S.A. Khan

Synthesis and characterization of ZnO thin film grown by electron beam evaporation

Highly transparent, conducting, highly oriented, and almost single phase ZnO films have been deposited by simple e-beam evaporation method, and the deposition parameters were optimized. The films were prepared by (a) evaporation of ZnO at different substrate temperatures and (b) evaporation of ZnO at room temperature and subsequent annealing of the films in oxygen ambient at different temperatures. The characterizations of the film were performed by optical absorption spectroscopy (UV-visible), Fourier transform infrared spectroscopy, resistivity measurement, transmission electron microscopy (TEM), photoluminescence, and x-ray diffraction measurement. Absorption spectra revealed that the films were highly transparent and the band gap of the pre- and postannealed films was in good agreement with the reported values. The band gap of the films increases on increasing the substrate temperature as well as annealing temperature, whereas the resistivity of the film decreases with substrate temperature and increa...

Formation of self-affine nanostructures on ZnO surfaces by swift heavy ions

The topography evolution using the high energy heavy ion irradiation revealed the fact that ion bombardment produces self-affine nanostructures, creating peculiar surface morphologies and regular structures on the surface of the ZnO thin film at certain fluences. The self-affine nanopatterns produced on the surface of ZnO thin film under swift heavy ion irradiation are different types of nanostructures such as nanodimensional grains aligned like a linear array. Scanning probe microscopy is used for investigating the ZnO surfaces and UV-visible spectroscopy for studying the effect of surface modification on optical properties. The two-dimensional power spectral density of the irradiated ZnO thin films have been evaluated for each image to extract the value of growth factor (β) and roughness exponent (α). The exponent n increases from 2.2 to 4.0 up to a critical value of fluence and beyond which it decreases. These values suggest that ion assisted∕induced diffusion process plays a crucial role in the evolution of self-affine nanostructures on ZnO surface.The topography evolution using the high energy heavy ion irradiation revealed the fact that ion bombardment produces self-affine nanostructures, creating peculiar surface morphologies and regular structures on the surface of the ZnO thin film at certain fluences. The self-affine nanopatterns produced on the surface of ZnO thin film under swift heavy ion irradiation are different types of nanostructures such as nanodimensional grains aligned like a linear array. Scanning probe microscopy is used for investigating the ZnO surfaces and UV-visible spectroscopy for studying the effect of surface modification on optical properties. The two-dimensional power spectral density of the irradiated ZnO thin films have been evaluated for each image to extract the value of growth factor (β) and roughness exponent (α). The exponent n increases from 2.2 to 4.0 up to a critical value of fluence and beyond which it decreases. These values suggest that ion assisted∕induced diffusion process plays a crucial role in the evolut...

Softening of phonons by lattice defects and structural strain in heavy ion irradiated nanocrystalline zinc oxide films

Origin of the Raman mode in nanocrystalline zinc oxide in the vicinity of A1 (LO) phonon mode induced by energetic heavy ions is reported. The evolution of this mode in the irradiated films is ascribed to the effect of disorder and the high density of lattice defects induced by irradiation. The presence of such defects is confirmed by the reduction in the intensity of E2 (high) mode and band bending of the near band edge absorption. A softening of the evolved Raman mode with increasing in ion fluence is also observed. This softening cannot be attributed to spatial confinement of phonons, as the sizes of the crystallites are large. Therefore, it is explained in terms of the combined effects of phonon localization by lattice defects and the structural strain in the lattice induced by electronic energy loss transferred by energetic heavy ions.

Enhancement of band gap and photoconductivity in gamma indium selenide due to swift heavy ion irradiation

γ‐In2Se3 thin films prepared at different annealing temperatures ranging from 100to400°C were irradiated using 90MeV Si ions with a fluence of 2×1013ions∕cm2. X-ray diffraction analysis proved that there is no considerable variation in structural properties of the films due to the swift heavy ion irradiation. However, photosensitivity and sheet resistance of the samples increased due to irradiation. It was observed that the sample, which had negative photoconductivity, exhibited positive photoconductivity, after irradiation. The negative photoconductivity was due to the combined effect of trapping of photoexcited electrons, at traps 1.42 and 1.26eV, above the valence band along with destruction of the minority carriers, created during illumination, through recombination. Photoluminescence study revealed that the emission was due to the transition to a recombination center, which was 180meV above the valence band. Optical absorption study proved that the defects present at 1.42 and 1.26eV were annealed out...

Tuberculosis of the foot and ankle in children.

Purpose. To report manifestations and management of tuberculosis of the foot and ankle in 21 children. Methods. Records of 12 girls and 9 boys aged 3 to 14 (mean, 7) years with tuberculosis of the foot and ankle were reviewed. The mean delay in presentation was 4.7 (range, 0.5–14) months. All the patients had local swelling, tenderness, and antalgic gait; 16 were limping; 5 had an antecedent trauma; 11 had an abscess; and 6 had a discharging sinus. The diagnosis was based on a smear positive for acid-fast bacilli (n=2), histopathology (n=15), or clinicoradiological findings (n=4). Nine patients had osteoarticular tuberculosis in other parts of the body. None had evidence of pulmonary tuberculosis. Lesions were classified into synovial (articular) and osseous. All 3 synovial lesions occurred in the ankle, 2 of which were at an advanced stage. Osseous lesions occurred in the calcaneus (n=5), metatarsal (n=5), talus (n=3), cuboid (n=3), medial cuneiform (n=1), and phalanx (n=1), and were sub-classified into stages 1 (n=3), 2 (n=5), and 3 (n=10) according to disease progression. All the patients were treated conservatively with splintage and chemotherapy. Results. The mean follow-up period was 21 (range, 7–51) months. All the 3 patients with stage 1 osseous lesions showed healing within 6 weeks and had complete recovery of function. Four of the 5 patients with stage 2 lesions also showed complete recovery of function and reformation of bony trabeculations; radiological incorporation of sequestrum was obvious by 6 months in most patients. In patients with stage 3 lesions, healing was delayed and there was residual alteration in bony architecture and joint changes. Sclerotic changes and joint involvement also increased the likelihood of poor outcomes. However, none of our patients had any residual tenderness or foot deformity at the final follow-up. Conclusion. Outcome after non-operative treatment is good, provided the lesions are treated early.

