Determination of the thickness distribution of a graphene layer grown on a 2" SiC wafer by means of Auger electron spectroscopy depth profiling

Auger electron spectroscopy (AES) depth profiling was applied for determination of the thickness of a macroscopic size graphene sheet grown on 2 inch 6H-SiC (0001) by sublimation epitaxy. The measured depth profile deviated from the expected exponential form showing the presence of an additional, buffer layer. The measured depth profile was compared to the simulated one which allowed the derivation of the thicknesses of the graphene and buffer layers and the Si concentration of buffer layer. It has been shown that the C made buffer layer contains about 30% unsaturated Si. The depth profiling was carried out in several points (diameter 50m), which permitted the constructing of a thickness distribution characterizing the uniformity of the graphene sheet

AlNiGe kao nov namjenski materijal za kontakte na n–GaAs

Al(150 nm)/Ni(30 nm)/Ge(40 nm) layers have been deposited onto n-type GaAs by thermal evaporation. The samples have been annealed for 20 minutes in flowing forming gas H2:N2 (30%:70%). The alloying behaviour of the specimens has been investigated by electron microscope. The contacts show a bilayer structure in the case of as-deposited samples. The top layer is pure Al and the second one is Ni-Ge. The metal-semiconductor interface is sharp. Annealing at 400 °C resulted in the formation of florets on the surface assumed to be AlGe eutectic; meanwhile, randomly distributed pits of size 10 nm have been grown into the GaAs. The samples annealed at 450 °C show bilayer structure. The top layer is pure Ge and the second one consists of Al-Ni(Ge). On samples annealed at 500 °C thick alloyed layer has been found with deep pyramidal pits of size 0.25 µm. The interface region between GaAs and the pits contains substantial amount of Al. Contrary to the published results, I-V (current-voltage) characteristics of the annealed specimens show that the contacts remained rectifying at each applied annealing process. The temperature dependence of parameters evaluated from either current-voltage or capacitance-voltage characteristics prove that the characteristic form of conductance is the anomalous thermionic-field emission.Slojevi Al(150 nm)/Ni(30 nm)/Ge(40 nm) termički su napareni na GaAs n–tipa. Uzorci su otpuštani u plinskoj smjesi H2(30%)+N2(70%) na 400 ◦C, 450 ◦C i 500 ◦C i njihovo legiranje je ispitivano elektronskom mikroskopijom. Suprotno objavljenim rezultatima, I − V krivulje pokazuju da spojevi zadržavaju ispravljačko svojstvo nakon otpuštanja na svim primijenjenim temperaturama. Temperaturna ovisnost parametara koji su bili određeni na osnovi ovisnosti struje o naponu ili kapaciteta o naponu potvrđuju da je vodenje struje posljedica anomalne termionske emisije polja

Kvantitatív elektronmikroszkópia = Quantitative transmission electron microscopy

A projekt keretében kvantitatív transzmissziós elektronmikroszkópos módszereket fejlesztettünk, majd e módszerek használhatóságát anyagtudományi problémák megoldása során demonstráltuk. "Imaging plate (IP)" segítségével végzett nagy pontosságú (egy millió szürkeségi fokozatot megkülönböztető) méréseinket használtuk mind a valós térbeli (HRTEM) képi információ, mind pedig a reciprok térbeli diffrakciós információ kisérleti rögzítésére. Új módszert dolgoztunk ki az elektron diffrakciós (ED) ábrák, valamint HRTEM képek kvantitatív feldolgozására nanokristályos vékonyrétegek kvalitatív és kvantitatív fázisanalízise, valamint egyes kristály szemcsék indexelése céljából. A méréseket szerkezeti modellekből számolt mennyiségekkel (HRTEM szimuláció, kinematikus diffrakció) hasonlítottuk össze. Inhomogén, összetett szerkezeti modellek megalkotását (atomi koordináták számítását) is saját fejlesztésű programunk segíti. Módszereinket a következő problémák megoldásánál használtuk: grafén sík-darabokat tartalmazó CNx-szerkezetek kialakulása; félvezetők (Ge, Si) és fémek reakcióinak kezdeti szakaszai; légköri eredetű koromszemcsék és vulkanikus szilikátok felépítése; beágyazottan izolált Co-szemcsék előállítása és fázisszelekciója; SiC poláros tulajdonságainak hatása a növekedésre; Cu/Mg multirétegekben az intermetallikus nukleációjának aszimmetriája. Eredményeinket nemzetközi konferenciákon és iskolákon mutattuk be és 11 referált folyóiratcikkben közöltük (kumulatív impakt faktor 27,24). | We developed quantitative transmission electron microscopy methods within the framework of the project and demonstrated the utility of them in solving problems from materials science. With the help of imaging plates, experimental images from real space (HRTEM) and from reciprocal space (diffraction patterns) were recorded with high accuracy (with one million gray levels). We developed a new method to process both the electron diffraction (ED) patterns and the HRTEM images quantitatively to result in both qualitative and quantitative phase analysis and to index patterns from individual crystal grains. The measured quantities were compared to similar ones (simulated HRTEM images and calculated kinematic diffraction), calculated from structural models. Construction of a structural model for inhomogeneous, complex structures is helped by a computer program also developed in this project. These methods helped us in solving the following problems: development of CNx structures from curved gaphene-sheets; initial stages of reaction between semiconductors (Ge, Si) and metals; structure of airborne soot particles and of volcanic silicates; formation of embedded, isolated Co nanoparticles and the phase selection during their formation; effect of the polarity of SiC on the growth; asymmetry in the nucleation of the intermetallic in Cu/Mg multilayer systems. Or results were presented at international conferences and schools and published in 11 papers in referenced journals (with cumulative impact factor of 27.24)

