Patterning: Direct Transfer Patterning of Electrically Small Antennas onto Three-Dimensionally Contoured Substrates

1. Carl Pfeiffer¹, 
2. Xin Xu², 
3. Stephen R. Forrest^3,*, 
4. Anthony Grbic^1,*

Article first published online: 24 FEB 2012

DOI: 10.1002/adma.201290043

A process to stamp conductors onto contoured surfaces is reported by S. R. Forrest, A. Grbic, and co-workers on page 1166. This process has the potential to provide an inexpensive and rapid method to print metallic patterns onto arbitrarily contoured substrates, which has extensive applications. Here, electrically small antennae are printed onto dielectric hemispheres. These antennae offer bandwidths approaching the fundamental limit, while maintaining some of the highest reported efficiencies to date. Cover design by C. Pfeiffer and P. Haley.

Site-Controlled Application of Electric Potential on a Conducting Polymer “Canvas”

Yutaka Ishiguro, Shinsuke Inagi*, and Toshio Fuchigami*

Department of Electronic Chemistry, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja211774z

Publication Date (Web): February 21, 2012

Copyright © 2012 American Chemical Society

A novel patterning method for conducting polymer films was successfully demonstrated using the concept of bipolar electrochemistry. The local application of an anodic potential to poly(3-methylthiophene) (PMT) and poly(3,4-ethylenedioxythiophene) (PEDOT) on a bipolar electrode (BPE) realized local electrochemical doping and reaction depending on the supporting salt used. The potential applied on the BPE was measured and corresponded well to the patterns. The array-type driving electrode system was able to draw complex patterns in a site-controlled manner.

Collective Conformations of DNA Polymers Assembled on Surface Density Gradients

Gabriel Shemer, Yahel Atsmon, Eyal Karzbrun, and Roy H. Bar-Ziv*

Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja2106543

Publication Date (Web): February 15, 2012

Copyright © 2012 American Chemical Society

To study dense double-stranded DNA (dsDNA) polymer phases, we fabricated continuous density gradients of binding sites for assembly on a photochemical interface and measured both dsDNA occupancy and extension using evanescent fluorescence. Despite the abundance of available binding sites, the dsDNA density saturates after occupation of only a fraction of the available sites along the gradient. The spatial position at which the density saturates marks the onset of collective stretching of dsDNA, a direct manifestation of balancing entropic and excluded-volume interactions. The methodology presented here offers a new means to investigate dense dsDNA compartments.

Synthesis of Monodisperse, Covalently Cross-Linked, Degradable “Smart” Microgels Using Microfluidics

1. Leah R. B. Kesselman¹, 
2. Siawash Shinwary², 
3. P. Ravi Selvaganapathy², 
4. Todd Hoare^1,*

Article first published online: 22 FEB 2012

DOI: 10.1002/smll.201102113

The development of a robust method for the synthesis of highly monodisperse microgels cross-linked with degradable covalent bonds offers the potential for fabricating microgels with the highly controllable porosities, cell interactions, and degradation half-lives required for biomedical applications. A microfluidic chip is designed that enables the on-chip mixing and emulsification of two reactive polymer solutions (hydrazide and aldehyde-functionalized carbohydrates) to form monodisperse, hydrazone cross-linked microgels in the size range of ≈40–100 μm. The device can be run continuously for at least 30 h without a significant drift in particle size. The resulting microgels have a homogeneous bulk composition and can swell and deswell as the solvent conditions change in predictable ways based on the chemistry of the reactive polymers used, thereby enabling improved control over both the chemistry and morphology of the resulting microgels relative to other reported approaches. The in situ gelation chemistry used facilitates rapid microgel formation within the droplets without requiring the use of UV light or heating to initiate polymerization, thus making this approach of particular potential utility in cell encapsulation or drug delivery (as demonstrated).

