Defining the Value of Injection Current and Effective Electrical Contact Area for EGaIn-Based Molecular Tunneling Junctions

Felice C. Simeone , Hyo Jae Yoon , Martin M. Thuo ,Jabulani R. Barber , Barbara Smith , and George M. Whitesides *

Department of Chemistry and Chemical Biology,Harvard University, Cambridge, Massachusetts 02138,United States

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja408652h

Publication Date (Web): November 4, 2013

Analysis of rates of tunneling across self-assembled monolayers (SAMs) of n-alkanethiolates SCn (with n = number of carbon atoms) incorporated in junctions having structure AgTS-SAM//Ga2O3/EGaIn leads to a value for the injection tunnel current density J0 (i.e., the current flowing through an ideal junction with n = 0) of 103.6±0.3 A·cm–2 (V = +0.5 V). This estimation of J0 does not involve an extrapolation in length, because it was possible to measure current densities across SAMs over the range of lengths n = 1–18. This value of J0 is estimated under the assumption that values of the geometrical contact area equal the values of the effective electrical contact area. Detailed experimental analysis, however, indicates that the roughness of the Ga2O3 layer, and that of the AgTS-SAM, determine values of the effective electrical contact area that are

10–4 the corresponding values of the geometrical contact area. Conversion of the values of geometrical contact area into the corresponding values of effective electrical contact area results in J0(+0.5 V) = 107.6±0.8A·cm–2, which is compatible with values reported for junctions using top-electrodes of evaporated Au, and graphene, and also comparable with values of J0 estimated from tunneling through single molecules. For these EGaIn-based junctions, the value of the tunneling decay factor β (β = 0.75 ± 0.02 Å–1; β = 0.92 ± 0.02 nC–1) falls within the consensus range across different types of junctions (β = 0.73–0.89 Å–1; β = 0.9–1.1 nC–1). A comparison of the characteristics of conical Ga2O3/EGaIn tips with the characteristics of other top-electrodes suggests that the EGaIn-based electrodes provide a particularly attractive technology for physical-organic studies of charge transport across SAMs.

Single-Molecule Tracking of Polymer Surface Diffusion

Michael J. Skaug , Joshua N. Mabry , and Daniel K. Schwartz *

Department of Chemical and Biological Engineering,University of Colorado Boulder, Boulder, Colorado 80309, United States

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja407396v

Publication Date (Web): November 10, 2013

The dynamics of polymers adsorbed to a solid surface are important in thin-film formation, adhesion phenomena, and biosensing applications, but they are still poorly understood. Here we present tracking data that follow the dynamics of isolated poly(ethylene glycol) chains adsorbed at a hydrophobic solid–liquid interface. We found that molecules moved on the surface via a continuous-time random walk mechanism, where periods of immobilization were punctuated by desorption-mediated jumps. The dependence of the surface mobility on molecular weight (2, 5, 10, 20, and 40 kg/mol were investigated) suggested that surface-adsorbed polymers maintained effectively three-dimensional surface conformations. These results indicate that polymer surface diffusion, rather than occurring in the two dimensions of the interface, is dominated by a three-dimensional mechanism that leads to large surface displacements and significant bulk–surface coupling.

The Role of Surface Oxygen in the Growth of Large Single-Crystal Graphene on Copper

Published Online October 24 2013Science 8 November 2013:
Vol. 342 no. 6159 pp. 720-723
DOI: 10.1126/science.1243879

The growth of high-quality single crystals of graphene by chemical vapor deposition on copper (Cu) has not always achieved control over domain size and morphology, and the results vary from lab to lab under presumably similar growth conditions. We discovered that oxygen (O) on the Cu surface substantially decreased the graphene nucleation density by passivating Cu surface active sites. Control of surface O enabled repeatable growth of centimeter-scale single-crystal graphene domains. Oxygen also accelerated graphene domain growth and shifted the growth kinetics from edge-attachment–limited to diffusion-limited. Correspondingly, the compact graphene domain shapes became dendritic. The electrical quality of the graphene films was equivalent to that of mechanically exfoliated graphene, in spite of being grown in the presence of O.

