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The hydroxylated carbon nanotubes (CNTs-OH), due to their propensity to trap electrons, are considered in many applications. Despite many case studies, the effect of the electronic structure of the CNT-OH electrode on its oxidation properties has not received in-depth analysis. In the present study, we used Fe(CN)63−/4− and Ru(NH3)63+/2+ as redox probes, which differ in charge. The CNT-OH and CNT electrodes used in the cyclic voltammetry were in the form of freestanding films. The concentration of holes in the CNTs-OH, estimated from the upshift of the Raman G-feature, was 2.9 × 10 13   c m − 2 . The standard rate constant of the heterogeneous electron transfer (HET) between Fe(CN)63−/4− and the CNTs-OH electrode was 25.9 × 10 − 4   c m · s − 1 . The value was more than four times higher than the HET rate on the CNT electrode ( k s = 6.3 × 10 − 4   c m · s − 1 ), which proves excellent boosting of the redox reaction by the holes. The opposite effect was observed for the Ru(NH3)63+/2+ redox couple. While the redox reaction rate constant at the CNT electrode was 1.4 × 10 − 4   c m · s − 1 , there was a significant suppression of the redox reaction at the CNT-OH electrode ( k s < 0.1 × 10 − 4   c m · s − 1 ). Based on the DFT calculations and the Gerischer model, we find that the boosting of the HET from the reduced form of the redox couple to CNT-OH occurs when the reduced forms of the redox couples are negatively charged and the occupied reduced states are aligned with acceptor states of the nanotube electrode. [ABSTRACT FROM AUTHOR]

Abstract Geometrically perfect S = ½ kagome lattices with frustrated magnetism are typically electrical insulators. Electron or hole doping is predicted to induce an exotic conducting state including superconductivity. Herein, an unconventional strategy of doping an S = ½ kagome lattice CoCu3(OH)6Cl2 is adopted – a structural analogue of a well‐known quantum spin liquid (QSL) candidate herbertsmithite (ZnCu3(OH)6Cl2) – by integrating it with reduced graphene oxide (rGO) via in situ redox chemistry. Such an integration drastically enhances the electrical conductivity, resulting in the transformation of an insulator to a semiconductor, corroborating the respective density of states obtained from the density functional theory calculations. Estimation of the magnetic moments, data on the Hall‐effect measurements, Bader charge analysis, and photoemission signals, altogether provide a bold signature of remote hole doping in CoCu3(OH)6Cl2 by rGO. The remote doping provides an alternative to the site doping approach to impart exotic electronic properties in spin liquid candidates, specifically, the generation of topological states like Dirac metal is envisioned.

Searching for multiferroic materials with ferromagnetic (FM) and ferroelectric (FE) properties holds promise for ultra‐high‐density and low‐energy‐consumption memory device applications, but 2D materials with both properties are rare. Herein, a general strategy to achieve nonvolatile electric field control of magnetism in the bilayer (BL) α‐In2Se3 by hole doping is proposed. By first‐principles calculations, it is demonstrated that hole doping can induce robust ferromagnetism in the bilayer α‐In2Se3 due to its unique flat Mexican‐hat‐shape valence band structure. Such band edges cause van Hove singularities (VHS), and proper hole doping can lead to time‐reversal symmetry breaking. The bilayer α‐In2Se3 exhibits ferromagnetism and ferroelectricity within a wide range of doping concentrations, resulting in an unexpected multiferroic phase. Furthermore, when the electrical polarization of α‐In2Se3 flips from downward to upward, it becomes non‐magnetic (NM) from ferromagnetic states in the As‐substituted bilayer α‐In2Se3, which can work as a nonvolatile magnetic storage unit. Remarkably, the As‐substituted bilayer α‐In2Se3 exhibits an enhanced magnetic moment of 1.2 μB per AsSe due to substantial charge transfer across the interface. Notably, the mechanism of electrically controlled magnetism is elucidated as the coupling among the Mexican‐hat‐like dispersion, ferromagnetism, and ferroelectricity. The findings offer a promising strategy for electrical writing and the magnetic reading memory device. [ABSTRACT FROM AUTHOR]

