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Vapor‐pressure mismatched materials such as transition metal chalcogenides have emerged as electronic, photonic, and quantum materials with scientific and technological importance. However, epitaxial growth of vapor‐pressure mismatched materials are challenging due to differences in the reactivity, sticking coefficient, and surface adatom mobility of the mismatched species constituting the material, especially sulfur containing compounds. Here, we report a novel approach to grow chalcogenides – hybrid pulsed laser deposition – wherein an organosulfur precursor is used as a sulfur source in conjunction with pulsed laser deposition to regulate the stoichiometry of the deposited films. Epitaxial or textured thin films of sulfides with variety of structure and chemistry such as alkaline metal chalcogenides, main group chalcogenides, transition metal chalcogenides and chalcogenide perovskites are demonstrated, and structural characterization reveal improvement in thin film crystallinity, and surface and interface roughness compared to the state‐of‐the‐art. The growth method can be broadened to other vapor‐pressure mismatched chalcogenides such as selenides and tellurides. Our work opens up opportunities for broader epitaxial growth of chalcogenides, especially sulfide‐based thin film technological applications.

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Phase change materials, which show different electrical characteristics across the phase transitions, have attracted considerable research attention for their potential electronic device applications. Materials with metal‐to‐insulator or charge density wave (CDW) transitions such as VO₂and 1T‐TaS₂have demonstrated voltage oscillations due to their robust bi‐state resistive switching behavior with some basic neuronal characteristics. BaTiS₃is a small bandgap ternary chalcogenide that has recently reported the emergence of CDW order below 245 K. Here, the discovery of DC voltage / current‐induced reversible threshold switching in BaTiS₃devices between a CDW phase and a room temperature semiconducting phase is reported. The resistive switching behavior is consistent with a Joule heating scheme and sustained voltage oscillations with a frequency of up to 1 kHz are demonstrated by leveraging the CDW phase transition and the associated negative differential resistance. Strategies of reducing channel sizes and improving thermal management may further improve the device's performance. The findings establish BaTiS₃as a promising CDW material for future electronic device applications, especially for energy‐efficient neuromorphic computing.

 

As one of the most fundamental physical phenomena, charge density wave (CDW) order predominantly occurs in metallic systems such as quasi‐1D metals, doped cuprates, and transition metal dichalcogenides, where it is well understood in terms of Fermi surface nesting and electron–phonon coupling mechanisms. On the other hand, CDW phenomena in semiconducting systems, particularly at the low carrier concentration limit, are less common and feature intricate characteristics, which often necessitate the exploration of novel mechanisms, such as electron–hole coupling or Mott physics, to explain. In this study, an approach combining electrical transport, synchrotron X‐ray diffraction, and density‐functional theory calculations is used to investigate CDW order and a series of hysteretic phase transitions in a diluted‐band semiconductor, BaTiS₃. These experimental and theoretical findings suggest that the observed CDW order and phase transitions in BaTiS₃may be attributed to both electron–phonon coupling and non‐negligible electron–electron interactions in the system. This work highlights BaTiS₃as a unique platform to explore CDW physics and novel electronic phases in the dilute filling limit and opens new opportunities for developing novel electronic devices.

 

Low-dimensional materials with chain-like (one-dimensional) or layered (two-dimensional) structures are of significant interest due to their anisotropic electrical, optical, and thermal properties. One material with a chain-like structure, BaTiS3 (BTS), was recently shown to possess giant in-plane optical anisotropy and glass-like thermal conductivity. To understand the origin of these effects, it is necessary to fully characterize the optical, thermal, and electronic anisotropy of BTS. To this end, BTS crystals with different orientations (a- and c-axis orientations) were grown by chemical vapor transport. X-ray absorption spectroscopy was used to characterize the local structure and electronic anisotropy of BTS. Fourier transform infrared reflection/transmission spectra show a large in-plane optical anisotropy in the a-oriented crystals, while the c-axis oriented crystals were nearly isotropic in-plane. BTS platelet crystals are promising uniaxial materials for infrared optics with their optic axis parallel to the c-axis. The thermal conductivity measurements revealed a thermal anisotropy of ∼4.5 between the c- and a-axis. Time-domain Brillouin scattering showed that the longitudinal sound speed along the two axes is nearly the same, suggesting that the thermal anisotropy is a result of different phonon scattering rates. 

An electro-optic modulator offers the function of modulating the propagation of light in a material with an electric field and enables a seamless connection between electronics-based computing and photonics-based communication. The search for materials with large electro-optic coefficients and low optical loss is critical to increase the efficiency and minimize the size of electro-optic devices. We present a semi-empirical method to compute the electro-optic coefficients of ferroelectric materials by combining first-principles density-functional theory calculations with Landau–Devonshire phenomenological modeling. We apply the method to study the electro-optic constants, also called Pockels coefficients, of three paradigmatic ferroelectric oxides: BaTiO 3 , LiNbO 3 , and LiTaO 3 . We present their temperature-, frequency-, and strain-dependent electro-optic tensors calculated using our method. The predicted electro-optic constants agree with the experimental results, where available, and provide benchmarks for experimental verification.