Dipak Paramanik

Formation of gold nanoparticles in polymethylmethacrylate by UV irradiation

Gold–polymethylmethacrylate (PMMA) nanocomposites were fabricated with a photoreduction method using UV irradiation. The irradiated samples are compared with unirradiated ones to investigate the mechanism of gold nanoparticle formation and the effect of UV irradiation and polymer matrix on the morphology of the particles. The triangular gold nanoparticles were formed in polymer medium at a specific concentration of gold salt and UV exposure. The particle size decreased when the gold salt to polymer ratio was increased. The samples were analysed using UV–Vis spectroscopy, Fourier transform infrared spectrometry, atomic force microscopy, x-ray diffraction, small angle x-ray scattering and x-ray photoelectron spectroscopy. The interfacial interaction of Au nanoparticles and PMMA polymer has been discussed.

Morphological evolution of InP nano-dots and surface modifications after keV irradiation

Evolution and coarsening behaviour of self-assembled nano-dots fabricated on an InP surface by 3 keV Ar ion sputtering have been studied in conjunction with the structural modifications at the surface. The dots have been produced in off-normal geometry but in the absence of rotation. For small sputtering durations, the dots coarsen and agglomerate, up to a critical time tc, while the surface roughens and experiences a tensile stress. A relaxation in this stress is observed after the surface becomes amorphized at tc, beyond which an inverse coarsening, fragmentation of dots and a smoothened surface are observed.

MeV N+-ion irradiation effects on α‐MoO3 thin films

In this work, modifications in the structural, vibrational, optical, and surface morphological properties of 2MeV N+-ion irradiated α‐MoO3 thin films are studied. Nitrogen irradiation up to the fluence of 1×1015ionscm−2 does not lead to any structural phase change. The irradiation induced formation of nanoscale defect structures at the film surface becomes more prominent at higher irradiation fluences, leading to the enhancement in the optical absorption behavior of the irradiated films. The possible role of energy loss process in the mechanism of modifying the surface morphology has been discussed.

Formation of large-area GaN nanostructures with controlled geometry and morphology using top-down fabrication scheme

This paper details the fabrication of GaN nanoscale structures using deep ultraviolet lithography and inductively coupled plasma (ICP) etching techniques. The authors controlled the geometry (dimensions and shape) and surface morphology of such nanoscale structures through selection of etching parameters. The authors compared seven different chlorine-based etch chemistries: Cl2, Ar, Cl2/N2, Cl2/Ar, Cl2/N2/Ar, Cl2/H2/Ar, and Cl2/He/Ar. The authors found that nitrogen plays a significant role in fabricating high quality etched GaN nanostructures. This paper presents the effects of varying the etch parameters, including gas chemistry, gas flow rate, ICP power, rf power, chamber pressure, and substrate temperature, on the etch characteristics, including etch rate, sidewall angle, anisotropy, mask erosion, and surface roughness. Dominant etch mechanisms in relation to the observed characteristics of the etched features are discussed. Utilizing such methods, the authors demonstrated the fabrication of nanoscale...

Nanoscale defect formation on InP (111) surfaces after MeV Sb implantation

We have studied the surface modifications as well as the surface roughness of the InP(111) surfaces after 1.5 MeV Sb ion implantations. A scanning probe microscope has been utilized to investigate the ion-implanted InP(111) surfaces. We observe the formation of nanoscale defect structures on the InP surface. The density, height, and size of the nanostructures have been investigated here as a function of ion fluence. The rms surface roughness, of the ion implanted InP surfaces, has also been investigated. Raman-scattering results demonstrate that at the critical fluence, where the decrease in surface roughness occurs, the InP lattice becomes amorphous.

Raman scattering characterization and electron phonon coupling strength for MeV implanted InP(111)

Structural modifications in InP(111) due to 1.5 MeV implantation of Sb have been characterized using first-order and second-order Raman spectroscopy. With both longitudinal optical (LO) and transverse optical (TO) modes allowed for InP(111), we have investigated the evolution of both these modes as a function of fluence. Investigations of both the first and second-order Raman modes indicate the presence of tensile stress in the lattice after implantation, which increases with fluence. Results show a coexistence of nanocrystalline InP regions and amorphous zones in the lattice. Consequently phonon confinement is observed and phonon confinement model (PCM) has been applied here to estimate the coherence length and the size of nanocrystalline zones in InP lattice after implantation. Nanocrystalline zones as small as 35 A have been observed here. A LO phonon-plasmon coupled mode, due to the charge layer in the vicinity of the surface, has also been observed. This coupled mode becomes sharper and more intense ...

