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NANOFABRICATION USING ATOMIC FORCE MICROSCOPY Ampere A. Tseng Professor of Engineering Arizona State University, Tempe, Arizona 85287 USA E-mail: [email protected] Co-Workers: L.A. Abril-Herrera, A.O. Adebo, C. Chaidilokpattanakul , R. V. Edupuganti , Ravi Gupta, Ivan A. Insua, C. J. Johnson, J. D. Kaplan, M. H. Lee, Bharath Leeladharan, Bo Li, W. D. Nath, Jong S. Park, Masahito Tanaka, C. L. Thomas, George P. Vakanas Collaborators: Professor Tu Pei Chen, Nanyang Technological University, Singapore Professor Rudy Diaz, Arizona State University, USA Dr. Shyankay Jou, National Taiwan University of Science and Technology, ROChina Dr. Gary Li, Freescale Semiconductor, USA Dr. Zhuang Li, Chinese Academy of Sciences, PRChina Professor M. F. Luo, National Central University, ROChina Dr. Andrea Notargiacomo, Roma TRE University, Italy Professor Jun-ichi Shirakashi, Tokyo University of Agriculture & Tech, Japan Sponsors: US National Science Foundation, Freescale Semiconductor, Intel, Pacific Technology, Walsin Lihwa WHAT IS AFM-BASED NANOFABRICATION ♦ AFM-based nanofabrication is using a functionalized cantilevered-tip for performing nanofabrication. ♦ Nanofabrication aims at building nanoscale structures (0.1 – 100 nm), which can act as components devices, components, devices or systems with desired properties, performance, reliability, reproducibility, in large quantities at low cost. • Methodology or Processing Technology • Toolbox (Equipment: hardware, software, system) • Nanostructured Materials or Raw Materials • Physical Product (Components, device, system….) Ampere A. Tseng, 2010 Atomic Force Microscope (AFM) AFM-Based Nanofabrication: Milestones 1982: Scanning Tunneling Microcopy (STM) invented by Binnig, Rohrer, and Gerber (1986 Nobel Physics Prize). 1986: Atomic Force Microcopy invented by Binnig (US Patent 4,724,318). 1990s: Lithography Using Scanning Tunnelling Micoscopy (STM) and AFM. 2000s: Lithography Using Scanning Near-Field Optical Microscopy (SNOM) and Dip Pen Nanofabrication (DPN). 2008: APMC (led by Zyvex Labs) Awarded US$9.7 Millions by DARPA & Texas ETF for Commercialization of Tip Based Nanofabrication (TBN) (focusing on AFM). 2009/10 DOE Solicitation Upcoming. • AFM works on insulating materials at room environment and is the most widely used scanning probe microscope (Low cost!!) • The AFM combines the technology developed for the surface profiler with the scanning tunnelling microscope. Ampere A. Tseng, 2010 2009/10 NSF Solicitation Upcoming. 2009-2013: $100 million in 5 years in USA. Ampere A. Tseng, 2010 NANOFABRICATION AND TECHNOLOGY Length scale realizable in nanofabrication Intel® 300mm wafer) Intel® 22 nm test chip (SRAM arrays and logic peripheral circuits) with 364 Mb array size and 2.9 billion transistors Ampere A. Tseng, 2010 Ampere A. Tseng, 2010 1 World Nanoproduct Market Ampere A. Tseng, 2010 http://nanopedia.case.edu/image/nanoscale.jpg Semiconductor Related Markets • Semiconductor world market grew by 6 % to $249 billion in 2006 and is $267 billion in 2007 and is expected to rise to 274 billions by 2008 (by Semiconductor Industry Association and IT research firm) • MEMS (MicroElectroMechanical Systems) companies: 80 in 1997 and 8,000 in 2007 in USA • World market of MEMS is $48 billion in 2005, and is expected to rise to $72 billion by 2008 and $95 billion by 2010 (In.Stat, An Industry in Transition: 2007 MEMS Forecast, Scottsdale, AZ) • Market Size of Nanoelectronics is US$ 1.8 Billion in 2005 and is forecasted to reach US$ 4.2 Billion by the year 2010. • Nanofood market will have an annual growth rate of 30.94% from 2006 to 2010 with a market value of US$ 20.40 Billion by 2010. • The market for textiles using nanotechnology will cross US$ 13.6 billion mark by 2007. By 2012, the market is expected to reach US$ 115 Billion. • US market for nanotech tools is projected to increase by nearly 30% per year with US$ 0.9 Billion in 2008, and to US$ 2.7 Billion in 2013. • US has the largest share of global investment in Nanotechnology. The US market had a share of 28% in 2005, followed by Japanese market with about 24% share. The western European market also had a quarter of the market share with major investment in countries like Germany, UK and France. Other countries like China, South Korea, Canada and Australia held the rest of the share. (The World Nanotechnology Market, Global Information Inc, 2006) General Nanotechnology Related Markets US National Science Foundation has made predictions of the of nanotechnology by 2015 • $340 $ billion for nanostructured materials, • $600 billion for electronics and information-related equipment, • $180 billion in annual sales from nanopharmaceuticals Ampere A. Tseng, 2010 Techniques in AFM-based Nanofabrication Atomic Force Microscopy (AFM) TYPICAL ATOMIC FORCE MICROSCOPE Digital Instruments Nanoscope IIIA * Nano-Manipulation: Atoms, molecules, Nanoparticles, nanoclusters… * Material Removal: Mechanical scratch, etching.. * Material Modification: Resist exposure, anodic oxidation,.. * Material Deposition and Growth: Electrical field-induced masstransfer, electrochemical deposition. ♦Dip-Pen Nanolithography (DPN) ♦Scanning Near-field Optical Microscopy (SNOM) 1. Tseng, A. A., Notargiacomo, A., and Chen, T. P. (2005), “Nanofabrication by scanning probe microscope lithography: a review,” J. Vac. Sci. Technol. B, Vol. 23, No. 3, pp. 877-894. 