S. V. S. Nageswara Rao

Studies of electronic sputtering of fullerene under swift heavy ion impact

The present work reports the dependence of electronic sputtering on thickness of fullerene film. The energetic ions of 200 MeV Au15+ are taken from NSC Pelletron at New Delhi and the Tandem accelerator at Munich. On-line elastic recoil detection analysis (ERDA) with ΔE–E telescope detector is used to determine the electronic sputtering yield. We observed systematic decrease in sputtering yield of carbon with increase in film (C60/silicon) thickness.

dE/dx measurements for heavy ions with Z = 6-29 in polycarbonate

Abstract d E /d x measurements for heavy ions with Z =6–29 in the polycarbonate (C 16 H 14 O 3 ) absorber in the energy range ∼0.3–3.0 MeV/u have been carried out utilizing the Pelletron accelerator facility at Nuclear Science Centre, New Delhi, India. The experimentally measured stopping power values have been compared with those calculated using Lindhard, Scharff and Schiott theory, Northcliffe and Schilling, Ziegler et al. (with and without bonding corrections) and extended Hubert et al. formulations. Merits and demerits of these formulations are highlighted.

Synthesis, characterization and radiation damage studies of high-k dielectric (HfO2) films for MOS device applications

The current trend in miniaturization of metal oxide semiconductor devices needs high-k dielectric materials as gate dielectrics. Among all the high-k dielectric materials, HfO2 enticed the most attention, and it has already been introduced as a new gate dielectric by the semiconductor industry. High dielectric constant (HfO2) films (10 nm) were deposited on Si substrates using the e-beam evaporation technique. These samples were characterized by various structural and electrical characterization techniques. Rutherford backscattering spectrometry, X-ray reflectivity, and energy-dispersive X-ray analysis measurements were performed to determine the thickness and stoichiometry of these films. The results obtained from various measurements are found to be consistent with each other. These samples were further characterized by I–V (leakage current) and C–V measurements after depositing suitable metal contacts. A significant decrease in the leakage current and the corresponding increase in device capacitance are observed when these samples were annealed in oxygen atmosphere. Furthermore, we have studied the influence of gamma irradiation on the electrical properties of these films as a function of the irradiation dose. The observed increase in the leakage current accompanied by changes in various other parameters, such as accumulation capacitance, inversion capacitance, flat band voltage, mid-gap voltage, etc., indicates the presence of various types of defects in irradiated samples.

Development of a large area two-dimensional position sensitive ΔE−E detector telescope for material analysis

A large area two-dimensional position sensitive detector telescope has been designed and fabricated at NSC, New Delhi for performing ERDA based material characterization experiments. This gas ionization detector is working well with position resolution better than 2 mm and good z-separation in both high and low mass regions. Large solid angle is a pre-request to minimize the possible unwanted radiation damage during the measurement. The consequent kinematic broadening has been corrected by recording the position information. Two-dimensional position sensitivity has also been obtained. Possibility of controlled modification is shown in this work.

Ion beam characterization and engineering of strain in semiconductor multi-layers

Abstract The objective of this work is to measure and engineer the strain in III–V compound semiconductor multi-layers using ion beams, which leads to spatial band-gap tuning for the integration of optoelectronics devices. Strained layer superlattices have been of unique interest due to their ability to tune the band gap, which depends on the strain at the interface. Therefore the strain measurements at the interface are of great interest. A large area two-dimensional positions sensitive Δ E − E detector telescope and a fully automated high energy channeling facility have been developed at NSC, New Delhi. An overview of the series of ERDA, RBS, Channeling, HRXRD and ion beam mixing experiments performed in this direction will be discussed in this paper.

Ion beam studies in strained layer superlattices

Abstract The potential device application of semiconductor heterostructures and strained layer superlattices has been highlighted. Metal organic chemical vapour deposition grown In 0.53 Ga 0.47 As/InP lattice-matched structure has been irradiated by 130 MeV Ag 13+ and studied by RBS/Channelling using 3.5 MeV He 2+ ions. Ion irradiation seems to have induced a finite tensile strain in the InGaAs layer, indicating thereby that ion beam mixing occurs at this energy. Other complementary techniques like high resolution XRD and STM are needed to conclude the structural modifications in the sample.

