We study data from an organization in which fund managers privately share and discuss detailed investment recommendations. Buy recommendations generate positive abnormal returns, and sell recommendations result in negative abnormal returns. In the context of these results, we explore an important economic question: Why do skilled investors share profitable ideas with others? Evidence suggests that the managers in our sample share to receive feedback on their ideas and to attract additional arbitrageur capital to the securities they recommend in order to correct mispricings.

Photochemical methods were developed to obtain a variation of the refractive index in aromatic polymer surfaces and a change in the photoluminescence characteristics of phenylene-vinylene-based polymers. Films of aromatic polymers, among them polystyrene (PS), poly(2-vinylnaphthalene) (PVN) and derivatives of poly(-phenylene-vinylene) (PPV) were UV irradiated in the presence of gaseous hydrazine (N2H4). The photoreaction led to a strongreduction of the refractive index of the polymers due to a hydrogenation of the aromatic units. In the case of PPV, we observed reductive photobleaching. This new technique was employed to produce photogenerated patterns in PPV. The results are compared to oxidative bleaching.

This study presents the results of surface investigation of the heteroepitaxial AIN/SiC interface. The analytical tools employed included UPS, XPS, Auger spectroscopy, and LEED. The surface electronic states were characterized by uv photoemission obtained at surface normal. Conclusions drawn from this study are that the AIN/SiC structure results in a negative electron affinity surface which is extremely sensitive to defect density. The surface Fermi level is found to be near the middle of the AlN gap, and a possible band alignment between the AlN and SiC is presented.

The morphology and interface chemistry occurring during the initial deposition of BN, AlN and GaN films via metal evaporation and N2 decomposition under UHV conditions have been determined. FTIR spectroscopy and TEM revealed the consecutive deposition of an initial 20Å layer of a-BN, 20–60Å of oriented h-BN, and a final layer of polycrystalline c-BN. This sequence is attributed primarily to increasing intrinsic compressive stress in the films. XPS analysis revealed the growth of GaN on sapphire to occur via the Stranski-Krastanov mode; growth on SiC showed characteristics of three-dimensional growth. AlN grew layer-by-layer on both substrates. Vicinal 6H-SiC(0001) substrate surfaces contain closely spaced, single bilayer steps. During deposition of Si and C at 1050°C, 6H layers initially form and step bunching occurs. The latter phenomenon results in more widely spaced steps, the nucleation of 3C-SiC both on the new terraces and at the larger steps and formation of double position boundaries. The C/Si ratio in the gaseous reactants also affects the occurrence of these three phenomena.

Organometallic vapor phase epitaxy (OMVPE) and molecular beam epitaxy (MBE) are the most common methods for the growth of thin films of A1N and GaN. Sapphire is the most common substrate; however, a host of materials have been used with varying degrees of success. Both growth techniques have been employed by the authors to grow AIN, GaN and AlxGa1−xN thin films primarily on 6H-SiC(0001). The mismatch in atomic layer stacking sequences along the growth direction produces double positioning boundaries in A1N and the alloys at the SiC steps; this sequence problem appears to discourage the two-dimensional nucleation of GaN. Films of these materials grown by MBE at 650°C are textured; monocrystalline films are achieved between 850°C (pure GaN) and 1050°C (pure A1N) by this technique and OMVPE. Donor and acceptor doping of GaN has been achieved via MBE without post growth annealing. Acceptor doping in CVD material requires annealing to displace the H from the Mg and eventually remove it from the material. High brightness light emitting diodes are commercially available; however, numerous concerns regarding metal and nitrogen sources, heteroepitaxial nucleation, the role of buffer layers, surface migration rates as a function of temperature, substantial defect densities and their effect on film and device properties, ohmic and rectifying contacts, wet and dry etching and suitable gate and field insulators must and are being addressed. Selected issues surrounding the growth of these materials with particular examples drawn from the authors' research are presented herein.

We report the dielectric functions of various GaN samples as measured by spectroscopic ellipsometry. Structure related to the A and B excitons is resolved at room temperature, in principle allowing strain to be assessed. However, the data indicate that dead-layer and dispersion effects are present, preventing a simple interpretation. We discuss various complications including the Edn/dE contribution to dispersion, which is important for laser action. Our data appear to indicate that the spin-orbit splitting of GaN is about 15 meV, somewhat larger than the currently accepted value of about 11 meV.

