Notre Dame extended Research Community 1 From the Human Eye Down to Microscopes at the Nano-Scale Michael Crocker Valerie Goss Pat Mooney Rebecca Quardokus

2 Outline  Discussion of Optics  History  Ranges of Visual Resolution  Scanning Electron Microscopy (SEM)  Fundamentals  Operation Scheme  Atomic Force Microscopy (AFM)  Scanning Tunneling Microscopy (STM)

3 Scanning Bunny A distant cousin of the energizer bunny who helps to explain nanoscience concepts. WELCOME PENN HIGH SCHOOL

4 target source How do we see an object? detector …and often you’ll need a lens

5 Requirements of Vision  The light that reaches the eye must have a color between red (760nm) and blue (400nm) – or a mixture of these colors  The light that reaches the eye must be sufficiently bright – usually requires a sufficiently bright source visible light wavelength in nm August 31, 2009 infrared UV UV UV C B A

6 Object and Source Matching

7 Seeing Atomic Structure  Light must be about 0.1nm in wavelength to see atomic structure: x-rays  But our eyes can’t detect x-rays - 0.1nm light - (5000 times smaller wavelength than we can see)  Options Use x-rays and detector (to replace the eye) Use particles (e.g. electrons) and detector  Electrons of the appropriate wavelength are easier to produce and direct than light – Scanning Electron Microscope (SEM)  Alternate imaging techniques Atomic Force Microscope (AFM) Scanning Tunneling Microscope (STM)

8 Scanning Electron Microscope Michael Crocker

9 Basic Idea? Let’s bounce something else at the surface! Animal sight and traditional microscopes collect deflected light e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- Some are absorbed Some are “reflected”

10 Electron Beam Column Beam created from heated filament Beam travels through a vacuum Electro-magnetic fields act as lenses Scattered and “secondary” electrons are detected Electron beam hits the sample in a precise location Beam scans back and forth

11 Electrons Hit Surface and Detection Primary electrons come from the beam Some scatter back, others dislodge electrons

12 Example Images

13 Atomic Force Microscope Valerie Goss

14 What is the AFM? We can sense with our hands by touching. An analogue!

15 AFM cantilever and AFM tips

16 The powerful, versatile AFM ~30 um scan Aug 27, 2009 Resolutions: X and Y nm Z 0.05 nm Microstructure of solids: CD, glass beads, circuits Biological samples: skin cross section, viruses, bacteria, blood, DNA and RNA

17 Scanning Tunneling Microscope Rebecca Quardokus

18 Scanning Tunneling Microscopy (STM)  Electrons tunnel!  With a higher probability than cars  STM measures the current created by tunneling electrons Images courtesy of and

19 Scanning Tunneling Microscopy (STM) Image courtesy of C60 “Bucky Balls” Each C60 diameter is ~ 10Å 1 Å = 1x m

20 Scanning Tunneling Microscopy (STM) Xenon on Nickel Iron on Copper Images courtesy of Individual atoms? That’s small!

21 I’ll show you more in the microscope laboratory!