The successful design of nanofluidic devices for the manipulation of biopolymers requires an understanding of how the predictions of soft condensed matter physics scale with device dimensions. Here we present measurements of DNA extended in nanochannels and show that below a critical width roughly twice the persistence length there is a crossover in the polymer physics. DOI: 10.1103/PhysRevLett.94.196101 PACS numbers: 81.16.Nd, 82.35.Lr, 82.39.Pj Top-down approaches to nanotechnology have the potential to revolutionize biology by making possible the construction of chip-based devices that can not only detect and separate single DNA molecules by size [1-4] but also-it is hoped in the future-actually sequence at the single molecule level [5]. While a number of top-down approaches have been proposed, all these approaches have in common the confinement of DNA to nanometer scales, typically 5-200 nm. Confinement alters the statistical mechanical properties of DNA. A DNA molecule in a nanochannel will extend along the channel axis to a substantial fraction of its full contour length [1,6]. Moreover, confinement is expected to alter the Brownian dynamics of the confined molecule [1]. While the study of confined DNA is interesting from a physics perspective, it is also critical for device design, potentially leading to new applications of nanoconfinement (for example, the use of nanochannels to prestretch and stabilize DNA before threading through a nanopore [5]). Moreover, available models [7][8][9][10][11] and simulations [12,13] are unable to account for the effect of varying confinement over the entire range of scales used in nanodevices. The theory gives asymptotic results valid only in limits that are not necessarily compatible with device requirements [1].Consider a DNA molecule of contour length L, width w, and persistence length P confined to a nanochannel of width D with D less than the radius of gyration of the molecule. When D P, the molecule is free to coil in the nanochannel and the elongation is due entirely to excluded volume interactions between segments of the polymer greatly separated in position along the backbone (see Fig. 1). de Gennes developed a scaling argument for the average extension of a confined self-avoiding polymer [8,12] which was later generalized by Schaefer and Pincus to the case of a persistent self-avoiding polymer [14]. The de Gennes theory predicts an extension r that scales with D in the following way:If the aspect ratio of the channel is not unity, i.e., the width D D 1 does not equal the depth D 2 , then Eq. (1) is still valid provided that D is replaced by the geometric average of the dimensions. As the channel width drops below the persistence length, the physics is dominated not by excluded volume but by the interplay of confinement and intrinsic DNA elasticity. In the strong confinement limit D P, backfolding is energetically unfavorable and contour length is stored exclusively in deflections made by the polymer with the walls. These deflections occur on average over th...

We report advances in nanoimprint lithography, its application in nanogap metal contacts, and related fabrication yield. We have demonstrated 5 nm linewidth and 14 nm linepitch in resist using nanoimprint lithography at room temperature with a pressure less than 15 psi. We fabricated gold contacts (for the application of single macromolecule devices) with 5 nm separation by nanoimprint in resist and lift-off of metal. Finally, the uniformity and manufacturability of nanoimprint over a 4 in. wafer were demonstrated.The field of nanotechnology is advancing rapidly. Applications of nanotechnology include subwavelength optical elements, biochemical analysis devices, photonic crystals, high-density single-domain magnetic storage, and singlemolecule devices, to name a few. Yet, key to the commercial success of these nanotechnology applications are low cost and high throughput manufacturing capabilities. State-of-theart manufacturing photolithography patterning tools are both too expensive and incapable of producing the necessary pitch and feature sizes of these applications. Thus, presently, researchers have been largely constrained to using lowthroughput lithography tools, such as electron-beam lithography (EBL), atomic force microscopy (AFM), and ion-beam lithography. For high-throughput and low-cost lithography, various "nanoprinting" technologies have been developed. 1-3 Here, we report our investigation of the resolution limit of nanoimprint lithography, where we demonstrated a nanoimprint record of 5 nm linewidth features and 14 nm pitch over a large area, its applications in nanogap metal contacts, and a study of fabrication yields.In photocurable nanoimprint lithography (P-NIL) (shown in Fig. 1), a mold is pressed into a low viscosity photocurable resist liquid to physically deform the resist shape such that it conforms to the topology of the mold. The resist is cured with exposure to UV light, crosslinking the various components in the resist liquid, producing a uniform, relatively rigid polymer network. The mold is then separated from the cured resist. Finally, an anisotropic reactive ion etch (RIE) removes the residual resist in the compressed area, exposing the substrate surface.In order to explore the performance of P-NIL, a variety of molds were fabricated to test specific attributes, including minimum pitch (maximum density), minimum feature size, and large-area uniformity patterning. Previously, 10 nm dots and 40 nm pitch have been demonstrated by NIL 1 with the resolution limited by our ability to fabricate the mold, as proximity effects inherent with EBL make sub-35 nm pitch patterning very difficult. To produce a mold with a pitch resolution surpassing EBL capabilities, we fabricated a NIL mold by selectively wet etching Al 0.7 Ga 0.3 As from a cleaved edge of a GaAs/ Al 0.7 Ga 0.3 As superlattice [grown by molecular-beam epitaxy (MBE)] with a dilute solution of hydrofluoric acid (HF). 4,5 This mold fabrication process offers many advantages, specifically very dense sub-50 nm pitch topologies can be ...

