Synaptic plasticity and learning behaviour in multilevel memristive devices

This research explores a novel two-terminal heterostructure of the Pt/Cu₂Se/Sb₂Se₃/FTO memristor, which exhibited essential biological synaptic functions. These synaptic functions play a critical role in emulating biological neural systems and overcoming the limitations of traditional computing architectures. By repeating a fixed pulse train, in this study, we realized a few crucial neural functions toward weight modulation, such as nonlinear conductance changes and potentiation/depression characteristics, which aid the transition of short-term memory to long-term memory. However, we also employed multilevel switching, which provides easily accessible multilevel (4-states, 2-bit) states, for high-density data storage capability along with endurance (10² pulse cycles for each state) in our proposed device. In terms of synaptic plasticity, the device performed well by controlling the pulse voltage and pulse width during excitatory post-synaptic current (EPSC) measurements. The spike-time-dependent plasticity (STDP) highlights their outstanding functional properties, indicating that the device can be used in artificial biological synapse applications. The artificial neural network with Pt/Cu₂Se/Sb₂Se₃/FTO achieved a significant accuracy of 73% in the simulated Modified National Institute of Standards and Technology database (MNIST) pattern. The conduction mechanism of resistive switching and the artificial synaptic phenomena could be attributed to the transfer of Se^2- ions and selenium vacancies. The neuromorphic characteristics of the Pt/Cu₂Se/Sb₂Se₃/FTO devices demonstrate their potential as futuristic synaptic devices.

A study on structural, optical, and electrical characteristics of perovskite CsPbBr3 QD/2D-TiSe2 nanosheet based nanocomposites for optoelectronic applications

Lead halide perovskite (CsPbBr₃) quantum dots (QDs) and two-dimensional (2D) layered transition metal dichalcogenides have a significant application in solution-processed optoelectronic devices. Here, we report the oleylamine-assisted exfoliation of TiSe₂ nanosheets (NSs) in dichlorobenzene with high concentration and stable dispersion. The functionalized TiSe₂ NSs were used to synthesize the solution-processed perovskite CsPbBr₃ QD/TiSe₂ NS-based nanocomposite. The perovskite QDs and TiSe₂ NSs were characterized by different techniques. The strong photoluminescence (PL) quenching and decreased lifetime decay of the nanocomposite indicates efficient charge transfer from photo-excited CsPbBr₃ to TiSe₂ NSs. The calculated charge-transfer rate constant (K_ET) from photo-excited CsPbBr₃ to TiSe₂ NSs increased from 1.50 × 10⁸ to 2.79 × 10⁸ s^-1 in different concentrations of TiSe₂ NSs (5 to 20 μg mL^-1), respectively. Furthermore, the photo-currents of CsPbBr₃ QD/TiSe₂ NS nanocomposite devices were dramatically enhanced ∼2 times compared to pristine CsPbBr₃ QD based devices, which supports the charge transfer and charge separation in nanocomposite devices.

A study on chemical exfoliation and structural and optical properties of two-dimensional layered titanium diselenide

Titanium diselenide (TiSe₂) is the least studied member of the transition metal dichalcogenide family due to a lack of available synthesis methodology, controlled bandgap engineering, and rapid characterization of layers. In this paper, we report the chemical exfoliation of TiSe₂ platelets synthesized by the chemical vapor transport route in ortho-dichlorobenzene (o-DCB) functionalized with oleylamine (OLA), for the first time to the best of our knowledge. It is found that the addition of OLA supports the formation of a stable dispersion of a large area of the TiSe₂ sheets due to surface capping with the OLA molecules indicating the importance of the ligand in dispersion behavior. The X-ray diffraction pattern confirms the hexagonal structure of the TiSe₂ platelets with the space group P3[combining macron]m1 while Raman spectroscopy reveals that two modes of vibration i.e. A_1g and E_2g exist with layered structures having dimensions in micrometers as confirmed by scanning electron microscopy. Fourier transform infrared spectroscopy confirms the successful functionalization of chemically exfoliated TiSe₂ nanosheets. Field-emission scanning electron microscopy reveals that exfoliated TiSe₂ has a thickness of 15-55 nm whereas high-resolution transmission electron microscopy indicates thicker sheets for ligand-free exfoliated TiSe₂ which are crystalline. Atomic force microscopy confirms the formation of nanosheets. UV-Visible, photoluminescence, and time-resolved PL spectroscopy showed an enhanced effect and better average lifetime of excitation for the exfoliated sheets with OLA than those without OLA. The C-V studies reveal that with increasing scan rate, the corresponding current also increases. The present study offers the possibility of their utilization in optoelectronics, advanced low-power electronics, voltage-controlled oscillators, ultra-fast electronics, and electrochemical devices.

