Paper TF-WeM5
Nanostructured Material Surface and Thin Film Interface Characterization by X-ray Photoelectron Spectroscopy

Wednesday, December 5, 2018, 9:20 am, Room Naupaka Salons 4

It is well known that X-ray photoelectron spectroscopy (XPS) is a very powerful tool for understanding the nature of solid surfaces. Although many newly developing tools with high spatial resolution play important role in the analysis of individual nanostructured features of materials XPS is still considered as an essential tool for understanding several important aspects of nanostructured materials that cannot easily be observed using other techniques. However, the question of how the nanostructured material features impact XPS data have been heavily debated in the scientific community, which limits its application in characterization of nanostructured materials. For example, there is consistent observation of cluster-size-dependent binding energy (BE) shifts. But there is substantial disagreement over the assignment of these shifts to initial or final state effects. As a result, the measured PES data can’t directly match to the electronic property of clusters because among the initial and final state effects, only the initial state effect involves information of changes in the electronic structure before photoemission, and hence is directly related to nanostructured material properties and is relevant for understanding other chemical process and reactions. In the first part of the presentation, I will talk to you the issues raised specifically for XPS analysis of nanostructured materials and followed by the method to overcome limitations through some examples of application of XPS to study nanostructured materials. In the second part, band energy alignment of different material interfaces such as semiconductor/semiconductor, metal/semiconductor, metal/insulator, semiconductor/insulator, 2D material interfaces determination by XPS will be presented. The performance of any type of hetero-junction device is determined by band energy alignment (band offsets) of material interfaces which form the hetero-junction. Therefore, accurately determining heterojunction band offsets and tuning them to a desired application would have an obvious impact on the optimization of the devices. The effects of chemical shift, differential charging, band bending and photoemission final state on the XPS measurement accuracy and reliability will be discussed.