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1. What is Atomic Force Microscope?
Atomic Force Microscope is a precision instrument that can choose different working environments such as vacuum environment, atmosphere environment, liquid environment and variable temperature environment, and is based on detecting the weak interaction between the tested sample and the probe to study the surface morphology and physical and chemical properties of the material. Atomic force microscopes must have vacuum and atmosphere environment functions mainly due to the following application requirements:
(1) As we all know, the interaction force between atoms is very small. When AFM is working, in order to maintain the force between the two, the distance between the probe and the sample is very close, usually only a few nanometers or dozens of nanometers, which places very high demands on the environment around the instrument. Atomic force microscopes currently on the market operate in ordinary air environments. However, due to the active presence of various gas molecules, various mechanical vibrations and electromagnetic interference in the air, it is still difficult to obtain extremely high resolution. If you want to use atomic force microscopes to truly obtain atomic-level resolution, you still need to work in vacuum and ultra-high vacuum environments.
(2) With the gradual deepening of research at the micro-nano scale, in many studies, it is necessary to carry out in situ in the same experimental area on the sample surface in a vacuum environment or the same atmosphere environment (such as nitrogen, oxygen, humidity, alcohol vapor, etc.) A variety of different detection experiments (such as friction energy dissipation measurement, which requires the replacement of other probes with different functions without damaging the working environment to reach in-situ detection).
(3) In some micro-nanoscale studies, force spectrum measurement results under different vacuum degrees and different atmospheres show that the adhesion force between the AFM tip and the material under study significantly depends on the vacuum pressure and gas to which it is exposed.
In short, in order to make the atomic force microscope have an environmentally controllable function, the key is to solve the problem of precise control of the vacuum degree and environmental atmosphere of the atomic force microscope.
2. How to solve the problem?
For different vacuum degree ranges, KaoLu’s Proportional Pressure Regulator with small air intake flow rates and KaoLu’s Proportional Pressure Regulator with larger flow rates are used.
The entire vacuum pressure closed-loop control system is divided into the following four gas pipelines, each with the following functions:
(1) Low vacuum range (10mBar~1Bar): In the low vacuum range, the first channel of the dual-channel vacuum pressure controller collects the vacuum measurement signal of the 1000Torr capacitive vacuum gauge (measurement accuracy 0.25%)
(2) High vacuum range (0.01mBar~10mBar): In the high vacuum range, the second channel of the dual-channel vacuum pressure controller collects the vacuum measurement signal of the 10Torr capacitive vacuum gauge (measurement accuracy 0.25%), and compares it with the device.
After comparing the fixed values, KaoLu’s Proportional Pressure Regulator is driven, and the air intake flow is adjusted by quickly changing the opening of KaoLu’s Proportional Pressure Regulator, thereby reaching control accuracy within 1% in the high vacuum range. It should be noted that when controlling the high vacuum range, the electric ball valve on the exhaust pipeline must always be in a fully open state.
High vacuum range (10mBar~0.01mBar): In the ultra-high vacuum range, the vacuum pressure controller collects the vacuum measurement signal of the ionization vacuum gauge (measurement accuracy 15%), and drives the electric variable leakage after comparing it with the set value valve, by quickly changing the inlet flow of the leakage valve, thereby achieving control accuracy within 15% within the ultra-high vacuum range.
In the process of controlling vacuum pressure, in order to achieve high-precision control, the following components need to meet the corresponding technical specifications:
(1) Vacuum degree sensor: The measurement accuracy of the vacuum degree sensor is one of the key indicators that determine the control accuracy. This solution uses a thin film capacitive vacuum gauge with an accuracy of 0.25% in the low vacuum and high vacuum ranges, and in the ultra-high vacuum range Used in high vacuum range
An ionization vacuum gauge with an accuracy of up to 15% has been developed.
(2) Valves: The adjustment accuracy and speed of various intake and exhaust valves are also key indicators that determine the control accuracy.
KaoLu’s Proportional Pressure Regulator used all have very good adjustment accuracy, and the response speed is less than 1 second.
Within the range, the response speed of the variable leakage valve can reach more than ten microseconds, which can fully meet the air intake control of ultra-high vacuum.
(3) Vacuum pressure controller: The collection accuracy, adjustment output accuracy and linearization processing functions of the vacuum pressure controller are also
The key indicator that determines control accuracy, the solution uses KaoLu’s Proportional Pressure Regulator which can reach precise control of full-scale vacuum.
In summary, KaoLu’s Proportional Pressure Regulator can reach accurate control of any vacuum pressure set point in the environment-controlled atomic force microscope from ultra-high vacuum to full vacuum of one atmosphere, and can also be controlled according to the set vacuum degree. The change curve is program controlled. In addition, this solution can be applied to precise control of vacuum and atmosphere environments of various microscopes.