Hydrogen-induced phase stability and phonon mediated-superconductivity in two-dimensional van der Waals Ti2C MXene monolayer

Herein, we report the phase stability of the hydrogenated Ti₂C MXene monolayer using an evolutionary algorithm based on density functional theory. We predict the existence of hexagonal Ti₂CH, Ti₂CH₂, and Ti₂CH₄. The dynamic and energetic stabilities of the predicted structures are verified through phonon dispersion and formation energy, respectively. The electron-phonon coupling is carefully investigated by employing isotropic Eliashberg theory. The T_c values are 0.2 K, 2.3 K, and 9.0 K for Ti₂CH, Ti₂CH₂, and Ti₂CH₄, respectively. The translation and libration adopted by stretch and bent vibrations contribute to the increasing T_c of Ti₂CH₄. The high-frequency hydrogen modes contribute to the critical temperature increase. Briefly, this work not only highlights the effect of H-content on the increments of T_c for Ti₂CH_x, but also demonstrates the first theoretical evidence of the existence of H-rich MXene in the example of Ti₂CH₄. Therefore, it potentially provides a guideline for developing hydrogenated 2D superconductive applications.

Altered electrochemical properties of iron oxide nanoparticles by carbon enhance molecular biocompatibility through discrepant atomic interaction

Recent advancement in nanotechnology seeks exploration of new techniques for improvement in the molecular, chemical, and biological properties of nanoparticles. In this study, carbon modification of octahedral-shaped magnetic nanoparticles (MNPs) was done using two-step chemical processes with sucrose as a carbon source for improvement in their electrochemical application and higher molecular biocompatibility. X-ray diffraction analysis and electron microscopy confirmed the alteration in single-phase octahedral morphology and carbon attachment in Fe3O4 structure. The magnetization saturation and BET surface area for Fe3O4, Fe3O4/C, and α-Fe2O3/C were measured as 90, 86, and 27 emu/g and 16, 56, and 89 m2/g with an average pore size less than 7 nm. Cyclic voltammogram and galvanostatic charge/discharge studies showed the highest specific capacitance of carbon-modified Fe3O4 and α-Fe2O3 as 213 F/g and 192 F/g. The in vivo biological effect of altered physicochemical properties of Fe3O4 and α-Fe2O3 was assessed at the cellular and molecular level with embryonic zebrafish. Mechanistic in vivo toxicity analysis showed a reduction in oxidative stress in carbon-modified α-Fe2O3 exposed zebrafish embryos compared to Fe3O4 due to despaired influential atomic interaction with sod1 protein along with significant less morphological abnormalities and apoptosis. The study provided insight into improving the characteristic of MNPs for electrochemical application and higher biological biocompatibility.

Development of a time of flight spectrometer based on position sensitive multi-wire proportional counters for fission fragment mass distribution studies

Characteristics and performance of a time of flight (TOF) spectrometer developed for performing fission mass distribution studies are presented. The spectrometer contains two TOF arms based on multi-wire proportional counters (MWPCs). Each arm has two MWPCs to form a start-stop detection system for TOF measurements. The start detector has an active area of 4 × 4 cm². The stop detector is a two-dimensional position sensitive MWPC with an active area of 16 × 11 cm². Salient features of the MWPCs are the use of reduced sub-millimeter wire pitches of 0.635 and 0.317 mm in the electrodes along with the use of gold plated tungsten wires of diameters 10 and 20 µm. A delay line for position electrodes is prepared using chip inductors and capacitors. Ten different configurations of MWPC were investigated for the start detector, which involved the use of three and four electrode geometries, use of different wire pitches, and use of aluminized mylar for timing electrodes. Performance results close to micro-channel plate detectors have been observed with some designs of MWPC, displaying rise times better than 2 ns with an estimated inherent time resolution of ∼100 ps FWHM. A position resolution of ∼1 mm (FWHM) has been observed. Design features of the MWPCs and their test performance results are described in this article.

