Vivian P. Chuang

Templated self-assembly of square symmetry arrays from an ABC triblock terpolymer.

Self-assembly provides the ability to create well-controlled nanostructures with electronic or chemical functionality and enables the synthesis of a wide range of useful devices. Diblock copolymers self-assemble into periodic arrays of microdomains with feature sizes of typically 10-50 nm, and have been used to make a wide range of devices such as silicon capacitors and transistors, photonic crystals, and patterned magnetic media(1-3). However, the cylindrical or spherical microdomains in diblock copolymers generally form close-packed structures with hexagonal symmetry, limiting their device applications. Here we demonstrate self-assembly of square-symmetry patterns from a triblock terpolymer in which one organometallic block imparts high etch selectivity and etch resistance. Long-range order is imposed on the microdomain arrays by self-assembly on topographical substrates, and the orientation of both square lattices and in-plane cylinders is controlled by the substrate chemistry. Pattern transfer is demonstrated by making an array of square-packed 30 nm tall, 20 nm diameter silica pillars. Templated self-assembly of triblock terpolymers can generate nanostructures with geometries that are unattainable from diblock copolymers, significantly enhancing the capabilities of block copolymer lithography.

Si-containing block copolymers for self-assembled nanolithography

Block copolymers can self-assemble to generate patterns with nanoscale periodicity, which may be useful in lithographic applications. Block copolymers in which one block is organic and the other contains Si are appealing for self-assembled lithography because of the high etch contrast between the blocks, the high etch resistance of the Si-containing block, and the high Flory–Huggins interaction parameter, which is expected to minimize line edge roughness. The locations and long range order of the microdomains can be controlled using shallow topographical features. Pattern generation from poly(styrene)-poly(ferrocenyldimethylsilane) and poly(styrene)-poly(dimethylsiloxane) block copolymers, and the subsequent pattern transfer into metal, oxide, and polymer films, is described

Nanoparticle assemblies in thin films of supramolecular nanocomposites.

We demonstrated a versatile approach to obtain layered nanoparticle sheets with in-plane hexagonal order and 3-D ordered arrays of single nanoparticle chains in thin films upon blending nanoparticles with block copolymer (BCP)-based supramolecules. Basic understanding on the thermodynamic and kinetic aspects of the assembly process paved a path to manipulate these assemblies to meet demands in nanoparticle-based device fabrication and understand structure-property correlations.

Multilayer magnetic antidot arrays from block copolymer templates

Antidot arrays (films with periodic arrays of holes) with periodicity of 26 or 40nm have been prepared from Co and Co∕Cu∕NiFe films using a block copolymer templating method. The magnetic properties of the antidot arrays differ from those of continuous films. The holes raise the coercivity of single-layer Co films and in the multilayers lead to an antiparallel alignment of the moments in the Co and NiFe layers at remanence, as a result of the strong magnetostatic interactions between the layers. These results are confirmed by micromagnetic modeling and the trend in coercivity is explained in terms of the interactions between the nanoscale holes and the domain walls in the films.

Nanoscale Rings Fabricated Using Self-Assembled Triblock Terpolymer Templates

Although there has been extensive work on the use of self-assembled diblock copolymers for nanolithography, there are few reports of the use of multiblock copolymers, which can form a more diverse range of nanoscale pattern geometries. Pattern transfer from a self-assembled poly(butadiene-b-styrene-b-methyl methacrylate) (PB-b-PS-b-PMMA) triblock terpolymer thin film has been investigated. Polymers of different total molecular weight were synthesized with a predicted morphology consisting of PMMA-core/PS-shell cylinders in a PB matrix. By adjusting the solvent-annealing conditions and the film thickness, thin films with vertically oriented cylinders were formed. The PMMA cylinder cores and the PB matrix were then removed using selective etching to leave an array of PS rings, and the ring pattern was transferred into a silica film by reactive ion etching to form 19 nm high silica rings. This result illustrates the design and use of triblock terpolymers for self-assembled lithography.

Templated self-assembly of Si-containing block copolymers for nanoscale device fabrication

Block copolymers have been proposed for self-assembled nanolithography because they can spontaneously form well-ordered nanoscale periodic patterns of lines or dots in a rapid, low-cost process. By templating the selfassembly, patterns of increasing complexity can be generated, for example arrays of lines with bends or junctions. This offers the possibility of using a sparse template, written by electron-beam lithography or other means, to organize a dense array of nanoscale features. Pattern transfer is simplified if one block is etch resistant and one easily removable, and in this work we use a diblock copolymer or a triblock terpolymer with one Sicontaining block such as polydimethylsiloxane or polyferrocenylsilane, and one or two organic blocks such as polystyrene or polyisoprene. Removal of the organic block(s) with an oxygen plasma leaves a pattern of Sicontaining material which can be used as an etch mask for subsequent pattern transfer to make metallization lines or magnetic nanostructures with feature sizes below 10 nm and periodicity below 20 nm.

Thickness dependence of magnetic film edge properties in Ni80Fe20 stripes

Measurements of “trapped spin wave” edge modes in transversely magnetized stripe arrays of Ni80Fe20 largely confirm previous theoretical predictions for the thickness dependence of the edge saturation field Hsat and the effective out-of-plane edge anisotropy field H2. The stripes were patterned using optical interference lithography with film thicknesses in the range from 10to65nm. Large linewidth values for edge modes relative to bulk modes indicate inhomogeneity of the edges. Elimination of an antireflective coating underlayer dramatically decreases the edge mode linewidth without affecting the bulk mode linewidth.