Person: Martinez, R
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Martinez
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Martinez, R
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Publication Nanoskiving Core–Shell Nanowires: A New Fabrication Method for Nano-optics(American Chemical Society (ACS), 2014) Watson, Douglas C.; Martinez, R; Fontana, Yannik; Russo-Averchi, Eleonora; Heiss, Martin; Fontcuberta i Morral, Anna; Whitesides, George; Loncar, MarkoThis paper describes the fabrication of functional optical devices by sectioning quantum-dotin-nanowires systems with predefined lengths and orientations. This fabrication process requires only two steps: embedding the nanowires in epoxy, and using an ultramicrotome to section them across their axis (“nanoskiving”). This work demonstrates the combination of four capabilities: i) the control of the length of the nanowire sections at the nanometer scale; ii) the ability to process the nanowires after cutting using wet etching; iii) the possibility of modifying the geometry of the wire by varying the sectioning angle; and iv) the generation of as many as 120 consecutive slabs bearing nanowires which have uniform size and approximately reproducible lateral patterns, and which can subsequently be transferred to different substrates. The quantum dots inside the nanowires are functional and of a high optical quality after the sectioning process, and exhibit photoluminescent emission with wavelengths in the range of 650-710 nm.Publication Elastomeric Origami: Programmable Paper-Elastomer Composites as Pneumatic Actuators(Wiley-VCH Verlag Berlin, 2012) Martinez, R; Fish, Carina; Chen, Xin; Whitesides, GeorgeThe development of soft pneumatic actuators based on composites consisting of elastomers with embedded sheet or fiber structures (e.g., paper or fabric) that are flexible but not extensible is described. On pneumatic inflation, these actuators move anisotropically, based on the motions accessible by their composite structures. They are inexpensive, simple to fabricate, light in weight, and easy to actuate. This class of structure is versatile: the same principles of design lead to actuators that respond to pressurization with a wide range of motions (bending, extension, contraction, twisting, and others). Paper, when used to introduce anisotropy into elastomers, can be readily folded into 3D structures following the principles of origami; these folded structures increase the stiffness and anisotropy of the elastomeric actuators, while being light in weight. These soft actuators can manipulate objects with moderate performance; for example, they can lift loads up to 120 times their weight. They can also be combined with other components, for example, electrical components, to increase their functionality.Publication Separation of Nanoparticles in Aqueous Multiphase Systems through Centrifugation(American Chemical Society (ACS), 2012) Akbulut, Ozge; Mace, Charles R.; Martinez, R; Kumar, Ashok Ashwin; Nie, Zhihong; Patton, Matthew Reiser; Whitesides, GeorgeThis paper demonstrates the use of aqueous multiphase systems (MuPSs) as media for rate-zonal centrifugation to separate nanoparticles of different shapes and sizes. The properties of MuPSs do not change with time or during centrifugation; this stability facilitates sample collection after separation. A three-phase system demonstrates the separation of the reaction products (nanorods, nanospheres, and large particles) of a synthesis of gold nanorods, and enriches the nanorods from 48 to 99% in less than ten minutes using a benchtop centrifuge.Publication Soft incommensurate reconstruction on Pb/Si(111): Structure, stress modulation, and phase transition(American Physical Society (APS), 1995) Hwang, Ing-Shouh; Martinez, R; Liu, Chien; Golovchenko, JeneWe resolve the atomic structure of the one-monolayer incommensurate (IC) reconstruction of Pb on Si(111) using a tunneling microscope. The local structure of this surface consists of two types of Pb trimers and a quasi-1×1 region, while on larger (>10 Å) scales the trimers are assembled into alternating domains discommensurate with the substrate. One feature of this surface is the sensitivity of the domain morphology to surface-stress inhomogeneities. This sensitivity dramatically alters the temperature at which the IC phase transforms locally to a 1×1 phase.Publication Phase-transforming and switchable metamaterials(Elsevier BV, 2016) Yang, Dian; Jin, Lihua; Martinez, R; Bertoldi, Katia; Whitesides, George; Suo, ZhigangThis paper demonstrates a new soft structure that uses a meso- or macro-scale elastic instability to generate a shape-memory effect similar to that exhibited by a ferroelastic material. It demonstrates the phase transitions, state switching, and shape-memory effects in this system, both in experiment and in simulation. The new class of materials described in the paper is potentially useful, since it comprises what are effectively ‘‘shape-memory alloys’’ of arbitrarily low modulus and arbitrarily large remnant strain. The reproduction of properties of materials usually associated with atomic- or molecular-level changes in structure using meso-scale structural opens the door to development of new, soft materials with new properties and functions.Publication Magnetic Assembly of Soft Robots with Hard Components(Wiley-Blackwell, 2013) Kwok, Sen W.; Morin, Stephen A.; Mosadegh, Bobak; So, Ju-Hee; Shepherd, Robert F.; Martinez, R; Smith, Barbara; Simeone, Felice; Stokes, Adam A.; Whitesides, GeorgeThis paper describes the modular magnetic assembly of reconfigurable, pneumatically actuated robots composed of soft and hard components and materials. The soft components of these hybrid robots are actuators fabricated