Low-field mobility in an electrostatically confined 2D rectangular nanowire: effect of density of states and phonon confinement.

Transport in GaN-based nanoscale devices is of supreme importance for various applications. While the transport in bulk and two-dimensional (2D) structures is relatively well understood, understanding one-dimensional (1D) transport is still at its nascent stage. More importantly, the nanoscale structures may not operate at an explicit dimension of 2D and 1D. The understanding of the transport becomes limited on such an occasion. Here, we investigate the evolution of low-field mobility in GaN-based nanostructures for increasing quantum confinement in a uniform framework. We have used a split-gate architecture to change the degree of quantum confinement electrostatically. The low-field mobility is experimentally determined, which is then matched using scattering theory. It is shown that acoustic phonon, polar optical phonon, and scattering from piezoelectric fields dominate these devices. Contrary to intuition, the piezoelectric fields play the most determining role in low-field regimes. In addition, the evolving density of states and 2D phonon confinement, in addition to electron confinement, lead to a non-monotonic change in mobility. A decrease in the number of states near conduction band minima tends to increase mobility by reducing the number of final scattering states for the electrons. A larger overlap between confined electrons and phonons aggravates scattering and reduces mobility. These two competing effects can lead to many possible values for mobility during device operation.

Utility of Contrast-Enhanced Ultrasound in Differentiation between Benign Mural Lesions and Adenocarcinoma of Gallbladder.

BACKGROUND: Mural lesions of gallbladder on ultrasound (US) are often difficult to characterize as benign or malignant. PURPOSE: The aim of the study was to evaluate the role of contrast-enhanced US (CEUS) in characterization of gallbladder (GB) wall lesions and making distinction between benign wall thickening and GB adenocarcinoma, utilizing both quantitative and qualitative parameters. METHODS: A total of 26 patients with GB wall lesions detected on sonography underwent CEUS. Lesions were evaluated on the basis of morphological imaging features, enhancement pattern, dynamic real-time contrast uptake, and intralesional vascularity. RESULTS: Overall, 19 patients had final diagnosis of GB adenocarcinoma, whereas seven patients had benign etiology. CEUS has enabled the differentiation of nonenhancing tumefactive sludge from enhancing mural lesions, thus improving the accuracy of morphological assessment of lesions. The intactness of outer wall was better assessed on CEUS. The dynamic postcontrast assessment showed that carcinoma showed early washout of contrast compared to benign thickening (P = 0.002). Nonlayered mural enhancement or thick enhancing inner layer with nonenhancing thin outer layer was associated with adenocarcinoma. The classification of intralesional vascularity on CEUS was not helpful in distinguishing benign lesions and adenocarcinoma. CONCLUSION: CEUS can increase the diagnostic confidence in differentiation between benign mural lesions and adenocarcinoma of GB.