1. Designing and creating the ultimate x-
ray diffractometer
By Robert Morien
under supervision of
Prof. Paul Lyman
REU PROGRAM
SUMMER 2004

2. Outline
 UWM’s x-ray machine
 What is x-ray radiation and what is it used
for
 Types of x-ray diffractometers
 Kappa reconfiguration
 Diffraction pattern of Si
 Pentacene used for OTFT’s

4. X-ray diffractometry is used for:
 A non-destructive technique in analyzing semi-conductor
wafers and thin films for contamination and atomic
spacings
 Determination of substrate and film coherence
 Information concerning the stresses and strains
between lattice and film mismatches
 Primary method for determining molecular structure of
proteins, particularly DNA which was determined by use
of x-ray diffraction
 Analysis of crystalline phases present in any sample

5. How are x-ray photons developed?
 X-rays are developed in an evacuated x-ray tube
 The tube is made of two electrodes, the anode and the cathode
 The cathode is usually constructed of a tungsten filament held at a high
negative potential
 The anode is held at ground potential
 The cathode is heated producing thermionic emission
 Electrons are accelerated towards the anode ejecting electrons of the
anode material
 The hole of the ejected electron is filled by an outer shell electron which
creates x-ray radiation – the x-ray source
 Energy and thus the wavelength of the x-ray beam is dependent upon
material selected for the anode

7. Types of x-ray diffractometers
 Picker 2 circle
 2 axes of rotation
 limited only to powder diffraction
 Standard four circle with eularian cradle
 4 axes of rotation
 Can diffract powders or crystals
 Kappa
 4 axes of rotation
 Allows better access to sample (no obstructing chi
circle)

8. 4 circle with eularian cradle

10. Kappa

11. Kappa under construction

13. Addition of the fifth circle will allow an additional degree of
freedom to detect out-of-surface plane scattering vectors
Can use additional constraint to use grazing incidence
angles for surface diffraction

14. Diffraction pattern for Si powder I ran on the 4-
circle Eularian X-ray diffractometer during REU
x-ray diffraction pattern
0
200
400
600
800
0 20 40 60
two-theta
c.p.s.
Detector
 d1 @ 1.28° = 34.06Ǻ = d
 d2 @ 14.1° = 3.16Ǻ = d111
 d3 @ 17.95° = 2.5Ǻ = d012
 d4 @ 23.6° = 1.92Ǻ = d022
a
dhkl =
aSi = 5.4305Ǻ
222
lkh
a

1.54λ αk  Ǻ

15. Pentacene is a promising molecule for growth on crystalline
substrates.
Currently we are growing pentacene crystals at UWM using
molecular beam epitaxy (MBE). Paul Lyman will take these crystals
with him as he leaves for Sabbatical at CERN to determine its
crystalline structure using synchrotron radiation

16. What can pentacene give us?
 Biodegradable and easy to reproduce
 Able to operate as a transistor at room
temperature
 High charge mobilitys and on/off ratios
 Low cost/Easy to manufacture
 Organic electronics
 Transistors
 Light emmiting diodes for display screens
 Flexible