fabrication of solid state nanopores

1. Fabrication of Solid State Nanopores Presented by Sabina Koukourinkova 28 March 2008

3. Nanopores Definition: a nanoscale pore in an electrically insulating membrane - a biological protein channel in a lipid membrane - a pore in a solid-state membrane (most commonly Si3N4) Detection Principle: - �translocation event� pulse Applications: - DNA sequencing - separation of ssDNA and dsDNA in solution - determining the length of polymers

4. Translocation of a DNA through a Biological Channel: 58mer DNA Strand Passing through a- Hemolysin Transmembrane Pore

5. Translocation of a DNA through a Synthetic Nanopore http://

6. Fabrication of Solid State Nanopores (Overview) Si3N4 thin membranes are deposited by sputtering on a 4-inch Si wafer. Photoresist (PR) is applied to both sides of the wafer. Anisotropic RIE is used to remove the thin layer of Si3N4 not protected by the photoresist Anisotropic Wet Etching uses a chemical agent KOH to remove bulk material from the wafer Focused Ion Beam is used to drill a hole through the free standing membrane

7. Fabrication of Solid State Nanopore (Step-by-Step Method) Wafer (Substrate): A thin piece of superconducting material (Si crystal): 1�� - 11.8�� The mechanical strength of the material determines the thickness of the wafer Fabrication: Czochralski method (1916)

8. Sputter Deposition of Si3N4 on Si Wafer Sputtering (Vacuum Evaporation/ Deposition Technique) Sputtering of light elements (Ne, Ar) versus heavy elements (Kr, Xe) Sputtering of conducting (DC) versus non-conducting materials (radiofrequency)

9. Photoresist (�Masking Material�) Application Remove any moisture from the wafer Clean the wafer from any contaminants Apply �adhesion promoter� HMDS (hexametyldisilazane) Apply viscous liquid photoresist to the wafer Spin the wafer to produce uniform coating 0.5 � 2.5�m: 1200-4800rpm, 30-60s Pre-bake the photoresist (90-100�C, 5-30 min) - removal of excess solvent Expose the photoresist to intense UV light (photolitography) Selectively remove material of a certain pattern using a photomask. Post-bake the photoresist (120�180�C) � solidification

10. Etching Anisotropic Reactive Ion Etching (RIE): precise Isotropic chemical etching: damage to the masking material and erosion of the substrate Wet Anisotropic KOH Etching:

11. Drilling a Hole Creating a hole (FIB): ~100nm Through hole versus blind hole The process can take place at room temperature or temperature as low as -120�C Focused ion beam (FIB): Ga LMIS (liquid metal ion source) Tungsten needle and heat Ionization of Ga, E= 5-50KeV

12. Sculpting of the Nanopore FIB Exposure Ga+ are implanted in the surface (amorphous surface): Hole closing Signal from ejected particles is collected to form an image Drawback: Hard to control the size of the hole Continuous sputtering of material during imaging of the hole Sculpting of the nanopore: Hole closing: large scan area and low rate of sputtering Hole opening: small scan area and high sputtering rate

13. Sculpting of the Nanopore Broad Area Ion Exposure: Ar+ source beam Ion Beam Sculpting Apparatus: close/open nanopores

14. Schematic of Ion Beam Sculpting Apparatus(Physics Dept., University of Arkansas)

15. Sculpting of Nanopores: Sputtering versus Lateral Mass Transport

16. Lateral Mass Transport Phenomenon which occurs when a surface of a solid is bombarded with heavy ion beams resulting in surface deformation

17. Lateral Mass Transport Ditch and Dike Formation (3D) The solid has to be deformable Sin? Cos? Dependence: ?: angle between the incident ion beam to the normal of the surface Sin ?: the direction of the mass transfer is in the direction of the off-normal component of the momentum parallel to the surface Cos ?: as ? increases, the incident beam penetrates less deep into surface, and results in lateral mass transport. Amount of Mass Displaced

18. Ion Beam Sculpting Apparatus Lateral mass transport is induced on the surface of a nanopore more quickly with heavier rather than lighter ions The thickness of the lateral mass build-up depends on the penetration depth of the ions: Heavier ions have less penetration depth, and so form thinner coating The flux of the ion beam is inversely proportional to the effectiveness of closing the pore. The size of the hole is affected by temperature changes For a constant flux and ion mass, the size of the hole is inversely related to the variable temperature.

19. Closing of a Nanopore

20. References: Aleksij Aksimentiev, Jiunn B. Heng, Gregory Timp and Klaus Schulten.Microscopic Kinetics of DNA Translocation through Synthetic Nanopores <www.biophysj.org/cgi/content/full/87/3/2086> Alpha-Hemolysin: Self-Assembling Transmembrane Pore. <http://www.ks.uiuc.edu/Research/hemolysin/> Bradley Ledden, Eric Krueger, Jiali Li. Study of Nanopore Sculpting with Noble Gas Ion Beams at Various Energies. 2006 APS Meeting: Poster Session II. Derek M. Stein, Ciaran J. McMullan, Jiali Li. Feedback-controlled Ion Beam Sculpting Apparatus. Rev. Sci. Instrum 75, 4 (2004) Introduction: Focused Ion Beam Systems < http://www.fibics.com/FIBBasics.html> Ion Beam Sculpting. <http://en.wikipedia.org/wiki/Ion-beam_sculpting> M. Chicoin, S. Roorda, and L. Clich�. Directional effects during ion implantation: Lateral mass transport and anisotropic growth. Phys Rev. B 56, 3 (1997) Nanopore. <http://en.wikipedia.org/wiki/Nanopore> Photolitography. <http://en.wikipedia.org/wiki/Photolithography> Qun Cai, Brad Ledden, and Eric Krueger. Nanopore Sculpting with Noble Gas Ions. J. Appl. Phys 100, 024914 (2006) Wafer (Electronics). <http://en.wikipedia.org/wiki/Wafer_%28electronics%29> What is Sputtering? <http://www.tcbonding.com/sputtering.html>