Pavel Čudek

Scintillation SE detector for variable pressure scanning electron microscopes

We present results obtained with a new scintillation detector of secondary electrons for the variable pressure scanning electron microscope. A detector design is based on the positioning of a single crystal scintillator within a scintillator chamber separated from the specimen chamber by two apertures. This solution enables us to decrease the pressure to several Pa in the scintillator chamber while the pressure in the specimen chamber reaches values of about 1000 Pa (7.5 Torr). Due to decreased pressure, we can apply a potential of the order of several kV to the scintillator, which is necessary for the detection of secondary electrons. Simultaneously, the two apertures at appropriate potentials of the order of several hundreds of volts create an electrostatic lens that allows electrons to pass from the specimen chamber to the scintillator chamber. Results indicate a promising utilization of this detector for a wide range of specimen observations.

Study of electrochemical properties and thermal stability of the high-voltage spinel cathode material for lithium-ion accumulators

This article deals with the properties of high-voltage cathode material LiNi0.5Mn1.5O4 synthesised by a solid-state reactions method. The sample—LiNi0.5Mn1.5O4—was synthesised by two steps of annealing process. A number of electrochemical and physical methods were used to analyse the samples. The obtained LiNi0.5Mn1.5O4 powder was characterised by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and galvanostatic charge/discharge measurements at different loads and high temperature in lithium-ion cells with metal lithium as a counter electrode. All these analyses were used for confirmation of the structure of the material LiNi0.5Mn1.5O4 and for investigating its electrochemical properties. A special analysis was used for this paper to understand and confirm the function of this type of material. It is called electron paramagnetic resonance (EPR) spectroscopy, which is used in the field of lithium-ion batteries and also which is not common. This analysis is typically used to analyse free radicals. It is possible to study changes of valence in cathode materials during charging and confirming the valence change of Mn from Mn3+ to Mn4+ and of Ni from Ni2+ to Ni3+ and then to Ni4+ with EPR analysis. Thermogravimetric (TG) analysis of stability of the material LiNi0.5Mn1.5O4 with in situ observation of structural changes by SEM was used as the last analysis.

The influence of used precursors on the properties of high-voltage cathode materials

This article deals with the influence of precursors used in the high-voltage cathode material LiNi0.5Mn1.5O4 based on the LiMn2O4 material on its properties. Precursors with various sizes of particles were used for making the cathode material. Consequently, its influence on the stability during cycling, change of load, and the influence of higher temperatures during cycling were investigated. Produced materials were further analyzed to discover the influence of the change of the used precursor on the structure of the cathode material. The structure of the material deposited on Al foil was investigated by atomic force microscopy (AFM), and also X-ray photoelectron spectroscopy (XPS) analysis was performed. The materials were then observed by SEM and analyzed by the EDAX method. The results show that smaller particle size enhances the properties of cathode material both in the stability during cycling and higher capacity and also the potential under higher load.

Effect of negative potential on the extent of PID degradation in photovoltaic power plant in a real operation mode

Abstract This paper deals with Potential Induced Degradation (PID) of p-type monocrystalline PV modules (Evergreen) from a photovoltaic power plant that has been in operation mode for 7 years. Within the PV module affected by the PID degradation, the effect of the electric field on individual PV cells is studied. The distribution of the electric field was simulated by SolidWorks software. The results show a random distribution of affected PV cells not related to the size and distribution of the electric field intensity. Furthermore, the dependencies of negative voltage potential on the range of PID degradation of individual PV modules located in the negative pole of the PV string is made. From measured current voltage characteristics (measured at STC), it is evident that the value of negative voltage potential is not directly proportional to the PID occurrence. These results are supplemented by electroluminescence images which confirm this finding.

Optimization of Signal Detection in Scintillation Secondary Electron Detector for ESEM and SEM

Scintillation secondary electron detector for environmental scanning electron microscope (ESEM) that uses two pressure limiting apertures to decrease pressure in scintillator chamber to values which allow to connect voltage of 10 kV to the scintillator while the water vapor pressure in the specimen chamber of the microscope reaches up to 1000 Pa was introduced in [1]. Furthermore the possibility of detection of secondary electrons with this detector, even at pressure of 0.01 Pa (vacuum conditions) in the specimen chamber was presented in [2]. In this detector, pictured on Fig.1, the space between two apertures A1 and A2 is vacuum pumped by a rotary pump and the scintillator chamber by a turbomolecular pump. Voltages connected to the grid, to electrodes E1 and E2 and to the electrostatic lens created by the apertures A1 and A2 produce an electrostatic field that attracts secondary electrons emitted from the specimen to the detector and allow them to pass to the scintillator chamber where they are accelerated to the scintillator.