Hall Effect Results Research Articles

Weyl fermion excitations in the ideal Weyl semimetal CuTlSe2

An ideal Weyl semimetal is characterized by a dispersion in which only Weyl cones intersect the Fermi level, with low-energy behavior being governed by Weyl fermions. Although ideal Weyl semimetals have long been anticipated, only a few are realized in nonmagnetic materials. In this study, we confirm the presence of Weyl-fermion excitations in the ideal Weyl semimetal CuTlSe2 via a combination of magnetoresistance, Hall-effect, magnetic-susceptibility, nuclear magnetic resonance (NMR), and muon-spin relaxation (µSR) experiments. Magnetoresistance measurements reveal a negative longitudinal magnetoresistance (LMR), which scales as B2, while Hall-effect results indicate a predominant contribution from Weyl fermions with a hole-type charge. Magnetic susceptibility and µSR measurements indicate the lack of any intrinsic spontaneous magnetic moments down to base temperature. Finally, the NMR results can be modeled by a two-component effective Hamiltonian, which reproduces well the temperature-dependent Cu63 NMR (T1T)−1 factor, shown to scale as T2 below 100 K and as T1 above 100 K. Overall, we find that the extremely low concentration (1017cm−3) of carriers in CuTlSe2 originates from an ideal nonmagnetic Weyl semimetallic state, persisting up to a thermal excitation energy of 9 meV (100 K), above which trivial electronic bands close to EF take over. Our findings highlight CuTlSe2 as a new member of the intriguing class of Weyl semimetals. Published by the American Physical Society 2024

Self-powered PEDOT: PSS/CSWCNT/Mxenes thermoelectric films and wearable electronics devices

In this work, Ti3C2–Cl is introduced into poly(3,4-ethylenedioxythiophene): poly(4-styrenesulfonic acid) / single-walled carbon nanotubes (PEDOT: PSS/SWCNT, noted as PPSC) films to prepare ternary thermoelectric films of PEDOT: PSS/SWCNT/Ti3C2–Cl (PPSCT). The microscopic morphology, structures, and thermoelectric properties of PPSC and PPSCT films show that the introduction of Ti3C2–Cl results in a tendency of decreasing electrical as well as thermal conductivity, and the Seebeck coefficient is increased. When the content of Ti3C2–Cl reaches 8 wt%, the conductivity, Seebeck coefficient, and thermal conductivity of the PPSCT films reach the optimum values of 1683 S/cm, 21.69 μV/K, and 14.97 W/mK, respectively, and the power factor (PF) and thermoelectric figure of merit (ZT) are 79.23 μW/mK2 and 1.58 × 10–3. The UPS and Hall effect results reveal that the improvement of the Seebeck effect of PPSCT mainly results from the ternary interfacial energy barrier as well as the change of carrier concentration. In addition, the wearable electronics devices demonstrate an output voltage of 4.5 mV and an output power of 54.36 nW under a 50 K temperature difference. The device displays a good monitoring sensitivity by reaching an output voltage of 0.6 mV at a 7 K temperature difference between the skin and the environment.

A differential scheme for the effective conductivity of microinhomogeneous materials with the Hall effect

A differential scheme is proposed for the calculation of the components of the effective electrical conductivity tensor of a microinhomogeneous material taking into account the Hall effect. The presence of the Hall effect results in an appearance of asymmetry of the components of the conductivity tensor and a dependence of these components on the magnitude of the magnetic field applied to the material. In this case, the differential scheme leads to a system of matrix differential equations that were solved numerically in the current work. This solution was obtained for materials containing spherical or cylindrical inclusions. In the case of cylindrical inclusions, the results were obtained for inclusions with the symmetry axes parallel or orthogonal to the magnetic field. A comparison of the results obtained by the proposed methodology to the low concentration approximation was carried out.

