Increase In Defect Concentration Research Articles

Modulation of micro-structural, opto-electronic and photo-induced fluorescence properties in sol-gel derived Pb1-xZnxO nanoparticles through the analytical study of vacancy-type defects

In the present work, the doping effect of Zn2+ ion (varying doping concentrations in the range of 0% to 30%) on PbO nanoparticles (NPs) has been investigated proficiently. This study aims at in-depth analysis of the structure-property relationships of the sol-gel derived Zn doped PbO (Pb1-xZnxO) NPs, especially the vacancy evolved properties and the luminescence properties. The X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), field emission scanning electron microscopy (FESEM) and Fourier-transform infrared (FT-IR) spectroscopic characterization analyses justified the nanocrystallinity of the Pb1-xZnxO powdered NPs while the mean crystallite sizes were located in between 12–36 nm range. Williamson – Hall (W – H) method revealed a monotonous increase of the lattice strain which is compatible with the decrease of NPs’ crystallite size by increase in the Zn2+ doping level. The replacement of Pb2+ ions with the Zn2+ ions caused the reduction of crystallite size by the higher Zn2+ doping level. Prominent peaks of Zn, Pb and O elements are noticed in energy dispersive X-ray spectroscopic (EDS) characterization. The elemental distributions of the chemicals present in the NPs were explored by the elemental mapping analysis. The optical absorption (OA) analysis indicated that the energy band gap (Eg) can be estimated to be 2.21, 2.36, 2.55 and 2.70 eV for 0, 10, 20 & 30% Zn doped PbO NPs, respectively. The positron annihilation lifetime (PAL) spectroscopic studies evidenced the presence of vacancy type defects within the NPs and an increase in defect concentrations has been observed by the increase in Zn concentrations. The photo-induced fluorescence (FL) emission spectra exhibited three luminescence peaks around the wavelengths 430 nm, 490 nm and 522 nm for all the NPs. The observations suggested the possibility of tailoring the characteristics of the synthesized NPs for practical applications in the field of optoelectronics.

Green Energy Generation via Water Splitting by Non-Photocatalytic Process based on Gd Doped Magnesium Ferrite Hydroelectric Cell

This study presents compelling empirical evidence that highlights the notable effect of increased defect concentration on the splitting of water molecules in MgGdxFe2-xO4 hydroelectric cells (HECs), which serve as a promising avenue for environmentally friendly electricity generation. The MgGdxFe2-xO4 (x = 0.00, 0.02, 0.06 and 0.10) series for eco-friendly electricity generation has been successfully synthesized using a facile sol-gel technique. These materials exhibit the characteristic spinel cubic structure with the Fd-3m space group confirmed using Rietveld analysis of X-ray diffraction plots. A maximum strain of 2.06×10-3 was observed in the MgGd0.10Fe1.90O4, indicating the formation of a probable defective structure. Moreover, the X-ray density values decrease with increase in Gd concentration, suggesting an increase in porosity of the samples. Langmuir hysteresis curve follows a typical type IV pattern further consolidating the mesoscopic nature of the materials. Furthermore, the conclusive identification of defects, particularly oxygen vacancies, through Photoluminescence and X-ray Photoelectron Spectroscopic (XPS) studies, holds an utmost importance in facilitating the water dissociation process at room temperature by ferrites. Impedance spectroscopy has been employed to scrutinize the contribution of small polaron hopping-assisted ionic conduction to the observed improved current density. The maximum short circuit output current of 6.8, 10.1, and 13.4mA was achieved for MgGd0.02Fe1.98O4 (GMF-1), MgGd0.06Fe1.94O4 (GMF-2) and MgGd0.10Fe1.90O4 (GMF-3) HECs, respectively. The corresponding open cell voltage values were found to be 0.85V, 0.92V and 0.98V. Off-load peak power output was 5.78mW, 9.29mW, and 13.13mW, respectively. The estimated Gibbs free energy values were -164.02, -177.53, and -189.11 kJ/mol. MgGdxFe2-xO4-based hydroelectric cells possess the advantages of being cost-effective and yielding eco-friendly by-products without reliance on photocatalytic activity, acid/alkali solutions, or electrolytes. The incorporation of Gadolinium (Gd) dopant not only enhances the hydroelectric current but also contributes to sustained current generation over extended periods. The extended operational lifespan of the cell positions it as an excellent candidate for practical applications

