Synthesis of metal chalcogenide nanodot arrays using block copolymer-derived nanoreactors

Soluble metal chalcogenide precursors are used to fabricate arrays of metal chalcogenide nanodots by spin-coating. Nanodots are formed after thermal decomposition of the precursors, which are collected in patterned nanowell arrays. These arrays are derived from block copolymer patterns and may consist of the polymer itself or result from etching to transfer the pattern to an inorganic substrate. Etching provides enhanced control over nanowell shape and the morphology of the resulting metal chalcogenide array.     

Non-lift-off block copolymer lithography of 25 nm magnetic nanodot arrays

Although nanolithographic techniques based on self-assembled block copolymer templates offer tremendous potential for fabrication of large-area nanostructure arrays, significant difficulties arise with both the lift-off and etch processes typically used for pattern transfer. These become progressively more important in the limit of extreme feature sizes. The few techniques that have been developed to avoid these issues are quite complex. Here, we demonstrate successful execution of a nanolithographic process based on solvent annealed, cylinder-forming, easily degradable, polystyrene-b-polylactide block copolymer films that completely avoids lift-off in addition to the most challenging aspects of etching. We report a "Damascene-type" process that overfills the polystyrene template with magnetic metal, employs ion beam milling to planarize the metal surface down to the underlying polystyrene template, then exploits the large etch rate contrast between polystyrene and typical metals to generate pattern reversal of the original template into the magnetic metal. The process is demonstrated via formation of a large-area array of 25 nm diameter ferromagnetic Ni(80)Fe(20) nanodots with hexagonally close-packed order. Extensive microscopy, magnetometry, and electrical measurements provide detailed characterization of the pattern formation. We argue that the approach is generalizable to a wide variety of materials, is scalable to smaller feature sizes, and critically, minimizes etch damage, thus preserving the essential functionality of the patterned material.     

Nanodomain Swelling Block Copolymer Lithography for Morphology Tunable Metal Nanopatterning

Ordered metal nanopatterns are crucial requirements for electronics, magnetics, catalysts, photonics, and so on. Despite considerable progress in the synthetic route to metal nanostructures, highly ordered metal nanopatterning over a large‐area is still challenging. Nanodomain swelling block copolymer lithography is presented as a general route to the systematic morphology tuning of metal nanopatterns from amphiphilic diblock copolymer self‐assembly. Selective swelling of hydrophilic nanocylinder domains in amphiphilic block copolymer films during metal precursor loading and subsequent oxygen based etching generates diverse shapes of metal nanopatterns, including hexagonal nanoring array and hexagonal nanomesh and double line array in addition to common nanodot and nanowire arrays. Solvent annealing condition of block copolymer templates, selective swelling of hydrophilic cylinder nanodomains, block copolymer template thickness, and oxygen based etching methods are the decisive parameters for systematic morphology evolution. The plasmonic properties of ordered Au nanopatterns are characterized and analyzed with finite differential time domain calculation. This approach offers unprecedented opportunity for diverse metal nanopatterns from commonly used diblock copolymer self‐assembly.     

Fabrication of nanostructure and formation of nanocrystal for non-volatile memory

In this work, we have demonstrated that the nanocrystal created by combining the self-assembled block copolymer thin film with regular semiconductor processing can be applicable to non-volatile memory device with increased charge storage capacity over planar structures. Self-assembled block copolymer thin film for nanostructures with critical dimensions below photolithographic resolution limits has been used during all experiments. Nanoporous thin film from PS-b-PMMA diblock copolymer thin film with selective removal of PMMA domains was used to fabricate nanostructure and nanocrystal. We have also reported about surface morphologies and electrical properties of the nano-needle structure formed by RIE technique. The details of nanoscale pattern of the very uniform arrays using RIE are presented. We fabricated different surface structure of nanoscale using block copolymer. We also deposited Si-rich SiNx layer using ICP-CVD on the silicon surface of nanostructure. The deposited films were studied after annealing. PL studies demonstrated nanocrystal in Si-rich SiNx film on nanostructure of silicon.     

