Adsorption Chemistry of Cyanogen Bromine and Cyanogen Chlorine on Silicon(100)

Abstract

The adsorption and decomposition of cyanogen halides, XCN (X ) Br, Cl), on Si(100) is investigated utilizing X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). For submonolayer exposures, XPS indicates that the CN triple bond of XCN remains intact upon adsorption at 100 K. The UPS spectrum contains two peaks assigned to the π-electrons in the CN triple bond. The splitting indicates that some fraction of the XCN molecules adsorbs molecularly at low temperature. XPS analyses of the C 1s photoelectron peak following submonolayer exposure at low temperature suggest a greater fraction of BrCN (60%) adsorbs molecularly than ClCN (40%). XPS and UPS measurements at room temperature show that the X-CN bond breaks, while the CN bond remains intact during room-temperature adsorption on Si(100). Thus, the UPS spectrum of XCN adsorbed at room temperature on Si(100) contains a peak at 6.0 eV due to the unperturbed π electrons of the CN species. Upon annealing a CN-saturated Si(100) surface to higher temperatures, the UPS spectra indicate that the CN bond remains intact until approximately 700 K. Simultaneous changes in the C 1s and N 1s photoelectron peaks are consistent with the idea that CN bond cleavage is correlated with silicon carbide and nitride formation. These results are compared with a previous study of ICN adsorption on Si(100).

Adsorption and Decomposition Pathways of Cyanogen Halides on Si(100)−(2×1)

“…10,11 Assuming that the reaction pathways shown in Figure 4 are followed experimentally, some tentative conclusions can be inferred. The initial dative bonded end-on adsorption structure (XCN1) is expected to form via a barrierless transition state.…”

“…Given the calculated barrier height, it is reasonable to assume that the reaction proceeds to the experimentally observed SiCN species at room temperature. 10,11 The driving force for the formation of this dissociated species is the replacement of the XC bond with the stronger XSi and SiC bonds.…”

“…Thus, for both pathways, the lowest energy structure is expected to form in agreement with experimental studies. 10,11 …”

“…13 The adsorption and thermal chemistry of the cyanogen halides (XCN, where X ) I, Br, Cl) have been investigated using ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). 10,11 Briefly, UPS measurements show that the CN triple bond of the XCN species remains intact upon adsorption. XPS analysis of the C 1s photoelectron peak following low XCN exposures (0.2-0.3 L) at low temperatures (100 K) indicates that some molecular adsorption occurs.…”

ADSORPTION AND DECOMPOSITION OF ClCN ON Si (100)-(2×1) SURFACE: A DENSITY FUNCTIONAL THEORY STUDY

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] However, most experimental and theoretical reports are on the adsorption of CN-containing molecules on the transition metal surfaces; [1][2][3][4][5][6] there are few experimental and theoretical reports about CN-containing molecule adsorption on semiconductor Si surface. [7][8][9][10][11][12][13] The interaction of CN-containing species with Si surfaces is not only fundamentally interesting [7][8][9] but also practically relvant to the chemical vapor deposition (CVD) of CN x films, 14 particularly SiCN x films which have been demonstrated to exhibit crystalline texture. 15 Lin et al 10 studied the adsorption and decomposition of HCN on Si (100)-(2×1) by using density functional theory calculation on the Si 9 H 12 model dimer clusters.…”