Entire Nanostructure Research Articles

Tuning Crystal Plane Orientation in Multijunction and Hexagonal Single Crystalline CsPbBr3 Perovskite Disc Nanocrystals

Two-dimensional-shaped CsPbBr3 platelet nanocrystals are widely studied for their bright high energy emission and self-assembly. These nanostructures are in orthorhombic phase, have a square shape, and have the vertical axis [001] perpendicular to the basal plane. Moreover, these are mostly single-crystalline structures with a continuous lattice and appear like slices of cube nanocrystals. In contrast, herein, multijunction and hexagonal single crystalline 2D discs of CsPbBr3 are reported to have all their vertical axes [100]. These are obtained by using the perovskite derivative of tetragonal Cs3MnBr5 as the parent material and subsequent B-site Pb(II) introduction in the presence of phenacyl bromide at different reaction temperatures. At low temperature, multijunction discs having random orientations of two horizontal axes [010] and [001] from one to another segment are observed. Orientations of planes remained random as both coherent and incoherent twin planes were observed at their boundaries. However, the number of junctions/segments was reduced at higher temperature, and finally hexagonal single crystalline discs remained as the ultimate product. Analysis suggested that the crystal nature of parent Cs3MnBr5 and temperature-dependent variation in the rate of Pb(II) insertions determined the nature of discs having randomly oriented or static planes in the entire nanostructure. Not only in 2D discs but also, 3D nanocrystals having similar segments with different orientations are formed upon Pb(II) exchange with Mn(II) alloyed cubic CsBr. Hexagonal single crystalline and segmented multijunction CsPbBr3 discs remain unique among 2D perovskites nanostructures, and their formation mechanism indeed introduced new fundamentals of the crystallization process of these emerging energy materials.

Wave reversal mode in permalloy wire-tube nanostructures

We have investigated hysteresis curves and magnetization reversal mechanisms in permalloy wire-tube nanostructures when an external magnetic field is applied perpendicular to the axis of the nanostructure, in the x direction. Our results show that the nanotube reverses its magnetization through the wave reversal mechanism, while the nanowire does so through pseudo-coherent rotation, according to the literature. The wire-tube nanostructure exhibits a more complex reversal mechanism, where each segment begins to revert depending on whether it is a wire or tube segment, but quickly the entire nanostructure adopts the wire segment reversal mechanism as its own, considerably reducing the area within of the hysteresis curve exhibited by the nanostructure. The possibility to alter the magnetization reversal mode in such nanostructures provides an attractive way to control the motion of the magnetic domain walls.

Ambient pressure drug loading on trimethylchlorosilane silylated silica aerogel in aspirin controlled-release system

Trimethylchlorosilane silylated silica aerogel (TS-SA) was loaded with a model drug, aspirin. TS-SA preparation, drug loading, and drying were performed through ambient pressure techniques in a safe and cheap manner. The sample structure, drug loading, and drug dissolution profiles were characterized by N2 adsorption and desorption analysis, FT-IR spectroscopy, UV absorption spectroscopy, FE-EM, EDX, XRD, and DSC. The characterization results indicated drug molecules are successfully loaded on the entire nanostructure of TS-SA. Specific surface area, total pore volume, and average pore size decrease with drug loading in TS-SA structure, as well as XRD and DSC results are indicating the amorphous state of loaded aspirin. Drug adsorption isotherm was measured and fitted well by the Freundlich model. Drug release kinetics from the samples were also evaluated in 0.1 N HCl (pH 1.2) and phosphate buffer (pH 7.4). The zero-order model, the first-order model, and the Higuchi model were employed to study the release kinetics. Better fitting to the Higuchi model showed that Fick's diffusion governs the aspirin release mechanism. The release rate of loaded samples was slower than the pure drug in both HCl and phosphate buffer. As pure aspirin dissolves totally in 0.1 N HCl and phosphate buffer within 40 min and 20 min, respectively, loaded drug dissolve 35% ± 4 and 80% ± 4 in 0.1 N HCl and phosphate buffer within 100 min. The ambient pressure drug loading on TS-SA could have interesting potential applications in controlled release drug delivery systems.

