Properties Of TTF-TCNQ Research Articles

Highly polarised Raman scattering anisotropy in tetrathiafulvalene tetracyanoquinodimethane single crystal

Tetrathiafulvalene tetracyanoquinodimethane (TTF-TCNQ) single crystal was prepared by a solution technique and studied by Raman spectra in the aspects of temperature dependence, polarised Raman spectra and the polarised Raman scattering anisotropy. Raman properties of TTF-TCNQ depend strongly on the temperature as the intensities of Raman scattering increase significantly with the decreasing of the temperature. Highly polarised Raman scattering anisotropy was found in the TTF-TCNQ single crystal, and this is caused by the dielectric properties of the crystal. The dielectric circumstance of the crystal leads to the reduction in the parallel field component inside the crystal; thus, the A(z) mode cannot be excited when the incident light polarised parallel to the b axis of the TTF-TCNQ single crystal.

Unipolar p-type single-walled carbon nanotube field-effect transistors using TTF–TCNQ asthe contact material

We demonstrate herein that organic metal tetrathiafulvalene–tetracyanoquinodimethane(TTF–TCNQ) can serve as an ideal material for source and drain electrodesto build unipolar p-type single-walled carbon nanotube (SWNTs) field-effecttransistors (FETs). SWNTs were synthesized by the chemical vapor deposition(CVD) method on silicon wafer and then TTF–TCNQ was deposited by thermalevaporation through a shadow mask to form the source and drain contacts. AnSiO2 layer served as the gate dielectric and Si was used as the backgate. Transfer characteristicsshow that these TTF–TCNQ contacted devices are Schottky barrier transistors just likeconventional metal contacted SWNT-FETs. The most interesting characteristic of theseSWNT transistors is that all devices demonstrate the unipolar p-type transport behavior.This behavior originates from the unique crystal structure and physical properties ofTTF–TCNQ and this device may have potential applications in carbon nanotubeelectronics.

Electronic structure of tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) and Nb by the pseudofunction energy-band technique.

The pseudofunction energy-band method is a full potential, ab initio technique with no adjustable parameters. The basis function is related to the pseudofunction used to create ab initio pseudopotentials. Orthogonalization of the pseudofunction to the core states is accomplished as in the augmented plane-wave method (APW) or linear augmented plane-wave method. The applicability of the pseudofunction method to both localized bonding as in molecules or to delocalized bonding as in metals is demonstrated with application to Nb and tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ). The electronic and structural properties calculated for Nb agree well with that of the APW and Korringa-Kohn-Rostoker (KKR) methods. The energy bands obtained from an ab initio self-consistent energy-band calculation for TTF-TCNQ are successful in providing new insight into the properties of TTF-TCNQ. The computed optical properties, Fermi surface wave vector, and charge transfer agree quantitatively with experiment for TTF-TCNQ.

The CDW transition with tripling of the period along the chains in quasi 1d crystals

It is shown that due to the influence of the interchain interaction the commensurate x3 CDW transition may be either I or II order. The possible types of 3d CDW ordering in this case are discussed. We point out also that for x3 transition the 2k F and 4k F anomalies coincide and add to increase the critical temperature and the gap or pseudogap. The results are discussed in connection with the properties of TTF-TCNQ under pressure.

Effect of x-ray irradiation on anisotropic properties of tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ)

We present the results of the effect of controlled disorder on the electrical resistivity of the one-dimensional conductor TTF-TCNQ. The resistivity was measured, both parallel (${\ensuremath{\sigma}}_{\ensuremath{\parallel}}$) and perpendicular (${\ensuremath{\sigma}}_{\ensuremath{\perp}}$) to the TTF-TCNQ chains, as a function of x-ray photon dose \ensuremath{\Phi}. The longitudinal resistivity increases with photon dose, saturates at about twice its original value, and then increases again. The effect of irradiation on the transverse resistivity is much less pronounced. This behavior, as well as the observed dependence of the anisotropy on temperature and defect concentration, is explained within the framework of the theory which takes into account the libron-drag effect on the metallic transport properties of TTF-TCNQ.

Electronic properties of TTF-TCNQ : a connection between theory and experiment

Electronic properties of TTF-TCNQ : a connection between theory and experiment

The structure, conductivity, and thermopower of HMTTF-TCNQ

The structure and some transport properties of a new organic conductor, HMTTF-TCNQ, are reported. A metallic conductivity and thermopower are found between room temperature and 50°K, with insulating behavior at lower temperatures. The conductivity data suggest that two phase transitions occur, one at 43±1° K and the other at 50±° K. Comparison with the properties of TTF-TCNQ and HMTSeF-TCNQ is made.

