ZnO catalysts

A445 886

Surface Science 189/190 (1987) 886-893 North-Holland, Amsterdam

AN INVESTIGATION OF METAL-SUPPORT INTERACTION IN BIMETALLIC Pt-Mo CATALYSTS DEPOSITED ON SILICA AND ALUMINA A. K A T R I B

*, C. P E T I T , P. LI~GARI~, L, H I L A I R E

a n d G. M A 1 R E

Laboratoire de Catalyse et Chimie des Surfaces, UA 423 du CNRS, Universit~ Louis Pasteur, 4 rue Blaise Pascal. 67070 Strasbourg Cedex, France

Received 25 March 1987; accepted for publication 16 April 1987 The argon ion bombardment of ammonium heptamolybdate reduced the Mo(VI) state to Mo(V) and Mo(IV) states successively as a function of the length of bombardment. However, when this compound (10% Mo) was supported on silica, it was possible to reduce it to metallic molybdenum by Ar + bombardment. Strong metal-support interaction in the form of Pt-O Si and Pt-O AI were induced by Ar + bombardment of vapour deposited platinum on silica and ct-Al203 single crystal. A similar situation was observed in the case of a 10% Pt/SiO2 catalyst. The effect of small Pt crystallite size on the Pt on silica or a-Al20~ results in the relative increase in binding energy of the Pt(4fT/2) (71.7 eV).

894

Surface Science 189/190 (1987) 894-902 North-Holland, Amsterdam

OPTICAL STUDIES OF PHASE IN Cu/ZnO CATALYSTS A. C H I O R I N O ,

F. B O C C U Z Z I

INTERACTION

a n d G, G H I O T I ' I

Istituto di Chimica Fisica, Universitgt di Torino, Corso M. D'Azeglio 48, 10125 Torino, Italy

Received 31 March 1987; accepted for publication 15 May 1987 Cu/ZnO samples with copper fractions ranging from 3 to 50 at% have been studied by diffuse reflectance spectroscopy, Besides the CuO phase absorptiom present in all the oxidized samples, only in the 3 at% sample the fundamental direct ZnO absorption is evident. The others show a modified absorption, interpreted as an indirect transition from CuO valence band to ZnO conduction band, as a consequence of a good contact between the phases. Reduction experiments have pointed out the growth of a Cu metal layer on ZnO particles thick enough to be responsible for the disappearance of the oxidic phases without formation of any new phase. Surface Science 189/190 (1987) 903-912 North-Holland, Amsterdam SURFACE

VIBRATIONAL

903

AND STRUCTURAL

PROPERTIES

OF P O L Y M E R S BY H R E E L S J.J. P I R E A U X , C. G R E G O I R E , a n d R. C A U D A N O

M. V E R M E E R S C H ,

P.A. T H I R Y

Institute for Research in Interface Sciences, Laboratoire InterdOpartemental de Spectroscopie Electronique, Facult& Universitaires Notre-Dame de la Paix, 61 rue de Bruxelles, B-5000 Namur, Belgium

A446 Received 12 April 1987: accepted for publication 7 May 1987 The extiemely promising applications of electron induced vibrational spectroscopy to study the surfaces of polymers and other organic materials are reviewed. It is demonstrated that this technique, which is known as HREELS: high-resolution electron-energy loss spectroscopy, is selectively surface sensitive: information on both the composition and morphology of the polymer surfaces is obtained. However, a quantitative interpretation of the data is not straightforward, as the exact interaction mechanism(s) between the probing electron and the molecular vibrations are not yet ascertained. One of the many illustrations given is the study of the incipient interface formation between a clean cured polyimide film and deposited aluminum which will demonstrate the specific completeness and capabilities of HREELS.

Surface Science 189/190 (1987) 913-918 North-Holland, Amsterdam

913

THE ELECTRONIC BAND STRUCTURE OF (GaAs).(AIAs). AND

(GaAs),(Znge),

G.P. SRIVASTAVA

SUPERLATIICES and A.C. FERRAZ

*

Pl~vsics Department, UnieersiO' of Ulster, Coleraine. Northern Ireland BT52 ISA, UK Received 23 March 1987: accepted for publication 15 April 1987 Using the self-consistent pseudopotential method, within the X a approximation, we have studied the electronic band structure of (GaAs),,(AIAs)~ and (GaAs),(ZnSe),, superlattices. Recent observation on the variation of the band gap in (GaAs),,(AIAs)n and its direct versus indirect nature is explained. Variation of the valence and conduction band discontinuities at G a A s / A 1 ,Ga~_ ~As is calculated as a function of x and a comparison is made with experiment. The difference between the electronic properties of the superlattice (GaAs)I(AIAs)I and the alloy Ga0.,A1 o 5As is investigated in detail. Finally, the variation of the band gap in (GaAs),,(ZnSe),, is compared and contrasted with that in (GaAs)~(A1As),,.

Surface Science 189/190 (1987) 919-926 North-Holland, A m s t e r d a m CONDUCTION

BAND

STRUCTURE

919 OF THE

l|l-Vl

LAYER

COMPOUND GaSe STUDIED WITH INVERSE PHOTOEMISSION J.M. NICHOLLS

* and J.M. DEBEVER

Groupe de Physique des Etats Condensds. UA CNRS 040783. Facult~ des Sciences de Luminv, Case 901, 13288 Marseille Cedex 9. France Received 1 April 1987: accepted for publication 16 April 1987 The conduction band structure of vacuum cleaved surfaces of GaSe is measured with k-resolved inverse photoemission (h~ = 9.5 eV). Several states are found for energies up to 9 eV above the Fermi level. The experimental band structure obtained is compared with that of a pseudopotential band calculation. Comparison is also made with the results of reflectivity measurements and tunneling spectroscopy. A contamination sensitive feature - 1.2 eV below the vacuum level is tentatively assigned to an image state.