Unconventional room-temperature negative magnetoresistance effect in Au/n-Ge:Sb/Au devices

Non-magnetic semiconductor materials and their devices have attracted wide attention since they are usually prone to exhibit large positive magnetoresistance (MR) effect in a low static magnetic field environment at room temperature. However, how to obtain a large room-temperature negative MR effect in them remains to be studied. In this paper, by designing an Au/n-Ge:Sb/Au device with metal electrodes located on identical side, we observe an obvious room-temperature negative MR effect in a specific 50 T pulsed high magnetic field direction environment, but not in a static low magnetic field environment. Through the analysis of the experimental measurement of the Hall effect results and bipolar transport theory, we propose that this unconventional negative MR effect is mainly related to the charge accumulation on the surface of the device under the modulation of the stronger Lorentz force provided by the pulsed high magnetic field. This theoretical analytical model is further confirmed by regulating the geometry size of the device. Our work sheds light on the development of novel magnetic sensing, magnetic logic and other devices based on non-magnetic semiconductors operating in pulsed high magnetic field environment.

Temperature dependent correlation of Hall effect and optical measurements of electron concentration in degenerate InN thin film

In this work, we study the thermal evolution of the optical and electrical features of an InN thin film. By correlating photoluminescence (PL) and Hall effect results, we determine the appropriate values of the correlation parameter to be used in the empirical power law that associates the electron concentration with the linewidth of the PL spectrum, in the scope of the Burstein–Moss effect across a wide range of temperatures. Additionally, by associating Raman and PL results, we observe the thermally induced compressive strain widening of the bandgap of the InN film. Our findings demonstrate the reliability of optical methods in providing contactless measurements of electrical and structural features of semiconductors.

Optoelectrical Properties of Treated CdSe Thin Films with Variations in Indium Chloride Concentration.

The effect of a nontoxic chloride treatment on the crystallinity and optoelectrical characteristics of a CdSe thin film was studied. A detailed comparative analysis was conducted utilizing four molarities (0.01 M, 0.10 M, 0.15 M, and 0.20 M) of indium (III) chloride (InCl3), where the results showed a notable improvement in CdSe properties. The crystallite size of treated CdSe samples increased from 31.845 nm to 38.819 nm, and the strain in treated films dropped from 4.9 × 10-3 to 4.0 × 10-3, according to XRD measurements. The highest crystallinity resulted from the 0.10 M InCl3-treated CdSe films. The In contents in the prepared samples were verified by compositional analysis, and FESEM images from treated CdSe thin films demonstrated compact and optimal grain arrangements with passivated grain boundaries, which are required for the development of a robust operational solar cell. The UV-Vis plot, similarly, showed that the samples were darkened after treatment and the band gap of 1.7 eV for the as-grown samples fell to roughly 1.5 eV. Furthermore, the Hall effect results suggested that the carrier concentration increased by one order of magnitude for samples treated with 0.10 M of InCl3, but the resistivity remained in the order of 103 ohm/cm2, suggesting that the indium treatment had no considerable effect on resistivity. Hence, despite the deficit in the optical results, samples treated at 0.10 M InCl3 showed promising characteristics as well as the viability of treatment with 0.10 M InCl3 as an alternative to standard CdCl2 treatment.

High density polarization-induced 2D hole gas enabled by elevating Al composition in GaN/AlGaN heterostructures

