Thin Films

Investigating Curie point transformations in thin film piezoelectric using a HFS91-PB4 stage

The piezoelectric charge is the charge which accumulates in certain solid materials such as crystals, ceramics and biological materials and is where an applied pressure generates an electrical charge. This characteristic of materials is useful for the production and detection of sound, generation of high voltages, generation of electron frequencies, and ultrafine focusing of optical assemblies. This affect also forms the basis of scanning probe microscopy techniques.

At the RMIT University in Melbourne, Australia, Dr. Sharath Sriram and his colleagues have been investigating reversal and pinning of Curie point transformation in thin film piezoelectrics.  

HFS91-PB4 Linkam stage is used to heat and cool PSZT thin films Using an HFS91-PB4 (HFS600) Linkam stage PSZT thin films were heated to 350°C and cooled at 10°C/min in situ with real-time collection of Raman spectra. This enabled the researchers to determine two main Raman peaks for the film at room temperature, ~575 and ~ 744cm¯¹ ( at which point the film had a rhombohedral structure). Controlled heating and cooling of the thin film causes peaks and intensity changes at the Curie point. This is indicative of a phase change occurring at the Curie point, where the film changes from a rhombohedral arrangement to a symmetrical cubic arrangement. This phase change coincides with loss of piezoelectric charge and piezoelectrical structure. With controlled cooling the cubic phase reverses back to the rhombohedral phase with minimum hysteresis, and piezoelectrical potential. 

The HFS91-PB4 stage in the RMIT Laboratory

This Curie point transformation from cubic to rhombohedral can be disrupted by uncontrolled cooling, which results in locking in place the peak positions and intensities indicating a permanent phase change and the material remaining “locked” in the cubic phase. This shows fast cooling permanently removes the piezoelectric charge within a material.

 

Posted by Caroline Feltham

Directional Crystallization Using a Thermal Gradient

Electroluminescent displays, lighting (organic light-emitting diodes (OLED), circuits on flexible substrates, and photovoltaic cells are all applications of organic electronics that rely on industrial organic semiconductors (OSC).

The Linkam GS350 Stage in the Université Libre de Bruxelles laboratoryDue to a fundamental lack of the understanding of how molecular structure and supramolecular organization affects optoelectronic properties Prof. Yves Henri Geerts and his colleagues at Université Libre de Bruxelles have undertaken a study of single crystal thin films of Terthiophene by directional crystallization by means of a thermal gradient using the Linkam GS350 stage.

Optoelectronic properties can also be affected by the method of fabrication, therefore determining a method to control deposition and crystallisation is important.

As part of his research Prof. Yves Henri Geerts used polarized optical microscopy (POM) and X-ray diffraction to characterise the shape, size, and orientation (in and out of the plane of the substrate) of the crystals produced by the thermal gradient technique.

A sample of Terthiophene was placed on a cover slip on the hot side of the stage and is slowly translated to the cold side at a constant speed until all the sample is on the cold side.

The cover slip and sample are slowly translated from the hot side to the cold side at a constant speed.One side is above the melting temperature (hot side) and the other at a temperature below the crystallization temperature (cold side).

The conclusion of the experiment was that temperature gradients could potentially be used to control crystal growth and these conditions induce a preferential fast growth direction perpendicular to the gradient direction. In addition it is found that nucleation and growth can be decoupled for OSC crystallizing from the melt in a temperature gradient and that these conditions lead to the generation of highly textured thin films with uniaxial in-plane orientation of crystallites.

By Caroline Feltham

Thin Film Tensile Testing App Note


We have received a couple more great application notes involving our Tensile Testing Stage the TST350.

These two come from the folks at the Ecole Polytechnique Federale de Lausanne (EPFL) in Switzerland.
Here's the 'Introduction' from the App Note,
'Fragmentation Test Method for Adhesion Analysis of Coatings In Situ in a Microscope'.
You can read the full application note on our website.
'Mechanical integrity is a key attribute of coatings, which should not crack and delaminate during processing and during service life. Numerous methods are available to determine the adhesion of coatings, including tape and pull-out tests, and indentation and scratch techniques. The accuracy of these methods is however compromised by the presence of 'third body interactions', such as indenter-coating friction in case of scratch and indentation tests, or adherent-coating traction in case of peel and pull-out tests. The fragmentation test method detailed in the present note is free of third-body interactions. It enables quantifying the cohesive properties (which control cracking) and the adhesive properties (which control delamination) of coatings on high-elongation substrates. The method has been used to analyze a broad range of coating/substrate combinations, including inorganic coatings on polymers [1-3] and steel (e.g, [4]) and organic coatings on polymers (e.g., [e.g, [5]). The following section introduces the theory of coating fragmentation and calculation of the adhesive strength. The experimental conditions are detailed in a further section. Finally two application examples are given to illustrate the method, with focus on adhesive strength of an organic coating on a PET substrate, and a transparent electrode on a PEN substrate.'
With Thanks to Dr. Manfred Feustel of Resultec Analytical Equipment for his collaboration.