Atomic Force Microscopy. July, 2011 R. C. Decker and S. Qazi

Transcription

1 Atomic Force Microscopy July, 2011 R. C. Decker and S. Qazi

2 Learning through Visualization Visualization of physical phenomena can confirm hypothesis Observation provides opportunities for study without damaging the sample Objects under study may be too small for our hands to handle or manipulate Our students are motivated by seeing for themselves!

3 Human Visual Acuity At about 300 mm (12 ), a person with 20/20 vision is able (at best) to resolve objects separated by not more than about mm ( ) under normal lighting conditions To see smaller objects, we use magnification systems including single convex lenses (magnifying glasses) and more complex vision enhancement systems such as optical microscopes.

4 Limits in Visualization Optical Microscopy Resolution Limits σ= kλ/na Where σ = minimum feature size λ=wavelength of light used NA = Numeric Aperture (lens) k = Constant (about 0.5) Shorter wavelengths of light and higher numerical aperture lenses are difficult to produce! High Index of Refraction materials are difficult to produce.

5 Some Options for Visualization Observe the sample with shorter wavelengths of light or radiation Need to convert the imaging result into something that we can visualize X-Ray film Scanning Electron Microscope Probe the sample physically Need to be very, very careful Mechanical feedback Motion to vision conversion required

6 AFM A Probing Solution Atomic Force Microscopy An imaging method for visualization of nanoscale objects 1 nanometer = 10-9 M A member of the scanning probe microscope family A tool to measure both topography and force-related material properties

7 AFM Very Brief History 1985 Gerd Binnig and Heinrich Rohrer win Nobel Prize for invention of a scanning tunneling microscope invented in 1981 Uses tunneling current to probe conductive surfaces to plot topography by measuring distance-dependent current Binnig, Quate and Gerber invent AFM in 1985 Uses nanoscale probe to make contact for nonconducting samples

8 AFM Block Diagram oscope_block_diagram.png

9 AFM Probing Operation The properties of the surface affect the position of the mirror Variations in height cause more deflection Interaction between surface and probe can be measured to provide information on the surface Atomic Scale Forces can be detected

10 Some Dimensional Reality AFM field of view is typically in the um range in x- and y- axis AFMs probing by contact or intermittent contact (dynamic) mode commonly have a z-axis limit of 5 15 um Samples must be flat within the z-axis limit but can be quite large in x-and y-axis Areas to be probed need to be identified

11 Project Rationale Utilize visualization tools to facilitate learning at the nanoscale Develop facilities at each college Initial learning/techniques at CC level Further learning/courses at BS Level Provide outreach activities in region Portable/remote access tools Professional Development Activities

12 Project Activities Develop understanding of techniques and advantages/limitations of instruments Visits to other AFM Sites Attendance at vendor-sponsored seminars Completion of workshops at NSF-ATE Centers Development of specifications for AFM Curriculum-specific needs Broader Applications

13 Project Activities (2) Development of AFM Capabilities Instrument Bid/Purchase Interface with Vendors Technique Development Sample Analysis and Preparation Cantilever/Probe Selection and Use Classroom Presentation

14 Project Activities (3) Activities and Outreach MVCC Summer Institute SUNY-IT IEEE Student Chapter Presentation High School Nanotechnology/Science Classes SUNY IT/MVCC lab classes High School Science Saturday workshop Faculty/Industry Workshop Project Presentations Industry Speakers

15 Project Activities (4) Materials/Activities Development AFM Narrative for Presenters PowerPoint presentations Laboratory Exercises (basic techniques) Lecture/lab visits Presentations on theory and demonstrations

16 AFMs Acquired

17 AFM - Lessons Learned Instrument Selection Dynamic mode options offered flexibility Anti-vibration systems improve image quality Tip exchange flexibility/ ease is important Tips can be damaged and require replacement Operator training and experience.vs. time Cantilever/tip costs Different grades of same type are often available Practice approaches and training are important

18 AFM Lessons Learned (2) Samples for Visualization Prepared sample kits were of value in improving technique and troubleshooting problems Known sample properties were helpful in exercise development Partnerships and sharing of good samples from other programs and/or departments stimulated project growth

19 AFM Visualization Samples I d like to look at my own materials, please! Tools for creating visualization samples are helpful Sputter/deposition systems for thin metal films Spinners for polymers and other films Chemical/mechanical polishing tools for sample prep Samples must be flat, fixed, clean and probeable Sample heights must be within the range of the z-axis Sample features must be in a definable region Flat, planar substrates for mounting are important TV camera/microscope for positioning is helpful

20 AFM Visualization Samples (2) Fixturing of samples is important Simple means and adhesives may work for dry samples Imaging in liquids requires specific instrument features Contamination of samples may be a concern Atomic level forces can include attraction or repulsion due to weak forces Environmental controls may be required Cleaning and handling of samples is important

21 Suggestions for Development Identify Partners Other Colleges Programs within your college Vendor-sponsored workshops, webinars, and conferences Shared Curriculum Materials NACK Penn State Nano-Link University Programs Collaborative Workshops

22 Laboratory Exercises Online Access to AFM Provides a method to have more tools in your lab Computer access identical to in-person use with the exception of sample loading Requires coordination and technician at remote site Consider this in your project to share with others Creative Scheduling Labs on flexible or open schedules Requires technician for open hours

23 Curriculum Development If you have precise imaging needs, you may have plenty to do Course integration ET 289 Intro to SMT ETC 290 Intro to Nanotechnology (SUNY IT) ETC 390 Intro to MEMS But partnerships stimulate applications! PH 263 Engineering Physics 3 (MVCC) MT 209 Materials Science (MVCC) BI??? Life Sciences!

24 Challenges, Opportunities, and Solutions AFM Imaging can be a time-intensive Line by line scanning can require several minutes to acquire Multiple scans may be required Capture images outside of real time Take a quick first pass and then zoom in Professional Development is Important Vendor-sponsored training and webinars University and Community College Workshops Partnerships with other NSF Projects and Centers

25 Applications beyond Visualization As a probing tool, AFM can provide additional information on the samples it visualizes Adhesion Conductivity Magnetic Forces Weak Forces AFM can also modify the sample Manipulation of Nanoscale objects Nano-lithography

26 Questions?

27 Disclaimer This project is sponsored in part by the National Science Foundation under grant # ). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect those of the National Science Foundation