We present a systematic study of the impact of disorder on the optical properties and intervalley scattering of monolayer MoS2 [1]. Using a helium ion microscope, we locally induce defects in the 2D crystal lattice. Optical spectroscopy reveals significant shifts of both first order Raman modes E’ and A1, which are well understood in the framework of a phonon confinement model, where increasing disorder links the ion dose to the inter-defect distance. Micro-photoluminescence measurements at T=10K show how a defect-related luminescence band emerges following irradiation, red-shifted by ~180 meV with respect to the delocalised excitons. This band has an intensity which can be engineered by varying the ion dose used for exposure. We attribute the observed luminescence to originate from chemisorbed atoms/molecules at monosulphur vacancies in good agreement with density functional theory calculations. Quasi-resonant polarisation-resolved photoluminescence measurements reveal a robust degree of circular polarization ~ 85% for doses over which ion-induced luminescence is observed, in good agreement with recent theoretical results [2]. Our results demonstrate that the excellent optical properties of MoS2 are preserved for helium ion doses typically used for nano-structuring via helium ion beam lithography. Embedding monolayer MoS2 into hBN, strongly reduces the linewidth of the delocalized excitons (<5meV), approaching the homogeneous limit, whilst simultaneously increasing their optical stability [3]. In combination with helium ion irradiation, this approach enables us to controllably realise single optical active emission centres in MoS2, which show clear indications of quantum dot-like behaviour [4]. Our results demonstrate the potential of helium ion irradiation to deterministically engineer the optical properties of 2D semiconductors at the nanoscale, gain new insights into disorder and valley depolarization processes and, moreover, represent a new route to realise optically active quantum emitters in transition metal dichalcogenides in a controlled manner. [1] Klein et al. 2D Mater. 5, 011007 (2018) [2] Kaasbjerg et al. Phys. Rev. B 96, 241411(R) (2017) [3] Wierzbowski et al. Sci. Rep. 7, 12383 (2017) [4] Klein et al. in preparation (2018)
This study examined the relationship between academic stress and health among students. The study also considered gender differences. Previous research showed that stress can have a direct effect on health. Results revealed significant correlation between academic stress and health, and existence of gender differences. World Health Organization defined health as “a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity“. The definition suggests multidimensionality of health construct and reveals its complex structure and exposure to other factors. Self-reported health is a very popular measure in health research nowadays, owing to its simplicity and validity. On the other hand, stress comprises of both a physiological and psychological response to external events or stressors. Certain level of stress could be stimulating, but trouble occurs when stress becomes overloading. Stress can appear in any area of life, whereas most prevalent are work-related stress and academic stress. It is well known that stress can have a direct effect on health. Moreover, various physical and emotional difficulties have been recognized as symptoms of stress, such as headaches and other body pains, insomnia, rashes or mood swings. The aim of this study was to examine the relationship between health and academic stress. Furthermore, the aim was to see whether there are differences in level of stress and health considering gender. Data collection was conducted online with 409 students of Josip Juraj Strossmayer University in Osijek, Croatia. There were 284 female participants and 124 male participants, aged from 18 to 31 (M=21.31, SD=1.839). Stress was measured using the 10-item Perceived Stress Scale (Cohen, Kamarck i Mermelstein 1983), which was adapted to measure academic stress. Health was measured using the 26-item WHOQOL- BREF Scale (WHO, 1996). Items are divided into 4 dimensions: Physical health, Psychological health, Social relationships and Environment. Results show that there are significant negative correlations between each dimension of health and academic stress. Furthermore, female participants report that they have significantly poorer Physical health than male participants, but significantly higher Social relationships than male participants. On the other hand, gender differences were not observed in academic stress. These results reveal a negative relationship between health and academic stress, which is a very important finding that has multiple implications for academic environment, such as university counselling or stress prevention. Results also show important difference in gender perception of health.
Mobile devices that are limited in terms of CPU power, memory or battery power are only capable of executing simple applications. To be able to run advanced applications we introduce a framework to split up the application and execute parts on a remote server. In order to dynamically adapt the deployment at runtime, techniques are presented to keep the migration time as low as possible and to prevent performance loss while migrating. Also methods are presented and evaluated to cope with applications generating a variable load, which can lead to an unstable system.