Samples of steel with high chrome content were implanted separately with 75 keV nitrogen ions and with 75 keV boron ions. Implanted doses of each ion species were 2-,4- and 8 × 1017 /cm2. Retained doses were measured using resonant non-Rutherford Backscattering Spectrometry. Tribological properties were determined using a pin-ondisk test with a 6-mm diameter ruby pin with a velocity of 0.94 m/min. Testing was done at 10% humidity with a load of 377g. Wear rate and coefficient of friction were determined from these tests. While reduction in the wear rate for nitrogen implanted materials was observed, greater reduction (more than an order of magnitude) was observed for boron implanted materials. In addition, reduction in the coefficient of friction for high-dose boron implanted materials was observed. Nano-indentation revealed a hardened layer near the surface of the material. Results from grazing incidence x-ray diffraction suggest the formation of Fe2N and Fe3N in the nitrogen implanted materials and Fe3B in the boron implanted materials. Results from transmission electron microscopy will be presented.

Low temperature cathodoluminescence has been used to investigate the spatial characteristics of light emission in InxGa1−xN single quantum wells. High spatial resolution, narrow band pass imaging shows the luminescence to be strongly inhomogeneous in wavelength as well as in intensity on a sub-micron scale. Cathodoluminescence spectra correlate favorably with photoluminescence spectra. However, when spectra are recorded from different areas in spot mode, the quantum emission varies significantly in wavelength. The observed variations are consistent with composition inhomogeneities in the quantum well.

Transmission electron microscopy has been applied to study defects in epitaxial doped and undoped GaN layers grown by MOCVD on sapphire and SiC substrates. Samples with InGaN/GaN and AlGaN/InGaN heterostructures have also been investigated. The results of this study show that incorporation of “foreign” atoms increases formation of nano-tubes and pinholes. The highest density of these defects was formed close to the interface with sapphire where oxygen outdiffusion might be expected, or in the subsurface area in the samples where oxygen was added deliberately. Addition of In (or Al) at QW's also leads to pinhole formation. Increased In fraction or a larger number of QW's results in a greater density of pinholes and more surface roughness. Many of the “hollow” nanotube defects are terminated during growth.

GaN, AlxGa1–xN, and AlN layers exhibit interference oscillations and bandgap-related features in their reflectance-difference (-anisotropy) (RD/RA) spectra. We concentrate on the interpretation of interference-related data, providing a general expression for these optical anisotropics and discussing mechanisms that originate in the layers themselves. These include anisotropic strain in the plane of the layer, a tilt of the c axis with respect to the surface normal, and non-normal-incidence illumination. We estimate the magnitudes of these contributions, and show that they are consistent with those observed. In principle these contributions can be separated by their different azimuthal dependences. The complex pattern of the data for AlxGa1–xN and AlN indicate that contributions from several layers are present.

The microstructure of lnxGal-xN quantum wells with intermediate indium concentrations (x = 0.28 and 0.52) has been studied using transmission electron microscopy. High-resolution lattice images and dark-field images taken under high tilt conditions indicate that the quantum wells are inhomogeneous in character. Most of the area of the quantum wells is pseudomorphic with the GaN adjacent layer. However, misfit dislocations are sometimes observed, although with an inhomogeneous distribution. Strained cluster regions are observed in the high-indium concentration quantum wells, with dimensions ranging fi'om 3 to 10 nm in diameter. Evidence is presented suggesting the extent of clustering depends on the exact orientation of the growth surface which is related to the columnar nature of the GaN/sapphire epitaxy.

Thin silicon dioxide (SiO2) on Si layers with embedded germanium nanocrystals (Ge-ncs) were fabricated using 74Ge+-implantation at 15 keV and subsequent annealing. Transmission electron microscopy and Rutherford backscattering spectrometry have been used to study the Ge redistribution in the SiO2 films as a function of implantation dose under specific annealing conditions. At low implantation doses, Germanium is found to segregate at the Si/SiO2 interface leading to poor electrical properties. At higher doses and when the disorder limit of one displacement per atom is reached at the interface, transmission electron microscopy revealed the formation of a Ge-nc layer array located close to the Si/SiO2 interface and an another one inside the SiO2 host material. This near-interface high density (>1012 ncs/cm2) nc-layer is found to act as a floating gate embedded within the silicon dioxide. Capacitance-voltage measurements performed on metal-oxide-semiconductor structures containing such implanted SiO2 layers show significant memory properties (few volts hysteresis) at low programming voltages (<|10V|) due to the presence of Ge-ncs near the Si/SiO2 interface