P-type Transport Research Articles

Membrane Anchoring and Ion-Entry Dynamics in P-type ATPase Copper Transport

Cu+-specific P-type ATPase membrane protein transporters regulate cellular copper levels. The lack of crystal structures in Cu+-binding states has limited our understanding of how ion entry and binding are achieved. Here, we characterize the molecular basis of Cu+ entry using molecular-dynamics simulations, structural modeling, and in vitro and in vivo functional assays. Protein structural rearrangements resulting in the exposure of positive charges to bulk solvent rather than to lipid phosphates indicate a direct molecular role of the putative docking platform in Cu+ delivery. Mutational analyses and simulations in the presence and absence of Cu+ predict that the ion-entry path involves two ion-binding sites: one transient Met148-Cys382 site and one intramembranous site formed by trigonal coordination to Cys384, Asn689, and Met717. The results reconcile earlier biochemical and x-ray absorption data and provide a molecular understanding of ion entry in Cu+-transporting P-type ATPases.

Facile Synthesis of Single Crystal PtSe2 Nanosheets for Nanoscale Electronics.

Ultrathin single crystal platinum diselenide (PtSe2 ) nanosheets are synthesized using H2 PtCl6 and Se as the precursors. The electronic properties are first investigated and exhibit p-type transport behavior with the mobility much larger than 7 cm2 V-1 s-1 . The further investigation on PtSe2 /MoS2 var der Waals p-n junction demonstrated that PtSe2 could be potentially applied in 2D electronics.

A scheme of simultaneous cationic–anionic substitution in CuCrO2 for transparent and superior p-type transport

Considering CuCrO2 to be a promising p-type transparent conducting oxide, unprecedented simultaneous cationic–anionic doping is carried out to achieve superior hole transport while maintaining its transparency. Magnesium and sulphur are doped at Cr and O-sites respectively by solid-state approach (CuCr1−xMgxO1−ySy, x, y ranging 0–5 atomic %) with significant doping confirmed by Rietveld refinement. UV–Vis spectroscopy is observed to imply promising optical properties of engineered materials. DC conductivity of co-doped CuCr0.95Mg0.05O1.9S0.1 is observed to be twice as large compared to CuCr0.95Mg0.05O2 at 300 K, which is consistent with the lower frequency shift of the negative differential susceptance () and the admittance peak, indicating higher ‘metallicity’ upon co-doping. Hole mobility of 16.26 cm2 V−1 s−1 at 300 K is observed for the co-doped CuCrO2. This strategy combines an established doping scheme at the cationic site with our newly developed anionic chalcogen doping, aiming to overcome a long-standing transport bottleneck in the field of semiconductor oxides.

Isoindigo-based fluorinated low band gap polymers for environmentally stable field effect transistor

Two isoindigo-based conjugated polymers, based on fluorinated elctron donor units (dithienyldifluorobenzothiadiazole(DT2FBT) and dithienyltetrafluorobenzene (DT4FBZ)), have been synthesized and their optical, electrochemical, morphological, and crystallinity features were evaluated. The combination of highly conjugated isoindigo moiety with fluorinated electron donor units induces high crystallinity of the derived polymers, resulting in p-type charge transport characteristics with high hole mobility exceeding 7.0 × 10−2 cm2 V−1 s−1. Furthermore, the low-lying energy levels due to the electron-deficient fluorinated electron donors allow not only effective electrical contact with the source/drain electrodes but also excellent ambient stability of the derived transistor devices, enabling the polymers to be promising candidates for the environmentally stable optoelectronics.

Strong compensation hinders the p-type doping of ZnO: a glance over surface defect levels

Abstract We propose a surface doping model of ZnO to elucidate the p-type doping and compensations in ZnO nanomaterials. With an N-dopant, the effects of N on the ZnO surface demonstrate a relatively shallow acceptor level in the band gap. As the dimension of the ZnO materials decreases, the quantum confinement effects will increase and render the charge transfer on surface to influence the shifting of Fermi level, by evidence of transition level changes of the N-dopant. We report that this can overwhelm the intrinsic p-type conductivity and transport of the ZnO bulk system. This may provide a possible route of using surface doping to modify the electronic transport and conductivity of ZnO nanomaterials.

Black Phosphorus Flexible Thin Film Transistors at Gighertz Frequencies.

