Metrology & Instrumentation : AFM / SPM

When measuring at these small scales, ground vibration and/or acoustic noise can be significant and can affect measurements substantially. To combat this, Veeco offers two products, the VT-103-3K Acoustic/Vibration Isolation System and the VT-102 Vibration Isolation Table.

There are many applications modules for the Dimension line: TUNA, CAFM, SCM and SSRM. These modules can map nanoscale resolution on a wide variety of materials including low-and mid-strength electrical currents, resistance and capacitance.

The Dimension™ Hybrid XYZ scanner for the Dimension V, Nanoman VS, and BioScope SZ SPM offers lower Z sensor noise and faster scanning than any other closed-loop system available. This patented hybrid head combines the benefits of the industry-leading Dimension tube scanner technology with a uniquely designed sensored Z scanner to deliver revolutionary accuracy in a three-axis closed loop scanner. These advanced capabilities significantly expand the benefits of the Dimension V, BioScope SZ, and Dimension Series SPMs by making it possible in a single head to perform highly accurate force curves, nanoindenting and "pulling" techniques, while still delivering high-resolution images. This is an excellent scanner for nanolithography and advanced nanomanipulation applications with its ability to define and control tip movement with nanoscale accuracy.

Click here for brochure [pdf]

Nanoindentation Software measures mechanical properties by nanoindenting to investigate hardness. Can also perform scratching and wear testing to investigate film adhesion and durability.

Specialized Software provides "point-and-click" control of probe position and motion via an intuitive and flexible user interface. The interface offers direct control of numerous parameters, including probe velocity, vertical position, oscillation amplitude/frequency, and applied voltages. A programmable script language mode permits customized functions, speeds up repeated measurements, and enables nanolithography of complex patterns.

Nanomanipulation Software provides the user with flexible, yet accurate control of the in-plane position and movement of the SPM probe. It allows direct, precise manipulation of nanoscale objects, such as nanotubes and nanoparticles, as well as high-definition nanolithography with a variety of "writing" techniques, in either a graphical point-and-click mode, or in a recipe-driven mode.

Nanolithography Software allows the user to create programs in the NanoScript software that will control tip movements on the surface. Typically, the tip is used as a tool to mechanically scribe the surface, or electrically oxidize it. (The Hybrid Head closed-loop scanner option vastly increases the accuracy and repeatability of the tip positioning for this application.)

NanoScope® Software offers unprecedented data control while delivering the greatest possible ease of use. Version 6 and higher software packages contain application routines designed specifically for force spectroscopy. Other features include

• Automatic cantilever spring constant calibration
• User-defined "scripting" for flexible design of experiments
• Powerful off-line export and processing tools, including batch processing

The Signal Access Modules SAM™ are in-line hardware accessories that allow access or interruption of signals between Dimension™, EnviroScope™, BioScope™, or MultiMode™ scanning probe microscopes (SPMs) and their NanoScope® controllers. Signals can be injected, tapped, and modified as they  flow between the SPM and the controller. Signal access is very useful for advanced  experimentation and diagnostic evaluation because it gives researchers the open architecture they need to conduct innovative experiments.

• SAM III: Works with the MultiMode, PicoForce, and EnviroScope and all SPMs using NanoScope Controllers prior to the NanoScope V. Since the signals between the controller and the SPM are already ground referenced, this
  is a passive device.
• SAM V: Works with the Dimension and Bioscope SPMs using NanoScope V controllers. The SAM V contains active electronics to convert the differential signals between these SPMs and the NanoScope V to ground referenced signals.

Click here for datasheet [pdf]

The standard open-loop head scans up to 90µm in X-Y and up to 6µm in Z. This scanner includes a piezoelectric tube scanner, a laser, and a quadrature optical detector. It uses advanced laser tracking to ensure that the laser beam reflects off the same spot on the cantilever throughout raster scan, maintaining a constant, low tip-sample force over the entire scan area. The NanoScope control systems provide patented waveforms that produce linear scan motion in X and Y as good as some closed loop systems. This head also maintains the low noise levels necessary for resolving single atomic steps on epitaxial thin films, or measuring sub-Angstrom surface roughness on ultrasmooth surfaces.

STM & Low-Current STM Converters provides STM capability for the MultiMode SPM with a TipView STM head. This mechanical design achieves very high quality atomic resolution STM scans with the appropriate scanner. The Low-Current STM Converter allows the scanning of poorly conductive samples with pA-scale tunneling currents.

The NanoScope V controller delivers reliable, high-speed data capture of high-pixel-density images (5120 x 5120), allowing researchers to record and analyze tip-sample interactions that probe nanoscale events at timescales previously inaccessible to SPMs. The NanoScope V enables up to eight images to be simultaneously displayed/captured with unprecedented signal-to-noise ratio.

The controller incorporates three independent lock-in amplifiers, provides thermal tune measurements of cantilever resonances up to 2MHz, affords easy access to most input and output signals through front-panel BNCs, and supports input data from an external source.

