Surfactant-mediated growth of ultrathin Ge and Si films and their interfaces: interference-enhanced Raman study

We report on the growth and interfaces of ultrathin polycrystalline Ge and Si films when they are grown on each other using ion beam sputter deposition with and without surfactant at different growth temperatures, studied using interference enhanced Raman spectroscopy. Ge films grown on Si without surfactant show Ge segregation at the interfaces forming an alloy of GexSi1-x as indicated by the Ge-Si Raman mode. However, use of Sb as surfactant strongly suppresses the intermixing. Also Si films grown on Ge have been observed to crystallize at low-substrate temperatures in the presence of the surfactant. In contrast to the growth of Ge on Si, the intermixing in the growth of Si on Ge is observed to be negligibly small even without the surfactant layer

Interference enhanced Raman spectroscopy of ultra thin crystalline Ge films

We report Raman study of ultra thin Ge films using interference enhanced Raman scattering which uses a trilayer structure of Al, CeO2 and crystalline Ge films. The use of CeO2 allows the growth of crystalline Ge films at relatively low substrate temperatures (300°C). With a decrease of Ge film thickness, the Raman line exhibits an increased red shift of the peak position and line broadening. The latter can be quantitatively explained on the basis of phonon confinement in the growth direction. Raman spectra of the 2 nm and 4 nm thick Ge films show shoulder at similar to -280 cm-1 which could be attributed to surface phonons. The changes in the Raman shift as a function of thickness showed that the films were compressively strained up to a thickness of similar to -7 nm beyond which the strain is released

In situ Raman monitoring of ultrathin Ge films

We report the in situ interference enhanced Raman spectroscopy of ultrathin crystalline Ge films grown at $300 ^oC$. The Raman spectra of the films show a peak at $\sim290 cm^{-1}$ attributed to the confined optical phonon and a broadband on the low-frequency side at $\sim254 cm^{-1}$ for 5 and 10 Å thick films. The latter is attributed to disordered surface with large number of dangling bonds. For thicker films, the low-frequency mode appears at $270 cm^{-1}$ assigned to surface optical phonons

Surfactant-mediated growth of ultrathin Ge and Si films and their interfaces: Interference-enhanced Raman study

We report on the growth and interfaces of ultrathin polycrystalline Ge and Si films when they are grown on each other using ion beam sputter deposition with and without surfactant at different growth temperatures, studied using interference enhanced Raman spectroscopy. Ge films grown on Si without surfactant show Ge segregation at the interfaces forming an alloy of GexSi1-x as indicated by the Ge-Si Raman mode. However, use of Sb as surfactant strongly suppresses the intermixing. Also Si films grown on Ge have been observed to crystallize at low-substrate temperatures in the presence of the surfactant. In contrast to the growth of Ge on Si, the intermixing in the growth of Si on Ge is observed to be negligibly small even without the surfactant layer

Interference enhanced Raman spectroscopy of ultra thin crystalline Ge films

We report Raman study of ultra thin Ge films using interference enhanced Raman scattering which uses a trilayer structure of Al, CeO2 and crystalline Ge films. The use of CeO2 allows the growth of crystalline Ge films at relatively low substrate temperatures (300 degrees C). With a decrease of Ge film thickness, the Raman line exhibits an increased red shift of the peak position and line broadening. The latter can be quantitatively explained on the basis of phonon confinement in the growth direction. Raman spectra of the 2 nm and 4 nm thick Ge films show shoulder at similar to 280 $cm^{-1}$ which could be attributed to surface phonons. The changes in the Raman shift as a function of thickness showed that the films were compressively strained up to a thickness of similar to -7 nm beyond which the strain is released

Optical and structural properties of reactive ion beam sputter deposited CeO<SUB>2</SUB> films

Optical and structural properties of reactive ion beam sputter deposited CeO2 films as a function of oxygen partial pressures (Po2) and substrate temperatures (Ts) have been investigated. The films deposited at ambient temperature with Po2 of 0.01 Pa have shown a refractive index of 2.36 which increased to 2.44 at 400 &#176;C. Refractive index and extinction coefficient are sensitive up to a Ts of ~ 200 &#176;C. Raman spectroscopy and X-ray diffraction (XRD) have been used to characterise the structural properties. A preferential orientation of (220) was observed up to a Ts of 200 &#176;C and it changed to (200) at 400 &#176;C and above. Raman line broadening, peak shift and XRD broadening indicate the formation of nanocrystalline phase for the films deposited up to a substrate temperature of 300 &#176;C. However, crystallinity of the films were better for Ts values above 300 &#176;C. In general both optical and structural properties were unusual compared to the films deposited by conventional electron beam evaporation, but were similar in some aspects to those deposited by ion-assisted deposition. Apart from thermal effects, this behavior is also attributed to the bombardment of backscattered ions/neutrals on the growing film as well as the higher kinetic energy of the condensing species, together resulting in increased packing density

Structure and composition related properties of titania thin films

The dependence of optical constants, structure and composition of titania thin films on the process parameters has been investigated. Films were deposited using both reactive electron beam evaporation and ion Assisted Deposition(IAD). If has been observed that the refractive index of IAD films is higher than that for the reactively deposited films, without much difference in the extinction coefficient. Electron paramagnetic resonance has been used to estimate qualitatively the presence of non-stoichiometry in the films. It has been found that these spectra correlate very well the optical behaviour of the films. X-ray diffraction studies revealed that the neutral oxygen deposited films were stress free, while the IAD films showed tensile stress. The lattice parameters showed anisotropic change with ion beam parameters

In situ Raman monitoring of ultrathin Ge films

We report the in situ interference enhanced Raman spectroscopy of ultrathin crystalline Ge films grown at 300 °C. The Raman spectra of the films show a peak at ~ 290 cm<SUP>−1</SUP> attributed to the confined optical phonon and a broadband on the low-frequency side at ~ 254 cm<SUP>−1</SUP> for 5 and 10 Å thick films. The latter is attributed to disordered surface with large number of dangling bonds. For thicker films, the low-frequency mode appears at 270 cm<SUP>−1</SUP> assigned to surface optical phonons

Characterization of ge nanocrystals in a-SiO2 synthesized by rapid thermal annealing

Applied Surface Science144-1450697-701ASUS