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Imaging of thermal treated thin films on silicon substrate in the scanning low energy electron microscope
Zobačová, Jitka ; Mikmeková, Šárka ; Polčák, J. ; Frank, Luděk
Structure of thin films usually requires to be examined on microscopic level. The research topics like growth and stability of thin films, phase transitions and separation, crystallization, diffusion and defect formation has a need for LEED or XPS as techniques adequate for investigation of atomic transport processes on short length scales. The low energy electron microscopy is a complementary solution for imaging of samples with special concern for knowledge of surface physics and material science. In this contribution the microscopic examination of as-deposited and thermal treated thin films on Si substrates is performed.
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Properties of Bi LMIS with ion clusters
Radlička, Tomáš
The ion beams used in SIMS are produced by liquid–metal ion sources (LMIS) which provide fine, optically bright ion beams even for low emission currents around 1 .mu.A or less. The typical energy of the primary beam varies from 10 to 40 keV. The properties of the LMIS are strongly limited by the effect of the Discrete Coulomb Interactions (DCI) near the source. The DCI increase the energy width (Boersh effect) and decrease the brightness of the source due to the trajectory displacement effect. Contrary to the Ga LMIS which contains mostly only Ga+ ions, in case of the Bi LMIS the ion beam consists of several ion types and clusters of ions with similar currents. Because each ion type has different charge and mass they will be accelerated to different velocities, which increase the number of interactions and decreases the quality of the source. The aim of this contribution is a simulation of the effect of the clusters on the source properties based on the MC simulation.
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Mapping the local density of states above vacuum level by very low energy electron reflectivity
Pokorná, Zuzana ; Frank, Luděk
The local density of states is an important characteristic of solids, crystalline matters in particular. What used to be a pure theoreticians’ toy is nowadays an experimentally accessible characteristic, e.g. by means of photoemission or scanning tunneling spectroscopy. Local density of states can reflect e.g. the local dopant concentration in semiconductors or discern between different crystal orientations, as each crystal face has a specific density of states. One way of probing the local density of states is to measure the reflectivity of very low energy electrons (units to tens of eV) from the sample surface. The reflectivity is principally inversely proportional to the local density of electronic states coupled to the impinging electron wave.
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Ray tracing, aberration coefficients and intensity distribution
Oral, Martin
In particle optics paraxial ray tracing (solution of the paraxial trajectory equation) provides the basic imaging properties of an optical system and real ray tracing (solution of the equation of motion with time as the parameter) gives the complete particle paths including all aberrations. While there are methods of computing the aberration coefficients directly, for example by evaluating the aberration integrals, ray tracing can also be used for this purpose.
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Transmission mode in scanning low enery electron microscope
Müllerová, Ilona ; Hovorka, Miloš ; Frank, Luděk
We incorporated the cathode lens (CL) principle, well known from the emission microscope, to the SEM in order to operate at very low landing energies. The primary beam electrons of several keV are decelerated to nearly zero energy of landing on the specimen negatively biased to high potential. Reflected electrons are collected on a grounded detector situated above the sample but the same can be done below the sample of a fair transparency for electrons. High collection efficiency and high amplification of both detectors is secured thanks to the cathode lens field. We use a scintillation detector for the reflected mode and a semiconductor structure for the transmitted electron (TE) mode. In this arrangement resolution of few nm is obtainable across the full energy range.
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Prospects of the scanning low energy electron microscopy in materials science
Mikmeková, Šárka ; Hovorka, Miloš ; Konvalina, Ivo ; Müllerová, Ilona ; Frank, Luděk
The use of the scanning low energy electron microscopy (SLEEM) has been slowly making its way into the field of materials science, hampered not by limitations in the technique but rather by the relative scarcity of these instruments in research institutes and laboratories. Various techniques exist which are capable of studying the material microstructure, with the scanning electron microscopy (SEM), (scanning) transmission microscopy ((S)TEM) and focused ion beam (FIB) microscopy being perhaps the most known. A specific way to visualizing the microstructure of materials at high spatial resolution, to achieve a high contrast between grains in polycrystals and very fast data acquisition is to use the cathode lens (CL) mode in SEM. The CL mode in the SEM enables us to detect slow but not only slow, high angle scattered electrons that carry mainly crystallographic contrast based on the electron channeling, mostly in the Mott scattering angular range.
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Imaging of dopants under presence of surface ad-layers
Mika, Filip ; Hovorka, Miloš ; Frank, Luděk
Scanning electron microscopy is widely used for imaging of semiconductor structures. Image contrast between differently doped areas is observable in the secondary electron emission. Quantitative relation exists between the image contrast and the dopant concentration. However, further examination has shown the dopant contrast level of low reproducibility and dependent on additional factors like the primary electron dose, varying energy and angular distributions of the SE emission and also presence of ad-layers on the semiconductor surface.
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Superconductive property and microstructure of MgB2/Al composite materials
Matsuda, K. ; Mizutani, M. ; Nishimura, K. ; Kawabata, T. ; Hishinuma, Y. ; Aoyama, S. ; Müllerová, Ilona ; Frank, Luděk ; Ikeno, S.
Scanning low energy electron microscopy (SLEEM) is a useful tool for observation of insulating samples and determination of microstructure on a specimen surface. In the present work, we have applied the SLEEM to examine the microstructure contrast between boride particles and Al matrix.
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