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The silicon diode array camera tube, recently developed for PICTURFPHONE® service, was modified to permit X-ray imaging. High quantum efficiency is attained without the use of a phosphor screen, since each photon absorbed in the silicon target generates several hundred hole-electron pairs for each keV of its energy, most of which can he usefully collected. The sensitivity and resolution are adequate to allow a continuous television display of the diffracted intensity as a crystal is oriented. Particular advantages of this technique include; high resolution (< 25 μm); electronically variable magnification; direct oscilloscope measurement of X-ray spot Intensity profiles and relative spot intensities because signal current is directly proportional to photon flux; high sensitivity in the range of 0.6 to 5.0 Å, potentially limited only "by counting statistics; integration times variable from < 1/60 second to minutes; and expected low cost, since the camera tube has no complicated electron imaging, and is directly interchangeable Mith a standard television vidicon. Applications which are described include crystal orientation and X-ray topography.
The Society of Precision Agriculture Australia Inc. (SPAA) is recognised as a leading, grower driven farming group in Australia. As an organisation it provides programs and services to its members and wider industry to promote the development and adoption of Precision Agriculture (PA) technologies as a means of enhancing the profitability and sustainability of agricultural production systems. This is achieved through publishing Australia’s only PA-dedicated magazine, delivering field days, seminars and conducting on-farm PA demonstrations and experiments. SPAA provides farmers with an independent source of advice on new concepts and equipment. The grains industry was the springboard for initial adoption, with winegrapes, horticulture and the sugar industry the focus sectors for further expansion. The purpose of this paper is to share the SPAA experience with a view to assisting the development of similar organisations in other countries
Ion angular current and energy distributions are important parameters for ion thrusters, which are typically measured at a few tens of centimetres to a few metres distance from the thruster exit. However, fully kinetic particle-in-cell (PIC) simulations are not able to simulate such domain sizes due to high computational costs. Therefore, a parallelisation strategy of the code is presented to reduce computational time. The calculated ion beam angular distributions in the plume region are quite sensitive to boundary conditions of the potential, possible additional source contributions (e.g. from secondary electron emission at vessel walls) and charge exchange collisions. Within this work a model for secondary electrons emitted from the vessel wall is included. In order to account for limits of the model due to its limited domain size, a correction of the simulated angular ion energy distribution by the potential boundary is presented to represent the conditions at the location of the experimental measurement in
distance. In addition, a post-processing procedure is suggested to include charge exchange collisions in the plume region not covered by the original PIC simulation domain for the simulation of ion angular distributions measured at
The origins of visible-band linear polarimetry of Algols and objects related to them are reviewed. It is pointed out, not for the first time, that the polarization signals of these systems can vary sporadically by significant amounts. The difficulty of evaluating the interstellar component of the observed polarization is discussed and these components are evaluated anew for each object studied in this paper. With one possible exception, the polarization signals intrinsic to these binaries derive from electron scattering. A well-defined model is applied to the constant and variable (but phase-locked) polarization signals. Limits to the mass associated with a scattering disk in each binary are derived. Within broad limits, concentrations of scattering mass within and above or below the orbital plane are also developed as are the centroid longitudes of these concentrations within the system. It is pointed out that very few measures of visible-band, circular polarization have been made but that cm-wavelength measures of Algol itself have been very informative.
We investigated electronic structure of one-dimensional biradical molecular chain which is constructed by exploiting the covalency between organic molecules of a diphenyl derivative of s-indacenodiphenalene (Ph2-IDPL). To control the crystallinity, we used gas deposition method. Ultraviolet photoelectron spectroscopy (UPS) revealed developed band structure with wide dispersion of the one-dimensional biradical molecular chain.
Structure-related ionization energy (IE) of vacuum-deposited titanyl-phthalocyanine (OTiPc) thin films was investigated by using in situ ultraviolet photoelectron spectroscopy (UPS) and X-ray diffractometry. Distinct molecular orientations (i.e. lying-flat and standing-up orientation) in different polymorphous (i.e. monoclinic β-phase and triclinic α-phase) were observed on a surface of polycrystalline (poly-) Au and octadecyltrichlorosilane-self assembled monolayer (OTS-SAM). For the two structures IE of the highest occupied molecular orbital (HOMO) of OTiPc thin films altered significantly by 0.55 eV. The different IE was attributed to surface dipole potential and strong intermolecular interaction.
