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Scanning very low energy electron microscopy for the characterization of polycrystalline metal samples
Pokorná, Zuzana; Knápek, Alexandr
2016 - anglický
We explored the possibility of a Scanning Electron Microscopy technique for the determination of crystallographic orientation, based on the measurement of the reflectivity of very low energy electrons. Our experiments are based on the concept that in the incident electron energy range 0–30 eV, electron reflectivity can be correlated with the electronic structure of the material, which varies with the local crystallographic orientation of the specimen.\nThe motivation for the development of this technique was to achieve a quick and highresolution means for determining the crystallographic orientation of very small grains in a polycrystalline material. The key limiting factor was the cleanliness of the sample surface and also the geometrical setup of the experiment.
Klíčová slova:
electron microscopy; SEM; crystallographic orientation
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Scanning very low energy electron microscopy for the characterization of polycrystalline metal samples
We explored the possibility of a Scanning Electron Microscopy technique for the determination of crystallographic orientation, based on the measurement of the reflectivity of very low energy ...
Using GPGPU in MR Data Processing
Mikulka, J.; Slíž, J.; Bartušek, Karel
2016 - anglický
The main tissue parameters targeted by MR tomography include, among others, relaxation times T-1 and T-2. This paper focuses on the computation of the relaxation time T-2 measured with the Spin Echo method. The maxima of measured echoes must be interleaved with an exponential function to compute the T2 relaxation. As this procedure needs to be repeated for each pixel of the scanned tissue, the processing of large images then becomes very intensive. This paper introduces the results provided by accelerated computation based on parallelization and carried out with a graphics card. By using the simple method of linear regression, we obtain a processing time of less than 36 ms. In the case of the Levenberg-Marquardt algorithm, the reconstruction was done in 96 ms. This period is at least 900 times shorter than that achievable with professional software.
Klíčová slova:
GPGPU; data processing
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Using GPGPU in MR Data Processing
The main tissue parameters targeted by MR tomography include, among others, relaxation times T-1 and T-2. This paper focuses on the computation of the relaxation time T-2 measured with the Spin Echo ...
New detectors for low-energy BSE
Lalinský, Ondřej; Schauer, Petr; Kučera, M.; Hanuš, M.; Lučeničová, Z.
2016 - anglický
Backscattered electrons (BSE) are mostly used to study the specimen’s topography. Nowadays, low energy (units of keV) electron beam imaging is often necessary for example for the research of nanomaterials, biomaterials or semiconductors. Because BSE detectors are mostly non-accelerating or low-accelerating, electrons with approximately the same energy as primary beam (PB) have to be detected. Therefore, BSE detectors need to become optimized for such low-energy electrons. For the scintillation detectors, the biggest problem probably lies in the scintillator. Semiconductor detectors aren’t studied in this work. Cerium activated bulk single crystals of yttrium aluminium garnet (YAG:Ce)Ce(X):Y(3-X)Al(5)O(12) are widely used as scintillators for the detection of high-energy backscattered electrons (BSE). However, commonly used YAG:Ce single crystal strongly loses its light yield (LY) with the decrease of the PB energy. As possible available alternatives for this application, bulk single crystals of yttrium aluminium perovskite (YAP:Ce) Ce(x)Y(1-X)AlO(3) and CRY018 can be predicted. However, similar LY drop can be expected also with these scintillators.
Klíčová slova:
BSE detector; cathodoluminescence; low-energy electron; scintillator
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
New detectors for low-energy BSE
Backscattered electrons (BSE) are mostly used to study the specimen’s topography. Nowadays, low energy (units of keV) electron beam imaging is often necessary for example for the research of ...
The information depth of backscattered electron imaging
Piňos, Jakub; Mikmeková, Šárka; Frank, Luděk
2016 - anglický
Of the conventional imaging signals in the scanning electron microscope (SEM), the secondary electrons generally reflect surface properties of the sample, while the backscattered electrons (BSE) are capable of providing information about complex properties of the target down to a certain subsurface depth. Contrast mechanisms are combined according to the energy of incident electrons and energy and angular acceptance of BSE detection. In all cases, a question arises concerning the information depth of this mode. No applicable answer provides a definition declaring this depth as that from which we still obtain useful information about the object. We can employ software simulating the electron scattering in solids,\nwhile experimental approaches are also possible. Moreover, two analytic formulas can be found in the literature.
