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1. Effect of Au/HfS ₃ interfacial interactions on properties of HfS ₃ -based devices

   https://doi.org/10.1039/d2cp01254e  

   Dhingra, Archit; Lipatov, Alexey; Loes, Michael J.; Abourahma, Jehad; Pink, Maren; Sinitskii, Alexander; Dowben, Peter A. (June 2022, Physical Chemistry Chemical Physics)

   X-ray photoemission spectroscopy (XPS) has been used to examine the interaction between Au and HfS 3 at the Au/HfS 3 interface. XPS measurements reveal dissociative chemisorption of O 2 , leading to the formation of an oxide of Hf at the surface of HfS 3 . This surface hafnium oxide, along with the weakly chemisorbed molecular species, such as O 2 and H 2 O, are likely responsible for the observed p-type characteristics of HfS 3 reported elsewhere. HfS 3 devices exhibit n-type behaviour if measured in vacuum but turn p-type in air. Au thickness-dependent XPS measurements provide clear evidence of band bending as the S 2p and Hf 4f core-level peak binding energies for Au/HfS 3 are found to be shifted to higher binding energies. This band bending implies formation of a Schottky-barrier at the Au/HfS 3 interface, which explains the low measured charge carrier mobilities of HfS 3 -based devices. The transistor measurements presented herein also indicate the existence of a Schottky barrier, consistent with the XPS core-level binding energy shifts, and show that the bulk of HfS 3 is n-type. 

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2. The Electronic Structure of Zirconium and Hafnium Monochalcogenides

   https://doi.org/10.1021/acs.jpca.5c05402  

   F_Romeu, João G; Joyner, Nickolas A; Kaye, Elliot; Peterson, Kirk A; Kawagoe, Thomas T; Stinson, Samantha L; Morse, Michael D; Dixon, David A (October 2025, The Journal of Physical Chemistry A)

   High-level ab initio CCSD(T) and spin-orbit icMRCI+Q calculations were used to predict potential energy curves (PECs) for the lowest-lying states of ZrO, ZrS, HfO, and HfS. The prediction of the ground state is basis set dependent at the icMRCI+Q level for ZrO and ZrS due to the small singlet-triplet splitting between the lowest 1Σ+ and 3Δ states. CCSD(T) with a spin orbit correction predicted the 1Σ+ ground state in agreement with experiment. New all-electron basis sets were developed for Hf to improve the results over those predicted by use of effective core potentials (ECPs) that subsume the 4f electrons into the definition of the core. The use of the new DK-4f basis sets rather than ECPs became more important for HfO and HfS where there is a lack of a good core-valence separation. icMRCI+Q, CCSD(T), and DFT calculations for the spectroscopic parameters of ZrO, ZrS, HfO, and HfS were benchmarked with available experimental data. Bond dissociation energies (BDEs) of these four systems were calculated at the Feller-Peterson-Dixon (FPD) level to be 762.1 (ZrO), 543.5 (ZrS), 803.8 (HfO), and 575.1 kJ/mol (HfS), in excellent agreement with experiment. The HfS BDE was remeasured using the R3PI method, providing an updated experimental measurement of D0(HfS) = 5.978 ± 0.002 eV = 576.8 ± 0.2 kJ/mol. This experimental value, combined with experimental measurements of the ionization energies of Hf and HfS, gives the cationic BDE of D0(Hf+-S) = 5.124 ± 0.002 eV = 494.4 ± 0.2 kJ/mol. 

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3. Cascade synthesis and optoelectronic applications of intermediate bandgap Cu3VSe4 nanosheets

   https://doi.org/10.1038/s41598-020-78649-9  

   Liu, Mimi; Lai, Cheng-Yu; Zhang, Meng; Radu, Daniela R. (December 2020, Scientific Reports)

   null (Ed.)