AlNiGe kao nov namjenski materijal za kontakte na n–GaAs

Al(150 nm)/Ni(30 nm)/Ge(40 nm) layers have been deposited onto n-type GaAs by thermal evaporation. The samples have been annealed for 20 minutes in flowing forming gas H2:N2 (30%:70%). The alloying behaviour of the specimens has been investigated by electron microscope. The contacts show a bilayer structure in the case of as-deposited samples. The top layer is pure Al and the second one is Ni-Ge. The metal-semiconductor interface is sharp. Annealing at 400 °C resulted in the formation of florets on the surface assumed to be AlGe eutectic; meanwhile, randomly distributed pits of size 10 nm have been grown into the GaAs. The samples annealed at 450 °C show bilayer structure. The top layer is pure Ge and the second one consists of Al-Ni(Ge). On samples annealed at 500 °C thick alloyed layer has been found with deep pyramidal pits of size 0.25 µm. The interface region between GaAs and the pits contains substantial amount of Al. Contrary to the published results, I-V (current-voltage) characteristics of the annealed specimens show that the contacts remained rectifying at each applied annealing process. The temperature dependence of parameters evaluated from either current-voltage or capacitance-voltage characteristics prove that the characteristic form of conductance is the anomalous thermionic-field emission.Slojevi Al(150 nm)/Ni(30 nm)/Ge(40 nm) termički su napareni na GaAs n–tipa. Uzorci su otpuštani u plinskoj smjesi H2(30%)+N2(70%) na 400 ◦C, 450 ◦C i 500 ◦C i njihovo legiranje je ispitivano elektronskom mikroskopijom. Suprotno objavljenim rezultatima, I − V krivulje pokazuju da spojevi zadržavaju ispravljačko svojstvo nakon otpuštanja na svim primijenjenim temperaturama. Temperaturna ovisnost parametara koji su bili određeni na osnovi ovisnosti struje o naponu ili kapaciteta o naponu potvrđuju da je vodenje struje posljedica anomalne termionske emisije polja

Preparation of Gold Nanocomposites with Tunable Charge and Hydrophobicity via the Application of Polymer/Surfactant Complexation

During the synthesis of gold nanoparticle (NP) assemblies, the interfacial charge and hydrophobicity of the primary particles play a distinguished role. In the present article, we demonstrate that the association of poly­(ethyleneimine) (PEI) capped gold NPs with sodium alkyl sulfates provide a powerful route for the manipulation of these interfacial properties. Dynamic light-scattering, electrophoretic mobility, UV–vis–near-infrared spectroscopy, nanoparticle tracking analysis, and transmission electron microscopy measurements were used to characterize the PEI/surfactant/gold nanoassemblies. The results indicate the formation of gold NPs surrounded by a PEI/surfactant shell with composition-dependent charge and hydrophobicity. The mean size and the aggregation of the nanoassemblies can be fine tuned by the amount of surfactant bound to the primary gold NPs as well as by the application of controlled mixing methods. The specific features of the prepared nanocomposites may be further exploited in next-generation applications

Encapsulation of the Graphene Nanoribbon Precursor 1,2,4-trichlorobenzene in Boron Nitride Nanotubes at Room Temperature

Graphene nanoribbons are prepared inside boron nitride nanotubes by liquid phase encapsulation and subsequent annealing of 1,2,4-trichlorobenzene. The product is imaged with high resolution transmission electron microscopy, and characterized by optical absorption and Raman spectroscopy. Carbon-containing material is detected inside the boron nitride nanotubes with energy-dispersive x-ray spectroscopy (EDS) and scanning transmission electron microscopy (STEM). The observed structures twist under the electron beam and the characteristic features of nanoribbons appear in the Raman spectra.Comment: 8 pages, 4 figure

Graphoepitaxy of High-Quality GaN Layers on Graphene/6H–SiC

The implementation of graphene layers in gallium nitride (GaN) heterostructure growth can solve self-heating problems in nitride-based high-power electronic and light-emitting optoelectronic devices. In the present study, high-quality GaN layers are grown on patterned graphene layers and 6H–SiC by metalorganic chemical vapor deposition. A periodic pattern of graphene layers is fabricated on 6H–SiC by using polymethyl methacrylate deposition and electron beam lithography, followed by etching using an Ar/O 2 gas atmosphere. Prior to GaN growth, an AlN buffer layer and an Al 0.2 Ga 0.8 N transition layer are deposited. The atomic structures of the interfaces between the 6H–SiC and graphene, as well as between the graphene and AlN, are studied using scanning transmission electron microscopy. Phase separation of the Al 0.2 Ga 0.8 N transition layer into an AlN and GaN superlattice is observed. Above the continuous graphene layers, polycrystalline defective GaN is rapidly overgrown by better quality single-crys- talline GaN from the etched regions. The lateral overgrowth of GaN results in the presence of a low density of dislocations ( ≈ 10 9 cm − 2 ) and inversion domains and the formation of a smooth GaN surface