physics

Magnetic resonance force microscopy

Magnetic resonance force microscopy is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Magnetic resonance force microscopy rather than just read about it. In short: Magnetic resonance force microscopy (MRFM) is an imaging technique that acquires magnetic resonance images (MRI) at nanometer scales, and possibly at atomic scales in the future. MRFM is potentially able to observe protein structures which cannot be seen using X-ray crystallography and protein nuclear magnetic resonance spectroscopy.

Key takeaways

Magnetic resonance force microscopy belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Magnetic resonance force microscopy to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Magnetic resonance force microscopy from memory before moving on to harder problems.

Reference excerpt

Magnetic resonance force microscopy (MRFM) is an imaging technique that acquires magnetic resonance images (MRI) at nanometer scales, and possibly at atomic scales in the future. MRFM is potentially able to observe protein structures which cannot be seen using X-ray crystallography and protein nuclear magnetic resonance spectroscopy. Detection of the magnetic spin of a single electron has been demonstrated using this technique. The sensitivity of a current MRFM microscope is 10 billion times greater than a medical MRI used in hospitals.

Basic principle The MRFM concept combines the ideas of magnetic resonance imaging (MRI) and atomic force microscopy (AFM). Conventional MRI employs an inductive coil as an antenna to sense resonant nuclear or electronic spins in a magnetic field gradient. MRFM uses a cantilever tipped with a ferromagnetic (iron cobalt) particle to directly detect a modulated spin gradient force between sample spins and the tip. The magnetic particle is characterized using the technique of cantilever magnetometry. As the ferromagnetic tip moves close to the sample, the atoms' nuclear spins become attracted to it and generate a small force on the cantilever. The spins are then repeatedly flipped, causing the cantilever to gently sway back and forth in a synchronous motion. That displacement is measured with an interferometer (laser beam) to create a series of 2-D images of the sample, which are combined to generate a 3-D image. The interferometer measures resonant frequency of the cantilever. Smaller ferromagnetic particles and softer cantilevers increase the signal-to-noise ratio. Unlike the inductive coil approach, MRFM sensitivity scales favorably as device and sample dimensions are reduced. Because the signal-to-noise ratio is inversely proportional to the sample size, Brownian motion is the primary source of noise at the scale in which MRFM is useful. Accordingly, MRFM devices are cryogenically cooled. MRFM was specifically devised to determine the structure of proteins in situ.

Milestones The basic principles of MRFM imaging and the theoretical possibility of this technology were first described in 1991. The first MRFM image was obtained in 1993 at the IBM Almaden Research Center with 1-μm vertical resolution and 5-μm lateral resolution using a bulk sample of the paramagnetic substance diphenylpicrylhydrazyl. The spatial resolution reached nanometer-scale in 2003. Detection of the magnetic spin of a single electron was achieved in 2004. In 2009 researchers at IBM and Stanford announced that they had achieved resolution of better than 10 nanometers, imaging tobacco mosaic virus particles on a nanometer-thick layer of adsorbed hydrocarbons.

References

External links University of Washington Quantum System Engineering and MRFM Home Page, https://web.archive.org/web/20060430032748/http://courses.washington.edu/goodall/MRFM/. Magnetic-Resonance Force Microscopy, http://www.medgadget.com/archives/2005/04/magneticresonan.html Archived 2007-10-22 at the Wayback Machine. Degen CL, Poggio M, Mamin HJ, Rettner CT, Rugar D (12 January 2009). "Nanoscale magnetic resonance imaging". PNAS. 106 (5): 1313–7. Bibcode:2009PNAS..106.1313D. doi:10.1073/pnas.0812068106. PMC 2628306. PMID 19139397. "Researchers Create Microscope With 100 Million Times Finer Resolution Than Current MRI". Phys.org. January 13, 2009. "IBM team boosts MRI resolution". BBC News. 13 January 2009. Retrieved 2009-01-14. Review Article: M. Poggio and C. L. Degen, Nanotechnology 21, 342001 (2010), Poggio, M.; Degen, C. L. (2010). "Force-detected nuclear magnetic resonance: recent advances and future challenges". Nanotechnology. 21 (34) 342001. arXiv:1006.3736. Bibcode:2010Nanot..21H2001P. doi:10.1088/0957-4484/21/34/342001. PMID 20671365. S2CID 10028988.

Worked examples

Example 1 — a first encounter with Magnetic resonance force microscopy

Start with the simplest possible case. Write down what Magnetic resonance force microscopy claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Magnetic resonance force microscopy before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Magnetic resonance force microscopy ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Magnetic resonance force microscopy

In research: Magnetic resonance force microscopy appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Magnetic resonance force microscopy in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Magnetic resonance force microscopy is common in secondary-school and first-year university syllabi. It links to neighbouring topics Nuclear magnetic resonance, Protein structure, Scanning probe microscopy, so understanding it makes those chapters shorter.
In everyday life: Look for Magnetic resonance force microscopy outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Magnetic resonance force microscopy in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Magnetic resonance force microscopy means in your own words.
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Frequently asked questions

What is Magnetic resonance force microscopy in simple terms?

Why does Magnetic resonance force microscopy matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Magnetic resonance force microscopy?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Magnetic resonance force microscopy.