Physics

The two-dimensional semiconductor HfSe2 is a promising candidate for future electronic, optical, and sensing applications due to its moderate bandgap (∼1.1 eV) and the spontaneous formation of a native high-κ dielectric in ambient conditions. In this study, a range of experimental techniques was employed to investigate the intrinsic surface properties of bulk HfSe2 grown by chemical vapor transport and to directly track oxidation in air. Scanning tunneling microscopy reveals a high defect density across the HfSe2 surface caused by Se vacancies and impurities, confirmed by XPS, inductively coupled plasma mass spectrometry, and high-resolution Rutherford backscattering spectrometry. Furthermore, XPS highlights the highly reactive nature of the HfSe2 surface in air, where the formation of HfOx is detected after a 1 min exposure to air, resulting in changes to the electronic properties, such as the work function and the valence band offset. Understanding the intrinsic surface properties, air stability, and material quality will facilitate the integration of 1T-HfSe2 in novel devices.

Reactive gases mixed with rare gases in capacitively coupled discharges are often used in etching and deposition processes in microelectronic device fabrication. Chlorine discharge and its mixtures are frequently applied in the etching of semiconductors and metals. Here, capacitive discharges in Ar/Cl2 mixture at 10 Pa in a 2.54 cm gap driven by sinusoidal rf voltage at 13.56 MHz are explored using one-dimensional particle-in-cell/Monte Carlo collision simulations. Chlorine is a highly electronegative discharge gas, whereas argon forms an electropositive discharge. By adding chlorine to an argon discharge, the plasma discharge can be transformed from being electropositive to become electronegative, and the electronegativity can be varied over a wide range. The electronegativity varies from 0 to 107, the electron energy distribution varies from bi-Maxwellian to Druyvsteyn like, and the plasma chemistry changes, as the Cl2 fraction in the admixture varies from 0% to 100%. We will discuss how the electron power absorption mechanisms, the electronegativity, the electron energy distribution function, the reaction rates, and the composition of the discharge vary with the addition of chlorine to the argon discharge. In particular, the influence of the metastable argon atoms and secondary electrons, emitted from the electrode surfaces, on the discharge properties, will be discussed.

We investigate the effects of isovalent Sb substitution at the As site in fluorine-doped PrFeAs 1- x Sb x O 0.7 F 0.3 (0 < x ≤ 1.0) through structural, Raman spectroscopy, density functional theory (DFT), transport, magnetotransport, and magnetic measurements. The superconducting transition temperature decreases gradually from ∼48 K for the parent compound to ∼44 K up to x ≈ 0.3, followed by a rapid suppression at higher Sb concentrations due to increasing disorder and secondary phase formation. Raman spectroscopy and DFT reveal lattice expansion and pronounced softening of pnictogen-related vibrational modes upon Sb substitution. Magnetotransport measurements up to 9 T show enhanced upper critical fields ( H c2 ∼ 200–350 T) and increased vortex activation energy for moderate Sb doping, indicating stronger vortex pinning. However, the critical current density remains low because of poor intergranular connectivity. The results demonstrate a crossover from an electronically tuned superconducting state to a disorder-dominated regime in isovalently substituted iron pnictides.