The Asylum Research Cypher AFMs are different from every other AFM in several important ways. This article describes how and why Cypher AFMs provide superior resolution, speed, environmental control, and productivity.
Cypher Routinely Achieves High Resolution
Resolution is the most important measure of AFM performance. Cypher AFMs routinely resolve features at a superior resolution to other AFMs, including single atomic point defects. Cypher is not the first AFM to solve atomic point defects, however it is the first and only commercial AFM that makes this performance routinely achievable.
There are a number of reasons why Cypher has higher resolution than other AFMs. The path between the tip and the sample is extremely short and stiff. This is the most critical contributor to low noise.
When combined with the integrated acoustic enclosure, Cypher is almost immune from environmental noise. Surprisingly, Cypher is normally used with no additional vibration isolation, however it achieves a vertical noise floor of less than 15pm, at least 50% less than most AFMs.
Figure 1. Successive tapping mode topography images of a calcite crystal in water. The repeated point defects demonstrate the true atomic resolution capabilities of the Cypher AFM. Arrows indicate scan direction. Scan size 20 nm.
What is Single Atomic Point Defect Resolution?
Crystals will usually contain defects. This includes point vacancy defects; where a uniform atomic lattice has a missing single atom in its structure.
However these defects may not always be captured by AFMs due to blunt AFM tips. When the AFM tip ends in a plateau of several atoms instead of a single protruding atom, the tip can scan over point defects without detecting them as shown in Figure 2. AFM images under these conditions may still show a uniform atomic lattice, but not point defects.
Figure 2. Blunt AFM tips skim over single point defects and have complex interactions with step edges. Most AFMs cannot preserve a sharp tip, so they only achieve lattice resolution
Cypher AFMs routinely observe single atomic point defects in the crystal face, isolated from step edges and often persisting from one scan frame to the next. This resolution is not routinely achieved by other AFMs.
It is not a case of simply finding a sharp tip, but preserving tip sharpness throughout the imaging procedure. The high stability of Cypher AFMs allows point defect resolution to continue from scan to scan for several hours. This can be observed in Figure 3.
Figure 3. An atomically sharp AFM tip can detect single point defects. Cypher AFMs are extremely stable, so the tip can remain sharp for hours.
Cypher – The Only Full Featured Fast Scanning AFM
Smaller cantilevers allow compatible AFMs to scan 10 to 100 times quicker than traditional AFMs. Cypher is unique in that it allows high speed tapping mode imaging while at the same time supporting all other accessories and modes expected. This does not happen with other AFMs.
Figure 4. (Left) Fast scanning cantilevers are 10–20x shorter than conventional cantilevers, (Right) The Cypher laser spot is perfectly sized for even the smallest commercially available cantilever
Small Fast Probes Used by Cypher
Since their resonance frequency scales with size, smaller cantilevers are faster. In order to use these probes, an AFM must focus its deflection sensing laser to a very small spot. The Cypher small laser spot is 3 x 9µm in size which allows use with even the smallest commercial probes.
Low Noise AFM
Small cantilevers enable higher resolution since they have intrinsically lower thermal noise in a bandwidth around their resonance compared to conventional cantilevers with the same spring constant.
Force mapping or contact modes operate in a higher noise regime dominated by larger 1/f noise sources. This is the key benefit of tapping mode with small cantilevers and one reason that Cypher achieves higher resolution than other AFMs.
Figure 5. Thermal noise spectrum of three different sizes cantilevers, conventional (green), intermediate (blue), and small (black). The thermal noise of a small cantilever is spread over a wider range of frequencies, so the noise in a bandwidth centered on the resonance is much lower, here about four times lower than a conventional probe. Click for larger figure.
No Compromise in the Cypher scanner
The performance of the Cypher S and Cypher ES scanners is exceptional. They have a 30μm XY and 5μm Z range. The XY scanner functions in closed loop for maximum scan accuracy, with less than 60pm XY sensor noise, which is over 50% lower than most competitors.
blueDrive Reinvents Tapping Mode AFM for Simple, Stable and Quantitative Results
The most prominent mode in the AFM world is tapping mode, which measures not just topography but also electrical, magnetic and mechanical properties. Piezoacoustic excitation is most often used to drive the cantilever oscillation.
Figure 6. AM-FM Viscoelastic Modulus Mapping of a polystyrene (PS) / polycaprolactone (PCL) polymer thin film on mica. Image was taken using blueDrive photothermal excitation on a Cypher S AFM at 2Hz. Scan sizes are 5µm (left) and 2µm (right).
Often used due to its ease of implementation, the piezo-driven response of cantilevers is however far from ideal in both air and liquids.
Asylum’s blueDrive excitation mechanism offers a near-perfect response by directly exciting the cantilever photothermally with the help of a modulated blue laser. Asylum Research Cypher AFMs exclusively feature photothermal excitation.
Simple Setup, even During Liquid Imaging
blueDrive uses light hence it excites only the cantilever and not other mechanical components in the AFM. This produces a clean response. This enables simple, reliable automated cantilever tuning, even in liquids and other challenging conditions.
Figure 7. (Top) Representative tunes for an Olympus BL-AC40TS cantilever. (Bottom) Amplitude stability measured under the same conditions.
Remarkably Stable Imaging
Piezo-driven cantilever responses are not just frequency dependent, but they also vary with time. As the response drifts relative to the setpoint, the tip-sample force changes. It can be difficult to differentiate true sample dynamics from artifacts of this drift.
The direct excitation provided by blueDrive is highly immune to drift, so the imaging force remains stable throughout the experiment and under full control. This allows stable imaging over extended durations with no need to readjust the amplitude setpoint.