2. Tseng, A. A. (2007), “Recent developments in nanofabrication using scanning near-field optical microscope lithography,” Optical & Laser Tech, Vol. 39, No. 3, pp. 514-526. 3. Tseng, A. A. and Li, Z. (2007), “Manipulations of atoms and molecules by scanning probe microscopy,” J. Nanoscience & Nanotechnology, Vol. 7, No. 8, pp. 2582-2595 . Ampere A. Tseng, 2010 2.5 x 2.5 nm simultaneous topographic and friction image of highly oriented pyrolytic graphic (HOPG). The bumps represent the topographic atomic corrugation, while the coloring reflects the lateral forces on the tip. The scan direction was right to left Ampere A. Tseng, 2010 2 FUNCTIONALITY OF AFM TIP Interaction Between Atoms or Molecules STM: d = tip gap Atoms & Molecules Feedback signal is the current (I) After discovered by Lord van der Waals, the vdW force was quantified by London (1930). The potential of the vdW interaction (pv) can be approximated as pv ( z ) = − A1 / z 6 AFM: d = tip gap Feedback signal is the force (F) London forces (ven der Waals) arise from the temporary variations in electron density around atoms and non-polar molecules (1) depicts the average electron clouds of two nonpolar molecules. However at any instant the electron distribution around an atom or molecule will likely produce a dipole moment (2) which will average out to zero over a period of time. But even a temporary or transient dipole moment can induce a (temporary) dipole moment in any nearby molecules (3) causing them to be attracted to the first molecule. Presently AFM is loaded with forces and electric voltages in ambient environment Ampere A. Tseng, 2010 Three Modes of Operation • Contact mode: also known as static mode, an AFM tip makes soft "physical contact" with the sample. The tip is attached to the end of a cantilever with a low spring constant. The contact force causes the cantilever to bend to accommodate changes in topography. Measurement: displacement (δ) Feedback signal: force (F) = kδ • Intermittent contact mode: also known as tapping mode, the cantilever is driven to oscillate up and down at near its resonance frequency by a small piezoelectric element mounted in the AFM tip holder. The amplitude of this oscillation is greater than 10 nm, typically 100 to 200 nm. A tapping AFM image is therefore produced by detecting the force of the oscillating contacts of the tip with the sample surface. Ampere A. Tseng, 2010 AFM HEIGHT IMAGES Topographical 3D Rendering of Red Blood Cells. Raw atomic force microscope data is visualized as 3D surface Data by Janelle Gunther, 3D Rendering by Ben Grosser (in www.itg.uiuc.edu/exhibits/gallery) Ampere A. Tseng, 2010 (1) where A1 is the interaction constant defined by London (1930) and dependent on the polarization and ionization potential associated and z is the distance between the centers of the paired atoms. In general, the above equation is effective only up to several tens nm. When the interactions are too far apart the dispersion potential, pv, decays faster than 1/z6; this is called the retarded regime (Israelachvilli, 1991). Ampere A. Tseng, 2010 Operation Modes and Van der Waals Curve AFM can be operated in three different modes. Each mode is operated in a different level of Van der Waals force Operated at Frequency Modulation or Amplitude Modulation Measurement: displacement, δ = δ(t) Feedback signal: dynamic force, Fd = F(k, δ, t) • Non-contact (NC) mode: also known as dynamic mode, the cantilever is vibrated near but not contact to the sample surface at a frequency slightly above its resonance frequency (typically, 100 - 400 kHz) ) where its amplitude is typically a few nm. Due to interaction of forces acting on the cantilever when the tip comes close or taps to the surface (within 10 nm), Van der Waals force or other forces (~1012 N) act to decrease the resonance frequency of the cantilever. This decrease in resonance frequency combined with the feedback loop system maintains a constant oscillation amplitude or frequency by adjusting the average tip-to-sample distance. Measuring the tip-to-sample distance at each data point allows the scanning software to construct a topographic image of the sample surface. The absence of repulsive forces in NC mode permits its use in the imaging “soft” samples. Ampere A. Tseng, 2010 IMAGING COMPARISON OF AFM AND SEM (AFM) (SEM) Atomic Force Microscopy - Contrast on flat samples - 3D magnification - Works in ambient air Scanning Electron Microscopy - Good depth of field - Fast scanning - 2⅓D magnification Ampere A. Tseng, 2010 3 Electric & Magnetic Forces Map by AFM Electrostatic Potential and Forces ● The Lennard-Jones potential is important for the interaction between neutral atoms or molecules. The electrostatic interaction force becomes important, if the particles are electrically charged and conductive. The corresponding Coulomb force (Fe) between two charges can be found as: −q Fe = ● Frequently, in calculating the interaction forces, the molecules with permanent dipoles can be treated as point charges. 