Group-III Nitride Field Emitters

Field-emission devices (cold cathodes) having low electron affinities can be fabricated through lattice-mismatched epitaxial growth of nitrides of elements from group III of the periodic table. Field emission of electrons from solid surfaces is typically utilized in vacuum microelectronic devices, including some display devices. The present field-emission devices and the method of fabricating them were developed to satisfy needs to reduce the cost of fabricating field emitters, make them compatible with established techniques for deposition of and on silicon, and enable monolithic integration of field emitters with silicon-based driving circuitry. In fabricating a device of this type, one deposits a nitride of one or more group-III elements on a substrate of (111) silicon or other suitable material. One example of a suitable deposition process is chemical vapor deposition in a reactor that contains plasma generated by use of electron cyclotron resonance. Under properly chosen growth conditions, the large mismatch between the crystal lattices of the substrate and the nitride causes strains to accumulate in the growing nitride film, such that the associated stresses cause the film to crack. The cracks lie in planes parallel to the direction of growth, so that the growing nitride film becomes divided into microscopic growing single-crystal columns. The outer ends of the fully-grown columns can serve as field-emission tips. By virtue of their chemical compositions and crystalline structures, the columns have low work functions and high electrical conductivities, both of which are desirable for field emission of electrons. From examination of transmission electron micrographs of a prototype device, the average column width was determined to be about 100 nm and the sharpness of the tips was determined to be characterized by a dimension somewhat less than 100 nm. The areal density of the columns was found to about 5 x 10(exp 9)/sq cm . about 4 to 5 orders of magnitude greater than the areal density of tips in prior field-emission devices. The electric field necessary to turn on the emission current and the current per tip in this device are both lower than in prior field-emission devices, such that it becomes possible to achieve longer operational lifetime. Moreover, notwithstanding the lower current per tip, because of the greater areal density of tips, it becomes possible to achieve greater current density averaged over the cathode area. The thickness of the grown nitride film (equivalently, the length of the columns) could lie between about 0.5 microns and a few microns; in any event, a thickness of about 1 micron is sufficient and costs less than do greater thicknesses. It may be possible to grow nitride emitter columns on glass or other substrate materials that cost less than silicon does. What is important in the choice of substrate material is the difference between the substrate and nitride crystalline structures. Inasmuch as the deposition process is nondestructive, an ability to grow emitter columns on a variety of materials would be advantageous in that it would facilitate the integration of field-emitter structures onto previously processed integrated circuits

Hesperidin effects on behavior and locomotor activity of diabetic Wistar rat

Today, there are sufficient validated scientific data that support the existence of relations between diabetes and certain neuropsychiatric disorders, such as behavioral disorders, anxiety, cognitive decline and depression. The objective of this work was to investigate the effect of a natural bioflavonoid, the antioxidant hesperidin on the neuro behavioral alterations and locomotor function in streptozotocine diabetic wistar rats. Twenty eight male rats were divided equally into four groups; control, and treated series (hesperidin, streptozotocine and hesperidin+ streptozotocine) then exposed to open field test, where animals were individually placed in the center of the compartment for a period of 5 min. Results of the open field test showed high level of anxiety and a slowdown in locomotion and mental flexibility on diabetic rats. Treatment with hesperidin, significantly module these disorders of the animals related to diabetes. Thus, our results confirm the capacity of hesperidin as an antioxidant, to correct neurobehavioral and locomotion disorders related to diabetes and its complications by neutralizing free radicals generated by this metabolic disease.Key words: Diabetes, oxidative stress, hesperidin, streptozotocine

Radiation and Temperature Hard Multi-Pixel Avalanche Photodiodes

The structure and method of fabricating a radiation and temperature hard avalanche photodiode with integrated radiation and temperature hard readout circuit, comprising a substrate, an avalanche region, an absorption region, and a plurality of Ohmic contacts are presented. The present disclosure provides for tuning of spectral sensitivity and high device efficiency, resulting in photon counting capability with decreased crosstalk and reduced dark current

Natural Radioactivity in Red Clay Brick Manufactured in Tlemcen-Algeria, Using Well-Shape NaI(Tl) Detector

The presence of natural radioactivity in brick and other building materials results in internal and external exposure to the general public. Therefore, it is desirable to determine the concentration of naturally occurring radionuclides. Bricks are one of the main components in building construction beside cements, granites and sand. Thus, this research has been carried out in order to investigate the levels of natural radioactivity and associated radiation hazard in Algerian red brick. The natural radioactivity due to the presence of 226Ra, 232Th and 40K in brick samples used as building materials in Tlemcen province - Algeria was measured by gamma spectrometry using NaI(Tl) scintillation well-shaped detector. In this context, brick samples were collected from two manufactories Tafna and Tounan. The mean values of activity concentrations for 226Ra, 232Th and 40K were found to be in the main value of 15.5Bq.kg-1, 11Bq.kg-1, and 196.5Bq.kg-1, respectively. The concentrations of these natural radionuclides were compared with the reported data for other countries and were found significantly lower than the world wide average (1,2). Radium equivalent activities were calculated (41.3 to 51.4) Bq.kg–1 for the analyzed samples to assess the radiation hazards arising due to the presence of these radionuclides in the samples. The calculated radium equivalent activities are lower than the limit set by the OECD report 370 Bq.kg–1 (3). The measured representative level index values for the investigated samples varied in the range (0.31 to 0.38) Bq.kg1.  External and internal hazard index (Hex,Hin), the specific dose rates in door (D) and the annual effective dose (DE) due to gamma radiation from building materials was calculated. Keywords: Brick, natural radioactivity, gamma radiation, absorbed dose, radiation exposure, Potassium, Thorium, Uranium; NaI(Tl) detector, Tlemcen

