Physics 18 05

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Precision Chemical Engineering Presentation at the Nanoscale Physics Seminar Series University of Birmingham 18th May 2005 - Jon A Preece - School of Chemistry, University of Birmingham j.a.preece@bham.ac.uk www.nanochem.bham.ac.uk www.crnnt.bham.ac.uk

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[1] Getting the Nano Length Scale into Perspective Bottom-Up Molecules and Biomolecules (Bio)molecular devices Top-Down Moore’s Law [2] Covergence of Bottom-Up and Top-Down [3] Integrating Bottom-Up and Top-Down Part 1: Writing Foundations with Electrons Part 2: Laying the Building Blocks Part 3: Writing to the Building Blocks with Electrons Part 4: Writing to the Building Blocks with Photons Part 5: Making Nanoelectronic Measurements [4] Conclusions Precision Chemical Engineering Outline of Talk

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The Molecular Length Scale

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Ethane C-C Bond 1.543 Å or 0.1543 nm or ~1/6 of a nanometer How Big is a Molecule?

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About as big as chemists have achieved as discrete molecular species

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The Biomolecular Length Scale and Function

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The biological example of writing information on a small scale has inspired me to think of something that should be possible. Biology is not simply writing information; it is doing something about it. A biological system can be exceedingly small. Many of the cells are very tiny, but they are very active; they manufacture various substances; they walk around; they wiggle; and they do all kinds of marvellous things – all on a very small scale. Also, they store information. Consider the possibility that we too can make a thing very small which does what we want – that we can manufacture an object that manoeuvres at that level! Richard Feynman (Nobel Laureate) There's Plenty of Room at the Bottom (1960) http://nano.xerox.com/nanotech/feynman.html What Nature’s Molecules Do?

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The cell's contact with the outer world  The wall that separates a cell from its surroundings - the membrane - is not an impermeable shell. It is pierced through by various sorts of protein channels. Proteins in Cell Membranes http://www.nobel.se/chemistry/laureates/2003/index.html The channels consist of proteins, each with its own function.

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Biological Nanotechnology Proteins Phospholipids Sugars Extreme Nanotechnology! And Extremely Old!

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Photosynthesis: A Biological Nano-Antenna

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20 nm Size not only brings complex nanoarchitectures but also function. Photosynthesis Chemical Energy

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Input Processing Output Vision Mechanism

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20 nm A Virus (adenovirus) 50 nm 252 proteins A Virus: A Nano-Robot [1] Uses a host to infect another host [2] Seeks out cells in the host [3] Recognises host cells [4] Docks onto the host cells [5] Ruptures the cell [6] Delivers its DNA into the cell [7] Replicates itself [8] Back to [1]

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The Molecular Length Scale and Function

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A Molecular Machine ‘Photochemical and Electrochemical Control of Molecular and Supramolecular Switches’ P.R. Ashton, S.E. Boyd, R. Ballardini, V. Balzani, A. Credi, M.T. Gandolfi, M. Gomez, S. Iqbal, D. Philp, J.A. Preece, H.G. Ricketts, J.F. Stoddart, M.S. Tolley, M. Venturi, D.J. Williams, and A.J.P. White, Chem. Eur. J., 1997, 3, 152-170. +2e -2e Purple Solution Colourless Solution ON State OFF State Binary Logic

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A Molecular Machine R.A. Bissell, E. Córdova, A.E. Kaifer and J.F. Stoddart, Nature, 1994, 369, 133-137. State 1 State 2 5 nm -1e

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Logic Operations With Molecules Prof AP de Silva An AND operator no no no no yes no yes no no yes yes yes Light Absorbed Na+ Added Light Emitted Input 1 Input 2 Output 0 0 0 0 1 0 1 0 0 1 1 1

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Problem These molecular machines and molecular logic gates are all solution based. i.e. they are moving about with millions of other molecules in solution. Therefore, it is not possible to write information to an individual molecule(s). And then read the information back from the same molecule(s) later. Solution The molecules need to be fixed in space. Attach the molecules to a surface and wire them up…simple!

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How Far is the World of Microelectronics from the Nanoscale?

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100 molecules of Benzene or 50 C60s Between the Source and Drain A Human Hair ~100 mm (0.1 mm) (100 000 nm) 1111 Transistors across a human hair Molecules, Biomolecules and the Intel Pentium Chip Microelectronics is now nanoelectronics Sizes of commercially lithographically produced materials are the size of biological entities.