Folding Paper-Based Lithium-Ion Batteries for Higher Areal Energy Densities

Qian Cheng †, Zeming Song †, Teng Ma ‡, Bethany B. Smith †, Rui Tang §, Hongyu Yu §, Hanqing Jiang ‡, and Candace K. Chan *†

Nano Lett., 2013, 13 (10), pp 4969–4974
DOI: 10.1021/nl4030374
Publication Date (Web): September 23, 2013
Copyright © 2013 American Chemical Society

Paper folding techniques are used in order to compact a Li-ion battery and increase its energy per footprint area. Full cells were prepared using Li4Ti5O12 and LiCoO2 powders deposited onto current collectors consisting of paper coated with carbon nanotubes. Folded cells showed higher areal capacities compared to the planar versions with a 5 × 5 cell folded using the Miura-ori pattern displaying a 14× increase in areal energy density.

Lithographically Defined Macroscale Modulation of Lateral Fluidity and Phase Separation Realized via Patterned Nanoporous Silica-Supported Phospholipid Bilayers

Eric L. Kendall †, Viviane N. Ngassam ‡, Sean F. Gilmore §, C. Jeffrey Brinker , and Atul N. Parikh *†‡§

J. Am. Chem. Soc., Article ASAP
DOI: 10.1021/ja408434r
Publication Date (Web): October 10, 2013
Copyright © 2013 American Chemical Society

Using lithographically defined surfaces consisting of hydrophilic patterns of nanoporous and nonporous (bulk) amorphous silica, we show that fusion of small, unilamellar lipid vesicles produces a single, contiguous, fluid bilayer phase experiencing a predetermined pattern of interfacial interactions. Although long-range lateral fluidity of the bilayer, characterized by fluorescence recovery after photobleaching, indicates a nominally single average diffusion constant, fluorescence microscopy-based measurements of temperature-dependent onset of fluidity reveals a locally enhanced fluidity for bilayer regions supported on nanoporous silica in the vicinity of the fluid–gel transition temperature. Furthermore, thermally quenching lipid bilayers composed of a binary lipid mixture below its apparent miscibility transition temperature induces qualitatively different lateral phase separation in each region of the supported bilayer: The nanoporous substrate produces large, microscopic domains (and domain-aggregates), whereas surface texture characterized by much smaller domains and devoid of any domain-aggregates appears on bulk glass-supported regions of the single-lipid bilayer. Interestingly, lateral distribution of the constituent molecules also reveals an enrichment of gel-phase lipids over nanoporous regions, presumably as a consequence of differential mobilities of constituent lipids across the topographic bulk/nanoporous boundary. Together, these results reveal that subtle local variations in constraints imposed at the bilayer interface, such as by spatial variations in roughness and substrate adhesion, can give rise to significant differences in macroscale biophysical properties of phospholipid bilayers even within a single, contiguous phase.

Villification: How the Gut Gets Its Villi

Amy E. Shyer1,*, Tuomas Tallinen2,3,*, Nandan L. Nerurkar1, Zhiyan Wei2, Eun Seok Gil4, David L. Kaplan4, Clifford J. Tabin1,†, L. Mahadevan2,5,6,7,8,†

Published Online August 29 2013Science 11 October 2013:
Vol. 342 no. 6155 pp. 212-218
DOI: 10.1126/science.1238842

The villi of the human and chick gut are formed in similar stepwise progressions, wherein the mesenchyme and attached epithelium first fold into longitudinal ridges, then a zigzag pattern, and lastly individual villi. We find that these steps of villification depend on the sequential differentiation of the distinct smooth muscle layers of the gut, which restrict the expansion of the growing endoderm and mesenchyme, generating compressive stresses that lead to their buckling and folding. A quantitative computational model, incorporating measured properties of the developing gut, recapitulates the morphological patterns seen during villification in a variety of species. These results provide a mechanistic understanding of the formation of these elaborations of the lining of the gut, essential for providing sufficient surface area for nutrient absorption.