A two-dimensional hole gas (2DHG) induced by polarization charges at the GaN/AlGaN hetero-interface is attracting much attention because of its potential to develop p-channel transistors required for GaN complementary logic integrated circuits. This platform is compatible with commercial AlGaN/GaN n-channel electronics, but the performance of GaN p-channel transistors has been far behind. In this work, 2DHGs in GaN/AlGaN/GaN heterostructures grown by plasma-assisted molecular beam epitaxy have been investigated. The Al composition of the AlGaN barrier has been pushed as high as possible without obvious strain relaxation, and the record high 2DHG sheet density and conductivity on the GaN/AlGaN/GaN platform have been obtained. By adopting a parallel conduction model, a dependent relationship of the 2DHG density on temperature has been extracted. The temperature dependent Hall-effect results have demonstrated that the 2DHG density boosts by 75 times and 46 times at room temperature and 77 K, respectively, when the Al composition is pushed from 0.18 to 0.45 for the AlGaN barriers. The 2DHG sheet density reaches 3.6 × 1013 and 2.1 × 1013 cm−2 at room temperature and 77 K, respectively, and the lowest sheet resistance is 8.9 kΩ/□ at 77 K. Such a 2DHG is beneficial for fabrication of p-channel GaN transistors with lower on-resistance on the already-industrialized platform.

Temperature dependence of the infrared dielectric function and the direct bandgap of InSb from 80 to 725 K

The temperature dependence of the complex pseudodielectric function of bulk InSb (100) near the direct band gap was measured with Fourier-transform infrared ellipsometry between 30 and 500 meV at temperatures from 80 to 725 K in ultrahigh vacuum. Using the Jellison–Sales method for transparent glasses, the thickness of the native oxide was found to be 25±5 Å, assuming a high-frequency dielectric constant of about 3.8 for the native oxide. After this surface correction, the dielectric function was fitted with a Herzinger–Johs parametric semiconductor model to determine the bandgap and with a Drude term to determine the electron concentration and the mobility. We find that the bandgap decreases from 230 meV at 80 K to 185 meV at 300 K, as expected from thermal expansion and a Bose–Einstein model for electron-phonon scattering renormalization of the bandgap. Between 450 and 550 K, the bandgap remains constant near 150 meV and then increases again at even higher temperatures, presumably due to a Burstein–Moss shift resulting from thermally excited electron-hole pairs. The broadening of the direct bandgap increases steadily with temperature. The electron concentration (calculated from the Drude tail at low energies assuming parabolic bands with a constant electron mass of 0.014m0) increases from 2×1016cm−3 at 300 K to 3×1017cm−3 at 700 K, in reasonable agreement with temperature-dependent Hall measurements. The electron mobility was found to decrease from 105cm2/Vs at 450 K to 2×104cm2/Vs at 700 K, also in good agreement with Hall effect results. We describe a theoretical model that might be used to explain these experimental results.

Physical properties of Cu2MgSnS4 thin films prepared by chemical spray pyrolysis technique: The effect of thiourea concentration

In this work, chemical spray pyrolysis is employed to prepare Cu2MgSnS4 thin films using different concentrations of thiourea (0.14, 0.16, 0.18, 0.20, 0.22, 0.24) M at a substrate temperature of 400 ℃ and thickness of (300±10) nm. The XRD results displayed that all thin films are polycrystalline with tetragonal structure and favorite orientation along the (112) plane. The crystallite size of films is estimated by Scherrer's equation and it was found that it increases with increasing thiourea concentration up to 0.20 M and then it decreases with further increase in thiourea concentration. The FESEM result exhibited the appearance of nanostructures with different particle sizes and shapes. The band gap was estimated using Tauc's relationship and it was found that the value of the band gap increases with increasing thiourea concentration from 1.68 eV at 0.14 M to 1.83 eV at 0.20 M and then it decreases to 1.60 eV at 0.24 M. Raman spectroscopy investigation confirms the purity of the sample formation phase. The main peak for all films is located at about 330 cm-1 . The broadening of this peak in solid solutions can be attributed to the disturbance effects related to the locations of the metal and sulfur atoms in the tetrahedral lattice due to chemical substitutions in the crystalline positions. Hall effect results showed that all films are P-type. The increase in carrier concentration and its motility with increasing thiourea concentrations leads to a decrease in the resistance of the films.

