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Supramolecular phase transitions triggered by external stimuli constitute a fascinating topic in materials science and supramolecular chemistry. Trimesic acid (TMA) represents a simple molecular bu...

Using scanning tunneling microscopy (STM), we investigated the effect of electrical pulses upon a supramolecular hybrid comprised of pentacenes and 1,3,5-tris(4-carboxyphenyl)-benzenes at the octanoic acid/graphite interface. STM results revealed that positive electrical pulses can promote the formation of such hybrids, whereas negative pulses selectively remove pentacene molecules from the complex. We attribute such results to the voltage-pulse-induced instant electrical attraction and repulsion between pentacene and substrate, thereby inducing the hybrid to form or to deform, respectively. Furthermore, these observed phenomena were elucidated via a coarse-grained molecular dynamic model using the continuum approximation.

Since the last decades, non-precious metal catalysts (NPMC), especially iron based electrocatalysts show sufficient activity, potentially applicant in oxygen reduction reaction (ORR), however they only withstand considerable current densities at low operating potentials. On the other hand iron based electrocatalysts are not stable at elevated cathode potentials, which is essential for high energy competence, and its remains difficult to deal. Therefore, via this research a simple approach is demonstrated that allows synthesis of nanosize Fe-doped mayenite electride, [Ca24Al28O64]4+·(e−)4 (can also write as, C12A7−xFex:e−, where doping level, x = 1) (thereafter, Fe-doped C12A7:e−), consist of abundantly available elements with gram level powder material production, based on simple citrate sol-gel method. The maximum achieved conductivity of this first time synthesized Fe-doped C12A7:e− composite materials was 249 S/cm. Consequently, Fe-doped C12A7:e− composite is cost-effective, more active and highly durable precious-metal free electrocatalyst, with 1.03 V onset potential, 0.89 V (RHE) half-wave potential, and ~5.9 mA/cm2 current density, which is higher than benchmark 20% Pt/C (5.65 mA/cm2, and 0.84 V). The Fe-doped C12A7:e− has also higher selectivity for desired 4e− pathway, and more stable than 20 wt% Pt/C electrode with higher immunity towards methanol poisoning. Fe-doped C12A7:e− loses was almost zero of its original activity after passing 11 h compared to the absence of methanol case, indicates that to introduce methanol has almost negligible consequence for ORR performance, which makes it highly desirable, precious-metal free electrocatalyst in ORR. This is primarily described due to coexistence of Fe-doped C12A7:e− related active sites with reduced graphene oxide (rGO) with pyridinic-nitrogen, and their strong coupling consequence along their porous morphology textures. These textures assist rapid diffusion of molecules to catalyst active sites quickly. In real system maximum power densities reached to 243 and 275 mW/cm2 for Pt/C and Fe-doped C12A7:e− composite, respectively.

ReS2 is an emerging member from the family of layered transition metal dichalcogenides (TMDCs) and has interesting optical and electrical properties due to its weak interlayer coupling. Systematically, layered ReS2 structures were successfully synthesized by hydrogen assisted controlled chemical vapor deposition method. DFT calculations were performed to determine the interface energies between ReS2 layer and SiO2/Si, sapphire and mica substrates. Calculated interface energy and % strain are lower for mica as compared to SiO2/Si and sapphire, which helps to grow smooth layers on mica substrate as compared to SiO2/Si. At atmospheric pressure, larger interface strains are produced between substrate and growing layers which transforms the 2D layered structure to 3D flower-like structures. Under the controlled conditions, substrates surface energy is playing a key role and mica with the freshly clean surface is probably facilitating the atoms to grow along in-plane direction to form smooth films. Finally, photo-detector measurements were made under the extreme conditions (high energy and intense light with large voltage sweep) to check the stability and reliability of the devices. The good stability, sensitivity (217 mAW−1) and fast response (Trise = 0.61 s, Tdecay = 1.59 s) of the devices reflects the quality of the synthesize product for their use in the future optoelectronic devices.

