WO2001055484A2 - Matières de bande interdite photonique à base de silicium - Google Patents

Matières de bande interdite photonique à base de silicium Download PDF

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WO2001055484A2
WO2001055484A2 PCT/CA2001/000049 CA0100049W WO0155484A2 WO 2001055484 A2 WO2001055484 A2 WO 2001055484A2 CA 0100049 W CA0100049 W CA 0100049W WO 0155484 A2 WO0155484 A2 WO 0155484A2
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silicon
silica
opal
microns
composite material
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PCT/CA2001/000049
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WO2001055484A3 (fr
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Sajeev John
Geoffrey Alan Ozin
Emmanuel Benjamin Chomski
Ceferino Lopez Fernandez
Francisco Javier Meseguer Rico
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The Governing Council Of The University Of Toronto
Universidad Politecnica De Valencia
Consejo Superior De Investigaciones Cientificas
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Priority to EP01946910A priority Critical patent/EP1279053A2/fr
Priority to US10/182,448 priority patent/US20030156319A1/en
Priority to CA002398632A priority patent/CA2398632C/fr
Priority to AU2001228217A priority patent/AU2001228217A1/en
Publication of WO2001055484A2 publication Critical patent/WO2001055484A2/fr
Publication of WO2001055484A3 publication Critical patent/WO2001055484A3/fr
Priority to US11/285,218 priority patent/US7333264B2/en

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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/122—Basic optical elements, e.g. light-guiding paths
    • G02B6/1225—Basic optical elements, e.g. light-guiding paths comprising photonic band-gap structures or photonic lattices
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals

Definitions

  • the present invention relates to a method of synthesis of periodic composite materials of silicon and another material with a dielectric constant less than silicon, and more particularly the invention relates to photonic band gap (PBG) materials based on silicon having complete photonic bandgaps.
  • PBG photonic band gap
  • Photonics is the science of molding the flow of light. Photonic band gap
  • PBG materials, as disclosed in S. John, Phys. Rev. Lett. 58, 2486 (1987), and E. Yablonovitch, Phys. Rev. Lett. 58, 2059 (1987), are a new class of dielectrics which carry the concept of molding the flow of light to its ultimate level, namely by facilitating the coherent localization of light, see S. John, Phys. Rev. Lett. 53, 2169 (1984), P. W. Anderson, Phil. Mag. B 52, 505 (1985), S. John, Physics
  • PBG materials infiltrated with suitable liquid crystals, may exhibit fully tunable photonic band structures [see K. Busch and S. John, Phys. Rev. Lett. 83, 967 (1999) and E. Yablonovitch, Nature 401 , 539 (1999)] enabling the steering of light flow by an external voltage.
  • PBG materials may play a role in photonics, analogous to the role of semiconductors in conventional microelectronics.
  • Sir John Maddox "If only it were possible to make dielectric materials in which electromagnetic waves cannot propagate at certain frequencies, all kinds of almost magical things would be possible.” John Maddox, Nature 348, 481
  • a silicon inverse opal With such a silicon inverse opal, a large number of photonic devices can be integrated into a single three-dimensional optical chip.
  • PBG photonic band gap
  • the present invention provides a method of producing artificial silica opals with high optical quality, which can be made by microspheres in a wide range of diameters from 0.22 to 1.3 microns.
  • a long-range face centered cubic (fee) ordering of the spheres in air medium has been achieved.
  • the porous lattice of these materials confers upon them the possibility to be employed as templates, in which different materials can be infiltrated. Hence, they inherit the fee order of the template.
  • the present invention provides a method for the synthesis of a 0.1 mm to 1.0 cm scale single crystal of a face centered cubic (fee) PBG material, comprising a close packed .870 micron diameter air spheres in pure silicon.
  • This silicon PBG material has a complete three-dimensional PBG centered in the range of 1.3 to 1.7 microns, the wavelength range of choice for fiber optic telecommunication systems.
  • the self-assembly synthetic approach that we employ is straightforward, mild, inexpensive, accurate, and yields single crystal, inverse opal structures made of silicon comprising up to 10,000 x 10,000 x 10,000 unit cells into which various defect network architectures can be imprinted during the initial stage of synthesis.
  • the methodology is compatible with, and can be easily integrated into, existing silicon fabrication manufacturing facilities.
  • a three dimensional periodic composite material comprising silicon and at least one other dielectric component having an effective dielectric constant smaller than a dielectric constant of silicon, the periodic composite material having a lattice periodicity ranging from about 0.28 microns to about 1.8 microns.
  • an inverse silicon opal comprising close packed spherical air voids in silicon, the spherical air voids having a diameter in a range from about 0.2 to about 1.3 microns.
