Patrick J. Pinhero

Theory and Manufacturing Processes of Solar Nanoantenna Electromagnetic Collectors

The research described in this paper explores a new and efficient approach for producing electricity from the abundant energy of the sun, using nanoantenna (nantenna) electromagnetic collectors (NECs). NEC devices target midinfrared wavelengths, where conventional photovoltaic (PV) solar cells are inefficient and where there is an abundance of solar energy. The initial concept of designing NECs was based on scaling of radio frequency antenna theory to the infrared and visible regions. This approach initially proved unsuccessful because the optical behavior of materials in the terahertz (THz) region was overlooked and, in addition, economical nanofabrication methods were not previously available to produce the optical antenna elements. This paper demonstrates progress in addressing significant technological barriers including: (1) development of frequency-dependent modeling of double-feedpoint square spiral nantenna elements, (2) selection of materials with proper THz properties, and (3) development of novel manufacturing methods that could potentially enable economical large-scale manufacturing. We have shown that nantennas can collect infrared energy and induce THz currents and we have also developed cost-effective proof-of-concept fabrication techniques for the large-scale manufacture of simple square-loop nantenna arrays. Future work is planned to embed rectifiers into the double-feedpoint antenna structures. This work represents an important first step toward the ultimate realization of a low-cost device that will collect as well as convert this radiation into electricity. This could lead to a broadband, high conversion efficiency low-cost solution to complement conventional PV devices.

SOLAR NANTENNA ELECTROMAGNETIC COLLECTORS

This research explores a new efficient approach for producing electricity from the abundant energy of the sun. A nantenna electromagnetic collector (NEC) has been designed, prototyped, and tested. Proof of concept has been validated. The NEC devices target mid-infrared wavelengths, where conventional photovoltaic (PV) solar cells are inefficient and where there is an abundance of solar energy. The initial concept of designing NEC was based on scaling of radio frequency antenna theory. This approach has proven unsuccessful by many due to not fully understanding and accounting for the optical behavior of materials in the THz region. Also, until recent years the nanofabrication methods were not available to fabricate the optical antenna elements. We have addressed and overcome both technology barriers. Several factors were critical in successful implementation of NEC including: 1) frequency-dependent modeling of antenna elements; 2) selection of materials with proper THz properties; and 3) novel manufacturing methods that enable economical large-scale manufacturing. The work represents an important step toward the ultimate realization of a low-cost device that will collect, as well as convert this radiation into electricity, which will lead to a wide spectrum, high conversion efficiency, and low-cost solution to complement conventional PVs.

Surface properties of quasicrystals

There is currently great interest in the surface reactivity of quasicrystalline materials, generated largely by a model, proposed by Janot, for the bulk atomic and electronic structure. This {open_quotes}hierarchical cluster{close_quotes} model predicts that quasicrystal surfaces should be intrinsically inert and rough, and is being used to rationalize their practical properties such as low friction coefficients and oxidation resistances Surface structure and surface preparation may play a role in the applicability of this model. In this talk, we examine these factors and present experimental measurements of the surface reactivity of Al-based icosahedral alloys. We make some comparisons with surface reactivity of pure, crystalline aluminum, and with that of crystalline alloys which are similar in composition to the quasicrystal.

The effect of localized electric fields on the detection of dissolved sulfur species from Type 304 stainless steel using scanning electrochemical microscopy

Abstract This paper discusses a method for imaging localized sulfur concentrations dissolved from sulfide inclusions in Type 304 stainless steels. The method involves amperometric detection using the I − /I 3 − redox couple as a mediator for sulfide oxidation. The microelectrode current for I − oxidation is amplified by chemical reduction of I 3 − to I − by dissolved thiosulfate and/or H 2 S. While galvanostatically inducing corrosion, an unexpected current inversion at the microelectrode was observed at higher sample current densities in close proximity to the area where sulfur was detected at lower sample current. In the article first describing this method, J. Electrochem. Soc. 147 (2000) 4120 did not observe this feature. It was found that the inverted feature resulted from the localized increase in the electric field at the corrosion site, shifting the potential of the microelectrode when positioned over the site. The electric field measurement is analogous to measurements performed using a scanning vibrating electrode technique (SVET). This paper presents the first known combination of localized electric fields and chemical detection for determining localized electrochemical activity at a corroding surface.