Tuning the Thermoelectric Material's Parameter: A Comprehensive Review

Thermoelectric is a device that converts heat into electricity. As thermodynamically it is not possible to make device which is 100 percent efficient, some amount of energy is wasted in the form of heat. Thermoelectric materials can play a major role in harnessing such waste energy. Although thermoelectric is a useful device still its efficiency is not good enough for commercialization. Therefore, lots of research have been carried out in finding out the best possible material, device geometry etc. There are thousands of papers describing various optimization processes. The present work reviews the basics of thermoelectric device parameters which determine the performance of the device and how to control these parameters for better thermoelectric efficiency. The efforts made to optimize parameters like power factor, thermal conductivity etc. have been summarized. Experimental results have been described with examples. Highest reported ZT values of various materials have been presented in this review.

Localized Surface Plasmon Resonance Studies on Pd/C Nano-Composite System: Effect of Metal Concentration and Annealing Temperature

The effects of metal concentration and annealing temperature on the localized surface plasmon resonance (LSPR) properties of the Pd nanoparticles (NP) dispersed in carbon were investigated. The Pd/C nano-composite thin films with 7 to 39 atomic % concentration of metal content were deposited using the atom beam co-sputtering techniques and subjected to annealing at temperature varying from 300 °C to 600 °C. The UV-vis spectroscopy studies on as-prepared films displayed a Mie scattering profile, but not well-defined LSPR bands were observed for all the values of Pd concentration. This is attributed to the smaller size (3-4 nm) of Pd NPs and rough Pd/C interface, as confirmed from TEM studies. When samples were annealed at a temperature of 300 °C, three broad LSPR absorption bands in the visible region, along with a sharp peak at 210 nm, were observed and the effect of Pd concentration variation was insignificant on their position. The multiple LSPR bands were observed due to agglomeration NPs, which is consistent with earlier reports and is also observed in the TEM images. When annealing temperature was subsequently increased to 500 °C, a blue shift in the LSPR peak position with an increase in the Pd concentration was observed, which phenomena is attributed to the formation of bigger NPs with the formation of sharp NPs-interface at high temperature upon annealing. A monotonic increase in the magnitude and decrease in the FWHM with an increase in concentration suggested change in the dielectric function of sample due to the growth of NPs. This is further confirmed from XRD studies, where strain relaxation and grain growth were observed. The intensity of the SPR peak decreased with an increase in the annealing temperature. The LSPR peak disappeared on annealing at a temperature of 600 °C, suggesting the formation of continuous polycrystalline thin films of Pd. In summary, NPs size, metalmatrix interface, and concentration of metal play key roles in the tailoring the LSPR properties of the Pd.

Experimental observation of spatially resolved photo-luminescence intensity distribution in dual mode upconverting nanorod bundles

A novel method for demonstration of photoluminescence intensity distribution in upconverting nanorod bundles using confocal microscopy is reported. Herein, a strategy for the synthesis of highly luminescent dual mode upconverting/downshift Y_1.94O₃:Ho³⁺_0.02/Yb³⁺_0.04 nanorod bundles by a facile hydrothermal route has been introduced. These luminescent nanorod bundles exhibit strong green emission at 549 nm upon excitations at 449 nm and 980 nm with quantum efficiencies of ~6.3% and ~1.1%, respectively. The TEM/HRTEM results confirm that these bundles are composed of several individual nanorods with diameter of ~100 nm and length in the range of 1–3 μm. Furthermore, two dimensional spatially resolved photoluminescence intensity distribution study has been carried out using confocal photoluminescence microscope throughout the nanorod bundles. This study provides a new direction for the potential use of such emerging dual mode nanorod bundles as photon sources for next generation flat panel optical display devices, bio-medical applications, luminescent security ink and enhanced energy harvesting in photovoltaic applications.

Tunable luminescence from two dimensional BCNO nanophosphor for high-contrast cellular imaging

Multi-colour emitting nanophosphors provide a paradigm shift in rare-earth free biocompatible nanoprobes for in vitro and in vivo imaging applications.

