Surface Studies of Solids by Total Reflection of X-Rays
TL;DR: In this paper, the shape of the curve of reflected x-ray intensity vs glancing angle in the region of total reflection was analyzed to study certain structural properties of the mirror surface about 10 to several hundred angstroms deep.
Abstract: Analysis of the shape of the curve of reflected x-ray intensity vs glancing angle in the region of total reflection provides a new method of studying certain structural properties of the mirror surface about 10 to several hundred angstroms deep. Dispersion theory, extended to treat any (small) number of stratified homogeneous media, is used as a basis of interpretation.Curves for evaporated copper on glass at room temperature are studied as an example. These curves may be explained by assuming that the copper (exposed to atmospheric air at room temperature) has completely oxidized about 150A deep. If oxidation is less deep, there probably exists some general reduction of density (e.g., porosity) and an electron density minimum just below an internal oxide seal. This seal, about 25A below the nominal surface plane, arrests further oxidation of more deeply-lying loose-packed copper crystallites.All measurements to date have been carried out under laboratory atmospheric conditions which do not allow satisfactory separation or control of the physical and chemical variables involved in the surface peculiarities. The method, under more controlled conditions of preparation and treatment of the surface, promises to be useful.
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TL;DR: The role of extended and point defects, and key impurities such as C, O, and H, on the electrical and optical properties of GaN is reviewed in this article, along with the influence of process-induced or grown-in defects and impurities on the device physics.
Abstract: The role of extended and point defects, and key impurities such as C, O, and H, on the electrical and optical properties of GaN is reviewed. Recent progress in the development of high reliability contacts, thermal processing, dry and wet etching techniques, implantation doping and isolation, and gate insulator technology is detailed. Finally, the performance of GaN-based electronic and photonic devices such as field effect transistors, UV detectors, laser diodes, and light-emitting diodes is covered, along with the influence of process-induced or grown-in defects and impurities on the device physics.
1,693 citations
TL;DR: This work demonstrates an organic circuit with very low power consumption that uses a self-assembled monolayer gate dielectric and two different air-stable molecular semiconductors (pentacene and hexadecafluorocopperphthalocyanine, F16CuPc) to implement transistors, circuits, displays and sensors on arbitrary substrates.
Abstract: Organic transistors and circuits show great promise for the realization of futuristic roll-up displays, adaptive sensors for humanoid robots and ubiquitous radio-frequency identification tags. But today's organic circuits require operating voltages of 15 to 30 volts (10 to 20 batteries' worth), and they draw enough power to drain those batteries in a day. To overcome this major hurdle, Hagen Klauk et al. have developed a method of fabricating organic circuits that run on a single 1.5-volt battery for several years. The key to the method is the use of a layer of an insulating organic material just one molecule thick; although the layer is very thin, it leaks only a small amount of current, while it provides for a large capacitance. Two different types of organic semiconductors are used to fabricate transistors, logic gates and ring oscillators. A report of the development of organic electronic circuits, which require only a single 1.5V battery and last for several years. The main ingredient is the use of a single layer of an insulating organic material. Although the layer is very thin, it leaks only small amount of current, while providing for a large capacitance. The prospect of using low-temperature processable organic semiconductors to implement transistors, circuits, displays and sensors on arbitrary substrates, such as glass or plastics, offers enormous potential for a wide range of electronic products1. Of particular interest are portable devices that can be powered by small batteries or by near-field radio-frequency coupling. The main problem with existing approaches is the large power consumption of conventional organic circuits, which makes battery-powered applications problematic, if not impossible. Here we demonstrate an organic circuit with very low power consumption that uses a self-assembled monolayer gate dielectric and two different air-stable molecular semiconductors (pentacene and hexadecafluorocopperphthalocyanine, F16CuPc). The monolayer dielectric is grown on patterned metal gates at room temperature and is optimized to provide a large gate capacitance and low gate leakage currents. By combining low-voltage p-channel and n-channel organic thin-film transistors in a complementary circuit design, the static currents are reduced to below 100 pA per logic gate. We have fabricated complementary inverters, NAND gates, and ring oscillators that operate with supply voltages between 1.5 and 3 V and have a static power consumption of less than 1 nW per logic gate. These organic circuits are thus well suited for battery-powered systems such as portable display devices2 and large-surface sensor networks3 as well as for radio-frequency identification tags with extended operating range4.
1,324 citations
TL;DR: The authors would like to thank M. Chabinyc, H. Ade, B. Noriega, K. Vandewal, and D. Duong for fruitful discussions in the preparation of this review and the Center for Advanced Molecular Photovoltaics for funding.
Abstract: The authors would like to thank M. Chabinyc, H. Ade, B. Collins, R. Noriega, K. Vandewal, and D. Duong for fruitful discussions in the preparation of this review. Stanford Synchrotron Radiation Lightsource (SSRL) is a national user facility operated by Stanford University on behalf of the U.S. Department of Energy, Office of Basic Energy Sciences. This publication was partially supported by the Center for Advanced Molecular Photovoltaics (Award No. KUS-C1-015-21), made by King Abdullah University of Science and Technology (KAUST).
1,072 citations
TL;DR: In this paper, the structures of various types of amorphous carbon films and common characterization techniques are described, which can be classified as polymer-like, diamond-like or graphite-like based on the main binding framework.
1,004 citations
TL;DR: In this article, the basic principles of x-ray diffraction of thin films and areas of special current interest, such as analysis of non-polar, semipolar and cubic III-nitrides, are reviewed, along with the basic principle of X-ray diffusion of thin thin films, and some useful values needed in calculations, including elastic constants and lattice parameters.
Abstract: The III-nitrides include the semiconductors AlN, GaN and InN, which have band gaps spanning the entire UV and visible ranges. Thin films of III-nitrides are used to make UV, violet, blue and green light-emitting diodes and lasers, as well as solar cells, high-electron mobility transistors (HEMTs) and other devices. However, the film growth process gives rise to unusually high strain and high defect densities, which can affect the device performance. X-ray diffraction is a popular, non-destructive technique used to characterize films and device structures, allowing improvements in device efficiencies to be made. It provides information on crystalline lattice parameters (from which strain and composition are determined), misorientation (from which defect types and densities may be deduced), crystallite size and microstrain, wafer bowing, residual stress, alloy ordering, phase separation (if present) along with film thicknesses and superlattice (quantum well) thicknesses, compositions and non-uniformities. These topics are reviewed, along with the basic principles of x-ray diffraction of thin films and areas of special current interest, such as analysis of non-polar, semipolar and cubic III-nitrides. A summary of useful values needed in calculations, including elastic constants and lattice parameters, is also given. Such topics are also likely to be relevant to other highly lattice-mismatched wurtzite-structure materials such as heteroepitaxial ZnO and ZnSe.
925 citations