Chemical exfoliation efficacy of semiconducting WS2 and its use in an additively manufactured heterostructure graphene–WS2–graphene photodiode

In the present work, various chemical exfoliation routes for semiconducting two-dimensional (2D) layered material WS₂ are explored, which include magnetic stirring (MS), shear mixing (SM), and horn-tip (HT) sonication. Current–voltage measurements, Raman spectroscopy, and photoluminescence (PL) spectroscopy were used to characterize the drop-casted WS₂ nanosheets produced by these three techniques and our analysis revealed that HT sonication produced the most optimal dispersions. Heterostructure photodetector devices were then fabricated using inkjet printing of the HT sonicated dispersions of WS₂ and graphene. The photodetector device performance was measured using a stream of ON/OFF light pulses generated using a red laser with wavelength λ ∼ 660 nm, and an arbitrary waveform generator. From this analysis, the photoresponsivity and detectivity of the graphene–WS₂–graphene heterostructure devices were calculated to be ∼0.86 A W⁻¹ and ∼10¹³ Jones, respectively. Capacitance–voltage (C–V) and C–frequency (f) measurements were also conducted, where the V was swept from –6 V to +6 V, while the change in C was measured from f ∼ 20 kHz up to 3 MHz to gain insights into the nature of the graphene–WS₂ interface. From the C–V measurements, the C plateaued at ∼324.3 pF from ∼−4 V to +4 V for the lowest f of 20 kHz and it reduced to ∼200 pF from −6 V to ∼−4 V, and similarly from ∼4 V to 6 V, C was ∼190 pF. The decrease in C for V > +4 V and V < −4 V was attributed to the reduction of the interfacial barrier at the electrodes which is suggestive of a Schottky-based photodiode at the graphene–WS₂ interface. A sharp decrease in C from ∼315.75 pF at 25.76 kHz to ∼23.79 pF at 480 kHz (at 0 V bias) from the C–f measurements suggests a strong effect of interface trap density on C built-up at the graphene–WS₂ interface and the ensuing Schottky barrier height. Our work confirms the excellent potential of solution-cast, trilayer graphene–WS₂–graphene heterostructures as a promising photodetector platform using additively manufactured inkjet printing.

Among magnetic stirring (MS), shear mixing (SM), and horn-tip (HT) sonication for the chemical exfoliation of semiconducting WS₂, HT sonication resulted in stable dispersions which were used to demonstrate ink-jet printed graphene–WS₂–graphene photodiodes.     

Electronic phase-crossover and room temperature ferromagnetism in a two-dimensional (2D) spin lattice

Tuning of system properties such as electronic and magnetic behaviour through various engineering techniques is necessary for optoelectronic and spintronic applications. In our current work, we employ first-principles methodologies along with Monte-Carlo simulations to comprehensively study the electronic and magnetic behaviour of 2-dimensional (2D) Cr₂Ge₂Te₆ (T_c = 61 K), uncovering the impact of strain and electric field on the material. In the presence of strain, we were able to achieve high temperature magnetic ordering in the layer along with observable phase crossover in the electronic state of the system, where the system exhibited transference from semiconducting to half-metallic state. Finally, on coupling strain and electric field remarkable increase in Curie temperature (T_c) ∼ 331 K (above 5-fold enhancement from pristine configuration) was observed, which is very well above room temperature. Our inferences have shed light on a relatively new type of coupling method involving strain and electric field which may have tremendous implications in the development of 2D spintronic architecture.

In the presence of strain, high temperature magnetic ordering in Cr₂Ge₂Te₆ was observed with electronic phase crossover from semiconducting to half-metallic state. On coupling strain and electric field, the Curie temperature reaches 331 K.     

