TiS3 Monolayer Research Articles

Exploring defect engineering in monolayer TiS[formula omitted] for next-generation electronic devices: Insights from first-principles study

Titanium trisulfide monolayer (TiS3) is a quasi-1D crystal with promising applications in a range of fields, including photoelectrochemical cells and thermoelectrics. Despite the emerging importance of monolayer TiS3, little is known regarding its intrinsic defects. In this work, we systematically investigate the stability, electronic, and magnetic properties of native defects in single layer TiS3, using Density Functional Theory. We consider S and Ti monovacancies, divacancies, extended Ti-nS (n=2−8) vacancy complexes, S and Ti antisites, as well as their complexes. We show that the likelihood of the formation of sulfur vacancies is strongly dependent on the symmetrically inequivalent lattice site at which the S vacancy is located. Under S-rich conditions, single sulfur vacancies are shown to be energetically more favorable than divacancies. In contrast, under Ti-rich conditions sulfur divacancies are more favorable than single S vacancies. We show that STi and TiS1 are most likely to form under S-rich and Ti-rich conditions, respectively, with low formation energies of -10.42 eV and -9.18 eV, and are therefore likely to be prevalent in single layer TiS3. We further consider defect levels in the band-gap, and show that several of these intrinsic defects are potential n-type or p-type dopants, while others will form deep electron/hole traps. Further, we show that while a number of these intrinsic defects induce no spin in the host, most intrinsic defects will induce a net magnetic moment in the host. The commonality of these defects in TiS3, will significantly impact applications such as spintronics, thermoelectrics, and the manufacturing of electronic devices.

Advancing intrinsic carrier mobility estimation in transition metal trichalcogenide monolayers using DFT-BTE

The Boltzmann transport equation (BTE) based intrinsic carrier mobility estimation significantly improves accuracy, which is crucial for assessing the performances of the materials within the devices. Herein, we explore the highly anisotropic, semiconducting 2D transition metal trichalcogenide monolayers (TMTC) MX3 (M = Ti, Zr, Hf and X = S, Se) for their transport properties. Remarkably, the electron carrier mobility obtained by combining BTE with density functional theory (DFT) in TiS3 monolayer has reached ∼1400 cm2/V.s. This finding stands in stark contrast to the electron mobility of ∼104 cm2/V·s obtained using a formalism built on the effective mass approximation. The marked disparity in mobility estimation underscores the crucial role played by the BTE in elevating precision. Alongside, a pronounced anisotropy in carrier mobility has been observed in these monolayers, particularly concerning lattice directions and electron-to-hole carrier mobility. Overall, this study seeks to fill out the voids and focuses on accurate estimation of high carrier mobility in TMTC monolayers using DFT-BTE.

High anisotropy in titanium trisulfide monolayer: Ultrahigh carrier mobilities and large excitonic absorption

Two-dimensional titanium trisulfide (TiS3) attracts much attention due to its high carrier mobilities and anisotropic physical properties. In this study, based on the ab-initio method, the vibrational, carrier transport and excitonic properties for TiS3 monolayer are investigated in detail. The results show that highly anisotropic structure of monolayer TiS3 leads to its anisotropic physical properties. The hole mobilities are larger than electron mobilities, which can be further enhanced by strain engineering. A strong absorption peak at 0.59 eV for light polarization along b direction is observed within the quasi-particle bandgap, which is 15 times larger than that at 0.98 eV for light polarization along a direction. The absorption peaks are contributed dominantly by bright excitons whose binding energies are 0.43 eV and 0.82 eV along a and b directions, both of which are delocalized Wannier-Mott types. The ultrahigh and flexibly strain-engineering transport properties and the significant excitonic effects of anisotropic TiS3 monolayer make possible applications in flexible electronic and optoelectronic devices.

