Laser Deposition Technique Research Articles

Preparation of GaN/Porous silicon heterojunction photodetector by laser deposition technique

In this work, gallium nitride (GaN) thin film was deposited on porous silicon (PSi) substrate via a pulsed laser deposition route with a 355 nm laser wavelength, 900 mJ of laser energy, and various substrate temperatures raging from 200 to 400 °C. The structural and optical properties of GaN films as a function of substrate temperature are investigate. XRD studies reveal that the GaN films deposited on porous silicon are nanocrystalline with a hexagonal wurtzite structure along (002) plane. The photoluminescence emission peaks of the GaN/PSi prepared at 300 °C substrate temperature are located at 368 nm and 728 nm corresponding to energy gap of 3.36 eV and 1.7 eV, respectively. The GaN/PSi heterojunction photodetector prepared at 300 °C exhibits the maximum performance, with a responsivity of 29.03 AW−1, detectivity of 8.6 × 1012 Jones, and an external quantum efficiency of 97.2% at 370 nm. Similarly, at 575 nm, the responsivity is 19.86 AW−1, detectivity is 8.9 × 1012 Jones, and the external quantum efficiency is 50.89%. Furthermore, the photodetector prepared at a temperature of 300 °C demonstrates a switching characteristic where the rise time and fall time are measured to be 363 and 711 μs, respectively.

Nanosecond laser irradiation of Yttria stabilized Zirconia: Pulsed laser ablation and surface treatment

Nanosecond pulsed laser irradiation resulting in material ablation and surface micro structuring of Yttria Stabilized Zirconia (YSZ) targets, has been investigated. Our study aims to evaluate suitable ablation conditions enabling either, creation of desired YSZ surfaces having micro porosity for directed use, or generation of YSZ vapors for deposition of homogenous, dense and particle free YSZ films via conventional Pulsed Laser Deposition (PLD) technique. The work being reported here involves a thermal model based theoretical simulation describing heat transport, melting and vaporization of a laser irradiated YSZ target. Our simulation has been validated against our experimental data on nanosecond laser ablation from a sample target of ceramic YSZ. Surface porosity generated on laser irradiated YSZ targets for low laser fluence levels ∼ 1 ​J/cm2 has been explained in terms of pore formation via entrapment of gas bubbles in the solidifying interface on laser melting and re-solidification thereafter, of the YSZ target. To understand surface crater formation on laser irradiated YSZ targets at high laser fluence levels ∼10 ​J/cm2 maximum temperature reached by the laser irradiated YSZ target has been compared with the thermodynamic critical temperature of YSZ. Our study confirms that judicious choice of laser fluence enables either, creation of surfaces having micro porosity of desired nature on YSZ target, or controlled generation of YSZ vapors for deposition of good quality YSZ films and coatings using laser deposition technique.

Wear characteristics of laser-deposited AlCoCrCuFeNi high entropy alloy with finite element analysis

BackgroundWear is a destructive phenomenon and one of the principal causes of material failure in moving components during surface interaction while in service. AlCoCrCuFeNi high-entropy alloy with its many properties is a potential material for aero-engine applications attributed to its outstanding relatively lightweight, high strength, good thermal, oxidation, and corrosion resistance properties. Hence, the investigation into the tribological behaviour of AlCoCrCuFeNi high-entropy alloys is essential to reduce maintenance costs and prolong the service life of this advanced material for aerospace applications. Most AlCoCrCuFeNi high-entropy alloy compositions were fabricated via arc melting, which has been reported to have defects attributed to slow solidification, consequently reducing the mechanical properties of the alloy with limited reports on other fabrication methods. Therefore, there is a need for the use of advanced manufacturing techniques for fabricating these alloys to improve the tribological properties. In this study, AlCoCrCuFeNi high-entropy alloy was fabricated via laser metal deposition. The influence of the laser processing parameters, rapid solidification, and the applied load on the tribological properties of the as-built alloys under dry conditions has been studied for aerospace applications. The counter ball rolling friction analysis was also investigated using COMSOL Multiphysics.ResultsThe results showed that at a high laser power of 1600 W and a scan speed of 12 mm/s, the lowest wear rates and highest hardness values were observed. The average coefficient of friction at room temperature was 0.1 and 0.3 at a speed of 21 m/s. The dominant wear mechanism at room temperature was abrasive wear as the wear rate increased linearly with an increase in load from 10 to 20 N. The scan speed had the most significant influence on the wear behaviour of the as-built high-entropy alloy attributed to the rapid rate of solidification which occurs at higher scan speeds.ConclusionsThe study examines the wear characteristics of high-entropy alloys fabricated via laser deposition technique in comparison with those fabricated via conventional routes. Although there were similarities in the phase structures of both techniques, the results showed that the wear resistance of the laser-deposited high-entropy alloy was comparatively higher than the same alloy prepared via conventional methods. Laser additive manufacturing was concluded to be a more successful method in fabricating high-entropy alloys.