Electron-electron interaction and instabilities in one-dimensional metals

The possible instabilities of a 1-dimensional itinerant electron gas are discussed, assuming electron-electron interaction to play the dominant role. As is well known, in the RPA, a 1-dimensional metal is prone to spin density wave (SDW), charge density wave (CDW) and Cooper pair (CP) instabilities. The spin channel decomposition of the irreducible scattering amplitude I is made and the spin channel projections are evaluated in terms of the matrix elements of bare electron-electron interactionV(x) for momenta of interest. It is found that if the bare electron interactionV(x) is repulsive and decreases monotonically with separation, only the SDW instability will occur. If the small separation (x≳(2k F )−1) part of the interaction is greatly reduced or is made attractive,V(x) is non-monotonic,V q (q≅2k F ) is negative, and a CDW instability is preferred. A CP instability is possible if the electron interaction is attractive,i.e., if [V q (0<q<k F )+V q (q⋍2k F )]<0. The above RPA results serve only as rough indicators, since in general there are important two-electron configurations with two-electron momentum close to zero and with electron hole momentum close to 2k F , an example being the near Fermi energy configurationk 1⋍k F ,k 2⋍−k F ,k 3⋍−k F k 4⋍k F . Therefore as pointed out first by Bychkov, Gorkov and Dzhyaloshinskii (BGD), cross channel coupling is especially significant. It is shown that the cross channel coupling is constructive is some cases,eg., exchange of CD fluctuations leads to an effective electron-electron spin singlet attraction and vice-versa. A formalism for studying such effects is set up, and the particular example mentioned above is discussed. An RPA-like approximation is made for the form of the reducible singlet electron hole scattering amplitudeγ s d and the resulting induced Cooper pair attraction is calculated to be $$\begin{gathered} [I_s ^e ]_{ind.} \rho _{{}^\varepsilon F} = [ln(\lambda \beta \omega _c )]^{ - 1} ln\{ [1 + 2\pi ^{ - 1} ln(\lambda \beta \omega _c )^2 ]/ \hfill \\ 1 + [8\pi ^{ - 1} \gamma _s ^d (q = 2k_F )^{ - 1} )^2 ]\} \hfill \\ \end{gathered} $$ where λ=1.14,β=(k B T)−1 andω 0 is an electronic energy cut-off ∼e F . The induced electron hole attraction due to the exchange of virtual Cooper pairs has a similar expression, but with a factor of (1/4) and withγ (q=0) replacingγ (q=2k F ). The induced Cooper pair attraction is seen to be quite large over a broad range of temperatures close to but aboveT CDW [i.e., aboveT such thatγ (q=2k F )−1=0]. There is no requirement thatγ (q=2k F ) andγ (q=0) become singular at the same temperature, as found by BGD. The BGD prediction is seen to arise from the neglect of real particle hole and particle-particle excitations while calculatingγ andγ . The effect of impurities, of electron-phonon coupling, of interchain coupling and of interaction between thermal order parameter fluctuations is discussed. The results are then applied to a discussion of the properties of TTF-TCNQ, where it is suggested that a CDW instability occurs becauseV q (q=2k F )<0,i.e., because the small separation electron repulsion is strongly reduced by the highly polarizable TTF. Because of substantial interchain coupling, the bulk CDW instability occurs close to the RPA instability temperature. The giant conductivity observed by Colemanet al is attributed to superconductive fluctuations in a 1-dimensional system with large mean field superconductive transition temperatureT CP MF of order 300°K. Such a largeT CP MF is shown to result from the induced Cooper pair attraction due to CD fluctuation exchange.

Thermoreflectance of Tetrathiafulvalinium Tetracyanoquinodimethanide (TTF-TCNQ)

We report the first observation of a marked temperature dependence in the optical properties of TTF-TCNQ, based on thermoreflectance spectroscopy. The structure just above the plasma edge exhibits an abrupt 25% drop with $\stackrel{\ensuremath{\rightarrow}}{\mathrm{e}}\ensuremath{\parallel}\stackrel{\ensuremath{\rightarrow}}{\mathrm{b}}$ as the temperature is lowered past 45-50 K; simultaneously, a strong response for this transition with $\stackrel{\ensuremath{\rightarrow}}{\mathrm{e}}\ensuremath{\perp}\stackrel{\ensuremath{\rightarrow}}{\mathrm{b}}$ emerges. This supports the suggestion that a librational distortion of the TCNQ ion may be responsible for a Peierls transition in the complex.