High-Temperature Excitonic Bose–Einstein Condensate in Centrosymmetric Two-Dimensional Semiconductors

The realization of high-temperature excitonic Bose-Einstein condensation (BEC) in practical materials poses great challenges, because of strict constraints in symmetry, exciton binding, lifetime, and interaction. Here, using first-principles methods and symmetry analysis, we propose a new route to realize high-temperature excitonic BEC in centrosymmetric 2D materials, exploiting the parity symmetry of band edges and reduced Coulomb screening. We demonstrate it by taking monolayer TiS3 as an example, whose lowest-energy exciton shows small exciton mass, small Bohr radius, large binding, and long lifetime simultaneously. The phase diagram of electron-hole systems is further constructed, showing that both BEC and superfluidity can be realized at high temperature and in a broad range of exciton density. Importantly, we reveal that the high-temperature character of excitonic BEC is robust against thickness, beneficial for its experimental observation. By application of this general strategy to 2D materials in the database, monolayer AuBr and BiS2 are identified as promising candidates for high-temperature excitonic BEC.

Study of Hydrogen Adsorption on a Monolayer Tis3 Decorated with Mg Cations

Study of Hydrogen Adsorption on a Monolayer Tis3 Decorated with Mg Cations

Theoretical Study on the Interfacial Properties of Monolayer TiS3–Metal Contacts for Electronic Device Applications

Recently, monolayer (ML) titanium trisulfide (TiS3) as a new group IVB transition-metal trichalcogenide material has been successfully prepared and aroused great interest in device applications. In this work, we contrastively investigate the interfacial nature of ML TiS3 with six metals (Au, Ag, Pd, Pt, Ir, and Ni) using the first-principles calculations. According to the analysis of effective potentials, no tunneling barriers appear in all contact systems. The band structures of ML TiS3 are disturbed with four metal electrodes (Pd, Pt, Ir, and Ni) strongly, accompanied by metallization of ML TiS3 due to the formation of covalent bonds between ML TiS3 and the metals, which indicates that the Schottky barrier heights (SBHs) are zero in the vertical direction. Furthermore, Ni and Ir are more appropriate contact electrodes according to the general analysis. Therefore, transport properties are further calculated by simulating dual-interface model using Ni and Ir as electrodes. The results demonstrate that Ir ...

TiS3 sheet based van der Waals heterostructures with a tunable Schottky barrier.

Monolayer titanium trisulfide (TiS3), synthesized recently through exfoliation [Adv. Mater., 2015, 27, 2595], has emerged as a new 2D material with outstanding electronic and optical properties. Here, using first-principles calculations we show for the first time the great potential of the TiS3 monolayer as a channel material when in contact with graphene and other 2D metallic materials to form van der Waals (vdW) heterostructures, where the intrinsic properties of both the TiS3 monolayer and the 2D materials are preserved, different from the conventional 3D metal/TiS3 semiconductor heterojunction [Nanoscale, 2017, 9, 2068]. Moreover, the TiS3 monolayer forms an n-type Schottky barrier (Φe) when in contact with graphene, exhibiting a tunneling barrier and a negative band bending at the lateral interface; the Schottky barrier character can also be changed from n-type to p-type by doping graphene with boron atoms or replacing graphene with other high-work-function 2D metals, while a Schottky-barrier-free contact can be realized by doping graphene with nitrogen atoms, thus providing a solution to the contact-resistance problem in 2D electronics.

Exfoliation, point defects and hydrogen storage properties of monolayer TiS3: an ab initio study.

The possibility of H2 molecule adsorption on the basal plane of monolayer TiS3 at various sites has been studied. Among the studied adsorption sites, few sites were found to be suitable for physisorption with binding energy up to 0.10 eV per H2. To increase the activity of hydrogen sorption, the possibility of generating S-vacancies, by removing sulfur atoms from the basal plane of monolayer TiS3, was investigated. Despite the fact that the structures containing vacancies were found to be stable enough, there was no increase in the activity towards hydrogen adsorption. The same effect was obtained with the use of common methods of increasing of the H2 adsorption energy: the decoration of the two-dimensional material with alkali metals (Li, Na). This might be caused by the negatively charged surfaces of single layer TiS3, which hinder the increase in binding by alkali metals through a weak electrostatic interaction.

Titanium Trisulfide Monolayer as a Potential Thermoelectric Material: A First-Principles-Based Boltzmann Transport Study.

