Khaliq Mahmood

Effect of ambient gas conditions on laser-induced copper plasma and surface morphology

The effect of different gases and their pressures on the intensity of spectral emission, electron temperature and density of laser-produced plasma has been investigated. For this purpose, Cu targets were ablated by employing Q-switched Nd:YAG laser pulses (λ~1064 nm, τ~10 ns, pulsed energy of 200 mJ) under various filling pressures of the background gases argon, air and helium. The optical emission spectroscopy of Cu plasma has been studied using the laser-induced breakdown spectroscopy system. The results obtained strongly indicate that the nature and pressure of the ambient atmosphere are one of the controlling factors of the plasma characteristics. A scanning electron microscopy analysis has been performed to investigate the dependence of surface morphological changes of an irradiated target on the nature and pressure of an ambient gas. The basic aim of this study is to improve the understanding of ablation mechanisms and plasma parameters (optical emission intensity, electron temperature and density) under various ambient conditions. The optimization of experimental conditions (the nature and pressure of the ambient environment) is very important for temperatures and densities of ablated species, which are consequently crucial for pulsed laser deposition of thin films and nanostructuring of materials.

Effect of laser irradiance on the surface morphology and laser induced plasma parameters of zinc

The effect of laser-irradiance on the surface morphology and laser induced breakdown spectroscopy of zinc has been investigated by employing Nd:YAG laser (wavelength λ= 1064 nm, pulse duration t∼ 10 ns, and repetition rate= 10 Hz) under ambient environment of argon at a pressure of 20 Torr. For this purpose, zinc targets were exposed to various laser irradiances ranging from 13 GW/cm to 100 GW/cm. Scanning electron microscope analysis has been performed to analyze the surface modification of irradiated zinc targets. Scanning electron microscope analysis revealed the formation of various kinds of structures such as ripples, cones, cavities, and wave like ridges at the center and peripheral regions of ablated zinc. In the central ablated region with increasing laser irradiance, the growth of distinct and well defined ripples is observed. Further increase in irradiance makes the appearance of these ripples diffusive and narrow. In order to correlate the plasma parameters with the surface modification, laser induced breakdown spectroscopy analysis has also been performed. The electron temperature and number density of zinc plasma have been evaluated at various laser irradiances. For both plasma parameters, an increasing trend up to a certain value of laser irradiance is observed which is due to enhanced energy deposition. Afterword a decreasing trend is achieved which is attributed to the shielding effect. With further increase in irradiance a saturation stage comes and almost no change in plasma parameters is observed. This saturation is explainable on the basis of the formation of a self-regulating regime near the target surface. A strong correlation between surface modification and plasma parameters is established.

EFFECTS OF SUBSTRATE TEMPERATURE ON STRUCTURAL, OPTICAL AND SURFACE MORPHOLOGICAL PROPERTIES OF PULSED LASER DEPOSITED ZnO THIN FILMS

The effect of substrate temperature on the structural, optical and morphological properties of ZnO thin films has been investigated. ZnO thin films were deposited on quartz substrate for various temperatures ranging from room temperature to 250°C by pulsed laser deposition (PLD) technique. Nd:YAG laser (532 nm, 100 mJ, 6 ns, 10 Hz) with corresponding fluence of 6 J/cm2 was employed for the ablation of ZnO target. Characterization of the thin films was carried out using X-ray diffraction (XRD), high resolution UV-visible spectrometer, atomic force microscope (AFM) and scanning electron microscope (SEM). From XRD analysis, the amorphous behaviors of films at room temperature and crystalline behavior along the preferred orientation of (002) is exhibited for higher substrate temperature. The transmittances of grown films increase with the increasing substrate temperature. The evaluated values of bandgap energies increase with increasing substrate temperature up to the range of 150°C and then monotonically decrease with the further increase in temperature. AFM and SEM analysis illustrates that the density and height of grains for deposited films increase significantly with increasing substrate temperature.