15μm scan Electric Force images showing reversed tip bias from A to B of polarized ferroelectric domains in an epitaxial, single crystalline Pb(Zr0.2Ti0.8)O3 thin film. The polarization pattern was created using the same metal-coated AFM tip that moments later captured these images (corresponding topography is featureless (not shown), with 0.2nm RMS roughness). Courtesy of T. Tybell, C.H. Ahn, and J.M. Triscone, 1 q2 4πε 0 r 2 The total interaction force can be found by integrating all charged particles involved. Analytical integration solutions do existing for very limited simple cases. The formula developed by Law and Rieutord (2002) ● An appropriate understanding of electrostatic for a conical tip with a spherical apex of r0 and a forces is of a wide interest for better controlling the electromagnetic induced reactions and the related rectangular include angle, 2θ is selected: Fe = πε 0V z ( zd ) charging mechanisms in performing many AFMbased nanopatterning processes, such as local where V is the applied voltage and z(zd) is a anodic oxidation and electrostatic nanolithography geometrical function including the contributions from as well as Kelvin probe microscopy. the spherical apex and conical part of the tip and the cantilever (as shown in the attached figure). By ● The electrostatic potential (pe), also known as assuming θ = 0, an approximation for z(zd) adopted by Coulomb potential, is an effective pair potential Butt et al. (2005) can be applied here. Then, the that describes the interaction between two point electrostatic force becomes: charges. It acts along the line connecting the two r02V 2 charges (q1, q2): q1q2 F = πε pe = 4πε 0 r where r is the distance between two charges and ε0 is the electric constant (permittivity of free space). B.M. Law, F. Rieutord, Phys. Rev. B 66 (2002) 035402; S. Watanabe, K. Hane, T. Ohye, M. Ito, T. Goto, J. Vac. Sci. Technol. B 11 (1993) 1774.; C. Bo¨hm, C. Roths, U. Mu¨ ller, A. Beyer, E. Kubalek, Mater. Sci. Eng. B 24 (1994). e 0 Topography (left) & Surface Potential (right) images of a CD-RW. SP image locates the position of the bits. Courtesy of Yasudo Ichikawa, z d ( z d + r0 ) If θ>>0, a more complicated solutions are needed. Numerical solutions for non-simplified geometries reported by Watanabe, et al. (1993) and Bohm et al. (1994) can also be used for the present electrostatic force calculation. Ampere A. Tseng, 2010 Nanofabrication Using Atomic Force Microscopy Magnetic Force Map of Surface of Zip Disk Ampere A. Tseng, 2010 AFM: Mechanical Scratching Material Removal: Mechanical scratch, Tunnel Barriers: Nano-Scale Modification AFM Tip Material Modification: Anodic oxidation,.. Nano-Manipulation: Atoms Molecules, Nanoparticles, nanoclusters… M Material t i lD Deposition iti and dG Growth: th Electrical El t i l fifieldld induced mass-transfer, electrochemical deposition.. Submicro-scale Modification Gate Drain Source Gate Automation of AFM Nanofabrication Ampere A. Tseng, 2010 AFM: Mechanical Scratching * Predictive model * CNC control with sub-nanometer precision * Multiple tips Ampere A. Tseng, 2010 AFM Scratching Versus Oblique Cutting SEM image of 6 scratched grooves with chips in NiFe substrate using normal force, Fn = 1, 2, 3, 5, 7 and 9 µN AFM scratching Operation in Contact mode Triangular pyramid tip Diamond coated Ampere A. Tseng, 2010 SEM image of 5 scratched grooves with chips in NiFe substrate using normal force, Fn = 9 µN with number of scan (No) equal to 1, 3, 5, 7, and 9 Ampere A. Tseng, 2010 4 Finite Element Modeling of AFM Scratching AFM Scratching of Silicon Static Model for normal AFM tip (negative rake angle) g ) Dynamic model For better tip design (positive rake angle) Ampere A. Tseng, 2010 CORRELATION OF GROOVE DEPTH WITH APPLIED NORMAL FORCE Color scale: Black to White is 4.65 nm. Ampere A. Tseng, 2010 SCRATCHING OF Ni80Fe20 NANOWIRE Nano-constriction made by AFM scratching: a) original configuration, b) after scratching AFM Scratchability Al/As2S3 Si I-V characteristics and geometric profile (insert) of NiFe nanoconstriction measured: a) before scratching (in µA domain), b) after scratching (in fA domain). Ni80Fe PGMA Ni Si Ampere A. Tseng, 2010 Mechanical Scratching and Etching by AFM AFM images of V-shaped grooves on mica substrate scratched by Si tip at contact mode: a) 2-nm deep and 60-nm wide grooves with one scratch at normal force of 500 nN, b) 20-30 nm groove by five repeated scratches with a normal force of 5 μN (Tseng et al., 2007). Ampere A. Tseng, 2010 AFM Scratching of Au-Pd Film Depletion of 2-D Electron Gas (2DEG) of GaAs/AlGaAS heterostructure scratched by AFM-tip with normal force of 50 μN at scan speed of 100μm/s: a) measured resistance against number of scans during scratching on GaAs/AlGaAs layers, the inset showing the schematic of the scanning and measuring process (Schumacher et al., 1999), b) Periodic hole arrays in a quantum well fabricated on InAs/AlSb surface by direct AFM mechanical scratching (Rosa et al., 1998). Ampere A. Tseng, 2010 A Chinese poem (20 characters) of Tang Dynasty was scratched on gold-palladium film (with r.m.s. of 0.2 nm), which was deposited on cleaved mica by ion sputtering. The scratch was performed by a Si AFM tip with a force constant of 35 N/m at a normal force of 20 μN. Scratched depth is about 2 nm. J. Song, Z. Liu, C. Li, H. Chen, H. He (1998),Appl. Phys. A 66, S715–S717. Ampere A. Tseng, 2010 5 AFM Local Anodic Oxidation (LAO) AFM Local Anodic Oxidation from silicon and metals to complex oxides Lines induced on Si substrate by AFM using −8-V DC and 1 m/s scanning speed • Nanometer-Scale Surface Modification Method Through Chemical and Physical Interactions between Tip and Surface • Anodic Oxidation on