Alexander Samokhvalov

Van der Waals (vdW) ferroelectric semiconductors provide a unique platform for exploring the interplay between spontaneous polarization, electronic transport, ion migration, and photocarrier generation at the nanoscale. Here, we establish a room‐temperature ferroelectric state in SnS ₂ and its sensitivity to structural polytype by directly contrasting the centrosymmetric 2H‐phase with the polar 4H‐phase. Raman spectroscopy distinguishes the 2H and 4H polymorphs of SnS ₂ through their characteristic phonon fingerprints. Piezoresponse force microscopy confirms room‐temperature ferroelectricity in the 4H phase, while the 2H phase exhibits no ferroelectric response. The built‐in polarization in a three‐terminal transistor device of the 4H‐SnS ₂ is modulated significantly by electrostatic gating and on exposure to linear and circularly polarized light. This device reveals polarization‐controlled output characteristics with distinct gate‐voltage induced hysteretic response and thermally activated carrier transport, confirming p ‐type semiconducting behavior strongly coupled to ferroelectric polarization. The photoresponse likewise exhibits polarization‐assisted carrier separation, sublinear power‐law scaling, a nonmonotonic temperature response correlated with the characteristic Raman modes, ferroelectric hysteresis, and a pronounced dependence on the circular and linear polarization states of the incident laser beam. These results establish 4H‐SnS ₂ as a promising material system for polarization‐driven electronic and optoelectronic technologies, including nonvolatile memory and photoferroelectric functionalities.

2H-WSe2 films were synthesized by magnetron co-sputtering of tungsten and selenium targets onto SiO2/Si(100), SiO2/Si(111), and Al2O3(0001) substrates in an Ar atmosphere at 150 °C, without any additional vacuum selenization step. After rapid thermal annealing at 700 °C in Ar, x-ray diffraction confirmed the formation of the optimal crystal phase. Films grown on SiO2/Si exhibited lower strain compared to those deposited on Al2O3. We demonstrated that (002)-textured WSe2 films with a thickness of approximately 50 nm can be achieved, and that planar-like growth is maintained for films thinner than about 60 nm. Raman spectroscopy showed the characteristic E2g and A1g modes of 2H-phase WSe2 at 248 cm−1 and 251 cm−1, corresponding to in-plane and out-of-plane vibrational phonon modes, respectively. The indirect optical bandgap of few-layer WSe2 was determined to be between 1.43 eV and 1.49 eV, with the bandgap varying as a function of film thickness—an expected property of 2D materials such as WSe2.

Background: gemcitabine is a cytidine analog and major anticancer drug functioning as an antimetabolite. However, its administration by systemic route is accompanied by “burst” and side effects. To limit this, drugs are encapsulated in matrices; metal–organic frameworks (MOFs) are coordination polymers with strong potential for drug encapsulation and delayed release. Methods: mechano-chemical synthesis of solid-state binary complex lag(CYCU-3)(Gem) is described from aluminum MOF (Al-MOF) CYCU-3 and gemcitabine free base (Gem). Synthesis is conducted by liquid-assisted grinding (LAG) with dimethyl sulfoxide (DMSO) followed by its outgassing. The alternative “dry” synthesis results in dry(CYCU-3)(Gem). Materials were characterized by FTIR spectroscopy and XRD, and delayed Gem release was tested to phosphate buffered saline (PBS) at 37 °C. The in vitro toxicity to pancreatic cancer PANC−1 and healthy cells hTERT−HPNE E6/E7/K−RasG12D was assessed by fluorometric assay. Results: in lag(CYCU-3)(Gem) interactions MOF-drug are via non-covalent bonds at O-H and COO⁻ groups of CYCU-3 as found by FTIR marker peak shifts and crystal structure is retained, while dry(CYCU-3)(Gem) shows significant amorphization and loss of functional groups. The lag(CYCU-3)(Gem) but not dry(CYCU-3)(Gem) shows delayed Gem release for 6000 min. The suppression of PANC−1 cells by lag(CYCU-3)(Gem) is time-dependent and it correlates with delayed Gem release. For the first time, a concept of ternary stoichiometric complex lag(CYCU-3)₁(Gem)₁(CIT)₂ is tested that also contains natural organic compound citronellol (CIT), and its structure, bonding and release of Gem are compared to those of binary complex. Bonding is at the O-H groups of CYCU-3 and this complex shows delayed Gem release. Conclusions: binary and ternary complexes of Gem with CYCU-3 yield delayed release and cytotoxicity. LAG is promising for synthesis of solid-state complexes of gemcitabine for delayed release and time-dependent suppression of cancer cells.