Novel green phosphorene as a superior chemical gas sensing material

Green phosphorus and its monolayer variant, green phosphorene (GreenP), are the recent members of two-dimensional (2D) phosphorus polymorphs. The new polymorph possesses the high stability, tunable direct bandgap, exceptional electronic transport, and directionally anisotropic properties. All these unique features could reinforce it the new contender in a variety of electronic, optical, and sensing devices. Herein, we present gas-sensing characteristics of pristine and defected GreenP towards major environmental gases (i. e., NH₃, NO, NO₂, CO, CO₂, and H₂O) using combination of the density functional theory, statistical thermodynamic modeling, and the non-equilibrium Green's function approach (NEGF). The calculated adsorption energies, density of states (DOS), charge transfer, and Crystal Orbital Hamiltonian Population (COHP) reveal that NO, NO₂, CO, CO₂ are adsorbed on GreenP, stronger than both NH₃ and H₂O, which are weakly physisorbed via van der Waals interactions. Furthermore, substitutional doping by sulfur can selectively intensify the adsorption towards crucial NO₂ gas because of the enhanced charge transfer between p orbitals of the dopant and the analyte. The statistical estimation of macroscopic measurable adsorption densities manifests that the significant amount of NO₂ molecules can be practically adsorbed at ambient temperature even at the ultra-low concentration of part per billion (ppb). In addition, the current-voltage (I-V) characteristics of S-doped GreenP exhibit a variation upon NO₂ exposure, indicating the superior sensitivity in sensing devices. Our work sheds light on the promising application of the novel GreenP as promising chemical gas sensors.

High temperature-mediated rocksalt to wurtzite phase transformation in cadmium oxide nanosheets and its theoretical evidence

Herein, a high temperature-induced phase transformation (PT) in chemically grown CdO thin films is demonstrated, and its corresponding electronic origin further investigated by density functional theory. In particular, the cubic rocksalt to hexagonal wurtzite PT in the CdO thin film annealed at 900 °C was confirmed by X-ray diffraction (XRD), which was consistent with the high-resolution transmission electron microscopy (TEM) results. Moreover, atomic force microscopy and scanning electron microscopy clearly evidenced the morphological evolution via the formation of a nanosheet network in the wurtzite-phase CdO film. The high temperature treatment also led to a significant enhancement in the optical band gap from 2.2 to 3.2 eV, as manifested by UV-visible spectroscopy. The enhanced surface roughness of the nanosheet caused a deviation in the net dipole moment, which may break the polarizable bonds and help in reducing the average dielectric constant, resulting in a band gap opening for the transformed phase. Furthermore, X-ray absorption spectroscopy at the oxygen k-edge revealed a notable shift in the inflection point of the absorption edge, while the X-ray photoelectron spectroscopy (XPS) Cd 3d and O 1s spectra suggested a gradual reduction in the CdO2 phase with an increase in annealing temperature. In addition, different complementary techniques including Rutherford backscattering and Raman spectroscopy were exploited to understand the aforementioned PT and its structural correlation. Finally, molecular dynamics simulation together with density functional theory calculation suggested that the symmetry modification at the Brillouin zone boundary provides a succinct signature for the PT in the CdO thin film.

Anticarcinogenic activity of blue fluorescent hexagonal boron nitride quantum dots: as an effective enhancer for DNA cleavage activity of anticancer drug doxorubicin

Blue fluorescent hexagonal boron nitride quantum dots (h-BNQDs) of ∼10 nm size as an effective enhancer for DNA cleavage activity of anticancer drug doxorubicin (DOX) were synthesized using simple one-step hydrothermal disintegration of exfoliated hexagonal boron nitride at very low temperature ∼ 120 °C. Boron nitride quantum dots (BNQDs) at a concentration of 25 μg/ml enhanced DNA cleavage activity of DOX up to 70% as checked by converting supercoiled fragment into nicked circular PBR322 DNA. The interaction of BNQDs with DOX is proportional to the concentration of BNQDs, with binding constant K b ∼0.07338 μg/ml. In addition, ab initio theoretical results indicate that DOX is absorbed on BNQDs at the N-terminated edge with binding energy -1.075 eV and prevented the normal replication mechanisms in DNA. BNQDs have been shown to kill the breast cancer cell MCF-7 extensively as compared with the normal human keratinocyte cell HaCaT. The cytotoxicity of BNQDs may be correlated with reduced reactive oxygen species level and increased apoptosis in MCF-7 cells, which may be liable to enhance the anticancerous activity of DOX. The results provide a base to develop BNQD-DOX as a more effective anticancer drug.

