Patent Publication Number: US-2009218028-A1

Title: Aligned surface-enhanced raman scattering particles, coatings made thereby, and methods of using same

Description:
TECHNICAL FIELD 
     When light is scattered from a molecule, most photons are elastically scattered. The scattered photons may have the same frequency and, therefore, wavelength, as the incident photons. However, a fraction of light (approximately 1 in 10 7  photons) may be scattered at optical frequencies different from the frequency of the incident photons. The process leading to this inelastic scatter is the termed the Raman effect. Raman scattering can occur with a change in vibrational, rotational or electronic energy of a molecule. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Embodiments of this disclosure are illustrated by way of example and not limitation in the Figures of the accompanying drawings, in which: 
         FIG. 1  is a cross-section elevation of a coated nanoparticle array during processing according to an example embodiment; 
         FIG. 2  is an elevational view of a coated particle during processing according to an example embodiment; 
         FIG. 3  is a side elevation of a mounting substrate during processing according to an example embodiment; 
         FIG. 4  is a cross-section elevation of a coated particle that is bonding to an array of receptor molecules. 
         FIG. 5  is a cross-section elevation of the mounting substrate depicted in  FIG. 4  after further processing according to an example embodiment; 
         FIG. 6  is a cross-section elevation of a method of using the mounting substrate depicted in  FIG. 5  according to an example embodiment; 
         FIG. 7  is a method flow diagram according to an example embodiment; 
         FIG. 8  is a schematic of an engine system  800  that uses a surface-enhanced Raman scattering particle apparatus according to an example embodiment; and 
         FIG. 9  is a schematic diagram illustrating a medium having an instruction set, according to an example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth. The following description and the drawing figures illustrate aspects and embodiments sufficiently to enable those skilled in the art. Other embodiments may incorporate structural, logical, electrical, process, and other changes; e.g., functions described as software may be performed in hardware and vice versa. Examples merely typify possible variations and are not limiting. Individual components and functions may be optional, and the sequence of operations may vary or run in parallel. Portions and features of some embodiments may be included in, substituted for, or added to those of others. The scope of the embodied subject matter encompasses the full ambit of the claims and substantially all available equivalents. 
       FIG. 1  is a cross-section elevation of a coated nanoparticle array  100  during processing according to an embodiment.  FIG. 1  depicts three occurrences of such particles disposed upon the precursor substrate  118 , one of which is designated with the reference numeral  101 . 
     The particle  101  is depicted with a particle core  110  that has been asymmetrically coated with a metallic shell  112 . In an embodiment, the particle core  110  has a diameter in a range from about 20 nanometer (nm) to about 1,000 nm. The particle core  110  may be a material such as hematite (an iron oxide) that can be obtained from nanoparticulate suppliers. In an embodiment, the particle core  110  is a dielectric material such as a metal oxide. 
     In an embodiment, the metallic shell  112  may be a metal such as gold that has been formed in contact with and covering the particle core  110 . In an embodiment, the metallic shell  112  is a metal such as gold that has been electrolessly plated onto the particle core  110  in a manner to cause the metallic shell  112  to form an assymetrical coating. The metallic shell  112  may also be referred to as an asymmetrical optical coating  112 . 
     The metallic shell  112  may have two locations, which are referred to herein as a shell first location  114  and a shell second location  116 . The shell second location  116  is depicted in  FIG. 1  as having a thinner skin (distance from the surface of the shell to the center of the particle core  110 ) than that of the shell first location  114 . The distance may be taken from a symmetry line  120  where the metallic shell  112  may be thinnest for the shell second location  116  and thickest for the shell first location  114 . In an embodiment, the metallic shell  112  enhances the largest diameter in a range from about 20% to about 60%. This largest diameter is delineated by the symmetry line  120 , beginning at the shell first location  114  and ending at the shell second location  116 . 
     The combination of the particle core  110  and the metallic shell  112  may result in light energy being uniquely reflected from the particle  101 . Other metals may be used for the metallic shell  112 . In an embodiment, the metallic shell  112  is a gold alloy that includes any of the platinum-group metals. In an embodiment, the metallic shell  112  is a platinum-group metal. 
