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This study presents a comprehensive simulation of a TiSe2‐based photodetector, an optoelectronic device adept at converting a spectrum of electromagnetic radiation spanning ultraviolet (UV), visible, and infrared wavelengths into electrical signals. The TiSe2 absorber material is characterized by a narrow direct bandgap of 1.2 eV, endowing the photodetector with superior optical and electronic attributes that enhance its photodetection capabilities. In‐depth analysis of the energy band diagram, the current‐voltage (J‐V) characteristics, and spectral responses is conducted. This article involves in methodical variations in the thickness, doping levels, and defect density across different layers to achieve optimal performance. The photodetector's current, JSC, and voltage, VOC are recorded at 37.30 mA cm−2 and 0.795 V, in turn. Additionally, the device achieves a peak responsivity, R of 0.67 A W−1 and a detectivity, D* of 12.9 × 1014 Jones at a wavelength of 920 nm. Notably, the spectral response is significantly enhanced between 760 and 1010 nm, indicating the photodetector's proficient detection of near‐infrared (NIR) light. The findings underscore the potential of TiSe2 as an effective material for photodetector applications, marking a significant advancement in the field and paving the way for future research endeavors in photodetector technology. [ABSTRACT FROM AUTHOR]

The interface of two-dimensional transition metal dichalcogenides hosts collective interactions between the electronic structures that tune the charge density wave (CDW) states and the photoelectrochemical (PEC) properties of heterostructures. This work reports the influence of the interface on the CDW and PEC of a sputtered Bi2Se3/TiSe2 heterostructure on Ti metal foils. The hexagonal nanoflakes on the spiral-pyramid-like surface morphology of pristine TiSe2 confirm the Bi2Se3 decoration on the TiSe2 sample. The stoichiometric growth of TiSe2 and Bi2Se3 was revealed from X-ray photoelectron spectroscopy and Raman spectroscopy. The temperature-dependent Raman spectroscopy demonstrates the evolution of EgCDW and A1gCDW optical phonon modes with increased CDW phase transition temperature for the Bi2Se3/TiSe2 heterostructure. The enhancement of photoresponsive properties of the Bi2Se3/TiSe2 heterostructure under a solar light intensity of 100 mW/cm2 (AM = 1.5 G) in 0.5 M Na2SO4 electrolyte solution toward suitable water splitting was validated from the PEC measurements. This engineered heterostructure can pave the futuristic path to studying light-active electrodes with tunable CDW properties of pristine TiSe2 and Bi2Se3/TiSe2 heterostructures grown on flexible Ti substrates. [ABSTRACT FROM AUTHOR]

Different from the direct delivery of chemodynamic agents into tumor tissue for chemodynamic therapy (CDT), this work reports the fabrication of heterojunction sonosensitizers (CD/TiSe2) for the in situ generation of chemodynamic agents by responding to tumor microenvironment (TME), realizing the in situ CDT‐enhanced sono‐immunotherapy. The in situ redox of TiSe2 in acidic TME leads to the formation of TiOxSe2−x containing Se (0), selenate, and Ti3+/Ti4+ redox couple, which can facilitate in situ CDT through a Ti3+‐mediated Fenton‐like reaction and consume overexpressed glutathione (GSH) via a Ti4+‐mediated GSH depletion. Moreover, Se ions generated through the in situ redox process promote the maturation of dendritic cells, consequently activating the adaptive immune responses. In another aspect, the construction of heterojunctions within carbon dots and TiSe2 improves the reactive oxygen species (ROS) generation efficiency of TiSe2 in a cascaded manner, which enhances the sonodynamic activity and amplifies the chemodynamic performance. More importantly, the ROS produced by in situ CDT and sonodynamic therapy efficiently triggers immunogenic cell death through a synergistic therapy based on the elicitation of antitumor immunity with the aid of an immune checkpoint blockade. This work thus provides a distinct paradigm of transition metal selenide‐originated in situ Fenton‐like agent generation for in situ CDT‐enhanced sono‐immunotherapy. [ABSTRACT FROM AUTHOR]