Recent advances in the fabrication and classification of amorphous carbon (a-Carbon) thin films play an active part in the field of surface materials science. In this paper, a pulsed laser deposition (PLD) technique through controlling experimental parameters, including deposition time/temperature and laser energy/frequency, has been employed to examine the substrate effect of amorphous carbon thin film fabrication over SiO2 and glass substrates. In this paper, we have examined the structural and magnetoresistance (MR) properties of these thin films. The intensity ratio of the G-band and D-band (ID/IG) were 1.1 and 2.4, where the C(sp2) atomic ratio for the thin films samples that were prepared on glass and SiO2 substrates, were observed as 65% and 85%, respectively. The MR properties were examined under a magnetic field ranging from −9 T to 9 T within a 2-K to 40-K temperature range. A positive MR value of 15% was examined at a low temperature of 2 K for the thin films grown on SiO2 substrate at a growth temperature of 400 °C using a 300 mJ/pulse laser frequency. The structural changes may tune the magnetoresistance properties of these a-Carbon materials. These results were demonstrated to be highly promising for carbon-based spintronics and magnetic sensors.

The optoelectronic properties of ZnS nanowires (NWs) and ZnS—Si core shell nanowires (CSNWs) oriented along different directions has been investigated using first principles calculations. Both NWs and CSNWs exhibit semiconductor characteristics in [100] and [111] directions while [110] oriented NWs and CSNWs exhibit metallic characteristics. The semiconductor characteristics of the ZnS NWs and ZnS—Si CSNWs in [100] and [111] directions have been confirmed from the electronic and optical energy gaps. We observed strong optical absorption in [110] directional ZnS—Si CSNWs throughout the spectrum from visible to UV region which represents significance to the optoelectronic and energy harvesting devices. Furthermore, the parallel and perpendicular parts of the optical absorption of ZnS—Si CSNWs show good improvement as compared to ZnS NWs. The refractive index and reflectivity spectra of ZnS—Si CSNWs also offered considerably upgraded values than ZnS NWs. Our predicated optical static dielectric constant e1(0) and static refractive index n(0) values are also much better than the previously reported one.

Using trimesic acid (TMA) as a model system by means of scanning tunneling microscope (STM) equipped with a temperature controller, here, we report a temperature-assisted method to cooperatively control electric-field-induced supramolecular phase transitions at the liquid/solid interface. Octanoic acid is used as a solvent due to its good solubility for TMA and its less complicated pattern formed under negative STM bias (e.g., only chicken-wire polymorphs existing). At positive substrate bias, STM revealed that TMA assembly based on temperature modulations underwent phase transitions from a porous (22 °C) to a flower (45 °C) and further to a zigzag (68 °C) structure. The transitions are ascribed to the partial deprotonation of the carboxyl groups of TMA. Both the temperature and electrical polarity of the substrate are crucial, i.e., the transitions only take place at positive substrate bias and elevated temperatures. Molecular mechanics simulations were carried out to calculate the temperature and electric field dependence of the adsorption enthalpy and free energy of the chicken-wire assembly of TMA on the two layers of graphene surface. The calculated decrease in adsorption enthalpy with the increase of temperature and electric field values that causes the TMA chicken-wire assembly to be less stable is proposed to promote the occurrence of the phase transition observed by STM. This study paves the way toward program-controlled supramolecular phase switching via the synergic effect of electrical and thermal stimuli.

In this study, we explored the thermoelectric properties of the host thermoelectric materials (TM), namely, binary skutterudites, using a combination of simulations based on density functional theory and post-DFT Boltzmann's semiclassical theory. The calculations were performed close to the Fermi surface for the Seebeck coefficient and other thermoelectric parameters. Our results demonstrated that CoSb3 exhibited the highest Seebeck value at room temperature among all the compounds (CoP3, CoAs3, CoSb3, IrP3, IrAs3, IrSb3, RhAs3, and RhSb3), which confirmed that this compound is an ideal host material for thermoelectric applications. Furthermore, the calculated electrical conductivity values show that RhAs3 has the largest value of 3.736 × 105 Ω−1 m−1. However, at high temperatures, the Seebeck values for all of these compounds are almost constant due to the activation of the minority charge carriers.

