Overview of Technique
Atomic Force Microscopy (AFM) provides the ability to image the surface topography of both conducting and insulating samples, as well as adsorbed molecules and nanoparticles. The Nanoscope Dimension 3100 Scanning Probe Microscope with the Nanoscope V controller (Veeco company) enables one to perform such measurements in air as well as in fluid, with nanometric scale resolution. Using the XY closed loop of the Hybrid XYZ scanner allows accurate and reproducible zooming, as well as high accuracy tip positioning. Using the XYZ closed loop makes it possible to perform highly accurate force-distance curves, current-voltage (I-V) curves, and "pulling" techniques, at specific points of high resolution images. In addition to the measurement capabilities, the scanner is also able to perform nanolithography (both scratching and oxidation) and advanced nanomanipulation applications (using the Nanoman software). It also provides the capability of measuring locally a wide variety of physical properties, some of them with the aid of special modules, as listed below.
Primary AFM Imaging Modes:
- Contact Mode (CM): high spatial resolution can be obtained, but may damage soft surfaces and adsorbed layers.
- Tapping Mode (TM): In this case the topography can be obtained by lightly tapping the surface with the oscillating probe. This mode is less destructive to the surface as compared to contact mode. It is the most used of all AFM modes. Imaging in fluid is available in both modes, Contact and Tapping.
- Torsion Resonance Mode (TR): is new technique that measures and controls dynamic lateral forces between the AFM probe and sample surface. This mode allows working close to the surface without actually contacting it, providing both high spatial resolution, and options for close range measurements (such as TUNA and lateral magnetic force imaging).
Secondary AFM imaging modes:
- Lateral Force Microscopy: provides information on variations of the local friction.
- Phase Microscopy: derived from TM and detects variations in composition, adhesion, friction, visco-elasticity, and as well as edge detection.
- Conductive Atomic Force Microscopy (C-AFM): measurement of the local conductivity variations across medium of conductive samples with the lateral resolution of a few nanometers. C-AFM has a current range of picoA to microA.
- Tunneling-AFM (TUNA): Similar to C-AFM, but with ultra-low current measurement capability, between 80 fA to 120 pA.
- Magnetic Force Microscopy (MFM): maps magnetic force gradient above the sample surface, with a special magnetic tip. This mapping is performed via two-pass technique, LiftMode.
- Electric Field Microscopy (EFM): similar to MFM, measures electric field gradient distribution above the sample. Voltage is applied between tip and sample.
- Surface Potential Imaging: maps the variation of the electrostatic potential across the sample surface.
- Scanning Capacitance Microscopy (SCM): maps variations in majority electrical carrier concentration (electrons or holes) across the sample surface, typically a doped semiconductor.
- Force modulation: can be used for imaging local sample stiffness or elasticity..
- Force Spectroscopy: provide information on the tip-surface adhesion, hardness and local elasticity of the sample.
- Force Volume: combines force measurement and topographic imaging capabilities. Possible applications include elasticity, adhesion, electrostatic, magnetic and binding studies.
- Spectroscopy: Force spectroscopy, I-V curve.
- Force Spectroscopy: produces force vs. distance curve, is used to analyze the adhesion of surface contaminations, as well as local variations in the elastic properties.
- Nanolithography: is "drawing" a nanometric-scale pattern on a sample surface by using an SPM probe. Scratching - mechanically scribing the surface by applying excessive force with an AFM tip. Oxidation - by applying highly localized electric fields with AFM tip.
- Nanomanipulation: allows direct, precise manipulation of nanoscale objects, such as nanotubes and nanoparticles in the plane of the sample surface.
- Nanoindentation: is a way to measuring mechanical properties, such as hardness and Young's Modulus, by nanoindenting a sample with an AFM tip.
Signal Access Module (SAM):
Designed to give researchers the open architecture they need to conduct innovative experiments. SAM is provided for up to 35 input/output separate SPM signals through BNC connectors.
Basics and Tutorials
In the early 1980s, scanning probe microscopes (SPMs) dazzled the world with the first real-space atomic-scale images of surfaces. Now, SPMs are used in a wide variety of disciplines, including fundamental surface science, routine surface roughness analysis, and spectacular three-dimensional imaging - from atoms of silicon to micron-sized protrusions on the surface of a living cell.
The scanning probe microscope is an imaging tool with a vast dynamic range, spanning the realms of optical and electron microscopes. It is also a profiler with unprecedented resolution. In some cases, scanning probe microscopes can measure physical properties such as surface conductivity, static charge distribution, localized friction, magnetic fields, and elastic modulus. Hence, SPM applications are very diverse.
Scanning probe microscopes are a family of instruments used for studying surface properties of materials from the micron all the way down to the atomic level. Two fundamental components that make scanning probe microscopy possible are the probe and the scanner.
The probe is the point of interface between the SPM and the sample; it is the probe that intimately interrogates various qualities of the surface. The scanner controls the precise position of the probe in relation to the surface, both vertically and laterally.
