6/11/13 Investigations into the Impact of the Template Layer on ZnO Nanowire Arrays Made Using Low Temperature Wet Chemical Growth

Paper:

Investigations into the Impact of the Template Layer on ZnO Nanowire Arrays Made Using Low Temperature Wet Chemical Growth

R obert Erd elyi, Takahiro Nagata, David J. Rogers, Ferechteh H. Teherani, Zsolt E. Horv ath, Zolt an L abadi, Zs ofia Baji, Yutaka Wakayama, and J anos Volk

Keywords: ZnO, seed layer, nanowire, hydrothermal, optoelectronics, 

Dead Body: We want something more than just epatxial ZnO as a substrate layer, and need to understand what happens with other substrates.

Prior work:there are many different deposition methods and the seed layer strongly influences the NW, 

Solution: Alternative substrate would (i) reduce the cost, (ii) integrate the nanostructure with conventional substrates, e.g. Si, sapphire, or glass, and (iii) attain light confinement in the NR/NW by refractive index contrast at the bottom of the cavity.

Want to be able to get uniform, highly ordered NWs on other substrates with other seed layers, instead of just epitaxial ZnO substrates.

Background: applied to LEDs, nanogenerator arrsy, electrodes for dye-sensitized solar cells, Photonic crystals, gas sensors, 

Lots of high aspect ratio work, with patterned placement being quite important for a number of the above applications.

What are the most interesting results: 

• PLD/Si and sputtered/Si had a lot of smaller grains, and non-c-plane directed crystals - based on AFM and XRD
• Also, PLD/Pt/sapp had a high roughness, maybe from the thick Pt that was deposited.

What are the most interesting discussions:

• Perpendicular Orientation: PLD/sapp, Bulk, and PLD/Si
• off-angle growth: PLD/Pt/sapp and Sputter/Si
• Single NW in hole: PLD/sapp, Bulk
• Multiple NW in hole: PLD/Si, PLD/Pt/sapp and Sputter/Si
• For single NWs, the grain size of the seed is larger than the hole diameter, but for smaller grain sizes, get multiple NWs
• XRD is used to determine thickness-crystalline, and in-plane crystallinity
• The surface roughness had less of an impact on the orientation of the NWs than the crystal size and direction - obtained from XRD
• Interesting suggestion that hydrothermal growth on Sapp could be the seeding template for larger growth with CVD.

Materials used: 

• Samples: ZnO epitaxial Crystal, PLD on c-sapphire, PLD on Si(111), PLD on c-sapphire with thick textured Pt, Sputtered Al-doped on Si(100)
• PMMA 300nm thick, EBL hex array pitch 500nm, 120-130nm diameter holes
• 4mM zinc nitrate hexahydrate and hexamethylene tretamine, 3 hours, 85C, 2um long @ 110-150nm diamter
• 
  

How this applies to my work:

• This directly applies to the MITEI work that I am doing for templated ZnO growth.
• seed layer: want larger grain sizes and better alignment of crystal grains for orthogonal growth
• PLD on an epitaxial substrate is best, but shows that testing the different substrates is worth while
• They haven't done any work with spin coated seed layers, or organic seed layers
• When we are comparing substrates, it is useful to create a table which characterizes the seed layers.  
• It will be important to determine a constant hole diameter for all of the substrates.

Applications:

Cited - Low-temp low cost fab of regular NW arrays with high conductivity and tunable positioning, active nanophotonic elements to energy harvesting and
sensor devices, UV/blue light emitting diodes

My own - PV solar cells

6/10/13 Conjugated Block Copolymer Photovoltaics with near 3% Efficiency through Microphase SeparationA Fully Integrated Nanosystem of Semiconductor Nanowires for Direct Solar Water Splitting

Paper:

Conjugated Block Copolymer Photovoltaics with near 3% Efficiency through Microphase SeparationA Fully Integrated Nanosystem of Semiconductor Nanowires for Direct Solar Water Splitting

Changhe Guo, Yen-Hao Lin, Matthew D. Witman, Kendall A. Smith, Cheng Wang,
Alexander Hexemer, Joseph Strzalka, Enrique D. Gomez, and Rafael Verduzco

Keywords: Organic solar cells, block copolymer, lamellae, self assembly, P3HT, thermal annealing, Resonant soft X-ray scattering

Dead Body: Some BCP PV have been attempted, but efficiencies are low.  Mostly this is attributed to nonconjugated insulating backbones.  For bulk heterojunction organic PVs, the main difficulty is getting a good bulk heterojunction, so control over the molecular interface is lacking.

