near-field scanning optical microscopy Near-field scanning optical microscopy (NSOM) or scanning near-field optical microscopy (SNOM) is a microscopy technique for nanostructure investigation that breaks the far field resolution limit by exploiting the properties of evanescent waves ...

the campanile probe is a tapered optical probe with a shape of a

campanile A bell tower is a tower that contains one or more bells, or that is designed to hold bells even if it has none. Such a tower commonly serves as part of a Christian church, and will contain church bells, but there are also many secular bell to ...

square pyramid In geometry, a square pyramid is a Pyramid (geometry), pyramid with a square base and four triangles, having a total of five faces. If the Apex (geometry), apex of the pyramid is directly above the center of the square, it is a ''right square p ...

). It is made of an optically transparent

dielectric In electromagnetism, a dielectric (or dielectric medium) is an Insulator (electricity), electrical insulator that can be Polarisability, polarised by an applied electric field. When a dielectric material is placed in an electric field, electric ...

, typically

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant f ...

, and its two facets are coated with a metal, typically

gold Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...

. At the probe tip, the metal-coated facets are separated by a gap of a few tens of nanometers, which determines the spatial resolution of the probe. Such a probe design allows collecting optical signals, usually

photoluminescence Photoluminescence (abbreviated as PL) is light emission from any form of matter after the absorption of photons (electromagnetic radiation). It is one of many forms of luminescence (light emission) and is initiated by photoexcitation (i.e. phot ...

(PL) or

Raman scattering In chemistry and physics, Raman scattering or the Raman effect () is the inelastic scattering of photons by matter, meaning that there is both an exchange of energy and a change in the light's direction. Typically this effect involves vibrationa ...

, with a subwavelength resolution, breaking the

diffraction limit In optics, any optical instrument or systema microscope, telescope, or camerahas a principal limit to its resolution due to the physics of diffraction. An optical instrument is said to be diffraction-limited if it has reached this limit of res ...

. The campanile probe is attached to an

optical fiber An optical fiber, or optical fibre, is a flexible glass or plastic fiber that can transmit light from one end to the other. Such fibers find wide usage in fiber-optic communications, where they permit transmission over longer distances and at ...

, which both provides a laser excitation of the studied sample and collects the measured signal. The probe is rastered over the sample with a standard

scanning probe microscopy Scanning probe microscopy (SPM) is a branch of microscopy that forms images of surfaces using a physical probe that scans the specimen. SPM was founded in 1981, with the invention of the scanning tunneling microscope, an instrument for imaging ...

scanner, keeping the distance to the sample surface at a few nanometers. Contrary to the traditional (circular) near-field probes, the campanile probe has no cut-off frequency and is insensitive to the spatial mode of the optical near field. Hence its application is not limited to thin-film samples. Another advantage of the campanile probe is a high signal collection efficiency, which exceeds 90%. Campanile probes are typically fabricated as follows: a standard cylindrical

single-mode optical fiber In fiber-optic communication, a single-mode optical fiber, also known as fundamental- or mono-mode, is an optical fiber designed to carry only a single mode (electromagnetism), mode of light - the transverse mode. Modes are the possible solutio ...

is etched with

hydrofluoric acid Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water. Solutions of HF are colorless, acidic and highly corrosive. A common concentration is 49% (48–52%) but there are also stronger solutions (e.g. 70%) and pure HF has a boiling p ...

to create a conical tip with a radius of ca. 100 nm. Then a square pyramid is carved on the tip using

focused ion beam Focused ion beam, also known as FIB, is a technique used particularly in the semiconductor industry, materials science and increasingly in the biological field for site-specific analysis, deposition, and ablation of materials. A FIB setup is a sc ...

(FIB) milling, and its two facets are coated with a metal by shadow evaporation. A nanometer gap is then opened on the tip by FIB. Alternative fabrication method uses

nanoimprint lithography Nanoimprint lithography (NIL) is a method of fabricating nanometer-scale patterns. It is a simple nanolithography process with low cost, high throughput and high resolution. It creates patterns by mechanical deformation of imprint resist and su ...

to replicate campanile pyramid from a mold. This approach significantly increases fabrication speed.

References

{{Reflist, refs= {{cite journal, doi=10.1038/ncomms8993, pmid=26269394, pmc=4557266, title=Visualizing nanoscale excitonic relaxation properties of disordered edges and grain boundaries in monolayer molybdenum disulfide, journal=Nature Communications, volume=6, pages=7993, year=2015, last1=Bao, first1=Wei, last2=Borys, first2=Nicholas J., last3=Ko, first3=Changhyun, last4=Suh, first4=Joonki, last5=Fan, first5=Wen, last6=Thron, first6=Andrew, last7=Zhang, first7=Yingjie, last8=Buyanin, first8=Alexander, last9=Zhang, first9=Jie, last10=Cabrini, first10=Stefano, last11=Ashby, first11=Paul D., last12=Weber-Bargioni, first12=Alexander, last13=Tongay, first13=Sefaattin, last14=Aloni, first14=Shaul, last15=Ogletree, first15=D. Frank, last16=Wu, first16=Junqiao, last17=Salmeron, first17=Miquel B., last18=Schuck, first18=P. James, bibcode = 2015NatCo...6.7993B {{cite journal, doi=10.1126/science.1227977 , pmid=23224550 , title=Mapping Local Charge Recombination Heterogeneity by Multidimensional Nanospectroscopic Imaging , journal=Science , volume=338 , issue=6112 , pages=1317–21 , year=2012 , last1=Bao , first1=W. , last2=Melli , first2=M. , last3=Caselli , first3=N. , last4=Riboli , first4=F. , last5=Wiersma , first5=D. S. , last6=Staffaroni , first6=M. , last7=Choo , first7=H. , last8=Ogletree , first8=D. F. , last9=Aloni , first9=S. , last10=Bokor , first10=J. , last11=Cabrini , first11=S. , last12=Intonti , first12=F. , last13=Salmeron , first13=M. B. , last14=Yablonovitch , first14=E. , last15=Schuck , first15=P. J. , last16=Weber-Bargioni , first16=A. , bibcode = 2012Sci...338.1317B {{cite book, author1=Chapelle, Marc Lamy de la , author2=Gucciardi, Pietro Giuseppe , author3=Lidgi-Guigui, Nathalie , title=Handbook of Enhanced Spectroscopy, url=https://books.google.com/books?id=fTPSCgAAQBAJ&pg=PA366, date=28 October 2015, publisher=Pan Stanford Publishing, isbn=978-981-4613-33-0, pages=366– Scanning probe microscopy