Description:

In scanning probe microscopy (SPM, commonly AFM), the interaction of a stylus probe and sample surface is quantified and mapped across the sample. The probe or "tip" is of nanometer-scale sharpness, and the standard image is 3D surface topography at resolution approaching the atomic or molecular scale. The tip is attached to a microfabricated cantilever of low spring constant. Property-sensitive imaging modes are performed simultaneous to topographic imaging. Gaseous or liquid media, plus sample temperature, can be controlled. Tip chemistry can be modified for controlled studies of probe-sample interaction.

Equipment:

Scanning Probe Microscope (SPM Station 1 / Hysitron), Digital Instruments Nanoscope III Multimode with auxiliary Extender electronics, Nikon optical microscope with CCD and image capture for tip positioning, Nano-K Biscuit vibration isolation platform, and Windows NT environment, plus Hysitron TriboScope. Special imaging capabilities include friction force, vertical force modulation with phase measurement, "tapping" mode / non-contact with phase measurement, electrostatic/magnetic force, surface potential, and force volume. Force Volume is 3D spatial mapping, i.e. the distance dependence of tip-sample interaction over a 2D grid of surface locations (low pixel resolution), in order to characterize adhesion, stiffness or dynamic interaction regimes. Hysitron-SPM combination enables nanoindentation, microscratch, and other mechanical tests along with in situ high-resolution imaging. The heart of the Hysitron attachment is a force/displacement transducer that allows both load and displacement data to be obtained simultaneously for indentation testing. Maximum load is approximately 2 mN and force resolution is 100 nN with Hysitron tester. Maximum lateral scan size is 150 µm.

Accessories:

• Optical access. Ability to acquire digital video image.
• Liquid cells: available for use (closed cell capability with in/out flow tubes).
• BNC breakout box: available for use.
• Custom adder circuit box for signal manipulation, for example to ramp set point during imaging
• Analog Witec pulsed force mode (adhesion and stiffness imaging).
• Infinitesima ActuResonance controller for manipulating the or quality factor (Q) of cantilever resonance.
• Mathematica and ICAdams available for quantitative analysis and modeling of force-distance data and dynamic tip-sample interactions, in order to extract sample storage/loss moduli, surface energy, etc.
• SPIP available for broad suite of image (e.g. grain size) and force curve (e.g. freely jointed chain model) analysis applications. Freeware programs WSXM and Gwyddion also available.
• XYZ manipulator to attach SiO2 or polystyrene microspheres to tipless cantilevers
• Plasma chamber and metal evaporator for chemical modification of tips by users. Tip modification services available, using silane linkage procedures customized by staff member Dr. Jinping Dong.

Applications:

• Sensitive to the following properties: surface chemistry, storage/loss modulus, hardness, interfacial energy, crystallinity, polarization, magnetization, surface charge, and local work function (surface potential).
• Applicable to conductive and non-conductive samples.
• Samples can be imaged in air or in liquid media in all modes of operation.
• Can measure tribological response versus load, scan velocity, temperature, relative humidity.

Capabilities:

• No sample pre-treatment needed and imaging can be performed in air.
• Sample can be conductive or nonconductive, hard or soft.
• Maximum scan size 150x150 µm laterally and 8 µm vertically
• Positioning resolution is 0.1 nm laterally and 0.01 nm vertically; imaging lateral resolution depends on sample/tip characteristics (adhesive contact mechanics) and typically is of order 1-10 nm.