Self-assembling materials are the building blocks of bottom-up nanofabrication processes, but they need to be templated to impose long-range order and eliminate defects. In this work, the self-assembly of a thin film of a spherical-morphology block copolymer is templated using an array of nanoscale topographical elements that act as surrogates for the minority domains of the block copolymer. The orientation and periodicity of the resulting array of spherical microdomains are governed by the commensurability between the block copolymer period and the template period and is accurately described by a free-energy model. This method, which forms high-spatial-frequency arrays using a lower-spatial-frequency template, will be useful in nanolithography applications such as the formation of high-density microelectronic structures.

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Templated self-assembly of a cylinder-forming poly(styrene-b-dimethylsiloxane) (PS−PDMS) diblock copolymer has been investigated for nanolithography applications. The large -parameter of the blocks and the use of a PDMS−brush substrate surface treatment are especially advantageous for achieving long-range ordering and minimizing defect densities, and the high Si content in PDMS leaves a robust oxide etch mask after two-step reactive ion etching. By adjusting mesa width and solvent-annealing vapor pressure and time, the cylinders can be intentionally oriented parallel or perpendicular to the trench walls. Pattern transfer into thin silica is also demonstrated. This block copolymer system has excellent characteristics for self-assembled nanolithography applications.The growing demand for nanoscale fabrication methods, combined with the inherent feature-size limitations of optical lithography and the low throughput of electron-beam lithography, have motivated a search for cost-effective nanoscale fabrication technologies, including nanoimprint lithography, 1 dip-pen nanolithography, 2 and block copolymer lithography. [3][4][5][6] In the case of block copolymer lithography, the use of a chemical or topographical template enables control over the long-range order of the self-assembled patterns, providing a simple and scalable nanopatterning method in which the feature sizes and geometries are controlled via the chain length and volume fractions of the block copolymer.In block copolymer lithography, arrays of holes or dots may be defined using a spherical-morphology block copolymer 3,5,6 or a cylindrical-morphology block copolymer with the cylinders oriented perpendicular to the substrate. 7,8 In contrast, patterns consisting of parallel lines may be defined using a cylindrical-morphology block copolymer with the cylinders parallel to the surface 9-12 or a lamellar block copolymer with a perpendicular orientation. 13,14 Such patterns have been templated using both chemical and topographical substrate features. For example, lamellar poly(styrene-bpolymethyl methacrylate) (PS-PMMA) patterns have been templated using a self-assembled monolayer patterned by extreme ultraviolet interference lithography (EUV-IL) or electron-beam (e-beam) lithography and have attracted much attention due to their high aspect ratio and absence of defects. 13,14 However, this process requires template generation on the same length scale as the period of the block copolymer. 15 On the other hand, well-ordered arrays of inplane cylinders templated by larger scale topographic patterns have been demonstrated by several groups. Horizontal cylinders from diblocks such as poly(styrene-b-ethylene propylene) (PS-PEP) 9 and PS-PMMA 10-12 have been successfully aligned in templates. The templates have critical dimensions an order of magnitude or more larger than the block copolymer period and can be made by optical lithography.In all these examples, the removal of one block leaves a structure made from the other block, typically PS, that could be...

Self-assembling materials are the building blocks for bottom-up nanofabrication processes, but many self-assembled nanostructures contain defects and lack sufficient long-range order for certain nanotechnology applications. Here we investigate the formation of defects in a self-assembled array of spherical block-copolymer microdomains, using topographical templates to control the local self-assembly. Perfect ordered sphere arrays can form in both constant-width templates and width-modulated templates. For modulated templates, transition between configurations having a constant number of rows and configurations of stable arrays with varying numbers of rows is shown to be analogous to dislocation formation in an epitaxial thin film system. Based on the configuration transition energy and fluctuation energy, designed templates with a high tolerance for lithographical imperfections can direct precisely modulated block-copolymer nanostructures. This study provides insights into the design of hybrid systems combining top-down and bottom-up fabrication.

