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Thermal desorption spectroscopy in prototype furnace for chemical vapor deposition
Průcha, Lukáš; Daniel, Benjamin; Piňos, Jakub; Mikmeková, Eliška
2018 - English
Cleaning of the sample surfaces is crucial for scanning electron microscopy, especially for\nlow energy electron microscopy or for the deposition of thin layers, such as graphene,\nwhere surface has to be well prepared. In the best case, every unwanted particle should be\ncleaned from the sample surface for best low energy electron microscopy observation or thin\nfilm deposition. Unfortunately, the standard cleaning procedures can leave residues on the\nsample surface. This work is focused on thermal desorption spectroscopy (TDS). TDS is a method of observing desorbed molecules from a sample surface during the increase of\ntemperature of the sample. The aim of this study was to determine optimum conditions:\ntemperature and time, to achieve clean surfaces in the shortest time.
Keywords:
thermal desorption spectroscopy; CVD; surface cleaning; silicon
Available at various institutes of the ASCR
Thermal desorption spectroscopy in prototype furnace for chemical vapor deposition
Cleaning of the sample surfaces is crucial for scanning electron microscopy, especially for\nlow energy electron microscopy or for the deposition of thin layers, such as graphene,\nwhere surface has ...
Electron optical properties of a new low-energy scanning electron microscope with beam separator
Radlička, Tomáš; Kolařík, V.; Oral, Martin
2018 - English
The low energy scanning electron microscope (SEM) which is currently at the Institute of\nScientific Instruments, suffers from low resolution and suboptimal detections systems. In the cathode lens regime, signal electrons are accelerated by the electric field between the sample and the objective lens, getting collimated. Those with low emission angles get through the bore in the BSE detector into the objective lens and cannot be detected by the available detectors now. The information about the sample provided by these electrons is lost, which limits our microscopy methods.\nThese two limitations are to be overcome with a new low-energy SEM, which was developed\nat Delong Instruments. It consists of a field emission gun with the energy width of 0.8 eV, a magnetic condenser lens, and an electrostatic triode objective lens. The acceleration voltage is 5 kV. The sample stage can be biased at up to -5 kV to provide low landing energy without strong decrease of the resolution – the effect of the cathode lens. A beam separator is placed in front of the deflection system for the detection of the signal electrons that get to the column. In a combination with standard detectors and cathode lens, it allows detecting all\nkinds of signal electrons.
Keywords:
low energy scanning electron microscopy; beam separation; aberrations
Available at various institutes of the ASCR
Electron optical properties of a new low-energy scanning electron microscope with beam separator
The low energy scanning electron microscope (SEM) which is currently at the Institute of\nScientific Instruments, suffers from low resolution and suboptimal detections systems. In the cathode lens ...
Inelastic mean free path from raw data measured by low-energy electrons time-of-flight spectrometer
Zouhar, Martin; Radlička, Tomáš; Oral, Martin; Konvalina, Ivo
2018 - English
The inelastic mean free path (IMFP) is a key parameter of electron transport in a solid. With\nthe rise of so-called meta-materials, materials of specific shape, such as 2D crystals, or\nmaterials with tailored functionality for next-generation electronic devices, the investigation\nof the IMFP is still topical and of high importance. This is true especially at low energies, landing energy of electrons below 100 eV, that are hard to study using well established\ntechniques of electron spectroscopy.
Keywords:
electron microscopy; time of flight; inelastic mean free path; low energy
Available at various institutes of the ASCR
Inelastic mean free path from raw data measured by low-energy electrons time-of-flight spectrometer
The inelastic mean free path (IMFP) is a key parameter of electron transport in a solid. With\nthe rise of so-called meta-materials, materials of specific shape, such as 2D crystals, or\nmaterials ...
