The effect of ion bombardment on the microstructure and properties of molybdenum films

Chromium thin films obtained by evaporation in a vacuum bell-jarr have different reactive properties. In order to determine these ones six techniques are used: X-rays and electron diffractions to study the crystallographical structures; EELS, AES, ESCA, and GXR (grazing X-ray reflection) methods in order to approach the chemical composition. The results permit to show the formation of compounds such as a suboxide (Cr3O) with a primitive cubic cell (A-15 type) and a hydrated oxyhydroxide with a rhombohedral structure. This study leads to show that the „new modification of chromium”, as „NMCr”, cannot be the metal itself.



Les couches minces de chrome obtenues par evaporation sous vide presentent des proprietes reactives diverses. Afin de les determiner nous avons utilise six techniques differentes: la diffraction de rayons-X et la diffraction electronique pour etudier les structures cristallographiques; et les methodes de mesures: EELS, AES, ESCA et GXR (rayons-X rasants par reflection) pour approcher la composition chimique. Les resultats ont permis de mettre en evidence la formation de plusieurs composes: un sous-oxyde de composition „Cr3O” de structure cubique primitive (type A-15) et un oxyhydroxyde hydrate de structure rhomboedrique. Cette etude a conduit a montrer que la „nouvelle modification du chrome”, appelee „NMCr”, ne peut etre assimilee au metal luiměme.

Analysis and crystallographic structures of chromium thin films

Thin films of Cr, Mo, and W rapidly evaporated in high vacuum (5 x 10 to the -7th torr) onto room-temperature substrates show anomalously low reflectance (compared to bulk samples). From electron and X-ray diffraction and electron microscopy, the normal bcc crystal structure is found, but with very fine grains. Columnar grains about 100 A in diameter were separated by a less dense grain-boundary network about 10-A wide. The measured optical conductivity agrees with an inhomogeneous-medium model that assumes the normal crystalline conductivity for the grain interiors, with model parameters that correlate to the observed columnar grain size. In contrast, V and Nb films rapidly evaporated onto room-temperature substrates have the reflectance of bulk crystalline material. On liquid-nitrogen temperature substrates, however, V and Nb have normal bcc crystal structure but with small flat-plate grains, and the same model, with appropriate parameters, accounts for the optical conductivity. The difference between these two groups apparently depends on residual gases segregated at the grain boundaries in the Cr-group films.

Structure and optical properties of evaporated films of the Cr- and V-group metals

Reflective metallic coatings for first mirrors on ITER

Secondary scintillation (defined here as photon emission originating from electron avalanches) was studied for two gaseous micropattern detectors: MSGC (MicroStrip Gas Chamber) and GEM (Gas Electron Multiplier) operated in pure CF4. For MSGC, the study was performed in the pressure range from 1 to 5 bar; for GEM all experiments were carried out at a fixed pressure of 1 bar. Charge gains from ~ 10 to ~ 150 were used in both cases. The primary ionization of the gas was produced by alpha particles from an Am-241 source. Emission spectra of the secondary scintillation were recorded in the wavelength range from 200 to 800 nm and corrected for the response of the detection system. Photon yields (number of photons generated per electron collected at MSGC or GEM) were measured for the integrated UV (200–500 nm) and visible (500–800 nm) emission bands. The obtained emission spectra and photon-per-electron ratios were compared to the corresponding data for the primary scintillation.

https://iopscience.iop.org/article/10.1088/1748-0221/7/02/P02008/pdf

Secondary scintillation in CF4: emission spectra and photon yields for MSGC and GEM

Chromium and molybdenum films deposited in a high vacuum at room temperature are shown to have anomalously low optical reflectance throughout the 0.2–2.5‐μm wavelength range. Deposition at about 700°C for chromium and 1000°C for molybdenum, or postdeposition annealing, gives films with bulk reflectance. X‐ray diffraction and transmission electron microscopy show the films deposited at room temperature to be very fine grained (80–100‐A grain size). Electrical resistivity of the fine grained films is high (3–5 times bulk). High‐temperature deposition or annealing gives larger grains (≳400 A) and lower resistivity. A simple model accounts for the resistivity behavior.

R. W. Christy

Papers

Reflectance and structure of evaporated chromium and molybdenum films