Advanced Nanostructures for Proton Exchange Membrane Fuel Cells: From Liquid Electrolyte to Membrane Electrode Assembly

During the last decade, the landscape of Pt-based electrocatalysts for the oxygen reduction reaction, cathodic reaction of the proton exchange membrane fuel cell, dramatically changed. Huge enhancements in specific and mass activity, versus the standard, mono-metallic platinum nanoparticles supported on carbon, have been achieved. This was made possible by following two different approaches, namely (i) the order-based and (ii) the disorder-based approaches. The order-based consists in modifying the platinum lattice parameter and coordination number, thus impacting its electronic structure, in an identical fashion throughout the nanostructure. To undergo this path, the Pt can be alloyed with 3d-transition metals or rare-earth elements, or the nanostructures can be shaped to exhibit a preferential orientation, such as (111) facets, with a specific Pt atoms packing. By opposition, the disorder-based approaches imply that the electrocatalytic activity is carried, not by the entire nanostructure, but by some specific active sites exhibiting an ideal generalized coordination number and an ideal distance with their nearest neighbour 1,2. Such approaches resulted in notable nanostructures, such as the PtNi octahedra 3, the PtNi nanoframes 4 or others that presented notable activity enhancements in liquid electrolyte vs. standard Pt/C. The highest activity improvement reported was for the PtNi nanowires 5, namely 35-fold higher specific activity than standard Pt/C. However, there is only little reports on their activity in membrane electrode assemblies. From these reports, it mainly appears that the liquid electrolyte activity is often not reproduced, and that the improvements factors in solid electrolyte environment range from 1 to 5 vs. standard Pt/C 6,7. However, an extensive comparison of the liquid vs. solid performance for a wide range of electrocatalysts is currently missing. In this work, a group of electrocatalysts was synthesized from using microwave-assisted syntheses, including standard Pt/C, PtM alloys, ordered (nano cubes, octahedra) and disordered nanostructures. These electrocatalysts were characterized in liquid electrolyte and solid electrolyte environment, and the changes in specific surface, mass and specific activity were assessed.(1) Calle-Vallejo, F.; Tymoczko, J.; Colic, V.; Vu, Q. H.; Pohl, M. D.; Morgenstern, K.; Loffreda, D.; Sautet, P.; Schuhmann, W.; Bandarenka, A. S. Science. 2015, 350, 185–189.(2) Le Bacq, O.; Pasturel, A.; Chattot, R.; Previdello, B.; Nelayah, J.; Asset, T.; Dubau, L.; Maillard, F. ChemCatChem 2017, 9, 2324–2338.(3) Cui, C.; Gan, L.; Li, H.-H.; Yu, S.-H.; Heggen, M.; Strasser, P. Nano Lett. 2012, 12, 5885–5889.(4) Chen, C.; Kang, Y.; Huo, Z.; Zhu, Z.; Huang, W.; Xin, H. L.; Snyder, J. D.; Li, D.; Herron, J. A.; Mavrikakis, M.; Chi, M.; More, K. L.; Li, Y.; Markovic, N. M.; Somorjai, G. A.; Yang, P.; Stamenkovic, V. R. Science. 2014, 343, 1339–1343.(5) Li, M.; Zhao, Z.; Cheng, T.; Fortunelli, A.; Chen, C.-Y.; Yu, R.; Zhang, Q.; Gu, L.; Merinov, B. V.; Lin, Z.; Zhu, E.; Yu, T.; Jia, Q.; Guo, J.; Zhang, L.; Goddard, W. A.; Huang, Y.; Duan, X. Science. 2016, 354, 1414–1419.(6) Li, B.; Wang, J.; Gao, X.; Qin, C.; Yang, D.; Lv, H.; Xiao, Q.; Zhang, C. Nano Res. 2019, 12, 281–287.(7) Mauger, S. A.; Neyerlin, K. C.; Alia, S. M.; Ngo, C.; Babu, S. K.; Hurst, K. E.; Pylypenko, S.; Litster, S.; Pivovar, B. S. J. Electrochem. Soc. 2018, 165, 238–245. Figure 1

Strain-induced non-linear optical properties of straddling-type indium gallium aluminum arsenic/indium phosphide nanoscale-heterostructures

Non-linear optical properties of indium gallium aluminum arsenic/indium phosphide (InGaAlAs/InP) material system based unstrained and strained lasing nano-heterostructures of straddled type (type-I) under TE (transverse electric) polarization mode have been studied. To produce the different states of strain at the heterointerfaces in the structure, the different layers of the active region of InGaAlAs (width ~6nm) with different lattice constants (due to different mole fractions) have been assumed to be deposited in between the barriers of In0.41Ga0.34Al0.25As followed by claddings of In0.52Al0.48As. The entire nano-structure is a type of step SCH (separate confinement heterostructure) and has been assumed to grow over InP substrate. To study the strain induced non-linear optical properties of the structure, single effective mass and Kohn–Luttinger Hamiltonian equations have been solved to obtain quantum states and envelope wave functions in the heterostructure. In addition, the optical gain, differential gain, and the anti-guiding factor in order to support the gain calculation have been computed and reported. On behalf of simulation and previously reported experimental results, it has been suggested that either unstrained or compressive strained InGaAlAs/InP nano-heterostructures are more suitable for novel applications in the emerging areas of nano-opto-electronics due to the maximum gain occurring at lasing wavelength of 1.55µm which is the wavelength of minimum optical attenuation.

