Application of Fresnel diffraction from a 2D array of reflective disks in optical profilometry of a flat surface

Since phase contrasts of STEM images, that is, Fresnel diffraction fringes or lattice images, manifest themselves in field emission scanning microscopy, the mechanism for image formation in the STEM mode has been investigated and compared with that in CTEM mode, resulting in the theory of reciprocity. It reveals that contrast in STEM images exhibits the same properties as contrast in CTEM images. However, it appears that the validity of the reciprocity theory, especially on the details of phase contrast, has not yet been fully proven by the experiments. In this work, we shall investigate the phase contrast images obtained in both the STEM and CTEM modes of a field emission microscope (100kV), and evaluate the validity of the reciprocity theory by comparing the experimental results.

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Simulation of high-resolution annular dark field STEM images

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010013657x ◽

1995 ◽

Vol 53 ◽

pp. 40-41

Author(s):

E. J. Kirkland

Keyword(s):

Electron Beam ◽

Atomic Layer ◽

Fresnel Diffraction ◽

Dark Field ◽

Objective Lens ◽

Image Simulation ◽

Small Probe ◽

Annular Dark Field ◽

Stem Image ◽

Uniform Plane

In a STEM an electron beam is focused into a small probe on the specimen. This probe is raster scanned across the specimen to form an image from the electrons transmitted through the specimen. The objective lens is positioned before the specimen instead of after the specimen as in a CTEM. Because the probe is focused and scanned before the specimen, accurate annular dark field (ADF) STEM image simulation is more difficult than CTEM simulation. Instead of an incident uniform plane wave, ADF-STEM simulation starts with a probe wavefunction focused at a specified position on the specimen. The wavefunction is then propagated through the specimen one atomic layer (or slice) at a time with Fresnel diffraction between slices using the multislice method. After passing through the specimen the wavefunction is diffracted onto the detector. The ADF signal for one position of the probe is formed by integrating all electrons scattered outside of an inner angle large compared with the objective aperture.

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Scanned tip measurement of deep vertical facets on a flat surface: Measuring roughness on gaas laser waveguide mirrors

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100148496 ◽

1993 ◽

Vol 51 ◽

pp. 532-533

Author(s):

Chang Shen ◽

Phil Fraundorf ◽

Robert W. Harrick

Keyword(s):

Integrated Circuits ◽

Flat Surface ◽

Scanning Force Microscopy ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Force Microscopy ◽

Optoelectronic Integrated Circuits ◽

Laser Waveguide ◽

Scanning Force ◽

Gaas Laser

Monolithic integration of optoelectronic integrated circuits (OEIC) requires high quantity etched laser facets which prevent the developing of more-highly-integrated OEIC's. The causes of facet roughness are not well understood, and improvement of facet quality is hampered by the difficulty in measuring the surface roughness. There are several approaches to examining facet roughness qualitatively, such as scanning force microscopy (SFM), scanning tunneling microscopy (STM) and scanning electron microscopy (SEM). The challenge here is to allow more straightforward monitoring of deep vertical etched facets, without the need to cleave out test samples. In this presentation, we show air based STM and SFM images of vertical dry-etched laser facets, and discuss the image acquisition and roughness measurement processes. Our technique does not require precision cleaving. We use a traditional tip instead of the T shape tip used elsewhere to preventing “shower curtain” profiling of the sidewall. We tilt the sample about 30 to 50 degrees to avoid the curtain effect.

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Calculation of many-beam dynamic electron diffraction without high-energy approximation

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100163101 ◽

1996 ◽

Vol 54 ◽

pp. 128-129

Author(s):

B. R. Ahn ◽

N. J. Kim

Keyword(s):

Electron Diffraction ◽

Flat Surface ◽

Dynamic Theory ◽

High Energy ◽

Perfect Crystal ◽

Zone Axis ◽

Beam Dynamic ◽

Diffraction Angle ◽

Energy Approximation ◽

The Many

High energy approximation in dynamic theory of electron diffraction involves some intrinsic problems. First, the loss of theoretical strictness makes it difficult to comprehend the phenomena of electron diffraction. Secondly, it is difficult to believe that the approximation is reasonable especially in the following cases: 1) when accelerating voltage is not sufficiently high, 2) when the specimen is thick, 3) when the angle between the surface normal of the specimen and zone axis is large, and 4) when diffracted beam with large diffraction angle is included in the calculation. However, until now the method to calculate the many beam dynamic electron diffraction without the high energy approximation has not been proposed. For this reason, the authors propose a method to eliminate the high energy approximation in the calculation of many beam dynamic electron diffraction. In this method, a perfect crystal with flat surface was assumed. The method was applied to the calculation of [111] zone axis CBED patterns of Si.

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