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Magnetic-order induced effects in nanocrystalline NiO probed by Raman spectroscopy
Get PDFThe magnetic-order induced effects in nanocrystalline NiO are investigated through the phonons and magnons observed in the Raman spectra. The key observations are (i) an anisotropy of the first-order transverse and longitudinal optical phonons, with a splitting on the order of 5 meV and (ii) a marked size and excitation wavelength variation of the two-magnon peak, which varies linearly with a redshift of similar to 50 cm(-1) with a size reduction from 105 to 30 mm The magnon-related peaks, in contrast to the phonons, are suppressed for near-resonance laser excitations. The experimental results are interpreted in terms of the exchange interactions and strong electron-electron correlations. The magnetization measurements shows a crossover to ferromagnetism with large coercivities and magnetization with decreasing size, which is shown to be due to the thermoinduced contribution
Measurement Uncertainty in Vibration Calibration in Frequency Range of 5 Hz to 10 kHz
Get PDFThe paper evaluates the measurement uncertainty in realizing the secondary vibration standard at CSIR-National Physical Laboratory, India, and presents a comparison of the measurement uncertainty of secondary standard with that of primary vibration standard. The relative expanded measurement uncertainty of 0.80% to 2.2% in frequency range of 5 Hz to 10 kHz is evaluated. The measurement uncertainty so calculated is verified by comparison with the results from primary vibration calibration standard of CSIR-National Physical Laboratory, New Delhi, and SPEKTRA Schwingungstechnik und Akustik GmbH Dresden, Germany primary calibrations. The study recommends calibrating the back-to-back accelerometer with minimal uncertainty by using a primary calibrated single-ended accelerometer mounted on the top of the back-to-back transducer.The paper serves a guiding document to the calibration laboratories, industries and other stake holders in India to understand the concept of traceability in vibration measurements and formulation of uncertainty budget as per the international standard
Accuracy Estimation of Propagation Velocity in Variable Path Ultrasonic Interferometer for Liquids
Get PDFIn this article, we describe the effects and the degree to which they cause error in the measurement of propagation velocity. Various effects include nonlinearity in path measurement, temperature stability and number of maxima or minima consideration. Double-distilled water was used as a sample to estimate various effects. Finally, it has been concluded that the variable frequency approach may be preferred for better accuracy. It has also been observed that the digital frequency selection is more precise than mechanical distance variation
Growth, photoluminescence, lifetime, and laser damage threshold studies of 1, 3, 5-triphenylbenzene (TPB) single crystal for scintillation application
Get PDFThe 1, 3, 5-triphenylbenzene (TPB) single crystal has been grown using slow cooling seed rotation technique. Optical transmittance of the grown crystal was obtained from UV-Visible analysis. The grown TPB crystal has good transmission in the entire visible region with a lower cutoff wavelength of 330 nm. The solubility of TPB material was determined using toluene as a solvent with different temperatures. The full width at half maximum is 18 arcsec, which indicates that the crystal is of good quality. The TPB crystal was excited (lambda (exc)) at 307 nm, and the corresponding emission (lambda (em)) has been observed at 352 nm. The laser-induced damage threshold (LDT) value of grown crystal is 1.25 GW/cm(2). Third-order nonlinear optical susceptibility chi (3) is determined using the Z-scan technique as 3.07422x10(-09) esu. The TPB crystal proves its suitability for scintillation applications and optoelectronic device fabrications
Long-Term Measurements of SO2 Over Delhi, India
No full textLong-term measurements (2011-2018) of ambient sulphur dioxide (SO2) and meteorology were carried out at an urban site of Delhi, India, to study the seasonal and inter-annual variations of SO2 over Delhi. The average mixing ratio of SO2 was estimated as 2.26 +/- 0.48 ppb for the entire study period. Mixing ratio of ambient SO2 was estimated as 2.19 +/- 0.64 ppb, 2.07 +/- 0.89 ppb, 2.49 +/- 1.05 ppb and 2.27 +/- 0.71 ppb during winter, pre-monsoon, monsoon and post-monsoon seasons, respectively. SO2 mixing ratio was recorded maxima during monsoon (2.49 +/- 1.05 ppb) season, whereas minima during pre-monsoon season (2.07 +/- 0.89 ppb). The mixing ratio of SO2 showed slightly increase in the trend during observational period. Surface wind speed and wind directions analysis indicates the influence of local sources on the mixing ratio of SO2 at the study site. Backward trajectories and potential source contributing factor (PSCF) analysis also showed the local as well as the regional sources (industrial activities, coal burning and thermal power plants etc.,) influencing the mixing ratio of SO2 over Delhi
Low-frequency dielectric processes in deformed helix ferroelectric liquid crystals
Get PDFA low-frequency dielectric relaxation mode in deformed helix ferroelectric liquid crystal (DHFLC) has been observed at the interface of strongly rubbed substrates and DHFLC material which may find applications in low power consumption FLC devices. The surface-induced dielectric relaxation process at the interface of DHFLC and substrate is called the partially unwound helical mode (p-UHM) due to the unwinding of the helical structure at this interface. After investigation of the material under various parameters such as temperature, variation of the amplitude of probing ac voltage and dc bias voltage, the relaxation frequency of p-UHM is found to be shifted towards Goldstone mode and merged with it. The relaxation frequency of Goldstone mode is found to decrease, whereas the relaxation frequency of p-UHM process increases with the increase in temperature of DHFLC. Finally, both the modes merge and the resultant relaxation frequency is found to be lower than Goldstone mode in SmC* phase. It seems that phason mode and partial helical unwinding mode are coupled together due to dipole moment that is resulting in a new relaxation frequency. p-UHM process is significant for low-power displays and non-displays applications like a part of sensor where weak electric signal is required to be realized without pre-amplification