the Metal/Semi. Surfaces under the AFM Tip • Operation Mode: Contact, Tapping and Noncontact. AFM Tip R. Garcia et al. Chem. Soc. Rev. 35, 29–38 (2006) Si+2h++2(OH-) Æ SiO2+ 2H+ + 2e- *LAO Patterning: forming of water memiscus *Wet etching … And other metals…. Nb, Cr, Mo, Al, Ni, Ti, Ta Ampere A. Tseng, 2010 (a) Silicon oxide dot is grown below the biased AFM tip in presence of a water meniscus. This dot can be removed by selective wet etching leaving corresponding trenches. AFM topographic images of 10 nm wide silicon oxide dots, (b) alternating insulating and semiconducting rings , and (c) first paragraph of “Don Quixote” written by LAO. Garcia et al. Chem. Soc. Rev. 35, 29, 2006. Oxidation kinetics involves the transport of ionic species across the growing oxide film and subsequent reaction at one or other of ambient/oxide and oxide/substrate interfaces. The process constitutes reaction and diffusion exhibiting relaxation-dissipation characteristics. Æ H2 A. A. Tseng et al., J Micro/Nanolith. MEMS MOEMS 84, 043050 (2009) Bouchiat et al. Appl. Phys. Lett. 79 123 (2001) OXIDE DOTS GROWTH BY MULTIPLE PULSES Oxide dot label* 1 2 3 4 5 6 7 8 9 10 11 12 Pulse type static static static modulated modulated modulated modulated modulated modulated modulated modulated modulated Total pulse duration, T [s] 0.20 1.00 5.00 0.50 1.25 2.50 2.00 5.00 10.0 10.0 25.0 50.0 Half cycle period, t [s] 0.20 1.00 5.00 0.25 0.25 0.25 1.00 1.00 1.00 5.00 5.00 5.00 Number of cycles (T/t) 1 1 1 2 5 10 2 5 10 2 5 10 AFM image of twelve oxide dots induced by a bias of -10 V with 60% humidity under twelve different pulse conditions. Ampere A. Tseng, 2010 MODELING OF AFM OXIDATION (aq) + 2e- Nb + 4h+ + x OH- Æ Nt EtchingbOx+ x H+ 500 nm AFM Local Anodic Oxidation (LAO) 2 H+ Ampere A. Tseng, 2010 Development of Wave-Interrogated Near-Field Array e‐dipole near field << λ/10 Open waveguide source Schematic of Wave Concentration by a Bowtie Resonant Element Typical Bowtie Shape Cabrera − Mott theory (1948) : During oxidation, OH- diffuse through material and H+ being liberated at Si/SiO2 interface: Si + 4h+ + 2OH– → SiO2 + 2H+ h dh = α exp( 0 ) dt h Teuschler empirical power law (1995) : h(t ) = β (V − Vth )t γ where α , β , γ are cons tan ts h0 is characteristic decay length Power Intensity at Free Space λ/8 Below Bowties Supported by BK-7 Superstrate Ampere A. Tseng, 2010 6 OXIDE BOWTIE INDUCED BY AFM TIP AS ETCHING MASK AFM Lithography Using Oxidation with SOI Substrate Si SOI (100 nm) SiO2 SiO2 a) Silicon on Insulator (SOI) Substrate Single bowtie c) Etching of Si using induced SiO2 as mask Exposure by scanning AFM tip Wave Interrogated Near-Field Array (WINFA) Oxidation is performed on SOI substrate in which top Si layer is n-type (0.01 Ω-cm) with (100) orientation by Soitec. AFM with Si tip is scanned in contact-mode at 60 nN, 60% ambient humidity, -10 voltages, and 1 µm/s scanning rate. The etchant used in c) is TMAH at 90 °C. SiO2 etch rate is 2 orders of magnitude lower than that of Si(100) Ampere A. Tseng, 2010 Bowtie SiO2 SiO2 b) AFM Tip Induced Oxidation d) Etching of remaining SiO2 Etchant used in c) can be either potassium hydroxide (KOH), tetramethyl ammonium hydroxide (TMAH) or hydrazine (N2H4). Using these echants, SiO2 etch rate is 1 to 2 orders of magnitude l lower than th Si(100). Si(100) Oxidation is performed on SOI substrate in which the top Si layer is n-type (0.01 Ωcm) with (100) orientation by Soitec. AFM with Si tip is scanned in contact-mode at 60 nN, 60% ambient humidity, -10 voltages, and 1 µm/s scanning rate. Ampere A. Tseng, 2010 Direct patterning of GaAs I. Local oxidation of Gallium Arsenide Fabricating tailored quantum devices high mobility two-dimensional electron gas (2DEG) below sample surface Ishii et al., Jpn. J. Appl. Phys. 34, 1329 (1 Matsumoto et al., APL 68, 34 (1996) Held et al., APL 73, 262 (1998) Oxidation of GaAs: reproducibility Insulators Transparent electronics Strain electronics ZnO SrTiO3 MgO LaAlO3 Al2O3 V2O3 TiO2 VO2 SnO2 Ca1-xSrxVO3 In2O3:Sn Superconductivity YBa2Cu3O7-x Epitaxial growth of functional oxides La2-xSrxCuO4 Multiferroics Ferroelectrics Pb(Zr,Ti)O3 BaTiO3 Spin electronics Fe3O4 (LaSr)MnO3 LaFeO3 La1-xSr1+xMnO4 Metal & Semiconductors BiMnO3 Thermoelectrics SrRuO3 LaCoO3 (La,Sr)TiO3 NaxCo2O4 BiFeO3 SrTiO3-x 7 Patterning TMOs Thin Crystalline Films Fabrication of Insulating Barriers & Nanocircuits on Oxides (Transition metal oxides) E-beam and Dry Etching Focused Ion Beam (FIB) La0.7Sr0.3MnO3 High energy processes !!! 16μm x 16 μm 15μm x 15 μm FIB damage of oxide thin films I. Pallecchi et al. Journal of Magnetism and Magnetic Materials 320 1945–1951 (2008) Surface S f d damages off oxide substrates T. Arnal et al. Microelectronic Engineering La 78–79 Sr 201–205 MnO (2005) 2/3 1/3 (La,Pr,Ca)MnO3 Nanochannels Ch Charge modulation d l ti on (La,Sr)MnO La,Sr)MnO3 channels SrTiO3-δ thin film side gate transistors 3 Advantages of using AFM lithography … • High contrast imaging and precise positioning on any kind of surface • Low energy processes (absence of lateral damages) • No Vacuum processes needed • Very high resolution can be achieved Y. Yanagisawa et al. J. Appl. Phys. 100, 124316 (2006) Why patterning crystalline Transition Metal Oxide (TMO) films IPallecchi et al. PRB 71, 014406 (2005) a) Studying different substrate materials and oxide composition. b) Studying oxide growth mechanism