Link between T-Linear Resistivity and Quantum Criticality in Ambipolar Black Phosphorus.

The interplay between strong Coulomb interactions and kinetic energy leads to intricate many-body competing ground states owing to quantum fluctuations in 2D electron and hole gases. However, the simultaneous observation of quantum critical phenomena in both electron and hole regimes remains elusive. Here, we utilize anisotropic black phosphorus (BP) to show density-driven metal-insulator transition with a critical conductance ∼e2/h which highlights the significant role of quantum fluctuations in both hole and electron regimes. We observe a T-linear resistivity from the deep metallic phase to the metal-insulator boundary at moderate temperatures, while it turns to Fermi liquid behavior in the deep metallic phase at low temperatures in both regimes. An analysis of the resistivity suggests that disorder-dominated transport leads to T-linear behavior in the hole regime, while in the electron regime, the T-linear resistivity results from strong Coulomb interactions, suggestive of strange-metal behavior. Successful scaling collapse of the resistivity in the T-linear region demonstrates the link between quantum criticality and the T-linear resistivity in both regimes. Our study provides compelling evidence that ambipolar BP could serve as an exciting testbed for investigating exotic states and quantum critical phenomena in hole and electron regimes of 2D semiconductors.

Rotational Set Up Uncertainly in Non-6D Couch and its Effects in Clinical Target Volume- Planning Target Volume Margin Calculation for Different Sites.

Purpose: The purpose of this study was to estimate and incorporate rotational error to translational error for clinical target volume (CTV) to planning target volume (PTV) margin calculations for non-6D couch. Materials and Methods: The study involved cone-beam computed tomography (CBCT) images of the patients who already had treatment in Varian Trilogy Clinac. The different sites studied were brain (70 patients, 406 CBCT images), head and neck (72 patients, 356 CBCT images), pelvis (83 patients, 606 CBCT images), and breast (45 patients, 163 CBCT images). Rotational and translational patient shifts were measured with the help of Varian eclipse offline review. The rotational shift introduces translational shift as it resolved along craniocaudal and mediolateral directions. Both rotational and translational error follow normal distribution and their respective errors were used to calculate CTV-PTV margin using van Herk model. Results: Rotational effect on CTV-PTV margin contribution increases with increase in size of CTV. It also increases with increase in distance between center of mass of CTV and isocenter. These margins were more pronounce in single isocenter supraclavicular fossa-Tangential Breast plans. Conclusions: There is always rotational error in all sites and it causes shift and rotation of the target. Rotational contribution to the CTV-PTV margin depends upon geometric center of CTV and isocenter distance and also on size of CTV. CTV-PTV margins should incorporate rotational error along with transitional error.

High-Performance MnO2 Nanowire/MoS2 Nanosheet Composite for a Symmetrical Solid-State Supercapacitor.

To improve the production rate of MoS2 nanosheets as an excellent supercapacitor (SC) material and enhance the performance of the MoS2-based solid-state SC, a liquid phase exfoliation method is used to prepare MoS2 nanosheets on a large scale. Then, the MnO2 nanowire sample is synthesized by a one-step hydrothermal method to make a composite with the as-synthesized MoS2 nanosheets to achieve a better performance of the solid-state SC. The interaction between the MoS2 nanosheets and MnO2 nanowires produces a synergistic effect, resulting in a decent energy storage performance. For practical applications, all-solid-state SC devices are fabricated with different molar ratios of MoS2 nanosheets and MnO2 nanowires. From the experimental results, it can be seen that the synthesized nanocomposite with a 1:4 M ratio of MoS2 nanosheets and MnO2 nanowires exhibits a high Brunauer-Emmett-Teller surface area (∼118 m2/g), optimum pore size distribution, a specific capacitance value of 212 F/g at 0.8 A/g, an energy density of 29.5 W h/kg, and a power density of 1316 W/kg. Besides, cyclic charging-discharging and retention tests manifest significant cycling stability with 84.1% capacitive retention after completing 5000 rapid charge-discharge cycles. It is believed that this unique, symmetric, lightweight, solid-state SC device may help accomplish a scalable approach toward powering forthcoming portable energy storage applications.

Phase-Engineered Molybdenum Telluride/Black Phosphorus Van der Waals Heterojunctions for Tunable Multivalued Logic.