Defect engineering or lattice distortion is considered an efficient strategy to enhance the intrinsic activity of an electrocatalyst. Multishell, hollow NiCoFe alloy spheres were prepared with vacancies, gaps or defect, and tilting of an atomic plane with incorporated graphitic carbon derived from the surfactant. The extra gaps or defects in the lattice, which can be verified by high-resolution transmission electron microscope, provide additional active edge sites for the hydrogen evolution reaction. As a result, three-dimensional NiCoFe alloy poses a very low overpotential of 16 mV in 0.5 M H2SO4 for the hydrogen evolution reaction and an unexpectedly small Tafel slope of 38 mV dec−1. This work can therefore broaden horizons and provide a new dimension for the design of new, highly efficient electrocatalysts for hydrogen evolution in an acidic medium.

Recently, exploring the unique properties of 2D materials has constituted a new wave of research, which lead these materials to enormous applications ranging from optoelectronics to healthcare systems. Due to the profusion of surface terminated functionalities, MXenes have become an emerging class of 2D materials that can be easily integrated with other materials. The versatility of MXenes allows to tune their finest material properties for further device applications. This review initiates with the classification of preparation methods of MXenes, where the authors elaborate on the significance of top-down approaches including the exfoliation of solid layers. Next, the focus is diverted toward the materials analysis of MXenes including their terminations analysis as well as their intriguing electrical and mechanical behaviors through scanning probe microscopy. Finally, critical challenges and perspectives for MXenes analysis and applications are explored and discussed. Therefore, this comprehensive review can encourage researchers, and offer a precise direction to employ MXenes in various applications.

Herein, we synthesized hollow cubic caves of CuO (HC) and wrapped it with N-rich graphitic C (NC), derived from a novel biogenic mixture composed of dopamine (DA) and purine. The synthesized NC wrapped HC (NC@HC) sensor shows enhanced electrocatalytic efficacy compared to unwrapped CuO with shapes including HC, sponge (SP), cabbage (CB), and solid icy cubes (SC). The shape and composition of synthesized materials were confirmed through field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), whereas interfacial surface energy was calculated through contact angle measurement. The designed NC@HC sensor shows a remarkable response toward the simultaneous detection of uric acid (UA) and xanthine (Xn) with detection limits of 0.017 ± 0.001 (S/N of 3) and 0.004 ± 0.001 μM (S/N of 3), respectively. In addition, this platform was successfully applied to monitor UA from the gout patient serum. To the best of our knowledge, this is the first report on using such novel NC@HC materials for the simultaneous monitoring of UA and Xn.

We demonstrate by using scanning tunneling microscopy that a series of trace organic solvent additives can efficiently promote the electrically triggered phase transition of trimesic acid (TMA), which would otherwise occur rather sporadically. DFT simulations taking into account the electric field effect elucidate such tailored phase transformations, based on the Gibbs activation and free energies of the deprotonation reactions of TMA.

Cesium halide double-perovskites (Cs2AgCrX6; X = Cl, Br, and I) have been investigated for potential applications in optoelectronic devices. Density functional theory (DFT) has been utilized to study the structural, chemical bonding, electronic, mechanical, optical, and thermoelectric properties of these materials. Structural analysis has revealed that these compounds favor a face-centered cubic double-perovskite crystal structure with space group Fm-3m. The electronic properties show that Cs2AgCrX6 (X = Cl, Br) are indirect whereas Cs2AgCrI6 is a direct band-gap semiconductor, and their band-gap values are 2.81, 2.1, and 0.9 eV, respectively. The bonding nature between Ag-X and Cr-X atoms is covalent, while ionic bonds exist between Cs-X atoms. The systems are good dielectric materials and have the potential to be used in optoelectronic devices. Post-DFT calculations have been performed to calculate thermoelectric parameters. The increase of the Seebeck coefficient in these materials with temperature up to 400 K satisfies the Mott formula. Above this temperature, thermal excitations of extrinsic carriers decrease the Seebeck coefficient. The mechanical properties of these compounds indicate that they are ductile and anisotropic.

