The possibility of creating a composite based on iron polyphthalocyanine (FePPc) and multi-walled carbon nanotubes (MWCNTs) grown directly on a flexible conductive substrate has been studied. The FePPc/MWCNT/Al composite has been formed by treating the prefunctionalized MWCNT/Al material in a solution of 100 mL of 1,2,4,5-tetracyanobenzene and 100 mg of ferrocene in 2 mL of acetone. The obtained material has been annealed for 4 h at a temperature of 360°C in a flow of argon and hydrogen mixed in a ratio of 1 : 1. The composite obtained under these conditions is characterized by a high specific capacitance: 141 mF/cm2 at a charging current of ‒1 mA and 73 mF/cm2 at a scanning speed of 2 mV/s. In addition to the high capacitive characteristics, the material is characterized by a good response speed (τr = 0.59 s) and a resistance against numerous charge‒discharge cycles (30 000 cycles).
A methodology for predicting the threshold power density of illumination for photodetectors with ultrabroad spectral sensitivity in the mid-wave infrared range has been proposed and validated. This approach enables the assessment of the capability to detect weak signals. For a photoresistor based on HgTe colloidal quantum dots, the threshold power density for SNR (signal-to-noise ratio) equal to 1 has been measured at 1.55 μm (467 mW cm–2) and predicted for similar SNR at 3.4 μm (747 mW cm–2). At the early stages of development, such sensors are characterized by high noise levels and weak response. The study of photosensitivity in the 3–5 μm range is complicated by the fact that the output power of widely used light‑emitting diodes for the mid‑infrared region is several orders of magnitude lower than that of radiation sources operating in the visible, near‑infrared, and short‑wave infrared ranges, due to fundamental limitations of the materials employed for radiation generation in the mid‑infrared. The sensitivity of photoresistor based on HgTe CQD in the mid‑infrared region was evaluated indirectly, by comparing the threshold illumination power density measured in the short‑wave infrared region with the spectral characteristics of the studied structures. The developed approach provides a tool for assessing progress in the development of photodetectors with an ultrawide spectral range.
The effect of sulfur vacancies on the electronic structure of a molybdenum disulfide (MoS2) monolayer has been studied using density functional theory (DFT) methods implemented in the VASP software package. The ideal structure and systems with one and two sulfur vacancies and various options of defect localization in the MoS2 structure have been discussed. A full geometric optimization with allowance for the spin polarization and subsequent analysis of band structures have been carried out, which made it possible to determine the band gap, the transition type (direct or indirect), and the Fermi level position. It has been shown that the formation of sulfur vacancies leads to the band gap narrowing from 1.70 to 0.64 eV, the Fermi level shift, and a change in the nature of the transition. The charge density redistribution, the emergence of localized states near defects, and partial spin polarization of molybdenum atoms have been established. The results obtained confirm a key role of sulfur vacancies in the formation of the donor states and n-type conductivity, demonstrating the prospects of defect engineering for controlling the electronic and quantum properties of MoS2-based 2D semiconductors.
The optimum conditions (reaction time and solution concentration) of the deposition of manganese(IV) oxide onto the surface of a porous silicon structure with a carbon coating have been experimentally established. The degree of penetration of the oxide coating into the porous matrix has been determined using Raman spectroscopy. The effect of the additional MnO2 layer on the electrochemical properties of the porous silicon structure with a carbon coating have been determined by cyclic voltammetry and galvanostatic charge‒discharge performance testing. It is shown that the electrochemical capacitance of the electrodes increases to 259 mF/cm2 after the MnO2 deposition. The obtained composites are highly stable: there is no capacitance loss after 20 000 measurement cycles.
The experimental results on the impact of a wide temperature range (80–300 K) on the internal photoelectric effect in a sample of a copper-doped indium phosphide semiconductor with a mechanically activated (sensitized) surface are reported. Based on the experimental data, the narrowing of the energy band gap with increasing temperature is noted. The goal of the mathematical description of the dependence of the InP:Cu photocurrent on two variables is outlined: the supplied radiation photon energy (1.2–1.6 eV) and the temperature factor (0–300 K). The empirical and semiempirical temperature dependences of the band gap for semiconductor materials are investigated: the linear approximation and the Varshni, O’Donnell‒Chen, Beide‒Vink, and Fan formulas. The results of approximation of the temperature dependence of the Eg value (for InP:Cu) are presented by three values: experimental (1.3 and 1.33 eV) and analytical (1.4 eV), which correspond to temperatures of 0, 80, and 300 K. It is concluded that the use of the Fan formula is preferable. The modeling of the semiempirical dependences of the intrinsic photoconductivity spectra of the material under study as a complex function of two variables is described in detail: the InP absorption coefficient as a function of photon energy and temperature and the coefficient proportional to the carrier lifetime as a function of temperature. The temperature effect on the Eg position (shift of maxima) and on the change in the amplitude of photoconductivity maxima is noted. The construction of the spectral dependences of the InP absorption coefficient as a function of temperature is presented. The temperature (0‒300 K) dependence of the InP:Cu intrinsic photoconductivity spectra is plotted. The desired dependence of the InP:Cu photoconductivity is shown in the form of a surface of two variables: quantum energy and temperature.
