Browsing by Author "D.K. Avasthi"

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High energy heavy ion irradiation in semiconductors
(Elsevier Science Publishers B.V., 1999) P.C. Srivastava; S.P. Pandey; O.P. Sinha; D.K. Avasthi; K. Asokan
Pd/n-Si and Pd/n-GaAs devices have been irradiated from high energy (approximately 100 MeV) heavy ions of Au7+ (gold) and Si7+ (silicon) to study the irradiation effects in these junction devices on semiconductor substrates. The devices have been characterized from I-V and C-V studies for electronic flow characterization. It has been found that the devices become high resistive on the irradiation and the substrates change the conductivity type from n- to p- on the irradiation of fluence of approximately 1012-1013 ions/cm2. The change in conductivity type has been understood as a result of creation of deep acceptors on the irradiation.
Measurement of the transverse kinetic energies of argon recoil ions produced in 120 MeV Si8+-Ar collisions
(Springer New York, 1998) M.J. Singh; S.K. Goel; R. Shanker; D.O. Kataria; N. Madhavan; P. Sugathan; J.J. Das; D.K. Avasthi; A.K. Sinha
Measurements were carried out to deduce the transverse kinetic energies of highly charged argon recoil ions produced in single collisions of 120 MeV Si8+ ions with argon atoms in which the post collision charge states of the projectiles were not determined. A time of flight spectrometer was designed and fabricated to detect the charge states of recoils. Experimental procedures for optimizing the spectrometer for extraction, transmission and detection of recoils are described. A simple approach for determining the transverse kinetic energy of the recoil ions from FWHM of the peaks is reported. This method is shown to be independent of the choice of collision partners and requires only the knowledge of the physical values of "optimized parameters" of time-of-flight spectrometer used in the experiment. The transverse kinetic energy of the recoil ions determined from the present approach is found to vary from 0.03 eV for Ar+ to 4.02 eV for Ar10+. These values are compared with the results reported by earlier workers and are shown to follow a g2-behaviour up to a charge state q = 8+ of the recoil ions. © EDP Sciences Springer-Verlag 1998.
Pd/Si device characteristics on 100 MeV gold ions irradiation
(Elsevier Ltd, 1997) P.C. Srivastava; S.P. Pandey; D.K. Avasthi; K. Asokan
Pd/p-Si and Pd/n-Si devices were irradiated from 100 MeV gold (7+) ions for varying doses (∼ 1011-1013 ions cm-2). The devices were characterized from I-V and C-V studies. It has been found that there is a change of conductivity type i.e. from n to p at a probed depth of ∼ 8 μm which is approximately the stopping range of the gold ions in silicon. A deep acceptor state (∼ 0.61 eV above V.B. edge) with a peak density of ∼ 109 cm-2 is observed for p-type irradiated devices at ∼ 3 μm which is attributed to the displacement damage caused by the high energy heavy ion irradiation. © 1998 Elsevier Science Ltd. All rights reserved.
Recrystallization in polyvinylidene fluoride upon low fluence swift heavy ion impact
(2001) A. Biswas; R. Gupta; N. Kumar; D.K. Avasthi; J.P. Singh; S. Lotha; D. Fink; S.N. Paul; S.K. Bose
Thin films (9 μm) of polyvinylidene fluoride (PVDF) are irradiated by swift heavy ions (180 MeV Ag14+) in the fluence range 1 × 1010-1 × 1012ions/cm2 with an electronic linear energy transfer LET∼11 keV/nm. In sharp contrast to the previous results, the most characteristic crystalline asymmetric and symmetric "CH2" doublets (located at 3025 and 2985 cm-1), have shown remarkable increase in their respective Fourier transform infrared (FTIR) absorbance intensities upon low fluence ion impact (1010 ions/cm2). This increase in absorbance is in consonance with the simultaneous decrease of the transmission intensities of other crystalline bending vibration bands located at 532 (CF2 bending), 614, 796, and 975 cm-1 (all due to CH2 bending) at the similar ion fluence. It appears most probable from the results that, being a polar polymer, the molecular dipoles in PVDF forming a hydrogen bond network get realigned upon irradiation into a highly ordered state of chain molecules in the crystalline regions and create volume elements as crystallites. © 2001 American Institute of Physics.