2次元金属ナノ構造体が示す強い局所光学活性：近接場円二色性イメージング

Nanostructures with chiral shapes show optical activity. The optical activity of the chiral nanostructure may be regarded approximately as an integration of contributions from optical activity of local sites over the entire nanostructure. In this article, we describe our recent experimental efforts to realize 100-nm-scale spatially resolved circular dichroism (CD) imaging. The results of CD imaging for S-shaped gold nanostructure are compared with the macroscopically obtained CD spectra. Local CD signals of both handednesses coexisted in the individual nanostructure, and the spatial distribution of the CD reflected the chiral symmetry of the nanostructure. When the local CD signal is integrated over the entire nanostructure, its value was approximately 1% of the maximum local CD signal, which roughly coincided with the macroscopic CD signal. This indicates that there are possibly prominent local CD signals even if only a tiny CD signal is observed in the macroscopic measurements of optical activity for nanostructured samples.

Optical properties and sensing in plexcitonic nanocavities: from simple molecular linkers to molecular aggregate layers

We present a theoretical study of a metal–molecular aggregate hybrid system consisting of a strongly coupled dimer connected by molecules characterized by an excitonic transition. The plasmonic resonances of the metallic dimer interact with the molecular excitations giving rise to coupled plasmon–exciton states, so called plexcitons. We compare the differences in the optical response when the excitonic material is placed only as a linker in the plasmonic gap of the dimer and when the material is distributed as an aggregate layer covering the dimer entirely. We also explore the efficiency of plexcitons for localized surface plamon resonance (LSPR) sensing in both situations. The ordinary shift-based sensing is more efficient for dimers connected through molecular linkers, whereas intensity-based sensing is more effective when the molecular aggregate covers the entire nanostructure. These results can serve to design the chemistry of excitons around metallic nanoparticles.

Highly oriented cupric oxide nanoknife arrays on flexible carbon fabric as high performing cold cathode emitter

Sharp knife edged copper oxide (CuO) nano architectures were directly grown on the surface of flexible carbon fabric by a facile chemical route with the assistance of nonionic surfactant PEG-6000. The carbon fabric substrate preserves its high flexibility even after the growth of the entire nanostructure. Moreover, it can be rolled-up and twisted to a large degree without affecting the electrical characteristics. The phase purity and degree of crystallinity of the developed nanostructures were systemically supported by X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy and high-resolution transmission electron microscopy. A proposed growth mechanism has been offered by thoroughly analyzing the field emission scanning electron microscopic images of the nanostructures grown at different concentrations of PEG. Among the as grown nanostructures, copper oxide nanoknives have exhibited remarkable field emission properties and high stability with a lower turn-on field of 0.9 V μm−1 (10 μA cm−2) at room temperature, which is sufficient for electron emission based devices like field emission displays and vacuum nano-electronic devices.

Strong Nanoscale Optical Activity Localized in Two-Dimensional Chiral Metal Nanostructures

Nanostructures with chiral shapes behave like chiral molecules and show optical activity. The optical activity of the chiral nanostructure should be given approximately by the summation of the local optical activities over the entire nanostructure. In this work, we report 100-nm-scale spatially resolved circular dichroism (CD) and compare the results with the macroscopically obtained CD spectrum of S-shaped gold nanostructures. Local CD signals with both directions of handedness coexisted in the individual nanostructures, and the spatial distribution of the CD reflected the chiral symmetry of the nanostructure. When integrated over the entire nanostructure, the local CD signal was approximately 1% of the maximum of the local CD signal, which approximately coincided with the macroscopic CD signal. This indicates that prominent nanoscale local CD signals might exist even if only a tiny CD signal is observed as the macroscopic optical activity of the nanostructured sample.

Carrier trapping and luminescence polarization in quantum dashes

We study experimentally and theoretically polarization-dependent luminescence from an ensemble of quantum-dot-like nanostructures with a very large in-plane shape anisotropy (quantum dashes). We show that the measured degree of linear polarization of the emitted light increases with the excitation power and changes with temperature in a nontrivial way, depending on the excitation conditions. Using an approximate model based on the $\mathbit{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{p}$ theory, we are able to relate this degree of polarization to the amount of light-hole admixture in the exciton states which, in turn, depends on the symmetry of the envelope wave function. Agreement between the measured properties and theory is reached under assumption that the ground exciton state in a quantum dash is trapped in a confinement fluctuation within the structure and thus localized in a much smaller volume of lower asymmetry than the entire nanostructure.

