Effects of Potassium on the Adsorption and Reactions of Nitric Oxide on Silicon Surface
- PDF / 422,826 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 90 Downloads / 238 Views
EFFECTS OF POTASSIUM ON THE ADSORPTION AND REACTIONS OF NITRIC OXIDE ON SILICON SURFACE Z. C. YING AND W. HO Laboratory of Atomic and Solid State Physics and Materials Science Center Cornell University, Ithaca, New York, 14853
ABSTRACT The adsorption, thermoreactions, and photoreactions of NO coadsorbed with K on Si(111)7X7 at 90 K have been studied and compared with the results obtained from the Kfree surface. The experiments were performed under ultra-high vacuum conditions using high resolution electron energy loss spectroscopy, work function change measurements, and mass spectrometry. NO adsorbs both molecularly and dissociatively on the K-free surface. Two molecular N-O stretching modes are observed at 188 and 225 meV. The concentration of these NO molecules on the surface decreases as the K exposure increases and vanishes at high K exposures. A new N-O stretching mode, attributed to adsorption of NO molecules on K clusters, is observed at 157 meV. After thermal heating or photon irradiation, the surface is covered with atomic 0 and N. The surface is more oxidized in the presence of K. A steady decrease in the photodesorption cross section is observed as the K exposure increases and is attributed to K-induced band structure changes. INTRODUCTION The adsorption of alkali metals on semiconductor surfaces has been observed to cause a decrease in the work function and to induce changes in the chemical and physical properties of the surface. Recent studies have focussed on the determination of the electronic properties of K chains on Si(100) surface' and the promotion of chemical reactions, such as oxidation 2 and nitridation 3 of the silicon surface by submonolayer coverages of K. The presence of alkali metals is also expected to promote or suppress photochemical reactions on solid surfaces. Studies of photoreactions on surfaces preadsorbed with alkali metals are expected to lead to an increase in our general understanding of the fundamental mechanisms of photo-induced reactions on solid surfaces. 4' 5 Furthermore, results from these studies can also have technological implications for microelectronic materials processing. The adsorption, thermoreactions, and photoreactions of NO coadsorbed with K on Si(111)7x7 at 90 K have been studied in detail and the main results are reported in this paper. The present study extends our previous investigation of NO on the K-free 6 Si(111)7x7 surface. ,7 EXPERIMENTAL ARRANGEMENT The experiments were performed under ultra-high vacuum (UHV) conditions, using high resolution electron energy loss spectroscopy (HREELS), thermal desorption spectroscopy (TDS), photon induced desorption spectroscopy (PIDS), and work function change (A0) measurements. An n-type (5.5 x 1014 cm- 3 ) Si(111) sample was used. The sample was cleaned by repeated cycles of sputtering and annealing. The clean surface, cooled down to 90 K, was exposed to K from a heated K getter. The surface was then exposed to a saturation exposure of NO. The coverage of K deposited on the surface was achieved reproducibly by
Data Loading...
