REU Summer 2004
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This document outlines Robert Morien's work during the 2004 REU program to design an improved x-ray diffractometer under the supervision of Prof. Paul Lyman. It provides background on x-ray diffraction and how it is used to analyze semiconductor wafers and determine molecular structures. It describes different types of x-ray diffractometers including 2-circle, 4-circle, and kappa configurations. It also includes the diffraction pattern Robert obtained from analyzing a silicon powder sample and discusses plans to use the diffractometer to analyze pentacene crystals grown at UWM for potential use in organic electronics.
REU Summer 2004
- 1. Designing and creating the ultimate x- ray diffractometer By Robert Morien under supervision of Prof. Paul Lyman REU PROGRAM SUMMER 2004
- 2. Outline UWMs 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 OTFTs
- 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
- 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属 = 34.06悩 = d d2 @ 14.1属 = 3.16悩 = d111 d3 @ 17.95属 = 2.5悩 = d012 d4 @ 23.6属 = 1.92悩 = d022 a dhkl = aSi = 5.4305悩 222 lkh a 1.54了 留k 悩
- 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