Metal deposition on a p-sexiphenyl (6P) film was studied by ultraviolet photoelectron spectroscopy (UPS), metastable atom electron spectroscopy (MAES), and X-ray photoelectron spectroscopy (XPS). The deposited metals were Au, Mg, and several alkali metals (K, Na, Rb, and Cs). No chemical reaction between 6P and Au or Mg was observed in the measured spectra, while additional gap states appeared in the UPS and MAES spectra by deposition of the alkali metals. The diffusion of Au and Mg atoms into the 6P film was observed in the MAES spectra. We found the trend of the vacuum level shift is different between the systems of the 6P on the Au and its reversed systems (Au on the 6P film), suggesting the different formation of the interface depending on the deposition sequence.
Effects of impurity (P and B) doping on the photoluminescence (PL) properties of Si nanocrystals (nc-Si) in SiO2 thin films are studied. It is shown that with increasing P concentration, PL intensity first increases and then decreases. In the P concentration range where PL intensity increases, quenching of the defect-related PL is observed, suggesting that dangling-bond defects are passivated by P doping. On the other hand, in the range where PL intensity decreases, optical absorptiondue to the intravalley transitions of free electrons generated by P doping appears. The generation of free electrons andthe resultant three-body Auger recombination of electron-hole pairs is considered to be responsible for theobserved PL quenching. In the case of B doping, the behavior is much different. With increasing B concentration, PL intensity decreases monotonously. By combining the results obtained for P and B doped samples, theeffects of donor and acceptor impurities on the PL properties of nc-Si are discussed.
A number of low workfunction metals (samarium, alkali metals) were deposited onto vacuum sublimed thin films of pentacene. The change in the valence electronic structure of the organic material was studied by in situ ultraviolet photoemission spectroscopy (UPS). Alkali metal intercalation leads to the appearance of a new photoemission feature within the pentacene energy gap, due to a charge transfer from the alkali atoms to the lowest unoccupied molecular orbital (LUMO) of the organic material. The energy spacing between this emission feature and the relaxed highest occupied molecular orbital (HOMO) of the pristine molecule is 1 eV. From X-ray photoemission spectroscopy core level analysis, we estimate a concentration ratio of two alkali metal atoms per pentacene molecule at maximum intercalation level, leading to a complete filling of the LUMO. This is consistent with the results from UPS that the new emission is always observed below the Fermi-level. Samarium is found to exhibit a more subtle interaction with pentacene: the molecular orbitals remain almost unperturbed upon Sm deposition. The resulting energy level alignment at this interface seems to be very favorable for the injection of electrons from Sm into pentacene, as the HOMO-onset is found at 1.8 eV below the metal Fermi edge. This value is close to the 2.2 eV HOMO-LUMO gap of pentacene measured by UPS and inverse photoemission spectroscopy, thus corresponding to a small electron injection barrier.
High temperature mechanical properties of various Zr and Cr strengthened single phase Ni3Al are investigated, with emphasis on the ability of each element to elevate Tp, the temperature corresponding to the peak yield strength. It is observed that Zr is a very effective strengthener, more so below Tp than above it, while a combination of Cr and Zr is capable of shifting Tp to a higher temperature. The combination results in an effective improvement of the rupture strength of Ni3Al. The strengthening mechanisms of each element will be discussed in this paper.
Electronic states of photocarriers in porous silicon have been investigated by photomodulated infrared and photoluminescence spectroscopies. Wet porous silicon is only weakly yellow-green luminescent, and contains photocarriers which exhibit a Drude-like absorption characteristic of free carriers. On the contrary, once dried or anodically oxidized, porous silicon becomes strongly red luminescent and photocarriers exhibit a broad Gaussian-like absorption, characteristic of localized carriers, which correlates in frequency, response time and intensity with the photoluminescence. This behavior does not appear to be related to surface chemistry. Instead, non-wetting of the surface seems to be mandatory in order to obtain localization of the photocarriers and strong red luminescence. This suggests that the driving effect for switching from green to red luminescence could be the dielectric screening of the Coulombic interactions by the embedding medium in which porous silicon is maintained. The electronic states bound to the potential generated by a charge in a cylindrical silicon wire have then been computed for various values of the dielectric constant of the embedding medium. It is shown that, when the dielectric constant is low, one may account for the red luminescence in terms of recombination through such shallow states, and that the finite time needed for the dielectric relaxation in electrolytes may also account for an inefficient trapping in such states in a wet environment. Preliminary luminescence results are consistent with the predictions of the model.
