Publications by authors named "Heiko Wolf"

36 Publications

Conversion of a Patterned Organic Resist into a High Performance Inorganic Hard Mask for High Resolution Pattern Transfer.

ACS Nano 2018 Nov 16;12(11):11152-11160. Epub 2018 Oct 16.

IBM Research - Zurich , Rüschlikon CH-8803 , Switzerland.

Polyphthalaldehyde is a self-developing resist material for electron beam and thermal scanning probe lithography (t-SPL). Removing the resist in situ (during the lithography process itself) simplifies processing and enables direct pattern inspection, however, at the price of a low etch resistance of the resist. To convert the material into a etch resistant hard mask, we study the selective cyclic infiltration of trimethyl-aluminum (TMA)/water into polyphthalaldehyde. It is found that TMA diffuses homogeneously through the resist, leading to material expansion and formation of aluminum oxide concurrent to the exposure to water and the degradation of the polyphthalaldehyde polymer. The plasma etch resistance of the infiltrated resist is significantly improved, as well as its stability. Using a silicon substrate coated with 13 nm silicon nitride and 7 nm cross-linked polystyrene, high resolution polyphthalaldehyde patterning is performed using t-SPL. After TMA/HO infiltration, it is demonstrated that pattern transfer into silicon can be achieved with good fidelity for structures as small as 10 nm, enabling >10× amplification and low surface roughness. The presented results demonstrate a simplified use of polyphthalaldehyde resist, targeting feature scales at nanometer range, and suggest that trimethyl-aluminum infiltration can be applied to other resist-based lithography techniques.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsnano.8b05596DOI Listing
November 2018

Capillary assembly as a tool for the heterogeneous integration of micro- and nanoscale objects.

Soft Matter 2018 Apr;14(16):2978-2995

IBM Research - Zurich, Säumerstrasse 4, 8803 Rüschlikon, Switzerland.

During the past decade, capillary assembly in topographical templates has evolved into an efficient method for the heterogeneous integration of micro- and nano-scale objects on a variety of surfaces. This assembly route has been applied to a large spectrum of materials of micrometer to nanometer dimensions, supplied in the form of aqueous colloidal suspensions. Using systems produced via bulk synthesis affords a huge flexibility in the choice of materials, holding promise for the realization of novel superior devices in the fields of optics, electronics and health, if they can be integrated into surface structures in a fast, simple, and reliable way. In this review, the working principles of capillary assembly and its fundamental process parameters are first presented and discussed. We then examine the latest developments in template design and tool optimization to perform capillary assembly in more robust and efficient ways. This is followed by a focus on the broad range of functional materials that have been realized using capillary assembly, from single components to large-scale heterogeneous multi-component assemblies. We then review current applications of capillary assembly, especially in optics, electronics, and in biomaterials. We conclude with a short summary and an outlook for future developments.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c7sm02496gDOI Listing
April 2018

Programmable Assembly of Hybrid Nanoclusters.

Langmuir 2018 02 6;34(7):2481-2488. Epub 2018 Feb 6.

Laboratory for Interfaces, Soft Matter, and Assembly, Department of Materials, ETH Zurich , Vladimir-Prelog-Weg 5, 8093 Zurich, Switzerland.

Hybrid nanoparticle clusters (often metallic) are interesting plasmonic materials with tunable resonances and a near-field electromagnetic enhancement at interparticle junctions. Therefore, in recent years, we have witnessed a surge in both the interest in these materials and the efforts to obtain them. However, a versatile fabrication of hybrid nanoclusters, that is, combining more than one material, still remains an open challenge. Current lithographical or self-assembly methods are limited to the preparation of hybrid clusters with up to two different materials and typically to the fabrication of hybrid dimers. Here, we provide a novel strategy to deposit and align not only hybrid dimers but also hybrid nanoclusters possessing more complex shapes and compositions. Our strategy is based on the downscaling of sequential capillarity-assisted particle assembly over topographical templates. As a proof of concept, we demonstrate dimers, linear trimers, and 2D nanoclusters with programmable compositions from a range of metallic nanoparticles. Our process does not rely on any specific chemistry and can be extended to a large variety of particles and shapes. The template also simultaneously aligns the hybrid (often anisotropic) nanoclusters, which could facilitate device integration, for example, for optical readout after transfer to other substrates by a printing step. We envisage that this new fabrication route will enable the assembly and positioning of complex hybrid nanoclusters of different functional nanoparticles to study coupling effects not only locally but also at larger scales for new nanoscale optical devices.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.langmuir.7b03944DOI Listing
February 2018

