The Line Emission Mapper (LEM) is an x-ray probe mission concept that is designed to provide unprecedented insight into the physics of galaxy formation, including stellar and black-hole feedback and flows of baryonic matter into and out of galaxies. LEM incorporates a light-weight x-ray optic with a large-format microcalorimeter array. The LEM detector utilizes a 14k pixel array of transition-edge sensors (TESs) that will provide <2.5 eV spectral resolution over the energy range 0.2 to 2 keV, along with a field-of-view of 30 arcmin. The microcalorimeter array and readout builds upon the technology developed for the European Space Agency’s (ESA’s) Athena/x-ray Integral Field Unit. Here, we present a detailed overview of the baseline microcalorimeter design, its performance characteristics, including a detailed energy resolution budget and the expected count-rate capability. In addition, we outline the current status and plan for continued technology maturation. Behind the LEM array sits a high-efficiency TES-based anticoincidence (antico) detector that will reject cosmic-ray background events. We will briefly describe the design of the antico and plan for continued development.
KEYWORDS: Field effect transistors, Crystals, Transistors, Doping, Raman spectroscopy, Chlorine, Modulation, Molybdenum, Control systems, Chemical species
In this study, electronic properties of field-effect transistors (FETs) fabricated from exfoliated MoTe2 single crystals are investigated as a function of channel thickness. The conductivity type in FETs gradually changes from n-type for thick MoTe2 layers (above ≈ 65 nm) to ambipolar behavior for intermediate MoTe2 thickness (between ≈ 60 and 15 nm) to ptype for thin layers (below ≈ 10 nm). The n-type behavior in quasi-bulk MoTe2 is attributed to doping with chlorine atoms from the TeCl4 transport agent used for the chemical vapor transport (CVT) growth of MoTe2. The change in polarity sign with decreasing channel thickness may be associated with increasing role of surface states in ultra-thin layers, which in turn influence carrier concentration and dynamics in the channel due to modulation of Schottky barrier height and band-bending at the metal/semiconductor interface.
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