Hidden lattice instabilities as origin of the conductive interface between insulating LaAlO3 and SrTiO3

The metallic interface between insulating LaAlO₃ and SrTiO₃ opens up the field of oxide electronics. With more than a decade of researches on this heterostructure, the origin of the interfacial conductivity, however, remains unsettled. Here we resolve this long-standing puzzle by atomic-scale observation of electron-gas formation for screening hidden lattice instabilities, rejuvenated near the interface by epitaxial strain. Using atomic-resolution imaging and electron spectroscopy, the generally accepted notions of polar catastrophe and cation intermixing for the metallic interface are discounted. Instead, the conductivity onset at the critical thickness of 4-unit cell LaAlO₃ on SrTiO₃ substrate is accompanied with head-to-head ferroelectric-like polarizations across the interface due to strain-rejuvenated ferroelectric-like instabilities in the materials. The divergent depolarization fields of the head-to-head polarizations cast the interface into an electron reservoir, forming screening electron gas in SrTiO₃ with LaAlO₃ hosting complementary localized holes. The ferroelectric-like polarizations and electron–hole juxtaposition reveal the cooperative nature of metallic LaAlO₃/SrTiO₃.

The origin of interfacial conductivity between two insulating oxides, LaAlO₃ and SrTiO₃, remains elusive despite a long time research. Here, Lee et al. report atomic-scale observation of electron-gas formation for screening hidden ferroelectric-like lattice instabilities, discounting the role of polar catastrophe and cation intermixing.

Luminomagnetic bifunctionality of Mn(2+)-bonded graphene oxide/reduced graphene oxide two dimensional nanosheets

Herein, we report the luminomagnetic bifunctional properties of two-dimensional (2D) Mn(2+) bonded graphene oxide (GO)/reduced graphene oxide (RGO) nanosheets synthesized using a facile route of oxidation followed by a solvothermal reduction method. Photoluminescence (PL) studies (excited by different wavelengths) revealed that the resonant energy transfer between Mn(2+) and sp(3)/sp(2) clusters of GO/RGO is responsible for the enhancement of emissions. Moreover, pH-sensitive PL behaviors have also been investigated in detail. The ferromagnetic behavior is believed to arise due to defects in Mn(2+) bonded GO composites. Thus, present reduction method provides a direct route to tune and enhance the optical properties of GO and RGO nanosheets bonded with Mn(2+) ions, which creates an opportunity for various technological applications.

Growth of dense CNT on the multilayer graphene film by the microwave plasma enhanced chemical vapor deposition technique and their field emission properties

Catalyst assisted carbon nanotubes (CNTs) were grown on multilayer graphene (MLG) on copper and silicon substrates by the microwave plasma enhanced chemical vapor deposition technique.

Band gap engineering from Vis to NIR range in CdPbS nanoparticles synthesized by one-step low-temperature decomposition of xanthate compound

In the present study, a generic method for the modification of optical band gap of CdS nanostructures material over a wide spectral range due to Pb doping and formation of Cd(1-x)Pb(x)S nanoparticles and its size confinement is reported. The composite investigated in this study was grown by thermal decomposition of metal xanthates and lead concentration was varied to obtain different lead doping. This is a direct decomposition one pot synthesis route that avoids use of toxic phosphine and injection of chemicals during the reaction. The prepared nanoparticles were characterized by XRD, SEM, EDX, and HRTEM. The optical absorption properties of the Cd(1-x)Pb(x)S nanostructures were investigated by UV-visible spectroscopy. Cd(1-x)Pb(x)S nanoparticles showed tuning of the band gap from 2.7 eV to 0.7 eV.

Room temperature lead-free relaxor–antiferroelectric electroceramics for energy storage applications

Round the globe, scientific communities have been searching for new materials for “green” energy, producing efficiently both high power as well as high energy density.

A commercial approach for the fabrication of bulk and nano phosphors converted into highly efficient white LEDs

A novel approach for the comparative study of bulk and nano phosphors converted into highly efficient white LEDs.

Highly luminescent-paramagnetic nanophosphor probes for in vitro high-contrast imaging of human breast cancer cells

Highly luminescent-paramagnetic nanophosphors have a seminal role in biotechnology and biomedical research due to their potential applications in biolabeling, bioimaging, and drug delivery. Herein, the synthesis of high-quality, ultrafine, europium-doped yttrium oxide nanophosphors (Y(1.9)O(3):Eu(0.1)(3+)) using a modified sol-gel technique is reported and in vitro fluorescence imaging studies are demonstrated in human breast cancer cells. These highly luminescent nanophosphors with an average particle size of ≈6 nm provide high-contrast optical imaging and decreased light scattering. In vitro cellular uptake is shown by fluorescence microscopy, which visualizes the characteristic intense hypersensitive red emission of Eu(3+) peaking at 610 nm ((5)D(0)-(7)F(2)) upon 246 nm UV light excitation. No apparent cytotoxicity is observed. Subsequently, time-resolved emission spectroscopy and SQUID magnetometry measurements demonstrate a photoluminescence decay time in milliseconds and paramagnetic behavior, which assure applications of the nanophosphors in biomedical studies.