Explaining the Transition from Diffusion Limited to Reaction Limited Surface Assembly of Molecular Species through Spatial Variations.

Langmuir 2018 01 29;34(1):73-80. Epub 2017 Dec 29.

IBM Research-Zurich , 8803 Rueschlikon, Switzerland.

Surface assembly is often decomposed into two classes: diffusion and reaction limited processes. The transition between the two cases is complex because the dynamics are so different. In this article, we simulate, explain, and experimentally discuss the evolution of the spatial distribution for surface assemblies with diffusion limited and reaction limited processes. Explicitly, we demonstrate that diffusion limited and reaction limited processes show some temporal differences, but more importantly, we show that the spatial arrangements are different enough to discriminate between the two cases. Using fundamental properties, such as the diffusion constant, we calculate the evolution of the spatial profile and derive from physical, heuristic models the assembly rate for reaction and diffusion limited processes based on the individual particle's interactions with the surface. Finally, we confirm the spatial profile differences between diffusion and reaction limited cases by experimentally measuring the surface assembly between two molecules of similar size, but having different assembly routes. Unique to our description is that we have derived and simulated everything through the particle picture in place of ensemble descriptions such as the diffusion equation, and we show the equivalence between our heuristic formulas and those derived from the diffusion equation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.langmuir.7b03050DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5763283PMC
January 2018

Testing the Equivalence between Spatial Averaging and Temporal Averaging in Highly Dilute Solutions.

Langmuir 2017 12 15;33(51):14539-14547. Epub 2017 Dec 15.

IBM Research-Zurich , Saumerstrasse 4, 8803 Ruschlikon, Switzerland.

Diffusion relates the flux of particles to the local gradient of the particle density in a deterministic way. The question arises as to what happens when the particle density is so low that the local gradient becomes an ill-defined concept. The dilemma was resolved early last century by analyzing the average motion of particles subject to random forces whose magnitude is such that the particles are always in thermal equilibrium with their environment. The diffusion dynamics is now described in terms of the probability density of finding a particle at some position and time and the probabilistic flux density, which is proportional to the gradient of the probability density. In a time average sense, the system thus behaves exactly like the ensemble average. Here, we report on an experimental method and test this fundamental equivalence principle in statistical physics. In the experiment, we study the flux distribution of 20 nm radius polystyrene particles impinging on a circular sink of micrometer dimensions. The particle concentration in the water suspension is approximately 1 particle in a volume element of the dimension of the sink. We demonstrate that the measured flux density is exactly described by the solution of the diffusion equation of an infinite system, and the flux statistics obeys a Poissonian distribution as expected for a Markov process governing the random walk of noninteracting particles. We also rigorously show that a finite system behaves like an infinite system for very long times despite the fact that a finite system converges to a zero flux empty state.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.langmuir.7b02730DOI Listing
December 2017

Sub-10 Nanometer Feature Size in Silicon Using Thermal Scanning Probe Lithography.

ACS Nano 2017 12 1;11(12):11890-11897. Epub 2017 Nov 1.

IBM Research Zurich , Säumerstrasse 4, 8803 Rüschlikon, Switzerland.

