Chemically induced charge carrier production and transport inPd∕SiO2∕n−Si(111)

Abstract

The energy transfer associated with reactions at metal surfaces produces energetic electrons and holes. Using ultrathin films of Pd on metal-semiconductor (MS) and metal-oxide-semiconductor (MOS) diode structures, we have investigated reaction-induced electrical phenomena associated with a variety of molecular and atomic interactions with the Pd surfaces. Distinct electronic signals are observable for species as diverse as atomic oxygen, xenon, and molecular hydrocarbons. Both MS and MOS devices allowed the detection of the chemically induced excitation of electron-hole pairs for highly exothermic chemisorption. Electronic signals from gas species with low adsorption energies were only observed in MOS devices with a thin oxide layer between the active metal film and the semiconductor. The density and distribution of interfacial states in the MOS devices have been found to be an important factor in understanding the origin and transport pathways of these "chemicurrents." A dynamic model is introduced to explain the displacement currents in the MOS devices during low-energy gas-surface interactions.

Subsurface excitations in a metal

“…3, where the backside current response shows a unique time dependence that is analogous to that seen in chemicurrent measurements of nonreactive species on MOS devices. 27 In that analysis, a sign-reversed and time-dependent response was attributed to interactions between hot holes and interface traps in the oxide layer of the MOS device. In conclusion we have measured internal hot carrier excitations generated by the bombardment of MOS devices with hyperthermal and low energy alkali and noble gas ions.…”

Isopotential Titration for Quantifying Metal-Adsorbate Charge Transfer

“…Previous studies of catalytic nanodiodes (i.e., devices without the insulating layer) exhibited current flow over a Schottky barrier, which was ascribed to nonadiabatic heat transfer which converted the energy released by the exothermic adsorption to electronhole pair formation in the metal catalyst. [52][53][54] This is likely a different phenomenon than observed in our catalytic condensers, because we see current for both exothermic adsorption of H2 (i.e., switching to higher H2 concentration) and for endothermic desorption (i.e., switching to lower concentrations).…”

Probing kinetically excited hot electrons using Schottky diodes

“…This direction of current flow is also consistent with previous measurements. 1,2,5,6,15 To obtain a value for the hot electron current generated, we subtracted the response of the device from the baseline background signal. For the data shown in Fig.…”

“…Using Schottky diode gas sensing devices, Nienhaus and others have performed measurements which give clear evidence for the electron-hole pair excitation channel under thermal energy gas exposure. 1,2 While their results indicate that electron-hole pair excitations are a common avenue for energy loss during a gas-surface interaction at thermal energies, there have been few studies that measure the role of this channel for higher energy projectiles.…”