Surface structure analysis by profilometry

The analysis of surface structures is of great importance in many industries, such as chip/sensor manufacturing, inkjet printing or membrane production. In these industries surface analyses are used for instance as quality control, checking surface roughness or finding the root cause of defects.


As an example, one of our customers had approached us to help solve an issue with a curable resin product. The application of this product requires a very flat surface. At first, the resin was cast on a Teflon film, in order to ‘copy’ the flat surface of these films onto the resin product. By the naked eye, such a film indeed appears very flat, but surface profiling revealed that the film has depth differences of 1-1,5 micrometers (see Figure 1). A silicon wafer, a known flat substrate material, shows depth differences of just 30 nanometers (see Figure 2). Using this silicon wafer as substrate for the curable resin did result in the desired smoothness of the final product. Therefore, surface profiling enabled our customer to choose the right substrate for their product.

PTG Eindhoven Surface structure analysis by profilometry
Surface profiling

Figure 1: Surface profile of Teflon foil.

Profilometry is a great way to analyse a surface of a product. There are two ways optical profilometry and stylus profilometry, For a soft surface optical profilometry will gif the best results.

Graph of surface profilometry. When a surface seems flat is doesn't mean it is. With this analysis technique we at PTG Eindhoven can analyse the surface of the material.

Figure 2: Surface profile of the silicon (Si) wafer with a line profile analysis, indicated by the pink raster. The line profile is represented in the graph.

Another example below shows a microchip, which can be found in everyday devices like laptops or smartphones. A detailed image of its complex surface profile can be used to inspect the chip for any damages or incorrect assembly. The surface images in Figure 3 were obtained by an optical surface profiling technique.

2D image of a surface structure analysis by profilometry.

3D structure analysis by profilometry, in this result it's easy to see the surface is not flat.

Figure 3: Surface profile in 2D and 3D of a microchip in common electronics.

Using this technique, surfaces can be analysed quickly and accurately. Surface profiling can be done optically (optical profilometry), in which case light is used to illuminate a surface. The reflected light is detected and translated into a 2D/3D profile image. However, profiling can also be performed physically (stylus profilometry), where a stylus is used to probe a surface. Both techniques are extremely sensitive, capable of measuring depth differences of less than 1 nanometer. The choice of which technique is preferred mostly depends on the sample surface. For a very soft surface, you want to choose optical profilometry, so the surface is not changed as a result of the measurement. If a surface is absorbing (almost) all light, stylus profilometry is preferred.

At PTG/e, we offer both optical and stylus profilometry, as each technique has its pros and cons (which can often be compensated by the other technique). As such, we will always decide together with our customers which technique is best suited for their samples.

Interested in optical and physical surface profiling? Please contact us, it’s our pleasure to discuss the possibilities.


Surface analysis

Identifying complex and unknown materials with TGA-IR-GC-MS ‘Hyphenation setup’

By combining the analysis techniques TGA, FT-IR and GC-MS via coupling of the devices one obtains a powerful analysis technique. With this TGA-IR-GC-MS ‘Hyphenation setup’ it is possible to identify complex and unknown materials.

PTG/e makes use of a TGA-IR-GC-MS ‘Hyphenation setup’ from PerkinElmer.
Some applications for this technique are:

  • The identification of additives, like plasticizers, in plastics
  • Determination of the primary components of a material
  • Analysis of unknown contaminations in a material, like fragrances or solvents

To characterize a material, it is first placed in the oven of the TGA, where it is heated with a programmed heating rate. During heating, weight loss can occur due to thermal decomposition or solvent evaporation. The evolved gases from these events are transferred via a transfer line to a heated chamber of the FT-IR. There, the gas is exposed to an infrared beam. The functional groups in the measured gas each respond differently to infrared radiation, which helps to identify the molecules.

TGA spectrum

IR spectrum

Following the FT-IR, the gas is transferred via another transfer line to be injected onto the column of the GC. Depending of the affinity of the injected gas with the column, the temperature of the column and the speed of the carrier gas, the injected gas has a certain retention time. Different components have a different retention time, which enables the GC to separate the individual components of the injected gas.

GC spectrum

An mass spectrometer (MS) is located at the end of the column. In the MS, the separated components are ionized and brought into an electric field. This field will accelerate the ionized components to a certain speed, depending on their mass and charge. The MS uses this principle to create a spectrum, which, together with the retention time of the GC, is unique for each component. Combining the data from FT-IR and GC-MS, the individual components of the evolved gases from TGA can be characterized.

MS spectrum

Aside from the fully hyphenated setup, it is also possible to use the individual analysis techniques, or a partially hyphenated setup, for example TGA – IR or TGA – GC-MS. The specific required setup will depend on what needs to be analyzed exactly.

Hyphenation setup

PerkinElmer equipment:
TGA 4000
FT-IR Frontier
Clarus 690 GC & SQ8T MS
RedShift Transferline

For more information about our equipment and techniques

Moisture content determination of PET

Determining moisture content in PET granulate. An explanation of which analysis technique is most suitable, but also why.

Polyethylene terephthalate (PET) is widely known from the PET bottle. It is a thermoplastic material with many other applications besides the PET bottle. Although it may sound contradictory, PET is sensitive to water, especially during processing at high temperatures and pressures. When the material contains water (> 0.02 %) and is subsequently heated, the water can cause the molecular chains to break down via hydrolysis. This can have a drastic effect on the quality of the material.

