Albert E. Miller

Self-ordered pore structure of anodized aluminum on silicon and pattern transfer

A practical approach of transferring a hexagonal array of nanosized pores produced in porous alumina into silicon and other substrates is discussed. The alumina pores have dimensions of 25–250 nm pore diameters and 50–300 nm pore spacings depending on the anodization conditions used. The characteristics of the alumina pores and the alumina–silicon interface are studied for different substrate materials and anodizing conditions. The unique structure of the barrier layer allows for the alumina to be directly used as an etch mask for pattern transfer into the silicon substrate.

Supercomputing with spin-polarized single electrons in a quantum coupled architecture

We describe a novel quantum technology for possible ultra-fast, ultra-dense and ultra-low-power supercomputing. The technology utilizes single electrons as binary logic devices in which the spin of the electron encodes the bit information. Both two-dimensional cellular automata and random wired logic can be realized by laying out on a wafer specific geometric patterns of quantum dots each hosting a single electron. Various types of logic gates, combinational circuits for arithmetic logic units, and sequential circuits for memory have been designed. The technology has many advantages such as (1) the absence of physical interconnects between devices (inter-device interaction is provided by quantum mechanical spin-spin coupling between single electrons in adjacent quantum dots), (2) ultra-fast switching times of approximately 1 picosecond for individual devices, (3) extremely high bit density approaching 10 terabits cm-2, (4) non-volatile memory, (5) robustness and possible room-temperature operation with very high noise margin and reliability, (6) a very low power delay product ( approximately 10-20 J) for switching between logic levels, and (7) a very small power dissipation of a few tens of nanowatts per switching event. In spite of the above advantages, the technology also has some serious drawbacks in that the fan-out of individual logic devices may be small, wiring crossover is very problematic and the devices themselves have no inherent gain so that isolation between input and output is virtually non-existent. These are problems that plague all similar quantum technologies although they are seldom recognized as such. We will discuss these problems, and where possible, offer plausible solutions. In spite of these drawbacks, however, there are still enough attractive features of this technology to merit serious research. In this paper, we will describe how the spin-polarized single-electron logic devices work, along with the associated circuits and architecture. Finally, we will propose a new fabrication technique for realizing these chips which we believe is much more compatible with the demands of the technology than conventional nanofabrication methods.

Nano-biosensor development for bacterial detection during human kidney infection: use of glycoconjugate-specific antibody-bound gold NanoWire arrays (GNWA).

Infectious disease, commonly caused by bacterial pathogens, is now the world’s leading cause of premature death and third overall cause behind cardiovascular disease and cancer. Urinary Tract Infection (UTI), caused by E. coli bacteria, is a very common bacterial infection, a majority in women (85%) and may result in severe kidney failure if not detected quickly. Among hundreds of strains the bacteria, E. coli 0157:H7, is emerging as the most aggressive one because of its capability to produce a toxin causing hemolytic uremic syndrome (HUS) resulting in death, especially in children. In the present study, a project has been undertaken for developing a rapid method for UTI detection in very low bacteria concentration, applying current knowledge of nano-technology. Experiments have been designed for the development of biosensors using nano-fabricated structures coated with elements such as gold that have affinity for biomolecules. A biosensor is a device in which a biological sensing element is either intimately connected to or integrated within a transducer. The basic principle for the detection procedure of the infection is partly based on the enzyme-linked immunosorbent assay system. Anti-E. coli antibody-bound Gold Nanowire Arrays (GNWA) prepared on anodized porous alumina template is used for the primary step followed by binding of the bacteria containing specimen. An alkaline phosphatase-conjugated second antibody is then added to the system and the resultant binding determined by both electrochemical and optical measurements. Various kinds of GNWA templates were used in order to determine the one with the best affinity for antibody binding. In addition, an efficient method for enhanced antibody binding has been developed with the covalent immobilization of an organic linker Dithiobissuccinimidylundecanoate (DSU) on the GNWA surface. Studies have also been conducted to optimize the antibody-binding conditions to the linker-attached GNWA surfaces for their ability to detect bacteria in clinical concentrations. Published in 2004.

Nanofabrication of a quantum dot array: atomic force microscopy of electropolished aluminum

One step required for the fabrication of a quantum dot array on an aluminum substrate is the preparation of a flat aluminum surface. To enable the optimization of the electropolishing procedure, atomic force microscopy was used to examine the morphology of electropolished polycrystalline aluminum surfaces that were prepared under different electropolishing conditions. The electropolishing voltage, time, and temperature were varied. Two distinctly different surface morphologies were observed for different electropolishing conditions and transitional structures were observed for intermediate conditions. It was found that the type of surface morphology and the surface roughness could be controlled primarily with the electropolishing voltage while temperature and time had relatively little effect over the range examined in this study.

