Steady-state intraband transition, which is a promising electronic transition of a colloidal quantum dot along with the band-gap transition, had been a long-standing challenge. The steady-state intraband transition occurring between discrete electronic states in the conduction band of a colloidal nanocrystal has been reported only from mercury chalcogenide nanocrystals for the past few years. Concerns about the toxicity of the mercury compound necessitate a new nontoxic system exhibiting a steady-state intraband transition.Here we present the steady-state intraband absorption and photoluminescence of Ag 2 Se colloidal nanocrystals under ambient conditions. The mid-IR intraband transition is carefully investigated by means of FT-IR emission spectroscopy, spectroelectrochemistry, compositional analysis, and transfer characteristics. Especially, the mid-IR intraband photoluminescence of the Ag 2 Se colloidal nanocrystal will open new avenues in the use of quantum-confined colloidal systems for mid-and longwavelength infrared light sources along with the band-gap transition that has been investigated for the last three decades.
Electrical properties for resistive microbolometer sensor materials including resistivity, temperature coefficient of resistance (TCR), and normalized Hooge parameter were explored in n-type a-Si:H and a-Si1−xCx:H prepared by plasma enhanced chemical vapor deposition. The complex dielectric function spectra (ε = ε1 + iε2) and structure were measured by spectroscopic ellipsometry. Two-dimensional drift-diffusion simulations were used to understand the band-tail slope dependency of TCR and 1/f noise.
Self-doping in nanocrystals allows accessing higher quantum states. The electrons occupying the lowest energy state of the conduction band form a metastable state that is very sensitive to the electrostatic potential of the surface. Here, we demonstrate that the high charge sensitivity of the self-doped HgSe colloidal quantum dot solid can be used for sensing three different targets with different phases through self-doped HgSe nanocrystal/ZnO thin-film transistors: the environmental gases (CO2 gas, NO gas, and H2S gas); mid-IR photon; and biothiol (l-cysteine) molecules. The self-doped quantum dot solid detects the targets through different mechanisms. The physisorption of the CO2 gas and the NO gas molecules, and the mid-IR photodetection show reversible processes, whereas the chemisorption of l-cysteine biothiol and H2S gas molecules shows irreversible processes. Considering the quenching of mid-IR intraband photoluminescence of the HgSe colloidal quantum dot solid by the vibrational mode of the CO2 gas molecule, sensing the CO2 gas could be involved in the electronic-to-vibrational energy transfer. The target molecules are quantitatively analyzed, and the limits of detection for CO2 and l-cysteine are 250 ppm and 10 nM, respectively, which are comparable to the performance of commercial detectors.
Doped n-and p-type hydrogenated silicon (Si:H) thin films prepared by plasma enhanced chemical vapor deposition have been investigated for uncooled microbolometer applications. The material microstructure has been studied by in situ real time spectroscopic ellipsometry collected during thin film deposition or ex situ spectroscopic ellipsometry measurements on a static sample with a multiple sample analysis technique. The key electrical properties of interest, including film resistivity (q), temperature coefficient of resistance (TCR), and 1/f noise, have been measured as a function of deposition conditions for p-type amorphous hydrogenated silicon (a-Si:H) films and microcrystalline content for n-type amorphous (a), microcrystalline (lc), and mixed-phase amorphous þ microcrystalline (a þ lc) Si:H films. The TCR and 1/f noise values were compared for p-and n-type a-Si:H samples in the resistivity range of 100 < q < 3000 X cm and show that for a given resistivity, amorphous p-type films exhibit a lower 1/f noise, which might be expected due to a larger density of majority carriers. V
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