Faster response of NO₂ sensing in graphene-WO₃ nanocomposites

Graphene-based nanocomposites have proven to be very promising materials for gas sensing applications. In this paper, we present a general approach for the preparation of graphene-WO(3) nanocomposites. Graphene-WO(3) nanocomposite thin-layer sensors were prepared by drop coating the dispersed solution onto the alumina substrate. These nanocomposites were used for the detection of NO(2) for the first time. TEM micrographs revealed that WO(3) nanoparticles were well distributed on graphene nanosheets. Three different compositions (0.2, 0.5 and 0.1 wt%) of graphene with WO(3) were used for the gas sensing measurements. It was observed that the sensor response to NO(2) increased nearly three times in the case of graphene-WO(3) nanocomposite layer as compared to a pure WO(3) layer at room temperature. The best response of the graphene-WO(3) nanocomposite was obtained at 250 °C.

Resistive switching in copper oxide nanorods: a bottom up approach applicable for enhanced scalability

Reversible, stable and reproducible resistive switching in a parallel network of Cu2O nanorods, observed in the present study, highlights the advantages of using nanorods in comparison to normally used thin films. Unipolar and symmetric current-voltage characteristics of the metal/insulator/metal structure consisting of Hg top contact/Copper oxide (Cu2O) nanorods/Ag bottom contact in a sandwich configuration shows electroforming at about 11 V, reproducible reset and set points at 0.53 +/- 0.03 and 4.2 +/- 0.02 V and a high OFF/ON resistance ratio > 10(3). Slope of current-voltage characteristics and current contrast in CAFM mapping indicate that filamentary conduction mechanism is responsible for resistive switching. This study sets the foundation for fabricating a nanorods based resistive random access memory device and thus a manifold increase in the device scalability.

Fast response and recovery of hydrogen sensing in Pd-Pt nanoparticle-graphene composite layers

This study reports the fast response and recovery of hydrogen sensing in nanoparticle-graphene composite layers fabricated using chemical methods and comprising of isolated Pd alloy nanoparticles dispersed onto graphene layers. For 2% hydrogen at 40 °C and 1 atm pressure, a response time of <2 s and a recovery time of 18 s are observed. The fast response and recovery observed during sensing are due to hydrogen-induced changes in the work function of the Pd alloy and modification in the distribution of defect states in the graphene band gap due to gas adsorption. The results of hydrogen sensing in the new class of Pd-Pt nanoparticle-graphene composite material are important for understanding the effect of gas adsorption on electronic conduction in graphene layers and for developing a new type of gas sensor based on changes in the electronic properties of the interface.

Photovoltaic response of a topotaxially formed CdS-Cu(x)S single nanorod heterojunction

In the present study, a combination of a hydrothermal route and a topotaxial conversion reaction has been used to grow a cadmium sulfide-copper sulfide (CdS-Cu(x)S) single nanorod heterojunction. The J-V characteristics of the CdS nanorods show Shockley behaviour consistent with the energy band diagram of the platinum conducting atomic force microscope (CAFM) probe-CdS nanorod combination. The photovoltaic response measured on the CdS-Cu(x)S nanorods using a CAFM probe shows the formation of a heterojunction with an open circuit voltage of 320 mV, a short circuit current density of 5.5 mA cm⁻² and a crossover of dark and light J-V curves related to the photoconductivity of the interfacial CdS layer. The lengthwise heterojunction fabricated in the present study has many potential advantages in comparison to other single nanorod junctions.