High-resolution lithography often involves thin resist layers which pose a challenge for pattern characterization. Direct evidence that the pattern was well-defined and can be used for device fabrication is provided if a successful pattern transfer is demonstrated. In the case of thermal scanning probe lithography (t-SPL), highest resolutions are achieved for shallow patterns. In this work, we study the transfer reliability and the achievable resolution as a function of applied temperature and force. Pattern transfer was reliable if a pattern depth of more than 3 nm was reached and the walls between the patterned lines were slightly elevated. Using this geometry as a benchmark, we studied the formation of 10-20 nm half-pitch dense lines as a function of the applied force and temperature. We found that the best pattern geometry is obtained at a heater temperature of ∼600 °C, which is below or close to the transition from mechanical indentation to thermal evaporation. At this temperature, there still is considerable plastic deformation of the resist, which leads to a reduction of the pattern depth at tight pitch and therefore limits the achievable resolution. By optimizing patterning conditions, we achieved 11 nm half-pitch dense lines in the HM8006 transfer layer and 14 nm half-pitch dense lines and L-lines in silicon. For the 14 nm half-pitch lines in silicon, we measured a line edge roughness of 2.6 nm (3σ) and a feature size of the patterned walls of 7 nm.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsnano.7b06307DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5746844PMC
December 2017

Enhanced Second-Harmonic Generation from Sequential Capillarity-Assisted Particle Assembly of Hybrid Nanodimers.

Nano Lett 2017 09 9;17(9):5381-5388. Epub 2017 Aug 9.

Optical Nanomaterial Group, Institute for Quantum Electronics, Department of Physics, ETH Zürich , Auguste-Piccard- Hof 1, 8093 Zürich, Switzerland.

We show enhanced second-harmonic generation (SHG) from a hybrid metal-dielectric nanodimer consisting of an inorganic perovskite nanoparticle of barium titanate (BaTiO) coupled to a metallic gold (Au) nanoparticle. BaTiO-Au nanodimers of 100 nm/80 nm sizes are fabricated by sequential capillarity-assisted particle assembly. The BaTiO nanoparticle has a noncentrosymmetric crystalline structure and generates bulk SHG. We use the localized surface plasmon resonance of the gold nanoparticle to enhance the SHG from the BaTiO nanoparticle. We experimentally measure the nonlinear signal from assembled nanodimers and demonstrate an up to 15-fold enhancement compared to a single BaTiO nanoparticle. We further perform numerical simulations of the linear and SHG spectra of the BaTiO-Au nanodimer and show that the gold nanoparticle acts as a nanoantenna at the SHG wavelength.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.nanolett.7b01940DOI Listing
September 2017

Hybrid Colloids Produced by Sequential Capillarity-assisted Particle Assembly: A New Path for Complex Microparticles.

Chimia (Aarau) 2017 Jun;71(6):349-353

Laboratory for Interfaces, Soft Matter, and Assembly Department of Materials, ETH Zurich Vladimir-Prelog-Weg 5, CH-8093 Zurich;, Email:

Colloidal particles have long been under the spotlight of a very diverse research community, given their ubiquitous presence in a broad class of materials and processes, and their pivotal role as model systems. More recently, intense efforts have been devoted to the development of micro- and nanoparticles combining multiple materials in objects with a controlled architecture, hence introducing multiple functionalities and a prescribed symmetry for interactions. These particles are often called hybrid colloids or colloidal molecules, given the analogy with classical molecules presenting well defined structures and chemical compositions. Here, we review the recent progress made in our group to fabricate a broad library of hybrid colloids exploiting a novel assembly route, which uses capillary forces at the moving edge of an evaporating droplet for the sequential composition of colloidal clusters, whose geometry and chemistry can be independently programmed.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.2533/chimia.2017.349DOI Listing
June 2017

Hybrid colloidal microswimmers through sequential capillary assembly.

Soft Matter 2017 Jun;13(23):4252-4259

Laboratory for Interfaces, Soft Matter, and Assembly, Department of Materials, ETH Zurich, Vladimir-Prelog-Weg 5, 8093 Zurich, Switzerland.

