M.L. Colaianni

Vibrational studies of CH3I on Si(100)-(2×1): adsorption and decomposition of the methyl species

Abstract The dissociative adsorption of CH 3 I to adsorbed CH 3 and I on a clean Si(100)-(2×1) surface has been studied by high resolution electron energy loss spectroscopy (HREELS), temperature-programmed desorption (TPD) and Auger electron spectroscopy. The thermal stability of CH 3 (a) to 600 K has been witnessed spectroscopically. At higher temperatures, CH 3 (a) decomposes to CH(a), possibly via the production of intermediate CH 2 (a) species. The CH(a) species is stable to ≈800 K. HREELS and TPD show that following CH 3 I dissociative adsorption at 100 K, a multilayer of undissociated CH 3 I is condensed on the substrate. Upon heating, this condensed overlayer is desorbed with a peak temperature of 225 K. H 2 and I desorption occur near 785 K, leaving adsorbed carbon on the Si(100) surface.

The Cu/Al2O3/Al(111) interface: initial film growth and thermally induced diffusion of copper into the bulk

Abstract High-resolution electron energy loss spectroscopy and Auger electron spectroscopy have been used to investigate the Cu/Al 2 O 3 /Al(111) interface at temperatures between 95 and 700 K. The copper overlayer was deposited by in situ evaporation, and the Al 2 O 3 substrate was prepared by controlled oxidation of an atomically clean Al(111) surface. It was found that the first monolayer of copper forms a smooth overlayer on the Al 2 O 3 /Al(111) substrate at 95 K. Heating the Cu/Al 2 O 3 /Al(111) layer causes an inward diffusion of the copper overlayer. The chemisorption of CO on the Cu/Al 2 O 3 /Al(111) substrate has been studied also and the results are compared to previous investigations of a Ni/Al 2 O 3 /Al(111) interface.

Direct vibrational detection of surface reaction channels leading to CO dissociation and to its inhibition on Mo(110)

Abstract Alternate surface reaction channels involving CO dissociation and the inhibition of dissociation on Mo(110) have been detected directly by vibrational studies using EELS. The CO species that exhibit a ν(CO) of 1345 cm −1 can be converted completely to adsorbed atomic carbon and atomic oxygen via an intermediate with ν(CO)=1130 cm −1 . Alternatively, when oxygen is chemisorbed with the CO species that exhibit a ν(CO) of 1345 cm −1 , CO dissociation is inhibited, and the CO is converted to CO species with ν(CO)≈2000 cm −1 via an intermediate species with ν(CO) of 1465-1535 cm − .

Silicon backbond strain effects on NH3 surface chemistry: Si(111)-(7 × 7) compared to Si(100)-(2 × 1)

Abstract The role of surface structure in controlling NH3 surface chemistry has been investigated by HREELS and TPD on Si(111)-(7 × 7) and Si(100)-(2 × 1). Following the initial NH3 dissociative adsorption producing NH2(a) and H(a), the production of NH(a) species is favored on Si(111)-(7 × 7) between 300 and 600 K. This is believed to occur through the insertion of NH(a) into the backbond of the Si adatom on Si(111)-(7 × 7) and to be driven by the relief of bond strain on the Si adatom backbonds. By contrast, this stepwise reaction step is disfavored on (Si(100)-(2 × 1). Instead, the surface NH2(a) species remain thermally stable until ~ 600 K, when a new reaction channel opens up leading to the 73% depletion of NH2(a) by recombination with H(a) to form NH3(g).

Spectroscopic studies of the thermal modification of the Fe/Al2O3 interface

Abstract A combination of high resolution electron energy loss spectroscopy (HREELS) and Auger electron spectroscopy (AES) has been applied to the investigation of thin metallic iron films on Al2O3. Two thermally-activated processes have been observed at the Fe/Al2O3 interface. In the temperature region 90–400 K, agglomeration of iron occurs to produce larger clusters of iron (process I). In the temperature region 400–900 K, little change is observed in the thin film, except for some enhancement of the elastic scattering of 3.8 eV electrons, and some small changes in Auger intensity. Above ∼ 900 K, diffusion of the iron into the Al2O3 film occurs, resulting in the production of a clean Al2O3 surface by 1200 K. (process II). It has been demonstrated that the diffusion of metallic iron into Al2O3 is not accompanied by oxidation of iron. In addition to the study of the Fe/Al2O3 interface, it was found that an iron oxide film on Al2O3 does not agglomerate into clusters below ∼ 900 K, but that iron oxide diffusion into Al2O3 occurs above ∼ 900 K.

