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.

Veeco’s Dimension™ Heater and Cooler Accessories enable atomic force microscopy (AFM) to be performed down to -35°C and at elevated temperatures up to 250°C, with precise control while stepping or cycling through thermal ranges.

• Auto Z-motor function control provides continuous tip/sample positioning while heating
• Closed-loop controlled operation enables accurate surface tracking during thermal cycling of samples 
• Software temperature control for heater, cooler and tip maintains thermal equilibrium and precise measurements
• Low-volume environment enables precise gas-flow control to avoid oxidation when heating sample or ice formation during cooling
• Flexible platform enables almost every AFM experiment or test while temperature cycling samples

Download Datasheet

• Dimension AFM Heater and Cooler Accessories
  
  Low Res [262 KB pdf ]

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.

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

Phaseimaging is a powerful extension of TappingMode. It is a key element in the use of a number of scanning probe techniques, including Phase Imaging, MFM, EFM, Surface Potential, SCM, SSRM, TUNA, and C-AFM, as well as other techniques. The Quadrex offers a method of detection that provides an improved noise floor and more sensitive measurement than other detection methods, such as amplitude detection. It also provides lock-in detection with advanced signal routing and access to signals for enhanced imaging measurement.

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.

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.

VITA (Veeco Instruments Thermal Analysis) technology adds high resolution thermal characterization capabilities to existing Veeco Scanning Probe Microscopes (SPM).

Now SPM users not only benefit from unmatched core performance, but can add a
traditional bulk characterization technique. The VITA option builds on Veeco’s extensive expertise with thermal measurements — providing extended thermal measurement
performance through:

• Improved lateral resolution capabilities (to <100 nm)
• Full digital control of heating cycles
• Productive VITA control integration enabled by Veeco systems open architecture

VITA technology provides superior material characterization in two ways:

• Nanoscale Thermal Analysis
• Scanning Thermal Microscopy

Veeco Instruments Thermal Analysis Webinar

Presenter: Thomas Mueller

Duration approx. 52 minutes

File size 48 MB

View it Now!

Install the GotoMeeting Codec to play the webinar video

VITA - Veeco Instruments Thermal Analysis Application Note

• High Res [1.1 MB pdf ]

• VITA Scanning Thermal Analysis
  
  Low Res [262 KB pdf ]

 
The NanoScope 3D is the world's best-selling and most productive SPM controller. It combines advanced analog and digital circuit designs with real-time software to provide superior multi-tasking control. The piezoelectric scanner enables 16-bit resolution on all three axes, and proprietary electronics allow zooms from scans of 100 micrometers to a few nanometers. Add-on Quadrex™ technology provides phase-measurement capabilities.

Click here for datasheet [pdf]

Conductive Atomic Force Microscopy (CAFM) is a secondary imaging mode derived from contact AFM that characterizes conductivity variations across medium- to low-conducting and semiconducting materials. CAFM performs general-purpose measurements, and has a current range of 2 pA to 1 µA. CAFM employs a conductive probe tip. Typically, a DC bias is applied to the tip, and the sample is held at ground potential. While the z feedback signal is used to generate a normal contact AFM topography image, the current passing between the tip and sample is measured to generate the conductive AFM image.



Current flow in conductive AFM (CAFM).

In contact AFM, the tip is in perpetual contact with the sample. The tip is attached to the end of a cantilever with a low spring constant, lower than the effective spring constant holding the atoms of most solid samples together. As the scanner gently traces the tip across the sample (or the sample under the tip) union the contact force causes the cantilever to bend and the Z-feedback loop works to maintain a constant cantilever deflection.

Electric Force Microscopy (EFM) is a secondary imaging mode derived from TappingMode that measures electric field gradient distribution above the sample surface. This is performed through LiftMode. In EFM, a voltage may be applied between the tip and the sample. The cantilever's resonance frequency and phase change with the strength of the electric field gradient and are used to construct the EFM image. For example, locally charged domains on the sample surface are mapped in a way that is similar to how MFM maps magnetic domains.



EFM

Force Modulation imaging is a secondary imaging mode derived from contact AFM that measures relative elasticity/stiffness of surface features, and is commonly used to map the distribution of materials of composite systems. As with LFM and MFM, Force Modulation imaging allows simultaneous acquisition of both topographic and material-property maps.

