Strain-shift coefficients for phonons in Si1-xGex epilayers on silicon

Polarized Raman spectroscopy-stress relationship considering shear stress effect

This Letter uses polarized Raman spectroscopy as a "strain rosette" to quantitatively determine all the in-plane components of the stress tensor for (110) silicon. Through polarized Raman spectroscopy, Raman wavenumber shifts can be obtained at the same point with different polarization directions of the incident and/or scattered light. With at least three measured Raman shifts in different polarized directions, the three stress components of a surface that contains two non-equal normal stresses and one shear stress can be calculated accordingly. We develop an analytical and linear Raman wavenumber shift-stress relationship when shear stress is considered. The experimental results verify the theoretical predictions. It shows that the simple stress condition assumption may lead to erroneous results.

Cooperative Electron-Phonon Coupling and Buckled Structure in Germanene on Au(111)

Germanene, a single-atom-thick germanium nanosheet in a honeycomb lattice, was proposed to be a Dirac fermion material beyond graphene. We performed scanning tunneling microscopy and in situ Raman spectroscopy studies combined with first-principles calculations on the atomic structures and the electronic and phonon properties of germanene on Au(111). The low-buckled 1 × 1 germanene honeycomb lattice was determined to exist in an unexpected rectangular √7 × √7 superstructure. Through in situ Raman measurements, distinctive vibrational phonon modes were discovered in √7 × √7 germanene, revealing the special coupling between the Dirac fermion and lattice vibrations, namely, electron-phonon coupling (EPC). The significant enhancement of EPC is correlated with the tensile strain, which is evoked by the singular buckled structure of √7 × √7 germanene on the Au(111) substrate. Our results present clear evidence for the existence of epitaxial germanene and elucidate the exotic properties of germanene on Au(111).

Tip-enhanced Raman imaging and nano spectroscopy of etched silicon nanowires

Tip-enhanced Raman spectroscopy (TERS) is used to investigate the influence of strains in isolated and overlapping silicon nanowires prepared by chemical etching of a (100) silicon wafer. An atomic force microscopy tip made of nanocrystalline diamond coated with a thin layer of silver is used in conjunction with an excitation wavelength of 532 nm in order to probe the first order optical phonon mode of the [100] silicon nanowires. The frequency shift and the broadening of the silicon first order phonon are analyzed and compared to the topographical measurements for distinct configuration of nanowires that are disposed in straight, bent or overlapping configuration over a microscope coverslip. The TERS spatial resolution is close to the topography provided by the nanocrystalline diamond tip and subtle spectral changes are observed for different nanowire configurations.

Composition and stress analysis in Si structures using micro-raman spectroscopy

Strained silicon (Si) technology enables improvements in complementary metal oxide semiconductor (CMOS) performance and functionality via replacement of the bulk, cubic-crystal Si substrate with an Si substrate that contains a tetragonally distorted, biaxially strained Si thin film at the surface. Here we use Raman spectroscopy to allow us to characterise growth processes of strained si, and to characterise the resulting level of strain/stress in the si and the effect it has on the underlying layer of graded SiGe.