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Origami design principles are scale invariant and enable direct miniaturization of origami structures provided the sheets used for folding have equal thickness to length ratios. Recently, seminal steps have been taken to fabricate microscale origami using unidirectionally actuated sheets with nanoscale thickness. Here, we extend the full power of origami-inspired fabrication to nanoscale sheets by engineering bidirectional folding with 4 nm thick atomic layer deposition (ALD) SiNx-SiO2 bilayer films. Strain differentials within these bilayers result in bending, producing microscopic radii of curvature. We lithographically pattern these bilayers and localize the bending using rigid panels to fabricate a variety of complex micro-origami devices. Upon release, these devices self-fold according to prescribed patterns. Our approach combines planar semiconductor microfabrication methods with computerized origami design, making it easy to fabricate and deploy such microstructures en masse. These devices represent an important step forward in the fabrication and assembly of deployable micromechanical systems that can interact with and manipulate micro- and nanoscale environments., Comment: This document is the unedited Author's version of a Submitted Work that was subsequently accepted for publication in Nano Letters, copyright American Chemical Society after peer review. To access the final edited and published work see: https://pubs.acs.org/articlesonrequest/AOR-JJHKJZVTJF4JFWSYZ2NW

We present a technique to precisely measure the surface energies between two-dimensional materials and substrates that is simple to implement and allows exploration of spatial and chemical control of adhesion at the nanoscale. As an example, we characterize the delamination of single-layer graphene from monolayers of pyrene tethered to glass in water and maximize the work of separation between these surfaces by varying the density of pyrene groups in the monolayer. Control of this energy scale enables high-fidelity graphene-transfer protocols that can resist failure under sonication. Additionally, we find that the work required for graphene peeling and readhesion exhibits a dramatic rate-independent hysteresis, differing by a factor of 100. This work establishes a rational means to control the adhesion of 2D materials and enables a systematic approach to engineer stimuli-responsive adhesives and mechanical technologies at the nanoscale.

Small-scale optical and mechanical components and machines require control over three-dimensional structure at the microscale. Inspired by the analogy between paper and two-dimensional materials, origami-style folding of atomically thin materials offers a promising approach for making microscale structures from the thinnest possible sheets. In this Letter, we show that a monolayer of molybdenum disulfide (MoS2) can be folded into three-dimensional shapes by a technique called capillary origami, in which the surface tension of a droplet drives the folding of a thin sheet. We define shape nets by patterning rigid metal panels connected by MoS2 hinges, allowing us to fold micron-scale polyhedrons. Finally, we demonstrate that these shapes can be folded in parallel without the use of micropipettes or microfluidics by means of a microemulsion of droplets that dissolves into the bulk solution to drive folding. These results demonstrate controllable folding of the thinnest possible materials using capillary origami and indicate a route forward for design and parallel fabrication of more complex three-dimensional micron-scale structures and machines.

Using the valleys in monolayer MoS 2 The electronic structure of the two-dimensional material MoS 2 has two distinct “valleys” of energy that may help to carry information in future electronic devices. Mak et al. observed the so-called valley Hall effect in a monolayer of MoS 2 . The electrons from different valleys moved in opposite directions across the sample, with one valley being overrepresented with respect to the other. The scientists achieved this by shining circularly polarized light on the material, which created an imbalance in the population of the two valleys. The findings may enable practical applications in the newly formed field of valleytronics. Science , this issue p. 1489

Bending and folding techniques such as origami and kirigami enable the scale-invariant design of 3D structures, metamaterials, and robots from 2D starting materials. These design principles are especially valuable for small systems because most micro- and nanofabrication involves lithographic patterning of planar materials. Ultrathin films of inorganic materials serve as an ideal substrate for the fabrication of flexible microsystems because they possess high intrinsic strength, are not susceptible to plasticity, and are easily integrated into microfabrication processes. Here, atomic layer deposition (ALD) is employed to synthesize films down to 2 nm thickness to create membranes, metamaterials, and machines with micrometer-scale dimensions. Two materials are studied as model systems: ultrathin SiO2 and Pt. In this thickness limit, ALD films of these materials behave elastically and can be fabricated with fJ-scale bending stiffnesses. Further, ALD membranes are utilized to design micrometer-scale mechanical metamaterials and magnetically actuated 3D devices. These results establish thin ALD films as a scalable basis for micrometer-scale actuators and robotics.

