Patent Publication Number: US-2007122313-A1

Title: Nanochannel apparatus and method of fabricating

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      N/A  
     BACKGROUND  
      1. Technical Field  
      The invention relates to nanotechnology. In particular, the invention relates to an apparatus having embedded nanochannels with open distal ends, a nanofluidic system including the apparatus, and the fabrication of the apparatus using nanowires as templates.  
      2. Description of Related Art  
      Nanotechnology is concerned with the fabrication and application of nano-scale structures, structures having at least one linear dimension between about 1 nm and about 200 nm. These nano-scale structures are often 50 to 100 times smaller than conventional semiconductor structures. Nanowires, nanopores and nanochannels are some examples of nano-structures useful in devices, such as sensors and lasers. There are many techniques known in the art for growing or synthesizing nanowires. However, there are fewer techniques for forming a nanochannel or a nanopore. Natural materials, such as the toxin protein alpha-hemolysin, form a microscopic pathway or tunnel through a cellular membrane having a pore size in the angstrom range. However, a natural pore material has an intrinsic short life time such that their use in device manufacture is limited. A nanofluidic device having a synthetic nanochannel or nanopore capable of mimicking the pathway provided by a natural protein like alpha-hemolysin would be useful in genome sequencing, chemical sensing, biological sensing, or both, and molecule separation, for example.  
      Synthetic inorganic nanopores and nanochannels have been made from silicon dioxide or silicon nitride, for example, which have greater stability over time than their natural organic counterparts. One or more of ion-sculpting, TEM drilling, and nanoimprinting have been used to form the synthetic nanopores and nanochannels. Such methods of fabrication require expensive instrumentation that lack precise control of one or both of the number and the dimensions of the nanochannels and the nanopores fabricated. This lack of precise control limits the applications for which these synthetic nanostructures are useful.  
      Moreover, nanotubes have been used as nanochannels in nanofluidic devices. The nanotube is fabricated using a nanowire as a sacrificial core on which a nanotube sheath is formed or grown. Two techniques of forming the nanotubes have been reported that include an epitaxial casting technique and an oxidation and etching technique. The fabricated nanotubes are subsequently harvested from the fabrication substrate for later installation or deposition in or on a device, which is a tedious serial process that may be impractical for some applications.  
      Accordingly, it would be desirable to have a fabrication technique for nanochannels or nanopores that is conducive to a manufacturing environment of a variety of nano-scale devices that utilize such nanochannels or nanopores. Moreover, it would be desirable if such a fabrication technique was also cost-efficient. Such a technique would solve a long-standing need in the developing area of a “bottom-up” fabrication approach in nanotechnology.  
     BRIEF SUMMARY  
      In some embodiments of the present invention, a nanochannel apparatus is provided. The nanochannel apparatus comprises a permanent support, and an array of nanochannels embedded in the permanent support. The array of nanochannels extends through a dimension of the support, such that distal ends of the nanochannels are exposed.  
      In some embodiments of the present invention, a nanofluidic system is provided. The nanofluidic system comprises a nanochannel apparatus that comprises an array of nanochannels embedded in a permanent support. The nanochannel array extends through a dimension of the permanent support, such that distal ends of the nanochannel apparatus are exposed. The nanofluidic system further comprises a fluidic interface adjacent to at least one of the distal ends of the nanochannel apparatus. The nanofluidic system further comprises a component interfaced to the nanochannel apparatus that facilitates one or more of analysis, detection and control of a fluid.  
      In some embodiments of the present invention, a method of fabricating a nanochannel apparatus is provided. The method of fabricating comprises encasing an array of nanowires in a support. The method of fabricating further comprises forming an array of nanochannels in situ through the support in locations of the nanowires, such. that distal ends of the nanochannels are exposed. The support is a permanent support for the nanochannels of the apparatus.  
      Certain embodiments of the present invention have other features that are one or more of in addition to and in lieu of the features described hereinabove. These and other features of some embodiments of the invention are detailed below with reference to the following drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The various features of embodiments of the present invention may be more readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, where like reference numerals designate like structural elements, and in which:  
       FIG. 1  illustrates a perspective view of a nanochannel apparatus according to an embodiment of the present invention.  
       FIG. 2A  illustrates a flow chart of a method of fabricating a nanochannel apparatus according to an embodiment of the present invention.  
       FIGS. 2B-2F  illustrate perspective views of a nanochannel apparatus during fabrication using the method of  FIG. 2A  according to an embodiment of the present invention.  
       FIG. 3A  illustrates a perspective view of a nanochannel apparatus according to another embodiment of the present invention.  
       FIG. 3B  illustrates a cross-sectional view of the nanochannel apparatus of  FIG. 3A .  
       FIG. 4A  illustrates a flow chart of a method of fabricating a nanochannel apparatus according to another embodiment of the present invention.  
       FIG. 4B-4F  illustrates perspective views of a nanochannel apparatus during fabrication using the method of  FIG. 4A  according to an embodiment of the present invention.  
