Abstract:
A nanoplasmonic device includes a nanoplasmonicly heatable layer having a heating side and a cooling side, the heatable layer including a plurality of localized energy receiving sites; and a cooling structure located adjacent to the cooling side, the cooling structure including a nanoscale structure to remove heat from the heated layer.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to nanoplasmonic devices and, in particular, to the cooling of nanoplasmonic devices. 
         [0002]    Nanoplasmonic techniques are being used increasingly to couple optical energy into devices. Examples of such applications include magnetic memory, photovoltaic cells, and sub-wavelength lithography. Besides efficient coupling of the energy, sub-wavelength resolutions are possible. 
         [0003]    Such applications make use of an optical spot smaller than the diffraction limit. This can result in substantial localized heating. Heat can be removed with a bulk metallic layer, but this can result in general heating by spreading the heat and may as well change the near-field characteristics of the device. In general, it may be difficult to obtain satisfactory cooling in an efficient and compact manner. 
       SUMMARY OF THE INVENTION 
       [0004]    A nanoplasmonic device includes a nanoplasmonicly heatable layer having a heating side and a cooling side, the heatable layer including a plurality of localized energy receiving sites; and a cooling structure located adjacent to the cooling side, the cooling structure including a nanoscale structure to remove heat from the heated layer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a schematic diagram of an example of a nanoplasmonic system according to an aspect of the invention; 
           [0006]      FIG. 2  is a schematic diagram of an example of a nanoplasmonic device according to another aspect of the invention; 
           [0007]      FIG. 3  is a schematic diagram of an example of a nanoplasmonic device according to an additional aspect of the invention; and 
           [0008]      FIG. 4  is a schematic diagram of an example of a nanoplasmonic device according to another additional aspect of the invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0009]    Referring to  FIG. 1 , an example nanoplasmonic system  10  includes optical sources  12 , nanotransducers  14 , and a nanoplasmonic device  20 . 
         [0010]    The nanoplasmonic device  20  includes a heatable layer  22  having a heating side  24  and a cooling side  26  and a cooling structure  28  adjacent to the cooling side  26 . The cooling structure  28  includes nanostructures described more fully below. 
         [0011]    The heatable layer  22  may be, for example, a magnetic memory material responsive to heat, a photovoltaic cell, or a lithography material. 
         [0012]    In operation, each optical source  12  and nanotransducer  14  combination can produce a sub-wavelength spot  16  of optical energy on the heatable layer  22 . The nanotransducers  14  may be, for example, known devices for localizing incident radiation into a sub-wavelength heated spots such as nanoparticles, nanoantennas and nanowaveguides. Each spot  16  corresponds to a localized energy receiving site. would also be possible to translate a single optical source  12  and nanotransducer  14  combination to successively illuminate the spots  16 . Radiative heat transfer at the nanoscale is the fundamental mechanism in coupling the sub-wavelength optical spots  16  produced by each optical spot  12  and nanotransducer  16  combination. 
         [0013]    When two objects are not in contact, i.e. when these two objects are separated by a distance, there is still a heat transfer between objects due to radiative heat transfer. The heat is transferred between these two bodies through electromagnetic radiation. Classically, this electromagnetic radiation from an object is related to the temperature of the object, and is known as the blackbody radiation. The electromagnetic radiative heat transfer from an object to another object not only depends on the temperature of the radiator, but also other factors as well, including the distance between two objects. Electromagnetic radiation from an object scales with 1/R, where R is the distance from the object. The electromagnetic power scales with 1/R̂2. 
         [0014]    However, at the nanoscale, that is, the sub-wavelength scale, when objects are separated by less than sub-wavelength scale, the radiative heat transfer between the surfaces can be several orders of magnitude higher than predicted by Planck&#39;s blackbody radiation. The radiative heat transfer at sub-wavelength distances can be three orders of magnitude higher than the prediction by Planck&#39;s blackbody radiation. This enhancement is due to electromagnetic energy tunneling of the evanescent fields, and excitation of surface plasmon or phonon polaritons on the structures. There are several ways to enhance this radiative heat transfer between objects. When the objects are brought into the sub-wavelength near-field regime, the radiative energy transfer between objects is enhanced due to evanescent coupling of the electromagnetic energy between objects. This phenomenon is also referred to as photon tunneling, and it is observed if the objects are separated by less than the wavelength of light. In addition, surface plasmon resonances or phonon resonances also improve the electromagnetic energy transfer. If the structures support surface plasmon resonances or surface phonon resonances, the electromagnetic energy transfer substantially increases. As used herein, plasmonic cooling or phononic cooling correspond to cooling an object through enhanced energy transfer when one or more of the structures supports surface plasmon resonances or surface phononic resonances, respectively. 
         [0015]    While the space or gap between objects may be, for example, air or vacuum, material such as dielectrics may also be used. 