Influence of magnetic field on electrical and thermal transport in the hole doped ferromagnetic manganite: La0.9Na0.1MnO3

We report the magnetization (M), magnetostriction, electrical resistivity (ρ), thermal conductivity (κ) and thermopower (S) of polycrystalline La_0.9Na_0.1MnO₃ over a wide temperature range of 5 to 360 K. This sample undergoes a paramagnetic to ferromagnetic transition around T_C = 274 K and electrical resistivity ρ shows an insulator–metal transition around T_IM = 292 K. The sign of thermopower S is positive in the entire temperature range which indicates that majority charge carriers are holes. Thermopower exhibits a peak and thermal conductivity shows a dip at T_C in the absence of magnetic field. Large difference between the experimentally determined activation energies of ρ and S in the insulating state indicates small polaron hopping dominant conduction above T_IM. Polaron formation above T_C, was further confirmed from the anomaly observed in thermal expansion (ΔL/L₀) which shows a change in slope at T_IM. In the vicinity of T_C at 3 T applied field, magneto-thermopower (∼61.5%) is larger than magnetothermal conductivity (∼12.7%) and magnetoresistance (∼49%).

Magnetic field dependent electrical resistivity (ρ), thermal conductivity (κ) and thermopower (S) of polycrystalline La_0.9Na_0.1MnO₃ have been reported and the possible mechanisms are discussed.     

Pressure dependent half-metallic ferromagnetism in inverse Heusler alloy Fe2CoAl: a DFT+U calculations

We report the electronic and magnetic properties along with the Curie temperature (T_C) of the inverse full Heusler alloy (HA) Fe₂CoAl obtained by using the first-principles computational method. Our calculations suggests that Fe₂CoAl is a magnetic metal when treated within PBE-GGA under the applied compressive pressures. However, the implementation of electron–electron (U) (i.e., GGA+U) with varying compressive pressure (P) drastically changes the profile of the electronic structure. The application of GGA+U along with pressure induces ferromagnetic half-metallicity with an integer value of total magnetic moment ∼4.0 μ_B per unit cell. The integer value is in accordance with the Slater–Pauling''s rule. Here, we demonstrate the variation of semiconducting gap in the spin down channel. The band gap increases from 0.0 eV to 0.72 eV when increasing the pressure from 0 to 30 GPa. Beyond 30 GPa, the electronic band gap decreases, and it is completely diminished at 60 GPa, exhibiting metallic behaviour. The analysis of the computed results shows that the treatment of electron–electron interactions within GGA+U and the application of compressive pressure in Fe₂CoAl enables d–d orbital hybridization giving rise to a half-metal ferromagnet. The T_C calculated from mean field approximation (MFA) decreases up to 30 GPa and then increases linearly up to 60 GPa.

We report the electronic and magnetic properties along with the Curie temperature (T_C) of the inverse full Heusler alloy (HA) Fe₂CoAl obtained using the first-principles computational method.     

Size-dependent magnetic and magnetothermal properties of gadolinium silicide nanoparticles

Gadolinium silicide (Gd₅Si₄) nanoparticles are an interesting class of materials due to their high magnetization, low Curie temperature, low toxicity in biological environments and their multifunctional properties. We report the magnetic and magnetothermal properties of gadolinium silicide (Gd₅Si₄) nanoparticles prepared by surfactant-assisted ball milling of arc melted bulk ingots of the compound. Using different milling times and speeds, a wide range of crystallite sizes (13–43 nm) could be produced and a reduction in Curie temperature (T_C) from 340 K to 317 K was achieved, making these nanoparticles suitable for self-controlled magnetic hyperthermia applications. The magnetothermal effect was measured in applied AC magnetic fields of amplitude 164–239 Oe and frequencies 163–519 kHz. All particles showed magnetic heating with a strong dependence of the specific absorption rate (SAR) on the average crystallite size. The highest SAR of 3.7 W g⁻¹ was measured for 43 nm sized nanoparticles of Gd₅Si₄. The high SAR and low T_C, (within the therapeutic range for magnetothermal therapy) makes the Gd₅Si₄ behave like self-regulating heat switches that would be suitable for self-controlled magnetic hyperthermia applications after biocompatibility and cytotoxicity tests.