Preparation of MAPbI3 perovskite film by pulsed laser deposition for high-performance silicon-based heterojunction photodetector

This study investigates the preparation and characterization of CH3NH3PbI3 (MAPbI3) perovskite thin films. The films were prepared using a one-step pulsed laser deposition technique at different laser fluences. Structural, optical, and electrical properties of CH3NH3PbI3 films were investigated at various laser fluences. The X-ray diffraction (XRD) studies confirm the formation of β-MAPbI3 films. The optical energy gap of MAPbI3 perovskite film was calculated and is found to be in the range of 1.53–1.68 eV. Scanning electron microscope (SEM) analysis reveals the formation of rod-like and platelet morphologies, while energy dispersive X-ray spectroscopy analysis reveals that the [I]/[Pb] ratio of the films prepared with 2, 2.5, and 3 J/cm2 was 1.3, 2.3, and 1.36, respectively. Hall effect results confirm that the MPPbI3 films are p-type and the mobility of MAPbI3 film decreases from 0.26 to 0.084 cm2V−1s−1 as laser fluence increases from 2 to 3 J/cm2. The optoelectronic characteristics of the p-MAPbI3/n-Si photodetector were investigated as a function of laser fluence. By selecting an optimum laser fluence, a maximum responsivity of 2.57 A/W and an external quantum efficiency of 7.08 × 102% at 450 nm were obtained. The energy band lineup of the p-MAPbI3/n-Si photodetector fabricated with 2.5 J/cm2 was constructed.

Hall effect in gated single-wall carbon nanotube films

The presence of hopping carriers and grain boundaries can sometimes lead to anomalous carrier types and density overestimation in Hall-effect measurements. Previous Hall-effect studies on carbon nanotube films reported unreasonably large carrier densities without independent assessments of the carrier types and densities. Here, we have systematically investigated the validity of Hall-effect results for a series of metallic, semiconducting, and metal–semiconductor-mixed single-wall carbon nanotube films. With carrier densities controlled through applied gate voltages, we were able to observe the Hall effect both in the n- and p-type regions, detecting opposite signs in the Hall coefficient. By comparing the obtained carrier types and densities against values derived from simultaneous field-effect-transistor measurements, we found that, while the Hall carrier types were always correct, the Hall carrier densities were overestimated by up to four orders of magnitude. This significant overestimation indicates that thin films of one-dimensional SWCNTs are quite different from conventional hopping transport systems.

Synergistic degradation of organic pollutants by poly (3,4-ethylenedioxythiophene) based photo-electrocatalysis

Poly (3,4-ethylenedioxythiophene) (PEDOT) had been explored as photosensitizer and hole transport agent. However, coating PEDOT on metal electrodes had issues with poor adhesion and delamination. In this work, the composite electrode with improved photo-electrocatalytic performance was constructed by potentiostatic polymerization of PEDOT on graphite plate and subsequent loading of ZnIn2S4. Solid micro-nanowires were observed in pure ZnIn2S4 electrode, which changed to polygon hollow tubular structure when loading ZnIn2S4 on PEDOT surface. From the Hall effect results, the resistance of composite electrode was reduced and the carriers density and mobility were increased. The charge carrier mobility value was 173.15 cm−2·V−1·s−1, which was almost two and four times higher than PEDOT (85.90 cm−2·V−1·s−1) and ZnIn2S4 (42.90 cm−2·V−1·s−1), respectively. The optimum EDOT concentration and polymerization time of PEDOT were 0.01 M and 20 min, respectively. The optimum scanning cycles for cyclic voltammetry deposition of ZIS and the ratio of ZnCl2, InCl·4H2O and Na2S2O3·5H2O were 400 cycles and 2:4:8, respectively. The radical capture experiment showed that singlet oxygen (1O2) and superoxide radical (O2−) were produced by PEDOT anode, while 1O2, O2− and hydroxyl radical (OH) were produced by the composite cathode. Through these reactive species, the removal of tetracycline and methylene blue reached 91% and 99% after 180 min reaction, respectively, under external voltage of 0.9 V.

