Recently Scientists Physicists at Osaka University in Japan to use the atomic force microscope AFM in the identification of the chemical composition and determine the type of each atom and their location on the map three-dimensional topography of the surface material at the atomic level. These scientists have discovered that interactions are atomic fingerprint to distinguish the atoms using a microscope AFM.
In this article, of how things work will shed light on this device and check how it works and the most important uses that can be carried out by atomic force microscope system.
Basic principle
Consists of an atomic force microscope AFM cantilever arm of the sensor probe at the end of the component from the top of mind known as a sharp tip is used to scan the surface of the sample. Arm are made of silicon or silicon nitride radius within a few nanometers. When approaching the top surface of the sample probe force generated between the head of the probe and the surface of the sample lead to the deviation of the force in the arm on the strength of the hook. The force would be a mutual mechanical strength or power or force or Vanderfal poetry Kahrostetekip force or magnetic force or the power of the Commonwealth of chemical or force Kzimar or other types of force, as this type of surface that is being studied. Can also study many kinds of force sensors using a special microscope and then called her name, such as magnetic force microscope, magnetic force Microscope (MFM) or scanning thermal microscope, scanning thermal microscopy or otherwise. In all of these mutual force microscopes occur in different kinds of deviation in the arm of an atomic force microscope, this deviation is measured by a laser beam deflection mirror installed on the arm of a microscope. And monitor the reflected laser beam on a matrix of linear Alfotodayud. Photodiodes. There are other ways to measure the deviation such as a scale interferometric optical interfermetry, or using Bisoketrk sensor or electrical capacity. According to the method of measuring the deviation is the design arm of the microscope example, if the measurement method relies on electricity compressibility (Bisoketrok), the arm made of materials Bisoketrok. But is the method of measuring laser rays deviation method more accurate and the most commonly used.
If the sensor is cleared when a certain height from the surface of the sample there may be a risk to the sensor that collide with the surface, In order to avoid this is to use feedback to control the distance between the sensor and the surface of the sample to keep them wrapped up Alambtadlp fixed. And is installed on the base of the sample material Bisoketrk move the sample in the z direction to maintain a constant value of force between the probe and the surface of the sample, as well as moving the sample in two dimensions x and y. There are other types of atomic force microscopes used Bisoketrik 3 crystals, each crystal is responsible for the direction of the traffic trends of the three. In modern designs are installed on the scanner arm Bisoketrik horizontal while the sample is moved only in directions x and y. In the end we get a map of space represent the topography of the surface of the sample.
Can run the atomic force microscope AFM in several types of operation and use this as required and the type of inspection you want. In general, patterns of operation can be divided into two types namely static operating style or mode of communication and the second type is the type of operating or dynamic pattern of non-contact.
Patterns of operation and taking pictures Imaging Modes
Reminded us that there are two major patterns of patterns of device driver and AFM Study are static, which is the withdrawal of the arm across the surface of the sample and not directly measure the topography of the surface through deviations in the arm. The Dynamic mode is oscillating arm near the surface at the resonant frequency of resonance frequency. Are measured by frequency and amplitude and phase and frequency resonance through force between the probe and the surface of the sample. These changes in frequency for the frequency reference gives information on the characteristics of the sample.
Study the pattern of contact or static
In this mode uses the deviation in the top of the sensor signal to the feedback and because the measured signal in this type of noise is being used less arm strength to enlarge the amount of signal deviations. And about the probe from the surface of the sample was designed to force repulsion caused by the electrons on the surface of the sample and the electron probe. Is to maintain a stable amount of power while scanning Altnarip this by maintaining the survival of deviation constant.
Dynamic mode or pattern of non-contact
Pattern of non-contact atomic force microscope
In this mode the sensor is not connected with the surface of the sample. But an arm oscillating at frequency slightly larger than the resonant frequency where the frequency capacity within a few nm (less than 10 nm). The force would be exchanged between the sensor and the surface of the sample is the strength of van der Waals Vanderfal which are dominant at that distance in any order of 1 to 10 nm above the sample, and this force acts to reduce the resonant frequency of the arm. This decrease in the resonant frequency is used in the feedback system that is maintaining the capacity to make the vibration fixed by re-adjust the distance between the sensor and the surface. By measuring the distance between the sensor and the surface while scanning in both directions x, y are plotted Tabgravep image to the surface of the sample using programs designed for it.
In this mode the sensor head is not exposed to any harm NH does not come into contact with the surface of the sample as occurs with the previous pattern. This makes it a preferred style of operating a dynamic and more particularly in the case dealing with the samples softball. But in the case of solid samples, the images taken with both types Tkona identical. But if you find a layer of nano-liquid on the surface of the sample types, the images will be going forward a bit different. Because the sensor in the style related to penetrate the liquid layer to give a picture of the surface below them, while the pattern is the caller will fluctuate over the surface and gives a picture of both the liquid and the surface together.
