Two future implications I’ve found are necessary for further optimization of our studies are:
- A Decrease in Substrate Roughness
- ZnO Nanotube Array Formation Through Ethanol Reconstruction
Monday, July 27, 2015
Conclusions & Future Implications: Osuji Lab
As my four weeks came dwindling down, my mentor and I were able to conclude our studies and determine what states provided the most optimal results of ZnO nanorod growth. Through the variation of acetone concentration, revolutions per minutes of spin coating, and the growth temperature, we somewhat optimized conditions for unseeded brass substrates. The conditions necessary for the optimal growth on brass would be a 15% acetone concentration and an RPM of 2000 revolutions. We ultimately decided, however, that unseeded substrates do not provide adequate control of array morphology as was shown by the uncorrelated molecular weight nanorod diameter data. During the last week, we seeded brass substrates with the hydrolyzed zinc solution expecting that the layer would fill the scratches on the brass substrates. This method worked, and we achieved more uniform growth. Although this process does not eliminate the time-consuming seeding step, it does provide an alternative set of substrates that are cheaper than silicon.
Two future implications I’ve found are necessary for further optimization of our studies are:
Two future implications I’ve found are necessary for further optimization of our studies are:
Results: Osuji Lab
We tested the following variables for array optimization: Acetone Concentration in Growth Solution (%), Spin-Coat RPM (1750-2500), Growth Temperature (60-80), & Molecular Weight of Ps-b-P4VP block copolymer. My mentor and I had initial expectations before conducting each variable. We expected that an increase in acetone concentration would give us a larger areal density of rods. This is because the acetone swells the PS coronas, which allows more reactants to come into contact with the cores. We also understood that the micelle cores were made of P4VP polymer chains. The size of the P4VP cores is directly related to the nanorod diameter, meaning that as the molecular weight of the P4VP increases, the diameter will as well.
We attained the following results.
We attained the following results.
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From our investigation, we were able to determine that 15% acetone concentration provided the best uniform growth of the four shown.
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We also determined that 2000 RPM was a soundly speed at which the nanorods could be most uniform.
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As you can see, there is no adequate growth pattern that is dependent on the molecular weight of the polymer.
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As you increase the temperature, the aerial density increases and the rod diameter decreases.
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Things Learned & Motivation: Osuji Lab
As with the completion of many tests and trial runs come results. These results helped distinguish which state certain variables should have been set at for optimal results. But, what are these results for? Why should we have an optimal array of nanorod arrays on brass nonetheless?
Over the course of my first two weeks at my internship, I slowly began to understand the worth of our results. By finding stable variants, we could take these optimized arrays and apply them to important devices. One specific device I learned about was “Hybrid Nanocomposite Photovoltaics”. Photovoltaics are devices used to convert sunlight directly into electricity. We want to make these devices more efficient with our research. Photovoltaic efficiency is directly related to the amount of interface contact between the polymer and the semiconductor. When you excite the polymer layer, the first particles from the layer become dipole-induced and expand to about ten nanometers. This length is known as an exciton diffusion length. The semiconductor collects these excitons. By nano-forming these electrodes we can increase the surface area of interface contact. We want to optimize the surface area, keeping in mind that the space between the nanorods cannot be too small. Otherwise, the polymer will not be able to fit in between the rods. For these reasons, I realized that it is important to systematically control the diameter and spacing between the ZnO nanorods for this specific application.
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| Inside: Photovoltaic Cell |
Sunday, July 26, 2015
Challenges & Frustrations: Osuji Lab
When you pose a research question and conduct an experiment, you always want to find some sort of result that is in favor of your hypothesis. You’re not always going to find the results you want when you conduct your experiments due to a variety of reasons, however. Human error, substrate wear-and-tear, and chemical inconsistencies are just a few reasons.
The internship I experienced was founded on top of a single research topic, “Optimal Growth of ZnO Nanorods on Brass”. We were given a single procedure that was tailored for silicon substrates, a couple research papers, and the liberty of testing any variable we deemed fit for optimal array growth. With this liberty, however, came good and bad consequences. Valeria and I were able to learn from these consequences—nonetheless being disappointed by bad results. Changing the acetone percentage in the growth solution bore great results! We were able to determine that 15% acetone concentration was the best level for nanorod growth.
Changing the molecular weight of the PS-b-P4VP block copolymer didn’t produce the quality results we assumed would occur. Theoretically, the micelle cores are comprised on P4VP polymer chains. This means that the size of the P4VP cores is directly related to the nanorod diameter. This relation would mean that as the molecular weight of the P4VP increases, the diameter would increase as well. When we characterized our nanorods for each molecular weight state (235K/23, 41K/24K, 15K/7K), we saw no adequate growth pattern that was dependent on the molecular weight of the polymer. Another important frustration was the difference in uniformity between brass and silicon substrates. No matter how optimized we could make unseeded ZnO nanorod arrays on brass look, the arrays were never going to be as uniform as the silicon substrates.
