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Contacting nanowires!

Contacting nanowires!. Groupmeeting 22-02-06 Christianne. Outline. Introduction The sample: CNT’s in suspension The contacts Outlook. Introduction. OR. EBPG. FEI NanoSEM. Fabrication process & current status. CNTs. Ethanol Hexane Chlorobenzene 1,2-Dichloroethane.

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Contacting nanowires!

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  1. Contacting nanowires! Groupmeeting 22-02-06 Christianne

  2. Outline • Introduction • The sample: CNT’s in suspension • The contacts • Outlook

  3. Introduction OR EBPG FEI NanoSEM • Fabrication process & current status

  4. CNTs • Ethanol • Hexane • Chlorobenzene • 1,2-Dichloroethane • 1,2-Dichloroethane ClCH2CH2Cl CH3CH2OH Apolar! CH3(CH2)4CH3 Recipe: • Ultrasonic bath ~ 30 min • Deposit a droplet on substrate • Wait until all solvent has evaporated ClCH2CH2Cl A stable suspension of CNTs should results!

  5. CNTs Length : ~ 300 – 500 nm

  6. EBPG • Write marker field (alignment) Lift-off Size: 5 x 5 μm Separation: 100 μm

  7. EBPG • Write marker field (alignment) • Deposit suspension on substrate

  8. EBPG • Write marker field (alignment) • Deposit suspension on substrate • Locate a CNT suitable for contacting • SEM • To much Carbon deposition • AFM • Need to “tag” the markers • Scan range of AFM smaller than marker separation • FEI NanoSEM • Easy to measure location of CNT • Much less Carbon deposition, cryo pump

  9. d ~ 30 nm d ~ 15 nm

  10. EBPG • Write marker field (alignment) • Deposit suspension on substrate • Locate a CNT suitable for contacting • Write mesoscopic contacts

  11. EBPG Dimensions in nm 500 500 500 250 250 400 400 Minimum length CNT: 3 μm!

  12. EBPG • Write marker field (alignment) • Deposit suspension on substrate • Locate a CNT suitable for contacting • Write mesoscopic contacts • Write macroscopic contacts

  13. EBPG • Three separate writing + sputtering steps. • Lift of: requires CNT larger than 3 μm.

  14. FEI NanoSEM • Write marker field EBPG (alignment) • Deposit suspension on substrate • Locate CNT suitable for contacting • Deposit structure with GIS (mesoscopic contacts) • Write macroscopic contacts with EBPG + sputtering

  15. FEI NanoSEM GIS deposition Electrons decompose adsorbed gas Possible materials: Pt, W, Au, Co, Fe and Pd

  16. FEI NanoSEM GIS deposition One GIS: Methylcyclopentadienyl trimethyl platinum Exposure: nonvolatile compounds formed Compounds should leave the substrate!

  17. FEI NanoSEM GIS deposition Strip: t = 500 nm w = 800 nm l = 6.5 μm Low Pt concentration! Can we improve conductivity?

  18. FEI NanoSEM GIS deposition Add H2O/O2 during deposition • Needle valve (H2O/O2) • Second GIS (H2O) Heating MgSO4 7H2O Substrate heating & annealing Low vacuum detector needed When mounted, impossible to insertGIS Aaltonen et al. Chem. Mater. 15, 1924, 2003 CVD deposition T = 200 – 350 °C Thermal decomposition of precursor ρ ~ 20 10-6 Ω cm! Tests by FEI lab show improvement: ρ ~ 1 Ω cm ρ ~ 5 10-2Ω cm Au : ρ ~ 2 10-6Ω cm!

  19. FEI NanoSEM GIS deposition Another option: Tungsten deposition Need second GIS Tungsten hexacarbonyl IBID results (FEI lab) show quality W is better than Pt

  20. FEI NanoSEM • Only two EBPG steps required • No limitations on length CNT • Pt not suitable as contact material

  21. Outlook • For now use EBPG for contacting • Implement GIS/needle valve for H2O/O2 • Implement GIS W deposition • Resistivity measurements on Pt and W strips

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