Pattern selection during electropolishing due to double-layer effects

We extend our earlier study of nanoscale pattern formation during electropolishing [Nanotechnology 7, 360 (1996); Phys. Rev. B 56, 12 608 (1997)]. The patterns are attributed to preferential adsorption of organic molecules on the convex portion of the electrode due to its enhanced electric field. This local enhancement occurs because of the effect of surface curvature on the double-layer potential drop. By allowing for transport correction to the double-layer potential drop at thermodynamic equilibrium, we estimate this anodic overpotential to be in the realistic mV range and hence verify the Debye-Huckel approximation used in our model. This small anodic overpotential suggests that pattern formation is a generic electropolishing phenomenon whose only requirement is that the polarizability of the organic additive relative to water must lie within a range specified by our theory. We verify this prediction experimentally with a variety of electrolyte solutions. The voltage ranges for specific hexagonal and ridge patterns are well correlated by our model with only a single parameter. (c) 1999 American Institute of Physics.

Nanoporous Alumina Template with In Situ Barrier Oxide Removal, Synthesized from a Multilayer Thin Film Precursor

A nanoporous alumina template made from a multilayer metal film structure has been developed that allows for the in situ removal of the electrically insulating alumina barrier layer, exposing a Pt electrode at the pore bases. This barrier-free nanoporous system is of great use for dc electrodeposition of a wide variety of materials in the alumina pores. This work in particular describes the development of a multilayer thin film precursor consisting of a Si substrate with thin Pt and Ti and a thicker Al layer in that order. After the Al is anodized, producing the porous alumina, the resulting TiO 2 is selectively removed at the base of the alumina pores exposing the Pt electrode. The metals in the precursor perform different roles in the fabrication and allow the alumina template to be fabricated directly on the final substrate with no film transfer technique involved. This allows Si to be used as the substrate, which could then include electronic circuitry. Several techniques are used to analyze the resulting template.

Self-assembled nanostructures using anodized alumina thin films for optoelectronic applications

Anodized aluminum has recently attracted much attention because of its desirable porous structure. The pore structure is a self-ordered hexagonal array of cells with cylindrical pores in an alumina matrix of variable sizes with diameters of 25 to 300 nm with depths exceeding 100 /spl mu/m depending on the anodizing conditions used. These properties make anodized aluminum a desirable material for many optoelectronic devices including polarizers, photonic crystals, low threshold current lasers, and investigation of light-surface plasmon interactions in metals. The conventional approach to fabricate porous alumina is to use bulk or thin sheets of aluminum and then replicate this pattern into the desired substrate by one of several methods involving a tedious film transfer. However, in this work, a more convenient and practical method of fabricating the porous alumina structure using an evaporated film of aluminum on silicon and other substrates, subsequent pattern transfer, and its use in optoelectronic applications will be discussed.

Formation of a high surface area, regular porous solid from the cluster of clusters, Zn4IIO[(CO)9Co3CCO2]6

The discrete molecular cluster of clusters, Zn4IIO[(CO)9Co3CCO2]6 (1), undergoes thermolysis with the sequential loss of 54 CO and 6 CO2 molecules without fusion resulting in the formation of a porous solid product. Density (fluid displacement and single crystal dimensions) and BET surface area measurements confirm the porous nature of the material. The calculated pore dimensions and regularity is corroborated by TEM of thermolyzed films supported on carbon. The formation of an α-Co phase is detectable by XRD and electron diffraction with crystallite size increasing with increasing heating temperature. The metallic nature of the cobalt environment is demonstrated by XPS of the films. Densification of the material occurs above 300°C with significant loss of surface area.