Nanoimprint Lithography: A Polyferroplatinyne Precursor for the Rapid Fabrication of L10-FePt-type Bit Patterned Media by Nanoimprint Lithography

1. Qingchen Dong¹, 
2. Guijun Li², 
3. Cheuk-Lam Ho¹, 
4. Mahtab Faisal³, 
5. Chi-Wah Leung⁴,
6. Philip Wing-Tat Pong^2,*, 
7. Kun Liu⁵, 
8. Ben-Zhong Tang³, 
9. Ian Manners^6,*, 
10. Wai-Yeung Wong^1,*

Article first published online: 14 FEB 2012

DOI: 10.1002/adma.201290034

W.-T. Pong, I. Manners, W.-Y. Wong, and co-workers report the simple and rapid fabrication of patterned L10-FePt alloy nanoparticles from a solution-processable bimetallic polyferroplatinyne polymer precursor. This approach holds great promise for fabricating L10-FePt-type bit-patterned media using high-throughput nanoimprint lithography, followed by controlled pyrolysis of the nanopatterned polymer. Each dot in the asgenerated FePt-containing nanodot array is magnetic, which can serve as a good platform for future ultrahigh-density perpen-dicular magnetic data recording systems.

Self-Assembled Flexible Microlasers

1. Van Duong Ta^†, 
2. Rui Chen^†, 
3. Han Dong Sun^*

Article first published online: 10 FEB 2012

DOI: 10.1002/adma.201103409

Hemispherical microresonators with tunable sizes are obtained based on the hydrophobic effect on distributed Bragg reflectors. Under optical excitation, whispering gallery mode lasing is observed from the dye-doped microresonators at room temperature. The results indicate the potential application of the flexible microresonators in photonic integrated circuits.

A General Approach to Synthesize Asymmetric Hybrid Nanoparticles by Interfacial Reactions

Jie He†, Maria Teresa Perez†, Peng Zhang‡, Yijing Liu†, Taarika Babu†, Jinlong Gong*‡, and Zhihong Nie*†

^† Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, United States

^‡ Key Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja210844h

Publication Date (Web): February 9, 2012

Copyright © 2012 American Chemical Society

Asymmetric multicomponent nanoparticles (AMNPs) offer new opportunities for new-generation materials with improved or new synergetic properties not found in their individual components. There is, however, an urgent need for a synthetic strategy capable of preparing hybrid AMNPs with fine-tuned structural and compositional complexities. Herein, we report a new paradigm for the controllable synthesis of polymer/metal AMNPs with well-controlled size, shape, composition, and morphology by utilizing interfacial polymerization. The hybrid AMNPs display a new level of structural–architectural sophistication, such as controlled domain size and the number of each component of AMNPs. The approach is simple, versatile, cost-effective, and scalable for synthesizing large quantities of AMNPs. Our method may pave a new route to the design and synthesis of advanced breeds of building blocks for functional materials and devices.

Zipping Effect on Omniphobic Surfaces for Controlled Deposition of Minute Amounts of Fluid or Colloids

1. Renaud Dufour^1,2, 
2. Philippe Brunet³,
3. Maxime Harnois¹, 
4. Rabah Boukherroub²,
5. Vincent Thomy¹, 
6. Vincent Senez^1,*

Article first published online: 16 FEB 2012

DOI: 10.1002/smll.201101895

When a drop sits on a highly liquid-repellent surface (super-hydrophobic or super-omniphobic) made of periodic micrometer-sized posts, its contact-line can recede with very weak mechanical retention providing that the liquid stays on top of the microsized posts. Occurring in both sliding and evaporation processes, the achievement of low-contact-angle hysteresis (low retention) is required for discrete microfluidic applications involving liquid motion or self-cleaning; however, careful examination shows that during receding, a minute amount of liquid is left on top of the posts lying at the receding edge of the drop. For the first time, the heterogeneities of these deposits along the drop-receding contact-line are underlined. Both nonvolatile liquid and particle-laden water are used to quantitatively characterize what rules the volume distribution of deposited liquid. The experiments suggest that the dynamics of the liquid de-pinning cascade is likely to select the volume left on a specific post, involving the pinch-off and detachment of a liquid bridge. In an applied prospective, this phenomenon dismisses such surfaces for self-cleaning purposes, but offers an original way to deposit controlled amounts of liquid and (bio)-particles at well-targeted locations.