and effects of applied DC voltage, d duration i time, i relative l i humidity, & pressure on oxide thickness. c) Comparison of stamp roughness and oxides roughness at different applied DC voltage, duration time, relative humidity, & pressure. V Drain • Nanosized TMO can be employed for the fabrication of functional nanodevices (Nanogaps, ferromagnetic nanoelectrodes for molecular electronics) Source Gate • Fabrication of nanochannels and functional devices (spin devices, field effect devices) Ampere A. Tseng, 2010 Imprint Local Anodic Oxidation (ILAO) Source • Physical properties of many TMOs are inhomogeneous at nanoscale Æ studying size effects and phase separation in TMOs (nanowires) L. Pellegrino, at al. Appl. Phys. Lett. 81, 3849 (2002) Gate Drai n • Thin film templates (nanodots, grids, interdigital circuits) Ampere A. Tseng, 2010 Comparison of AFM LAO & Imprint LAO a) AFM images and corresponding cross sections of oxide features obtained on ZrN thin film as they go through the sequence of AFM oxidation, HF and TMAH etching from top to bottom. b) Schematic representation of the sequence of oxidation, HF and TMAH etching processing steps. c) AFM images and corresponding cross sections of oxide patterns obtained on ZrN (using a silicon stamp with posts) as they go through the sequence of Imprint oxidation, HF and TMAH etching from top to bottom. (Farkas et al., 2010 in JNN) Quantum ring coupled to quantum dot Lithography on 8nm Ti top gates: 7 gates 7 degrees of freedom Martin Sigrist, Andreas Fuhrer Ampere A. Tseng, 2010 8 AFM Tip Induced Deposition Electrochemical deposition (ECD) Gold Nanowire Made by Tip Induced Deposition Electric field-induced mass transfer (EFTM) In ECD, the tip and substrate act as two electrodes to form a nanoscale electrochemical cell to perform a chemical reaction. AFM images of electrochemically induced carbonaceous mounds and lines on Au surface: a) mounds with a height increasing from 4 nm to 11 nm produced over a sweeping voltage varying from -4 to -12V, b) lines with a height increasing from 3 nm to 15 nm produced by a voltage varying from -4 V to -8 V. B. M. Kim et al., Jpn. J. Appl. Phys. Part 1, 40, 4340, 2001. Ampere A. Tseng, 2010 Brushes Grafted by Photopolymerization Using Thiol-Based Iniferters on Au Nanowire a) A gold-coated tip is operated at oscillating noncontact mode onSi (100) surface with 2-nm native oxide, b) a voltage of 10-15 V with 0.5-5.0 ms pulse is loaded to produce the gold transport from the tip to surface. M. Calleja et al., 2001 appl. Phys Lett * To prevent the formation of local silicon oxides, the sample is biased negatively with respect to tip. a) AFM image of a gold nanowire on a * Each voltage pulse produces a gold dot on 4.3 nm oxide film, which was formed by the insulating (oxide) surface and nanowire the application of pulses of 5 ms at -18 V. consists of a succession of gold dots which b) I –V characteristics of the nanowire is separations are smaller than their diameter. obtained at room temperature. Ampere A. Tseng, 2010 Nano-xerography: Patterning by Deposited Charges a) & b) gold nanowires asembled on hydrideterminated Si using AFM tip with HAuCl4 coating c) & d) UV-initiated photopolymerization of PMMA brushes using thiol-based iniferters (DTCA) assembled on Au nanowire platform Ampere A. Tseng, 2010 Nanomanipulation Lateral Manipulation Nano-xerography (a) Charge patterns are written into an electret layer on a solid substrate by applying voltage pulses to a conductive AFM tip. (b) The sample is developed in a suspension of nano-objects. (c) After rinsing and drying, the nano-objects remain selectively attached to the predefined pattern. A Stemmer, D Ziegler, L Seemann, J Rychen N Naujoks,J. Physics: Conference Series 142, 012048 (2008) Vertical manipulation Ampere A. Tseng, 2010 Nanoscale Manipulation (Bottom-up) Forces 8 Push Objects 4 6 4 2 1 0 0 -2 AFM images of lateral manipulation of 24-nm Au nanoparticles to create chain-like nanostructure by FM-AFM: a) pushing nanoparticles labeled with 2 and 3 along direction shown by arrows, b) nanoparticles 2 and 3 are pushed close to nanoparticle 1, c) moving nanoparticle 4 towards nanoparticle 1, d) final chain-like nanostructure (A. A. Tseng and Z. Li, J. Nanosci. Nanotech., 2007) Adatom remains bound to surface and pushed or dragged by tip: a) pulling where adatom discontinuously follows tip from one adsorption site to another due to attractive forces, b) sliding where adatom is trapped under tip and follows its motion instantaneously and continuously, c) tip is retracted at desired place. Adatom is transferred from surface to STM tip and back to surface: a) tip picking adatom from adsorption site and adatom dissociation occurring, b) tip lifting adatom from surface and moving to desired place due to attractive forces, c) tip with adatom is loaded at desired site. Ampere A. Tseng, 2010 -4 Lift-Drop 3 500 6 1000 1500 2 Time (msec) 2000 2500 3000 5 -6 1 6 2 5 3 4 Ampere A. Tseng, 2010 9 ATOMIC AND MOLECULAR MANIPULATION How to Move an Atom STM image of atomic manipulation of iron atoms on copper(111) surface in writing Chinese characters for "atom” by C. P. Lutz and D. M. Eigler, to which the literal translation is something like "original child" (courtesy of IBM Research, Almaden Research Center) STM image of nanoscale millennial numbers “2000” are constructed with 47 CO-molecules regulated