P. V. Satyam

Study of sputtered particles from gold nano-islands due to MeV self-ion irradiation

Abstract Very thin films of gold deposited on silicon substrates form isolated nano-island structures due to the non-wetting nature of gold. Thick films are more homogeneous and do not have the isolated island structures. Thin gold films of various thicknesses (≈0.4–21.4 nm) are deposited under high vacuum condition and irradiated with 1.5 MeV Au2+ ions. The sputtered particles are collected on catcher grids (carbon coated) during the irradiation and are analyzed with transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS). The average sputtered particle size is determined from TEM measurements, whereas the amount of gold on the catcher grid is found by RBS. The average sputtered particle size from thin (up to a thickness of ≈2 nm) discontinuous films is larger compared to the average particle size from thick continuous films. The coverage of the sputtered particles on the catcher grids is also discussed. Energy spike and its distribution in the nano-islands is proposed to be the main reason for the variation in the particle size and the coverage of the sputtered particles on the catcher grid.

Low current MeV Au2+ ion-induced amorphization in silicon: Rutherford backscattering spectrometry and transmission electron microscopy study

Abstract The amorphization due to MeV Au2+ ion implantation in Si(1xa01xa01) has been studied using Rutherford backscattering spectrometry/channeling (RBS/C) and transmission electron microscopy (TEM) methods. 1.5 MeV Au2+ ions were implanted into Si(1xa01xa01) substrates at various fluences at low currents (0.02–0.04 μAxa0cm−2) while the samples were kept at room temperature. The RBS/C results for as-implanted specimen shows the onset fluence for amorphization to be ≈5×1013 ionsxa0cm−2 which is much lower than the fluence reported earlier. Selected area diffraction (TEM) for a sample implanted at a of 1×1014 ionsxa0cm−2 confirms the occurrence of the amorphization. Earlier, amorphization studies by Alford and Theodore, using 2.4 MeV gold ions in silicon (1xa00xa00) reported a threshold fluence of 1.8×1015 ionsxa0cm−2 for amorphization when the implantation was carried out at higher currents (0.2–5 μAxa0cm−2) [J. Appl. Phys. 76 (1994) 7265]. The nuclear energy loss (Sn) for 1.5 MeV gold ions in silicon is ≈13% greater than the value for 2.4 MeV and cannot be the sole reason for lower threshold fluence for the amorphization. The amorphization at a relatively lower fluence for the low current implantations could be possible due to reduction in the dynamical annealing effects.

Thickness dependent lattice expansion in nanogranular Nb thin films

We report on the dependence of the lattice parameter on thickness (t) and grain size (D) in nanogranular Nb thin films deposited on Si (100) substrates by using dc magnetron sputtering. The lattice parameter is found to exponentially increase with decreasing thickness as well as grain size. We analyze the lattice expansion in terms of the excess free volume in the grain boundaries, which is found to decrease with the grain size in large thickness limit. The thickness dependence of the lattice expansion and the grain size dependence of the excess free volume are discussed in terms of the oxygen content in the grain boundaries.

Oxide mediated liquid–solid growth of high aspect ratio aligned gold silicide nanowires on Si(110) substrates

Silicon nanowires grown using the vapor-liquid-solid method are promising candidates for nanoelectronics applications. The nanowires grow from an Au-Si catalyst during silicon chemical vapor deposition. In this paper, the effect of temperature, oxide at the interface and substrate orientation on the nucleation and growth kinetics during formation of nanogold silicide structures is explained using an oxide mediated liquid-solid growth mechanism. Using real time in situ high temperature transmission electron microscopy (with 40 ms time resolution), we show the formation of high aspect ratio ( approximately 15.0) aligned gold silicide nanorods in the presence of native oxide at the interface during in situ annealing of gold thin films on Si(110) substrates. Steps observed in the growth rate and real time electron diffraction show the existence of liquid Au-Si nano-alloy structures on the surface besides the un-reacted gold nanostructures. These results might enable us to engineer the growth of nanowires and similar structures with an Au-Si alloy as a catalyst.

Formation of aligned nanosilicide structures in a MBE-grown Au/Si(110) system: a real-time temperature-dependent TEM study.

Thin Au films (∼2xa0nm) were deposited on an Si(110) substrate epitaxially under ultra-high vacuum (UHV) conditions in a molecular beam epitaxy (MBE) system. Real-time in situ transmission electron microscopy (TEM) measurements were carried out at various temperatures (from room temperature to 700u2009°C), which shows the formation and growth of aligned gold silicide nanorod-like structures. The real-time selected-area electron diffraction patterns show the presence of silicon and unreacted gold at lower temperatures (up to 363u2009°C), while at higher temperatures only the signature of silicon has been observed. The diffraction analysis from room temperature cooled systems show the presence of gold silicide structures. Around 700u2009°C, 97% of the nanostructures were found to be aligned nanosilicide-rod-like structures with a longer side of ≈37xa0nm and aspect ratio of 1.38. For a high temperature annealed system (at 600u2009°C), selected-area diffraction (SAD) and high resolution lattice (after cooling down to room temperature) confirmed the formation of nano- Au(5)Si(2) structures. The alignment of gold silicide structures has been explained on the basis of lattice matching between the substrate silicon and silicide structures.

