Can we exfoliate graphene with the aid of solution?

The most common preparation of graphene is to exfoliate the graphite with scotch tape.

On the other hand, the researchers try to seek an alternative way to exfoliate the graphite stacks, that is, using various kinds of solvent to intercalate the graphite and exfoliate the stacks.

The most representational work is

http://www.nature.com/nnano/journal/v3/n9/full/nnano.2008.215.html

Since the experiments in this paper seems to be relatively simple. I made a test immediately.

The solvent I chose is NMP (N-Methyl-2-pyrrolidone) which is the best solvent they concluded.

The mechanism is easily comprehended by the solvent-graphene interaction, but the main problem is that NMP is hard to evaporate in ambient condition. It can only be removed in vacuum with heat assistance.

After drying the solvent, the graphene flakes is so small to the extent that are difficult to process.

Meanwhile, something came to my mind, can we exfoliate the graphene sheets by similar technique used for dispersing CNT bundle? 

So I test this idea with a surfactant called NaDDBS (sodium dodecylbenzenesulfonate) which were used in our previous study of CNT-FET biosensor. The results is better, I was so happy with that !

Immediately, I searched the literature to see whether it has been published or not....

And then.......I found this one.....

http://pubs.acs.org/doi/abs/10.1021/ja807449u

I was so depressed about it..............

It was too late, they already published their work in Feb, 2009.

The early bird catches the worm.......

Terpyridine and Graphene

A paper published at 2005 discussed the interaction between terpyridine and CNT.

http://onlinelibrary.wiley.com/doi/10.1002/smll.200500132/abstract

That triggered me to think what if we put terpyridine on the top of graphene?

Could Terpy serve as a nanoparticle template for graphene?

To test this idea, I've tried to immerse the graphene-contained silicon chip into the 50 mM ethanolic solution for 1 hr just like the way they do. But turns out, the outcome is far beyond what I expected.

The Raman spectroscopy results showed that the peaks does not change at all, neither does the electrical properties. 

Furthermore, I also tried to immerse the Terpy-modified samples into metal ions solution for the nanoparticle formation test. And I scanned the surface with AFM and tried to find the nanoparticles that should be formed on the surface of graphene. But the result was not as good as I anticipated. Only little amount of nanoparticles were formed and located everywhere without spatial selectivity. 

The paper claimed that the terpyridine would associate CNT through nitrogen-mediated interactions instead of the π-π interactions. But if this statement is true, why it can not be applied in the case of graphene?

The possible reason is that the curvature of CNT is the crucial character for the interaction between Terpy and CNT.

Reducing GO with Flash light !??

Although the use of camera lash has been reported in CNT, Si nanowire and conducting polymer. This work still gave me a big shock.
http://pubs.acs.org/doi/abs/10.1021/ja902348k

Researchers from Northwestern University (the alma mater of my master adviser) had invented a new way to reduce graphite oxide. They used the commercial camera's flash light to irradiate the GOs and make them back to graphite and accounted for this effect by using photothermal heating mechanism. They found that the flash method is effective enough to compare with themal annealed samples. The basic principle is about the water evaporation from the GO, and the enough photo energy to trigger the deoxygenating process.

Taking advantage of flash light, they even make a photomask to define the device region. This is a very useful method for GO approach, and they demonstrated again that the camera flash is able to be a tool for reduction proecess.

I just wondering why the flash light irradiation in ambient condition could be a reducing agent for GO while being a oxide agent in other cases. @_@

Over 1 square centimeter graphene debut!!

http://www.sciencemag.org/cgi/content/full/324/5932/1312

No doubt this accomplishment is definitely an enormous progress for graphene research.

A famous group from UT Austin, lead by Rodney S. Ruoff, a leader who first carved up graphite into graphene in 1998, he also wrote a review article in Nature Nanotechonlogy in just few months earlier.

They found if the growth substrate for CVD graphene is replaced by a copper foil, the growth of graphene would be self-limited, which means it is hard to build the second layer on the top of the first layer graphene. With the help of the poor carbon solubility in copper during the synthesis process, the graphene is formed continuously across a vast area of substrate. Eventually, they concluded that the precipitation process of carbon on the surface of copper is suppressed at the high temperature, which enabled a large continuous graphene to be obtained.

The realization of getting a wafer scale and atomically thin graphene is a great progress, however, the absence of band gap in SLG has strongly limited the potential application in electronic industry. Nowadays, a vigorous trend is to open a band gap in graphene electronic device without degrading the transport properties. As far as I know, there are many groups are eagerly working on band gap engineering of graphene, one of these possibility is bilayer graphene, which has been shown to be able to get a band gap under the dual gate configuration. I believe that one day the dream of wafer scale CVD bilayer graphene will be realized. Unfortunately, in spite of my previous work is related to build a CVD system, I don't have chance and enough time to work on it...

Raman spectroscopy in our lab again !!

In fact, we have a confocal Raman system in the lab already, but the alignment is completely lost...