       FIG. 4G  illustrates a perspective view of the nanochannel apparatus of  FIG. 4F  according to another embodiment of the present invention.  
       FIG. 5A  illustrates a side view of a nanofluidic sensor system according to an embodiment of the present invention.  
       FIG. 5B  illustrates a side view of a nanofluidic sensor system according to another embodiment of the present invention.  
       FIG. 6  illustrates a side view of a nanofluidic transistor system according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION  
      Some embodiments of the present invention are directed to a nanochannel formed from a nanowire grown to bridge between horizontally spaced apart vertical surfaces, wherein the nanowire is embedded in a support material and subsequently removed from the material. The vertical surface from which the horizontal nanowire grows is a (111) surface of a [110] oriented semiconductor crystal lattice. Other embodiments of the present invention are directed to a nanochannel formed from a nanowire grown vertically from a horizontal surface, wherein the nanowire is embedded in a support material and subsequently removed from the material. The horizontal surface from which the nanowire grows is a (111) surface of a [110] oriented semiconductor crystal lattice.  
      A semiconductor nanowire will grow preferentially nearly normal to the (111) surface. On a vertically oriented (111) surface, the nanowire will grow horizontally from, or essentially perpendicular to, the vertical (111) surface. On a horizontally oriented (111) surface, the nanowire will grow vertically from, or essentially perpendicular to, the horizontal (111) surface. The nanowire will grow substantially perpendicular to the (111) surface until the growth is intentionally stopped or until the nanowire contacts a facing surface that is respectively vertical or horizontal. By ‘essentially perpendicular’, ‘substantially perpendicular’ and ‘nearly normal’ it is meant that the nanowire will grow from the (111) surface predominantly in a direction to contact the respective facing surface. Once contacted, the nanowire will attach or connect to the respective facing surface.  
      The use of brackets ‘[ ]’ herein in conjunction with such numbers as ‘111’ and ‘110’ pertains to a direction or orientation of a crystal lattice and is intended to include directions ‘&lt; &gt;’ within its scope, for simplicity herein. The use of parenthesis ‘( )’ herein with respect to such numbers ‘111’ and ‘110’ pertains to a plane or a planar surface of a crystal lattice and is intended to include planes ‘{ }’ within its scope for simplicity herein. Such use is intended to follow common crystallographic nomenclature known in the art.  
      The materials useful for the various embodiments of the present invention include, but are not limited to, group IV, group IV-IV, group III-V and group II-VI materials, including compound semiconductor materials, from the Periodic Table of the Elements. For example and not by way of limitation, the nanowire may be made from a semiconductor including, but not limited to, any of silicon (Si), germanium (Ge), silicon carbide (SiC), gallium arsenide (GaAs), gallium nitride (GaN), gallium phosphide (GaP), indium phosphide (InP), indium arsenide (InAs), aluminum nitride (AlN), zinc oxide (ZnO), indium oxide (InO), indium tin oxide (ITO) and cadmium sulfide (CdS), for example, or a metal-semiconductor alloy. Numerous nanowire materials are known in the art. The scope of the various embodiments of the present invention is intended to include all such materials. In some embodiments, the nanowire is a single crystal structure, while in other embodiments, the nanowire may be an amorphous or multi-crystalline structure. A semiconductor nanowire can be grown such that one or more of length, diameter, shape, direction of growth, and position of the semiconductor nanowire are controlled in accordance with some embodiments of the present invention. Moreover, the nanowires may be grown from a substrate used for semiconductor device fabrication.  
      The substrate material comprises one or more of the semiconductor materials listed above, and may include, but is not limited to, the list of nanowire materials from above. For example, a silicon nanowire will grow in a direction that is nearly normal to a (111) plane of a crystal lattice of, for example, a semiconductor substrate or wafer made of Si or GaAs. Moreover, the support material described below comprises one or more of the semiconductor materials listed above, an insulator material and a metal. For example, the support material may be an oxide or a nitride of the above materials including, but not limited to, silicon dioxide, silicon nitride and aluminum oxide. For the purposes of the embodiments herein, the support material is intended to be a permanent support for the nanochannel, while the substrate may provide either temporary or permanent support to the apparatus.  
      In some embodiments of the present invention, a nanochannel apparatus  10  is provided.  FIG. 1  illustrates a perspective view of the nanochannel apparatus  10  according to an embodiment of the present invention. The nanochannel apparatus  10  comprises a support or block  12  having an array of nano-scale size channels or pores  16  through a dimension of the support  12 . Hereafter, the term ‘nanochannel’ will be used to interchangeably to refer to a ‘channel’ or a ‘pore’ having a nano-scale dimension, for simplicity and without limitation. The nanochannels of the array each has distal ends that are open or exposed. Moreover, the term ‘array’ used herein defines a quantity equal to or greater than two, i.e., a plurality.  FIG. 1  illustrates only one nanochannel  16  of the array, for the purpose of simplicity herein and not by way of limitation. The nanochannel  16  has a predominant or principal dimension a (i.e., length) and extends laterally through the support  12 . In some embodiments, the nanochannel apparatus  10  further comprises a substrate adjacent to the support  12 . In these embodiments, the nanochannel array is horizontally oriented or essentially parallel to a horizontal plane of the substrate. Embodiments of the nanochannel apparatus that further include a substrate are described below with respect to  FIGS. 2A-2F .  
