Ordered nanoparticle assemblies can exhibit collective properties that are quite different from those displayed by the individual nanoparticles or their bulk counterpart. This paper reviews recent progress on the assembly of superparamagnetic nanoparticles, with emphasis on different strategies for their chemical fabrication with highly ordered nanostructures as well as their novel properties. Prospective applications of superparamagnetic nanoparticles in the fields of photonic crystals, biomedicine, and biology are also discussed.

This paper provides an overview of directed self-assembly (DSA) options that exhibit potential for enabling extensible high-volume patterning of nanoelectronics devices. It describes the current set of research requirements, which a DSA technology must satisfy to warrant insertion consideration, and summarizes the state-of-the art. The primary focus is on chemical patterning and graphoepitaxial approaches to directing block copolymer (BCP) based assembly. These options exhibit the nearest-term potential, among the emerging DSA technologies, for satisfying projected International Technology Roadmap for Semiconductors (ITRS) patterning requirements. The paper concludes with a selected set of additional challenges, which represent potential barriers to the integration of directed BCP patterning into a nanoelectronics manufacturing line, as well as a few emerging application opportunities for related functional materials. A glossary of acronyms and terms may be found at the end of this manuscript.

Controlled bottom-up assembly of nanocylinders (e.g., nanotubes, nanorods, nanowires) into large area aligned arrays is widely recognized as a key obstacle impeding application development. Processing of lyotropic liquid crystal phases is a promising route for overcoming this obstacle, but nanocylinder liquid crystalline science is a nascent field that tends to be fractionated based on material type. This review explores the common challenges and achievements of nanocylinder liquid crystal research by focusing on three types of systems: (i) carbon nanotubes, (ii) inorganic nanocylinders, and (iii) cellulose nanocrystals.

Reliable and cost-effective techniques to process surface nanoscale metallic structures with controllable and complex nanomorphologies is important toward progress in technologies related to sensing, energy harvesting, information storage, and computing. Here we discuss how pulsed laser melting and the ensuing self-organization by dewetting of ultrathin films can be utilized to fabricate various nanomorphologies in a predictable manner. Ultrathin metal films (1–100 nm) on inert substrates like SiO2 are generally unstable, with their free energy resembling that of a spinodal system. The energy rate theory of self-organization, which is based on balancing the rate of thermodynamic free energy change to the rate of energy dissipation, predicts the appearance of characteristic length scales. This is borne out in experiments of nanosecond pulsed laser melting of a variety of metal films. We review this laser-based self-organization technique with various examples from the behavior of Ag and Co metals on SiO2 substrates. Specifically, film thickness and film roughness can be used to control dewetting length scales, whereas knowledge of the intermolecular forces responsible for the free energy of the system control the type of morphology. Furthermore, novel dewetting is observed that is attributable to nanoscale heating effects resulting from the thickness-dependent pulsed laser heating. These results help elucidate the basic mechanisms of pulsed laser induced dewetting of metal films, but they also provide potential routes for cost-effective nanomanufacturing of metallic surfaces for applications in sensing, energy harvesting, and information processing.

Surface-enhanced Raman scattering (SERS) coupled with micro- or nanofluidics integrated into optofluidic devices offer many advantages over conventional SERS conducted under static conditions. Higher reproducibility, larger intensity, as well as greater enhancement can be achieved by efficient mixing of analytes and SERS enhancers under a continuous flow. Progress and advances in the past 10 years, including the design of channels and efficient mixing conditions, assemblies of SERS substrates for optimal enhancement, and advantages of optofluidic-SERS analysis, are reviewed. Recent results show that optofluidic-SERS effectively overcomes many of the difficulties and limitations plaguing conventional SERS and the novel technique has enormous application potential.

Anodized aluminum oxide (AAO), well-known hexagonally ordered vertical pore nanostructure, can be altered to form nanotubular AAO arrays potentially having many favorable properties due to its large surface area and unique geometry. We present here a creation of novel nanotubular AAO structure by the hard anodization technique. Because of the guided formation of void channels at triple cell junctions during the course of the controlled anodization process, periodically spaced-apart aluminum oxide nanotubular geometry could be achieved over large areas. Further separation to well-defined individual AAO nanotube arrays was obtained when etched in a mixed CuCl2/HCl solution during Al substrate removal. Nanotubular geometry AAO with periodic and mechanically robust structure can be useful not only for biomedical applications such as to enhance cell adhesion and viability or drug delivery vehicles, but also as a large-surface-area catalyst support or sensor elements.