Innovative Technologies to Improve the Corrosion Resistance of Stainless Steels

Oxidation is one of the main degradation mechanisms that affects most industrial components. Stainless steels are used in components and equipment in the chemical and petrochemical industries (e.g., valves, plates, columns, capacitors and desalination units). Generally, the steels used in these applications have physical, mechanical and chemical properties that give them corrosion resistance. However, contaminants existing in the processed fluids are the main factor causing the increase in corrosion rate, leading to significant financial losses, which requires the development of innovative technologies to protect the metal from the action of aggressive environment. The paper presents two innovative surface protection techniques used to improve the corrosion resistance of stainless steels. Thus, Matrix-Assisted Pulsed Laser Evaporation (MAPLE) and Pulsed Laser Deposition (PLD) techniques are used to obtain deposition of hybrid nanostructures of binary oxides and porphyrins on W1.4034 martensitic stainless steel, according to EN 10083-3.

Comparison of laser deposition methods for the synthesis of AlxCoCrFeNi multi-principal element alloy

Additive manufacturing (AM) of multi-principal element alloys (MPEAs) has enabled high throughput synthesis for rapid alloy design and development for targeted structural properties. However, the complex solidification cycles endured by the material during processing often yield disparate outcomes when porting the processing conditions between different laser deposition techniques. With difference in the cooling rates being a primary difference between laser metal deposition (LMD) and powder bed fusion (PBF), understanding the effects of the processing on the microstructures and material properties is critical to assess the printability of such complex alloys. Here, we compare the fabricability, quality, and structural properties of AlxCoCrFeNi MPEA synthesized by LMD and PBF. Our results indicate that the equiatomic MPEA processed using PBF exhibits interfacial cracks due to warping and bending between successive deposit layers, while the LMD produces crack free near-dense deposits. XRD characterization corroborates a relatively high lattice strain of 1.8 × 10−3 in the PBF sample resulting from the high residual stresses arising from the relatively high cooling rates (∼106 K/s) during the processing. While the PBF sample assumes smaller grains relative to the LMD processed alloy, no significant differences are noted in the crystallographic phases of the alloys produced by the two approaches. Also, the tool path employed to fabricate the alloy by LMD can facilitate gradation in the structural properties driven by the variation in thermal gradient during the synthesis. Further, we propose methods to map material space while porting processes within AM, enabling fabricability of alloys using PBF and DED.

Graphene and its Effect on the Structural and Optical Properties of TiO2 Nano Thin Films Prepared by PLD Technique

In this study, thin films were prepared from pure titanium dioxide doped with graphene (1, 3, 5, 7%) wt using pulsed laser deposition (PLD) technique. The X-ray diffraction results showed that the prepared films were polycrystalline with a quaternary structure. It is noted that there are diffraction peaks corresponding to the levels (101, 004, 200, 211), and in the preferential direction (101), we notice that the intensity of the peak (101) decreases with increasing doping with the appearance of a new peak when doping at rates (5, 7%)and angle (26.5 ) This peak represents graphene oxide, and that the grain size decreased with increasing doping with graphene, where the grain size ranged between (20-40) nm. EDX analysis also shows that the results of the ratios were close to the required ratios, The results showed in the scanning electron microscope that the increase in the percentage of doping leads to the crystallization and agglomeration of graphene oxide and its rise over the Titanium dioxide (TiO2) until the surface reaches the state of collapse. The optical properties revealed an increase in the value of the energy gap by increasing the doping with graphene oxide, as it ranged between (3.15-3.7) eV.