Hole-doped high-temperature copper oxide-based superconductors (cuprates) exhibit complex phase diagrams where electronic orders like a charge density wave (CDW) and superconductivity (SC) appear at low temperatures. The origins of these electronic orders are still open questions due to their complex interplay and correlated nature. These electronic orders can modify the phonons in the system, which has also been experimentally found in several cuprates as a softening in the phonon frequency at the CDW vector. Recent experiments have revealed that the softening in phonons in cuprates due to CDW shows intriguing behavior with increasing hole doping. Hole doping can also change the underlying Fermi surface. Therefore, it is an interesting question whether the doping-induced change in the Fermi surface can affect the softening of phonons, which in turn can reveal the nature of the electronic orders present in the system. In this work, we investigate this question by studying the softening of phonons in the presence of CDW and SC within a perturbative approach developed in an earlier work. We compare the results obtained within the working model to some experiments. [ABSTRACT FROM AUTHOR]

Abstract Searching for multiferroic materials with ferromagnetic (FM) and ferroelectric (FE) properties holds promise for ultra‐high‐density and low‐energy‐consumption memory device applications, but 2D materials with both properties are rare. Herein, a general strategy to achieve nonvolatile electric field control of magnetism in the bilayer (BL) α‐In2Se3 by hole doping is proposed. By first‐principles calculations, it is demonstrated that hole doping can induce robust ferromagnetism in the bilayer α‐In2Se3 due to its unique flat Mexican‐hat‐shape valence band structure. Such band edges cause van Hove singularities (VHS), and proper hole doping can lead to time‐reversal symmetry breaking. The bilayer α‐In2Se3 exhibits ferromagnetism and ferroelectricity within a wide range of doping concentrations, resulting in an unexpected multiferroic phase. Furthermore, when the electrical polarization of α‐In2Se3 flips from downward to upward, it becomes non‐magnetic (NM) from ferromagnetic states in the As‐substituted bilayer α‐In2Se3, which can work as a nonvolatile magnetic storage unit. Remarkably, the As‐substituted bilayer α‐In2Se3 exhibits an enhanced magnetic moment of 1.2 μB per AsSe due to substantial charge transfer across the interface. Notably, the mechanism of electrically controlled magnetism is elucidated as the coupling among the Mexican‐hat‐like dispersion, ferromagnetism, and ferroelectricity. The findings offer a promising strategy for electrical writing and the magnetic reading memory device.

Hole-doped high-temperature copper oxide-based superconductors (cuprates) exhibit complex phase diagrams where electronic orders like a charge density wave (CDW) and superconductivity (SC) appear at low temperatures. The origins of these electronic orders are still open questions due to their complex interplay and correlated nature. These electronic orders can modify the phonons in the system, which has also been experimentally found in several cuprates as a softening in the phonon frequency at the CDW vector. Recent experiments have revealed that the softening in phonons in cuprates due to CDW shows intriguing behavior with increasing hole doping. Hole doping can also change the underlying Fermi surface. Therefore, it is an interesting question whether the doping-induced change in the Fermi surface can affect the softening of phonons, which in turn can reveal the nature of the electronic orders present in the system. In this work, we investigate this question by studying the softening of phonons in the presence of CDW and SC within a perturbative approach developed in an earlier work. We compare the results obtained within the working model to some experiments.

2D semiconductors show promise as a competitive candidate for developing future integrated circuits due to their immunity to short-channel effects and high carrier mobility at atomic layer thicknesses. The inherent defects and Fermi level pinning effect lead to n-type transport characteristics in most 2D semiconductors, while unstable and unsustainable p-type doping by various strategies hinders their application in many areas, such as complementary metal-oxide-semiconductor (CMOS) devices. In this study, an intralayer/interlayer codoping strategy is introduced that stabilizes p-type doping in 2D semiconductors. By incorporating oppositely charged ions (F and Li) with the intralayer/interlayer of 2D semiconductors, remarkable p-type doping in WSe 2 and MoTe 2 with air stability up to 9 months is achieved. Notably, the hole mobility presents a 100-fold enhancement (0.7 to 92 cm 2 V -1 s -1 ) with the codoping procedure. Structural and elemental characterizations, combined with theoretical calculations validate the codoping mechanism. Moreover, a CMOS inverter and more complex logic functions such as NOR and XNOR, as well as large-area device arrays are demonstrated to showcase its applications and scalability. These findings suggest that stable and straightforward intralayer/interlayer codoping strategy with charge-space synergy holds the key to unlocking the potential of 2D semiconductors in complex and scalable device applications., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