  • a method of growing an inverse silicon opal comprising: providing a three dimensional opal template comprising particles having an effective geometry and composition; infiltrating the opal template with an effective amount of silicon into voids between said particles; and etching out the particles to produce an inverse silicon opal.
  • the present invention also provides a method of growing an inverse silicon opal, comprising: providing a three dimensional silica opal template made of silica spheres; infiltrating voids in the silica opal template with enough silicon to fill between about 80% to about 100% of said voids; and etching the silica spheres out of the template to produce an inverse silicon opal.
  • the present invention also provides a method of growing an inverse silicon opal with a complete three dimensional photonic bandgap, comprising: providing a three dimensional silica opal template including substantially mono-disperse silica spheres having a diameter in a range from about 0.55 to about 1.3 microns; infiltrating voids in the silica opal template with enough silicon to fill between about 80% to about 100% of said voids; and etching all the silica out of the template to produce an inverse silicon opal.
  • a method of growing silica spheres having a diameter between about 0.55 microns to about 1.3 microns comprising: growing silica seed particles by rapidly adding a first amount of tetraethylorthosilicate (TEOS) to a stirred alcohol solution comprising water and aqueous ammonia to form a suspension of silica seed particles; after a first effective period of time of stirring enlarging the silica seed particles to silica spheres with a preselected diameter by slowly adding a second amount of tetraethylorthosilicate (TEOS) with stirring and thereafter stirring the suspension for a second effective period of time; and collecting the silica spheres with a diameter between about 0.6 microns to about 1.3 microns from said suspension.
  • TEOS tetraethylorthosilicate
  • the present invention provides method of synthesizing an opal from silica spheres, comprising; providing a suspension of silica spheres in a liquid, the silica spheres having an effective diameter and the liquid having an effective viscosity and density so said silica spheres settle with an effective velocity; settling the silica spheres from said suspension at a first effective temperature to form a sediment of preselected dimensions; and drying the sediment at a second effective temperature.
  • Figure 1 shows a transmission electron micrograph (TEM) image of silica spheres (left) and the corresponding size distribution (right);
  • TEM transmission electron micrograph
  • Figure 2 shows a scanning electron micrograph (SEM) image of silica spheres made by a re-growth process on seeds having a diameter of 0.853 ⁇
  • Figure 3 shows an SEM image of a cleft edge of a crystallized sediment of 0.448 micron diameter silica spheres
  • Figure 4 shows an SEM image of a cleft edge of the crystallized sediment of 0.853 microns diameter silica spheres
  • Figure 5 is a vertical view of an electrophoretic cell used to grow silica opals
  • Figure 6 are plots of settling times versus height for sedimentation of SiO 2 spheres of 0.500 micron diameter settling in the presence and absence of an electric field;
  • Figure 7 shows SEM images of a cleaved edge of a silica opal produced using 0.870 micron diameter SiO 2 spheres according to the present invention, a) the spheres settled without an electric field, its Fourier transform (inset) showing the absence of order while the opal shown in b) was settled using an electric field, its Fourier transform (inset) showing the presence of periodicity;
  • Figure 8 shows Bragg diffraction from two different silica opals at different temperatures, (a) silica opal produced by sintering 0.870 micron diameter SiO 2 spheres according to the present invention whose sedimentation was slowed and (b) silica opal produced from as grown 0.205 micron diameter SiO 2 spheres settled under acceleration;
  • Figure 9 shows scanning electron micrographs for a silica opal template sintered at 950°C for 3 hours (left) and sintered at 1025°C 12 hours (right);
  • Figure 10(a) is a scanning electron micrograph (SEM) of an internal [113] facet of a Si infiltrated opal produced in accordance with the present invention
  • Figure 10(b) is an atomic force microscopy (AFM) image of a surface showing smooth growth of silicon on an opal template;
  • Figure 11a shows an SEM image of an internal [110] facet of a silicon inverse opal
  • Figure 11 b shows an SEM image of an internal [111] facet of a silicon inverse opal
  • Figure 12 shows the photonic band structure of a silicon inverse opal
  • Figure 13 shows the measured reflectivity spectrum of silicon inverse opal, the shaded regions centered around 2.5 ⁇ m and 1.46 m show the calculated positions of the first stop band and the complete photonic bandgap.
  • a three dimensional periodic composite material comprising silicon and a dielectric component having a dielectric constant smaller than the dielectric constant of silicon.
  • the periodic composite material has a cubic lattice periodicity (center to center distance between adjacent cubic repeating units) ranging from about 0.28 microns to about 1.8 microns.