Black phosphorus (BP) has attracted rapidly growing attention for high speed and low power nanoelectronics owing to its compelling combination of tunable bandgap (0.3 to 2 eV) and high carrier mobility (up to ∼1000 cm(2)/V·s) at room temperature. In this work, we report the first radio frequency (RF) flexible top-gated (TG) BP thin-film transistors on highly bendable polyimide substrate for GHz nanoelectronic applications. Enhanced p-type charge transport with low-field mobility ∼233 cm(2)/V·s and current density of ∼100 μA/μm at VDS = -2 V were obtained from flexible BP transistor at a channel length L = 0.5 μm. Importantly, with optimized dielectric coating for air-stability during microfabrication, flexible BP RF transistors afforded intrinsic maximum oscillation frequency fMAX ∼ 14.5 GHz and unity current gain cutoff frequency fT ∼ 17.5 GHz at a channel length of 0.5 μm. Notably, the experimental fT achieved here is at least 45% higher than prior results on rigid substrate, which is attributed to the improved air-stability of fabricated BP devices. In addition, the high-frequency performance was investigated through mechanical bending test up to ∼1.5% tensile strain, which is ultimately limited by the inorganic dielectric film rather than the 2D material. Comparison of BP RF devices to other 2D semiconductors clearly indicates that BP offers the highest saturation velocity, an important metric for high-speed and RF flexible nanosystems.

Stable electrical performance observed in large-scale monolayer WSe2(1−x)S2x with tunable band gap

Two-dimensional (2D) semiconductor materials have attracted broad interest due to their unique structures and physical properties. The stability of the 2D-material-based devices plays a key role in their practical applications. Here, we report the promising stable electrical performance in the large-scale monolayer WSe2(1−x)S2x with a tunable band gap. Photoluminescence (PL) spectroscopy was utilized to verify the tunable band gap in the as-grown monolayer with a tuning capability of 120 meV. Gated field effect transistor (FET) performance confirmed the p-type transport behavior in monolayer WSe2(1−x)S2x with a high on/off ratio (>104). Top-gated FET configuration improves the carrier mobility with two orders larger than that in the back-gated FET device. After exposure to air for three months, the device performance manifested excellent stability with no source-drain current drop observed. P-type WSe2(1−x)S2x with a tunable band gap is the ideal complement to n-type tunable monolayers in the application of pn junction-related flexible nanodevices.

Ambipolar Charge Transport in Isoindigo-Based Donor–Acceptor Polymers

A series of donor–acceptor isoindigo (iI)-based copolymers synthesized with increasing numbers of thiophene rings in the repeat unit (from zero to three thiophene rings, including silole and germole-bridged fused bithiophene units) is applied toward solution-processed OFET devices. Differential pulse voltammetry on thin films of the polymers recorded LUMO energy levels confined within a 0.1 eV range around 3.9 eV, while their bandgaps are estimated at 1.5 to 1.7 eV. The interchain π-stacking distance of each sample was evaluated from the 2D-WAXS diffraction patterns of annealed extruded filaments and the GIWAXS patterns of thin films, and were found to be all in the same range, between 3.65 and 3.75 Å for the thin films. Both p-type and n-type charge transport in thin film bottom gate, bottom contact transistor devices were recorded. In particular, the copolymer P(T-iI) containing one thiophene ring afforded well-balanced ambipolar p-type and n-type mobilities of 0.04 cm2/(V s) and 0.1 cm2/(V s), respectively. Under our processing conditions, the charge transport properties evolved from exclusively n-type to solely p-type as the number of thiophene rings within the repeat unit is increased to three rings in the case of P(T3-iI). This was observed despite all polymers displaying similar LUMO energy levels, interchain π-stacking distances, and microscopic thin film morphology (all face-on arrangement on the dielectric surface). This prompted a molecular-scale morphological analysis of P(T-iI) and P(T3-iI) in particular, using solid-state NMR spectroscopy in order to further investigate the stark difference in n-type mobilities between these two polymers. Using the complete assignment of solution 2D-NMR spectra of a thiophene-iI-thiophene model compound as guideline, the analysis of proton–carbon correlations in the solid-state 2D 13C{1H} FSLG-HETCOR NMR spectra of P(T-iI) and P(T3-iI) revealed differences in the molecular environment surrounding each iI unit. The latter suggests a stronger correlation of neighboring iI units in P(T-iI), whereas a stronger intermixing of iI and thiophenes prevails in P(T3-iI). We conclude that, in this study, the choice of the donor unit length within the primary structure of the D–A polymer can be responsible for hindering its n-type character.