Strong Perpendicular Anisotropy and Anisotropic Landé Factor in Bismuth-Doped Thulium Garnet Thin Films

With the development of spintronics, garnet films with perpendicular magnetic anisotropy (PMA) have been attracting the attention of researchers for decades. In this work, bismuth-doped thulium iron garnet (Tm2BiFe5O12, TmBiIG) films of varying thickness having strong PMA effect were fabricated on substituted Gd3Ga5O12 (sGGG) (111) substrates using the pulsed laser deposition (PLD) technique. Crystallographic characterization and magnetic properties of TmBiIG films were investigated using high-resolution scanning transmission electron microscopy, X-ray diffraction, vibrating sample magnetometry, and broadband ferromagnetic resonance (FMR). A high perpendicular anisotropic field of H⊥ = 4,445 ± 7.5 Oe in a 10-nm-thick film and H⊥ = 4,582 ± 7.7 Oe in a 30-nm-thick film at room temperature were obtained and analyzed in detail. Surprisingly, an additional spin-wave mode was observed in the in-plane FMR spectra. The discrepancy between in-plane and the out-of-plane Landé g-factors established a correlation with the PMA effect in the TmBiIG films. The Landé g-factor of the TmBiIG films is much lower than that of free electrons, indicating that the strong spin–orbit coupling is caused by Tm and Bi heavy elements. The Gilbert damping factor α changed from 0.007 to 0.012 in various thicknesses of TmBiIG films.

The Status of High Entropy Alloys Studies in Africa: An Overview

One valid way to access the state of knowledge in a specific research area is by assessing the availability of quality publications in that research area. In this work, we assess the level of high entropy research in Africa considering that it is a hot topic in the field of materials engineering. Precedent on the independent studies of Cantor and Yeh, the conventional alloying techniques are evolving towards the high entropy approach. To determine the extent of high entropy research in Africa, SCOPUS database was used following specific keywords searches. The result ranked South Africa as the most publisher of high entropy alloy-related articles in Africa followed by Egypt then Kenya, Nigeria and Algeria. Notably, most high entropy alloy articles published from South Africa and Egypt are within the last two years. In South Africa, the high entropy alloys are majorly fabricated via arc melting, spark plasma sintering and laser deposition techniques while Egypt shows proficiency in studies focusing on mechanical alloying, sintering and casting processes for high entropy alloys. Conclusively, the research output from Africa is still lagging when compared to those of other continents however, maximizing the limited infrastructure within Africa and improving collaborations will go a long way towards improving Africa’s research output on high entropy alloys.

Photo-resistor applications of Bi:ZnSe nano-composition deposited on micro-glass

Bi:ZnSe films at different concentrations (0, 5, 10, and 15%) were made by the laser deposition technique. The scanning electron microscopy and Uv–visible spectroscopy were used to investigate the surface topography and optical properties of the prepared films, respectively. The calculated energy gap was (3.0, 2.6, 3.2, and 3.1 eV) due to differences in lattice parameters. Moreover, the electrical characteristics reveal enhanced dark current with all samples probably due to the essential property of p-type doped ZnSe Nano-composition. The density, refractive index, permittivity, and reflection loss were also studied versus Bi-dopant. The structural characteristics of the coated films have been tested by an X-ray diffractometer. In addition, the interstitial or substitutional Zn ion by Bi ion in the lattice was also explained in this paper.