  • the dielectric constant of the lower dielectric component is in a range from about 1 to about 2.1 and said composite material is characterized by at least one complete photonic bandgap centered in the range of 1.3 to 1.7 microns.
  • a preferred method of producing this silicon/dielectric material composite involves producing an inverse silicon opal from a silica opal with the silica opal produced using monodisperse silica spheres of selected diameter.
  • a major advantage obtained by producing an inverse silicon opal in this way is that composites with complete photonic bandgaps can be economically synthesized which heretofore has not been realized.
  • the fabrication of artificial opals requires several stages including 1) synthesis of monodisperse silica spheres with diameter between 0.2 and 1.3 microns; 2) growth of silica opal template; and 3) sintering the three dimensional periodic structure to increase the mechanical stability and control the volume filling fraction.
  • silicon silicon alloys
  • etching to remove the silica.
  • silica opal template comprising a weakly sintered face centered cubic (fee) lattice of monodisperse silica (SiO 2 ) spheres having a diameter chosen between 0.6 microns and 1.3 microns.
  • the inverse opal is produced by infiltration of the template with the desired amount of silicon then etching away the silica, described more fully hereinafter.
  • a method of synthesizing suspensions of silica colloidal spheres of diameters in the range 0.2-1.3 microns which are monodisperse with a narrow size distribution (standard deviation ⁇ 5%) in such a way as to reduce formation of defects in the spheres, which advantageously reduces imperfections in opal structures produced from the silica spheres.
  • the inventors have discovered that the synthesis of monodisperse (typically less than 5% variation in diameter) large silica spheres may be achieved by a modified St ⁇ ber method [W. St ⁇ ber, A. Fink, E. Bohn; J. of Colloid and Interface Science, Vol. 26, pp. 62-69, 1968].
  • silica spheres (0.2-0.6 micron diameter) were grown by mixing two different solutions, one containing a mixture of water, ammonia and ethanol and the other containing a mixture of tetraethylorthosilicate (TEOS) and ethanol were mixed.
  • concentrations employed are shown in Table 1.
  • Water was used as a varying parameter to control the sphere size.
  • the solution was thoroughly agitated and the temperature kept constant by using a thermally stabilised bath at 27°C. This was done in order to prevent lack of homogeneity in the solution during particle growth.
  • suspensions of spherically shaped, well dispersed silica particles of diameters between 0.2 and 0.55 microns were obtained.
  • Example 1 gives an illustrative, non-limiting example of growth of silica spheres smaller than 0.6 microns in diameter.
  • the first solution contained 0.727 ml of tetraethylorthosilicate (TEOS) and 4.5 ml of ethanol.
  • the second solution included 1.219 ml (28% weight in water) of NH 3 , and 0.864 ml of double distilled water and 4.69 ml of ethanol.
  • the solutions were kept at 27°C in a thermally stabilised bath for 1 hour.
  • the solutions were then mixed and stirred and the reaction allowed to proceed for two hours.
  • SEM scanning electron microscopy
  • Suspensions of colloidal silica spheres with diameters in the range 0.55- 1.3 microns were produced starting with suspensions of 0.55 micron diameter spheres grown according to Example 1 above.
  • the 0.55 micron silica spheres were used as seeds on which a continuous silica growth process was carried out.
  • Silica seed particles were grown to diameters of about 0.55 microns by mixing 74 ml of absolute ethanol, 10 ml of aqueous ammonia (32% wt) and 4 ml of double distilled water and stirring the mixture in a flask with a magnetic stirrer.
  • TEOS tetraethylorthosilane
  • TEOS concentration employed in the sphere re-growth process. Seed concentration: 0.64% volume. Seeds: 0.55 microns diameter spheres. [TEOS] is given in volume percentage.
  • Silica seeds of diameter of 0.55 microns were grown as described above in Example 2. To a stirred suspension of these seed particles 5 ml of TEOS was added rapidly. After 2 hours of stirring the seed suspension, 74 ml of absolute ethanol, 10 ml of aqueous ammonia (32% wt) and 4 ml of double distilled water were added (0.32% volume of seeds) while the suspension was stirred. The first re-growth cycle was initiated by adding 10 ml of TEOS (5.52% volume) drop by drop, over a period of 90 minutes while the suspension was stirred. After all the TEOS was added the stirring was continued for another 2 hours.
  • the second re- growth step was initiated by transferring 100 ml of this suspension to another flask and adding 10 ml of TEOS (10% volume) drop by drop, to the suspension over a period of 90 minutes with stirring. After stirring the suspension for 3 hours the colloidal suspension was washed as described above in Example 2.