      According to another embodiment of the present invention, a method of fabricating a nanochannel apparatus is provided. The method of fabricating comprises encasing a plurality of nanowires in a support on a substrate; and forming an array of nanochannels in the support in the locations of the nanowires, such that the nanochannels of the array have distal open ends. The support is a permanent support for the nanochannels of the apparatus, while the substrate is either temporary or permanent, depending on the embodiment. Moreover, the nanowires are grown in situ on the substrate before being encased, and the nanochannels are formed in situ in the support. The nanochannels correspond in size to that of the encased nanowires. The resultant nanochannel apparatus is an in situ nanochannel apparatus.  
      In some embodiments, a method  200  of fabricating a nanochannel apparatus having an array of horizontal-oriented nanochannels is provided.  FIG. 2A  illustrates a flow chart of the method  200  of fabricating a nanochannel apparatus according to an embodiment of the present invention.  FIGS. 2B-2F  illustrate perspective views of a nanochannel apparatus  20  during fabrication according to the method  200 . The method  200  of fabricating comprises creating  210  spaced apart parallel islands  201  of a first layer of a material supported by a substrate  202 . In some embodiments, the substrate  202  is a semiconductor material having an insulator material layer  207  on the substrate  202  surface. The substrate  202 ,  207  materials include, but are not limited to, a silicon wafer with a layer of either silicon dioxide or silicon nitride on the surface, for example and not by way of limitation. The first layer is a crystalline material polished in a [110] direction such that the horizontal surface is a (110) plane. For example, the first layer may be a silicon layer having a [110] crystal orientation. At least one of the created islands  201  has a vertical (111) planar surface that faces a vertical surface of the other created island  201 , wherein the (111) surface is vertical relative to the (110) horizontal planar surface.  
      As illustrated in  FIG. 2B , both of the created islands  201  have a vertical surface that is (111) planar surface and that faces the other vertical surface in some embodiments. The created  210  islands are essentially parallel vertical walls of a trench when viewed from an end or in cross-section. The parallel islands  201  having vertical (111) surfaces may be created  210  using the techniques described in co-pending U.S. patent application, Ser. No. 10/738,176, filed Dec. 17, 2003, U.S. Publication  2005 / 0133476 -A1, published Jun. 23, 2005, incorporated herein by reference in its entirety. For example, the first layer of material may be one or more of mechanically cut, laser cut, wet chemical etched and dry etched, for example and not by way of limitation, along (111) lattice planes down to the substrate  202  surface or down to a insulator layer  207  on the substrate  202  surface to create a trench that has vertical sidewalls. An internal surface of the vertical sidewalls are aligned with vertical (111) lattice planes of the first layer. The vertical sidewalls of the trench are the parallel islands  201 .  
      The method  200  of fabricating further comprises growing  220  nanowires from the vertical (111) surface of a first island of the created islands  201  to a second island of the created islands  201 . Since a nanowire preferentially grows nearly normal to a (111) surface, the nanowire will grow preferentially horizontal to the vertical (111) surface.  FIG. 2C  illustrates an array of such nanowires  203 , for example, grown  220  preferentially horizontal to the vertical (111) surface of the first island  201  to laterally bridge across the trench and contact the other (or second) spaced apart island  201 . The grown nanowires  203  are effectively suspended between the spaced apart, parallel islands  201 .  
      There are many techniques known in the art for growing nanowires that may be used in this embodiment. In particular, nanowires are grown in the location where they will be used to form a nanochannel in the apparatus (i.e., in situ). Nanowires may be ‘grown’ using methods such as, but not limited to, vapor-liquid-solid (VLS), vapor-solid-solid (VSS), solution-liquid-solid (SLS), which are known in the art, using a catalyst particle. The growth method may be referred to as catalyzed growth or in some embodiments, metal-catalyzed growth. However, any of the in situ growth methods may be substituted for the metal-catalyzed growth and still be within the scope of the embodiments described herein. Metal-catalyzed growth is described in more detail in the co-pending U.S. patent application, Ser. No. 10/738,176, cited and incorporated by reference supra.  
      For example, in some embodiments, a catalyst material is deposited on the vertical (111) surface of one or both of the parallel islands  201 . The catalyst material may be annealed into activated catalyst (i.e., a nanoparticle catalyst) or may be deposited in an activated form. The catalyst material may include, but is not limited to, gold (Au), nickel (Ni), titanium (Ti), iron (Fe), cobalt (Co), and gallium (Ga), and respective alloys thereof. Other catalyst materials may include, but are not limited to, nonmetals, such as SiO x , where x ranges from about 1 to less than 2, for example. The catalyst materials used for growing a Si nanowire, for example, include, but are not limited to, Ti, Au, TiSi 2  alloy and Au—Si alloy.  