Active colloids, also known as artificial microswimmers, are self-propelled micro- and nanoparticles that convert uniform sources of fuel (e.g. chemical) or uniform external driving fields (e.g. magnetic or electric) into directed motion by virtue of asymmetry in their shape or composition. These materials are currently attracting enormous scientific attention as models for out-of-equilibrium systems and with the promise to be used as micro- and nanoscale devices. However, current fabrication of active colloids is limited in the choice of available materials, geometries, and modes of motion. Here, we use sequential capillarity-assisted particle assembly (sCAPA) to link microspheres of different materials into hybrid clusters of prescribed shapes ("colloidal molecules") that can actively translate, circulate and rotate powered by asymmetric electro-hydrodynamic flows. We characterize the active motion of the clusters and highlight the range of parameters (composition and shape) that can be used to tune their trajectories. Further engineering provides active colloids that switch motion under external triggers or perform simple pick-up and transport tasks. By linking their design, realization and characterization, our findings enable and inspire both physicists and engineers to create customized active colloids to explore novel fundamental phenomena in active matter and to investigate materials and propulsion schemes that are compatible with future applications.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c7sm00443eDOI Listing
June 2017

Understanding How Charged Nanoparticles Electrostatically Assemble and Distribute in 1-D.

Langmuir 2016 12 15;32(51):13600-13610. Epub 2016 Dec 15.

IBM Research - Zurich , Säumerstrasse 4, CH-8803 Rüschlikon, Switzerland.

The effects of increasing the driving forces for a 1-D assembly of nanoparticles onto a surface are investigated with experimental results and models. Modifications, which take into account not only the particle-particle interactions but also particle-surface interactions, to previously established extended random sequential adsorption simulations are tested and verified. Both data and model are compared against the heterogeneous random sequential adsorption simulations, and finally, a connection between the two models is suggested. The experiments and models show that increasing the particle-surface interaction leads to narrower particle distribution; this narrowing is attributed to the surface interactions compensating against the particle-particle interactions. The long-term advantage of this work is that the assembly of nanoparticles in solution is now understood as controlled not only by particle-particle interactions but also by particle-surface interactions. Both particle-particle and particle-surface interactions can be used to tune how nanoparticles distribute themselves on a surface.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.langmuir.6b03471DOI Listing
December 2016

Programmable colloidal molecules from sequential capillarity-assisted particle assembly.

Sci Adv 2016 Apr 1;2(4):e1501779. Epub 2016 Apr 1.

IBM Research-Zurich, Säumerstrasse 4, 8803 Rüschlikon, Switzerland.

The assembly of artificial nanostructured and microstructured materials which display structures and functionalities that mimic nature's complexity requires building blocks with specific and directional interactions, analogous to those displayed at the molecular level. Despite remarkable progress in synthesizing "patchy" particles encoding anisotropic interactions, most current methods are restricted to integrating up to two compositional patches on a single "molecule" and to objects with simple shapes. Currently, decoupling functionality and shape to achieve full compositional and geometrical programmability remains an elusive task. We use sequential capillarity-assisted particle assembly which uniquely fulfills the demands described above. This is a new method based on simple, yet essential, adaptations to the well-known capillary assembly of particles over topographical templates. Tuning the depth of the assembly sites (traps) and the surface tension of moving droplets of colloidal suspensions enables controlled stepwise filling of traps to "synthesize" colloidal molecules. After deposition and mechanical linkage, the colloidal molecules can be dispersed in a solvent. The template's shape solely controls the molecule's geometry, whereas the filling sequence independently determines its composition. No specific surface chemistry is required, and multifunctional molecules with organic and inorganic moieties can be fabricated. We demonstrate the "synthesis" of a library of structures, ranging from dumbbells and triangles to units resembling bar codes, block copolymers, surfactants, and three-dimensional chiral objects. The full programmability of our approach opens up new directions not only for assembling and studying complex materials with single-particle-level control but also for fabricating new microscale devices for sensing, patterning, and delivery applications.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1126/sciadv.1501779DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4820371PMC
April 2016

Accurate Location and Manipulation of Nanoscaled Objects Buried under Spin-Coated Films.