Hybrid and Nonhybrid Lipids Exert Common Effects on Membrane Raft Size and Morphology

Frederick A. Heberle *†, Milka Doktorova ‡#, Shih Lin Goh ‡, Robert F. Standaert †§

, John Katsaras†

, and Gerald W. Feigenson *‡

†Biology and Soft Matter and §Biosciences Divisions,Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States

‡Department of Molecular Biology and Genetics and#Tri-Institutional Training Program in Computational Biology and Medicine, Cornell University, Ithaca, New York 14853, United States

Departments of Biochemistry and Molecular & Cellular Biology and

Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996,United States

Joint Institute for Neutron Sciences, Oak Ridge, Tennessee 37831, United States

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja407624c

Publication Date (Web): September 16, 2013

Nanometer-scale domains in cholesterol-rich model membranes emulate lipid rafts in cell plasma membranes (PMs). The physicochemical mechanisms that maintain a finite, small domain size are, however, not well understood. A special role has been postulated for chain-asymmetric or hybrid lipids having a saturated sn-1 chain and an unsaturated sn-2 chain. Hybrid lipids generate nanodomains in some model membranes and are also abundant in the PM. It was proposed that they align in a preferred orientation at the boundary of ordered and disordered phases, lowering the interfacial energy and thus reducing domain size. We used small-angle neutron scattering and fluorescence techniques to detect nanoscopic and modulated liquid phase domains in a mixture composed entirely of nonhybrid lipids and cholesterol. Our results are indistinguishable from those obtained previously for mixtures containing hybrid lipids, conclusively showing that hybrid lipids are not required for the formation of nanoscopic liquid domains and strongly implying a common mechanism for the overall control of raft size and morphology. We discuss implications of these findings for theoretical descriptions of nanodomains.

Shape Memory and Superelastic Ceramics at Small Scales

Alan Lai1, Zehui Du2, Chee Lip Gan2,3, Christopher A. Schuh1,*

Shape memory materials are a class of smart materials able to convert heat into mechanical strain (or strain into heat) by virtue of a martensitic phase transformation. Some brittle materials such as intermetallics and ceramics exhibit a martensitic transformation but fail by cracking at low strains and after only a few applied strain cycles. Here we show that such failure can be suppressed in normally brittle martensitic ceramics by providing a fine-scale structure with few crystal grains. Such oligocrystalline structures reduce internal mismatch stresses during the martensitic transformation and lead to robust shape memory ceramics that are capable of many superelastic cycles up to large strains; here we describe samples cycled as many as 50 times and samples that can withstand strains over 7%. Shape memory ceramics with these properties represent a new class of actuators or smart materials with a set of properties that include high energy output, high energy damping, and high-temperature usage.

Solid Colloids with Surface-Mobile DNA Linkers

Stef A. J. van der Meulen * and Mirjam E. Leunissen

FOM Institute AMOLF, Science Park 104, 1098 XG, Amsterdam, The Netherlands

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja406226b

Publication Date (Web): September 16, 2013

Surface functionalization with bioinspired binding groups is increasingly used to steer nano- and microscale self-assembly processes, with complementary DNA “sticky ends” as one of the most notable examples. The fabrication of well-organized structures is complicated, however, by the sharp association/dissociation transitions and the slow rearrangement kinetics intrinsic to collections of discrete, surface-immobilized binding groups and is aggravated by natural nonuniformities in the surface coating. Here, we demonstrate a novel system of solid microparticles functionalized with specific binding groups—in this case DNA linkers—that are fully mobile along the particle surface. These colloids display qualitatively new behavior and circumvent many of the commonly encountered issues. Importantly, the association/dissociation transition, and thereby the temperature window for equilibrium self-assembly, is much broader. We further find that the linkers are uniformly distributed above the DNA melting temperature, while visibly accumulating at the interparticle contacts below this temperature. The unique combination of binding group mobility with nondeformability, monodispersity, and facile manipulation of solid particles should have a profound impact on DNA-mediated and other bioinspired self-assembly approaches.

Fatty Acid Chemistry at the Oil−Water Interface: Self-Propelled Oil Droplets

Martin M. Hanczyc ,† Taro Toyota ,‡ Takashi Ikegami ,‡ Norman Packard ,† and Tadashi Sugawara *‡
Contribution from ProtoLife Srl, Parco Vega, Via della Liberta 12, Marghera, Venice 30175, Italy, and Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan

Fatty acids have been investigated as boundary structures to construct artificial cells due to their dynamic properties and phase transitions. Here we have explored the possibility that fatty acid systems also demonstrate movement. An oil phase was loaded with a fatty acid anhydride precursor and introduced to an aqueous fatty acid micelle solution. The oil droplets showed autonomous, sustained movement through the aqueous media. Internal convection created a positive feedback loop, and the movement of the oil droplet was sustained as convection drove fresh precursor to the surface to become hydrolyzed. As the system progressed, more surfactant was produced and some of the oil droplets transformed into supramolecular aggregates resembling multilamellar vesicles. The oil droplets also moved directionally within chemical gradients and exhibited a type of chemotaxis.

