Byeong-Hyeok Sohn

Exposure of 38 nm period grating patterns with extreme ultraviolet interferometric lithography

Extreme ultraviolet (EUV, λ=13 nm) lithography is considered to be the most likely technology to follow ultraviolet (optical) lithography. One of the challenging aspects is the development of suitable resist materials and processes. This development requires the ability to produce high-resolution patterns. Until now, this ability has been severely limited by the lack of sources and imaging systems. We report printing of 38 nm period grating patterns by interferometric lithography technique with EUV light. A Lloyd’s Mirror interferometer was used, reflecting part of an incident beam with a mirror at grazing incidence and letting it interfere with the direct beam at the wafer plane. High-density fringes (38 nm pitch) were easily produced. Monochromatized light of 13 nm wavelength from an undulator in an electron storage ring provided the necessary temporal and spatial coherence along with sufficient intensity flux. This simple technique can be extended to sub-10 nm resolution.

Magnetic properties of iron oxide nanoclusters within microdomains of block copolymers

Abstract The magnetic properties of γ-Fe 2 O 3 nanoclusters grown within the microdomains of optically transparent block copolymer films were investigated. SQUID magnetometry and 57 Fe Mossbauer spectroscopy were employed with characteristic measurement times of 100 s and 10 −8 s, respectively. The observed magnetism of the ca. 5 nm diameter particles was dominated by quantum-size effects, collective magnetic excitations, and superparamagnetic relaxation processes associated with the sub-magnetic domain γ-Fe 2 O 3 nanoclusters. The combination of these two techniques allowed determination of the values of the magnetic anisotropy constant ( K = 1.58 × 10 5 J/m 3 ) and the pre-exponential factor ( τ 0 = 4.2 × 10 −12 s) which determine the magnetic behavior of the nanocomposites. At low temperatures, the nanocomposite films exhibited hysteresis with the saturated coercivity, H c 0 , equal to 530 Oe.

Templated Organic and Hybrid Materials for Optoelectronic Applications

The review highlights different approaches to template organic materials as well as hybrid materials that find or are expected to find application in optoelectronic devices. The first templating approach focuses on the use of preformed nanoporous membranes as templates for organic materials and polymeric materials. Such nanoporous templates can be track-etched membranes, anodic aluminum oxide membranes and other variants thereof, or block copolymer templates. Further, opals have been described as templates. In the second part, we have summarized developments that take advantage of self-assembly processes to pattern hybrid materials. Examples are sol-gel templating techniques using amphiphiles, evaporation-induced self-assembly, lyotropic templating as well as templating from block copolymers. Both routes are very promising templating approaches for optoelectronic materials and represent complementary rather than competing techniques.

Multilevel Data Storage Memory Devices Based on the Controlled Capacitive Coupling of Trapped Electrons

Since the fi rst conceptualization of non-volatile memory devices using a fl oating gate in 1967, [ 1 ] tremendous efforts have been made to develop high-density, low-cost, and non-volatile solidstate memory devices for portable electronics. [ 2–17 ] Among the many kinds of non-volatile memory devices, fl ash memories which use an array of fl oating gate transistors to store information are the most widely used. [ 12–20 ] One of the main limitations of conventional fl ash memory devices is the easy discharge of the stored information from the fl oating gate to the silicon substrates through the thin tunneling oxide. [ 12–20 ] To improve the device reliability, the recent trend for fl ash memory devices is to store information in discrete charge trapping sites such as in silicon nitride [ 17–20 ] or metal nanoparticles. [ 21–29 ] Recently, we reported that ordered arrays of metallic nanoparticles obtained by a micellar route and multilayered metallic nanoparticles can be used as charge storage media for non-volatile memory devices with tailored performances. [ 27–29 ] However, most of the research on nanoparticle-based memory devices has focused on binary data storage in the charge trapping layer. In this work, multiple data storage memory devices based on the controlled capacitive coupling of trapped electrons operated at room temperature have been fabricated by using highly ordered arrays of metal nanoparticles as the charge trapping elements. We present results from metal nanoparticle-based memory devices with controlled nanoparticle charge trapping elements, which undergo gate-voltage-adjustable multilevel memory states. Experimental and theoretical analysis of multilevel data manipulations and visualization of memory states has been done on the nanometer scale. Electrical multilevel data programming and data access of fi ve well-defi ned data levels were

Photocatalytic thin films containing TiO2 nanoparticles by the layer-by-layer self-assembling method

Photocatalytic thin films consisting of ionic polymers and positively charged TiO2 nanoparticles were fabricated by the layer-by-layer self-assembling (LBL-SA) method, i.e. successive ionic adsorption from their aqueous solutions. Regular increases of the film thickness and the film weight by each deposition were characterized using ellipsometry, UV–Vis spectroscopy, and a quartz crystal microbalance (QCM). Uniformly distributed TiO2 nanoparticles in the thin film were also observed in scanning and transmission electron microscopic images. Photocatalytic properties of the LBL-SA thin film containing TiO2 nanoparticles were confirmed by oxidation of iodide and decomposition of methyl orange. These results indicate a controllable LBL-SA process to immobilize photocatalytic TiO2 nanoparticles in thin films.

