#atomic microscope

PinPointing Polymers: Nanomechanical Characterization of Functional Polymer Blends | Park Webinar

Polymer based blends and composites are a key area of materials research activity.For example, blends of polymers are used in optoelectronic devices for charge extraction, and biopolymers which change their mechanical character upon environmental influences.

To many researchers and scientists, the availability of an atomic force microscope and the nearly miraculous way it processed images were the best thing that ever happened in their careers. It provided them with the chance to break through barriers which used to be impossible and find solutions, make advances and take their research forward. Yet, according to the team at Park Systems, a global leader in the field of atomic force microscopy, even this highly advanced device has its limitations. They shared an overview of what the many advantages of the device are and the slight shadow of limitations following it like a trail.

One of the features of AFM which set it apart from its predecessor the SEM was the fact that now life sciences could also reap the benefits of nanotechnology as the materials which you can observe did not have to be conductive or semi-conductive anymore and researchers could explore biological tissue.

The AFM provides a three-dimensional view of the surface of the profile you want to explore and the process does not require any kind of advanced treatments. With the SEM a surface would need special treatments with carbon or metal coating causing irreversible damage to your object. Now it was no longer the case.

The AFM could break free from the very expensive vacuum environment which was a necessary feature when you work with SEM. As scanning electron microscopes only function accurately within a vacuum environment, it had several limitations often set by limited budgets. The AFM broke through all these barriers as it works perfectly well and provided high accuracy and precision even in ambient air and liquid settings. The result was that now researchers could study living objects. Lastly, AFM image processing is possible at far higher resolutions than with SEM, bringing greater visibility and accurate insights into the field of study.

While there are many breakthroughs in several fields of study that took place thanks to the wonderful contributions of AFM image processing, even this highly advanced device still has some limitations. One of the limitations is that the AFM has a relatively slow scanning speed. Every scan can take up to several minutes, this is much slower than the rate at which SEM image processing takes place. It is all fine to wait slightly longer for the scanning process but the growing concern during the longer processing time is the increasing risk of thermal drift in the image. The result of this is that AFM becomes a less accurate tool to measure the distances present between various topographical features.

Another concern is the restrictions AFM has towards the size of the object it can scan at any single moment. With an SEM it is possible to scan areas of several square millimetres while it also has a depth of field of several millimetres. This is not the case with the AFM. During AFM image processing, the area which it can scan is small and no bigger than 10-20 micrometres while the maximum area it can scan is no larger than 150x150 micrometres. One technique which scientists use to overcome this concern is to rely on parallel probes in a way which resembles the same techniques as used in millipede data storage.

Factors such as an unsuitable tip, the quality of the sample material you are scanning and even environmental factors can influence the accuracy of your ATM image processing.

Yet, it is important to remember that researchers can overcome many of these restrictions through various techniques. While the team of experts at Park Systems is always available to provide the support, you need to achieve optimal functionality from your highly advanced equipment.

Before looking at the many great benefits of electron microscopes, get to know some of the history behind this versatile microscope used in many research projects globally each year. The first electron microscope was built in 1931 by Ernst Ruska, a German academic professor and engineer. The same principles he used still govern the modern day electron microscope. With an understanding that electron wavelengths are shorter than light wavelengths, Ruska applied his knowledge to develop a powerful microscope. He developed an even more powerful electron microscope at the end of the 1930's. He won the Nobel Prize for Physics in 1986.

The electron microscope focuses a beam of energized electrons to examine specimens in nano scales. The specimens do need to be prepared differently to light microscopes, in that they need to be placed in a vacuum chamber with an image being viewed on a screen. The electron microscope relies on electromagnetic or electrostatic lenses, sometimes both. These have a coil of wire wrapped on the outside of a tube, this is a solenoid. The microscope then uses digital displays, software for analysis and a pressure chamber to provide accurate results of the research being carried out.

Electron microscopy samples have to be prepared with care and placed in a microscope vacuum before research can begin. There are numerous techniques used, which are determined based on the analysis and specimen including fixation, cryofixation, embedding, dehydration, sectioning, steining, sputter coating and freeze fracturing or freeze etching. The majority of these techniques need a trained operator due to the manipulation of the specimen, which can cause an artifact or inadvertent change to the specimens structure.

