Radiation from Relativistic Electrons in Periodic Structures "RREPS-15"
Orientation Effects for the Grazing Interaction of Fast Electrons
with a Dielectric Surface
K. A. Vokhmyanina1, A. S. Kubankin1,2, V.S. Levina1, I.S. Nikulin1
and G. P. Pokhil3
1
Laboratory of Radiation Physics, Belgorod State University, Belgorod,
Russia
2 National Research Tomsk Polytechnic University, Tomsk, Russia
3 Skobel’tsyn Research Institute of Nuclear Physics, Moscow State
University, Moscow, Russia
A series of experiments has been conducted to investigate the spectral and angular characteristics
of the beam of fast electrons interacting with dielectric surfaces in a grazing mode. The scheme of the
experimental setup is presented in figure 1.
The study of such processes using metal coated gratings on dielectric substrate is of great interests
because of its potential benefit of reducing the total impact parameter of the electron beam interacting
with the target, which opens the possibility to increase the effectiveness of radiation sources based on
diffraction mechanisms.
Metal coated gratings on dielectric substrate
The contribution of the structure of the target surface to the scattering of the incidence primary
electrons was observed for different geometries for the interaction process of a 10 keV electron beam
with a diffraction grating.
A 600 G/mm diffraction grating was used as target in our experiments. The grating relief measured
by a probe microscope Integra Aura is presented in figure 5. We used the 30x30 mm2 size samples of
aluminum coated diffraction grating formed in 15 mm thickness glass substrate. The front and back
sides of the grating were shielded by metal masks to prevent charge accumulation due to the
electrons interaction with the glass side of the target (Fig.6). All the masks were placed 1 mm apart
the samples without contact with the front and back sides of the samples in order to avoid grounding
and damaging the thin coating layer. The upper edges of the front masks were approximately 1 mm
above the surfaces to prevent charging up the front sides of the samples by the incident beam. The
edge of the back mask had the same level as the surface of a sample.
Fig.1.Experimental setup: 1 – electron gun, 2 –
beam of electrons, 3 – collimator Ø 2 mm, 4 –
solenoid magnetic lens, 5 – magnetic corrector,
6 – plane target in the goniometer, 7 – screen, 8
– cam
The cases of flat, conical and surface-structured targets were considered. The experimental
results have shown the ability to control the angular characteristics of the electron beam when
changing the orientation of the plane or the axis of the target relative to the axis of the electron
beam.
All the experiment were made with 10 keV electrons. The incident beam current could be
changed in the range 100-350 nA with FWHM=1.9 mm and angular divergence less than 0.28º.
Tapered channels
Fig. 5. Profile of aluminum
diffraction grating and the
test sample
Fig. 6. Schemes of grounding of the plates (a) front side
grounded. b) both sides grounded
Figure 7 shows the plot of the displacement of the beam trace on the screen under tilting of two
identical plates for different directions of the beam with respect to the surface structure (grounding
scheme fig.6 (a) was used). Each set was taken after a 20 min pause and distinguishes from the previous
set by the point of incidence of the beam.
For example in order to study the guiding effect using a tapered capillary we studied a glass
tapered tube of a simple geometry (on top of Fig. 2). The angular shift of the maximum transmitted
current position relatively to the straight beam position depending on the tilt angle of the capillary
is shown in Fig. 2 (bottom). The shift was measured by the beam trace in the screen (Fig. 1).
In order to study the profile of the beam passing through the channel at different tilt angles and
determine the fraction of electrons that have retained their original energy it was used a parallelplate system coupled with a Faraday cup that allowed scanning the beam in the horizontal
direction with a resolution of 1 mm (Fig. 3, top). The parallel-plate system was placed with the
capillary on the same platform right after the capillary outlet. The platform could be tilted with
respect to the initial beam axis.
Fig.7.Displacement of the beam trace
on the screen under tilting of two
identical plates (left and right
columns) for different directions of the
beam with respect to surface structure
(rows). Curves 1,2 and 3 on each plot
correspond to different sets of
experiments.
The same behavior of the beam was
observed for the longitudinal direction
of the incident electrons with respect
to the surface structure for both
samples.
Fig. 2. Sketch of the studied capillary (all
sizes in mm) on the top and guiding of the
electron beam by the capillary on the
bottom
More detailed explanations of the
experiments with tapered capillaries can be
found in[1].
Fig. 3. Scheme of the parallel-plate
system coupled with the FC (top), the
transmitted current vs. position of FC:
left peaks correspond to zero voltage on
the deflector plates and right peaks
correspond to 330 V on one of the
deflector plate. Metal tube transmitted
current was normalized on its maximum,
the rest peaks are the current in nA
In case of the second grounding scheme (Fig.6(b)) it seems that there is no any lifting of the beam
above the surface. In contrary, position of the beam trace on the screen even moves downward
while the surface tilt up with respect to the beam axis (Fig.8,9).
Fig.8. Photos of the displacement of the
beam trace on the screen under tilting of the
plate for the cross direction of the beam with
respect to surface structure
Fig.9. Displacement of the beam
trace on the screen under positive
and negative tilting of the plates
for the cross direction of the
beam with respect to surface
structure
Plane Plexiglass surface
Experiments on the interaction of the grazing electron beams with flat dielectric surfaces revealed a
number of features [2]. Surface charge distribution generated by grazing electron beam defines the
possibility to guide the beam and also affects the shape of the beam cross section (Fig 4). The deflection
angle of the beam from the surface of the Plexiglas plate depends, first of all, on the grounding scheme
of the sides of the insulator.
e-
Fig. 4. Separation of the trace of the
beam on the screen into two parts
upon inclination of the Plexiglass
plate of 5 cm length. Scheme of the
plate grounding: only front of the
plate is grounded (bottom)
In case of both sides (front and back side of the plate) are grounded, no guiding was observed. More
detailed explanations of the experiments with tapered capillaries can be found in [3].
The effect of “pressing” the beam towards the insulator surface when both sides are grounded occurs
because of the complete absence of charging up processes on the front and back sides of the
dielectric. So the only processes of grazing interaction of the beam with dielectrics take place and
enable to attract the beam of electrons to the surface.
Thus the experimental results show the possibility to “press” the beam of fast electrons to the
surface of the combined metal-dielectric sample in order to study more efficiently the radiation
arising during electron movement above the periodically structured surface.
REFERENCES
1. K.A. Vokhmyanina, G.P. Pokhil, P.N. Zhukova, E. Irribarra, A.S. Kubankin, V.S. Levina, R.M.
Nazhmudinov, A.N. Oleinik, I.A. Kishin//Nuclear Instruments and Methods in Physics Research B
355 (2015) 307–310
2. K.A. Vokhmyanina, P.N. Zhukova, A.S. Kubankin, Le Thu Hoai, R.M. Nazhmudinov, A.A. Pleskanev,
A.N. Oleinik, N.N. Nasonov, G.P. Pokhil //Journal of Surface Investigation. X-ray, Synchrotron and
Neutron Techniques, 2014, Vol. 8, No. 2, pp. 356–359
3. K.A. Vokhmyanina, P.N. Zhukova, A.S. Kubankin, R.M. Nazhmudinov, A.N. Oleinik, I.A. Kishin, A.S.
Klyuev, G.P. Pokhil//Journal of Surface Investigation. Xray, Synchrotron and Neutron Techniques,
2015, Vol. 9, No. 2, pp. 286–289
The work was supported by a program of the ministry of education and science of The Russian Federation for higher education establishments,
project 14.578.21.0063 (RFMEFI57814X0063).