Perpendicular lamellae induced at the interface of neutral self-assembled monolayers in thin diblock copolymer films

Abstract We obtained perpendicular lamellar orientations in thin films of symmetric polystyrene- block -poly(methyl methacrylate), PS- b -PMMA, on self-assembled monolayers (SAMs) of 3-( p -methoxyphenyl)propyltrichlorosilane (MPTS) prepared on silicon wafers. In contrast to completely parallel lamellae on silicon wafers having a native oxide layer, perpendicular lamellae at the MPTS interface with parallel lamellae at the air interface were directly observed by transmission electron microscopy (TEM) in cross-sectional view. The perpendicular lamellae at the MPTS interface were attributed to the non-preferential (neutral) MPTS-covered substrate to both PS and PMMA blocks. The neutrality of the SAMs of MPTS was confirmed by the similar interfacial tension values of the SAMs of MPTS with PS and PMMA, estimated by contact angle measurements.

Brief review of metal nanoclusters in block copolymer films

We provide a brief non-comprehensive survey of some recent work on the insitu production of metal nanoclusters in polymer films. The synthesis schemes rely on the well-known spontaneous microphase separation of block copolymers to restrict metal species within nanoscale regions in the bulk morphology. In one variation of the scheme, organometallic monomers are used to form one of the block sequences of the block copolymer. A second approach relies on metal-sequestering moieties in one of the blocks which assemble to produce ‘nanoreactors’ capable of being loaded with metal species for later reduction to zerovalent clusters. Morphological evidence is provided to assess the success of these schemes. A few properties of the metal-containing nanocomposite films are discussed here. These include electrical properties and catalytic activity in hydrogenation reactions.

Multifunctional layer-by-layer self-assembly of conducting polymers and magnetic nanoparticles

Multifunctional thin films having both electrical conductivity and ferrimagnetic properties were successfully fabricated by the layer-by-layer self-assembling (LBL-SA) method, i.e. successive ionic adsorption of polypyrrole (PPy) and ferrite nanoparticles from their aqueous solutions. Using an ellipsometer, a constant increase of the film thickness by each deposition was characterized, implying a controllable process of the LBL-SA for multifunctional thin films. Uniformly distributed ferrite nanoparticles in the thin film were also observed in scanning and transmission electron microscopic images. The thin film consisting of six PPy and two ferrite nanoparticle layers had a conductivity of 0.18 S/cm and simultaneously showed a magnetic hysteresis.

Single layers of diblock copolymer micelles for the fabrication of arrays of nanoparticles

Recent advances in the process of using single layers of diblock copolymer micelles for the fabrication of arrays of nanoparticles were highlighted. The technique using a monolayer of diblock copolymer micelles as an effective nanostructured template allowed precise control over the type, size, location, and ordering regularity of nanoparticles. The approach using copolymer micelles was fully compatible with top-down lithographical methods for micropatterning of nanoparticles. In addition, an array of two types of nanoparticles in specific positions was effectively fabricated for a multifunctional array. A near-perfect hexagonal array of nanoparticles was also created by solvent annealing in situ on a single layered film of copolymer micelles prior to synthesizing nanoparticles.

Switching Off FRET in the Hybrid Assemblies of Diblock Copolymer Micelles, Quantum Dots, and Dyes by Plasmonic Nanoparticles

Recently, it has been noticed that surface plasmon resonance of metal nanoparticles can alter the intrinsic properties of nearby fluorophores. Field enhancement and radiative decay engineering are major principles for understanding a number of experimental observations such as enhanced and quenched emission of fluorophores in the vicinity of metal nanoparticles. At the same time, there are apparent similarities between surface-plasmon-coupled fluorescence and fluorescence resonance energy transfer (FRET), as both are near-field through-space interactions. From this perspective, we hypothesize that donor-acceptor interaction in the FRET can be altered by metal nanoparticles. Our approach is based on diblock copolymer micelles, which have been widely applied for nanoscale arrangement of functionalities. By applying self-assembling techniques of copolymer micelles to organize the spatial location of semiconductor quantum dots, fluorescent dyes, and metal nanoparticles, the FRET in hybrid assemblies can be switched off by plasmonic effects.