Hidden strange metallic state in underdoped electron-doped cuprates

The low-temperature linear-in-T resistivity of ``strange metals,'' such as the metallic state of the cuprate high-temperature superconductors, has long been thought to be associated with a quantum critical point. However, recent transport studies of the cuprates have found this behavior persists over a finite range of overdoping. In this work, we report magnetoresistance and Hall effect results for electron-doped films of the cuprate superconductor ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Ce}}_{x}{\mathrm{CuO}}_{4}$ (LCCO) for temperatures from 0.7 to 45 K and magnetic fields up to 65 T. For $x=0.12$ and 0.13, just below the Fermi surface reconstruction (FSR) at $x=0.14$, the normal state in-plane resistivity exhibits a well-known upturn at low temperature. Our new results show that this resistivity upturn is eliminated at high magnetic field and the resistivity becomes linear-in-temperature from \ensuremath{\sim}40 K down to 0.7 K. The magnitude of the linear coefficient scales with Tc and doping, as found previously [K. Jin, Nature(London) 476, 73 (2011), T. Sarkar, Sci. Adv. 5, eaav6753 (2019)] for dopings above the FSR. This striking observation suggests that the strange metal is not confined to a single ``critical point'' in the phase diagram, but rather is a robust universal feature of the metallic ground state of the cuprates.

Physical properties of ultrasonically spray deposited Yttrium-doped SnO2 nanostructured films: supported by DFT study

The physical properties of ultrasonically spray deposited Yttrium (Y) doped tin dioxide (SnO2) are experimentally and theoretically investigated. The different diagnostics techniques such as X-ray diffraction (XRD), UV–Vis, scanning electron microscopy (SEM) and Hall effect measurements were performed to analyze the influence of yttrium doping ratio on the structural, optical and electrical properties of Y-doped SnO2 nanostructured films. Additionally, density functional theory (DFT) is applied to calculate and check the energy gap, lattice parameters and optical properties of SnO2 with different Y doping ratios. Super cell of Y-doped SnO2 was formed using Wien2k, and analyzed to physical properties of un-doped and Y doped stoichiometry with different ratios. Theoretical results are in agreement with the experimental results and the literature reports. Experimental results show that the optical band gap of fabricated sample increases with the increasing the Y doping amount in the tin dioxide film. The same tendency of energy band gap is observed with DFT calculation for Y-doped SnO2 compound. Theoretical results also show that the lattice parameter is nearly the same for pure and Y-doped SnO2 case, attributed to a change in the stoichiometry owing to metal doping. XRD results reveal that the all fabricated films are polycrystalline in the tetragonal Bravais lattice of tin dioxide, and the crystallite size, the crystalline orientation are affected by the Y doping level. The nanosized grains of the produced films are manipulated with increasing the Y dopant confirmed by the SEM. Y doped nanostructured films show the higher optical transmittance about 90% in ultra-violet region. Optical band gap gets widen from 3.689 to 3.810 eV with increasing the dopant amount. From Hall effect results, lower resistivity, higher carrier concentration and high enough mobility have been achieved by Y doping for the sample 5 at% Y:SnO2 based TCO film. The obtained results declared that Yttrium doping has an important effect on the optoelectronic properties, in particular, transparency and conductivity of SnO2 nanostructured film.

