Diamond Optical Properties Measurement System

Dan Schulz, Adam Tayloe, Allen Lin, Chunyu Li, Dan KuangMichigan State University, East Lansing, MI, 48823, USA

Introduction Problem Diagnosis and Solution

Michigan State University Engineering Design Day East Lansing, MI April 25, 2014

The present work shows that nanofibrillar versus planar surface architectures can be directive for specific implementations of long-distance interactions. Cell-cell interactions of astrocytes cultured on nanofibrillar surfaces were shown to differ in connective extension type, cell body type, and the number of interactions. Epi-fluorescence microscopy versus AFM has the potential to lead to different conclusions about the lack or presence of cellular connections, as well as their types.

The Fraunhofer Center for Coatings and Laser Applications is interested in improvements to the accuracy and sensitivity of their diamond optical properties measurement system.

Some of the highest quality diamond in the world is grown at Fraunhofer. A senior capstone team was tasked with creating the measurement system in the spring of 2013, and Fraunhofer was dissatisfied with the result. The goal of this project is to improve upon the previous system in all areas, including computer interface, hardware components, and the resulting measurements.

Fraunhofer makes very high quality synthetic diamonds. They produce three-dimensional geometries by using chemical vapor deposition (CVD). CVD is a process where diamond is chemically deposited on a substrate from the gas phase. A pretreated silicon is coated with diamond by means of microwave plasma in an ellipsoidal reactor. The advantage to CVD over other processes such as high temperature high pressure methods is that it allows Fraunhofer to coat larger substrates, and it produces diamonds of high enough quality for use in electronic applications.

The measurement system is physics intensive, and uses the optical property of birefringence to calculate stresses and impurities in diamond samples. Stressed diamonds exhibit properties of birefringence, and this is detected by placing the diamond sample between two linearly polarized filters.

Once the image reaches the camera and is uploaded to the computer, the image is processed in visual studio. This allows Fraunhofer to see the location and magnitude of stresses in the diamond sample.

ConclusionsFraunhofer grows synthetic diamonds used chemical

vapor deposition (CVD). These diamonds are often subject to stresses and impurities. The goal of this project is to identify the location and magnitude of these impurities in diamond samples, with a clean and easy to use interface.

Diamonds that have stresses and impurities exhibit an optical property called birefringence. Birefringent materials spread light into an ordinary wave and an extraordinary wave. If we can detect the extraordinary wave, we can compute the birefringence.

To find this extraordinary wave, the system involves moving light from an LED through a 90 degree linear polarizer. This polarized light then travels through the diamond, and is split into an ordinary and extraordinary wave. These waves are then passed through a polarizer perpendicular to the original. The ordinary wave will be filtered out. The extraordinary wave will continue on to the camera for our detection.

Once an image has been taken, image processing is done in visual studio to quantify the birefringent properties in the diamond.

The primary causes of birefringence that we encounter

are molecular dislocations. These dislocations create a clover pattern in our data.

ACKNOWLEDGEMENTS The electrical and computer engineering department at Michigan State University for the opportunity, the Fraunhofer center and Shannon Demlow for the project, and Dr. Virginia Ayres for providing guidance as the groups facilitator.

REFERENCES[1] Friel, I., S.l. Clewes, H.k. Dhillon, N. Perkins, D.j. Twitchen, and G.a. Scarsbrook. "Control of Surface and Bulk Crystalline Quality in Single Crystal Diamond Grown by Chemical Vapour Deposition." Diamond and Related Materials 18.5-8 (2009): 808-15. Print.[2Lang, A. R. "Causes of Birefringence in Diamond." Nature 213.5073 (1967): 248-51. Print.

By passing linearly polarized light through a diamond, ordinary and extraordinary waves are observed. When those rays pass through a perpendicularly polarized filter, only the extraordinary waves pass through. The team collects this light through a 5 megapixel camera to observe and calculate the diamond’s birefringence.

To the left is an image collected by the 5 MP camera after light has traveled through the system. The areas of higher intensity represent higher levels of birefringence, and therefore higher levels of stress. LEDs of different wavelengths (which visually corresponds to different colors) are capable of being placed into the system to compare separate results. The LED used in the image to the left had an approximate wavelength of 650 nm.

Light Source

-90 Polarizer

90 Polarizer

Diamond Sample

5 MP Camera

Computer

Image Processing

Final Results

Birefringence Algorithm:δ = (2π/λ) * (Δn)d

Algorithm that relates pixel intensity to birefringence:

I/I0≈1/2*sin^2(δ/2)

Conclusions