      The activated (111) surface is exposed to a controlled temperature, pressure and a gas containing a material of the nanowire to be grown. In some embodiments, the activated vertical (111) surface is exposed to the gas in the reactor chamber of the material deposition system. As such, the temperature and pressure are regulated, and the gas or a gas mixture is introduced and controlled during nanowire growth  220 . In some embodiments, the activated (111) surface is exposed to the gas in the reactor chamber under conditions at which the uncatalyzed (i.e., normal) deposition rate is low. The catalyst accelerates the decomposition of the gas, allowing a high ratio of catalyzed-to-normal growth. Material deposition systems including, but not limited to, chemical vapor deposition (CVD) systems, metal organic vapor phase epitaxy (MOVPE) systems, molecular beam epitaxy (MBE) systems, plasma-enhanced CVD (PECVD) systems, resistance-heated-furnace diffusion/annealing systems, and rapid thermal processing (RTP) systems may be employed for the nanowire growth  220 , for example. For a Si nanowire, growth  220  using a CVD system and a process that employs a Si-containing gas including, but not limited to, a gas mixture of silane (SiH 4 ) and hydrogen chloride (HCl), a gas of dichlorosilane (SiH 2 Cl 2 ), or a silicon tetrachloride (SiCl 4 ) vapor in a hydrogen (H 2 ) ambient may be used, for example and not by way of limitation.  
      The nanowire grows  220  in a columnar shape from the vertical (111) surface adjacent to the activated catalyst particle. A free end of the columnar-shaped growing nanowire contains the activated catalyst particle. The nanowire continues to grow in the environment described above until the free end of the nanowire  203  contacts the vertical surface of the other parallel island  201 . In some embodiments, contact of the free end is accompanied by attachment to the vertical surface of the other island  201 . The grown nanowires  203  are effectively suspended to bridge across the trench.  
      The method  200  of fabricating further comprises encasing or enveloping  230  the laterally bridging nanowires  203  in a second layer  204  of material. The second layer  204  may fill the trench formed by the spaced apart islands  201 .  FIG. 2D  illustrates the second layer  204  between the islands  201  that encases or envelops  230  the array of nanowires  203 . The material of the second layer  204  is different from the materials of the nanowire  203  and the islands  201  (i.e., the first layer) and is intended as a permanent support or block for the subsequently formed nanochannels. Various materials may be used for the second layer  204  including, but not limited to, silicon dioxide, silicon nitride, aluminum oxide, aluminum nitride, a polymeric material, and a metal.  
      Encasing  230  the nanowires  203  comprises depositing the material of the second layer  204  to completely surround the horizontally suspended nanowires  203 . The material of the second layer  204  is deposited using any of the deposition or growth techniques known in the art including, but not limited to, one or more of chemical vapor deposition (CVD) and plasma enhanced CVD (PECVD), for example and not by way of limitation, and may depend in part on the material chosen for the second layer  204 . Moreover, angled deposition may be used to facilitate the material surrounding the nanowires  203 , for example and not by way of limitation.  
      In some embodiments, encasing  230  the nanowires  203  further comprises removing excess deposited material of the second layer  204  to expose the horizontal (110) planar surface of the islands  201  and form the second layer  204 .  FIG. 2D  further illustrates that horizontal (110) planar surfaces of the islands  201  are exposed. Removing excess second material includes, but is not limited to, one or more of chemical etching, mechanical polishing, chemical mechanical planarization (CMP) and lithography. In some embodiments, encasing  230  further comprises masking the islands  201  and a portion of the nanowires  203  that is adjacent to at least one of the islands  201  before the material of the second layer  204  is deposited, and subsequently removing the mask to expose the islands  201  and the nanowire portions after the second layer  204  material is deposited.  
      The method  200  of fabricating further comprises forming  240  nanochannels in a permanent support of the nanochannel apparatus  20 . In some embodiments, forming  240  nanochannels comprises removing  240  the nanowires  203  from the second layer  204  while leaving the second layer  204  or a majority thereof permanently intact. In some embodiments, forming  240  nanochannels further comprises removing  240  the islands  201  either simultaneously or sequentially with the removal of the nanowires. Moreover in some embodiments, forming  240  nanochannels further comprises removing a section of the second layer  204  at an interface immediately adjacent to one or both of the islands  201  to expose a portion of the nanowires  203  from the section.  FIG. 2E  illustrates the apparatus with the section of the second layer  204  removed and the nanowire  203  portions exposed according to an embodiment.  