         [0016]    Referring to  FIG. 2 , the nanoplasmonic device  20  includes a heatable layer  22  and a cooling structure  28 ′ formed on a substrate  30 . The substrate may be for example a semiconductor or dielectric material such as silicon or any other suitable material such as ceramic glass or amorphous glass and is generally much thicker than the other layers. The heatable layer may be, for example, 5 nm to 30 nm thick. The cooling structure  28 ′ may be, for example, 5 nm to 200 nm thick. 
         [0017]    The cooling structure  28 ′ is formed from a dielectric or semiconductor  32  with embedded nanoparticles  34  that support surface plasmon or phonon resonance. 
         [0018]    The size of the nanoparticles  34  can be between 5 nm and 200 nm. It is expected that particle sizes on the order of 5 nm to 20 nm is preferable. The alternating pattern of particles as a percentage of total width can be referred to as the duty cycle. A typical duty cycle for the particles is around 50 percent. 
         [0019]    The dielectric  32  can be, for example, an oxide such as silicon dioxide, titanium dioxide, or tantulum pentoxide. The nanoparticles  32  can be made of metals such as gold, silver, aluminum, platinum, or copper to support surface plasmon resonances. Alternatively, the nanoparticles  32  can be made of SiC, cubic boron nitride (cBN), hexagonal boron nitride (hBN), or boron carbide BC to support surface phonon resonances. 
         [0020]    These structures can be fabricated using different techniques. One potential way to fabricate these structures is the thin-film deposition and patterning techniques, which are well-known and heavily utilized by semiconductor companies and hard-disk drive companies. Thin film layers can be deposited using different techniques such as sputtering, thermal evaporation, or ion beam deposition. The patterning of these structures can be achieved using photolithographic techniques. Alternatively, patterning of these structures can also be achieved using more recently developed techniques including self-ordered arrays or nanoimprint lithography. 
         [0021]    Different patterns can be made of nanoparticles embedded into a dielectric or semiconductor layer. Different patterns can be obtained by using different duty-cycles between particles. Also, different patterns include the possible shapes that can form the cross section of the layer. Different patterns can refer to different cross sections of nanoparticles, including, for example, spherical, cylindrical, rectangular and square. Different patterns can also refer to different arrangements of these particles with respect to each other, including regular distribution with constant duty-cycle and random distribution. 
         [0022]    This utilizes the coupling between fundamental electromagnetic and thermal phenomena. Placing patterned structures that can support surface plasmon resonances and phonon resonances improve the localized electromagnetic and optical field distribution around these regions. Such localized and improved optical fields improve the radiative energy transfer between these particles and the heatable layer thereby improving the localized heating and cooling. 
         [0023]    Referring to  FIG. 3 , the nanoplasmonic device  20  includes a heatable layer  22  and a cooling structure  28 ″ formed on a substrate  30 . The substrate may be for example a semiconductor or dielectric material such as silicon or any other suitable material such as ceramic glass or amorphous glass and is generally much thicker than the other layers. The heatable layer may be, for example, 5 nm to 30 nm thick. The cooling structure  28 ″ may be, for example, 5 nm to 200 nm thick. 
         [0024]    The cooling structure  28 ″ includes a gap  36  between the heatable layer  22  and the polariton layers  38 ,  40 ,  42 ,  44 . The gap  36  facilitates the radiative energy transfer between the layers. This gap should be very small, i.e. nanoscale scale or sub-wavelength scale, to facilitate phonon tunneling (or evanescent energy coupling) between the structures. The layer underneath is selected so that it supports surface phonon resonances or alternatively it can be selected to support surface plasmon resonances. This way the radiative energy transfer between the objects is further enhanced. 
         [0025]    The polariton layers  38 ,  40 ,  42 ,  44  are a multilayer structure, where each layer may have a different thickness and material property. Each layer may have a different property from the other. The stack supports surface plasmon resonances or surface phonon resonances. These are surface waves that can be excited under specific conditions. The layers can be surface plasmon resonance supporting metals such as gold or silver; or surface phonon resonance materials such as SiC, cubic boron nitride (cBN), hexagonal boron nitride (hBN), or boron carbide BC. In between the layers are dielectric layers. 
         [0026]    Referring to  FIG. 4 , the nanoplasmonic device  20  includes a heatable layer  22  and a cooling structure  28 ′″ formed in the substrate  30 . 
         [0027]    The cooling structure  28 ′″ includes sub-micron channels  46  in the substrate  30  for use with a circulating cooling fluid, for example, water. Inside of each channel  46  are nanorods  48  to improve heat absorption by the cooling fluid. Shapes other than rods could also be employed. 
         [0028]    The cooling structure  28 ′″ may be, for example fabricated in a silicon substrate. The substrate  30  can be formed from two halves anodically bonded together and similarly bonded to the heatable layer  22 . E-beam lithography techniques can be used to form the channels in each half. Before bonding, the nanostructures can be deposited by glancing angle deposition (GLAD). The nanostructures can be rods of copper for example. 
         [0029]    It should be noted that the cooling structure  28 ′″ is localized under the spot  16 . This localization can be employed in the other embodiments herein as well. This allows not only the more rapid cooling possible with nanoscale structures, but also the focusing of the cooling effects more closely to where they are needed. 
         [0030]    It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.