Sunday, July 31, 2011

What we did last week...

...was that we prepared our SAM layers using a more rigorous procedure than we used before. We cleaned the chips in piranha for 5 minutes instead of a couple of seconds, and increased the amount of purging when loading MUA in a vial in the "glove box". We also purged the jars with the chips in MUA solutions for 10 minutes as opposed to 3-5 minutes. As a result, when we inspected our chips with the FTIR we were able to see the absorption peaks corresponding to MUA's vibrational modes. At the same time, the thickness measurements were inconclusive. It appeared that we needed to explore deeper fitting the thickness of a layer and its optical constants. This week taught me that a true researcher should always look for a way to improve experimental procedures and not be afraid to start all over if the existing procedure proves to be ineffective.

Monday, July 25, 2011 the ellipsometry saga continues...

The first three weeks were gone and...can you believe it? I am still excited! Ellipsometry? Fun! SAM layers? Fun!! Surface chemistry? I love it!!! This is the most exciting program I have ever participated in! Triple-fun!
So, last week went under the sign of ellipsometry. We made a lot of measurements using the ellipsometer. It seems that we have mastered the art of measuring thickness, given the index of refraction. Our measurements were lower than it was expected, but they were our actual results, and they were consistent with each other. It means that the thickness of MUA layers was greater than the thickness of MUA+MBA layers. And I am not going to decipher the MUA/MBA acronyms for you! Google it for extra-credit. 3 extra-credit points valid for the next test if correctly deciphered. Diagrams will be helpful.
I loved ellipsometry so much that I even dedicated my homework assignment to it. Watch it if you dare!
My super ellipsometry movie!
Guess what, this week we are going to expand our knowledge of ellipsometry to learning how to measure optical constants of a material. Stay tuned!

Wednesday, July 13, 2011

What about an ellipsometer? (aka You Should Always Take Notes!)

Making wafers!
Yesterday, we had an interesting and learning experience with an ellipsometer. This experience became even more interesting and learning today! But before I tell you the ellipsometer story, let me introduce you briefly (no more than a couple of thousands words – just kidding!) to what we did on Monday-Tuesday. First of all, I was happy to come on time to our clean room training session at 8:00 am on Monday. Phew! I live in Acton, and morning traffic to Boston is usually unpredictable. So, on Monday morning, we put our fancy “bunny suits” on and entered the fascinating realm of cleanliness. Our training session took place in the “yellow” part of the clean room, where researchers work with photo-sensitive materials and, therefore, plain white light is not allowed. Surrounded by the yellow radiance, we started making our first wafers. No, we did not bake any crispy, delicious, whipped cream-covered things. Though, some sort of baking was involved in the process of making our special wafers. We just took thin glass disks (wafers), about 4-5 inches in a diameter. Then, we poured some amount of photoresist on each disk and put the disks, one by one, on a spinner - to produce a thin uniform film of photoresist on the surface of each disk. Then, we soft-baked them (for 1 min on a hot plate) and imprinted several sets of nanoholes on our disks using a special mask and a light source. We practically made pictures of nanoholes on our wafers with photosensitive films! What fun! Then the exposed wafers were developed in a special developer and rinsed in water. Then we dried them off with nitrogen, hard-baked (for 5 minutes on a hot plate), and inspected using a microscope. Oh no! The microscope inspection showed ugly-looking wavy patterns on some of my pretty nanohole imprints. Well, now I have a valuable experience, and next time my wafer will be better.
Then, David and I made our first set of thiols. A thiol is a mono(molecular) layer of a substance self-attached to a metal-coated glass substrate when it is submerged in a solution of the substance. We prepared the necessary solutions and put our gold-coated chips in the solutions. On the next day, we rinsed the chips, dried them of and went to an ellipsometer to measure the thickness of thiols. And now it happened. When we were first trained on using this ellipsometer, everything appeared to be so easy. There was a detailed manual. Just follow the steps and you will be there. So, I did not take notes on this training, because I was sure that I would be able to handle the thickness measurements easily. So, we came to the clean room. Everything started well. We successfully calibrated the ellipsomer. However, when we had to take actual measurements we realized that we were not quite sure what parameters we should use for a spectroscopic scan. …So, we had to seek help.
Conclusion: take notes! Always! It helps!
….and I will continue my ellipsometer story later…

Sunday, July 10, 2011

No, it was an FTIR spectrometer!

FTIR spectroscopy is a method for determining the structure of a material. FTIR stands for Fourier Transform Infra Red. Infrared refers to the part of the electromagnetic spectrum that lies between visible light and microwaves. We perceive some parts of the infrared range radiation as heat.
Now let's describe how FTIR spectroscopy works. An FTIR spectrometer consists of a source of infrared radiation, an interferometer, and a detector. All atoms and molecules vibrate at specific frequencies. When the frequency of infrared radiation matches the vibration frequency of an atom, molecule, or a group of atoms bonded together within a molecule (a so-called "functional group"), the infrared radiation will be absorbed. The amount of absorbed radiation depends on the strength of a bond. Each functional group absorbs its own unique frequency. So, if we measure absorbances of different frequencies of infrared radiation from a sample, we can obtain information about the chemical structure of the sample. A radiation source produces a broadband beam of infrared radiation. An interferometer converts the infrared beam into an interference signal (interferogram) containing all of the infrared frequencies. The interference signal goes to the sample, where some radiation is absorbed, and then to a detector. The final interferogram is then mathematically transformed (Fourier transformation) into an absorption spectrum containing the structural "fingerprint" of the sample.

Thursday, July 7, 2011


When I came home from BU, I told my son that today we learned how to work with two devices: an ellipsometer and a ..."Let me guess," said my son, "circlometer?"

Wednesday, July 6, 2011

I am excited!

My office place!
A great window view
from the nanoscale optics lab.
Today was my fourth RET day at BU. I cannot express in words how much I am excited to participate in the RET program. I will be working on one of the most interesting projects: Resonant Optical Virus Reader (ROVR) for Protein Detection. My partner, David B., is a very knowledgeable chemistry teacher (Yay! chem isn't one of my strong areas and I hope to use his help in conquering the chemistry aspects of our project). The BU faculty participants are very helpful and supportive. Today, my partner and I learned some secrets of surface chemistry involved in preparing gold-covered chips. Tomorrow, we will learn how to work with an FTIR spectrometer. What is FTIR? I will explain it to you later. Stay tuned!