Prior work: High open-circuit voltages have indeed been demonstrated for solar cells where the active layer is comprised of blends of P3HT and other dioctylfluorene bisthienyl-benzothiadiazole alternating copolymers, 25 ternary blends composed of similar conjugated block copolymers as P3HT-b-PFTBT with donor and acceptor homopolymers,26 or polymer blends with fluorene benzothiadiazole alternating copolymers as acceptor  molecules.

Solution: Use fully conjugated BCPs where phase separation is on order of 10nm for exciton extration.  Lamellae is a good morphology because it has a large amount of surface area for a small amount of required exciton diffusion. the importance is getting blocks which line up well to transport the charge efficiently and have different enough HOMO and LUMO levels for a voltage separation.

Background: difference between the lowest unoccupied molecular orbital of PFTBT (∼ 3.5 eV)24 and the highest occupied molecular orbital of P3HT (∼ 4.9 eV)25 can yield open-circuit voltages above 1 V.

What are the most interesting results: 

• 3% efficiency, 1.2 Voc, 5mA/cm2 Isc
• higher temperature, and shorter annealing, gave better PV results
• homopolymer blends of the individual BCPs didn't result in very good PV cells
• they didn't test the capacitance, might be interesting to see C-V curve

What are the most interesting discussions:

• Interestingly, an EQE value of 31% was recorded at 400 nm where the exciton generation is mostly  attributed to the optical absorption of PFTBT, suggesting efficient exciton dissociation from photoexcitations in the acceptor domains.
• RSXRS is useful for measurement because PFTBT and P3HT differ by 285.4eV in the core electron transitions.
• They suggest that the 18nm domain spacing means that the individual domains are roughly 9nm, or similar to the exciting diffusion length
• The XRS measurments both say that at a higher annealing temperature, the BCP self-assembles into a perpendicular lamellae, so that is why the lower temp annealing isn't as good for PV
• the face-on stacking of the P3HT enhance hole extraction because higher conduction along pi-pi stacking.
• suggested that the PFTBT assembly helps to orient the P3HT to be face-on instead of head-on
• covalent bonding across the donor−acceptor interface has the potential to control charge separation and charge recombination rates
• choosing bcp blocks with complementary, instead of overlapping, absorption spectra could help performance

Materials used: 

• poly(3-hexylthiophene)−block−poly-((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(thiophen-5-yl)-2,1,3-benzothiadiazole]-2′,2″-diyl) (P3HT-b-PFTBT)
• 56 wt% P3HT, 29 kg/mol total
• 18nm domain spacing
• 60-70 nm thick from anhydrous chloroform

How this applies to my work:

• could this use templating? if so, how much could it increase the ordering.  Or could it decrease defects which might recombine excitons
• could plasmonic NPs be incorportated to assist in the absorption?
• It makes sense that the lamellae would be short circuiting across both electrodes. Is there a way to ensure that only a single block be on the top and bottom respectively?
• The importance of high chi here...with higher chi, the intersection of the two blocks will be finer and therefore offer a better voltage liley
• couldn't solvent annealing be used? It will probably give btter order
• they didn't image with SEM or TEM.  That can help with testing the order of the film.
• 
  

Applications:

Cited - 

My own - 

6/9/13 A transparent electrode based on a metal nanotrough network

Paper:

A transparent electrode based on a metal nanotrough network

Hui Wu, Desheng Kong, Zhichao Ruan, Po-Chun Hsu, Shuang Wang, Zongfu Yu, Thomas J. Carney, Liangbing Hu, Shanhui Fan & Yi Cui

Keywords: Transparent conductor, plasmonics, thermal evaporation, nanotube, thinfilm, electrospinning, flexible electronics, nanotrough, transfer film

Dead Body: conventional TCOs are good, but most are not flexible, transparent, and highly conducting at the same time. Furthermore, TCOs can have low infrared transmittance.  CNTs and NW transparent conductors are good, but they aren't usually conducting enough.

Prior work: lots of citations on previous transparent conductors such as ITO, graphene, CNTS, Ag NWs, Ag grid, and Ni film.

Solution: 

Background: electrospun PET can be spun over large lengths, and therefore is good for larger industrial applications. Also, electrospinning achieves a spatially uniform distribution of nanofibers, which helps to achieve a high percolation parameter (aspect important to make sure that current doesn't have to travel through a non-uniform network).