We have developed three classes of techniques to produce micron-size and submicron-size light emitting porous Si (LEPSi) patterns and to protect the rest of the wafer. In the 1st class, LEPSi lines down to 2 µm width have been made using a photoresist/silicon nitride trilayer mask, followed by anodization. PL mapping of the structures indicates that the protected regions have not been etched. Using electron beam lithography sub-0.5 micron porous Si lines have been generated. In the 2nd class, formation of porous Si is inhibited by amorphizing Si using ion implantation followed by anodization and annealing. The crystallinity and electrical properties of the implanted region have been fully characterized after annealing. Using focussed ion-beam implantation, LEPSi patterns of the order of 100 nm have been obtained. The 3rd class consists of enhancing the formation of porous Si by a low energy/low dose bombardment (ion-milling) with argon ions prior to anodization. Under appropriate conditions, we have observed a strong enhancement of the formation rate of LEPSi where bombardment took place, possibly due to the generation of a large number of defects on the wafer surface.
We performed an X-ray diffraction study of amorphous-tetrahedrally-coordinated carbon (a-tC) films prepared by pulsed laser deposition (PLD). The samples' properties were analyzed as a function of laser energy and thickness. For all thicknesses and laser energies, films were made up of clusters with a basic unit size of 7 -11 nm. Thicker films, as well as films prepared at higher laser densities exhibit larger clusters, in the tens of nanometers. The clusters are not readily observable by AFM, which may indicate the presence of a flat (graphitized) top film surface.
Single crystal-silicon quantum well layers with SiO2 barriers were grown from silicon-on-insulator substrates. Photoluminescence in the red and near-infrared was observed for average layer thickness < 8 nm, with peak signal for 2-nm thickness. The luminescence spectrum was essentially independent of well width for SiO2 barriers, but the photoluminescence intensity decreased sharply after annealing in Ar. These results suggest the importance of radiation from surface states. In contrast to oxide-passivated silicon nanocrystals and to porous silicon, the room-temperature photoluminescence quantum efficiency is low (10-4-10-5), probably due to variations in layer thickness and to diffusion of photoexcited carriers to fast nonradiative recombination centers.
The structure and composition of tetrahedral-coordinated amorphous diamondlike carbon films (a-tC) grown by pulsed laser deposition (PLD) of graphite has been studied with atomic force microscopy (AFM). The nanometer-scale surface structure has been studied as a function of growth parameters (e.g., laser energy density and film thickness) using contact-mode and tapping-mode AFM. Although the surfaces were found to be generally smooth, they exhibited reproducible structural features on several size scales which correlate with the variation of laser energy and the effects of excited ion etching.
The technologies of laser crystallization and methods of SiO2 formation in remote plasma chemical vapor deposition or SiO evaporation with an oxygen ambient realize the fabrication of n-channel polycrystalline and amorphous silicon thin film transistors (poly-Si and a-Si TFTs) at a temperature lower than 300 °C. The defect density was achieved to be 2∼3×1011 cm−2eV−1 and threshold voltage was about IV for both TFTs. The maximum field effect mobility was 600 cm2/Vs for poly-Si TFTs and 2.6 cm2/Vs for a-Si TFTs. The mobility of poly-Si TFT decreased as the gate voltage increases. This is interpreted as that the electrons are confined in the narrow inversion layer and electron scattering with phonon is enhanced for higher normal electric field.
Multicomponent nickel base intermetallics with the L12 structure were evaluated as high temperature structural materials. The compounds were based on the γ' composition of PWA 1480, a high strength single crystal nickel base superalloy. The best balance of properties in the compound was achieved with <111> oriented single crystals but no significant advantage could be demonstrated over the precipitation hardened superalloys. Insufficient impact resistance was a major deficiency of the L12 compounds. Other nickel base intermetallics were also evaluated but showed little advantage over superalloys.