Non-linear to linear negative magnetoresistance (MR) was studied under the magnetic field ranging from &minus, 7 T to 7 T with a change in measurement temperature from 2 K to 300 K. Under the magnetic field of 7 T, a maximum MR magnitude of 8.2% was observed at 2 K. The chemical vapor deposition technique was adopted to synthesize the amorphous carbon thin films. Non-saturated and non-linear negative MR was observed for the lower temperatures, while 10 K was observed as transition temperature. Afterwards, the more likely linear MR behavior was observed up to 300 K. MR shape change was correlated with the structural morphology of metallic disordered graphitic layers or the random stacking of graphene layers with amorphous carbon. The negative MR mechanism for such a non-linear to linear shift was partially assumed as a combined effect of the diffused scattering theory and the weak localization theory. The negative MR effect has a direct relation with the degree of structural order.

In the present work, first principles calculations were applied to study the structural, electronic, optical and thermoelectric properties of perovskites (XRuO3; X = Ca, Sr) for the first time. The CaRuO3 and SrRuO3 are semiconductor materials with an average band gap of 1.27 eV and 0.27 eV, respectively. The dielectric function of CaRuO3 and SrRuO3 perovskites, which gives response to light in the infrared and visible region, represents its application in the optical devices. To extensively study the optical properties of CaRuO3 and SrRuO3 semiconductor material, we have discussed the dielectric constant and energy loss function in detail. The thermoelectric properties such as Seebeck coefficient, thermal conductivity and electrical conductivity as a function of chemical potential are investigated for both perovskites CaRuO3 and SrRuO3, using BoltzTrap code. The calculated values of Seebeck coefficients are 700 μV/K (CaRuO3) and 500 μV/K (SrRuO3) are much higher than the reported one. The exciting thermoelectric properties show that CaRuO3 and SrRuO3 semiconductor material can be a potential candidate for the thermoelectric application. The obtained results are in close agreement with the experimental data and existing literature.

Magnetoresistance (MR) of pure amorphous carbon thin films deposited by pulsed laser deposition at various deposition temperatures was studied. Maximum MR of 46% was observed at 2 K under the magnetic field of 7 T for the sample deposited at temperature of 500 °C. No tendency of MR saturation was observed up to 7 T. The MR decreases rapidly with the increase in measurement temperature and vanishes after 40 K. The transport mechanism of all the samples follow Efros-Shklovskii variable range hopping model. The characteristics temperature decreasing from 2540 K to 1290 K and localization length increasing from 5.3 nm to 10.7 nm with increasing fraction of C(sp2) from 72% to 84%. The lower disorder degree may results in higher MR.

Herein, for the first time, anisotropic magnetotransport phenomenon in amorphous carbon (a-C) thin films has been examined on the basis of Brysksin – Klein (B-K) model. The sign of magnetoresistance turns negative at (θ, ϕ) = (0°, 90°) to positive at (θ, ϕ) = (90°, 90°) where θ and ϕ are the angle between applied magnetic field and normal to the plane and the angle between applied magnetic field and current, respectively. The sign of magnetoresistance of a-C thin films varies continuously at θ = 0–360° and ϕ=0–90°, suggesting good potential for the position sensing of large magnetic field.

Negative magnetoresistance (MR) up to 13% was observed at 2 K under the magnetic field of 7 T in amorphous carbon thin films synthesized by chemical vapor deposition. No tendency of saturation of MR is observed up to the magnetic field of 7 T. Shift of structural morphology from disordered amorphous carbon to ordered graphitic like carbon was studied by using Raman, X-ray Diffraction, High Resolution Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy. Negative MR effect increases with the increase in structural order. The mechanism of this negative MR could be ascribed to the Weak Localization and Grain Boundary Scattering Conduction depending on the different temperature regimes.

