Scanning near-field ultrasound holography (SNFUH) is a method for performing nondestructive nano-scale high-resolution imaging of buried and embedded structures. SNFUH is critical for analysis of materials, structures and phenomena as they continue to shrink at the micro/nano scale. SNFUH is a type of

scanning probe microscopy Scan may refer to: Acronyms * Schedules for Clinical Assessment in Neuropsychiatry (SCAN), a psychiatric diagnostic tool developed by WHO * Shared Check Authorization Network (SCAN), a database of bad check writers and collection agency for bad ...

(SPM) technique that provides depth information as well as spatial resolution at the 10 to 100 nm scale.

History

Gajendra S. Shekhawat and Vinayak P. Dravid of Northwestern University (Evanston, IL, USA) developed SNFUH in 2005. Observing copper damascene structures of a void in an opaque material was made possible by this technique.

Technique

Scanning near-field ultrasound holography combines atomic force acoustic microscopy and

ultrasonic force microscopy Acoustic microscopy is microscopy that employs very high or ultra high frequency ultrasound. Acoustic microscopes operate non-destructively and penetrate most solid materials to make visible images of internal features, including defects such as c ...

. Two transducers producing high frequencies are used. Usually frequency is higher than the

resonant frequency Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillatin ...

of the cantilever. One transducer is placed below the sample and the other attached to the cantilever. The cantilever can be called as SPM acoustic antenna which senses the interference of acoustic waves sent by the transducers. The interference of these waves forms surface acoustic standing waves. The wave's

frequencies Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...

are slightly different. The

perturbations Perturbation or perturb may refer to: * Perturbation theory, mathematical methods that give approximate solutions to problems that cannot be solved exactly * Perturbation (geology), changes in the nature of alluvial deposits over time * Perturbatio ...

to phase and amplitude of the surface acoustic standing wave are locally monitored by the antenna via the lock-in approach and the SPM electronic module. This electronic module was developed by Shekhawat and Dravid. It was implemented with a radio frequency (RF) lock in approach. Two modes are used:Gajendra S. Shekhawat and Vinayak P. Dravid "''Nano Scale imaging of buried Structures via SNFUH''
Science 2005
/ref> Soft contact mode is for hard structures. In the near contact mode, the tip is first made to touch the surface and then lift f 2-5 nm is used for biological samples.

Advantages over other SPM techniques

This technique takes advantage of both the phase and amplitude of scattered ultrasound waves to produce nanoscale resolution images of internal substructures. It is nondestructive and provides real space imaging, depth information, hidden information in materials, spatial resolution at the 10- 100 nm scale and can study various material systems.

References

{{reflist Holography

History

Technique

Advantages over other SPM techniques

See also

References