Furthermore, the NanoScope V offers both outstanding software functionality and compatibility. An expansive set of functions controls the SPM for custom experiments and nanoscale research.

Veeco’s new NanoScope-based control system sets the standard for power, ease of use, and flexibility, enabling greater reproducibility and productivity, even multi-user environments

• High speed data capture
• 5120 x 5120 data points
• HarmoniX Nanoscale Material Property Mapping
• Automatic Spring Constant calibration
• Capture 8 channels of data

Click here for datasheet [pdf]

Force Volume produces a two-dimensional array of force-distance measurements over a specified area to display images of force variations and topography along with individual force curves at any point.

Force-Distance Measurements are performed to study attractive and repulsive forces on a tip as it approaches and retracts from the sample surface. Commonly applied to investigating fundamental force interactions, nano-scale adhesive and elastic response, binding forces, colloidal studies, and chemical sensing.

Lateral Force Microscopy (LFM) is a secondary contact AFM mode that detects and maps relative differences in the frictional forces between the probe tip and the sample surface. In LFM, the scanning is always perpendicular to the long axis of the cantilever. Forces on the cantilever that are parallel to the plane of the sample surface cause twisting of the cantilever around its long axis. This twisting is measured by a quad-cell Position Sensitive PhotoDetector (PSPD) union as with TRmode.

AFM tip lateral movement in LFM.

Twisting of the cantilever usually arises from two sources: changes in surface friction and changes in topography. In the first case, the tip may experience greater friction as it traverses some areas, causing the cantilever to twist more. In the second case, the cantilever may twist when it encounters edges of topographical features. To separate one effect from the other, usually three signals are collected simultaneously: the trace and retrace LFM signals, and the AFM height (topography) signal.

LFM applications include identifying transitions between different components in polymer blends and composites, identifying contaminants on surfaces, delineating coverage by coatings, and chemical force microscopy (CFM) using probe tips functionalized for specific chemical or biological species.

Magnetic Force Microscopy (MFM) is a secondary imaging mode derived from TappingMode mode that maps magnetic force gradient above the sample surface. This is performed through a patented two-pass technique, LiftMode. LiftMode separately measures topography and another selected property (magnetic force, electric force, etc.) using the topographical information to track the probe tip at a constant height (Lift Height) above the sample surface during the second pass.




Lift Mode AFM.
The MFM probe tip is coated with a ferromagnetic thin film. While scanning, it is the magnetic field’s dependence on tip-sample separation that induces changes in the cantilever’s resonance frequency or phase. MFM can be used to image both naturally occurring and deliberately written domain structures in magnetic materials. An image of a hard disk acquired in MFM mode is shown.

Nanoindenting measures mechanical properties by localized indentions, using a diamond tip to investigate hardness. AFM can also perform nano-scratching and wear testing to investigate film adhesion and durability.

Scanning Capacitance Microscopy (SCM) is 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.

SCM is commonly used for two-dimensional profiling of dopants in semiconductor process evaluation and failure analysis.



Contact Mode topography (left) and SCM dC/dV images of a cross-sectioned transistor in a Pentium-II chip. 1.25µm scans.

Scanning Tunneling Microscopy (STM) measures topography of surface electronic states using a tunneling current that is dependent on the separation between the probe tip and a sample surface. STM is typically performed on conductive and semiconductive surfaces. Common applications consist of atomic resolution imaging, electrochemical STM, Scanning Tunneling Spectroscopy (STS) union and low current imaging of less conductive samples.

TRmode is a major new technique exclusive to Veeco that measures and controls dynamic lateral forces between the probe tip and sample surface. Utilizing advanced sensing hardware and electronics to characterize torsion oscillations of the cantilever, TRmode enables detailed, nanoscale examination of in-plane anisotropy, and provides new perspectives in the study of material structures and properties. It can also be interleaved with TappingMode AFM to provide complementary lateral and vertical characterization. In TRmode, the probe is oscillated along the cantilever's long axis, creating a rotational oscillation, i.e., a twisting motion. This oscillation causes a dithering motion of the tip. As the probe encounters lateral forces on the sample surface, the corresponding changes in the cantilever's twisting motion is measured. This twisting can be measured by using a quad-cell position-sensitive photo-detector (PSPD). Contact AFM uses a bi-cell PSPD to measure the vertical deflection of the cantilever, indicating changes in sample topography. With a quad-cell PSPD, both vertical and lateral deflections can be measured, as shown in the figure below.



Figure 4. Bi-cell vs. quad-cell PSPD used in TRmode AFM

TR-TUNA is an enhanced TUNA option for our MultiMode and Dimension platforms. It allows TUNA to be used on soft or otherwise delicate samples by using torsional resonance (TR) mode instead of contact mode. This greatly reduces vertical and lateral tip forces on samples while keeping the tip in the near field where the TUNA currents can be measured. This capability is especially important for polymer, thin film, and nanoelectronics applications.

Click here for datasheet [pdf]