George M. Whitesides

Bio: George M. Whitesides is an academic researcher from Harvard University. The author has contributed to research in topics: Microcontact printing & Self-assembled monolayer. The author has an hindex of 240, co-authored 1739 publications receiving 269833 citations. Previous affiliations of George M. Whitesides include University of California, Davis & University of Texas at Austin.

Fabrication of Conjugated Polymer Nanowires by Edge Lithography

Abstract: This paper describes the fabrication of conjugated polymer nanowires by a three stage process: (i) spin-coating a composite film comprising alternating layers of a conjugated polymer and a sacrificial material, (ii) embedding the film in an epoxy matrix and sectioning it with an ultramicrotome (nanoskiving), and (iii) etching the sacrificial material to reveal nanowires of the conjugated polymer. A free-standing, 100-layer film of two conjugated polymers was spin-coated from orthogonal solvents: poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) from chloroform and poly(benzimidazobenzophenanthroline ladder) (BBL) from methanesulfonic acid. After sectioning the multilayer film, dissolution of the BBL with methanesulfonic acid yielded uniaxially aligned MEH-PPV nanowires with rectangular cross sections, and etching MEH-PPV with an oxygen plasma yielded BBL nanowires. The conductivity of MEH-PPV nanowires changed rapidly and reversibly by >103 upon exposure to I2 vapor. The result suggests...

Microcontact printing and electroplating on curved substrates: Production of free‐standing three‐dimensional metallic microstructures

Abstract: Microelectromechanical systems (MEMS) often require three-dimensional parts with micrometer-sized features. Currently, mechanical or laser micromachining tools,['] or multistep planar lithographic schemes are used to construct these parts. In this communication, we describe a convenient means for fabricating three-dimensional microstruc-tures. The method begins with the generation of thin patterns of metal produced by microcontact printing (pCP)[*I on curved substrates. Electrodeposition increases the thickness and rigidity of these structures,[31 and removal of the substrate results in freestanding, three-dimensional objects. We demonstrate this method through the fabrication of structures whose dimensions and mechanical properties are appropriate for micro-coil springs and medical devices known as coronary stents. Stents are small expandable tubular structures that are used to hold open anatomical structures and they are increasingly used to prevent blood vessels from collapsing after balloon angi~plasty.~~] Figure 1 summarizes the sequence of fabrication for mi-crostructures with the geometries of micro-coil springs and coronary stents. We first coated all sides of glass cylinders (Kimble Products, KIMAX-51, outer diameter-1.60 mm for the stents, and Polymicro Technologies, outer diameter-134 pm for the micro-coil springs) with titanium (-25 A) and silver (-500 A) using an electron beam evaporator and a system of mechanical rotation stages.[51 pCP was then used to pattern the surface of these cylinders with a self-assembled monolayer of he~adecanethiolate.[".~~ In pCP, contact of an 'inked' elastomeric stamp with a substrate transfers ink from the stamp to the substrate. We printed the entire outer surface of our cylinders by rolling them over a stamp inked with a solution of hexadecanethiol. The stamping process was controlled with an arrangement of precision rotation and translation stages.[71 evaporate titanium (25& adhesion promoter) and silver (500A) 1 microcontact print; etch unprotected silver and titanium 1 make electrical contact; electroplate silver 1 dissolve capillary in HF and release structure 1 1-3 cm Fig. 1. Scheme for fabricating a stent using Microcontact Printing (pCP). Glass cylinders were coated with titanium (-25 A) and silver (-500 A) using an electron beam evaporator. pCP of hexadecanethiol onto the cylinder created a monolayer resist with the geometry of the stamp. A selective wet chemical etch removed silver not protected by the monolayer. Immersion of the patterned cylinder in 1 % H F removed exposed titanium. Electrodeposi-tion of silver increased the thickness of the silver by a few hundred microns. Removal of the glass substrate using concentrated HF produced a rigid. free-standing structure made of silver. For …

Fluid delivery system and method

Abstract: Method and device for storing and/or delivering fluids, wherein at least a first and a second fluid, such as chemical or biochemical reagents or rinse solutions, are maintained separately from each other in a common vessel and transferred in series from the vessel to a reaction site to carry out a predetermined chemical or biochemical reaction. Separation may be achieved by interposing a third fluid, e.g., a gaseous fluid plug, between the first and second fluids.

Fabrication of microstructures using shrinkable polystyrene films

Abstract: This paper demonstrates the combination of reactive ion etching (RIE) and shrinkable polystyrene (PS) films to reduce the feature size of microstructures and to generate microstructures with high aspect ratios on both planar and curved surfaces. A shrinkable PS film is patterned with relief structures using RIE through a physical mask. The patterned surface is heated and shrinks. After shrinking, the size of microstructures decreases by a factor of four to five, and their height increases by a factor of ∼ 20. Thermal shrinkage results in a 100-fold increase in the aspect ratio of the patterned microstructures in the PS film. Microstructures as high as ∼ 126 μm with aspect ratio of ∼9.5 have been generated. The smallest structures fabricated using this strategy are rectangular pits ∼ 1.4 μm × 1.7 μm in size. Fabrication of microstructures on curved surfaces has been demonstrated by folding a patterned PS film and allowing it to shrink in place.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

The Theory of Island Biogeography

Abstract: Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

Large-scale pattern growth of graphene films for stretchable transparent electrodes

Abstract: Problems associated with large-scale pattern growth of graphene constitute one of the main obstacles to using this material in device applications. Recently, macroscopic-scale graphene films were prepared by two-dimensional assembly of graphene sheets chemically derived from graphite crystals and graphene oxides. However, the sheet resistance of these films was found to be much larger than theoretically expected values. Here we report the direct synthesis of large-scale graphene films using chemical vapour deposition on thin nickel layers, and present two different methods of patterning the films and transferring them to arbitrary substrates. The transferred graphene films show very low sheet resistance of approximately 280 Omega per square, with approximately 80 per cent optical transparency. At low temperatures, the monolayers transferred to silicon dioxide substrates show electron mobility greater than 3,700 cm(2) V(-1) s(-1) and exhibit the half-integer quantum Hall effect, implying that the quality of graphene grown by chemical vapour deposition is as high as mechanically cleaved graphene. Employing the outstanding mechanical properties of graphene, we also demonstrate the macroscopic use of these highly conducting and transparent electrodes in flexible, stretchable, foldable electronics.

Fuzzy Nanoassemblies: Toward Layered Polymeric Multicomposites

Abstract: Multilayer films of organic compounds on solid surfaces have been studied for more than 60 years because they allow fabrication of multicomposite molecular assemblies of tailored architecture. However, both the Langmuir-Blodgett technique and chemisorption from solution can be used only with certain classes of molecules. An alternative approach—fabrication of multilayers by consecutive adsorption of polyanions and polycations—is far more general and has been extended to other materials such as proteins or colloids. Because polymers are typically flexible molecules, the resulting superlattice architectures are somewhat fuzzy structures, but the absence of crystallinity in these films is expected to be beneficial for many potential applications.