The effects of microcrystal size and shape on the one phonon Raman spectra of crystalline semiconductors

http://nathan.instras.com/documentDB/paper-69.pdf

Porous silicon: a quantum sponge structure for silicon based optoelectronics

https://hal.archives-ouvertes.fr/hal-00120432/document

Raman Spectroscopy of Nanomaterials: How Spectra Relate to Disorder, Particle Size and Mechanical Properties

Nanostructured oxides in chemistry: characterization and properties.

Two-dimensional (2D) transition metal dichalcogenide (TMD) nanosheets exhibit remarkable electronic and optical properties. The 2D features, sizable bandgaps and recent advances in the synthesis, characterization and device fabrication of the representative MoS2, WS2, WSe2 and MoSe2 TMDs make TMDs very attractive in nanoelectronics and optoelectronics. Similar to graphite and graphene, the atoms within each layer in 2D TMDs are joined together by covalent bonds, while van der Waals interactions keep the layers together. This makes the physical and chemical properties of 2D TMDs layer-dependent. In this review, we discuss the basic lattice vibrations of 2D TMDs from monolayer, multilayer to bulk material, including high-frequency optical phonons, interlayer shear and layer breathing phonons, the Raman selection rule, layer-number evolution of phonons, multiple phonon replica and phonons at the edge of the Brillouin zone. The extensive capabilities of Raman spectroscopy in investigating the properties of TMDs are discussed, such as interlayer coupling, spin–orbit splitting and external perturbations. The interlayer vibrational modes are used in rapid and substrate-free characterization of the layer number of multilayer TMDs and in probing interface coupling in TMD heterostructures. The success of Raman spectroscopy in investigating TMD nanosheets paves the way for experiments on other 2D crystals and related van der Waals heterostructures.

Phonon and Raman scattering of two-dimensional transition metal dichalcogenides from monolayer, multilayer to bulk material

The one phonon Raman spectrum in microcrystalline silicon

The red shift and the broadening of the Raman signal from microcrystalline silicon films is described in terms of a relaxation in the q-vector selection rule for the excitation of the Raman active optical phonons. The relationship between width and shift calculated from the known dispersion relation in c-Si is in good agreement with available data. An increase in the decay rate of the optical phonons predicted on the basis of the same model is confirmed experimentally.

The one phonon raman spectrum in microcrystalline silicon

Microcrystalline silicon (grain size ∼100 A) films have been prepared at temperatures below 400 °C through an H2‐plasma assisted transport process. The films contain an average of ∼2 at. % of hydrogen which is predominantly situated in the grain boundary regions in the form of Si‐H2. The optical absorption coefficient of these films exceeds that of crystalline Si by up to two orders of magnitude below 3.0 eV. The films can be doped by adding PH3 to the hydrogen plasma. The highest room‐temperature conductivity so achieved was ∼1 (Ω−1 cm−1). From an analysis of the activation energies vs dopant concentration we deduce that the high‐temperature transport (T≳330 °K) is barrier limited. The upper limit for the density of trapping states in the grain boundaries is 1×1013 cm−2.

Optical properties and transport in microcrystalline silicon prepared at temperatures below 400 °C

Using in-situ Raman spectroscopy, we have studied the growth of microcrystal 1 i ne s il icon films prepared by plasma-assi sted transport at sub- strate temperatures around 300~~. Me find that initially the m aterial grows as an amorphous film. At thicknesses over about 15 nm, crystallites are detec- ted. Further growth increases the ratio of crystal 1 ine to amorphous material in the film. Subsequent etching of the film reveals a crystallization of the initially amorphous layer during the growth process. Measurements of the Anti stokes/Stokgs ratio during film growth indicate that local temperatures are at least 300 C below the crystall ization tempegature of the amorphous layer, that has been separately determined to be 700 C, the same as that of thick amorphous silicon films. We therefore conclude that the crystal1 ization cannot be expl ai ned by a thermal annealing process. The experimental facts are compared with the low temperature crystallization of amorphous sil icon in a hydrogen plasma observed by Bustarret et a1 . (1 ) and they are discussed in the light of the crystallization model proposed by Veprek et a1 .(2)

https://hal.archives-ouvertes.fr/jpa-00221791/document

Growth of plasma-transport microcrystalline silicon as studied by in-situ raman spectroscopy

We have studied the interface formation at 550 K between Sb(111) and evaporated indium with angle‐resolved photoemission using synchrotron radiation. At ultralow coverages (0.007–0.02 ML), simultaneous formation of small In clusters, and two‐dimensional growth of InSb is detected. At higher coverages, the formation of an epitaxial layer of InSb is observed. The valence‐band energy distribution curves exhibit pronounced angular variations which are consistent with the formation of a highly ordered InSb(111) overlayer.

H. Richter

Papers

The one phonon Raman spectrum in microcrystalline silicon

The one phonon raman spectrum in microcrystalline silicon

Optical properties and transport in microcrystalline silicon prepared at temperatures below 400 °C

Growth of plasma-transport microcrystalline silicon as studied by in-situ raman spectroscopy

InSb growth on Sb(111) single crystals studied by angle-resolved photoemission