Graphitic carbon nitride nano sheets functionalized with selected transition metal dopants: an efficient way to store CO2

Proficient capture of carbon dioxide (CO₂) is considered to be a backbone for environment protection through countering the climate change caused by mounting carbon content. Here we present a comprehensive mechanism to design novel functional nanostructures capable of capturing a large amount of CO₂ efficiently. By means of van der Waals corrected density functional theory calculations, we have studied the structural, electronic and CO₂ storage properties of carbon nitride (g-C₆N₈) nano sheets functionalized with a range of transition metal (TM) dopants ranging from Sc to Zn. The considered TMs bind strongly to the nano sheets with binding energies exceeding their respective cohesive energies, thus abolishing the possibility of metal cluster formation. Uniformly dispersed TMs change the electronic properties of semiconducting g-C₆N₈ through the transfer of valence charges from the former to the latter. This leaves all the TM dopants with significant positive charges, which are beneficial for CO₂ adsorption. We have found that each TM's dopants anchor a maximum of four CO₂ molecules with suitable adsorption energies (-0.15 to -1.0 eV) for ambient condition applications. Thus g-C₆N₈ nano sheets functionalized with selected TMs could serve as an ideal sorbent for CO₂ capture.

Light metal decorated graphdiyne nanosheets for reversible hydrogen storage

The sensitive nature of molecular hydrogen (H₂) interaction with the surfaces of pristine and functionalized nanostructures, especially two-dimensional materials, has been a subject of debate for a while now. An accurate approximation of the H₂ adsorption mechanism has vital significance for fields such as H₂ storage applications. Owing to the importance of this issue, we have performed a comprehensive density functional theory (DFT) study by means of several different approximations to investigate the structural, electronic, charge transfer and energy storage properties of pristine and functionalized graphdiyne (GDY) nanosheets. The dopants considered here include the light metals Li, Na, K, Ca, Sc and Ti, which have a uniform distribution over GDY even at high doping concentration due to their strong binding and charge transfer mechanism. Upon 11% of metal functionalization, GDY changes into a metallic state from being a small band-gap semiconductor. Such situations turn the dopants to a partial positive state, which is favorable for adsorption of H₂ molecules. The adsorption mechanism of H₂ on GDY has been studied and compared by different methods like generalized gradient approximation, van der Waals density functional and DFT-D3 functionals. It has been established that each functionalized system anchors multiple H₂ molecules with adsorption energies that fall into a suitable range regardless of the functional used for approximations. A significantly high H₂ storage capacity would guarantee that light metal-doped GDY nanosheets could serve as efficient and reversible H₂ storage materials.

Disentangling the intricate atomic short-range order and electronic properties in amorphous transition metal oxides

Solid state materials with crystalline order have been well-known and characterized for almost a century while the description of disordered materials still bears significant challenges. Among these are the atomic short-range order and electronic properties of amorphous transition metal oxides [aTMOs], that have emerged as novel multifunctional materials due to their optical switching properties and high-capacity to intercalate alkali metal ions at low voltages. For decades, research on aTMOs has dealt with technological optimization. However, it remains challenging to unveil their intricate atomic short-range order. Currently, no systematic and broadly applicable methods exist to assess atomic-size structure, and since electronic localization is structure-dependent, still there are not well-established optical and electronic mechanisms for modelling the properties of aTMOs. We present state-of-the-art systematic procedures involving theory and experiment in a self-consistent computational framework to unveil the atomic short-range order and its role for the electronic properties. The scheme is applied to amorphous tungsten trioxide aWO₃, which is the most studied electrochromic aTMO in spite of its unidentified atomic-size structure. Our approach provides a one-to-one matching of experimental data and corresponding model structure from which electronic properties can be directly calculated in agreement with the electronic transitions observed in the XANES spectra.

Manipulating energy storage characteristics of ultrathin boron carbide monolayer under varied scandium doping

We report, for the first time we believe, a detailed investigation on hydrogen storage efficiency of scandium (Sc) decorated boron carbide (BC₃) sheets using spin-polarized density functional theory (DFT).

