Stephen A. Joyce

The chemisorption of chlorosilanes and chlorine on Si(111)7 × 7

Abstract The chemisorption of SiCl4, Si2Cl6, and chlorine on Si(111)7 × 7 has been characterized using soft X-ray photoemission with synchrotron radiation, thermal desorption spectroscopy, and Auger electron spectroscopy. SiCl4 dissociatively chemisorbs on room temperature Si(111)7 × 7 with an extremely low sticking coefficient, with only SiCl remaining on the surface. In contrast, Si2Cl6 chemisorbs with ∼ 500 times greater probability and then partly dissociates into SiClx (x = 1, 2, 3) fragments. A monolayer of Cl deposited directly also contains SiCl, SiCl2, and SiCl3 surface species, but they are created via reaction with substrate Si atoms and have lower Si2p core level binding energies. Upon heating the surface all the adsorbed Cl is removed via desorption of silicon chlorides, primarily SiCl2, indicating that SiCl4, Si2Cl6, and chlorine will etch Si(111)7 × 7 if an additional reactant is not avail to remove the surface Cl. Interestingly, the different reactivities of SiCl4 and Si2Cl6 upon adsorption can be explained by the dynamics of different adsorption mechanisms.

Desorption Induced by Electronic Transitions

Bombardment of a surface by electrons or photons can cause rupture of surface bonds and desorption from the surface, by inducing transitions to repulsive electronic states. The phenomenon of desorption induced by electronic transitions (DIET) includes both electron stimulated desorption (ESD) and photon stimulated desorption (PSD) [4.1–3]. DIET processes are of widespread importance in many areas of science and technology, including beam damage in surface analysis using x-rays or electrons, in electron and photon beam lithography, and in radiation physics of interstellar space, to name a few.

Methodology for electron stimulated desorption ion angular distributions of negative ions

The electron stimulated desorption angular distributions technique has been extended to measure the angular distributions of negative ions desorbing from surfaces. The apparatus is a modification of an existing display‐type detector. Time‐of‐flight methods have been employed to separate the negative ions from the large background of electrons, and to permit mass‐resolved measurements of both positive and negative ions. General trends in negative ion desorption from a series of fluorinated molecules (PF3 , NF3 , and hexafluoroacetone) adsorbed on Ru(0001) are presented. In these systems, negative ions arise primarily from molecularly intact adsorbates while positive ions can arise from both intact and dissociated species with similar probability.

Radiation damage in an adsorbed monolayer: PF3 on Ru(0001)

Abstract The chemisorption of PF3 on Ru(0001) has been studied using soft X-ray photoemission spectroscopy (SXPS) and photon stimulated desorption (PSD). The initial adsorption of PF3 on ruthenium is predominantly molecular. PF3 is found to be extremely sensitive to both electron and photon beam exposure, leading to the formation of adsorbed PFx fragmentation products and the desorption of fluorine. Annealing the beam-damaged overlayers results in the reformation of some adsorbed PF3. PSD ion yields at photon energies near the P 2p absorption edge show that direct photoexcitations of the adsorbed PF3 and PF2 species lead to F + desorption. Photoexcitation of the the P 2p level of an adsorbed PF unit does not lead to direct F+ emission, however.

British vacuum council annual address—1988: Electron and photon stimulated deosrption: benefits and difficulties

Abstract Some of the benefits and pitfalls of electron and photon stimulated desorption (ESD/PSD) processes at surfaces are described. The benefits include useful information about the local structure of surface molecules, provided by electron stimulated desorption ion angular distributions (ESDIAD), ESDIAD is an effective surface structural tool because the directions of ion desorption are determined by the orientation of the surface bonds ruptured by electron or photon bombardment. Other benefits of electron and photon-stimulated damage processes at surfaces include electron and photon beam lithography in microelectronics. The pitfalls of ESD/PSD include beam damage in surface analysis (by Auger electron spectroscopy, X-ray photoelectron spectroscopy and high resolution transmission electron microscopy), the PSD of gases from vacuum walls in fusion reactors and synchrotron radiation sources, and inaccurate pressure readings due to ESD effects in ionization gauges.

The Structure of Molecules on Surfaces as Determined Using Electron-Stimulated Desorption

The structure of molecules on surfaces is an area of great importance in surface science, and a variety of surface-sensitive methods have been applied to structural problems. Many of these techniques [including Angle Resolved Ultraviolet Photo-emission Spectroscopy (ARUPS), X-ray absorption near-edge structure (XANES), surface extended X-ray absorption fine structure (EXAFS), high-resolution electron energy loss spectroscopy (HREELS), and photoelectron diffraction (PD)] are discussed in other chapters in this volume.