What are the most interesting results: 

• The nanotrough design is sufficiently thin to be mostly transparent, but also doesn't cover as large of an areas as a nanoribbon, so it doesn't block as much light.
• the transmission spectral is flat, meaning that they don't absorb at any particular wavelength from 300-2000nm.  This is possibly because they are below this spectrum cutoff (about 200nm diameter), but also not small enough to show quantum characteristics like NPs.
• They are decently chemically stable
• They are extremely flexible and stretchable.  Bending to a radius of 2mm or 20mm X 2000 bendings didn't reduce the conductivity.  Furthermore, they could be stretched at 50% and still only increase resistance by 40%. Lastly, on paper, they were crumpled up, then shown to still conduct
• They can be transferred with tape.
• 
  

What are the most interesting discussions:

• FE simulation was done to test the TM and TE excitation of light based on the nanotroughs.  It is interesting to note the magnification (up to 8 times) of fields was either at the tips of the troughs, or at the U's of the trough.  As is appropriate, they suggested that this might be useful for applications where the fields need to be magnified inside this conductor. The TE polarization "focuses" the light into the U of the trough, which is pretty neat! 
• Pretty interesting that the nanotroughs are so useful.  it seems that it is simply because they have a smaller x-sectional area that they let more light through than nanowires, and the e-beam deposition means that the metal grains have fewer defects.  otherwise, why is a nanotrough better?

Materials used: 

• PVA nanofibers electrospun
• Au, Ag, Cu, Al thermally evaporated
• transfer substrate: glass, PET, plastic, textile, paper, curved flask

How this applies to my work:

• Do I have anything that needs to be patterned inside of these nanotroughs?  They are interesting, but what could they be used for?
• The electrospinning of nanofibers could be used as a substrate for polymers as well.
• Could this work as a TEM grid? or suspension grid for annealing between the troughs?
• If the diameter of the trough is commensurate with a particular self-assembly system, or synthesis of a nanomaterial, it might help to make higher order structures or materials.

Applications:

Cited - optoelectronic devices, resistive-touch-screen devices, solar cells, solar fuel, photo-assisted chemical reactions, and optical sensors

My own - templated assembly within the nanotroughs, TEM grids, something that requires this transverse electric field along the length of the nanotrough, 

6/8/13 Electrically Controlled Nanoparticle Synthesis inside Nanopores

Paper:

Electrically Controlled Nanoparticle Synthesis inside Nanopores

Kimberly Venta, Meni Wanunu,† and Marija Drndić*

Keywords: : Nanopores, nanoparticles, silicon nitride, synthesis, transmission electron microscopy, metallic nanostructures

Dead Body: Controlled placement and synthesis of NPs is difficult, and the smaller NPs are limited by some processing methods

Prior work: Doesn't seem to be a lot, except using nanopores for translocation of single molecules in very small pores

Solution: Use nanopores drilled into SiN as reaction sites for NP synthesis driven by electric field, and measure synthesis with changes in electricity.

Background: Limiting reaction volume to form other materials: organic particles in solution, high
aspect ratio nanowires, and electrofunctionalized micropores as well as studies of precipitation-induced ion current fluctuations in nanopores and related mathematical modeling

What are the most interesting results: 

• The NP forms in a single nanopore. It fills the entire width of the nanopore and is self-limiting when the precursors can't reach each other though the pore anymore.
• The dI/dt derivative of the reaction current was measured to show the nucleation, growth, and the filling growth characteristics.
• The voltages were a few hundred mV, and nA of current.
• they created a model for the growth of the NP that has some constants such as the particle growth constant and constraint constant (rep. difficulty for reagents to meet in the narrow pore), and gives a function for the radius vs. time.
• Use of an alpha-lipoic acid capping on the Au made the NP form much faster (there was almost no time delay) and suggests that it helps with the nucleation of the NP. 
• From TEM analysis, the AuNPs were single xstalline and didn't show a lot of gold formation surrounding the single NP
• They did a nanopore array of 4 different pores, and found a stepwise reduction in current as the nanopores were closed.  without the addiction of alpha lipoic acid, there was a lot of extra gold accumulation as well connecting the 4 NPs.

What are the most interesting discussions: 

• The concentrations of the precursors was chosen to minimize NP formation time without going to unsafe amounts of hydrazine
• The reaction is self limiting because when the reagents can't reach each other anymore, the reaction stops
• They added a thicker layer of SiO2 and a silicone elastomer to reduce the capacitance and therefore decrease the current spike when the switched the voltage
• There was a long delay between switching the voltage and the formation of the NP.  They suggested that during this delay, smaller particles or coagulants might form in parts of the pore.  These would need to be minimized for future applications.
• Decreasing the KCl molarity (and therefore ionic strength) reduced this time delay by 1-2 orders of magnitude
• 
  

Materials used: 

KCl (5mM - 1M) as electrolyte
HAuCl4 5 mg/mL solution for 2.94 mM
hydrazine 0.0312 mM


How this applies to my work:

• Does this actually need to be SiN, or can anything be used?
• Why do the pore sizes need to be so small, or can they be bigger?
• If they can be bigger, than BCP can be used to etch the pores and make tons of NPs all over.  
• If there is a huge array of NPs, will the yield be 100%?
• Would HIBL be faster at making these nanopores?
• Can the BCP film itself be the actual nanopore thinfilm?