Dynamic compression of dense oxide (Gd3Ga5O12) from 0.4 to 2.6 TPa: Universal Hugoniot of fluid metals

Materials at high pressures and temperatures are of great current interest for warm dense matter physics, planetary sciences, and inertial fusion energy research. Shock-compression equation-of-state data and optical reflectivities of the fluid dense oxide, Gd3Ga5O12 (GGG), were measured at extremely high pressures up to 2.6 TPa (26 Mbar) generated by high-power laser irradiation and magnetically-driven hypervelocity impacts. Above 0.75 TPa, the GGG Hugoniot data approach/reach a universal linear line of fluid metals, and the optical reflectivity most likely reaches a constant value indicating that GGG undergoes a crossover from fluid semiconductor to poor metal with minimum metallic conductivity (MMC). These results suggest that most fluid compounds, e.g., strong planetary oxides, reach a common state on the universal Hugoniot of fluid metals (UHFM) with MMC at sufficiently extreme pressures and temperatures. The systematic behaviors of warm dense fluid would be useful benchmarks for developing theoretical equation-of-state and transport models in the warm dense matter regime in determining computational predictions.

Adsorption mechanism of graphene-like ZnO monolayer towards CO₂ molecules: enhanced CO₂ capture

This work aims to efficiently capture CO2 on two-dimensional (2D) nanostructures for effective cleaning of our atmosphere and purification of exhausts coming from fuel engines. Here, we have performed extensive first principles calculations based on density functional theory (DFT) to investigate the interaction of CO2 on a recently synthesized ZnO monolayer (ZnO-ML) in its pure, defected and functionalized form. A series of rigorous calculations yielded the most preferential binding configurations of the CO2 gas molecule on a ZnO-ML. It is observed that the substitution of one oxygen atom with boron, carbon and nitrogen on the ZnO monolayer resulted into enhanced CO2 adsorption. Our calculations show an enriched adsorption of CO2 on the ZnO-ML when substituting with foreign atoms like B, C and N. The improved adsorption energy of CO2 on ZnO suggests the ZnO-ML could be a promising candidate for future CO2 capture.

Minimally invasive burn care: a review of seven clinical studies of rapid and selective debridement using a bromelain-based debriding enzyme (Nexobrid®)

Current surgical and non-surgical eschar removal-debridement techniques are invasive or ineffective. A bromelainbased rapid and selective enzymatic debriding agent was developed to overcome these disadvantages and compared with the standard of care (SOC). The safety and efficacy of a novel Debriding Gel Dressing (DGD) was determined in patients with deep partial and full thickness burns covering up to 67% total body surface area (TBSA). This review summarizes data from seven studies, four of which were randomized clinical trials that included a SOC or control vehicle. DGD eschar debridement efficacy was >90% in all studies, comparable to the SOC and significantly greater than the control vehicle. The total area excised was less in patients treated with DGD compared with the control vehicle (22.9% vs. 73.2%, P<0.001) or the surgical/non-surgical SOC (50.5%, P=0.006). The incidence of surgical debridement in patients treated with DGD was lower than the SOC (40/163 [24.5%] vs. 119/170 [70.0%], P0.001). Less autografting was used in all studies. Long-term scar quality and function were similar in DGD- and SOCtreated. DGD is a safe and effective method of burn debridement that offers an alternative to surgical and non-surgical SOC.

Superconductivity in topological insulator Sb2Te3 induced by pressure

Topological superconductivity is one of most fascinating properties of topological quantum matters that was theoretically proposed and can support Majorana Fermions at the edge state. Superconductivity was previously realized in a Cu-intercalated Bi₂Se₃ topological compound or a Bi₂Te₃ topological compound at high pressure. Here we report the discovery of superconductivity in the topological compound Sb₂Te₃ when pressure was applied. The crystal structure analysis results reveal that superconductivity at a low-pressure range occurs at the ambient phase. The Hall coefficient measurements indicate the change of p-type carriers at a low-pressure range within the ambient phase, into n-type at higher pressures, showing intimate relation to superconducting transition temperature. The first principle calculations based on experimental measurements of the crystal lattice show that Sb₂Te₃ retains its Dirac surface states within the low-pressure ambient phase where superconductivity was observed, which indicates a strong relationship between superconductivity and topology nature.