Optical binding of polystyrene particles in tractor beam
Damková, Jana; Chvátal, Lukáš; Oulehla, Jindřich; Ježek, Jan; Brzobohatý, Oto; Zemánek, Pavel
2018 - English
The motion of a particle illuminated by a laser beam is usually driven by the photon flow due\nto the radiation pressure and therefore for particle trapping, one has to employ gradient forces. But in a tractor beam, objects are illuminated by the uniform light intensity and even so they can be pulled against the beam propagation. There have been developed several techniques how to create such a tractor beam. In our case, the tractor beam is created by two identical Gaussian beams that interfere under the defined angle. It creates the\nstanding wave, where in the transversal plane the particle is trapped by means of the gradient\nforce, but in the total beam propagation direction, the particle manipulation is driven by the non-conservative force. It is remarkable that this force can for the specific combinations of\nparameters pull the micro-particle against the beam propagation. This kind of behavior is\nbecause of the particle scattering where the majority of the incident photons is scattered in the forward direction and, based on the principle of action and reaction, the transfer of\nmomentum leads to a backward movement of the object. The pushing and pulling force is\nsensitive to the polarization of the laser beam, its incident angle and the particle size so this\ntechnique can be used for example for sorting of objects of different sizes.
Keywords:
optical binding; self-organization; optical force; tractor beam; holographic video microscopy
Available at various institutes of the ASCR
Optical binding of polystyrene particles in tractor beam
The motion of a particle illuminated by a laser beam is usually driven by the photon flow due\nto the radiation pressure and therefore for particle trapping, one has to employ gradient forces. But in ...
Field emission from W5O14 nanowires
Saqib, M.; Knápek, Alexandr; Jelenc, J.; Pirker, L.
2018 - English
The W5O14 (O/W=2.8) nanowires are metallic oxides with specific resistivity of 25 microOhm/cm and\ndiameters bellow 100 nm [1]. They were synthesized by iodine transport method using nickel\nas a growth promoter and WO3 as source of tungsten and oxygen. The field emission\ncharacteristics of single nanowires [2] and the films composed of these nanowires have been\nreported [3]. The emitting current densities up to 6.4 mA/cm2 have been obtained at relatively\nlow average electric field of about 3 V/Ohm*m. The samples were allowed to emit for more than\n100 hours without showing significant decays of the emitting current and without substantial\ncurrent oscillations. Here, we present field emission properties of single W5O14 nanowires\nexposed to two ranges of average electric fields (0.7–0.85 V/Ohm*m and up to 37–39 V/Ohm*m.
Keywords:
field emission; W5O14 nanowires
Available at various institutes of the ASCR
Field emission from W5O14 nanowires
The W5O14 (O/W=2.8) nanowires are metallic oxides with specific resistivity of 25 microOhm/cm and\ndiameters bellow 100 nm [1]. They were synthesized by iodine transport method using nickel\nas a ...
Stable Ce4+ centres - a tool to optimize cathodoluminescence performance in garnet scintillators
Lalinský, Ondřej; Schauer, Petr; Rathaiah, M.; Kučera, M.
2018 - English
Garnet single crystals are widely used as scintillators in electron detectors. Cerium activated lutetium aluminum garnet Cex:Lu3-xAl5O12 (LuAG:Ce) is a promising example of such material for these applications. This is mainly due to its high light yield (LY) of 25 kph/MeV, short decay time of 60–80 ns, high atomic density (6.7 g/cm3), and high radiation stability with no hygroscopicity. The cathodoluminescence (CL) performance can be improved by Ga and Gd doping the garnet matrix. Proper admixture of these elements can increase the LY to 50–60 kph/MeV in addition to eliminating unwanted slower decay components. There was an idea that further decay acceleration can be achieved by doping the garnet with monovalent (Li+) or divalent ions (Mg2+, Ca2+). This should increase the valency of some Ce3+ centres to Ce4+ which should better compete with electron traps, and thus accelerate the decay. Our previous work proved the same decay trend, however, at a price of the LY. Such LY loss may induce the idea, if the stable Ce4+ centres are really participating in Ce3+ emission.
Keywords:
garnet scintillators; cathodoluminescence performance
Available at various institutes of the ASCR
Stable Ce4+ centres - a tool to optimize cathodoluminescence performance in garnet scintillators
Garnet single crystals are widely used as scintillators in electron detectors. Cerium activated lutetium aluminum garnet Cex:Lu3-xAl5O12 (LuAG:Ce) is a promising example of such material for these ...
