METHOD AND APPARATUS FOR THERMAL-TO-ELECTRICAL ENERGY CONVERSION

Abstract

An improved method and apparatus for thermal-to-electric conversion involving relatively hot and cold juxtaposed surfaces separated by a small vacuum gap wherein the cold surface provides an array of single charge carrier converter elements along the surface and the hot surface transfers excitation energy to the opposing cold surface across the gap through Coulomb electrostatic coupling interaction.

Claims

1-57. (canceled)

58. A thermal-to-electric conversion apparatus comprising: a cold side element having: a first cold side quantum element with at least one cold side charge carrier; a second cold side quantum element; and a potential barrier between the first and second cold side quantum element; and a hot side element juxtaposed to the cold side element and separated by a small gas-filled or vacuum gap, the hot side element having a hot side quantum element with at least one hot side charge carrier, wherein the at least one cold side charge carrier electrostatically Coulomb-couples across the gap to the at least one hot side charge carrier, such that when the hot side charge carrier undergoes a transition to a lower energy level from an upper energy level in the hot side quantum element, energy is transferred across the gap through excitation transfer mediated by electrostatic Coulomb coupling causing the at least one cold side charge carrier in the first cold side quantum element to be promoted to an upper energy level from a lower energy level and, in turn, the at least one promoted cold side charge carrier tunnels through the potential barrier to the second cold side quantum element.

59. A thermal-to-electric conversion apparatus as recited in claim 58, wherein the gap is in a range of 1 nanometer to 100 nanometers.

60. A thermal-to-electric conversion apparatus as recited in claim 58, wherein: the at least one cold side charge carrier is supplied from a first cold side reservoir to the first cold side quantum element; and the second cold side quantum element is connected to a second cold side reservoir at elevated voltage.

61. A thermal-to-electric conversion apparatus as recited in claim 60, wherein the second cold side reservoir is connected to the first cold side reservoir through an electrical load.

62. A thermal-to-electric conversion apparatus as recited claim 58, wherein the quantum elements are selected from the group consisting of dots, cylinders, wires, wells, quantum well sheets, molecules, rectangular boxes and bar elements.

63. A thermal-to-electric conversion apparatus comprising: a cold side element having: a first cold side quantum element with at least one cold side charge carrier; a second cold side quantum element; and a potential barrier between the first cold side quantum element and the second cold side quantum element; and a hot side element comprising at least one hot side dipole juxtaposed to the cold side element and separated by a small gas-filled or vacuum gap, the at least one cold side charge carrier electrostatically Coulomb-couples across the gap to the at least one hot side dipole such that excitation energy is transferred across the gap through excitation transfer mediated by electrostatic Coulomb coupling causing the at least one cold side charge carrier in the first cold side quantum element to be promoted to an upper energy level from a lower energy level and, in turn, the at least one promoted cold side charge carrier tunnels through the potential barrier to the second cold side quantum element.

64. A thermal-to-electric conversion apparatus as recited in claim 63, wherein the gap is in a range of 1 nanometer to 100 nanometers.

65. A thermal-to-electric conversion apparatus as recited in claim 61, wherein: the at least one cold side charge carrier is supplied from a first cold side reservoir to the first cold side quantum element; and the second cold side quantum element is connected to a second cold side reservoir at elevated voltage.

66. The thermal-to-electric conversion apparatus as recited claim 63, wherein the quantum elements are selected from the group consisting of dots, cylinders, wires, wells, quantum well sheets, molecules, rectangular boxes and bar elements.

67. The thermal-to-electric conversion apparatus of claim 65, wherein the one or more second cold side reservoirs are connected to the one or more first cold side reservoirs through one or more electrical loads.

68. The thermal-to-electric conversion apparatus of claim 63, wherein the second cold side quantum element is selected from the group consisting of dots, cylinders, wires, wells, quantum well sheets, molecules, rectangular boxes and bar elements.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] These and other features, aspects and advantages of the present invention will become better understood with regard to the following description and accompanying drawings wherein:

[0020] FIG. 1 of which is a basic schematic diagram of an idealized conception underlying the invention;

[0021] FIG. 2 is an expanded isometric schematic view of a preferred device for practicing the methodology of the invention embodying solid state conversion arrays as implementation;

[0022] FIG. 3 is a similar diagram of such an array of the novel thermal-to-electric converter elements of the type shown in FIG. 2; and

[0023] FIGS. 4 and 5 are respective load power density and efficiency of performance graphs attainable with such an embodiment of the invention.

