Single
Crystal
Diamond

SCD probe is a sharp micro-sized monocrystal diamond tip that provide highly reproducible results in AFM imaging, nanoindentation and lithography. The probe consists of two parts that are manufactured separately: a cantilever on a chip-holder and a tip. The tips grow in batches and then glued onto cantilevers using a specially developed micromanipulation technique.

The manufacturing technology of diamond probes provides high product quality at reasonable costs. Images below illustrate key stages of the production.
 

Diamond is just an option of what can be a probe tip for AFM, but it's a very promising material because of its durability, hardness, outstanding chemical stability, high temperature conductivity and potential ability to conduct electric current. There are a number of ways to make artificial diamond, and chemical vapor deposition (CVD) technique is among them. This technique is widely used for application of diamond coatings or production of polycrystalline diamond structures by molding.

Still these techniques do not utilize the ability of a crystal to anisotropic growth, when it can get itself a shape specific for AFM probe tips. Such a diamond monocrystal must have higher hardness comparing to the polycrystals and better durability comparing to the films. This opportunity emerges when diamond crystals grow fast in the <100> direction; in this case the tip also obtains a square basis convennient for mounting it onto a cantilever.

The fact that diamond crystals of this kind are possible to grow by CVD was established in the middle of 1990's [1]. The same technique under similar conditions allows getting fullerenes, graphenes and nanotubes, and the range of the technological parameters providing growth of each structure is quite narrow. Our know-how consists in the growth of monocrystal diamond pyramids with the {001} facet in the basis having a controllable shape along the <001> axis. What's challenging here in the view of AFM application perspective, it is to attain good sharpness and aspect ratio at the tip end.

There are just some examples below on how the growth of the diamond pyramids may go. The growth usually starts from the formation of nanometer-sized nuclei with random orientations over the substrate. Along with the growth of the diamond crystals in the preferred direction, secondary nucleation starts on their lateral surfaces. All these crystallites form a ballas-like film contaning tips of the needed size and orientation and the "wadding" of satellites. Additional treatment is needed to remove the ballas-like diamond crystallites, while the large single crystal diamonds of pyramidal shape must remain untouched or just get "polished" in this process.
 

A method for production of diamond tips is proposed in patent application [2]. The technology was developed by following to protocols introduced in the work [3] and now is brought to a state when the tip shape and sharpness are reproducible. Besides application in AFM as a probes or indentors, the diamond tips can be used as nanosized temperature sensors [4] and X-ray detectors [5]. Studies of color center fluorescence and spin manipulation [6] show that the tips can be used for measuring magnetic fields with high sensitivity via photo luminescence detection.
 

Attachment is another stage of the manufacturing technique that allows positioning and gluing of the micro-sized object on a cantilever with high precision. Certainly, this manipulation technique can be used to attach not only diamond tips and not only on silicon cantilevers. Our experience shows that other objects like carbon fibers or micro-sized particles can be handled the same way, see examples below. For AFM, the objects can also be glued to silicon nitride cantilevers, piezo cantilevers or tuning forks.

After the tip is selected and glued to the cantilever, its shape and sharpness are controlled individually on SEM to guarantee the full cone angle at last 200 nm of 10° and radius of 10 nm.
 

After the tip is mounted onto a cantilever, the cantilever with the tip can be detached from the chip holder and glued to another surface. Images below show tuning forks with cantilevers having pre-mounted SCD tips. The cantilever is projecting from the quartz prong to facilitate tip positioning on the sample surface. Tuning forks with SCD tips can be used for tapping mode AFM without use of optical system. When the cantilever is attached to the prone face, the tip can be used in shear force mode AFM.
 

Another example below is the SCD tip glued onto a piezo-resistive self-sensing cantilever. This type of cantilevers features integrated piezo-resistive Wheatstone bridge that measures deflection directly, without the space-consuming optical laser readout widely used in AFM. The self-sensing technology enables easy and seamless integration with various instruments like SEM, TEM, and many others. The cantilever chip holder is bonded onto a small PCB with a connector for quick replacement. These probes are commercially available from SCL-Sensor.Tech. Fabrication, GmbH.
 

SCD probes can be functionalized for a number of applications providing unique results as diamond chemistry and physical properties are quite different from that of Si or Si₃N₄ AFM tips. Two R&D projects of this kind were supported by Enterprise Estonia in 2015 and 2016.
 

Contact us if you have an idea how the diamond tips or micromanipulation technique can be used for your research. We also offer a service of cutting a pattern of your design on your substrate by SPM nanolithography methods.