Corrosion Nature in [CoN/AlN]n Multilayers Obtained from Laser Ablation

The aim of this work is the improvement of the electrochemical behavior of industrial steel using [CoN/AlN]n multilayered system via reactive Pulsed Laser Deposition (PLD) technique with a Nd: YAG laser (λ = 1064 nm) on Silicon (100) and AISI 302 steel substrates. In this work was varied systematically the bilayer period (Λ) and the coatings were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and the chemical composition was determined by means of X-ray photoelectron spectroscopy (XPS). The maximum corrosion resistance for the coating with (Λ) equal to 34.7 nm, corresponding to n = 30 bilayered. The polarization resistance and corrosion rate were around 7.62 × 105 kOhm × cm2 and 7.25 × 10−5 mm/year, these values were 6.3 × 105 and 78.6 times better than those showed by the uncoated 302 stainless steel substrate (1.2 kOhm × cm2 and 0.0057 mm/year), respectively. The improvement of the electrochemical behavior of the steel 302 coated with this [CoN/AlN]n can be attributed to the presence of several interfaces that act as obstacles for the inward and outward diffusions of Cl− ions, generating an increment in the corrosion resistance. The electrochemical results found in the [CoN/AlN]n open a possibility of future applications in mechanical devices that require high demands in service conditions.

Enhanced Spin Accumulation in Semiconductor at Room Temperature Using Ni0.65Zn0.35Fe2O4(NZFO) as Spin Injector in NZFO/MgO/p-Si Device

In this article, the fabrication of a Ni0.65Zn0.35Fe2O4/MgO/p-Si heterostructure device has been optimized using the pulsed laser deposition (PLD) technique, and a detailed investigation of its structural, electrical, and magnetic features has been performed experimentally. The electronic and magneto-transport characteristics have been explored in the temperature range of 100–300 K. The current-voltage (I-V) characteristics of the heterojunction have been recorded, which displayed an excellent rectifying magnetic tunnel diode-like behavior throughout that temperature regime. The application of an external magnetic field parallel to the plane of the NZFO film causes the current (I) across the junction to decrease, clearly indicating positive junction magnetoresistance (JMR) of the heterostructure. The root of displaying positive magnetoresistance in our heterojunction has been well justified using the standard spin injection model. The electrical injection of spin-polarized carriers and its accumulation and detection in a p-Si channel have been demonstrated using the NZFO/MgO tunnel contact using a three-terminal (3-T) Hanle device. The parameters such as spin lifetime (99 ps), spin diffusion length (276 nm), and spin polarization (0.44) have been estimated from the Hanle curve detected in our heterostructure at room temperature, making the Ni0.65Zn0.35Fe2O4/MgO/p-Si device a very favorable promising junction structure in the field of spintronics for several device appliances in the future.

Modification of a silicon surface visible light reflectivity by the carbon nanofilm

Crystalline silicon substrate visible light reflectivity is finely modified by a discrete growth of carbon nanofilm (CNF) on it by nanosecond pulsed laser deposition (PLD) technique. It is established that 71 nm thick CNF effectively reduces the high reflection of the substrate on average to 5% in the visible light wave range. The exact values of the thickness and refractive index of the carbon nanofilm are also determined via an analysis of reflection spectra.

Comparison of electrical and photovoltaic parameters of the hetero-junction solar cells based on CZTS and CIGS ultrathin films

ABSTRACT Copper-Zinc-Tin-Sulphide (CZTS)/n-Si and Copper-Indium-Gallium-Selenide (CIGS)/n-Si hetero-junction solar cells have been manufactured using Pulse Laser Deposition (PLD) technique. Properties of both CZTS&CIGS ultrathin films have been produced in comparable thicknesses, analysed and compared to each other. CIGS ultrathin film has smaller main crystalline size but absorbs more light compared to CZTS. characteristics of CZTS/n-Si and CIGS/n-Si hetero-junctions have been obtained in the darkness and under light conditions. The ideality factor, barrier height, serial resistances of these hetero-junctions have been calculated by the traditional and Cheung-Cheung methods for the darkness. Although the serial resistance of CZTS hetero-junction has been found to be very low compared to CIGS hetero-junction, the efficiency and photocurrent of CZTS solar cell have been higher compared to those of CIGS solar cell. The photoelectric outputs of CZTS/n-Si and CIGS/n-Si cells have been studied using SCAPS-1D programme. We have found/concluded difference in characteristics between CZTS/n-Si and CIGS/n-Si structures.