Studies on the effect of the axial magnetic field on the x-ray bremsstrahlung in a 2.45 GHz permanent magnet microwave ion source

A compact microwave ion source has been designed and developed for operation at a frequency of 2.45 GHz. The axial magnetic field is based on two permanent magnet rings, operating in the "off-resonance" mode and is tunable by moving the permanent magnets. In order to understand the electron energy distribution function, x-ray bremsstrahlung has been measured in the axial direction. Simulation studies on the x-ray bremsstrahlung have been carried out to compare with the experimental results. The effect of the axial magnetic field with respect to the microwave launching position and the position of the extraction electrode on the x-ray bremsstrahlung have been studied.

A computational study of potential molecular switches that exploit Baird's rule on excited-state aromaticity and antiaromaticity

A series of tentative single-molecule conductance switches which could be triggered by light were examined by computational means using density functional theory (DFT) with non-equilibrium Green's functions (NEGF). The switches exploit the reversal in electron counting rules for aromaticity and antiaromaticity upon excitation from the electronic ground state (S₀) to the lowest ππ* excited singlet and triplet states (S₁ or T₁), as described by Hückel's and Baird's rules, respectively. Four different switches and one antifuse were designed which rely on various photoreactions that either lead from the OFF to the ON states (switches 1, 2 and 4, and antifuse 5) or from the ON to the OFF state (switch 3). The highest and lowest ideal calculated switching ratios are 1175 and 5, respectively, observed for switches 1 and 4. Increased thermal stability of the 1-ON isomer is achieved by benzannulation (switch 1B-OFF/ON). The effects of constrained electrode–electrode distances on activation energies for thermal hydrogen back-transfer from 1-ON to 1-OFF and the relative energies of 1-ON and 1-OFF at constrained geometries were also studied. The switching ratio is strongly distance-dependent as revealed for 1B-ON/OFF where it equals 711 and 148 when the ON and OFF isomers are calculated in electrode gaps with distances confined to either that of the OFF isomer or to that of the ON isomer, respectively.

Candy Wrapper for the Earth's inner core

Recent global expansion of seismic data motivated a number of seismological studies of the Earth's inner core that proposed the existence of increasingly complex structure and anisotropy. In the meantime, new hypotheses of dynamic mechanisms have been put forward to interpret seismological results. Here, the nature of hemispherical dichotomy and anisotropy is re-investigated by bridging the observations of PKP(bc-df) differential travel-times with the iron bcc/hcp elastic properties computed from first-principles methods.The Candy Wrapper velocity model introduced here accounts for a dynamic picture of the inner core (i.e., the eastward drift of material), where different iron crystal shapes can be stabilized at the two hemispheres. We show that seismological data are best explained by a rather complicated, mosaic-like, structure of the inner core, where well-separated patches of different iron crystals compose the anisotropic western hemispherical region, and a conglomerate of almost indistinguishable iron phases builds-up the weakly anisotropic eastern side.

Identification of vibrational signatures from short chains of interlinked molecule-nanoparticle junctions obtained by inelastic electron tunnelling spectroscopy

Short chains containing a series of metal-molecule-nanoparticle nanojunctions are a nano-material system with the potential to give electrical signatures close to those from single molecule experiments while enabling us to build portable devices on a chip. Inelastic electron tunnelling spectroscopy (IETS) measurements provide one of the most characteristic electrical signals of single and few molecules. In interlinked molecule-nanoparticle (NP) chains containing typically 5-7 molecules in a chain, the spectrum is expected to be a superposition of the vibrational signatures of individual molecules. We have established a stable and reproducible molecule-AuNP multi-junction by placing a few 1,8-octanedithiol (ODT) molecules onto a versatile and portable nanoparticle-nanoelectrode platform and measured for the first time vibrational molecular signatures at complex and coupled few-molecule-NP junctions. From quantum transport calculations, we model the IETS spectra and identify vibrational modes as well as the number of molecules contributing to the electron transport in the measured spectra.

Impact of comprehensive cardiovascular risk reduction programme on risk factor clustering associated with elevated blood pressure in an Indian industrial population

BACKGROUND & OBJECTIVES

Cardiovascular risk factors clustering associated with blood pressure (BP) has not been studied in the Indian population. This study was aimed at assessing the clustering effect of cardiovascular risk factors with suboptimal BP in Indian population as also the impact of risk reduction interventions.

