Esta es la versión de autor del artículo publicado en: This is an author produced version of a paper published in: a.castellanosgomez@tudelft.nl ABSTRACT Isolation and characterization of mechanically exfoliated black phosphorus flakes with a thickness down to two single-layers is presented. A modification of the mechanical exfoliation method, which provides higher yield of atomically thin flakes than conventional mechanical exfoliation, has been developed. We present general guidelines to determine the number of layers using optical microscopy, Raman spectroscopy and transmission electron microscopy in a fast and reliable way. Moreover, we demonstrate that the exfoliated flakes are highly crystalline and that they are stable even in free-standing form through Raman spectroscopy and transmission electron microscopy measurements. A strong thickness dependence of the band structure is found by density functional theory calculations. The exciton binding energy, within an effective mass approximation, is also calculated for different number of layers. Our computational results for the optical gap are consistent with preliminary photoluminescence results on thin flakes. Finally, we study the environmental stability of black phosphorus flakes finding that the flakes are very hydrophilic and that long term exposure to air moisture etches black phosphorus away. Nonetheless, we demonstrate that the aging of the flakes is slow enough to allow fabrication of field-effect transistors with strong ambipolar behavior. Density functional theory calculations also give us insight into the water-induced changes of the structural and electronic properties of black phosphorus.

Control over the morphology of TiS3 is demonstrated by synthesizing 1D nanoribbons and 2D nanosheets. The nanosheets can be exfoliated down to a single layer. Through extensive characterization of the two morphologies, differences in the electronic properties are found and attributed to a higher density of sulphur vacancies in nanosheets, which, according to density functional theory calculations, leads to an n-type doping.

A technique to determine accurately transport properties of integrable and non-integrable quantum-spin chains at finite temperatures by Quantum Monte-Carlo is presented. The reduction of the Drude weight by interactions in the integrable gapless regime is evaluated. Evidence for the absence of a Drude weight in the gapless regime of a non-integrable system with longer-ranged interactions is presented. We estimate the effect of the non-integrability on the transport properties and compare with recent experiments on one-dimensional quantum-spin chains.PACS numbers: 75.30.Gw, 75.10.Jm, 78.30.-j Introduction -During the last few years several families of materials containing well characterized quasi onedimensional spin-1/2 structures have been synthesized. The charge-transfer gap is in many cases large and the spin excitations contribute significantly to the thermal and magnetization transport at low temperatures. For example,63 Cu NMR studies 1 in Sr 2 CuO 3 have measured a spin diffusion coefficient (equivalent to diffusive magnetization transport) several orders of magnitude larger than the value for conventional diffusive systems, and thermal transport measurements in Sr 2 CuO 3 and SrCuO 2 indicate 2 quasi-ballistic transport with a mean-free path of several thousands ofÅ.These unusual results have been related to the peculiar physics of one-dimensional quantum chains. It is known that the spin transport in the XXZ chain

Temperature dependent high resolution photoemission spectra of quasi-one-dimensional Li(0.9)Mo(6)O(17)evince a strong renormalization of its Luttinger-liquid density-of-states anomalous exponent. We trace this new effect to interacting charge neutral critical modes that emerge naturally from the two-band nature of the material. Li(0.9)Mo(6)O(17) is shown thereby to be a paradigm material that is capable of revealing new Luttinger physics.

We study the thermal transport properties of several quantum spin chains and ladders. We find indications for a diverging thermal conductivity at finite temperatures for the models examined. The temperature at which the non-diverging prefactor κ (th) (T ) peaks is in general substantially lower than the temperature at which the corresponding specific heat cV (T ) is maximal. We show that this result of the microscopic approach leads to a substantial reduction for estimates of the magnetic mean-free path λ extracted by analyzing recent experiments, as compared to similar analyses by phenomenological theories.