Different from the direct delivery of chemodynamic agents into tumor tissue for chemodynamic therapy (CDT), this work reports the fabrication of heterojunction sonosensitizers (CD/TiSe2) for the in situ generation of chemodynamic agents by responding to tumor microenvironment (TME), realizing the in situ CDT‐enhanced sono‐immunotherapy. The in situ redox of TiSe2 in acidic TME leads to the formation of TiOxSe2−x containing Se (0), selenate, and Ti3+/Ti4+ redox couple, which can facilitate in situ CDT through a Ti3+‐mediated Fenton‐like reaction and consume overexpressed glutathione (GSH) via a Ti4+‐mediated GSH depletion. Moreover, Se ions generated through the in situ redox process promote the maturation of dendritic cells, consequently activating the adaptive immune responses. In another aspect, the construction of heterojunctions within carbon dots and TiSe2 improves the reactive oxygen species (ROS) generation efficiency of TiSe2 in a cascaded manner, which enhances the sonodynamic activity and amplifies the chemodynamic performance. More importantly, the ROS produced by in situ CDT and sonodynamic therapy efficiently triggers immunogenic cell death through a synergistic therapy based on the elicitation of antitumor immunity with the aid of an immune checkpoint blockade. This work thus provides a distinct paradigm of transition metal selenide‐originated in situ Fenton‐like agent generation for in situ CDT‐enhanced sono‐immunotherapy.

Compound TiSe2 has received much attention among the transition metal chalcogenides because of its thrilling physical properties concerning atypical resistivity behavior, the emergence of charge density wave (CDW) state, induced superconductivity, etc. Here, we report the discovery of a new feature of TiSe2, namely, the observation of resistive switching in voltage biased point contacts (PCs) based on TiSe2 and its derivatives doped by S and Cu (TiSeS, CuxTiSe2). The switching occurs between a low resistive mainly "metallic-type" state and a high resistive "semiconducting-type" state when a bias voltage is applied (usually < 0.5 V), and reverse switching occurs when a voltage of opposite polarity is applied (usually < 0.5 V). The difference in resistance between these two states can reach up to two orders of magnitude at room temperature. The origin of this effect can be attributed to the variation of stoichiometry in the PC core due to the drift/displacement of Se/Ti vacancies under a high electric field. Additionally, we demonstrated that heating occurs in the PC core, which can facilitate the electric field-induced effect. At the same time, we did not find any evidence for CDW spectral features in our PC spectra for TiSe2. The observed resistive switching allows proposing TiSe2 and their derivatives as promising materials, e.g., for non-volatile resistive random access memory (ReRAM) engineering. [ABSTRACT FROM AUTHOR]

Compound TiSe2 has received much attention among the transition metal chalcogenides because of its thrilling physical properties concerning atypical resistivity behavior, the emergence of charge density wave (CDW) state, induced superconductivity, etc. Here, we report the discovery of a new feature of TiSe2, namely, the observation of resistive switching in voltage biased point contacts (PCs) based on TiSe2 and its derivatives doped by S and Cu (TiSeS, CuxTiSe2). The switching occurs between a low resistive mainly "metallic-type" state and a high resistive "semiconducting-type" state when a bias voltage is applied (usually < 0.5 V), and reverse switching occurs when a voltage of opposite polarity is applied (usually < 0.5 V). The difference in resistance between these two states can reach up to two orders of magnitude at room temperature. The origin of this effect can be attributed to the variation of stoichiometry in the PC core due to the drift/displacement of Se/Ti vacancies under a high electric field. Additionally, we demonstrated that heating occurs in the PC core, which can facilitate the electric field-induced effect. At the same time, we did not find any evidence for CDW spectral features in our PC spectra for TiSe2. The observed resistive switching allows proposing TiSe2 and their derivatives as promising materials, e.g., for non-volatile resistive random access memory (ReRAM) engineering. [ABSTRACT FROM AUTHOR]