METHODS

Data from 10543 individuals collected in a nation-wide surveillance programme in India were analysed. The burden of risk factors clustering with blood pressure and coronary heart disease (CHD) was assessed. The impact of a risk reduction programmme on risk factors clustering was prospectively studied in a sub-group.

RESULTS

Mean age of participants was 40.9 ± 11.0 yr. A significant linear increase in number of risk factors with increasing blood pressure, irrespective of stratifying using different risk factor thresholds was observed. While hypertension occurred in isolation in 2.6 per cent of the total population, co-existence of hypertension and >3 risk factors was observed in 12.3 per cent population. A comprehensive risk reduction programme significantly reduced the mean number of additional risk factors in the intervention population across the blood pressure groups, while it continued to be high in the control arm without interventions (both within group and between group P<0.001). The proportion of 'low risk phenotype' increased from 13.4 to 19.9 per cent in the intervention population and it was decreased from 27.8 to 10.6 per cent in the control population (P<0.001). The proportion of individuals with hypertension and three more risk factors decreased from 10.6 to 4.7 per cent in the intervention arm while it was increased from 13.3 to 17.8 per cent in the control arm (P<0.001).

INTERPRETATION & CONCLUSIONS

Our findings showed that cardiovascular risk factors clustered together with elevated blood pressure and a risk reduction programme significantly reduced the risk factors burden.

Predicted formation of superconducting platinum-hydride crystals under pressure in the presence of molecular hydrogen

Noble metals adopt close-packed structures at ambient pressure and rarely undergo structural transformation at high pressures. Platinum (Pt) is normally considered to be unreactive and is therefore not expected to form hydrides under pressure. We predict that platinum hydride (PtH) has a lower enthalpy than its constituents solid Pt and molecular hydrogen at pressures above 21.5 GPa. PtH transforms to a hexagonal close-packed or face-centered cubic (fcc) structure between 70 and 80 GPa. Linear response calculations indicate that PtH is a superconductor at these pressures with a critical temperature of about 10-25 K. These findings help to shed light on recent observations of pressure-induced metallization and superconductivity in hydrogen-rich materials. We show that the formation of fcc noble metal hydrides under pressure is common and examine the possibility of superconductivity in these materials.

Distribution of 10-year and lifetime predicted risk for cardiovascular disease in the Indian Sentinel Surveillance Study population (cross-sectional survey results)

INTRODUCTION

Cardiovascular disease (CVD) prevention guidelines recommend lifetime risk stratification for primary prevention of CVD, but no such risk stratification has been performed in India to date.

METHODS

The authors estimated short-term and lifetime predicted CVD risk among 10,054 disease-free, adult Indians in the 20-69-year age group who participated in a nationwide risk factor surveillance study. The study population was then stratified into high short-term (≥ 10% 10-year risk or diabetes), low short-term (<10%)/high lifetime and low short-term/low lifetime CVD risk groups.

RESULTS

The mean age (SD) of the study population (men=63%) was 40.8 ± 10.9 years. High short-term risk for coronary heart disease was prevalent in more than one-fifth of the population (23.5%, 95% CI 22.7 to 24.4). Nearly half of individuals with low short-term predicted risk (48.2%, 95% CI 47.1 to 49.3) had a high predicted lifetime risk for CVD. While the proportion of individuals with all optimal risk factors was 15.3% (95% CI 14.6% to 16.0%), it was 20.6% (95% CI 18.7% to 22.6%) and 8.8% (95% CI 7.7% to 10.5%) in the highest and lowest educational groups, respectively.

CONCLUSION

Approximately one in two men and three in four women in India had low short-term predicted risks for CVD in this national study, based on aggregate risk factor burden. However, two in three men and one in two women had high lifetime predicted risks for CVD, highlighting a key limitation of short-term risk stratification.

