A hyperfine look at titanium dioxide

Titanium dioxide is a commonly used material in a wide range of applications, due to its low price, and the increasing demand for it in the food- and pharmaceutical industries, and for low- and high-tech applications. Time-differential perturbed angular correlation (TDPAC) and Mössbauer spectroscopy measurements have a local character and can provide important and new information on the hyperfine interactions in titanium dioxide. With the application of characterization techniques and radioactive beams, these methods have become very powerful, especially for the determination of temperature dependence of hyperfine parameters, even at elevated temperatures. Such measurements lead to a better understanding of lattice defects and irregularities, including local environments with low fractions of particular defect configurations that affect electric quadrupole interactions. At ISOLDE-CERN, physicists benefit from the many beams available for the investigation of new doping configurations in titanium dioxide. We report the annealing study of titanium dioxide by means of the time differential perturbed γ-γ angular correlation of 111mCd/111Cd in order to study the possible effects of vacancies in hyperfine parameters. This paper also provides an overview of TDPAC measurements and gives future perspectives

Optical properties of MoSe2_2 monolayer implanted with ultra-low energy Cr ions

The paper explores the optical properties of an exfoliated MoSe$_2$ monolayer implanted with Cr$^+$ ions, accelerated to 25 eV. Photoluminescence of the implanted MoSe$_2$ reveals an emission line from Cr-related defects that is present only under weak electron doping. Unlike band-to-band transition, the Cr-introduced emission is characterised by non-zero activation energy, long lifetimes, and weak response to the magnetic field. To rationalise the experimental results and get insights into the atomic structure of the defects, we modelled the Cr-ion irradiation process using ab-initio molecular dynamics simulations followed by the electronic structure calculations of the system with defects. The experimental and theoretical results suggest that the recombination of electrons on the acceptors, which could be introduced by the Cr implantation-induced defects, with the valence band holes is the most likely origin of the low energy emission. Our results demonstrate the potential of low-energy ion implantation as a tool to tailor the properties of 2D materials by doping

Low-energy Se ion implantation in MoS2 monolayers

Abstract In this work, we study ultra-low energy implantation into MoS2 monolayers to evaluate the potential of the technique in two-dimensional materials technology. We use 80Se+ ions at the energy of 20 eV and with fluences up to 5.0·1014 cm−2. Raman spectra of the implanted films show that the implanted ions are predominantly incorporated at the sulfur sites and MoS2−2xSe2x alloys are formed, indicating high ion retention rates, in agreement with the predictions of molecular dynamics simulations of Se ion irradiation on MoS2 monolayers. We found that the ion retention rate is improved when implantation is performed at an elevated temperature of the target monolayers. Photoluminescence spectra reveal the presence of defects, which are mostly removed by post-implantation annealing at 200 °C, suggesting that, in addition to the Se atoms in the substitutional positions, weakly bound Se adatoms are the most common defects introduced by implantation at this ion energy