DETAILED DESCRIPTION

[0024] Turning first to the roadmap of our said FIG. 1, this involves an idealized theoretical explanatory scheme consisting of a hot-side surface S.sub.H and a juxtaposed cold-side carrier charge-to-electricity converter surface S.sub.C separated by a small vacuum gap g. On the cold side, there is schematically shown a first quantum well W.sub.C1 having a lower electron potential level 1 and an upper level 2 and wherein an electron is introduced or supplied into the lower level or state 1 from a source of electrons called a reservoir r.sub.1, which may be at relative ground potential. As later explained, in practical implementation, the well W.sub.C1 may be inherently provided in a quantum dot, such as an appropriate semi-conductor dot, and the electron reservoir r.sub.1 may be a conductor of a conducting network interconnecting such dots in an array or matrix of dots distributed along the cold-side S.sub.C as later more fully described in connection with the embodiments of FIGS. 2 and 3.

[0025] Electrostatic coupling to charges on the hot side surface S.sub.H produces a quantum-correlation. This appears schematically in FIG. 1 as a well W.sub.H with two levels connected to an electron reservoir r.sub.a. As an electron is supplied from the cold-side reservoir r.sub.1 to the cold-side level 1 of the well W.sub.C1, accordingly, Coulomb electrostatic coupling between that electron and a charge on the hot side produces a quantum correlation between the cold side electron and such carrier, providing electrostatic interaction U that leads to excitation energy transfer from the hot side to the cold side, thereby elevating the electron in the cold-side well W.sub.C1 up to higher potential level or state 2, as indicated by the upward arrow portion shown below the symbol U. From this upper state 2, the electron may tunnel, as shown schematically at V, through a potential barrier PB to a matched level 2.sup.1 in a second quantum dot well W.sub.cr on its way to a second reservoir r.sub.2 which is at elevated voltage relative to ground, as schematically illustrated at +. The well W.sub.cr permits only one level—level 2.sup.1. The two cold-side reservoirs r.sub.1 and r.sub.2 are connected together through an electrical load, so-labeled. Thus, when elections are promoted in the first quantum well W.sub.C1, they have the possibility of tunneling to the second well W.sub.cr and then continuing on to do electrical work before ending up in the first reservoir r.sub.1 at ground.

[0026] The levels of the hot-side relax to an electron reservoir r.sub.A comprising a continuum of excitation levels, wherein the level “a” is coupled to each level in the reservoir with matrix element m.sub.2 and m.sub.3.

[0027] Electric fields between an electron on the hot side well W.sub.H and an electron on the cold side, couple the product states |b>|1> and |a>|2> with coupling U such that excitation transfer can occur across the gap g. Level 1 of the well W.sub.C1, in turn, relaxes to reservoir r.sub.1 with matrix element m.sub.1 and level 2.sup.1 of well W.sub.cr relaxes to reservoir r.sub.2 with matrix element m.sub.4.

[0028] In Coulomb-coupling energy is transferred from a hot-side electron to a cold-side electron through the Coulomb force between the two electrons. The basic mechanism of the device is that high temperature on the hot side results in excited electrons in the hot-side image, with excitation transferred via electrostatic interaction coupling U (between the hot-side charge, which is itself coupled to excited electrons and phonon modes, and the cold-side electron) to promote a cold-side electron from level 1 to level 2 in well W.sub.C1. The invention of FIG. 1 can also functions as a refrigerator where the load is a power source providing energy into the system to cool the cold-side down and to heat up the hot-side.

