U.S.Patent #5,689,603
November 1st, 2003 | No Comments »An Optically Interactive Nanostructure
Summary Of The Invention And Discussion Of Potential Applications
I have attempted to describe the interaction as succinctly as possible encoding the “engineering rules” for varying optical wavelength. In physics terms this means varying cavity dimensions adjacent to quantum confined electron sites. A summary of the invention and discussion of possible applications.
The principle contained in this invention followed from an initial interest of mine in a U.S. patent of Alvin Marks (see below) which employed “antenna lengths” of optical dimensions to absorb and utilize light energy. Another invention (Fletcher/Bailey, again see below) used generally the same principle but was even more prescient in it’s embodiment. Then….while considering the idea of such antennas and, while viewing a diagram of the architecture of the rods and cones of the retina of the eye, it became apparent to me that nature had evolved this light detecting structure using the same dimensional principle, i.e., it was designed to detect light as a wave immediately (and, necessarily) adjacent to quantum confined electron spaces. This single insight seemed to explain much about the eye and vision…….why, for example, the retina was formed of only two sizes of receptors ….and , for the first time gave a “map” of the trichromicity of the retinal surface. Following this it became clear to me that the “granal/stromal” structure of the light interactive chloroplast organelle of green plants seemed to have evolved using the same principle. Almost at this same time (circa 1990) an entirely unexpected optical luminescence phenomenon in the solid state realm was discovered by Canham in England (again see below). This effect is now termed “porous silicon”. Visible luminescence was found to be emitted from electro-etched silicon surfaces of entirely unexpected deep “pillar and pore”character in a surface nanostructure that uncannily resembles the receptors of the retina of the eye. I thought I saw at this time an experimental approach to studying the phenomenon in silicon namely that the etched pores were probably nucleated in the etching process by dopant atoms appearing at the surface in the silicon single crystal. In a series of experiments that I conducted it became clear that the wavelength of the optical emission indeed followed the same principle that I had proposed for light interaction with the retina of the eye and could actually be controlled using this principle (I consider this experiment definitive and I can lead any silicon experimental group through it). The experiment itself has been subsequently replicated by a Japanese photonics company.
I realize the implications of my assertions re: this principle versus the concept of the nature of “pigments”,etc. Can a pigment possibly be defined as “a quantum confined electron space adjacent to a spatially extended ’surround” whose dimension determines wavelength specificity”? To my way of thinking there is much (some of which is enumerated herein) to support this view. Energy conduction within this “surround” must be lossless and I would propose that such has been observed - in Kuhn’s seminal “photon funnel” experiment with the mechanism being probably, as shown in my studies of “Shiebe aggregates”, via solitonic conduction.
Marks in his U.S. Patent No. 4,445,050 (”A Solar Energy Converter”) discloses a type of spatial device for the absorption of optical wavelength solar radiation in the form of a dipole antenna of finite and specified length relative to the wavelength of light. Arrays of these antennae are then formed in this disclosure and coupled with electrical rectification devices in nearby (but, crucially, remote from the viewpoint of this invention) locations to perform subsequent radiant energy power conversion. In Marks’ concept, therefore, absorbed light energy is assumed to generate in some unspecified manner a thermalized electron somewhere near or at the dipole antenna absorption site.
Fletcher/Bailey in U.S. Patent No. 3,070,257 (”A Radiant Energy Converter”) disclose another spatial antenna optical absorption concept that utilizes the space between two adjacent receptors formed from either conductive or dielectric materials as the region of spatial extent wherein light or other forms of electromagnetic energy are absorbed. This results in a voltage difference being generated between adjacent receptors. This voltage difference is subsequently sensed in an electrical rectification circuit formed in a specific circuit disclosed between the adjacent receptors but, again, spatially distant from the absorption site. This invention again is directed toward solar energy conversion application. This disclosure is vague on the subject of dimensions required other than to state that they must be of “less than the wavelength of light”
Thus both Marks and Fletcher/Bailey both describe physically extended structures generally having nanometer spatial dimensions that they propose as being effective for absorbing light or other electromagnetic radiation. Regarding specific, quantified, design rules, Marks in his disclosure gives an optical wavelength-specific formula for calculating the length of his dipole antenna; such being given as lambda/2n where lambda is the optical wavelength of interest and n is the index of refraction of the material used to form the antenna. Antenna width is proposed as being “about 10 nanometers” . Fletcher/Bailey go beyond a specified length and indicate that a still rather generalized “aspect ratio” is desirable for operation of their invention. In their receptor array design, receptor height is given as “several” (up to seventy five) wavelengths of the longest wavelength of incident radiation of interest, and the centerline spacing between adjacent receptors is given as on the order of, or less than, the wavelength of interest.
The crucial point is that both Marks and Fletcher/Bailey are vague on the point of exactly where the transition from photon (Marks) or classical wave energy (Fletcher/Bailey) to thermalized electron conversion takes place in the device structures that they propose - in essence both simply assume that this transition does occur…somewhere.
