deposition for Surface Acoustic Wave H2 Gas Sensor
摘要： The influence of sensitive porous films obtained by pulsed laser deposition (PLD) on the response of surface acoustic wave (SAW) sensors on hydrogen at room temperature (RT) was studied. Monolayer films of TiO2 and bilayer films of Pd/TiO2 were deposited on the quartz substrates of SAW sensors. By varying the oxygen and argon pressure in the PLD deposition chamber, different morphologies of the sensitive films were obtained, which were analyzed based on scanning electron microscopy (SEM) images. SAW sensors were realized with different porosity degrees, and these were tested at different hydrogen concentrations. It has been confirmed that the high porosity of the film and the bilayer structure leads to a higher frequency shift and allow the possibility to make tests at lower concentrations. Thus, the best sensor, Pd-1500/TiO2-600, with the deposition pressure of 600 mTorr for TiO2 and 1500 mTorr for Pd, had a frequency shift of 1.8 kHz at 2% hydrogen concentration, a sensitivity of 0.10 Hz/ppm and a limit of detection (LOD) of 1210 ppm. SAW sensors based on such porous films allow the detection of hydrogen but also of other gases at RT, and by PLD method such sensitive porous and nanostructured films can be easily developed.
关键词： bilayer films,pulsed laser deposition (PLD),palladium,hydrogen sensor,surface acoustic wave (SAW),Pd/TiO2,porous morphology,titanium dioxide
更新于2025-09-23 15:19:57
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Synthesis of Nanostructured PLD AlN Films: XRD and Surface-Enhanced Raman Scattering Studies
摘要： Thin films of AlN on Si were fabricated by pulsed laser deposition in vacuum and in nitrogen ambient, and at laser repetition rate of 3 Hz or 10 Hz. The films were nanostructured according to the X-ray diffraction analysis and TEM imaging. Films deposited in vacuum were polycrystalline with hexagonal AlN phase and with columnar structure, while films deposited in nitrogen were predominantly amorphous with nanocrystallites inclusions. The Al-N phonon modes in the surface-enhanced Raman spectra were largely shifted due to stress in the films. Phonon mode of Al-O related to film surface oxidation is observed only for deposition at low pressures.
关键词： microstructure,nanostructured thin film,Transmission electron microscopy,pulsed laser deposition,Aluminium nitride,Raman spectroscopy,X-ray diffractometry
更新于2025-09-19 17:15:36
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Structural, electrical and mechanical properties of ВС films prepared by pulsed laser deposition from mixed and dual boron-diamond/graphite targets
摘要： Relatively low and high deposition rates of BCх films were realized by pulsed laser ablation of mixed B–diamond and dual B–graphite targets, respectively. Deposition was performed at 500 °C and the rate of film deposition was determined with respect to the number of atomic monolayers (obviously less or more than one monolayer) grown for one laser pulse. In the case of BCх films formation with a low deposition rate, doping with B facilitated the growth of the nanocomposite structure, which possessed an increased fraction of sp3 bonds, a very low electrical resistance, and an improved mechanical performance. The change of the sheet resistance of these films as the temperature was reduced from 300 to 65 K had a metallic character. For about 95-nm-thick films with bulk compositions of BC1.7 and BC0.6, the resistivity at room temperature were approximately equal to 1.5 mΩ·cm, and the lowest resistivity of 0.23 mΩ·cm was detected for B-enriched film at 85 K. With an increase in the B atom concentration in such films, the charge carrier (holes) concentration decreased, and their mobility increased from 180 to 10,500 cm2·V?1·s?1 due to samples cooling. The application of a higher deposition rate from the dual B–graphite target activated surface migration of condensed atoms, which caused the development of granular morphology, the B segregation and the reduction of the sp3 bond fraction. The hardness and electrical conductivity of such films were obviously inferior to those of the films obtained by PLD with a low deposition rate.
关键词： Hardness,Thin films,Resistivity,Pulsed laser deposition,Boron,Diamond-like carbon
更新于2025-09-19 17:15:36
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[IEEE 2018 International Semiconductor Conference (CAS) - Sinaia (2018.10.10-2018.10.12)] 2018 International Semiconductor Conference (CAS) - Effect of the Deposition Conditions on Titanium Oxide Thin Films Properties
摘要： This paper presents the fabrication and characterization of titanium oxide thin films deposited by Pulsed Laser Deposition in different experimental conditions. The scope of this work is to investigate the effect of the oxygen pressure in the deposition chamber on the material properties. Thin films characterizations include the mechanical and tribological properties such as the modulus of elasticity, hardness and the adhesion force. The mechanical and tribological properties of the materials are experimentally determined by using the atomic force microscopy technique. The effect of the oxygen pressure on the film thickness is analyzed. As the pressure in the deposition process decreases, the thickness of the thin films increases, respectively. The surfaces roughness increases as the deposition pressure decreases that leads to a decrease of adhesion forces. Hardness and modulus of elasticity increases as the deposition pressure decreases. This study shows that the mechanical and tribological properties of the investigated thin films strongly depend on the grain size and the films density, which are influenced by the deposition conditions (the oxygen pressure in the deposition chamber).
关键词： pulsed laser deposition,thin films,adhesion force,hardness,modulus of elasticity
更新于2025-09-19 17:15:36
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Structure and transport properties of titanium oxide (Ti2O, TiO1+, and Ti3O5) thin films
摘要： Titanium oxides have partially filled or empty d orbital and are stable at various oxidation states with different structures and unique properties. Here, three kinds of titanium oxide thin films of hexagonal Ti2O metal, cubic TiO1+d superconductor, and monoclinic g-Ti3O5 semiconductor, were successfully grown on a-Al2O3 substrates by a pulsed laser deposition technique, through ablating a pure titanium target under different oxygen pressures. The electrical resistivities of these films increase with increasing oxygen content. The metallic behaviors of Ti bulk and Ti2O film can be described by the Bloch-Grüneisen formula, and the semiconducting behaviors of TiO1+d films in normal state and g-Ti3O5 film obey the variable range hopping and the small polaron hopping conduction mechanisms, respectively. For titanium monoxide TiO1+d (1.05 ≤ 1+d ≤ 1.17) films, increasing oxygen content is accompanied by an increase of disorder, a decrease of electron density of states at the Fermi level, and an enhancement of carrier localization, leading to a suppression of superconductivity.
关键词： Electron energy-loss spectroscopy,Oxygen content,Superconductivity,Transport properties,Titanium oxide thin films,Pulsed laser deposition
更新于2025-09-19 17:15:36