Snapshots of P-Type ATPases - From Crystal Structures to Single-Molecule Studies

P-type ATPases maintain essential ion gradients and asymmetric distributions of lipids across cell membranes. They encompass well-known ion pumps such as the Na+,K+-ATPase and Ca2+-ATPases. Much knowledge has been obtained on general principles of P-type ATPase structure, function and inhibition, including a vast database of P-type ATPase structures, mutational studies and transport kinetics studies. Our studies have revealed large conformational changes associated with the Post-Albers transport cycle of e.g. sarcoendoplamic reticulum Ca2+-ATPase and pig kidney Na,K-ATPase, where the enzyme alternates between inward-oriented E1 forms and outward-oriented E2 forms. We also seek to contribute with new structures representing missing functional states or inhibited forms, regulatory mechanisms and complexes, and structures of P-type ATPases which have remained so far uncharacterized. Overall, the cycle is driven in a forward direction by ATP hydrolysis through a two-step mechanism of autophosphorylation (E1 to E1P) and autodephosphorylation (E2P to E2) of the enzyme. Critical transitions take place when the orientation shifts sides (E1P to E2P and E2 to E1). However, most information on the cycle has so far been derived from bulk measurements, and insights into the actual coupling and kinetics at a single-molecule level has been missing. We have established a P-type ATPase model for single-molecule studies based on the Listeria Ca2+-ATPase 1 (LMCA1). Laursen M et al. 2015. Structures and characterization of digoxin- and bufalin-bound Na+,K+-ATPase compared with the ouabain-bound complex. PNAS 112:1755 Nyblom M et al. 2013. Crystal Structure of Na+, K+-ATPase in the Na+-Bound State. Science 342:123 Winther AM et al. 2013. The Sarcolipin-bound Calcium Pump Stabilizes Calcium Sites exposed to the Cytoplasm. Nature 495:265 Faxen K et al. 2011. Characterisation of a Listeria monocytogenes calcium pump - a SERCA type ATPase with only one Ca2+-binding site. J Biol Chem 286:1609

Donor–Acceptor Conjugated Polymers Based on Dithieno[3,2-b:3′,2′-b′]naphtho[1,2-b:5,6-b′]dithiophene: Synthesis and Semiconducting Properties

A polycyclic aromatic unit comprising six rings, i.e., 5,11-bis(2-octyldodecyl)dithieno[3,2-b:3′,2′-b′]naphtho[1,2-b:5,6-b′]dithiophene (DTNDT), was developed. Four donor–acceptor (D–A) conjugated polymers, which are named P-BT, P-2FBT, P-IID, and P-DPP, were synthesized with DTNDT as the D-unit and 2,1,3-benzothiadiazole (BT), 5,6-difluorobenzo[c][1,2,5]thiadiazole (2FBT), isoindigo (IID), and diketopyrrolopyrrole (DPP) as the A-unit, respectively. All four polymers are thermally stable with decomposition temperature above 390 °C and show pseudo-straight-shaped backbones. Their ordered thin films were prepared via solution spin-casting, in which conjugated backbones mainly adopted edge-on alignment on the substrate. The semiconducting properties of the polymers were characterized with bottom gate and top contact (BGTC) organic thin film transistors (OTFTs). All four polymers showed p-type transport behavior, and the hole mobilities were 0.023, 0.078, 0.50, and 1.80 cm2/(V s) for P-BT, P-2FBT, P-IID, and ...

Modeling p-type charge transport in thienoacene analogs of pentacene

The charge transport properties of two fused-ring thienoacenes, (a) the syn-isomer of dibenzo-thieno-dithiophene (DBTDT), packing in the solid state with a π–π stacking arrangement and also known as bis-benzo-thieno-thiophene (BBTT) and (b) C6-DBTDT, an alkylated derivative, packing in the more conventional herring-bone arrangement, are investigated computationally in the framework of the non-adiabatic hopping mechanism. Charge transfer rate constants are computed within the Marcus–Levich–Jortner formalism including a single effective mode treated quantum mechanically and are injected in a kinetic Monte Carlo scheme to propagate the charge carrier in the crystal. Charge mobilities are computed at room temperature with and without the influence of an electric field and are shown to compare very well with the measured mobilities in single-crystal devices. Both systems show an almost 1D charge transport with C6-DBTDT displaying about a ten times larger mobility value, in agreement with experiment. It is shown that the role of the HOMO-1 orbital is not relevant for BBTT, while it might contribute to a more marked 2D charge transport character for C6-DBTDT.