Recently, multivalued logic (MVL) circuits have attracted tremendous interest due to their ability to process more data by increasing the number of logic states rather than the integration density. Here, we fabricate logic circuits based on molybdenum telluride (MoTe2)/black phosphorus (BP) van der Waals heterojunctions with different structural phases of MoTe2. Owing to the different electrical properties of the 2H and mixed 2H +1T' phases of MoTe2, tunable logic devices have been realized. A logic circuit based on a BP field-effect transistor (FET) and a BP/MoTe2 (2H + 1T') heterojunction FET displays the characteristics of binary logic. However, a drain voltage-controlled transition from binary to ternary logic has been observed in BP FET- and BP/ MoTe2 (2H) heterojunction FET-based logic circuits. Also, a change from binary to ternary characteristics has been observed in BP/MoTe2 (2H)-based inverters at low temperature below 240 K. We believe that this work will stimulate the assessment of the structural phase transition in metal dichalcogenides toward advanced logic circuits and offer a pathway to substantialize the circuit standards for future MVL systems.

Carrier Induced Hopping to Band Conduction in Pentacene.

Charge transport in organic thin films which are generally polycrystalline is typically limited by the localization of the carriers at lattice defects resulting in low carrier mobilities and carriers move from one state to another state by hopping. However, charge transport in organic semiconductors in their single crystalline phase is coherent due to band conduction and mobilities are not limited by disorder resulting in higher carrier mobility. So it is a challenge to enhance the carrier mobility in a thin film which is the preferred choice for all organic devices. Here, we show that it is possible to increase the carrier mobility in polycrystalline thin films by injecting sufficient carriers such that Fermi level can be moved into the region of high density in Gaussian density of states of molecular solids. When the hopping transport happens through the molecular energy levels whose density is low, mobility is decided by incoherent transport however, when the the hopping transport happens through the energy levels with high density, mobility is decided by coherent transport, as in band conduction. We present results highlighting the observation of both band-like and hopping conduction in polycrystalline organic thin films by varying the concentration of injected charge. More importantly the transition from hopping to band transport is reversible. The observed carrier mobilities in both the regimes match well with theoretical estimates of hopping mobility and band mobility determined from first principles density functional theory.

Ferromagnetism from non-magnetic ions: Ag-doped ZnO.

To develop suitable ferromagnetic oxides with Curie temperature (TC) at or above room temperature for spintronic applications, a great deal of research in doping ZnO with magnetic ions is being carried out over last decade. As the experimental results on magnetic ions doped ZnO are highly confused and controversial, we have investigated ferromagnetism in non-magnetic ion, Ag, doped ZnO. When Ag replaces Zn in ZnO, it adopts 4d9 configuration for Ag2+ which has single unpaired spin and suitable exchange interaction among these spins gives rise to ferromagnetism in ZnO with above room temperature TC. Experimentally, we have observed room temperature ferromagnetism (RTFM) in Ag-doped ZnO with Ag concentration varied from 0.03% to 10.0%. It is shown that zinc vacancy (VZn) enhances the ferromagnetic ordering (FMO) while oxygen vacancy (VO) retards the ferromagnetism in Ag-doped ZnO. Furthermore, the theoretical investigation revealed that VZn along with Ag2+ ions play a pivotal role for RTFM in Ag-doped ZnO. The Ag2+-Ag2+ interaction is ferromagnetic in the same Zn plane whereas anti-ferromagnetic in different Zn planes. The presence of VZn changes the anti-ferromagnetic to ferromagnetic state with a magnetic coupling energy of 37 meV. Finally, it has been established that the overlapping of bound magnetic polarons is responsible for RTFM in low doping concentration. However, anti-ferromagnetic coupling sets in at higher doping concentrations and hence weakens the FMO to a large extent.

Origin of ferromagnetism in Cu-doped ZnO.