Gadolinium silicide (Gd₅Si₄) nanoparticles prepared by surfactant-assisted ball milling exhibit a size-dependent reduction in magnetic ordering temperature and a high magnetothermal effect making them suitable for magnetic hyperthermia applications.     

The spin–orbit–phonon coupling and crystalline elasticity of LaCoO3 perovskite

Based on an integrated study of magnetic susceptibility, specific heat, and thermal expansion of single-crystal LaCoO₃ free from cobalt and oxygen vacancies, two narrow spin gaps are identified before and after the phonon softening of gap size ΔE ∼ 0.5 meV in a CoO₆-octahedral crystal electric field (CEF) and the thermally activated spin gap Q ∼ 25 meV, respectively. Significant excitation of Co³⁺ spins from a low-spin (LS) to a high-spin (HS) state is confirmed by the thermal activation behavior of spin susceptibility χ^S of energy gap Q ∼ 25 meV, which follows a two-level Boltzmann distribution to saturate at a level of 50% LS/50% HS statistically above ∼200 K, without the inclusion of a postulated intermediate spin (IS) state. A threefold increase in the thermal expansion; coefficient (α) across the same temperature range as that of thermally activated HS population growth is identified, which implies the non-trivial spin–orbit–phonon coupling caused the bond length of Co^3+(LS↔HS)–O fluctuation and the local lattice distortion. The unusually narrow gap of ΔE ∼ 0.5 meV for the CoO₆ octahedral CEF between e_g–t_2g indicates a more isotropic negative charge distribution within the octahedral CEF environment, which is verified by the Electron Energy Loss Spectroscopy (EELS) study to show nontrivial La–O covalency.

Considering the before and after phonon softening, the gap in a CoO₆-octahedral crystal electric fields (CEF) and the thermally activated spin gap, were observed of ∼0.5 meV and Q ∼ 25 meV in defect-free LaCoO₃ single crystal, respectively.     

Composition design,electrical properties,and temperature stability in (1 − x)K0.44Na0.56Nb0.96Sb0.04O3-xBi0.45La0.05Na0.5ZrO3 lead-free ceramics

In this work, we designed a new system of (1 − x)K_0.44Na_0.56Nb_0.96Sb_0.04O₃-xBi_0.45La_0.05Na_0.5ZrO₃ (KNNS-xBLNZ, 0 ≤ x ≤ 0.06) ceramics, and systemically investigated both their electrical performance and temperature stability. Through optimizing the composition, a relatively good comprehensive performance (e.g., d₃₃ ∼ 455 ± 10 pC N⁻¹, k_p ∼ 0.47 ± 0.02, T_C ∼ 266 °C, strain ∼ 0.148%, and ) is obtained in the ceramics with x = 0.040, which is attributed to the construction of a rhombohedral–orthorhombic–tetragonal (R–O–T) phase boundary. Moreover, a good temperature stability of remnant polarization (P_r) as well as strain value (P_{r100 °C}/P_rRT ∼ 89.6%, P_{r180 °C}/P_rRT ∼ 73.2%, S_{100 °C}/S_RT ∼ 92.6%, S_{180 °C}/S_RT ∼ 74.1%) is gained in KNNS-0.040BLNZ ceramics with a broad temperature range from room temperature to 180 °C. Hence, we believe that KNNS-xBLNZ ceramics opens a window for the practical application of lead-free ceramics.

A new system of (1 – x)K_0.44Na_0.56Nb_0.96Sb_0.04O₃-xBi_0.45La_0.05Na_0.5ZrO₃ (KNNS-xBLNZ, 0 ≤ x ≤ 0.06) ceramics was designed, and systemically investigated both their electrical performance and temperature stability.     