Effect of induced shape anisotropy on magnetic properties of ferromagnetic cobalt nanocubes

We report on the synthesis of ferromagnetic cobalt nanocubes of various sizes using thermal pyrolysis method and the effect of shape anisotropy on the static and dynamic magnetic properties were studied. Shape anisotropy of approximately 10% was introduced in nanocubes by making nanodiscs using a linear chain amine surfactant during synthesis process. It has been observed that, ferromagnetism persisted above room temperature and a sharp drop in magnetic moment at low temperatures in zero-field cooled magnetization may be associated with the spin disorder due to the effective anisotropy present in the system. Dynamic magnetic properties were studied using RF transverse susceptibility measurements at different temperatures and the singularities due to anisotropy fields were probed at low temperatures. Symmetrically located broad peaks are observed in the frozen state at the effective anisotropy fields and the peak structure is strongly affected by shape anisotropy and temperature. Irrespective of size the shape anisotropy gave rise to higher coercive fields and larger transverse susceptibility ratio at all temperatures. The role of shape anisotropy and the size of the particles on the observed magnetic behaviour were discussed.

Biosynthesis of Silver Nanoparticles from Desmodium triflorum: A Novel Approach Towards Weed Utilization

A single-step environmental friendly approach is employed to synthesize silver nanoparticles. The biomolecules found in plants induce the reduction of Ag⁺ ions from silver nitrate to silver nanoparticles (AgNPs). UV-visible spectrum of the aqueous medium containing silver ions demonstrated a peak at 425 nm corresponding to the plasmon absorbance of silver nanoparticles. Transmission electron microscopy (TEM) showed the formation of well-dispersed silver nanoparticles in the range of 5–20 nm. X-ray diffraction (XRD) spectrum of the AgNPs exhibited 2θ values corresponding to the silver nanocrystal. The process of reduction is extracellular and fast which may lead to the development of easy biosynthesis of silver nanoparticles. Plants during glycolysis produce a large amount of H⁺ ions along with NAD which acts as a strong redoxing agent; this seems to be responsible for the formation of AgNPs. Water-soluble antioxidative agents like ascorbic acids further seem to be responsible for the reduction of AgNPs. These AgNPs produced show good antimicrobial activity against common pathogens.

Self-catalytic synthesis, structure and properties of ultra-fine luminescent ZnO nanostructures for field emission applications

A facile method to produce high-quality ZnO nanostructures; either tetrapod (TP), nanotetraneedle (NTN) or multipod (MP) with a high degree of homogeneity for advanced field emission (FE) applications is presented. Among these nanostructures, NTN has been successfully employed to demonstrate enhanced current densities (2.6 mA cm(-2)), turn-on field (1.5 V microm(-1)) and field-enhancement factors (6930) over conventional multiwalled carbon nanotubes (MWCNTs), TP, MP and ZnO-spheroids. A comparative study of FE from various ZnO nanostructures, morphologies and site densities has lead to the conclusion that diameter of the tip is one of the vital parameters in enhancing the overall FE properties.

Synthesis and characterization of ultra-fine Y2O3:Eu3+ nanophosphors for luminescent security ink applications

We report a simple method for the synthesis of ultra-fine Eu(3+)-doped yttria (Y(2)O(3)) nanophosphors with an average diameter of approximately 5 nm for development of a transparent colloid that could be used as a luminescent security ink. This has been achieved by suitably substituting Eu(3+) ions at the favorable C(2) symmetry sites of Y(3+) ions and quantum mechanically confining the growth of the nanophosphor using a novel acid-catalyzed sol-gel technique. This is one of the few reports that depict the development of a transparent aqueous-stable Y(2)O(3):Eu(3+) colloidal solution for strategic applications related to security codes. High resolution transmission electron microscopy images showed excellent lattice fringes that in turn support the presence of better crystal quality and enhanced photoluminescence (PL) emission from the Y(1.9)O(3)Eu(0.1)(3+) nanophosphor system. Time resolved emission spectroscopy measurement indicated a PL decay time in the range of a few milliseconds, suitable for making luminescent security ink and other advanced applications in optoelectronic devices and bio-labeling.

Formation of water-soluble and biocompatible TOPO-capped CdSe quantum dots with efficient photoluminescence

In this work, polysorbate surfactants with same functional groups but with varying molecular masses (Tween-80, Tween-40 and Tween-20) in different concentrations (0.1% to 20% w/w) were used to study the effect of the length of the surfactant chain on the luminescence of the entrapped TOPO-capped CdSe nanocrystals. Various phospholipids with different functional headgroups such as ethylene glycol (-PEG) and amine (-NH2) were used to improve biocompatibility and provide sites for bioconjugation respectively. It is understood that that the hydrophobic ends of the surfactant binds with the water repelling groups of the cap layer, thus modifying the CdSe cap layer and making it soluble in aqueous media. It was observed that the PL emission intensity of CdSe increases with increase in concentration of Tween-series surfactant unlike in the case of thiol-coated CdSe nanoparticles. However, higher PL intensity was obtained in the case of stoichiometric CdSe with Tween-40 corresponding to 20% w/w. The efficient PL sustainability of water-soluble CdSe QD's can be attributed to the simpler chain structure of Tween-40 surfactant resulting in better passivation of the micelle.