Sub-10 nm copper chromium oxide nanocrystals as a solution processed p-type hole transport layer for organic photovoltaics

Solution processed <10 nm CuCrO2 nanocrystals are demonstrated as an efficient p-type hole transport layer for organic photovoltaic devices.

P-i-n/n-i-p type planar hybrid structure of highly efficient perovskite solar cells towards improved air stability: synthetic strategies and the role of p-type hole transport layer (HTL) and n-type electron transport layer (ETL) metal oxides

There has been fast recent progress in perovskite solar cells (PSCs) towards low cost photovoltaic technology. Organometal mixed halide (MAPbX or FAPbX) perovskites are the most promising light absorbing material sandwiched between the electron transport layer (ETL) and hole transport layer (HTL). These two layers play a critical role in boosting the power conversion efficiency (PCE) and maintaining air stability. However, the device stability is a serious issue in regular as well as p-i-n inverted type perovskite solar cells. This mini-review briefly outlines the state-of-art of p-i-n/n-i-p type planar hybrid perovskite solar cells using MAPbX/FAPbX perovskite absorbing layers. Later, we will focus on recent trends, progress and further opportunities in exploring the air stable hybrid planar structure PSCs.

Genetic characterization and identification of single nucleotide polymorphisms of ATP1A1 gene in Indian humped cattle

Climate change in India is likely to aggravate the heat stress in dairy animals due to rise in temperature coupled with increased precipitation. In animals heat stress affects the alteration of plasma Potassium (K (+)) and Sodium Na (+) ions. ATP1A1 gene belongs to the family of P-type cation transport ATPases, and to the subfamily of Na+/K+ -ATPases. Na+/K+ -ATPase is an integral membrane protein responsible for establishing and maintaining the electrochemical gradients of Na+ and K+ ions across the plasma membrane. The present study is aimed to investigate the polymorphisms in the entire coding region of ATP1A1 gene in Bos indicus (Deoni) cattle by PCR- Single-Strand Conformation Polymorphism (PCR- SSCP) and direct sequencing of variants. Sequence analysis showed 16 SNPs, of which 5 SNPs were in the coding region and the remaining 11 SNPs were detected in the non-coding region of ATP1A1 gene. All the observed variations in the coding regions of ATP1A1 gene were silent mutations. The genotypic, allelic frequencies, c<sup>2</sup> test for Hardy-Weinberg equilibrium and Shannon’s information index were calculated using POPGENE-32. The study revealed a high degree of genetic variability in ATP1A1 gene in the Deoni cattle population which indicated the utility of this gene for further studies for identification of markers associated with heat tolerance in Indian humped cattle for using in marker assisted selection for heat tolerance.

Epindolidione-Based Conjugated Polymers: Synthesis, Electronic Structures, and Charge Transport Properties

Development of new electron-deficient building blocks is essential to donor-acceptor conjugated polymers. Herein, epindolidione (EPD) as electron-deficient unit was integrated into conjugated polymers for the investigation of field-effect transistors for the first time. We systematically studied the electronic structures and charge transport properties of the EPD-based donor-acceptor polymers. They exhibit p-type transport characteristics with the highest mobility of up to 0.40 cm(2) V(-1) s(-1), thus demonstrating its great potential as a building block for polymer field-effect transistors and photovoltaics.

Synthesis, characterization and semiconducting properties of dioctyl substituted vanadyl phthalocyanines

