Raman and infrared spectra of rhombohedral selenium have been measured and the fundamental bands observed in these spectra are assigned by analogy to the S6 ring molecule. Calculation of the normal mode vibration for the Se6 ring using a modified Urey-Bradley force field confirms this assignment. Anomalous softening of the A1g stretching mode relative to other modes and to the corresponding A1 mode in the Se8 ring was observed. This phenomenon is explained by the idea of interference of inter-molecular interaction with the intra-molecular bonding. Comparison of the observed spectra of rhombohedral selenium with those of other allotropes (α-monoclinic, trigonal, and amorphous selenium) suggests that Se6 ring molecules may exist in amorphous selenium.

Scanning probe microscopy (SPM) has been one of the most important tools to image and, hopefully, to manipulate bio-structures at micro/nanoscales. However, the current out-of-plane cantilever design makes it very difficult to extend the spectrum of the current SPM technology to meet many new functionalities arising from bio-engineering applications. An in-plane scanning probe concept is developed to accommodate the new functional requirements. It is designed to have a single-strand multi-walled carbon nanotube (CNT) tip assembled at the end of the probe, a built-in actuator and a tip deflection sensor, all in the same plane. The coplanar design is compatible with most of the standard MEMS processes and would facilitate the assembly of a carbon nanotube tip to the micromachined probe. The in-plane design features a switchable stiffness which adapts the scanning probe's stiffness to the changing surface hardness of the sample. This paper describes how the variable stiffness is accomplished by engaging or disengaging electrostatically actuated clutches, in addition to the discussions on many possible benefits of the in-plane scanning platform.