Radioactivity Investigation of Sand from the Northern Region of Tlemcen-Algeria, Using Well-Shape NaI(Tl) Detector

The presence of natural radioactivity in sand and other building materials results in internal and external exposure to the general public. Therefore, it is desirable to determine the concentration of naturally occurring radionuclides. Sand is one of the main components in building construction beside cements, granites and bricks. Thus, this research has been carried out in order to investigate the levels of natural radioactivity and associated radiation hazard in some Algerian sand. The natural radioactivity due to the presence of 226Ra, 232Th and 40K in sand samples used as building materials in Tlemcen province - Algeria was measured by gamma spectrometry using NaI(Tl) scintillation well-shaped detector. In this context, sand samples were collected from four different locations of northern areas of Tlemcen city, Behira seabeach sand, Targa sand, Boukdasen sand, Sidi Bourzin sand. The measured activity in the sand samples ranged from 4.70 to 7.85 Bq.kg-1, 0.80 to 3.00Bq.kg-1 and 22 to 53 Bq.kg-1 for 226Ra, 232Th and 40K, respectively. The concentrations of these natural radionuclides were compared with the reported data for other countries and were found significantly lower than the worldwide average as reported by United Nations Scientific Committee on the Effects of Atomic Radiation (1,2). Radium equivalent activities were calculated (9.25 to 16.39) Bq·kg–1for the analyzed samples to assess radiation hazards arising due to the presence of these radionuclides in the samples. Most of the calculated radium equivalent activities are lower than the limit set in the OECD report at 370Bq.kg–1(3). The measured representative level index values for the investigated samples varied in the range (0.068 to 0.118) Bq.kg-1. External and internal hazard index (Hex,Hin), the specific dose rates indoor (D) and the annual effective dose (DE) due to gamma radiation from building materials was calculated. Keywords. Sand, natural radioactivity, gamma radiation, absorbed dose, radiation exposure, Potassium, Thorium, Uranium, NaI(Tl) Detector, Tlemcen

Coating MCPs with AlN and GaN

A development effort underway at the time of reporting the information for this article is devoted to increasing the sensitivity of microchannel plates (MCPs) as detectors of photons and ions by coating the MCPs with nitrides of elements in period III of the periodic table. Conventional MCPs are relatively insensitive to slowly moving, large-mass ions for example, ions of biomolecules under analysis in mass spectrometers. The idea underlying this development is to coat an MCP to reduce its work function (decrease its electron affinity) in order to increase both (1) the emission of electrons in response to impingement of low-energy, large-mass ions and (2) the multiplying effect of secondary electron emission. Of particular interest as coating materials having appropriately low or even negative electron affinities are gallium nitride, aluminum nitride, and ternary alloys of general composition Al(x)Ga(1-x)N (where 0<x<1). These materials exhibit attractively high degrees of chemical, mechanical, and thermal stability plus acceptably high resistance to sputtering. The electron-excitation cross sections of these materials are expected to exceed those of several other materials (including diamond) that are, variously, in use or under development for the same purpose. Moreover, by doping these materials with silicon, one can render them partly electrically conductive, thereby suppressing the undesired accumulation of electric charge that could otherwise occur during bombardment by ions. For experiments, thin films of AlN and GaN both undoped and doped with Si were deposited on commercial MCPs by radio-frequency molecular-beam epitaxy (also known as plasma-assisted molecular-beam epitaxy) at temperatures <200 C. This deposition technique is particularly suitable because (1) MCPs cannot withstand the higher deposition-substrate temperatures used to decompose constituent compounds in some other deposition techniques and (2) in this technique, the constituent Al, Ga, and N are supplied in elemental form, so that there is no need for thermal decomposition at the substrate surface. The nitride films thus formed were, variously, amorphous or polycrystalline. The nitride films were coated with surface layers of gold <100 thick. The MCPs were tested in a standard configuration in which the output stage of a first MCP was coupled to the input stage of a second MCP. Each pair of MCPs was mounted in a standard holder that included front and back contact rings and an anode for collecting the output electrons of the second MCP. The MCP pairs were biased at potentials between 1.7 and 1.9 kV, and count rates measured after preamplification and discrimination. To enable a direct comparison, in one pair, the second MCP was uncoated while the first MCP was coated over half its surface. The coated and uncoated sides of the half-coated MCP were exposed to fluxes of argon ions at kinetic energies of 1.0 and 0.5 keV. At 1.0 keV, the count rate for the coated side was about 2.3 times greater than that for the uncoated side; at 0.5 keV, the count rate for the coated side was about 1.8 times greater than that for the uncoated side

Solid-State Neutron Detector Device

The structure and methods of fabricating a high efficiency compact solid state neutron detector based on III-Nitride semiconductor structures deposited on a substrate. The operation of the device is based on absorption of neutrons, which results in generation of free carriers

Strained quantum well photovoltaic energy converter

An indium phosphide photovoltaic cell is provided where one or more quantum wells are introduced between the conventional p-conductivity and n-conductivity indium phosphide layer. The approach allows the cell to convert the light over a wider range of wavelengths than a conventional single junction cell and in particular convert efficiently transparency losses of the indium phosphide conventional cell. The approach hence may be used to increase the cell current output. A method of fabrication of photovoltaic devices is provided where ternary InAsP and InGaAs alloys are used as well material in the quantum well region and results in an increase of the cell current output