Chiral templating of self-assembling nanostructures by circularly polarized light

PMCID: PMC4387888.-- et al.The high optical and chemical activity of nanoparticles (NPs) signifies the possibility of converting the spin angular momenta of photons into structural changes in matter. Here, we demonstrate that illumination of dispersions of racemic CdTe NPs with right- (left-)handed circularly polarized light (CPL) induces the formation of right- (left-)handed twisted nanoribbons with an enantiomeric excess exceeding 30%, which is â 1/410 times higher than that of typical CPL-induced reactions. Linearly polarized light or dark conditions led instead to straight nanoribbons. CPL templating of NP assemblies is based on the enantio-selective photoactivation of chiral NPs and clusters, followed by their photooxidation and self-assembly into nanoribbons with specific helicity as a result of chirality-sensitive interactions between the NPs. The ability of NPs to retain the polarization information of incident photons should open pathways for the synthesis of chiral photonic materials and allow a better understanding of the origins of biomolecular homochirality.This material is based on work partially supported by the Center for Solar and Thermal Energy Conversion, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences under award number #DE-SC0000957, and by ARO MURI W911NF-12-1-0407 ‘Coherent Effects in Hybrid Nanostructures for Lineshape Engineering of Electromagnetic Media’ (N.A.K. and S.L.). We acknowledge support from the NSF under grant ECS-0601345; CBET 0933384; CBET 0932823; and CBET 1036672. Financial support from the Robert A. Welch Foundation (C-1664) is also acknowledged (S.L.). Support from the NIH grant GM085043 (P.Z.) is gratefully acknowledged. The work of P.K. was supported by the NSF DMR grant No. 1309765 and by the ACS PRF grant No. 53062-ND6.Peer Reviewe

Virus-Templated Near-Amorphous Iron Oxide Nanotubes

© 2016 American Chemical Society. We present a simple synthesis of iron oxide nanotubes, grown under very mild conditions from a solution containing Fe(II) and Fe(III), on rod-shaped tobacco mosaic virus templates. Their well-defined shape and surface chemistry suggest that these robust bionanoparticles are a versatile platform for synthesis of small, thin mineral tubes, which was achieved efficiently. Various characterization tools were used to explore the iron oxide in detail: Electron microscopy (SEM, TEM), magnetometry (SQUID-VSM), diffraction (XRD, TEM-SAED), electron spectroscopies (EELS, EDX, XPS), and X-ray absorption (XANES with EXAFS analysis). They allowed determination of the structure, crystallinity, magnetic properties, and composition of the tubes. The protein surface of the viral templates was crucial to nucleate iron oxide, exhibiting analogies to biomineralization in natural compartments such as ferritin cages

Real-space observation of ultraconfined in-plane anisotropic acoustic terahertz plasmon polaritons

Thin layers of in-plane anisotropic materials can support ultraconfined polaritons, whose wavelengths depend on the propagation direction. Such polaritons hold potential for the exploration of fundamental material properties and the development of novel nanophotonic devices. However, the real-space observation of ultraconfined in-plane anisotropic plasmon polaritons (PPs)-which exist in much broader spectral ranges than phonon polaritons-has been elusive. Here we apply terahertz nanoscopy to image in-plane anisotropic low-energy PPs in monoclinic Ag2Te platelets. The hybridization of the PPs with their mirror image-by placing the platelets above a Au layer-increases the direction-dependent relative polariton propagation length and the directional polariton confinement. This allows for verifying a linear dispersion and elliptical isofrequency contour in momentum space, revealing in-plane anisotropic acoustic terahertz PPs. Our work shows high-symmetry (elliptical) polaritons on low-symmetry (monoclinic) crystals and demonstrates the use of terahertz PPs for local measurements of anisotropic charge carrier masses and damping.The work was financially supported by the Spanish Ministry of Science and Innovation under the María de Maeztu Units of Excellence Program (CEX2020-001038-M/MCIN/AEI/10.13039/501100011033) (R.H., A.C., L.E.H. and E.A.); Projects PID2021-123949OB-I00 (R.H.), PID2019-109905GB-C21 (M.G.V. and I.E.), RTI2018-094861-B-100 (L.E.H.), PID2019-107432GB-I00 (J.A.) and PID2019-107338RB-C61 (E.A.) funded by MCIN/AEI/10.13039/501100011033 and by ‘ERDF—A Way of Making Europe’; the National Natural Science Foundation of China (NSFC) (52225207 and 11934005) and the Shanghai Pilot Program for Basic Research—Fudan University 21TQ1400100 (21TQ006) (F.X.X.); NSFC grant no. 61988102 and the Science and Technology Commission of Shanghai Municipality (nos. 23010503400 and 23ZR1443500) (S.C.); the Czech Science Foundation GACR under the Junior Star grant no. 23-05119M (A.K.); the European Research Council (ERC) under grant agreement no. 101020833 (M.G.V.); the German Research Foundation (DFG) under project nos. 467576442 (I.N.) and GA 3314/1-1–FOR 5249 (QUAST) (M.G.V.); the Gipuzkoa Council (Spain) in the frame of the Gipuzkoa Fellows Program (B.M.-G.); and the University groups of the Basque Government (IT1526-22) (J.A.).Peer reviewe

