CCVD synthesis of carbon nanotubes from (Mg,Co,Mo)O catalysts: influence of the proportions of cobalt and molybdenum

Carbon nanotubes have been synthesised by catalytic chemical vapour deposition of a H2–CH4 mixture (18 mol% CH4) over (Mg,Co,Mo)O catalysts. The total amount of cobalt and molybdenum has been kept constant at 1 cat% and the proportion of molybdenum with respect to cobalt has been varied from x(Mo) = 0.25–1.0. This variation has important effects on both the yield and the nature (number of walls, straight walls or bamboo-like structures) of the carbon nanotubes. It also has an influence on the purity of the samples (amount of encapsulated metal particles, presence or not of amorphous carbon deposits). For x = 0.25, the nanotubes were mainly double- and triple-walled (inner diameter less than 3 nm); samples prepared from catalysts with higher molybdenum ratios contained larger multi-walled carbon nanotubes (inner diameter up to 9 nm), having up to 13 concentric walls. It is proposed that different growth mechanisms may occur depending on the initial composition of the catalyst

Topography induced optical spectral shifts and finite size effect of focal spot

We observe topography induced spectral shifts using high resolution grating spectrometers which we attribute to the fact that the focal spot has a finite size. The topography induced spectral shifts depend on spectrometer grating orientation and numerical aperture of the microscope objective. This is demonstrated by spectroscopic imaging trenches in GaAs in directions parallel and perpendicular the spectrometer entrance slit. Differences along the two directions of the LO phonon band show that the spectral shift is due to the variation of the grating angle across the non uniform illuminated focal spot caused by topography. Alignment errors of the optical axis lead to additional spectral shifts. Topography induced spectral shifts can be detected by recording spectra by scanning the sample in two perpendicular orientations with respect to the spectrometer entrance slit.Comment: 9 pages, 3 figure

Local optical field variation in the neighborhood of a semiconductor micrograting

The local optical field of a semiconductor micrograting (GaAs, 10x10 micro m) is recorded in the middle field region using an optical scanning probe in collection mode at constant height. The recorded image shows the micro-grating with high contrast and a displaced diffraction image. The finite penetration depth of the light leads to a reduced edge resolution in the direction to the illuminating beam direction while the edge contrast in perpendicular direction remains high (~100nm). We use the discrete dipole model to calculate the local optical field to show how the displacement of the diffraction image increases with increasing distance from the surface.Comment: 12 pages, 3 figure

Exeter fogadta 2011-ben az oktatáskutatókat

„The City and the University of Exeter proud to welcome the educational researchers from all over the world.” – ez a kifeszített felirat fogadta és üdvözölte Exeter elegáns belvárosi utcáján azt a több mint ezerhatszáz oktatáskutatót, aki részt vett a 2011. augusztus 30. és szeptember 3. között megrendezett 14. EARLI Konferencián (A konferencia hivatalos elnevezése: 14th Biennial Conference for Research on Learning and Instruction, és tudományos háttérszervezete az EARLI: European Association for Research on Learning and Instruction). E délnyugat-angliai város, amely méretét és hangulatát tekintve Szegeddel mérhető, joggal büszke, hiszen az általuk szervezett konferencia az eddigi legnagyobb tudományos konferencia, amelynek valaha helyet adott nem csak a város és az egyetem, hanem az Egyesült Királyság

A tanulási célok vizsgálata az angol nyelvtanulás tükrében

A tanulási célok kutatása az utóbbi évtizedekben vált jelentőssé a nemzetközi szakirodalomban. A motivációkutatásból indult el, teljesen új területet tárva fel a pedagógiai kutatásban. A célok tanulmányozása azonban szorosan kapcsolódik az önszabályozó tanulás, a motiváció, az önhatékonyság és a metakogníció területeihez, s a hazai kutatások több szinten is érintik. Molnár Éva (2002) az önszabályozó tanulás szakirodalmi áttekintésében foglalkozik a célok meghatározásával, csoportosításával, Jámbori Szilvia (2003) a személyes célok szerepét vizsgálta kutatásaiban, míg Réthy Endréné (2002, 2003) és Józsa Krisztián (2002, 2005) a motiváció kutatása kapcsán tértek ki a célok szerepére