The narrow-gap magnesium silicide semiconductor Mg2Si is a promising mid-temperature (600–900 K) thermoelectric material. It intrinsically possesses n-type conductivity, and n-type dopants are generally used for improving its thermoelectric performance; however, the synthesis of p-type Mg2Si is relatively difficult. In this work, the hole doping of Mg2Si with various impurity atoms is investigated by performing first principles calculations. It is found that the Ag-doped systems exhibit comparable formation energies ΔE calculated for different impurity sites (Mg, Si, and interstitial 4b ones), which may explain the experimental instability of their p-type conductivity. A similar phenomenon is observed for the systems incorporating alkali metals (Li, Na, and K) since their ΔE values determined for Mg (p-type) and 4b (n-type) sites are very close. Among boron group elements (Ga and B), Ga is found to be favorable for hole doping because it exhibits relatively small ΔE values for Si (p-type) sites. Furthermore, the interstitial insertion of Cl and F atoms into the crystal lattice leads to hole doping because of their high electronegativity.

The narrow-gap magnesium silicide semiconductor Mg2Si is a promising mid-temperature (600–900 K) thermoelectric material. It intrinsically possesses n-type conductivity, and n-type dopants are generally used for improving its thermoelectric performance; however, the synthesis of p-type Mg2Si is relatively difficult. In this work, the hole doping of Mg2Si with various impurity atoms is investigated by performing first principles calculations. It is found that the Ag-doped systems exhibit comparable formation energies ΔE calculated for different impurity sites (Mg, Si, and interstitial 4b ones), which may explain the experimental instability of their p-type conductivity. A similar phenomenon is observed for the systems incorporating alkali metals (Li, Na, and K) since their ΔE values determined for Mg (p-type) and 4b (n-type) sites are very close. Among boron group elements (Ga and B), Ga is found to be favorable for hole doping because it exhibits relatively small ΔE values for Si (p-type) sites. Furthermore, the interstitial insertion of Cl and F atoms into the crystal lattice leads to hole doping because of their high electronegativity. [ABSTRACT FROM AUTHOR]

Abstract The perovskite oxide LaNiO3 is a promising oxygen electrocatalyst for renewable energy storage and conversion technologies. Here, it is shown that strontium substitution for lanthanum in coherently strained, epitaxial LaNiO3 films (La1−x SrxNiO3) significantly enhances the oxygen evolution reaction (OER) activity, resulting in performance at x = 0.5 comparable to the state‐of‐the‐art catalyst Ba0.5Sr0.5Co0.8Fe0.2O3−δ. By combining X‐ray photoemission and X‐ray absorption spectroscopies with density functional theory, it is shown that an upward energy shift of the O 2p band relative to the Fermi level occurs with increasing x in La1−xSrxNiO3. This alloying step strengthens Ni 3d–O 2p hybridization and decreases the charge transfer energy, which in turn accounts for the enhanced OER activity.