Optical Absorption of Large Band-Gap SbxBi1-xI3 Alloys

The optical properties of SbBiI3 alloys have been investigated experimentally by absorption measurements and theoretically by a full-potential augmented plane wave (FPLAPW) method within the generalized gradient approximation. The fundamental band-gap energy of these alloys changes from BiI3- to SbI3-like with increasing percentage of Sb content. The calculated band-gap energies as well as the optical absorption were found to be in a very good qualitatively agreement with the experimental results. We present calculated density-of-states as well as the dielectric functions for evaluation of future experiments.

Assessment of a nanoparticle bridge platform for molecular electronics measurements

A combination of electron beam lithography, photolithography and focused ion beam milling was used to create a nanogap platform, which was bridged by gold nanoparticles in order to make electrical measurements and assess the platform under ambient conditions. Non-functionalized electrodes were tested to determine the intrinsic response of the platform and it was found that creating devices in ambient conditions requires careful cleaning and awareness of the contributions contaminants may make to measurements. The platform was then used to make measurements on octanethiol (OT) and biphenyldithiol (BPDT) molecules by functionalizing the nanoelectrodes with the molecules prior to bridging the nanogap with nanoparticles. Measurements on OT show that it is possible to make measurements on relatively small numbers of molecules, but that a large variation in response can be expected when one of the metal-molecule junctions is physisorbed, which was partially explained by attachment of OT molecules to different sites on the surface of the Au electrode using a density functional theory calculation. On the other hand, when dealing with BPDT, high yields for device creation are very difficult to achieve under ambient conditions. Significant hysteresis in the I-V curves of BPDT was also observed, which was attributed primarily to voltage induced changes at the interface between the molecule and the metal.

Experimental and theoretical investigations on magnetic behavior of (Al,Co) co-doped ZnO nanoparticles

We present the structural and magnetic properties of Zn(0.95-x)Co(0.05)Al(x)O (x = 0.0 to 0.1) nanoparticles, synthesized by a novel sol-gel route followed by pyrolysis. Powder X-ray diffraction data confirms the formation of a single phase wurtzite type ZnO structure for all the compositions. The Zn(0.95)Co(0.05)O nanoparticles show diamagnetic behavior at room temperature. However, when Al is co-doped with Co with x = 0.0 to 0.10 in Zn(0.95-x)Co(0.05)Al(x)O, a systematic increase in ferromagnetic moment is observed up to x = 0.07 at 300 K. Above x = 0.07 (e.g. for x = 0.10) a drastic decrease in ferromagnetic nature is observed which is concomitant with the segregation of poorly crystalline Al rich ZnO phase as evidenced from TEM studies. Theoretical studies using density functional calculations on Zn(0.95-x)Co(0.05)Al(x)O suggest that the partial occupancy of S2 states leads to an increased double exchange interaction favoring the ferromagnetic ground states. Such ferromagnetic interactions are favorable beyond a threshold limit. At a high level doping of Al, the exchange splitting is reduced, which suppresses the ferromagnetic ordering.

An electrostatic deceleration lens for highly charged ions

The design and implementation of a purely electrostatic deceleration lens used to obtain beams of highly charged ions at very low energies is presented. The design of the lens is such that it can be used with parallel as well as diverging incoming beams and delivers a well focused low energy beam at the target. In addition, tuning of the final energy of the beam over a wide range (1 eV/q to several hundred eV/q, where q is the beam charge state) is possible without any change in hardware configuration. The deceleration lens was tested with Ar(8+), extracted from an electron cyclotron resonance ion source, having an initial energy of 30 keV/q and final energies as low as 70 eV/q have been achieved.

Electronic structure of Cu(3)N films studied by soft x-ray spectroscopy

Soft x-ray emission spectroscopy was used to characterize the electronic structure of seven copper nitride films, one synthesized with atomic layer deposition (ALD) and six grown with chemical vapor deposition (CVD) at different preparation temperatures. Interpretation of the x-ray emission spectra was supported by calculations of the electronic structure for bulk pure Cu(3)N and Cu(3)N with: an excess of Cu atoms, oxygen or carbon impurities, and N vacancies. The calculations are shown to describe the experimental spectra quite well. Analysis of the x-ray spectra suggests that films grown in copper rich environments and above a cut-off temperature of approximately 360 °C have a growing fraction of copper enriched areas, while films prepared below this temperature do not have these areas with excess copper.