[0029] In summary, thus, an electron reservoir on the cold side supplies an electron to a lower state; and coupling with the hot side causes the electron to be promoted to an excited state, and then the electron proceeds to a second electron reservoir at elevated potential. An electrical load connected between the two reservoirs can be driven from the electrical current caused by the promoted electrons. Such a scheme can work with either electrons or holes. We have called it a “single carrier converter” since, in accordance with the invention, it is only a single carrier that is promoted at a time (either an electron or a hole but not both), as opposed to a photovoltaic in which electron-hole pairs are created and photon exchange coupling occurs, namely an electron on the hot side emits a photon and an electron on the cold side accepts the photon. This photon exchange coupling is in contrast to Coulomb coupling. The magnitude of the photon exchange coupling and the Coulomb coupling have different distance dependencies (that is, the distance between the hot-side and the cold-side) where Coulomb coupling has a 1/R.sup.3 dependence on distance while the photon exchange coupling has a 1/R dependence. Coulomb coupling dominates over the photon exchange coupling at narrow distances roughly shorter than the wavelength corresponding to the energy separation of the cold-side single level and higher level excitation quantum state elements divided by 2π or at distances roughly shorter than λ/2π. At larger distances, the Coulomb coupling decays rapidly.

[0030] FIG. 2 presents an exploded view of a preferred physical structure of a thermal-electric converter constructed in accordance with the invention to operate in accordance with the methodology thereof as outlined in FIG. 1. As explained previously, the cold-side surface S.sub.C of the device is shown juxtaposed to the hot-side heat emitter surface S.sub.H with a small vacuum gap g there between. The cold-side converter comprises an array of appropriate semi-conductor small elements or dots, two of which are shown as “Dot 1” and “Dot 2”, implemented as by well-known chip technology and in a chip substrate matrix schematically illustrated by S. In practice, these semi-conductor converter dots may assume any desired geometry, such as the rectangular boxes or bar elements shown, supporting and serving as quantum-confined electron energy excitation state wells (W.sub.C1 and W.sub.cr, FIG. 1) along (at or near) the surface S.sub.C. Other forms of these semi-conductor elements may include small cylinders or wires, small quantum-well sheets or even molecules. The array of dot elements or the like will be conductor-interconnected, as earlier mentioned by, a network of conductors feeding and outputting electrons to and from the respective elements (reservoir r.sub.1, r.sub.2, etc. in FIG. 1) interconnecting the array of dot elements in series and/or in parallel fashion, as appropriate, and also formed into the substrate matrix S of the converter chip side of the device. In the device of FIG. 2, moreover, segments of these electron “reservoir” conductors are shown at “Reservoir 1” (r.sub.1 in FIG. 1) and at “Reservoir 2” (r.sub.2 in FIG. 1) as rectangular cross-section bus portions.

[0031] In accordance with the invention, in an appropriately dimensioned structure, the charge in the quantum dot on the cold side surface S.sub.c will couple to a charge on the nearby conductive hot-side surface S.sub.H, providing a coupling to surface currents, resulting in the two-level system model of the invention herein presented.

[0032] In the device of FIG. 2, the hot side surface S.sub.H may accordingly be a simple flat surface comprising aluminum oxide or a metal, semi-metal or highly doped semiconductor. The metal surface has surface charges and the charges act as an effective dipole with zero energy separation that is coupled to thermally excited electrons and phonons. Across the gap g, the cold-side is shown as comprising the before-mentioned two quantum dots on the surface S.sub.C; Dot 1 having two levels (well W.sub.C1 of FIG. 1) and they couple to the hot-side dipole via the electrostatic Coulomb coupling interaction before described. Dot 2 has one level (in well W.sub.cr of FIG. 1) and it couples to the excited upper level of Dot 1 (state 2 in well W.sub.C1 of FIG. 1) through the tunneling (V). The lower level of Dot1 (level 1 in well WO, as before stated, relaxes to the ground voltage conductor Reservoir 1 (r.sub.1 in FIG. 1). The Dot 2 level relaxes to conductor Reservoir 2 which is at the elevated voltage+. Reservoir conductor 1 is shown having a horizontal branch bus portion extending from the vertical leg of the bus conductor in order to couple the lower level of Dot 1, the branch being oriented horizontally to Dot 1 and facing the center of Dot 1, with a distance. Reservoir conductor 2 is shown parallel to Dot 1 and it runs parallel along the surface S.sub.C next to Dot 2, with a distance. Where desired, these dot and conductor elements may also be oriented at other angles, including substantially perpendicular to the plane of the surface S.sub.C.