Superior radiation resistance of ODS-RAFM steels revealed by Positron annihilation spectroscopy study

Oxide-dispersion-strengthened (ODS) reduced-activation ferritic/martensitic (RAFM) steels are considered as most promising structural materials for fusion reactors and other advanced nuclear systems due to its excellent irradiation resistance under high dose irradiations. However, the extreme complex synergistic effect between transmuted helium/hydrogen and displacement damage which most seriously affects the structure and mechanical properties of ODS-RAFM steels is very difficult to understand, especially the role of hydrogen still remains unclear. Taking advantage of very sensitive to small vacancy clusters of Positron annihilation spectroscopy (PAS) method, we conducted irradiation defect study on ODS-RAFM, RAFM and its corresponding model alloy Fe–9Cr and α-Fe to investigate their anti-swelling properties at the early stage of irradiation with hydrogen-helium synergism and the mechanism. Three distinct irradiation schemes including (1) single Fe ion beam, (2) simultaneous Fe and He (named Fe + He) ion beam, (3) subsequent H ion injection after Fe + He (named Fe + He/H) ion beam irradiation were performed. Hydrogen-helium synergistic effects on vacancy evolution within these steels were explored combining the first-principles calculation. The implantation of He was observed to significantly increase defect concentration among all four steels, while H exhibited interestingly complexity on affecting the evolution of helium bubbles. The H post-injection increased defect concentration obviously in the materials with abundant sinks, but improved poorly in ones with rare sinks. Through the systematic study of the interactions between H, He, and vacancies, it was revealed that even at the early irradiation stage, ODS-RAFM steels has already exhibited excellent irradiation resistance compared to other alloys across three irradiation schemes.

Enhanced photocatalytic activity of Er doped ZnO nanospindles and nanorods for degradation of organic pollutants

Rare earth doping in ZnO is an efficient way to improve the photocatalytic performance. In the present work, Er doped ZnO nanospindles and nanorods were prepared through a simple cost effective wet chemical approach and were thoroughly characterized by FESEM, XRD, Raman spectroscopy, UV–vis-DRS, UV–vis absorption and PL spectroscopy. Nanospindle and nanorod-like morphologies of the fabricated samples were revealed by FESEM. XRD analyses revealed hexagonal wurtzite structure of Er doped ZnO nanostructures and confirmed Er doping into ZnO. PL studies showed increased defect concentration in ZnO nanostructures doped with Er ions. The photodegradation ability of nanostructures was investigated using cationic and anionic dyes and photodecomposition rate of 0.042 min−1 was achieved for MB decolorization using 0.5 % Er doped ZnO sample upon 32 min of solar light illumination. The probable photodecomposition mechanism supported by in-situ radical trapping experiments and repeatability test have also been discussed and results suggest that Er doped ZnO photocatalyst exhibit potential for use as commercial solar-active photocatalysts.

Phase Relationship and Ni Solubility in Nanoparticles of Ce0.9Zr0.1O2

AbstractThe phase relationship, defect formation, and incorporation of Ni in Ce0.9Zr0.1O2 have been investigated in samples of nominal composition (Ce0.9Zr0.1)1‐xNixO2‐δ with x=0.03, 0.05 and 0.1, synthesized by a cation complexation route and heat treated at 600, 800 and 1000 °C. Several structural (XRD, XAS, HRTEM) and spectroscopic (XPS, Raman) techniques have been used. Our data show the lattice parameters determined from XRD do not significantly vary with the Ni content or annealing temperature. The increasing defect concentration with increasing Ni content revealed by Raman spectra was associated to the formation of oxygen vacancies in the bulk due to coexistence of NiO and Ce0.9Zr0.1O2. On the other hand, no variation in the oxygen vacancies concentration was detected at the surface with increasing the Ni content by XPS data. In those samples with the lowest Ni concentrations (3 and 5 %) and heat treated at 600 °C, the analysis of the EXAFS zone of the K‐edge of Ni indicates that local order around Ni cations is not long‐range, suggesting the presence of a noncrystalline phase. When the Ni content is higher (10 %) and/or the temperature of the thermal treatment is increased, the crystallization of NiO is clearly detected by XRD, EXAFS and HRTEM.