      A section of the second layer  204  may be removed using a variety of techniques known in the art including, but not limited to, one or more of dry etching, for example, reactive ion etching (RIE) or ion milling, wet chemical etching, and lithography, and depends on the material used for the second layer  204 . In some embodiments, the technique selectively removes the section of the second layer  204  but not the adjacent islands  201  or the nanowires  203 . As such, one or more other techniques that are selective to the removal of the nanowires  203  is used to further remove the nanowires  203 , while the islands  201  may be optionally removed also, depending on the embodiment.  
      In some embodiments, the islands  201  and the nanowires  203  are removed with selective etching, such as using one or more of XeF 2  dry chemical etching and a selective wet etching technique, for example and not by way of limitation, and depends on the materials of the islands  201  and of the nanowires  203 . The nanowires  203  are removed from the support layer  204  selectively, such that nanochannels  206  in the support layer  204  are created  240  where the horizontally suspended nanowires  203  are removed.  FIG. 2F  illustrates the resultant nanochannel apparatus  20  with the nanowires  203  and the parallel islands  201  removed  240 . Respective nanochannels  206  extending laterally through the second layer  204  take the place of (i.e., remains as a result of the removal of) the array of nanowires  203 . The second layer  204  forms the permanent support  205  for the laterally or horizontally extending nanochannels  206  of the nanochannel apparatus  20 .  
      The nanochannel apparatus  20  illustrated in  FIG. 2F  is similar to the nanochannel apparatus  10  illustrated in  FIG. 1 , except that the nanochannel apparatus  20  of  FIG. 2F  includes the substrate  202  and illustrates the array of the nanochannels  206 . In some embodiments, the nanochannel apparatus  10  is fabricated using the method  200  described above. As such, the method  200  may further comprise separating the support  205  from the substrate  202  (and insulator layer  207 , when present), such as by using one or more of the etching techniques mentioned above, to remove the substrate  202 ,  207  from the support  205 .  
      In another embodiment of the present invention, a nanochannel apparatus  30  is provided.  FIGS. 3A and 3B  illustrate perspective views of the nanochannel apparatus  30  according to an embodiment of the present invention.  FIG. 3B  is a perspective cross sectional view of the nanochannel apparatus  30  along line B-B in  FIG. 3A . The nanochannel apparatus  30  comprises a support  32  having an array of nanochannels  36  that extends through a dimension of the support  32 .  FIGS. 3A and 3B  illustrate only one of the nanochannels  36  of the array for simplicity and not by way of limitation. In  FIGS. 3A and 3B , the nanochannel  36  has a predominant or principal dimension b (i.e., length) that extends through an equivalent dimension b (i.e., height or thickness) of the support  32 , such that the nanochannel  36  is vertically oriented or parallel to the dimension b of the support  32 . In some embodiments, the nanochannel apparatus  30  further comprises a substrate  34  having an opening  35 . The substrate  34  has a horizontal (111) planar surface that is adjacent to the support  32 . In these embodiments, the vertically oriented nanochannel  36  is essentially perpendicular to the horizontal surface plane of the substrate  34 . The nanochannel  36  extends vertically relative to the substrate plane in a location coaxial with the opening  35 .  
      In another embodiment of the present invention, a method  400  of fabricating a nanochannel apparatus having an array of vertical-oriented nanochannels is provided.  FIG. 4A  illustrates a flow chart of the method  400  of fabricating a nanochannel apparatus according to an embodiment of the present invention.  FIGS. 4B-4F  illustrate perspective views of a nanochannel apparatus  40  during fabrication according to the method  400 . The method  400  of fabricating comprises providing  410  a substrate  401  having a [111]-oriented crystal lattice. In some embodiments, the substrate  401  is polished in a [111] direction. The provided substrate  401  has an exposed surface that is a horizontal (111) lattice plane.  
      The method  400  of fabricating further comprises growing  420  an array of nanowires from the horizontal (111) surface. Since a nanowire preferentially grows nearly normal to a (111) surface, the nanowires will grow preferentially vertical to the horizontal (111) surface.  FIG. 4B  illustrates the array of nanowires  403 , for example, grown  420  preferentially vertical to the horizontal (111) surface of the substrate  401 . The nanowires  403  are grown using any of the growth techniques described or referenced above for the method  200  of fabricating. Moreover, vertical growth of nanowires from horizontal (111) planar surfaces is described in more detail in co-pending U.S. patent application, Ser. No. 10/982,051, filed Nov. 5, 2004, incorporated by reference herein in its entirety.  
      A nucleating catalyst material is deposited on the (111) surface in a very thin layer and annealed in a controlled environment (i.e., chamber) to form isolated nanoparticles of the catalyst material. Alternatively, when the nanoparticle catalyst is directly deposited, annealing may be optional. The catalyst material may be lithographically patterned using techniques known in the art to define target locations of the catalyst material on the horizontal (111) surface of the substrate  401  from which nanowires  403  are to be grown  420 . As described above for the method  200 , a nanowire material-containing gas is introduced into the controlled environment. The nanoparticle catalyst accelerates decomposition of the gas, such that atoms of the nanowire material precipitate between the nanoparticle catalyst and the horizontal (111) surface to initiate nanowire growth  420 .  