The overall signal-to-noise ratio per unit dose for X-ray diffraction data from protein crystals can be improved by reducing the mass and density of all material surrounding the crystals. This article demonstrates a path towards the practical ultimate in background reduction by use of atomically thin graphene sheets as a crystal mounting platform for protein crystals. The results show the potential for graphene in protein crystallography and other cases where X-ray scatter from the mounting material must be reduced and specimen dehydration prevented, such as in coherent X-ray diffraction imaging of microscopic objects.

Precise vertical stacking and lateral stitching of two-dimensional (2D) materials, such as graphene and hexagonal boron nitride (h-BN), can be used to create ultrathin heterostructures with complex functionalities, but this diversity of behaviors also makes these new materials difficult to characterize. We report a DUV-vis-NIR hyperspectral microscope that provides imaging and spectroscopy at energies of up to 6.2 eV, allowing comprehensive, all-optical mapping of chemical composition in graphene/h-BN lateral heterojunctions and interlayer rotations in twisted bilayer graphene (tBLG). With the addition of transmission electron microscopy, we obtain quantitative structure-property relationships, confirming the formation of interfaces in graphene/h-BN lateral heterojunctions that are abrupt on a micrometer scale, and a one-to-one relationship between twist angle and interlayer optical resonances in tBLG. Furthermore, we perform similar hyperspectral imaging of samples that are supported on a nontransparent silicon/SiO2 substrate, enabling facile fabrication of atomically thin heterostructure devices with known composition and structure.

A major achievement of the past decade has been the realization of macroscopic quantum systems by exploiting the interactions between optical cavities and mechanical resonators. In these systems, phonons are coherently annihilated or created in exchange for photons. Similar phenomena have recently been observed through phonon-cavity coupling - energy exchange between the modes of a single system mediated by intrinsic material nonlinearity. This has so far been demonstrated primarily for bulk crystalline, high-quality-factor (Q > 105) mechanical systems operated at cryogenic temperatures. Here, we propose graphene as an ideal candidate for the study of such nonlinear mechanics. The large elastic modulus of this material and capability for spatial symmetry breaking via electrostatic forces is expected to generate a wealth of nonlinear phenomena, including tunable intermodal coupling. We have fabricated circular graphene membranes and report strong phonon-cavity effects at room temperature, despite the modest Q factor (∼100) of this system. We observe both amplification into parametric instability (mechanical lasing) and the cooling of Brownian motion in the fundamental mode through excitation of cavity sidebands. Furthermore, we characterize the quenching of these parametric effects at large vibrational amplitudes, offering a window on the all-mechanical analogue of cavity optomechanics, where the observation of such effects has proven elusive.

We use atomic force microscopy to image grain boundaries and ripples in graphene membranes obtained by chemical vapor deposition. Nanoindentation measurements reveal that out-of-plane ripples effectively soften graphene's in-plane stiffness. Furthermore, grain boundaries significantly decrease the breaking strength of these membranes. Molecular dynamics simulations reveal that grain boundaries are especially weakening when subnanometer voids are present in the lattice. Finally, we demonstrate that two graphene membranes brought together form membranes with higher resistance to breaking.

We achieve direct electrical readout of the wavelength and polarization dependence of the plasmon reso- nance in individual gold nanogap antennas by positioning a graphene nanoconstriction within the gap as a localized photo- detector. The polarization sensitivities can be as large as 99%, while the plasmon-induced photocurrent enhancement is 2� 100. The plasmon peak frequency, polarization sensitivity, and photocurrent enhancement all vary between devices, indicating the degree to which the plasmon resonance is sensitive to nanometer-scale irregularities.

Over the past decade, transport measurements on individual single-wall nanotubes have played a prominent role in developing our understanding of this novel carbon conductor. These measurements have identified both metallic and semiconducting nanotubes, determined their dominant electronic scattering mechanisms, and elucidated in great detail the properties of their quantized energy spectrum. Recent technological breakthroughs in nanotube device fabrication and electronic measurement have made possible experiments of unprecedented precision that reveal new and surprising phenomena. In this review, we present the fundamental properties of nanotubes side by side with the newest discoveries and also discuss some of the most exciting emerging directions.