In situ synthesis and electronic transport of the carbon-coated Ag@C/MWCNT nanocomposite

A nanocomposite of Ag@C nanocapsules dispersed in a multi-walled carbon nanotube (MWCNT) matrix was fabricated in situ by a facile arc-discharge plasma approach, using bulk Ag as the raw target and methane gas as the carbon source. It was found that the Ag@C nanocapsules were ∼10 nm in mean diameter, and the MWCNTs had 17–32 graphite layers in the wall with a thickness of 7–10 nm, while a small quantity of spherical carbon cages (giant fullerenes) were also involved with approximately 20–30 layers of the graphite shell. Typical dielectric behavior was dominant in the electronic transport of Ag@C/MWCNT nanocomposites; however, this was greatly modified by metallic Ag cores with respect to pure MWCNTs. A temperature-dependent resistance and I–V relationship provided evidence of a transition from Mott–David variable range hopping [ln ρ(T) ∼ T^−1/4] to Shklovskii–Efros variable range hopping [ln ρ(T) ∼ T^−1/2] at 5.4 K. A Coulomb gap, Δ_C ≈ 0.05 meV, was obtained for the Ag@C/MWCNT nanocomposite system.

An electric transition from ln ρ(T) ∼ T^−1/4 to ln ρ(T) ∼ T^−1/2 hopping conduction happened at 5.4 K in situ synthesis of Ag@C/MWCNTs nanocomposite.     

Electrical,magnetic and magnetotransport properties of Na and Mo doped Ca3Co4O9 materials

We report the electrical, magnetic and magnetotransport properties of Na and Mo dual doped Ca_3−2xNa_2xCo_4−xMo_xO₉ (0 ≤ x ≤ 0.15) polycrystalline samples. The results indicate that the strength of ferrimagnetic interaction decreases with increase in doping, as is evident from the observed decrease in Curie temperatures (T_C). The substitution of non-magnetic Mo⁶⁺ ions (4d⁰) in CoO₂ layers and the presence of oxygen vacancies are responsible for decrease in ligand field strength, which results in an enhanced magnetization in the low doped x = 0.025 sample due to a change from the low spin to partial high spin electron configuration. The electrical resistivity of samples exhibits a semiconducting-like behavior in the low temperature range, a strongly correlated Fermi liquid-like behavior in the intermediate temperature range, and an incoherent metal-like behavior in the temperature range 210–300 K. All the samples show a large negative magnetoresistance (MR) at low temperature with a maximum MR value of −59% for the x = 0.025 sample at 2 K and 16 T applied field. The MR values follow the observed trend in magnetization at 5 K and sharply increase below the Curie temperatures of the samples, suggesting that the ferrimagnetic interactions are mainly responsible for the decrease in electrical resistivity under an applied magnetic field.

We report the electrical, magnetic and magnetotransport properties of Na and Mo dual doped Ca_3−2xNa_2xCo_4−xMo_xO₉ (0 ≤ x ≤ 0.15) polycrystalline samples.     

Magnetic carbon nanotubes for self-regulating temperature hyperthermia

Magnetic hyperthermia can enhance the anti-tumor effects of chemotherapy. As carbon nanotubes are ideal drug carriers for chemotherapy, their combination with magnetic nanoparticles provides a novel chance for multi-modal thermo-chemotherapy. Most related work focuses on attaching Fe₃O₄ nanoparticles on carbon nanotubes, however the hyperthermia temperature for this combination can not be self-regulated due to the high Curie temperature of Fe₃O₄. In this work, magnetic Zn_0.54Co_0.46Cr_0.6Fe_1.4O₄ nanoparticles with low Curie temperature were attached onto carbon nanotubes to obtain the magnetic carbon nanotubes. The morphology, formation mechanism, magnetic properties, heat generation ability and cytotoxicity of the magnetic carbon nanotubes were investigated. These magnetic carbon nanotubes show a Curie temperature of 43 °C and a self-regulating temperature at 42.7 °C under clinically applied magnetic field conditions (frequency: 100 kHz, intensity: 200 Oe). The evaluation of in vitro cytotoxicity suggests no obvious toxicity effects under the concentrations of 6.25 μg ml⁻¹ to 100 μg ml⁻¹. This study proposed a methodology for the bespoke synthesis of magnetic carbon nanotubes with a low Curie temperature for self-regulating magnetic hyperthermia, which may be used for further research on loading drugs for multi-modal cancer therapy.

