The possibilities of the quantitative analysis of elemental composition of multicomponents solid state surface with resolution on depth in a mode of measurement of elastic electron scattering coefficient in a narrow solid angle is analyzed.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2064

Barchenko, V.T.

Grebnev, O.I.

Luchinin, V.V.

Pronin, V.P.

Ryzhov, I.V.

Electronic Sumy State University Institutional Repository

Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part II              339  ANGULAR-RESOLVED ELASTIC PEAK ELECTRON SPECTROSCOPY for ANALYSIS of NANOSCALE  SOLIDS V.T. Barchenko1 V.V. Luchinin1, O.I. Grebnev1, V.P. Pronin2, I.V. Ryzhov2  1 Saint Petersburg Electrotechnical University «LETI», Russia, Saint-Petersburg 2 Herzen State Pedagogical University of Russia, Russia, Saint-Petersbur  ABSTRACT The possibilities of the quantitative analysis of elemental composition of multi-components solid state surface with resolution on depth in a mode of measurement of elastic electron scattering coefficient in a narrow solid angle is analyzed.  Key words: electron spectroscopy, elastic electron scattering, surface composi-tion.  INTRODUCTION Now electron spectroscopy is an essential tool for analyzing the surface area of solids. In this case, all methods of electron spectroscopy in one way or another need knowledge of the elementary processes of interaction of electrons with solids, including the elastic interaction of electrons with solids. Without knowledge of the quantitative principles of elastic scattering of electrons we can not solve problems of quantitative diagnostics of surface and near-surface area of solids. Meanwhile, analyzing the characteristics of flows of the elas-tically reflected electrons, we can develop techniques that can itself solve quan-titatively certain problems of diagnostics of solids. RESULTS AND DISCUSSION The development of nanotechnology is impossible without progress in methods of analysis of nanostructures. Electron spectroscopy in all modifica-tions is the most significant method of such analysis. In recent years one method of electron spectroscopy – elastic peak electron spectroscopy (EPES) is being intensively developed. One of its modification is called angular resolved elastic peak electron spectroscopy (AREPES) [1-3]. In this article we discuss the poten-tial of AREPES in the mean electron energy range for investigation element composition of disordered solids. The reporting depth in this energy range varied from fractions to several dozens of nanometers. One of the most important ad-vantages of AREPES is relative simplicity of experiment results interpretation by means of analytical calculations and Monte Carlo method.  340                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part II              The task of this study was to find the sensibility of AREPES in determin-ing the surface content. The results presented in figure 1 are received by means of calculation of the coefficient of elastic electron scattering in a narrow spatial angle for Au covered by a monolayer of C. The results were received based on Monte Carlo method. As seen from the figure fractions of C monolayer result in substantial change in the coefficient of elastic electron scattering.   For analytical calculation of the coefficient of elastic electron scattering r(ș) for multicomponent solids we used phenomenological model of multiple scattering. In the context of this model we calculated r(ș) using formula (1):  (1 ( )) (1 ( ))( , ) ( )cos(1 )cosM DT M O V TMD    ¦ ¦] ɭz i izz iP Pr n W S  (1) Where ĳ, ș are the electron incidence and scattering angles, Į = ʌ – ș – ĳ is the electron es-cape angle, ɊĮ), Ɋĳ) are the probabilities of surface losses, Ȝ is the effective mean free path of electrons in the target: O = OyOɧ/(Oy + Oɧ), where Oɧ and Oy – are the electrons mean free path to the elastic and inelastic collisions, nz is the atomic con-centrations of zith component, ıɭz is the corresponding integral cross section for elastic scattering, Wi is the probability of electron es-cape into vacuum after ith scatter-ing event; and Siz(ș) is the nor-malized probability of electron scattering by angle ș after the ith event. To find out the responsive-ness  of  the  method  we  used  dis-ordered structures based on Pb xOy. Based on experimentally measured and calculated using formula (1) values of r(ș) we showed that with measurement accuracy ~ 1% for r(ș) one can find depth pro-files of element concentration with similar accuracy. In measures we used NIST electron elastic-scattering cross-section database [4].  