A study of surface hydroxyl groups on .gamma.-alumina

Abstract

Publicatlon costs assisted by Universidad de SevillaA statistical-mechanic study of the surface dehydration of y-alumina is made. The surface monolayer is considered as a monomer-asymmetrical dimer system on a square lattice, so that only nearest neighbors interact. The evolution of a wide set of surface ionic groups is studied. The results explain successfully the experimental data of thermogravimetric analysis, infrared spectra, and mobility of surface ions at T > 600 "C. The contributions to the activation energy of the different surface interactions have been estimated, giving eoo N 2 kcal/mol (oxide-oxide interaction), eHO = 1 kcal/mol (hydroxyl-oxide interaction), and e " N 0 (hydroxyl-hydroxyl interaction). The adsorbed water molecule energy is a surface coverage function and falls between -26 and -89 kcal/mol, within the expected range.

Cryo-ePDF: Overcoming Electron Beam Damage to Study the Local Atomic Structure of Amorphous ALD Aluminum Oxide Thin Films within a TEM

“… 64 The decrease in surface hydroxyl coverage at elevated temperature is significant, with an expected ∼40% reduction in surface *OH density on the growth surface upon increasing the growth temperature from 150 to 300 °C. 80 , 81 The decrease in the number of *OH growth sites at elevated growth temperatures is expected to (a) introduce a preference for TMA to react via single-reaction sites (Al(CH 3 ) 3 + *OH → *OAl(CH 3 ) 2 ) over dual reaction sites (Al(CH 3 ) 3 + 2*OH → *O 2 AlCH 3 ) during the TMA ALD half reaction and (b) lead to the incorporation of unreacted Al–O–Al groups within the bulk AlO x structure. We expect that the combination of these effects would lead to a higher O-content and lower O–Al CN values at elevated growth temperatures, consistent with the observations in Figure 10 c,f, respectively.…”

“…The TMA ALD half reaction requires surface hydroxyls, and the equilibrium surface hydroxyl density is expected to decrease at elevated growth temperature. 12,15,64,[80][81][82][83][84] This decrease in hydroxyl density with increasing temperature arises from recombinative desorption of *OH groups (* indicates a surface-bound species) to release H2O via the reaction 2*AlOH → *Al-O-Al* + H2O. 64 The decrease in surface hydroxyl coverage at elevated temperature is significant, with an expected ~40% reduction in surface *OH density on the growth surface upon increasing the growth temperature from 150°C to 300°C.…”

FTIR Spectroscopy of Adsorbed Probe Molecules for Analyzing the Surface Properties of Supported Pt (Pd) Catalysts

“…It should be noted that modern concepts of the surface structure of aluminum oxides, which were developed in recent 50 years, are based mainly on the vibrational spectroscopy data. Various structural models of the aluminum oxide surface were suggested to explain the experimental data www.intechopen.com (Egorov, 1961;Peri, 1965;Tsyganenko & Filimonov, 1973;Zamora & Córdoba, 1978;Knözinger & Ratnasamy, 1978). These models are based on the spinel structure of transitional alumina modifications.…”

Effect of residual H 2 O on epitaxial AlN film growth on 4H-SiC by alternating doses of TMA and NH 3

“…It is well-known that the annealing temperature decreases the concentration of the surface hydroxyl group [25,39,40], and that the quantitative values are well matched with the GPC of TMA/H 2 O deposition process [14]. Hydroxyl groups can be lost by the recombinative desorption of two AlOH species to produce gas phase H 2 O and to leave an Al-O-Al bond on the surface [36,[41][42][43]. Fig.…”