Computational analysis of electronic structure and optical properties of monocrystalline silicon-vacancy defect system based on density functional theory

Monocrystalline silicon is an important substrate or base material for manufacturing integrated circuit chips, mirrors, etc. However, it is a typical hard and brittle material, which is very prone to produce defects during processing. This paper investigates the electronic structure and optical properties of sphalerite monocrystalline silicon with vacancy concentrations of 1.5625%, 3.125%, 4.6875%, and 6.25% using the first principles method based on density functional theory. The results demonstrate that the introduction of impurities results in the formation of impurity bands (IB) within the band structure, thereby facilitating electronic transitions. However, vacancy defects do not alter the properties of monocrystalline silicon as an indirect semiconductor. Regarding optical properties, an increase in defect concentration leads to a decrease in the macroscopic symmetry of the system, resulting in noticeable anisotropy in each property. Also found that the main spectral peaks of the defect system are red-shifted, and the vacancy defects introduce new peaks in the near-infrared region and the visible region with increasing intensity, but the peaks in the ultraviolet region gradually decrease with the increase of the defect concentration. The refractive index peak gradually decreases with the increase of defect concentration, and the calculated average refractive index is around 1.2. In the high-energy region, the refractive index takes a very small value, and the reflection of electromagnetic waves from the doped system is also weak at this time, which indicates that the system has a high transmittance property. Importantly, there is a higher intensity of energy loss at photon energies around 16.5 eV. Consequently, these calculations are deemed valuable for advancing research and applications involving monocrystalline silicon optical mirrors.

Interfacial thermal conductance of multilayer graphene/MoS2 heterostructure

We investigated the Interfacial thermal conductance (ITC) with a heterogeneous structure of a bilayer of MoS2 embedded in the middle of four graphene layers by non-equilibrium molecular dynamics (NEMD). Surprisingly, the ITC of MoS2/MoS2 (M/M) is significantly higher than that of the graphene/MoS2 (G/M). Interestingly, changes in the cross-sectional dimensions do not affect the ITC of the G/M and M/M, as the constant interface spacing preserves their structural characteristics so that phonon mean free range remains unchanged. Intriguingly, the interfacial strain affects the ITC notably. A 10% compression strain increases the G/M ITC by 100%, while a 10% tension strain reduces it by 70%. Unexpectedly, increasing defect concentration near the G/M interface leads to a decrease in thermal conductance. We find that graphene plays a dominant role in heat conduction within the heterostructure, while defects primarily enhanced low-frequency phonon vibrations of graphene, with MoS2 vibrations remaining largely unaffected. Due to the increase in defect rate, the out-of-plane phonon coupling is weakened, thus leading to a decrease in G/M ITC. These findings provide concise insights into the heat conduction of G/M heterostructures.

Improving high-field strain and temperature stability on KNN-based ceramics sintered in reducing atmosphere via defect engineering