Good electronic transport capacity and low lattice thermal conductivity are beneficial for thermoelectric applications. In this study, the potential use as a thermoelectric material for the recently synthesized two-dimensional TiS3 monolayer is explored by applying first-principles method combined with Boltzmann transport theory. Our work demonstrates that carrier transport in the TiS3 sheet is orientation-dependent, caused by the difference in charge density distribution at band edges. Due to a variety of Ti-S bonds with longer lengths, we find that the TiS3 monolayer shows thermal conductivity much lower compared with that of transition-metal dichalcogenides such as MoS2. Combined with a high power factor along the y-direction, a considerable n-type ZT value (3.1) can be achieved at moderate carrier concentration, suggesting that the TiS3 monolayer is a good candidate for thermoelectric applications.

Quantum-Transport Characteristics of a p-n Junction on Single-Layer TiS3.

By using density functional theory and non-equilibrium Green's function-based methods, we investigated the electronic and transport properties of a TiS3 monolayer p-n junction. We constructed a lateral p-n junction on a TiS3 monolayer using Li and F adatoms. An applied bias voltage caused significant variability in the electronic and transport properties of the TiS3 p-n junction. In addition, the spin-dependent current-voltage characteristics of the constructed TiS3 p-n junction were analyzed. Important device characteristics were found, such as negative differential resistance and rectifying diode behaviors for spin-polarized currents in the TiS3 p-n junction. These prominent conduction properties of the TiS3 p-n junction offer remarkable opportunities for the design of nanoelectronic devices based on a recently synthesized single-layered material.

Group IVB transition metal trichalcogenides: a new class of 2D layered materials beyond graphene

The discovery of graphene, a single atomic layer of carbon in a hexagonal lattice, has invigorated enormous research interests in two‐dimensional (2D) layered materials and their one‐dimensional (1D) derivatives not only owing to their extraordinary physical and chemical properties but also their high potential for applications in electronic and photonic devices. A weakness of the graphene however is its lack of a bandgap—a prerequisite for building field‐effect transistors (FETs). A stream of new 2D layered materials have been developed over the past 5 years, including, among many others, silicene, phosphorene, and transition metal dichalcogenides. Monolayers of many of these 2D materials exhibit a bandgap, either direct or indirect. In 2015, a new class of 2D layered materials, namely, group‐IVB transition metal trichalcogenides (TMTCs), has been uncovered. A prototypical representative of this new class of 2D materials is TiS3 whose monolayer is predicted to possess a direct band gap of about 1 eV [close to that (1.17 eV) of bulk silicon], and relatively high carrier mobility. Isolation of the few‐layer TiS3 sheets and TiS3 nanoribbons via mechanical exfoliation has been realized in the laboratory in 2015. The modest 1‐eV band gap, relatively high carrier mobility, as well as high chemical stability in open air render TiS3 monolayer a promising 2D material for nanoelectronic and nanophotonic applications. In this study, we give an overview of the emerging area of 2D and 1D TMTC materials and suggest future research directions related to these novel materials. WIREs Comput Mol Sci 2016, 6:211–222. doi: 10.1002/wcms.1243This article is categorized under: Structure and Mechanism > Computational Materials Science

A first-principles study on the magnetic properties of Sc, V, Cr and Mn-doped monolayer TiS3

Substitutional doping of V, Cr and Mn atoms can induce the magnetic moment in monolayer TiS3.

Titanium Trisulfide Monolayer: Theoretical Prediction of a New Direct‐Gap Semiconductor with High and Anisotropic Carrier Mobility

AbstractA new two‐dimensional (2D) layered material, namely, titanium trisulfide (TiS3) monolayer, is predicted to possess novel electronic properties. Ab initio calculations show that the perfect TiS3 monolayer is a direct‐gap semiconductor with a bandgap of 1.02 eV, close to that of bulk silicon, and with high carrier mobility. More remarkably, the in‐plane electron mobility of the 2D TiS3 is highly anisotropic, amounting to about 10 000 cm2 V−1 s−1 in the b direction, which is higher than that of the MoS2 monolayer, whereas the hole mobility is about two orders of magnitude lower. Furthermore, TiS3 possesses lower cleavage energy than graphite, suggesting easy exfoliation for TiS3. Both dynamical and thermal stability of the TiS3 monolayer is examined by phonon‐spectrum calculation and Born–Oppenheimer molecular dynamics simulation. The desired electronic properties render the TiS3 monolayer a promising 2D atomic‐layer material for applications in future nanoelectronics.