Synthesis and characterization of ferromagnetic cobalt nanospheres, nanodiscs and nanocubes

We report the synthesis of cobalt nanoparticles with different shapes and sizes by rapid pyrolysis of cobalt carbonyl in the presence of various surfactants. The size and shape of the nanoparticles were influenced by reaction conditions, such as type of the surfactant, molar ratio of surfactant to precursor, reflux temperature and reaction time. The shapes that we have achieved include spherical, nearly spherical, disc and cube. The presence of linear amine yielded nanodiscs and they spontaneously self-assembled into long ribbons. The effect of shape anisotropy on magnetic nanoparticles has been investigated. Spherical nanoparticles of diameter 14.5 nm show strong ferromagnetic behavior at low temperature and superparamagnetism at room temperature. On the other hand the cubic nanoparticles of 45 nm sides showed negligible coercive field at T=10 K and ferromagnetism that persisted above T=300 K. The cobalt nanospheres were oxidized to grow cobalt oxide shell of varying thickness to study exchange bias effect. A pronounced exchange bias and a strong temperature dependant magnetization were observed in oxidized cobalt nanospheres.

Tunable synthesis of indium oxide octahedra, nanowires and tubular nanoarrow structures under oxidizing and reducing ambients

We report the effect of oxidizing and reducing ambients on the growth of indium oxide (IO) nanostructures in the vapor phase evaporation method. Our results show that the oxidizing reagent, water, results in the growth of IO nanowires and preserves the In/O stoichiometry throughout the length of the nanowires. The reducing reagent, ethanol, makes the growth environment indium rich, resulting in the growth of indium-filled IO tubular nanoarrow structures. The growth of solid IO nanowires is attributed to a vapor-liquid-solid mechanism, whereas for indium-filled tubular nanoarrow structures a modified bottom-vapor-solid growth mechanism is proposed. The tunable synthesis of IO nanostructures in different morphologies with correction of their stoichiometry may have potential applications in future nanodevices.

Synthesis and properties of nanocrystalline copper indium oxide thin films deposited by Rf magnetron sputtering

Nanocrystalline copper indium oxide (CuInO2) thin films with particle size ranging from 25 nm to 71 nm have been synthesized from a composite target using reactive Rf magnetron sputtering technique. X-ray photoelectron spectroscopy (XPS) combined with glancing angle X-ray diffraction (GAXRD) analysis confirmed the presence of delafossite CuInO2 phase in these films. The optical absorption studies show the presence of two direct band gaps at 3.3 and 4.3 eV, respectively. The resistance versus temperature measurements show thermally activated hopping with activation energy of 0.84 eV to be the conduction mechanism.

Effect of Substrate Morphology on Growth and Field Emission Properties of Carbon Nanotube Films

Carbon nanotube (CNT) films were grown by microwave plasma-enhanced chemical vapor deposition process on four types of Si substrates: (i) mirror polished, (ii) catalyst patterned, (iii) mechanically polished having pits of varying size and shape, and (iv) electrochemically etched. Iron thin film was used as catalytic material and acetylene and ammonia as the precursors. Morphological and structural characteristics of the films were investigated by scanning and transmission electron microscopes, respectively. CNT films of different morphology such as vertically aligned, randomly oriented flowers, or honey-comb like, depending on the morphology of the Si substrates, were obtained. CNTs had sharp tip and bamboo-like internal structure irrespective of growth morphology of the films. Comparative field emission measurements showed that patterned CNT films and that with randomly oriented morphology had superior emission characteristics with threshold field as low as ~2.0 V/μm. The defective (bamboo-structure) structures of CNTs have been suggested for the enhanced emission performance of randomly oriented nanotube samples.