  • Silica seeds of diameter of 0.55 microns were grown as described above in Example 2. After 2 hours of stirring the suspension of 0.55 micron diameter seeds a solution comprising 74 ml of absolute ethanol, 10 ml of aqueous ammonia (32% wt ) and 4 ml of double distilled water was added (0.32% volume of seeds) while the suspension was continuously stirred. The first re-growth process was initiated by adding 10 ml of TEOS (5.52% of volume) drop by drop over a period of 70 minutes while the suspension was stirred. After this the stirring was maintained for 2 hours.
  • the second re-growth process was initiated by transferring 98 ml of this suspension to another flask to which was added 15 ml of TEOS (15.31% volume) drop by drop over a period of 140 minutes while the suspension was stirred with a magnetic stirrer. The resulting mixture was stirred for 4 hours.
  • the third regrowth step was initiated by adding 15 ml of TEOS (15.31% volume) drop by drop to the suspension over a period of about 150 minutes. The stirring was maintained for a further 4 hours and then the colloidal suspension is washed as in the above Example 2. Table 3 gives the TEOS concentrations used in the re-growth process.
  • TEOS concentration employed in the sphere re-growth process. Seed concentration: 0.32%. Seeds: 0.55 microns diameter spheres. [TEOS] is given in volume percentage.
  • the method of silica sphere growth disclosed herein very advantageously provides monodisperse spheres with a dispersity less than 5%. These are the essential building-blocks needed to produce the silica opal templates from which the inverted silicon opals are produced. 2) Growth Of Silica Opal Template The next step in the fabrication of an artificial opal is the crystallization of the silica spheres into a three dimensional periodic structure or template. The inventors have discovered that different methods for settling silica spheres are needed depending on the sphere diameter. 2i) Crystallisation Of Spheres Of Diameters Between 0.2 And 0.55 Microns
  • spheres having a diameter of 0.853 ⁇ 0.012 microns were dispersed in 180 cm 3 of a mixture of 40% weight of etyleneglycol and 60% of double distilled water. Spheres were allowed to settle during 4 days on the above mentioned substrate. Then the supernatant liquid was removed until a 2 mm height liquid column was left above the sediment. The sedimentation tube was then placed in an oven at 60°C during 1 day and later at 100°C during 5 days.
  • the electrophoretic mobility can be obtained in a straightforward manner if Stokes velocity is subtracted from the experimental velocity of the sample under a known electric field. Once the mobility is determined, the electric field necessary to achieve a given velocity can be stated beforehand.
  • the electrophoresis cell shown in Figure 5 comprised a cylindrical tube (2 cm of diameter) of poly(methylacrylate) fixed to the base where the opal should settle, obtained from a standard silicon wafer sputtered with titanium or gold (with less than 0.1 nm of rugosity and thick enough to assure a good conductivity).
  • the material used for the upper electrodes were platinum because it has the highest redox potential so that electrolysis is avoided.
  • Both electrodes are connected to a dc source in order to develop an electrical field.
  • sediments with thickness ranging between a few monolayers and 1 mm (depending on the amount of silica spheres used) with surface areas about 3.1 cm 2 are produced.
  • the height descended by the colloid/clear water interface (setting 0 mm the initial height) was monitored with time.
  • Electrophoretic assisted deposition has been shown to be an efficient way to control the sedimentation velocity of silica spheres over a wide range of diameters.
  • Crystalline sediments of silica spheres suffer from low mechanical stability which makes them difficult to handle.
  • as-grown samples were sintered at different final temperatures. The sintering process leads to the necking, or the formation of small necks, between neighboring silica spheres.
  • Necking is the thermally induced softening and flow of silica into the regions defined by the touching of silica spheres in the colloidal silica crystal to create a silica neck with a diameter that facilitates infiltration of silicon into the voids of the silica opal and etching of silica from the infiltrated opal to create the inverse silicon opal.
  • Another extremely important parameter of the opals when used as matrices for other compounds, is the filling fraction (ratio between the volume occupied for each compound and the total volume of the structure). Sintering provides an accurate way to control the filling fraction between 74% and 100% of silica in opals.
  • the process of necking allows tuning of the dimensions of the silica opal and the resulting inverse silicon opal.
  • the process of necking also provides mechanical stability to the template in addition to providing a control over the opal void volume for subsequent synthesis and providing the connected network topology for removal of the template by an etching process.
  • silica opals sintered at 950°C for 3 hours have a mechanically stabilized compact face centered cubic (fee) structure with a silica filling factor of
  • Figure 9a shows an SEM of a silica opal sintered at 950°C for 3 hours compared to a silica opal sintered at 1025°C for 12 hours, Figure 9b.
  • Example 8 provides an illustrative, non-limiting example of use of sintering temperature for tuning the optical and physical properties of a silica opal.
