Atomic-Scale Desorption Through Electronic and Vibrational Excitation Mechanisms

Abstract

The scanning tunneling microscope has been used to desorb hydrogen from hydrogen-terminated silicon (100) surfaces. As a result of control of the dose of incident electrons, a countable number of desorption sites can be created and the yield and cross section are thereby obtained. Two distinct desorption mechanisms are observed: (i) direct electronic excitation of the Si-H bond by field-emitted electrons and (ii) an atomic resolution mechanism that involves multiple-vibrational excitation by tunneling electrons at low applied voltages. This vibrational heating effect offers significant potential for controlling surface reactions involving adsorbed individual atoms and molecules.

Manipulation of atoms across a surface at room temperature

“…We did not use voltages below 10 meV in the motion experiments, so there is always enough energy available to excite the Br motion. Multiple excitation before relaxation is also possible 17,19 , which might allow use of even lower voltages, but we do not have direct evidence to indicate this at present. We point out that all surface atoms become very unstable in general STM when the currents reach values around 100 nA.…”

“…A variety of mechanisms of atom manipulation have now been reported 1,19,20 . The type of mechanism acting in a particular case depends on the atom species being manoeuvred, and more than one threshold process might be present in more complex chemical and molecular systems.…”

Field-directed sputter sharpening for tailored probe materials and atomic-scale lithography

“…STM can be used to eff ect the electron-stimulated desorption (ESD) of hydrogen from silicon 1,30,31 , providing a lithographic mask for subsequent deposition. Hydrogen desorption patterning can be achieved at the atomicscale 32,33 with a low patterning rate (vibrational heating).…”

Writing with atoms: Oxygen adatoms on the MoO2/Mo(110) surface

“…The tunneling current should be above a critical value due to the finite vibrational lifetime for the oxygen adatom on MoO2/Mo(110) surface, as has been observed for the Si-H system discussed in the first publications on desorption by inelastic electron tunneling. 32 Because of the finite lifetime of the (previously) unoccupied oxygen adatom electron states above 1.5 eV, a minimum number of available tunneling electrons which can occupy these states is crucial to increase the probability of adatom desorption. The requirement of reaching a minimal current value rather than the cumulative number of electrons transferred leads to the different saturation threshold voltages observed at different tip-sample distances in Fig.…”

“…If these electrons are conducted away through the sample or tip (depending on the bias) without depositing their energy, this is termed elastic tunneling, however if the electrons lose energy through interactions with adsorbates or the surface, inelastic tunneling occurs. 5,[32][33][34][35][36] Inelastically tunneling electrons can cause the controlled excitation of adsorbed atoms or molecules, and can be used to manipulate or charge adsorbates or to break the bonds between molecular fragments. In this process low energy tunneling electrons (or holes) are injected to the atom (or molecule) located on a surface by positioning the tip above the target.…”