Formation of Heteroepitaxy in Different Shapes of Au–CdSe Metal–Semiconductor Hybrid Nanostructures

Formation of heteroepitaxy and designing different‐shaped heterostructured nanomaterials of metal and semiconductor in solution remains a frontier area of research. However, it is evident that the synthesis of such materials is not straightforward and needs a selective approach to retain both metal and semiconductor identities in the reaction system during heterostructure formation. Herein, the epitaxial growth of semiconductor CdSe on selected facets of metal Au seeds is reported and different shapes (flower, tetrapod, and core/shell) hetero‐nanostructures are designed. These results are achieved by controlling the reaction parameters, and by changing the sequence and timing for introduction of different reactant precursors. Direct evidence of the formation of heteroepitaxy between {111} facets of Au and (0001) of wurtzite CdSe is observed during the formation of these three heterostructures. The mechanism of the evolution of these hetero‐nanostructures and formation of their heteroepitaxy with the planes having minimum lattice mismatch are also discussed. This shape‐control growth mechanism in hetero‐nanostructures should be helpful to provide more information for establishing the fundamental study of heteroepitaxial growth for designing new nanomaterials. Such metal–semiconductor nanostructures may have great potential for nonlinear optical properties, in photovoltaic devices, and as chemical sensors.     

Estimation of quartz resonator Q and other figures of merit by an energy sink method

An important determinant of the quality factor Q of a quartz resonator is the loss of energy from the electrode area to the base via the mountings. The acoustical characteristics of the plate resonator are changed when the plate is mounted onto a base substrate. The base substrate affects the frequency spectra of the plate resonator. A resonator with a high Q may not have a similarly high Q when mounted on a base. Hence, the base is an energy sink and the Q will be affected by the shape and size of this base. A lower bound Q will be obtained if the base is a semi-infinite base since it will absorb all acoustical energies radiated from the resonator. A scaled boundary finite element method is employed to model a semi-infinite base. The frequency spectra of the quartz resonator with and without the base are presented. In addition to the loss of energy via the base, there are other factors which affect the resonator Q, such as, for example, material dissipation, and damping at the interfaces of quartz and electrodes. The energy dissipation due to material damping increases with the resonant frequency and the reduction of resonator size; hence material damping becomes important in the current and future miniaturized resonators operating at very high frequencies. An energy sink model along with material dissipation would provide realistic Q, motional capacitance, motional resistance, and other figures of merit useful for designing resonators. The model could be used for evaluating resonator and mountings designs of microelectromechanical systems and miniaturized devices. The effect of the mountings, and plate and electrode geometries on the resonator Q and other electrical parameters are presented for AT-cut quartz resonators. Model results from the energy sink method were compared with experimental results and were found to be good.     

Structural, magnetic, and electron transport studies on nanocrystalline layered manganite La1.2Ba1,8Mn2O7 system

The structure property relationship for Ru doped La1.2Ba1.8Mn2-RuxO7 system has been studied systematically. The system crystallizes in the single-phase tetragonal structure with space group of 14/mmm. The unit cell volume is found to increase with Ru doping. The sheet type microstructure could be seen in this system, which is important for anisotropic nature of layered structure. The crystallite size is found to be 25 nm indicating nanocrystalline nature of the system. Ferromagnetic to paramagnetic (Tc) transition above the room temperature is observed in all except the highest doped Ru (x = 1.0) where the Tc is 254 K using a.c. susceptibility measurement. The large values of magnetoresistance for the x = 0.0 sample at 10 K is found to be 57% and 64% at applied fields of 5 and 10 T, respectively.     

Development and Experimental Study of Milling Electrochemical Spark Micromachining (M-ECSMM) of Silicon

Silicon - Milling Electrochemical Spark Micromachining (M-ECSMM) is hybrid micromachining process which is used to create microfeatures in non-conducting materials. Silicon is one of the abundantly...     

Densification behaviour in forming of sintered iron–0.35% carbon powder metallurgy preform during cold upsetting

Plastic deformation is an important process to improve and obtain final product for sintered powder materials to compete with solid metal formed parts. The densification behaviour and forming limits of sintered iron–0.35% carbon steel preforms with different aspect ratios, during cold upsetting with two different lubricating constraints namely nil/no and graphite lubricant were investigated experimentally and is presented in this work. Powder preforms having initial theoretical density value of 84%, with two different aspect ratios were prepared using a suitable die-set assembly on a 1 MN capacity hydraulic press. Sintering operation was carried in an electric muffle furnace at the temperature of 1200 °C for a holding period of 1.5 h. Each sintered compact was subjected to incremental compressive loading of 0.05 MN under two different lubricant conditions till a visible crack appeared at the free surface. The densification mechanism is developed by studying the behaviour of densification against induced strain and Poisson’s ratio. Further, attained density is considered to establish flow stress and formability stress index behaviour. Increased frictional constraints produces high circumferential stress on the free surface due to barreling effect and hence inhibits forming limits. The present work provides a guideline for producing P/M components free from open surface pores.     