Magnetic carbon nanotubes with low Curie temperature are synthesized for self-regulating temperature in hyperthermia.     

Effect of H2 Blockade and Food on Single-Dose Pharmacokinetics of GSK1322322, a Peptide Deformylase Inhibitor Antibacterial

GSK1322322 is first in a new class of antibiotics, peptide deformylase inhibitors, and is active against multidrug-resistant respiratory and skin pathogens. Part 1 of this phase 1, randomized, single-dose (1,000 mg) study in 20 healthy volunteers compared the relative bioavailability of three different tablet formulations of GSK1322322 (fast release, intermediate release, and slow release) to that of the previously studied powder-in-bottle formulation to assess the optimal formulation for progression into clinical trials. Part 2 assessed the effect of a high-fat meal and drug interaction with an H₂ blocker and an H₂ blocker plus vitamin C on the pharmacokinetic profile of GSK1322322. Of the three tablet formulations, fast-release GSK1322322 provided pharmacokinetic profiles similar to those of the powder-in-bottle reference formulation (∼93% relative bioavailability) and was selected for progression in part 2. When GSK1322322 was administered with a high-fat meal, the maximum observed plasma concentration (C_max) was reduced by 20%, and the time to maximum plasma concentration (T_max) was delayed by 1.9 h. The exposure (area under the concentration-time curve [AUC]) increased by ∼20% compared to that in volunteers in the fasted state. Coadministration of GSK1322322 with an H₂ blocker resulted in a slight delay in absorption (T_max ∼0.75 h later) and 58 and 38% decreases in the C_max and AUC_0–∞ values, respectively, compared to GSK1322322 alone. This effect was reversed with vitamin C intake (i.e., no delay in T_max and the C_max and AUC_0–∞ values decreased by only 21 and 12%, respectively). GSK1322322 was generally well tolerated, and most adverse events were mild in intensity during both parts of the study.     

Electronic,magnetic, optical and thermoelectric properties of Ca2Cr1−xNixOsO6 double perovskites

With the help of density functional theory calculations, we explored the recently synthesized double perovskite material Ca₂CrOsO₆ and found it to be a ferrimagnetic insulator with a band gap of ∼0.6 eV. Its effective magnetic moment is found to be ∼0.23 μ_B per unit cell. The proposed behavior arises from the cooperative effect of spin–orbit coupling and Coulomb correlation of Cr-3d and Os-5d electrons along with the crystal field. Within the ferrimagnetic configuration, doping with 50% Ni in the Cr-sites resulted in a half-metallic state with a total moment of nearly zero, a characteristic of spintronic materials. Meanwhile, the optical study reveals that both ε₁^xx and ε₁^zz decrease first and then increase rapidly with increasing photon energy up to 1.055 eV. We also found optical anisotropy up to ∼14 eV, where the material becomes almost optically isotropic. This material has a plateau like region in the σ_xx and σ_zz parts of the optical conductivity due to a strong 3d–5d interband transition between Cr and Os. In addition, we performed thermoelectric calculations whose results predict that the material might not be good as a thermoelectric device due to its small power factor.

With the help of density functional theory calculations, we explored the recently synthesized double perovskite material Ca₂CrOsO₆ and found it to be a ferrimagnetic insulator with a band gap of ∼0.6 eV.     

Large magnetic entropy change and prediction of magnetoresistance using a magnetic field in La0.5Sm0.1Sr0.4Mn0.975In0.025O3