Klíčová slova:
electron microscopy; SEM; BSE
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
The information depth of backscattered electron imaging
Of the conventional imaging signals in the scanning electron microscope (SEM), the secondary electrons generally reflect surface properties of the sample, while the backscattered electrons (BSE) are ...
Secondary electron spectroscopy and energy selective imaging for the engineering of carbon based materials
Rodenburg, C.; Masters, R.; Lidzey, D.; Unčovský, M.; Vystavěl, Tomáš; Mika, Filip
2016 - anglický
That the fine structure of secondary electron emission spectra (SES) from carbon fibres is effected by fibre crystallinity and molecular orientation and linked to engineering materials properties such as modulus was reported over three decades ago. In spite of this\nlongstanding knowledge SES are not yet widely exploited for materials engineering of carbon based materials, probably due to a lack of instrumentation that is suitable to collect SES from beam sensitive materials and also has the capability to visualise, local variation based on SES shape. Thanks to rapid advances in low voltage SEM that offer energy selective imaging, it was recently demonstrated that differences in SES for different carbon based materials can be used to map chemical variations with sub-nanometer resolution when only SE 8 < eV were\nselected to form the SEM images. Such high resolution is not surprising as the implementation of energy filtering in SEMs to improve image resolutions was previously advocated. To fully exploit energy selective imaging for materials engineering the nature of the features in the SES must be determined.
Klíčová slova:
emission spectroscopy; SES
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Secondary electron spectroscopy and energy selective imaging for the engineering of carbon based materials
That the fine structure of secondary electron emission spectra (SES) from carbon fibres is effected by fibre crystallinity and molecular orientation and linked to engineering materials properties such ...
Golden nanoparticle in optical tweezers: influence of shape and orientation on optical trapping
Šiler, Martin; Brzobohatý, Oto; Chvátal, Lukáš; Karásek, Vítězslav; Paták, Aleš; Pokorná, Zuzana; Mika, Filip; Zemánek, Pavel
2016 - anglický
Noble metal nanoparticles (NPs) have attracted increased attention in recent years due to various applications of resonant collective oscillations of free electrons excited with light (plasmon resonance). In contrast to bulk metal materials, where this plasmon resonance frequency depends only on the free electron number density, the optical response of gold and silver NPs can be tuned over the visible and near-infrared spectral region by the size and shape of the NP. Precise and remote placement and orientation of NPs inside cells or tissue would provide another degree of control for these applications. A single focused laser beam – optical tweezers – represents the most frequently used arrangement which provides threedimensional (3D) contact-less manipulation with dielectric objects or living cells ranging in size from tens of nanometers to tens of micrometers. It was believed that larger metal NPs behave as tiny mirrors that are pushed by the light beam radiative force along the direction of beam propagation, without a chance to be confined. However, recently several groups have reported successful optical trapping of gold and silver particles as large as 250 nm. We\noffer an explanation based on the fact that metal nanoparticles naturally occur in various nonspherical\nshapes, and their optical properties differ significantly due to changes in localized plasmon excitation.
Klíčová slova:
NPs; plasmon resonance
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Golden nanoparticle in optical tweezers: influence of shape and orientation on optical trapping
Noble metal nanoparticles (NPs) have attracted increased attention in recent years due to various applications of resonant collective oscillations of free electrons excited with light (plasmon ...
Reverse Monte Carlo as MRS quantitation quality assessment
Jabłoński, Michal; Starčuková, Jana; Starčuk jr., Zenon
2016 - anglický
Data analysis of Magnetic Resonance Spectroscopy (MRS) using quantitation algorithms, such as AQSES, QUEST, AMARES or LCModel produces estimates of relative metabolite concentrations and their precision, estimated as the Cramer Rao Lower Bounds (CRLB). This assessment does not guarantee the uniqueness of the fit, and thus is not a true representation of the concentration uncertainty. In this publication authors propose to verify the quality of fitting by Reverse Monte Carlo method, which is independent of the estimator and has weaker requirements on the solution and model accuracy.
Klíčová slova:
reverse Monte Carlo; MRS quantitation quality
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Reverse Monte Carlo as MRS quantitation quality assessment
Data analysis of Magnetic Resonance Spectroscopy (MRS) using quantitation algorithms, such as AQSES, QUEST, AMARES or LCModel produces estimates of relative metabolite concentrations and their ...