A novel corrosion inhibitor for aluminum alloys using the beef lipids

Vigorous efforts are being made at many research institutes and academic institutions to find a substitute for chromates which are extremely good inhibitors for mild steel and aluminum alloys but are known to be carcinogenic due to Cr(VI) ions. The Environmental Protection Agency (EPA) is the main regulator of chromate uses and emissions through several different acts including the Clean Water Act, the Comprehensive Environmental Response, Compensation and Liability Act (CRCLA) and Toxic Substances Control Act (TSCA) [1]. Many of the organic inhibitors that are being studied are really promising as they have low toxicity and are readily biodegradable. Fatty acids are chains of covalently linked carbon atoms, bearing hydrogen atoms, which terminate in a carboxyl group that is responsible for their properties as acids. These fatty acids, also known as monocarboxylic acids, are known to be extremely good corrosion inhibitors for mild steel and aluminum alloys, particularly in neutral media [2, 3]. These carboxylic acids get absorbed on the aluminum surface and raise the pitting corrosion resistance [3]. Lipids are a heterogeneous group of substances which occur in biological materials [4]. The lipid family is comprised of 1) fatty acids; 2) neutral fats; 3) phosphatides; 4) glycolipids; 5) aliphatic alcohols and waxes; 6) terpenes and 7) steroids [5]. Since lipids contain both saturated and unsaturated fatty acids, it was decided to study the effect of these lipids on the localized corrosion resistance of aluminum alloys. In order to separate lipids from the beef, about 500 g of fresh beef fat (raw) was cut into small pieces and placed in a 2-liter clean beaker. To this one liter of a mixture of chloroform and methanol (both AR grade) was added. The mixture in the beaker was constantly stirred and the beef fat was allowed to dissolve for 3 h. After this period the supernatant solution was filtered off and the solvent was evaporated using the rotary evaporator. The lipids (44 g) that collected were stored in a glass vial with a stopper and kept in a freezer to avoid any decomposition. A 0.1 wt.% solution was prepared from these lipids in a suitable alcohol and all the dilutions were prepared from this stock solution using the same alcohol. This solution was stored in a cooler. Electrochemical corrosion studies were conducted on high purity aluminum (Al 99.99%, Aldrich Chemical Company, Inc.) sheet (50× 50× 1 mm) and Al 6061 T6 sheet (75× 75× 3 mm) by using a GAMRY CMS/100 system. These specimens were polished mechanically up to 1500 grit, cleaned in soap solution and degreased in acetone before the commencement of the experiments. These experiments were conducted by using a EG&G PARC flat cell where 1 cm2 area of the specimen is exposed to the electrolyte. The corrosion potential measurement was carried out for 30 min. The electrochemical impedance spectroscopic (EIS) experiments were conducted in the frequency range of 5 kHz to 10 mHz at open circuit potential (OCP) by applying a alternating current (AC) signal of 10 mV peak-to-peak. In order to determine the pitting potential (Epp), potentiodynamic anodic polarization experiments were conducted at a scan rate of 1 mV/s in aerated solutions at room temperature until the current increased monotonically. All the potential measurements of the working electrode were conducted against a saturated calomel electrode (SCE). The lipids were studied in the concentration range of 0.0002 wt.% to 0.05 wt.% comprising of two decades of concentration change. These solutions were prepared by taking the required aliquots from the stock solution and diluting them in a 50:50 mixture of a buffer solution (pH= 7.0) and an alcohol (which was used to prepare the stock solution) along with the addition of 200 ppm of AR grade NaCl to them. The profiles of the corrosion potential for pure aluminum and Al 6061 are shown in Fig. 1a and b. The corrosion potential profile at 0.001 wt.% could not be determined for pure Al. It was observed that there was rapid ennoblement of the corrosion potentials in the initial 30 min for both the alloys indicating a passivating tendency of the lipids. Aluminum 6061 showed more ennoblement at higher concentrations of lipids as very active initial OCP values were noted at these concentrations. More active OCP values suggested a better chemisorption of the inhibitor molecules on the electrode/electrolyte interface. From the EIS

Magnetic moment distribution in Ni3Al

A polarized‐neutron diffraction study was made of the unpaired‐spin density distribution in the Cu3Au‐type ordered alloy Ni3Al at 4.2°K in a 10 kOe field. The system Ni3+xAl1−x is weakly ferromagnetic for x≳−0.02; for our single‐crystal specimen (x?0.035) the average Ni moment is 0.125 μB and Tc?70°K. The measured fundamental (fcc) reflections describe a 3d magnetic form factor whose radial dependence and asphericity (82% T2g, 18% Eg) are similar to those for pure nickel. Consistent with the tetragonal symmetry at each Ni site, the superlattice reflection measurements show that the cubic T2g and Eg distributions split into 3% (xy), 79% (yz,zx), 6% (3z2−r2), and 12% (x2−y2), z being the tetragonal axis. Hence, much less unpaired‐spin moment is associated with the xy lobes directed toward nearest‐neighbor Al atoms than with the yz and zx lobes directed toward nearest‐neighbor Ni atoms. These results appear to agree with recent band calculations on Ni3Al, which indicate that the electrons in xy‐type orbitals...