It is widely reported during last decade on the observation of room temperature ferromagnetism (RTFM) in doped ZnO and other transition metal oxides. However, the origin of RTFM is not understood and highly debated. While investigating the origin of RTFM, magnetic ion doped oxides should be excluded because it is not yet settled whether RTFM is intrinsic or due to the magnetic ion cluster in ZnO. Hence, it is desirable to investigate the origin of RTFM in non-magnetic ion doped ZnO and Cu-doped ZnO will be most suitable for this purpose. The important features of ferromagnetism observed in doped ZnO are (i) observation of RTFM at a doping concentration much below than the percolation threshold of wurtzite ZnO, (ii) temperature independence of magnetization and (iii) almost anhysteretic magnetization curve. We show that all these features of ferromagnetism in ZnO are due to overlapping of bound magnetic polarons (BMPs) which are created by exchange interaction between the spin of Cu2+ ion and spin of the localized hole due to zinc vacancy [Formula: see text]. Both the experimental and theoretical investigation show that the exchange interaction between Cu2+-Cu2+ ions mediated by [Formula: see text] is responsible for RTFM in Cu-doped ZnO.

Multifunctional van der Waals Broken-Gap Heterojunction.

The finite energy band-offset that appears between band structures of employed materials in a broken-gap heterojunction exhibits several interesting phenomena. Here, by employing a black phosphorus (BP)/rhenium disulfide (ReS2 ) heterojunction, the tunability of the BP work function (Φ BP ) with variation in flake thickness is exploited in order to demonstrate that a BP-based broken-gap heterojunction can manifest diverse current-transport characteristics such as gate tunable rectifying p-n junction diodes, Esaki diodes, backward-rectifying diodes, and nonrectifying devices as a consequence of diverse band-bending at the heterojunction. Diversity in band-bending near heterojunction is attributed to change in the Fermi level difference (Δ) between BP and ReS2 sides as a consequence of Φ BP modulation. No change in the current transport characteristics in several devices with fixed Δ also provides further evidence that current-transport is substantially impacted by band-bending at the heterojunction. Optoelectronic experiments on the Esaki diode and the p-n junction diode provide experimental evidence of band-bending diversity. Additionally, the p+ -n-p junction comprising BP (38 nm)/ReS2 /BP(5.8 nm) demonstrates multifunctionality of binary and ternary inverters as well as exhibiting the behavior of a bipolar junction transistor with common-emitter current gain up to 50.

Van der Waals Broken-Gap p-n Heterojunction Tunnel Diode Based on Black Phosphorus and Rhenium Disulfide.

The broken-gap (type III) van der Waals heterojunction is of particular interest, as there is no overlap between energy bands of its two stacked materials. Despite several studies on straddling-gap (type I) and staggered-gap (type II) vdW heterojunctions, comprehensive understanding of current transport and optoelectronic effects in a type-III heterojunction remains elusive. Here, we report gate-tunable current rectifying characteristics in a black phosphorus (BP)/rhenium disulfide (ReS2) type-III p-n heterojunction diode. Current transport in this heterojunction was modeled using the Simmons approximation through direct tunneling and Fowler-Nordheim tunneling in lower- and higher-bias regimes, respectively. We showed that a p-n diode based on a type-III heterojunction is mainly governed by tunneling-mediated transport, but that transport in a type-I p-n heterojunction is dominated by majority carrier diffusion in the higher-bias regime. Upon illumination with a 532 nm wavelength laser, the BP/ReS2 type-III p-n heterojunction showed a photo responsivity of 8 mA/W at a laser power as high as 100 µW and photovoltaic energy conversion with an external peak quantum efficiency of 0.3%. Finally, we demonstrated a binary inverter consisting of BP p-channel and ReS2 n-channel thin film transistors for logic applications.

Alternating Current Dielectrophoresis Optimization of Pt-Decorated Graphene Oxide Nanostructures for Proficient Hydrogen Gas Sensor.

Alternating current dielectrophoresis (DEP) is an excellent technique to assemble nanoscale materials. For efficient DEP, the optimization of the key parameters like peak-to-peak voltage, applied frequency, and processing time is required for good device. In this work, we have assembled graphene oxide (GO) nanostructures mixed with platinum (Pt) nanoparticles between the micro gap electrodes for a proficient hydrogen gas sensors. The Pt-decorated GO nanostructures were well located between a pair of prepatterned Ti/Au electrodes by controlling the DEP technique with the optimized parameters and subsequently thermally reduced before sensing. The device fabricated using the DEP technique with the optimized parameters showed relatively high sensitivity (∼10%) to 200 ppm hydrogen gas at room temperature. The results indicates that the device could be used in several industry applications, such as gas storage and leak detection.