Nanoparticle formation by swift heavy ion irradiation of indium oxide thin film

In this study, a novel approach for the formation of indium oxide (IO) nanoparticles by irradiating IO thin film using 100 MeV Ag(8+) ions has been reported. High resolution transmission electron microscopy and energy dispersive x-ray analysis confirm the presence of single-crystalline IO nanoparticles after irradiation. The electronic excitations induced by 100 MeV Ag(8+) ions followed by thermal relaxation of the energy spike in IO thin film is responsible for the formation of latent tracks in the film. The electronic energy loss (S(e)) of 100 MeV Ag(8+) ions in IO is greater than the threshold electronic energy loss (S(eth)) required for the track formation in IO film, but is less than S(eth) required for crystalline silicon. Therefore, the tracks are formed in the IO film and not in the silicon substrate. This results in a stress induced at the IO film and silicon substrate interface which is responsible for dewetting of the tracks and the formation of nanoparticles. The theoretically calculated value of nanoparticle diameter using the thermal spike model is found to be in good agreement with the experimentally observed value of 30 nm.

Size-dependent gas sensing properties of indium oxide nanoparticle layers

In2O3 nanoparticle layers having an average size of 8, 11, 15, 21, and 29 nm have been deposited using a two-step method consisting of chemical capping and dip coating techniques. The gas sensing properties in terms of sensor response and response time of the nanoparticle layers towards ethanol have been studied as a function of ethanol concentration and operating temperature. It has been observed that the sensor response increases and the response time decreases with decreasing size in the size range of 5-15 nm. The increase in sensor response at smaller nanoparticle size has been explained in terms of the increase in surface area and particle size becoming comparable to the electron Debye length.

Nanoparticle size-dependent lowering of temperature for phase transition from In(OH)3 to In2O3

Phase transformation of In(OH)3 to In2O3 has been studied as a function of nanoparticle size without any alteration of nanoparticle size during transformation. Chemically capped In(OH)3 nanoparticles having sizes of 15, 11, and 8 nm transform to In2O3 at temperatures of 285, 272, and 255 degrees C, respectively. This first-time unambiguous observation of size-dependent lowering of transformation temperature represents a thermodynamic characteristic of the nanoparticle system. The results have been explained in terms of a lower cohesive energy of surface atoms and an increase in surface-to-volume ratio with a decrease in nanoparticle size.

The role of gas analysis with exercise testing

Evaluation of exercise performance is an integral component of every medical history. Currently, it is accomplished by means of subjective history taking. Routine exercise testing adds very little information; however, the addition of gas analysis (or cardio pulmonary exercise [CPX] testing) provides the crucial objective assessment by analyzing breath-by-breath oxygen uptake, carbon dioxide production, and anaerobic threshold (AT). Cardiac and pulmonary causes can be reliably differentiated, e.g., cardiac patients cross AT and attain VO2max, use less than 50% of maximal voluntary ventilation (MVV) at peak exercise, and do not develop desaturation. Pulmonary patients, on the contrary, fail to cross AT or achieve VO2max, utilize more than 70% of MVV at peak exercise, and develop arterial desaturation. In the current cost-conscious health care system, CPX proves to be a better cost-effective test because it is objective and more directly targeted to the issues than the conventional exercise test. CPX provides an important link between the disease process and its effect on exercise performance, which is crucial to a comprehensive clinical evaluation, diagnosis, prognosis, exercise prescription, and follow-up after medical or surgical intervention in patients with various diseases causing cardiopulmonary dysfunction.

Effects of a 6-month vitamin intervention on DNA damage in heavy smokers

Because their formation is associated with tumor development in specific tissues, DNA adducts have potential usefulness as intermediate end points in chemoprevention studies. To determine the efficacy of a combination of antioxidant vitamins (vitamins C and E and beta-carotene), a randomized clinical trial was conducted among heavy smokers using DNA damage as the end point. Immunological methods were used to measure polycyclic aromatic hydrocarbon-DNA adducts and oxidative DNA damage (8-oxo or hydroxydeoxyguanosine) in mononuclear and oral cells. A total of 121 subjects were randomized to the 6-month intervention and received either vitamins or placebo. Dropout rates were higher in the placebo than in the vitamin group; 65% of subjects in the vitamin group, but only 47% in the placebo group, provided specimens at 6 months. Plasma levels of all three antioxidants rose significantly in the vitamin group but not in the placebo group. All four measures of DNA damage decreased in both groups; the between-group differences were not statistically significant. These data do not provide clear evidence that antioxidant vitamin intake prevents DNA damage. However, the study demonstrates that DNA damage is a useful end point in chemoprevention trials.