High-field strain and its temperature stability of (1–x) K0.48Na0.52Nb0.96Ta0.04O3-xBaZrO3+8%MnO+3%ZrO2 (in mole, KNNT-xBZ+8Mn) ceramics sintered in reducing atmosphere are improved simultaneously via defect design in A and B site. There is a conducting type transition from n-type to p-type at x = 0.07. The BaZrO3 dopant not only induces the increase of defects (ZrNb′, BaNa·, BaK·) concentration, but also results in the increase of defect (MnNb‴) concentration, because more Mn ions as +2 oxidation state in ceramics is triggered by BaZrO3 doping modification. Defect dipoles (MnNb′′′−Vo··, ZrNb′-Vo··, BaNa·-VNa′, BaK·-VK′) in poled and aged ceramics enhance the reversibility of the non–180° domains switching, which increases the high-field strain of KNNT-xBZ+8Mn ceramics. The reversibility of non–180° domain switching can be preserved to high temperature due to stable defect dipoles (BaNa·-VNa′, BaK·-VK′) in A-site. The KNNT-xBZ+8Mn ceramics at x = 0.07 show the largest high-field strain coefficient (543 pm/V@20 kV/cm) and the highest temperature stability (125 °C). The KNNT-xBZ+8Mn ceramic is a lead-free material with great potential to be applied in the fabrication of multilayer ceramic actuators with Ni inner electrodes in the future.

MgF2-based microwave dielectric ceramics with ultra-low sintering temperature and high thermal expansion coefficient

Ultralow-temperature co-fired ceramic (ULTCC) materials with low permittivity and dielectric loss are considered promising materials for 5 G communication applications. Herein, a novel multiphase xMgF2-(1x)LiF (x = 0.20, 0.35, 0.50, 0.65) microwave dielectric ceramic was prepared via a conventional solid-state method for ULTCC applications. The ceramic achieves densification at a sintering temperature of 625 °C. The xMgF2-(1-x)LiF ceramics exhibit tunable permittivity ranging from 5.21 to 7.30, Q×f from 39400 to 52800 GHz, and τf from − 61 to − 98 ppm °C−1. Analysis of the crystal structure and microstructure revealed that the volatilisation of fluoride ions in the ceramics led to an increase in defect concentration, contributing to an unfavourable decrease in dielectric loss. The 0.35MgF2-0.65LiF ceramic shows comprehensive properties with the highest Q×f value (52800 GHz) and low permittivity (6.40). Furthermore, the thermal expansion coefficient is an important performance parameter in ceramic packaging with the 0.35 MgF2-0.65 LiF ceramic exhibiting a colossal thermal expansion coefficient of 28.69 ppm °C−1, thus enabling excellent compatibility with printed circuit board (PCB) substrates. Moreover, these high thermal expansion coefficient ceramics are excellent candidates for packaging.

New insights into the effect of hard carbons microstructure on the diffusion of sodium ions into closed pores

Closed pores formed in hard carbons play an essential role in sodium storage at plateau region. However, the effect of different structural features on the diffusion of sodium ions into closed pores remains unclear. Herein, a precursor reconstruction strategy is conducted to regulate carbon microstructures including interlayer spacing, defect concentration, and closed pore volume by changing the ratio of aromatic and polysaccharide components. Aromatic structure parts tend to develop disordered carbons with fewer defects, larger interlayer spacing, and smaller closed pore volume, while polysaccharide components prefer to form disordered carbons with more defects, smaller interlayer spacing, and larger closed pore volume. Through the correlation analysis of microstructure features and the sodium storage capacity below 0.1 V. It finds that the intercalation capacity is proportional to the ratio of pseudo-graphitic domains, whereas the pore filling capacity appeared at lower potential gradually decreases with the increasing defect concentration due to homo-ionic repulsion effect, without linear correlation with short-range microcrystalline and closed pore volume. The optimized sample with suitable interlayer spacing and defect concentration exhibits a high plateau capacity of 241.7 mAh/g. This work provides insights into the exploitation of closed pore sodium storage performance.

