Angstrom Advanced Knowledge Base: Introduction of Atomic Force Microscope and Scanning Force Microscope

The AFM consists of a cantilever with a sharp tip (probe) at its end that is used to scan the specimen surface. The cantilever is a silicon or silicon nitride with a tip radius of curvature on the order of nanometers. When the tip is brought into proximity of a sample surface, forces between the tip and the sample lead to a deflection of the cantilever according to Hooke's law. Depending on the situation, forces that are measured in AFM include mechanical contact force, van der Waals forces, capillary forces, chemical bonding, electrostatic forces, magnetic forces, Casimir forces, solvation forces, etc. Along with force, additional quantities may simultaneously be measured through the use of specialized types of probe. Typically, the deflection is measured using a laser spot reflected from the top surface of the cantilever into an array of photodiodes. Other methods that are used include optical interferometry, capacitive sensing or piezoresistive AFM cantilevers. These cantilevers are fabricated with piezoresistive elements that act as a strain gauge. Using a Wheatstone bridge, strain in the AFM cantilever due to deflection can be measured, but this method is not as sensitive as laser deflection or interferometry.

Atomic force microscope topographical scan of a glass surface. The micro and nano-scale features of the glass can be observed, portraying the roughness of the material. The image space is (x,y,z) = (20um x 20um x 420nm). If the tip was scanned at a constant height, a risk would exist that the tip collides with the surface, causing damage. The feedback mechanism is employed to adjust the tip-to-sample distance to maintain a constant force between the tip and the sample. The sample is mounted on a piezoelectric tube, that can move the sample in the z direction for maintaining a constant force, and the x and y directions for scanning the sample. The tip is mounted on a piezo scanner while the sample is being scanned in X and Y using another piezo block. The resulting map of the area z = f(x,y) represents the topography of the sample.

The AFM can be operated in a number of modes, depending on the application. In general, possible imaging modes are divided into contact modes and a non-contact modes where the cantilever is vibrated.

Our goal is to provide our customers with the best products with highest standard of service at cost efficient pricing.

Angstrom Advanced Atomic Force Microscope and Scanning Force Microscope Software

The Software is available with the following data types of images: AFM Contact Mode: Topography — the rise and fall of the sample surface. Deflection — cantilever flexes because of the rise and fall of sample topography and the amount of this deflection can be reflected by the photodetector’s Up-Down signal. Friction — lateral forces between tip and sample, which causes the torsion of the cantilever and can be reflected by the photodetector’s Left-Right signal. AFM Tapping Mode: Topography — the rise and fall of the sample surface. Amplitude — cantilever oscillating amplitude changes because of the rise and fall of sample topography. Phase — cantilever oscillating phase changes because of the sample material characteristics. Scanning Tunneling Microscope: Topography —the rise and fall of the sample surface. Current — Tunneling current changes between tip and sample surface.

Our goal is to provide our customers with the best products with highest standard of service at cost efficient pricing.

Atomic Force Microscope Modes (Angstrom Advanced)

Angstrom Advanced STM relies on “tunneling current” between the probe and the sample to sense the topography of the sample. The STM probe, a sharp metal tip (in the best case, atomically sharp), is positioned a few atomic diameters above a conducting sample which is electrically biased with respect to the tip. At a distance under 1 nanometer, a tunneling current will flow from sample to tip. In operation, the bias voltages typically range from 10 to 1000 mV while the tunneling currents vary from 0.1 to10 nA. 
The tunneling current changes exponentially with the tip-sample separation, typically decreasing by a factor of two as the separation is increased 0.2 nm. The exponential relationship between the tip separation and the tunneling current makes the tunneling current an excellent parameter for sensing the tip-to-sample separation. In essence, a reproduction of the sample surface is produced by scanning the tip over the sample surface and sensing the tunneling current. 

STM relies on a precise scanning technique to produce very high-resolution, three-dimensional images of sample surfaces. The STM scans the sample surface beneath the tip in a raster pattern while sensing and outputting the tunneling current to the SPM Controller. The digital signal processor (DSP) in the Controller controls the Z position of the Piezo Scanner based on the tunneling current error signal. The STM operates in both “constant height” and “constant current” data modes, depending on the Feedback Gain settings. The DSP always adjusts the height of the tip based on the tunneling current error signal, but if the feedback gains are set extremely low (e.g., Integral Gain < 15 and Proportional Gain < 15), the piezo remains at a nearly constant height while tunneling current data is collected. With the Feedback Gains high (e.g., Integral Gain >15 and Proportional Gain >15), the Scanners Piezo height changes to keep the tunneling current nearly constant, and changes in piezo height are used to construct the image. The exponential relationship between tip-sample separation and tunneling current allows the tip height to be controlled very precisely. Angstrom Advanced AFM systems are available with multi-function setups to cover the broadest range of laboratory and academic applications.

Our goal is to provide our customers with the best products with highest standard of service at cost efficient pricing.