Multifunctional Lipid Multilayer Stamping

1. Omkar A. Nafday¹, 
2. Troy W. Lowry², 
3. Steven Lenhert^1,*

Article first published online: 6 FEB 2012

DOI: 10.1002/smll.201102096

Nanostructured lipid multilayers on surfaces are a promising biofunctional nanomaterial. For example, surface-supported lipid multilayer diffraction gratings with optical properties that depend on the microscale spacing of the grating lines and the nanometer thickness of the lipid multilayers have been fabricated previously by dip-pen nanolithography (DPN), with immediate applications as label-free biosensors. The innate biocompatibility of such gratings makes them promising as biological sensor elements, model cellular systems, and construction materials for nanotechnology. Here a method is described that combines the lateral patterning capabilities and scalability of microcontact printing with the topographical control of nanoimprint lithography and the multimaterial integration aspects of dip-pen nanolithography in order to create nanostructured lipid multilayer arrays. This approach is denoted multilayer stamping. The distinguishing characteristic of this method is that it allows control of the lipid multilayer thickness, which is a crucial nanoscale dimension that determines the optical properties of lipid multilayer nanostructures. The ability to integrate multiple lipid materials on the same surface is also demonstrated by multi-ink spotting onto a polydimethoxysilane stamp, as well as higher-throughput patterning (on the order of 2 cm² s⁻¹ for grating fabrication) and the ability to pattern lipid materials that could not previously be patterned with high resolution by lipid DPN, for example, the gel-phase phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or the steroid cholesterol.

Zhe Jiang†, Quan Qing†, Ping Xie†, Ruixuan Gao†, and Charles M. Lieber*†‡

^†Department of Chemistry and Chemical Biology and^‡School of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts 02138, United States

Nano Lett., Article ASAP

DOI: 10.1021/nl300256r

Publication Date (Web): February 6, 2012

Semiconductor nanowires and other semiconducting nanoscale materials configured as field-effect transistors have been studied extensively as biological/chemical (bio/chem) sensors. These nanomaterials have demonstrated high-sensitivity from one- and two-dimensional sensors, although the realization of the ultimate pointlike detector has not been achieved. In this regard, nanoscale p–n diodes are attractive since the device element is naturally localized near the junction, and while nanowire p–n diodes have been widely studied as photovoltaic devices, their applications as bio/chem sensors have not been explored. Here we demonstrate that p–n diode devices can serve as a new and powerful family of highly localized biosensor probes. Designed nanoscale axial p–n junctions were synthetically introduced at the joints of kinked silicon nanowires. Scanning electron microscopy images showed that the kinked nanowire structures were achieved, and electrical transport measurements exhibited rectifying behavior with well-defined turn-on in forward bias as expected for a p–n diode. In addition, scanning gate microscopy demonstrated that the most sensitive region of these nanowires was localized near the kinked region at the p–n junction. High spatial resolution sensing using these p–n diode probes was carried out in aqueous solution using fluorescent charged polystyrene nanobeads. Multiplexed electrical measurements show well-defined single-nanoparticle detection, and experiments with simultaneous confocal imaging correlate directly the motion of the nanobeads with the electrical signals recorded from the p–n devices. In addition, kinked p–n junction nanowires configured as three-dimensional probes demonstrate the capability of intracellular recording of action potentials from electrogenic cells. These p–n junction kinked nanowire devices, which represent a new way of constructing nanoscale probes with highly localized sensing regions, provide substantial opportunity in areas ranging from bio/chem sensing and nanoscale photon detection to three-dimensional recording from within living cells and tissue.

Thermally Induced Structural and Morphological Changes of CdSe/CdS Octapods

1. Bart Goris¹, 
2. Marijn A. Van Huis², 
3. Sara Bals^3,*, 
4. Henny W. Zandbergen⁴, 
5. Liberato Manna⁵, 
6. Gustaaf Van Tendeloo⁶

Article first published online: 31 JAN 2012

DOI: 10.1002/smll.201101897

Branched nanostructures are of great interest because of their promising optical and electronic properties. For successful and reliable integration in applications such as photovoltaic devices, the thermal stability of the nanostructures is of major importance. Here the different domains (CdSe cores, CdS pods) of the heterogeneous octapods are shown to have different thermal stabilities, and heating is shown to induce specific shape changes. The octapods are heated from room temperature to 700 °C, and investigated using (analytical and tomographic) transmission electron microscopy (TEM). At low annealing temperatures, pure Cd segregates in droplets at the outside of the octapods, indicating non-stochiometric composition of the octapods. Furthermore, the tips of the pods lose their faceting and become rounded. Further heating to temperatures just below the sublimation temperature induces growth of the zinc blende core at the expense of the wurtzite pods. At higher temperatures, (500–700 °C), sublimation of the octapods is observed in real time in the TEM. Three-dimensional tomographic reconstructions reveal that the four pods pointing into the vacuum have a lower thermal stability than the four pods that are in contact with the support.