A detailed study of the structural, magnetic, magnetocaloric and electrical effect properties in polycrystalline manganite La_0.5Sm_0.1Sr_0.4Mn_0.975In_0.025O₃ is presented. The X-ray diffraction pattern is consistent with a rhombohedral structure with R$\bar{3}$c space group. Experimental results revealed that our compound prepared via a sol–gel method exhibits a continuous (second-order) ferromagnetic (FM) to paramagnetic (PM) phase transition around the Curie temperature (T_C = 300 K). In addition, the magnetic entropy change was found to reach 5.25 J kg⁻¹ K⁻¹ under an applied magnetic field of 5 T, corresponding to a relative cooling power (RCP) of 236 J kg⁻¹. We have fitted the experimental data of resistivity using a typical numerical method (Gauss function). The simulation values such as maximum resistivity (ρ_max) and metal–semiconductor transition temperature (T_M–Sc), calculated from this function, showed a perfect agreement with the experimental data. The shifts of these parameters as a function of magnetic field for our sample have been interpreted. The obtained values of β and γ, determined by analyzing the Arrott plots, are found to be T_C = 298.66 ± 0.64 K, β = 0.325 ± 0.001 and γ = 1.25 ± 0.01. The critical isotherm M (T_C, μ₀H) gives δ = 4.81 ± 0.01. These critical exponent values are found to be consistent and comparable to those predicted by the three-dimensional Ising model with short-range interaction. Thus, the Widom scaling law is fulfilled.

Rietveld refinement for the sample LSSMIO. Experimental data (the point symbols), calculated data (the solid lines), difference between them is shown at the bottom of the diagram and Bragg positions are marked by vertical bars.     

Tetrathiafulvalene: effective organic anodic materials for WO3-based electrochromic devices

Finding a new, effective anodic species is a challenge for achieving simpler low-voltage tungsten trioxide (WO₃)-based electrochromic devices (ECDs). In this work, we utilize tetrathiafulvalene (TTF) and demonstrate its reversible redox behaviors as an electrolyte-soluble anodic species. The concentration of TTF in the electrolyte is varied to optimize device performance. When the TTF concentration is low (0.01 M), a smaller maximum transmittance difference (ΔT_max ∼ 34.2%) and coloration efficiency (η ∼ 59.6 cm² C⁻¹) are measured. Although a better performance of ΔT_max ∼ 93.7% and η ∼ 74.5 cm² C⁻¹ is achieved at 0.05 M TTF, the colored state could no longer return to its original form. We conclude that 0.03 M of TTF is the appropriate concentration for high-performance WO₃ ECDs with high optical contrast and reversible EC behaviors. The irreversible EC transition at high concentrations of TTF is attributed to the agglomeration of TTF molecules.

Tetrathiafulvalene (TTF) is employed as an effective electrolyte-soluble anodic species for achieving low-voltage tungsten trioxide (WO₃)-based electrochromic devices (ECDs).     

Bilayer graphene/HgCdTe based very long infrared photodetector with superior external quantum efficiency,responsivity, and detectivity

We present a high-performance bilayer graphene (BLG) and mercury cadmium telluride (Hg_1−xCd_x=0.1867Te) heterojunction based very long wavelength infrared (VLWIR) conductive photodetector. The unique absorption properties of graphene enable a long carrier lifetime of charge carriers contributing to the carrier-multiplication due to impact ionization and, hence, large photocurrent and high quantum efficiency. The proposed p⁺-BLG/n-Hg_0.8133Cd_0.1867Te photodetector is characterized and analyzed in terms of different electrical and optical characteristic parameters using computer simulations. The obtained results are further validated by developing an analytical model based on drift-diffusion, tunneling and Chu''s methods. The photodetector has demonstrated a superior performance including improved dark current density (∼1.75 × 10⁻¹⁴ µA cm⁻²), photocurrent density (∼8.33 µA cm⁻²), internal quantum efficiency (QE_int ∼ 99.49%), external quantum efficiency (QE_ext ∼ 89%), internal photocurrent responsivity (∼13.26 A W⁻¹), external photocurrent responsivity (∼9.1 A W⁻¹), noise equivalent power (∼8.3 × 10⁻¹⁸ W), total noise current (∼1.06 fA), signal to noise ratio (∼156.18 dB), 3 dB cut-off frequency (∼36.16 GHz), and response time of 9.4 ps at 77 K. Furthermore, the effects of different external biasing, light power intensity, and temperature are evaluated, suggesting a high QE_ext of 3337.70% with a bias of −0.5 V near room temperature.

