A high-throughput lithographic method with 25-nanometer resolution and smooth vertical sidewalls is proposed and demonstrated. The technique uses compression molding to create a thickness contrast pattern in a thin resist film carried on a substrate, followed by anisotropic etching to transfer the pattern through the entire resist thickness. Metal patterns with a feature size of 25 nanometers and a period of 70 nanometers were fabricated with the use of resist templates created by imprint lithography in combination with a lift-off process. With further development, imprint lithography should allow fabrication of sub-10-nanometer structures and may become a commercially viable technique for manufacturing integrated circuits and other nanodevices.

A nanoimprint process that presses a mold into a thin thermoplastic polymer film on a substrate to create vias and trenches with a minimum size of 25 nm and a depth of 100 nm in the polymer has been demonstrated. Furthermore, the imprint process has been used as a lithography process to fabricate sub-25 nm diameter metal dot arrays of a 100 nm period in a lift-off process. It was found that the nanostructures imprinted in the polymers conform completely with the geometry of the mold. At present, the imprinted size is limited by the size of the mold being used; with a suitable mold, the imprint process should mold sub-10 nm structures with a high aspect ratio in polymers. The nanoimprint process offers a low cost method for mass producing sub-25 nm structures and has the potential to become a key nanolithography method for future manufacturing of integrated circuits and integrated optics.

Nanoimprint lithography, a high-throughput, low-cost, nonconventional lithographic method proposed and demonstrated recently, has been developed and investigated further. Nanoimprint lithography has demonstrated 25 nm feature size, 70 nm pitch, vertical and smooth sidewalls, and nearly 90° corners. Further experimental study indicates that the ultimate resolution of nanoimprint lithography could be sub-10 nm, the imprint process is repeatable, and the mold is durable. In addition, uniformity over a 15 mm by 18 mm area was demonstrated and the uniformity area can be much larger if a better designed press is used. Nanoimprint lithography over a nonflat surface has also been achieved. Finally, nanoimprint lithography has been successfully used for fabricating nanoscale photodetectors, silicon quantum-dot, quantum-wire, and ring transistors.

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...

New developments, further details, and applications of imprint lithography are presented. Arrays of 10 nm diameter and 40 nm period holes were imprinted not only in polymethylmethacrylate (PMMA) on silicon, but also in PMMA on gold substrates. The smallest hole diameter imprinted in PMMA is 6 nm. All the PMMA patterns were transferred to a metal using a liftoff. In addition, PMMA mesa’s of a size from 45 nm to 50 μm were obtained in a single imprint. Moreover, imprint lithography was used to fabricate the silicon quantum dot, wire, and ring transistors, which showed the same behavior as those fabricated using electron (e)-beam lithography. Finally, imprint lithography was used to fabricate nanocompact disks with 10 nm features and 400 Gbits/in.2 data density—near three orders of magnitude higher than current critical dimensions (CDs). A silicon scanning probe was used to read back the data successfully. The study of wear indicates that due to the ultrasmall force in tapping mode, both the nano-CD and the scanning probe will not show noticeable wear after a large number of scans.

We show that genomic-length DNA molecules imaged in nanochannels have an extension along the channel that scales linearly with the contour length of the polymer, in agreement with the scaling arguments developed by de Gennes for self-avoiding confined polymers. This fundamental relationship allows us to measure directly the contour length of single DNA molecules confined in the channels, and the statistical analysis of the dynamics of the polymer in the nanochannel allows us to compute the SD of the mean of the extension. This statistical analysis allows us to measure the extension of DNA multimers with a 130-nm SD in 1 min.T he location of landmark restriction sites on chromosomallength DNA molecules is a powerful way to guarantee that the assembled DNA sequences in shotgun DNA sequencing represent the native genome faithfully. The restriction sites can be determined by measuring the length of restriction fragments by gel electrophoresis (1). Alternatively, they can be located by using optical mapping of stretched DNA molecules trapped on a surface (2). To measure the contour length of a single molecule by using optical techniques directly, it is necessary to extend the polymer such that a one-to-one mapping can be established between the spatial position along the polymer and position within the genome.Confinement elongation of genomic-length DNA has several advantages over alternative techniques for extending DNA, such as flow stretching and͞or stretching relying on a tethered molecule. Confinement elongation does not require the presence of a known external force because a molecule in a nanochannel will remain stretched in its equilibrium configuration, and hence, the mechanism is in equilibrium. Second, it allows for continuous measurement of length.Some fundamental statistical mechanical problems are associated with confinement of a polymer in a channel whose width D is much less than the radius of gyration of the unconfined polymer, such as (i) the dependence of the end-to-end length L z of the confined polymer on the length L of the polymer and (ii) the dependence of the effective spring constant k of the confined polymer on the length L. The spring constant sets the scale of end-to-end length fluctuations for the confined polymer because of thermal effects. For the measurement process, an understanding of the relaxation time is also crucial. A key element for understanding these questions is the influence of the selfavoiding nature of random walk of the polymer in the channel, as we show in Fig. 1.The effect of self-avoidance on flexible polymers that are freely coiled in solution was first understood by Flory (3) and later generalized to the semiflexible case by Schaefer et al. (4). The rms radius of gyration R g of a self-avoiding persistent polymer in solution scales according to Flory-Pincus with the persistence length p, molecule width w, and contour length L, such that (pw) 1/5 L 3/5 . Compare this form with the result expected for an ideal, non-self-avoiding polymer R g Ϸ (pL) 1/2 . Thus, self-av...