More recently a totally new phenomenon in regard to light interaction with matter has been discovered by Canham (App. Physic. Lett., Vol. 57, (10), 3 September 1990) in the very unexpected and intense visible light emission from silicon semiconductor surfaces that have been electrolytically etched in hydroflouric acid mixtures (an acid that has not traditionally been considered to etch silicon single crystal). This development has generated intense interest in the scientific community with the phenomenon now generally termed “porous silicon” - a term that indicates the character of the etched silicon surface, i.e., very deep, high aspect ratio, pores etched orthogonal to the silicon surface. This development is surprising in that the extremely well characterized indirect energy bandgap of silicon did not predict this behavior. The morphology of these etched light emitting surfaces generally shows a field of irregularly spaced silicon “pillars” and intervening hollow pores with the composite forming an exceptionally high aspect ratio structure. Specification of the emitted wavelength from these etched silicon surfaces is not yet possible with the exception that it has been experimentally found that “increased etching time generally shifts the emitted radiation to shorter, i.e. ‘blue shifted’ wavelengths”. Progression of color change in most etching experiments has been from a red-orange to greenish. There is an ongoing debate in the scientific community as to the mechanism involved in this new light conversion process. It is, however, now becoming increasingly accepted that a quantum mechanism is involved, i.e., the sizes of the “pillar” structures must be reduced generally to quantum dimensions before visible light is emitted. Canham from the outset recognized that reduction of this dimension to electron quantum confinement dimension (~100 nm) had to be attained before optical luminescence could be achieved.
There has been additional experimental evidence elicited in recent years that visible light effects are involved in semiconductor integrated circuitry devices and structures as these are fabricated with increasingly small dimensions - now well into the nanospatial domain. One such report by Koch et al ( Physics & Technology of Sub micron Structures, Springer-Verlag, p 253) shows visible light emission from MOS-FET semiconductor device structures attributed to degradation under electrical stress of micron-sized device features into sub-micron light emitting structures.
The light interactive nanostructure invention follows from the above considerations and defines the fundamental interaction of light with matter from an entirely new viewpoint, i.e, that physical dimensional bodies of the order of, and less than, the wavelength of light (generally termed “nanostructure”) actually determine the aspects (optical wavelength, light conversion efficiency, etc.) of the interaction. In this new view one might envision that optical antenna structures exist in the nanometer domain that resonate with incident (or emitted) light. In the patent a very specific and unique new type of antenna structure is defined wherein light is treated as a wave, i.e., employing classical wave optics, but having a necessarily adjacent absorbing mass (the electron) which is defined in quantum confinement spatial terms (or is in effect quantized). The fundamental interaction of light can thus be viewed either from the classical, wave viewpoint or, alternatively, as a quantum event - both regimes of physics seem to exist “side-by-side” in the nanometer spatial domain. This principle forms the essence of the patent.
Beyond this, the patent defines the equations and rules which allow f the engineering of such light interactive nanostructures designed to perform optical tasks. Such structures are very similar to contemporary high density computer integrated circuits - thus their fabrication is almost immediately possible. But initially, without even resorting to such patterned structures, the patent defines the basis for simple processes for the fabrication of an entirely new class of inexpensive light emitting solid state devices emitting light from near -infrared to blue wavelengths. Such light emitting structures would use inexpensive silicon single crystal rather than expensive and toxic compound semiconductor materials. It also follows from the invention that the light emitted from such devices can be “spectrally tailored” uniquely employing the principle of the invention - a capability that has never existed before. Perhaps most importantly, the principle predicts that the all important light conversion efficiency of such devices to be controlled - and that high efficiency values areattainable by controlling the spatial regularity of the light interactive pore structure. Current porous silicon structures displat very low efficiency values (of the order of a few percent) due, I believe, to the random, chaotic character of the distribution of pores. This single factor may determine the ultimate commrecial viability of the PS phenomenon.
Antennas by their nature inherently emit or absorb light. Thus these structures can be operated in either manner. By injecting electrons from an underlying solid state structure light - again of any specified wavelength or spectral character - .can be emitted from an electrical input. This would seem to make optical displays possible possessing unparalleled spatial resolution and inherent brightness. The principle of this patent in fact implies the ultimate in the achievement of these properties.
“Surface texturing” or the creation of roughened surfaces is commonly employed on the surface of solar photovoltaic conversion devices to enhance optical absorption and thus increase their overall efficiency. Such methods possess only limited wavelength specificity or spectral enhancement characteristics. The principles of this invention allow for the first time “educated” texturing to achieve more optimum matching of the absorption characteristic of the device with the incident solar spectrum.
The basic light interactive nanostructure of this invention may also be used, for example, to encode color information onto the heretofore only position-specific sites used to encode image information in optical data storage (”CCD”) devices.. The potential for direct encoding of additional color information within the dimension of each discrete site will vastly increase the information storage capability of this medium.
These are only a few of the applications that I envision applying the principle disclosed in the patent. The fundamental nature of this principle implies that there will be many others - from optical links between electrical computer functions to…?