Defect-induced electron rich nanodomains in CoSe0.5S1.5/GA realize fast ion migration kinetics as sodium-ion capacitor anode

Optimizing charge migration and alleviating volume expansion in anode materials are the key to improve the electrochemical performance for sodium-ion storage devices. Herein, a hierarchical porous conducting matrix confining defect-rich selenium doped cobalt dichalcogenide (CoSe0.5S1.5/GA) is constructed as a promising SICs anode based on the guidance of theoretical calculation analysis. The increased defect concentration significantly enhanced the disorder degree of the compound and presented electron aggregation around the S atoms, which effectively modulated the electronic structure, further enabling high rate and ultra-capacity sodium storage. Moreover, strong interfacial coupling could construct spatial constraint to alleviate volume expansion as well as maintain electrode integrity and stability. The CoSe0.5S1.5/GA electrode can deliver a high capacity of 310.1 mA h g−1 after 2000 cycles at 1 A g−1, and the CoSe0.5S1.5/GA//AC sodium ion capacitor can exhibit an outstanding energy density of 237.5 W h kg−1. A series of characterization and theoretical calculation convincingly reveal that the defect moieties can regulate the Na+ storage and diffusion kinetics, which prove that our defect manufacture coupling with space-confined strategy can provide deep insights into the development of high-performance Na+ storage devices.

Concentration characterization of underlying intrinsic defects accompany with surface structural defects and their effect on laser damage resistance

During ultra-precision processing of potassium dihydrogen phosphate (KDP) crystals, various macro-structural surface defects are inevitably introduced, but there is no monotonic relationship between different macro-defects and laser-induced damage threshold (LIDT). Therefore, a single macro-perspective cannot fundamentally reveal the causation for low LIDT. In this work, energy, photoelectron spectra characterization and photoluminescence characteristics of surface were adopted to determine the type and concentration of intrinsic defects accompany with macro-structural defects. First-principles calculation was applied to explore the influence of oxygen vacancy (VO) defect concentration on performance in terms of crystal structure, electronic structure, and optical properties. The results show that the causation for low LIDT of cracks is VO defects. With the increase of VO defect concentration, PO43- group would collapse, leading to a decrease in the stability of crystal structure. High concentration of VO defects would introduce defective-energy level, causing irreversible alteration in energy level. Free electrons are susceptible to absorb photons and transition due to defective-energy level, severely reducing the laser damage resistance of components. This work reveals the influence of surface defects on laser damage from intrinsic defects at atomic-level, which is significance for the suppression of surface defects during ultra-precision processing and effective improvement of laser damage resistance of KDP.

Non-monotonic effect of growth pressure on the responsivity of AlGaN ultraviolet Schottky detectors

Three AlGaN-based Schottky detector samples grown with varying pressure conditions are prepared and their responsivity is investigated. It is found that the responsivity of the three samples first increases and then decreases with the increase of pressure. In addition, the vacancy defect concentration increases and carbon impurities concentration decreases when the reactor pressure increases from 100 mbar to 200 mbar during the i-AlGaN layer growth. It is assumed that carbon impurities and vacancy defects play a negative role in detector’s performance, which increase the recombination of photogenerated carriers and reduce detector responsivity. The relationship between growth pressure and detector responsivity is not linear. It is necessary to select a suitable growth pressure to improve the performance of AlGaN detectors.

The effect of defects induced by polarization on bandgap evolution and photovoltaic performance in KN-based semiconducting ferroelectric ceramics

The high-field polarization enables bandgap-engineered ferroelectric perovskite oxides to further enhance their photovoltaic performance. However, research on the mechanism of the high-field polarization-enhanced ferroelectric photovoltaic effect lacks understanding in terms of bandgap evolution. In this work, the ceramics [KNbO3]1−x−[SrNi0.5Hf0.5O3−δ]x(KNSNH100x, x = 0.02 − 0.08), prepared by the solid phase method, exhibit good ferroelectricity and four absorption bandgaps, three of which have sub-bandgaps generated by Ni. The effect of increased defects induced by high-field polarization on bandgap evolution and photovoltaic properties was investigated. The increase in defect concentration in KNSNH2 induced by high-field polarization is the cause of the variation in bandgap structure in KNSNH2. Structural refinement suggests that the change in the bandgap after polarization can be induced by the lattice distortion. The evolution of bandgap structure after polarization in KNSNH2 lead to an enhancement of visible light absorption, which further improve the photovoltaic performance by produced more carriers. A two-fold enhancement of short-circuit photocurrent density (Jsc) under simulated solar irradiation is achieved in the KNSNH2 sample by polarization. This work provides new insights into the effect of defect induced by polarization on enhancing ferroelectric photovoltaic performance and the mechanism of bandgap evolution.

