View source for Physics:Scanning near-field ultrasound holography

[[File:SNFUH Principle.png|thumb|right|300px| Scanning near-field ultrasound holography principle]]
''' 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 [[Physics:Scanning probe microscopy|scanning probe microscopy]] (SPM) technique that provides depth information as well as spatial resolution at the 10 to 100&nbsp;nm scale.<ref>Gajendra S. Shekhawat, Shraddha Avasthy, Arvind K. Srivastava, Soo-Hyun Tark, and Vinayak P. Dravid "''Probing Buried Defects in Extreme Ultraviolet Multilayer Blanks Using Ultrasound Holography''" [http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=05491187 IEEE transactions 2010]</ref>

==History==
Gajendra S. Shekhawat and Vinayak P. Dravid of Northwestern University (Evanston, IL, USA) developed SNFUH in 2005.<ref>{{Cite journal|last1=Shekhawat|first1=Gajendra S.|last2=Dravid|first2=Vinayak P.|date=2005-10-07|title=Nanoscale Imaging of Buried Structures via Scanning Near-Field Ultrasound Holography|journal=Science|language=en|volume=310|issue=5745|pages=89–92|doi=10.1126/science.1117694|issn=0036-8075|pmid=16210534|bibcode=2005Sci...310...89S|s2cid=9906164 }}</ref><ref>Gajendra Shekhawat and Vinayak P. Dravid "''Seeing the Invisible: Scanning Near-Field Ultrasound Holography (SNFUH) for High Resolution Buried Imaging and Pattern Recognition''" [http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=1213376 Microscopy and Microanalysis 2007]</ref> Observing [[Engineering:Copper interconnect|copper damascene]] structures of a void in an opaque material was made possible by this technique.<ref>Alain C. Diebold "''Subsurface Imaging with Scanning Ultrasound Holography''" [https://www.science.org/doi/pdf/10.1126/science.1119259 Science magazine 2005]</ref>

==Technique==
Scanning near-field ultrasound holography combines [[Physics:Atomic force acoustic microscopy|atomic force acoustic microscopy]] and [[Physics:Ultrasonic force microscopy|ultrasonic force microscopy]]. Two transducers producing high frequencies are used. Usually frequency is higher than the [[Physics:Resonant frequency|resonant frequency]] of the cantilever. One transducer is placed below the sample and the other attached to the cantilever.  The cantilever can be called as SPM [[Physics:Acoustics|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 are slightly different. The [[Physics:Perturbation theory|perturbations]] to [[Physics:Phase (waves)|phase]] and [[Physics:Amplitude|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 [[Engineering:Radio frequency|radio frequency]] (RF) lock in approach.

Two modes are used:<ref>Gajendra S. Shekhawat and Vinayak P. Dravid "''Nano Scale imaging of buried Structures via SNFUH''" [https://www.science.org/doi/full/10.1126/science.1117694  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&nbsp;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.{{fact|date=August 2016}} It is nondestructive and provides real space imaging, depth information, hidden information in materials, spatial resolution at the 10- 100&nbsp;nm scale and can study various material systems.

==See also==
* [[Physics:Acoustic microscopy|Acoustic microscopy]]
* [[Engineering:Scanning acoustic microscope|Scanning acoustic microscope]]

==References==
{{reflist}}

[[Category:Holography]]

{{Sourceattribution|Scanning near-field ultrasound holography}}