Fig. – 1 Monte Carlo simulation of probability of elastic electron scattering for: gold ( < < < < ); gold with monolayer of carbon (, , , , ); gold with 0.5 monolayer of carbon (D D D D ) Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part II              341  Taking into account a significant difference of the [2] and [5] results, we can conclude the following: 1) The fraction of electrons elastically reflected by a solid surface is large enough, and in the considered energy range it  is a few percent of the incident electron beam; 2) If an element has high atomic number Z, the integral coefficient of elas-tic reflection r in the considered electron energy range varies non-monotonically with energy, reaches the maximum at Emax ~ Z2/8 (eV), and then decreases with increasing electron energy. The elements with low atomic num-ber Z show monotonic decrease of the dependence r(E); 3) If E  1,5  keV,  the  r  coefficient  is  a  nonmonotonic  function  of  the  atomic number Z of the tested sample. When energies of incident electrons are high, r is an increasing function of Z. For example, if E = 2 keV, r = 0,08% for carbon, r = 0,3% for aluminum, while r = 4% for gold. CONCLUSIONS Practical implementation of the EER (Elastic Electron Reflection) spec-troscopy options can be achieved in the experimental apparatus meeting the following requirements. 1. Due to the high sensitivity of the EER characteristics to surface contam-ination, they should be measured in ultrahigh vacuum with the residual gas pressure p <10-7 Pa. 2. The device should measure the absolute values of the EER coefficient in the narrow solid angle, that usually requires special calibration of the elec-tron detector-analyzer. 3. As an electron analyzer in the narrow solid angle, it is advisable to use an analyzer with the retarding field allowing to measure the total current of elastically reflected electrons. 4. The energy resolution of the analyzer ǻE/E should be at 0.1% to ensure sufficient accuracy of the absolute values of the EER coefficient in the narrow solid angle. 5. Necessary angular resolution of the analyzer ǻș depends on the differ-ential cross sections of electron elastic scattering dıy(ș)/dȍ on the atoms of a solid and must not exceed 2°. 6. As an electron detector, it is advisable to use a detector operating in the mode of registration of individual pulses, which allows measurements at low currents of the primary electron beam and provides respectively non-destructive nature of the analysis. 7. When analyzing the elemental composition, it is advisable to do meas-urements at angles of electron incidence ĳ to the sample close to normal and the scattering angles ș > 150°. In this area of angles there are no special spatial distributions of elastically reflected electrons, almost no effects of electron 342                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part II              refraction on the solid border, and the effects of surface roughness are mini-mized. 8. To do the experimental determination of the surface loss probability, the device should ensure measurements of the absolute values of the rșș) coef-ficient in a wide range of incidence angles ĳ. Note that the correct solution of surface diagnostic problems by elastic electron reflection spectroscopy, in particular the problems of determining the analysis depth, needs knowledge of the differential cross sections of elastic scattering of the electrons on the atoms in the condensed state, which may sig-nificantly differ (especially if angles of scattering are small) of those for isolat-ed atoms . REFERENCES [1] A. Jablonski, J. Zemek, Surface Science, 2006, vol. 600, P.4464-4474.    [2] A. Jablonski. Analytical applications of elastic electron backscattering from surfaces // Progress in Surface Science. 2003. V. 74. P. 357-374. [3] V.P. Pronin, I.I. Khinich, I.A.Chistotin, Technical Physics Letters, 2008, 34, 825. [4] C.J. Powell, A. Jablonski. NIST electron elastic-scattering cross-section database. Version 3.1, Standard Reference Data Program Database 64. – National Institute of Standards and Technology, Gaithersburg, MD, 2003. [5] Gergely G. Elastic peak electron spectroscopy // Scanning, 1986. V. 8. P. 203–214.    