Self-Propelled Oil Droplets Consuming “Fuel” Surfactant

Taro Toyota †‡, Naoto Maru †, Martin M. Hanczyc §,Takashi Ikegami

and Tadashi Sugawara *†

Department of Basic Science and Department of General Systems Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan, Department of Applied Chemistry and Biotechnology, Graduate School of Engineering, Chiba University, 1-33 Yayoi-cho, Inage, Chiba 263-8522, Japan, and Department of Physics and Chemistry, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark

A micrometer-sized oil droplet of 4-octylaniline containing 5 mol % of an amphiphilic catalyst exhibited a self-propelled motion, producing tiny oil droplets, in an aqueous dispersion of an amphiphilic precursor of 4-octylaniline. The tiny droplets on the surface of the self-propelled droplet were conveyed to the posterior surface and released to the aqueous solution. Thus the persistent movement becomes possible in this chemical system, because the processing of chemical energy to mechanical movement proceeds by consuming exogenous fuel, not consuming the oil droplet itself. The mechanism of the unidirectional motion is hypothesized in terms of an asymmetric interfacial tension around the surface of the oil droplet.

Programmed Vesicle Fusion Triggers Gene Expression

Filippo Caschera †, Takeshi Sunami ‡, Tomoaki Matsuura ‡§, Hiroaki Suzuki ‡

, Martin M. Hanczyc†, and Tetsuya Yomo *‡

Center for Fundamental Living Technology (FLinT), Institute of Physics and Chemistry, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark

Exploratory Research for Advanced Technology (ERATO), Japan Science and Technology Agency, Yamadaoka 1-5, Suita, Osaka 565-0871

Department of Biotechnology, Graduate School of Engineering, Osaka University, Yamadaoka 2-1, Suita, Osaka 565-0871, Japan

Department of Bioinformatic Engineering,

Graduate School of Information Science and Technology, and Department of Frontier Biosciences,

Graduate School of Frontier Biosciences, Osaka University, Yamadaoka 1-5, Suita, Osaka 565-0871, Japan

The membrane properties of phospholipid vesicles can be manipulated to both regulate and initiate encapsulated biochemical reactions and networks. We present evidence for the inhibition and activation of reactions encapsulated in vesicles by the exogenous addition of charged amphiphiles. While the incorporation of cationic amphiphile exerts an inhibitory effect, complementation of additional anionic amphiphiles revitalize the reaction. We demonstrated both the simple hydrolysis reaction of β-glucuronidase and the in vitro gene expression of this enzyme from a DNA template. Furthermore, we show that two vesicle populations decorated separately with positive and negative amphiphiles can fuse selectively to supply feeding components to initiate encapsulated reactions. This mechanism could be one of the rudimentary but effective means to regulate and maintain metabolism in dynamic artificial cell models.

Liposome, self assembly, Oil i water emulsion

Speciﬁc and reversible DNA-directed self-assembly of oil-in-water emulsion droplets

Center for Fundamental Living Technology, Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, 5230 Odense M, Denmark;
and b
Artiﬁcial Intelligence Laboratory, Department of Informatics, University of Zurich, 8050 Zurich, Switzerland
Edited by David A. Weitz, Harvard University, Cambridge, MA, and approved October 24, 2012 (received for review August 18, 2012)

Higher-order structures that originate from the speciﬁc and reversible DNA-directed self-assembly of microscopic building blocks hold great promise for future technologies. Here, we functionalized biotinylated soft colloid oil-in-water emulsion droplets withbiotinylated single-stranded DNA oligonucleotides using streptavidin as an intermediary linker. We show the components of this
modular linking system to be stable and to induce sequencespeciﬁc aggregation of binary mixtures of emulsion droplets. Three length scales were thereby involved: nanoscale DNA base pairing
linking microscopic building blocks resulted in macroscopic aggregates visible to the naked eye. The aggregation process was reversible by changing the temperature and electrolyte concentration and by the addition of competing oligonucleotides. The system was reset and reused by subsequent refunctionalization of the emulsion droplets. DNA-directed self-assembly of oil-in-water
emulsion droplets, therefore, offers a solid basis for programmable and recyclable soft materials that undergo structural rearrangements on demand and that range in application from information technology to medicine.

