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Organoaluminum cations for carbonyl activation
No full textIn search of stable, yet reactive aluminum Lewis acids, we have isolated an organoaluminum cation, (Me2NC6H4)(2)Al(C4H8O)(2)](+), coordinated with two labile tetrahydrofuran ligands. Its catalytic performance in aldehyde dimerization reveals turn-over frequencies reaching up to 6000 h(-1), exceeding that of the reported main group catalysts. The cation is further demonstrated to catalyze hydroelementation of ketones. Mechanistic investigations reveal that aldehyde dimerization and ketone hydrosilylation occur through carbonyl activation
Outstanding Absolute Electromagnetic Interference Shielding Effectiveness of Cross-Linked PEDOT:PSS Film
No full textConducting polymer ultrathin films with high absolute electromagnetic interference (EMI) shielding effectiveness (SE) is highly desirable for their facile processability. The conducting polymer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), possesses excellent conductivity. However, a thin film of PEDOT:PSS is water soluble, making it disadvantageous for EMI shielding. Here, a cross-linked, water-insoluble, ultrathin film of PEDOT:PSS for EMI shielding is evaluated. A 9 +/- 1 mu m thick cross-linked PEDOT:PSS film exhibits an average EMI SE of 40 dB. Standard electrodynamics simulation also confirms the experimental data. The most realistic parameter of EMI shielding for practical application is the absolute SE. The absolute SE of cross-linked PEDOT:PSS film is obtained to be 51 480 dB cm(2) g(-1), highest ever reported. Mechanistically, the absorption predominant SE originates from the cross-linking of PEDOT:PSS, resulting in a higher conductivity (769 S cm(-1)) and creating internal reflecting surfaces. The mechanical strength, solution processability, and outstanding absolute EMI SE make cross-linked PEDOT:PSS film to be an attractive EMI shield for real-time applications such as in defense arena
Generalizable Data-Free Objective for Crafting Universal Adversarial Perturbations
No full textMachine learning models are susceptible to adversarial perturbations: small changes to input that can cause large changes in output. It is also demonstrated that there exist input-agnostic perturbations, called universal adversarial perturbations, which can change the inference of target model on most of the data samples. However, existing methods to craft universal perturbations are (i) task specific, (ii) require samples from the training data distribution, and (iii) perform complex optimizations. Additionally, because of the data dependence, fooling ability of the crafted perturbations is proportional to the available training data. In this paper, we present a novel, generalizable and data-free approach for crafting universal adversarial perturbations. Independent of the underlying task, our objective achieves fooling via corrupting the extracted features at multiple layers. Therefore, the proposed objective is generalizable to craft image-agnostic perturbations across multiple vision tasks such as object recognition, semantic segmentation, and depth estimation. In the practical setting of black-box attack scenario (when the attacker does not have access to the target model and it's training data), we show that our objective outperforms the data dependent objectives to fool the learned models. Further, via exploiting simple priors related to the data distribution, our objective remarkably boosts the fooling ability of the crafted perturbations. Significant fooling rates achieved by our objective emphasize that the current deep learning models are now at an increased risk, since our objective generalizes across multiple tasks without the requirement of training data for crafting the perturbations. To encourage reproducible research, we have released the codes for our proposed algorithm.(1
Nanodelivery in Scrolls-Based Nanocarriers: Efficient Constructs for Sustainable Scavenging of Heavy Metal Ions and Inactivate Bacteria
No full textNanodelivery is a well-known and efficient strategy andherein, we attempted to mimic this strategy using graphene-based nanoscrolls containing metal-organic frameworks (Zn-3(BTC)(2)MOF) for efficient capture of heavy metal ions and inactivate bacterial cells in water. Zn-3(BTC)(2) and graphene scrolls have been used in different fields independently, yet the potential scope of these materials is unexplored. Mimicking metamorphosis of a caterpillar was adapted to design deliverable nanoscroll-encapsulated rod-like Zn-3(BTC)(2)MOF. These constructs lead to targeted inactivation of bacterial cells by puncturing the cells showing a 3 log-fold reduction in E. coli and S. aureus. Additionally, after hydration, the activated porous MOFs result in scavenging heavy metals like lead and arsenic from water sources with a rejection > 99.5%. The uniqueness of these constructs was explored as an easy-to-deploy point of use device (hand-held and in-line kit) for water remediation applications
High Hole Mobility and Efficient Ambipolar Charge Transport in Heterocoronene-Based Ordered Columnar Discotics
No full textHeterocoronene, a new redox-active core fragment, is utilized for the synthesis of room-temperature columnar discotic liquid crystals (DLCs). Three wedge-shaped side chains having different lengths of alkyl tails are introduced at the periphery of the heterocoronene core to prepare three kinds of discotic molecules, 1 (R = C10H21), 2 (R = C12H25), and 3 (R = C14H29). X-ray diffraction (XRD) analysis confirmed the packing variation in the columnar lattices regulated by alkyl chains of discrete length and steric bulk. When used in space charge limited current devices, compound 1 exhibits a high hole mobility value of 8.84 cm(2)/V s at ambient temperature, whereas compounds 2 and 3 show efficient ambipolar charge transport behavior with maximum hole (mu(h)) and electron (mu(e)) mobilities of 0.70 and 3.59 cm(2)/V s, respectively, for compound 3. The mobility values (mu(h) = 8.84 cm(2)/V s for 1 and mu(e) = 3.59 cm(2)/V s for 3) are remarkable and the highest ever disclosed for any DLC-based organic semiconductor, promising to deliver a good balance between mobility and processability in devices. The grazing incidence small- and wide-angle X-ray scattering experiments are employed to quantify the extent of alignment in the film state, which correlates with the observed trend of mobility values
