Chapter 32: spectrometer

　　 Chen Wanqing led Xu Qiu to the black laboratory platform on the side with three instruments and a computer.
　　 "These three instruments are UV-Vis spectrophotometer, fluorescence spectrometer, and electrochemical workstation." She introduced them and pointed them to Xu Qiu.
　　 "The first two instruments are mainly used today. They can be used to obtain the light absorption and fluorescence spectra of thin film samples, generally referred to as UV-vis and PL."
　　 Chen Wanqing turned on the power of the UV-Vis spectrophotometer and fluorescence spectrometer, and then turned on the UV-vis test software in the computer.
　　 After waiting for a few seconds, the computer shows that the connection with the instrument is successful, and the control page pops up.
　　 Chen Wanqing explained while operating:
"The principle of UV-vis testing is to pass monochromatic light of each wavelength through the sample. During this process, part of the photons are absorbed by the sample, and then the intensity of the incident light and the emitted light are measured. The transmittance of light.
　　 The range we can test is roughly 200-1000 nanometers.
　　The experimental procedure is also very simple.
　　The first step is to start the light source;
　　 The second step is to test a blank sample, which is a glass sheet, paste it on the sample table, and click the ‘’ button;
　　 The third step is to test the sample, and also paste it on the sample table, click the "sample" button, the software will automatically test and deduct the background.
　　 This set of equipment can also be used to test solution samples, but we usually use it to test thin films. "
　　 The test speed is very fast. The light absorption spectrum of the sample appears on the computer screen, and the main absorption peak is at 400-650 nanometers.
　　 Xu Qiu still doesn't understand notation, so he asked: "Senior sister, how is it, is the guess correct?"
"Um..." Chen Wanqing considered for a while, and said, "From this chart, compared to the sample under normal spin coating conditions, the half-width of its absorption peak is now smaller. If its light absorption coefficient is also at the same time If it increases, it can be explained by the increase in polymer crystallinity, but the film thickness is not known now, so the light absorption coefficient cannot be calculated."
　　 "How do you measure the film thickness?" Xu Qiu said.
　　"The thickness of our spin-coated organic films is generally about 100 nanometers. The thickness of them is generally measured by ellipsometer or SEM.
The former requires fitting parameters, while the latter requires breaking the substrate under the condition of liquid nitrogen cooling, and then testing the SEM of the section. In short, it is not very convenient, and even if it is measured, the light absorption coefficient can be calculated. This data can only be used as Proof, because it is not intuitive enough.
　　 If you want to get more intuitive evidence, you still need to go to the Modu Synchrotron Radiation Center and do a grazing X-ray diffraction experiment on the sample. "
　　 Chen Wanqing finished testing the other five samples, saved the data, and said:
　　 "The fluorescence spectrometer needs to be warmed up for a while after it is turned on. It should be almost there now."
　　 She opened the instrument cover of the fluorescence spectrometer, took out the sample holder inside, pasted one of the samples and put it back, and then said:
　　" Its principle is to irradiate the surface of the sample with monochromatic light, the sample molecule absorbs the energy of the photon and emits fluorescence, and the instrument collects its fluorescence signal.
　　According to the principle of conservation of energy, under single photon excitation, the energy of fluorescence is less than the energy of excitation light, that is, the wavelength of fluorescence is longer than the wavelength of excitation light.
　　The instrument has two modes, one is to set the wavelength of the excitation light, and collect the fluorescence signal of the sample at the full wavelength within the detection range of the instrument;
　　 The other is to give a range of excitation light wavelength and collect the fluorescence signal of the sample at a given wavelength.
　　We use the first mode. Normally, the wavelength of the excitation light selects the wavelength corresponding to the peak in the light absorption spectrum of the sample.
　　 Therefore, it is generally necessary to test UV-vis first, and then test PL. "
　　 Chen Wanqing opened the PL test software and started to set the parameters: excitation light wavelength 550 nanometers, fluorescence detection range 570 to 850 nanometers.
　　"This does not require a blank substrate, just measure directly. The limit test range is roughly 300-850 nanometers.
　　The operation is very simple. Put the sample in, rotate the sample stage to make the sample and the excitation light source have an angle of 60 degrees, then close the lid and start the test. "
　　 Chen Wanqing presses the start button.
　　 "Woo"
　　 "Dang, Dang, Dang..."
　　 "The sound of this instrument is quite unique." Xu Qiu said.
　　 "It should be the sound of the transmission and grating inside," Chen Wanqing said: "Have you learned the operation of these two instruments?"
　　 "I learned it." Xu Qiu nodded, and at the same time copied the two skills of the senior sister in the system.
　　 Now, he has more than 20 skills in his system list.
　　…………
　　 Xu Qiu continued to experiment, and today he will make another batch of devices, which is another day of overtime work.
　　Clean the substrate and spin-coated zinc oxide.
　　 During the annealing of the zinc oxide substrate, the senior sister came over and used the glove box for a while to prepare the chloroform solutions of P3HT, PC[60]BM, and PC[70]BM.
　　 After the senior sister got it right, Xu Qiu continued to spin coat the effective layer.
　　 This time the variable is only the speed, so he only prepared 12 substrates and designed six sets of speeds, each with 2 pieces.
　　The speeds are 1200, 1500, 1800, 2000, 2300, 2500r.p.m. respectively.
　　 After some operations, a piece of 1200 rpm was scrapped.
　　 But the problem is not big. Today’s focus is on samples above 1500 rpm. UU reading www.uukanshu.com
　　 He transferred the substrate to the vapor deposition chamber and began to vacuum.
　　 Returning to the desk, Xu Qiu leaned in curiously when he saw that the senior sister was processing the data just measured.
　　 "When drawing pictures, is Teacher Wei very strict in this respect?" Xu Qiu said.
　　"Yes, he pays special attention to the style of pictures, such as:
　　 Font size, physical quantity and unit should use 36-point font, the number on the coordinate axis should use 26-point font, Chinese uses Song Ti, and English uses TimesNewRoman font. Chinese cannot appear in the picture;
　　 The scale of the coordinate axis, there must be a coordinate axis up, down, left and right, there must be a scale on the left and bottom, and there must be no scale on the upper and right sides, and the tip of the scale must point into the figure;
　　 The default black box cannot be used in the legend, it must be manually changed to no border;
　　 When there are multiple curves in the picture, the curve in the control group must be black, and the curve in the experimental group with the best data is red.
　　 In addition, there are many other details that need attention. "Chen Wanqing said.
　　 "Senior sister can remember so many requests," Xu Qiu said.
"It's not practice makes perfect. At the beginning, every picture basically needs to be changed," Chen Wanqing said: "Later, I used the template function of the origin software to save the templates for all types of pictures, and now I directly set the templates, making mistakes. The odds are much smaller."
　　 "Sister, you know." Xu Qiu stretched out his hand and said.
　　 "What?" Chen Wanqing pretended to be incomprehensible.
　　 "Template, origin, sister, your acting is too exaggerated." Xu Qiu smiled.
　　 "Oh -" Chen Wanqing also smiled: "Well, I will pack a copy for you when you want to draw a picture."