Fabrication of Cr2O3: ZnO Nanostructure Thin Film Prepared by PLD Technique as NH3 Gas Sensor

Chromium oxide (Cr2O3) doped ZnO nanoparticles were prepared by pulsed laser deposition (PLD) technique at different concentration ratios (0, 3, 5, 7 and 9 wt %) of ZnO on glass substrate. The effects of ZnO dopant on the average crystallite size of the synthesized nanoparticles was examined By X-ray diffraction. The morphological features were detected using atomic force microscopy (AFM). The optical band gap value was observed to range between 2.78 to 2.50 eV by UV-Vis absorption spectroscopy, with longer wavelength shifted in comparison with that of the bulk Cr2O3 (~3eV). Gas sensitivity, response, and recovery times of the sensor in the presence of NH3 gas were studied and discussed. In the present work, we found that the sensitivity was increased upon increasing the concentration ratio from 3 to 5%wt of ZnO, whereas it was decreased again over that value. Also, we found that the sensitivity was increased when increasing operating temperature, while the response time was decreased. The optimum concentrations ratio for NH3 gas sensitivity at 5%wt ZnO revealed sensitivity of 66.67% and response time of 14s at operating temperature of 300oC and 700mJ PLD energy.

Improvement in microstructure uniformity and mechanical properties of surface modified graphene reinforced Ni-based composites by laser deposition

Graphene (Gr) is regarded as one of the promising nano reinforcement of metal matrix composites (MMCs) to improve the comprehensive performance owing to its superior physical and mechanical properties recently. However, the agglomeration and survivability at high-temperature of Gr as well as the compatibility between Gr and metal, have severely restricted the application of Gr in MMCs. Herein, the surface modification coupled with a mixing method without ball-milling was employed to protect Gr from the structural damage. Then, the modified Gr (CoFe@Gr) reinforced Ni-based alloy composites were fabricated via laser deposition technique in an argon protective atmosphere. The results showed that the pristine Gr nanosheets were successfully incorporated into composites, but some of them were transformed into the nanospheres while others formed “core-shell” structure with carbides under the high-energy laser irradiation. Compared with alloys adding Gr directly, the addition of CoFe@Gr composite powders not only promoted the uniform distribution of the second phases in matrix phase but also inhibited the generation of the pores defects resulted from the burning of Gr without surface modification. The changes in microstructure contributed to the lower coercivity of composites. Moreover, the micro-hardness and compressive strength values of composites were increased by 12.55% and 45.50% as compared with that of as-deposited alloys, respectively. This was mainly attributed to the improved interface compatibility between Gr and Ni matrix, the thermal mismatch effect and the second phase strengthening effect. This work is expected to provide a technique guidance for Gr reinforced MMCs that the fabrication conditions requiring high temperature.

Effect of laser power on the microstructure and mechanical properties of laser deposited titanium aluminide composite

ABSTRACT In this work, titanium aluminide alloy have been fabricated via the laser deposition technique. The effect of some selected deposition parameters on the microstructure and mechanical properties of produced deposits were studied. The relationship between the laser power, and the microhardness of deposited samples on laser preheated substrate showed an incremental change in laser power from 200 to 600 W. This led to an overall decrease in microhardness of deposited samples from 426 to 373 HV. Sample deposited at 500 W gave the lowest Icorr of 1.8 x 10-8 and the highest Ecorr of -0.138 V. It is evident from the nanoindentation results that indentation modulus and stiffness of sample deposited at 600 W laser power had a lower value compared with 400 W laser power. However, the modulus of both samples fell within titanium alloy modulus range between 105-120 GPa. The microstructures of the deposits are mainly characterized with γ-TiAl and α2-Ti3Al phases and an improved hardness property almost two times higher than that of commercially pure titanium were achieved. It was concluded that changes in the laser power directly causes changes in the microstructure, hardness, stiffness, modulus of elasticity and corrosion resistance of the deposits.

