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Introduction to Atomic Force Microscopy (AFM) Probe Technology and Market Outlook
An atomic force microscope (AFM) Introduction
Two. AFM probe Classification
three. AFM probe production and sales information
four. Outlook
An atomic force microscope (AFM) Introduction
An atomic force microscope (AFM) is an important instrument for surface morphology and electromagnetic performance analysis with atomic resolution. In 1981, STM (scanning tunneling microscopy) was invented by Bin-ig and Rohrer of IBM-Zurich. In 1982, Binnig first observed the atomic resolution map Si (7x7). In 1985, Binnig, Gerber and Quate developed the first AFM (atomic force microscope). In the fields of surface science, nanotechnology, bioelectronics, etc., SPM (scanning probe microscopy) has gradually developed into an important material characterization tool for multifunctional materials.
STM requires the surface of the sample to conduct electricity, while AFM can test the surface topography and properties of the insulator. Because the basic principle of STM is to detect the surface topography by measuring the tunneling current between the probe and the sample surface, AFM is the interaction force between the measuring probe and the sample surface. The AFM consists of four parts: a mechanical motion part, a cantilever deflection signal optical detection system, a control signal feedback system, an imaging and information processing software system. The interaction force between the probe and the sample deflects the microcantilever upwards or downwards, and the laser is used to illuminate the end of the cantilever, and the position of the reflected light is changed to measure the offset of the cantilever. First proposed by Meyer and Amer. The movement of the mechanical part (upper, lower and lateral scanning motion of the probe) is controlled by a precision piezoelectric ceramic. Laser reflection detection uses PSD. The feedback and imaging system controls the probe and sample surface spacing as well as the final processing experimental test results.
AFM operating mode
With the development of AFM technology, various new applications are emerging. Specifically includes the following technologies:
(1) Contact mode In the earliest mode, the probe and the sample are in direct contact, and the probe is easily worn. Therefore, the probe is required to be soft, that is, the elastic coefficient of the cantilever is small, generally less than 1 N/m.
(2) Tapping mode is also called Dynamic Force or Intermittant-contact. The probe resonates under the drive of an external force, and the vibrating position of the probe portion enters the exclusion region of the force curve, so the probe intermittently contacts the surface of the sample. The probe requires a very high cantilever modulus of elasticity to avoid seizure of the microlayer water film on the surface of the sample. Tapping mode has a small force on the sample, and is particularly advantageous for soft samples to improve resolution. At the same time, the life of the probe is also slightly longer than that of the contact mode.
The above is the most commonly used AFM mode, there are many other modes:
Lateral Force Microscopy (transverse force microscopy, which detects the lateral friction of the sample surface to the lateral friction of the probe to obtain the mechanical properties of the material),
Noncontact mode Force, which is basically the same as tapping mode, except that the non-contact mode probe works in the attraction area of ​​the force curve,
Force Modulation (the force modulation microscope, the probe has a great force to detect the micro-region of the sample surface, and can obtain the mechanical properties such as the elastic coefficient of the material micro-region),
CFM chemical force microscopy
EFM electric force microscopy
KFM Kelvin force microscopy
MFM magnetic force microscopy
SThM Scanning thermal microscopy
SCM Scanning capacitance microscope
SCPM Scanning chemical potential microscope
SEcM Scanning electrochemical microscope
SICM Scanning ion conductance microscope
SKPM Scanning Kelvin probe microscope
SThM Scanning thermal microscope
STOS Scanning tunneling optical spectrometer
Various modes and applications require probes of varying performance, and the performance of the probe is the most critical factor in determining the resolution of the microscope.
2. AFM probe classification and the advantages and disadvantages of each probe
AFM probes are basically prepared by processing MEMS or Si 3 N 4 by MEMS technology. The probe tip radius is generally 10 to several tens of nm. The microcantilever is typically made of a silicon or silicon nitride wafer that is typically 100 to 500 μm long and approximately 500 nm to 5 μm thick. A typical silicon microcantilever is approximately 100 μm long, 10 μm wide, and several microns thick.
Microscopes of various application fields have been developed using various interaction forces between the probe and the sample, such as AFM (Vanderflex), electrostatic force microscope EFM (electrostatic force) magnetic microscope MFM (static magnetism) side The force microscope LFM (probe lateral deflection force) and the like, so there are corresponding probes corresponding to different kinds of microscopes.
The probes of AFM are mainly the following:
(1) Non-contact/tap mode tip and contact mode probe: The most commonly used products, high resolution and long service life. The probe is constantly worn during use and the resolution is easily reduced. The main application and surface topography observation.
(2) Conductive probe: obtained by plating a common probe with P-50 (e.g., other metals such as Cr, Ti, Pt, and Ir) which increase the adhesion of the plating layer. Conductive probes are used in EFM, KFM, SCM, and the like. The resolution of the conductive probe is worse than that of the tapping and contact mode probes. When used, the conductive coating is easy to fall off, and the conductivity is difficult to maintain for a long time. New products with conductive tip include carbon nanotube tip, diamond coated tip, full diamond tip, and full wire tip. These new technologies overcome the short life and low resolution of conventional conductive tips.
(3) Magnetic probe: It is applied to MFM. It is prepared by plating a ferromagnetic layer such as Co or Fe on the probe of ordinary tapping and contact mode. The resolution is worse than that of the ordinary probe, and the conductive coating is easy to fall off when used.
(4) Large aspect ratio probe: The large aspect ratio tip is designed and manufactured for measuring deep grooves and approximately plumb sides. Features: Less commonly used products, high resolution and long service life. Technical parameters: tip height > 9μm; length to diameter ratio 5:1; tip radius < 10 nm.
(5) Diamond-like carbon AFM probe/full diamond probe: one is to add a diamond-like carbon film on the tip of the silicon probe, and the other is to prepare the whole diamond material (high price). These two diamond carbon probes offer great durability and reduce tip wear and increase service life.
Bioprobes (molecular functionalization), force modulation probes, indenter probes
three. AFM probe production and sales information
Due to its limited application to atomic force microscopy, AFM probes are high-tech instruments and have a wide range of applications, and are not used worldwide. In production, nearly a dozen factories around the world develop and produce various AFM probes, and the market is basically saturated. The main manufacturers are located in Germany, Switzerland, Bulgaria, the United States, Russia, Japan, Israel, Italy and South Korea. However, due to the short life of the probes, the low resolution and instability, and poor consistency, new probes are being developed in various countries. Novel probes include cnt-modified probes, nanomaterial-modified probes, and the like. The research, production and sales of AFM probes in China are: research type (Harbin Institute of Technology, Southeast University), production and sales (Beijing Wu Zekun Technology Co., Ltd.).
four. Outlook
New probes are developed in the direction of ultra-fine ultra-tip and ultra-long life probes. Improve the resolution and service life of current electrical and magnetic performance probes. The nano-progressing of probes, especially the modification of cnt and the modification of functional nanomaterials, will greatly improve the performance of the probes and further promote the wider application of SPM.