0000000000205455
AUTHOR
A. Von Czarnowski
Infrared and Raman spectroscopy of WO3 and CdWO4
Abstract Infrared reflection and Raman spectroscopy have been applied to study the vibrational modes of tungsten trioxide (WO 3 ) and cadmium tungstate (CdWO 4 ). Kramers–Kronig relations are employed to yield the refractive index as well as TO and LO functions of these materials at frequencies from 50 to 1200 cm −1 . The symmetry of the vibrations of CdWO 4 is reported.
Electron beam induced optical and electronical properties of SiO 2
Abstract Ionizing radiation in dielectric and optically transparent silica as well as thin SiO 2 layers produces defect luminescence as well as charge storage. A comparison of different excitation–relaxation processes like cathodoluminescence, charge injection and trapping, secondary electron field emission, and exoelectron emission leads to a generally similar excitation dose behaviour described by an electron beam saturation dose of 0.01–0.1 C/cm 2 . This suggests a correlation of these four electron excitation mechanisms likely related to the same kind of defect in glassy SiO 2 , the 2-fold-coordinated silicon Si: centre with typical electronic singlet–singlet and singlet–triplet transit…
Radiation induced defects in SiO 2
The main luminescent centers in SiO 2 films are the red luminescence R (650 v nm; 1.85 v eV) of the non-bridging oxygen hole center (NBOHC) and the twofold-coordinated (divalent) silicon with a blue B (460 v nm; 2.7 v eV) and a UV band (285 v nm; 4.4 v eV). Especially the latter ones are produced under irradiation, but from existing precursors assumed as silicon related oxygen deficient centers (SiODC). Therefore, in order to prove these models we compare a direct oxygen implantation with a direct silicon implantation into SiO 2 layers. The main result is: implanting oxygen increases the red band R but does not affect the blue band B. Silicon surplus increases the amplitude of the blue (B) …
Structure and luminescence of GaN layers
Abstract GaN films grown on 〈1 1 1〉 Si substrate by means of low pressure MOCVD technique in a horizontal flow quartz reactor are characterized by different thin layer analysis methods. The polycrystalline hexagonal structure of the GaN layers has been checked by means of grazing incidence X-ray diffractometry and IR spectroscopy. Cathodoluminescence (CL) spectra and their time kinetics are studied. The mean decay time of the 3.44 eV UV bound exciton transition is below 1 ns, whereas the 3.26 eV violet band shows a slow hyperbolical decay over about 1 μs. A third yellow band appears at 2.12 eV due to transitions via localized states.
Cathodoluminescence of Ge+, Si+, and O+ implanted SiO2 layers and the role of mobile oxygen in defect transformations
Abstract Thermally grown SiO 2 layers of thickness d =500 nm have been implanted by Ge + , Si + , and O + ions of energy 350, 150, and 100 keV, respectively, and a uniform implantation dose of D i =5×10 16 ions/cm 2 . Thus the implantation profiles are expected with a concentration maximum of nearly 4 at.% at the half-depth d m ≅250 nm of the SiO 2 layers. After thermal annealing to 900 °C for 1 h in dry nitrogen or vacuum the typical violet luminescence band ( λ =400 nm) of the Ge + implanted centers is increased more than 200-fold and the Ge luminescent center depth profile is shifted from about 250 to 170 nm towards the surface as determined by cathodoluminescence (CL) depth profiling. I…
Cathodoluminescence and IR absorption of oxygen deficient silica – influence of hydrogen treatment
Abstract The cathodoluminescence (CL) and IR absorption of silica samples with normal stoichiometry as well as with an extremely high level of oxygen deficit were studied. Additionally, some samples have been treated in hydrogen at 800°C. Crystalline quartz was used for reference measurements and the CL data have been compared with those of X-ray excited luminescence (XL). The luminescence spectra of silica have a band at 1.85 eV due to non-bridging oxygens and the two bands at 2.7 and 4.4 eV due to twofold-coordinated silicons. The energetic yield for CL is about 0.1%, for XL it approaches 0.15%. Cathodoluminescence of quartz at temperatures >130 K exhibits the self-trapped exciton lumines…
IR Spectroscopy of Monoclinic Tungsten Oxide
Stoichiometric tungsten trioxide WO3 has several polimorphous crystal phases [1] in the temperature region from 4 up to 1200K. These WO3 phases have more or less distorted ReO3 — type crystal structures, and ReO3 lattice topology is identical to topology of the BO3 sublattice of perovskite ABO3.