High temperature grown transition metal oxide thin films: tuning physical properties by MeV N+-ion bombardment

In this paper, we present a systematic study on tuning the physical properties of high temperature (373 K) grown transition metal oxide thin films by the effect of 2 MeV nitrogen ion irradiation. Although we observe irradiation induced growth in crystallite sizes for both WO3 and MoO3 films, no structural phase change takes place in the films due to N+-ion beam irradiation even up to the fluence of 1 × 1015 N+ cm−2. On the other hand, irradiation leads to a significant increase in the optical absorption and the surface roughness of the films. These observations are corroborated by micro-Raman analysis. The results are attributed to the MeV ion–matter interaction.

Top-down fabrication of large-area GaN micro- and nanopillars

Large-area gallium nitride (GaN) micro- and nanopillar (NP) arrays were fabricated by plasma etching of lithographically patterned GaN thin-film grown on Si substrate. Deep-ultraviolet lithography, inductively coupled plasma (ICP) etching, and subsequent chemical treatments were effectively utilized to fabricate GaN pillars with diameters ranging from 250 nm to 10 μm. The impact of various plasma etching process parameters and chemical etchants on the morphology, strain, and surface defects of these NPs were studied using scanning-electron microscopy, photoluminescence (PL), and Raman spectroscopy. It was found that the shape of the NPs can be controlled by the substrate temperature during the plasma etch and by using different gas chemistries. Room-temperature PL and Raman spectroscopy measurements revealed significant strain relaxation in 250 nm diameter pillars as compared to 10 μm diameter pillars. PL measurement also indicated that the surface damage from the plasma etch can be removed by etching in KOH-ethylene glycol solution. Post-ICP selective wet chemical etch enabled us to fabricate functional structures such as micro- and nanodisks of GaN, which potentially could be utilized in nitride-based resonators and lasers.Large-area gallium nitride (GaN) micro- and nanopillar (NP) arrays were fabricated by plasma etching of lithographically patterned GaN thin-film grown on Si substrate. Deep-ultraviolet lithography, inductively coupled plasma (ICP) etching, and subsequent chemical treatments were effectively utilized to fabricate GaN pillars with diameters ranging from 250 nm to 10 μm. The impact of various plasma etching process parameters and chemical etchants on the morphology, strain, and surface defects of these NPs were studied using scanning-electron microscopy, photoluminescence (PL), and Raman spectroscopy. It was found that the shape of the NPs can be controlled by the substrate temperature during the plasma etch and by using different gas chemistries. Room-temperature PL and Raman spectroscopy measurements revealed significant strain relaxation in 250 nm diameter pillars as compared to 10 μm diameter pillars. PL measurement also indicated that the surface damage from the plasma etch can be removed by etching in ...

Formation and Shape Transition of Nanostructures on Si(100) surfaces after MeV Sb Implantation

Abstract We have studied the formation of nanostructures on Si(100) surfaces after 1.5 MeV Sb implantation. Scanning Probe Microscopy has been utilized to investigate the ion implanted surfaces. We observe the formation of nanostructures after a fluence of 1 × 1 0 13  ions/cm 2 . These surface structures are elliptical in shape with an eccentricity of 0.86 and their major and minor axes having dimensions of about 11.6 nm and 23.0 nm, respectively. The area of the nanostructure is 210 nm 2 at this fluence. Although the nanostructures remain of elliptical shape, their area increase with increasing fluence. However, after a fluence of 5 × 1 0 14  ions/cm 2 a transition in shape of nanostructures is observed. Nanostructures become approximately circular with an eccentricity of 0.19 and a diameter of about 30.1 nm. At this fluence we also observe a large increase in the area of the nanostructures to 726 nm 2 . Surface morphology and surface roughness of the ion implanted surfaces has also been discussed.

Formation of patterns and scaling properties of tantalum surfaces after low-energy ion beam irradiation

Here we study the pattern formation on tantalum foils after low-energy ion irradiation with 3 keV Ar ion beams. Surfaces display a variety of patterns decorated with nanodots. The associated surface roughness demonstrates an initial increase but a subsequent decrease as a function of ion fluence. The decrease in roughness, after critical fluence, is related to the development of several linear modulations on the surface which subsequently transform to ripples. The growth and roughness parameters of the ion-sputtered surfaces indicate scaling behaviors.