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Electron Beam Lithography can create structuresof less than 10 nm. Bottom-up is meeting Top-Down Length Scales for Top-D and B-Up Scales Compared The molecular world has met the engineered world

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What strikes one is that the top-down engineering and bottom-up self-assembly and self-organisation are converging. This raises the question where does the engineering stop and the (bio)chemistry begin, on the nanoscale? Precision Chemical Engineering… Central to the Preece Research is integrating top-down and bottom-up approaches for making nanostructures.

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Precision Chemical Engineering

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Methodologies for Integrating Top-Down and Bottom-Up Chemistry SAM Formation Engineering Lithographically Writing Chemistry Chemistry Assembly Chemistry Assembly Engineering Lithographically Writing Chemistry Chemistry Dis-Assembly Structures will not only have chemical properties but mechanical properties

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The m-Nano Device Top-Down Lithography Bottom-up Self-assembly Integration of top-down engineering and bottom-up self-assembly allows the potential for a scaleable strategy single electron devices, and other devices requiring sub 100 nm structures.

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Part 1 Lithography: Chemically Modifying Surfaces ‘The Chemical Modification of an Organic Nitro Group to an Organic Amine Group by X-Ray Photoelectron Radiation’ P. Mendes, M. Belloni, M. Ashworth, C. Hardy, K. Nikitin, D. Fitzmaurice, K. Critchley, S.D. Evans, J.A. Preece ChemPhysChem, 2003, 4, 884-889 .

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e b e a m W. Eck, V. Stadler, W. Geyer, M. Zharnikov, A. Gölzhäuser, M. Grunze, Adv. Mater. 2000, 12, 805-808. Writing with X-Rays and Electrons

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Film Formation Immerse Si/SiO2 into 5 mM/anhy. THF under Ar (Sonication at 25°C) Reaction times: 2 hours Sonicate twice in fresh THF for 5 min Rinse intensively with CHCl3, EtOH and UHP H2O Dry under Ar Film Characterisation: Contact Angle (surface type) AFM (roughness) Elipsometry (thickness) XPS (elemental composition) NPPTMS Procedure from: N. Tillman, A. Ulman, J.S. Schildkraut, TL. Penner, J. Am. Chem. Soc., 1988, 110, 6136-6144. SAM on Si/SiO2

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Patterning: Mask and Parallel Exposure to Radiation NO2 Terminated SAM Electron energy = 5 and 6 keV Doses = 50 to 100 µCcm-2,

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Patterning: Direct-Beam Writing primary beam energy = 5 and 6 keV doses between = 25 and 300 µCcm-2

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Part 2 Self Organisation: Sticking Particles to the Surface ‘Gold Nanoparticle Patterning of Silicon Wafers Using Chemical e-Beam Lithography’ P. Mendes, S. Jacke, Y. Chen, S.D. Evans, K. Kritchley, K. Nikitin, R. E. Palmer, D. Fitzmaurice, J.A. Preece Langmuir, 2004, 20, 3766-3768. ‘Integrating Nanolithography and Nanoassembly: Does Precision Chemical Engineering Hold the Key to Future Nanofabrication?’ P.M. Mendes, J.A. Preece RSC Materials Chemistry Forum, Issue 6, 2004, 8-9.

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Adsorbing the Nanoparticles to SiO2 Substrates NO2 NH2 Karine Mougin, Hamidou Haidara, G. Castelein Colloids and Surfaces A: Physicochemical and Engineering Aspects 2001, 193, 231–237 Controlling the two-dimensional adhesion and organization of colloidal gold nanoparticles

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Au Nanoparticle Citrate Stabiliser The Mechanism of Interaction pH-Dependent Adsorption of Gold Nanoparticles on Aminothiophenol-Modified Gold Substrates Tao Zhu, Xiaoyi Fu, Tao Mu, Jian Wang, Zhongfan Liu Langmuir 1999, 15, 5197-5199

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Adsorption of Particles to e-Beam Patterned Surface at pH 4.5

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90 nm And Our Smallest Result to Date!