Metal Deposition on a Self‐Generated Microfibril Network to Fabricate Stretchable Tactile Sensors Providing Analog Position Information

Stretchable conductors and sensors have attracted great attention for use in electronic skin and healthcare monitoring. Despite the development of many stretchable conductors, there are still very few studies that utilize the conventional methods making electrodes and circuits used in current industry. A method is proposed to fabricate a stretchable electrode pattern and a stretchable tactile sensor by simply depositing linear metal lines through a mask on a stretchable substrate. A method is developed of a self‐generating microfibril network on the surface of stretchable block copolymer substrates. The formation mechanism of the microfibril network is studied with finite element method simulations. Metals (Au and Ag nanowires) are deposited directly on the substrate through a patterned mask. This study shows that strain‐insensitive circuit and strain‐sensitive sensor can be fabricated in a controlled way by adjusting the thickness of the deposited metal, which makes it easy to fabricate a tactile sensor by metal deposition. Also, by using the characteristic that the sensor has different sensitivity depending on the line pattern width, a novel sensor structure simultaneously providing analog‐type position information and pressure value is proposed.     

Simple orientational control over cylindrical organic-inorganic block copolymer domains for etch mask applications

Bottom-up patterning methodologies, predicated on chemical self-assembly, have the potential to transcend limitations associated with more traditional lithographies. By controlling the domain orientation of a cylinder-forming organic-inorganic block copolymer, poly(styrene-block-ferrocenyldimethylsilane), it is possible to straightforwardly fabricate massive arrays of either nanoscale dots or wires out of a film composed of a wide variety of materials. In the work reported here, orientational control is achieved by manipulating the polymer film thickness in concert with the annealing treatment. For films much thinner than the equilibrium periodicity of the microdomains, the cylinders spontaneously orient themselves perpendicular to the substrate. Films with thickness close to the equilibrium periodicity exhibit the more common in-plane orientation following thermal annealing. Solvent annealing leads to an in-plane orientation for the full range of film thicknesses studied. As a demonstration of the effectiveness of this method, semiconductor substrates were patterned with arrays of posts and wires, respectively, using the same starting polymeric material as the etch mask. Compatibility of this polymer with various substrate materials is also demonstrated.     

Site-specific fabrication and epitaxial conversion of functional oxide nanodisk arrays

Nanodisk arrays of technologically important magnetic (CoFe(2)O(4)) and ferroelectric (BaTiO(3)) oxides are fabricated on diverse substrates with well-defined size and separation using the soft-eBL approach. We demonstrate that below a certain pattern size, the as-deposited amorphous nanodisks can be readily converted into dense, single-crystal form that exhibit cube-on-cube heteroepitaxy with respect to the underlying single-crystal substrate. Such single-crystal disks show well-defined truncated-pyramid morphology that is consistent with Wulff construction. The mechanism of morphology development with the pattern size change is discussed. Localized characterization of the crystallinity, chemical composition, and magnetic behavior of the CFO nanodisk patterns are carried out using analytical transmission electron microscopy and magnetic force microscopy. Such solution-based epitaxial conversion of patterned arrays of multifunctional oxides has potential for viable cost-effective technological applications.     

Controlled Segmentation of Metal Nanowire Array by Block Copolymer Lithography and Reversible Ion Loading

Spatial arrangement of 1D nanomaterials may offer enormous opportunities for advanced electronics and photonics. Moreover, morphological complexity and chemical diversity in the nanoscale components may lead to unique properties that are hardly anticipated in randomly distributed homogeneous nanostructures. Here, controlled chemical segmentation of metal nanowire arrays using block copolymer lithography and subsequent reversible metal ion loading are demonstrated. To impose chemical heterogeneity in the nanowires generated by block copolymer lithography, reversible ion loading method highly specific for one particular polymer block is introduced. Reversibility of the metal ion loading enables area‐selective localized replacement of metal ions in the self‐assembled patterns and creates segmented metal nanowire arrays with different metallic components. Further integration of this method with shear aligning process produces high aligned segmented metal nanowire array with desired local chemical compositions.     

Patterning of various silicon structures via polymer lithography and catalytic chemical etching

We demonstrate a facile fabrication of a rich variety of silicon patterns with different length scales by combining polymer lithography and a metal-assisted chemical etching method. Several types of polymer patterns were fabricated on silicon substrates, and silver layers were deposited on the patterned silicon surfaces and used to etch the silicon beneath. Various silicon patterns including topographic lines, concentric rings, and square arrays were created at a micro-?and nanoscale after etching the silicon and subsequent removal of the patterned polymer masks. Alternatively, the arrays of sub-30?nm silicon nanowires were produced by a chemical etching of the silicon wafer which was covered with highly ordered polystyrene-block-polyvinylpyridine (PS-b-PVP) micellar films. In addition, silicon nanohole arrays were also generated by etching with hexagonally packed silver nanoparticles that were prepared using PS-b-PVP block copolymer templates.     

