Ak Sharma

Electrical properties of amorphous and crystalline InSb and InAs thin films

Abstract Amorphous films of indium antimonide (0.02–0.26 μm) and indium arsenide (0.03–0.3 μm) were formed on goldseal glass, freshly cleaved mica and NaCl substrates by using a “flash evaporation” technique. The post-deposition heat treatment was carried out on these films when the amorphous → crystalline transformation was observed. The transformation was characterized by a sudden and large fall in the resistance of the film at a particular temperature depending on the thickness. This transformation was confirmed by transmission electron micrographs and diffraction patterns obtained on the films before and after heat treatment. The transformation temperatures lie between 495–525 K for indium antimonide and 550–575 K for indium aresenide, for the thickness range involved in our investigations. The electrical conductivity measurements showed a temperature dependent activation in the high temperature region and hopping conduction in the low temperature region (Motts theory). The activation energies, at different temperatures for various thicknesses were calculated and presented. While no Hall mobility could be observed in as-deposited films, very low mobilities were observed in annealed thick films (t > 2000 A). Thermoelectric power for InSb films was found to vary from 0.075–0.17 mV/K for films of thickness ranging from 1000–2300 A, whereas for InAs films, its value varied from 0.09–0.27 mV/K for the thickness range, 1250–2500 A. These measurements indicated the conductivity to be n-type and supported the hopping conduction mechanism observed in low temperature conductivity measurements.

Physical investigations on amorphous films of some semiconducting compounds

Abstract The electrical conductivity, Hall effect and thermo-electric power of variable thickness GaSb, InSb, InAs, InTe, InSe and In0.5Ga0.5Sb films formed on glass, mica and NaCl substrates held at room temperature in a vacuum of approximately 5 × 10−6 torr, are discussed in this paper. All the films were found to be amorphous in nature with the presence of microcrystals in the films of some materials like InAs. A systematic post-deposition heat treatment was done on these films when the amorphous - crystalline transformation was observed. This transformation was characterised by a sudden and steep fall in the resistance of the film at a particular temperature depending on the thickness. This transformation was confirmed by selected area diffraction patterns obtained on the films before and after heat-treatment. The electrical conductivity measurements below transition temperature showed that the relation exp ( −Δ E kT ) does not hold over a significant range. The measurements at low temperatures obeyed T − 1 4 law. Hall effect, thermoelectric power and optical absorption measurements were made in both amorphous and crystalline phases.

LIVER RESECTION FOR METASTASES FROM COLORECTAL CANCER

Five percent of patients with liver secondaries from colorectal carcinoma are potentially resectable and several studies have demonstrated significantly improved survival following resection. Two hundred and ten patients operated for colorectal carcinoma were followed up. Computed tomography confirmed potentially resectable metastasis to the liver in 38. On exploration 18 patients who had 4 or less hepatic metastases and no extrahepatic disease, underwent resection of their secondaries. Fourteen were males and 4 females with a mean age of 43.5 (SD 13.6, range 18-72) years. Ten patients presented with synchronous liver metastasis and 8 had metachronous disease. There was no post-operative mortality. All 18 have been followed up. for a median period of 23.5 (range 12-38) months. Seven patients are alive and well with no evidence of recurrence at a median period of 28 months (survival 39%). Four are alive with local recurrence in the liver. Median time to recurrence was 22 months. Seven patients have died of disseminated disease. The disease free survival at 28 months is 39% and the overall survival 61%. A close follow-up protocol for all patient undergoing curative surgery for colorectal cancer is essential, if such patients are to be selected early.

Actinomycetoma of hand and foot.

Mycetoma refers to the chronic suppurative pathological process in which exogenous etiological agents generate pus and sulphur like granules. These agents belong to two groups: true fungi and the actinomycetes. Eumycetoma (caused by fungi) and actinomycetoma (caused by actinomycetes) must be distinguished as their treatment is different. These causative agents are introduced into the skin by minor trauma. Most cases of mycetoma occur in tropical regions such as Asia, Africa and Central and South America but this disease is endemic in India. Nocardia brasiliensis is the most common isolate found in India [1]. The pathologic process is characterized by tumefaction, subcutaneous nodules and in most cases discharging sinuses that drain exudate containing granules. It gradually invades the tissues and bones causing a functional disability. Bone involvement depends on the duration of the disease and the causative agent. Here we present two cases of actinomycetoma, one affecting the hand and the other the foot. The pathogenesis, radiological features and the therapeutic management of this entity are reviewed. Case Report A 32-year old individual, tailor by profession reported with a gradually increasing painless swelling of the left hand associated with progressive development of multiple discharging sinuses, of 8 years duration. He did not give any positive history of direct prick or any injury. Local examination revealed a diffuse swelling of the left hand involving mainly the palm and the dorsum, sparing the fingers and thumb. The feel of the swelling was woody and there were multiple discharging sinuses present all over the dorsum and palmar aspect of the hand (Fig 1). The granules contained in the discharge were yellowish in colour. 1–2 mm in size, multiple and discharging intermittently. The surrounding skin was thickened, unhealthy and hyperpigmented. Systemic examination was normal. There was no evidence of any distant spread. Gram stain of the granules showed gram positive branching bacillary filaments (1μ in diameter) having a distinct sunray appearance, diagnostic of actinomycetoma. Repeated culture both under aerobic and anaerobic conditons did not grow any organism.(the patient gave history of prior antibiotic treatmment). X-ray of the left hand showed a patchy resoiption of all the metacarpal bones with lucent filling defects and thickened cortex with partial destruction of the carpal bones (Fig 2). There was no involvement of the small joints. He was managed with high dosage of penicillin along with dapsone (DDS) and rifampicin to which he responded well. The chemotherapy was then switched over to dapsone (DDS) and trimethoprim-sulfamethoxazole combination at the time of discharge, for the patients convenience. He is under close follow up. Open in a separate window Fig. 1 Palmar view of the left hand showing massive soft tissue swelling, subcutaneous nodules and multiple discharging sinuses.

ROLE OF RADIOLOGY IN THE DIAGNOSIS AND MANAGEMENT OF HYDATID DISEASE OF THE LIVER

Twelve patients with hepatic hydatid cysts were studied for radiological features. All had undergone plain radiography abdomen (AP view) and ultrasound study. Six patients had undergone computerised tomography (CT). On plain radiography, curvilinear calcification was the only important positive finding (3 cases). Ultrasonographic findings were - single thick walled cyst (2 cases), multiple cysts (3 cases), multilocular cysts (3 cases), internal septum/floating membrane (2 cases), hydatid sand (1 case), and ill-defined cyst (1 case). CT findings of 6 patients were : single cyst (2 cases), multiple cyst (1 case), multilocular cysts (1 case), and ill-defined cysts (2 cases).

Hall mobility of evaporated InAs films prepared at different temperatures

The behaviour of the Hall mobilityμH and the carrier concentrationn have been investigated on InAs films as a function of thickness, substrate temperature and annealing treatment. While the Hall mobility showed an increasing trend with substrate temperature and thickness for both as-deposited and annealed films, the carrier concentration for asdeposited films showed a maximum at a particular substrate temperature range while that for annealed films showed a monotonous decreasing behaviour.