Angular-resolved elastic peak electron spectroscopy for analysis of nanoscale solids

SocioEconomic Challenges Journal (Sumy State University)

Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part II              339 
 
ANGULAR-RESOLVED ELASTIC PEAK ELECTRON 
SPECTROSCOPY for ANALYSIS of NANOSCALE  
SOLIDS 
V.T. Barchenko1 V.V. Luchinin1, O.I. Grebnev1, V.P. Pronin2, I.V. Ryzhov2 
 
1 Saint Petersburg Electrotechnical University «LETI», Russia, Saint-Petersburg 
2 Herzen State Pedagogical University of Russia, Russia, Saint-Petersbur 
 
ABSTRACT 
The possibilities of the quantitative analysis of elemental composition of multi-
components solid state surface with resolution on depth in a mode of measurement of 
elastic electron scattering coefficient in a narrow solid angle is analyzed. 
 
Key words: electron spectroscopy, elastic electron scattering, surface composi-
tion. 
 
INTRODUCTION 
Now electron spectroscopy is an essential tool for analyzing the surface 
area of solids. In this case, all methods of electron spectroscopy in one way or 
another need knowledge of the elementary processes of interaction of electrons 
with solids, including the elastic interaction of electrons with solids. Without 
knowledge of the quantitative principles of elastic scattering of electrons we 
can not solve problems of quantitative diagnostics of surface and near-surface 
area of solids. Meanwhile, analyzing the characteristics of flows of the elas-
tically reflected electrons, we can develop techniques that can itself solve quan-
titatively certain problems of diagnostics of solids. 
RESULTS AND DISCUSSION 
The development of nanotechnology is impossible without progress in 
methods of analysis of nanostructures. Electron spectroscopy in all modifica-
tions is the most significant method of such analysis. In recent years one method 
of electron spectroscopy – elastic peak electron spectroscopy (EPES) is being 
intensively developed. One of its modification is called angular resolved elastic 
peak electron spectroscopy (AREPES) [1-3]. In this article we discuss the poten-
tial of AREPES in the mean electron energy range for investigation element 
composition of disordered solids. The reporting depth in this energy range varied 
from fractions to several dozens of nanometers. One of the most important ad-
vantages of AREPES is relative simplicity of experiment results interpretation 
by means of analytical calculations and Monte Carlo method.  
340                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part II             
 
The task of this study was to find the sensibility of AREPES in determin-
ing the surface content. The results presented in figure 1 are received by means 
of calculation of the coefficient of elastic electron scattering in a narrow spatial 
angle for Au covered by a monolayer of C. The results were received based on 
Monte Carlo method. As seen from the figure fractions of C monolayer result 
in substantial change in the coefficient of elastic electron scattering.   
For analytical calculation of the coefficient of elastic electron scattering 
r(ș) for multicomponent solids we used phenomenological model of multiple 
scattering. In the context of this model we calculated r(ș) using formula (1): 
 (1 ( )) (1 ( ))( , ) ( )cos(1 )
cos
M DT M O V TM
D
    

¦ ¦] ɭz i iz
z i
P Pr n W S  (1) 
Where ĳ, ș are the electron 
incidence and scattering angles, 
Į = ʌ – ș – ĳ is the electron es-
cape angle, ɊĮ), Ɋĳ) are the 
probabilities of surface losses, Ȝ is 
the effective mean free path of 
electrons in the target: 
O = OyOɧ/(Oy + Oɧ), where Oɧ and 
Oy – are the electrons mean free 
path to the elastic and inelastic 
collisions, nz is the atomic con-
centrations of zith component, ıɭz 
is the corresponding integral cross 
section for elastic scattering, Wi 
is the probability of electron es-
cape into vacuum after ith scatter-
ing event; and Siz(ș) is the nor-
malized probability of electron 
scattering by angle ș after the ith 
event. 
To find out the responsive-
ness  of  the  method  we  used  dis-
ordered structures based on Pb 
xOy. Based on experimentally 
measured and calculated using 
formula (1) values of r(ș) we 
showed that with measurement accuracy ~ 1% for r(ș) one can find depth pro-
files of element concentration with similar accuracy. In measures we used 
NIST electron elastic-scattering cross-section database [4]. 
 