The internship I experienced was founded on top of a single research topic, “Optimal Growth of ZnO Nanorods on Brass”. We were given a single procedure that was tailored for silicon substrates, a couple research papers, and the liberty of testing any variable we deemed fit for optimal array growth. With this liberty, however, came good and bad consequences. Valeria and I were able to learn from these consequences—nonetheless being disappointed by bad results. Changing the acetone percentage in the growth solution bore great results! We were able to determine that 15% acetone concentration was the best level for nanorod growth.
Changing the molecular weight of the PS-b-P4VP block copolymer didn’t produce the quality results we assumed would occur. Theoretically, the micelle cores are comprised on P4VP polymer chains. This means that the size of the P4VP cores is directly related to the nanorod diameter. This relation would mean that as the molecular weight of the P4VP increases, the diameter would increase as well. When we characterized our nanorods for each molecular weight state (235K/23, 41K/24K, 15K/7K), we saw no adequate growth pattern that was dependent on the molecular weight of the polymer. Another important frustration was the difference in uniformity between brass and silicon substrates. No matter how optimized we could make unseeded ZnO nanorod arrays on brass look, the arrays were never going to be as uniform as the silicon substrates.
Procedures: Osuji Lab
During the course of my four weeks, we tested the following variables for array optimization: Acetone Concentration in Growth Solution (%), Spin-Coat Rotations Per Minute (1750-2500 RPM), Growth Temperature (60-80 Degrees Celsius), & Molecular Weight of Ps-b-P4VP block copolymer.
In order to prepare for the experimental process, brass substrates were sonicated in a water-soap, ethanol, and acetone solution-each state for 15 minutes. Afterwards, the substrates were UV irradiated for further elimination of organic contaminants.
About 4 mL of micelle solution are coated above the brass substrate by spin coater revolving from ranges 1750 RPM to 2500 RPM. By adjusting the solution concentration and spin speed, we achieve a block copolymer monolayer. The machine used to spin-coat our substrates is called the “WS-650-23 Spin Coater”.
The spin-casted substrate was then placed in a growth solution containing hexamethylenetetramine (HMTA) and zinc acetate dihydrate dissolved in deionized water and acetone. The vial was sealed and then placed in a water bath that was variably heated at 60, 70, 75, and 80 degrees Celsius between 15, 20, and 30-minute increments. The final step before rod characterization was a water and ethanol cleansing, each done for 45 seconds. In order to later characterize our nanorod at high resolutions, we took our substrate samples to the Hitachi SU-70 SEM machine.
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| © Candice Pelligra, Osuji Lab |
In order to prepare for the experimental process, brass substrates were sonicated in a water-soap, ethanol, and acetone solution-each state for 15 minutes. Afterwards, the substrates were UV irradiated for further elimination of organic contaminants.
About 4 mL of micelle solution are coated above the brass substrate by spin coater revolving from ranges 1750 RPM to 2500 RPM. By adjusting the solution concentration and spin speed, we achieve a block copolymer monolayer. The machine used to spin-coat our substrates is called the “WS-650-23 Spin Coater”.
The spin-casted substrate was then placed in a growth solution containing hexamethylenetetramine (HMTA) and zinc acetate dihydrate dissolved in deionized water and acetone. The vial was sealed and then placed in a water bath that was variably heated at 60, 70, 75, and 80 degrees Celsius between 15, 20, and 30-minute increments. The final step before rod characterization was a water and ethanol cleansing, each done for 45 seconds. In order to later characterize our nanorod at high resolutions, we took our substrate samples to the Hitachi SU-70 SEM machine.
Research Summary: Osuji Internship
The current approaches to controlling the geometry of nano-arrays are nanoimprint lithography and unconstrained hydrothermal growth. Nanoimprint lithography is when a polymer imprint is used to form nanoscale patterns that are later cured by UV radiation. This procedure is not suitable for scaling, because it is expensive. Unconstrained hydrothermal growth is another method. Despite many developments in ZnO seed-layer thicknesses, precursor concentrations, and chemical etching treatments, this specific growth does not provide adequate control over the morphology of nanorod arrays.
The approach that we’ve been using to systematically customize ZnO nanorod arrays is the self-assembly of block copolymer chains. When two incompatible monomers are chemically linked, a block copolymer forms. Due to the homopolymers in the chains and their separation response, the block copolymers phase-separate into nanoscale microdomains. The following microdomains covered are spherical (s), cylindrical (c), gyroidal (g), and lamellar (l). For this particular method, the BCP PS-b-P4VP is used at ratios that form spherical microdomains. The solution used creates P4VP micelles that are surrounded by a corona of PS chains. The block copolymer is dissolved in toluene, which is a strongly selective solvent for polystyrene (PS).