Tunable near-infrared and visible-light transmittance in nanocrystal-in-glass composites

Amorphous metal oxides are useful in optical^1, 2, electronic^3, 4, 5 and electrochemical devices^6, 7. The bonding arrangement within these glasses largely determines their properties, yet it remains a challenge to manipulate their structures in a controlled manner. Recently, we developed synthetic protocols for incorporating nanocrystals that are covalently bonded into amorphous materials^8, 9. This ‘nanocrystal-in-glass’ approach not only combines two functional components in one material, but also the covalent link enables us to manipulate the glass structure to change its properties. Here we illustrate the power of this approach by introducing tin-doped indium oxide nanocrystals into niobium oxide glass (NbOx), and realize a new amorphous structure as a consequence of linking it to the nanocrystals. The resulting material demonstrates a previously unrealized optical switching behaviour that will enable the dynamic control of solar radiation transmittance through windows. These transparent films can block near-infrared and visible light selectively and independently by varying the applied electrochemical voltage over a range of 2.5 volts. We also show that the reconstructed NbOx glass has superior properties—its optical contrast is enhanced fivefold and it has excellent electrochemical stability, with 96 per cent of charge capacity retained after 2,000 cycles.

Synthetic Self-Localizing Ligands That Control the Spatial Location of Proteins in Living Cells

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja4046907

Publication Date (Web): August 14, 2013

Small-molecule ligands that control the spatial location of proteins in living cells would be valuable tools for regulating biological systems. However, the creation of such molecules remains almost unexplored because of the lack of a design methodology. Here we introduce a conceptually new type of synthetic ligands, self-localizing ligands (SLLs), which spontaneously localize to specific subcellular regions in mammalian cells. We show that SLLs bind their target proteins and relocate (tether) them rapidly from the cytoplasm to their targeting sites, thus serving as synthetic protein translocators. SLL-induced protein translocation enables us to manipulate diverse synthetic/endogenous signaling pathways. The method is also applicable to reversible protein translocation and allows control of multiple proteins at different times and locations in the same cell. These results demonstrate the usefulness of SLLs in the spatial (and temporal) control of intracellular protein distribution and biological processes, opening a new direction in the design of small-molecule tools or drugs for cell regulation.

Cell bilayer - protein interaction visualized under confocal fluorescence microscope

Membrane bending by protein–protein crowding

Nature Cell Biology

14,

944–949

(2012)

doi:10.1038/ncb2561

Received: 07 October 2011
Accepted: 12 July 2012
Published online: 19 August 2012

Curved membranes are an essential feature of dynamic cellular structures, including endocytic pits, filopodia protrusions and most organelles^1, 2. It has been proposed that specialized proteins induce curvature by binding to membranes through two primary mechanisms: membrane scaffolding by curved proteins or complexes^3, 4; and insertion of wedge-like amphipathic helices into the membrane^5, 6. Recent computational studies have raised questions about the efficiency of the helix-insertion mechanism, predicting that proteins must cover nearly 100% of the membrane surface to generate high curvature^7, 8, 9, an improbable physiological situation. Thus, at present, we lack a sufficient physical explanation of how protein attachment bends membranes efficiently. On the basis of studies of and , proteins involved in clathrin-mediated endocytosis, we propose a third general mechanism for bending fluid cellular membranes: protein–protein crowding. By correlating membrane tubulation with measurements of protein densities on membrane surfaces, we demonstrate that lateral pressure generated by collisions between bound proteins drives bending. Whether proteins attach by inserting a helix or by binding lipid heads with an engineered tag, protein coverage above ~20% is sufficient to bend membranes. Consistent with this crowding mechanism, we find that even proteins unrelated to membrane curvature, such as green fluorescent protein (GFP), can bend membranes when sufficiently concentrated. These findings demonstrate a highly efficient mechanism by which the crowded protein environment on the surface of cellular membranes can contribute to membrane shape change.