on a Cu(211) surface using lateral manipulation at 15 K (courtesy of Dr. Gerhard Meyer of IBM Zurich Research Laboratory, Rüschlikon, Switzerland). Ampere A. Tseng, 2010 In e, silicon, tin and hydrogen atoms are represented by yellow, blue and white spheres, respectively, and the tip apex and surface models correspond to the atomic arrangements in the upper and lower halves respectively. a) By gently exploring the repulsive forces of the bonding interaction between the foremost atom of the AFM tip and atoms probed at a surface, it is possible to induce the vertical interchange of the interacting atoms. Here, a Si defect of the Sn/Si(111)-(3x3)R30° surface (white circle) was replaced by a Sn atom coming from the AFM tip. In a subsequent process, the newly deposited Sn atom (dark circle) was substituted by a Si atom coming from the tip. Applying this manipulation method in heterogeneous semiconductor surfaces enables one to 'write' (b) and 'erase' (c) atomic markers by respectively depositing and removing the atoms in lower concentration (Si in the case of b and c). Reproducibility of this manipulation method provides another way to create atomic designs on surfaces with an AFM at room temperature (d). These vertical-interchange manipulations involve complex multi-atom contacts between tip and surface. Ampere A. Tseng, 2010 (Custance et al., Nature Nanotechnology 2009). MOLECULAR DYNAMICS SIMULATION “Atom Inlay”, that is, atom letters ”Sn” consisted of 19 Sn atoms embedded in Ge(111)-c(2 × 8) substrate Sugimoto et al. Nature Mater. 4, 156-159, 2005 Schematic models of lateral atom manipulation (a) IBM group (STM low temperature), (b) Hitachi group (AFM low temperature), and (c) Osaka group (AFM room temperature). Ampere A. Tseng, 2010 AFM Operation In Dynamic Mode (a), and of the onset of the chemical bonding between the outermost tip atom and a surface atom (highlighted by the green stick) that gives rise to the atomic contrast (b). However, the tip experiences not only the shortrange force associated with this chemical interaction, but also longrange force contributions that arise from van der Waals and electrostatic interactions between tip and surface (though the effect of the latter is usually ll minimized i i i d through th h appropriate choice of the experimental set-up). c) Curves obtained with analytical expressions for the van der Waals force, the shortrange chemical interaction force, and the total force to illustrate their dependence on the absolute tip– surface distance. d–e), Dynamic force microscopy topographic images of a single-atomic layer of Sn (d) and Pb (e) grown, respectively, over a Si(111) substrate. At these surfaces, a small concentration of substitutional Si defects, characterized by a diminished topographic contrast, is usually found. The green arrows indicate atomic positions where force spectroscopic measurements were performed. Image dimensions are (4.3 4.3) nm2; for the acquisition parameters (Sugimoto et al., Nature 2007). Ampere A. Tseng, 2010 What Is Dip-Pen Nanolithography (DPN) In DPN, the cantilevered tip is coated with a thin film of ink molecules that can react with the substrate surface to create a chemical or biological reaction, which can be controlled at the nanoscale level. A scene from a molecular dynamics simulation of an atomic force microscope. Here a hard nickel tip comes down to a soft gold substrate. Before the tip can touch, the surface gold atoms jump up and coat the tip, leaving a neck of gold joining the surface with the tip. Elongation of the atomic spheres and spot coloring are used to indicate elongation/compressive and shear forces. Ampere A. Tseng, 2010 The tip in DPN is not only used for energy transfer to substrate surfaces as it does in AFM but also used for coating material transfer for further chemical or biological reactions Ampere A. Tseng, 2010 10 Dip-Pen Nanolithography (DPN) a) Schematic showing the generation of CdS features through the simultaneous reaction of ink precursors, b) AFM morphology image of CdS patterns created (Ding et al., 2005) d) AFM image of Cu nanowires fabricated with DPN, in which ascorbic acid was dropped onto freshly cleaved mica first, and then writing on the mica with AFM tip adsorbed with CuSO4 molecules (Tseng and Li, 2007). Ampere A. Tseng, 2010 Biological-based Nanostructures by DPN Mesa-like nanostructure of BSA (bovine serum albumin) on mica surface written with tip contact force of 5 nN: a) AFM image, b) crosssection profile along the black line shown in a). R6G (rhodamine 6G, organic dyes) nanostructures written on mica surface with tip writing speed of: a) 0.01 μm/s, b) 0.04 μm/s. (A. A. Tseng and Z. Li, J. Nanosci. Nanotech., 2007) Detection of HIV-1 p24 antigen using a nanoarray of anti-p24 antibody: a) DPN-generated nanoarrays of MHA are used to immobilize anti-p24 antibodies on a Au substrate. The bare Au regions were passivated with 11-mercaptoundecyl-tri(ethylene glycol) (PEG), and nonspecific protein adsorption was minimized by blocking with bovine serum albumin (BSA). The presence of HIV-1 p24 in patient plasma is probed by measuring the height profile of the anti-p24 antibody array. The height increase signal as a result of specific antigen–antibody binding is further amplified by a nanoparticle sandwich assay. b–d, AFM images that demonstrate the detection of HIV-1 p24 antigen. b) Anti-p24 IgG