Graphical abstract Highlights • The TcS 2 monolayer has ferromagnetic half-metallicity via hole doping. • Half-metallicity is derived from p orbital and the Curie temperature is higher than room temperature. • The interlayer interaction can affect ferromagnetic coupling in the TcS 2 bilayer. Abstract Here, we study the magnetism of the distorted 1 T - TcX 2 (X = S,Se) based on first-principles calculation. The magnetism originates from the hole doping due to the density of states near the valence band edge having van Hove singularity feature. The calculated results show that the TcS 2 monolayer can develop an interesting ferromagnetic (FM) half-metallic phase with tunable spin-polarization orientation. The FM half-metallicity and magnetic moments of the hole-doped TcS 2 monolayer are primarily derived from the p orbital of S atoms, then, a FM ground phase with a high Curie temperature (T C) (larger than 800 K) is obtained due to the strong S p – S p direct exchange interaction. The magnetic order is robust against thermal excitations at finite temperatures because of magnetic anisotropic energy. In the TcS 2 bilayer, the electrons near Fermi level are redistributed when introducing the interlayer interaction, which suppresses the ferromagnetism induced by hole doping. The ferromagnetism can be recovered when the interlayer interaction is weakened. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Hole-doped ZnO monolayer transits from nonmagnetic state to magnetic state. • The critical hole density in ZnO monolayer can be modulated by the biaxial strain. • The O- p z states play a vital role for the induced magnetism in hole-doped ZnO monolayer with applying biaxial strain. Abstract The influences of the hole-doped and biaxial strain applied on the electronic structure and magnetism of graphene-like ZnO monolayer are systematically investigated by the first-principles calculations. The results show that hole-doped ZnO monolayer transits from nonmagnetic state to magnetic state once the hole density reaches a certain value (3.65 × 1014 cm−2), and the average spin magnetic moment increases by 1.0 μ B /hole upon increasing the hole density from 0.3 × 1014 to 8.2 × 1014 cm−2. More interestingly, the critical hole density can be effectively reduced by applying the biaxial strain. The magnetism of hole-doping ZnO monolayer with biaxial strian comes from the O- p z states. Our study demonstrates that the combined effect of the hole doping and biaxial strain on ZnO monolayer can modulate its electronic and magnetic properties, which can be applied in nanoelectronics and spintronics. [ABSTRACT FROM AUTHOR]

We present a T = 0 K renormalization group (RG) phase diagram for the hole-doped 2D Hubbard model on the square lattice. The RG method employed is nonperturbative in treating quantum fluctuations of the single-particle occupation number via the unitarily decoupling of one electronic state at every RG step. As a result, the RG phase diagram possesses the quantum fluctuation energy scale ( ω ) as one of its axes. Using effective Hamiltonians and wavefunctions for the low-energy many-body eigenstates for the doped Mott liquid obtained from the stable fixed point of the RG flows, we demonstrate the collapse of the pseudogap for charge excitations (Mottness) at a quantum critical point (QCP) possessing a nodal non-Fermi liquid with superconducting fluctuations, and spin-pseudogapping near the antinodes. The QCP is characterised using both thermodynamic and quantum information-theoretic measures. d-wave superconducting order is shown to arise from this quantum critical state of matter. The pseudogap phase possesses a variety of fluctuations that lead to several symmetry-broken phases at low-energies. Benchmarking of the ground state energy per particle and the double-occupancy fraction obtained from a finite-size scaling analysis against existing numerical results yields excellent agreement. We present detailed insight into the T = 0 origin of several experimentally observed findings in the cuprates, including Homes law and Planckian dissipation. We also establish that the heirarchy of temperature scales for the pseudogap ( T _PG ), onset temperature for pairing ( T _ons ), formation of the Mott liquid ( T _ML ) and superconductivity ( T _C ) obtained from our analysis is quantitatively consistent with that observed experimentally for some members of the cuprates. Our results offer insight on the ubiquitous origin of superconductivity in doped Mott insulating states, and pave the way towards a systematic search for higher superconducting transition temperatures in such systems.

Abstract We examined the effect of X-ray irradiation on the magnetic properties of REBa 2 Cu 3 O y (REBCO; RE = Y, Nd, or Gd). In all the samples, T c0 , which is defined as the temperature below which the magnetic susceptibility is lower than zero, did not change significantly after irradiation within the measurement accuracy. On the other hand, the magnetic susceptibilities after irradiation were lower than those before irradiation in all the samples. These results, which are consistent with those observed under light irradiation, indicate that X-ray irradiation enhances the superconductive properties of these materials. This enhancement results from hole doping in the CuO 2 plane via the generation of electron–hole pairs by X-ray irradiation and subsequent trapping of the electrons at oxygen vacancies. Relaxation of the irradiation effect and the electron behavior after irradiation were studied by analyzing the magnetic properties and Raman spectra. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract The seeking of room temperature ferromagnetic semiconductors, which take advantages of both the charge and spin degrees of freedom of electrons to realize a variety of functionalities in devices integrated with electronic, optical, and magnetic storage properties, has been a long-term goal of scientists and engineers. Here, by using the spin-polarized density functional theory calculations, we predict a new series of high temperature ferromagnetic semiconductors based on the melilite-type oxysulfide Sr 2 MnGe 2 S 6 O through hole (K) and electron (La) doping. Due to the lack of strong antiferromagnetic superexchange between Mn ions, the weak antiferromagnetic order in the parent compound Sr 2 MnGe 2 S 6 O can be suppressed easily by charge doping with either p -type or n -type carriers, giving rise to the expected ferromagnetic order. At a doping concentration of 25%, both the hole-doped and electron-doped compounds can achieve a Curie temperature ( T c ) above 300 K. The underlying mechanism is analyzed. Our study provides an effective approach for exploring new types of high temperature ferromagnetic semiconductors. [ABSTRACT FROM AUTHOR]