Efficient Carbon Nanotube Photodiodes A single photon absorbed in a single-walled carbon nanotube device can generate multiple unbound particles carrying an electric charge. Gabor et al. (p. 1367 ) report that in such a device at low temperatures, excitation with light of increasing energy leads to well-defined stepwise increases in current. Interestingly, because of the unique band structure of carbon nanotubes, this behavior is analogous to particle-antiparticle creation commonly observed in high-energy particle physics. These observations point to the promise of investigations in other nanoscale carbon systems, such as graphene, and could lead to numerous applications, including highly sensitive photon detection and ultra-efficient photovoltaics.

We report on a method to produce free-standing graphene sheets from epitaxial graphene on silicon carbide (SiC) substrate. Doubly clamped nanomechanical resonators with lengths up to 20 microm were patterned using this technique and their resonant motion was actuated and detected optically. Resonance frequencies of the order of tens of megahertz were measured for most devices, indicating that the resonators are much stiffer than expected for beams under no tension. Raman spectroscopy suggests that the graphene is not chemically modified during the release of the devices, demonstrating that the technique is a robust means of fabricating large-area suspended graphene structures.

We introduce a new technique of probing the local potential inside a nanostructure employing Au nanoparticles as electrometers and using single-electron force microscopy to sense the charge states of the Au electrometers, which are sensitive to local potential variations. The Au nanoelectrometers are weakly coupled to a carbon nanotube through high-impedance molecular junctions. We demonstrate the operation of the Au nanoelectrometer, determine the impedance of the molecular junctions, and measure the local potential profile in a looped nanotube.

Understanding the physics of low-dimensional systems and the operation of next-generation electronics will depend on our ability to measure the electrical properties of nanomaterials at terahertz frequencies (∼100 GHz to 10 THz). Single-walled carbon nanotubes are prototypical one-dimensional nanomaterials because of their unique band structure1,2 and long carrier mean free path3,4,5. Although nanotube transistors have been studied at microwave frequencies (100 MHz to 50 GHz)6,7,8,9,10,11, no techniques currently exist to probe their terahertz response12. Here, we describe the first terahertz electrical measurements of single-walled carbon nanotube transistors performed in the time domain. We observe a ballistic electron resonance that corresponds to the round-trip transit of an electron along the nanotube with a picosecond-scale period. The electron velocity is found to be constant and equal to the Fermi velocity, showing that the high-frequency electron response is dominated by single-particle excitations rather than collective plasmon modes. These results demonstrate a powerful new tool for directly probing picosecond electron motion in nanostructures.

Carbon nanotube transistors combine molecular-scale dimensions with excellent electronic properties, offering unique opportunities for chemical and biological sensing. Here, we form supported lipid bilayers over single-walled carbon nanotube transistors. We first study the physical properties of the nanotube/supported lipid bilayer structure using fluorescence techniques. Whereas lipid molecules can diffuse freely across the nanotube, a membrane-bound protein (tetanus toxin) sees the nanotube as a barrier. Moreover, the size of the barrier depends on the diameter of the nanotube--with larger nanotubes presenting bigger obstacles to diffusion. We then demonstrate detection of protein binding (streptavidin) to the supported lipid bilayer using the nanotube transistor as a charge sensor. This system can be used as a platform to examine the interactions of single molecules with carbon nanotubes and has many potential applications for the study of molecular recognition and other biological processes occurring at cell membranes.

We couple magnetic tweezer techniques with standard lithography methods to make magnetically actuated single-walled carbon nanotube (SWNT) devices. Parallel arrays of 4-10 μm-long SWNT cantilevers are patterned with one end anchored to the substrate and the other end attached to a micron-scale iron magnetic tag that is free to move in solution. Thermal fluctuations of this tag provide a direct measurement of the spring constant of the SWNT cantilevers, yielding values of 10(-7)-10(-8) N/m. This tag is also a handle for applying forces and torques using externally applied magnetic field gradients. These techniques provide a platform on which interaction forces between SWNTs and other objects such as biomolecules and cells can be measured in situ.

We demonstrate optomechanically induced amplification of carbon nanotube (CNT) mechanical modes using optical microcavities. We also show direct imaging of the spatial profile of CNT mechanical modes using optical readout.