Bismuth selenide (Bi2Se3) is a promising 2D quantum nanomaterial for thermoelectric and optoelectronic devices; however, several growth techniques lack crystalline uniformity and scalability. Through multiple corroborating methods, we study the optical properties of Bi2Se3 in conjunction with its structural properties for a uniquely comprehensive description. The Raman spectra of films of Bi2Se3 prepared using a radio frequency (RF) source of magnetron sputtering reveal the characteristic Eg2 and A1g2 peaks of Bi2Se3 at ∼120 and 175 cm−1, which undergo spectral blue shifts as film thickness is increased due to the quantum size effect. Numerical analysis of the width of the Raman peaks suggests that the films are crystalline with nanocrystal sizes of 13–22 nm, confirmed by Scherrer's analysis of complementary x-ray diffraction. A strong optical absorption was observed in the visible–near infrared (NIR) range with an optical direct bandgap Eg determined from visible–NIR spectra within a 1.8–1.4 eV range, depending on film thickness and nanoparticulate structure. The interplay between film thickness and surface roughness strongly influences the optical response of Bi2Se3, where thinner, rougher films exhibit enhanced scattering and Urbach tailing, while thicker, smoother films display sharper absorption edges and bulk-like behavior. The deposition of nanometer Bi2Se3 films using RF magnetron sputtering constitutes a promising scalable platform for quantum thermoelectric and optoelectronic devices.

Scalable and controlled doping of two-dimensional transition metal dichalcogenides is essential for tuning their electronic and optoelectronic properties. In this work, we demonstrate a robust approach for the substitution of vanadium in tungsten diselenide (WSe2) via the selenization of pre-deposited V2O5/WO3 thin films. By adjusting the thickness of the vanadium oxide layer, the V concentration in W1−xVxSe2 is systematically varied. Electrical measurements on field-effect transistors reveal a substantial enhancement in hole conduction, with drain current increasing by nearly three orders of magnitude compared to undoped WSe2. Temperature-dependent electrical resistivity indicates a clear insulator-to-metal transition with increasing V content, likely due to band structure modifications. Concurrently, the photoconductive gain decreases, suggesting enhanced recombination and charge screening effects. These results establish vanadium doping via selenization of V2O5/WO3 films as a scalable strategy for modulating the transport and photoresponse of WSe2, offering promising implications for wafer-scale optoelectronic device integration.

Atomically thin layers of tungsten disulfide (WS2) have attracted much attention due to their unique optical and electronic properties. The controllable, scalable, and cost-effective development of defect-free monolayers of WS2 for the fabrication of electronic devices remains a challenge. A few experiments have indicated the efficacy of halide salts as growth promoters for the low temperature growth of WS2 monolayers. However, the optical and electronic behavior of materials grown with halide assistance remains to be addressed fully. Herein, a large-area synthesis of WS2 on Si/SiO2 substrates with sodium chloride (NaCl) as a growth promoter in a chemical vapor deposition process is reported. Temperature-dependent Raman and photoluminescence (PL) spectroscopy of monolayer WS2 carried out from 77 to 433 K reveals phonon softening and a redshift in the energy bandgap at higher temperatures. The effect of the laser power on the Raman and PL spectra has also been investigated, demonstrating spectral changes and peak shifts due to laser-induced heating and enhanced electronic excitations across the gap. A comparative study of the temperature and power dependent spectra has yielded a threshold laser power beyond which sample damage may occur due to excessive heating. Electrostatic gating of the sample during PL measurements reveals distinct effects of electronic doping on the spectral content of the trionic emission. Furthermore, the photodetection capability of monolayer WS2 is demonstrated under 532 nm laser illumination, exhibiting good responsivity (∼400 A/W) and detectivity (4.89 × 109 Jones). This comprehensive analysis of monolayer WS2 provides valuable insights into its potential applications in optoelectronic devices.