Atomic Force Microscopy

Atomic Force Microscopy (AFM) is a microscopy technique that can measure surface morphology down to atomic resolution. The principles of AFM can be simple: a tip of nanometer scale sharpness is mechanically contacted with the surface to probe the morphology. High instrument resolution is obtained using a very sharp silicon nitride probe. The sample is mounted under the probe and it's moved on X, Y and Z by a ceramic piezo-scanner. Tip is mounted on the edge of an elastic cantilever (100-200 µm) of low spring constant to keep the probe in contact with surface. Deflection of the tip along Z axis, due to different height on the surface of the sample, is monitored by an optical laser. With all this information is possible to obtain a 3D scan of the surface. Property-sensitive imaging modes can also be performed simultaneous to topographic imaging. Tip chemistry can be modified for controlled studies of probe-sample interaction.

The institute operates a Difital Instrument Nanoscope III Multimode AFM primarily used to study the topography of semiconductor surfaces and other materials. It can operate in contact mode (where the tip is in continuous physical contact with the probed surface) or in tapping mode. The MultiMode system features multiple scanners that permit the user to tailor the system for individual research. Scanners with large scan ranges up to 120 microns on the X–Y axes, and a Z range up to 5 microns, as well as high-resolution scanners with 0.4 microns X–Y axes and submicron Z range are available. The MultiMode's image analysis and presentation software contains powerful algorithms for the measurement and presentation of research results including: Cross sectional analysis, roughness measurement , grain size analysis, depth analysis, power spectral density, histogram analysis, bearing measurement and fractal analysis. This instrument can also perform Scanning Capacitance Microscopy (SCM) as a secondary imaging mode derived from contact AFM that maps variations in majority electrical carrier concentration (electrons or holes) across the sample surface (typically a doped semiconductor). An AC bias voltage is applied between the tip and sample. The tip scans across the sample surface, and changes in capacitance between the tip and the sample surface are monitored by an extremely sensitive high-frequency resonant circuit.

The institute also jouses a Digiteal Instruments EnviroScope which constitutes a multipurpose platform for scanning probe microscopy under a variety of environments, including elevated temperature (185°C in ambient environment, 300°C in vacuum, and 60°C in fluid), vacuum (10-5 torr), and in the presence of introduced gases. It incorporates contact AFM, tapping mode, fluid imaging, force imaging. Other specific features: large sample size (up to 2”), real-time sample monitoring and instant shots. The instrument resolution is ~5 nm X-Y (limited by the tip size); < 0.1 nm Z with a scan size of 90µm X-Y; 5µm Z.

Obtain surface topograghy of various electronic materials at the nm scale and under various environment. Study of the electrical characteristics of micro-devices.

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Institutes:

• NRC Institute for Microstructural Sciences