Direct observation of site-specific valence electronic structure at theSiO2∕Siinterface

Abstract

Atom specific valence electronic structures at interface are elucidated successfully using soft x-ray absorption and emission spectroscopy. In order to demonstrate the versatility of this method, we investigated SiO 2 /Si interface as a prototype and directly observed valence electronic states projected at the particular atoms of the SiO 2 /Si interface; local electronic structure strongly depends on the chemical states of each atom. In addition we compared the experimental results with first-principle calculations, which quantitatively revealed the interfacial properties in atomic-scale.Interfaces change atomic structures and chemical compositions of matters, providing not only fascinating physical properties such as metal-insulator transition [1], band gap narrowing [2], and superconductivity [3] but also affecting electronic properties of semiconductor devices [4]. Therefore, observing valence and/or conduction electronic states projected at an individual atom of the interface is in particular important to obtain atom-based picture of physical properties of matters. In spite of many studies on interfaces, the interfacial electronic states have been evaluated mostly as the average and not as individual states. Thus, what we need is a method that allows us to probe atom-specific electronic states at the interfaces directly.Soft X-ray absorption (SXA) spectroscopy [5] is a method to study an excitation from a core level to conduction states, providing an element-specific conduction states. Soft X-ray emission (SXE) spectroscopy [6,7] probes n photon emission process involving a core hole decay process predominantly from valence states to a core level state, which addresses valence states of a particular element. Moreover, since the core electrons are localized to a particular atom we can in an atom-specific way study the valence and conduction states using SXA and SXE spectroscopy. Thus, the selective photo-absorption at interfaces is realized by tuning the incident photon energy to only allow the electronic excitation from a core level to conduction band levels, using SXA. Once the core level at the interfaces is

Schottky Barrier Formation and Strain at the (011)GdN/GaNInterface from First Principles

“…To visualize the real-space band structure across the interface, we evaluate the real-space density of states ρðz; EÞ projected onto the normal direction z of the interface [54][55][56][57][58][59][60][61]. This projection is calculated for majority and minority spins σ ¼ AE as…”

An in situ x-ray photoelectron spectroscopy study of the initial stages of rf magnetron sputter deposition of indium tin oxide on p-type Si substrate

“…A narrower band gap for suboxides in a SiO 2 /n-type Si(111) interface region is calculated by Yamashita et al 24 They have shown that the main oxides in a thin interface region between a Si substrate and a SiO 2 film are Si 2 O and Si 2 O 3 and that the band gap increases as the oxidation state increases (E g ðSi 2 OÞ < E g ðSi 2 O 3 Þ < E g ðSiO 2 Þ). A different band gap alignment of the ITO/Si interface than in the case of SiO 2 as the main silicon oxide and the presence of metallic In and Sn at the interface may play a significant role in the carrier transport mechanism in the ITO/Si junction.…”

Direct Observation of Valence and Conduction States near the SiO2/Si(100) Interface

“…2(d)). According to the previous study, these edge structures were attributed to valence band maximums (VBMs) of the suboxide species [7]. Thus, the VBMs, conduction band minimums (CBMs), and band-gaps (E g s) of the suboxide species are obtained, which is summarized in Table I.…”

“…Recently we successfully observed conduction and valence electronic structures at solid-solid interfaces directly using soft x-ray absorption (SXA) and emission (SXE) spectroscopy [7][8][9]. This method is based on site-specific photo absorption and emission, which gives us the local valence electronic states at the interface [10,11].…”