Resonant electron tunneling in single quantum well heterostructure junction of electrodeposited metal semiconductor nanostructures using nuclear track filters
(Elsevier Science Publishers B.V., 1999) A. Biswas; D.K. Avasthi; Benoy K. Singh; S. Lotha; J.P. Singh; D. Fink; B.K. Yadav; B. Bhattacharya; S.K. Bose
We report on resonant electron tunneling through a Cu-Se heterostructure junction grown electrochemically in the submicron size pores (0.8 μm) of a nuclear track filter (Polycarbonate). The prominent feature of negative differential resistance (NDR) has been observed in the current-voltage (I-V) characteristic of the so-fabricated array of resonant tunneling diodes (RTDs) even at room temperature, along with a significant peak to valley current ratio (2.5) of the resonance. Tunneling structures of the nanofabricated RTDs around zero bias are also observed at room temperature. Our results show that the low cost and relatively easy electrodeposition method can be a very effective way to prepare resonant quantum tunneling devices, using the pores of nuclear track filters.
SCORPION: A system for coincidences between recoil and projectile ions at NSC, New Delhi
(Indian Academy of Sciences, 1997) M.J. Singh; S.K. Goel; R. Shanker; D.O. Kataria; N. Madhavan; P. Sugathan; J.J. Das; D.K. Avasthi; A.K. Sinha
An on-line facility to measure coincidences between the recoil ions and the scattered projectiles (SCORPION) has been designed, fabricated and commissioned at Nuclear Science Centre (NSC), New Delhi. The facility consists of a four jaw slit assembly, a time of flight (TOF) spectrometer, a parallel plate electrostatic charge analyser and a one dimensional position sensitive parallel plate avalanche counter (PPAC). Details of the design and working principles of various components and the test results obtained for the Siq+-Ar collision system are presented to highlight the performance of the system. A multiple loss of up to four electrons has been observed for 60 MeV Si4+ ions colliding with argon atoms in a single collision condition. Spectra of recoil ions detected in coincidence with a particular charge state of the scattered projectile show a bell shaped distribution as a function of the recoil charge state (r) for the electron loss events. However, the yield of recoil ions drops as r increases for the direct ionization channel. Also for electron loss, the peak of the recoil ion distribution is seen to shift to a higher recoil charge state as the number of lost electrons from the projectile increases.
Study of hydrogen in hydrogenated Pd/semiconductor device by ERDA
(1996) P.C. Srivastava; U.P. Singh; S.P. Pandey; D.K. Avasthi
The content of hydrogen in Pd/n-Si, Pd/p-Si, and Pd/p-GaAs devices have been measured, both in the semiconducting substrates and the palladium thin film deposited on p-type Si, n-type Si and p-type GaAs, by ERDA (Elastic Recoil Detection Analysis) using 55 Mev Si ions. The samples were hydrogenated by keeping them in the atmosphere of molecular hydrogen at a pressure of 1 aim at room temperature. It is found that there is a fairly large amount of hydrogen in the semiconductor substrates and the palladium overlayers. It seems that the hydrogen absorbed by the palladium overlayers diffuses to the semiconducting substrates through the Pd/Semiconductor interface. It is found that the p-type semiconducting substrates accommodate more hydrogen than n-type semiconducting substrates in such hydrogenated samples. Copyright © 1996 Elsevier Science Ltd.
Study on evolution of gases from Mylar under ion irradiation
(Elsevier, 1998) D.K. Avasthi; J.P. Singh; A. Biswas; S.K. Bose
A swift heavy ion produces a zone of damage area along its path through polymers. The dominant gases hydrogen, carbon monoxide and ethylene released under 180 MeV Ag ion irradiation of Mylar i.e. polyethylene terephthalate (PET) were studied. The evolved gases were monitored as a function of ion fluence by quadrupole mass analyzer (QMA). The logarithmic decrease in the release of gaseous products provide an estimate of track diameter. It also indicates two zones of varying damages within the ion track. © 1998 Elsevier Science B.V. All rights reserved.