Lead-free relaxor-ferroelectric thin films for energy harvesting from low-grade waste-heat

One of the ways to mitigate the world energy crisis is to harvest clean and green energy from waste-heat, which is abundant, ubiquitous, and free. Energy harvesting of this waste-heat is one of the most encouraging methods to capture freely accessible electrical energy. Ferroelectric materials can be used to harvest energy for low power electronic devices, as they exhibit switchable polarization, excellent piezoelectric and pyroelectric properties. The most important characteristic of ferroelectric materials, in the context of energy harvesting, is their ability to generate electric power from a time-dependent temperature change. In this work, we grew highly c-axis oriented heterostructures of BaZr0.2Ti0.8O3 (barium zirconium titanate, BZT)/Ba0.7Ca0.3TiO3 (barium calcium titanate, BCT) on SrRuO3 (strontium ruthenate, SRO) and deposited on SrTiO3 (strontium titanate, STO) single crystalline substrate using pulsed laser deposition (PLD) technique. We investigated the structural, electrical, dielectric, and pyroelectric properties of the above-mentioned fabricated heterostructures. The wide range of θ–2θ X-ray diffraction (XRD) patterns only shows (00l) reflection peaks of heterostructures and the substrate which confirmed that the films are highly c-axis oriented. We are also capable to convert the low-grade waste-heat into electrical energy by measuring various temperature-dependent ferroelectric hysteresis loops of our nanostructure films via pyroelectric Ericsson cycles and the structures show an energy conversion density ~ 10,970 kJ/m3 per cycle. These devices exhibit a large pyroelectric current density of ~ 25 mA/m2 with 11.8 °C of temperature fluctuation and the corresponding pyroelectric coefficient of 3425 μC/m2K. Our research findings suggest that these lead-free relaxor-ferroelectric heterostructures might be the potential candidates to harvest electrical energy from waste low-grade thermal energy.

Comparative Study on Structural, Optical, and Electrical Properties of ZnO Thin Films Prepared by PLD and Sputtering Techniques

ZnO thin films were formed on c-plane sapphire and p-GaN substrates by pulsed laser deposition (PLD) and radio frequency (RF) magnetron sputtering techniques. XRD analysis including omega scan depicted the formation of highly textured wurtzite ZnO with c-axis. The texture was primarily introduced by the substrate effects as the planes lying at oblique angles also exhibited six-fold symmetry during phi scan. Atomic force microscopy exhibited the surface roughness of 4.33 and 12.99 nm for PLD and sputtered ZnO films, respectively. In photoluminescence (PL) measurements, a strong UV emission was observed at 3.30 eV for both ZnO films. However, deep-level emission was observed at around 2.61 eV in PLD film, but it had a wide range from 2.61 to 2.29 eV in case of sputter-deposited film. From the transmission spectra, the optical band gap values were found to be 3.29 and 3.28 eV for PLD and sputtered ZnO films, respectively. Hall measurement revealed the resistivity values of 0.0792 and 0.4832 Ω cm and carrier concentrations of 2.28 × 1018 and 1.73 × 1018 cm–3 for respective PLD and sputtered films. I(V) current–voltage curves clearly demonstrated the n-ZnO|p-GaN hetero-junction with turn-on voltage of 3.8 and 5.2 V for PLD and sputtered samples, respectively.

レーザーアブレーション法を用いたフッ素化アパタイト薄膜の作製とin vitro 評価

レーザーアブレーション法を用いたフッ素化アパタイト薄膜の作製とin vitro 評価

Pulsed Laser Deposition Deposited Layers of Pseudo-Binary Zinc Oxides and Zinc-Porphyrin for Steel Corrosion Inhibition

Obtaining of ZnTa2O6 and ZnV2O6 pseudo-binary oxide materials by hydrothermal and coprecipitation methods and of Zn(II) 5-pyridyl-10,15,20-tris-(3,4-di-methoxy-phenyl) porphyrin (ZnPydiMeOPP) are presented. Mixed thin films of pseudo-binary oxide materials and Zn-porphyrin were realized by pulsed laser deposition (PLD) technique on steel disks and corrosion tests in 0.1 M HCl solution were performed. The inhibition efficiency (IE) in all cases containing porphyrin was always higher than 80%. The best IE (84.50%) was obtained for the sandwich structure using the hydrothermally obtained ZnV2O6 oxide as the first layer and the ZnPydiMeOPP porphyrin as the second layer. The mechanism of corrosion protection can be explained by the physical/mechanical barrier effect.