Component mode synthesis approaches for quantum mechanical electrostatic analysis of nanoscale devices

In this paper, two component mode synthesis (CMS) approaches, namely, the fixed interface CMS approach and the free interface CMS approach, are presented and compared for an efficient solution of 2-D Schrodinger-Poisson equations for quantum-mechanical electrostatic analyses of nanostructures and devices with arbitrary geometries. In the CMS approaches, a nanostructure is divided into a set of substructures or components and the eigenvalues (energy levels) and eigenvectors (wave functions) are computed first for all the substructures. The computed wave functions are then combined with constraint or attachment modes to construct a transformation matrix. By using the transformation matrix, a reduced-order system of the Schrodinger equation is obtained for the entire nanostructure. The global energy levels and wave functions can be obtained with the reduced-order system. Through an iteration procedure between the Schrodinger and Poisson equations, a self-consistent solution for charge concentration and potential profile can be obtained. Numerical calculations show that both CMS approaches can largely reduce the computational cost. The free interface CMS approach can provide significantly more accurate results than the fixed interface CMS approach with the same number of retained wave functions in each component. However, the fixed interface CMS approach is more efficient than the free interface CMS approach when large degrees of freedom are included in the simulation.

New Ultra-Thin Pure Silicon Window Grids for Transmission Electron Microscopy Samples

Abstract Traditional sample preparation supports for electron microscopy have usually been thin films of amorphous or holey carbon stretched over a metallic grid. More recently introduced formats include organic polymers over metallic grids or silicon nitride and silicon oxide membranes over silicon frames. Here, the application of a nanofabricated silicon membrane technology as a novel sample preparation support for electron microscopy is described. These new supports offer several unique characteristics, including nanoscale thickness and pores, which may improve imaging and analysis of materials and biological molecules. Recently developed technology permits the fabrication of pure silicon membranes that are among the world's thinnest materials—only 5 to 15 nm thick. See Striemer et al., Nature (2007) 445: 749-751 for more details. These silicon membranes are also among the world's first membrane technologies to offer nanoscale pores of 5 to 50 nm. This combination of characteristics is unique and not shared by the materials currently employed as sample supports. Moreover, it suggests that these silicon membranes could overcome many of the problems associated with current generation materials. For example, the holes of lacey and holey carbon grids (1-5 micron diameter) are incompatible with the size of most nanotubes and nanoparticles (2-40 nm). Obtaining background-free images of the entire nanostructure is rarely possible with this incompatible combination of sizes. Another significant issue is the inability to vigorously plasma clean samples on carbon grids. In some cases, this inability to remove organic contaminants can prevent high-resolution imaging of samples.

A multilevel component mode synthesis approach for the calculation of the phonon density of states of nanocomposite structures

In this paper, a multilevel component mode synthesis (MCMS) approach is presented for the calculation of the phonon density of states (PDOS) of nanocomposite structures. In this approach, the nanocomposite structures are described by hierarchical levels of substructures. The phonon frequencies and modes are first computed for the bottom level substructures by using the theory of lattice dynamics. The computed component modes are then synthesized by using a quasi-static component mode synthesis (QSM) technique to obtain the phonon modes of the upper-level substructures in a bottom-up manner. By repeating this procedure, the PDOS of the entire nanostructure can be obtained. The proposed approach, while retains the atomic description of the nanocomposite structure, significantly reduces the computational cost of the calculation. Numerical calculations show that the proposed approach provides accurate results with a much less computational cost. The PDOS of several 1-D atom chains and 2-D atom sheets are computed by using the MCMS.

Electric- and magnetic-field-induced evolution of transport windows in a vertical quantum dot

A theoretical description is presented for the quantum Coulomb blockade observed in a vertical gated quantum dot. We have applied a self-consistent approach to a solution of the Poisson-Schr\odinger problem, which takes into account the electrostatics of the entire nanostructure. The conditions under which the Coulomb blockade and the transport windows appear in the current-voltage characteristics of the nanodevice are determined as functions of the external magnetic field and the potentials applied to the electrodes. We have discussed the magnetic-field induced ground-state transformations in the system of electrons confined in the quantum dot and their consequences for the measured characteristics of the nanodevice. The results of the present calculations are in a good agreement with the experimental data.