NIMS: SEM + AFM. Current People, Overall Funding. SEM/AFM Concept. Russell M. Taylor II

Transcription

1 Russell M. Taylor II Russ Taylor, Fall 02 Slide 1 Current People, Overall Funding Sustained hard work across disciplines CS:Russ Taylor, Leandra Vicci, Steve Pizer, Paul Morris, David Marshburn, Adam Seeger, David Borland, Yoni Fridman P&A/MS:Rich Superfine, Sean Washburn, Mike Falvo, Stefan Seelecke, Stergios Papadakis, Michael Stadermann, Onejae Sul, Hakan Deniz, Adam Hall, Aarish Patel, Rohit Prakash Sustained funding ARO/DURIP (2 yr), ONR/MURI (5 yr) Russ Taylor, Fall 02 Slide 2 SEM/AFM Concept Combine the best of: SEM: Imaging elemental analysis ebeam lithography Hitachi S4700 AFM: topography local (mech., elect,..) properties manipulation nm: Manipulation (XYZ control) Multiple Data Set Rendering Registration Topometrix Observer Russ Taylor, Fall 02 Slide 3

2 SEM/AFM System + Thermomicroscopes Observer AFM System Hitachi S-4700 SEM AFM cantilever AFM tip Simultaneous AFM & SEM imaging Sample Russ Taylor, Fall 02 Slide 4 AFM Scanner: 4.3 microns XY range 1 micron Z range AFM Head for SEM/AFM Primary XY translation stage Mounted AFM tip goes here Mounted sample goes here Russ Taylor, Fall 02 Slide 5 AFM Installation Observer before attachment to SEM Close-up of Observer attached to the SEM Russ Taylor, Fall 02 Slide 6

3 SEM/AFM Challenges Challenges: Real-Time overlay/registration E Beam Lith Integration Optimized Integration of Data Sets 3D manipulation-where is the tip? Russ Taylor, Fall 02 Slide 7 EDX: Color and Texture Russ Taylor, Fall 02 Slide 8 EDX: Oriented Slivers Background color shows backscattered electrons Reveals dark slivers Shows region boundary Chris Weigle Close-up Russ Taylor, Fall 02 Slide 9

4 AFM + Simulate BSE from SEM Calibration grid from NIST Adam Seeger s SEM simulator Russ Taylor, Fall 02 Slide 10 AFM + Simulate BSE from SEM Russ Taylor, Fall 02 Slide 11 NIMS: Overlaying Model Model of spider AFM Image Project Solve for pose Solve for model Russ Taylor, Fall 02 Slide 12

5 SEM/AFM: Successes Twanging a suspended nanotube Pick-and-place nanotube on MEMS Measuring force to twist a paddle on suspended tube Russ Taylor, Fall 02 Slide 13 Hand-controlled AFM Zooms in on nanotube Twangs nanotube SEM/AFM in action Russ Taylor, Fall 02 Slide 14 MEMS for properties: CNT/MEMS Hybrids from Manipulation Phillip Williams Create Test devices now Broaden measurement settings for basic science A. Grab CNT from storage B. Position and place C. Repeat Russ Taylor, Fall 02 Slide 15

6 MEMS Chip Mike Sinclair, Microsoft Research Space between pointer and reticule is about 2 microns reticle (movable) pointer Russ Taylor, Fall 02 Slide 16 Designing MEMS: CNT electrical conductivity vs. stress/strain Spring constants and parameters chosen to measure simultaneously strain and current Russ Taylor, Fall 02 Slide 17 CNT Cartridge MWNT Cartridge (Aarish Patel) Russ Taylor, Fall 02 Slide 18

7 Grabbing CNT from Storage Cartridge from electrodepostion Tip grabs with vanderwaals force or ebeam welding AFM Tip Carbon Nanotube Russ Taylor, Fall 02 Slide 19 Position and Place CNT end position, welded CNT stretched to other side, welded Russ Taylor, Fall 02 Slide 20 Actuate MEMS for CNT properties/devices Russ Taylor, Fall 02 Slide 21

8 Testing CNT/Weld Strength CNT did not break; failure occurred at the welds Russ Taylor, Fall 02 Slide 22 NEMS Devices Phillip Williams Design of nanorelay CNT forms conductor Left lead opens/closes Current through other two Adhesion keeps tube stuck Perhaps place higher CO 2 critical point drying Add another tube beneath to act as a bearing Russ Taylor, Fall 02 Slide 23 NEMS next steps CO 2 critical point drying Another tube acts as bearing Russ Taylor, Fall 02 Slide 24

