Reversible modifications of linear dispersion - graphene between boron nitride monolayers

Electronic properties of the graphene layer sandwiched between two hexagonal boron nitride sheets have been studied using the first-principles calculations and the minimal tight-binding model. It is shown that for the ABC-stacked structure in the absence of external field the bands are linear in the vicinity of the Dirac points as in the case of single-layer graphene. For certain atomic configuration, the electric field effect allows opening of a band gap of over 230 meV. We believe that this mechanism of energy gap tuning could significantly improve the characteristics of graphene-based field-effect transistors and pave the way for future electronic applications.Comment: 5 pages, v2 with slightly modified introduction and summar

Domains of doping in graphene on polycrystalline gold: first-principles and scanning tunneling spectroscopy studies

We have studied the graphene/gold interface by means of density functional theory (DFT) and scanning tunneling spectroscopy (STS). Weak interaction between graphene and the underlying gold surface leaves unperturbed Dirac cones in the band-structure, but they can be shifted with respect to the Fermi level of the whole system, which results in effective doping of graphene. DFT calculations revealed that the interface is extremely sensitive to the adsorption distance and to the structure of metal's surface, in particular strong variation in doping can be attributed to the specific rearrangements of substrate's atoms, such as the change in the crystallographic orientation, relaxation or other modifications of the surface. On the other hand, STS experiments have shown the presence of energetic heterogeneity in terms of the changes in the local density of states (LDOS) measured at different places on the sample. Randomly repeated regions of zero-doping and p-type doping have been identified from parabolic shape characteristics and from well defined Dirac points, respectively. The doping domains of graphene on gold seem to be related to the presence of various types of the surface structure across the sample. DFT simulations for graphene interacting with Au have shown large differences in doping induced by considered structures of substrate, in agreement with experimental findings. All these results demonstrate the possibility of engineering the electronic properties of graphene, especially tuning the doping across one flake which can be useful for applications of graphene in electronic devices

Energy gap tuning in graphene on hexagonal boron nitride bilayer system

We use a tight binding approach and density functional theory calculations to study the band structure of graphene/hexagonal boron nitride bilayer system in the most stable configuration. We show that an electric field applied in the direction perpendicular to the layers significantly modifies the electronic structure of the whole system, including shifts, anticrossing and other deformations of bands, which can allow to control the value of the energy gap. It is shown that band structure of biased system may be tailored for specific requirements of nanoelectronics applications. The carriers' mobilities are expected to be higher than in the bilayer graphene devices.Comment: 10 pages, 7 figures, submitted to Physical Review

Analysis of initiation cavitation erosion process mechanism of the chosen alloys based on intermetallic Ni3Al phase

W pracy przedstawiono wyniki badań zużycia kawitacyjnego, w okresie inkubacji, wybranych stopów na bazie fazy międzymetalicznej Ni3Al z dodatkami stopowymi boru, cyrkonu, chromu, molibdenu i żelaza. Badania prowadzono na materiale w stanie po odlewaniu oraz po procesie homogenizacji w temperaturze 1200°C. Stwierdzono podobny charakter inicjowania zużycia kawitacyjnego w postaci mikropęknięć i lokalnych ubytków zarówno w stanie po odlewaniu, jak i po homogenizacji.In the paper the results of research on initial stage - incubation period of a cavitation wear in the intermetallic Ni3Al alloys with boron, zirconium, chromium, molybdenum and iron are presented. Investigations were carried out both for as-cast and materials after homogenisation treatment at the temperature 1200°C. Initiation of the cavitation consumption in material as microcracking and local dents had similar character after casting as well as homogenization

Cavitation wear of intermetallic Ni₃Al alloy

W referacie zaprezentowano wyniki badań erozji kawitacyjnej w okresie inkubacji stopu odlewniczego na bazie fazy międzymetalicznej Ni₃Al z dodatkami stopowymi boru, cyrkonu, chromu, molibdenu i żelaza. Badania prowadzono na materiale w stanie po odlewaniu oraz po procesie homogenizacji w temperaturze 1200°C, w czasie do 100 godzin, w atmosferze powietrza. Stwierdzono podobny charakter inicjowania zużycia kawitacyjnego w postaci mmikropęknięć i lokalnych ubytków zarówno w stanie po odlewaniu, jak i po homogenizacji.The result of research on initial state-incubation period of a cavitation wear in the intermetallic Ni₃Al alloy with boron, zirconium, chromium molybdenum, and iron are presented in this paper. Investigations were carried out both for as-cast and material after homogenization treatment. Experiments show that first micro-cracks are formed in the matrix-diphase regions (ɣ' + β) regions occur during further interaction of a liquid with alloy surface. After complete pulling out of surface layer fragments, a separation surface shows clear tracks of both brittle cleavable and fatigue cracking

Investigation of Structure and Conductivity of Superionic Conducting Materials Obtained on the Basis of Silver Iodide

Conductivity and structure of materials belonging to pseudo-binominal group $(AgI-Ag_2MoO_4)$ were investigated. Structure was investigated by X-ray and scanning electron microscopy techniques. It was found that described materials present a variety of internal structures. This type of structures affects conductivity at room temperature, so there is correspondence between conductivity and structure

Zmiany chropowatości powierzchni intermetali Ni3Al w wyniku oddziaływania erozyjnego i kawitacyjnego

Alloys based on the Ni3Al intermetallic phase belong to a group of new generation special materials. Their main advantages are resistance to oxidising and carbonising atmospheres, high fatigue strength, high creep resistance, and very high wear and corrosion resistance. This paper presents an analysis of the influence of chemical composition and heat treatment on the structure, thermomechanical strengthening homogeneity, and resistances to erosion wear and cavitation wear of alloys based on Ni3Al intermetallic phase. Investigations of the alloy roughness in the primary stage and after erosion and cavitation wear tests are described. The analysis indicates that erosion and cavitation wear progresses with time and strongly depends on the chemical composition.Stopy na osnowie fazy międzymetalicznej Ni3Al to grupa materiałów specjalnych nowej generacji. Do podstawowych zalet tych stopów należy zaliczyć: odporność na działanie atmosfer utleniających i nawęglających, wysoką wytrzymałość zmęczeniową, wysoką odporność na pełzanie, bardzo dobrą odporność na zużycie ścierne i korozję. Ponadto istotną zaletą intermetali z układu Ni-Al jest niski koszt materiałowy, wynikający ze stężenia aluminium. W pracy przedstawiono analizę wpływu składu chemicznego oraz obróbki cieplnej na strukturę, jednorodność umocnienia i odporność na zużycie erozyjne i kawitacyjne stopów na osnowie fazy międzymetalicznej Ni3Al. Przeprowadzono również chropowatości analizowanych stopów w stanie wejściowym i po próbach zużycia erozyjnego i kawitacyjnego. Badania prowadzono na intermetalach Ni3Al z dodatkami stopowymi boru, cyrkonu, chromu, molibdenu i żelaza, w stanie po odlewaniu i wygrzewaniu ujednorodniającym. Przeprowadzona analiza chropowatości wykazała, że zużyciu erozyjne i kawitacyjne rośnie wraz z czasem trwania prób i zależy istotnie od składu chemicznego