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Part 3 Making Gold Nanowires With Electrons: E-Beam Lithography ‘Dialkyl Sulfides: Novel Passivating Agents for Gold Nanoparticles’ E.J. Shelley, D. Ryan, M. Couillard, D. Fitzmaurice, R.E. Palmer, P.D. Nellist, J.A. Preece, Y. Chen. Langmuir, 2002, 18, 1791-1795. ‘HREELS Studies of Gold Nanoparticles with Dialkyl Sulfide Ligands’ Y. Chen, R.E. Palmer, E.J. Shelley, J.A. Preece. Surface Science, 2002, 502/503, 208-213. ‘Nanostructures From Nanoparticles’ P. Mendes, Y. Chen, R. E. Palmer, K. Nikitin, D. Fitzmaurice, J.A. Preece, J. Phys.: Condens. Matter, 2003, 15, S3047-S3063.

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The nanopartices are rinsed away with an organic solvent, leaving the gold nanowire. Writing Gold Nanowires: Negative Tone E-Beam Resist Gold nanoparticles fuse together, and organic evaporates in UHV.

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Organic passivant stops the nanoparticles aggregating Gold-Thiolate Bond The Organic Passivant

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E-beam degrades the passivant, leaving carbonaceous residue in the gold. Not exactly a good conductor. But

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SAM on planar gold formed from dialkylsulfides Dialkyl Sulfides SAM on planar gold formed from alkylthiols Au-S Bond = 60 kJ mol-1 A New Passivant for Gold Nanoparticles Alkyl Thiols R.G. Nuzzo, F.A. Fusco, D.L. Allara J. Am. Chem. Soc., 1987, 109, 2358 E.B. Troughton, C.D. Bain, G.M. Whitesides Langmuir, 1988, 4, 365

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Synthesis of Nanoparticles HAuCl4 (H2O) N(Oct)4Br (PhMe) 45 minutes Separate PhMe layer Precipitation (MeCN) Centrifugation Brust, M.; Walker, M.; Bethell, D.; Schiffrin, D. J.; Whyman, R. J. Chem. Soc., Chem. Commun. 1994, 801. Inoue, K.; Shinkai, S.; Huskens, J.; Reinhoudt, D. J. Mater. Chem. 2001, 11, 1919.

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TEM Characterisation H21C10SC10H21: 5.31 ± 0.76 nm (H21C10SH: 2.21 ± 0.12 nm) Nanoparticles assembled on graphite from solution (CDCl3) drop. 1 mg ml-1 on HOPG

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1H NMR Characterisation a g b IR (1265 cm-1) Oxidation in SAMs: M.T. Lee, C.C. Hsueh, M.S. Freund, G.S. Ferguson Langmuir, 1998, 14, 6419

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Exposure of Nanoparticles to Electrons HREELS

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Writing Nanogaps with an e-Beam SEM Image

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Part 4 Making Gold Nanowires with Photons: Scanning Near Field Photolithography S. Sun,a P.M. Mendes,b K. Kritchley,c S.D. Evans,c G.J. Leggett,a J.A. Preeceb Manuscript Submitted. aSchool of Chemistry, University of Sheffield bSchool of Chemistry, University of Birmingham cSchool of Physics, University of Leeds

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Background: Organic Photochemistry On Planar Gold Surfaces Brewer NJ, Rawsterne RE, Kothari S, Leggett GJ. Oxidation of self-assembled monolayers by UV light with a wavelength of 254 nm. J. Am. Chem. Soc. 2001, 123, 4089. Strong Interaction Weaker Interaction

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S N O M Background: Scanning Near Field Photolithography Nanoscale Molecular Patterns Fabricated by Using Scanning Near-Field Optical Lithography Shuqing Sun, Karen S. L. Chong, and Graham J. Leggett J. Am. Chem. Soc., 2002, 124, 2414 Planar Surface

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Proposal: Extending to non-Planar Gold Surfaces

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Making 3D Micron Scale Structures Decane thiol passivated gold nanoparticles (1-3 nm) M. Brust, M. Walker, D. Bethell, D. J. Schiffrin, R. Whyman, J. Chem. Soc., Chem. Commun., 1994, 801-802. The nanoparticulate film was spincoated

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Film shrinks upon irradiation Unirradiated particles rinse away Irradiating the Surface: AFM Images

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Before Irradiation Chemistry on Sulfur: XPS Au S-R Au SO3-R

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Proposal: Scanning Near Field Photolithography (SNP)

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250 x 14 nm ‘Wires’ Some differences to micron scale structures [1] Not pitted [2] Sonication removes structure from surface [3] Structure is tented