Fig. – 1 Monte Carlo simulation of 
probability of elastic electron scattering for: 
gold ( < < < < ); gold with monolayer of carbon 
(, , , , ); gold with 0.5 monolayer of 
carbon (D D D D ) 
Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part II              341 
 
Taking into account a significant difference of the [2] and [5] results, we 
can conclude the following: 
1) The fraction of electrons elastically reflected by a solid surface is large 
enough, and in the considered energy range it  is a few percent of the incident 
electron beam; 
2) If an element has high atomic number Z, the integral coefficient of elas-
tic reflection r in the considered electron energy range varies non-
monotonically with energy, reaches the maximum at Emax ~ Z2/8 (eV), and then 
decreases with increasing electron energy. The elements with low atomic num-
ber Z show monotonic decrease of the dependence r(E); 
3) If E  1,5  keV,  the  r  coefficient  is  a  nonmonotonic  function  of  the  
atomic number Z of the tested sample. When energies of incident electrons are 
high, r is an increasing function of Z. For example, if E = 2 keV, r = 0,08% for 
carbon, r = 0,3% for aluminum, while r = 4% for gold. 
CONCLUSIONS 
Practical implementation of the EER (Elastic Electron Reflection) spec-
troscopy options can be achieved in the experimental apparatus meeting the 
following requirements. 
1. Due to the high sensitivity of the EER characteristics to surface contam-
ination, they should be measured in ultrahigh vacuum with the residual gas 
pressure p <10-7 Pa. 
2. The device should measure the absolute values of the EER coefficient 
in the narrow solid angle, that usually requires special calibration of the elec-
tron detector-analyzer. 
3. As an electron analyzer in the narrow solid angle, it is advisable to use 
an analyzer with the retarding field allowing to measure the total current of 
elastically reflected electrons. 
4. The energy resolution of the analyzer ǻE/E should be at 0.1% to ensure 
sufficient accuracy of the absolute values of the EER coefficient in the narrow 
solid angle. 
5. Necessary angular resolution of the analyzer ǻș depends on the differ-
ential cross sections of electron elastic scattering dıy(ș)/dȍ on the atoms of a 
solid and must not exceed 2°. 
6. As an electron detector, it is advisable to use a detector operating in the 
mode of registration of individual pulses, which allows measurements at low 
currents of the primary electron beam and provides respectively non-destructive 
nature of the analysis. 
7. When analyzing the elemental composition, it is advisable to do meas-
urements at angles of electron incidence ĳ to the sample close to normal and 
the scattering angles ș > 150°. In this area of angles there are no special spatial 
distributions of elastically reflected electrons, almost no effects of electron 
342                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part II             
 
refraction on the solid border, and the effects of surface roughness are mini-
mized. 
8. To do the experimental determination of the surface loss probability, 
the device should ensure measurements of the absolute values of the rșș) coef-
ficient in a wide range of incidence angles ĳ. 
Note that the correct solution of surface diagnostic problems by elastic 
electron reflection spectroscopy, in particular the problems of determining the 
analysis depth, needs knowledge of the differential cross sections of elastic 
scattering of the electrons on the atoms in the condensed state, which may sig-
nificantly differ (especially if angles of scattering are small) of those for isolat-
ed atoms . 
REFERENCES 
[1] A. Jablonski, J. Zemek, Surface Science, 2006, vol. 600, P.4464-4474.    
[2] A. Jablonski. Analytical applications of elastic electron backscattering from surfaces 
// Progress in Surface Science. 2003. V. 74. P. 357-374. 
[3] V.P. Pronin, I.I. Khinich, I.A.Chistotin, Technical Physics Letters, 2008, 34, 825. 
[4] C.J. Powell, A. Jablonski. NIST electron elastic-scattering cross-section database. 
Version 3.1, Standard Reference Data Program Database 64. – National Institute of 
Standards and Technology, Gaithersburg, MD, 2003. 
[5] Gergely G. Elastic peak electron spectroscopy // Scanning, 1986. V. 8. P. 203–214. 
 
  


https://essuir.sumdu.edu.ua/bitstream/123456789/20645/1/16.pdf

Angular-resolved elastic peak electron spectroscopy for analysis of nanoscale solids

Abstract

Similar works

Full text

Available Versions

Electronic Sumy State University Institutional Repository

SocioEconomic Challenges Journal (Sumy State University)