Abstract Background Pancreatic cancer remains among the most prevalent and aggressive forms of cancer. While immunotherapeutic treatment strategies have shown some promise in affected patients, the benefits of these interventions have been limited by insufficient tumor infiltration by activated T cells. Results Here, Titanium diselenide (TiSe2) nanosheets were synthesized with good stability. When exposed to ultrasound (US), the TiSe2 nanosheets served as a reliable nano-sensitizer capable of inducing large amounts of reactive oxygen species (ROS) mediating sonodynamic therapy (SDT) under hypoxic and normoxic conditions. The tumor-released TAAs induced by TiSe2 nanosheet-mediated SDT promoted immunogenic cell death (ICD) conducive to the maturation of dendritic cells (DCs), and cytokine secretion and the subsequent activation and infiltration of T cells into the tumor. Combining TiSe2-mediated SDT with anti-PD-1 immune checkpoint blockade treatment led to the efficient suppression of the growth of both primary tumor and distant tumor, while simultaneously preventing lung metastasis. These improved immunotherapeutic and anti-metastatic outcomes were associated with activated systematic antitumor immune responses, including the higher levels of DC maturation and cytokine secretion, the increased levels of CD8+ T cells and the decreased levels of Treg cells infiltrated in tumors. Conclusion TiSe2 can be used as a sonosensitizer with good efficacy and high safety to mediate efficient SDT. The combination treatment strategy comprised of TiSe2-mediated SDT and PD-1 blockade activate anti-tumor immune responses effectively thorough inducing ICD, resulting in the inhibition the growth and metastasis of tumor. The combination therapy holds promise as a novel immunotherapy-based intervention strategy for pancreatic cancer patients.

Background: Pancreatic cancer remains among the most prevalent and aggressive forms of cancer. While immunotherapeutic treatment strategies have shown some promise in affected patients, the benefits of these interventions have been limited by insufficient tumor infiltration by activated T cells. Results: Here, Titanium diselenide (TiSe2) nanosheets were synthesized with good stability. When exposed to ultrasound (US), the TiSe2 nanosheets served as a reliable nano-sensitizer capable of inducing large amounts of reactive oxygen species (ROS) mediating sonodynamic therapy (SDT) under hypoxic and normoxic conditions. The tumor-released TAAs induced by TiSe2 nanosheet-mediated SDT promoted immunogenic cell death (ICD) conducive to the maturation of dendritic cells (DCs), and cytokine secretion and the subsequent activation and infiltration of T cells into the tumor. Combining TiSe2-mediated SDT with anti-PD-1 immune checkpoint blockade treatment led to the efficient suppression of the growth of both primary tumor and distant tumor, while simultaneously preventing lung metastasis. These improved immunotherapeutic and anti-metastatic outcomes were associated with activated systematic antitumor immune responses, including the higher levels of DC maturation and cytokine secretion, the increased levels of CD8+ T cells and the decreased levels of Treg cells infiltrated in tumors. Conclusion: TiSe2 can be used as a sonosensitizer with good efficacy and high safety to mediate efficient SDT. The combination treatment strategy comprised of TiSe2-mediated SDT and PD-1 blockade activate anti-tumor immune responses effectively thorough inducing ICD, resulting in the inhibition the growth and metastasis of tumor. The combination therapy holds promise as a novel immunotherapy-based intervention strategy for pancreatic cancer patients. [ABSTRACT FROM AUTHOR]

TiSe 2 as a potential electrode for potassium-ion batteries, has garnered significant attention owing to its stable ion storage property. Nevertheless, the inadequate electronic conductivity of TiSe 2 impedes its practical implementation. In this investigation, we adopt a polymerization method to fabricate TiSe 2 @PPy, which boasts enhanced conductivity and exceptional performance. Once coated with polypyrrole, the TiSe 2 @PPy composites demonstrate the optimum electrochemical performance, providing a charge capacity of 67.4 mAh g−1 at 1 C with a capacity retention of 68.4 % after 170 cycles. The PPy coating enhances the conductivity of TiSe 2 and enables potassium-ion batteries to exhibit outstanding electrochemical performance. Ex-situ Raman and FTIR tests are utilized to comprehend the electrochemical reaction between K+ and the TiSe 2 @PPy electrode during cycling. Overall, this work introduces a PPy coating on TiSe 2 , which presents a novel concept for the development. • A polypyrrole layer has been coated onto TiSe 2 , resulting in stable potassium-ion storage. • The synthesis of TiSe 2 @PPy via a polymerization approach is simple and efficient. • The capacity retention of TiSe 2 @PPy is 68.4 % at 1 C after 170 cycles. • The reaction mechanism of TiSe 2 @PPy is analyzed by ex-situ Raman and FTIR tests. [ABSTRACT FROM AUTHOR]

