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.

The isolation of graphene and transition metal dichalcongenides has opened a veritable world to a great number of layered materials which can be exfoliated, manipulated, and stacked or combined at will. With continued explorations expanding to include other layered materials with unique attributes, it is becoming clear that no one material will fill all the post-silicon era requirements. Here we review the properties and applications of layered, quasi-one dimensional transition metal trichalcogenides (TMTCs) as novel materials for next generation electronics and optoelectronics. The TMTCs present a unique chain-like structure which gives the materials their quasi-one dimensional properties such as high anisotropy ratios in conductivity and linear dichroism. The range of band gaps spanned by this class of materials (0.2 eV-2 eV) makes them suitable for a wide variety of applications including field-effect transistors, infrared, visible and ultraviolet photodetectors, and unique applications related to their anisotropic properties which opens another degree of freedom in the development of next generation electronics. In this review we survey the historical development of these remarkable materials with an emphasis on the recent activity generated by the isolation and characterization of atomically thin titanium trisulfide (TiS3).

We present characterizations of few-layer titanium trisulfide (TiS3) flakes which, due to their reduced in-plane structural symmetry, display strong anisotropy in their electrical and optical properties. Exfoliated few-layer flakes show marked anisotropy of their in-plane mobilities reaching ratios as high as 7.6 at low temperatures. Based on the preferential growth axis of TiS3 nanoribbons, we develop a simple method to identify the in-plane crystalline axes of exfoliated few-layer flakes through angle resolved polarization Raman spectroscopy. Optical transmission measurements show that TiS3 flakes display strong linear dichroism with a magnitude (transmission ratios up to 30) much greater than that observed for other anisotropic two-dimensional (2D) materials. Finally, we calculate the absorption and transmittance spectra of TiS3 in the random-phase-approximation (RPA) and find that the calculations are in qualitative agreement with the observed experimental optical transmittance.

Stochastic methods are ubiquitous to a variety of fields, ranging from physics to economics and mathematics. In many cases, in the investigation of natural processes, stochasticity arises every time one considers the dynamics of a system in contact with a somewhat bigger system, an environment with which it is considered in thermal equilibrium. Any small fluctuation of the environment has some random effect on the system. In physics, stochastic methods have been applied to the investigation of phase transitions, thermal and electrical noise, thermal relaxation, quantum information, Brownian motion and so on. In this review, we will focus on the so-called stochastic Schrödinger equation. This is useful as a starting point to investigate the dynamics of open quantum systems capable of exchanging energy and momentum with an external environment. We discuss in some detail the general derivation of a stochastic Schrödinger equation and some of its recent applications to spin thermal transport, thermal relaxation, and Bose-Einstein condensation. We thoroughly discuss the advantages of this formalism with respect to the more common approach in terms of the reduced density matrix. The applications discussed here constitute only a few examples of a much wider range of applicability.

This is the post-peer reviewed version of the following article: J. Quereda et al. "Strong quantum confinement effect in the optical properties of ultrathin α-In2Se3".Advanced The isolation of atomically thin semiconductors has attracted the interest of the nanoscientists as these materials can complement graphene in those applications where its lack of an electronic band gap hinders its use. [1][2][3][4][5] In fact, two dimensional semiconductors have been recently employed in the fabrication of field effect transistors, [6,7] photodetectors [8][9][10][11][12][13][14] and solar cells. [15][16][17][18][19] Inherent to their reduced out-of-plane dimension, atomically thin semiconductors present a marked thickness-dependent band structure due to the quantum confinement of the charge carriers. For instance, the band gap in Mo-and W-based transition metal dichalcogenides increases from its bulk value (~1.3 eV, indirect gap) up to 1.9 eV (direct gap) in the single-layer limit. [20,21] More recently, black phosphorus has also shown a pronounced thickness-dependent band gap ranging from ~0.3 eV (direct gap) for bulk to ~1.75 eV (direct gap) for single-layer black phosphorus. [22] This thickness-dependent band gap can be very advantageous for applications as photodetectors as one can select the sensing photon energy window by simply selecting the right material thickness for the photodetector device. Up to now, however, there is a broad spectral window from 2.0 eV to 3.0 eV uncovered by 2D materials that could be very relevant for applications requiring 'solar blind' This is the post-peer reviewed version of the following article: J. Quereda et al. "Strong quantum confinement effect in the optical properties of ultrathin α-In2Se3". In this work we demonstrate a very strong quantum confinement effect in the optical properties of atomically thin α-In 2 Se 3 crystals. We observe a marked thickness-dependent shift in the optical absorption spectra acquired on mechanically exfoliated Figure S1). In order to study the optical absorption of the In 2 Se 3 crystals we used a home-made hyperspectral imaging setup, described in detail elsewhere.[25] The hyperspectral imaging is carried out by sweeping the excitation wavelength in steps and acquiring transmission mode images of the In 2 Se 3 crystals for each wavelength.The collected data is then arranged in a three-dimensional matrix, being the first two matrix According to Tauc et al. [26] , near the absorption edge the absorption coefficient of a direct-gap semiconductors iswhere A is a material-dependent constant and E g opt is the optical energy gap of the material.Equation (2) can be rewritten asThis is the post-peer reviewed version of the following article: J. Quereda et al. "Strong quantum confinement effect in the optical properties of ultrathin α-In2Se3".Advanced The usual method for determining the value of E g opt involves representing (αℏω) 2 versus the photon energy, ℏω, and fitting the absorption band edge to a linear function. According to Equation (3), the int...

A study of the electronic and optical bandgap is presented in layered TiS3, an almost unexplored semiconductor that has attracted recent attention because of its large carrier mobility and inplane anisotropic properties, to determine its exciton binding energy. Scanning tunneling spectroscopy and photoelectrochemical measurements are combined with random phase approximation and Bethe–Salpeter equation calculations to obtain the electronic and optical bandgaps and thus the exciton binding energy. Experimental values are found for the electronic bandgap, optical bandgap, and exciton binding energy of 1.2 eV, 1.07 eV, and 130 meV, respectively, and 1.15 eV, 1.05 eV, and 100 meV for the corresponding theoretical results. The exciton binding energy is orders of magnitude larger than that of common semiconductors and comparable to bulk transition metal dichalcogenides, making TiS3 ribbons a highly interesting material for optoelectronic applications and for studying excitonic phenomena even at room temperature.

TiS3 nanosheets have proven to be promising candidates for ultrathin optoelectronic devices due to their direct narrow band-gap and the strong light-matter interaction. In addition, the marked in-plane anisotropy of TiS3 is appealing for the fabrication of polarization sensitive optoelectronic devices. Herein, we study the optical contrast of TiS3 nanosheets of variable thickness on SiO2/Si substrates, from which we obtain the complex refractive index in the visible spectrum. We find that TiS3 exhibits very large birefringence, larger than that of well-known strong birefringent materials like TiO2 or calcite, and linear dichroism. These findings are in qualitative agreement with ab initio calculations that suggest an excitonic origin for the birefringence and linear dichroism of the material.

By combining ab initio calculations and experiments we demonstrate how the band gap of the transition metal tri-chalcogenide TiS 3 can be modified by inducing tensile or compressive strain. We show by numerical calculations that the electronic band gap of layered TiS 3 can be