Changes in LDH isozyme pattern in uterine fluid of mice during early pregnancy

The total LDH activity in the uterine fluid of mice shows a rising trend from the first day after mating (DAM-1) to the seventh day after mating (DAM-7). This suggests that LDH activity increases as gestation progresses. During early pregnancy, M-isozymes of LDH show a predominance from DAM-1 to DAM-3 in the uterine luminal fluid of mice, while H-isozyme shows a rising level from DAM-5 (implantation day) and attains a maximum level at DAM-7 (the post-implantation period). Such shift of M-isozymes into H-isozymes of LDH (lactate dehydrogenase) during pre-implantation (DAM-3) to post-implantation (DAM-7) period changes the uterine luminal environment from anaerobic to aerobic condition which is more conducive for the normal development, implantation and survival of the growing blastocyst.

Use of antioxidant supplements in the treatment of human oral leukoplakia

An increasing public awareness of antioxidants may prompt a patient's request to be treated without surgery if a leukoplakic lesion is discovered. However, surgical excision remains the treatment of choice for oral leukoplakia. The use of antioxidant supplements has shown some promise, but the predictability of success remains uncertain and long-term results are unavailable. Before the decision to use any antioxidant is made, it is critical to obtain a histopathologic diagnosis of the lesion. When dealing with a lesion diagnosed as hyperkeratosis, it may be appropriate to choose an antioxidant that may take some time for clinical improvement to occur. However, as the grade of epithelial dysplasia becomes more severe, consideration must be given to the possibility of malignant transformation during antioxidant treatment. We do not recommend the use of antioxidant supplements in the treatment of any carcinoma. The therapeutic use of antioxidant supplements outside of clinical trials conducted at academic medical centers should be done with considerable caution by practitioners in private practice. It should be emphasized that in these clinical trial patients were seen at frequent intervals to monitor their progress and to intervene if there was a noticeable deterioration in the clinical appearance of the lesion. In spite of the uncertainty with respect to antioxidant treatment, there are circumstances in which it should be considered. Recurrence after surgical excision when there is little reason to believe that a second surgical excision would be any more successful is an ideal candidate. Also, patients with widespread leukoplakia that involves a large area of the oral mucosa might be suitable for treatment with antioxidants, as well as patients who have extensive medical problems that make them surgical risks. The choice of which antioxidant(s) to use is complex because thus far there is no combination that is superior to the others. Beta-carotene with ascorbic acid or alpha-tocopherol is attractive because of a lack of side effects, but the range in reported values for lesion improvement has been broad and the clinical improvement typically takes several months. Clinical response with 13-cRA is faster but requires baseline and periodic serologic testing, as well as close monitoring for side effects. In those circumstances in which time is an important consideration, 13-cRA might be useful because clinical improvement can be evaluated within a matter of weeks as compared with beta-carotene. The group from M.D. Anderson Hospital has shown the value of an induction dose of 13-cRA that is followed by a lower maintenance dose. Unfortunately, the problem of recurrence after discontinuation of 13-cRA is quite common. One aspect that has not been evaluated is the combination of conventional surgical excision and the administration of postoperative antioxidants. This would have the obvious advantage of conventional treatment of surgery together with the possible protective effect of the antioxidants. Although this is an attractive hypothesis, we do not know of any studies that have proven this to be beneficial.

Effect of beta-carotene supplementation on serum alpha-tocopherol concentration

Conflicting reports of the effects of beta-carotene supplementation on serum alpha-tocopherol concentration led us to evaluated serum alpha-tocopherol in subjects with and without beta-carotene (30 mg/day) supplementation for up to 2 years duration in an ongoing chemoprevention trial. No adverse effect has been observed at any of the time periods examined.

Estrogen dependent LDH-Y, a new LDH isozyme and fertility factor in mice uterus during early pregnancy

In estrogen treated ovariectomized and pregnant mice on the first day after mating a sixth LDH isozyme appeared at Relative mobility (Rm) 0.08 to 0.15 and for convenience this isozyme is provisionally designated as LDH-Y. The appearance of a sixth LDH isozyme (LDH-Y) in mice uterus after ovariectomy and estrogen treatment favours the idea that this isozyme is estrogen dependent. Presence of this LDH-Y in mice uterus during preimplantation and finally its sudden disappearance during implantation and post implantation periods further suggest that LDH-Y is estrogen dependent and responsible for restoring fertility in mice.

Human uterine amylase in relation to infertility

In the uterine fluid of infertile women the amylase activity is significantly lower (90.00 to 357.75 mg/hr/100 ml) than that in parous women (172.14 to 536.99/hr/100 ml) during the different phases of menstrual cycle. Possibly the low enzyme activity in infertile women can impair the sperm capacitation and thus adversely affect the fertility of these infertile women.