ACS Nano 2015 Jun 11;9(6):6188-95. Epub 2015 Jun 11.

†IBM Research - Zurich, Rueschlikon 8803, Switzerland.

Detection and precise localization of nanoscale structures buried beneath spin-coated films are highly valuable additions to nanofabrication technology. In principle, the topography of the final film contains information about the location of the buried features. However, it is generally believed that the relation is masked by flow effects, which lead to an upstream shift of the dry film's topography and render precise localization impossible. Here we demonstrate, theoretically and experimentally, that the flow-shift paradigm does not apply at the submicrometer scale. Specifically, we show that the resist topography is accurately obtained from a convolution operation with a symmetric Gaussian kernel whose parameters solely depend on the resist characteristics. We exploit this finding for a 3 nm precise overlay fabrication of metal contacts to an InAs nanowire with a diameter of 27 nm using thermal scanning probe lithography.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsnano.5b01485DOI Listing
June 2015

Insights into mechanisms of capillary assembly.

Faraday Discuss 2015 ;181:225-42

Laboratory for Interfaces, Soft Matter and Assembly, Department of Materials, ETH Zurich, Vladimir-Prelog-Weg 5, 8093 Zurich, Switzerland.

Capillary assembly in a topographical template is a powerful and flexible method for fabricating complex and programmable particle assemblies. To date, very little attention has been paid to the effects that the trap geometry--in particular the trap depth--has on the outcome of the assembly process. In this paper, we provide insights into the mechanisms behind this directed assembly method by systematically studying the impact of the trap depth and the surface tension of the suspension. Using confocal microscopy, we investigate the assembly process at the single-particle level and use these observations to formulate a simple mechanical model that offers guidelines for the successful assembly of single or multiple particles in a trap. In particular, single particles are assembled for shallow traps and moderate surface tensions, opening up the possibility to fabricate multifunctional particle dimers in two consecutive assembly steps.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c4fd00250dDOI Listing
October 2015

Cascaded assembly of complex multiparticle patterns.

Langmuir 2014 Jan 30;30(1):90-5. Epub 2013 Dec 30.

IBM Research - Zurich , Säumerstrasse 4, 8803 Rüschlikon, Switzerland.

A method for the cascaded capillary assembly of different particle populations in a single assembly cycle is presented. The method addresses the increasing need for fast and simple fabrication of multicomponent arrays from colloidal micro- and nanoscale building blocks for constructing nanoelectronic, optical, and sensing devices. It is based on the use of a microfluidic device from which two independent capillary bridges extend. The menisci of the capillary bridges are pulled over a template with trapping sites that receive the colloidal particles. We describe the parameters for simultaneous, high-yield assembly from both menisci and demonstrate the applicability of the process by means of the size-selective assembly of particles of different diameters and also by the fabrication of two-component particle clusters with defined shape and composition. This approach allows the fabrication of multifunctional particle clusters having different functionalities at predetermined positions.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/la403956eDOI Listing
January 2014

Deterministic assembly of linear gold nanorod chains as a platform for nanoscale applications.

Nanoscale 2013 Sep;5(18):8680-8

IBM Research-Zurich, Säumerstrasse 4, 8803 Rüschlikon, Switzerland.

We demonstrate a method to assemble gold nanorods highly deterministically into a chain formation by means of directed capillary assembly. This way we achieved straight chains consisting of end-to-end aligned gold nanorods assembled in one specific direction with well-controlled gaps of ∼6 nm between the individual constituents. We determined the conditions for optimum quality and yield of nanorod chain assembly by investigating the influence of template dimensions and assembly temperature. In addition, we transferred the gold nanorod chains from the assembly template onto a Si/SiO2 target substrate, thus establishing a platform for a variety of nanoscale electronic and optical applications ranging from molecular electronics to optical and plasmonic devices. As a first example, electrical measurements are performed on contacted gold nanorod chains before and after their immersion in a solution of thiol end-capped oligophenylenevinylene molecules showing an increase in the conductance by three orders of magnitude, indicating molecular-mediated transport.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c3nr02358cDOI Listing
September 2013

Directed placement of gold nanorods using a removable template for guided assembly.