We have fabricated high performance field-effect transistors made from semiconducting single-walled carbon nanotubes (SWNTs). Using chemical vapor deposition to grow the tubes, annealing to improve the contacts, and an electrolyte as a gate, we obtain very high device mobilities and transconductances. These measurements demonstrate that SWNTs are attractive for both electronic applications and for chemical and biological sensing.

Single-walled carbon nanotubes (SWNTs) have emerged as a very promising new class of electronic materials. The fabrication and electronic properties of devices based on individual SWNTs are reviewed. Both metallic and semiconducting SWNTs are found to possess electrical characteristics that compare favorably to the best electronic materials available. Manufacturability issues, however, remain a major challenge.

Solid-state devices in which electrons are confined to two-dimensional planes have provided some of the most exciting scientific and technological breakthroughs of the last 50 years. From metal-oxide-silicon field effect transistors to high-mobility gallium-arsenide heterostructures, these devices have played a key role in the microelectronics revolution and are critical components in a wide array of products from computers to compact-disk players. From a more parochial perspective, the study of electrons in two-dimensional systems has also been responsible for two Nobel prizes in physics – to Klaus von Klitzing in 1985 and to Robert Laughlin, Horst Stormer and Daniel Tsui in 1998. This is testimony to the basic as well as applied interest of such devices (see Heiblum and Stern in further reading).

In order to study the electronic properties of single-walled carbon nanotube junctions we have fabricated several devices consisting of two crossed nanotubes with electrical leads attached to each end of each nanotube. We correlate the properties of the junctions with the properties of the individual nanotubes: metal–metal, metal–semiconductor, and semiconductor–semiconductor junctions are all formed. We find that metal–metal SWNT junctions exhibit surprisingly high conductances of 0.1– 0.2 e 2 /h . Semiconductor–semiconductor junctions also show significant linear response conductance. Metal–semiconductor junctions behave as p-type Schottky diodes. All the junction types can reliably pass currents of hundreds of nanoamps.

We address the effects of disorder on the conducting properties of metal and semiconducting carbon nanotubes. Experimentally, the mean free path is found to be much larger in metallic tubes than in doped semiconducting tubes. We show that this result can be understood theoretically if the disorder potential is long-ranged. The effects of a pseudospin index that describes the internal sublattice structure of the states lead to a suppression of scattering in metallic tubes, but not in semiconducting tubes. This conclusion is supported by tight-binding calculations., Comment: four pages

Single-walled carbon nanotubes - nanometer diameter graphene cylinders — are a new class of one-dimensional (1D) conductors. Recent STM[1] and transport[2–8] experiments have shown that these tubes can be either semiconductors or 1D metals. Here we review our group's recent electrical studies[3–5] of these novel 1D conductors.

The ability to control the stacking structure in layered materials could provide an exciting approach to tuning their optical and electronic properties. Because of the lower symmetry of each constituent monolayer, hexagonal boron nitride (h-BN) allows more structural variations in multiple layers than graphene; however, the structure-property relationships in this system remain largely unexplored. Here, we report a strong correlation between the interlayer stacking structures and optical and topological properties in chemically grown h-BN bilayers, measured mainly by using dark-field transmission electron microscopy (DF-TEM) and optical second harmonic generation (SHG) mapping. Our data show that there exist two distinct h-BN bilayer structures with different interlayer symmetries that give rise to a distinct difference in their SHG intensities. In particular, the SHG signal in h-BN bilayers is observed only for structures with broken inversion symmetry, with an intensity much larger than that of single layer h-BN. In addition, our DF-TEM data identify the formation of interlayer topological defects in h-BN bilayers, likely induced by local strain, whose properties are determined by the interlayer symmetry and the different interlayer potential landscapes.