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Part 5 Nanoelectronic Measurements: Some Interesting Chemistry! M. Biancardo,a A.J. Quinn,a L. Floyd,a P.M. Mendes,b S.S. Briggs,b J.A. Preece,b C.A. Bignozzi,c G. Redmonda Manuscript Submitted. aTyndall Institute (formerly the NMRC), University of Cork bSchool of Chemistry, University of Birmingham cSchool of Chemistry, University of Ferrara

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Au Cr 80 nm 8 mm 100 nm 10 nm 300 K a.c. (frequency 20 – 800 kHz) Evaporation of Water/Ethanol Solution of Particles Internanoparticle separation ~ 1 nm Metallic lustre across the whole chip and TEM Probing the Low Frequency Charge Transport Mechanism: Room Temp Impedance Spectroscopy

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Skewed arc: indicates the nanoparticle assembly behaves as network of parallel resistor-capacitor elements The array is an insulator No inductive component to the impedance: indicates no strong (i.e. metallic) internanoparticle coupling (despite the metallic sheen of the layer) Low value of t (1.1 ms) related to electron transfer

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The low value of t (1.1 ms), which is related to electron transfer suggests either: • large internanoparticle separation, and therefore a low electron transfer rate This is ruled out because of metallic sheen and SEM data suggesting close interparticle separation • slow environmental process associated with charge transport, such as re-organization of the capping ligand This is ruled out because it is several orders of magnitude greater that values associated with electronic or vibrational transitions • ionic motion linked to proton transfer….interesting for a chemist….. precision chemical electrical engineering!

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Au Cr 80 nm 50 nm 25 nm 5 nm 5 nm T = 3 K – 400 K d.c. Internanoparticle separation ~ 1 nm Metallic lustre across the whole chip _ + e Probing I-V Characteristics on the Nanoscale: Proton Transfer?

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Linear I-V Characteristics Charging Energy, Ec = 31 meV Electron tunnel transport through an array of discrete metal islands, separated by insulating barriers (the organic passivant). What was expected Probing I-V Characteristics at 80 k and Above Nothing particularly interesting. At least not for a chemist!!

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38 K 4 K (1st) 4 K (2nd) Probing I-V Characteristics Below 40 K Hysteresis at 4 K Reorganisation of the nanoparticles in the film, through the hydrogen bonded network, via proton transfer… At least that is the proposed mechanism! Reproducible Hysteresis on second run Potential sensor or memory device More interesting for the chemist as we now have the possibility of developing integrated nanoparticle sensors or memory devices via the tuning of the ligand chemistry Non-Linear I-V Characteristics Electrons tunnelling through the film only after a threshold voltage is reached…Coulomb Blockade

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-6.5 4.8 10 16 50 4.4 Probing the Proposed Mechanism: pKa Modulation Strong acid Weak acid Hysteresis Reduces? Hysteresis Increases? Designing the Electronics With Chemistry…to be continued…

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Conclusions and Outlook

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Precision Chemical Engineering The term precision chemical engineering encapsulates [1] the precision engineering of writing to surfaces in a spatially controlled fashion to direct the surface chemistry. [2] the engineering that is involved in fabricating three- dimensional nanoarchitectures from the surface from molecular and condensed phase entities. [3] the chemical interactions required to control the assembly. [4] the fact that the three-dimensional architectures are held together by both mechanical and chemical interactions. The integration of the top-down and bottom-up methodologies is representing a new paradigm for creating nanostructured surfaces with function.

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Outlook: Self-Assembling Nanochannels EC Project: Nano3D: Precision Chemical Nanoengineering 2M Euro: 5 Academics 2 Industrial Partners Fabrication of environmentally adaptive nanofluidic channels and devices. Walls Channels: Walls with roofs Channels with retractable roofs Starts in June….

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Nanotech? The integration of the self-assembly of nanomaterials and lithography will have a large part to play.

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GR/126547N/01 GR/S71514101 HPRN-CT-2000-00028 Prof Stephen Evans, Physics, University of Leeds Prof Donald Fitzmaurice, Chemistry, University College Dublin Prof Graham Leggett, Chemistry, University of Sheffield Prof Richard Palmer, Physics, University of Birmingham Dr Gareth Redmond, Tyndall Institute (NMRC), University of Cork Acknowledgements

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Thank you www.nanochem.bham.ac.uk www.crnnt.bham.ac.uk ‘Precision Chemical Engineering: Integrating Top-Down and Bottom-Up Methodologies’ P.M. Mendes, J.A. Preece, Current Opinion in Colloid and Inferface Science, Invited Review Article, 2004, 9, 236-248