Chem 125 Lecture 6 9/18/06 Projected material This material is for the exclusive use of Chem 125 students at Yale and may not be copied or distributed further. It is not readily understood without reference to notes from the lecture.

flat to flat 62 mm convex to flat Newton’s Rings ~1 mm gap at rim 1 mm

Simpler Measurement of Smaller Distance 1774

Benjamin Franklin Philosophical Transactions of the Royal Society 1774 Portrait by Paulze Lavoisier

Benj. Franklin to Wm. Brownrigg (1773) …I had, when a youth, read and smiled at Pliny's account of a practice among the seamen of his time, to still the waves in a storm by pouring oil into the sea; as well as the use made of oil by the divers... I think that it has been of late too much the mode to slight the learning of the ancients. The learned, too, are apt to slight too much the knowledge of the vulgar.

In 1757, being at sea in a fleet of ninety-six sail bound against Louisbourg, I observed the wakes of two of the ships to be remarkably smooth, while all the others were ruffled by the wind, which blew fresh. Being puzzled with the differing appearance, I at last pointed it out to our captain and asked him the meaning of it. "The cooks," said he, "have I suppose been just emptying their greasy water through the scuppers, which has greased the sides of those ships a little." … Benj. Franklin to Wm. Brownrigg (1773) recollecting what I had formerly read in Pliny, I resolved to make some experiment of the effect of oil on water when I should have the opportunity.

Franklin's Experiment London, 1762 Clapham Common

for I had applied it first on the leeward side of the pond where the waves were greatest; and the wind drove my oil back upon the shore. I then went to the windward side where they began to form; and there the oil, though not more than a teaspoonful, produced an instant calm over a space several yards square which spread amazingly and extended itself gradually till it reached the lee side, making all that quarter of the pond, perhaps half an acre, as smooth as a looking glass. Benj. Franklin to Wm. Brownrigg (1773) At length being at Clapham, where there is on the common a large pond which I observed one day to be very rough with the wind, I fetched out a cruet of oil and dropped a little of it on the water. I saw it spread itself with surprising swiftness upon the surface; but the effect of smoothing the waves was not produced; 1 tsp ≈ 5 cm acre ≈ 2000 m 2 = 2 x 10 7 cm 2 layer thickness ≈ 5 cm 3 / 2 x 10 7 cm 2 = 2.5 x cm = 2.5 nm = 25 Å

Benj. Franklin to Wm. Brownrigg (1773) When put on water it spreads instantly many feet round, becoming so thin as to produce the prismatic colours for a considerable space, and beyond them so much thinner as to be invisible except in its effect of smoothing the waves at a much greater distance. It seems as if a mutual repulsion between its particles took place as soon as it touched the water

Are there Electron Pairs? Scanning Probe Microscopy for Feeling Individual Molecules, Atoms, Bonds?

The Challenge of Resolution

Scanning Tunneling Microscopy (1981) Heinrich Rohrer Gerd Binnig Nobel Prize (1986)

Atomic Force Microscopy

Cantilever Choice Only one of these five cantilevers is used in any one experiment. They differ in stiffness and ability to twist. The smallest scale division is 20  m Hair

Scanning Electron Micrographs of AFM Cantilever & Tip ~20 nm wide at bottom

Cantilever/Chip Holder Tips

Cantilever/Chip Holder Sensitive to < 1 molecule change in height !

COOH tip

Scanning Tunneling Microscopy (1999) Geo. Flynn D. Yablon (Columbia Univ) Br O Br(CH 2 ) 11 COOH on graphite

Quantum corral STM Image of Fe atoms on Cu

SNOM Scanning Near-Field Optical Microscope Scanning Near-Field Optical Microscope Glass Fiber Aluminum Coating 100 nm Aperture Lens Emitted Light Detector Sample (scanned) Light

SNOM image of nanofabricated material  m scale red wavelength

Scanning Probe Microscopies (AFM, STM, SNOM) are really powerful. Sharp points can resolve individual molecules and even atoms but not bonds

Lux

A lonely architectural curiosity on Sterling Chemistry Laboratory at Yale University (1923)

Micrographia Robert Hooke (1665) “But Nature is not to be limited by our narrow comprehension; future improvements of glasses may yet further enlighten out understanding, and ocular inspection may demonstrate that which as yet we may think too extravagant either to feign or suppose.”

"Seeing" Individual Molecules, Atoms, and Bonds? Problem:

What IS light?

How is Light a Wave? Force on Charge at One Position Up Down 0 Time Charged Particle

Charged Particle How is Light a Wave? Force at Different Positions - OneTime Up Down 0 Position

Interference of Ripples

"Seeing" Individual Molecules, Atoms, Bonds Collectively by X-Ray Crystallography

End Be sure you have read the webpage on x-ray diffraction.

Blurring Problem Blurring Problem from Motion and Defects Time Averaging Space Averaging in Diffraction (Cooperative Scattering) Advantage for SPM (Operates in Real Space)

In 1895 Röntgen Discovers X-Rays Shadow of Frau Röntgen's Hand (1895) In 1912 Laue Invents X-Ray Diffraction CuSO 4 Diffraction (1912)

Wm. Lawrence Bragg ( ) Determined structure of ZnS from Laue's X-ray diffraction pattern (1912) Youngest Nobel Laureate (1915)

B-DNA R. Franklin (1952)

Science, 11 August 2000

25 nm (250 Å) >100,000 atoms + hydrogens!

What can X-ray diffraction show? How does diffraction work? Like all light, X-rays are waves. Atoms?Molecules?Bonds?

Wave Machines

Bragg Machine Breaks?

Real Space "Reciprocal" Space Material Diffraction Photo Molecular Structure Fuzzy Pattern Crystal Lattice Viewing Holes Decreasing Spacing Increasing Spacing

Direct Two Scattering Directions are Always Exactly in Phase “scattering vector” Specular perpendicular to scattering vector All electrons on a plane perpendicular to the scattering vector scatter in-phase at the specular angle ! Specular

Simplification from Electrons-on-a-Plane Trick scattering vector

10 Simplification from Electrons-on-a-Plane Trick scattering vector Net in-phase scattering Total Electrons

Water Oil “Thickness” ~ 200 nm Path Difference = 400 nm = 0.5 Strong 400 nm Scattering No 800 nm Scattering = 1

10 Simplification from Electrons-on-a-Plane Trick scattering vector Suppose first path difference is half a wavelength. (Change or angle) Net in-phase scattering Total Electrons

Benzene Snowflake Slide with Random (but Oriented) "Benzenes"

Benzene Snowflake Isolated “Benzenes”

Benzene Snowflake 1 √3 [1] Reciprocal Isolated “Benzenes” Closely-spaced planes give high angles.

Benzene Snowflake Isolated “Benzenes”

2D Lattice of “Benzenes”

Filament Light Bulb Filament (helix)

Filament Light Bulb Filament (helix) X angle tells helix pitch Spot spacing tells scale Spot spacing tells scale Spots weaken successively (from wire thickness) (given & screen dist)

HELIX w S S vw S Curious Intensity Sequence B-DNA R. Franklin (1952)

Even Double Helix Would cancel "Odd reflections"

w S S vw S Curious Intensity Sequence B-DNA R. Franklin (1952)

Offset Double Helix

BASE STACKING B-DNA R. Franklin (1952) w S S vw S MAJOR & MINOR GROOVES HELIX DIAMETER

“Confus’d Pulses of Light” mica