Neuroscience is at a crossroads. Great effort is being invested into deciphering specific neural interactions and circuits. At the same time, there exist few general theories or principles that explain brain function. We attribute this disparity, in part, to limitations in current methodologies. Traditional neurophysiological approaches record the activities of one neuron or a few neurons at a time. Neurochemical approaches focus on single neurotransmitters. Yet, there is an increasing realization that neural circuits operate at emergent levels, where the interactions between hundreds or thousands of neurons, utilizing multiple chemical transmitters, generate functional states. Brains function at the nanoscale, so tools to study brains must ultimately operate at this scale, as well. Nanoscience and nanotechnology are poised to provide a rich toolkit of novel methods to explore brain function by enabling simultaneous measurement and manipulation of activity of thousands or even millions of neurons. We and others refer to this goal as the Brain Activity Mapping Project. In this Nano Focus, we discuss how recent developments in nanoscale analysis tools and in the design and synthesis of nanomaterials have generated optical, electrical, and chemical methods that can readily be adapted for use in neuroscience. These approaches represent exciting areas of technical development and research. Moreover, unique opportunities exist for nanoscientists, nanotechnologists, and other physical scientists and engineers to contribute to tackling the challenging problems involved in understanding the fundamentals of brain function.

We present experimental and theoretical results of confined plasmons in graphene micro- and nano-structures. We present a FDTD technique to accurately model the measured data and demonstrate the importance of interactions between plasmonic structures.

We discuss the use of a conducting-tip atomic force microscope (AFM) for the imaging and electrical measurement of chemically derived nanostructures. First, scanning probe microscopy of CdSe and Au nanocrystals bound to a substrate with a self assembled monolayer will be discussed. It is found that imaging in liquids is necessary to avoid removing the nanocrystals. We then address some issues in performing electrical measurements in liquids. In particular, we examine the conducting properties of the AFM tip when imaging a flat surface, highly oriented pyrolytic graphite, in a non-polar liquid, hexadecane. We find that the solvation layers between the tip and the substrate strongly influence the electrical properties.

Single-molecule imaging at nanometre resolution using noncontact AFM has been applied to image a protein complex on mica using single-wall carbon nanotube (CNT) technology. Hydrated RNA polymerase (RNAP)–DNA complex was imaged using constant-amplitude tapping mode AFM. CNT tips (1–2 nm diameter) prepared by chemical vapour phase deposition were mounted onto standard Pt/Ir coated AFM tips. The effectiveness of the CNT tip scanning was tested by imaging the profile of an RNAP–DNA complex. The results demonstrate the merits of high-resolution carbon nanotube nc-AFM scanning and suggest that CNT tips may provide a general tip–surface reference standard for defining tip–surface interactions on molecular-bonde do rganic surfaces. (Some figures in this article are in colour only in the electronic version)

By virtue of their low mass and stiffness, atomically thin mechanical resonators are attractive candidates for use in optomechanics. Here, we demonstrate photothermal back-action in a graphene mechanical resonator comprising one end of a Fabry–Perot cavity. As a demonstration of the utility of this effect, we show that a continuous wave laser can be used to cool a graphene vibrational mode or to power a graphene-based tunable frequency oscillator. Owing to graphene’s high thermal conductivity and optical absorption, photothermal optomechanics is efficient in graphene and could ultimately enable laser cooling to the quantum ground state or applications such as photonic signal processing.

Graphene's unparalleled strength, stiffness, and low mass per unit area make it an ideal material for nanomechanical resonators, but its relatively low quality factor is an important drawback that has been difficult to overcome. Here, we use a simple procedure to fabricate circular mechanical resonators of various diameters from graphene grown by chemical vapor deposition. In addition to highly reproducible resonance frequencies and mode shapes, we observe a striking improvement of the membrane quality factor with increasing size. At room temperature, we observe quality factors as high as 2400 ± 300 for a resonator 22.5 μm in diameter, about an order of magnitude greater than previously observed quality factors for monolayer graphene. Measurements of quality factor as a function of modal frequency reveal little dependence of Q on frequency. These measurements shed light on the mechanisms behind dissipation in monolayer graphene resonators and demonstrate that the quality factor of graphene resonators relative to their thickness is among the highest of any mechanical resonator demonstrated to date.

We fabricated large arrays of suspended, single-layer graphene membrane resonators using chemical vapor deposition (CVD) growth followed by patterning and transfer. We measure the resonators using both optical and electrical actuation and detection techniques. We find that the resonators can be modeled as flat membranes under tension, and that clamping the membranes on all sides improves agreement with our model and reduces the variation in frequency between identical resonators. The resonance frequency is tunable with both electrostatic gate voltage and temperature, and quality factors improve dramatically with cooling, reaching values up to 9000 at 10 K. These measurements show that it is possible to produce large arrays of CVD-grown graphene resonators with reproducible properties and the same excellent electrical and mechanical properties previously reported for exfoliated graphene.

