Improvement of energy resolution of VEELS spectra with deconvolution method for electronic and optical properties analysis on ferroelectric oxides in nano-scale

Abstract

Electron Energy Loss Spectra of low-energy loss regions below 50eV, which is called VEELS, is the signature of valence band structures, displaying the inter-band transition (single excitation), plasma oscillation (collective excitation), etc. It can also be employed to reveal electronic and optical properties of materials [1]. VEELS analysis can elucidate a local variation of electronic and optical properties of materials in nanoscale using the transmission electron microscope (TEM) in the nano-probe mode. TEM-VEELS method has several advantages over conventional optical spectroscopy, such as UV-VIS-IR spectrometry, because it could measure a wider energy (wave length) range and local electronic and optical properties from a small volume. However, the energy resolution of TEM-EELS spectrum is less than that of high resolution EELS (HREELS) or reflective EELS methods used with a lower incident energy, or conventional optical measurements such as UV/VIS/IR spectrometry. In TEM-EELS methods operated under a high voltage, the monochromater has been applied for improving the energy resolution. However, this method is restricted for the limited number of instruments, and there exist the cost of loss of intensity. On the othr hand, a software besed monochromater, which was a deconvolution method, is free from these difficulties [2]. This technique has been applied to improve the energy resolution of core-loss spectra by eliminating the energy spread of incident electrons and shown to be effective. However, it has not been reported for application of VEELS.