Mass spectrometric identification of silver nanoparticles: the case of Ag32(SG)19

Mass spectrometry has played a key role in identifying the members of a series of gold clusters, which has enabled the development of magic-number cluster theory. The successes of the gold cluster system have yet to be repeated in another metal cluster system, however. Silver clusters in particular have proven to be challenging due to their relative instability compared with gold clusters. Using the well-characterized gold nanocluster, Au(25)(SG)(18), we present optimized electrospray ionization mass spectrometry (ESI-MS) instrumental parameters for the maximal transmission of the intact cluster. Parameters shown to have the largest effect on intact cluster transmission/detection include trap and transfer collision energy, source temperature, and cone gas flow rate. Herein we describe a general strategy to acquire mass spectra of fragile metal clusters with reliable mass assignments. By also optimizing sample solution conditions, high-quality ESI mass spectra of a prototypical silver:glutathione (Ag:SG) cluster were obtained without significant fragmentation. By using gentle conditions and solution conditions designed to stabilize the clusters, fragmentation was dramatically reduced and mass spectra with isotopic resolution were measured. Using this strategy, we have made the first formula assignment for a ligand-protected Ag cluster of Ag(32)(SG)(19).     

Synthesis and characterization of multi-walled carbon nanotubes functionalized with hyperbranched poly(urea-urethane)

Two types of hyperbranched poly(urea-urethane)-functionalized multi-walled carbon nanotubes (GHPU) have been synthesized in the presence of bis- and tris-hydroxy terminated carbon nanotubes (MWNT-OH). For comparison of the grafting efficiency on carbon nanotubes, pure hyper-branched poly(urea-urethane)s (HPUs) were also synthesized to prepare pristine carbon nanotubes-reinforced nanocomposites (HPNTs). Better MWNT dispersion in the polymer matrix was obtained for GHPU than for HPNT, and the effect was superior in the case of highly branched GHPU from tris-hydroxy-functionalized MWNTs, compared to GHPU from bis-hydroxy-functionalized MWNTs. TEM measurements for GHPUs clearly showed hyperbranched polymer-wrapped MWNT structures. Crystallization of hyperbranched polymers in GHPU was more developed than that of the HPNT nanocomposites, although MWNT-induced crystallization was observed for both the GHPU and HPNT samples. The hyperbranched polymer-grafting effect on MWNTs resulted in greater enhancement of the mechanical properties of GHPU at the same nanotube loading, compared to the case of HPNT nanocomposites. However, a too highly branched structure was found to lower the crystallization and mechanical properties of both the GHPUs and HPNTs.     

An experimental investigation on the application potential of heterogeneous catalyzed Nahar biodiesel and its diesel blends as diesel engine fuels

From the inception of commercialization of biodiesel, feedstock scarcity is a major issue to be pondered upon in developing countries. In this study, an attempt has been made to use an abundantly available underutilized high oil content (67% of Nahar seed kernel) feedstock derived biodiesel in a compression ignition engine. The experimental investigation on diesel engine reveals slightly reduced brake thermal efficiency and excellent exhaust emissions up to 40% blending of Nahar biodiesel with conventional diesel fuel. At full load, compared to diesel fuel, the BTE dropped by 1.64% and 1.83%, whereas the BSFC increased by 5.07% and 6.76% for B30 and B40 blends, respectively. The tested emission parameters such as CO, HC, NOx, and smoke were decreased by 12.66%, 17.99%, 8.31%, and 10.61% for B30 and 4.87%, 12.76%, 7.98%, and 11.78% for B40, respectively, compared to diesel fuel.

Abbreviation: BD: Biodiesel; DF: Diesel fuel     

A modified approach for collimation testing using Lau interferometry

A modified approach for the collimation testing of an incoherent optical beam using the Lau effect coupled with moiré readout is proposed. In the experimental set-up a white-light incoherent source illuminates a coarse grating G_1. The collimating lens is mounted on a translation stage, so that the grating G₁ can be adjusted to be at the ‘in-focus’, ‘at-focus’ or ‘out-of-focus’ position. Grating G₂ and grating G₃ are mounted on a precision rotational stage and are so positioned that the lines of the gratings make a small but equal and opposite angle with the vertical. The inclination angle of the resulting moiré fringe demonstrates the quality of collimation of optical beam. The proposed technique can also be conveniently used for measurement of the focal length of a collimating lens, at a very low cost.     