Transparent conducting oxides (TCOs) are a unique series of materials combining electrical conductivity with optical transparency. Most of the commercially available TCOs are of the n-type. The performance of p-type TCOs, however, is far behind their n-type TCO counterparts primarily due to the doping bottleneck and low hole mobility. Herein, a Mott-Hubbard insulator of LaVO3 is proposed as the starting point for exploring p-type TCOs. Substitution of La3+ by Sr2+ can introduce high hole carrier concentration at the top of the valence band to overcome the doping bottleneck. Combining a modest carrier mobility with weak absorption in the visible region, La1-xSrxVO3 compounds can serve as new p-type TCOs and exhibit good balance of the tradeoffs between electrical conductivity and optical transparency. It is demonstrated that La2/3Sr1/3VO3 thin films exhibit a high conductivity of 742.3-872.3 S cm-1 at room temperature and a high transmission of 53.9-70.1% in the visible region, which leads to the highest figure of merit among p-type TCOs so far. [ABSTRACT FROM AUTHOR]

The structure, microstructure and resistivity of three bulk samples with different compositions corresponding to the (La-Sr) 1.55 (Nd-Ce) 0.45 CuO 4 series, were studied. As the previously studied undoped La 1.55 Nd 0.45 CuO 4 system, these three compositions are biphasic, with orthorhombic T and tetragonal T' phases in two cases, as main and secondary phases, with the exception of La 1.4 Sr 0.15 Nd 0.4 Ce 0.05 CuO 4 , with a secondary T* phase instead of the T' one. Commensurate superstructures are present in La 1.5 Sr 0.05 Nd 0.43 Ce 0.02 CuO 4 . All the samples behave as semiconductor at low temperatures, with a metal insulator transition temperature in the 50–100 K range; a second transition temperature at 274 K, can be seen for La 1.5 Sr 0.05 Nd 0.4 Ce 0.05 CuO 4 . An improvement in electrical conductivity have been found with increasing doping, independently of the nature of the dopant agent −hole or electron-. No superconducting transitions have been detected. [ABSTRACT FROM AUTHOR]

This letter investigates the response of a wide detection range mercury ion sensor based on Si MOSFET having a floating-gate (FG) and a control-gate (CG) in horizontal direction. Single-walled carbon nanotubes (SWNTs) are formed between the FG and the CG by using an inkjet-printing method. The interaction between themercury ions and SWNTs is studied by measuring transient current response (I–t). Conductance change is measured from 1 fM to \sim 10~\mu \textM in saturated transient current region. The measured transient response shows that the drain current ( I{D} ) is appreciably changed in pMOSFET sensor and almost notchanged in nMOSFET sensor. By analyzing the conductance change of the pMOSFET sensor with the concentration of mercury ions, it is shown that the work-function of SWNTs increases due to hole doping and the I{D} increases as a result. [ABSTRACT FROM AUTHOR]