In Tapping Mode, a cantilever is oscillating in free air at its resonant frequency. A piezo stack excites the cantilever’s substrate vertically, causing the tip to bounce up and down. As the cantilever bounces vertically, the reflected laser beam is deflected in a regular pattern over a photodiode array, generating a sinusoidal electronic signal. And this signal is converted to a root mean square (RMS) amplitude value. 

When the same cantilever is oscillating at the sample surface, Although the piezo stack continues to excite the cantilever’s substrate with the same energy, the tip is deflected in its encounter with the surface. The reflected laser beam reveals information about the vertical height of the sample surface.

The feedback system controls the scanner’s Z voltage to maintain the tip-sample force constant, which leads the Up-Down signal equals to the Setpoint. The Z voltage is recorded for calculating the sample topography. Figure 1: No force between tip and sample, no cantilever deflection. Figure 2: Repulsion between tip and sample, cantilever deflects upside. Figure 3: Repulsion between tip and sample, cantilever deflects upside: X: Deflection of cantilever k: Force constant of cantilever F=kx

Angstrom Advanced Inc

Angstrom Advanced Inc. designs, manufactures and supplies variety of scientific instruments and Hydrogen & Nitrogen plants for academic and industrial fields. Angstrom Advanced instruments and plants have been delivered to many renowned organizations. Angstrom Advanced goal is to provide customers with the best products with highest standard of service at cost efficient pricing. Angstrom Advanced now provides several product lines including Spectrophotometer, X-ray Diffractometer, Gas Generator, Atomic Force Microscope/Scanning Probe Microscope, Hydrogen Generating Plant and Nitrogen Generating Plant. Angstrom Advanced corporate headquarters are located  in Massachusetts, USA. Angstrom Advanced have numerous partnerships, representatives in countries around the world.

Angstrom Advanced delivers a reputable and highly efficient world accepted Hydrogen and Nitrogen Generating Plants for refinery, petrochemical and other industrial applications. Angstrom Advanced services for Hydrogen Plant projects typically include conceptual design, detailed engineering, procurement, fabrication, construction, start-up and operational training. The production line of Gas Generators includes Hydrogen Plant, Nitrogen Plant and Air Plant. The combination Plants for both Hydrogen and Nitrogen, and Air and Hydrogen are available. These generators have state of the art technology, stability and functionality for scientific instruments, industry and solar and wind energy. Angstrom Advanced provide a lump-sum, turnkey solution, handling everything from concept to start-up with our own resources whenever possible. k

Angstrom Advanced Hydrogen Generating Plant product line include technologies such as:

• Hydrogen Plant by Water Electrolysis
• Hydrogen plant by Natural Gas Steam Reforming
• Hydrogen Plant by Pressure Swing Adsorption with Purifying System
• Hydrogen Plant by Ammonia Decomposition with Purifying System
• Hydrogen Plant by Methanol Decomposition

Angstrom Advanced offers gas and liquid Nitrogen Generating Plants from 0.5 m3/hr to 10000 m3/hr. Angstrom Advanced is on the forefront of technologies for Pressure Swing Adsorption (PSA) and Membrane Separation and providing turn-key nitrogen generation projects to meet different industrial applications. We also offer Nitrogen Purifying System to purify the nitrogen up to 99.9995%. Nitrogen/Oxygen Plant by Pressure Swing Adsorption (PSA).

Angstrom Advanced Nitrogen Generating Plant product line include technologies such as:

• Nitrogen Plant by Membrane Separation
• Nitrogen Purifying System
• Liquid Nitrogen, Oxygen, Argon Plant by Cryogenic Technology

Angstrom Advanced Atomic Force Microscope / Scanning Probe Microscope include AFM, SPM, STM, LFM, EFM. All of Angstrom Advanced microscope line-up bring state the art technology to meet the most advanced applications and are designed to provide images of atomic scale up to 100 micrometer. With a Digital Signal Processor inside the system, Angstrom Advanced systems can handle complicated multi-functional tasks efficiently. Angstrom Advanced Atomic Force Microscopes (AFM) which has full coverage of Contacting Mode, Tapping Mode, Phase Imaging and Lifting Mode, Lateral Force Microscope (LFM), Scanning Tunneling Microscope (STM), Conductive AFM, SPM in liquid, Environmental Control SPM, Nano-Processing System including Lithography Mode and Vector Scan Mode.

Angstrom Advanced has been bringing forth the latest advancements in all fields of technology and was founded by a group of engineers that realized the importance to research and development for the better of mankind. Angstrom Advanced location in the heart of high technology schools and Institutes made us a leading developer and manufacturer of Scientific instruments. Angstrom Advanced instruments have been delivered to many renowned universities, research institutes and companies worldwide. Angstrom Advanced goal is to supply the most accurate and sustainable scientific instrument with the highest standard of customer satisfaction.

Our goal is to provide our customers with the best products with highest standard of service at cost efficient pricing.

Learn more by visiting the Angstrom Advanced website at: www.angstrom-advanced.com