Spectroscopic and morphological study of laser ablated Titanium

The laser-induced breakdown spectroscopy (LIBS) and surface morphology of Titanium (Ti) plasma as a function of laser irradiance have been investigated under ambient environment of argon at fixed pressure of 50 Torr. Ablation was performed by employing Q-switched Nd:YAG laser pulses (λ ≈ 1064 nm, τ ≈ 10 ns, repetition rate ≈ 10 Hz). Ti targets were exposed to various laser intensities ranging from 6 to 50 GW/cm2. LIBS analysis has been employed for the investigation of plasma parameters. Scanning Electron Microscope (SEM) analysis was employed for investigation of surface morphology. Ablation depth was measured by optical microscopy technique. It was observed that both plasma parameters, i.e., excitation temperature and electron density have been significantly influenced by laser irradiance. It is observed that with increasing laser irradiance up to 13 GW/cm2, the electron temperature decreases whereas number density significantly increases and attains its maxima. Afterwards by increasing irradiance electron temperature increases, attains its maxima and a decrease in electron number density is observed at irradiance of 19 GW/cm2. Further increase in irradiance causes saturation with insignificant changes in both electron temperature and electron number density. This saturation in both excitation temperature and electron number density is explainable on the basis of self-sustaining regime. SEM micrographs reveal the ripple and coneformation at the boundaries of ablated region of Ti. The height of cones as well as the ablation depth is maximum at irradiance of 13 GW/cm2 whereas electron number density is also maximum. The maximum electron number density is considered to be responsible for maximum ablation as well as mass removal. A strong correlation between plasma parameters and surface morphology is established.

Optical emission spectroscopy of magnetically confined laser induced vanadium pentoxide (V2O5) plasma

Optical emission spectra of a laser induced plasma of vanadium pentoxide (V2O5) using a Nd:YAG laser (1064 nm, 10 ns) in the presence and absence of the magnetic field of 0.45 T have been investigated. The effect of the magnetic field (B) on the V2O5 plasma at various laser irradiances ranging from 0.64 GW cm−2 to 2.56 GW cm−2 is investigated while keeping the pressure of environmental gases of Ar and Ne constant at 100 Torr. The magnetic field effect on plasma parameters of V2O5 is also explored at different delay times ranging from 0 μs to 10 μs for both environmental gases of Ar and Ne at the laser irradiance of 1.28 GW cm−2. It is revealed that both the emission intensity and electron temperature of the vanadium pentoxide plasma initially increase with increasing irradiance due to the enhanced energy deposition and mass ablation rate. After achieving a certain maximum, both exhibit a decreasing trend or saturation which is attributable to the plasma shielding effect. However, the electron density shows a decreasing trend with increasing laser irradiance. This trend remains the same for both cases, i.e., in the presence and in the absence of magnetic field and for both background gases of Ar and Ne. However, it is revealed that both the electron temperature and electron density of the V2O5 plasma are significantly enhanced in the presence of the magnetic field for both environments at all laser irradiances and delay times, and more pronounced effects are observed at higher irradiances. The enhancement in plasma parameters is attributed to the confinement as well as Joule heating effects caused by magnetic field employment. The confinement of the plasma is also confirmed by the analytically calculated value of magnetic pressure β, which is smaller than plasma pressure at all irradiances and delay times, and therefore confirms the validity of magnetic confinement of the V2O5 plasma.Optical emission spectra of a laser induced plasma of vanadium pentoxide (V2O5) using a Nd:YAG laser (1064 nm, 10 ns) in the presence and absence of the magnetic field of 0.45 T have been investigated. The effect of the magnetic field (B) on the V2O5 plasma at various laser irradiances ranging from 0.64 GW cm−2 to 2.56 GW cm−2 is investigated while keeping the pressure of environmental gases of Ar and Ne constant at 100 Torr. The magnetic field effect on plasma parameters of V2O5 is also explored at different delay times ranging from 0 μs to 10 μs for both environmental gases of Ar and Ne at the laser irradiance of 1.28 GW cm−2. It is revealed that both the emission intensity and electron temperature of the vanadium pentoxide plasma initially increase with increasing irradiance due to the enhanced energy deposition and mass ablation rate. After achieving a certain maximum, both exhibit a decreasing trend or saturation which is attributable to the plasma shielding effect. However, the electron density show...