Trapping and cooling of single ions for frequency metrology and quantum optics experiments
Slodička, L.; Pham, Minh Tuan; Lešundák, Adam; Hucl, Václav; Čížek, Martin; Hrabina, Jan; Řeřucha, Šimon; Lazar, Josef; Obšil, P.; Filip, R.; Číp, Ondřej
2016 - anglický
Single trapped ions trapped in Paul traps correspond to ideal candidates for realization of extremely accurate optical atomic clocks and practical studies of the light–atom interactions and nonlinear mechanical dynamics. These systems benefit from both, the superb isolation of the ion from surrounding environment and excellent control of its external and internal\ndegrees of freedom, at the same time, which makes them exquisite platforms for experimental studies and applications of light matter interaction at its most fundamental level. The exceptional degree of control of single or few ion's state enabled in past decade number of major advancements in the applications from the fields of experimental quantum information\nprocessing and frequency metrology, including recent realization of scalable Shor's\nalgorithm, fractional uncertainties of the frequency measurements close to 10-18 level, or simulations of complex quantum many-body effects. These results, together with the rapid advancements in the production of low-noise segmented micro-traps, promise prompt access to long-desired regimes of quantum optomechanics and further development and applications\nof optical atomic clocks.
Klíčová slova:
quantum optics experiments; frequency metrology
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Trapping and cooling of single ions for frequency metrology and quantum optics experiments
Single trapped ions trapped in Paul traps correspond to ideal candidates for realization of extremely accurate optical atomic clocks and practical studies of the light–atom interactions and nonlinear ...
Treatment of surfaces with slow electrons
Frank, Luděk; Mikmeková, Eliška
2016 - anglický
Historically, the most annoying obstacle to acquiring SEM micrographs, in particular higher magnification micrographs taken with the ambition of resolving the finest observable details, may be said to be carbonaceous contamination “highlighting” the previous field of view with a black rectangle contoured by an even darker frame. This contamination is generated by decomposition of adsorbed hydrocarbon molecules with incident electrons leaving a crosslinked\nlayer of carbon atoms as a surface coating. The darker contours come from high surface mobility of hydrocarbon molecules from outside the field. The situation has been improved in recent decades by a lower pressure and dryer vacuum in specimen chambers, but even under ultrahigh vacuum (UHV) conditions the phenomenon occurs due to hydrocarbon molecules deposited on the specimen when loaded. Therefore, only in-situ cleaning with an\nattachment producing an ion beam solves this problem in UHV, while some plasma cleaners have also started appearing in standard-vacuum SEM chambers. The goal of complete removal of hydrocarbons is motivated by the supposed unavoidability of their decomposition with primary electrons. However, we have found hydrocarbon molecules being released, rather than their decomposition, when the energy of the impinging electrons drops beneath 50 eV or so.
Klíčová slova:
electron microscopy; SEM; STEM
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Treatment of surfaces with slow electrons
Historically, the most annoying obstacle to acquiring SEM micrographs, in particular higher magnification micrographs taken with the ambition of resolving the finest observable details, may be said to ...
Field emission from the surface of highly ordered pyrolytic graphite
Knápek, Alexandr; Pokorná, Zuzana
2016 - anglický
This paper deals with the electrical characterization of highly ordered pyrolytic graphite (HOPG) surface based on field emission of electrons. The effect of field emission, occurs only at disrupted surface, i.e. surface containing ripped and warped shreds of the uppermost layers of graphite. These deformations provide the necessary field gradients which are required for measuring tunneling current caused by field electron emission. Results of the field emission measurements are correlated with other surface\ncharacterization methods such as scanning near-field optical microscopy (SNOM) or atomic force microscopy. A simple method utilizing the field emission of electrons has been devised to characterize the sample surface. Electron and probe microscopies were used to determine the structure of both the bulk sample and the partially exfoliated shreds of the uppermost layers of graphite in locations where field emission is observed.
Klíčová slova:
electron microscopy; HOPG; SNOM
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Field emission from the surface of highly ordered pyrolytic graphite
This paper deals with the electrical characterization of highly ordered pyrolytic graphite (HOPG) surface based on field emission of electrons. The effect of field emission, occurs only at disrupted ...
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