     A plasmon is a ripple of electron-cloud waves in the “electron sea” that flows constantly across metal surfaces. A plasmon on the surface of the metallic shell  112  can convert light into electrical energy when the frequency of the light resonates with the same frequency for oscillation of the plasmon. This resonant effect can create large local electrical fields that radiate around the particle  101 . In an embodiment, the particle  101  at the shell second location  116  may be optically active differently than the particle  101  at the shell first location  114 . In an embodiment, the particle  101  at the shell second location  116  may be more optically active than the particle  101  at the shell first location  114 . 
     The particle  101  is depicted disposed upon the precursor substrate  118 . In an embodiment, the treatment of the particle  101  has resulted in selected acceptor molecules  122  being located upon the particle  101  at the shell first location  114  where the metallic shell  112  is thicker than at the shell second location  116 . In an embodiment, these acceptor molecules  12   y  2_acceptor molecules have formed principally at the shell first location  114  due to intermolecular forces such as Van der Waal&#39;s forces, the close packing of one particle next to an adjacent particle, and other causes. An example molecule for  122  is a thiol group that will bond with the Au coating and link with a mercaptosilane chemistry  334  attached to the substrate  332 . 
       FIG. 2  is a cross-section elevation of a particle  201  during processing according to an embodiment. In an embodiment, the particle  201  has been removed from a precursor substrate such as the precursor substrate  118  depicted in  FIG. 1 . The acceptor molecules  122  have caused the shell first location  114  to be a less likely site for allowing bonding of a different molecule and the shell second location  116  to be a more likely site for such bonding. As depicted in  FIG. 2 , a coating of Raman-active molecules  124  mabe either a Raman active site. In an embodiment, there may be a bond site for Raman active analytes. There may also be a bond site that is Raman active that also has polarization sensitivity to specific analytes according to an embodiment. Further the material is selected according to a useful Raman spectral response when the analyte of interest bonds to the molecule. The Raman-active film  124  is depicted as bonded with the particle at the shell second location  116  where the metallic shell  112  is thinner. In an embodiment, the Raman-active film  124  is formed by selectively treating the asymmetrically coated particle  201 . “Selectively treating” means forming the Raman-active film  124  at the shell first location  114  where the shell first location  114  is thinner. This selective treating means the Raman-active film  124  is not formed everywhere over the coated particle  201 . Consequently, an anisotropric configuration of the coated particle  201  has occurred with acceptor molecules  122  at the shell first location  114  and Raman-active film  124  at the shell second location  116 . The Raman-active film  124  is depicted as a coating that is substantially symmetrically disposed over the particle  201  at the shell second location  116 . 
     In an embodiment, the Raman-active film  124  includes Raman active compositions such as a Raman-active molecule. In an embodiment, the film  134  is a bond site for a Raman active analyte. For example, it is the the material that is to be sensed, or it can be a Raman active material that changes properties when exposed to certain analytes. 
     Several Raman active molecules may be selected such as bismethylstyrylbenzene (BMSB) according to an embodiment. In an embodiment, naphthalene is used as the Raman-active molecule. 
     One factor which makes for a useful Raman-active molecule is sufficient coupling between the vibrational mode and polarizability of the molecule. In other words, we want molecules that change their polarization in response to incident light 
     In an embodiment, the particle  201  is removed from a precursor substrate such as the precursor substrate  118  ( FIG. 1 ) by liquid action such as a liquid wash that frees the particle  201 . The wash may be a liquid that is laden with a substance that can form the Raman-active film  124 . In an embodiment, the particle  201  is simultaneously removed from a precursor substrate and treated with a substance that results in deposition of the Raman-active film  124  that is in solution or in suspension. The Raman-active film  124  is allowed to attach by the available space of the shell second location  116 . In an embodiment, the presence of the acceptor molecules  122  may be sufficient to prevent the Raman-active film  124  from affixing at the shell first location  114  where the metallic shell  112  is thinnest. 