These microscopes offer nanoscale imaging. Images are developed through an interaction between the energetic electrons and the sample carefully prepared in the vacuum chamber. The beam passes through one or more solenoids and is directed down a column and onto the chosen sample. Electron beams are sent and in turn, create a high resolution image.

If you increase voltage you will find an increase in resolution. When the electrons contact the sample, they provide topographical information including surface texture, size, shape, surface particles detected, element composition and more.

There are two types of electron microscopes with the first being discussed is the transmission electron microscope, which can produce images of one nanometer in size. This microscope requires high voltage to increase the speed of the electrons. The black and white image can be viewed on a screen or printed onto a plate.

The second electron microscope is the scanning electron microscope which is used to gather useful topographical information. These use solenoids to pull the beam back and forth over the sample while scanning the surface.  Secondary electrons which are emitted from the surface produce the high quality and high resolution image.

The scanning electron microscope is less powerful than the transmission electron microscope, but produces a very high quality, black and white 3D image of the specimen being studied.

These microscopes are advantageous for providing powerful magnification of specimens, which can be used in medical and forensic science, biotechnology, biology and so much more. They are also used in industrial applications, computer chip manufacturing, quality control and more.

These are large pieces of equipment, so you need to ensure you have ample space in your laboratory to house them, keeping them away from other equipment which could result in the machine picking up sounds and vibratos which could negatively impact its performance.

Atomic force microscopy principle is based on the assembly of the cantilever tip that is responsible for interacting with samples. The assembly is often called the probe. The Atomic force microscopy (AFM) probe interacts with substrates using a raster scanning motion, up down and side to side motions are used by the tip as it scans the surface using a laser beam which reflects off the cantilever. This laser is tracked by position sensitive photo detectors that are responsible for picking up the motion of the probe.

In order to achieve tapping modes, the probe is mounted onto a holder with shaker piezo. The shaker piezo offers the opportunity for the probe to oscillate at a number of frequencies. How the AFM works is determined by numerous factors including the AFM theory, cantilever and assembly.

Assembly is a detailed process that relies on a sharp tip hanging from the bottom of the narrow cantilever. The cantilever tip assembly is the AFM probe, the height and length of the probe is determined by the cantilever. The most common cantilevers is the rectangular and the triangular. The probe material is silicone or silicon nitride, which is reserved for the softer cantilevers that have lower spring constants. The dimensions are essential in determining the spring constant or stiffness. The stiffness manages the interaction between the surface and the probe. If you choose incorrectly it could result in bad image quality.

The sensitivity is calibrated to convert the volts that are measured on the photodetector to nanometers of the motion. The calibration is done by measuring a force curve of the surface.  Then there is the calibration of the spring constant of rectangular cantilevers. The length and width of the cantilever is recorded, this often includes the thermal noise spectrum where room temperature thermal motion helps to drive the cantilever. A harmonic oscillating model helps extract resonance frequency and the quality factor, which are added to the cantilever in a set environment, which helps to calculate the spring constant.

Frequency sweeps can also be used for the calibration of the spring constant. This calibration is essential to ensure that accurate thermal sweeps occur.  Finally you need to ensure that the AFM operation is focused on feedback. Feedback perimeters are important. Based on the different modes, the parameter will serve as a set point. The feedback loop can be controlled, which helps the feedback loop adjust to the difference against the set point value.

The proportional gain may offer improvements after optimization of the integral gain, while the derivative gain is there for tall edged samples. Gains that are set too low makes it harder for the PID loop to keep to the set point. Gains that are set too high can cause an electrical noise which will cause interference to the feedback.

Scan rate and set point are also important to ensure that the scan rate isn't too fast to provide sufficient feedback. Slow scan rates shouldn't be too much of a concern except it can take a long period to acquire the feedback.

Atomic Force Microscopes can be configured to scan the tip over the sample or scan the sample under the tip.. This offers the advantage of flexibility based on the sample size. The scanning instruments can handle large samples with the limitation that they must fit into the instrument. This flexibility makes atomic force microscopy popular in a wide range of industries on a global scale.

Surface Potential Imaging via Sideband KPFM | Park Systems Webinar

Park Systems Webinar - New Surfactant Design

The Park Systems 2019 Material Science Research and AFM Webinar Series continues with New Surfactant Design.