Raman microprobe determination of local crystal orientation

Abstract

The analysis of local crystal orientation with micron spatial resolution is of prime importance in understanding the dynamics of crystal growth processes with potential for device applications. Examples of such processes are laser annealing, lateral epitaxial growth over oxides, and molecular-beam-epitaxial growth over structured substrates. We present here a nondestructive technique for obtaining such information based on polarization selective Raman scattering from near-diffraction limited O(1 μm) regions of the sample. Depth resolution is limited by the optical penetration depth at the laser wavelength, which is on the order of 1.0 μm for Si at visible wavelengths. By rastering the sample with respect to the probe laser beam, maps of the local crystal orientation can be obtained. Abrupt changes in crystal orientation at grain boundaries are readily apparent. This paper details the experimental apparatus and the method for extracting local crystal orientation information for the particular case of Si. Experiments on single crystals of known orientation are presented which confirm our theoretical predictions and serve to calibrate the technique. Practical examples of mapping of laser annealed silicon-on-oxide structures are given. The analysis shows the loss of the lateral epitaxial seed, with many grains exhibiting 〈110〉 surface normals, in agreement with qualitative results obtained from a destructive selective chemical-etching procedure. Signal intensities are such that orientation information at a single point can be recorded in less than 30 s, thus providing the potential for a real time in situ monitor of slow growth processes.

The effects of environment on <i>Arctica islandica</i> shell formation and architecture

“…Polarized Raman microscopy is known to provide comprehensive information about the crystallographic properties of the materials (Hopkins and Farrow, 1985). The aragonite spectrum is characterized by two lattice modes (translation mode T a , 152 cm −1 and librational mode L a , 206 cm −1 ) and the two internal modes (in-plane band ν 4 , 705 cm −1 and symmetric stretch ν 1 , 1085 cm −1 ).…”

“…The aragonite spectrum is characterized by two lattice modes (translation mode T a , 152 cm −1 and librational mode L a , 206 cm −1 ) and the two internal modes (in-plane band ν 4 , 705 cm −1 and symmetric stretch ν 1 , 1085 cm −1 ). The ratio (R ν1/T a ) between peak intensities belonging to ν 1 and T a is caused by different crystallographic orientations of the aragonitic units (Hopkins and Farrow, 1985;Nehrke and Nouet, 2011). Within each scan, R ν1/T a was calculated for each data point.…”

Evaluation of methods for application of epitaxial layers of superconductor and buffer layers

“…By observing the 500 cm -1 in the proper polarization the oxygen content can be found. (53,(55)(56)(57)(58) Crystal orientation can also be obtained by observing several Raman spectra of the HTSC film. By applying different polarizations to the laser, using different orientations of the crystal axes and studying different places on the film an accurate measurement can be made of the crystal orientation.…”

“…With some technique development, real time measurements should be possible under the appropriate conditions. (52,58) Argon Ion Laser In order to scale-up the current know-how on the selected three candidates to commercially viable processes to manufacture long-lengths of coated conductor wires/tapes, a significant amount of development work is needed. Areas of major technical concerns/issues and significant gaps in the useful data for each of these candidate options are as follows.…”

“…By applying different polarizations to the laser, using different orientations of the crystal axes and studying different places on the film an accurate measurement can be made of the crystal orientation. (58)(59)(60)(61) For example, by comparing the relative intensities of the 500cm -1 line and the 335 cm -1 line in the proper Raman mode the degree of c-axis tilting away from the normal can be determined. (60) The main difficulty with Raman spectroscopy is the data acquisition speed.…”