Hassle-Free Environmental Control
The Cypher ES was designed for environmental control, including temperature, operation in liquids with or without perfusion, and broad chemical compatibility. Most AFM designs are more suited for ambient operation in air with limited environmental control only considered later.
Fully Sealed for Gas or Liquids
Every Cypher ES comprises a sealed cell, pressure tested to at least 35kPa. For use in liquid, this ensures that there will be no leaks anywhere that could cause damage and creates an equilibrium that prevents evaporation of the liquid volume.
Sealed tubing connections are used to perfuse or exchange gas or liquid. The entire sealed cell can be handled independently from the AFM, for instance, to transfer a sample from a dry glovebox.
Figure 8. Whether used in gas or liquid, the Cypher ES operates in a sealed cell for superior environmental control in all situations. Here operation is depicted in a liquid droplet.
Exquisite Temperature Control
Temperature control of the sample is achieved in the sealed cell, which is beneficial to prevent oxidation of samples at high temperature or condensation on samples at low temperature. Two temperature control ranges are available, ambient to 250°C and 0°C to 120°C. Both may be used in either gas or liquid environments.
Chemical Compatibility even in Harshest Environments
All materials in contact with the sample and environment were chosen for superior chemical compatibility. When used in liquid, the liquid only touches the samples, cantilever holder (fused silica) and probe clip (choice of stainless steel or PEEK).
Gases and liquid vapors also contact the FFKM O-ring that seals the cantilever holder and the FFKM bellows that seals around the scanner. These materials enable the use of strong acids and bases, aggressive organic solvents, and most other gases and liquids.
Hassle-free Design for Easy Operation
The environmental control options were designed to not just be effective, but also easy to use. The number of required components is minimized, including no external controller and no liquid coolant pump for heat exchange. A built-in pressure sensor can be used to verify that the cell is sealed.
Components are developed to be cleaned easily, without crevices that might accumulate contamination. Experienced users of other AFMs might be conditioned to avoid environmental control wherever possible. The Cypher ES is designed to be hassle-free so that environmental control can be used whenever it is beneficial.
Electrochemistry Cell for the Cypher ES AFM
The Electrochemistry Cell for the Asylum Research Cypher ES AFM is an advanced solution for in situ AFM characterization of electrochemical processes. It has a simple modular design, providing great versatility and compatibility with a variety of materials. Most importantly, the cell is based on the Cypher ES AFM - the world's highest resolution, fast scanning AFM with ease of use and superior environmental control for maximum productivity.
Time series of AFM images showing the electrochemical stripping of copper from a gold electrode in an acidic 0.1 M copper sulfate solution, 2 µm scans. Imaged in tapping mode using blueDrive™ photothermal excitation. Graph: Voltammogram showing reductive deposition and oxidative stripping corresponding to the process shown in the images.
Designed for the Rigors of EC Research
- The EC Cell liquid cup has a working volume of ~200 µL, which is small enough to save reagents and large enough to prevent significant reaction-induced concentration changes, and eliminates low surface tension liquids from leaking
- The EC Cell probe clip and liquid cup are offered in both glass-filled PEEK and PPS (Ryton®) for better compatibility with most of the solvent electrolyte materials. A perfluoroelastomer O-ring (FFKM, P-Rex®) provides sealing against the working electrode.
- Quartz-constructed probe holder submerges the reference electrode and the AFM probe into the liquid volume
- Sample chamber eliminates electrolyte evaporation and offers secondary containment against spills
- Ring-shaped counter electrode eliminates directional artifacts
- The liquid cup creates a well-defined working electrode surface area of ~55 mm2, facilitating quantitative electrochemistry and removing electric field edge effects
- With shielded electrode connections, highly sensitive signals are preserved and routed neatly to an external potentiostat
- Optional glovebox integration for the ultimate sub-ppm control of oxygen and water levels
EC Cell liquid cup and sample stage
Partial bottom view of the EC probe holder
Experimental Versatility and Simplest User Experience
- Two gas ports and two optional liquid perfusion ports allow for hassle-free electrolyte and gas exchange
- Modular counter and reference electrodes facilitate the selection of the most appropriate materials
- Users can connect to their choice of commercial potentiostats, or Asylum Research can recommend a suitable general-purpose model
- EC Cell is compatible with square and round samples, with a diameter range of 9-15 mm
- All components are fast and convenient to clean and assemble, even wearing gloves
- Optional heating and cooling stages enable analysis of electrochemical thermodynamics
Cutaway drawing and exploded views of the Cypher EC cell
The Cypher ES equipped with the EC Cell performs extremely well at a broad range of measurements:
- Monitoring morphology over time of microorganisms, electrode-attached biocatalysts, and other biophysical research
- Nucleation and growth of nanoparticles
- Investigating kinetics of corrosion
- Electrodeposition and stripping of metals
- Characterization of energy storage materials under bias, including solution-electrode interfaces, membranes, and battery electrodes
Aqueous cyclic voltammetry of 1 mM ferro-/ferricyanide in 100 mM KCl with a Au-sputtered mica working electrode (WE). Each colored trace represents two scan cycles and shows the one-electron process [Fe(CN)6 ]4- ⇌ [Fe(CN)6 ]3-+e-. (Top) Current response as a function of temperature, T, at a scan rate of 100 mV s-1. Inset shows Arrhenius-type behavior with an activation energy of 0.17 eV (16.6 kJ mo-1). Temperature is controlled in the Cypher ES sample chamber with the Heater or HeaterCooler stages. (Bottom) Current response as a function of scan rate, ν, at ambient temperature (29 °C). The potentiostat may be used to vary ν over many orders of magnitude. Inset plots show the scan rate dependence of peak potential (Epeak) and peak current amplitude (ipeak).
This information has been sourced, reviewed and adapted from materials provided by Asylum Research - An Oxford Instruments Company.
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