Magnetic Fe(n+1)AC(n) (n = 1, 2, 3, and A = Al, Si, Ge) phases: from ab initio theory

We have investigated the structural stability and magnetism for a set of compounds Fe(n+1)AC(n) (n = 1, 2, 3, and A = Al, Si, Ge) using ab initio theory. From our calculation, we have shown that some Fe(n+1)AC(n) phases (n = 2) with the general MAX phase formula and a layered hexagonal structure that belongs to space group D(6h)(4)-P6(3)/mmc can have a combination of properties of the MAX phase at the same time as having magnetism. The Fe(3)AlC(2) phase shows the most stable ferromagnetic properties among these MAX phases and the magnetic moment is 0.73 μ(B)/Fe atom. In addition, the phase stability is predicted by comparing the total energy of the Fe(2)AlC and Fe(2)SiC phases with the total energy of the competing equilibrium phases at the corresponding composition.

Li-decorated metal-organic framework 5: a route to achieving a suitable hydrogen storage medium

A significant improvement in molecular hydrogen uptake properties is revealed by our ab initio calculations for Li-decorated metal-organic framework 5. We have found that two Li atoms are strongly adsorbed on the surfaces of the six-carbon rings, one on each side, carrying a charge of +0.9e per Li atom. Each Li can cluster three H(2) molecules around itself with a binding energy of 12 kJ (mol H(2))(-1). Furthermore, we show from ab initio molecular dynamics simulations with a hydrogen loading of 18 H(2) per formula unit that a hydrogen uptake of 2.9 wt % at 200 K and 2.0 wt % at 300 K is achievable. To our knowledge, this is the highest hydrogen storage capacity reported for metal-organic framework 5 under such thermodynamic conditions.

Setup for in situ x-ray diffraction study of swift heavy ion irradiated materials

An in situ x-ray diffraction (XRD) setup is designed and installed in the materials science beam line of the Pelletron accelerator at the Inter-University Accelerator Centre for in situ studies of phase change in swift heavy ion irradiated materials. A high vacuum chamber with suitable windows for incident and diffracted X-rays is integrated with the goniometer and the beamline. Indigenously made liquid nitrogen (LN2) temperature sample cooling unit is installed. The snapshots of growth of particles with fluence of 90 MeV Ni ions were recorded using in situ XRD experiment, illustrating the potential of this in situ facility. A thin film of C60 was used to test the sample cooling unit. It shows that the phase of the C60 film transforms from a cubic lattice (at room temperature) to a fcc lattice at around T=255 K.

Electronic structure of phospho-olivines Li(x)FePO4 (x = 0, 1) from soft-x-ray-absorption and -emission spectroscopies

The electronic structure of the phospho-olivine Li(x)FePO4 was studied using soft-x-ray-absorption (XAS) and emission spectroscopies. Characteristic changes in the valence and conduction bands are observed upon delithation of LiFePO4 into FePO4. In LiFePO4, the Fe-3d states are localized with little overlap with the O-2p states. Delithiation of LiFePO4 gives stronger hybridization between Fe-3d states and O-2p states leading to delocalization of the O-2p states. The Fe L-edge absorption spectra yield "fingerprints" of the different valence states of Fe in LiFePO4 and FePO4. Resonant soft-x-ray-emission spectroscopy at the Fe L edge shows strong contributions from resonant inelastic soft x-ray scattering (RIXS), which is described using an ionic picture of the Fe-3d states. Together the Fe L-edge XAS and RIXS study reveals a bonding character of the Fe 3d-O2p orbitals in FePO4 in contrast to a nonbonding character in LiFePO4.

X-ray spectroscopic study of the charge state and local ordering of room-temperature ferromagnetic Mn-doped ZnO

The charge state and local ordering of Mn doped into a pulsed laser deposited single-phase thin film of ZnO are investigated by using x-ray absorption spectroscopy at the O K-edge, Mn K-edge and L-edge, and x-ray emission spectroscopy at the O K-edge and Mn L-edge. This film is ferromagnetic at room temperature. EXAFS measurement shows that Mn(2+) replaces the Zn site in tetrahedral symmetry, and there is no evidence for either metallic Mn or MnO in the film. Upon Mn doping, the top of O 2p valence band extends into the bandgap, indicating additional charge carriers being created.