Nano-scale Characterization Techniques In Auger Electron Spectroscopy

Inspired by the rapid progresses and wide applications of nanostructure materials, high-resolution characterization techniques have played the important role in nanoscience.To investigate properties,e.g.,atomic and electronic structures,force field, electrical features,optical properties,magnetic responses et al.in nano-materials and nano-devices,exploration and development of new methods and techniques of nanoscale characterizations becomes more and more crucial.Although conventional tools such as XRD,XAFS,Raman spectroscopy,SEM,HRTEM,and STM have been widely used in various nanoscale investigations,however,ever and again they meet their ends in approaching many nano-scale characterizations.Therefore,built upon the Auger electron spectroscopy with electron beam probe,here we report the establishments of advanced nanoscale,intrinsic,and non-contact characterization methods and techniques.In this thesis,based on the fundamentals of Auger electron spectroscopy,the physical essence was discussed and the theoretical expression of valence-band Auger spectrum was described.By first-principles calculations,the electronic structures of GaN and ZnO were obtained and the theoretical Auger spectra under different physical environments were simulated.In practice,a couple of advanced nanoscale characterization techniques for important physical quantities,including local stress field, intrinsic local charges,internal electric field,local structural phase,conducting type et al.,have been established on Auger electron spectroscopy.Main approaches in our works are following:In theory,the concept of General Auger Shift were proposed for the first time. Based on this concept,it unifies all(including the chemical,physical,ect.)factors leading to the energetic shift and the lineshape deformation of the valence-band Auger spectra.Thus,the methods of novel measurements of important quantities in materials were setup:(â… )Calculations of electronic structures under different environments;(â…¡) Fitting of the theoretical Auger spectrum by convolution integration of density of electron states;(â…¢)Calibration of relationship between the specific quantities with the General Auger Shift;(â…£)Characterization of specific object by surveying valence-band Auger spectra at local area of interest and obtaining the properties.The sensitivity and high-resolution of these AES techniques shows their power in the investigations for weak signals and local properties for nano-structured materials. Establishment of measurement of local stress field in nanoscale.The electron densities of states(DOS)of GaN under different biaxial stress field were calculated. The theoretical Auger spectra N KVV of various stress conditions were obtained by convoluting the DOS and fitting the experimental spectra.Then the relation between biaxial stress and the energetic shift of N KVV peak was determined for measurement use.In practice,the mapping of stress field distributions of epitaxial-lateral-overgrowth GaN was carried out and the value on GaN surface is consistent well with that by Raman scattering.These results reveal the refined distribution of stress field,which could only be simulated by theoretical methods before,and the complex mechanism of stress release in the lateral region.The accuracy and pertinence of this technique was verified.Establishment of non-contact nanoscale measurement of local electrical properties (local charge and local electric field).The local electron concentration of N atom in Al_xGa_1-xN with different Al mole fraction were calculated and the concentration was found to increase with the increase of Al fraction.At the same time,acquirement of N KVV Auger spectra in different Al_xGa_1-xN showed the proportional relation of peak height ratio N_ppN_spwith the Al mole fration,also.Therefore,the calibration curve of N_pp/N_spas a function of local charge concentration was obtained.With this approach, the measurement of internal electric field was established.Applying in heterointerfaces of GaN/Al_xGa_1-xN/GaN,the embedded polarization charges and distribution of internal electric field at the interfaces were precisely detected,which demonstrates the existence and accurate value of 2 dimension electron gas at different interfaces.Establishment of techniques of structural phase identification for local area.With theoretical and experimental methods,the relation of the General Shift of valence-band Auger spectrum was determined for zinc-blend and wurtzite GaN structures.The techniques of structural identification for local nano-area were achieved.In applications, the complex structural phases of ZnO tetrapod nanocrystals were investigated and determined.The results showed the wurtzite and zinc-blend phase in the leg part and the core part,respectively,which also agreed well with the Raman spectra and calculation data.This approach proved the validity of this advanced measurement technique and its capability in the phase determination for nano-structured systems.