Parallel Alignment of Nanowires for Fast Fabrication of Nanowire Based Gas Sensors

Transcription

1 Parallel Alignment of Nanowires for Fast Fabrication of Nanowire Based Gas Sensors R. Jiménez-Díaz 1, J.D. Prades 1 F. Hernández-Ramírez, J. Santander 3 C. Calaza 3, L. Fonseca 3, C. Cané 3 A. Romano-Rodriguez 1 1 MIND-IN UB, Dept. Electrònica, Universitat de Barcelona, Spain IREC, Barcelona, Spain 3 Instituto de Microelectrónica de Barcelona, IMB-CNM-CSIC, Bellaterra, Spain Previous work Nanowires offer attractive features to improve many of the issues in solid state gas sensors

2 Previous work Sensitivity Adv. Funct. Mater. 18, 99 (8) Previous work Stability Nanotechnol. 18, (7) Sens.Actuatators B 144, 1 (1)

3 Previous work Response time PCCP 11, 715 (9) Previous work Working temperature response S(%) UV - OFF (T=5ºC) UV - ON (T=5ºC) 1 1 [NO ] (ppm) time (minutes) Sens. Actuators B 14, 337 (9) PCCP, in press (1)

4 Previous work Power consumption very low power consumption: less than μw (measurement AND HEATING included!!!) APL 93, 1311 (8) APL 95, 5311 (9) Previous work Nanowires offer attractive features to improve many of the issues in solid state gas sensors Sensitivity radius response Stability pristine surface fully reversible response Response time indiv. nanowire no gas diffusion Working temperature UV light room temperature operation Power consumption indiv. nanowire self-heating effect ultra-low power consumption fully autonomous gas sensors faster devices Challenge: dealing with nanofabrication issues

5 Contacting & Measuring One Single Nanowire Dual-beam Focused-Ion Beam Ion-assisted deposited platinum stripe among 4 gold microelectrodes Deposit Pt-containing material (from PtC 9 H 16 ) Auger Electron Spectr.: C (67%) + Pt (7%) With ions or with electrons ρ ions = 1 ρ Pt-metal ρ electrons = 1 5 ρ Pt-metal 1 1 A/m Thermally stable up to 65 K Contacting & Measuring One Single Nanowire Nanowires are dispersed over a substrate with pre-patterned patterned μelectrodes SnO Nanowires Nanotechnology 17, (6)

6 Contacting & Measuring One Single Nanowire Nanolithography Process - Sequential e-beam e & i-beam i depositions L = 11 μm r 5 nm Nanotechnology 17, (6) - Platinum contacts - Reproducible process - Can be used on demand Contacting & Measuring One Single Nanowire Electrical Characterization (- & 4-probes) Metal oxide NW Mostly non-ohmic responses High contact resistances Study of the NW requires 4p Current (na) Self-heating at contacts Voltage (V) Nanotechnology 17, (6) Physical Review B 76, 8549 (7)

7 Dielectrophoretic alignment of NWs Self-assembly technique When a polarizable NW is subject to a non-uniform electric field a dipole moment is induced that tends to align the nanowire in the direction of the electric field Proof of concept experiments Dielectrophoretical force when applying an electrical field in a dielectric medium: 1 FDEP = π r l ε m Re{ K} E RMS 6x1 5 ω Re{ K} = ( ε ε ε ) + ( σ σ σ ) m p m ε m ω + σ m p m m 5x1 5 4 Re{K} (a.u.) 4x1 5 3x1 5 x1 5 1x1 5 Re{K} Experimental results Alignment Yield (a.u.) Frequency (Hz) Dielectrophoretic alignment of NWs Design of electrodes Based on big electrodes with sharp tips opposed. Gaps of different lengths Au SiO Au Au SiO SiO Au Au SiO SiO

8 Dielectrophoretic alignment of NWs Results on alignment of nanowires: Dielectrophoretic alignment of NWs Big difference! BEFORE NOW!

9 Dielectrophoretic alignment of NWs -probes configuration rectifying behavior Schottky diodes (NW // Pt FIB). Phys.Rev.B 76, 8549 (7) 4-probes configuration SnO -NW ρ EIB =.4 ±. (Ωcm) -1 ρ DEP =.38 ±. (Ωcm) -1 Gas Sensor Measurements Carbon monoxide Aligned SnO -NW Diameter: 9nm R CO /R SA 1,,8,6,4, R CO /R SA at T = 375 K R CO /R SA at T = 45 K CO concentration, time (hours) [CO] (ppm)

10 Gas Sensor Measurements Comparison with non-dep experiments: Adv. Funct. Mater. 18, 99 (8) Conclusions Individual NWs can be electrically contacted with the help of FIB lithography techniques Gas nanosensors can be fabricated using these techniques, responding to different gases (SA, N, CO, H O) Alignment of nanowires by dielectrophoretic feasible techniques is Gas nanosensors with equivalent properties as non-dep aligned NWs can be fabricated This allows the increase of the throughput in gas sensor fabrication based on individual NWs

11 Acknowledgments This work was partially supported by: European Union through projects NANOS4 and ARI (Access to Research Infrastructures) Spanish Ministry of Science and Technology, through the projects MAGASENS, CROMINA and NAWACS (NanoSciERA programme) and FPU grants. This work has been developed partially using the capacities of ICTS Clean room of micro & nano fabrication of IMB-CNM (CSIC). Thank you all for your attention!