The properties of polycrystalline materials are often dominated by the size of their grains and by the atomic structure of their grain boundaries. These effects should be especially pronounced in two-dimensional materials, where even a line defect can divide and disrupt a crystal. These issues take on practical significance in graphene, which is a hexagonal, two-dimensional crystal of carbon atoms. Single-atom-thick graphene sheets can now be produced by chemical vapour deposition on scales of up to metres, making their polycrystallinity almost unavoidable. Theoretically, graphene grain boundaries are predicted to have distinct electronic, magnetic, chemical and mechanical properties that strongly depend on their atomic arrangement. Yet because of the five-order-of-magnitude size difference between grains and the atoms at grain boundaries, few experiments have fully explored the graphene grain structure. Here we use a combination of old and new transmission electron microscopy techniques to bridge these length scales. Using atomic-resolution imaging, we determine the location and identity of every atom at a grain boundary and find that different grains stitch together predominantly through pentagon-heptagon pairs. Rather than individually imaging the several billion atoms in each grain, we use diffraction-filtered imaging to rapidly map the location, orientation and shape of several hundred grains and boundaries, where only a handful have been previously reported. The resulting images reveal an unexpectedly small and intricate patchwork of grains connected by tilt boundaries. By correlating grain imaging with scanning probe and transport measurements, we show that these grain boundaries severely weaken the mechanical strength of graphene membranes but do not as drastically alter their electrical properties. These techniques open a new window for studies on the structure, properties and control of grains and grain boundaries in graphene and other two-dimensional materials.

We report the effects of potassium doping on the conductance of individual semiconducting single-walled carbon nanotube ropes. We are able to control the level of doping by reversibly intercalating and de-intercalating potassium. Potassium doping changes the carriers in the ropes from holes to electrons. Typical values for the carrier density are found to be ∼100–1000 electrons/μm. The effective mobility for the electrons is μeff∼20–60 cm2 V-1 s-1, a value similar to that reported for the hole effective mobility in nanotubes [R. Martel et al., Appl. Phys. Lett. 73, 2447 (1998)].

An overview is presented of an approach for treating cancer that uses nanoparticles to deliver heat to diseased areas after absorbing energy from a laser of the appropriate wavelength. The implications are discussed of the relationship of parameters necessary to raise the temperature to therapeutically beneficial levels. Tight focusing is required for a continuous-wave laser to sufficiently heat individual nanoparticles because of heat loss to the surrounding fluid during the period of exposure. The natural thermal confinement of pulse lasers minimizes this effect because of the finite thermal diffusion time, which restricts the absorbed energy to a region around the particle, that offers the potential for achieving high temperatures that can promote phase change on the surface of a nanoparticle or even melting of the particle. A discussion of a way to potentially measure temperature on the scale of an individual nanoparticle is included based on using a single-walled nanotube (SWNT) of carbon as a thermistor. The challenges of this undertaking are that SWNTs do not always follow Ohm's law, they may exhibit metallic or semiconductor behavior with an often unpredictable result in manufacturing, and no two SWNTs behave identically, which necessitates calibration for each SWNT. Some results are presented that show the electrical characteristics of SWNTs and their potential for exploitation in this application.

We describe the first terahertz electrical measurements of single-walled carbon nanotube transistors. A picosecond ballistic electron resonance is directly observed in the time-domain. These results demonstrate a powerful new tool for directly probing picosecond electron motion in nanostructures.

A simple yet highly reproducible method to fabricate metallic electrodes with nanometer separation is presented. The fabrication is achieved by passing a large electrical current through a gold nanowire defined by electron-beam lithography and shadow evaporation. The current flow causes the electromigration of gold atoms and the eventual breakage of the nanowire. The breaking process yields two stable metallic electrodes separated by ∼1 nm with high efficiency. These electrodes are ideally suited for electron-transport studies of chemically synthesized nanostructures, and their utility is demonstrated here by fabricating single-electron transistors based on colloidal cadmium selenide nanocrystals.