EFFECT OF SUBSTRATE TEMPERATURE ON THE GROWTH OF COPPER OXIDE THIN FILMS DEPOSITED BY PULSED LASER DEPOSITION TECHNIQUE

The effect of substrate temperature on growth of pulsed laser deposited copper oxide thin films has been investigated by employing Nd: YAG laser (532nm, 6ns, 10Hz) irradiation at a fluence of 8.2J/cm2. XRD analysis reveals that copper oxide films deposited at room temperature are amorphous in nature, whereas films deposited at higher substrate temperatures are polycrystalline in nature. SEM and AFM analyses revealed that films deposited at substrate temperatures, ranging from room temperature to 300∘C are comprised of large sized clusters, islands and particulates, whereas uniform films with an appearance of granular morphology and distinct bump formation are grown at higher substrate temperatures of 400∘C and 500∘C. The optical bandgap of deposited films is evaluated by UV-VIS spectroscopy and shows a decreasing trend with increasing substrate temperature. Four point probe analysis reveals that electrical conductivity of the deposited films increases with increase in the substrate temperature, and is maximum for highest growth temperature of 500∘C. It is revealed that growth temperature plays a significant role for structure, texture, optical and electrical behavior of copper oxide thin films. The surface and structural properties of the deposited films are well correlated with their electrical and optical response.

Synthesis, Crystallization Behavior and Surface Modification of Ni-Cr-Si-Fe Amorphous Alloy

A quaternary Ni86Cr7Si4Fe3 amorphous alloy was synthesized by melt spinning technique. Surface modification was done by electron beam melting (EBM), neutron irradiation and γ-rays. Microstructure of as cast, annealed and modified samples was examined by scanning electron microscope. Crystallization behavior was studied by annealing the samples in vacuum at different temperatures in the range 773-1073 K. Techniques of X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used for characterization. Differential scanning calorimetry (DSC) was conducted at various heating rates in the range 10-40 K/min. Thermal parameters like glass transition temperature Tg, crystallization temperature Tx, supercooled liquid region ΔTx and reduced glass transition temperature Trg were measured. The Ni86Cr7Si4Fe3 alloy exhibits wide supercooled liquid region of 60 K indicating good thermal stability. The activation energy was calculated to be 160±4 kJ/mol using Kissinger and Ozawa equations respectively which indicates high resistance against crystallization. The XRD results of the samples annealed at 773 K, 923 K, 973 K and 1073 K/20 min show nucleation of Ni2Cr3 and NiCrFe crystalline phases. Vickers microhardness of the as cast ribbon was measured to be 680.. About 30-50 % increase in hardness was achieved by applying EBM technique.

CARBON ION IRRADIATION EFFECTS ON PULSED LASER DEPOSITED TITANIUM NITRIDE THIN FILMS

Pulse laser deposited thin films of TiN are irradiated by 1 MeV carbon (C+) ions beam for various doses ranging 0.4 to 2.8 × 1014 ions/cm2. Atomic force microscopy (AFM) analysis reveals the formation of hillocks like structures after ion irradiation. X-ray diffraction (XRD) investigations show that the film crystallinity increases for lower doses ranging from 0.4 to 1.2 × 1014 ions/cm2 and decreases for higher doses (2 to 2.8 × 1014 ions/cm2) of ions. No new bands are identified from Raman spectroscopy. However, a noticeable change in microhardness has been observed. The hillock densities as well as hardness are strongly dependent upon ion dose.