In Force Modulation imaging mode, the probe tip tracks the sample topography as in normal contact AFM.  In addition, a periodic signal mechanically drives the cantilever (and tip) in the Z-direction.  The amplitude of cantilever modulation that results from this applied signal varies according to the elastic properties of the sample

The resulting force modulation image is a map of the sample’s elastic response. The frequency of the applied signal is typically a few kilohertz, which is faster than the z feedback loop is set up to track. Thus, topographic information can be separated from local variations in the sample’s elastic properties, and the two types of images can be collected simultaneously, as shown below.



Contact-AFM (left) and Force Modulation (right) images of a carbon fiber/polymer composite collected simultaneously.
5µm scan.

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.

Phase imaging is a secondary imaging mode derived from TappingMode that goes beyond topographical data to detect variations in composition, adhesion, friction, viscoelasticity, and other properties, including electric and magnetic. Applications include contaminant identification, mapping of components in composite materials, differentiating regions of high and low surface adhesion or hardness and regions of different electrical or magnetic properties.
Phase imaging is the mapping of the phase lag between the periodic signal that drives the cantilever and the oscillations of the cantilever. Changes in the phase lag often indicate changes in the properties of the sample surface.



The phase lag varies in response to the properties of the sample surface.

The system's feedback loop operates in the usual manner, using changes in the cantilever's oscillation amplitude to map sample topography. The phase lag is monitored while the topographic image is being taken so that images of topography and material properties can be collected simultaneously.




This figure shows simultaneously acquired topography (left) and phase (right) AFM images of silicone hydrogel in saline solution. The four outer areas were exposed to a sequence of chemical processing steps. The central cross-like region was masked and so protected from the processing steps and hence retained its hydrophobicity.

In the phase image (right) union a marked phase shift is clearly seen across the boundaries. However, the hydrophilic and hydrophobic regions show no topographic contrast (left). The phase image is clearly providing material property contrast on this well-defined experimental hydrogel surface.

The phase signal is sensitive to both short- and long-range tip-sample interactions. Short-range interactions include adhesive forces and visco-elastic forces; long-range include electric fields and magnetic fields.

Phase imaging is a key element in the use of a number of scanning probe techniques, including Magnetic Force Microscopy (MFM) union Electric Force Microscopy (EFM) and Scanning Capacitance Microscopy (SCM). This method of detection provides a more sensitive measurement than other detection methods, such as amplitude detection.

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.

Surface Potential (SP) imaging is a secondary imaging mode derived from TappingMode that maps the electrostatic potential on the sample surface. SP is a nulling technique. As the tip travels above the surface in LiftMode (see “Magnetic Force Microscopy” for description of LiftMode) union the tip and the cantilever experience a force wherever the potential on the surface is different than the potential of the tip. The force is nullified by varying the voltage of the tip so that the tip is at the same potential as the region of the sample surface underneath it. SP imaging can be used to detect and quantify contact potential differences (CPD) on the surface.



TappingMode Topography (left) and Surface Potential (Right) images of an area on a CD-RW. The bits are depicted only in the Surface Potential image. 5µm scans, courtesy Yasudo Ichikawa, Toyo Corp. Japan.

TappingMode AFM, the most commonly used of all AFM modes, is a patented technique (Veeco Instruments) that maps topography by lightly tapping the surface with an oscillating probe tip. The cantilever’s oscillation amplitude changes with sample surface topography, and the topography image is obtained by monitoring these changes and closing the z feedback loop to minimize them.

TappingMode has become an important AFM technique, as it overcomes some of the limitations of both contact and non-contact AFM. By eliminating lateral forces that can damage soft samples and reduce image resolution, TappingMode allows routine imaging of samples once considered impossible to image with AFM, especially in contact mode.

Another major advantage of TappingMode is related to limitations that can arise due to the thin layer of liquid that forms on most sample surfaces in an ambient imaging environment, i.e., in air or some other gas. The amplitude of the cantilever oscillation in TappingMode is typically on the order of a few 10’s of nanometers, which ensures that the tip does not get stuck in this liquid layer. The amplitude used in non-contact AFM is much smaller, as different forces are being measured. As a result, the non-contact tip often gets stuck in the liquid layer unless the scan is performed at a very slow speed.

In general, TappingMode is much more effective than non-contact AFM for imaging larger scan sizes that may include large variations in sample topography. TappingMode can be performed in gases, liquids, and some vacuum environments.

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.