We made uniform arrays of nanometer scale structures using nanoimprint lithography over large areas ͑100 mm wafers͒. The nanofluidic channels were further narrowed and sealed by techniques that are based on nonuniform deposition. The resulting sealed channels have a cross section as small as 10 nm by 50 nm, of great importance for confining biological molecules into ultrasmall spaces. These techniques can be valuable fabrication tools for Nanoelectromechanical Systems and Micro/ Nano Total Analysis Systems.

In this article we report on the fabrication of subwavelength antireflection structures on silicon substrates using a trilayer resist nanoimprint lithography and liftoff process. We have fabricated cone-shaped nanoscale silicon pillars with a continuous effective index gradient, which greatly enhances its antireflective performances. Our measurements show that the two-dimensional subwavelength structure effectively suppresses surface reflection over a wide spectral bandwidth and a large field of view. A reflectivity of 0.3% was measured at 632.8 nm wavelength, which is less than 1% of the flat silicon surface reflectivity.

High density metal cross bars at 17 nm half-pitch were fabricated by nanoimprint lithography. Utilizing the superlattice nanowire pattern transfer technique, a 300-layer GaAs/AlGaAs superlattice was employed to produce an array of 150 Si nanowires (15 nm wide at 34 nm pitch) as an imprinting mold. A successful reproduction of the Si nanowire pattern was demonstrated. Furthermore, a cross-bar platinum nanowire array with a cell density of approximately 100 Gbit/cm(2) was fabricated by two consecutive imprinting processes.