Solution processible organic semiconductors have attracted great attention in recent years due to their applications in printable electronics, such as organic thin-film transistor (OTFT). This type of device requires semiconductors characterized by low reorganization energies and strong intermolecular electronic interaction. Phthalocyanines are 18 π -electron disc-like aromatic macrocycles with two-dimensional (2D) π -electron delocalization over the whole molecule, and are featured with low reorganization energies and close π - π stacking. Moreover, tight 2D cofacial π - π stacking, which is beneficial for charge transport in the channel of OTFTs, can be realized by incorporating axially substituted metals or large metals in the core of phthalocyanines. Introducing alkyl substituents can endow phthalocyanines good solubility in organic solvents. However, the number and positions of alkyl substituents have great influence on the packing structures thereby OTFT performance of phthalocyanines. In the current paper, four dioctyl substituted vanadyl phthalocyanines, i.e. 2,3-dioctyl vanadyl phthalocyanine (2,3-C8OVPc), 2,16(17)-dioctyl vanadyl phthalocyanine ( dp - C8OVPc), 1,15-dioctyl vanadyl phthalocyanine (1,15-C8OVPc) and 1,18-dioctyl vanadyl phthalocyanine ( dp -C8OVPc), were synthesized, and the effect of the positions of octyl groups on their photophysical properties, OTFT performance was studied in detail. All four compounds are soluble in organic solvents such as chloroform and exhibit excellent thermal stability with the decomposition temperature ( T d) beyond 400°C. In dilute solution, the positions of octyl groups have negligible influence on their absorption spectra and frontier molecular orbital energy levels. Their absorption maxima ( λ max) are all at ca. 700 nm and the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels are - 5.2 and - 3.8 eV, respectively. From solution to film, their absorption spectra exhibited a remarkable bathochromic shift. In film state, four compounds all can form ordered thin films, in which they arrange in an edge-on way. Bottom gate and top contact OTFTs based on thermally annealed films of these four compounds were fabricated via solution spin-casting. All compounds showed p-type transport behavior with field-effect mobility above 0.1 cm2/(V s) 2,3-C8OVPc displayed the best OTFT device performance. A mobility of 0.19 cm2/(V s) has been demonstrated when the films were annealed at 150°C.

Ba2TeO as an optoelectronic material: First-principles study

The band structure, optical, and defects properties of Ba2TeO are systematically investigated using density functional theory with a view to understanding its potential as an optoelectronic or transparent conducting material. Ba2TeO crystallizes with tetragonal structure (space group P4/nmm) and with a 2.93 eV optical bandgap [Besara et al., J. Solid State Chem. 222, 60 (2015)]. We find relatively modest band masses for both electrons and holes suggesting applications. Optical properties show infrared-red absorption when doped. This could potentially be useful for combining wavelength filtering and transparent conducting functions. Furthermore, our defect calculations show that Ba2TeO is intrinsically p-type conducting under Ba-poor condition. However, the spontaneous formation of the donor defects may constrain the p-type transport properties and would need to be addressed to enable applications.

Suppressing spontaneous polarization of p-GaN by graphene oxide passivation: augmented light output of GaN UV-LED.

GaN-based ultraviolet (UV) LEDs are widely used in numerous applications, including white light pump sources and high-density optical data storage. However, one notorious issue is low hole injection rate in p-type transport layer due to poorly activated holes and spontaneous polarization, giving rise to insufficient light emission efficiency. Therefore, improving hole injection rate is a key step towards high performance UV-LEDs. Here, we report a new method of suppressing spontaneous polarization in p-type region to augment light output of UV-LEDs. This was achieved by simply passivating graphene oxide (GO) on top of the fully fabricated LED. The dipole layer formed by the passivated GO enhanced hole injection rate by suppressing spontaneous polarization in p-type region. The homogeneity of electroluminescence intensity in active layers was improved due to band filling effect. As a consequence, the light output was enhanced by 60% in linear current region. Our simple approach of suppressing spontaneous polarization of p-GaN using GO passivation disrupts the current state of the art technology and will be useful for high-efficiency UV-LED technology.

Slow recombination in quantum dot solid solar cell using p–i–n architecture with organic p-type hole transport material

The interfaces between different materials in the heterojunction colloidal quantum dot (QD) solar cell play an important role for charge carrier separation, recombination and collection.

NaCu6Se4: a layered compound with mixed valency and metallic properties.

A new ternary compound NaCu6Se4 was synthesized from the reaction of Cu in a molten sodium polyselenide flux. The compound crystallizes in trigonal space group R3̅m with a = 4.0465(3) Å and c = 41.493(5) Å. The crystal structure contains flat two-dimensional slabs of (1)/∞[Cu6Se4] with a unique structural arrangement, separated by Na cations. The compound contains mixed valency and has a high conductivity of ∼3 × 10(3) S cm(-1) at room temperature, and exhibits increasing conductivity with decreasing temperature, indicating metallic behavior. A small positive thermopower (4-11 μV K(-1) from 300 to 500 K) and Hall effect measurements indicate p-type transport with a carrier concentration of ∼2.8(3) × 10(21) cm(-3) and a hole mobility of ∼8.75 cm(2) V(-1) s(-1) at 300 K. NaCu6Se4 exhibits temperature-independent Pauli paramagnetism.