9 Moving Devices: Torsional Oscillators Frequency Sources, Mixers, Sensors Single Paddles released Double Paddles released Russ Taylor, Fall 02 Slide 25 NanoElectroMechanical Systems Materials: Si down to <50 nm! But - Materials issues limit energy loss CNT may be better material Route to 1 nm Si Paddle Craighead group (Cornell) CNT CNT Torsional Beam SiO2 NSRG (UNC) Au/Cr Russ Taylor, Fall 02 Slide 26 Measuring Torsional Properties Press with AFM tip Measure along the paddle F F F F F F F Russ Taylor, Fall 02 Slide 27

10 SEM/AFM in action Two paddles Suspended on tube Tip comes down Paddle sticks Tries to pry off Game over Russ Taylor, Fall 02 Slide 28 Is the nanotube really twisting? Use double paddle: twist one, does the other move? 1 2 Russ Taylor, Fall 02 Slide 29 Typical Force vs. Distance Curves Slope tells stiffness Russ Taylor, Fall 02 Slide 30

11 Measuring Torsional Properties Each press provides force curve Steeper force curve = stiffer effective spring constant F F F Substrate Calibration Russ Taylor, Fall 02 Slide 31 Measuring Torsional Properties Plot each force curve slope versus relative displacement Fit for torsional stiffness (width) Substrate Calibration Russ Taylor, Fall 02 Slide 32 Torsional constant increases with number of force curves Russ Taylor, Fall 02 Slide 33

12 20X Torsion Increase! Force curves all at single point (+/- 50nm)on single paddle Force gets 20x larger after repeats Russ Taylor, Fall 02 Slide 34 Models for MWNT Shear Moduli r All shells equally strained 4 r r G 4 outer inner e 2 l ( ) Initially strain only on outer shell, then increased coupling = πκ r outer -r inner =0.34 nm, Single shell r outer >> r inner Approximate as solid cylinder Russ Taylor, Fall 02 Slide 35 CNTs as Field Emitters Motivation Interesting mechanical and electrical properties of carbon nanotubes (CNTs) gelectron field emission mapping out the electric field for individual MWNT Measurement of the MWNT resonance frequency via FE current low turn-on voltage Applications CNTs as components in field emission devices: Displacement sensors/transducers, MEMS/NEMS devices, switches, oscillators Russ Taylor, Fall 02 Slide 36

13 Electric Field near CNT tip Calculated field line and field intensity distribution near the nanotube end. Field is dramatically enhanced near the tip. Calculations by Lu s group (UNC-CH Physics): The enhancement factor is sensitive to both tube length and the applied field. I-V characteristics deviate from F-N straight line. Turn-on field is about 1V/µm for tube length of few µm. Russ Taylor, Fall 02 Slide 37 Experiment Setup/Procedure 1 Combined SEM/ AFM system -simultaneous AFM & SEM imaging -nm-scale control of tip motion -manipulate objects w/ SEM observation -mechanical and electrical measurements AFM cantilever Sample AFM tip Individual, cantilevered MWNTs MWNTs suspended by either direct deposition on substrate or lithographic techniques Russ Taylor, Fall 02 Slide 38 Experiment Setup/Procedure 2 + _ V AFM or STM metal tip I MWNT f Goals Reproducible field emission from individual pinned nanotube Map out the local electric field and FE characteristics around the CNT Measure resonance frequency of oscillating CNTs via FE current Russ Taylor, Fall 02 Slide 39

14 MWNT Preliminary Measurements: Z Distance Dependence PtIr tip Y MWNT: 100nm diam.;1 µm long X Tip: ~250 nm diam. Z Curve# Relative Z dist. 1: 0 nm 2: 18.4 nm 3: 49.6 nm 4: 61.1 nm 5: 79.1 nm I0 I1 I2 I3 I4 I vs V as a function of Z distance Increasing Z distance UNC NanoScale 0 Science Lectures Russ Taylor, Fall 02 V (volts) Slide 40 TAMS: Thermally Actuated MicroStructures Can we create freely moving, mobile structures? What are the physical principles as we scale them to molecular size? Who cares? Russ Taylor, Fall 02 Slide 41 TAMS: Thermally Actuated MicroStructures Can we create freely moving, mobile structures? What are the physical principles as we scale them to molecular size? Who cares? (a) (b) Silicon=Micro CNT=route to nano? Russ Taylor, Fall 02 Slide 42

15 TAMS: Example structures Hakan Deniz Russ Taylor, Fall 02 Slide 43 Thermal Actuator Nanoscale Movement from Temperature Control Onejae Sul Russ Taylor, Fall 02 Slide 44 Method Evaporate Metal on Cooled TEM Grid. Russ Taylor, Fall 02 Slide 45

16 Initial Experiment Results Slight bending Room Temperature 160 º C Russ Taylor, Fall 02 Slide 46 Russ Taylor, Fall 02 Slide 47 Credits for non-unc Inclusions MEMS device design: Mike Sinclair, Microsoft Research Hardware Lab. Russ Taylor, Fall 02 Slide 48