from silicone elastomers using soft lithography,and the hard components are acrylonitrile-butadiene-styrene (ABS) structures made using three-dimensional (3D) printing. Neodymium-iron-boron (NdFeB) ring magnets are embedded in these components to make and maintain the connections between components. The reversibility of these magnetic connections allows the rapid reconfiguration of these robots using components made of different materials (soft and hard) that also have different sizes, structures, and functions; in addition, it accelerates the testing of new designs, the exploration of new capabilities, and the repair or replacement of damaged parts. This method of assembling soft actuators to build soft machines addresses some limitations associated with using soft lithography for the direct molding of complex 3D pneumatic networks. Combining the self-aligning property of magnets with pneumatic control makes it possible for a teleoperator to modify the structures and capabilities of these robots readily in response to the requirements of different tasks.Publication Omniphobic “R F Paper” Produced by Silanization of Paper with Fluoroalkyltrichlorosilanes(Wiley-Blackwell, 2013) Glavan, Ana; Martinez, R; Subramaniam, Anand; Yoon, Hyo; Nunes, Rui M. D.; Lange, Heiko; Thuo, Martin M.; Whitesides, GeorgeThe fabrication and properties of “fluoroalkylated paper” (“\(R^F\) paper”) by vapor-phase silanization of paper with fluoroalkyl trichlorosilanes is reported. \(R^F\) paper is both hydrophobic and oleophobic: it repels water \((θ_{app}^{H2O} > 140^{\circ})\), organic liquids with surface tensions as low as \(28 \space mN \space m^{-1}\), aqueous solutions containing ionic and non-ionic surfactants, and complex liquids such as blood (which contains salts, surfactants, and biological material such as cells, proteins, and lipids). The propensity of the paper to resist wetting by liquids with a wide range of surface tensions correlates with the length and degree of fluorination of the organosilane (with a few exceptions in the case of methyl trichlorosilane-treated paper), and with the roughness of the paper. \(R^F\) paper maintains the high permeability to gases and mechanical flexibility of the untreated paper, and can be folded into functional shapes (e.g., microtiter plates and liquid-filled gas sensors). When impregnated with a perfluorinated oil, \(R^F\) paper forms a “slippery” surface (paper slippery liquid-infused porous surface, or “paper SLIPS“) capable of repelling liquids with surface tensions as low as \(15 \space mN \space m^{-1}\). The foldability of the paper SLIPS allows the fabrication of channels and flow switches to guide the transport of liquid droplets.Publication Low-temperature homoepitaxial growth on Si(111) mediated by thin overlayers of Au(AIP Publishing, 1994) Wilk, G. D.; Martinez, R; Chervinsky, John; Spaepen, Frans; Golovchenko, JeneHigh quality homoepitaxialgrowth of Si on Si(111) through an overlayer of Au is shown to occur at 450–500 °C, far below the temperature required for growth of Si of similar quality on bare Si(111). Films of unlimited thickness can be obtained with excellent crystalline quality, as revealed by Rutherford backscattering spectrometry ion channeling measurements (χmin=2.2%). A distinct range of Au coverage (0.4–1.0 monolayer) results in the best quality epitaxy, with no measurable amount of Au trapped at either the interface or within the grownfilms. Cross‐sectional transmission electron microscopy reveals that in filmsgrown with Au coverages below and above the optimum range, the predominant defects are twins on (111) planes and Auinclusions, respectively.Publication Soft Actuators and Robots that Are Resistant to Mechanical Damage(Wiley-Blackwell, 2014) Martinez, R; Glavan, Ana; Keplinger, Christoph; Oyetibo, Alexis I.; Whitesides, GeorgeThis paper characterizes the ability of soft pneumatic actuators and robots to resist mechanical insults that would irreversibly damage or destroy hard robotic systems—systems fabricated in metals and structural polymers, and actuated mechanically—of comparable sizes. The pneumatic networks that actuate these soft machines are formed by bonding two layers of elastomeric or polymeric materials that have different moduli on application of strain by pneumatic inflation; this difference in strain between an extensible top layer and an inextensible, strain-limiting, bottom layer causes the pneumatic network to expand anisotropically. While all the soft machines described here are, to some extent, more resistant to damage by compressive forces, blunt impacts, and severe bending than most corresponding hard systems, the composition of the strain-limiting layers confers on them very different tensile and compressive strengths.Publication Structural determination of the Si(111) √3×√3-Bi surface by x-ray standing waves and scanning tunneling microscopy(American Physical Society (APS), 1994) Woicik, J. C.; Franklin, Gillian; Liu, Chien; Martinez, R; Hwong, I.-S.; Bedzyk, M. J.; Patel, J. R.; Golovchenko, JeneX-ray standing-wave measurements and tunneling microscopy have been combined to solve the atomic geometry of the √3×√3R30° honeycomb phase of Bi on Si(111). The standing-wave measurements utilize three different diffracting planes to triangulate the surface position of Bi atoms. The unoccupied surface sites required to completely determine the structure can be deduced from Rutherford-backscattering coverage and low-energy electron-diffraction symmetry arguments. These arguments are completely confirmed by a tunneling-microscope study, which is free of the ambiguities of previous studies. The final result is a 2/3-ML √3×√3R30° structure with Bi atoms in the T1 sites directly above first-layer Si atoms.