eMIL: advanced emission Mössbauer spectrometer for measurements in versatile conditions

The current work presents a contemporary design of an advanced emission Mössbauer Spectrometer: eMIL equipped with a parallel-plate avalanche detector, which has been devised and built for the Mössbauer collaboration at ISOLDE/CERN. The setup is based on emission geometry, combined with on-line/off-line isotope implantation and provides numerous advantages over conversion electron, common emission (where isotope is deposited chemically on a sample) or transmission Mössbauer spectroscopy. eMIL is designed to measure hyperfine interactions in solids under various exposures. The implemented design overcomes limitations and improves performance and handling. In the current revision, the chamber is supplied with an UV extension — allowing to perform studies of photo-catalytic materials under external light exposure. A specifically designed motorized lid-samples-holder is fully automatized, and makes it possible to study up to 4 samples loaded in a magazine within a temperature range from RT up to 1100 K and to perform angular dependent measurements in high vacuum. This work additionally briefly describes data acquisition with additional electronic blocks, vacuum and data-acquisition system construction

Investigation of the local environment of SnO2 in an applied magnetic field

This paper presents the results of time-differential perturbed gamma–gamma angular correlation measurements of SnO2 thin films carried out in an applied magnetic field. The measurements were performed upon the implantation of Fe at 80 keV and 111In (111Cd) at 160 keV. The samples were further characterized by energydispersive X-ray spectroscopy. The hyperfine parameters were studied at room temperature with and without an applied magnetic field. The results indicate the presence of two distinct local environments for the probe nuclei. Both occupy a paramagnetic state and correspond to a substitutional Sn site in the rutile phase of SnO2 with different numbers of electrons added to SnO2:Cd0. In addition, the crystal homogeneity of the site 1 increases upon applying the magnetic field

Perturbed Angular Correlation Technique at ISOLDE/CERN Applied for Studies of Hydrogenated Titanium Dioxide (TiO2): Observation of Cd-H Pairs

Profound understanding of the local electronic and defect structure in semiconductors always plays a vital role in the further developing of applications of such materials. In the present work an investigation of the electronic structure in hydrogenated TiO2 (rutile) thin films is conducted by virtue of Time-Differential γ-γ Perturbed Angular Correlation spectroscopy (TDPAC or PAC) with 111mCd/Cd isotope, produced and implanted at ISOLDE/CERN. The measurements were performed at 581 K as a function of the temperature of the samples during hydrogenation. Despite the fact, that rutile single crystals usually show the presence of two local environments, when are studies with Cd/In isotopes, the current pristine thin films sample had a single electric field gradient. Upon various degrees of hydrogenation, Cd probe atoms showed underwent alterations, resulting in up to 3 different local surroundings, generally with high electric field gradients. Broad EFG distributions are likely due to randomly distributed point defects in the neighbourhood of Cd acceptors. Observed results suggest that hydrogenations performed at RT and 423 K are not able to promote unique defect configurations, while in the range of 473-573 K the formation of such configurations is observed. Therefore, one may assume that the formation of Cd-defect complexes (Cd-H pairs) is temperature enhanced. At higher levels of hydrogenation (663 K), the samples become partly amorphous that further hinders any atomistic studies with strong damped PAC spectra. Cd-H complexes seem to be stable up to annealing up to 581 K annealing. The obtained results give a deep insight into complex hydrogen defects, their interactions and bond formations with Cd acceptor

Perturbed Angular Correlation Technique at ISOLDE/CERN Applied for Studies of Hydrogenated Titanium Dioxide (TiO2): Observation of Cd-H Pairs

Profound understanding of the local electronic and defect structure in semiconductors always plays a vital role in the further developing of applications of such materials. In the present work an investigation of the electronic structure in hydrogenated TiO2 (rutile) thin films is conducted by virtue of Time-Differential γ-γ Perturbed Angular Correlation spectroscopy (TDPAC or PAC) with 111mCd/Cd isotope, produced and implanted at ISOLDE/CERN. The measurements were performed at 581 K as a function of the temperature of the samples during hydrogenation. Despite the fact, that rutile single crystals usually show the presence of two local environments, when are studies with Cd/In isotopes, the current pristine thin films sample had a single electric field gradient. Upon various degrees of hydrogenation, Cd probe atoms showed underwent alterations, resulting in up to 3 different local surroundings, generally with high electric field gradients. Broad EFG distributions are likely due to randomly distributed point defects in the neighbourhood of Cd acceptors. Observed results suggest that hydrogenations performed at RT and 423 K are not able to promote unique defect configurations, while in the range of 473-573 K the formation of such configurations is observed. Therefore, one may assume that the formation of Cd-defect complexes (Cd-H pairs) is temperature enhanced. At higher levels of hydrogenation (663 K), the samples become partly amorphous that further hinders any atomistic studies with strong damped PAC spectra. Cd-H complexes seem to be stable up to annealing up to 581 K annealing. The obtained results give a deep insight into complex hydrogen defects, their interactions and bond formations with Cd acceptor

Hyperfine interactions and diffusion of Cd in TiO2_{2} (rutile)

In the current work, we present an investigation of the electronic and defect structure in (TiO$_{2}$) rutile monocrystals by virtue of time differential perturbed angular $\gamma$ - $\gamma$ correlation spectroscopy. Studies were performed using $^{111m}$Cd, implanted at ISOLDE/CERN complemented with diffusion studies and density functional theory calculations. Hyperfine field parameters have been probed as a function of temperature between 298 K and 873 K. The results demonstrate that $^{111m}$Cd implanted rutile has two local environments. The first environment is characterized with parameters attributed to Cd localized at the cationic site which goes relatively along with a specific case where a charged supercell Cd:Ti(2e$^{−}$) is in the scope. The origin of the second fraction could be rising from the subsurface regions where according to a tracer diffusion study the major part of implant is bounded featuring different diffusion mechanisms. Performed $ab initio$ calculations suggest that the disruptive surface environment could contain apical or equatorial vacancies near the probe, inducing high electric field gradients for the second fraction. Current results seem to differ from those obtained before with different methods of probing (Ag/Cd and In/Cd)

Temperature dependence of the local electromagnetic field at the Fe site in multiferroic bismuth ferrite

In this paper, we present a study of the temperature-dependent characteristics of electromagnetic fields at the atomic scale in multiferroic bismuth ferrite (BiFeO$_3$ or BFO). The study was performed using time differential perturbed angular correlation (TDPAC) spectroscopy on implanted 111In (111Cd) probes over a wide temperature range. The TDPAC spectra show that substitutional $^{111}$In on the Fe$^{3+}$ site experiences local electric polarization, which is otherwise expected to essentially stem from the Bi$^{3+}$ lone pair electrons. Moreover, the TDPAC spectra show combined electric and magnetic interactions below the Néel temperature $T_N$. This is consistent with simulated spectra. X-ray diffraction (XRD) was employed to investigate how high-temperature TDPAC measurements influence the macroscopic structure and secondary phases. With the support of ab initio DFT simulations, we can discuss the probe nucleus site assignment and can conclude that the $^{111}$In ($^{111}$Cd) probe substitutes the Fe atom at the B site of the perovskite structure