The sodium dual ion battery (Na‐DIB) technology is proposed as highly promising alternative over lithium‐ion batteries for the stationary electrochemical energy‐storage devices. However, the sluggish reaction kinetics of anode materials seriously impedes their practical implementation. Herein, a Na‐DIB based on TiSe2‐graphite is reported. The high diffusion coefficient of Na‐ions (3.21×10−11–1.20×10−9 cm2 s−1) and the very low Na‐ion diffusion barrier (0.50 eV) lead to very fast electrode kinetics, alike in conventional surface capacitive storage systems. In‐situ investigations reveal that the fast Na‐ion diffusion involves four insertion stage compositions. A prototype cell shows a reversible capacity of 81.8 mAh g−1 at current density of 100 mA g−1, excellent stability with 83.52 % capacity retention over 200 cycles and excellent rate performance, suggesting its potential for next‐generation large scale high‐performance stationary energy storage systems. [ABSTRACT FROM AUTHOR]

The combination of 2D materials and noble metallic nanostructure is becoming an attractive research domain for label-free, highly sensitive surface-enhanced Raman spectroscopy (SERS) applications. This study demonstrated photocatalysis degradation and SERS enhancements of organic fluorophore (Rhodamine 6G) on two-dimensional (2D) TiSe 2 using Raman spectroscopy. The Au nanoparticles (NPs) were decorated on TiSe 2 thin films by thermal annealing at variable temperatures. The selective deposition of Au NPs on the hexagonal TiSe 2 nanocrystals increases surface roughness, creating a larger surface area for molecule adsorption. It has been observed that the Au decoration at 250 °C on TiSe 2 exhibits efficient detection capabilities for R6G with the Raman intensity enhancement factors of the order of ≈10 5 along with the significantly improved visible light-induced photodegradation efficiency. The optimized Au NP size creates large electromagnetic hot spots produced by strong plasmon coupling that assists in the charge transfer mechanism among TiSe 2 , Au NPs, and R6G for enhanced SERS and photocatalysis activities. It has been observed that the intensity of Raman scattering decreases as the Au NP size increases on the TiSe 2 material. A possible charge transfer mechanism is proposed with an energy band diagram. The simultaneous measurement of SERS and photocatalytic dye degradation in Au decorated TiSe 2 can be used as a sensitive technique for water pollution treatment and biodegradable organic contaminants for the environmental ecosystem., (© 2023 IOP Publishing Ltd.)

Graphical abstract Abstract By using scanning tunneling microscopy (STM)/spectroscopy (STS), we systematically characterize the electronic structure of lightly doped 1 T -TiSe 2 , and demonstrate the existence of the electronic inhomogeneity and the pseudogap state. It is found that the intercalation induced lattice distortion impacts the local band structure and reduce the size of the charge density wave (CDW) gap with the persisted 2 × 2 spatial modulation. On the other hand, the delocalized doping electrons promote the formation of pseudogap. Domination by either of the two effects results in the separation of two characteristic regions in real space, exhibiting rather different electronic structures. Further doping electrons to the surface confirms that the pseudogap may be the precursor for the superconducting gap. This study suggests that the competition of local lattice distortion and the delocalized doping effect contribute to the complicated relationship between charge density wave and superconductivity for intercalated 1 T -TiSe 2. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) metallic transition-metal dichalcogenides (TMDCs), such as 1 T-TiSe2, have recently emerged as unique platforms for exploring their exciting properties of superconductivity and the charge density wave (CDW). 2D 1 T-TiSe2 undergoes rapid oxidation under ambient conditions, significantly affecting its CDW phase-transition behavior. We comprehensively investigate the oxidation process of 2D TiSe2 by tracking the evolution of the chemical composition and atomic structure with various microscopic and spectroscopic techniques and reveal its unique selenium-assisting oxidation mechanism. Our findings facilitate a better understanding of the chemistry of ultrathin TMDCs crystals, introduce an effective method to passivate their surfaces with capping layers, and thus open a way to further explore the functionality of these materials toward devices. [ABSTRACT FROM AUTHOR]

