Pressure dependence of raman modes in double wall carbon nanotubes filled with 1D tellurium

The preparation of highly anisotropic one-dimensional (1D) structures confined into carbon nanotubes (CNTs) in general is a key objective in nanoscience. In this work, capillary effect was used to fill double wall carbon nanotubes (DWCNTs) with trigonal Tellurium. The samples are characterized by high resolution transmission electronic microscopy and Raman spectroscopy. In order to investigate their structural stability and unravel the differences induced by intershell interactions, unpolarized Raman spectra of radial and tangential modes of DWCNTs filled with 1D nanocrystalline Te excited with 514 nm were studied at room temperature and high pressure. Up to 11 GPa we found a pressure coefficient of 3.7 cm−1 GPa−1 for the internal tube and 7 cm−1 GPa−1 for the external tube. In addition, the tangential band of the external and internal tubes broaden and decrease in amplitude. All findings lead to the conclusion that the outer tube acts as a protection shield for the inner tube (at least up 11 GPa). No pressure-induced structural phase transition was observed in the studied range

Gate-dependent magnetoresistance phenomena in carbon nanotubes

We report on the first experimental study of the magnetoresistance of double-walled carbon nanotubes under magnetic field as large as 50 Tesla. By varying the field orientation with respect to the tube axis, or by gate-mediated shifting the Fermi level position, evidences for unconventional magnetoresistance are presented and interpreted by means of theoretical calculations

Ab Initio Study of the Electronic and Vibrational Properties of 1-nm-Diameter Single-Walled Nanotubes

The electronic structure, band gap, density of states of the (8,8), (14,0) and (12,3) single-walled carbon nanotubes by the SIESTA (Spanish Initiative for Electronic Simulations with Thousands of Atoms) method in the framework density-functional theory (DFT) with the generalized gradients approximation (GGA) were studied. Also, we studied the vibrational properties of the (8,8) and (14,0) nanotubes. Only the calculated relaxed geometry for (12,3) nanotube show significant deviations from the ideal rolled graphene sheet configuration. The electronic transition energies of van Hove singularities were studied and compared with previous results. The calculated band structures, density of states and dispersion curves for all tubes were in good agreement with theoretical and experimental results

Preparation and characterization of α-Fe nanowires located inside double wall carbon nanotubes

Capillary effect was used to fill double wall carbon nanotubes (DWCNT) with iron. The samples are characterized by Mössbauer and Raman spectroscopies, TEM, SAED, and magnetization. The experimental results indicate the presence of a-Fe nanowires inside the DWCNTs. The samples are ferromagnetic at room temperature. There are three striking results due to the confinement effects on the physical behavior of a-Fe: the hyperfine fields increase, the Debye temperature decreases and Raman modes are observed

Nanodevices for correlated electrical transport and structural investigation of individual carbon nanotubes

We report a new approach to the correlation of the structural properties and the transport properties of carbon nanotubes. Through an original combination of UV lithography, custom-made photosensitive sol–gel resist and deep reactive ion etching (RIE), we have successfully integrated membrane technology and nanodevice fabrication for the electrical connection of individual carbon nanotubes. After single wall nanotube (SWNT) deposition by molecular combing and contacting using high resolution electron beam lithography, we obtain a device that allows both the investigation of the nanotubes and the contact regions by transmission electron microscopy (TEM) and the measurement of the electronic transport properties of the same individual nano-object. The whole fabrication process is detailed and the demonstration that the micro membranes are suitable for both TEM inspection and nanoelectrode fabrication is given

Trigonal field acting at the Cr3+ 2 E states in ruby from magneto-optical measurements under high pressure

Magneto-optical measurements on ruby under high-pressure conditions provided direct determination of the trigonal crystal field acting at the t2g orbitals of Cr3+ in Al2O3 CrO6 and its dependence with pressure. The correlation study between the measured trigonal splitting and the trigonal distortion at the Al3+-substituted site indicates that the trigonal splitting increases with pressure whereas the trigonal distortion slightly reduces. The result is interpreted in terms of an enhancement of the electron-lattice coupling due to trigonal distortion upon reduction in the Al-O bond distance, i.e., the Cr-O bond distance R. The observed variations can be explained on the basis of empirical R dependence of the trigonal crystal field as VtrR?n with n=6. It is shown that this exponent does not change when we consider the pressure variation of the local structure around Cr3+ obtained from ab initio calculations. By the way, we also demonstrate that a methanol-ethanol mixture is a good pressure transmitting medium at cryogenic temperaturesFinancial support from the Spanish Ministerio de Ciencia e Innovación Project No. MAT2008-06873-C02-01, MALTA INGENIO-CONSOLIDER 2010 Grant No. CDS2007-0045, and EuroMagnet II FP7 program are acknowledged

Electronic structure of indium selenide probed by magnetoabsorption spectroscopy under high pressure

We report on an investigation of the peculiar electronic structure of the layered semiconductor InSe by magneto-optical experiments under high pressure up to 5 GPa. Magneto-absorption spectroscopy is performed under pulsed magnetic field up to 53 T using a specific setup. Excitonic magnetofingerprints and high-field oscillatory magnetoabsorption yield significant details on the band structure. In addition, the application of an external pressure unveils phenomena that confirm the specific k·p model proposed for this compound on the basis of earlier measurements

Anharmonic effects in ZnO optical phonons probed by Raman spectroscopy

We report Raman spectroscopy measurements on ZnO crystals grown by the vapor transport method and annealed. Vacuum annealing is found to yield single crystals with ultra low density of defects. We focus on the optical E2 phonon linewidth temperature dependence in the 10?500 K range. The linewidth decrease at low temperature is analyzed and discussed in the light of anharmonic up- and down-conversion processes, unveiling strongly different behaviors for the two E2 phonons

Unveiling the Landau Levels Structure of Graphene Nanoribbons

Magnetotransport measurements are performed in ultraclean (lithographically patterned) graphene nanoribbons down to 70 nm. At high magnetic fields, a fragmentation of the electronic spectrum into a Landau levels pattern with unusual features is unveiled. The singular Landau spectrum reveals large magneto-oscillations of the Fermi energy and valley degeneracy lifting. Quantum simulations suggest some disorder threshold at the origin of mixing between opposite chiral magnetic edge states and disappearance of quantum Hall effect

Alignment and nano-connections of isolated carbon nanotubes

We report a new approach for the alignment and the electrical nano-connection of isolated carbon nanotubes (CNTs). Through a novel combination of proven technics, we have been able to align isolated carbon nanotubes and selectively contact those CNTs by high resolution electron beam lithography (HREBL). Resistance versus temperature (R(T)) experiments have been carried out to determine the reliability of the metal–CNTs interface and to probe the electronic conductance of the CNT