Dielectric and Raman Spectroscopic Studies of Na0.5Bi0.5TiO3–BaSnO3 Ferroelectric System

A series of lead‐free perovskite solid solutions of (1 ? x) Na_0.5Bi_0.5TiO₃(NBT)—x BaSnO₃(BSN), for 0.0 ≤ x ≤ 0.15 have been synthesized using a high‐temperature solid‐state reaction route. The phase transition behaviors are studied using dielectric and Raman spectroscopic techniques. The ferroelectric to relaxor phase transition temperature (T_FR) and the temperature corresponding to maximum dielectric permittivity (T_m) are estimated from the temperature‐dependent dielectric data. Dielectric studies show diffuse phase transition around ~335°C in pure NBT and this transition temperature decreases with increase in x. The disappearance of x‐dependence of A₁ mode frequency at ~134 cm^?1 for x ≥ 0.1 is consistent with rhombohedral‐orthorhombic transition. In situ temperature dependence Raman spectroscopic studies show disappearance and discontinuous changes in the phonon mode frequencies across rhombohedral (x < 0.1)/orthorhombic (x ≥ 0.1) to tetragonal transition.     

Free and bound triacontanol in tea leaves

A direct gas chromatographic method of identification and determination of 1-triacontanol, a plant growth substance, in tea leaves is reported. Treatment of the tea leaves with calcium oxide releases more triacontanol, showing that the compound occurs also in a bound form in tea leaves.     

Achieving the Best Yield in Glycolipid Biosurfactant Preparation by Selecting the Proper Carbon/Nitrogen Ratio

Pseudomonas aeruginosa RS29, the native biosurfactant-producing strain isolated from the oil fields of Assam, India was used to investigate the influence of the carbon nitrogen ratio on production of the biosurfactant. The biosurfactant producing ability of the strain was measured based on surface tension (ST) reduction of the culture medium and the emulsification (E24) index. Production was greatly influenced by the sources of nitrogen and carbon as well as the carbon to nitrogen (C/N) ratio. Sodium nitrate was the best nitrogen source and the water miscible carbon source, glycerol was observed as the best carbon source for maximum biosurfactant production. The C/N ratio 12.5 allowed the maximum production of biosurfactant by the RS29 strain. At this C/N ratio, 55 % ST of the culture medium was reduced by the produced biosurfactant. Concentrations of crude and rhamnolipid biosurfactant obtained at this particular C/N ratio were 5.6 and 0.8 g/l respectively. The RS29 strain was novel as it was able to produce a sufficient amount of biosurfactant utilizing a much lower amount of the water miscible carbon source, glycerol. Extraction of the biosurfactant by a chloroform–methanol (2:1) mixture was the best method to obtain the highest biosurfactant from the culture medium of the strain. The biosurfactant was confirmed as a mixture of mono and di-rhamnolipid congeners, Rha–C₁₀–C₁₀–CH₃ being the most abundant one. The biosurfactant was a good foaming and emulsifying agent.     

Jatropha oil and karanja oil as carbon sources for production of sophorolipids

Biosurfactants like sophorolipids (SL) are mild and environmentally friendly surfactants to be used in cosmetics and health care products. In addition to surfactant properties, SL also possess antimicrobial and skin healing properties. SL are produced by microbial fermentation using refined vegetable oils with glucose as a carbon source. This affects the economics of the production of SL. In the present work, non‐traditional oils like jatropha oil, karanja oil, and neem oil were used as newer feedstock for fermentative production of SL using Starmerella bombicola (ATCC 22214). In the fermentation, jatropha oil and karanja oil gave 6.0 and 7.6 g/L of SL (mainly lactonic form), respectively. HPLC, liquid chromatography–mass spectrometer, and ¹H NMR of crude SL obtained from fermentation broth showed lactonic form of two major SL. Oleic acid and linoleic acid were preferentially consumed over other fatty acids by the organism. Neem oil gave lower yield, i.e., 2.63 g/L of SL (mainly acidic form). Practical applications: Jatropha oil and karanja oil are one of the non‐traditional oils grown wildly in India that have large potential that is still to be explored. These oils contain non‐glycerides components that exclude their use as edible oil. These oils can be used as substrate for SL that can find novel applications like in soil remediation, skin care production, antimicrobial agents, low foaming detergents, and food additives. The current study has provided proof of concept work that has indicated the potential of these oils to be used as substrate for SL. It has opened new avenues and there is further scope to improve the yield by validating the process parameters like aeration rate, residual substrate recycle and pH control.     

Assessment of land grabbing from protected forest areas of Bhawal National Park in Bangladesh

Land grabbing has become the major problem in all the protected forest areas of Bangladesh during the last two decades. The study was conducted in Bhawal National Park, the tropical moist deciduous Sal (Shorea robusta C.F. Gaertn) forest ecosystem of Bangladesh. This area is going through a critical situation caused by industrial revolution. Already, 255.3 ha forest lands have been grabbed by 354 illegal industrial set-ups from the study area. In this study, grabbing of protected forestland by industries, their types, future grabbing trends, increasing population inside the forest area, causal factors of grabbing and impact on biodiversity have been analysed. Increasing practical conservation efforts supported by strong political will and ordinance for specific areas is essential to conserve the protected areas. Community-based conservation approaches need to be applied for mass awareness regarding the value of this ecosystem for sustainability.