Applications:

Cited - transport measurements, self-assembly, and catalysis, expansion to arrays of NPs with individual addressing from electric field, expand to other materials and metals, TEM study of individual nanoparticles

My own - applications of gold NPs as antenna arrays? Nucleation for VLS? Can the NPs then be placed down on another surface?

6/7/13 Epidemiological study of health hazards among workers handling engineered nanomaterials

Paper:

Epidemiologicalstudy of health hazards among workers

handling engineered nanomaterials

Saou-Hsing Liou • Tsui-Chun Tsou • Shu-Li Wang • Lih-Ann Li • Hung-Che Chiang •

Wan-Fen Li • Pin-Pin Lin • Ching-Huang Lai • Hui-Ling Lee • Ming-Hsiu Lin •

Jin-Huei Hsu • Chiou-Rong Chen • Tung-Sheng Shih • Hui-Yi Liao •

Yu-Teh Chung

Keywords: : nanoparticle, health hazard, antioxidant, inflammation, risk level

This was a pretty long paper, so I didn't include all the details.

Dead Body: what are the potential health hazards among workers handling nanomaterials who are potentially exposed to nanoparticles?

Prior work: Tons of previous work both on animals and humans.  All of it cited, and seem that they are good examples.

Only evidence in humans that nps are bad is for polyacrylate NPs, but in animals, there are lots of lung issues,

Lots of evidence that NPs, over fine particles, lead to oxidative stress markers.

Solution: Study to see the results of different tests with different risk groups.

Background: there are natural and engineering NPs (latter including carbon nanotubes, black carbon, nanogold and nanoresins) (former from traffic pollution and combustion). A lot of the natural particles have shown links to respiratory illness, lung inflammation, oxidative damage, worsening of heart disease, atherosclerosis, asthma and possibly lung cancer. Only carbon nanotubes, black carbon and titania have shown negative effects for the engineered nanoparticles.

Route of entry for lung issues: Inhalation (1) <100nm np in alveoli, (2) clearance of np inlung slow, (3) migration of nps from lungs to circulatory system, (4) np migration to brain, interstitial tissues, and regional lymph nodes, 

What are the most interesting results: 

• Studies: antioxidant enzyme activity, lung inflammation and oxidative damage or lipid peroxidation, cardiovascular disease markers, DNA damage and genotoxicity, pulmonary function, and neurobehavioral function.
• Risk Levels 1-4 based on the type of material, the type of nanoparticle, and general exposure.  4 was the worst, while 1 was the least probable. Some confounding variables were accounted for.
• Antioxidant enzyme activity was generally lower in risk groups
• Lung inflammation and markers of oxidative damage or lipid peroxidation did not differe between the groups
• Generally, CVD risk markers were higher in risk groups
• No difference in DNA damage or genotoxicity, or pulmonary lung function
• Risk groups had lower 7-digit memory, but not for 5- and 6-digit memory.

What are the most interesting discussions: 

• There is a discrepancy in this study compared to other studies.  This one didn’t find a big issue with the lungs, but found more problems with oxidative damage, memory, and cardio.  Past studies have focused more on the lungs, including animal studies.  They suggest one difference may be the low dose of exposure to the handling workers as opposed to the studies where animals were actually dosed with nanoparticles.  
• the study was pretty small, with a diverse group of nanoparticles, and only a few years in length.  They call for a study that is more systematic
• Open up the discussion of looking at SOD and cardiovascular response to NPs as a new place for investigation

Materials used: 

 subjects (exposed and unexposed to handling of NPs) from 14 manufacturing plants in Taiwan.  Tests were performed on 227 exposed workers, and 137 unexposed workers.

Blood and urine samples tested, as well as exhaled breath condensates

Tested: pulmonary function, heart rate variability, and neurofunctional behavior. 

How this applies to my work:

• I need to be safe!  As a researcher in this area, it is important to take into consideration the safety of my product/service.  I'll have to watch what future research comes out of this area.