[0033] The converter elements may comprise an array of semi-conductor elements that are chip-integrated along the cold surface in a matrix substrate and interconnected by a network of electron reservoir conductors or buses, interleaved within the chip substrate to provide the appropriate series and/or parallel connections amongst and between the elements of the array.

[0034] The cold-side structure is repeated as an array over the surface S.sub.C as shown in FIG. 3, with the Reservoir 1 conductor buses linked together, and the Reservoir 2 conductor buses linked together, and within Reservoirs 1 and 2 connected through the load as in FIG. 1.

[0035] In one embodiment, a simulated specific structural design of this implementation, we obtained the following exemplary results. The temperature on the hot-side is 1300K, and that on the cold-side, 300K. Dot 1 has x×y×z dimension 120 Å×100 Å×100 Å and is of the preferred material InSb. The energy separation of the Dot 1 levels is 0.2 eV. The relaxation time of InSb at 0.2 eV is 1.ps. The hot-side is metallic copper, in this equipment, of which relaxation time at 0.2 eV is 0.57 fs. In one embodiment, Dot 2 has dimension 50 Å×100 Å×100 Å and is horizontally pointing to the top part of Dot 1. (FIG. 2 is not drawn to scale). Dot 2 is of material Ga.sub.0.31In.sub.0.69Sb but may also be comprised of other materials as described herein. The distance between Dot 1 and Dot 2 is 100 Å. Reservoir 1 branch is horizontally positioned 50 Å away from the center of Dot 1. Reservoir 2 is located 50 Å next to Dot 2. Both reservoirs are preferably made up of n-type InSb doped such that its relaxation time at 0.2 eV is 10 ps. The relaxation time for an n-type InSb with doping level 3×10.sup.17 cm.sup.−3 at 0.2 eV is 52 ps, and it is expected that the relaxation time will decrease to zero as the doping increases, since this is the behavior at DC. Therefore there exists a doping level with any desired relaxation time. The surrounding matrix material substrate on the cold side may be GaSb. In other embodiments, the quantum element dimensions, spacing there between and materials may differ as described herein.

[0036] Electrostatic interaction increases with smaller vacuum gap thickness. Radiative heat transport occurs between the hot and cold region, however, if two surfaces are close together, the amount of useful power transferred from the hot to cold side increases much more rapidly because of the effects of Coulomb coupling. In a vacuum, Coulomb coupling dominates over photon contribution by the absorption wavelength in the divided by 2 it. For example, the absorption wavelength corresponding to 0.2 eV is 6.2 μm, and hence the gap should be below about 1 μm for that case in a vacuum. in the calculations, Coulomb coupling dominates below about 500 Angstroms because of the dielectric constants. Therefore if the gap between the hot surface and the cold surface is sufficiently small, the effects of transverse photon generation are minimized relative to the amount of thermal energy transferred by the Coulomb interaction. The converted power per unit area is improved as the gap becomes smaller at very small distances due to Coulomb-coupling interactions. The amount of power converted per unit area is important since it fundamentally impacts the cost of power conversion. If the gap between the hot surface and the cold surface is sufficiently small the converted power per unit area will be increased due to Coulomb-coupling interactions. Gaps below 50-100 nanometers with a lower limit as small as practically possible such as 1 nanometer may facilitate the maximization of the amount of thermal energy transferred by the Coulomb interaction.

[0037] Shown in FIG. 4 and FIG. 5 are the power on load density and efficiency, respectively, as a function of voltage for the device. An initial estimate for maximum power per unit active area is 202 W/cm.sup.2 occurring at voltage 107 mV. FIG. 5 shows that the maximum efficiency 49.8% occurs at voltage 129 mV.

[0038] While the invention has been described with references to its preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teaching of the invention without departing from its essential teachings.