Nanotechnology Now - Press Release: Development of Algorithm for Accurate Calculation of Average Distance Travelled by Low-Speed Electrons without Energy Loss that Are Sensitive to Surface Structure

Home > Press > Development of Algorithm for Accurate Calculation of Average Distance Travelled by Low-Speed Electrons without Energy Loss that Are Sensitive to Surface Structure

Inelastic mean free path (IMFP) of copper in relation to electron energy. Theoretical prediction using conventional algorithm (red band), theoretical prediction using newly developed algorithm (red solid line), and experimental data with improved accuracy (■).

Abstract:
The research team consisting of postdoctoral researcher Da Bo, former postdoctoral researcher Hiroshi Shinotsuka, group leader Hideki Yoshikawa and special researcher Shigeo Tanuma, Surface Chemical Analysis Group, Nano Characterization Unit, NIMS; and professor Ding Zejun, University of Science and Technology of China, has developed a theoretical algorithm to accurately calculate the average distance traveled by low-energy/low-speed electrons without energy loss that are sensitive to the surface structures of materials through which they travel while retaining their energy information. The results of this research have been published in Physical Review Letters Vol.113, 063201 (2014). DOI: 10.1103/PhysRevLett.113.063201

Development of Algorithm for Accurate Calculation of Average Distance Travelled by Low-Speed Electrons without Energy Loss that Are Sensitive to Surface Structure

Tsukuba, Japan | Posted on September 11th, 2014

The research team consisting of postdoctoral researcher Da Bo, former postdoctoral researcher Hiroshi Shinotsuka, group leader Hideki  Yoshikawa and special researcher Shigeo Tanuma, Surface Chemical  Analysis Group, Nano Characterization Unit, NIMS (Sukekatsu Ushioda, president); and professor Ding Zejun, University of Science and  Technology of China, has developed a theoretical algorithm to accurately  calculate the average distance traveled by low-energy/low-speed electrons without any energy loss that are sensitive to the surface  structures of materials through which they travel while retaining their  energy information. This information on the average traveling distance is vital in terms of measuring the amount of electrons released from  materials and gaining information about the depth at which surface  analysis is conducted.

The nanometer-scale surface layers and interface layers influence the  properties of various materials such as catalysts, batteries, semiconductors, sensors and anticorrosion materials. It is imperative to identify the amount of elements present and chemical bonding state in these layers in terms of improving the performance of functional  materials and developing new materials. And to achieve this, it is  essential to accurately analyze and measure electrons (bonding electrons) that indicate the state of elements present in the surface and interface  layers. This procedure involves measurement of bonding electron energy  extracted from materials due to external stimuli applied to them in such forms as X-rays and electrons, and of the intensity distribution of that energy. During this process, it is critical to identify the depth from the surface at which these measurements were taken. The range of the  measurement depth can be determined by measuring a physical quantity  called the inelastic mean free path (IMFP), which defines how far an electron can travel in a material while retaining its original energy level in a statistical sense. Experimental and theoretical attempts to  quantify IMFP have been pursued globally since the 1970s. However, since  it is difficult to take measurements on low-speed electrons that are sensitive to the surface structure (especially at 200eV or below), this  quantification had been an issue for a long time.

In theory, accurate calculation of IMFP in a material is feasible  provided that the energy loss function of that material is fully known.  The energy loss function represents the level of interaction between the material and electromagnetic waves, and is expressed in terms of the change in the amount of energy lost from electrons and the change in  momentum due to corresponding scattering events occurring in the  material. The conventional model function (so-called optical energy loss  function) only enabled calculating a partial energy loss function under limited conditions assuming zero-momentum, however, lacking of the  accompanied changing in momentum as electrons lose energy. As such, this is an incomplete energy loss function in view of obtaining IMFP. The  conventional function was particularly problematic when that or similar  functions were applied to low-speed electrons that are sensitive to the  surface structure. To overcome this problem, we described the optical energy loss function in terms of a composite function resulting from  combining many functions, and also used a new model function that accurately expresses the change in momentum. With this method, we  succeeded in determining a nearly complete energy loss function. This calculation method enabled us to more accurately perform theoretical  prediction of IMFP compared to the experimental value, which was  obtained by applying spectrometry (extended X‐ray absorption fine  structure spectrometry) to low-speed electrons of Copper and molybdenum at the high-brilliant synchrotron radiation facility, and to explain the  relationship between energy measurement and the types of materials.  Through this endeavor, we found a hint to solve this long-lasting  problem.

Based on this research, more accurate quantification of elements and analysis of chemical bonding states have become feasible in the several atom thick surface layer of materials using electrons. The results of this study will behave been published in the online version of Physical Review Letters Vol.113, 063201 (2014).  DOI: 10.1103/PhysRevLett.113.063201.

B. Da, H. Shinotsuka, H. Yoshikawa, Z. J. Ding, and S. Tanuma Extended Mermin Method for Calculating the Electron Inelastic Mean Free Path Physical Review Letters Vol.113, 063201 (2014).  DOI: 10.1103/PhysRevLett.113.063201.     

####

About National Institute for Materials Science (NIMS)
Only one Public Institution for Materials Science in Japan

For more information, please click here

Contacts:
Press Office

Inquiry for this research:
 Hideki Yoshikawa 
Group Leader
Surface Chemical Analysis Group
 Nano Characterization Unit
Advanced Key Technologies Division
NIMS TEL：+81-29-859-2451
 FAX：+81-29-859-2723
 E-Mail: YOSHIKAWA.Hideki=nims.go.jp (Please change "=" to

For general inquiry
 NIMS Public Relations Office
 TEL:+81-29-859-2026
 FAX:+81-29-859-2017    