  • Pieces of an opal synthesized from 0.426 micron diameter spheres were sintered at 1025°C for different periods of time.
  • One piece of the opal was placed in an oven and heated up to 70°C employing a temperature gradient of 1°/min. Once the temperature reached 70°C it was kept constant at 70°C for 3 hours to prevent rapid or abrupt water de-sorption from the opal. After this, the temperature was increased up to 1025°C employing a temperature gradient of 1°/min. The opal was maintained at this temperature for 3 hours.
  • Two other pieces of the starting opal were sintered using the same procedure but one piece was sintered for 6 hours and the other for 12 hours. Characterization of the optical properties of the differently sintered opals reveal the free volume of the three opal pieces were different, decreasing with increasing temperature. 4) Infiltration of Silicon Into The Silica Opal
  • Silicon was grown inside the void spaces of the silica opal template by means of chemical vapor deposition (CVD) using disilane (Si 2 H 6 ) gas as a precursor.
  • the temperature during infiltration may be in the range from 100°C to about 500°C, but preferably the temperature is varied from 250°C for low in-filling samples to 350°C for high in-filling ones.
  • Example 9 below provides illustrative, non-limiting examples of use of silicon infiltration into the silica opal template and annealing of the silicon in the template.
  • the silica opal was placed in a quartz cell and dried under vacuum for about 5 hours. Disilane gas was added to the cell to raise the pressure to about 200 torr, but the pressure may be in the range from 0.1 to about 760 Torr.
  • the cell was heated at 350°C for different periods of time hours, Table 5.
  • the cell was evacuated by vacuum to remove disilane that remained unreacted and annealed to 500°C for 30 minutes.
  • the maximum PBG is obtained with a 90% to 97% infilling of the opal voids in the form of a uniform, thick, wetting layer on the silica surfaces.
  • the reaction time was typically 24 hours and the disilane pressure was about 200 torr.
  • the samples are annealed or heated to 500°C to assist diffusion of silicon into the voids in the template to provide substantially uniform spatial distribution of silicon in the voids.
  • the annealing temperature is varied depending on whether crystallization of the silicon is required.
  • the silica-silicon composite may be annealed in the temperature range from about 400°C to 950°C.
  • the silica template is subsequently removed using fluoride-based etching procedures designed to minimize the dissolution of the macroporous silicon framework.
  • the inverse silicon opal may be annealed in the temperature range from about 400°C to 1100°C. Examples below provide illustrative, non-limiting examples of silica opal removal from the composite silicon-silica opal material.
  • silica colloidal crystals opals
  • Examples of other silicon precursors, other deposition techniques, other forms of silicon for synthesizing the inverse silicon opal comprise, but are not limited by, the following.
  • Capped silicon clusters like octasilacubanes (R ⁇ Si ⁇ ) could be used as a Si source for CVD.
  • Octa-tert-butyloctasilacubane vaporizes around 200°C and decomposes to silicon from 350-450°C.
  • Kanemitsu Y Silicon and germanium nanoparticles, Light Emission in Silicon From Physics to Devices, Semiconductors and Semimetals, Academic Press, San Diego 1998, pp 157-202. Brus L; Silicon polymers and nanocrystals, Light Emission in Silicon From Physics to Devices, Semiconductors and
  • Micro-Raman spectroscopy was used to ascertain the nature and quality of the sample.
  • the silicon phonon peak observed in the inverse silicon opal samples was narrow and centered at 515 cm "1 , suggesting the presence of crystalline silicon.
  • Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the silicon growth.
  • Figure 10(a) shows an internal [113] face of the silicon, infiltrated opal.
  • the SEM picture reveals a large single domain of fee order and a thick, uniform layer of silicon surrounding the silica spheres, indicating a high degree of infiltration.
  • FIG. 10(b) an AFM image of a local area of the infiltrated opal surface is shown, highlighting the smoothness of the silicon coating. From the AFM measurements, the surface roughness was estimated to be 2 nm.
  • the growth of the silicon- wetting layer is quite homogeneous and is independent of the local characteristics of the opal template. The nearly complete and homogeneous infiltration of silicon occurs throughout the depth of the sample.
  • Figure 11a is an SEM image of an internal [110] face of the inverse silicon opal taken after etching and Figure 11b shows an internal [111] facet of an inverse opal structure.
  • These images clearly show an infiltrated structure having an interconnected network of air spheres surrounded by thin silicon shells, inheriting the face centered cubic structure of the opal template. The adjacent air spheres are connected via windows, defining the neck regions which result from the sintering process.