Technological progress in the synthesis and characterization of nanometer-scale structures has improved understanding of molecular and colloidal aggregation, self-assembly, and crystal growth. While substrates are commonly used to control nucleation and growth in metal and semiconductor crystals, their use in protein epitaxy has been limited by the lack of substrate structures commensurate with protein sizes. In this paper we describe the use of polished cross sections of amorphous alumina–silica nanolaminates whose periods varied from 8 to 200 nm in the formation of self-assembled monolayers of the protein macromolecule aspartate transcarbamoylase (ATCase). Scanning force microscopy images of rapidly deposited ATCase demonstrates one-dimensional protein ordering along 13.5 nm wide silica nanolaminate. Numerical studies of irreversible adhesion indicate that patterning can induce a higher degree of ordering by varying the substrate periodicity. We expect this to have implications for nucleation and growth of both two-dimensional crystalline layers and bulk protein crystals.

Small FePt grain size is one of the candidates for ultrahigh density magnetic recording material. We investigate increasing grain density of FePt grains fabricated on nanostructured substrates. One of them is nanodent-array (NDA) (period = 14 nm), and another is self-assembled silica nanoparticles (SASP) (period = 18 nm). In this paper, the influence of difference in nanostructured substrates on grain density Np is investigated in detail. FePt films were fabricated by sputtering and rapid thermal annealing (RTA) [Y. Itoh, T. Aoyagi, A. Tsukamoto, K. Nakagawa, A. Itoh, and T. Katayama, Jpn. J. Appl. Phys.43(12), 8040 (2004)]. FePt grains on those substrates show almost the same areal density; however, experimental results show that FePt grains on SASP has the largest Np while the initial film thicknesses are the same. Electron diffraction measurements indicate the existence of ordered FePt crystalline. The magnetic hysteresis loops are also shown.

A novel nanoparticle self-assembly process is demonstrated. Nanoparticles were fabricated by a DC magnetron sputtering process. A silicon substrate was initially patterned with arrays of peak and valley photoresist structures using inexpensive patterning techniques. When the nanoparticles were deposited onto the prepatterned substrate, due to surface topography induced local increase in the electric field created by the charges on the nanoparticles, the nanoparticles were self-assembled onto the peaks of the structures and formed long nanowire arrays.

Alternating current (AC) electric fields generated by coplanar electrodes are used to externally direct the assembly of submicrometer sized disk-shaped zeolite particles. At the edge of the electrode, zeolite particles assemble in a brushlike structure that forms because of an interplay between an induced dipolar interaction and the drag force due to AC electroosmotic flow. Far from the electrode edge, where the fluid is quiescent, the disk-shaped particles form a nearly hexagonally close-packed structure, similar to suspensions of spherical particles. These results demonstrate a surprising generality of field-directed structures and offer promise for a hierarchical fabrication of nanostructures from zeolites.

Highly aligned microstrip patterns consisting of biaxial CaF2 nanorods have been successfully self-assembled by simply using capillary pressure. The alignment direction of the microstrips is perpendicular to the flux direction during nanorod growth. Aligning behavior and pattern width can be controlled by changing wetting time and surface tension of the liquid. Higher surface tension and longer wetting time result in wider pattern width and better alignment. Taller nanorod height also results in better pattern alignment. Simple and cost-effective self-aligned microstrip patterns can be potentially used as a template for various applications, such as superhydrophobic surfaces, tissue scaffolds, microchannels, and optical polarizers.

Molecular films have been extensively used for crystal growth. The Langmuir–Blodgett (LB) technique allows the oriented molecules film to be produced in a controllable manner. By controlling the LB film surface pressure and tuning quenching temperature of the supersaturated solution, single NaCl (100) crystal planes are successfully produced under the surface pressure of 30 mN/m with quenching temperature 5 °C of the NaCl supersaturated solution. The mechanism of single NaCl (100) crystal growth can be further explained based on the best matching between NaCl (100) crystal plane distance and the lattice parameter of LB film among all other crystal planes.

The heterocomponent films of polypyridine ruthenium(II) complexes and methyl viologen derivatives, and polypyridine ruthenium(II) complexes and alkyl chain derivatives have been successfully obtained using a layer-by-layer fabrication method. We determined their photocurrent generation properties and noted that the photocurrent generation strongly depended on the inner layer. A higher photocurrent generation in the donor–acceptor film was obtained than in a single-component film of the chromophore.