Gamma irradiation-induced effects on the electrical properties of HfO2-based MOS devices

ABSTRACT Hafnium Oxide (HfO2) thin films were synthesized by e-beam evaporation and Radio frequency magnetron sputtering techniques. Au/HfO2/Si-structured Metal Oxide Semiconductor capacitors have been fabricated to study the effects of gamma irradiation on the electrical properties, leakage current versus voltage (I–V) and capacitance versus voltage (C–V) characteristics, as a function of irradiation dose. Systematic increase in leakage current as well as accumulation capacitance has been observed with increase in the irradiation dose. The influence of gamma irradiation and pre-existing defects on the evolution of oxide and interface traps have been studied in detail.

Ion channeling, high resolution x-ray diffraction and Raman spectroscopy in strained quantum wells

InGaAs strained epitaxial layers on GaAs are of considerable interest in semiconductor devices. An important feature is the critical thickness of the epitaxial layer beyond which relaxation occurs, affecting the device performance. With this in view, a series of such structures have been grown by organometallic vapor phase epitaxy and characterized by ion channeling, high resolution x-ray diffraction and Raman spectroscopy. The results of these three techniques are compared for the samples in this study which are fully strained, nominally and by experimental measurements. Beam steering effect that occurs at low energy channeling is also addressed.

Studies on linear, nonlinear optical and excited state dynamics of silicon nanoparticles prepared by picosecond laser ablation

We report results from our studies on the fabrication and characterization of silicon (Si) nanoparticles (NPs) and nanostructures (NSs) achieved through the ablation of Si target in four different liquids using ∼2 picosecond (ps) pulses. The consequence of using different liquid media on the ablation of Si target was investigated by studying the surface morphology along with material composition of Si based NPs. The recorded mean sizes of these NPs were ∼9.5 nm, ∼37 nm, ∼45 nm and ∼42 nm obtained in acetone, water, dichloromethane (DCM) and chloroform, respectively. The generated NPs were characterized by selected area electron diffraction(SAED), high resolution transmission microscopy(HRTEM), Raman spectroscopic techniques and Photoluminescence(PL) studies. SAED,HRTEM and Raman spectroscopy data confirmed that the material composition was Si NPs in acetone, Si/SiO2 NPs in water, Si-C NPs in DCM and Si-C NPs in chloroform and all of them were confirmed to be polycrystalline in nature. Surface morphological information of the fabricated Si substrates was obtained using the field emission scanning electron microscopic (FESEM) technique. FESEM data revealed the formation of laser induced periodic surface structures (LIPSS) for the case of ablation in acetone and water while random NSs were observed for the case of ablation in DCM and chloroform. Femtosecond (fs) nonlinear optical properties and excited state dynamics of these colloidal Si NPs were investigated using the Z-scan and pump-probe techniques with ∼150 fs (100 MHz) and ∼70 fs (1 kHz) laser pulses, respectively. The fs pump-probe data obtained at 600 nm consisted of single and double exponential decays which were tentatively assigned to electron-electron collisional relaxation ( 1 ps). Large third order optical nonlinearities (∼10−14 e.s.u.) for these colloids have been estimated from Z-scan data at an excitation wavelength of 680 nm suggesting that the colloidal Si NPs find potential applications in photonic devices.

Quantum description for the effects of strained layered superlattices on channeling radiation

Abstract The transverse motion of relativistic electrons (e − ) and positrons (e + ) during their motion along the crystallographic channels is quantized and the spontaneous transitions among these energy levels lead to what is known as channeling radiation. Quantum mechanical formulation is developed for dechanneling of these light particles, by incorporating the effects of deformations across the interfaces of the strained multi-layered structures. Simple harmonic type (one dimensional hydrogen atom type) potential is used to describe the transverse motion of planar-channeled positrons (electrons). In addition, the transitions among these bound states are considered for e − , e + and the corresponding radiation characteristics like initial populations and the re-distribution due to the strain are studied in quantum mechanical framework. Channeling angular scans are obtained using the simple quantum mechanical concepts.