Monolayer (ML) MoSe2 and WSe2 are promising materials for novel two-dimensional high-performance electronic and optoelectronic devices. Although ML MoSe2 and WSe2 possess the same crystal structure and similar chemical composition and band gap, they are experimentally observed to have distinct carrier types in conduction, i.e., ML MoSe2 is usually a n-type and ML WSe2 usually a p-type semiconductor. The reasons for such distinction are not fully understood so far. In this paper, by first-principles systematic investigation of the properties of intrinsic point defects and some inevitable unintentional extrinsic impurities under normal growth environments for ML MoSe2 and WSe2, we find that intrinsic defects are neither efficient p-type nor n-type dopants in these materials. Instead, hydrogen interstitial (H i inside ) is a shallow donor in both ML MoSe2 and WSe2, while nitrogen-substituting host selenium (N Se ) is a relatively shallow acceptor in both ML MoSe2 and WSe2. However, in the presence of both H and N doping, the compensation between the two type dopants pinned the Fermi energy close to the conduction band edge for ML MoSe2 and close to the valence band edge for ML WSe2. Our study, therefore, provides insights into the origin of the distinct types of conduction of ML MoSe2 and WSe2 and provides guidelines on how to dope transition metal dichalcogenides.

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Neurons in sensory cortices are more naturally and deeply integrated than any current neural population recording tools (e.g. electrode arrays, fluorescence imaging). Two concepts facilitate efforts to observe population neural code with single-cell recordings. First, even the highest quality single-cell recording studies find a fraction of the stimulus information in high-dimensional population recordings. Finding any of this missing information provides proof of principle. Second, neurons and neural populations are understood as coupled nonlinear differential equations. Therefore, fitted ordinary differential equations provide a basis for single-trial single-cell stimulus decoding. We obtained intracellular recordings of fluctuating transmembrane current and potential in mouse visual cortex during stimulation with drifting gratings. We use mean deflection from baseline when comparing to prior single-cell studies because action potentials are too sparse and the deflection response to drifting grating stimuli (e.g. tuning curves) are well studied. Equation-based decoders allowed more precise single-trial stimulus discrimination than tuning-curve-base decoders. Performance varied across recorded signal types in a manner consistent with population recording studies and both classification bases evinced distinct stimulus-evoked phases of population dynamics, providing further corroboration. Naturally and deeply integrated observations of population dynamics would be invaluable. We offer proof of principle and a versatile framework.

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