Ultra-long silicon nanostructures, and methods of forming and transferring the same
View Patent ↗Under one aspect, a plurality of silicon nanostructures is provided. Each of the silicon nanostructures includes a length and a cross-section, the cross-section being substantially constant along the length, the length being at least 100 microns. Under another aspect, a method of making nanostructures is provided that includes providing a silicon wafer including a thickness and first and second surfaces separated from one another by the thickness; forming a patterned layer of metal on the first surface of the silicon wafer; generating a current through the thickness of the silicon wafer, the metal oxidizing the silicon wafer in a region beneath the patterned layer of the metal; and exposing the silicon wafer to an etchant in the presence of the current, the etchant removing the oxidized region of the silicon wafer so as to define a plurality of nanostructures. Methods of transferring nanowires also are provided.
1. A method of making nanostructures, the method comprising:
providing a silicon wafer including a thickness and first and second surfaces separated from one another by the thickness;
forming a patterned layer of metal on the first surface of the silicon wafer;
generating a current through the thickness of the silicon wafer, the metal oxidizing the silicon wafer in a region beneath the patterned layer of the metal; and
exposing the silicon wafer to an etchant in the presence of the current, the etchant removing the oxidized region of the silicon wafer so as to define a plurality of nanostructures.
2. The method of claim 1 , each of the silicon nanostructures including a length of at least 100 microns.
3. The method of claim 1 , each of the silicon nanostructures including a length of at least 250 microns.
4. The method of claim 1 , each of the silicon nanostructures including a length of at least 500 microns.
5. The method of claim 1 , the current flowing in a direction that is substantially perpendicular to the first and second surfaces.
6. The method of claim 1 , comprising generating the current with first and second electrodes.
7. The method of claim 1 , comprising generating the current by illuminating the silicon wafer with light.
8. The method of claim 1 , wherein the patterned layer of metal defines a plurality of rectangularly shaped apertures, and the nanostructures include rectangularly shaped cross-sections substantially corresponding to the plurality of rectangularly shaped apertures.
9. The method of claim 8 , wherein the rectangularly shaped apertures are elongated, and wherein the nanostructures include nanoribbons.
10. The method of claim 1 , wherein the patterned layer of metal defines a plurality of curved apertures, and the nanostructures include curved cross sections substantially corresponding to the plurality of curved apertures.
11. The method of claim 10 , wherein the plurality of curved apertures include circles.
12. A method of transferring nanowires, the method comprising:
providing a plurality of nanostructures coupled to a silicon wafer, each nanowire including a length and a cross-sectional area;
generating a current along the lengths of the nanowires; and
exposing the nanowires and the silicon wafer to an etchant in the presence of a current, the etchant weakening the coupling between the nanowires and the silicon wafer.
13. The method of claim 12 , each of the silicon nanostructures including a length of at least 100 microns.
14. The method of claim 12 , each of the silicon nanostructures including a length of at least 250 microns.
15. The method of claim 12 , each of the silicon nanostructures including a length of at least 500 microns.