Applications:

Cited = 

My own -

6/6/13 Achieving a New Controllable Male Contraception by the Photothermal Effect of Gold Nanorods

Paper:

Achieving a New Controllable Male Contraception by the Photothermal Effect of Gold Nanorods

Wen-qing Li, Chun-yang Sun, Feng Wang, Yu-cai Wang, Yi-wen Zhai, Meng Liang, Wen-jing Liu, Zhi-min Liu, Jun Wang, and Fei Sun

Keywords: gold nanorods, sterilization, near-infrared, plasmonics, hyperthermia, poly(ethylene glycol),

I didn't summarize all of this paper, because the last half of the paper was more about actual mechanism of the infertility instead of the actual intervention.

Dead Body: No one has tried controllable male infertility with use of gold nanorods before and they think it can be done.


Prior work:


Solution: Coat the AuNRs with α-lipoyl-ω-hydroxyl polyer(ethylene glycol), injection them in the testes, and irradiate with 800 nm light to achieve the long or short term infertility

Background: hyperthermia driven extinction of cancer cells has been shown before. Furthermore, hyperthermia will destroy testicular function and spermatogenesis.

What are the most interesting results:

high concentration GNRs with higher irradiation achieved >50°C after 5 minutes in solution and >45°C in the mouse testes.
Furthermore, this treatment completely destroyed the testes.
What are the most interesting discussions:

They determined that the infertility was the result of protein degredation at the higher temperatures
Au presence after the treatment was concentrated mainly in the liver and spleen because of the bodies typical clearing mechanism – reticuloendothelial system uptakeMaterials used:
α-lipoyl-ω-hydroxyl polyer(ethylene glycol) coated AuNRs 10nm diameter x 40nm long, phosphate buffered saline

How this applies to my work:

All of these are in solution, and not in a nanostructure, so it is hard to suggest that it is directly applicable.
It shows the promise of hyperthermia treatment through AuNPs and AuNRs, or just plasmonics in general
Is there any reason that you would want to template the AuNRs?
Could the NRs be encapsulated in a BCP, and then transported to the testes?
Applications:
Cited - testicular infertility, cancer treatement

My own -

6/5/13 Injectable Nano-Network for Glucose-Mediated Insulin Delivery

Paper:

Injectable Nano-Network for Glucose-Mediated Insulin Delivery

Zhen Gu,

Alex A. Aimetti,

Qun Wang,

Tram T. Dang, Yunlong Zhang, Omid Veiseh,

Hao Cheng, Robert S. Langer, and Daniel G. Anderson†

ACS Nano, 7(5) (2013) 4194
Keywords: diabetes treatment, nano network, nanoparticles, drug delivery, nanoparticle self-assembly

I didn't summarize all of this paper, because the last half of the paper was more about the drug interaction instead of the nano-network.

Dead Body: Open-loop insulin/glucose control is tough for the patient.  Semi-automated control is a little better (with blood glucose monitor and external insulin infusor), but problems are guaranteed accurate signal feedback and preventing biofouling. Closed loop systems can be better, though bulk hydrogels are slow and membranes aren't strong enough to limit release of insulin.

Prior work: See Citation 4 for something that might be really interesting.

Solution: Use biocompatible matrix of modified dextran which degrades in acid, and releases insulin

Background: GOx catalyzes glucose to gluconic acid and changes the pH of the solution.  This pH change can be recognized by certain biosystems to allow for tailored release of insulin

What are the most interesting results: 

• NPs, coated with either positively-charged chitosan or negatively-charged alginate, both polysaccharides, will self assemble! The charge makes them for a high-surface area, nano gel-like network.
• Fully coated NPs were 340 and 293 nm, for chitosan and alginate NPs respectively.
• The structure broke down really well in response to hyperglycemic solution

What are the most interesting discussions: 

• the nano network is stabalized in equilibrium from attractive (agglomeration) and repulsion (pores) energy.
• 
  

Materials used: 

NPs: 4 components 1) acid-degradeable polymer matrix, 2) polyelectroyte-based surface coatings, 3) encapsulated glucose-specific enzymes (GOx and catalase) and 4) insulin.

How this applies to my work:

• creating nanonetworks can be pretty important for closed-loop drug delivery systems.
• The sizes of the NPs (100s of nm) is much larger than what I deal with, but I wonder if going smaller is better.  
• Is there an imagine technique that can be used to better determine the breakdown of the NP coatings and therefore understand the drug release better.
• Why do you need the nanonetwork?  why can't you just have the coated NPs?
• Is it possible that some of these materials could be loaded into a different matrix which will magnify the reaction rate?  
• It seems like the lump from the nano-network was quite large.  In what way can the size be reduced?

Applications:

Cited - treating diabetes 

My own - other forms on drug delivery