Single crystals of Li-doped SrFe2As2 up to 2 × 2 mm2 in size were grown from LiCl flux. The obtained material contains only a minor amount of Li, but shows distinct differences in physical properties as compared to the pure material synthesized via other techniques. It orders antiferromagnetically below 6.2 K and does not show any indication of superconductivity above 1.2 K. The large negative Curie-Weiss temperature θW⊥ = −206.5 ( μW|| = −200.5 K) points to the dominance of antiferromagnetic Fe-Fe interactions. The reduced effective magnetic moments of Fe2+ μeff⊥ = 2.31 μB ( μeff|| = 2.27 μB) indicate itinerant character of magnetism in this system. According to electrical resistivity measurements this material is a semimetal. In the temperature range of 12-70 K ρ( T) follows a Fermi-liquid T2-dependence. In the vicinity of antiferromagnetic ordering ρ( T) deviates from Fermi-liquid behavior. Below about 12 K, a transport law of the obtained single crystals requires a substantial linear non-Fermi contribution to successfully describe the data. [ABSTRACT FROM AUTHOR]

Two-dimensional van der Waals magnetic heterostructures based on intrinsic ferromagnetic materials have potentially useful for realizing novel spintronic devices. Here, the electronic structure and magnetic property of BN/CrOBr heterostructures are investigated by using first-principles calculations. The calculations show that stacking patterns have no significant effects on the band structure of BN/CrOBr heterostructures, BN/CrOBr heterostructures are semiconductors with indirect band gap. The band gaps of CrOBr monolayer in BN/CrOBr heterostructures are reduced compared with the individual one. The total magnetic moment of CrOBr monolayer is not affected by h-BN monolayer. The h-BN monolayer enhances the in-plane magnetic anisotropy of CrOBr monolayer in BN/CrOBr heterostructures depends on stacking pattern. Furthermore, hole doping can switch the easy magnetization axis of BN/CrOBr heterostructure from in-plane to out-of-plane direction. The theoretical results show that BN/CrOBr heterostructure has potential applications in spintronics for its controllable magnetic anisotropy. • The BN/CrOBr heterostructures with different stacking patterns are semiconductors. • The h-BN monolayer enhances the in-plane magnetic anisotropy of CrOBr monolayer in BN/CrOBr heterostructure. • Hole doping can switch the easy axis of BN/CrOBr heterostructure from in-plane to out-of-plane direction. [ABSTRACT FROM AUTHOR]

Recent research work on searching for high mobility p -type oxides has identified substantial promising p -type oxide candidates. However, very few of them have been experimentally proven with high p -type conductivity, due to their limited p -type dopability caused by the deep valence band edge (VBE). In this work, we report amorphous phase Ta 2 SnO 6 (a -Ta 2 SnO 6) possessing unusually shallow VBE that permits high p -type doping without hole-killing oxygen vacancy defects spontaneous formation, contrasting to crystalline Ta 2 SnO 6 (c -Ta 2 SnO 6). The shallow VBE in a -Ta 2 SnO 6 also allows a low Schottky barrier height with contact metals and unique a −/ c - Ta 2 SnO 6 heterostructure device. The shallow VBE in a -Ta 2 SnO 6 is due to the local structure disorder that circumvents the strong electrostatic Coulombic interaction between positively charged Ta5+ and Sn-5 s lone-pair electrons which accounts for the deep VBE and low p -type dopability in c -Ta 2 SnO 6. [Display omitted] • Many high hole mobility oxides cannot be p -type doped because of their deep valence band edge positions. • Band alignments and band edge positions are investigated to access the p -type dopability of oxides. • Amorphous Ta 2 SnO 6 has different electronic structure and carrier transport property than its crystalline counterpart. • Shallow valence band edge in amorphous Ta 2 SnO 6 allows a low Schottky barrier with contact metal. • A novel heterostructure device based on amorphous/crystalline Ta 2 SnO 6 is designed for better electron transport. [ABSTRACT FROM AUTHOR]