Nano Lett 2011 Sep 25;11(9):3957-62. Epub 2011 Aug 25.

IBM Research-Zurich, Säumerstrasse 4, 8803 Rüschlikon, Switzerland.

We have used a temperature sensitive polymer film as a removable template to position, and align, gold nanorods onto an underlying target substrate. Shape-matching guiding structures for the assembly of nanorods of size 80 nm × 25 nm have been written by thermal scanning probe lithography. The nanorods were assembled into the guiding structures, which determine both the position and the orientation of single nanorods, by means of capillary interactions. Following particle assembly, the polymer was removed cleanly by thermal decomposition and the nanorods are transferred to the underlying substrate. We have thus demonstrated both the placement and orientation of nanorods with an overall positioning accuracy of ≈10 nm onto an unstructured target substrate.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/nl202276qDOI Listing
September 2011

High-grade optical polydimethylsiloxane for microfluidic applications.

Biomed Microdevices 2011 Dec;13(6):1027-32

IBM Research GmbH, Säumerstrasse 4, 8803 Rüschlikon, Switzerland.

Commercially available polydimethylsiloxane (PDMS) elastomers, such as Sylgard 184® are widely used in soft lithography and for microfluidic applications. These PDMS elastomers contain fillers to enhance their mechanical stability. The reinforcing fillers, often sub-micrometer small SiO(2) particles, tend to aggregate, swell with water, and thereby become cognoscible in a way that can strongly interfere with the visualization of micro-scale events taking place next to PDMS structures. As PDMS microfluidics are often used for studying cells and micro-/nanoparticles and for creating/handling nanodroplets, it has become highly desirable to employ a PDMS having high optical quality and that allows microscopy observation without artifacts. Here, we present a PDMS formulation that is free of fillers and has sufficiently low viscosity to perform a filtration step of the mixed prepolymers before curing. By molding a bi-layer microfluidic network (MFN), composed of a thin filler-free PDMS layer and a thicker Sylgard 184® backing layer, PDMS MFNs featuring both high optical quality and mechanical stability, can be fabricated.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s10544-011-9572-0DOI Listing
December 2011

Precise placement of gold nanorods by capillary assembly.

Langmuir 2011 May 14;27(10):6305-10. Epub 2011 Apr 14.

IBM Research-Zurich, Säumerstrasse 4, 8803 Rüschlikon, Switzerland.

Capillary assembly was explored for the precise placement of 25 nm × 70 nm colloidal gold nanorods on prestructured poly(dimethylsiloxane) template surfaces. The concentration of nanorods and cationic surfactant cetyltrimethylammonium bromide (CTAB), the template wettability, and most critically the convective transport of the dispersed nanorods were tuned to study their effect on the resulting assembly yield. It is shown that gold nanorods can be placed into arrayed 120-nm diameter holes, achieving assembly yields as high as 95% when the local concentration of nanorods at the receding contact line is sufficiently high. Regular arrays of gold nanorods have several benefits over randomly deposited nanorod arrangements. Each assembled nanorod resides at a precisely defined location and can easily be found for subsequent characterization or direct utilization in a device. The former is illustrated by collecting scattering spectra from single nanorods and nanorod dimers, followed by subsequent SEM characterization without the need for intricate registration schemes.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/la2001128DOI Listing
May 2011

Precision patterning with luminescent nanocrystal-functionalized beads.

Langmuir 2010 Sep;26(17):14294-300

Department of Chemistry, University of Bari, Via Orabona 4I, Bari 70126, Italy.

