|
|
Study of beta phase in Al-Mg-Si alloys by means of unconventional methods of electron microscopy
Ligas, Aleš ; Julišová, Martina (referee) ; Mikmeková, Šárka (advisor)
Aluminium Al-Mg-Si alloys are the most commonly used in automotive and construction industry. Hexagonal ’-phase is one of the metastable phases occured in this type of alloys. Unlike classic square -phase, this ’-phase is characterized by different crystalographic orientation to the matrix and shape. Standard method used for identification of aluminium alloys is scanning electron microscopy (SEM), because of its quickness and efficiency, but in case of very thin or damaged structures (as a result of metallographic process) it’s insufficient. Scanning low energy electron microscopy (SLEEM) can be appropriate for identification of mentioned precipitates due to its physical principles resulting in many advantages compared to SEM. So the most important benefits are interaction volume reduction (which leads to improvement of surface sensitivity), increase of material contrast (ability to change matrix / precipitates contrast) as well as crystalographic contrast.
|
|
|
Study of metals by low voltage SEM
Ligas, Aleš ; Jánský, Pavel (referee) ; Mikmeková, Šárka (advisor)
The aim of this thesis is to demonstrate the advantages of the scanning low energy electron microscopy (SLEEM) in the field of materials science. The SLEEM can be very effectively used for investigation of wide range of materials, such as steels, alloys, ceramics and thin films. Experimental part of this work was performed on the scanning electron microscope TESCAN VEGA TS 5310 equipped with cathode lens mode at Institute of Scientific Instruments of the ASCR, v.v.i..
|
|
|
Direct Imaging of Deformation of Metallic Materials by Means of Slow Electrons
Piňos, Jakub ; Kolíbal, Miroslav (referee) ; Kasl, Josef (referee) ; Frank, Luděk (advisor)
Scanning electron microscopy is one of the common tools for the analysis of advanced engineering materials. The development of various techniques allows choosing an appropriate mode of observation to obtain new information about sample structure and properties. The thesis deals with direct imaging of deformation in metal samples by scanning low energy electron microscopy during the in-situ tensile test. Experiments were performed on pure copper samples. Images obtained during the tensile test allow us to observe the effect of deformation in the structure of metal from the first appearance of these effects in structure at deformation intensities about 3-4% up to extreme plastic deformation at the crack tip.
|
|
|
Real time observation of strain in the SEM sample
Piňos, Jakub ; Frank, Luděk
The SEM with various detector arrangements and analytical attachments represents an\nirreplaceable tool in material research. One of the techniques available in most contemporary\nmicroscopes is the scanning low energy electron microscopy (SLEEM) with biased specimen, marketed as the beam deceleration mode, gentle beam and others. The SLEEM allows\ncontrolling the information depth of the backscatter electron (BSE) imaging within a wide\nrange by altering the landing energy of electrons.
|
|
|
Very low energy STEM/TOF system
Daniel, Benjamin ; Radlička, Tomáš ; Piňos, Jakub ; Frank, Luděk ; Müllerová, Ilona
Scanning low energy electron microscopes (SLEEMs) have been built at ISI for over 20 years, either by modification of commercially available SEMs with a cathode lens or completely self-built in case of a dedicated ultra-high vacuum scanning low energy electron microscope (UHV SLEEM). Recently, the range of detection methods has been extended\nby a detector for electrons transmitted through ultrathin films and 2D crystals like graphene. For a better understanding of interaction between low energy electrons and solids in general, and the image contrast mechanism in particular, it was considered useful to measure the energy of transmitted electrons. This allows a better comparison with simulations, which suffer from increasing complexity due to a stronger interaction of electrons with the density of states at low energies.
|
|
|
Study of beta phase in Al-Mg-Si alloys by means of unconventional methods of electron microscopy
Ligas, Aleš ; Julišová, Martina (referee) ; Mikmeková, Šárka (advisor)
Aluminium Al-Mg-Si alloys are the most commonly used in automotive and construction industry. Hexagonal ’-phase is one of the metastable phases occured in this type of alloys. Unlike classic square -phase, this ’-phase is characterized by different crystalographic orientation to the matrix and shape. Standard method used for identification of aluminium alloys is scanning electron microscopy (SEM), because of its quickness and efficiency, but in case of very thin or damaged structures (as a result of metallographic process) it’s insufficient. Scanning low energy electron microscopy (SLEEM) can be appropriate for identification of mentioned precipitates due to its physical principles resulting in many advantages compared to SEM. So the most important benefits are interaction volume reduction (which leads to improvement of surface sensitivity), increase of material contrast (ability to change matrix / precipitates contrast) as well as crystalographic contrast.
