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.

Fluid Imaging Cells provide contact mode and TappingMode AFM imaging in fluid environments. Fluid cells consist of a glass cantilever holder and silicon o-ring to form an enclosed fluid environment with the ability to exchange liquids. TappingMode can be conducted by oscillating the cantilever acoustically (traditional) or by Magnetic Actuated Drive. For electrochemical experiments, fluid cells allow contact mode and TappingMode imaging in electrochemical solutions with the addition of the electrochemical STM/AFM converters.

Click here for datasheet [pdf]

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

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]

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 PicoAngler™ Tool allows the user to easily explore tip-sample interactions with highly sensitive approach and retraction of the cantilever tip. This innovative, handheld tool is particularly useful for techniques in catching single molecules. Four different levels of sensitivity for manual control of the Z-axis and force-feedback allows exploration of interactions over a wide range of distances and forces.

Tip Evaluation helps users quickly identify tip problems which can degrade images and measurements which could lead to faulty interpretation of data. The Tip Evaluation feature compares user-selected thresholds with calculated tip characteristics obtained directly from the AFM image. This capability provides better and more consistent results, better comparison of data collected with different tips.

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 Spreading Resistance Microscopy (SSRM) is a Veeco-patented secondary imaging mode derived from contact AFM that maps two-dimensional carrier concentration profiles (resistance) in semiconductor materials. A conductive probe is scanned in contact mode across the sample, while a DC bias is applied between the tip and sample. The resulting current between the tip and sample is measured using a logarithmic current amplifier providing a range of 10 pA to 0.1 mA.



SSRM (left) and contact mode topography (right) scans of an InP-based heterostructure. 7mm scans. Sample courtesy Lucent Technologies. The contrast in the SSRM image shows the different regions of the heterostructure: alternating Zn-doped p-type and S-doped n-type layers.

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] 

Tunneling AFM (TUNA) works similarly to Conductive AFM, but with higher sensitivities. TUNA characterizes ultra-low currents (<1 pA) through the thickness of thin films. The TUNA application module can be operated in either imaging or spectroscopy mode. Applications include gate dielectric development in the semiconductor industry.