Photocatalysis is attracting huge interest for addressing current energy and environmental issues by converting solar light into chemical energy. For this purpose, we investigated the effect of La3+ and Se4+ co-doping on the photocatalytic activity of BiFeO3. BiFeO3 and Bi0.92La0.08FeO3 nanoparticles containing different Se4+ doping content (BiFe(1−x)SexO3, x = 0.0, 0.02, 0.05, and Bi0.92La0.08Fe(1−x)SexO3, x = 0.0, 0.02, 0.05, 0.075, 0.1) were synthesized by a double solvent sol–gel route. The co-doped nanoparticles were characterized by X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), and UV-vis diffuse reflectance spectroscopy (DRS), and their photocatalytic activity was studied by the photocatalytic degradation of Congo Red (CR) in aqueous solution under different wavelengths of light illumination. The band-gap of the pure BiFeO3 was significantly decreased from 2.06 eV to 1.94 eV. It was found that La3+ and Se4+ co-doping significantly affected the photocatalytic performance of pure BiFeO3. Moreover, with the increment of Se4+ doping into Bi0.92La0.08FeO3 up to an optimal value, the photocatalytic activity was maximized. In order to study the photosensitization process, photo-degradation of a colourless organic compound (acetophenone) was also observed. On the basis of these experimental results, the enhanced photocatalytic activities with La3+ and Se4+ co-doping could be attributed to the increased optical absorption, and efficient separation and migration of photo-generated charge carriers with the decreased recombination of electrons–holes resulting from co-doping effects. The possible photocatalytic mechanism of La3+ and Se4+ co-doped BiFeO3 was critically discussed.

Chromium (III) oxide (Cr2O3) is a unique material which possesses a layered structure in the corundum structure phase, quite similar to the graphene and other transition metal dichalcogenides (TMDCs). Systematically, layered 2D-Cr2O3 hexagonal flakes were synthesized by chemical vapor deposition (CVD) method with Iodine as an assisting material. Under the controlled conditions (temperature, N2:H2 in carrier gas, etc), Iodine is playing a key role in transforming the crystal structure into hexagonal phase and grows in the form of layers. Incident light polarization dependent Raman spectroscopy was employed to see the coupling of in-plane Eg mode with spin to predict the anti-ferromagnetic ordering of spin in Cr2O3 hexagonal flake. Due to layer stacking and ordering, strong feature of creation of magnon states has been observed in photoluminescence (PL) spectroscopy. Finally, photo-detector response was measured to test the stability and reliability of the as-grown flakes for their use in spintronic devices.

We have investigated the electronic properties of heterostructures MoS2-ReS2 and ReS2-MoS2 with hybrid density functional theory. Contrary to the reported work, we found that ReS2 is an indirect band gap semiconductor material in the 2H phase, in good agreement with experimental work. Furthermore, the calculated charge density profile and weighted bands show that MoS2-ReS2 heterostructures have type-II band alignment whereas ReS2-MoS2 have type-I band alignment with indirect band gaps, which are in good agreement with the literature. In MoS2-ReS2 heterostructures, both electrons and holes were positioned in ReS2 layer in the form of an exciton, while in ReS2-MoS2 the electrons and holes were located in different layers which separated the electrons and holes into two different regions. The former heterostructure material is useful to the photovoltaic devices and the later is for the application of optoelectronic devices.

The present study is focused on the conductivity enhancement of the doped ceria. Composite mediated hydrothermal method (CMHM) was employed to produce the material. X-ray diffraction was used to determine phase of nanocrystalline Ce 1−2 x Gd x La x O δ and Ce 1−2 x Gd x Nd x O δ ( x = 0.1, 0.25). Conduction mechanism (dc conductivity and ac conductivity) in prepared samples was observed as a function of temperature and frequency. DC conductivity was measured in temperature range 300–700 °C. AC conductivity was measured in frequency range 1 kHz to 3 MHz at temperatures 300, 400, 500, 600, and 700 °C. The enhancement in conductivity was observed due to availability of oxygen vacancy sites which was dependent on composition. The Raman measurements supported the electrical conductivity results and more vacancy sites were observed in Raman spectrum in samples which showed maximum conductivities. The maximum conductivity achieved was 1.78 S cm −1 (at 600 °C) for Ce 0.5 Gd 0.25 Nd 0.25 O δ , which is quite a higher value in these compounds. This made this material a potential candidate for its use as an electrolyte material for Intermediate Temperature Solid Oxide Fuel Cells (ITSOFCs).