       FIG. 3  is a side elevation  300  of a mounting substrate  330  during processing according to an embodiment. In an embodiment, the mounting substrate  330  is an inorganic material such as a ceramic that is capable of withstanding high temperatures such as are found in the exhaust stream of an internal combustion engine. A metallic film  332  is disposed upon the mounting substrate  330  and a film of receptor molecules  334  is formed upon the metallic film  332 . The array of active receptor molecules  334  is provided to bond with the acceptor molecules that are attached to the particle embodiments. In an embodiment, the metallic film  332  is treated to form nucleation sites for deposition of the receptor molecules  334 . In an embodiment, the nucleation sites are an array of grid-scratch imperfections in the metallic film  332  that allow the receptor molecules  334  to deposit in a pattern. 
       FIG. 4  is a cross-section elevation  400  of a particle  401  that is bonding to an array of receptor molecules  334  from the mounting substrate  330  depicted in  FIG. 3 .  FIG. 4  depicts the mounting substrate  330  depicted in  FIG. 3  after further processing according to an embodiment. The particle  401  may be similar or identical to the coated particle  101  depicted in  FIG. 1 . The particle  401  is depicted with a particle core  410  and a metallic shell  412 . Further, a metallic shell  412  is a metal such as gold that has been electrolessly plated onto a particle core  410  in a manner to cause the metallic shell  412  to form an asymmetrical coating. The metallic shell  412  may have two locations, which are referred to herein as a shell first location  414  and a shell second location  416 . The shell second location  416  is depicted in  FIG. 4  as having a thinner skin (distance from the surface of the metallic shell to the center of the core  410 ) than that of the shell first location  414 . The distance may be taken from a symmetry line  420  where the metallic shell  412  may be thinnest for the shell second location  416  and thickest for the shell first location  414 . 
     The particle  401  also includes acceptor molecules  422  and a Raman-active film  224  disposed over the particle  401  at the shell second location  416  of the metallic shell  412 . 
       FIG. 5  is a cross-section elevation  500  of a particle array disposed upon a mounting substrate  330  according to an embodiment. A plurality of particles  501 , such as the particle  401  depicted in  FIG. 4 , are disposed upon a mounting substrate such as the mounting substrate  330  depicted in  FIG. 3 . As the plurality of particles  501  is depicted in cross-section, the plurality of particles  501  exhibit an array configuration that can be manufactured by pretreating the metallic film  332 . In an embodiment, the metallic film  332  is treated to form nucleation sites for deposition of the receptor molecules  334 . In an embodiment, the nucleation sites are an array of grid-scratch imperfections in the metallic film  332  that allow the receptor molecules  334  to deposit in a pattern 
       FIG. 6  is a cross-section schematic  600  of a particle array disposed upon a mounting substrate  630  according to an embodiment. The particle array  601  is depicted disposed upon a metallic film  632  that is disposed upon a mounting substrate  630 . The particle array  601  includes aligned particles, and a Raman-active film  624  is also depicted. An exhaust corridor  640  is depicted. The exhaust corridor may be an exhaust pipe of an external combustion engine such as a diesel engine. However, the exhaust corridor may be any gas corridor that may carry a gas that is responsive to Raman scattering analysis, according to an embodiment. 
     The Raman-active film  624  is either a Raman-active material that changes the spectral response based on exposure to analyte materials. Alternatively, there are provided bond bond sites for gas stream analytes of interest that are inherently Raman active. For the embodiment of bond sites, once the gas stream analytes bond to the Raman-active film  624 , the sensor is able to sense these analytes due to SERS enhancement. The sensor senses the change in response due to molecular changes in the Raman-active material. 
     In an embodiment, a gas corridor  642  forms a diversion from the main flow direction made possible in the exhaust corridor  640 . In an embodiment, where the gas that flows in the exhaust corridor  640  is exhaust gas from an internal combustion engine, the gas corridor  642  channels a bleed stream  650  that is taken from the larger exhaust stream  648  within the exhaust corridor  640 . 
     In an embodiment, the gas corridor  642  is coupled with a cooling-stream corridor  644 . In order to protect the particle array  601  from excessive conditions, the cooling-stream corridor  644  allows a cooling gas  646  to mix with the bleed stream  650  such that analysis of the bleed stream  650  may be done without damaging the particle array  601 . In an embodiment, the bleed stream  650  is monitored and the cooling gas  646  is added at a temperature and flow volume that forms a pre-mix gas  652  at a temperature just above the dew point. This allows the pre-mix gas  652  to condense in part upon the particle array  601 , particularly upon exposed portions of the Raman-active film  624 , without materially changing temperature and pressure conditions for the particle array  601 . 