  • the refractive index of silicon is 3.5, well above the theoretically determined threshold of 2.8 for a PBG in a fee lattice of air spheres disclosed in K. Busch and S. John, Phys. Rev. E 58, 3896 (1998).
  • the optical absorption edge of the silicon backbone occurs at a frequency well above the frequency range of the
  • the hatched region highlights a complete PBG with a gap to mid-gap ratio of 5.1 %.
  • the calculations were performed using the plane wave expansion method, following the model of K. M. Ho, C. T. Chan and C. M. Soukoulis, Phys. Rev. Lett. 65, 3152 (1990), using a basis of 2662 plane waves.
  • the optical properties of the inverse opal were characterized by measuring the reflection spectrum and comparing the spectral positions of the observed stop bands with predictions from band structure.
  • a Bohmen Fourier transform infrared (FTIR) spectrometer was used to measure the specular reflectance spectrum.
  • FTIR Fourier transform infrared
  • the lattice constant is related to the sphere size of the original silica opal template. It was. obtained by fitting the spectral positions of the first stop band edges in the T-L direction of the bare opal to the. positions predicted by band structure calculations (the band edges were obtained by measuring the 3dB points of the reflectance peak).
  • the refractive index of the silica spheres was measured to be 1.456 using index matching experiments.
  • the degree of silicon infiltration is determined by both direct and indirect means.
  • the SEM image is analysed by a computer graphics program.
  • the graphics program provides a means of identifying image pixels in a 2d coordinate system.
  • the resolution of the SEM picture (measured in nanometeres/pixel) is obtained by measuring the pixel extension of the ruler drawn at the bottom of the SEM picture.
  • the thickness of the silicon coating layer on the silica sphere is measured at a large number of points at locations on the picture where the thickness is clearly visible and the angle of viewing is known. The average value and the standard deviation is recorded.
  • the (cubic) lattice constant can also be obtained from the center to center distance between adjacent spheres and multiplying by 1.4142.
  • the degree of infiltration is evaluated.
  • This formula is based on a model of the structure in which the silica spheres are in a close packed fee (or other as the case may be) lattice and the silicon uniformly coats all exposed silica surfaces in the form of a spherical shell.
  • the photonic band structure associated with the mathematical model described above is computed. This determines the precise frequency ranges spanned by all of the photonic stop bands (in specific directions) as well as the complete photonic band gap (spanning all directions).
  • the optical reflectivity from the sample (at normal incidence to the sample) probing the lowest frequency stop gap is then fitted to the photonic band structure calculated for different silicon coating layer thicknesses.
  • the best fit yields the actual coating thickness, and hence the degree of infiltration. It has been found that both the direct and the indirect methods yield the same result for the degree of silicon infiltration.
  • the lattice constant which is preserved after infiltration and inversion, was independently determined from reflectivity measurements of the bare silica opal at normal incidence (the L-point).
  • a (cubic) lattice constant of 1.23 microns was obtained by fitting the spectral positions of the first stop band edges to those predicted by band structure calculations (using 1.45 as a refractive index for silica). This corresponds to center-to-center distance between adjacent spheres of 0.87 microns.
  • the cubic lattice constant is 1.4142 x (the center to center distance) for the fee lattice.)
  • the silicon inverse opal crystals obtained after etching were then measured.
  • a microscope coupled to the FTIR was used to probe a single crystal domain and also cover a wide range of angles in a single measurement.
  • the microscope produced a spot size of approximately 20 x 20 ⁇ m 2 and an incident cone of wave vectors with an angular bandwidth spanning 15-35° from normal incidence.
  • the measured spectrum shown in Figure 13, exhibits a broad peak with a center wavelength of 2.5 ⁇ m followed by a series of three peaks in the near-IR regime. One of these latter peaks is centered at 1.46 microns with a width of 5.1% and corresponds to 88% silicon infiltration. Calculations show that this gap is sensitive to percent silicon, for example with 90 % silicon infiltration the gap center moves to 1.5 microns.
  • the band structure also reveals something very surprising and unexpected. Namely, that as the degree of silicon infiltration is increased gradually from 88% to about 97%, somewhere in between, there will be observed a full PBG as large as 9% rather than 5%. The exact position of the optimum depends somewhat on the details of the sintering. Nevertheless an optimum of roughly 9% does appear in almost all of the models that were studied. At 100% infiltration the gap again reduces to about 5%.
  • silicon based PBG material offers a number of imminent possibilities, involving further infiltration of this highly open structure with light sensitive (i.e. light emitting) molecules or atoms, magnetically sensitive dopants and electrically sensitive dopants.
  • Preferred dopants for these silicon based photonic crystals are those that luminescence in a wavelength range located in or near the photonic bandgap.
