| Since the advent of the first scanning tunneling microscope (STM), human could observe atoms directly and even manipulate the atoms. In the last thirty years, scientists have forged ahead for the development of STM, making it more mature, diversification, specialization and professionalization. Today, people can observe, detect and control the micro world relying on scanning probe microscope in the field of condensed matter physics, physical electronics, biology, electrochemistry, aeronautics and so on.The study of surface electronic states in strong magnetic field is always the focus of research, because lots of novel physical phenomena can be observed using STM in the strong magnetic field. However, there are some important things need ultra strong magnetic field STM to observe, such as explaining the micro mechanism of metal-insulator transition in Single-walled Carbon Nanotubes, which requires ultra strong magnetic field of45Tesla; verifing the theory of Vortex in Quantum Dots, which needs about25Tesla; obsveing the micro behavior of HTS in their Upper Critical Magnetic Field also needs about45Tesla. For that sharp tools make good work, the construction of STM in strong magnetic field is particularly important. Over the years, many teams in the word had developed outstanding STM in strong magnetic field. However, the record obtaining atomic resolution STM in magnetic field is only18Tesla, which is far from our needs. At present, the commercial superconduct magnet on sale has the highest23Tesla. Although one team had made a30Tesla superconduct magnet, it is a long way to sale. As a consequence, people need water-cooled magnet and even hybrid magnet to obsever the surface electronic states in ultra strong magnetic field. However, the vibrations of water-cooled magnets and the hybrid magnets are violent, and the noises are very lound, which are the biggest difficulties to obtain the atomic resolution images in the magnet. So far, there have no reports about building STM in water-cooled magnet or hybrid magnet in the world.At High Magnetic Field Laboratory of Chinese Academy of Sciences, there one water-cooled magnet has officially come into service, which has the maximum magnetic field of27Tesla and the center aperture of32mm. This is the first water-cooled magnet in China. At the end of next year, there will the first hybrid magnet be built in China, which has the maximum magnetic field of45Tesla. On this water- cooled magnet with small aperture, we have built up a set of STM system. The biggest difficulties are the lound noise and the violent vibration of the magnet. In addition, the small aperture is also the limit. The STM in such harsh conditions and small aperture must have ultra rigid structure. Generally, the scanner is connected to the step motor, so the stability of motor directly related to the stability of tunnelling current. As a consequence, an outstanding step motor is necessary. The motor should have the following properties:1. simple structure, because the simple structure brings reliability;2. low control voltage, which will reduce the noise and improve the control accuracy;3. compactness, because small volume brings small thermal drift, and also the suitability in small aperture;4. rigidity, which is the most important indicator of vibration resistance. However, all of the fashionable motor in the world has one or more shallows, which are not suitable for water-cooled magnet. The manuscript of this STM has accepted by Scanning.In the second chapter, in order to make the best STM for harsh conditions, we developed a rigid and compact piezoelectric stack motor with its diameter of only13mm. The motor consists of two branches (six pieces of piezoelectric plates), which then flexibly fixed on the surface of two parallel polishing corundum rods. The advantages of the motor are apparent:simple and compact structure, high rigidity, unlimited travel range. The STM using such motor shows high rigidity and vibration resistance, and even obtained quite clear atomic resolution images in the73dB surrounding noise, which has no difference from the one in the sound proof box. In addition, we developed a method to effectively reduce the working voltage of the motor, reducing the threshold voltage of1/3-1/2. This STM is also compatible in the low temperature. Because of its high rigidity and compactness, the STM is very suitable for harsh conditions like voilent vibration, lound noise and strong magnetic field. The preamplifier circuit, high voltage amplifier circuit and filter circuit which the STM needed are home-designed and manufactured.In the third chapter, we built up a complete set of STM system in the water-cooled magnet of WM4(center aperture of32mm and the highest field of27Tesla). The whole system, including the damping system, vacuum insulation system and the STM body, adopts non-magnetic or weakly magnetic material. The whole system used the integral spring suspension mechanism, leading to the resonance frequency less than3Hz. The STM body is used the mechanism of three stages of spring suspension, which has a very good effect. The vacuum system used the method of cold trap, i.e. using the large surface and elasticity of soft bellows to make a low-temperature pump and operating lever, leading to the best vacuum degree of3×10-5mbar, which is the key point of sound insulation and heat insulation. The STM body had further improvement based on the motor introduced in the second chapter. We used the method of scanner-motor separation, which cause the interference signal of motor dividing from the tunnelling signals, and improve the quality of the image. Finally, we obtained very clear highly oriented pyrolytic graphite atomic image when the water-cooled magnet having maximum water flow and even the0.42Tesla magnetic field. It is the first atomic resolution STM image in water-cooled magnet, which has great significance because it is the foundation of building atomic resolution STM in the future hybrid magnet. The reasons are:1. the vibration of hybrid magnet is the same with the one of water-cooled magnet;2. the noise of hybrid magnet is the same with the one of water-cooled magnet;3. the central aperture of hybrid magnet is also32mm;4. the hybrid magnet has room temperature aperture, too.In the fourth chapter, we designed and manufactured a five piezo stacks motor with the character of self-cancelling friction, and then assembled a STM with high rigidity and large output force. The advantages of this motor include:1. very high density of piezo material utilized, which provides high output force per unit space;2. the travel range is limited by the lengths of the rails which can be arbitrarily long;3. small size of only16mm diameter;4. large rage of work temperature because the spring forces are long range forces and do not change in a wide temperature range since the thermal expansion mismatch is negligible compared with the range of the spring force;5. very high positioning precision as confirmed by the measured tunneling current curve, which is very important for the approaching of probe and sample. In addition, we defined the static-dynamic ratio, which is used to measure the output force of motor. Our motor has the static-dynamic ratio of less than10%, leading to far larger output force than other friction motor. Because of the characte of high output force of motor, the clamping force of scanner is up to0.82N, which is very rigid. The manuscript of this STM has accepted by Rev. Sci. Instrum. Finally, we get very clear atomic resolution images using this STM. In order to make the STM body compatible with our superconduct magnet of18/20Tesla, we built a set of vacuum and sample cutting system for it. |
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