      The nanowire  403  will grow  420  from under the nanoparticle on the (111) horizontal surface in columnar form, taking the nanoparticle with it at its tip or free end. The nanowires  403  will continue to grow until growth is terminated, such as by terminating the growth environment in the chamber or removing the substrate  401  from the chamber, for example.  
      The method  400  of fabricating further comprises encasing or enveloping  430  the grown nanowires  403  in a support layer  404  of material. The support layer  404  may fully encase the nanowires  403  or in some embodiments, may encase a portion of a length of the nanowires  403 , such that the free ends of the nanowires  403  are exposed or otherwise not encased  430  in the material of the support layer  404 .  FIG. 4C  illustrates the support layer  404  that encases or embeds  430  the array of nanowires  403 . The material of the support layer  404  is different from the materials of the nanowire  403  and the substrate  401  and is intended as a permanent support or block  405  for the subsequently formed nanochannels  406 . Any of the materials provided above for the support material or the second layer  204  of the method  200  of fabricating may be used for the material of the support layer  404 , for example. Encasing  430  the nanowires  403  comprises depositing the material of the support layer  404  to completely surround the nanowires  403 . The material of the support layer  404  is deposited using any of the deposition or growth techniques described above for the method  200  of fabricating, and may depend in part on the material chosen for the support layer  404 .  
      In some embodiments, encasing  430  the nanowires  403  further comprises removing excess deposited material of the support layer  404  to expose the free ends of the vertically grown nanowires  403 .  FIG. 4C  further illustrates that the free ends of the nanowires  403  are exposed. Removing excess material of the support layer  404  includes, but is not limited to, one or more of chemical etching, mechanical polishing, chemical mechanical planarization (CMP).  
      The method  400  of fabricating further comprises forming  440  an array of nanochannels in the support layer  404  of the apparatus  40 . Forming  440  the nanochannels comprises removing  440  at least a section of the substrate  401  and removing the nanowires  403  from the support layer  404  while leaving the support layer  404  permanently intact.  FIG. 4D  illustrates the apparatus with the section of the substrate  401  removed to expose the nanowires  403  in an opening  407  created in the substrate  401  by the removed section that is coaxial with the array of nanowires  403 .  
      A section of the substrate  401  may be removed using a variety of techniques known in the art including, but not limited to, one or more of dry etching, for example reactive ion etching (RIE) or ion milling, wet chemical etching, and lithography, and depends on the material used for the substrate. The technique or techniques used will selectively remove the section of the substrate  401 , and optionally, will remove the material of the nanowires  403 , depending on the embodiment, but will not remove the material of the support layer  404 . In some embodiments, the technique(s) used for the removal of the substrate  401  section selectively does not remove the nanowires  403 . Where the nanowires  403  are not removed with the section of the substrate  401 , another of the above described techniques may be used to selectively remove the nanowires  403 . In some embodiments, the entire substrate  401  is removed instead of a section thereof that is coaxial with the nanowires  403 . In other embodiments, the section of the substrate  401  is removed, followed by the removal of the nanowires  403 , and then the removal of a remainder of the substrate  401 .  
      The nanowires  403  are removed from the support layer  404  selectively, such that an array of nanochannels  406  in a support or block  405  are created  440  where the nanowires  403  are removed.  FIG. 4E  illustrates the resultant nanochannel apparatus  40  with the nanowires  403  removed  440 .  FIG. 4F  illustrates a perspective view of an opposite end of the resultant nanochannel apparatus  40  that illustrates the opening  407  formed as a result of removing a section of the substrate  401  that is coaxial with the formed nanochannels  406 .  FIG. 4G  illustrates a perspective view of the nanochannel apparatus  40 , according to another embodiment, that has the substrate  401  completely removed, such that the nanochannel apparatus  40  essentially is the nanochannel support block  405 .  
      The nanochannel apparatus  40  illustrated in  FIGS. 4E and 4F  is similar to the nanochannel apparatus  30  illustrated in  FIGS. 3A and 3B , except that the nanochannel apparatus  40  has the array of nanochannels  406  illustrated. In some embodiments, the nanochannel apparatus  30  is fabricated using the method  400  described above. Moreover, while not illustrated, in some embodiments, the support layer  404  may envelop the nanowires  403  but not cover one or more portions of the substrate  401  surface that do not include the grown nanowires  403 . As a result, some embodiments of the nanochannel apparatus  40  may have exposed horizontal (111) surfaces of the substrate  401  adjacent to the support block  405  having nanochannels  406 . The embodiment illustrated in  FIG. 2F  may be representative of these features. For example, the nanochannel apparatus  40  having exposed substrate surfaces is similar to that depicted for the nanochannel apparatus  20  in  FIG. 2F , except that vertically extended nanochannels  406  coaxial with an opening  404  in the substrate would replace the illustrated horizontally extended nanochannels  206 .  