A soft lithographic approach to fabricate patterned microfluidic channels

The control of surface properties and spatial presentation of functional molecules within a microfluidic channel is important for the development of diagnostic assays and microreactors and for performing fundamental studies of cell biology and fluid mechanics. Here, we present a simple technique, applicable to many soft lithographic methods, to fabricate robust microchannels with precise control over the spatial properties of the substrate. In this approach, the patterned regions were protected from oxygen plasma by controlling the dimensions of the poly(dimethylsiloxane) (PDMS) stamp and by leaving the stamp in place during the plasma treatment process. The PDMS stamp was then removed, and the microfluidic mold was irreversibly bonded to the substrate. The approach was used to pattern a nonbiofouling poly(ethylene glycol)-based copolymer or the polysaccharide hyaluronic acid within microfluidic channels. These nonbiofouling patterns were then used to fabricate arrays of fibronectin and bovine serum albumin as well as mammalian cells. In addition, further control over the deposition of multiple proteins onto multiple or individual patterns was achieved using laminar flow. Also, cells that were patterned within channels remained viable and capable of performing intracellular reactions and could be potentially lysed for analysis.     

Substrate wetting and topographically induced ordering of amorphous PI-b-PFS block-copolymer domains

The substrate wetting of an amorphous, low-glass-transition-temperature spherical poly(isoprene-block-ferrocenylsilane) (PI-b-PFS) block copolymer and the alignment of the microdomains in grooves of various geometry are studied. Compositional analysis by time-of-flight secondary ion mass spectrometry depth profiling (TOF-SIMS) indicates the presence of both PI and PFS directly at the film-substrate interface on silicon and silica substrates. The TOF-SIMS depth-profiling study indicates a transition in the packing of the domains between the two-dimensional (2D) monolayer and 3D, thicker layers. In a monolayer of domains, a hexagonal packing is adopted. In films of two or three layers, the hexagonal packing reorganizes towards a body-centered cubic (bcc) packing by the extension of the copolymer chains in the direction normal to the substrate, as indicated by an increase in spacing between PFS layers and an increase in domain size. For thicker layers, a bcc morphology with the (110) plane parallel to the substrate is found to extend from the free surface downwards. Films of one monolayer of domains of the copolymer exhibit long-range lateral ordering on the micrometer scale on flat substrates without high-temperature annealing. On topographically patterned silicon substrates the position of the domains of the minority PFS phase directly near the side walls is fixed by the neutral wetting condition. Successful positioning of the block-copolymer spheres in linear and hexagonal grooves is achieved in grooves up to 1.3 microm wide, whereby the hexagonal grooves demonstrate complete 2D alignment. In circular pits, this graphoepitaxial effect is absent.     

Self-assembled one-dimensional nanostructure arrays

A range of proposed devices relies on the electronic, optical or magnetic properties of one-dimensional (1D) chains of nanoparticles. Here, well-controlled 1D arrays have been formed by templating a spherical-morphology block copolymer within a narrow groove. Significantly, the domains are distorted into ellipses with aspect ratio and major axis orientation controlled by the groove width. This technique gives unprecedented control over the period, particle size, aspect ratio, and orientation of nanoparticles in 1D arrays, making it valuable for creating self-assembled masks for the fabrication of novel devices.     

Directed assembly of cylinder-forming block copolymer films and thermochemically induced cylinder to sphere transition: a hierarchical route to linear arrays of nanodots

A morphological transition from cylinders to spheres was induced in an asymmetric diblock copolymer, poly(styrene)-block-poly(tert-butyl acrylate) (PS-b-PtBA). The periodic arrays of the poly(tert-butyl acrylate) (PtBA) domains were transformed to the ordered poly(acrylic anhydride) (PAA) spheres via the thermal deprotection of tert-butyl acrylate linkages and the subsequent volume change of the minority block. Coupled with techniques to direct the assembly of cylinder-forming block copolymers, this finding provides new routes to fabricate ordered geometries of nanodot arrays.     

Graphoepitaxial Directed Self‐Assembly of Polystyrene‐Block‐Polydimethylsiloxane Block Copolymer on Substrates Functionalized with Hexamethyldisilazane to Fabricate Nanoscale Silicon Patterns

In block copolymer (BCP) nanolithography, microphase separated polystyrene‐block‐polydimethylsiloxane (PS‐b‐PDMS) thin films are particularly attractive as they can form small features and the two blocks can be readily differentiated during pattern transfer. However, PS‐b‐PDMS is challenging because the chemical differences in the blocks can result in poor surface‐wetting, poor pattern orientation control and structural instabilities. Usually the interfacial energies at substrate surface are engineered with the use of a hydroxyl‐terminated polydimethylsiloxane (PDMS‐OH) homopolymer brush. Herein, we report a facile, rapid and tuneable molecular functionalization approach using hexamethyldisilazane (HMDS). The work is applied to both planar and topographically patterned substrates and investigation of graphoepitaxial methods for directed self‐assembly and long‐range translational alignment of BCP domains is reported. The hexagonally arranged in‐plane and out‐of‐plane PDMS cylinders structures formed by microphase separation were successfully used as on‐chip etch masks for pattern transfer to the underlying silicon substrate. The molecular approach developed here affords significant advantages when compared to the more usual PDMS‐OH brushes used.     