The polymer polystyrene-b-poly-4-vinylpyridine (PS-b-P4VP) is amphiphilic (partially hydrophobic, partially hydrophilic), allowing for the selective permeation (penetration through a solid) of aqueous reactants in the growth solution. As shown in the image, aqueous reactants permeate through P4VP micellar bodies to react with the substrate and form rods. The addition of acetone to the hydrothermal growth solution swells PS chains that surround the P4VP cores enough to allow the aqueous reactions to reach the depth at which the micelles are located.
A procedure that controls nanorod synthesis through block copolymer self-assembly has already been created for silicon-seeded substrates. Rather than using silicon, my research involved ZnO rod growth on top of brass substrates. Brass is an alloy of zinc and copper. This means that the growth procedure for these substrates would not require Zinc seeding, which would speed up the process. Brass substrates are also cheaper, making the procedure more scalable.
The approach that we’ve been using to systematically customize ZnO nanorod arrays is the self-assembly of block copolymer chains. When two incompatible monomers are chemically linked, a block copolymer forms. Due to the homopolymers in the chains and their separation response, the block copolymers phase-separate into nanoscale microdomains. The following microdomains covered are spherical (s), cylindrical (c), gyroidal (g), and lamellar (l). For this particular method, the BCP PS-b-P4VP is used at ratios that form spherical microdomains. The solution used creates P4VP micelles that are surrounded by a corona of PS chains. The block copolymer is dissolved in toluene, which is a strongly selective solvent for polystyrene (PS).
The polymer polystyrene-b-poly-4-vinylpyridine (PS-b-P4VP) is amphiphilic (partially hydrophobic, partially hydrophilic), allowing for the selective permeation (penetration through a solid) of aqueous reactants in the growth solution. As shown in the image, aqueous reactants permeate through P4VP micellar bodies to react with the substrate and form rods. The addition of acetone to the hydrothermal growth solution swells PS chains that surround the P4VP cores enough to allow the aqueous reactions to reach the depth at which the micelles are located.
A procedure that controls nanorod synthesis through block copolymer self-assembly has already been created for silicon-seeded substrates. Rather than using silicon, my research involved ZnO rod growth on top of brass substrates. Brass is an alloy of zinc and copper. This means that the growth procedure for these substrates would not require Zinc seeding, which would speed up the process. Brass substrates are also cheaper, making the procedure more scalable.
First Impressions: Osuji Internship
Good evening, everyone.
My name is Sofia Azmal, and I’m a rising high schooler who was given the opportunity to work inside the Osuji Lab. didn’t have any high expectations coming into my internship, because I wanted a fresh template to work off of. If my expectations were too high, I would just disappointment myself. Rather than visualizing my future, I focused on the “now” and found myself in a wonderful intern position. Past experiences from EVO goers were misleading. I’d heard some were scrubbing mud off of fossils, while others categorized and filed papers. I never assumed that my work would just be “cleaning up the office space”, but I also didn’t have expectations that would put me into a critical position in the lab. When I first arrived, other in the lab greeted me with questionable expressions—nonetheless with “Hellos”. The days following that first meet were simple, my mentor and I were given a research question to investigate for us. The Osuji lab was our oyster to cultivate this project, and we began testing different variables that would lead to the most optimal zinc-oxide nanorod arrays on brass. On paper, the project seemed like a difficult synthesis that focused on the development of block-copolymer self assembly. I realized during my first week that this wasn’t the case. The concepts were simple to understand with a little explanation. Rather than a jumbled mess of chemical phrases, I understood my mission in the lab for the next month.
My mission was to control the geometry of ZnO nanorods on brass substrates with the use of block copolymer self-assembly.
My name is Sofia Azmal, and I’m a rising high schooler who was given the opportunity to work inside the Osuji Lab. didn’t have any high expectations coming into my internship, because I wanted a fresh template to work off of. If my expectations were too high, I would just disappointment myself. Rather than visualizing my future, I focused on the “now” and found myself in a wonderful intern position. Past experiences from EVO goers were misleading. I’d heard some were scrubbing mud off of fossils, while others categorized and filed papers. I never assumed that my work would just be “cleaning up the office space”, but I also didn’t have expectations that would put me into a critical position in the lab. When I first arrived, other in the lab greeted me with questionable expressions—nonetheless with “Hellos”. The days following that first meet were simple, my mentor and I were given a research question to investigate for us. The Osuji lab was our oyster to cultivate this project, and we began testing different variables that would lead to the most optimal zinc-oxide nanorod arrays on brass. On paper, the project seemed like a difficult synthesis that focused on the development of block-copolymer self assembly. I realized during my first week that this wasn’t the case. The concepts were simple to understand with a little explanation. Rather than a jumbled mess of chemical phrases, I understood my mission in the lab for the next month.
My mission was to control the geometry of ZnO nanorods on brass substrates with the use of block copolymer self-assembly.
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