We present a high-performance bilayer graphene (BLG) and mercury cadmium telluride (Hg_1−xCd_x=0.1867Te) heterojunction based very long wavelength infrared (VLWIR) conductive photodetector.     

Solvent assisted size effect on AuNPs and significant inhibition on K562 cells

Herein, the synthesis and characterization of ideal size (∼10 and 40 nm, in diameter) AuNPs (gold nanoparticles) were reported. Two different organic solvents such as DMF (dimethyl formamide) and NMPL (N-methyl-2-pyrrolidone) were used to synthesize AuNPs along with agents reducing agents such as NaBH₄ (sodium borohydrate) and Na₃C₆H₅O₇ (sodium citrate). The combination of [(HAuCl₄)–(DMF)–(NaBH₄)] gives AuNPs with an avg. size of 10.2 nm. Similarly, the combination of [(HAuCl₄)–(NMPL)–(Na₃C₆H₅O₇)] gives AuNPs with an avg. size of 40.4 nm. The morphology of these nanoscale AuNPs has been characterized through TEM and HRTEM imaging followed by SAED for lattice parameters such as d-spacing value (2.6 Å/0.26 nm) of crystalline metal (Au) nanoparticles. Further, these unique and ideal nanoscale AuNPs were used to evaluate the potential working efficacy by using in vitro cell based studies on K562 (leukaemia) blood cancer cells. From the MTT assay results around 88% cell inhibition was measured for ∼10 nm sized AuNPs. The treated cells were stained with different fluorescent dyes such as FITC, DAPI, Rho-6G and their ruptured morphology has been reported in the respective sections. These types of ideal sized metal (Au) nanoparticles are recommended for various theranostics such as to cure breast, colon, lung and liver cancers.

Herein, the synthesis and characterization of ideal size (∼10 and 40 nm, in diameter) AuNPs (gold nanoparticles) were reported.     

Hydrazone connected stable luminescent covalent–organic polymer for ultrafast detection of nitro-explosives

Developing promising luminescent probes for the selective sensing of nitro-explosives remains a challenging issue. Porous luminescent covalent–organic polymers are one of the excellent sensing probes for trace hazardous materials. Herein, fluorescent monomers 1,1,2,2-tetrakis(4-formyl-(1,1′-biphenyl))ethane (TFBE) and 1,3,5-benzenetricarboxylic acid trihydrazide (BTCH) were selected to build a novel hydrazone connected stable luminescent covalent–organic polymer (H-COP) of high stability by typical Schiff-base reaction. The N₂ sorption study, BET surface area analysis, and TGA profile indicate the porosity and stability of this H-COP material. Such properties of the H-COP material enable a unique sensing platform for nitro-explosives with great sensitivity (Ksv ∼ 10⁶ M) and selectivity up to μM. This polymer material shows attractive selectivity and sensitivity towards phenolic nitro-explosives and other common explosives among earlier reported COP-based sensors.

A novel H-COP was synthesized through Schiff-base condensation reaction, which shows high sensitivity (K_sv ∼ 10⁶ M⁻¹) and selectivity (μM level) towards nitro-explosives.     

Futuristic electron transport layer based on multifunctional interactions of ZnO/TCNE for stable inverted organic solar cells