      According to some embodiments of the present invention, a diameter of the nanochannels  16 ,  206 ,  36 ,  406  may be controlled or adjusted in the respective nanochannel apparatuses  10 ,  20 ,  30 ,  40 . For example, in some embodiments of the methods  200 ,  400  of fabricating a nanochannel apparatus, a thermal oxide may be grown on the nanowires  203 ,  403 , such that a diameter of the nanowires  203 ,  403  is reduced by the thickness of the thermal oxide layer. During forming  240 ,  440  nanochannels, the reduced-diameter nanowires  203 ,  403  (or core nanowire materials) are removed, such that the resultant nanochannels  206 ,  406  are actually narrower in diameter (by approximately the thickness of the thermal oxide layer) than they would have been without thermal oxidation of the nanowires  203 ,  403 . In an example, silicon nanowires having a diameter of approximately 5 nanometers (nm) may be thermally oxidized prior to forming  240 ,  440  nanochannels to achieve a resultant nanochannel diameter of approximately 2 nm to approximately 3 nm.  
      In some embodiments, the nanochannel apparatus  10 ,  20 ,  30 ,  40  may be further processed to include one or more components and structures to provide a variety of nanofluidic devices or systems. For example, one or more of the nanochannels  206 ,  406  of the apparatus  20 ,  40  may be interfaced to one or more fluidic components and structures formed on the surface of the substrate  202 ,  401  for one or more of holding, processing and sensing fluids that travel through the one or more nanochannels  206 ,  406 . A fluid is defined to include one or both of a liquid and a vapor herein. In some embodiments of the present invention, any of the nanochannel apparatuses  10 ,  20 ,  30 ,  40  described above may be used in a variety of miniaturized systems for analysis, detection and control.  
      In some embodiments of the present invention, a nanofluidic system is provided. The nanofluidic system comprises a nanochannel apparatus  10 ,  20 ,  30   40 ; a fluidic interface adjacent to at least one open end of the nanochannel apparatus  10 ,  20 ,  30   40 ; and a component interfaced to the nanochannel apparatus  10 ,  20 ,  30   40 . The component is defined herein as a structure or element that facilitates one or more of analysis, detection and control. In some embodiments, the component comprises one or more of an electrode and a sensor. The electrode comprises one or more of a gate electrode, a source electrode and a drain electrode, for example and not by way of limitation. The sensor comprises one or more detectors, nano-detectors and nano- emitters. The sensor includes, but is not limited to, one or more of a nanowire-based sensor, a single electron transistor, an optical detector, and an optoelectronic structure, such as a vertical cavity surface emitting laser (VCSEL), including a nano-VCSEL, for example and not by way of limitation. See, U.S. Pat. No. 6,815,706 B2, issued Nov. 9, 2002; co-pending U.S. patent application Ser. No. 10/982,051, cited supra; and co-pending U.S. patent application Ser. No. 11/084,886, filed Mar. 21, 2005, incorporated herein by reference in their entireties, for some examples of a nano-detector or a nano-device useful in various embodiments of a nanofluidic system according to the present invention. In some embodiments, the nanochannel apparatus  10 ,  20 ,  30 ,  40  may be integrated with a component, as described above, and optionally other devices to form miniaturized systems for fluidic processing of biological materials, such as DNA.  
       FIGS. 5A and 5B  illustrates a nanofluidic sensor system  500  according to embodiments of the present invention. The nanofluidic sensor system  500  comprises a nanochannel apparatus  50 ; a fluidic interface  501  at a first open end  51  of the nanochannel apparatus  50  and a sensor  510  interfaced to the nanochannel apparatus  50 . The nanochannel apparatus  50  is similar to any of the nanochannel apparatus embodiments  10 ,  20 ,  30 ,  40  described above. In some embodiments, the nanofluidic sensor system  500  further comprises another fluidic interface  503  at a second open end  53  that is distal to the first open end  51  of the nanochannel apparatus  50 . In some embodiments, the nanofluidic sensor system  500  is supported by a substrate  502 .  
      As illustrated in  FIG. 5A , the sensor  510  is incorporated into or embedded in the nanochannel apparatus  50  of the nanofluidic sensor system  500  in some embodiments. By ‘incorporated into’ or ‘embedded in’ it is meant that the component forms an integral portion of at least one of the nanochannels of the array. Moreover, the fluidic interfaces  501 ,  503  illustrated in  FIG. 5A  are exemplary fluid reservoirs  501 ,  503 . In other embodiments, such fluidic interfaces include, but are not limited to, one or more of a conduit, a valve, a via, and another nanochannel apparatus, for example, and not by way of limitation. As such, when a fluid is moved from a first fluid interface  501  to a second fluid interface  503 , the fluid passes through or by the sensor  510  embedded in the nanochannel apparatus  50 , such that one or more characteristics of the fluid may be analyzed or detected using the sensor  510 . In some embodiments, the sensor  510  or another sensor, such as any of those mentioned above, may be located adjacent to one or both of the open ends  51 ,  53  in addition to or in lieu of that illustrated in  FIG. 5A . See, for example, co-pending U.S. patent application Ser. No. 11/145,038, filed Jun. 3, 2005, incorporated herein by reference in its entirety.  