Soft ferrites are useful for various applications due to their high resistivity and low eddy current losses. Nanoferrites of manganese (MnFe2O4) were prepared by chemical co-precipitation method. Synthesis conditions were optimized for phase purity. The prepared MnFe2O4 were characterized by using X-ray diffraction (XRD) and AC and DC measurements for electrical conductivity and advantageous transient plane source (ATPS) method for thermal transport properties (thermal conductivity, thermal diffusivity, and volumetric heat capacity). The XRD results confirmed the spinel structure of as-prepared nanoferrites. Samples were sintered at 750°C for 2 h, and after sintering, the structure of the material changed from spinel to garnet. The sintering procedure was repeated for five times and its effect was observed on Mn ferrite nanoparticles. These materials are useful for various purposes of applications, e.g., as a core material to increase the efficiency of switch-mode power supply (SMPS). Using data of DC electrical resistivity as a function of temperature, activation energy was calculated. Thermal transport properties of the synthesized samples are reported and these are rarely found in literature.

The synthesis of cerium oxide (CeO2) nanoparticles through composite mediated hydrothermal approach is reported. A composite of sodium hydroxide and potassium hydroxide was used as precursor with cerium nitrate as the raw material. With the help of X-ray diffraction (XRD), we observed that the crystal structure of prepared ceria nanoparticles is cubic. Scanning electron microscopy (SEM) has been utilized to study the surface morphology of the material. Conductivity of synthesized cerium oxide was measured by standard two probes method. Cerium oxide is nonconductive at room temperature, but when we increase the temperature, it becomes conductive. It is observed that ionic conductivity depends on nature of nanoparticles and temperature. The oxygen ions conductivity was 2.32 ×10−8 S cm−1 at 300 ± 5 ∘C. In the region of 300 ± 5 to 400 ± 5 ∘C, the conductivity increases slightly. Above 400 ± 5 ∘C, it increases rapidly and gave a maximum value of 1.01 × 10 −7 S cm−1 at 700 ± 5 ∘C. Also, the effect of applied frequency on the conductivity, dielectric constant, and dissipation factor was observed as a function of temperature. The studied material is a strong potential candidate for electrolyte material in intermediate temperature solid oxide fuel cells (ITSOFC).

Both semiconductor and magnetic material properties are highly dependent on the environment temperature, and this is one of the critical obstacles limiting the application of these materials at high temperatures. In this work, a negative differential resistance-assisted anomalous Hall effect-based magnetic device has been fabricated and its thermal stability has been studied. The magnetic device was found quite stable and gave a reliable output current ratio of >104% in the temperature range of 0 °C–100 °C. The load-line analysis was performed to study the mechanism of thermal stability of this device in 0 °C–100 °C. It was found that the magnetic device exhibits improved thermal stability, with resistance variation in the range of 0 °C–100 °C being reduced by ∼40% compared to semiconductor-only devices. This study suggests that integrating magnetic and semiconductor properties together not only offer flexibility to integrate a number of applications in one simple device but also possible to provide thermal stability.

Nanoparticles of cerium oxide were synthesized by Composite Mediated Hydrothermal Approach (CMHA). The synthesis conditions were optimized to enhance the conduction properties and for narrow range of nanocrystallites. The synthesis parameters like hydrothermal treatment temperature (at 180 °C and 220 °C) and time (for 45 min, 70 min and 90 min) were optimized. The structural properties of the prepared ceria were examined by X-ray diffraction (XRD) data. Scherrer’s formula was used to calculate the crystallite sizes of average and most intense peak. Temperature dependent dc conductivity was measured in temperature range 200–700 °C and found to be increasing with the increase in measuring temperature and controlling the other synthesis conditions. The frequency dependent ac conductivity and dielectric properties were measured in frequency range 20 Hz–3 MHz at different temperatures. The ac conductivity increased (from 0.00091 to 2.661 S cm−1) with the increase in temperature (from 200 to 700 °C). Raman spectrum was observed for the different bands of cerium oxide and oxygen vacancies at 514 nm excitation laser line.