In order to dealing with our new baby--graphene, I told to my boss that I want to refurbish the previous Raman system in the lab. Since it is has long fallen into disuse. And once again, I gave myself a challenge, just like the previous work in redesigning the CVD system.

But I have to say this is definitely a wearing job to save this old Raman system.

The confocal Raman system has several parts, laser, confocal microscope, spectrometer, CCD, the most difficult task is how to adjust the laser spot and make it align to the identical light path of signal from sample. I spent almost two weeks adjusting a small piece of filter, namely "notch filter" which is an essential part of confocal Raman system. This small filter is responsible for filtering out the original laser signal from the reflected Raman signal of sample. Even the most subtle adjustment of this filter could lead to significant change in the position of light spot. That's why no one in the lab want to solve this thorny problem!

Anyway, through this experience of refurbishing our old Raman system, I have learned the alignment of optical path, and the basic sense of the optical component as well. After about 1 month wearing job of alignment, the Raman started to work normally with graphene.

Graphene Times !?

Incredibly, I found a website named "Graphene Times"!!

The guy who built this website is almost doing the same thing as me!!

But, the difference is that I catch the RSS feeds with a software called "Newsfire" (Mac only). NewFire is the best RSS reader I ever used, since it has the major and most important function -- filter. The filter just as the name implies, it filters out the unwanted and huge amount of RSS feeds except the keyword I set, for example, graphene as a keyword. With the help of filter in NewsFire, I can easily follow the newest publication related to graphene which were just updated in each journal website all around the world.

In comparison with "Graphene Times", my solution is even better, because the number of journal I monitored is more than he did, in addition, I could set more keywords to seek more research combination with graphene.

Substrate engineering of graphene?

I always think that the substrate has enormous effect on the graphene.

It is not difficult to imagine because the vast area of graphene have contacted with substrate, and the substrate has long been considered as major source of charge impurities. (though no one knows where they came from)

The clues can be found from the previous work done by Andrei group in Rutgers, they reported that they could approach ballistic transport by suspending the graphene and measured the highest mobility ever in low-temperature about 200,000 cm2/ Vs.
http://www.nature.com/nnano/journal/v3/n8/full/nnano.2008.199.html
And the work related to Raman Spectroscopy
http://pubs.acs.org/doi/abs/10.1021/nn900130g
And the work that focus on the doping effect of the substrate
http://prb.aps.org/abstract/PRB/v79/i11/e115402

Since the previous work I focused is the surface modification of silica surface.
One of the various kinds modification I did is that I capped the silanol groups with HMDS which make silica to be hydrophobic.

And I analyzed the sensing signal change when I injected the buffer with stepwise concentration.
I found that the influence of surface silanol groups is quite important, since they are greatly responsible for the surface potential change in SiNW-FET biosensor. Moreover, I think the ionic behavior is quite different when we replaced the surface groups or capped them.

So, a question has now appeared--
If the so called "charge impurity" mainly came from the ions or ion-like molecules that associated with substrate, what would happen if I capped the surface silanol groups of SiO2 substrate with trimethylsilane?

I think it would be better, at least the mobility should increase, since the ion-like charge impurities would reduce the amount of them which associated with silica prior to the graphene attaching.

Can graphene quench the light from FITC?

I found that when I try to excite an FITC-tag protein linked to graphene with blue light, it seems graphene quench the light every time. No matter how many times I tried, it still became the darkest one on the screen. In order to find the answers, I've searched the literature and only found these two.

http://link.aip.org/link/JCPSA6/v130/i8/p086101/s1
http://link.aip.org/link/JCPSA6/v129/i5/p054703/s1

I also repeated this experiment with almost identical condition simply by replacing graphene with CNT.
The results is quite different from graphene, it emitted green light normally.
But I think this may be due to some of CNTs are semiconductor which would not quench the light so effectly whereas the metallic one would do.
Maybe graphene behaves just like a metal, since the metal marks in the surrounding area were able to quench all the light as well.
But, what would happen if we put the FITC-tag protein on the top of the GO?
GO should have a band gap due the disruption of the π network, but it seems to depend on some specially distributed oxidized sites to open the "gap". I  believe that one day the GO will be a band gap controllable materials in the future, but now, still long way to go.

UCLA researchers found the way to form GNR by Si-NW etching mask!!

I have to say this is really a brilliant idea to form a GNR by simply applying the nanowire as a mask.

Two groups from UCLA, lead by Yu Huang and Xiangfeng Duan, published this work in Nano Letters

http://pubs.acs.org/doi/abs/10.1021/nl900531n

I think it is very suitable for us to produce GNR in this way, since we have plenty of Si nanowires. In order to test it, I try to disperse Si nanowires by suspending them in an enthanolic solution. I found that it is hard to control the distribution and orientation of nanowires. Even though the nanowire has been deposit on the top of graphene, it is no guarantee that the nanowire would firmly contact the graphene to the extent that is able to protect the underlying graphene, which is hard to verify as well.

I think I would try to use some physical ways to deposit the nanowire if I have time to test it.