I Have a Research Support System

Xu Qiu, we are going to prepare samples of the light source. Chen Wanqing said.

Light source? Xu Qiu thought for a while and said, It must be the Synchrotron Radiation Center of the Demon City.

That's right, they are also called Modu Light Source, which is the latest generation of synchrotron radiation light source in China. Chen Wanqing said.

Then when are we going to take the test? Xu Qiu asked.

Two days later, July 25th, Friday, starting at nine o'clock, the time is 12 hours. Chen Wanqing said.

It takes 12 hours to test, it's so long. Xu Qiu said.

There's no way. When they allocate machines, they allocate them in units of half a day. Chen Wanqing said.

Their light source is running 24 hours a day, so some unlucky people have to test it all night, wait a minute... Xu Qiu seemed to realize something suddenly.

We can't be the unlucky ones.

That's right, we were scheduled to start at nine o'clock in the evening. Chen Wanqing nodded.

After the test, it will be nine o'clock in the morning on the 26th. I will have a rest for the day, and I will have a postgraduate interview on the 28th. It shouldn't be a big problem. After analyzing inwardly, Xu Qiu said:

Okay, senior sister, come and teach me how to prepare samples.

…………

Came to the laboratory, Chen Wanqing introduced:

The substrate we use for light source samples is a single crystal silicon wafer, because its background signal is easy to identify and subtract.

First of all, it is necessary to cut the silicon wafer into small pieces with a glass knife, and the area of ​​each piece should be more than 2 square centimeters, roughly square.

After speaking, Chen Wanqing took out a round silicon wafer from the silicon wafer box.

Its diameter is about 15 cm, its thickness is about 2-3 mm, and it is polished on one side.

She took a glass knife, compared it with a ruler, and drew a set of parallel straight lines about 1.5 centimeters apart on the unpolished side.

Then, use two tweezers with flat tips to respectively clamp the two ends of the straight line imprinted by the glass knife, and break it off with force at the same time.

In this way, a group of long silicon wafers with a width of about 1.5 cm was obtained.

Then, with the help of a glass knife again, she broke the long silicon wafers into small square silicon wafers.

Of course, because large silicon wafers are round, there is inevitably a certain curvature at the corners.

After Xu Qiu learned it, he did the same thing. He took two round silicon wafers and broke them into small silicon wafers.

The two got a total of more than 90 small silicon wafers, which is enough for this sample.

Next, wash and dry the small silicon wafers. There are special tools for cleaning silicon wafers.

Chen Wanqing brought a beaker with a plastic stand.

Put the silicon wafers neatly one by one on the plastic support, then pour the solution, seal the mouth of the beaker with aluminum foil, and then use an ultrasonic cleaner to sonicate.

The solutions were deionized water, acetone, and isopropanol, and each was sonicated for 10 minutes. Finally, the silicon wafer was blown dry with a nitrogen gun and placed in a petri dish.

This is similar to the steps of cleaning a glass substrate, except that no soapy water is used. Xu Qiu said.

Yes, but be careful when using a nitrogen gun. Silicon wafers are more likely to fly off than ITO glass substrates. Chen Wanqing reminded.

Okay. Xu Qiu said, By the way, don't Wu Feifei and Duan Yun need to make samples?

Wu Feifei's three-dimensional perovskite material will directly deteriorate when it encounters oxygen, so there is no way to test it;

Duan Yun mainly makes inorganic thermoelectric materials. He can use XRD to test them in school, and he doesn’t need to go to the light source to test them. Chen Wanqing said.

…………

With the reminder from the senior sister, Xu Qiu didn't make any big mistakes when drying the silicon wafers, only blowing one piece away.

Then, he discussed with his senior sister what samples to make.

For P3HT, Chen Wanqing has 6 blend systems, 3 separate components, a total of 9 types;

Spin coating methods include normal spin coating and spray coating, a total of 2 kinds;

Set 2 groups of speeds for each type;

A total of 36 sets of conditions.

PTB7-TH system, 1 blend system, 2 separate components, 3 types in total.

There are 3 kinds of solvent additives including no addition and 2 different volume fractions;

Annealing and non-annealing, a total of 2 types;

Set 2 groups of speeds for each type;

A total of 36 sets of conditions.

In fact, the rotational speed has little effect on the final result, but the signal of organic samples is generally weak. In order to prevent accidents and ensure that each system can measure the signal, it is necessary to prepare as many samples as possible.

Because the area of ​​the silicon wafer is small, numerical numbers are used, from 1 to 72, and Xu Qiu records the experimental conditions corresponding to the numbers in the experiment record book.

He then ozonizes the blow-dried silicon wafers and transfers them into the glove box, ready to be spin-coated.

The spin-coating operation of the silicon wafer is almost the same as the normal one. Although the area of ​​the silicon wafer is relatively small, its surface is flat and has high hardness.

Therefore, it is only necessary to change the suction table of a small coating machine to firmly suck the silicon wafer, and it does not need to be attached to the glass for spin coating like the PEN substrate.

Two hours later, Xu Qiu prepared all the samples and marked the number on the back of each silicon wafer.

For samples containing numbers 6 and 9, a horizontal line needs to be drawn under it to confirm whether it is 6 or 9.

…………

Back at the desk, Xu Qiu did not forget to ask the senior sister for the principle of the test.

Chen Wanqing introduced:

Ordinary X-ray diffraction experiment, also known as XRD, is to shoot an X-ray to a crystal sample, and when the X-ray passes through the crystal, diffraction will occur.

The generated diffraction signals are collected by the equipment, and after data analysis, information about the arrangement of atoms in the crystal can be obtained.

This kind of test has no distinction in dimension. For example, if the crystal crystallizes differently in different directions, it cannot be seen through the XRD signal.

What we are testing is grazing incidence wide-angle X-ray diffraction, abbreviated as GIWAXS, which can be understood as two-dimensional XRD.

That is, we can analyze how crystals crystallize in two dimensions.

For example, when a polymer is crystallized, its main chain and branch chain can be crystallized, and the direction of crystallization is generally vertical.

We prepare it as a film, then one dimension is the film plane, and the other dimension is out of the plane perpendicular to the film plane, and the crystallization signals in the two dimensions are different.

Therefore, GIWAXS can be used to see the crystallization properties of the polymer main chain and branch chains, but using XRD, their signals will be mixed together and cannot be distinguished.

Is this test difficult to do? Xu Qiu asked: Our general characterization can be tested on the public instrument platform in the laboratory or school, but this one has to go to Zhang Jiang.

Actually, we're pretty good, the school happens to be in Shanghai, and it's only an hour's taxi ride to Zhangjiang.

When I was testing before, I met researchers from all over the country, such as those from the University of Hong Kong. They all flew here one day in advance by plane and had to book a hotel.

At present, there are only four synchrotron radiation sources in the country, and the Modu synchrotron radiation source is the most advanced one, which is the third generation of synchrotron radiation sources.