Ultraviolet photon absorption in single- and double-wall carbon nanotubes and peapods: Heating-induced phonon line broadening, wall coupling, and transformation

Ultraviolet photon absorption has been used to heat single- and double-wall carbon nanotubes and peapods in vacuum. By increasing the laser intensity up to 500 mW, a downshift and a broadening of the optical phonons are observed corresponding to a temperature of 1000°C. The UV Raman measurements are free of blackbody radiation. We find that the linewidth changes for the G+ and G− bands differ considerably in single-wall carbon nanotubes. This gives evidence that the phonon decay process is different in axial and radial tube directions. We observe the same intrinsic linewidths of graphite (highly oriented pyrolytic graphite) for the G band in single- and double-wall carbon nanotubes. With increasing temperature, the interaction between the walls is modified for double-wall carbon nanotubes. Ultraviolet photon induced transformations of peapods are found to be different on silica and diamond substrates

Narrow diameter double-wall carbon nanotubes: synthesis, electron microscopy and inelastic light scattering

Double-wall carbon nanotubes are themolecular analogues to coaxial cables. Narrow diameter double-walled carbon nanotubes (DWNTs) have been obtained by catalytic chemical vapour deposition process with high yield and characterized by scanning and transmission electron microscopy. We examine the inelastic light scattering spectrum of mostly DWNTs with internal tubes of subnanometre diameter. We observe particularly narrow radial breathing modes corresponding to the internal tubes of diameter less than 0.7 nm of double-walled tubes. The D band is found to be strongly helicity dependent and the tangential modes in narrow diameter DWNTs are found to be often down-shifted