Titanium trisulfide monolayer: theoretical prediction of a new direct-gap semiconductor with high and anisotropic carrier mobility.

A new two-dimensional (2D) layered material, namely, titanium trisulfide (TiS3 ) monolayer, is predicted to possess novel electronic properties. Ab initio calculations show that the perfect TiS3 monolayer is a direct-gap semiconductor with a bandgap of 1.02 eV, close to that of bulk silicon, and with high carrier mobility. More remarkably, the in-plane electron mobility of the 2D TiS3 is highly anisotropic, amounting to about 10 000 cm(2) V(-1) s(-1) in the b direction, which is higher than that of the MoS2 monolayer, whereas the hole mobility is about two orders of magnitude lower. Furthermore, TiS3 possesses lower cleavage energy than graphite, suggesting easy exfoliation for TiS3 . Both dynamical and thermal stability of the TiS3 monolayer is examined by phonon-spectrum calculation and Born-Oppenheimer molecular dynamics simulation. The desired electronic properties render the TiS3 monolayer a promising 2D atomic-layer material for applications in future nanoelectronics.

Vacancy Formation and Oxidation Characteristics of Single Layer TiS3

The structural, electronic, and magnetic properties of pristine, defective, and oxidized monolayer TiS3 are investigated using first-principles calculations in the framework of density functional theory. We found that a single layer of TiS3 is a direct band gap semiconductor, and the bonding nature of the crystal is fundamentally different from other transition metal chalcogenides. The negatively charged surfaces of single layer TiS3 makes this crystal a promising material for lubrication applications. The formation energies of possible vacancies, i.e. S, Ti, TiS, and double S, are investigated via total energy optimization calculations. We found that the formation of a single S vacancy was the most likely one among the considered vacancy types. While a single S vacancy results in a nonmagnetic, semiconducting character with an enhanced band gap, other vacancy types induce metallic behavior with spin polarization of 0.3-0.8 {\mu}B. The reactivity of pristine and defective TiS3 crystals against oxidation was investigated using conjugate gradient calculations where we considered the interaction with atomic O, O2, and O3. While O2 has the lowest binding energy with 0.05-0.07 eV, O3 forms strong bonds stable even at moderate temperatures. The strong interaction (3.9-4.0 eV) between atomic O and TiS3 results in dissociative adsorption of some O-containing molecules. In addition, the presence of S-vacancies enhances the reactivity of the surface with atomic O, whereas it had a negative effect on the reactivity with O2 and O3 molecules.

An ab initio study of TiS3: a promising electrode material for rechargeable Li and Na ion batteries

First-principles calculations have been used to study the electronic properties of bulk and monolayer TiS3 and its characteristics as an electrode material in rechargeable Li and Na ion batteries.

Single layer of MX₃ (M = Ti, Zr; X = S, Se, Te): a new platform for nano-electronics and optics.

A serial of two-dimensional titanium and zirconium trichalcogenides nanosheets MX3 (M = Ti, Zr; X = S, Se, Te) were investigated based on first-principles calculations. The evaluated low cleavage energy indicates that stable two-dimensional monolayers can be exfoliated from their bulk crystals in the experiment. Electronic studies reveal the very rich electronic properties in these monolayers, including metallic TiTe3 and ZrTe3, direct band gap semiconductor, TiS3, and indirect band gap semiconductors, TiSe3, ZrS3 and ZrSe3. The band gaps of all the semiconductors are between 0.57 and 1.90 eV, which implies their potential applications in nano-electronics. In addition, the calculated effective masses demonstrate the highly anisotropic conduction properties for all the semiconductors. Optically, TiS3 and TiSe3 monolayers exhibit good light absorption in the visible and near-infrared region, respectively, indicating their potential applications in optical devices. In particular, the highly anisotropic optical absorption of the TiS3 monolayer suggests it could be used in designing nano-optical waveguide polarizers.