1,512 research outputs found
Health risks of irrigation with untreated urban wastewater in the southern Punjab, Pakistan
Irrigation water / Water quality / Water reuse / Waste waters / Risks / Public health / Diseases / Farmers / Pakistan / Southern Punjab / Haroonabad
Study of interface asymmetry in InAsâGaSb heterojunctions
We present reflection high energy electron diffraction, secondary ion mass spectroscopy, scanning tunneling microscopy and xâray photoelectron spectroscopy studies of the abruptness of InAsâGaSb interfaces. We find that the interface abruptness depends on growth order: InAs grown on GaSb is extended, while GaSb grown on InAs is more abrupt. We first present observations of the interfacial asymmetry, including measurements of band alignments as a function of growth order. We then examine more detailed studies of the InAsâGaSb interface to determine the mechanisms causing the extended interface. Our results show that Sb incorporation into the InAs overlayer and As exchange for Sb in the GaSb underlayer are the most likely causes of the interfacial asymmetry
Scanning tunneling microscopy of lnAs/GaSb superlattices: Subbands, interface roughness, and interface asymmetry
Scanning tunneling microscopy and spectroscopy is used to characterize InAs/GaSb superlattices, grown by molecular-beam epitaxy. Roughness at the interfaces between InAs and GaSb layers is directly observed in the images, and a quantitative spectrum of this roughness is obtained. Electron subbands in the InAs layers are resolved in spectroscopy. Asymmetry between the interfaces of InAs grown on GaSb compared with GaSb grown on In As is seen in voltage-dependent imaging. Detailed
spectroscopic study of the interfaces reveals some subtle differences between the two in terms of their valence-band onsets and conduction-band state density. These differences are interpreted in a model in which the GaSb on InAs interface has an abrupt InSb-like structure, but at the InAs on GaSb interface some Sb grading occurs into the InAs overlayer
Urban wastewater: A valuable resource for agriculture - A case study from Haroonabad, Pakistan
Waste waters / Irrigation water / Water reuse / Economic analysis / Soil properties / Households / Water availability / Water use / Water quality / Groundwater / Public health / Risks / Case studies
Effects of hydrogen on the morphology and electrical properties of GaN grown by plasma-assisted molecular-beam epitaxy
We study the effect of introducing hydrogen gas through the rf-plasma source during plasma-assisted molecular-beam epitaxy of GaN(0001). The well-known smooth-to-rough transition that occurs for this surface as a function of decreasing Ga flux in the absence of H is found to persist even with H present, although the critical Ga flux for this transition increases. Under Ga-rich conditions, the presence of hydrogen is found to induce step bunching (facetting) on the surface. Conductive atomic force microscopy reveals that leakage current through dislocation cores is significantly reduced when hydrogen is present during the growth
Friedel Oscillation-Induced Energy Gap Manifested as Transport Asymmetry at Monolayer-Bilayer Graphene Boundaries
We show that Friedel charge oscillation near an interface opens a gap at the
Fermi energy for electrons with wave vectors perpendicular to the interface. If
the Friedel gaps on two sides of the interface are different, a nonequlibrium
effect - shifting of these gaps under bias - leads to asymmetric transport upon
reversing the bias polarity. The predicted transport asymmetry is revealed by
scanning tunneling potentiometry at monolayer-bilayer interfaces in epitaxial
graphene on SiC (0001). This intriguing interfacial transport behavior opens a
new avenue towards novel quantum functions such as quantum switching.Comment: accepted for publication in PR
Prevalence of intestinal parasites in the southern Punjab, Pakistan
Public health / Diseases / Irrigation programs / Villages / Households / Waste waters / Sanitation / Pakistan / Southern Punjab / Bahawalnagar District / Hakra / Haroonabad
Sub-nanosecond, time-resolved, broadband infrared spectroscopy using synchrotron radiation
A facility for sub-nanosecond time-resolved (pump-probe) infrared
spectroscopy has been developed at the National Synchrotron Light Source of
Brookhaven National Laboratory. A mode-locked Ti:sapphire laser produces 2 ps
duration, tunable near-IR pump pulses synchronized to probe pulses from a
synchrotron storage ring. The facility is unique on account of the broadband
infrared from the synchrotron, which allows the entire spectral range from 2
cm-1 (0.25 meV) to 20,000 cm-1 (2.5 eV) to be probed. A temporal resolution of
200 ps, limited by the infrared synchrotron-pulse duration, is achieved. A
maximum time delay of 170 ns is available without gating the infrared detector.
To illustrate the performance of the facility, a measurement of electron-hole
recombination dynamics for an HgCdTe semiconductor film in the far- and mid
infrared range is presented.Comment: 11 pages with 9 figures include
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