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Test sample for tip's curvature radius estimation: qualitative - by comparison of AFM scans, taken by different probes; quantitative - using "blind" tip's estimation (deconvolution) algorithm.

Test sample TSD01 is intended for:

  • Qualitative estimation of AFM tip’s sharpness based on topography image of its surface;
  • Quantitative estimation of AFM tip’s curvature radius using deconvolution algorithm.

TSD01 consists of large variety of densely packed particles with average diameter around 60 nm. Particles’ shape is not ideally round. Some of them are rather cylindrical, some ones have got vertical walls and sharp corners (like as on the REM photo). These features are necessary to collect enough statistics for further “blind” tip estimation using Deconvolution algorithm.

Qualitative tip’s shape estimation with TSD01

Qualitative tip’s shape estimation could be done by comparison of AFM images of TSD01 surface of different AFM probes. Below you may find AFM images of TSD01, performed by two cantilevers of the same model.







Looking at images’ scales, the one may notice that particles’ height on the left image is more than on the right one. That means that tip #1 penetrates deeper into gaps between particles during the scan. And the tip #1 is just the sharpest one between them both.

Quantitative tip's shape estimation: “Blind” reconstruction of AFM tip’s shape using Deconvolution algorithm

Deconvolution algorithm for AFM surface reconstruction was suggested by J.S. Villarrubia in 1997 and now it is implemented in many different AFM-image-processing programs. It also includes the part, that allows so-called "blind" tip's estimation, when analysing a scan of specific surface program draws tip's profile.

For better understanding of this method let’s imagine an ideal vertical bulk (on the image below) which width is equal to “0”. It’s not difficult to calculate that when a probe passes such an object, its image on AFM topography scan will be just the inverted probe’s shape (a dotted line).

Thus, every particle of topography imaged, which size is comparable to a tip, should hold some information about its real shape. The algorithm of “blind reconstruction” compares shapes of all particles (local maximums) of the topography scan and finds common features between them. On the basis of such comparison it outputs approximated tip’s shape. Reliability of the result depends on particles amount (it should be enough to collect statistics) and their shape (then closer to an “ideal bulk” – than better, as we have seen previously).

Knowing details of "blind" tip's estimation algorithm we could formulate the next criteria to the test sample that could be used for its realization:

  • Obviously, it should be rigid;
  • It should have got many particles of 20-100 nm approximate diameter, so that their size should be comparable to tip’s one;
  • All the particles should densely sit on the surface. For detailed analysis each particle should contain, say 10x10 points. From the other hand, there should be 50, 100 or more particles in range of one scan so that we had enough statistics;
  • As we discussed above, speaking about “ideal bulk approximation”, only AFM images of vertical objects of “zero” width hold the most exact information about tip’s shape. If even they don’t exist in nature, every vertical wall and sharp corner of our particle holds exact information about tip’s shape. Thus, the test structure for tip’s shape “blind” estimation should have got irregular shape with many vertical walls and corners.

Quantitative tip’s shape estimation with TSD01

TSD01 manufacture process determines its physical properties: all particles are being grown chaotically around small, several nanometers, cores. Thus, they have got similar, but very irregular shapes. Some of them may have got sections, close to cylindrical, some of them look to be rounder. They have got many sharp corners too. Writing several dozens of such particles during the same AFM image a tip leaves much information about its true shape from each side. And usually this statistic is enough to get reasonable tip’s images after tip’s “blind” estimation by standard deconvolution procedure.

Below you may find the results of “blind” tip’s shape reconstruction from the AFM scans of TSD01 test structure, which were posted previously:

As the one may notice, the results of tip’s shape estimation correspond to our previously-made suggestion that the probe #1 is sharper than the probe #2.

AFM probes with a Full Diamond (FD) tip, attached to a tipless cantilever HA_NC. Each chip contains 1 cantilever with 140 kHz resonance frequency, 3.5 N/m force constant, <25 degrees tip's curvature radius and <12 nm tip's end.

Full Diamond (FD) cantilevers HA_NC/FD consist of standard polysilicon chips and consoles and high quality single crystal diamond needle grown in CVD process and fixed on a lever. Manufacturing a diamond tip with tip's curvature radius less than 12nm and attaching this tip to our own-made polysilicon lever, together with our partners we're glad to present on the market the very special offer: the highest quality AFM tips for routine measurements for the reasonable prices! Our new probes are remarkable for the next features:

  • Full diamond tip is harder than a standard silicone one. Its wear is about 10 times lower and it allows to measure surfaces that grind fast silicon needles. More of all, such cantilevers will be the best for measurements of surface elasticity properties. Their deformation during force curves processing will be minimal respectively to other-material tips;
  • Full Diamond tip has got small cone angle (<25 degrees) and tip's curvature radius (<12 nm) that allows to get high quality scans of various type samples;
  • Low surface energy of diamond makes FD cantilevers to be well-usable for long time scanning of sticky biological samples;
  • Narrow and hard tips are also suitable for simple nanoindentation experiments with standard AFM parts;
  • Experimental results have showed that Full Diamond tips are less sensitive to static charges on sample’s surface. That results in more detailed topography scans in comparison with Si cantilevers in the same conditions

Great utility of FD AFM cantilevers for precise measurements is accompanied by a detailed quality control. After gluing a tip to a lever each cantilever is being observed by SEM before shipment. Thus only good probes reach the customers.