   Abstract Two-dimensional (2D) ternary materials recently generated interest in optoelectronics and energy-related applications, alongside their binary counterparts. To date, only a few naturally occurring layered 2D ternary materials have been explored. The plethora of benefits owed to reduced dimensionality prompted exploration of expanding non-layered ternary chalcogenides into the 2D realm. This work presents a templating method that uses 2D transition metal dichalcogenides as initiators to be converted into the corresponding ternary chalcogenide upon addition of copper, via a solution-phase synthesis, conducted in high boiling point solvents. The process starts with preparation of VSe 2 nanosheets, which are next converted into Cu 3 VSe 4 sulvanite nanosheets (NSs) which retain the 2D geometry while presenting an X-ray diffraction pattern identical with the one for the bulk Cu 3 VSe 4 . Both the scanning electron microscopy and transmission microscopy electron microscopy show the presence of quasi-2D morphology. Recent studies of the sulfur-containing sulvanite Cu 3 VS 4 highlight the presence of an intermediate bandgap, associated with enhanced photovoltaic (PV) performance. The Cu 3 VSe 4 nanosheets reported herein exhibit multiple UV–Vis absorption peaks, related to the intermediate bandgaps similar to Cu 3 VS 4 and Cu 3 VSe 4 nanocrystals. To test the potential of Cu 3 VSe 4 NSs as an absorber for solar photovoltaic devices, Cu 3 VSe 4 NSs thin-films deposited on FTO were subjected to photoelectrochemical testing, showing p-type behavior and stable photocurrents of up to ~ 0.036 mA/cm 2 . The photocurrent shows a ninefold increase in comparison to reported performance of Cu 3 VSe 4 nanocrystals. This proves that quasi-2D sulvanite nanosheets are amenable to thin-film deposition and could show superior PV performance in comparison to nanocrystal thin-films. The obtained electrical impedance spectroscopy signal of the Cu 3 VSe 4  NSs-FTO based electrochemical cell fits an equivalent circuit with the circuit elements of solution resistance (R s ), charge-transfer resistance (R ct ), double-layer capacitance (C dl ), and Warburg impedance (W). The estimated charge transfer resistance value of 300 Ω cm 2 obtained from the Nyquist plot provides an insight into the rate of charge transfer on the electrode/electrolyte interface. 

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4. Families of asymmetrically functionalized germanene films as promising quantum spin Hall insulators

   https://doi.org/10.1039/D0CP06231F  

   Shi, Lawrence; Li, Qiliang (February 2021, Physical Chemistry Chemical Physics)

   null (Ed.)

   Topological insulators (TIs), exhibiting the quantum spin Hall (QSH) effect, are promising for developing dissipationless transport devices that can be realized under a wide range of temperatures. The search for new two-dimensional (2D) TIs is essential for TIs to be utilized at room-temperature, with applications in optoelectronics, spintronics, and magnetic sensors. In this work, we used first-principles calculations to investigate the geometric, electronic, and topological properties of GeX and GeMX (M = C, N, P, As; X = H, F, Cl, Br, I, O, S, Se, Te). In 26 of these materials, the QSH effect is demonstrated by a spin–orbit coupling (SOC) induced large band gap and a band inversion at the Γ point, similar to the case of an HgTe quantum well. In addition, engineering the intra-layer strain of certain GeMX species can transform them from a regular insulator into a 2D TI. This work demonstrates that asymmetrical chemical functionalization is a promising method to induce the QSH effect in 2D hexagonal materials, paving the way for practical application of TIs in electronics. 

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5. Investigation of Key Electronic States in Layered Mixed Chalcogenides With a d ⁰ Transition Metal as Li‐Ion Cathodes

   https://doi.org/10.1002/adfm.202408060  

   Kumar, Khagesh; Sunariwal, Neelam; Louis, Jacques; Leube, Bernhard T; Roy, Indrani; Sterbinsky, George E; Tarascon, Jean‐Marie; Cabana, Jordi (September 2024, Advanced Functional Materials)

   Abstract Lithium‐rich transition metal chalcogenides are witnessing a revival as candidates for Li‐ion cathode materials, spurred by the boost in their capacities from transcending conventional redox processes based on cationic states and tapping into additional chalcogenide states. A particularly striking case is Li₂TiS_3‐ySe_y, which features a d⁰metal. While the end members are expectedly inactive, substantial capacities are measured when both Se and S are present. Using X‐ray absorption spectroscopy, it is shown that the electronic structure of Li₂TiS_3‐ySe_yis not a simple combination of the end members. The data confirm previous hypotheses that, in Li₂TiS_2.4Se_0.6, this behavior is underpinned by concurrent and reversible redox of only S and Se, and identify key electronic states. Moreover, wavelet transforms of the extended X‐ray absorption fine structure provide direct evidence of the formation of short Se–Se units upon charging. The study uncovers the underpinnings of this intriguing reactivity and highlights the richness of redox chemistry in complex solids. 

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