Due to its high permeability, Mn–Zn ferrite is the material of choice for high frequency applications up to a few MHz. At increased operational frequency, Ni–Zn ferrites are more suitable than Mn–Zn ferrites due to their low eddy current losses and low dielectric losses. To combine all these properties and to increase the operational frequency up to GHz, we have prepared Ni 0.5 Zn 0.5 Cr x Mn 0.5− x Fe 1.5 O 4 ( x = 0.1, 0.2, 0.3, 0.4, 0.5), with a simplified sol gel method. Prepared samples show high saturation magnetization, low coercivity, and low dielectric loss. The dielectric loss in the frequency range 1 MHz to 1.3 GHz remained almost constant as the Cr content was increased in the samples. The crystallite size and lattice parameters of these samples were calculated from X-ray Diffraction (XRD) data analysis. The crystallite size for each sample was calculated using the Scherrer formula considering the most intense peak (3 1 1) and the results were compared with the Scanning Electron Microscope (SEM) images of these samples. Powder X-ray diffraction (XRD) patterns confirmed the single phase spinel structure for these samples. Wayne Kerr Precession Component Analyzer 6440B and Agilent E4991 Impedance Analyzer were used to study the dielectric constant ( e ′) and the dielectric loss tangent (tan δ ) of these samples as a function of frequency in the frequency range 100 Hz to 1 MHz and 1 MHz to 1.29 GHz respectively. Quantum design PPMS model 6700 was used to study the magnetic properties of these samples.

Cerium oxide (CeO2) nanoparticles were synthesized by using sol–gel methods and the Composite Mediated Hydrothermal Method (CMHM). Sol–gel synthesis was done for 0.6 M molarity of the precursor solution of cerium nitrate hexa hydrated [Ce(NO3)3⋅6H2O] and the hydrothermal synthesis was done at 180 °C for 45 min. X-Ray diffraction (XRD) was used to measure the structural properties of the prepared ceria. Scherrer’s formula was used to calculate the crystallite sizes of average and most intense peak. Temperature dependent (200 °C to 700 °C) dc conductivity was measured and found to be increasing with the increase in measuring temperature. The frequency dependent (20 Hz to 3 MHz) ac conductivity and dielectric properties were measured at different temperatures. The comparison of electric and dielectric properties was studied. Both synthesis techniques were further analyzed by the Raman spectrum at 514 nm excitation laser line for the different bands of cerium oxide and oxygen vacancies.

Nanoparticles of cerium oxide were synthesized by the co-precipitation method. Synthesis conditions were optimized for phase purity, particularly the effect of pH (=14,13,11) of solutions during reaction, was studied. The phase analysis and structural properties of the prepared particles were determined by X-ray diffraction analysis. The average crystallite size decreased with the increase in pH of solution. The temperature-dependent DC conductivity was measured in the temperature range 300 °C to 700 °C and was found to be increasing with the increase in measurement temperature. AC conductivity and dielectric constants were measured in the frequency range of 1 kHz to 3 MHz and also at different temperatures.

Cerium oxide (Rare earth oxide ceramic) films were coated on ITO glass slides where CeO 2 was obtained by a simplified sol-gel method. The layer of molten NiO (Metal oxide) was physiosorped on ceria. The synthesis parameters like molarity of the precipitating agent and annealing temperature of the as prepared films were optimized. The X-ray diffraction was used for the confirmation of the phase, crystal structure and determination of crystallite sizes. The morphology of annealed films was studied using atomic force microscopy. The ac electrical measurements were done using LCR meter at room temperature and in frequency range 1 kHz to 3 MHz. The ac conductivity, dielectric constant and dielectric loss were determined using the electrical data.

Rare earth hydroxides (R(OH) 3 ) were synthesized by Composite mediated hydrothermal (CMH) method, a facile technique to prepare functional materials, and stoichiometric change in composition and morphology was observed. Ce(OH)3, La(OH) 3 and Nd(OH) 3 were the synthesized samples. X-ray diffraction (XRD) confirmed the hexagonal structures of the prepared samples. The crystallite size corresponding to the most intense peaks were 18, 33 and 41 nm for Nd-, La- and Ce-hydroxides. SEM revealed very interesting and fascinating morphologies. Ce(OH) 3 has belts like structures, Nd(OH) 3 has needles like structures and La(OH) 3 has wires like structures. The growth of structures can be ascribed to chemical potential, maintained through precipitating agent, the pressure inside the vessel, the temperature provided for the hydrothermal treatment and time for hydrothermal treatment time. The shape evolution can be explained by Gibbs-Curie-Wulff model which relate the shape evolution with the face energies. When the equilibrium energy is obtained for respective faces the Ostwald ripening is stopped. On heat treatment, the La(OH) 3 first converted into LaOOH at ca. 400 °C and finally into La 2 O 3 at ca. 600 °C as observed in DSC plot. The increase of conductivity with temperature is evident from the plots. Nd(OH) 3 achieved maximum conductivity and Ce(OH) 3 acquired minimum among the three possibly due to smaller crystallite sizes in the former case. The smaller grains increase the grain boundaries and charges can pile up on boundaries which increase the conductivity. The ac conductivity showed a direct dependence on frequency (1kHz–3MHz). The corresponding dc conductivity values of Ce(OH) 3 , La(OH) 3 and Nd(OH) 3 were 0.372, 6.648 and 20.369 S-cm−1, respectively. The interesting morphologies make these materials potential candidates for sensing and functionalization.