Mechanical Properties of Giant Liposomes Compressed between Two Parallel Plates: Impact of Artificial Actin Shells

Edith Schäfer , Torben-Tobias Kliesch , and Andreas Janshoff *
Institute of Physical Chemistry, Georg-August-University of Goettingen, Tammannstr. 6, 37077 Goettingen

Langmuir, Article ASAP
DOI: 10.1021/la401969t
Publication Date (Web): July 19, 2013
Copyright © 2013 American Chemical Society

The mechanical response of giant liposomes to compression between two parallel plates is investigated in the context of an artificial actin cortex adjacent to the inner leaflet of the bilayer. We found that nonlinear membrane theory neglecting the impact of bending sufficiently describes the mechanical response of liposomes consisting of fluid lipids to compression whereas the formation of an actin cortex or the use of gel-phase lipids generally leads to substantial stiffening of the shell. Giant vesicles are gently adsorbed on glassy surfaces and are compressed with tipless cantilevers using an atomic force microscope. Force–compression curves display a nonlinear response that allows us to determine the membrane tension σ0 and the area compressibility modulus KA by computing the contour of the vesicle as a function of the compression depth. The values for KA of fluid membranes correspond well to what is known from micropipet-suction experiments and computed from monitoring membrane undulations. The presence of a thick actin shell adjacent to the inner leaflet of the liposome membrane stiffens the system considerably, as mirrored in a significantly higher apparent area compressibility modulus.

Fabricating Nanoscale Chemical Gradients with ThermoChemical NanoLithography

Keith M. Carroll †‡, Anthony J. Giordano §, Debin Wang , Vamsi K. Kodali , Jan Scrimgeour †‡, William P. King #, Seth R. Marder §, Elisa Riedo †§, and Jennifer E. Curtis *†‡

Langmuir, 2013, 29 (27), pp 8675–8682

DOI: 10.1021/la400996w

Publication Date (Web): June 10, 2013

Production of chemical concentration gradients on the submicrometer scale remains a formidable challenge, despite the broad range of potential applications and their ubiquity throughout nature. We present a strategy to quantitatively prescribe spatial variations in functional group concentration using ThermoChemical NanoLithography (TCNL). The approach uses a heated cantilever to drive a localized nanoscale chemical reaction at an interface, where a reactant is transformed into a product. We show using friction force microscopy that localized gradients in the product concentration have a spatial resolution of 20 nm where the entire concentration profile is confined to sub-180 nm. To gain quantitative control over the concentration, we introduce a chemical kinetics model of the thermally driven nanoreaction that shows excellent agreement with experiments. The comparison provides a calibration of the nonlinear dependence of product concentration versus temperature, which we use to design two-dimensional temperature maps encoding the prescription for linear and nonlinear gradients. The resultant chemical nanopatterns show high fidelity to the user-defined patterns, including the ability to realize complex chemical patterns with arbitrary variations in peak concentration with a spatial resolution of 180 nm or better. While this work focuses on producing chemical gradients of amine groups, other functionalities are a straightforward modification. We envision that using the basic scheme introduced here, quantitative TCNL will be capable of patterning gradients of other exploitable physical or chemical properties such as fluorescence in conjugated polymers and conductivity in graphene. The access to submicrometer chemical concentration and gradient patterning provides a new dimension of control for nanolithography.

Bubbles are the new lenses for nanoscale light beams

These are laboratory images of a light beam without a bubble lens, followed by three examples of different bubble lenses altering the light. Credit: Tony Jun Huang, Penn State

Read more at: http://phys.org/news/2013-08-lenses-nanoscale.html#jCp

Anisotropic Nanoparticles as Shape-Directing Catalysts for the Chemical Etching of Silicon

Guoliang Liu †, Kaylie L. Young †, Xing Liao ‡, Michelle L. Personick †, and Chad A. Mirkin *†‡
†Department of Chemistry and International Institute for Nanotechnology and ‡Department of Materials Science and Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States

J. Am. Chem. Soc., Article ASAP
DOI: 10.1021/ja4061867
Publication Date (Web): August 1, 2013
Copyright © 2013 American Chemical Society

Anisotropic Au nanoparticles have been used to create a library of complex features on silicon surfaces. The technique provides control over feature size, shape, and depth. Moreover, a detailed study of the etching rate as a function of the nanoparticle surface facet interfaced with the silicon substrate suggested that the etching is highly dependent upon the facet surface energy. Specifically, the etching rate for Au nanocubes with {100}-terminated facets was 1.5 times higher than that for triangular nanoprisms with {111} facets. Furthermore, this work gives fundamental insight into the mechanism of metal-catalyzed chemical etching.