An investigation of the organisational features, commodities and situations associated with contract farming and outgrower schemes in Sub Saharan Africa and of the factors which are critical to their successful operation

This desk review is funded under ODA's Crop Post Harvest Programme. The framework for the research is the improvement of marketing and financing services for traders and farmers in liberalising economies. The Terms of Reference required the researcher to identify the types of scheme, the commodities and situations for which contract farming/outgrower schemes are appropriate as well as the critical success factors

Analysis of defect structure in silicon. Characterization of samples from UCP ingot 5848-13C

Statistically significant quantitative structural imperfection measurements were made on samples from ubiquitous crystalline process (UCP) Ingot 5848 - 13 C. Important trends were noticed between the measured data, cell efficiency, and diffusion length. Grain boundary substructure appears to have an important effect on the conversion efficiency of solar cells from Semix material. Quantitative microscopy measurements give statistically significant information compared to other microanalytical techniques. A surface preparation technique to obtain proper contrast of structural defects suitable for QTM analysis was perfected

Photoluminescence of Shallow Acceptors in Epitaxial AlGaAs

Journal ArticleThe low-temperature (2 K) photoluminescence (PL) of AlxGa1-xAs (0<x<0.25 was studied in an effort to characterize shallow acceptors in material grown by organometallic vapor phase epitaxy and liquid phase epitaxy techniques. The dominant shallow acceptor in nominally undoped AlxGa1-xAs specimens grown by both techniques was identified as Carbon, with EA=26 meV for x=0. EA was observed to increase with increasing x to ~36 meV at x~0.20, as expected for an effective mass like center where EA [proportional][m*(x)/epsilon(x)2]. The PL peak due to the conduction band to acceptor transition was found to become progressively broader with increasing x, which is attributed to increasing donor plus acceptor concentration. The acceptor Ge was studied in intentionally doped LPE specimens. It also behaves as a simple effective masslike center, with EGe~40 meV for GaAs and 55 meV for Al0.2Ga0.8As, contrary to earlier reports of anomalous behavior

It\u27s Raining in the Archives: Practical Lessons and Impactful Results from Moving an Academic Archives

This article explores the move of the Central Washington University Archives and Special Collections (CWUASC) to a new location from the fourth floor to the second floor of the James E. Brooks Library in 2018. The history of the CWUASC, reasons for the move, the planning and designing of the new space, the actual move of the collection by the archives staff, lessons learned, and the impact of the move in reaching a larger audience of faculty, staff, students, and the general public are described. A review of literature on other moves of archives and special collections is also provided

Analysis of defect structure in silicon. Characterization of SEMIX material. Silicon sheet growth development for the large area silicon sheet task of the low-cost solar array project

Statistically significant quantitative structural imperfection measurements were made on samples from ubiquitous crystalline process (UCP) Ingot 5848 - 13C. Important correlation was obtained between defect densities, cell efficiency, and diffusion length. Grain boundary substructure displayed a strong influence on the conversion efficiency of solar cells from Semix material. Quantitative microscopy measurements gave statistically significant information compared to other microanalytical techniques. A surface preparation technique to obtain proper contrast of structural defects suitable for quantimet quantitative image analyzer (QTM) analysis was perfected and is used routinely. The relationships between hole mobility and grain boundary density was determined. Mobility was measured using the van der Pauw technique, and grain boundary density was measured using quantitative microscopy technique. Mobility was found to decrease with increasing grain boundary density

Radiative pair transitions in p-type ZnSe:Cu crystals

Journal ArticleShallow levels with an ionization energy of 0.012 eV play an important role in the photoelectronic properties of p-type ZnSe:Cu crystals. These levels exhibit the characteristics of the higher-lying member of an imperfection pair involved in luminescence emission, as well as of a trap determining long-time decay rates of luminescence and photoconductivity, and of a center causing low-temperature reduction of free-electron lifetime

A review of the storage and marketing systems of major food grains in Northern Ghana

This study was conducted to determine the constraints to maintaining good quality grain in store on the farm and to marketing produce surplus to food needs. Two regions were visited, Northern Region, where maize is the main cereal staple, and Upper East, where maize is replaced by millet and sorghum. Farmers and traders were interviewed in groups or individually in both villages and markets

How to Have a Successful Archives Crawl on a Shoestring Budget

Central Washington University Archives and Special Collections hosts an annual archives crawl. This article reports about evolution and promotion of the event, and describes the archives and museums that participated in 2016

Controlled MOCVD growth of Bi2Se3 topological insulator nanoribbons

Topological insulators are a new class of materials that support topologically protected electronic surface states. Potential applications of the surface states in low dissipation electronic devices have motivated efforts to create nanoscale samples with large surface-to-volume ratios and highly controlled stoichiometry. Se vacancies in Bi2Se3 give rise to bulk conduction, which masks the transport properties of the surface states. We have therefore developed a new route for the synthesis of topological insulator nanostructures using metalorganic chemical vapour deposition (MOCVD). MOCVD allows for control of the Se/Bi flux ratio during growth. With the aim of rational growth, we vary the Se/Bi flux ratio, growth time, and substrate temperature, and observe morphological changes which indicate a growth regime in which nanoribbon formation is limited by the Bi precursor mass-flow. MOCVD growth of Bi2Se3 nanostructures occurs via a distinct growth mechanism that is nucleated by gold nanoparticles at the base of the nanowire. By tuning the reaction conditions, we obtain either single-crystalline ribbons up to 10 microns long or thin micron-sized platelets.Comment: Related papers at http://pettagroup.princeton.ed

Development and operation of research-scale III-V nanowire growth reactors

III-V nanowires are useful platforms for studying the electronic and mechanical properties of materials at the nanometer scale. However, the costs associated with commercial nanowire growth reactors are prohibitive for most research groups. We developed hot-wall and cold-wall metal organic vapor phase epitaxy (MOVPE) reactors for the growth of InAs nanowires, which both use the same gas handling system. The hot-wall reactor is based on an inexpensive quartz tube furnace and yields InAs nanowires for a narrow range of operating conditions. Improvement of crystal quality and an increase in growth run to growth run reproducibility are obtained using a homebuilt UHV cold-wall reactor with a base pressure of 2 X 10$^{-9}$ Torr. A load-lock on the UHV reactor prevents the growth chamber from being exposed to atmospheric conditions during sample transfers. Nanowires grown in the cold-wall system have a low defect density, as determined using transmission electron microscopy, and exhibit field effect gating with mobilities approaching 16,000 cm$^2$(V.s).Comment: Related papers at http://pettagroup.princeton.ed