Insights into the carbonization mechanism of bituminous coal-derived carbon materials for lithium-ion and sodium-ion batteries

Despite recent interest in the low-temperature carbonization of coal to prepare disordered carbon materials for the anodes of lithium-ion (LIBs) and sodium-ion batteries (SIBs), the carbonization mechanism is still poorly understood. We selected bituminous coal as the raw material and investigated the chemical, microcrystal, and pore structure changes during the carbonization process from coal to the resulting disordered carbon. These structural changes with temperature below 1 000 °C show an increase in both interlayer spacing (3.69–3.82 Å) and defect concentration (1.26–1.90), accompanied by the generation of a large amount of nano-microporous materials. These changes are attributed to the migration of the local carbon layer and the release of small molecules. Furthermore, a decrease in interlayer spacing and defect concentration occurs between1 000 °C and 1 600 °C. In LIBs, samples carbonized at 1 000 °C showed the best electrochemical performance, with a reversible capacity of 384 mAh g−1 at 0.1 C and excellent rate performance, maintaining 170 mAh g−1 at 5 C. In SIBs, samples carbonized at 1 200 °C had a reversible capacity of 270.1 mAh g−1 at 0.1 C and a high initial Coulombic efficiency of 86.8%. This study offers theoretical support for refining the preparation of carbon materials derived from coal.

Low-temperature sintering of PLSZT-based antiferroelectric ceramics in reducing atmosphere for energy storage

Due to their elevated sintering temperature, pure PLZST-based antiferroelectric ceramics are unsuitable for co-firing with copper internal electrodes as MLCC dielectric materials. In this work, PLZST ceramic materials sintered at low temperature in reducing atmosphere were obtained through a unique BASK glass additive and Y3+ co-doping. While the sintering temperature of ceramics is reduced to 1040 °C, stable defect association (YPb∙,YZr′) is formed by Y3+ solution entering A/B site, which effectively inhibits the increase of defect concentration and promotes ceramic sintering. The high breakdown strength of PLSZT ceramics is attributed to their compact grain and excellent insulation resistivity, which enhance their tolerance to electric fields. An ultrahigh recoverable energy density (Wrec) of 4.9 J/cm3 with a high energy storage efficiency (η) of 92.8% are achieved at an electric field of 400 kV/cm. Moreover, the AFE ceramics possess excellent discharge energy storage properties with a high discharge energy density (Wd) of 4.4 J/cm3 and a large power density (Pd) of 125 MW/cm3.

Response of CH3NH3PbI3 films to thermal exposure and proton irradiation

For the purpose of the space application, the thermal stability and proton irradiation effects of the methylammonium lead iodide (MAPbI3, MA+ = CH3NH3+) films have been investigated via the experimental and molecular dynamics (MD) simulation methods. Surface decomposition of MAPbI3 is found to occur at 100 °C, which leads to the formation of a PbI2 layer on the sample surface that suppresses the decomposition of the underlying MAPbI3. PbI2 can be further decomposed into Pb and I2 at 150 °C, creating a porous structure of the film. After 100 keV proton irradiation, the photoluminescence yield from the MAPbI3 keeps almost unchanged with proton fluences up to 1 × 1013 p/cm2, followed by a rapid decrease at the higher fluences. The proton irradiation-induced damage evolution in MAPbI3 is dominated by a pronounced defect recovery, which is owing to the fast migration of the defects in MAPbI3. However, the defect recovery efficiency decreases with increasing defect concentration. The MA component in MAPbI3 is preferentially destroyed by proton irradiation, which accounts for the optical degradation of the film. The reported results provide atomic-level insights into the thermal decomposition processes and the proton irradiation-induced damage accumulation in MAPbI3.