Material Study of Co2CrAl Heusler Alloy Magnetic Thin Film and Co2CrAl/n-Si Schottky Junction Device
Get PDFThe structural, optical, magnetic, and electrical properties of Co2CrAl Heusler alloy magnetic thin films grown on n-type silicon (100) substrate (n-Si) and glass substrate were studied. The films were deposited using DC magnetron sputtering. X-ray diffraction (XRD) analysis confirmed the polycrystalline nature of the films. The effect of grain size on transmittance was investigated. Magnetic measurements revealed the presence of magnetic ordering in the films. Partial densities of states (PDOS) of the Co2CrAl were calculated by density functional theory (DFT) methods using the Vienna Ab initio Simulation Package (VASP). Co2CrAl thin film deposited over a silicon substrate was investigated for I-V characteristics. The electrical behaviour confirmed the existence of a Co2CrAl/n-Si Schottky contact, which suggests a spin injection phenomenon from Co2CrAl to n-Si by tunnelling through the lowered Schottky barrier
Melt-Spun SiGe Nano-Alloys: Microstructural Engineering Towards High Thermoelectric Efficiency
Get PDFSilicon-germanium (SiGe) alloys are prominent high-temperature thermoelectric (TE) materials used as a powering source for deep space applications. In this work, we employed rapid cooling rates for solidification by melt-spinning and rapid heating rates for bulk consolidation employing spark plasma sintering to synthesize high-performance p-type SiGe nano-alloys. The current methodology exhibited a TE figure-of-merit (ZT) approximate to 0.94 at 1123 K for a higher cooling rate of similar to 3.0 x 10(7) K/s. This corresponds to approximate to 88% enhancement in ZT when compared with currently used radioisotope thermoelectric generators (RTGs) in space flight missions, approximate to 45% higher than pressure-sintered p-type alloys, which results in a higher output power density, and TE conversion efficiency (eta) approximate to 8% of synthesized SiGe nano-alloys estimated using a cumulative temperature dependence (CTD) model. The ZT enhancement is driven by selective scattering of phonons rather than of charge carriers by the high density of grain boundaries with random orientations and induced lattice-scale defects, resulting in a substantial reduction of lattice thermal conductivity and high power factor. The TE characteristics of synthesized alloys presented using the constant property model (CPM) and CTD model display their high TE performance in high-temperature regimes along with wide suitability of segmentation with different mid-temperature TE materials
A comparative study of circularity of artefact detecting circle using CMM and form tester with different filters
No full textThis paper presents a study of circularity of the different workpiece using CMM for smooth functioning of manufactured parts. The present work to study of roundness of different artefact using different algorithm and filters. For the present study have been conducted on RA-2200CNC form tester and LEGEX 9106 CMM by selecting two filters and four types of algorithm with different range of spectral wave numbers in terms of undulations per revolution (UPR) and fitting software techniques. Instrument data set help the designer and operator to satisfy the best fit for roundness in nano scale metrology
A facile approach for enhancing device performance of excitonic solar cells with an innovative SnO2/TCNE electron transport layer
No full textThe spread of the Internet of things created the need for huge amounts of off-grid energy sources for tens of billions of electronic devices with low power consumption for indoor applications. Excitonic solar cells may provide a better solution as compared with other solar cells due to their advantages such as low-cost, large-area module, and fabrication by solution printing and coating techniques. However, the organic solar cells (OSCs) or perovskite solar cells (PSCs) should have a low energy loss, suitable absorption spectrum, and minimum trap mediated charge recombination for its proper commercialization. Interface engineering is one of the ways of achieving better performance for these devices. Herein, we report a facile and effective strategy for interfacial modulation to achieve the improved performance of inverted bulk heterojunction (BHJ) solar cells with a solution-processable SnO2 electron transport layer (ETL) modified by an organic small molecule tetracyanoethylene (TCNE). We can say that a few nano-meter thin film of TCNE supports to reduce the energy barrier of SnO2, resulting in the efficient extraction and transport of negative charge carriers toward the cathode. The TCNE also passivates the surface defects of SnO2 and hence decreases the charge recombination rate for iOSCs. Furthermore, it brings the better interfacial contact between SnO2 and BHJ blend in which the polymer PTB7 and fullerene PC71BM are the donor and acceptor, respectively, showing average power conversion efficiencies of similar to 4.58%, similar to 4.98%, and similar to 2.95% with varying concentrations of TCNE (0.5 mg/ml, 1 mg/ml, and 2 mg/ml), respectively, in methanol, on top of SnO2, as ETLs, which are comparably better than that of pristine SnO2 (3.28%). We assumed that the TCNE modified SnO2 method is a potent and easy way to get efficient inverted BHJ solar cells with higher efficiency and may also be an appropriate alternative for other organic semiconducting devices where an ETL is required, such as organic light-emitting diodes and PSCs