Applications: Scanning sticky biological samples

Our colleague from University of Nebraska Medical Center, Mohtadin Hashemi, have reported about outstanding FD probes utility for measurements of sticky biological samples. He tried both FD and Si probes for scanning of fibril and globular amyloid aggregates. When standard Si tip could be used only for 2-3 hours (then its surface became too dirty, catching sample's material), FD cantilever didn't show any degradation during 7 hours continous repeated scan of the same area. Images from the both sides were taken with 3 hours difference - no tip's or sample's degradation can be noticed.

Applications: Less sensitivity to surface charges

Our experiment have showed that FD cantilevers are less sensitive to effect of image distortion due to surface charges. To the left you may find an image of silver nanoparticles on mica by a standard Si cantilever in low humidity conditions. It took around 1 hour of parameters' adjustment to get this image. The engineer had to decrease contact amplitude of cantilever's oscillation 10 times in respect to free oscillations. To the right you may find a scan of the same surface, obtained by FD probe without any special adjustments. Image is more sharp and particles' sizes are much lower, as they should be in accordance to non-AFM investigation of this sample.

Cantilever specification

Chip thickness H: 0,4mm.
Reflective side coating: Au.
Tip's cone angle: < 25 degrees.
Tip's aspect ratio: > 1:5.
Tip's curvature radius: < 12 nm.
Chip has one rectangular spring.

Cantilever type A Typical dispersion
Length, L (µm) 124 ± 2
Width, W (µm) 34 ± 3
Thickness, H (µm) 1.85 ± 0.15
Force Constant (N/m) 3.5 ±20%
Resonant frequency (kHz) 140 ± 10%

***HA_C/FD probe could be produced with another type of HA_NC lever (235 kHz resonance frequency) by request.




Etalon Premium: pencil-shape tips for HQ AFM topography scans

We're glad to present the new product line in our assortment: Etalon Premium probes with pencil-shape tips for high-quality AFM scanning!

Etalon Premium tips have got conical apex and cylindrical body to minimize tip-related widening of objects investigated. Excellent geometry provides high resolution of AFM scans:
 - Conical apex of 5-8 nm typical curvature radius and cone angle < 30° suits well for imaging of small objects and nanoparticles;
 - Narrow cylindrical body with diameter of 300 - 700 nm and height 8 mkm allow getting detailed images of high objects, making Etalon Premium probes being similar to high aspect ratio probes models.

In our experience (and by reports of our customers), these probes show better scanning data for almost all types of surfaces. They are especially effective for high objects of 1 um and higher.

To check performance of Etalon Premium probes in application to high objects we scanned with AFM hemi-spherical particles of 2,5 um diameter. 
Below you may find comparison of topography scans of these objects, obtained with Etalon Premium (the left one) and standard pyramidal (the right one) probes.  Scan area: 12x12 um. Ridge of tip’s pyramid gives the same artifact in the bottom of each sphere on the right scan. As Etalon Premium probe is narrower, no artifacts are seen when it draws a surface on the left scan.

At the moment Etalon Premium probes presented only with HA_NC-based lever parameters. But in the first half of 2019 we plan to expand this product line by HA_C, HA_CNC, HA_FM and HA_HR Premium models. Condutive Etalon Premium cantilevers will be also designed soon.

More detailed technical data can be found on Etalon Premium product page. We hope that our new products will suit well for your investigations!

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In the end of August together with our colleagues from Ostec-Instruments we were attending International conference Scanning Probe Miscroscopy - 2018 in Ekaterinburg.

We appreciate our colleagues from Ural Federal University - for warm wellcome and excellent organization of all events and lectures, and many interesting people who we met during the conference - for great pastime and valuable ideas for our next developments and common projects.

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Test sample for AFM tip's radius investigation

The necessity of tip's shape estimation arises very often during AFM measurements. Even if manufacturer claims this parameter with high accuracy, fast tip's wear off during scanning leads to the need of its repeated re-calculation.

One of the most popular and cheapest methods to control tip's apex is so-called "blind" tip's shape estimation, suggested by J.S. Villarrubia in 1997. Now it is implemented in many different AFM-image-processing programs. But proper choice of a test sample for such investigation is also a tricky task. It should include many densely packed and respectively hard particles, which size will of the same order that tip's curvature radius.

Today we present our new product: TSD01, the test sample for tip's curvature radius estimation. TSD01 consists of large variety of densely packed particles with average diameter around 60 nm. Particles’ shape is not ideally round. Some of them are rather cylindrical, some ones have got vertical walls and sharp corners (like as on the REM photo). These features are necessary to collect enough statistics for further “blind” tip estimation using Deconvolution algorithm.

Another possible usage of this test sample - qualitative tip's quality control by simple comparison of TSD01 scans "before" and "after" scanning.

More information about TSD01 is presented on its product page. We will be also glad to discuss deconvolution method, its possible applications and correct usage of TSD01 for it. Please, contact us if any questions will appear.

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