Energy spike induced effects in MeV ion-irradiated nanoislands

Abstract Transmission electron microscopy (TEM), atomic force microscopy (AFM) and Rutherford backscattering spectrometry (RBS) have been used to study the modification of Au nanoislands, grown on silicon substrates under high vacuum condition by MeV self-ion irradiation. Upon irradiation with 1.5 MeV Au 2+ ions, interesting observations were found for the nanoislands in comparison with continuous films: (i) higher probability of crater formation, (ii) larger sputtered particle size as well as coverage and (iii) enhanced sputtering yield. Crater formation has been studied as a function of impact angle at a fluence of 1xa0×xa010 14 ionsxa0cm −2 and we found that crater formation is prominent at high impact angles (i.e. at glancing angle geometry). AFM has been used to determine the crater formation, TEM to study the sputtered particles as well as craters and RBS has been used to determine the sputtering yield from the nanoisland and continuous films.

Growth of Au capped GeO2 nanowires for visible-light photodetection

A single step process to grow Au capped oxygen deficient GeO2 crystalline nanowires via generation of growth species through the metal induced surface decomposition of Ge substrate is reported. Without the external source supply, the growth of the Au-GeO2 nanowires on the Ge substrate is addressed with possible mechanism. Despite high band gap, application of GeO2 as a possible new material for visible light photodetection is presented. The as-grown samples were found to have a photo-response of ≥102 with 17% external quantum efficiency at −2.0u2009V applied bias upon visible-light illumination (λu2009=u2009540u2009nm, 0.2 mW/cm2). This visible-light detection can be attributed to the oxygen vacancy related defect states as well as localized surface plasmon resonance induced absorption and subsequent hot electron injection from Au to conduction band of GeO2. The photodetection performance of the devices has been understood by the proposed energy band diagrams. In addition, ≈4 times enhancement in the efficiency has been ...

Swift heavy ion induced formation of preferentially oriented Au0.6Ge0.4 alloy

Formation of Au0:6Ge0:4 alloy on Si (1 0 0) substrate has been observed upon irradiating Au/Ge bilayer with 120 MeV Au ions and subsequent vacuum annealing at 360 � C. Transmission electron microscopy measurements on irradiated and vacuum annealed Au/Ge samples show a possibility of formation of oriented Au0:6Ge0:4 alloy, in agreement with X-ray diffraction data. These measurements reveal that although 120 MeV Au irradiation alone can not lead to a large scale mixing, it acts as a seed by forming nanoislands of Au0:6Ge0:4 alloy. Further post-irradiation annealing leads to vigorous intermixing of Au and Ge followed by the formation of large, closely packed and oriented Au0:6Ge0:4 islands. These results have been discussed on the basis of irradiation induced effects followed by subsequent thermal annealing. � 2003 Elsevier B.V. All rights reserved.

Facile Synthesis of Semiconducting Ultrathin Layer of Molybdenum Disulfide

In this paper, we have reported a simple and efficient method for the synthesis of uniform, highly conducting single or few layer molybdenum disulfide (MoS2) on large scale. Scanning Electron Microscopy (SEM) and High Resolution Transmission Electron Microscopy (HRTEM) have been used for the confirmation of mono or few layered nature of the as-synthesized MoS2 sheets. X-ray Photoelectron Spectroscopy (XPS), X-Ray Diffraction (XRD) and Raman Spectroscopy have also been used to study the elemental, phase, and molecular composition of the sample. Optical properties of as-synthesized sample have been probed by measuring absorption and photoluminescence spectra which also compliment the formation of mono and few layers MoS2 Current-voltage (I-V ) characteristics of as-synthesized sample in the pellet form reveal that MoS2 sheets have an ohmic character and found to be highly conducting. Besides characterizing the as-synthesized sample, we have also proposed the mechanism and factors which play a decisive role in formation of high quality MoS2 sheets.

Adsorption of Ru, Ce and Eu radionuclides within naturally precipitated polycrystalline calcium carbonate under acidic environment

Abstract106Ru, 144Ce and 152+154Eu radiotracers sorption experiments (pH: 1–6) have been carried out with polycrystalline columnar/microcrystalline calcite and aragonite obtained from a stalagmite of Dharamjali cave, India. The different domains of the sample were powdered and thoroughly studied using electron microscopic and X-ray spectroscopic techniques. Both 106Ru and 144Ce exhibited higher sorption within calcite varieties compared to aragonite and increased with rising pH, while it showed reverse relation in case of 152+154Eu. Further, it is noted that aragonite offers the highest Kd values for 152+154Eu, whereas 106Ru and 144Ce prefer calcite.