Organometal-trihalide-perovskite-based solar cells have exhibited high efficiencies when incorporated into mesoscopic NiO (NiOnc) hole-transport layers. The integration of a NiOnc-perovskite heterojunction provides an inorganic alternative as a p-type contact material with efficient hole extraction for perovskite-based solar cells. Herein the origin of such highly efficient carrier transport is studied in terms of electronic, chemical and transport properties of a NiOnc-perovskite heterojunction with X-ray photoelectron spectra, ultraviolet photoelectron spectra, near-edge X-ray absorption fine structure spectra, a scanning transmission X-ray microscope, and calculations of electronic structure. A pronounced chemical redox reaction is found at an NiOnc-perovskite heterojunction such that PbI2 is oxidized to PbO with subsequent formation of hole-dopant CH3NH3PbI3-2δOδ at the heterojunction. The generation of hole-doping CH3NH3PbI3-2δOδ induced by the redox reaction at the NiOnc/perovskite heterojunction plays a significant role to facilitate the carrier transport, and thus enhances the photovoltaic efficiencies. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hole doping of metallic carbon nanotubes contained in unsorted species is detected by Raman spectroscopy. • The effect of hole doping is manifested stronger in Raman spectra of metallic nanotubes. • Increase of electron–phonon coupling in metallic nanotubes at hole doping removal is revealed. • More complete DNA coverage of nanotubes partially mitigates hole doping removal. Single-walled carbon nanotubes have unique photophysical and electronic properties that can be tuned by means of redox chemistry and charge transfer. In this work the removal of hole doping from the DNA-suspended unsorted nanotubes using reducing agent (dithiothreitol) was examined by Raman spectroscopy. Raman spectra of two nanotube:DNA aqueous suspensions with different amount of holes on the free nanotube surface obtained due to different biopolymer coverage were analyzed in the range of the radial breathing mode, tangential modes, as well as defect-induced and two-phonon modes. Noticeable transformation of intensity, spectral position and lineshape was revealed for bands assigned to metallic nanotubes contained in unsorted species while bands of semiconducting nanotubes remained unchanged. This band transformation is explained by diminished hole doping of metallic nanotubes. Tighter DNA coverage of the nanotube surface partially mitigated hole doping removal which indicates an important role of biopolymer coverage on nanotube response to reducing agent influence. [ABSTRACT FROM AUTHOR]

In this study, a linear relationship between the doping level ( p ) and the temperature coefficient of electrical resistance (TCR) is shown and substantiated for 20 nanostructured superconducting ceramics based on YBa 2 Cu 3 O 7-δ (YBCO). Variations of ceramic production parameters, ceramic particles' porosity and dispersion, average values of oxygen index or the normal phase conductivity type (metallic or semiconducting) do not violate this dependence. A distinctive feature of these ceramics is the decomposition of YBCO main superconducting phase into superconducting phases with different oxygen stoichiometries during nanostructuring. The values of p and ТCR and the change in the width of the superconducting transition (Δ T c) associated with this decay were obtained in situ by studying the temperature dependence of the resistance of each sample. The correlations between p and ТCR with Δ T c are shown. Slater's theory of elementary charge excitations formation in condensed medium, which is a system of interacting polarized ions and atoms, was used for interpretation of relationship between p and TCR established on the basis of these correlations. [Display omitted] • Nanostructured YBCO ceramics with different levels of doping. • Correlations of the level of doping and the temperature coefficient of resistance with the width of the superconducting transition. • The linear relationship between the level of doping for nanostructured YBCO with the temperature coefficient of resistance. [ABSTRACT FROM AUTHOR]

Single-walled carbon nanotube (SWNT) electrodes that are chemically and mechanically robust are fabricated using a simple drop cast method with thermal annealing and acid treatment. An electronic-type selective decrease in sheet resistance of SWNT electrodes with HNO3 treatment is shown. Semiconducting SWNTs show a significantly higher affinity toward hole doping in comparison to metallic SWNTs; a ≈12-fold and a ≈fivefold drop in sheet resistance, respectively. The results suggest the insignificance of the electronic type of the SWNTs for the film conductivity after hole doping. The SWNT films have been employed as transparent hole extracting electrodes in bulk heterojunction (BHJ) organic photovoltaics. Performances of the devices enlighten the fact that the electrode film morphology dominates over the electronic type of the doped SWNTs with similar sheet resistance and optical transmission. The power conversion efficiency (PCE) of 4.4% for the best performing device is the best carbon nanotube transparent electrode incorporated large area BHJ solar cell reported to date. This PCE is 90% in terms of PCEs achieved using indium tin oxide (ITO) based reference devices with identical film fabrication parameters indicating the potential of the SWNT electrodes as an ITO replacement toward realization of all carbon solar cells. [ABSTRACT FROM AUTHOR]