Browsing by Subject "Binding energy shifts"

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Open Access
Electrical properties from photoinduced charging on Cd-doped (100) surfaces of CuInSe2 epitaxial thin films
(AVS Science and Technology Society, 2016) Johnson, N.; Aydogan, P.; Süzer, Şefik; Rockett, A.
The photoresponse of Cd-doped CuInSe2 (CIS) epitaxial thin films on GaAs(100) was studied using x-ray photoelectron spectroscopy under illumination from a 532 nm laser between sample temperatures of 28-260 °C. The initial, air-exposed surface shows little to no photoresponse in the photoelectron binding energies, the Auger electron kinetic energies or peak shapes. Heating between 50 and 130 °C in the analysis chamber results in enhanced n-type doping at the surface and an increased light-induced binding energy shift, the magnitude of which persists when the samples are cooled to room temperature from 130 °C but which disappears when cooling from 260 °C. Extra negative charge trapped on the Cu and Se atoms indicates deep trap states that dissociate after cooling from 260 °C. Analysis of the Cd modified Auger parameter under illumination gives experimental verification of electron charging on Cd atoms thought to be shallow donors in CIS. The electron charging under illumination disappears at 130 °C but occurs again when the sample is cooled to room temperature.
Open Access
Gate-tunable photoemission from graphene transistors
(American Chemical Society, 2014) Copuroglu, M.; Aydogan, P.; Polat, E. O.; Kocabas, C.; Süzer, S.
In this Letter, we report gate-tunable X-ray photoelectron emission from back-gated graphene transistors. The back-gated transistor geometry allows us to study photoemission from graphene layer and the dielectric substrate at various gate voltages. Application of gate voltage electrostatically dopes graphene and shifts the binding energy of photoelectrons in various ways depending on the origin and the generation mechanism(s) of the emitted electrons. The gate-induced shift of the Fermi energy of graphene alters the binding energy of the C 1s electrons, whereas the electric field of the gate electrodes shift the binding energy of core electrons emitted from the gate dielectric underneath the graphene layer. The gradual change of the local potential through depths of the gate dielectric provides quantitative electrical information about buried interfaces. Our results suggest that gate-tunable photoemission spectra with chemically specific information linked with local electrical properties opens new routes to elucidating operation of devices based especially on layered materials.