Very high resolution angular resolved photoemission (ARPES) spectra on TiSe 2 in two distinct polarization geometries (vertical and horizontal) at temperatures between 300 K and 22 K enabled the observation of details of bands near the Fermi level not reported so far. Calculations of the electronic band structure based on density functional theory (DFT) using B3LYP hybrid functional and MBJ potential (with and without spin-orbit coupling) were performed to obtain the orbital symmetry and dispersion. Two degenerate conduction bands (CB’s) were observed at the Γ-point, a weak CB- emission at the A-point, and two non degenerate CB’s (i.e. splitting of CB) at the M/L-point of the Brillouin Zone (BZ). The splitting was detected at L for both polarizations, while at M remarkably only for horizontal polarization. These results cannot be fully accounted for by current theories for the charge density wave (CDW) and point to a reduced symmetry of the electronic states, possibly due to the chiral CDW. [ABSTRACT FROM AUTHOR]

We systematically examined the properties of the polycrystalline 1 T -TiSe 2±α series synthesized by solid-state method, combined chemical analysis and physical property characterization, including Energy-dispersive X-ray spectroscopy (EDXS), x-ray photoelectron spectroscopy (XPS) x-ray diffraction (XRD), resistivity, hall effect and magnetization measurement have been employed to study how Ti/Se ratio influences the charge density wave (CDW) formation, the crystal structure, and the electrical characteristics. The electrical resistivity of Se-rich -TiSe 2 (Ti/Se ​= ​0.484) is found to be a metallic behavior with decreased CDW transition temperature. This study emphasizes how sensitive 1T-TiSe 2 characteristics are to defects and stoichiometry. TOC: The transport properties of TiSe 2±α occurs varies on decreasing Ti/Se ratio. The resistivity maximum related to the CDW state enlarges and slightly shifts to lower temperatures with decreasing Ti/Se ratio until it becomes unobserved for S6 with Ti/Se ratio ∼ 0.478. The over-all resistivity decreases as Ti/Se ratio decreases and the high-temperature curves become metallic and linear in T (Ti/Se ratio: 0.484 to 0.478) [Display omitted] • The electrical transport revealed a decreasing T CDW with decreasing Ti/Se ratio due to the high defect concentration. • Since elements analysis and the cell constants variations both point to an increase in Se content, we propose that 1 T -TiSe 2 becomes Se rich system. • Th change ratio of Ti to Se gave effective electron doping, as the Se-3d core levels shift toward higher binding energies. • The carrier type and its associated transport behavior are found to be highly sensitive to both the Ti/Se ratio and temperature. [ABSTRACT FROM AUTHOR]

[Display omitted] • D3 Grimme's dispersion showed low correction for all evaluated properties. • HSE06 functional presented more deviation because of Hartree-Fock exchange term. • Low vibrations were poorly described. • PBE0 functional described better the properties. Superconductivity is one of the most interesting electrical phenomena found in Physical Science. The null electrical resistance provides a unique free displacement for the electrons into the material. TiSe 2 is a superconductor material below 4K, creating a charge density wave as electrical propagation. Gaussian basis sets or exchange–correlation functionals poorly described the high interaction distance as van der Waals force because of low exchange–correlation energy. One physical–mathematical tool to indicate long-range distance is the Grimme's or D3 dispersion. In this work, quantum simulations based on DFT using periodic models depicted in CRYSTAL17 code investigated the TiSe 2 material regarding PBE0, HSE06, and B3LYP functionals and Grimme's dispersion. In particular, the high covalent feature on the Ti–Se chemical bond is challenging for DFT functionals, while van der Waals interaction between lamellas is essential for crystalline structure. Then, relative errors quantified the functional descriptions to evaluate the influence of hybrid and parameterized hybrid functionals on this critical material's structural, electronic, and vibrational properties. [ABSTRACT FROM AUTHOR]