Pattern you
Single polymer chain, (thickness 0.4nm), recorded the pattern you Tapping mode in aqueous medium at different pH values
Often consists of a layer of water above the surface of the sample. Because we make the sensor very close to the top of the sample to obtain a reference to the measure of mutual force is likely to stick to the sensor head in the sample and to prevent this from happening is to develop the style of others connected to the pattern you tapping mode in order to overcome this problem.
In the pattern you fluctuate arm up and down near the resonant frequency and vibration have a capacity greater than 10 nm, ranging between 100 and 200 nm. Given the strength of the mutual influence on the arm when approaching from the surface of the sample Vanderfal the strength or power pole interacting binaries or electrostatic forces cause a change in capacity and less frequency, the closer the sensor head from the surface of the sample. Up the arm is controlled by Bisoketrk working to adjust the height of the arm during a survey sample. The pattern of this operating mode an ongoing pattern of non-communication.
Measure the deviation of the beam in your AFM
Reflected laser beam diode on the back side of the growers and is controlled through the detector is sensitive to the subject position sensitive detector (PSD) consists of two Votodiodin near each other and outlet of the microphone connector Votodayud differential amplifier. Angular displacement of the arm makes one Aldieudin pick up a signal is greater than Aldieud other. This gives a signal proportional to the deviation of the arm. And reach the sensitivity of the device to detect a deviation of less than 10 nm. Change can be enlarged in the corner, up along the beam path of the laser beam a few centimeters.
Force spectroscopy Force Spectroscopy
In addition to the use of atomic force microscope to obtain images at the atomic level using the microscope in the analysis of force, relationship to the measurements of force between the head of the probe and the surface of the sample as a function of the distance between them get results, known as the power curve and the distance force-distance curve. In this way be extended probe head and dragging the surface of the sample during the control arm as a function of deviation in removing Albisoketrik. This functionality is used in the measurements at the nanoscale such as links to the atomic forces and the forces of Vanrdval Kaysamar and the forces of decay in liquids and individual molecules and the forces of expansion and rupture. This force is very small within Allbeckonewton piconewton can not be measured in any other device and now it's measured AFM device and on the analytical precision of up to 0.1 nm. Can be obtained on the force spectroscopy measurements in both a typical operating static and dynamic.
To identify atoms and excellence
Image crystallize sodium chloride by atomic force microscope
alt=""id="BLOGGER_PHOTO_ID_5490049682064093826" />Uses standard atomic force AFM to obtain images of atoms, but also moved to the surfaces of materials. An atom at the top of the sensor sensitive to the atoms on the surface of an atom atom sample and a force with all the chemical atom. Because of these interactions alter the precise frequency vibration sensor head, they can be measured and sketched. On this basis, the distinction between atoms of silicon and tuna on the surface and lead alloy, by comparing the fingerprint Atomic and enlarge. Been observed that the head of the probe interacts strongly with the silicon atoms while the atoms interact with the tuna and lead less powerful. For this, the different atoms can be characterized in the form of a matrix during the passage of the sensor head on the surface of the sample.
Advantages and disadvantages
Atomic force microscope AFM has several advantages for scanning electron microscope SEM. It is also not the same as scanning electron microscope, which provides images two-dimensional Femicroskub atomic force gives three-dimensional images of the surface, in addition to that the samples do not require address the special as in the electron microscope Kngtitha carbon or gold, this invalidate the sample, and the microscope works in normal circumstances in while the electron microscope requires that the work in a vacuum. This has made atomic force microscope to study the organ of the living cell. The atomic force microscope has a high analytical capacity beyond the capacity of SEM and STM.
One disadvantage of AFM compared to a device with a SEM is the size of the image. The move, SEM is able to size up to a few millimeters and a depth of up to a few millimeters, but the AFM device works on an area of 150x150 micrometers and a depth of 10-20 micrometer. However, this defect has been dealt with through the development of devices by AFM, IBM is working Bmjsin parallel.
The use of the head sensor tip is not suitable may give some defects in the resulting image. In addition to the AFM works slowly compared with the SEM, which gives a vivid picture of the sample, the AFM requires that works for a few minutes to give a picture. This delay leads to thermal drift in the image, which makes atomic force microscope is not suitable for accurate measurements of distances on the topographic image. Devices are being developed AFM to overcome this problem with known videoAFM and running more quickly than in SEM.
AFM images are affected by hysteresis in the material retardation Albisoketrik and overlap in the signals captured for each of the x, y during the survey but this was overcome by using sophisticated software and special filters or by using separate orthogonal scanners.
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