A Planar Scanning Probe Microscope

Abstract

Scanning probe microscopy (SPM) is traditionally based on very sharp tips, where the small size of the apex is critical for resolution. This paradigm is about to shift, since a novel generation of planar probes (color centers in diamond 1 , superconducting sensors 2 and single electron transistors 3 ) promises to image small electric and magnetic fields with hitherto inaccessible sensitivity. To date, much effort has been put into fabricating these planar sensors on tip-like structures. This compromises performance and poses a considerable engineering challenge, which is mastered by only a few laboratories. Here we present a radically simplified, tipless, approach -a technique for scanning an extended planar sensor parallel to a planar sample at a distance of few tens of nanometers. It is based on a combination of far-field optical techniques 4,5 to measure both tilt and distance between probe and sample with sub-mrad and sub-nm precision, respectively. Employing these measurements as a feedback signal, we demonstrate near-field optical imaging of plasmonic modes in silver nanowires by a single NV center. Our scheme simultaneously improves the sensor quality and enlarges the range of available sensors beyond the limitations of existing tip-based schemes.The rise of nanotechnology has been largely fueled by scanning probe microscopy, most prominently atomic force and scanning tunneling microscopy, which have provided a tool to image topography, friction and electronic structure with a resolution down to the atomic level 6,7 . Today, the imaging of quantities other than forces and electric transport properties stands out as a frontier in this field of research. Scanning electron transistors (SETs) are being used to image weak electric stray fields 3,8 while weak magnetic fields are accessible to scanning Hall bars 9 , nitrogenvacancy (NV) centers in diamond 1,10-12 and scanning superconducting interference devices (SQUIDs) 13-15 .These two latter sensors have, more recently, even imaged surface temperature 16 and thermal conductivity 17 .Fig 1 -Planar scanning probe microscope. a, An extended planar sensor (blue) can be brought into 10 nm-scale proximity with a planar sample (orange) if tilt is controlled to the sub-mrad level. NV: nitrogen-vacancy center, SQUID: superconducting sensor, SET: single electron transistor. b, Optical measurement of tilt by interference reflection microscopy. Reflections in a multilayer interfere, forming Newton's fringes. c, Optical measurement of the sensor-sample gap Δ by a combination of total internal reflection microscopy (TIRM) and Brewster angle microscopy (BAM). A sample scatters light from an evanescent field at the sensor surface, changing the intensity and/or polarization of the reflected beam. Effects of both b and c are imaged via a microscope looking from above.Most of these novel techniques share a central challenge: the sensors are extended planar devices -circuits fabricated on a substrate or crystals -but scanning probe positioning requires a sharp tip to provide forc...

An Integrated Widefield Probe for Practical Diamond Nitrogen-Vacancy Microscopy

“…The NV layer is first moved into focus, then the sample is brought up until it is seen to contact the diamond through the NV PL video feed (sample features come into focus, and the sample is stabilized when the diamond comes into contact). Compared with the method of Ernst et al 23 , this method is manual and does not allow estimation of the actual standoff directly.…”

“…Overcoming standoff limitations will require finer angular and vertical control of the probe, easily accomplished using robotic stages 23 . Keeping the surfaces clean and flat to further reduce d SO should be readily achiev- able.…”

“…Our approach follows the method demonstrated by Ernst et al 23 . They reported the application of interferometry to scanning planar probe microscopy, showing that in situations involving a planar sensor parallel to a planar sample, the distance between probe and sample can be reliably minimized by first rotationally aligning the surfaces using interferometry as a feedback mechanism.…”

Recent Advances in Single Crystal Diamond Device Fabrication for Photonics, Sensing and Nanomechanics

“…In an alternative approach, the sample is attached to the cantilever of a commercial scanning probe microscope and scanned over an NV embedded ≈ 5 nm below an SCD surface and is equivalent to scanning of diamond probes over the sample surface [ 61 , 62 ]. Ernst et al [ 63 ] recently demonstrated another method of using planar SCD (50 µm thick) with single NV centers as scanning probes for imaging planar samples, which required highly precise alignment (radial) and proximity control between sensor and sample. While initial scanning probes relied on grafting color center containing diamond nanocrystals to AFM tips, the focus recently shifted to realization of top-down fabricated SCD nanoprobes [ 20 , 60 ].…”

Trendbericht: Elektronen‐Paramagnetische‐Resonanzspektroskopie

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