To solve the severe polarization, a combined Sb-etching-doping route is adopted to synthesis Sb doped TiSe 2 @C core–shell structure. Benefitting from nano-crystallization and built-in electric field, Sb-TiSe 2 @C shows low polarization effect and high pseudocapacitance storage ability. [Display omitted] • Sb doped TiSe 2 @C core–shell is synthesized by a combined Sb-etching-doping route. • Local built-in electric field and nano-crystallization are demonstrated. • Enough active sites and enhancing interfacial ion transfer kinetics are obtained. • Sb-TiSe 2 @C shows low polarization effect/high pseudocapacitance storage ability. The critical challenge of TiSe 2 anode for lithium-ion battery (LIB) lies in the severe polarization due to the accumulation of excessive lithium ions and Li 3 TiSe 2 phase during charge/discharge process, resulting in reduced active sites and sluggish interfacial transport kinetics. To solve the issues, Sb doped TiSe 2 @C core–shell is synthesized via a combined ion etching-doping route. During the process, the introduced Sb element in MIL-125 triggers a synergistic etching-ion exchanging reaction, leading to a structure change of TiSe 2 from bulk to core–shell as well as homogeneous Sb-doping in TiSe 2. The unique structure demonstrates nano-crystallization of bulk TiSe 2 and the formation of local built-in electric field, providing enough achievable active sites and enhancing interfacial charge/ion transfer kinetics. Benefitting from the synergistic effect of structural engineering and electronic structural engineering, polarization effect is weakened and pseudocapacitance storage ability is improved, leading to the high specific capacity and cycle stability of 502 mAh g−1 after 100 cycles at 0.1 A g−1. Therefore, the synthetic route of Sb doped TiSe 2 @C core–shell anode can be extended to related nanostructured systems for high performance energy storage device application. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis and physical properties of the new misfit compound (BiSe)1.15(TiSe2)2 are reported. Transmission electron microscopy and powder X-ray diffraction show that the structure consists of alternating rock-salt type BiSe layers and hexagonal (TiSe2)2 double layers. Resistivity, specific heat, and magnetization measurements show that it has metallic and diamagnetic behaviors. These results are interpreted and discussed in the context of the transition between single-layer (BiSe)1.13(TiSe2), which shows no charge density wave, and infinite-layered (bulk) 1T-TiSe2, which undergoes a charge density wave transition at T=202K. Intercalation with copper, Cu x (BiSe)1.15(TiSe2)2, (0≤x≤0.10) is also reported, but unlike Cu x TiSe2, no superconductivity is observed down to T=0.05K. Thus, the series Cu x (BiSe)1+δ (TiSe2) n provides an effective approach to elucidate the impact of dimensionality on charge density wave formation and superconductivity. [Copyright &y& Elsevier]

Rechargeable zinc-based aqueous system is attractive for energy storage technology due to its safety, low cost, and ecological friendliness. However, the growth of Zn dendrites in anode severely limits the development of the energy storage system. Here, TiSe 2 is verified as an intercalated anode for aqueous zinc ion batteries (ZIBs) and zinc ion hybrid supercapacitors (ZHSCs) by a series of experimental and theoretical studies. The interlayer spacing of 0.601 nm makes TiSe 2 suitable for (de)intercalation of zinc ions and its good electronic conductivity endows TiSe 2 with excellent electrical charge transport characteristics. The TiSe 2 electrode shows a capacity of 128.0 mA h g−1 at 0.20 A g−1, low working potential window (0.00–0.60 V vs Zn2+/Zn), and a recyclability of 70.0% retention after 300 cycles. Fabricated by TiSe 2 anode and VO 2 cathode, an aqueous ZIBs is successfully demonstrated, delivering a capacity of 44.3 mA h g−1 at 0.20 A g−1. Fabricated by TiSe 2 anode and activated carbon (AC) cathode, a ZHSC is demonstrated with a specific capacitance of 60.6 F g−1 at 0.20 A g−1. This work brings an attempt and exploration of electrode materials about a (de)intercalation battery-type anode instead of Zn metal anode for aqueous ZIBs and ZHSCs. [Display omitted] • TiSe 2 is verified as an intercalated anode for ZIBs and ZHSCs by a series of experimental and theoretical studies. • The interlayer spacing of 0.601 nm makes TiSe 2 suitable for (de)intercalation of zinc ions. • The TiSe 2 electrode shows low working potential window, high capacity, and stable cyclic performance. • The ZIBs and ZHSCs based on TiSe 2 anode both exhibit good capacity and stability. [ABSTRACT FROM AUTHOR]