Synthesis and characterization of new hyperbranched poly(ether ketones) with various number of phenylene units

A new series of AB₂ type monomers with aromatic thio and various number of phenylene units were prepared. Three series of AB₂ type monomers, 4-thio-3′,5′-bis(4-fluorobenzal)biphenyl 1, 4-thio-3′′,5′′-bis(4-fluorobenzal)-p-terphenyl 2 and 4-thio-3′′′,5′′′-bis(4-fluorobenzal)-p-quarterphenyl 3 were synthesized in a stepwise manner starting from 3,5-bis(4-fluorobenzoyl)phenol 4 by repeating a series of conversions of the hydroxy group to the triflate, cross-coupling reaction of the triflate with (p-methoxythiophenyl)boronic acid, reduction of carbonyl groups followed by conversion of methylthio to thio group. Three kinds of hyperbranched poly(ether ketones) were prepared by the polymerization of the these three AB₂ type monomers. All compounds were characterized by elemental analysis, thermal analysis, ¹H and ¹³C NMR spectrometry.     

Physiochemical,circular dichroism‐induced helical conformation and optical property of chitosan azo‐based amino methanesulfonate complex

We have demonstrated the efficient procedure for the preparation of chitosan azo‐based amino methanesulfonate complex in isopropyl alcohol under mild condition. The ionic complexation between chitosan and {4‐[(4‐nitrophenyl)azo]phenyl}amino methanesulfonate is confirmed by ultraviolet (UV) and Fourier transform infrared spectroscopy. The circular dichroism spectra of chitosan complex showed positive at λ = 298 nm band with 3.88 mdeg having UV absorbance maximum up to a narrow band at λ= 290 nm in dimethyl sulfoxide, indicating that the polymer adopted helical (right handed) secondary structure. Physical properties, thermal stability, and surface morphology were analyzed by X‐ray diffraction, thermogravimetric analysis, differential scanning calorimetry and scanning electron microscopy. Optical properties of chitosan complex are evaluated by photoluminescence spectroscopy that showed blue shift (λ_em) peak at 400 nm at excitation wavelength 325 nm. Overall, it may open new perspectives for the use of chitosan azo‐based biohybrid in biomedical applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Analytical modeling for 3D potential distribution of rectangular gate (RecG) gate-all-around (GAA) MOSFET in subthreshold and strong inversion regions

In this paper, we have introduced an analytical subthreshold and strong inversion 3D potential model for rectangular gate (RecG) gate-all-around (GAA) MOSFET. The subthreshold and strong inversion potential distribution in channel region of a RecG MOSFET is obtained respectively by solving 3D Laplace and 3D Poisson equations. The assumed parabolic potential distribution along the z-axis in channel direction is appropriately matched with 3D device simulator after consideration of z-depended characteristic length in subthreshold region. For accurate estimation of short channel effects (SCE), the electrostatics near source and drain is corrected. The precise gate-to-gate potential distribution is obtained after consideration of higher order term in assumed parabolic potential profile. The model compares well with numerical data obtained from the 3D ATLAS as a device simulator and deckbuild as an interactive runtime of Silvaco Inc.     

Photovoltaics literature survey (no. 92)

In order to help keep readers up‐to‐date in the field each issue of Progress in Photovoltaics will contain a list of recently published journal articles most relevant to its aims and scope. This list is drawn from an extremely wide range of journals, including IEEE Transactions on Electron Devices, Journal of Applied Physics, Applied Physics Letters, Progress in Photovoltaics and Solar Energy Materials and Solar Cells. To assist the reader, the list is separated into broad categories, but please note that these classifications are by no means strict. Also note that inclusion in the list is not an endorsement of a paper's quality. If you have any suggestions please email Santosh Shrestha at s.shrestha@unsw.edu.au.