ABSTRACT
The existence of barrier inhomogeneities at metal-semiconductor interfaces is believed to be one of the reasons for the non-ideal behaviour of Schottky contacts. In general, barrier inhomogeneities are modelled using a Gaussian distribution of barrier heights of nanoscale patches having low and high barrier heights, and the standard deviation of this distribution roughly estimates the level of barrier inhomogeneities. In the present work, we provide direct experimental evidence of barrier inhomogeneities by performing electrical characterizations on individual nanoscale patches and, further, obtaining the magnitude of these inhomogeneities. Localized current-voltage measurements on individual nanoscale patches were performed using conducting atomic force microscopy (CAFM) whereas surface potential variations on nanoscale dimensions were investigated using Kelvin probe force microscopy (KPFM) measurements. The CAFM measurements revealed the distribution of barrier heights, which is attributed to surface potential variations at nanoscale dimensions, as obtained from KPFM measurements. The present work is an effort to provide direct evidence of barrier inhomogeneities, finding their origin and magnitude by combining CAFM and KPFM techniques and correlating their findings.
ABSTRACT
The electrical behaviour of Schottky barrier diodes realized on vertically standing individual GaN nanorods and array of nanorods is investigated. The Schottky diodes on individual nanorod show highest barrier height in comparison with large area diodes on nanorods array and epitaxial film which is in contrast with previously published work. The discrepancy between the electrical behaviour of nanoscale Schottky diodes and large area diodes is explained using cathodoluminescence measurements, surface potential analysis using Kelvin probe force microscopy and 1ow frequency noise measurements. The noise measurements on large area diodes on nanorods array and epitaxial film suggest the presence of barrier inhomogeneities at the metal/semiconductor interface which deviate the noise spectra from Lorentzian to 1/f type. These barrier inhomogeneities in large area diodes resulted in reduced barrier height whereas due to the limited role of barrier inhomogeneities in individual nanorod based Schottky diode, a higher barrier height is obtained.
ABSTRACT
INTRODUCTION: Thalassemia is one of the most common genetic disorder of hemoglobin synthesis in Jammu region. Although RBC transfusion is life saving for these patients, it may be associated with some complications like RBC alloimmunization. Thus, the aim of this study was to determine the frequency of alloimmunization and the most common alloantibodies involved. MATERIAL AND METHODS: This was a descriptive study involving a total of 70 thalassemic patients in the age range of 2-17 years receiving regular blood transfusions, registered at SMGS Blood Bank, Jammu. Relevant clinical and laboratory data was collected with reference to age at the start of transfusions, total number of transfusions received and splenectomy status. Antibodies screening, antibody identification, and cross matching was done on allpatient samples included in the study, during the period between November 2009 and October 2010. RESULTS: In this study, a total of six alloantibodies six patients (8.5%) and one autoantibody (1.42%) was detected. All identified alloantibodies belonged to Rh system (i.e. anti-E, in 3 patients (50%), anti D, in one patient (16.66%)) and Kell system (anti-K, in two patients (33.34%)). Higher frequency of alloimmunization was found, with increase in number of transfusions and in those who received transfusions after 1 year of age. Alloimmunization was not significantly associated with gender and splenectomy status (P-value > 0.05). CONCLUSION: Red cell alloantibodies developed in 8.5% of thalassemic patients and 1.42% had autoantibodies. The most common alloantibodies identified were anti Rh system antibodies (anti-E and anti-D) present in 50% and 16.66% of patients respectively. Alloimmunization is not an uncommon problem faced by blood banks and finding compatible units for regularly transfused thalassemic patients may become very difficult. In order to reduce alloimmunization, a policy for performing extended red cell phenotyping of these patients is essential and at least antigen E and Kell negative blood should be provided for transfusion to these patients.