Abstract: To get insight into the influence of different growth conditions of 1T-TiSe2 onto its charge density wave (CDW) phase transition, we have performed angle-resolved photoelectron spectroscopy (ARPES) on TiSe2 in its CDW phase at low temperatures comparing the results with resistivity measurements. Though the local resistivity maxima become less pronounced with increasing growth temperatures, we do not find this trend in ARPES. While shape and intensity of the emission near E F change drastically, the backfolded valence bands are not affected. The question of the significance of the peaking resistivity as a characteristical ‘fingerprint’ of the CDW phase transition arises. [Copyright &y& Elsevier]

Abstract: A method for creating a patterned array of sub-micron crystals on the surface of a doped layered dichalcogenide using a scanning electron microscope has been developed. Exposing the surface of copper doped TiSe2 to iodine vapor induces sub-micron CuI crystals to form upon the surface. The copper ions diffuse to the surface from within the crystal to react with the iodine vapor, with larger crystals forming at higher temperatures. The amount and size of the crystals formed in a given area could be controlled by first exposing of portions of the surface to electron radiation within the microscope. Increasing the radiation exposure results in the formation of fewer and smaller CuI crystallites, and it is possible to completely prevent their formation using large exposures. It appears that the electron beam creates a thin barrier that limits the diffusion of copper ions to the surface. The system is sufficiently inert that exposing the surface to air for a few hours has no significant effect. The resultant surface features can be arranged with a lateral resolution limited mainly by the size of the features themselves. [ABSTRACT FROM AUTHOR]

The sodium dual ion battery (Na-DIB) technology is proposed as highly promising alternative over lithium-ion batteries for the stationary electrochemical energy-storage devices. However, the sluggish reaction kinetics of anode materials seriously impedes their practical implementation. Herein, a Na-DIB based on TiSe 2 -graphite is reported. The high diffusion coefficient of Na-ions (3.21×10 -11 -1.20×10 -9  cm 2  s -1 ) and the very low Na-ion diffusion barrier (0.50 eV) lead to very fast electrode kinetics, alike in conventional surface capacitive storage systems. In-situ investigations reveal that the fast Na-ion diffusion involves four insertion stage compositions. A prototype cell shows a reversible capacity of 81.8 mAh g -1 at current density of 100 mA g -1 , excellent stability with 83.52 % capacity retention over 200 cycles and excellent rate performance, suggesting its potential for next-generation large scale high-performance stationary energy storage systems., (© 2021 Wiley-VCH GmbH.)

• The similarities and differences in the electrochemical behavior and mechanism of the bulk phase and monolayer in TiSe 2 were discussed. • Theoretical calculations illustrated that there are two stages of redox reaction in the lithiation process, both in bulk phase and monolayer TiSe 2. • Monolayer TiSe 2 was found to be a promising anode material for lithium-ion batteries with high theoretical capacity(780 mA·h·g−1 with a voltage window of 0.18–1.43 V) and fast diffusion kinetics (≤161 meV). Two-dimensional transition metal dichalcogenides (TMDs) have been intensively studied as electrode materials for lithium-ion batteries. But, most of TMDs are low electronic conductors, and there is lack of research on the distinct electrochemical mechanisms of monolayer and bulk TMDs. In this work, the Li+ storage properties of monolayer and bulk TiSe 2 are studied by first-principles calculations based on the density functional theory. Calculations showed that bulk TiSe 2 works on the intercalation mechanism, which results in a theoretical capacity of 260 mA·h·g−1 in the voltage window of 1.14–2.09 V. In comparison, monolayer TiSe 2 works on the adsorption mechanism which gives a theoretical capacity of 780 mA·h·g−1 in 0.18–1.43 V. A two-stage redox process was revealed for both TiSe 2 forms. In the initial stage, Se acted as the main redox species; then both Ti and Se participated in the redox reaction. In addition, the material possesses low Li+ diffusion barriers. Especially, a very small diffusion barrier of 163 meV at high Li+ concentration and 39 meV at low Li+ concentration was obtained for monolayer TiSe 2 , which provide great potential as a high rate anode material for lithium ion batteries. [ABSTRACT FROM AUTHOR]