For many companies that process PET, it is therefore extremely important to dry PET as much as possible before processing. But how can one check whether this drying process has taken place correctly?
This can be done in two ways, following the weight loss of the material during drying or via Karl Fischer titration.

Monitoring the weight loss of the material during drying seems to be the most obvious method. However, in order to be able to indicate small amounts of water in ppm range (parts per million), one must have a very accurate balance, such as a thermogravimetric analysis (TGA). With this analysis technique, it must be taken into account that not only the decrease in weight of water is monitored, but the decrease of all volatile components (such as used solvents or gaseous degradation products). This can lead to incorrect assumptions about the volatile component present when a small weight decrease is registered.

PerkinElmer TGA 4000 at PTG/e
PerkinElmer TGA 4000 at PTG/e

The most suitable technique for determining the amount of water is by Karl Fischer titration. The PET granulate is heated in a glass vial, so that water is released and blown into a titration liquid by means of a dry nitrogen flow. The liquid only reacts with water and the amount of water can be accurately determined on a ppm scale. An additional advantage is that the granulate can be sampled at various locations or after various time intervals in hermetically sealed bottles in order to determine the course of the drying process.

Metrohm 831 KF Coulometer in combination with a Thermoprep 832 oven at PTG/e

PTG /e has a wide range of analysis techniques and can therefore choose the most suitable technique or choose to combine techniques.

Interested in the various techniques and what they can be used for?

Download our overview of analysis equipment and techniques.

Polymers PTG Eindhoven

Material identification

One of our customers was using a certain grade of plastic for injection molding of their top-selling product. However, they had recently switched supplier and wanted to make sure that the material they ordered was exactly the same as they were used to. Therefore they sent us a sample of the product and asked if we could identify the material.

When identifying an organic material, a technique we use regularly is Infrared (IR) spectroscopy. With IR, the sample is irradiated with a beam of infrared light at different wavelengths. Functional groups interact with the infrared light, creating a unique signal. Combining all these signals yields a spectrum that is characteristic for that specific material, comparable to a fingerprint.

We recorded an initial IR spectrum and it was immediately evident that the sample was some kind of Nylon. However, there are several variations of Nylon that exhibit very similar IR spectra. Therefore, we made a detailed comparison of the IR spectra of the sample (yellow) to several different kinds of Nylon from our database, as shown in the figure below. Based on small differences of characteristic peaks, indicated with the colored arrows, we were able to exclude Nylon 6/6 (blue), Nylon 6/10 (pink) and Nylon 6/12 (green) as possible candidates. The best match was obtained with Nylon 6 (red).

To confirm our IR hit we used Differential Scanning Calorimetry (DSC) and determined the melting point (Tm) to be around 220°C. To finalize the material identification, we performed thermogravimetric analysis (TGA) to determine whether the Nylon contained any filler. The sample was heated to 900°C to remove the organic material, whilst recording the weight loss in weight percentage (wt%). At 900 °C, the residue was 24 wt%, which can be attributed to inorganic filler material (like glass fiber, which is commonly used to reinforce Nylon 6).

So, by a smart selection of three different techniques and with the help of our extensive database, we were able to determine quickly that the material was indeed Nylon 6 containing an inorganic filler. With this crucial information, the customer was fully reassured and could continue production without interruption.

Interested in our IR analysis? Please contact us via and we will be happy to discuss the possibilities.

Chocolate viscosity

With Easter upon us, many of us enjoy eating the associated chocolate eggs. It’s often easy to overlook the numerous steps between cacao harvesting, transporting, processing, and ultimately enjoying the taste of the final chocolate confection. As PTG/e, we’ve provided support in one of those many steps, related to the manufacturing process of chocolate products.

One of our customers approached us for viscosity measurements on raw cacao, an intermediate product in the chocolate production process. The viscosity data was required for the pump design needed to transport the cacao through pipes from one vessel to another. To correctly size such a pump, it is important to know what the viscosity of the material is, and particularly what the range of viscosities could be at different pumping speeds and temperatures.

Therefore, we used our TA Instruments DHR-2 rheometer, equipped with a Peltier heating system, with a 60 mm parallel plate configuration. We measured the viscosity of the raw cacao over a wide range of shear rates (simulating different pumping speeds), and at different temperatures as well. An example of such a flow sweep measurement performed at 90 °C is shown in the plot below.

While at low shear rates the raw cacao has a more or less constant viscosity, it can clearly be seen that the viscosity decreases dramatically at increased shear rates. This kind of material behavior is usually referred to as ‘shear thinning’, where the viscosity decreases as the flow increases and a certain yield stress is overcome. You could compare this behavior to peanut butter, which does not flow if you tilt the jar upside down, but spreads easily once you start smearing it on a sandwich. Such information on the shear thinning behavior of any material can be very useful in process design, because less energy is needed to pump a lower viscous material of course.

With all the viscosity data we collected under various circumstances, our customer could complete his pump design and thus satisfy their customer needs.

Besides raw cacao, we have had the pleasure of measuring a wide variety of foodstuffs, such as fruit juices, bread paste and pesto. Similarly, we have had the (arguable) pleasure of measuring cattle feed ingredients as well as filtered sewer sludge. Most importantly in all cases, we were able to provide our customers with useful viscosity data in order to aid in their process design.

Interested in viscosity measurements of your fluids? Please contact us at, we will be glad to discuss the possibilities.

Happy Easter!

Viscosity of chocolate