Influence of pressure and radio frequency power on deposition rate and structural properties of hydrogenated amorphous silicon thin films prepared by plasma deposition

The influence of radio frequency (rf) power and pressure on deposition rate and structural properties of hydrogenated amorphous silicon (a-Si:H) thin films, prepared by rf glow discharge decomposition of silane, have been studied by phase modulated ellipsometry and Fourier transform infrared spectroscopy. It has been found two pressure regions separated by a threshold value around 20 Pa where the deposition rate increases suddenly. This behavior is more marked as rf power rises and reflects the transition between two rf discharges regimes. The best quality films have been obtained at low pressure and at low rf power but with deposition rates below 0.2 nm/s. In the high pressure region, the enhancement of deposition rate as rf power increases first gives rise to a reduction of film density and an increase of content of hydrogen bonded in polyhydride form because of plasma polymerization reactions. Further rise of rf power leads to a decrease of polyhydride bonding and the material density remains unchanged, thus allowing the growth of a-Si:H films at deposition rates above 1 nm/s without any important detriment of material quality. This overcoming of deposition rate limitation has been ascribed to the beneficial effects of ion bombardment on the a-Si:H growing surface by enhancing the surface mobility of adsorbed reactive species and by eliminating hydrogen bonded in polyhydride configurations.

[8 phot. de l'inlandsis du Groenland par J. Jaeger, phot. à Stockholm, d'après des dessins du docteur Berggren, juillet 1870, don A. E. Nordenskild]

Donateur : Nordenskjöld, Adolf Erik (1832-1901)

[41 phot. de Tchouktches prises lors du voyage de la Vega en 1879, expédition de A.E. Nordenskild le long des côtes de la Sibérie, des collections du prince Roland Bonaparte]

Donateur : Bonaparte, Roland (1858-1924)

José Ramón Mélida. Arqueología Española. Edición de Margarita Díaz Andreu

Dentro de la serie de Urgoiti Editores sobre los grandes nombres de la ciencia histórica en España, se publica la tercera obra dedicada a los arqueólogos y prehistoriadores de la primera mitad del siglo XX. Tras los estudios de Jordi Cortadella sobre Pere Bosch Gimpera (1981-1974) y Fernando Wulff sobre Adolf Schulten (1870-1960), y a la espera del trabajo de Gloria Mora sobre Hugo Obermaier (1877-1946), ve la luz el estudio que Margarita Díaz Andreu ha dedicado a una de las figuras más nombradas, pero a la par más desconocidas, de la arqueología española: José Ramón Mélida y Alinari (1856-1933).

Uplifted spirits, earthbound machines : studies on artists and the dream of flight, 1900-1935

Doctoral dissertation, Academy of Fine Arts