Bottom-up assembly of structures on a substrate
Examples of the present invention include methods of assembling structures, such as nanostructures, at predetermined locations on a substrate. A voltage between spaced-apart electrodes supported by substrate attracts the structures to the substrate, and positional registration can be provided the substrate using topographic features such as wells. Examples of the present invention also include devices, such as electronic and optoelectronic devices, prepared by such methods.
1. A method of assembling structures at predetermined locations on a substrate surface, the method comprising:
providing a substrate assembly, the substrate assembly having the substrate surface,
the substrate assembly including spaced-apart electrodes, the spaced-apart electrodes including a pair of electrodes having an electrode gap therebetween,
the pair of electrodes being covered by a dielectric layer,
the substrate assembly further having topographic features, the topographic features being depressions in the substrate surface;
exposing the substrate surface to a fluid suspension of the structures; and
applying an alternating voltage between the spaced-apart electrodes so as to attract the structures towards the substrate surface,
the topographic features locating the structures at the predetermined locations on the substrate surface,
the alternating voltage inducing an electric field, the electric field having electric field gradients that preferentially attract the structures to the depressions in the substrate surface,
the structures being centered relative to the electrode gap by electrostatic forces between the structures and the spaced-apart electrodes,
positional registration of the structures on the substrate surface being provided by the topographic features.
2. The method of claim 1 , the structures being nanostructures having at least one dimension less than 1 micron.
3. The method of claim 1 , the structures having a shape anisotropy of at least 2:1.
4. The method of claim 1 , the structures being attracted to the substrate surface by a dielectrophoretic force induced by the alternating voltage.
5. The method of claim 1 , wherein the depressions are wells having an elongation direction, the electric field being applied generally parallel to the elongation direction.
6. The method of claim 5 ,
the structures being elongate, the electric field aligning the structures with the elongation direction of the wells.
7. The method of claim 1 , the topographic features being formed in a sacrificial dielectric layer.
8. The method of claim 7 ,
the method further comprising connecting the structures at the predetermined locations by forming an electrical connection between the structures and at least one of the spaced-apart electrodes.
9. The method of claim 7 , further comprising removing structures at locations other than the predetermined locations by selectively removing the sacrificial dielectric layer using a lift-off process.
10. The method of claim 1 , wherein the spaced-apart electrodes are provided by interdigitated electrodes.
11. The method of claim 1 , the substrate including electronic components, the topographic features positioning the structures relative to the electronic components with a positional accuracy of less than 1 micron.
12. The method of claim 11 , the electronic components being CMOS electronic components.
13. The method of claim 1 , further comprising chemically or biochemically functionalizing the structures before assembly of the structures on the substrate,
the method being used to provide an array of analyte-sensitive elements on the substrate.
14. The method of claim 1 , the method providing an array of structures on the surface,
the array of structures having a surface density of at least 1,000,000 elements per square centimeter.
15. The method of claim 1 , the structures being selected from a group of structures consisting of wires, disks, tubes, rings, spheroids, and sheets,
the substrate comprising a substrate material selected from a group of substrate materials consisting of semiconductors, inorganic dielectrics, glasses, ceramics, and polymers.
16. The method of claim 1 , the structures comprising graphene sheets.
17. An apparatus fabricated using the method of claim 1 , the apparatus being an electronic device, an optoelectronic device, or an analyte sensor.
18. A method of assembling a plurality of structures at predetermined locations on a substrate, the plurality of structures including at least a first structure species and a second structure species, the method comprising:
providing the substrate, the substrate having a substrate surface and including a plurality of electrodes, the electrodes being located below the substrate surface and covered by a dielectric layer;
exposing the substrate to a fluid suspension of the first structure species;
applying a first alternating voltage to a first set of electrodes from the plurality of electrodes, so as to assemble the first structure species at a first set of predetermined locations,
the first set of predetermined locations being defined by a first set of depressions in the substrate surface;
exposing the substrate to a fluid suspension of the second structure species; and
applying a second alternating voltage to a second set of electrodes from the plurality of electrodes, so as to assemble the second structure species at a second set of predetermined locations,
the second set of predetermined locations being defined by a second set of depressions in the surface,
thereby assembling the plurality of structures at predetermined locations on the substrate,
positional registration of the first structure species being provided by the first set of topographic features,
positional registration of the second structure species being provided by the second set of topographic features.
19. The method of claim 18 , each structure species having a different chemical or biochemical functionality,
functionalization of the structure species being achieved before exposing the substrate to a fluid suspension of the structure species.
20. The method of claim 19 , structure species being functionalized using DNA before exposing the substrate to a fluid suspension of the structure species.
21. The method of claim 19 , the method being used to assemble a multi-analyte sensor.
22. The method of claim 18 , each structure species having a different semiconductor composition, the method being used to assemble an electronic device or optoelectronic device.
23. The method of claim 18 , the method further comprising:
preparing at least one structure species by growth on a different substrate.
24. A method of assembling structures at predetermined locations on a substrate surface, the method comprising:
providing a substrate, the substrate having the substrate surface,
the substrate including spaced-apart electrodes, the spaced-apart electrodes including a pair of electrodes with an electrode gap therebetween,
the pair of electrodes being buried below the substrate surface by a dielectric layer,
the substrate further having topographic features, the topographic features being depressions in the substrate surface,
the depressions being formed in a sacrificial dielectric layer;
exposing the substrate to a fluid suspension of the structures;
applying an electric field between the spaced-apart electrodes so as to attract the structures towards the substrate,
the topographic features locating the structures at the predetermined locations, so as to assemble the structures at the predetermined locations; and
selectively removing the sacrificial dielectric layer, leaving the structures located at the predetermined locations,
the substrate including electronic components, the structures being in electrical communication with the electronic components after assembly at the predetermined locations,
the positional accuracy of assembled structures relative to at least one electronic component being less than 1 micron.
25. The method of claim 24 , the structures being nanostructures having at least one dimension less than 1 micron.
26. The method of claim 25 , the structures being nanowires.
27. The method of claim 24 , the method further comprising:
connecting the structures to the substrate so as to provide mechanical resonators, and
providing an electronic circuit operable to detect a change in mechanical properties of the mechanical resonators in response to an analyte.
28. The method of claim 24 , further comprising:
connecting the structures to the substrate so as to provide chemoresistive elements, and
providing an electronic circuit operable to detect a change in electrical properties of the chemoresistive elements in response to an analyte.
29. The method of claim 24 , the structures including a semiconductor, the method further comprising:
preparing the structures by growth on a different substrate; and
removing the structures from the different substrate, so as allow preparation of the fluid suspension of the structures.