Héctor Corte-León explores the benefits and downsides of the completely different methods used to calibrate a magnetic power microscope.
What’s Magnetic Pressure Microscopy?
Essentially the most basic time period is scanning probe microscope (SPM), which englobes all of the microscopes that use a bodily probe to sense the floor of pattern. Usually, these microscopes have a subject of view of about 100 µm and may obtain atomic decision. Inside the SPM techniques, people who use van der Waals interactions to sense the floor of the pattern are generally referred as ‘atomic power microscopes’ (AFMs). Within the AFM household there are numerous completely different modes, that are devoted to sensing a number of bodily properties. As an illustration, some modes sense the friction, the electrical subject or the stiffness, some measure the conductivity…
Within the case of a normal 2-pass MFM (that’s the technical name), the AFM system makes use of an oscillating silicon-based probe with a magnetic coating to sense the gradient of a magnetic subject (once more, that is basic: each day new fashions of probes and variations on the usual imaging mode are recommended – see this very exotic proposal from us utilizing nanostructures constructed into the probe). The gradient of the sphere provides to the forces performing on the probe and, consequently, shifts the probe’s oscillation from that of the excitation factor.
To simplify: in MFM, what you get are scaled photos whose colours signify levels and are proportional to magnetic subject gradients. Due to how MFM photos are fashioned, calibrating them again to quantitative values of the stray subject just isn’t straight ahead, and normally requires one among two choices: utilizing reference samples whose subject is thought (both by calculations or by measuring utilizing different strategies), or; by measuring the probe’s stray subject with another methodology after which calculating again the stray subject of the pattern.
Measuring the Probe’s Stray Area
Within the case of measuring the probe, electron microscopy-based methods are most well-liked, however generally individuals have additionally used identified fields from micron-sized coils, or magnetic nanostructures whose switching subject is thought.
When utilizing nanostructures, the thought is that the exterior subject plus the probe’s subject is what switches the magnetization; nonetheless, as a result of the probe’s subject is extremely non-uniform, the belief just isn’t sturdy sufficient and solely offers a tough estimation of the probe’s subject.
When coils are used (and it has been tried a number of instances), the dimensions of the coils impacts the outcomes as a result of, with a bigger coil, a bigger quantity of the probe’s magnetic materials contributes to the whole power. Therefore a previous data of the sorts of samples which are going to be imaged afterwards is required.
Electron-based methods, resembling differential section imaging or electron holography, add extra problems. The pictures produced with these methods are additionally not calibrated and, typically, are proportional to the mixing of the magnetic subject alongside the electron’s path inside the microscope, therefore are tough to calibrate. As well as, in MFM, probe degradation is a really massive challenge and it’s required to calibrate the probe earlier than and after every calibrated picture. If the calibration protocol contains electron-based imaging, this an extra constraint that will increase the price when it comes to time and assets.
Imaging a Pattern of Recognized Magnetization
Within the case of utilizing samples of identified magnetization (micron-sized coils is an instance), the thought is that the magnetization is thought and thus, by evaluating the section picture with the identified magnetization, is feasible to acquire the tip switch operate which converts one into the opposite. This system, which we comply with right here, just isn’t new (it was first proposed by Hug et al. in 1998), however it’s the most profitable due to its ease of use. What we showed in our paper, and what was developed within the NanoMag project, is learn how to systematically apply the calibration (i.e., a calibration protocol examined and validated many instances), its implementation within the open-source software program Gwyddion, and a few minor tweaks that enhance the calibration.
In a way, our publication was a working instance of the usual that has been developed inside the NanoMag challenge: it explains the calibration strategies, establishes a protocol, and builds on previous experiences of making an attempt to realize calibrated MFM measurements.
For extra complete info and tips about learn how to carry out a correct calibration, try his necessary paper ‘Comparison and Validation of Different Magnetic Force Microscopy Calibration Schemes’ in Small.
