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Layered GeI 2 is a two-dimensional wide-bandgap van der Waals semiconductor, which is theorized to be a promising material for thermoelectric applications. While the value of the experimentally extrapolated indirect optical bandgap of GeI 2 is found to be consistent with the existing theoretical calculations, its potential as a thermoelectric material still lacks experimental validation. In this Perspective, recent experimental efforts aimed towards investigating its dynamical properties and tuning its bandgap further, via intercalation, are discussed. A thorough understanding of its dynamical properties elucidates the extent of electron-phonon scattering in this system, knowledge of which is crucial in order to open pathways for future studies aiming to realize GeI 2 -based thermoelectric devices. 

Few-layered HfS₃nanoribbons exhibit n-type conductivity and a large photoresponse to visible light. The photocurrent strongly depends on the polarization direction of the excitation laser due to the highly anisotropic quasi-1D crystal structure of HfS₃.

 

Transition metal trichalcogenides (TMTs) are two-dimensional (2D) systems with quasi-one-dimensional (quasi-1D) chains. These 2D materials are less susceptible to undesirable edge defects, which enhances their promise for low-dimensional optical and electronic device applications. However, so far, the performance of 2D devices based on TMTs has been hampered by contact-related issues. Therefore, in this review, a diligent effort has been made to both elucidate and summarize the interfacial interactions between gold and various TMTs, namely, In₄Se₃, TiS₃, ZrS₃, HfS₃, and HfSe₃. X-ray photoemission spectroscopy data, supported by the results of electrical transport measurements, provide insights into the nature of interactions at the Au/In₄Se₃, Au/TiS₃, Au/ZrS₃, Au/HfS₃, and Au/HfSe₃interfaces. This may help identify and pave a path toward resolving the contemporary contact-related problems that have plagued the performance of TMT-based nanodevices.

Graphical abstract

I–Vcharacteristics of (a) TiS3, (b) ZrS3, and (c) HfS3

 

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. 

Abstract Applications of quantum information science (QIS) generally rely on the generation and manipulation of qubits. Still, there are ways to envision a device with a continuous readout, but without the entangled states. This concise perspective includes a discussion on an alternative to the qubit, namely the solid-state version of the Mach–Zehnder interferometer, in which the local moments and spin polarization replace light polarization. In this context, we provide some insights into the mathematics that dictates the fundamental working principles of quantum information processes that involve molecular systems with large magnetic anisotropy. Transistors based on such systems lead to the possibility of fabricating logic gates that do not require entangled states. Furthermore, some novel approaches, worthy of some consideration, exist to address the issues pertaining to the scalability of quantum devices, but face the challenge of finding the suitable materials for desired functionality that resemble what is sought from QIS devices. 

Abstract GeI 2 is an interesting two-dimensional wide-band gap semiconductor because of diminished edge scattering due to an absence of dangling bonds. Angle-resolved x-ray photoemission spectroscopy indicates a germanium rich surface, and a surface to bulk core-level shift of 1.8 eV in binding energy, between the surface and bulk components of the Ge 2p 3/2 core-level, making clear that the surface is different from the bulk. Temperature dependent studies indicate an effective Debye temperature ( θ D ) of 186 ± 18 K for the germanium x-ray photoemission spectroscopy feature associated with the surface. These measurements also suggest an unusually high effective Debye temperature for iodine (587 ± 31 K), implying that iodine is present in the bulk of the material, and not the surface. From optical absorbance, GeI 2 is seen to have an indirect (direct) optical band gap of 2.60 (2.8) ± 0.02 (0.1) eV, consistent with the expectations. Temperature dependent magnetometry indicates that GeI 2 is moment paramagnetic at low temperatures (close to 4 K) and shows a diminishing saturation moment at high temperatures (close to 300 K and above). 

In this review, an attempt has been made to compare the electronic structures of various 5d iridates (iridium oxides), with an effort to note the common features and differences. Both experimental studies, especially angle-resolved photoemission spectroscopy (ARPES) results, and first-principles band structure calculations have been discussed. This brings to focus the fact that the electronic structures and magnetic properties of the high- Z 5d transition iridates depend on the intricate interplay of strong electron correlation, strong (relativistic) spin–orbit coupling, lattice distortion, and the dimensionality of the system. For example, in the thin film limit, SrIrO 3 exhibits a metal–insulator transition that corresponds to the dimensionality crossover, with the band structure resembling that of bulk Sr 2 IrO 4 .