Optofluidic techniques for directed evolution of enzymes
Pilát, Zdeněk; Ježek, Jan; Samek, Ota; Zemánek, Pavel; Buryška, T.; Damborský, J.; Prokop, Z.
2018 - English
Enzymes are highly versatile and ubiquitous biological catalysts. They can greatly accelerate\nlarge variety of reactions, while ensuring appropriate catalytic activity and high selectivity.\nThese properties make enzymes attractive biocatalysts for a wide range of industrial and\nbiomedical applications. Over the last two decades, directed evolution of enzymes has\ntransformed the field of protein engineering.
Keywords:
optofluidics; Raman spectroscopy; enzymes
Available at various institutes of the ASCR
Optofluidic techniques for directed evolution of enzymes
Enzymes are highly versatile and ubiquitous biological catalysts. They can greatly accelerate\nlarge variety of reactions, while ensuring appropriate catalytic activity and high selectivity.\nThese ...
Real time observation of strain in the SEM sample
Piňos, Jakub; Frank, Luděk
2018 - English
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.
Keywords:
SEM; SLEEM; deformation
Available at various institutes of the ASCR
Real time observation of strain in the SEM sample
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 ...
Grazing incidence interferometer for form measurement of hollow cylinders
Šarbort, Martin; Řeřucha, Šimon; Holá, Miroslava; Lazar, Josef
2018 - English
Optical metrology of cylindrical specimens represents an interesting task in scientific and\nindustrial practice. The most precise measurement methods use principles of laser\ninterferometry where the phase difference between the reference wave and the object wave reflected from the tested surface is detected. The form measurement of hollow cylindrical tubes can be advantageously realized by an object wave with conical wavefronts generated by an axicon lens or an equivalent diffractive optical element. An axicon characterized by large apex angle forms a conical wave that fulfills the conditions of the grazing incidence, which results in suppression of the speckle noise. The previous experimental setups were relatively complex since they involved a pair of mutually reversed axicons or a pair of diffractive optical elements that transform the object wave from planar to conical and vice\nversa.
Keywords:
interferometry; surface metrology; hollow cylinders
Available at various institutes of the ASCR
Grazing incidence interferometer for form measurement of hollow cylinders
Optical metrology of cylindrical specimens represents an interesting task in scientific and\nindustrial practice. The most precise measurement methods use principles of laser\ninterferometry where the ...
Imaging via multimode optical fiber: recovery of a transmission matrix using internal references
Šiler, Martin; Jákl, Petr; Traegaardh, Johanna; Ježek, Jan; Uhlířová, Hana; Tučková, Tereza; Zemánek, Pavel; Čižmár, Tomáš
2018 - English
Current research of life shows a great desire to study the mechanics of biological processes\ndirectly within the complexity of living organisms. However, majority of practical techniques\nused nowadays for tissue visualization can only reach depths of a few tens of micrometres as\nthe issue obscures deep imaging due to the random light scattering. Several imaging\ntechniques deal with this problems from different angels, such as optical coherence\ntomography, light sheet microscopy or structured light illumination A different and promising strategy to overcome the turbid nature of scattering tissues is to employ multimode optical fibers (MMF) as minimally invasive light guides or endoscopes to provide optical access inside. Although the theoretical description of light propagation through such fibers has been developed a long time ago it is frequently considered inadequate to describe real MMF. The inherent randomization of light propagating through MMFs is typically attributed to undetectable deviations from the ideal fiber structure. It is a commonly believed that this\nadditional chaos is unpredictable and that its influence grows with the length of the fiber.\nDespite this, light transport through MMFs remains deterministic and can be characterized by a transmission matrix (TM) which connects the intensity and phase patterns on the fiber input and output facets. Once the TM is known it can be used to create focus in any desired 3D\ncoordinates beyond the distal fiber facet, see figure 1, and perform e.g. fluorescence based\nlaser scanning microscopy or optical trapping.
Keywords:
multimode optical fiber
Available at various institutes of the ASCR
Imaging via multimode optical fiber: recovery of a transmission matrix using internal references
Current research of life shows a great desire to study the mechanics of biological processes\ndirectly within the complexity of living organisms. However, majority of practical techniques\nused ...
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