Shielding Effect of Oxide Isolating Layer on Surface Potential Measured by Kelvin Probe Force Microscopy

Tato diplomová práce je zaměřená na experimentální studium stínícího efektu oxidové izolační vrstvy na povrchový potenciál měřený Kelvinovým silovým mikroskopem. Pro studium povrchového potenciálu byly vytvořeny struktury na bázi Au/SiO2 pomocí elektronové litografie a metod depozice monovrstev a multivrstev. Povrchový potenciál byl zkoumaný v závislosti na vlhkosti a tloušťce oxidové vrstvy.The diploma thesis deals with the experimental study of shielding effect of oxide isolating layer on surface potential measured by Kelvin Probe Force Microscopy. For the study of surface potential were created Au/SiO2 based nanostructures by Electron Beam Lithography, Atomic Layer Deposition and Multilayer Deposition. Surface potential was measured depending on the relative humidity and thickness of oxide isolating layer.

Study of Water Meniscus Formation between the AFM Tip and NaCl Surface

Tato bakalářská práce je zaměřená na studium tvorby vodního menisku mezi hrotem AFM a povrchem NaCl. Jedná se o nepřímou metodu studia menisku, a to sledováním vzniku kráterů a pahorků na povrchu NaCl v závislosti na relativní vlhkosti, čištění hrotu, době přiložení hrotu a napětí mezi vzorkem a hrotem.This bachelor's thesis deals with the study of water meniscus formation between the AFM tip and NaCl surface. This is an indirect method for the study of meniscus by observation of holes and hillocks created on the NaCl surface, in dependence on the relative humidity, cleaning the tip, time of keeping the on the surface apllied voltage tip-surface.

Sub-0.1 degree phase locking of a single-photon interferometer

We report a single-photon Mach-Zehnder interferometer stabilized to a phase precision of 0.05 degrees over 15 hours. To lock the phase, we employ an auxiliary reference light at a different wavelength than the quantum signal. The developed phase locking operates continuously, with negligible crosstalk, and for an arbitrary phase of the quantum signal. Moreover, its performance is independent of intensity fluctuations of the reference. Since the presented method can be used in a vast majority of quantum interferometric networks it can significantly improve phase-sensitive applications in quantum communication and quantum metrology

Density functional study of gallium clusters on graphene: electronic doping and diffusion

Motivated by experimental results on transport properties of graphene covered by gallium atoms, the density functional theory study of clustering of gallium atoms on graphene (up to a size of 8 atoms) is presented. The paper explains a rapid initial increase of graphene electron doping by individual Ga atoms with Ga coverage, which is continually reduced to zero, when bigger multiple-atom clusters have been formed. According to density functional theory calculations with and without the van der Waals correction, gallium atoms start to form a three-dimensional cluster from five and three atoms, respectively. The results also explain an easy diffusion of Ga atoms while forming clusters caused by a small diffusion barrier of 0.11 eV. Moreover, the calculations show this barrier can be additionally reduced by the application of an external electric field, which was simulated by the ionization of graphene. This effect offers a unique possibility to control the cluster size in experiments only by applying a gate-voltage to the graphene in a field-effect transistor geometry and thereby without growth temperature assistance.Grant Agency of the Czech RepublicGrant Agency of the Czech Republic [17-21413S]; Ministry of Education, Youth and Sports from the Large Infrastructures for Research, Experimental Development and Innovations project 'IT4 Innovations National Super-computing Center' [LM2015070

Mechanism and Suppression of Physisorbed-Water-Caused Hysteresis in Graphene FET Sensors

Hysteresis is a problem in field-effect transistors (FETs) often caused by defects and charge traps inside a gate isolating (e.g., SiO2) layer. This work shows that graphene-based FETs also exhibit hysteresis due to water physisorbed on top of graphene determined by the relative humidity level, which naturally happens in biosensors and ambient operating sensors. The hysteresis effect is explained by trapping of electrons by physisorbed water, and it is shown that this hysteresis can be suppressed using short pulses of alternating gate voltages.Grant Agency of the Czech RepublicGrant Agency of the Czech Republic [17-21413S]; H2020 Twinning Programme (Project SINNCE) [810626]; MEYS CR [LQ1601 CEITEC 2020, LM2015041

Preparation cutting edge of solid milling tools by the means of drag-finishing process

Tato diplomová práce se zabývá možnostmi preparace břitu monolitních frézovacích nástrojů pomocí technologie vlečného omílání, při použití rozdílných médií a procesních časů preparace břitu. Dále se zabývá kvalitativními výsledky drsnosti povrchu dosažených pomocí vlečného omílání. Takto připravené nástroje dále poslouží pro testování trvanlivosti.Katedra technologie obráběníObhájenoThis thesis deals with the possibilities of cutting edge preparations of solid milling tools by the means of drag finishing technology, using different media and their relation to procedural times of the cutting edge preparing. It also deals with qualitative outcomes of the roughness of the tool surface achieved by drag finishing. These tools will be further used for endurance testing

Side charge propagation in simultaneous KPFM and transport measurement of humidity exposed graphene FET sensor

The surface diffusion (dissipation) of charge carriers enhanced by water molecules in solution-based biosensors and ambient operating gas sensors strongly influence their resistance response, sensitivity, and stability in time. Therefore, the information on the charge distribution at interfaces of conductive and insulating parts is essential for the operating sensors. This work presents the simultaneous measurement of the longitudinal macroscopic resistance response and local surface potential (SP) mapping by Kelvin probe force microscopy (KPFM) on a graphene Hall bar sensor. The results show the propagation of an electric charge from the main graphene channel onto the neighboring SiO2 surface. The charge propagation strongly increases with the relative humidity and can be controlled by a bottom-gate voltage used in most sensors based on a field effect transistor (FET) architecture. As proved by the longitudinal resistance measurements, the resulting side charge accumulation has a very small impact on the 2D resistivity of the graphene channel. It has been explained by an application of the Thomas-Fermi theory, proving an efficient screening of side accumulated charge potential caused by a redistribution of the charge inside the wide graphene channel. The combination of a transport resistance response and KPFM provides a deeper understanding of sensors/biosensors functionality and their design features than a simple resistance response usually observed. © 2023 Elsevier LtdMinisterstvo Školství, Mládeže a Tělovýchovy, MŠMT, (LM2023051, LQ1601 – CEITEC 2020); Grantová Agentura České Republiky, GA ČR, (23-07617S); European Regional Development Fund, ERDF, (CZ.1.05/1.1.00/02.0068