Atomic Force Microscopy (AFM)
The atomic force microscope (AFM) grew out of the scanning tunneling microscopy (STM) and today it is by far the more prevalent of the two. Unlike STMs, AFMs can be used to study insulators, as well as semiconductors and conductors. The probe used in an AFM is a sharp tip, typically less than 5micrometer tall and often less than 10nm in diameter at the apex. The tip is located at the free end of a cantilever that is usually 100-500 micrometer long. Forces between the tip and the sample surface cause the cantilever to bend, or deflect. A detector measures the cantilever deflections as the tip is scanned over the sample, or the sample is scanned under the tip. The measured cantilever deflections allow a computer to generate a map of surface topography. Several forces typically contribute to the deflection of an AFM cantilever. To a large extent, the distance regime (i.e., the tip-sample spacing) determines the type of force that will be sensed. Variations on this basic scheme are used to measure topography as well as other surface features. There are numerous AFM modes. Each is defined primarily in terms of the type of force being measured and how it is measured.
For basic education and principle understanding of the SPM, we kindly ask you to use following web resources:
Brief description of the microscope and control electronics
|Scanner Piezo Resolution:
||16 bits (all axes)
|Max. scan size
||Xand Y axis 100 micrometers; Z axis 7.5 micrometers
|Max. sample size
||Wafers and disk media: 150-mm diameter; 12 mm thick
150 mm vacuum chuck for wafers and other samples; Magnetic holder for small samples up to 6 mm thick
Precise motorizes positioning; 125 mm x 100 mm inspected area; Resolution: 2 micrometer;
||Fluid cell and tip holder for working with liquid.
10 x objective, field of view of 180-810 micro meter; motorized zoom and focus;
1.5 micrometer resolution; computer-controlled illumination; video image capture
Silicone vibration pad; Vibration isolation table
The Nanoscope Dimension 3100 Scanning Probe Microscope (SPM) is a low-noise system specifically designed to produce measurements at the nanometer (lateral) and sub-angstrom (vertical) scales. An Integrated Acoustic/Vibration Isolation System is used, which provides true acoustic isolation for Dimension 3000 microscopes by enclosing the vibration isolation platform within the acoustic hood and the legs of the isolation table. This isolation system important for users who are interested in imaging surfaces with roughness levels of <10nm RMS, such as those encountered in the semiconductor, data storage, and optics industries.
NanoScope V Controller is new atomic force/scanning probe microscopy control system, that has many enhansements over its predecessors, including several synchronization outputs, reference signal outputs for three lock-ins, and five analog inputs which can be sampled with Analog-to-Digital Converters (ADCs). The NanoScope V Controller provides more speed, more resolution, more sensitivity and more flexibility:
- Highest Pixel Density: The resolution of the NanoScope V has been increased to 5k x 5k points per image. The high pixel density improves "time to results" by reducing the need to capture several images at lower resolution. It also allows observation of large structures and small features in the same image. NanoScope V offers up to 10 times faster scanning with new TappingMode+TM technology (Fast scan). To achieve this, the NanoScope V employs micro-actuator probe technology, which uses its own feedback loop to move the probe in the Z-direction at speeds much faster than the scanner can by itself
- Q control: improves sensitivity by either enhancing or suppressing a selectable narrow band within the tuning spectrum. Q enhancement can also improve the signal-to-noise ratio. This can then enable, for example, improved Phase contrast, as may be desirable for MFM imaging. Q control is also useful for damping and unwanted resonance in a multi-peaked spectrum.
- Fast, Dependable Data Capture (HSDC): NanoScope V Controller utilizes advanced electronics, including A/D and D/A converters operating at 50 MHz, to deliver reliable, high-speed data capture. It allows researchers to record and analyze tip-sample interactions, such as at pull-off in force spectroscopy. HSDC is simultaneous with imaging or ramping and is independent of microscope mode.
- The NanoScope V enables up to eight images to be simultaneously displayed in real-time and offline visualization/analysis, correlating information about unprecedented number of sample properties.
- Three Lock-In Amplifiers: The controller incorporates two independent high-speed lock-ins (1 kHz - 5 MHz) and one mid speed lock-in (0.1 Hz - 50 kHz) allow sampling and determining amplitude and phase of up to three independent signals, or analyzing higher harmonics of a signal.
- User-accessible hardware input/output: The controller also affords easy access to most input and output signals through front-panel BNCs. Input data into the controller from an external source is supported, as is user access to lock-in amplifiers and to signals to/from a microscope, e.g. XYZ sensors, amplitude, phase.
- Thermal tune: the thermal tune method provides an automated and quick determination of cantilever spring constant. The Nanoscope V provides thermal tune measurements of cantilever resonances up to 2 MHz.
- High speed and expanded AC capabilities: The NanoScope V SPM controller has . Two high speed 14-bit A/D converters (ADC) for sampling and digitizing the probe signal (+/-2V); . Two high speed 16-bit ADCs that provide sinusoids (+/-10V); . Nine mid-speed 18-bit ADCs enable multiple digital feedback loops to operate at 2 microseconds speed, allowing faster scanning and data capture with fast actuators.
- Easy-AFM, Remarkable simplicity: For the ultimate in streamlined operational simplicity, the Nanoscope v controller's Easy-AFM, easy-of-use feature, offers an intuitive, easy-to-follow graphic user interface. Easy-AFM reduces the time for initial setup, including probe, laser, and detector alignments, adjusting the scanning parameters, and obtaining Tapping Mode images on most samples.
- Open architecture provides new options to design and run customized experiments, including with third-party software.