A reliable strategy is presented to combine the preparation of functional building blocks based on polymer beads decorated with luminescent nanocrystals (NCs) and their precise positioning onto suitable patterns by capillary assembly technique. In particular, a layer-by-layer (LbL) polyelectrolyte (PE) deposition procedure has been implemented to provide uniform NC coverage on PS beads, thus conveying the optical properties of luminescent nanocrystals to highly processable PS beads. The latter have then been integrated into patterned stamps by means of template-driven capillary assembly. Their selective positioning has been directed by means of pattern geometry. The use of luminescent (CdSe)ZnS NCs offers a direct optical probe to evaluate the efficiency of the positioning procedure on the substrate, enabling the extension of the method to a wide range of materials, i.e., NCs with different compositions and specific geometry-dependent properties. Moreover, the precise control over the pattern geometry and the micrometer accuracy in positioning achieved by capillary assembly make such functional patterned structures excellent candidates for integration into devices exploiting specific size-dependent NC properties.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/la1023339DOI Listing
September 2010

Selective assembly of sub-micrometer polymer particles.

Adv Mater 2010 Jul;22(25):2804-8

IBM Research - Zurich, Säumerstrasse 4, 8803 Rüschlikon, Switzerland.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/adma.201000396DOI Listing
July 2010

Nanoscale three-dimensional patterning of molecular resists by scanning probes.

Science 2010 May 22;328(5979):732-5. Epub 2010 Apr 22.

IBM Research-Zurich, Säumerstrasse 4, 8803 Rüschlikon, Switzerland.

For patterning organic resists, optical and electron beam lithography are the most established methods; however, at resolutions below 30 nanometers, inherent problems result from unwanted exposure of the resist in nearby areas. We present a scanning probe lithography method based on the local desorption of a glassy organic resist by a heatable probe. We demonstrate patterning at a half pitch down to 15 nanometers without proximity corrections and with throughputs approaching those of Gaussian electron beam lithography at similar resolution. These patterns can be transferred to other substrates, and material can be removed in successive steps in order to fabricate complex three-dimensional structures.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1126/science.1187851DOI Listing
May 2010

Nanoparticle printing with single-particle resolution.

Nat Nanotechnol 2007 Sep 2;2(9):570-6. Epub 2007 Sep 2.

IBM Research GmbH, Zurich Research Laboratory, Säumerstrasse 4, 8803 Rüschlikon, Switzerland.

Bulk syntheses of colloids efficiently produce nanoparticles with unique and useful properties. Their integration onto surfaces is a prerequisite for exploiting these properties in practice. Ideally, the integration would be compatible with a variety of surfaces and particles, while also enabling the fabrication of large areas and arbitrarily high-accuracy patterns. Whereas printing routinely meets these demands at larger length scales, we have developed a novel printing process that enables positioning of sub-100-nm particles individually with high placement accuracy. A colloidal suspension is inked directly onto printing plates, whose wetting properties and geometry ensure that the nanoparticles only fill predefined topographical features. The dry particle assembly is subsequently printed from the plate onto plain substrates through tailored adhesion. We demonstrate that the process can create a variety of particle arrangements including lines, arrays and bitmaps, while preserving the catalytic and optical activity of the individual nanoparticles.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/nnano.2007.262DOI Listing
September 2007

Matrix effects on the surface plasmon resonance of dry supported gold nanocrystals.

Opt Lett 2008 Apr;33(8):806-8

Department of Materials, Laboratory for Surface Science and Technology, Department of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich, Switzerland.