T he latter half of the 20th century has seenexplosiveprogress in thefieldsof microelectronics and biotechnology. The roots of these advances lie in the 19th century, when the doorswere opening on the molecular world. James Clerk Maxwell demonstrated once and for all that atoms exist and then wrote down the electromagnetic laws that govern their interactions. He immediately began to wonder about whether he could controlatoms and speculated where thatmight lead. Two years earlier, Gregor Mendel, an Austrianmonk studying peas in his garden, discerned that inherited traits in his peas were binary. Tall or short. Smooth or wrinkled. Mendel had discovered genes. Moreover, he’d found the patterns by which genes were handed down. By selecting for a desired trait, he could affect the genetic makeup of a population. These two discoveries, Maxwell’s and Mendel’s, followed separate developmental paths after their joint birth in the late 1860s. The biggest steps for both happened in the 1950s. With the invention of transistors and integrated circuits, Maxwell’s dream of control over the small was finally realized, giving birth to the modern computer industry. It was not atoms that got sorted but electrons, pushed and pulled through the hierarchical semiconductor societies by transistors opening and closing tiny doorways. After decade upon decade of Moore’s Law, electronic societies have reached the nanoscale, possessing the complexity of large cities in a space the size of a postage stamp. Furthermore, these cities run on a sped-up clock so fast that they have a lifetime of thoughts every second. The biotech revolution got underway about the same time, when Watson and Crick unlocked the structure of the double helix of DNA in 1953. The microscopic origins of Mendel’s genes were finally resolved, and biology’s evolution from a taxonomy-based discipline to an information-based one was fully underway. This genetic revolution has transformed the way we think about ourselves and the way we practice medical science. A few decades later, we have usurped nature’s tools, cutting and pasting genes between organisms with ever-increasing skill. These two paths, Maxwell’s and Mendel’s, represent two completely separate visions for controlling matter at the nanoscale. They play with different materials and work by different rules, the former corresponding to the rigid control of computer circuits and the latter the flexible variability of biological systems. Now, these two approaches are crashing together. Biologists dream of controlling the machinery of life like engineers control device layouts on a computer chip, and engineers dream of evolving adaptive architectures that can, among other things, build themselves.What will happen as these two worlds collide? What is the future of bio meets nano? In June 2007, we held a symposium to address this question, sponsored by the *Corresponding author, mceuen@ccmr.cornell.edu.

5 pages, 4 figures.-- Printed version published May 14, 2008., Supporting information available: A detailed description of fabrication technique, a description of the FEM model, a comparison of the FEM model to analytical predictions for a beam under tension as well as recent simulations on nanotubes with slack, and a detailed description of the SFM technique to detect mechanical vibrations. Available at: http://pubs.acs.org/doi/suppl/10.1021/nl080201h/suppl_file/nl080201h-file002.pdf, We carried out measurements on nanoelectromechanical systems based on multilayer graphene sheets suspended over trenches in silicon oxide. The motion of the suspended sheets was electrostatically driven at resonance using applied radio frequency voltages. The mechanical vibrations were detected using a novel form of scanning probe microscopy, which allowed identification and spatial imaging of the shape of the mechanical eigenmodes. In as many as half the resonators measured, we observed a new class of exotic nanoscale vibration eigenmodes not predicted by the elastic beam theory, where the amplitude of vibration is maximum at the free edges. By modeling the suspended sheets with the finite element method, these edge eigenmodes are shown to be the result of nonuniform stress with remarkably large magnitudes (up to 1.5 GPa). This nonuniform stress, which arises from the way graphene is prepared by pressing or rubbing bulk graphite against another surface, should be taken into account in future studies on electronic and mechanical properties of graphene., The research has been supported by a EURYI grant and FP6-IST-021285-2 and by the NSF through the Cornell Center for Materials Research. Sample fabrication was performed at the Cornell Nanoscale Science and Technology Facility, a National Nanotechnology Infrastructure Network node, funded by NSF.

We present a resist-free patterning technique to form electrically contacted graphene nanochannels via localized burning by a pulsed white light source. The technique uses end-point detection to stop the burning process at a fixed resistance to produce channels with resistances of 10 kΩ to 100 kΩ. Folding of the graphene sheet takes place during patterning, which provides very straight edges as identified by AFM and SEM. Electrical transport measurements for the nanochannels show a non-linear behavior of the current vs source-drain voltage as the resistance goes above 20 kΩ indicating conduction tunneling effects. Electrochemical gating was performed to further electrically characterize the constrictions produced. The method described can be interesting not only for fundamental studies correlating edge folded structures with electrical transport but also as a promising path for fabricating graphene devices in situ. Additionally, this method might also be extended to create nanochannels in other 2D materials.

