• FREQUENTLY ASKED QUESTIONS

    General
    Probes
    How To Use


    Answers

    General

    AFM (Atomic Force Microscopy) is a widely-used instrument and technique for non-destructive surface investigations as well as for surface modifications at the nanoscale. Besides topography, AFM is capable of collecting information that relates to local material properties such as adhesion, stiffness, elasticity, conductivity, coercitivity, etc.

    The principle of AFM consists in registering the force experienced by the probe from the sample as the probe scans its surface. There are other scanning techniques like STM or NSOM, where the probe is designed to register other physical values. All these techniques and instruments are referred to as SPM (Scanning Probe Microscopy). So AFM is a part of SPM.

    AFM is a widely used technique in life science, chemistry and materials research, where the structures and processes at micro and nanoscale are of interest.

    MikroMasch offers AFM probes and test structures.

    The probe is a key part of any AFM experiment. One of the most important characteristics of a probe is its sharpness, that determines the resolution. Extremelly sharp probes with subnanometer radius can provide true submolecular resolution in ambient conditions. Any probe also have to provide means to transfer the force signal to the AFM system.

    The test structures provide means to check the system performance in many aspects. In combination with special techniques, the test structures can be used for calibration purposes.

    Basically a chip is a relatively large piece of silicon to which one or several cantilevers are attached (see Fig.). Cantilevers (or just levers) are thin beams of silicon or silicon nitride. They usually have rectangular or triangular shape and well-defined mechanical properties. Finally, a tip is a very sharp protrusion at the end of a cantilever, although cantilevers themselves are often referred to as 'tips' as in 'contact tips', for example.

    Fig.1 Chip, cantilever, and tip

    Our products are compatible with the microscopes of all major SPM manufacturers, including Bruker (Veeco, Digital Instruments, ThermoMicroscopes), Agilent, Asylum Research, JEOL, PSIA, Burleigh, and others. Note that to use cantilevers in ThermoMicroscopes SPM you need to mount them first.

    The dimensions of the chip are 1.6 mm x 3.4 mm x 0.3 mm.

    No.

    Contact MikroMasch tech support team using request form.

    Probes

    We use monocrystalline silicon for manufacturing cantilevers.

    The tips point in the <100> direction, the edges of cantilevers are along the <110> direction.

    Young's modulus of elasticity E = 1.69*1011 N/m2 (in the <110> direction)

    Shear modulus G = 0.5*1011 N/m2

    Density = 2330 kg/m3

    Our cantilevers are n-doped. The specific resistance of the doped silicon material is 0.01-0.025 Ohm*cm. However, in air, silicon always has a native oxide layer, which is not conductive. You can try to remove it in UHV and use cantilevers in UHV immediately, because in air the native SiO2 layer will grow again very soon. You can also purchase cantilevers with conductive coating like Pt.

    The thickness of the native oxide layer is about 1 - 2 nm.

    Reflective coating is deposited on the backside of cantilevers to increase the reflected laser signal and prevent interference of light reflected from the two surfaces of the cantilever (silicon is semi-transparent, so some portion of the incident beam is reflected from the backside, and some from the tip side). The most popular reflective coatings are gold and aluminum. A reflective coating is not used when cantilever already has another type of overall coating (for example conductive).

    Important! Use uncoated cantilevers whenever experimental conditions may lead to corrosion of the reflective coating.

    To answer your question, we removed coatings from different cantilevers. Typically, after removal the frequency goes down very slightly. For example, for HQ:CSC17 series the difference in the frequencies of coated and uncoated cantilevers is in the order of 30 - 50 Hz (the fundamental frequency is about 13 kHz).

    The cantilever does not behave like harmonic oscillator and its spectrum has additional resonance peaks at higher frequencies. These peaks can be assigned to different oscillation modes of the cantilever or even oscillations of the microscope head.

    If you use autotune, you probably see a resonance of high order. Try manual tune and limit the range of scanning frequencies.

    The elastic modulus of Si changes as a function of temperature, which brings about the variation of the resonant frequency. The composition of the atmosphere is also crucial when you are talking about such precision. In the case the difference in gas density and friction influences the Q-factor and the shift of the resonant frequency with respect to that in vacuum.

    A: Some of our chips have more than one cantilever. In this case, instead of calling them "left short cantilever" or "middle long cantilever" we use one-letter names. The letters by themselves do not have any meaning, refer to the description of a specific series for specifications.

    Fig.2 Silicon chip with cantilevers.

    The package sizes of our cantilevers are 5, 15, 50, 100, 200 and 400. Not all cantilevers are offered in all package sizes. Please check the available package sizes for the specific model of interest to you on its webpage.

    How To Use

    It is not necessary. Although you cannot control the force applied by the lever you are not using, in most cases nothing will happen to it and you will be able to use it later (e.g. by realigning the laser).

    Unfortunately, this important question does not have a simple answer. A lot will depend on the properties of your sample and imaging conditions and there is often a trade-off of some sort. Here are a couple of general remarks.

    In contact mode soft levers should be used to minimize damage to the sample and the tip. However, very soft levers are noisy.

    In tapping mode stiff levers are used so that the tip does not stick to the sample surface. Cantilevers with very high resonance frequencies (and force constants) allow faster scanning but can damage very soft samples. Rectangular cantilevers are preferable because they typically have better Q-factors than triangular ones.

    Basic techniques and recommended types of cantilevers for different SPM applications are described in our "how-to-choose" chapter.

    We do offer contact mode probes with hard DLC coated tips (HQ:CSC17/Hard/Al BS). However, the coating is very thin in order to keep tip radius low. Therefore, we do not recommend this model for scratching hard surfaces.

    The best choice will be Hi'Res-C probes, which have a curvature radius of about 1 nm. The choice of the force constant of the cantilever basically depends on the mechanical and adhesion properties of your sample. As the probe is very sharp, it requires special care in use, especially in engagement procedure. Our experience shows that many users break the tips during the first tests.

    Yes. Try the HQ:NSC36/Cr-Au BS probes. These cantilevers are the shortest and suffer the least dumping forces in liquid media. Corresponding resonance peaks (10 - 35 kHz in water) are clearly seen in a cantilever tune.

    We produce the PA01 test sample for this purpose. It has pyramidal nanostructures with sharp edges over the surface. The pyramids are triangular with base length in the range 50 – 100 nm and height 50 – 150 nm. The radius of curvature of the sharpest edges is below 5 nm.

    You also need a deconvolution program. We recommend to use Image Metrology software SPIP available for downloading from Image Metrology.

    The shelf life of the tip varies depending on conditions of storage. In a desiccator, the shelf life is from half year to one year. When without desiccation, the shelf life will depend on humidity. Generally, it's recommended to use the tips within three months from the shipment date.

    The best way to get rid of dust particles (not organic contamination) will be to softly blow on the grating with pure nitrogen or Ar. Cleaning in consecutive acetone, isopropanol and DI water ultrasonic baths is also possible.

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