Non-reciprocal photonic devices, including optical isolators and circulators, are indispensible components in optical communication systems. However, the integration of such devices on semiconductor platforms has been challenging because of material incompatibilities between semiconductors and magneto-optical materials that necessitate wafer bonding, and because of the large footprint of isolator designs. Here, we report the first monolithically integrated magneto-optical isolator on silicon. Using a non-reciprocal optical resonator on an silicon-on-insulator substrate, we demonstrate unidirectional optical transmission with an isolation ratio up to 19.5 dB near the 1,550 nm telecommunication wavelength in a homogeneous external magnetic field. Our device has a small footprint that is 290 mm in length, significantly smaller than a conventional integrated optical isolator on a single crystal garnet substrate. This monolithically integrated non-reciprocal optical resonator may serve as a fundamental building block in a variety of ultracompact silicon photonic devices including optical isolators and circulators, enabling future low-cost, large-scale integration.Non-reciprocal photonic devices that break the time-reversal symmetry of light propagation provide critical functionalities such as optical isolation and circulation in photonic systems. Although widely used in optical communications, such devices are still lacking in semiconductor integrated photonic systems 1,2 because of challenges in both materials integration and device design. On the materials side, magneto-optical garnets used in discrete nonreciprocal photonic devices show large lattice and thermal mismatch with semiconductor substrates, making it difficult to achieve monolithic integration of garnets with phase purity, high Faraday rotation and low transmission loss 3,4 , and requiring wafer bonding to incorporate them on a semiconductor platform. On the device side, non-reciprocal mode conversion (NRMC) and non-reciprocal phase shift (NRPS) integrated optical isolators have large footprints with length scales from millimetres to centimetres 5,6 , which severely limits the feasibility of large-scale and low-cost integration. Efforts have been pursued both in the monolithic integration of iron garnet and the exploration of other magneto-optical materials with better semiconductor compatibility. Polycrystalline Y 3 Fe 5 O 12 (YIG) films 3 , epitaxial Sr(Fe-doped InP films 9 have been demonstrated to have promising magneto-optical performance at a wavelength of 1,550 nm. In relation to device design, several monolithic non-reciprocal photonic devices capitalizing on optical resonance effects (for example, magneto-optical photonic crystals 10 , garnet thin-film based optical resonators 11 , silicon ring resonators with magneto-optical polymer cladding 12 and modulated ring resonators using non-reciprocal photonic transitions 1 ) have been theoretically analysed with a view to reducing the device footprint. However, the experimental realization of monolit...

Single‐domain cobalt dot arrayswith high magnetic particle density, patterned over large areas (e.g., 10 cm diameter wafers) are fabricated by self‐assembled block copolymer lithography, using a polystyrene–poly(ferrocenyldimethylsilane) copolymer as a template. By varying the copolymer type and etching conditions the magnetic properties can be tuned. The Figure shows a typical array of Co dots with tungsten caps obtained via this procedure.

Crystal structures of HIV-1 reverse transcriptase (RT) complexed with a range of chemically diverse non-nucleoside inhibitors (NNIs) have shown a single pocket in which the inhibitors bind and details of the inhibitor-protein interactions. To delineate the structural requirements for an effective inhibitor, we have determined the structures of three closely related NNIs which vary widely in their potencies. Crystal structures of HIV-1 RT complexed with two very potent inhibitors, MKC-442 and TNK-651, at 2.55 angstroms resolution complement our previous analysis of the complex with the less effective inhibitor, HEPT. These structures reveal conformational changes which correlate with changes in potency. We suggest that a major determinant of increased potency in the analogues of HEPT is an improved interaction between residue Tyr181 in the protein and the 6-benzyl ring of the inhibitors which stabilizes the structure of the complex. This arises through a conformational switching of the protein structure triggered by the steric bulk of the 5-substituent of the inhibitor pyrimidine ring.

Self‐assembly of a block copolymer into cylindrical and/or perforated lamellar arrays within substrate trenches can be extensively tuned during the solvent‐annealing process. Following reactive‐ion etching, SEM images reveal that the solvent mixing ratio and the vapor pressure determine the type of array obtained and influence the dimensions of the repeat unit.