We show the fractionation of whole blood components and isolation of blood plasma with no dilution by using a continuousflow deterministic array that separates blood components by their hydrodynamic size, independent of their mass. We use the technology we developed of deterministic arrays which separate white blood cells, red blood cells, and platelets from blood plasma at flow velocities of 1,000 m͞sec and volume rates up to 1 l͞min. We verified by flow cytometry that an array using focused injection removed 100% of the lymphocytes and monocytes from the main red blood cell and platelet stream. Using a second design, we demonstrated the separation of blood plasma from the blood cells (white, red, and platelets) with virtually no dilution of the plasma and no cellular contamination of the plasma.

The PMMA opal film was infiltrated with SiO 2 using a homemade CVD setup operating at atmospheric pressure and room temperature with SiCl 4 and H 2 O as precursors [12]. The CVD process is based on the hydrolysis of silicon tetrachloride (SiCl 4 ) on the hydrophilic surface of the spheres; these had been previously wetted with water vapor. SiCl 4 and water are both separately bubbled by a N 2 flow that sweeps the vapor phases to the reactor where the sample is placed. Controlled filling fractions can be achieved by adjusting the N 2 -flow rate and time.Patterning of the PMMA/SiO 2 composite was performed by EBL, using a Hitachi S-800 and a LEO 1455 scanning electron microscope equipped with a Raith Elphy Plus EBL control unit, at an accelerating voltage of 25 kV and exposure doses between 100 and 850 lC cm ±2 . The samples were developed for 40 s in methyl isobutyl ketone and then placed in isopropanol for 10 s to stop the developing process.The optical characterization was performed with a FTIR spectrometer, IFS 66 from Bruker with an attached IR Scope II microscope. 15 and 36 Cassegrain objectives were used to focus and collect the light from the patterned motifs. The incident and collected light cover external angles from 5 to 15 (15 objective) and 20 to 57 (36 objective) from normal incidence with respect to the (111) family of planes.HRSEM was used to observe the alterations in the opal structure. Before examination, samples had been cleaved and sputtered with a thin film of gold. Block copolymer thin films are currently of great interest as contact masks for inexpensive, large-area lithography. Films of the order of 50 nm thickness, containing a single layer of spherical or cylindrical microdomains formed by one block in a matrix of the other, have been successfully used to pattern semiconductors, [1±3] fabricate ultradense arrays of metal [4,5] and III±V semiconductor quantum dots, [6] and condense and isolate magnetic storage media. [7,8] Progress has been impeded by the lack of a versatile technique for inducing long-range order and orientation of the microdomains in a predetermined direction. For example, the striped patterns [9] formed by either cylinders or edge-on lamellaeÐwhich, if aligned, could serve as precursors to arrays of metal nanowiresÐinstead form curved, wormlike patterns with no long-range order. Techniques capable of aligning these striped patterns over areas of several lm 2 include electric fields, [10] graphoepitaxy (where the substrate is topographically prepatterned at the micrometer length scale [11,12] ), and directional crystallization of a suitable solvent. [13] Ordering over even larger areas is potentially achievable by prepatterning the substrate with the desired nanometer-scale pattern, [14,15] and then replicating this pattern in the block copolymer film; however, the aim of COMMUNICATIONS 1736