Uncovering the Neglected Similarities of Arynes and Donor-Acceptor Cyclopropanes
No full textArynes and donor-acceptor (D-A) cyclopropanes are two classes of strained systems having the potential for numerous applications in organic synthesis. The last two decades have witnessed a renaissance of interest in the chemistry of these species primarily because of the mild and robust methods for their generation or activation. Commonly, arynes as easily polarizable systems result in 1,2-disubstitution, whereas D-A cyclopropanes as polarized systems lead to 1,3-bisfunctionalization thereby showing striking similarities. Transformations with 1,2- and 1,3-dipoles afford cyclic structures. With arynes, emerging four-membered rings as intermediates might react further, whereas the analogous five-membered rings obtained from D-A cyclopropanes are most often the final products. However, there are a few cases where these intermediates behave surprisingly differently. This Minireview highlights the parallels in reactivity between arynes and D-A cyclopropanes thereby shedding light on the neglected similarities of these two reactive species
Microstructural Characterization of GaN Grown on SiC
No full textGaN films have been grown on SiC substrates with an AlN nucleation layer by using a metal organic chemical vapor deposition technique. Micro-cracking of the GaN films has been observed in some of the grown samples. In order to investigate the micro-cracking and microstructure, the samples have been studied using various characterization techniques such as optical microscopy, atomic force microscopy, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy (TEM). The surface morphology of the AlN nucleation layer is related to the stress evolution in subsequent overgrown GaN epilayers. It is determined via TEM evidence that, if the AlN nucleation layer has a rough surface morphology, this leads to tensile stresses in the GaN films, which finally results in cracking. Raman spectroscopy results also suggest this, by showing the existence of considerable tensile residual stress in the AlN nucleation layer. Based on these various observations and results, conclusions or propositions relating to the microstructure are presented
SPR Sensing Enhancement with Dynamic Radiative Damping Stimulated by Graphene Conductivity Under Temperature Variation in NIR
No full textThe dynamic nature of radiation damping is exploited in a fluoride fiber-based plasmonic sensor in terms of variable temperature (T) and Ag layer thickness (d(m)) at certain near-infrared wavelengths. The optimum point of radiation damping, which is stimulated by the presence of a graphene monolayer and its dynamic dispersive and thermo-optic properties as per Kubo formulation, causes extremely huge enhancement in sensor's performance (analyzed in terms of its figure of merit, i.e., FOM). The simulation indicates that at lambda = 1550 nm, the optimum radiation damping is achieved at d(m) = 35 nmand T = 322.7Kleading to a peak FOM value of 27,086 RIU-1. At. = 1310 nm, the peak FOM is 16,736.65 RIU-1 for d(m) = 35.4 nm and T = 315.6 K. The above peak FOM values are significantly greater than those presently available with plasmonic sensors
One Hundred Years After the Latimer and Rodebush Paper, Hydrogen Bonding Remains an Elephant!
No full textLatimer and Rodebush (J Am Chem Soc 42: 1419-1433, 1920) discussed the ways a Lewis dot structure could be drawn for liquid water and proposed that the H held between two octets constitutes a bond in 1920. When it was realized that the other molecule of life, DNA, owes its double helix structure to specific hydrogen bonds between A-T (two) and C-G (three) base pairs, the interest in hydrogen bonding grew dramatically. While hydrogen bonding could be readily seen in water and DNA, it was not so easy to understand leading to continuous debates about what it means. This article gives a personal perspective of the evolution of hydrogen bonding since the Latimer and Rodebush paper to the recent IUPAC definition of hydrogen bond, published in 2011 and now. Is there a third C-H center dot center dot center dot O hydrogen bond in the A-T base pair
Tailoring light-matter interaction in WS2-gold nanoparticles hybrid systems
No full textRecently, considerable attention has been paid to tune the emission using hybrid systems composed of layered transition-metal dichalcogenides and metal nanoparticles (NPs) since metal NPs have the ability to enhance and localize the incident electromagnetic field. Furthermore, these hybrid systems show great interest from the standpoint of fundamental science as it constitutes an atomic scale prototype of charge-transfer complexes. Here, we realized WS2-gold (Au) NPs hybrids by chemically growing Au NPs at the edges of the mechanically exfoliated bilayer WS2. The Au NPs significantly increase the light-matter interaction which has been studied through Raman and photoluminescence (PL) spectroscopy. A substantial enhancement of the PL intensity in the WS2-Au composite concerning the pristine WS2 has been observed, and it increases as the number and size of the Au NPs on WS2 is increased. Geometry-dependent modification of plasmon resonance energy of Au NP alters the coupling strength between the emission pathways of WS2 and the plasmon which is manifested by a change in relative intensity between trion (X-) and exciton (X) emissions. We probe the mechanism of the PL intensity modulation through polarization-dependent measurements and simulation. We have demonstrated that, in WS2, the internal quantum efficiency increases and activation energy decreases due to coupling with Au NPs. Compared to pristine WS2, a faster change in optical band gap with temperature in WS2-Au may be due to enhancing electron-phonon interaction and lattice expansion in the latter. Our paper indicates the possibility to develop high performance transition-metal dichalcogenide-based photonic devices