protein nanoarray. Topography trace of adsorbed anti-p24 IgG on MHA. C) After p24 binding to anti-p24 IgG, a height increase for the IgG features is observed. d, p24 detection after amplification with anti-p24 IgG coated gold nanoparticles (20 nm) (courtesy of C. A. Mirkin of Northwestern Uni) Ampere A. Tseng, 2010 DIP-PEN NANOLITHOGRAPHY (DPN) DPN Multiple Tips & Parallel Processing Nanofountain pen: a) Schematic of writing mechanism of DPN probe, where molecular ink fed from reservoir forms liquid-air interface at annular aperture of volcano tip, b) ink from reservoir is delivered to the tip via capillary forces, c) SEM image of volcano tip, d) SEM image of volcano dispensing system (courtesy of C. A. Mirkin of Northwestern University) Nanostructures fabricated by DPN using 55,000 pyramidal tips: a) SEM image of part of a 2D 55,000-tip array, b) AFM image of miniaturized replica of five-cent coin generated by depositing 1-octadecanethiol on gold-on-SiOx substrate followed with wet etching, where background is optical image of representative region of the substrate on which approximately 55,000 duplicates were generated (courtesy of C. A. Mirkin of Northwestern University). Ampere A. Tseng, 2010 Scanning Near-field Optical Microscopy (SNOM) In SNOM, the cantilevered tip is used as a nanoscale light source/collector or as a scatterer. Because the distance between the probe and the sample surface is much smaller than the wavelength of the light source, SNOM works in "nearfield" and the optical excitation of materials at spatial resolutions is well below the far-field diffraction limit. A wide variety of induced energy sources, including electrostatic, optical, optochemical optochemical, optoelectrical, optomagnetic, mechanical and thermal have been adopted by SNOMbased techniques, to enhance its capability. a) aperture SNOM, b) apertureless SNOM Ampere A. Tseng, 2010 Material Oxidation by SNOML AFM images of three oxide patterns on Si substrate generated by NSOM: a) with optical illumination at intermediate oscillation amplitude, b) no illumination at relatively low oscillation amplitude, and c) no illumination at high oscillation amplitude, with all other parameters held constant (courtesy of Matthew B. Johnson of University of Oklahoma) Tseng, 2007 Optics & Lasers Eng. Ampere A. Tseng, 2010 Ampere A. Tseng, 2010 11 Material Removal by SNOML (Ablation) Nanoholes in anthracene crystal film by ballistic ablation through SNOM radiation; the shear force topographic image is shown in the top figure, while the profile measurement is plotted below (courtesy of Renato Zenobi of Swiss Federal Institute of Technology). Material Deposition by SNOML Two Zn nanodots deposited on glass substrate by SNOM photodissociation of precursor diethylzinc gas: a) shearforce image, (b) the cross-sectional profile taken along the white dashed line in Panel (a) (after Yamamoto et al., 2000). Ampere A. Tseng, 2010 Material Modification by SNOML Ampere A. Tseng, 2010 Equipment to Have Precision Of ~1 nm • Develop closed-loop control strategy to reduce the geometric errors induced by equipment including hysteresis creep by piezo scanner, AFM tip, mechanical drift, thermal drift…, - To reduce the hysteresis creep, feedback signal uses direct-measuring, direct measuring non-contact non contact capacitive position sensors (high motion linearity, long-term stability, phase fidelity) - To reduce mechanical drift, positioning and scanning use frictionless flexure guidance (within 0.01 nm/s) Photopatterning of nanostructure in SAM: a) 3 major steps for photopatterning: SNOM selective exposure, photooxidation of exposed region, and contrasting thiol replacing oxidized region, b) FFM image of a 39-nm wide line of dodecanethiol written into SAM of mercaptoundecanoic acid, c) five ~40-nm wide lines of mercaptoundecanoic acid written into dodecanethiol by reversed procedure (courtesy of Graham J. Leggett of University of Sheffield). - To reduce thermal drift, invar or low thermal expansion materials is used for the stage (within 0.01 nm/s) - The total inaccuracy should be less than 1 nm/mm and 0.01 nm/s. Ampere A. Tseng, 2010 DESIGN SOFTWARE FOR PRECISION PARTERNING • Dimension and accuracy of patterns are highly affected by operating parameters: contact mode, tip material, scanning speed, humidity, applied voltage…. • Accuracy of patterning scheme requires further refining, and better processing procedures need to be developed. • Height and width modulation by adjusting the phase and the duration time of pulsed voltage (short pulse voltage restricting lateral diffusion while high voltage pulse producing fast growing in height). • Develop CAD software for the design and control of AFM (including DPN, STM, SNOM) oxidation and scratching patterning. Nano- and Macro-Integrated Manufacturing Desk Top Based System Manufacturing Execution System Vehicle & Stocker C t ll Controllers Material Handling Equipment Station Prod. Equipment Controllers Execution Control Material Control System APC View Dispatch Lists Move Queue Dispatch Job Control/Trigger Wafer control SPC Real-time Scheduler/ Dispatcher Decision Support Systems Ampere A. Tseng, 2010 12 Parallel Processing & Multi-Resolution (IBM Millipede and Special Tip Design) Schematics and SEM image of a cantileverSWNT-based sensing device. The white arrows indicate the location of the suspended SWCNT. Deflections of