By the controlling of oxygen flow rate, the oxygen content has been altered in the (CoFeTaB)(100−x)Ox system, a newly reported possible magnetic semiconductor. The electric and magnetic properties of (CoFeTaB)(100−x)Ox films are dependent on the oxygen content of (CoFeTaB)(100−x)Ox films. The resistivity of the grown (CoFeTaB)(100−x)Ox films could be altered from 3.77 × 10 − 4 Ω · cm to insulator. Correspondingly, the magnetic behavior of the grown (CoFeTaB)(100−x)Ox films was varied from ferromagnetism to paramagnetism. The increase in the resistivity was mainly attributed to the enhanced oxidization of metal Co; and the magnetism conversion was resulted from the decrease of ferromagnetic Fe3+ and increase of paramagnetic Co2+ in the grown films. These findings provide the fundamental reference for tailoring the electric and magnetic properties of (CoFeTaB)(100−x)Ox materials for potential applications in spintronics.

The combined effect of metal inhomogeneity and diode assisted geometry changes on magnetoresistance (MR) of silicon has been studied at a low magnetic field by both finite element modeling (FEM) and experiments. The diode rectifying characteristic is utilized with rectangular shaped metal inhomogeneity to enhance the MR value. It is found that the MR value increases with the increase in the filling factor and reaches a maximum of 72% at 50 mT for a filling factor of 0.416. The FEM studies show that a large differential resistance ratio and critical current shift are the main factor for such a high MR value, which is in good agreement with our experimental results. This study could open another way to design MR devices that can show large MR and good magnetic field sensitivity.

Amorphous carbon thin films with a negative magnetoresistance (MR) of 13% and a positive MR of 31% at 2 K under a magnetic field of 7 T were fabricated through chemical vapor deposition (CVD) and pulsed laser deposition (PLD), respectively. Graphitic like carbon and amorphous structures of the thin films were observed by high-resolution transmission electron microscopy and X-ray diffraction. The MR decreases rapidly with the increase in temperature and vanishes after 40 K for the PLD grown sample, whereas for the CVD grown sample, the MR is observed up to 300 K. The negative MR may be due to the ordered graphitic like structures and its mechanism is explained by the weak localization theory for a lower temperature range of 2–50 K and the grain boundary scattering model for a higher temperature range of 50–300 K, whereas the positive MR may be due to its disordered amorphous structure and its mechanism is explained by the Efros-Shklovskii-type variable range hopping model.

Amorphous carbon thin films were fabricated on a SiO2 substrate using a chemical vapor deposition (CVD) technique. The structural and surface morphology of the films were analyzed by Raman spectrometry and high resolution transmission electron microscopy (HRTEM), respectively. The atomic ratio % of C(sp 2) and C(sp 3) bonds was estimated using x-ray photoelectron spectroscopy (XPS). The film shows angular magnetoresistance (MR) of 18% and 1.6% at 2 K and room temperature respectively. The mechanism of this angular MR was discussed by use of a grain boundary scattering (GBS) model.

Thin films of undoped amorphous carbon thin film were fabricated by using Chemical Vapor Deposition and their structure was investigated by using High Resolution Transmission Electron Microscopy and Raman Spectroscopy. Angular magnetoresistance (MR) has been observed for the first time in these undoped amorphous carbon thin films in temperature range of 2 ∼ 40 K. The maximum magnitude of angular MR was in the range of 9.5% ∼ 1.5% in 2 ∼ 40 K. The origin of this angular MR was also discussed.