Smoothing, roughening and sputtering: the complex evolution of immiscible Fe/Bi bilayer system

In this work, swift heavy ion (SHI) induced surface smoothing, roughening and sputtering of thermally immiscible Fe/Bi bilayer system has been investigated. The pristine and irradiated samples were analysed by Rutherford backscattering spectrometry (RBS), grazing angle x-ray diffraction (XRD), atomic force microscopy and scanning electron microscopy including x-ray dispersive energy analyzer. RBS analysis revealed that steepness of the low energy edge of the Bi signal increases at a fluence of 3 ? 1013?ions?cm?2, beyond which the slope of the rear edge decreases. The increased steepness is due to smoothing induced at initial fluence; however, the decrease in the slope of rear edge beyond 3 ? 1013?ions?cm?2 fluence is a result of surface roughening. XRD reveals the increase in the crystalline nature of Bi after irradiation at 3 ? 1013?ions?cm?2. Irradiation at higher fluences from 6 ? 1013 to 1 ? 1014?ions?cm?2 leads to a decrease in the crystalline nature of Bi. Surface roughness of pristine and irradiated samples from AFM analysis revealed that initially roughness decreases with a fluence of 3 ? 1013?ions?cm?2. However, at higher fluences, beyond 3 ? 1013?ions?cm?2, the agglomeration of smaller grains has been observed due to the shear flow mechanism, which results in surface roughening. The observed behaviour of surface smoothing and roughening under SHI irradiation may be explained on the basis of the thermal spike model.

Studies of swift heavy ion induced colour centres in LIF thin films deposited on silica substrates

Swift heavy ion induced colour centres in polycrystalline LiF thin films deposited on silica substrate were studied. LiF thin films of 200 nm thickness, deposited by the electron beam evaporation method, and silica substrates were irradiated with 120 MeV Au9+ ions in the fluence range 5 × 1010–1 × 1013 ions cm−2. Optical absorption, photoluminescence (PL) and glancing angle x-ray diffraction (GAXRD) techniques were used for the characterization of the irradiated films. Optical absorption spectroscopy was performed on irradiated LiF films by using irradiated silica substrates as reference sample. The resulting spectra show three bands at 260 nm, 380 nm and 445 nm corresponding to F, F3 and F2 colour centres, respectively. Absorbance of colour centres increases with fluence and seems to saturate at higher fluences. PL spectra, performed by an excitation source of 442 nm, show two broad bands of F2 and colour centres. The intensity of both the centres increases upto 3 × 1011 ions cm−2 followed by some decrease. The GAXRD results show that the average grain size decreases systematically from 35 nm for the pristine film to 20 nm for the sample irradiated at a fluence of 1 × 1013 ions cm−2.

Large aneurysmal bone cyst of iliac bone in a female child: a case report

BackgroundSymptomatic aneurysmal bone cysts in pediatric age group with an expansile lesion in ilium is a rare occurrence.CaseAn 11-year-old female presented with a swelling over her right iliac region and numbness along the medial aspect of thigh. Clinicoradiological diagnosis was aneurysmal bone cyst confirmed on fine needle aspiration cytology. Excision curettage (wide margin excision of the soft tissue tumor and intralesional curettage in the region of acetabulum) of the tumor was performed in view of proximity to acetabular roof and endangered hip stability.ResultAt follow up of 18 months, the child has full painless range of movements in the hip joint with no recurrence.ConclusionsPelvic aneurysmal bone cysts are distinctly rare in pediatric age. The lesion was associated with an atypical symptom of numbness along the femoral nerve distribution. Hip stability and range of movements were major concern in this patient. Although many treatment options are described, surgical excision still remains the mainstay. In our case, we performed excision curettage, with good outcome.

Fast ion surface energy loss and straggling in the surface wake fields.

We have measured the stopping powers and straggling of fast, highly ionized atoms passing through thin bilayer targets made up of metals and insulators. We were surprised to find that the energy losses as well as the straggling depend on the ordering of the target and have small but significantly different values on bilayer reversal. We ascribe this newly found difference in energy loss to the surface energy loss field effect due to the differing surface wake fields as the beam exits the target in the two cases. This finding is validated with experiments using several different projectiles, velocities, and bilayer targets. Both partners of the diatomic molecular ions also display similar results. A comparison of the energy loss results with those of previous theoretical predictions for the surface wake potential for fast ions in solids supports the existence of a self-wake.

Investigation of swift heavy ion-induced mixing in metal/polymer systems

We have investigated swift heavy ion-induced mixing in Ni/Teflon and Au/Teflon systems using 120 MeV Au ions. Our earlier studies showed that the Ni/Teflon system exhibits strong interface mixing, as determined by Rutherford backscattering spectrometry (RBS). In the present work, the Ni/Teflon system is further studied by scanning electron microscopy and Fourier transform infrared spectroscopy. Moreover, RBS studies are extended to demonstrate interface mixing in the Au/Teflon system. The observed mixing is explained on the basis of the chemical activeness (or reactivity) of the metal/polymer systems leading to a chemical reaction. The chemical reaction occurs in the hot zone around the ion path between the Ni and reactive polymer species. Thermodynamic property bond dissociation energy has been taken into account for the reactivity of the systems.