nano-TA, TTM

Localized nanoscale thermal imaging and analysis

Localized thermal analysis on sub-100 nm scale, nano-TA (nanoscale Thermal Analysis), provides the ability to locally measure the thermal properties of thin films and coatings on substrate and to create detailed images to identify thermal inhomogeneities invisible to other forms of microscopy. The NanoTA2™ is an accessory that enables a number of commercially available AFMs to perform localized Thermo Mechanical Analysis on a nano scale.

Background
Bulk thermal analysis techniques are widely used for materials analysis. But bulk analysis methods like Hot Disk™, DSC, TMA, DMA and others are limited to measuring average or aggregate properties of the entire sample. This masks critical variations in material properties that can have a huge impact on material performance. Materials and pharmaceutical developers increasingly need information about the spatial variation of thermal properties to engineer materials with desired properties. With the exception of Hot Disk™, bulk thermal analysis is also difficult to apply to thin films and coatings, where the underlying substrate may complicate or render bulk measurements impractical.

Methods (nano-TA, TTM, HT-AFM, SThM)

nano-TA, nanoscale Thermal Analysis is a TMA (thermo mechanical analysis) method that uses a nanoscale thermal probe, ThermaLever™, to locally heat samples and measure their transition temperatures by the relaxation of the probe tip deflection. TTM, Transition Temperature Microscopy is performed by repeated nano-TA measurements over the surface to generate a raster image.

Application example of TTM:

Identification of Processing Artifacts: The optical microscopy image (left) revealed a skin around the microfibers which was an artifact that formed during the microfiber embedding process, but could not identify the artifact. The TTM image (middle 100 x100 um) determined that it was the use of 'aged' epoxy resin monomer and catalyst that had hydrolyzed during storage and led to this formation. (Right) Density distribution of the transition temperatures obtained over the sample.

HT-AFM, Heated Tip AFM
The ThermaLever™ probes can be used to perform a variety of SPM measurements but with the addition of heating the probe. While this will not give the quantitative measurements obtainable with the nano-TA mode it can be used to differentiate the different materials at the sample surface.

These probes have been used in the contact, intermittent contact, force curve, pulsed force mode and nanolithography while heated up to temperatures as high as 400 º C. As opposed to sample heating stages, the temperature can be changed rapidly while inducing minimal thermal drift due to the small heated area.

SThM, Scanning Thermal Microscopy
Scanning Thermal Microscopy monitors and maps the local temperature and/or the localized thermal conductivity properties of a sample as a raster image is created.
SThM uses specially designed probes that incorporate a thin metal film near the apex of the probe. The system can very sensitively measure the resistance of this metal film which is an indication of its temperature.

Example:
 
AFM (left) and SThM (right) images of a Cu trace and solder joint in a cross sectioned Ball Grid Array. Scan size = 75 x 75 μm

The SThM mode works by applying a fixed voltage to the probe. This voltage can be varied which allows control of the temperature of the probe. When measuring active heated samples such as magnetic recording heads, electrical circuits or laser diodes, the voltage applied is kept low to reduce self heating. Alternately, when measuring qualitative variations in local thermal conductivity, the voltage can be increased to more easily sense the heat flow from the probe into the sample.

Features:
-System includes TA Studio software, a power supply box, the TMA controller, a CAL box, bridge cable, calibration samples and 10 ThermaLever™ silicon probes.

-The probes come premounted for easy exchange and allow high resolution AFM imaging and heating up to 400° C for the ThermaLever™ probes. The SThM probes have a maximum temperature of 160° C.

-Rapid controllable Thermo-Mechanical Analysis with heating rates up to 600,000°C / min.

-Temperature mapping via Scanning Thermal Microscopy (SThM) with a probe temperature resolution of <0.1°C and a lateral resolution of <100 nm.

-Identify/characterize individual phases from their onset and peak temperatures and by measuring their thermal properties.

-Currently compatible with a number of commercially available AFMs, contact K-analys to see if your system will operate with the NanoTA2 system.

Requirements:
-AFM system must have available a spare input channel and one spare USB connections.

-The operating system for the AFM must be Windows 2000 or XP.

Controller Specifications:
Controller:                        67XX DSP with FGPA

Connection to PC:           USB or RS-232

Input Signals:                  3 16 bit ADCs 100 ksps, 1 16 bit ADC 1.2 Msps

Input Gain (Vs-Vr):        10X, 100X or 1000X (software controlled)

SW Signals:                      SW can record up to 4 independent channels including the following options (Deflection, Resistance, Power, Vs, Vi, Vs-Vr, Delta Power, Vheat, and FbOut)

Output (to Probe):          0-10V or 0-40V (4 16 bit DACs, 100 ksps SW selectable range)

SThM Output:                   +/-4.2 V (equivalent to probe resistance)

Feedback:                        Digital feedback to ramp power, resistance or delta power

AC Input:                          BNC connector on the CAL box allowing up to 50 kHz sine waves to be summed onto the output to the probe

nano-TA/HT-AFM Specifications:
Measurement Mode:      Single or Dual Probe (SW selectable)

Ramp Modes:                   Voltage, Power (single), Resistance (single) Delta Power (dual)

Imaging Modes:              Contact Mode / Intermittent Contact Mode (SPM Dependent)

Temp. Ramp Rate:          Up to 600,000°C / min

Max. Controllable
Temp. of Probe:              400°C (dependent on probe)

Probe Spring Const:       ranges from 0.1 N/m to 5 N/m

Probe Res. Freq.:            ranges from 20 to 80 kHz

Tip Radius:                   10-30 nm

Tip Height:                        3-6 microns

Cantilever Length:          200 - 350 μm

SThM Specifications:
Measurement Mode:      Temperature contrast

Lateral Resolution:         <100 nm (dependent on probe)

Temp. Resolution:           <0.1 ˚C (dependent on probe)

Max. Temp. of Probe:     160°C (dependent on probe)

Spring Constant:             ~0.5 N/m

Resonant Frequency:     ~50 kHz

Tip Radius:                   <100 nm

Tip Height:                        ~10 microns

Cantilever Length:          ~150 microns