Ösztrán vázas vegyületek A- és D-gyűrűben történő módosítása

Our work was started with the aromatic halogenation of 13α-estrone. 3-O-Methyl- and 3-O-benzyl-protected 13α-estrone were successfully reacted with N-iodo-, N-bromo- or N-chlorosuccinimide to afford 2-, 4- and 2,4-bis-substituted derivatives at ring A. These were formed in short reaction times and good yields. Conversions could be significantly influenced by changing the solvent of the reaction and varying the quantity of the reactant. The presence of the phenolic OH group facilitates both mono- and double substitution. 3-Protected compounds yielded only monosubstituted derivatives. The 3-O-benzyl ether showed reduced reactivity, only bromination and chlorination occurred in this case. Similar halogenations of 17-deoxy-13α-estrone with N-halosuccinimide were carried out to synthesize 2-, 4- and 2,4-bis-substituted derivatives. A comparison of the results obtained in the halogenation of 17-oxo and 17-deoxy starting compounds allowed the conclusion that analogous derivatives were formed in different ratios. In the 17-deoxy series in some cases major changes in conditions were required to have the desired compounds. We have developed a convenient synthetic microwave procedure for Sonogashira coupling using the synthesized halogen compounds as starting materials. The reaction of 2-iodo-3-O-methyl-13α-estrone with phenylacetylene could efficiently be achieved using Pd(PPh3)4 catalyst and CuI cocatalyst in dimethylformamide in the presence of Et3N as a base, at 50 °C in 20 min in a microwave reactor. After establishing the most favourable reaction conditions using phenylacetylene as the alkyne partner, the method was successfully adapted to compounds with phenolic 3-OH function by the change of solvent to acetonitrile. We extended the scope of the steroid component to 4-iodo derivatives. We found that elevation of the reaction temperature to 80 °C and the change of catalyst to Pd(PPh3)2Cl2 facilitated substitution at C-4. Iodo compounds bearing phenolic OH required the changing of solvent to tetrahydrofuran. We isolated the desired 4-phenethynyl compound in short time and excellent yield. The protocol developed for phenylacetylene was successfully extended to the synthesis of 4-(4’-subst.)phenethynyl derivatives. We carried out the semihydrogenation of certain compounds synthesized by Sonogashira coupling. Microwave-assisted partial saturation of (4’-methoxyphenyl)ethynyl compounds was achieved in the 3-methyl ether series. We applied DMF/KOH as the hydrogen source and Pd(PPh3)2Cl2 as the catalyst. Under the applied conditions, cis-alkenes were formed from 2-phenethynyl derivatives while 4-phenethynyl derivatives led to trans-alkenes chemo- and stereoselectively. Semihydrogenation of compounds bearing phenolic OH did not result in 2- or 4-phenethenyl compounds; rather, formation of benzo[b]furans occurred. Additionally, we transformed 2- and 4-phenethynyl derivatives in ethyl acetate under 20 bar H2 with palladium-on-charcoal to 2- and 4-phenethyl derivatives, respectively, in excellent yields. We performed not only C–C but C–N cross couplings as well starting from the ring A halogenated derivatives. We have developed an efficient protocol for the Buchwald–Hartwig amination of 2-bromo-3-O-methyl-13α-estrone with aniline. An optimization process was performed by the systematic changes of catalyst, base and ancillary ligand. We compared conventional heating and microwave-assisted heat transfer and found that microwave irradiation shortened reaction times significantly. The highest yields were achieved by using Pd(OAc)2 as catalyst, KOtBu as base and XPhos as ancillary ligand at 100 °C in a microwave reactor. With the best reaction conditions in hand, couplings at C-2 were extended to monosubstituted anilines bearing substituents at ortho, meta or para positions with varied electronic properties. All couplings proceeded with high yields. We noticed that the electronic nature of the substituents influenced the conversion slightly but their position did not have any effect. 4-Bromo-3-O-methyl- and 2- or 4-bromo-3-O-benzyl-13α-estrone were successfully aminated with aniline without the need for changing reaction conditions established for couplings at C-2. Coupling with benzophenone imine instead of aniline was performed in order to gain 2- or 4-amino derivatives. 2- and 4-(N-diphenylmethylideneamino)-13α-estrones were efficiently transformed into the appropriate amino counterparts in a subsequent reaction step. Liberation of the NH2 function was achieved by Brønsted acid in the case of 3-methyl ethers and via hydrogenolysis from the 3-benzyl ether using palladium-on-charcoal catalyst..

Spectroscopic detection of carbon nanotube interaction with amphiphilic molecules in epoxy resin composites

Incorporation of carbon nanotubes into epoxy resin composites has the effect of increasing electrical conductivity at low percolation levels. An amphiphilic molecule such as palmitic acid has been used to increase the surface contact area and improve the dispersion of the carbon nanotube bundles in the prepolymer. The chemical environment of the dispersed nanotubes has been probed using vibrational Raman spectroscopy. Spectroscopic Raman maps, on sample surfaces (60x60 µm2) with ratios of nanotubes to palmitic acid varying from 1:2 to 2:1 by weight, have been recorded to test the uniformity of the dispersion. Substantial spatial inhomogeneities have been observed in the G-band shift and an additional spectral band at 1450 cm-1. The 1450 cm-1 band has been attributed to the CH3 group of the amphiphilic molecules adsorbed onto the nanotube surface. The maps are correlated with the measured electrical conductivity values. The highest conductivity has been observed for the best dispersed nanotubes and nanotubes with the highest degree of interaction

Raman G and D band in strongly photoexcited carbon nanotubes

We observe clear differences in the spectral shift of the Raman D and G bands when heating double wall carbon nanotubes through intense photon irradiation and by varying the temperature in a thermostat. These spectral differences are attributed to modifications of the defect induced double-resonance Raman process, and are consistent with Stokes–anti-Stokes anomalies observed for single and double wall carbon nanotubes, not present in graphite. We find that the Raman intensity for double wall carbon nanotubes increases superlinearly in the red spectral region and sublinearly in the UV spectral region