Self-assembly Fabrication Research Articles

FePt and CoPt Magnetic Nanoparticles Film for Future High Density Data Storage Media

AbstractFor Abstract see ChemInform Abstract in Full Text.

Self-assembled single wall carbon nanotube field effect transistors and AFM tips prepared by hot filament assisted CVD

The ability of the HFCVD to synthesize SWNTs using cobalt as catalyst has been applied to the preparation of self-assembled single wall carbon nanotube field effect transistor and tips for AFM imaging. This self-assembling batch process fabrication technique has allowed us to fabricate carbon nanotube-based devices that are directly usable without any post-treatment.

Modeling and simulation for a nano-photonic quantum dot waveguide fabricated by DNA-directed self-assembly

We propose a nano-photonic waveguide structure by DNA-directed self-assembled fabrication. In this paper, we focus on the study of quantum dot (QD) behavior under optical stimulation in terms of gain, absorption, and emission characteristics. Both continuous wave (CW) and pulsed operations are considered and the results are compared utilizing the CdSe/ZnS and In/sub 0.47/Ga/sub 0.53/As/InP core/shell material systems. Gain coefficients reach optima at pump powers of 0.055 and 0.05 nW for the former and 0.11 and 0.019 /spl mu/W for the latter in 100 ps pulsed and CW cases, respectively. Due to their unique properties and size, QDs provide a means to create integrated photonic circuits on the nanoscale. Accordingly, the optical propagation of a QD waveguide array in a single line formation is simulated and demonstrates a viable subdiffraction limit optical energy transfer for high coupling coefficient between adjacent QDs. A proposed fabrication process by DNA-directed self-assembly is also described.

The design of DNA self-assembled computing circuitry

We present a design methodology for a nanoscale self-assembling fabrication process that uses the specificity of DNA hybridization to guide the formation of electrical circuitry. Custom design software allows us to specify the function of a structure in a way similar to that used by VLSI circuit designers. In an analogous manner to generating masks for a photolithographic process, our software generates an assembly procedure including DNA sequence allocation. We have found that the number of unique DNA sequences needed to assemble a structure scales with its surface area. Using a simple face-serial assembly order we can specify an unambiguous assembly sequence for a structure of any size with only 15 unique DNA sequences.

DNA self-assembled parallel computer architectures

New varieties of computer architectures, capable of solving highly demanding computational problems,are enabled by the large manufacturing scale expected from self-assembling circuit fabrication(1012–1019 devices). However, these fabrication processes are in their infancy and even at maturity areexpected to incur heavy yield penalties compared to conventional silicon technologies.To retain the advantages of this manufacturing scale, new architectures mustefficiently use large collections of very simple circuits. This paper describes two sucharchitectures that are enabled by self-assembly and examines their performance.

Growth temperature effect on a self-assembled SiC nanostructure

Self-assembled nanostructure fabrication technology holds much potential to further the interests of nanoscience and nanotechnology. Using a low-energy mass-selected ion beam deposition system, we fabricated self-assembled silicon carbide (SiC) nanotiles. Methylsilicenium ions (SiCH 3 +) used as single precursors were generated from dimethylsilane (SiH 2(CH 3) 2). Low-energy SiCH 3 + ions (100 eV) were deposited on a Si(100) substrate at 500–600 °C. The characteristics of the self-assembled SiC nanotiles were analyzed by reflection high-energy electron diffraction (RHEED), a scanning electron microscope (SEM) and an atomic force microscope (AFM). The self-assembled SiC nanostructure displayed the properties of a zinc-blende structure (3C–SiC) and heteroepitaxial growth. The shape of the self-assembled SiC nanotiles was rectangular with an edge length of 150–200 nm and a height of 10–30 nm. Optimum temperature was found to be 600 °C due to the sensitivity of crystal quality and shape of the self-assembled SiC nanotiles to growth temperature.

DNA-conjugated polymers for self-assembled DNA chip fabrication.

We developed two DNA-conjugated polymers, one based on polyallylamine and the other on polyacrylic acid, for use in DNA chips. A 30-mer single-stranded DNA probe and thioctic acid were covalently attached to polyallylamine as sidechains. The same single-stranded DNA and 3-(pyridyldithio)propionyl hydrazide were covalently attached to polyacrylic acid as sidechains. Both DNA-conjugated polymers could be specifically immobilized onto a gold sensor substrate by a self-assembly technique. The interactions between fully matched DNA and each DNA-conjugated polymer were investigated by surface plasmon resonance. A gold surface modified with either DNA-conjugated polymer recognized fully matched DNA much better than unmatched DNA. The hybridization selectivity and efficiency of DNA-conjugated polyallylamine was optimized by adjusting the pH so as to reduce the effects of cationic polymer sidechains. The hybridization selectivity and efficiency of DNA-conjugated polymers were higher than those of a conventional immobilized thiol-based DNA. The coating of DNA-conjugated polymers reduced nonspecific adsorption of DNA by the gold substrate. DNA-conjugated polyacrylic acid was more selective toward fully matched DNA than was DNA-conjugated polyallylamine. Therefore, DNA-conjugated polymers show promise for application in novel DNA chips.