We investigated a simple and low-cost route for the formation of metallic nanodots on Si substrates ordered in size and position and laterally isolated by SiO2. The method was based on a two-step process: (i) the formation of a nanopattern of ordered cylindrical pores on oxidized Si substrates through self-assembly of diblock copolymers, and successive oxide dry etching down to the Si; (ii) the deposition of gold nanodots and thermal diffusion over the nanopatterned oxide substrates. After diffusion, the nanodot density outside the nanopores was found to decrease, and most of the nanodots were found to saturate the nanopores. The process was followed in situ by transmission electron microscopy (TEM) and ex situ by scanning electron microscopy (SEM) analysis for different thermal budgets. This patterned substrate can be used for catalyst mediated growth, for example, through vapor-liquid-solid (VLS), of nanowires for the formation of absorber materials in novel photovoltaic architectures.

We demonstrate the formation of non-close-packed binary colloidal structures through a novel layer-by-layer directed self-assembly methodology. In this approach we deposit colloidal suspensions of particle concentration and controlled electrostatic potential onto a planar template with a periodic array of features that is able to trap the particles, nucleating ordered domains with a template-defined symmetry and periodicity that permits subsequent, sequential deposition to produce an ordered heterostructure. Specifically, a silicon template with a hole pattern formed by interference lithography that corresponds to [100] symmetry of a cubic system has been used. At low particle concentrations, and using a Debye length that is on the order of the particle diameter, ordered domains in which polystyrene (PS) particles occupy every other site in the template are formed. The remaining sites on the 2D template are then filled by identically sized silica particles using vertical deposition. This process is repeated to produce a second layer of the same structure. Upon removing the PS particles, a two-layer non-close-packed structure that is a half-unit-cell precursor to the diamond cubic structure is obtained. To our knowledge this is the first demonstration of colloidal self-assembly to obtain a non-close-packed multilayer structure. Challenges that remain in applying the approach to create extended three-dimensional structures are discussed.

An increasing number of technologies benefit from or require patterned surfaces on a micro- and nanoscale. Methods developed to structure polymer films can be adapted to fabricate low-cost patterned ceramics using nonlithographic techniques, for example, dewetting and phase separation in thin films. In this paper we describe a simple patterning process that does not require a template and is able to produce Fe2O3 microdots with a spatial periodicity. Our method involves the dewetting of a silicon substrate by a thin metal oxide precursor film, in which the liquid film breaks up because of fluctuations in the film thickness induced by solvent evaporation or an external applied electric field. The patterning is followed by a thermal treatment at 550 °C to produce crystalline Fe2O3 microdots with a diameter range of 200 nm to 3 μm.

Self-assembled monolayers (SAMs) were formed on gold at anodic potentials from solutions containing two different alkyl thiosulfates, CH3(CH2)10S2O3Na and HO2C(CH2)10S2O3Na. The resulting two-component SAMs were analyzed using x-ray photoelectron spectroscopy to relate their compositions to those of the solutions from which they were adsorbed. This relationship was more linear than reported for analogous SAMs adsorbed from mixed solutions of alkanethiols. The wettability of these surfaces by water and by hexadecane was also measured and compared to analogous SAMs prepared by chemisorption of thiols from solution.

We present a versatile and flexible method to sequentially self-assemble micron-scale components at specific locations onto unconventional substrates, such as glass and plastic. In this method, components are independently batch fabricated and assembled onto a series of receptor sites incorporated onto a substrate in a fluid medium. Initially, all self-assembly sites are blocked with a photoresist polymer. Controlled light exposure can be used to remove the polymer and make a site available for receiving a microcomponent. By repeating this procedure, various microcomponents may be integrated onto specific locations on the substrate. To demonstrate the process, we prepared four types of 20 μm thick, 320 μm diameter circular silicon components and showed their optically controllable self-assembly in arrays of 640 receptor sites on glass and plastic with yields reaching 85%. The integration and operation of two types of functional components, red light-emitting diodes and silicon resistors, on plastic substrates was also demonstrated.

Thin film Cu-Ni alloys ranging from 2–8 nm were synthesized and their optical properties were measured as-deposited and after a laser treatment which dewet the films into arrays of spatially correlated nanoparticles. The resultant nanoparticle size and spacing are attributed to a laser induced spinodal dewetting process. The evolution of the spinodal dewetting process is investigated as a function of the thin film composition which ultimately dictates the size distribution and spacing of the nanoparticles. The optical measurements of the copper rich alloy nanoparticles reveal a signature absorption peak suggestive of a plasmon peak that red-shifts with increasing nanoparticle size and blue-shifts and dampens with increasing nickel concentration.