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

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

NONLINEAR SCANNING ELECTRON ACOUSTIC MICROSCOPY

La microscopie électronique acoustique par balayage non-linéaire est une technique spéciale de la microscopie acoustique, qui utilise les amplitudes et les phases des harmoniques, particulièrement le second harmonique de l'onde acoustique provenant d'un faisceau électronique modulé sur une certaine fréquence de base. Comme ces harmoniques sont déterminés par le couplage non-linéaire entre le son et le solide, ils détectent d'une manière très sensible les inhomogénéités du matériau avec une grande résolution spatiale.Nonlinear scanning electron acoustic microscopy is a special technique of acoustic microscopy which uses amplitudes and phases of higher harmonics, especially the second harmonic, of the sound wave originated by an electron beam modulated at a certain ground frequency. As these harmonics are determined by the nonlinear coupling between sound and the solid , they reveal very sensitively material inhomogeneities with high spatial resolution

SCANNING ELECTRON ACOUSTIC MICROSCOPY WITH SUBNANOSECOND TIME RESOLUTION

En microscopie électronique acoustique par balayage le signal acoustique de l'échantillon peut être analysé complètement par des mesures résolues en temps. L'utilisation d'un "boxcar" permet de réaliser des micrographies électroniques acoustiques avec un déphasage déterminé par rapport aux implusions du faisceau primaire électronique. En principe ces micrographies peuvent être appliquées aux analyses en profondeur de façon non destructive. On montre des exemples d'application aux semiconducteurs et aux dispositifs.In scanning electron acoustic microscopy the local acoustic response of the specimen can be analysed by time resolved experiments. Use of boxcar integration techniques enables the production of electron acoustic images with fixed time delays with respect to the primary electron beam pulse. In principle, these micrographs should allow a non-destructive depth profiling. Examples are shown for semiconducting materials and devices

Application of scanning electron acoustic microscopy to the characterization of n-type and semiinsulating GaAs

A series of GaAs wafers with different doping levels and electrical resistivity has been used to investigate the scanning electron acoustic microscopy (SEAM) application to the characterization of this material. It has been found that SEAM is particularly useful to characterize semi-insulating GaAs as compared with n-type material. The SEAM signal generation mechanisms in GaAs are discussed