We present a method to characterize surface-chemical properties of gold nanocrystals. Spherical, 60 nm gold nanocrystals were immobilized on quartz substrates by a coupling agent and cleaned in a hydrogen plasma. The nanocrystals were then functionalized with alkanethiol self-assembled monolayers (SAM) of varying chain lengths by adsorption from the gas phase, and localized surface plasmon resonance (LSPR) spectroscopy was performed on the samples. Depending on the alkanethiol chain length, the adsorption of the SAM redshifted the LSPR to different extents, in accordance with Mie theory. SAM thickness differences below 1 nm could be easily resolved. Our results demonstrate that LSPR spectroscopy can be applied to characterize thin organic layers on dry supported gold particles with high sensitivity.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/ol.33.000806DOI Listing
April 2008

Controlled particle placement through convective and capillary assembly.

Langmuir 2007 Nov 2;23(23):11513-21. Epub 2007 Oct 2.

IBM Research GmbH, Zurich Research Laboratory, Säumerstrasse 4, 8803 Rüschlikon, Switzerland.

A wide variety of methods are now available for the synthesis of colloidal particle having controlled shapes, structures, and dimensions. One of the main challenges in the development of devices that utilize micro- and nanoparticles is still particle placement and integration on surfaces. Required are engineering approaches to control the assembly of these building blocks at accurate positions and at high yield. Here, we investigate two complementary methods to create particle assemblies ranging from full layers to sparse arrays of single particles starting from colloidal suspensions of gold and polystyrene particles. Convective assembly was performed on hydrophilic substrates to create crystalline mono- or multilayers using the convective flow of nanoparticles induced by the evaporation of solvent at the three-phase contact line of a solution. On hydrophobic surfaces, capillary assembly was investigated to create sparse arrays and complex three-dimensional structures using capillary forces to trap and organize particles in the recessed regions of a template. In both methods, the hydrodynamic drag exerted on the particle in the suspension plays a key role in the assembly process. We demonstrate for the first time that the velocity and direction of particles in the suspension can be controlled to perform assembly or disassembly of particles. This is achieved by setting the temperature of the colloidal suspension above or below the dew point. The influence of other parameters, such as substrate velocity, wetting properties, and pattern geometry, is also investigated. For the particular case of capillary assembly, we propose a mechanism that takes into account the relative influences of these parameters on the motion of particles and that describes the influence of temperature on the assembly efficiency.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/la700852cDOI Listing
November 2007

An in situ study of the adsorption behavior of functionalized particles on self-assembled monolayers via different chemical interactions.

Langmuir 2007 Sep 18;23(20):9990-9. Epub 2007 Aug 18.

Laboratories of Molecular Nanofabrication and Supramolecular Chemistry and Technology, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, Enschede 7500 AE, The Netherlands.

The formation of particle monolayers by convective assembly was studied in situ with three different kinds of particle-surface interactions: adsorption onto native surfaces, with additional electrostatic interactions, and with supramolecular host-guest interactions. In the first case carboxylate-functionalized polystyrene (PS-COOH) particles were assembled onto native silicon oxide surfaces, in the second PS-COOH onto protonated amino-functionalized (NH3+) self-assembled monolayers (SAMs), and in the third beta-CD-functionalized polystyrene (PS-CD) particles onto beta-CD SAMs with pre-adsorbed ferrocenyl-functionalized dendrimers. The adsorption and desorption behaviors of particles onto and from these surfaces were observed in situ on a horizontal deposition setup, and the packing density and order of the adsorbed particle lattices were compared. The desorption behavior of particles from surfaces was evaluated by reducing the temperature below the dew point, thus initiating water condensation. Particle lattices on native oxide surfaces formed the best hexagonal close packed (hcp) order and could be easily desorbed by reducing the temperature to below the dew point. The electrostatically modified assembly resulted in densely packed, but disordered particle lattices. The specificity and selectivity of the supramolecular assembly process were optimized by the use of ferrocenyl-functionalized dendrimers of low generation and by the introduction of competitive interaction by native beta-CD molecules during the assembly. The fine-tuned supramolecularly formed particle lattices were nearly hcp packed. Both electrostatically and supramolecularly formed lattices of particles were strongly attached to the surfaces and could not be removed by condensation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/la701671sDOI Listing
September 2007