|
|
|
Study of metals by low voltage SEM
Ligas, Aleš ; Jánský, Pavel (referee) ; Mikmeková, Šárka (advisor)
The aim of this thesis is to demonstrate the advantages of the scanning low energy electron microscopy (SLEEM) in the field of materials science. The SLEEM can be very effectively used for investigation of wide range of materials, such as steels, alloys, ceramics and thin films. Experimental part of this work was performed on the scanning electron microscope TESCAN VEGA TS 5310 equipped with cathode lens mode at Institute of Scientific Instruments of the ASCR, v.v.i..
|
|
|
Characterization of .beta.-phase in Al-Mg-Si alloys by SLEEM and STLEEM techniques
Ligas, A. ; Hida, S. ; Matsuda, K. ; Mikmeková, Šárka
Knowledge of the distribution and morphology of the Mg2Si precipitates (i.e. .beta.-phase) in Al-Mg-Si alloys are very important for many practical reasons and the scanning electron microscopy (SEM) technique is widely used for their visualization. Unfortunately, in the standard SEM images these precipitates are barely visible and finding them can be very difficult. Using the cathode lens (CL) mode in the SEM (so called SLEEM) these difficulties have been overcome and a very high contrast between the hexagonal-shaped .beta.-phase and the matrix has been obtained. Moreover, it has been found that the SLEEM images offer the possibility to distinguish between the hexagonal-shaped and the conventional .beta.-phase based on their different brightness, not only on their shape, which can be in some cases difficult or even impossible. Mg2Si precipitates have been also characterized by means of the scanning transmission low energy electron microscopy (STLEEM) method based on the using of a STEM detector in the SEM operated in the CL mode.
|
|
|
Microstructural characterization of metallic materials using advanced SEM techniques
Piňos, Jakub ; Konvalina, Ivo ; Kasl, J. ; Jandová, D. ; Mikmeková, Šárka
The development of advanced materials is inseparably connected with detailed knowledge of the relationship between microstructure and mechanical properties. Traditional high-voltage scanning electron microscopy (SEM) is one of the most commonly used techniques for microstructure analysis, though it may be insufficient particularly for the characterization of advanced materials exhibiting a complex microstructure. The benefits of using slow electrons have been described in several articles. Experiments have been performed with a XHR SEM Magellan 400L (FEI Company) equipped with two detectors for secondary electrons (SE), an Everhart Thornley detector and an in-lens TLD detector, and solid-state BSE detector (CBS) located below the pole piece. This microscope can also be operated in the beam deceleration (BD) mode. The field of the BD not only decelerates the primary electrons, but also accelerates the emitted (signal) electrons towards the detector. Furthermore, high-angle backscattered electrons (BSE) are also collimated towards the optical axis and are detected. These electrons carry, first and foremost, crystal orientation contrast. SE and low-angle BSE can be detected by the TLD detector located inside the objective lens. Angle-resolved detection of BSE is performed using a CBS detector divided into four concentric segments.
|
|
|
Influence of annealing to stress in CNx:(H) films observed by SLEEM
Mikmeková, Eliška ; Mikmeková, Šárka ; Müllerová, Ilona ; Sobota, Jaroslav
The effect of high residual stress on the quality of thin sputtered carbon nitride films has been studied by Scanning Low Energy Electron Microscopy (SLEEM). Basically, two different types of stress can be identified in thin films: compressive stress and tensile stress. Compressive stress leads to wrinkling and film delamination and tensile stress can cause the fracturing of thin films. Experiments were made in the Tescan TS 5130 MM equipped with the Cathode Lens system (CL), which enable us to observe samples at arbitrary landing energies of the illuminating electrons. Operating of a SEM at low energies offers several advantages: an increase of materials contrast via low energy, high ratio SE, BSE signal and noise, smaller interaction volume and elimination of charging effects. The effect of annealing in vacuum to residual stress (calculated from Stoney’s equation) was measured. The porous character of films was observed by thermal desorption spectroscopy (TDS).
|
guest ::