Molecule Dynamics Simulation of the Effects of Temperature and Vacancy Defects on the Eutectic Sensitivity of CL-20_TNT

For contemporary applications, CL-20’s energy density is the highest of any explosive, but it has a very high susceptibility and very low stability. Eutectic techniques can successfully lower CL-20’s susceptibility. However, the eutectic susceptibility can be significantly impacted by the high temperature and many flaws found in its manufacture. By removing CL-20 molecules in Materials Studio (MS) using a molecular dynamics approach, a CL-20/TNT eutectic model with various vacancy concentrations was created in this study. Equilibrium state simulations of the model were run at various temperatures to determine the corresponding kinetic parameters. The susceptibility of CL-20/TNT eutectic-containing vacancy defects is found to increase with the increase in defect concentration and with the increase in temperature, which guides the study of CL-20’s stability and the reduction of susceptibility methods in engineering preparation. Cohesive energy density and binding energy are used at the molecular level as the evaluation criteria of the susceptibility at the macroscopic level.

Change in the gas sensing mechanism and improved sensing response on ion-irradiated palladium-graphene oxide nanocomposite

In this study, we synthesized Pd-graphene oxide (Pd-GO) nanocomposite layers on SiO2/Si substrates using chemical method. Pd-GO layers were treated with swift heavy ion irradiation (100 MeV Ag ions, 1013 ions/cm2). The structural properties of the pristine as well as the ion irradiated samples were investigated using synchrotron grazing incidence x-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) techniques. XRD shows peaks corresponding to Pd (FCC, space group-Fd-3m), GO and synthetic graphite. The relative graphite peak intensities increased after ion irradiation, indicating reduction of GO. The sensor responses of nanocomposite layers towards exposure of 35 ppm H2 at 100 °C, were measured for several cycles. Ion-irradiated Pd-GO samples show enhancement in the sensing response of H2 gas by about 24% and with lower recovery times (25%), as compared to pristine Pd-GO nanocomposite samples. The change in type of conductivity from p-type gas sensing layer in pristine nanocomposite to n-type conductivity, along with an increase in conductivity (about 500 times) in ion irradiated samples were observed. The change in type of conductivity on ion-irradiation is attributed to the reduction of GO layer and the changes in conductivity on hydrogen exposure is explained due to hydrogen spill-over effect in the two-component system. The improvement in sensitivity upon ion-irradiation was due to the increase in concentration of structural defects due to electronic energy loss, as studied by SRIM simulation. This study points towards using ion induced electronic energy loss as a new tool for varying the gas sensing properties of GO based sensors.

Prediction and Control of Thermal Transport at Defective State Gr/h-BN Heterojunction Interfaces.

The control of interfacial thermal conductivity is the key to two-dimensional heterojunction in semiconductor devices. In this paper, by using non-equilibrium molecular dynamics (NEMD) simulations, we analyze the regulation of interfacial thermal energy transport in graphene (Gr)/hexagonal boron nitride (h-BN) heterojunctions and reveal the variation mechanism of interfacial thermal energy transport. The calculated results show that 2.16% atomic doping can effectively improve interfacial heat transport by more than 15.6%, which is attributed to the enhanced phonon coupling in the mid-frequency region (15-25 THz). The single vacancy in both N and B atoms can significantly reduce the interfacial thermal conductivity (ITC), and the ITC decreases linearly with the increase in vacancy defect concentration, mainly due to the single vacancy defects leading to an increased phonon participation rate (PPR) below 0.4 in the low-frequency region (0-13 THz), which shows the phonon the localization feature, which hinders the interfacial heat transport. Finally, a BP neural network algorithm is constructed using machine learning to achieve fast prediction of the ITC of Gr/h-BN two-dimensional heterogeneous structures, and the results show that the prediction error of the model is less than 2%, and the method will provide guidance and reference for the design and optimization of the ITC of more complex defect-state heterogeneous structures.