Solution-processed inverted bulk heterojunction (BHJ) organic solar cells (OSCs) are expected to play a significant role in the future of large-area flexible devices and printed electronics. In order to catch the potential of this inverted BHJ technology for use in devices, a solar cell typically requires low-resistance ohmic contact between the photoactive layers and metal electrodes, since it not only boosts performance but also protects the unstable conducting polymer-based active layer from degradation in the working environment. Interfacial engineering delivers a powerful approach to enhance the efficiency and stability of OSCs. In this study, we demonstrated the surface passivation of the ZnO electron transport layer (ETL) by an ultrathin layer of tetracyanoethylene (TCNE). We show that the TCNE film could provide a uniform and intimate interfacial contact between the ZnO and photo-active layer, simultaneously reducing the recombination of electron and holes and series resistance at the contact interface. After successful insertion of TCNE between the ZnO film and the active layer, the parameters, such as short circuit current density (J_sc) and fill factor (FF), greatly improved, and also a high-power conversion efficiency (PCE) of ∼8.59% was achieved, which is ∼15% more than that of the reference devices without a TCNE layer. The devices fabricated were based on a poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b : 4,5-b′]dithiophene-2,6-diyl]-[3-fluoro-2[(2-ethylhexyl)-carbonyl]-thieno[3,4-b]thiophenediyl]] (PTB7):(6,6)-phenyl C71 butyric acid methyl ester (PC71BM) blend system. These results suggest that this surface modification strategy could be readily extended in developing large-scale roll-to-roll fabrication of OSCs.

Solution-processed inverted bulk heterojunction (BHJ) organic solar cells (OSCs) are expected to play a significant role in the future of large-area flexible devices and printed electronics.     

Study of magnetic and electrical properties of Pr0.65Ca0.25Ba0.1MnO3 manganite

The magnetic properties and magnetocaloric effect (MCE) in Pr_0.65Ca_0.25Ba_0.1MnO₃ have been investigated supplemented by electrical data. X-ray diffraction shows that the sample crystallizes in the distorted orthorhombic system with the Pnma space group. Pr_0.65Ca_0.25Ba_0.1MnO₃ undergoes paramagnetic–ferromagnetic (PM–FM) phase transition at T_C ∼ 85 K. For a magnetic field change of 5 T, the maximum value of the magnetic entropy change (−ΔS^max_M) is estimated to be 4.4 J kg⁻¹ K⁻¹ around T_C with a large relative cooling power (RCP) value of 263.5 J kg⁻¹. While the modified Arrott plots suggested that the magnetic transition belongs to the second order phase transitions, the universal curves of the rescaled magnetic entropy (ΔS_M) proved the opposite. The electrical properties of Pr_0.65Ca_0.25Ba_0.1MnO₃ have been investigated using impedance spectroscopy techniques. The dc-resistivity (σ_dc) study shows the presence of semiconductor behavior. Ac-conductivity (σ_ac) analysis shows that the conductivity is governed by a hopping process. From the analysis of the alternating regime, the exponent s variation obtained is in good agreement with Mott theory. The impedance spectrum analysis reveals the presence of a relaxation phenomenon. Based on these analyzes, the sample can be modeled by an electrical equivalent circuit.

The magnetic properties and magnetocaloric effect in Pr_0.65Ca_0.25Ba_0.1MnO₃ compound have been investigated supplemented by electrical data.     

Pressure-induced phase transition of 1,5-diamino-1H-tetrazole (DAT) under high pressure

Nitrogen-rich energetic materials have attracted certain interest as promising high energy density materials (HEDMs) in recent years. Pure N₂ and nitrogen-based molecular crystals are ideal HEDMs that would polymerize under high pressure, as reported in previous literature. We selected a 1,5-diamino-1H-tetrazole (DAT) crystal, which has two kinds of molecular structures and hydrogen bonds, to study under high pressure by spectroscopy and diffraction due to its high nitrogen percentage and low sensitivities. Pressure-induced structure transitions occur at pressures of 2.3–6.6 GPa, ∼8.5 GPa, and ∼17.7 GPa. The phase transition at 2.3–6.6 GPa is related to the rotation of NH₂, and the latter two transitions are caused by both the rotation of NH₂ and the distortion of the heterocycle. Significantly, the reconstitution of the hydrogen bond may induce the rotation/distortion of the NH₂/heterocycle in the second phase transition. There is no evidence showing a transformation between the two molecular structures in the whole pressure range studied. Our investigation uncovers the phase transition mechanism of DAT under pressure, which will help to find targeted HEDMs.

DAT experiences phase transitions under pressure related to rotation of NH₂ and distortion of the heterocycle.