Low-energy electron-stimulated desorption of cations and neutrals from Si(111)-(7×7):C2D2

Abstract

The interactions of low-energy (5-50 eV) electrons with acetylene-d(2) (C(2)D(2)) adsorbed on the Si(111)-(7x7) surface have been examined by monitoring the stimulated desorption products. These include primary cation desorbates, D(+) and C(2)D(2)(+) (C(2)HD(+)), the fragment ion C(2)D(+), smaller amounts of C(2)(+), CDH(+) (CH(3)(+)), and neutral D((2)S). The approximately 23-25 eV threshold energies for D(+) and hydrocarbon fragment ion detection indicate involvement of two-hole or two-hole one electron final states that Coulomb explode. These multihole states can be created via Auger decay of single holes in shallow core levels localized on C or Si surface atoms. The approximately 12 eV appearance threshold for the C(2)D(2)(+) molecular ion can be correlated with direct excitation of an adsorbate-induced surface state, which may initially possess character of the A(3) surface state of Si. The 18 eV threshold for C(2)D(+) correlates with decomposition of C(2)D(2)(+) with excess vibronic energy. C(2)D(+) desorption via direct excitation of the dissociative (2)Sigma(u)(+)-type state of the C(2)D(2)(+) ion is also possible. The approximately 8 eV threshold energy for production and desorption of neutral D((2)S) may correlate with excitation of the perturbed/mixed F (1)Sigma(u)(+)<--X (1)Sigma(g)(+) and E (1)Sigma(u)(+)<--X(1)Sigma(g)(+) dissociative transitions of adsorbed acetylene molecules. Time-of-flight distributions of D((2)S) indicate both nonthermal (557 and 116 meV; 4300 and 900 K) and thermal (17 meV; 130 K) components. The two fast components can be related to the geometry of di-sigma bonded acetylene on the Si(111)-(7x7) surface.

Molecular and atomic manipulation mediated by electronic excitation of the underlying Si(111)-7x7 surface

“…The Si(111)-7x7 surface has been extensively used in studies of molecular adsorption, desorption and more particularly STM induced manipulation both of atomic and molecular adsorbates and the silicon surface itself [20][21][22][23][24][25]. It has also demonstrated photo-induced silicon atom desorption through laser irradiation [26][27][28].…”

Photodissociation of methyl iodide adsorbed on low-temperature amorphous ice surfaces

“…Both ground-state I( 2 P 3/2 ) and excited-state I( 2 P 1/2 ) atomic iodine desorbates were detected by focusing a tunable pulsed ionization laser beam above and parallel to the surface. 40,41 The distance between the surface and the detection region was 0.8 mm for 260 nm and 1.2 mm for 290 nm. The ground and excited states of neutral iodine were detected using the I(6p [3] 5/2 ← 5p 2 P 3/2 ) and I(6p[1] 3/2 ← 5p 2 P 1/2 ) (2+1) REMPI schemes at 304.67 and 305.57 nm, respectively.…”