Surface oxidation of Al-Cu-Fe alloys: A comparison of quasicrystalline and crystalline phases

Abstract We have used X-ray photoelectron spectroscopy and Auger electron spectroscopy to examine the characteristics of oxide surfaces on a family of Al-Cu-Fe alloys. The alloys studied are compositionally similar but structurally different: two are crystalline and one is quasicrystalline. The samples all are formed by consolidation of powders, resulting in multiple grains with random surface orientations. They are oxidized to saturation in a variety of environments at room temperature. Under the conditions of our experiments, there is no detectable difference in the oxidation characteristics of the three phases. That is, there is no difference in the elemental constituents which oxidize, or in the relative extent of oxygen-induced Al segregation, or in the depth of the oxide formed. Hence, the oxidation chemistry of these alloys is determined by their Al-rich chemical composition, and not by their atomic or electronic bulk structure, under these conditions.

Effect of water on the surface oxidation of an Al-Pd-Mn quasicrystal

Abstract X-ray photoelectron spectroscopy is used to determine the effect of water on the oxidation of a quasicrystalline alloy at room temperature. We use a singlegrain sample, oriented with the fivefold axis perpendicular to the surface plane, and with nominal bulk composition Al70Pd21Mn9. We compare the oxide which forms upon exposure to four basic environments: pure oxygen in ultrahigh vacuum, ambient air, humid air and liquid water. These environments are increasingly aggressive toward the alloy, as judged by the number of alloy constituents oxidized and by the thickness of the oxide layer.

Scanning Electrochemical Microscopy Study of Corrosion Dynamics on Type 304 Stainless Steel

Scanning electrochemical microscopy was utilized to study dynamics of corrosion on type 304 SS. The I - /I 3 - redox couple was used in the substrate generation/tip collection mode to determine active sites. Scanning the sample sequentially revealed that the electrochemical activity (where I - 3 was detected) was localized and dynamic in nature. Subsequent microscopy indicated pitting occurred at many of the sites where electrochemical activity was detected. Currently, the technique is limited by the time required to raster a single probe through the scan area. In future studies, parallel (multielectrode) image acquisition is proposed to address this issue.

Surface oxidation of a quasicrystalline Al–Cu–Fe alloy: No effect of surface orientation and grain boundaries on the final state

We have used x-ray photoelectron spectroscopy and Auger electron spectroscopy to examine the characteristics of oxides on two types of quasicrystalline Al{endash}Cu{endash}Fe samples. One type was formed by consolidation of powders, resulting in multiple grains with random surface orientations. The other was a single grain, oriented to expose a fivefold surface. Both were oxidized to saturation in a variety of environments at room temperature. We measured the elemental constituents that oxidized, the extent of oxygen-induced Al segregation, and the depth of the oxide. Under the conditions of our experiments, there was little, if any, significant difference between the two types of samples. Hence, surface orientation and bulk microstructure played little or no role on the final state of the oxide under these conditions. {copyright} {ital 1999 Materials Research Society.}

The five-fold surface of quasicrystalline AlCuFe: preparation and characterization with LEED and AES

We report the first surface characterization of a large, single-grain sample of quasicrystalline AlCuFe. The sample is oriented with its surface perpendicular to a five-fold axis, and has the bulk composition 63.4-24.0-12.6 at%. Following our method of preparation, the surface yields an exceptionally sharp and rich five-fold pattern in low-energy electron diffraction. The spot spacings and symmetries are consistent with expectations for this surface, based upon the unreconstructed structure.

Corrosion of thermal spray hastelloy C-22 coatings in dilute HCl

The microstructure and corrosion behavior of Hastelloy C-22 coatings produced using the high velocity oxygen fuel (HVOF) method have been determined and related to in-flight measurements of the particle velocity and temperature. Average particle temperatures ranged from 1280–1450 °C and velocities ranged from 565–640 ms−1. All of the coatings were greater than 98% of theoretical density and exhibited passivating behavior in 0.1 M HCl during cyclic potentiodynamic polarization testing. The passive current density was somewhat higher compared with wrought C-22 alloy and an active-passive peak attributed to the formation of a Cr-rich surface layer was observed. Resistance of corrosion and deposition efficiency improved as the particle temperature decreased. There was little effect of particle velocity on the corrosion behavior over the range of deposition conditions examined. Our results suggest that feedback control based on measurement of the particle temperature can be used to process coatings with optimum properties.