      In another embodiment, the nanofluidic sensor system  500  comprises a sensor  512  interfaced with an open end  51 ,  53  of the nanochannel apparatus  50 , as illustrated in  FIG. 5B . In particular, the sensor  512  is located or formed on the substrate  502  within one or both of the fluidic interfaces  501 ,  503 .  FIG. 5B  illustrates the sensor  512  within fluidic reservoir  503  by way of example and not by way of limitation. While not illustrated in  FIG. 5B , the sensor  512  may be in addition to rather than in lieu of the sensor  510  that is embedded in the nanochannel apparatus  50  of  FIG. 5A , depending on the embodiment. Moreover, a sensor in addition to or in lieu of the sensor  512  may be located in the reservoir  501 , depending on the embodiment. Assuming fluid flow is primarily in the direction of the horizontal arrow illustrated in  FIG. 5B , a terminally located sensor  512  in the nanofluidic sensor system  500  can detect one or both of a substance and characteristics about the substance as the substance exits the nanochannel apparatus  50  and enters the reservoir  503 .  
      In some embodiments, the embedded sensor  510  is replaced by an embedded electrode, such as a metal or semiconductor gate of a nanofluidic transistor.  FIG. 6  illustrates a nanofluidic transistor  600  according to another embodiment of the present invention. The nanofluidic transistor  600  comprises a nanochannel apparatus  60 , such as that described above for the nanochannel apparatus  50  in  FIG. 5 , that includes a first electrode  610  embedded in the nanochannel apparatus  60 . The nanofluidic transistor  600  further comprises a first fluidic interface  601 , and a second fluidic interface  603 , such as reservoirs  601 ,  603 , for example and not by way of limitation, associated with distal open ends  61 ,  63  of the nanochannel apparatus  60  in much the same way as that described above for the nanofluidic sensor system  500  in  FIG. 5 . The nanofluidic transistor  600  further comprises a source or second electrode  604  interfaced with the first reservoir  601  and a drain or third electrode  606  interfaced with the second reservoir  603 . The nanofluidic transistor  600  controls the flow of fluid through the nanochannel apparatus  60  in the same way as a switch, for example and not by way of limitation. The nanofluidic transistor  600  may further comprise a substrate  602  that supports the nanofluidic transistor  600 .  
      The sensors  510 ,  512  and the electrodes  604 ,  606  and  610  may be fabricated using standard semiconductor processing and materials. For example, the sensor  510  or the electrode  610  may be incorporated into the nanochannel apparatus  50 ,  60  during the fabrication of the nanochannel apparatus. Referring back to the method  200  of fabricating the nanochannel apparatus  20  in  FIG. 2A  and  FIG. 2D , for example, after the nanowires  203  are grown  230  and embedded in the support material  204 , one or both of the sensor  510  and the electrode  610  may be added. In some embodiments, another section of the support material  204  may be removed at a respective location along the horizontal length a of the grown nanowire  203  where the potential sensor  510  or electrode  610  is to be located. Then, the sensor  510  or the electrode  610  may be formed in the respective location using semiconductor processing techniques and materials known in the art. These steps may be performed prior to when a portion of the support material  204  is removed as illustrated in  FIG. 2E  and described above for the fabrication of the nanochannel apparatus  20 .  
      In another example, referring back to the method  400  of fabricating the nanochannel apparatus  40  in  FIG. 4A  and  FIG. 4B , encasing  430  the grown  420  nanowires  403  in the support material  404  may comprise encasing a first portion of the vertical length b of the nanowire  403  in the support material  404 , then depositing material(s) used to form one or both of the sensor  510  and the electrode  610  in a second portion at a respective location along the vertical length b of the nanowires  403  and then, encasing a remaining portion of the vertical length b of the nanowires  403  in the support material  404 , as described above for the nanochannel apparatus  40 .  
      Any of the embodiments of the nanofluidic system  500 ,  600  illustrated in  FIGS. 5A, 5B  and  6  may further comprise a cover or lid that encloses at least the fluidic interfaces  501 ,  503 ,  601 ,  603 . For example and not by way of limitation, the cover or lid may be deposited to extend over the entire system  500 ,  600 , such that the respective sensor  510 ,  512  and electrodes  610 ,  604 ,  606  remain accessible. The cover or lid may include a layer of a material compatible with the use of the nanofluidic system.  
      Thus, there have been described various embodiments of a nanochannel apparatus, a method of fabricating a nanochannel apparatus and a nanofluidic system. It should be understood that the above-described embodiments are merely illustrative of some of the many specific embodiments that represent the principles of the present invention. Clearly, those skilled in the art can readily devise numerous other arrangements without departing from the scope of the present invention as defined by the following claims.