Terahertz Spectroscopy of 
CdSe Quantum Dots

†††††††††††††††††††††††††††††††††††† Fadzai Fungura

†††††††††††††††††††††††††††††††††††††††† Mentor: Prof Viktor Chikan

Kansas State University Physics Department  REU Program, sponsored by NSF

Welcome to my webpage. This page summarizes my experience doing research in Victor Chikanís lab for the summer of 2008.Hereís a picture of me and the amazing people I was working with:

††††††††††††††††††††††††††††††††††††††††††††††† ††††††††††† group2

 

Below, I describe the Project Goals, my Project Statement, Research Progress, Final Presentation and Final Paper.  Scroll all the way down to learn more About Me

 

Project Goals:Comparing the refractive index and the absorption of doped quantum dots to indium doped and tin dope quantum dots.Also to compare these results to what was obtained when there was a comparison between charged and uncharged quantum dots.

 

Project Statement: My project was on the terahertz spectroscopy of undoped, tin doped and indium doped CdSe Quantum dots.I purified the quantum dots, added some polystyrene and dissolved all in toluene and then evaporated the toluene leaving a small circular solid cast behind and then did the terahertz measurement of that.The polystyrene is transparent in terahertz. The terahertz time domain spectroscopic technique directly measures the terahertz wave temporal electric field that allows precise measurements of the refractive index and the absorption coefficients. This way Iíll be able to compare the refractive indexes of doped and undoped quantum dots.Quantum dots are a special class of semiconductors, which are a cornerstone of modern electronics industry and make possible applications such as the light emitting diode and personal computers.They are very small ranging from 2 to 10 nanometers in diameter and at these very small sizes materials have unprecedented tunability enabling never before seen applications in science and technology. Doping or the use of intentional impurities (in this case tin and indium) to control the behavior of materials lies in the heart of many technologies.Doping is critical for semiconductors that can be otherwise electrically insulating or to increase the conductivity of semiconductors hence changing its electrical and optical properties.Doped and undoped quantum dots have many unique applications in industries such as in the making of medical devices, bio-reagents and electronics.Comparing different doping materials and undoped materials is useful so as to tell which materials are suitable for the particular applications they are needed for.

 

 

Research Progress: 

Week 1:Read through a number of papers such as Plasmon-Phonon Coupling in Charged n-Type CdSe Quantum dots; A THz Time Domain Spectroscopic study so that by understanding what people have done before with Quantum dots and since some of the hiongs are similar to what I would be doing I would get a feel for my project.

Week 2; Read through more papers that described laserssince I had never worked with lasers before, and more papers on doping, phonons and the generation and Detection of the infrared Radiation.Started on working on trying to make polystyrene cylinders that did not contain quantum dots just for practicesí sake. They did not come out well.

Week 3:Read more on lasers.Worked some more successfully on producing smooth cylinders that were of the required thickness.Also that is when I first worked with a laser.We cleaned it up, realigned it and worked on optimizing its power output.

Week 4: I made the cylinders with some undoped CdSe dots.Also we mode locked the laser and took some terahertz measurement of the cylinders I had produced.Also I made some cylinders with someCdSe dots that are doped with tin (Sn).

Week 5: I made some cylinders with some Indium dope in them after purifying the quantum dots.Put an indium doped sample to take the terahertz measurement of the sample.

Week 6: Took the samples with tin, undoped samples with some quantum dots and one without and took some measurements of it.Also read on several articles on terahertz spectrometry.

Week 7: Purified more quantumdots and made one more cylinder with indium dope.Gave Kristan Corwin a tour in the lab.Read more in detail about what quantum dots are and how the terahertz signal is produced.Gave a presentation in the group meeting.

Week 8:Made more undoped samples.Took terahertz measurements of some samples

Week 9: Took more terahertz measurements of my samples.Read on a previous study that had been done with charged and uncharged quantum dots

Week 10:Worked on my powerpoint presentation, final paper and did the final presentation!

 

 

Final PresentationClick here to download my presentation in PowerPoint and Pdf file.

Final Paper:Click here to also view my final paper.

About Me:  I am an international student from Zimbabwe and I go to Cornell College.I have a double major in Mathematics and Physics.I hope to go to graduate school and hopefully do medical physics, aerospace or nuclear engineering.

This had been a great summer.Would like to thank Larry Weaver, Kristan Corwin, Prof Viktor Chikan, all those I worked with in the lab for being such wonderful people and helping us get some experience in the physics world