Microelectronics based on silicon is probably the technology that has most changed the twentieth century. But in the coming century, carbon may take over. An early sign of that promise is the construction of a transistor based on a single large molecule & a semiconducting carbon nanotube.

We have used single-walled carbon nanotube transistors to measure changes in the chemical potential of a solution due to redox-active transition-metal complexes. The interaction of the molecules with a gold electrolyte-gate wire changes the electrostatic potential sensed by the nanotube, which in turn shifts the gate-voltage dependence of the nanotube conductance. As predicted by the Nernst equation, this shift depends logarithmically on the ratio of oxidized to reduced molecules.

Carbon nanotube adhesion force measurements were performed on single-walled nanotubes grown over lithographically defined trenches. An applied vertical force from an atomic force microscope (AFM), in force distance mode, caused the tubes to slip across the 250-nm-wide silicon dioxide trench tops at an axial tension of 8 nN. The nanotubes slipped at an axial tension of 10 nN after being selectively coated with a silicon dioxide layer.

We present electrical measurements of single Au and CdSe nanocrystals. The devices are fabricated using a hybrid scheme which combines electron beam lithography and wet chemistry to bind nanocrystals in tunneling contact between two closely spaced metallic leads. The current–voltage characteristics of these devices exhibit a Coulomb staircase with a charging energy of ∼50 meV. This technique is readily adapted to the study of a host of nanocrystals made by solution chemistry.

Nanoelectromechanical systems (NEMs) hold promise for a number of scientific and technological applications. In particular, NEMs oscillators have been proposed for use in ultrasensitive mass detection, radio-frequency signal processing, and as a model system for exploring quantum phenomena in macroscopic systems. Perhaps the ultimate material for these applications is a carbon nanotube. They are the stiffest material known, have low density, ultrasmall cross-sections and can be defect-free. Equally important, a nanotube can act as a transistor and thus may be able to sense its own motion. In spite of this great promise, a room-temperature, self-detecting nanotube oscillator has not been realized, although some progress has been made. Here we report the electrical actuation and detection of the guitar-string-like oscillation modes of doubly clamped nanotube oscillators. We show that the resonance frequency can be widely tuned and that the devices can be used to transduce very small forces., 9 pages, 3 figures

We use an Atomic Force Microscope (AFM) tip to locally probe the electronic properties of semiconducting carbon nanotube transistors. A gold-coated AFM tip serves as a voltage or current probe in three-probe measurement setup. Using the tip as a movable current probe, we investigate the scaling of the device properties with channel length. Using the tip as a voltage probe, we study the properties of the contacts. We find that Au makes an excellent contact in the p-region, with no Schottky barrier. In the n-region large contact resistances were found which dominate the transport properties., 4 pages, 5 figures

DNA possesses many desirable chemical/physical properties as a polymeric material. With the myriad of tools available to manipulate DNA, there is great potential for using DNA as a generic instead of a genetic material. Although much progress has been made in DNA computing and DNA nanotechnology, the full achievement of DNA-based materials has not yet been realized. As almost all DNA molecules are either linear or circular, to rationally construct DNA materials one must first create additional shapes of DNA as basic building blocks. In addition, these DNA building blocks must be readily incorporated into larger structures in a controlled manner. Here, we show the controlled assembly of dendrimer-like DNA (DL-DNA) from Y-shaped DNA (Y-DNA). The synthesis of Y-DNA and controlled assembly of DL-DNA were robust and efficient; the resulting DL-DNA was stable and almost monodisperse. The multivalent DNA dendrimers can be either isotropic or anisotropic, providing great potential to link other entities.

We show that the band structure of a carbon nanotube (NT) can be dramatically altered by mechanical strain. We employ an atomic force microscope tip to simultaneously vary the NT strain and to electrostatically gate the tube. We show that strain can open a bandgap in a metallic NT and modify the bandgap in a semiconducting NT. Theoretical work predicts that bandgap changes can range between +100meV and -100meV per 1% stretch, depending on NT chirality, and our measurements are consistent with this predicted range., Comment: 5 pages, 5 figures; minor changes and corrections