Communication: Enhancement of dopant dependent x-ray photoelectron spectroscopy peak shifts of Si by surface photovoltage

Cataloged from PDF version of article.Binding energies measured by x-ray photoelectron spectroscopy (XPS) are influenced by doping, since electrons are transferred to (p-type) and from (n-type) samples when they are introduced into the spectrometer, or brought into contact with each other (p-n junction). We show that the barely measurable Si2p binding energy difference between moderately doped n- and p-Si samples can be enhanced by photoillumination, due to reduction in surface band-bending, which otherwise screens this difference. Similar effects are also measured for samples containing oxide layers, since the band-bending at the buried oxide-Si interfaces is manifest as photovoltage shifts, although XPS does not probe the interface directly. The corresponding shift for the oxide layer of the p-Si is almost twice that of without the oxide, whereas no measurable shifts are observable for the oxide of the n-Si. These results are all related to band-bending effects and are vital in design and performance of photovoltaics and other related systems. (C) 2011 American Institute of Physics

XPS for chemical- and charge-sensitive analyses

Cataloged from PDF version of article.By recording X-ray photoelectron spectroscopic binding energy shifts, while subjecting samples to a variety of optical and electrical stimuli, information about charge accumulation on materials or surface structures can be obtained. These stimuli included d.c. as well as a.c. electrical and/or optical pulses covering a wide frequency range (10−3 to 106 Hz) for probing charging and/or photovoltage shifts, stemming from impurities, dopants, defects, etc., whether created intentionally or not. The methodology is simple to implement and provides several new dimensions for thin films and materials analyses

Probing the charge build-up and dissipation on thin PMMA film surfaces at the molecular level by XPS

Cataloged from PDF version of article.What's the charge? X-ray photoelectron spectroscopy was used to determine the charge state and dynamics of charge build-up and decay on a thin poly(methyl methacrylate) film. The film is initially negatively charged to around −2 V and becomes progressively positively charged during the course of the XPS analysis

High insecticidal activity of Leclercia adecarboxylata isolated from Leptinotarsa decemlineata (Col.: Chrysomelidae)

Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), is an important pest on solanaceous crops worldwide. CPB has developed resistance to insecticides used for its control. In this study, in order to find a more effective and safer biological control agent against L. decemlineata, we studied the bacterial flora of CPB, and tested them for insecticidal effects on it. The highest insecticidal effect determined on L. decemlineata within 5 days was 100% and this effect was exhibited by Ld1 isolate. According to the morphological, physiological and biochemical tests, and 16S rRNA sequencehomologies, Ld1 was identified as Leclercia adecarboxylata. This is the first time that this bacterium has been isolated from any insect pests. Our results indicate that Lecl. adecarboxylata may be valuable as a biological control agent for L. decemlineata

XPS Investigation of a CdS-Based Photoresistor under Working Conditions: Operando−XPS

Cataloged from PDF version of article.A noncontact chemical and electrical measurement X-ray photoelectron spectroscopy (XPS) technique is performed to investigate a CdS-based photoresistor during its operation. The main objective of the technique is to trace chemical- and location-specified surface potential variations as shifts of the XPS Cd 3d(5/2) peak position without and under photoillumination with four different lasers. The system is also modeled to extract electrical information. By analyzing the measured potential variations with this model, location-dependent resistance values are represented (i) two dimensionally for line scans and (ii) three dimensionally for areal measurements. In both cases, one of the dimensions is the binding energy. The main advantage of the technique is its ability to assess an element-specific surface electrical potential of a device under operation based on the energy deviation of core level peaks in surface domains. Detection of the variations in electrical potentials and especially their responses to the energy of the illuminating source in operando, is also shown to be capable of detecting, locating, and identifying the chemical nature of structural and other types of defects

Chemical Visualization of a GaN p-n junction by XPS

We report on an operando XPS investigation of a GaN diode, by recording the Ga2p 3/2 peak position under both forward and reverse bias. Areal maps of the peak positions under reverse bias are completely decoupled with respect to doped regions and allow a novel chemical visualization of the p-n junction in a 2-D fashion. Other electrical properties of the device, such as leakage current, resistivity of the domains are also tapped via recording line-scan spectra. Application of a triangular voltage excitation enables probing photoresponse of the device

Transient surface photovoltage in n- and p-GaN as probed by x-ray photoelectron spectroscopy

Cataloged from PDF version of article.Transient surface photovoltage (SPV) of n and p-GaN was measured using x-ray photoelectron spectroscopy (XPS) with a time resolution of 0.1 s. The measured SPV transients for both n- and p-GaN are << 0.1 s, and for the n-GaN they are not affected by flood-gun electrons. However, for the p-GaN, the transient character of the SPV is dramatically changed in the presence of flood-gun electrons. The combination of time-resolved XPS, flood gun, and laser illumination give us a new way to study the surface electronic structure and other surface properties of semiconducting materials in a chemically specific fashion. (C) 2011 American Institute of Physics