Measurement of local optomechanical properties of a direct bandgap 2D semiconductor

Strain engineering is a powerful tool for tuning physical properties of 2D materials, including monolayer transition metal dichalcogenides (TMDs)—direct bandgap semiconductors with strong excitonic response. Deformation of TMD monolayers allows inducing modulation of exciton potential and, ultimately, creating single-photon emitters at desired positions. The performance of such systems is critically dependent on the exciton energy profile and maximum possible exciton energy shift that can be achieved under local impact until the monolayer rupture. Here, we study the evolution of two-dimensional exciton energy profile induced in a MoSe2 monolayer under incremental local indentation until the rupture. We controllably stress the flake with an atomic force microscope tip and perform in situ spatiospectral mapping of the excitonic photoluminescence in the vicinity of the indentation point. In order to accurately fit the experimental data, we combine numerical simulations with a simple model of strain-induced modification of the local excitonic response and carefully account for the optical resolution of the setup. This allows us to extract deformation, strain, and exciton energy profiles obtained at each indentation depth. The maximum exciton energy shift induced by local deformation achieved at 300 nm indentation reaches the value of 36.5 meV and corresponds to 1.15% strain of the monolayer. Our approach is a powerful tool for in situ characterization of local optomechanical properties of 2D direct bandgap semiconductors with strong excitonic response

Abnormalities of Neurotransmission in Drug Addiction

Substance use disorders are prevalent and severe conditions associated with numerous health, social, and economic harms. While the neurobiological mechanisms are still not fully understood, adaptations in multiple neurotransmitter systems have been implicated in the development and maintenance of substance use disorders. The advent of molecular imaging techniques has provided a unique opportunity to better understand abnormalities of neurotransmission in humans with substance use disorders, and this insight may ultimately lead to improved treatment options in the future. This chapter provides a summary of positron emission tomography (PET) and single photon emission computed tomography (SPECT) studies in humans with alcohol, tobacco, cannabis, opioid, and stimulant use disorders. Studies to date provide consistent evidence that the dopaminergic system is disrupted in populations with substance use disorders, although there has been little research in other neurotransmitter systems and findings of existing studies have been mixed. Many PET and SPECT studies investigating abnormalities of neurotransmission in substance use disorder are limited by small sample sizes and over-reliance on male samples without comorbid conditions. In addition, the use of cross-sectional study designs does not make it possible to draw conclusions about causality