A 1 9 0

evaluated. Water and tetradecane particle interaction potentials for the same size particles are also calculated to illustrate size effects due to the retardation of the interaction. These potentials are then used to calculate the enhancement of the particle collision rates above their value in the absence of any potential at various gas pressures. The roles of the interaction potential in collision among identical pairs of particles of differing compositions is also briefly discussed.

Surface Science 106 (1981) 538-543 North-Holland Publishing Company

P H O T O E L E C T R O N E M I S S I O N F R O M S M A L L P A R T I C L E S

S U S P E N D E D IN A G A S

A. S C H M I D T - O ' I T * and B. F E D E R E R

Atmospheric Physics ETH, CH-8093 Ziirich, Switzerland Received 8 September 1980; accepted for publication 11 November 1980

Photoelectron emission from small particles (d - 100 A) suspended in air and other gases is measured for the first time. The electrons photoemitted from the particles lead to an aerosol photoconductivity 2 which is measured by means of an AC bridge circuit. E(t) is governed by the photoemission rate, the rate of attachment of electrons (or negative ions in electronegative gases) to particles and the diffusion loss of ions and particles. It is related to the particles' size, concentration and photoelectric yield Y (electrons emitted per incident photon). Y(hv) is determined near the photothreshold ~b (~ < hv < ~ + 1.5 eV) for particles of Ag, Au and various metaloxides in an Nz-O2 mixture. It is demonstrated that Y is abnormally high (e.g. a factor of 102 for Ag!) compared to photo yields of large surfaces in ambient gases. The sensitivity of Y(hv) to adsorbates on the particle surface is demonstrated for H20 adsorption on W oxide particles. Due to the enhanced photoelectric yield, photoelectric charging is very efficient for small particles. The electrical mobility spectrum of aerosol particles photoelectrically charged to a Coulomb limit is related to their size distribution and their photothresholds. Such measurements are performed with atmospheric aerosols ~ and compared with size distributions obtained with the commercially available Withby electrostatic aerosol analyzer based on charging by small ion attachment and mobility analysis. Implications of the high photo yield on atmospheric processes are discussed.

Surface Science 106 (1981) 5-44-550 North-Holland Publishing Company

F I L M F O R M A T I O N T E C H N I Q U E BY I O N I Z E D - C L U S T E R B E A M

T. T A K A G I * , I. Y A M A D A * * a n d H. T A K A O K A * * *

Kyoto University, Sakyo, Kyoto 606, Japan Received 8 September 1980; accepted for publication 27 October 1980

The ionized-cluster beam (ICB) technique (deposition and epitaxial growth) does not use ionized atoms or molecules as in the conventional ion plating method. The cluster is formed from a loosely coupled aggregate of about 103 atoms by an adiabatic expansion of pure evaporant material without any inert gas mixing, through a nozzle into high vacuum (10-7-10-STorr). We have previously shown that the crystal structure could be changed from an amorphous state to a single crystal by changing the acceleration voltage for the deposition at a particular substrate temperature. These experimental data suggested to us the possibility of forming a hydrogenated amorphous Si film useful for electron devices. By using the ICB technique, hydrogenated amorphous Si can be prepared at hydrogen pressure lower than 10 -4 Torr, whereas in the conventional fabrication methods such as glow discharge and reactive

A191

sputtering, hydrogenated amorphous Si film is deposited from reactive gas plasma at the pressure higher than 10-2Torr. The operation condition requiring high gas pressure may cause serious contamination by gases, and complicates the diagnosing of the deposition conditions. On the other hand, the ICB technique is preferable to overcome these difficulties. In this paper, the required deposition conditions of amorphous Si films are described from a standpoint of the behaviour of incident clusters onto a substrate. The thermally stable amorphous Si film properties are also shown.

Surface Science 106 (1981) 551-555 North-Holland Publishing Company

SOME ASPECTS OF HEAT CONDUCTION IN FERROFLUIDS J.P. BRANCHER LEMTA, Laboratoire d'Energ~tique et de M~canique Th~orique et Appliqu~e, 2 Rue de la Citadelle, F-54011 Nancy C~dex, France

Received 8 September 1980; accepted for publication 19 September 1980

The aim of this paper is to introduce the contribution of internal rotations in colloidal suspensions of magnetic particles, in heat transfer phenomena. The conduction phenomenon can be taken from a macroscopic point of view. However, the microscopic convection disturbs the isotropy of the medium. New parameters like the Peclet number must be introduced.

Surface Science 106 (1981) 556-562 North-Holland Publishing Company

CLUSTER INFLUENCE ON ELECTRICAL PROPERTIES OF AI-Zn SOLID SOLUTIONS J. MERLIN, G. VIGIER, J.M. PELLETIER and R. BORRELLY Groupe d'Etudes de M~tallurgie Physique et de Physique des Mat~riaux ERA 463, INSA de Lyon, t:-69621 Villeurbanne C~dex, France Received 8 September 1980; accepted for publication 15 December 1980

The existence of small atom clusters in metallic solid solutions leads to electrical resistivity and thermoelectric power variations. Such variations are studied in the present work in AI-Zn alloys, in a temperature range where no precipitation phenomenon occurs.

Surface Science 106 (1981) 563-568 North-Holland Publishing Company

PRODUCTION AND BEAM ANALYSIS OF ENERGETIC SMALL HYDROGEN CLUSTER IONS FOR STUDY OF THEIR INTERACTION WITH TARGETS AND OF THEIR STRUCTURE Y. CHANUT, J. MARTIN and R. SALIN [nstitut de Physique NuclJaire et IN2P3, Universit~ Lyon-l, 43 Bd. du 11 Novembre 1918, F-69622 Villeurbanne Cedex, France

and