We have obtained spectra of second-harmonic generation, third harmonic generation, and fourwave mixing from a fishnet metamaterial around its magnetic resonance. The resonant behaviors are distinctly different from those for ordinary materials. They result from the fact that the resonance is plasmonic, and its enhancement appears through the local field in the nanostructure. PACS numbers:Optical metamaterials with nanoscale metal building blocks have been studied extensively in recent years [1]- [8]. With each metal unit much smaller than optical wavelength, they can be viewed as continuous media and the metal units act as 'artificial molecules'. The optical properties of metamaterials can be engineered by proper design of the 'artificial molecules' and they can exhibit unusual behavior nonexistent in nature, such as negative refractive indices. While linear optical properties of metamaterials have been well investigated [2]-[8], nonlinear optical properties began to attract interest only recently [9]-[19]. Such interest stems from possible strong enhancement of nonlinear response from plasmon resonances of the metal nanostructures together with spectral tunability offered by design of 'artificial molecules'. A crucial aspect in understanding nonlinear optical properties of metamaterials is their spectral responses, which have not yet been reported.In this letter, we present the first spectroscopic study of second harmonic generation (SHG), third harmonic generation (THG) and four-wave mixing from a metamaterial comprising a monolayer of "fishnet" structure [20], [21]. It was designed to have negative refractive index in the near-IR range, with a magnetic resonance around 1.55 µm [22]. The spectra of SHG and THG with the fundamental input scanned over the magnetic resonance were obtained with different fundamental and harmonic polarizations. Resonant enhancement were clearly observed. Interestingly, the observed resonances are much sharper than that in linear absorption. This is distinctly different from typical molecular cases, where resonant excitation at the fundamental wavelength yields the same resonance spectrum in linear and nonlinear responses. Such difference originates from the fact that, unlike molecular resonances, the plasmon resonances in metal nanostructures are collective oscillations and their resonance enhancement appears through the local field effect in the nonlinear processes.The measurements were carried out on a "fishnet" metamaterial composed of two silver sheets with hole arrays separated by a SiO 2 layer. It was fabricated us- * Electronic address: evgenia˙kim@berkeley.edu ing combination of nanoimprint lithography (NIL) and electron-beam lithography (EBL) [23]. The SEM image of the structure is shown in Fig. 1a and the structural configuration of the broad wire and its dimensions in Fig. 1b. Linear optical response of this metamaterial exhibits a magnetic resonance at 1.55 µm when the magnetic field component of the input wave threads the loop formed by linking the broad metal wires of...

A reflective polarizer consisting of two layers of 190 nm period metal gratings was fabricated using nanoimprint lithography. Measurements with a He–Ne laser (wavelength=632.8 nm) showed that at normal incidence, this polarizer reflects light polarized perpendicular to the grating lines (transverse magnetic polarization) with a reflectance of 54%, but strongly absorbs parallel-polarized light (transverse electric polarization) with a reflectance of only 0.25%. The enhanced polarization extinction ratio of over 200 at this wavelength is possibly related to the resonance between the two layers of metal gratings. This polarizer is thin, compact, and is suited for integrated optical systems.

Thermal emission is the process by which all objects at non-zero temperatures emit light, and is welldescribed by the classic Planck, Kirchhoff, and Stefan-Boltzmann laws. For most solids, the thermally emitted power increases monotonically with temperature in a one-to-one relationship that enables applications such as infrared imaging and non-contact thermometry. Here, we demonstrate ultrathin thermal emitters that violate this one-to-one relationship via the use of samarium nickel oxide (SmNiO3), a strongly correlated quantum material that undergoes a fully reversible, temperature-driven solid-state phase transition. The smooth and hysteresis-free nature of this unique insulator-to-metal (IMT) phase transition allows us to engineer the temperature dependence of emissivity to precisely cancel out the intrinsic blackbody profile described by the Stefan-Boltzmann law, for both heating and cooling. Our design results in temperature-independent thermally emitted power within the long-wave atmospheric transparency window (wavelengths of 8 -14 µm), across a broad temperature range of ~30 °C, centered around ~120 °C. The ability to decouple temperature and thermal emission opens a new gateway for controlling the visibility of objects to infrared cameras and, more broadly, new opportunities for quantum materials in controlling heat transfer. Main text:The total amount of power thermally emitted by a surface in free space can be obtained by integrating its spectral radiance-given by Planck's law and an emissivity-over all wavelengths and hemispherical angles 1 2 . Assuming negligible angular dependence of the emissivity and wrapping the angular integral into the blackbody distribution, ( , ), this relationship can be expressed as:where is the surface area, ( , ) is the spectral emissivity, is the free-space wavelength, is the temperature, and is the Stefan-Boltzmann constant. The total emissivity, ( ), can have a gradual temperature dependence even if the spectral emissivity has no such dependence, due to the integration of ( ) ( , ) 3 ; nevertheless, this dependence is usually dwarfed by the 4 term, and so can often be considered to be approximately constant. Thus, the Stefan-Boltzmann law yields a one-to-one mapping