  • These luminescent dopants include, but are not restricted to, rare earth atoms such as erbium, organic dyes, inorganic dyes, organic polymers and inorganic polymers which luminesce.
  • Variations of the present invention comprise the inverse silicon opals having optically sensitive molecules adsorbed or chemically bonded to the surface of the silicon.
  • optically sensitive molecules include luminescent dyes and luminescent polymers adsorbed or chemically anchored to the surface in the form of monolayers or multilayers.
  • the silicon surface may also be modified with physically or chemically anchored/adsorbed monolayers or multilayers including hydrophobic and hydrophylic organic molecules that could facilitate the infiltration of other optically, electrically, magnetically interesting species.
  • the infiltrated silicon may be in the form of single crystal silicon, amorphous silicon, polycrystalline silicon, porous silicon and nanocrystalline silicon.
  • Literature examples cited above for different precursors and different deposition techniques could be used to create these different forms of silicon which comprise the inverse silicon opal.
  • alloys of silicon may be used to produce composite silicon-based materials with different optical/electronic properties than those with pure silicon- air.
  • silicon alloys that may be used include, but are not restricted to, silicon-germanium alloys Si x Ge ⁇ -x , 0 ⁇ x ⁇ 1 , silicon-carbide alloys Si x C ⁇ -x ,
  • silicon-tungsten alloys silicon-nickel alloys, silicon-titanium alloys, silicon-chromium alloys, silicon-aluminum alloys and silicon-molybdenum alloys.
  • These alloys facilitate changes in the electronic band gap as well as the photonic band gap of the periodic composite. In this way electrical and optical properties of the material can be tailored for specific device applications.
  • the achievement disclosed herein of a periodic silicon-air composite material with a complete photonic bandgap realizes a long standing goal in photonic materials research and opens a new door for complete control of radiative emission from atoms and molecules, light localization and the integration of micron scale photonic devices into a three-dimensional all-optical micro-chip.
  • the inverse silicon opals grown by the method disclosed herein, which may form the basis of photonic circuit elements, may be grown with a variety of geometries, shapes or morphologies including fibers, films, spheres, lithographic patterns and monoliths from microsopic to macroscopic dimensions.
  • the opals may be grown with dimensions in a range from 2 x 2 x 2 unit cells to a x b x c unit cells, wherein 2 ⁇ a ⁇ 10,000, 2 ⁇ b ⁇ 10,000, 2 ⁇ c ⁇ 10,000 .
  • Three dimensional inverse silicon opals may be grown having a planar thin film geometry with dimensions in a range from 1 x 2 x 2 unit cells to a x b x c unit cells, wherein 1 ⁇ a ⁇ 100, 10 ⁇ b, c ⁇ 100,000.
  • the method of producing the periodic silicon-air composites starting with silica opals and producing the inverse opals therefrom is a preferred or best mode known at present since the periodicity of the opal can be efficiently transferred to the inverse opal.
  • synthesis of periodic silicon-air composites or variants thereof as disclosed herein will not be restricted to conversion of silica opals.
  • Other silica templates and non-silica templates may be employed.
  • Silica templates involving lattice structures other than the close packed face center cubic lattice may be used and templates using two or more different sphere sizes may be used. These include for example the hexagonal close packed structure, the body center cubic structure, the diamond lattice structure, the hexagonal AB 2 structure.
  • Non-silica templates include periodically arrrayed block co-polymers and other self- assembling organic materials. In this case non-spherical, repeating units can be realized.
  • a multi-stage infiltration process is required since the polymeric material may not withstand the high temperatures required for silicon CVD. Therefore, a material such as silica would be infiltrated into the polymer template and the polymer template will be removed, prior to the final infiltration with silicon and the final removal of silica.
  • the local density of states controls the rate of spontaneous emission of light from atoms and molecules at particular locations in the photonic crystal, for lasing and optical switching applications.
  • the pseudogap material encompasses a broader range of materials and composites than the rather restricted set of materials which exhibit a complete PBG.
  • materials with a complete gap or pseudogap in the LDOS encompass an even broader range of materials than those which exhibit corresponding gaps in the total density of states.
  • the LDOS is the density of states as felt by an atom or molecule in a particular position in the photonic crystal. As stated above, a gap in the LDOS may occur under less restrictive conditions than those required for a gap in the total DOS. For microlaser device applications, it is contemplated that low threshold laser action may be achieved with a gap only in the LDOS where the light emitting atoms are actually situated. The LDOS is what actually controls the radiative dynamics of individual atoms and molecules. Finally, it should be noted that whereas the total DOS may only have a gap of only 10% in a silicon inverse opal with a "complete 3-d PBG", the LDOS may exhibit a gap of up to 20% in the same material.