Thermal Stability of Cu-Al-Ni Shape Memory Alloy Thin Films Obtained by Nanometer Multilayer Deposition

Cu-Al-Ni is a high-temperature shape memory alloy (HTSMA) with exceptional thermomechanical properties, making it an ideal active material for engineering new technologies able to operate at temperatures up to 200 °C. Recent studies revealed that these alloys exhibit a robust superelastic behavior at the nanometer scale, making them excellent candidates for developing a new generation of micro-/nano-electromechanical systems (MEMS/NEMS). The very large-scale integration (VLSI) technologies used in microelectronics are based on thin films. In the present work, 1 μm thickness thin films of 84.1Cu-12.4 Al-3.5Ni (wt.%) were obtained by solid-state diffusion from a multilayer system deposited on SiNx (200 nm)/Si substrates by e-beam evaporation. With the aim of evaluating the thermal stability of such HTSMA thin films, heating experiments were performed in situ inside the transmission electron microscope to identify the temperature at which the material was decomposed by precipitation. Their microstructure, compositional analysis, and phase identification were characterized by scanning and transmission electron microscopy equipped with energy dispersive X-ray spectrometers. The nucleation and growth of two stable phases, Cu-Al-rich alpha phase and Ni-Al-rich intermetallic, were identified during in situ heating TEM experiments between 280 and 450 °C. These findings show that the used production method produces an HTSMA with high thermal stability and paves the road for developing high-temperature MEMS/NEMS using shape memory and superelastic technologies

Nanometer-Sized MoS₂ Clusters on Graphene Flakes for Catalytic Formic Acid Decomposition

MoS₂ was deposited on graphene flakes via decomposition of MoS₃ in vacuum at different temperatures (500–800 °C). The materials obtained were tested for catalytic formic acid decomposition, giving mainly hydrogen and carbon dioxide. According to atom-resolved transmission electron microscopy study, a considerable amount of MoS₂ clusters with a mean size of 1 nm was formed on the graphene surface at 500 °C. Simulation of the structure of a cluster revealed the presence of Mo-edge atoms. Raising the preparation temperature up to 800 °C led to agglomeration of MoS₂ clusters and formation of thin crystalline MoS₂ particles 20–30 nm in size. The sample enriched with the MoS₂ clusters showed 6 times higher catalytic activity at 160 °C than the sample with the crystalline MoS₂ particles. This demonstrates that the observed nanometer-sized MoS₂ clusters are responsible for catalysis

Support effect for nanosized Au catalysts in hydrogen production from formic acid decomposition

Catalysts with about 2.5 wt% of gold supported on Al2O3, ZrO2, CeO2, La2O3 and MgO oxides and with the same mean metal particle sizes of 2.4-3.0 nm have been studied in hydrogen production via formic acid decomposition. A strong volcano-type relation of the catalytic activity on the electronegativity of the support's cation was demonstrated with the Au/Al2O3 catalyst on the top. This indicated that the activity is affected by the acid-base properties of the support. A study of the most active Au/Al2O3 catalyst with aberration-corrected HAADF/STEM, XPS and EXAFS proved that gold is in metallic state. The content of single supported gold atoms/cations was negligible. Therefore, the mechanism of the reaction was related to the activation of formic acid on the catalyst's support followed by further decomposition of the formed reaction intermediate on the Au/support interface

Hydrogen Production from Formic Acid over Au Catalysts Supported on Carbon: Comparison with Au Catalysts Supported on SiO₂ and Al₂O₃

Characteristics and catalytic activity in hydrogen production from formic acid of Au catalysts supported on porous N-free (Au/C) and N-doped carbon (Au/N-C) have been compared with those of Au/SiO2 and Au/Al2O3 catalysts. Among the catalysts examined, the Au/N-C catalyst showed the highest Au mass-based catalytic activity. The following trend was found at 448 K: Au/N-C > Au/SiO2 > Au/Al2O3, Au/C. The trend for the selectivity in hydrogen production was different: Au/C (99.5%) > Au/Al2O3 (98.0%) > Au/N-C (96.3%) > Au/SiO2 (83.0%). According to XPS data the Au was present in metallic state in all catalysts after the reaction. TEM analysis revealed that the use of the N-C support allowed obtaining highly dispersed Au nanoparticles with a mean size of about 2 nm, which was close to those for the Au catalysts on the oxide supports. However, it was by a factor of 5 smaller than that for the Au/C catalyst. The difference in dispersion could explain the difference in the catalytic activity for the carbon-based catalysts. Additionally, the high activity of the Au/N-C catalyst could be related to the presence of pyridinic type nitrogen on the N-doped carbon surface, which activates the formic acid molecule forming pyridinium formate species further interacting with Au. This was confirmed by density functional theory (DFT) calculations. The results of this study may assist the development of novel Au catalysts for different catalytic reactions