The stepwise dissociation of NH3 on the Si(111)–(7×7) surface: Low‐temperature dissociative adsorption and thermal effects

The molecular and dissociative adsorption of NH3 on a clean Si(111)–(7×7) surface has been studied using high‐resolution electron‐energy‐loss spectroscopy (HREELS), Auger electron spectroscopy, and temperature‐programmed desorption (TPD). All NHx (3≥x≥1) species have been observed vibrationally under varying experimental conditions. Adsorbed molecular ammonia is observed by both HREELS and TPD below 200 K. The absence of a strong δs(NH3) mode in our vibrational spectra suggests that NH3 is bound as a tilted species to the Si(111)–(7×7) surface. Ammonia exposures above 1.7×1014 NH3/cm2 at 110 K populate a weakly bound NH3(a) state which desorbs upon heating with a peak desorption temperature of 115 K. The NH2(a) species is observed to form at 80 K at all coverages and exhibits an enhanced thermal stability at higher ammonia exposures. The NH(a) species is detected above 200 K by an energy‐loss feature at 1100 cm−1, which we assign to the δ(NH) mode. NH(a) is stable to 750 K on high coverage layers. Finally...

Inhibition of atomic hydrogen etching of Si(111) by boron doping

Abstract : Subsurface boron doping reconstructs the Si(111) surface and alters the electronic character of the surface Si atoms. The interaction of atomic hydrogen with the boron-modified Si(111) - (V3xV3) - R30 surface was studied using temperature programmed desorption (TPD), high resolution electron energy loss spectroscopy (HREELS) and low energy electron diffraction (LEED). In comparison to the Si(111) - (7x7) surface, we observe a significantly reduced hydrogen saturation coverage, measured by TPD and HREELS, and the absence of silane production. The ordered (1/3 ML) subsurface boron atoms passivate the surface Si atoms and reduce their reactivity with atomic hydrogen. This leads to a surface condition causing suppression of silicon etching by atomic hydrogen, compared to the unmodified Si(111) - (7x7) surface.

Fragmentation of molecular adsorbates by electron and ion bombardment: Methoxy chemistry on Al(111)

(High resolution) electron energy loss spectroscopy [(HR)EELS] has been used successfully to provide direct spectroscopic evidence regarding details of the molecular fragmentation of methoxy (CH3O) on Al(111) caused by energetic electron and ion beams. Chemisorbed methoxy on Al(111) is produced by heating of adsorbed CH3OH. Irradiation of CH3O(a) by either energetic (∼300 eV) electrons or Ar+ ions results in C–O and C–H bond scission with simultaneous formation of Al–O and Al–C bonds. During electron stimulated desorption the CH3O(a) species undergo sequential fragmentation first to CHx groups that are captured by the surface and in the final decay process to adsorbed carbon. C–O bonds in CH3O(a) are depleted preferentially compared to C–H bonds in CHx(a) species. The electron induced sequential fragmentation of the parent CH3 group (from methoxy) to resultant CHx(a) occurs with an efficiency ∼3 orders of magnitude greater then the subsequent process of CHx(a) →C(a). Cross sections for various bond scissi...

The thermal dissociation of decaborane on Si(111)‐(7×7) and doping effects in the near surface region

The thermal decomposition of decaborane (B10H14) and its doping effects on Si(111)‐(7×7) has been investigated by surface spectroscopies. Upon adsorption between 100 and 300 K, molecular decaborane was identified on the surface by high‐resolution electron‐energy‐loss spectroscopy (HREELS) by the absence of Si‐H surface species production. The thermal decomposition of adsorbed decaborane molecules at higher temperatures involves a preferential removal of hydrogen from the weaker B—H—B linkage. H2 thermal desorption was observed to cover a wide temperature range between 300 and 900 K. Clean boron deposition on the surface was achieved at ∼900 K. Upon heating to ∼1275 K, extensive boron diffusion into bulk silicon produced a highly B‐doped region below the surface (∼103 A) with a carrier hole concentration on the order of ∼1019 cm−3 depending upon the initial surface boron coverage and annealing conditions. The surface adopted a (√3×√3)R30° reconstruction with a nominal 1/3 ML boron occupying subsurface subs...

Dissociative adsorption of PH3 on Si(111)-(7 × 7): a high resolution electron energy loss spectroscopy study

Abstract Dissociative adsorption of PH 3 on Si(111)-(7 × 7) has been observed at 80 K. The Si-H species is observed to be produced upon PH 3 adsorption. Depending upon the PH 3 surface coverage, PH 3 (a) (minority species) and PH 2 (a) species are found on the surface. The thermal dissociation of the surface PH 2 species occurs between 450 and 500 K, resulting in the capture of hydrogen and phosphorus on the surface.