FePt and CoPt magnetic nanoparticles film for future high density data storage media

Controlled self-assembly of magnetic L10 FePt and CoPt nanoparticles has stimulated great interest recently and may serve as future ultrahigh-density data storage media. This article reviews chemical synthesis of self-assembled FePtCu nanoparticles film and fabrication of CoPt/C and FePt/C granular thin films by sputtering. Their novel structural characterisation and unique magnetic properties are also reviewed. Firstly, monodispersed nanoparticle arrays of FePtCu with varying composition were synthesized by chemical reduction of Pt and Cu reagents and thermal decomposition of Fe pentacarbonyl in the presence of oleic acid and oleyl amine stabilizers. As prepared particles had FCC structure with an average diameter of 3.5 nm and were superparamagnetic. The particles were well dispersed in hydrocarbon solvents and could be self-assembled into two or three dimensions particles arrays with a variety of close-packing arrangements. Heat-treatment of the self-assembled films at temperatures above 550°C transformed the particles from the FCC to the L10 phase, giving in-plane coercivities as high as 9 kOe. X-ray diffraction revealed that the Cu remained in the annealed FePtCu films. The magnetic hysteresis curves could be decomposed into a hard component (Hc > 5 kOe) and a soft component (Hc < 2 kOe). On the other hand, CoPt and FePt nanoparticles embedded in non-magnetic C matrix have been obtained by annealing CoPt/C and FePt/C multilayer precursors deposited onto Si substrate at different substrate temperature. The magnetic and structural properties of the films were investigated with respect to bilayer thickness, annealing conditions and temperature. Ordered FePt nanoparticles with average particle size from a few nanometers to about 20 nm were obtained directly by depositing at high substrate temperature. These particles showed higher magnetic ordering than particles made via multilayer precursors. With a certain FePt to C ratio, films showed strong perpendicular anisotropy.

Corrections to "performance simulation of nanoscale silicon rod field-effect transistor logic"

We have simulated the behavior of a rod shaped nanoscale ring-gated field-effect transistor (RG-FET) using the PISCES-IIb as in the report by M. R. Pinto et al. semiconductor drift-diffusion solver. The results from these simulations are used by a customized SPICE 3f5, as in the report by T. Quarles, kernel to simulate several simple logic gates. The usefulness of this kind of transistor is examined within the context of a self-assembling fabrication technique that we outline. Our simulation results, SPICE kernel modifications, and input decks may be found at ftp://ftp.cs.unc.edu/pub/packages/GRIP/publication_ad- denda/TSNSRFET.

Performance simulation of nanoscale silicon rod field-effect transistor logic

We have simulated the behavior of a rod shaped nanoscale ring-gated field-effect transistor (RG-FET) using the PISCES-IIb semiconductor drift-diffusion solver. The results from these simulations are used by a customized SPICE 3f5 kernel to simulate several simple logic gates. The usefulness of this kind of transistor is examined within the context of a self-assembling fabrication technique that we outline.

Direct observation of defect-mediated cluster nucleation.

Ion implantation is widely used to introduce electrically or optically active dopant atoms into semiconductor devices. At high concentrations, the dopants can cluster and ultimately form deactivating precipitates, but deliberate nanocrystal formation offers an approach to self-assembled device fabrication. However, there is very little understanding of the early stages of how these precipitates nucleate and grow, in no small part because it requires imaging an inhomogenous distribution of defects and dopant atoms buried inside the host material. Here we demonstrate this, and address the long-standing question of whether the cluster nucleation is defect-mediated or spontaneous. Atomic-resolution illustrations are given for the chemically dissimilar cases of erbium and germanium implanted into silicon carbide. Whereas interstitial loops act as nucleation sites in both cases, the evolution of nanocrystals is strikingly different: Erbium is found to gather in lines, planes and finally three-dimensional precipitates, whereas germanium favours compact, three-dimensional structures.

Self-assembled fabrication of aluminum–silicon nanowire networks

Uniquely structured two-dimensional aluminum–silicon alloy nanowire networks are fabricated on glass and silicon substrates by dealloying an aluminum–silicon thin film through selective chemical etching. The nanowire network is comprised of 3–6 nm diameter wires with lengths of 50–200 nm, and a wire density of approximately 1010 wires/cm2. The spatial extent of the fabricated nanowire network is limited only by the substrate dimensions. Current–voltage measurements reveal the metallic nature of the nanowires, with current propagating throughout the nanowire network. The fabrication route offers the possibility for achieving billion wire/cm2 devices as a relatively low cost production commodity.