Bottom-up Nanostructures just a research hype?

Fakultät Maschinenwesen, Institut für Werkstoffwissenschaft, Professur Materialwissenschaft u. Nanotechnik Bottom-up Nanostructures just a research hype? Dr.-Ing. Alexander Nerowski Dresden, 22.09.2017 Pd Coaly flower

Why (bottom-up) Nano? Today s applications of nanotechnology Zinc-Oxide Nanoparticles UV light diffraction Lotos effect (paint, cars ) Catalyst Dr. A. Nerowski Folie Nr. 2/19

Top-Down vs. Bottom-Up E Photoresist Substrate Silicon Nanowire 5 nm R. G. Hobbs et al. Chem. Mater. 24, 1975 (2012) Well defined, integrated structures For < 500 nm: relatively expensive equipment (e.g. e-beam lithography) Surface tension, external fields Silicon Nanowire with 3D kink 200 nm Relatively well defined structures 3D structures feasible Hard to integrate into microcircuits B. Tian et al. Science 329, 830 (2010) Dr. A. Nerowski Folie Nr. 3/19

Content 1. (Example for) Fabrication of Metal Nanowires 2. (Example for) Metal Nanowire Sensor Application 3. (Example for) Silicon Nanowire Sensor Application 4. Conclusion & Outlook Dr. A. Nerowski Folie Nr. 4/19

1. Fabrication of Metal Nanowires Combining bottom-up and top-down Au Au Insulating substrate Dr. A. Nerowski Folie Nr. 5/19

1. Fabrication of Metal Nanowires Combining bottom-up and top-down Pt containing solution Au Au Insulating substrate Dr. A. Nerowski Folie Nr. 6/19

1. Fabrication of Metal Nanowires Combining bottom-up and top-down V 0, f ~ Pt containing solution Au Pt nanowire Insulating substrate Au Advantages Integration Costs Speed Conditions (T, p) Dr. A. Nerowski Folie Nr. 7/19

1. Fabrication of Metal Nanowires Combining bottom-up and top-down V 0, f ~ Pt containing solution Au Pt nanowire Insulating substrate Au Advantages Integration Costs Speed Conditions (T, p) Dr. A. Nerowski Folie Nr. 8/19

1. Fabrication of Metal Nanowires Challenges 2 µm 1 µm 1 µm Growth influenced by many parameters Voltage Frequency Solution type Concentration of solution Goal: growth control straight, thin and unbranched wires Dr. A. Nerowski Folie Nr. 9/19

1. Fabrication of Metal Nanowires Nanowire is modeled as sphere capacitor Flux of Pt complexes j is influenced by: r 0 r Dielectrophoretic force Concentration gradient F DEP c Tip Boundary conditions: A. Nerowski & M. Poetschke et al. Langmuir 28, 7498 (2012) Far from tip (r ): bulk concentration c At tip surface: reaction rate k r (T) Resulting differential equation for concentration c: 2 cr () r L FDEP kbt log 0 r r c Convection Diffusion Dr. A. Nerowski Folie Nr. 10/19

Growth velocity v g [nm/s] 1. Fabrication of Metal Nanowires Growth kinetics temperature dependence Reaction limitation Diffusion limitation 30 Experimental data for c = 10 µm Fitted curves 20 10 0 288 293 298 303 308 313 318 Temperature T [K] Qualitative agreement with theory A. Nerowski & M. Poetschke et al. Langmuir 28, 7498 (2012) Dr. A. Nerowski Folie Nr. 11/19

1. Fabrication of Metal Nanowires Morphology: Signal variation N=2 N=3 N=5 N Scalebars: 500 nm Variation of voltage slope during polarity change Morphology from branched to straight A. Nerowski et al. Langmuir 30, 5655 (2014) 200 nm 20 nm Dr. A. Nerowski Folie Nr. 12/19

2. Metal Nanowire Sensor Application Impedimetric nanobiosensor 2 µm Solution with bacteria 120 nm Nanogap with bacterium.5 µm Production of nanogap using electromigration Dielectrophoretic attraction of nanoscaled objects into gap Electrical impedance measurement of single objects A. Nerowski et al., Utility patent DE 20 2013 002 076.8 Dr. A. Nerowski Folie Nr. 13/19

-Reactance X p [GΩ] 2. Metal Nanowire Sensor Application 200 2 µm 10 100 0 1 0.1 10 2 10 3 Before trapping 10 1 10 2 10 3 10 4 Frequency f [Hz] After trapping Impedance spectroscopy of E. Coli reveals parallel RC-circuit in accordance with literature (50 GΩ, 3 ff) High frequencies: substrate resistance is equal to analyte resistance A. Nerowski et al., Utility patent DE 20 2013 002 076.8 Dr. A. Nerowski Folie Nr. 14/19

3. Silicon Nanowire Sensor Application Microfluidic ph sensor(s) Bubbles with analyte pass nanostructures Sensitive, optics-less analysis of biochemical processes Use of a single device for thousands of independent sensors J. Schuett et al. Nano Lett. 16, 4991 (2016) Dr. A. Nerowski Folie Nr. 15/19

3. Silicon Nanowire Sensor Application Droplet microfluidics with silicon nanowire based FET Increase in current when droplet passes Current characteristics dependent on size of droplet Current amplitude dependent on content of bubble Here: ph-sensor, but also others feasible J. Schuett et al. Nano Lett. 16, 4991 (2016) Dr. A. Nerowski Folie Nr. 16/19

Conclusion for Bottom-Up Nanotechnology Research hype? Already: Fabrication of controlled bottom-up nanostructures on industry scale Electronics like OLED TVs Research in applications still ongoing: Biosensorics Chemosensorics ToDo: Environmental sustainability/health, longevity Dr. A. Nerowski Folie Nr. 17/19

Acknowledgements Thanks to: Prof. Cuniberti, Dr. Baraban, Dr. Bobeth and my PhD colleagues at Max- Bergmann-Center! This work was supported by the European Union (European Social Fund) and the Free State of Saxony (Sächsische Aufbaubank) in the young researcher group "InnovaSens" (SAB-Nr. 080942409). Support from the German Excellence Initiative via the Cluster of Excellence EXC 1056 "Center for Advancing Electronics Dresden" (cfaed) is gratefully acknowledged. Funded by the European Union and the Free State of Saxony