Diamond Luminescence

Luminescence spectroscopy is an established tool to investigate natural, high pressure synthesized, and chemical vapour deposited (CVD) diamond. The spectral range extends from 5.3 eV in the ultraviolet to approximately 1.2 eV in the near-infrared. More than 100 optical centres have been observed. Since the early 1930\u27s, semiconducting diamond for electronic devices has been of interest to science. The large bandgap (5.5 eV), low dielectric constant (5.7), and high thermal conductivity (about 5 times larger then that of Ag), as well as the superior charge-carrier transport properties, such as electron and hole mobility (µ-: 2200 cm2/Vs, μ+: 1600 cm2/Vs), lead to applications in active and passive electronics. At the beginning of the 1980\u27s, the first successful experiments of diamond films synthesis by low pressure chemical vapour deposition method were presented. Cathodoluminescence (CL) and photoluminescence (PL) are important techniques for characterising the defects present in CVD films and natural diamond. In this presentation, the most significant luminescence bands, the defects and the problems with the models used to interpret the bands are discussed

Quantitative Scanning Electron Acoustic Microscopy of Silicon

So far results of scanning electron acoustic microscopy (SEAM) have retained a widely qualitative meaning only due to the enormous uncertainty in understanding sound generation and contrast mechanisms in SEAM micrographs. In this work, a detailed treatment of these mechanisms has been undertaken for silicon resulting in precise knowledge of the signal generation processes and a well understood interpretation of the contrast mechanisms involved in imaging thermo-mechanical and electronic features

Numerical Simulation of the Influence of Electron Beam Induced Excess Charge Carriers on Potential and Charge Carrier Density Distributions in GaAs MESFET

Such scanning electron microscopy modes as electron beam induced current (EBIC), cathodoluminescence (CL) and scanning electron acoustic microscopy (SEAM) are widely used for the characterization of semiconductor specimens and devices. These methods are based on the generation of excess charge carriers by an electron beam inside of the investigated specimen. Usually, theoretical models used to explain the physics of these methods presuppose the low injection case. However, in experimental investigations, the low injection condition cannot always be observed. Thus, for the interpretation of such measurement results more complicated simulation models have to be used. Such simulations can be carried out by means of numerical simulation programs. Important results of such simulations are how the charge carrier density distributions as well as the potential distributions are influenced by the electron beam induced excess charge carriers inside of investigated semiconductor devices, as for example Gallium Arsenide (GaAs) Metal Semiconductor Field Effect Transistors (MESFET). Additionally, processes such as the recharging of deep levels by the excess charge carriers and the effects of the recharging on the electrical potential distribution can be investigated

Signal Generation and Contrast Mechanisms in Scanning Electron Acoustic Microscopy

In scanning electron acoustic microscopy (SEAM) until now the signal generation is explained mainly by an intermediate production of thermal waves. Though this so-called thermal wave approach has proven to give realistic results for metals, from experimental evidence it seems to fail for other material groups such as ceramics, dielectrics, piezoelectrics and semiconductors. As these material groups are of major technological importance, it is necessary to develop theories which help interpreting those SEAM micrographs obtained for these types of material. In a comparative manner three different models are discussed in this paper, the well known thermal coupling, the piezoelectric coupling and the excess carrier coupling. The relevant parameters for the signal formation are determined and the contrasts achieved in electron acoustic micrographs explained by means of these models. The experimental evidence discussed for all important material groups supports the three models significantly, and the results obtained can be interpreted quantitatively in terms of material properties and primary electron beam parameters

Tau Polarization in Λb→Xcτνˉ \Lambda_b \to X_c \tau \bar{\nu} and B→XcτνˉB \to X_c \tau \bar{\nu}

We discuss the longitudinal and transverse $\tau$-polarization in inclusive decays of hadrons containing $b$-quarks. The calculation is performed by means of an OPE in HQET. Some mathematical difficulties in calculating transverse polarizations are explained. Numerical results are presented for longitudinal and for transverse polarizations, both in and perpendicular to the decay plane.Comment: LATEX, 20 pages, 5 Postscript figure

High Resolution Electron Beam Induced Current Measurements in an Scanning Tunneling Microscope on GaAs-MESFET

Recently, the first results of electron beam induced current (EBIC) measurements in a scanning tunneling microscope (STM) have been reported. Although the acquired results match with those obtained in conventional EBIC investigations, the interpretation of the obtained results is still restricted solely to a qualitative discussion. In this paper, a quantitative approach is used for two-dimensional numerical simulations of induced currents in GaAs-MESFET leading to a first starting point for a sophisticated interpretation of the dependence of induced currents on experimental and device parameters

Signal generation mechanisms in scanning-electron acoustic microscopy of ionic crystals

MgO crystals have been studied by scanning‐electron acoustic microscopy under different experimental conditions. Contrast mechanisms in imaging are discussed and compared. The experimental results obtained by earthing or nonearthing the specimen‐transducer interface suggest the existence of a signal generation mechanism that is related to the ionic nature of these kind of crystals. Electron‐acoustic microscopy appears then to be a useful tool for the characterization of ionic materials

Scanning electron‐acoustic microscopy of MgO crystals

The capability of scanning electron‐acoustic microscopy in the characterization of MgO crystals has been studied. The conditions for the observation of different surface and subsurface features in as‐grown and deformed crystals are described and the results are discussed on the basis of thermal and nonthermal mechanisms of acoustic signalgeneration

Measurements of Nanoscale Domain Wall Flexing in a Ferromagnetic Thin Film

We use the high spatial sensitivity of the anomalous Hall effect in the ferromagnetic semiconductor Ga1-xMnxAs, combined with the magneto-optical Kerr effect, to probe the nanoscale elastic flexing behavior of a single magnetic domain wall in a ferromagnetic thin film. Our technique allows position sensitive characterization of the pinning site density, which we estimate to be around 10^14 cm^{-3}. Analysis of single site depinning events and their temperature dependence yields estimates of pinning site forces (10 pN range) as well as the thermal deactivation energy. Finally, our data hints at a much higher intrinsic domain wall mobility for flexing than previously observed in optically-probed micron scale measurements