Role of Cu dilute on microstructures, optical, photoluminescence, magnetic and electrical properties of CdS film

Thin films of CdS1-xCux (with 0 ≤ x ≤ 0.10) were deposited using electron beam evaporation. Using XRD, EDX, SEM and UV–Vis–NIR spectroscopy, the impact of [Cu]/[S] on the film properties was examined. The influences of various concentrations of Cu are also elucidated on the optical parameters of the films. The XRD analysis shows that the thin films of CdS1-xCux have been improved and have hexagonal polycrystalline structure with the increase of Cu doping ratio. Additionally, the crystallite size is reduced while the micro-strain ε increases with enhancement of the incorporation of Cu in CdS lattice. The envelope method was used to extract the optical parameters of the undoped and Cu-doped CdS films. With the increase of Cu concentration, the energy optical bandgap decreased, and the variation values of band gap could play an important role in solar cell applications. Another optical parameters such as, dissipation factor and real/imaginary dielectric constant parts were evaluated and demonstrated a strong Cu doping dependence. The shift observed in the photoluminescence spectra emission band confirmed Cu's substitution to CdS lattice. The measurements of magnetization using vibrating sample magnetometer illustrated a hysteresis loop in Cu-doped CdS films, and confirmed the room temperature ferromagnetism. Finally, the Hall effect results show that the pure CdS film corresponds to an n-type semiconductor with a resistivity of 8.11 × 10-2 Ω cm and a carrier concentration of 29.6 × 1019 cm-3, and the CdS:Cu film is a p-type semiconductor and the resistivity is reduced from 6.8 × 10-2 to 3.7 × 10-2 Ωcm, and the carrier concentration is reduced from 26.4 × 1019 to 4.1 × 1019 cm-3, which has potential application prospects in solar cells.

Impact of Cu addition on the optoelectronic properties of Zn3N2 thin films: n to p-type transitions

Copper-doped Zinc Nitride (Cu:Zn3N2) films are grown on glass and Si substrates at various concentration of Cu (2.7, 4.9 and 5.7 at.%) by reactive RF magnetron co-sputtering. The impact of Cu atomic concentration on the structural and optoelectronic properties of Zn3N2 films is discussed in detail. Incorporation of Cu ions into Zn3N2 host lattice is confirmed by EDAX analysis. Hall Effect results indicate that the fabricated film exhibited p-type conductivity with high hole concentration of 1.78–1.36 × 1018 cm−3, resistivity of 0.48–0.56 Ω cm, and high hole mobility of ~8 cm2 V−1 s−1. The transmittance of Cu:Zn3N2 films are found to be in the range of 11–18% at the wavelength of 500 nm and hence the band gap decreases from 1.80 to 1.61 eV when Cu doping content is increased. These findings would assist Cu:Zn3N2 as a potential candidate for p-type layer in thin film solar cells.

Evolution of microstructure, defect, optoelectronic and magnetic properties of Cu1-xCaxFeO2 ceramics

Microstructures, defect characteristics, optoelectronic, and magnetic properties of polycrystalline delafossite Cu1-xCaxFeO2 (x = 0.00–0.08) samples have been systemically investigated. Our investigation results distinctly show that divalent Ca2+ ions can successfully substitute partial Cu+ ions and prompt the grain size and induce the partial Fe3+ valence variation to Fe2+. The positron annihilation lifetime spectra signifies that the cation vacancy clusters exist in all samples, the size and concentration of vacancy defects are redistributed with increasing Ca2+ ions content, while the overall defect environment of CuFeO2 system is not changed. The Hall-effect measurement results indicate the transition of semiconductor type from p-type to n-type. The UV–Visible absorption spectroscopy results indicate that the calculated band gap of the prepared samples is estimated to be 3.42–3.58 eV, indicating the series can be applied to the transparent conductive oxide materials. The magnetic measurements reveal that the transition temperature TN1 and TN2 are independent of Ca2+ content x, while the coexistence of antiferromagnetism and weak ferromagnetism for all the doped samples are observed. A moderate Ca2+ content, i.e. x = 0.02, can distinctly promote weak ferromagnetism. The above internal mechanism is probably relevant to the evolution of lattice structure and defect characteristics caused by Ca2+ ions doping.

Photoconductive mechanism of IR-sensitive iodized PbSe thin films via strong hole-phonon interaction and minority carrier diffusion.