the cantilever induce strains in the CNT leading to a change in its resistivity (Stampfer et al., 2006). Millipede chip: the electrical wiring for addressing the 1,024 tips etched out in a square of 3mm by 3mm (The chip's size is 7 mm by 14 mm http://domino.research.ibm.com/Comm/bios.nsf/pages/millipede.html Parallel Processing of AFM Tip Arrays A key element when developing probe array devices is a convenient read-out system for measurements of the probe deflection. Such a readout should be sufficiently sensitive, resistant to the working environment, and compatible with the operation of large number of probes working in parallel. Schematic of three main classes of sensory used for deflection detection in AFM 1) external sensor: sensor is not integrated in the cantilever, 2) self sensing: sensor is integrated in the cantilever, 3) Tip-surface interaction sensor: other tip-surface than force interactions are detected, e. g. thermal or electrochemical interactions (Courtesy of J. PoleselMaris). Ampere A. Tseng, 2010 Capacitive Devices for AFM Tip Sensing and Actuating a) SEM image of array of mircofabricated capacitive cantilever sensors, b) and c) enlarged view of cantilever ends, showing the gap between cantilever counter-electrode as well the tip. The perforation of cantilever promotes the removal of SiO2 between the cantilever and the counter-electrode. Sensing and Actuating for Arrays of AFM Tip Ampere A. Tseng, 2010 Other Applications Using Atomic Force Microscope Schematic of AFM Capacitive Sensor and Actuator (Brook et al., 2003) Schematic of AFM with integrated g p piezoresistive sensor and p piezoelectric ZnO actuator. The cantilever is divided into a actuator and sensor region (Minne et al., 1998). Ampere A. Tseng, 2010 AFM DESK TOP NAMOFABRICATION TIP BASED DIRECT WRITING PROTOTYPING Ampere A. Tseng, 2010 Roadmap for Tip-Based Nanofabrication* Developed in 2007 for Commercialization Metric Feature Position Accuracy [nm] Feature Size Variation [% of dimension] Heterogeneity in Parameter: Size Shape, Size, Shape or Orientation 2010 50 2012 25 2014 5 10 3 1 Two values of one parameter 1/min Feature Fabrication Rate Single tip (No. of structure/min/tip with array tips) Height < 10%, Tip Shape Variation Radius < 20% [% of dimension with 100 operations required operations] In-situ Tip Height Sensing 20 [nm] Ampere A. Tseng, 2010 Five values of Continuous two parameters control over two parameters 5/min/tip 60/min/tip Five-tip array Thirty-tip array Height < 5%, Radius < 10% 1000 operations 10 * A. A. Tseng, S. Jou, A. Notargiacomo, T. P. Chen, J. Nanosci. Nanotech., May 2008 Height < 1%, Radius < 3% 106 operations 2 Ampere A. Tseng, 2010 13 For All of Us in Nano Worlds Life Is Limited! Learning Is Unlimited! Nanorization Is Unlimited! Prospective Applications Are Unlimited! Thank You!! Nanofabrication Using Atomic Force Microscopes Atomic force microscopy (AFM) has been used as a nanofabrication tool for localized material deposition, removal, and modification for near two decades. The recent development of several AFM-based techniques will be introduced with the emphasis on their abilities in creating a variety of nanoscale components and devices. Th nanostructures made The d by b these h techniques, h i especially i ll the techniques of mechanical scratching, local anodic oxidation, and deposition are presented to illustrate the characteristics and uniqueness of their versatility and advancement. Recommendations for future research in making the AFM-based techniques more controllable and in widening their applicability in nanofabrication are also addressed. IBM AFM Moving Individual Atoms: www.youtube.com/watch?v=YcqvJI8J6Lc&NR=1&feature=fvwp Nano, the next dimension, for EU(27:04 min): www.youtube.com/watch?v=eCpkq_AeX50&NR=1&feature=fvwp Ampere A. Tseng, 2010 Ampere A. Tseng Bio Ampere A. Tseng is a Professor of Engineering at Arizona State University (ASU). He received his Ph.D. in Mechanical Engineering from Georgia Institute of Technology in 1978 and has published more than two hundred fifty referred papers with nine US patents under his credentials. Dr. Tseng has edited more than ten technical monographs and has been an editor for more than ten different technical journals. Professor Tseng was a recipient of the Superior Performance Award of Martin Marietta Laboratories, RCA Service Award, Alcoa Foundation Research Award, and ASU 1999-2000 Faculty Award. He chaired the ASME Materials Division in 1991-1992 and was selected as an ASME fellow in 1995. Also, he chaired the 2000 NSF Workshop on Manufacturing of MEMS and 1st International Workshop on Tip-Based Nanofabrication in 2008 as well as he co-chaired 1992 International Conference on Transport Phenomena in Processing and the 1999 NSF USA-China Workshop on Advanced Machine Tool Research. Dr. Tseng has received more than three million dollars in research funding directly from government agencies and industries. In 1990, Professor Tseng managed to secure twelve million dollars from US Department of Energy to establish Center for Automation Technology and became its first center director at Drexel University. From 1996 to 2001, Dr. Tseng was the founding Director of the Manufacturing Institute at ASU and the nine million dollars' donation from Motorola to Manufacturing Institute in 1997 was the largest single gift in ASU history. Ampere A. Tseng, 2010 14