     In a method embodiment, a cooling gas  646  is mixed with a bleed stream  650 , and the pre-mix gas  652  condenses in part upon the particle array  601 . In an embodiment, a light source  654  projects coherent (laser) light onto the particle array  601 , and Raman-scattered light is detected at a light receptor  656 . The light that is detected at the receptor light  656  may be compared to the light that was projected from the light source  654 . In an embodiment, where a known gas is passing over the particle array  601 , a lookup table may be used for known Raman-active scattered light for known systems. For example in a diesel engine, fuel impurities may be detected in the pre-mix gas  652  based upon standardized tests that are recorded in a database. In an embodiment where the gas is other than an exhaust gas, impurities or anomalies may be detected in the pre-mix gas  652  based upon standardized tests that are recorded in a database. 
     Although the apparatus is depicted with a bleed stream  650  to cool the gas, the bleed stream may be heat exchanged instead of mixed with the cooling gas  646 ; the cooling gas may simply pass through an exchanger instead of mixing directly with the bleed stream  650 . 
     In an embodiment, the apparatus needs no cooling-stream mix or nor heat exchanger, as a selected gas that is susceptible to Raman-scattering analysis may impinge the particle array  601  at temperatures and flow rates that are not damaging to the particle array  601 . 
       FIG. 7  represents a method  700  of analyzing a gas stream. 
     At  710  the method includes passing a gas stream over a surface-enhanced Raman scattering (SERS) particle. 
     At  720 , the method includes projecting light through the gas stream under conditions to allow the light to impinge the SERS particle and to scatter in the Raman spectrum. In an embodiment, the light is single frequency coherent (laser) light. Consequently, the coherent light is scattered under Raman scattering conditions. 
     At  730 , the method includes receiving the Raman-scattered light at a detector. 
     At  740 , the method includes comparing the scattered light with the projected light. 
       FIG. 8  is one version of a loop  800  for engine control based on gas stream analysis that uses the passing of a gas stream over a SERS particle according to an embodiment. After a gas stream passes through an engine intake  872  and is combined with combustion materials, an engine  850  may output an exhaust  852  which is sensed by a SERS apparatus  810 , which in turn may output a signal  854  to a processor  856 . 
     The output from the processor  856  may include an electronic indication of the qualities in the exhaust gas stream that can be correlated to known peculiarities in a gas stream for process control reasons. This electronic indication may go to an output signal  866  which may be correlated with other various inputs of engine data. Examples of various inputs include timing, temperature, percent exhaust-gas recirculation (EGR), valve position, and others. 
     It can now be appreciated that several and complex combinations of engine performance can be monitored in part at least by use of a SERS particle apparatus embodiment set forth in this disclosure. 
       FIG. 9  is a schematic diagram illustrating a medium having an instruction set, according to an example embodiment that uses a SERS particle apparatus. A machine-readable medium  900  includes any type of medium such as a link to the Internet or other network, or a disk drive or a solid state memory device, or the like. A machine-readable medium  900  includes instructions within an instruction set  950 . The instructions, when executed by a machine such as an information handling system or a processor, cause the machine to perform operations that include charachterization of gas stream embodiments. 
     In an example embodiment of a machine-readable medium  900  that includes a set of instructions  950 , the instructions, when executed by a machine, cause the machine to perform operations including gas stream analysis that use a SERS particle apparatus embodiment. In an embodiment, the machine-readable medium  900  and instructions  950  are disposed in a module and are locatable within the engine compartment of the internal combustion engine such as a diesel tractor. In an embodiment, the machine-readable medium  900  and instructions  950  are disposed in a module and are locatable within the cab, such as near the firewall of the engine compartment of an internal combustion engine such as a diesel tractor. 
     Thus, a system, method, and machine-readable medium including instructions for Input/Output scheduling have been described. Although the various calibration, in situ recalibration, and methods have been described with reference to specific example embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader scope of the disclosed subject matter. Accordingly, the specification and drawings are to be regarded in an illustrative rather that a restrictive sense.