Photoconductive PbSe thin films are highly important for mid-infrared imaging applications. However, the photoconductive mechanism is not well understood so far. Here we provide additional insight on the photoconductivity mechanism using transmission electron microscopy, x-ray photoelectron microscopy, and electrical characterizations. Polycrystalline PbSe thin films were deposited by a chemical bath deposition method. Potassium iodide (KI) was added during the deposition process to improve the photoresponse. Oxidation and iodization were performed to sensitize the thin films. The temperature-dependence Hall effect results show that a strong hole-phonon interaction occurs in oxidized PbSe with KI. It indicates that about half the holes are trapped by KI-induced self-trapped hole centers (Vk center), which results in increasing dark resistance. The photo Hall effect results show that the hole concentration increases significantly under light exposure in sensitized PbSe, which indicates the photogenerated electrons are compensated by trapped holes. The presence of KI in the PbSe grains was confirmed by I 3d5/2 core-level x-ray photoelectron spectra. The energy dispersive x-ray spectra obtained in the scanning transmission electron microscope show the incorporation of iodine during the iodization process on the top of PbSe grains, which can create an iodine-incorporated PbSe outer shell. The iodine-incorporated PbSe releases electrons to recombine with holes in the PbSe layer so that the resistance of sensitized PbSe is about 800 times higher than that of PbSe without the iodine-incorporated layer. In addition, oxygen found in the outer shell of PbSe can act as an electron trap. Therefore, the photoresponse of sensitized PbSe is from the difference between the high dark resistance (by KI addition and iodine incorporation) and the low resistance after IR exposure due to electron compensation (by electron traps at grain boundary and electron-hole recombination in KI hole traps).

Highly Conductive P-Type MAPbI3 Films and Crystals via Sodium Doping.

To regulate the optical and electrical properties of the crystals and films of the intrinsic methylammonium lead iodide (CH3NH3PbI3), we dope them with sodium (Na) by selecting sodium iodide (NaI) as a dopant source. The highly conductive p-type sodium-doped CH3NH3PbI3 (MAPbI3: Na) perovskite single crystals and thin films are successfully grown using the inverse temperature crystallization (ITC) method and antisolvent spin-coating (ASC) method, respectively. With the increase of Na+ doping concentration, the grain size of the film increases, the surface becomes smoother, and the crystallinity improves. Hall effect results demonstrate that both the MAPbI3: Na thin films and single crystals change their quasi-insulating intrinsic conductivity to a highly conductive p-type conductivity. The room-temperature photoluminescence (PL) peaks of doped MAPbI3 films slightly blue shift, while the photocarriers' lifetime becomes longer. The optical fingerprints of the doped levels in MAPbI3: Na perovskites can be identified by temperature-dependent PL. Obvious fingerprints of Na-related acceptor (A0X) levels in the doped MAPbI3: Na were observed at 10 K. These results suggest that sodium doping is an effective way to grow highly conductive p-type MAPbI3 perovskites.

Enhanced acetone sensing performance in black TiO2 by Ag modification

The application of TiO2 acetone monitor is highly limited by the high operating temperature and poor sensitivity. In this work, black TiO2 (B-TiO2) is produced by Ti3+ self-doping and is followed by Ag modification to form B-TiO2@Ag. It is first demonstrated that the operating temperature and sensitivity of TiO2 to acetone can be promoted evidently. By introducing a Ti3+ self-doped layer on the surface of TiO2, as observed in TEM images, the band gap of TiO2 is reduced to 3.01 eV. Ag surface decoration is carried out for the enhancement of electron generation. Optical absorption and the Hall effect results prove that B-TiO2@Ag exhibits highest photoelectrical properties. As a result, the B-TiO2@Ag gas sensor with a low operating temperature at 250 °C and high response of 68.19 to 50 ppm acetone is realized. The low detection limit of B-TiO2@Ag sensor reaches 887 ppb, which provides an applicable way for non-invasive detection of blood glucose.