  • Certain silicon-air composites comprising doped silicon are useful as sensors.
  • the silicon may be doped silicon, n-type by doping with phosphorus or p-type silicon obtained by doping with boron.
  • the dopant is incorporated by infiltrating the silicon in the presence of gaseous phosphenes or boranes.
  • Such a three dimensional periodic composite material comprising silicon and a dielectric component having a dielectric constant small than a dielectric constant of silicon is treated by anodic oxidation to render it luminescent.
  • the doped macroporous silicon crystal with controlled porosity silicon walls functions as a chemoselective sensor to discriminate optically between molecules in a mixture, depending on the diameter of the pores that grown in the silicon walls.

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Abstract

L'invention concerne un procédé de synthèse de matières de bande interdite photonique. L'invention concerne plus particulièrement la synthèse et la caractérisation de matières de bande interdite photonique cubiques à faces centrées, à très grande échelle et de qualité élevée, constituées de silicium pur, présentant une bande interdite photonique tridimensionnelle complète centrée sur une longueur d'onde de 1,5 νm. On procède, à cet effet, à un dépôt chimique en phase vapeur et à l'ancrage de disilane en un gabarit de silice opaline auto-assemblé, à l'humidification d'une épaisse couche de silicium sur les surfaces intérieures du gabarit, puis à la suppression du gabarit. L'invention atteint ainsi un but fixé de longue date dans le domaine des matières photoniques et ouvre de nouvelles perspectives pour le contrôle total des radiations émises par les atomes et par les molécules, la localisation de la lumière et l'intégration de dispositifs photoniques à l'échelle micronique en une micropuce tout optique tridimensionnelle.
PCT/CA2001/000049 2000-01-28 2001-01-24 Matières de bande interdite photonique à base de silicium WO2001055484A2 (fr)

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EP01946910A EP1279053A2 (fr) 2000-01-28 2001-01-24 Mati res de bande interdite photonique base de silicium
US10/182,448 US20030156319A1 (en) 2000-01-28 2001-01-24 Photonic bandgap materials based on silicon
CA002398632A CA2398632C (fr) 2000-01-28 2001-01-24 Matieres de bande interdite photonique a base de silicium
AU2001228217A AU2001228217A1 (en) 2000-01-28 2001-01-24 Photonic bandgap materials based on silicon
US11/285,218 US7333264B2 (en) 2000-01-28 2005-11-23 Photonic bandgap materials based on silicon

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WO2001086038A2 (fr) * 2000-05-05 2001-11-15 Universidad Politecnica De Valencia Materiaux a bande interdite photonique a base de germanium
EP1423881A1 (fr) * 2001-08-27 2004-06-02 Sandia Corporation Emetteur a incandescence photonique
WO2004063432A1 (fr) * 2003-01-10 2004-07-29 The Governing Council Of The University Of Toronto Procede de cristaux colloidaux photoniques de silicium 3d par micromoulage dans de l'opale de silice inverse (miso)
US7106938B2 (en) 2004-03-16 2006-09-12 Regents Of The University Of Minnesota Self assembled three-dimensional photonic crystal
US7655376B2 (en) 2003-12-05 2010-02-02 3M Innovative Properties Company Process for producing photonic crystals and controlled defects therein

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CN115009207A (zh) * 2021-03-05 2022-09-06 北京航空航天大学 仿生双相力学超材料及大学生方程式赛车吸能盒

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Publication number Priority date Publication date Assignee Title
WO2001086038A2 (fr) * 2000-05-05 2001-11-15 Universidad Politecnica De Valencia Materiaux a bande interdite photonique a base de germanium
WO2001086038A3 (fr) * 2000-05-05 2002-05-10 Univ Valencia Politecnica Materiaux a bande interdite photonique a base de germanium
EP1423881A1 (fr) * 2001-08-27 2004-06-02 Sandia Corporation Emetteur a incandescence photonique
EP1423881A4 (fr) * 2001-08-27 2007-05-09 Sandia Corp Emetteur a incandescence photonique
WO2004063432A1 (fr) * 2003-01-10 2004-07-29 The Governing Council Of The University Of Toronto Procede de cristaux colloidaux photoniques de silicium 3d par micromoulage dans de l'opale de silice inverse (miso)
US7655376B2 (en) 2003-12-05 2010-02-02 3M Innovative Properties Company Process for producing photonic crystals and controlled defects therein
US7106938B2 (en) 2004-03-16 2006-09-12 Regents Of The University Of Minnesota Self assembled three-dimensional photonic crystal

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EP1279053A2 (fr) 2003-01-29
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WO2001055484A3 (fr) 2002-04-18

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