图形化硅纳米线阵列的制备

本文主要研究了在常态(常温、常压等)条件下,利用金属催化化学腐蚀方法在硅片表面上大面积制备排列整齐、取向一致的硅纳米线阵列.同时,出于对后续制作硅纳米线传感器考虑,利用微电子标准加工工艺,以氮化硅做掩膜,通过选择合适的实验参数,在硅片表面选择性生长纳米线阵列,得到图形化的硅纳米线阵列.     

Ordered arrays of <100>-oriented silicon nanorods by CMOS-compatible block copolymer lithography

Dense, ordered arrays of <100>-oriented Si nanorods with uniform aspect ratios up to 5:1 and a uniform diameter of 15 nm were fabricated by block copolymer lithography based on the inverse of the traditional cylindrical hole strategy and reactive ion etching. The reported approach combines control over diameter, orientation, and position of the nanorods and compatibility with complementary metal oxide semiconductor (CMOS) technology because no nonvolatile metals generating deep levels in silicon, such as gold or iron, are involved. The Si nanorod arrays exhibit the same degree of order as the block copolymer templates.     

Three-dimensional self-assembly of spherical block copolymer domains into V-shaped grooves

The self-assembly of a spherical-morphology block copolymer into V-shaped grooves has been investigated. Although spherical morphology block copolymers typically form a bcc sphere array in bulk, the V groove promotes the formation of a well-ordered fcc close-packed sphere array with the (111) planes of the array parallel to the groove walls. The sphere size in the block copolymer adjusts depending on the commensurability between the periodicity of the block copolymer and the film thickness within the V groove. The top surface of the close-packed array, parallel to the substrate, shows a square symmetry, unlike the hexagonal symmetry seen in monolayers of spherical domains, which may provide a useful geometry for block copolymer lithography.     

Nanometer-scale pattern registration and alignment by directed diblock copolymer self-assembly

We describe a fabrication method that combines the alignment capabilities of optical lithography with the sub-lithographic dimensions achievable using self-assembled diblock copolymer films. We use surface topography to direct the assembly of in-plane cylindrical copolymer domains so as to subdivide larger patterns defined using optical lithography, in the process registering the location of each 20-nm polymer domain to the lithographic pattern. Our approach provides an application for self-assembly in the fabrication of complex microelectronic circuits entailing alignment of multiple patterned layers. We detail the influence of such process parameters as lithographic pattern dimensions and density, copolymer film thickness, and anneal time on the quality of the resulting nanometer-scale-domain registration.     

Chemical alignment of DNA origami to block copolymer patterned arrays of 5 nm gold nanoparticles

We have used block copolymer patterned arrays of 5 nm gold nanoparticles (AuNPs) for chemically aligned surface attachment of DNA origami. Addition of single-stranded DNA-thiol to AuNPs allowed a base paired attachment of sticky end modified DNA origami. Results indicate a stable, selective attachment between the DNA origami and ssDNA modified AuNPs. Yield data showed 74% of AuNP binding sites forming an attachment with a DNA origami rectangle, and control surfaces showed less than 0.5% nonspecific adsorption.     

Nanostructuration of self-assembled poly(styrene-b-isoprene-b-styrene) block copolymer thin films in a highly oriented pyrolytic graphite substrate

Highly oriented pyrolitic graphite (HOPG) is a useful substrate to visualize epitaxial formation due to its crystallographic structure. The morphology of a poly(styrene-b-isoprene-b-styrene) block copolymer thin film on a HOPG substrate was investigated by atomic force microscopy. Block copolymer domains generated a morphology with triangular regularity. This arrangement was induced by the HOPG substrate structure due to van der Waals attraction between the HOPG π-conjugated system and aromatic ring of polystyrene domains. However, increasing the film thickness, the substrate effect on the surface morphology decreased. As a consequence, film surfaces showed the coexistence of different structures such as highly aligned cylinders and perforated lamellae. When film thickness exceeded a threshold value, the substrate did not have effect in the surface arrangements and the surface showed a similar morphology to that existing in bulk.