Abstract: We have examined core-level photoemission spectra of 1T-TiSe2 and 1T-TaS2 to study chemical shifts associated with unusual superlattice formation. While large temperature-dependent core-level splitting was observed for TaS2, temperature-dependent chemical shift was not observed for TiSe2. On the other hand, angle-resolved valence-band photoemission spectra of TiSe2 showed appearance of a new branch (band-folding) at the L points in the ordered phase at 50K. These results suggest smaller lattice distortion in TiSe2 than that in TaS2. [Copyright &y& Elsevier]

Multivalent-ion batteries (MVIBs) provide economical and energy-dense alternatives to Li-ion batteries. In the academic pursuit to finding high-performance beyond Li-ion batteries, identifying a suitable cathode is a primary issue. More specifically, a cathode that supports high energy density, competitive charge/discharge rates, diffusion kinetics, and cyclability is desireable. In this regard, we computationally investigate layered TiSe 2 as a cathode for beyond Li-ion batteries. We find voltages as high as 2.0, 2.0, 1.1, and 1.8 V for Li, Na, Mg, and Ca respectively. We compute voltage profiles, diffusion energy barriers, and formation energies, as well as consider the impact of swelling and electronic properties. While we consider several intercalants, we are especially interested in Ca, which we find to experience an energy barrier of approximately 0.4 eV, similar to the energy barrier experienced by Li, and lower than that of Mg. While Mg is the popular choice for multivalent-ion battery materials, we find that TiSe 2 is able to accept more Ca per formula unit than Mg, and exhibits higher voltages than Mg, while experiencing improved diffusion kinetics. We advocate for the exploitation of TiSe 2 layered cathodes for beyond Li-ion batteries, and especially for Ca-ion batteries. Image 1 • We model the intercalation of M = Li, Na, Mg, Ca within a layered MxTiSe2 cathode. • CaxTiSe2 yields a voltage range of 1.8 V - 0.5 V, which is competitive with other Ca-ion batteries. • We find that Ca experiences an energy barrier of approximately 0.4 eV, which is quite low for a Ca-ion battery. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) metallic transition-metal dichalcogenides (TMDCs), such as 1T-TiSe 2 , have recently emerged as unique platforms for exploring their exciting properties of superconductivity and the charge density wave (CDW). 2D 1T-TiSe 2 undergoes rapid oxidation under ambient conditions, significantly affecting its CDW phase-transition behavior. We comprehensively investigate the oxidation process of 2D TiSe 2 by tracking the evolution of the chemical composition and atomic structure with various microscopic and spectroscopic techniques and reveal its unique selenium-assisting oxidation mechanism. Our findings facilitate a better understanding of the chemistry of ultrathin TMDCs crystals, introduce an effective method to passivate their surfaces with capping layers, and thus open a way to further explore the functionality of these materials toward devices., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Abstract: We synthesized single crystals of TiSe2 with various Cu concentrations, and have performed an angle-resolved photoemission spectroscopy (ARPES) study in order to understand the CDW mechanism and to reveal the role of the Cu atoms in Cu-doped 1T-TiSe2. The measurements reveal that during the well-known charge density wave (CDW) transition the pristine TiSe2 sample undergoes a transition from a very small indirect gap semiconductor to a larger one. No nesting sign was observed in the Fermi surface in the CDW phase. The transition is suppressed in the Cu-doped samples, and an electron pocket appears near the L point, which may help appearance of the superconductivity of Cu x TiSe2 through the BCS–Eliashberg relation. [ABSTRACT FROM AUTHOR]