The electron is a subatomic particle, belonging to a lepton. For a long time, because of its small quality (9.1x10-31 kg), fast (a week around the atomic nucleus only need 1.8x10^-16 seconds), although the use of a wide range, it is difficult to observe. In February 2008, a number of scientists from Sweden for the first time to take a single video recording, to achieve a historic breakthrough. However, want to shoot electronic solid inside, because the electronic large number and complicated environment is more difficult. Scientists have not found any direct observation for a long time. Until a few days ago, from the Okinawa Institute of Science and Technology Graduate University scientists use their "femtosecond camera" succeeded for the first time to take the material internal electron trajectory, once again to achieve a breakthrough. Since Thompson was discovered in 1897, scientists have tried to describe the motion of the sub atomic particles in many ways. Electrons laser pointer 5mw are too small to move too fast, not to say the naked eye, or even an optical microscope. So, how to measure the movement of electrons, stumped generations of scientists. However, Institute of Science and Technology Graduate University Okinawa femtosecond spectroscopy laboratory, so that human beings to observe the electronic movement of the goal of a big step forward.
Kesha Dani (Keshav Dani) professor is in charge of the laboratory, he said, the motion of the electron observation materials, and not only is to estimate the motion of the electron interaction based on photoelectric materials, his dream has been. Observation of electronic motion, the need for the instrument with a high spatial and temporal resolution, but the traditional instrument can not meet these two requirements. Dr. Mitchell Man (Man Michael) is a postdoctoral fellow in the laboratory. He combines ultraviolet pulse technology with electron microscopy to observe the movement of electrons in a solar cell. Schematic diagram of the high time resolution imaging principle of electron motion by femtosecond spectroscopy. 800 nm wavelength of the 50mw laser pointer excitation material in the electron, 266 nm wavelength (blue) laser is responsible for the measurement of electron motion.
Under normal circumstances, when the material is exposed to light, the electron absorbs light energy, and transitions from the low energy state to the high energy state. If the pulse time is very short duration -- 1 FS femtosecond, equal to 1/1000000000000000 seconds, then it will stimulate short response in the material, the electrons are excited will then quickly return to the ground state. For such a solar equipment, we need it in the high-energy state when the "extraordinary" energy, therefore, the scientists want to know is how to change the state of battery materials and energy release. Of course, it is not possible to directly observe the electronic energy state change on the femtosecond time scale. Therefore, to achieve the purpose of indirect observation scientists -- first with high power 30mw laser pointer pulse irradiation materials through reflection measurement of material change in light, causing material state changes lag after a period of time to launch a weak laser pulse and reflected light measurement. The energy of the first strong laser can rapidly heat the material, and the reflection of the photon produced change. When the material begins to cool, the reflection begins to move towards the normal value. Therefore, the scientists can infer the dynamic change of the internal state of the material according to the reflected light. Professor Dani said that the problem of this approach is that you can not see what happened in the material, but only according to the interpretation of the reflection of the data, to explain the changes in the internal electronic materials.
In order to solve this problem, Professor Dani's team developed a way to visualize the electronic state of the semiconductor material. Some of the electrons on the surface of the material will pop up when the weak laser beam is irradiated, and the scientists will collect the electrons and form the image with electron microscope. Under the continuous irradiation of the weak laser, these electrons will gradually accumulate, and finally form a picture of the internal electron distribution of the material. "You first use a laser to stimulate the material, and so on for a while, and then another 20mw laser pointer detection materials. So you can repeat the experiment, each time to maintain the same time difference. So you will eventually get a picture of the majority of the electronic location in this particular time difference." Professor Dani said. Next, the research team changed the time difference between the strong (excitation) and weak (detected using) laser, and got a new electronic distribution. When the picture is complete, they will further increase the time difference, and finally get a series of pictures, so that we can establish the relationship between the electronic position and the length of time after the excitation.
Finally, the pictures made by the various moments made video, you can visually display the electronic excitation, from the excited state to return to the ground state of the whole process. It is the first time that human beings are able to directly observe the changes in the electronic state, rather than the indirect one.10mw laser pointer electron excitation imaging method provides a new tool for the observation of electron motion in semiconductor materials. Scientists will be more in-depth understanding of the working mechanism of solar cells and other semiconductor devices, and is expected to produce a higher performance, lower power consumption of electronic products.
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