GID -- Jul.7th, 2004 1

GID=Grazing Incidence Diffraction

“Grazing incidence X-ray diffraction” by Pulak Dutta,

Current Science, Vol. 78 (12), 2000

GID -- Jul.7th, 2004 2

Two Sides of X-Ray

Advantage• Bulk materials• Penetrate significant

distance (0.1~10mm)• Obtain microscopic

structural information averaged over a large ensemble of atoms or molecules

Disadvantage• Surface/interface

• Thin film (10~100Å)

GID -- Jul.7th, 2004 3

Two possible ways for surface

• “Truncation rod” analysis

• ??? (Thin substrate)

Intense sources of X-ray 3D 2D

q q’

Good Single Crystal

(Lateral structure of a surface/thin film)

GID -- Jul.7th, 2004 4

What makes GID possible?

AIR

THIN LAYER

SUBSTRATE

X-RAY

αN=1

N= 1-ε

α 0.05o ~ 1.5o

GID -- Jul.7th, 2004 5

Limitations of GID• Smooth surface

for total reflection condition• Most of incoming X-ray is wasted

0.1o20um*

* In the paper, 2um

α > critical angle increase the number of photons substrate crystalline

1cm

GID -- Jul.7th, 2004 6

Schematics of GID experiment

GID -- Jul.7th, 2004 7

Generic phase diagram*

* For fatty acid Langmuir monolayers

• Horizontal-plane lattice

• Whether tilt and direction

• Degree of positional order

Descriptions

GID -- Jul.7th, 2004 8

Reciprocal space for a 2D lattice

GID -- Jul.7th, 2004 9

When Points Molecules …

NN = nearest-neighbor direction

NNN = next-nearest-neighbor direction

Intensity

form factor of the molecule

Structure and orientation of molecules

Cigar-shaped molecule

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1

1 1 1 1

2

2 2 2 2

3

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3 3