PCGG - Reports

Report: Project Week in the Krebs Group

Tutors : Joerg Faupel, Erick Sueske, Thorsten Scharf

In this project week I was actively involved in learning the technique of Pulse Laser Deposition (PLD) which is a versatile technique to form thin films of polymers.

Introduction:
Thin films of polymers, amphiphilic molecules, metals etc. will play a very important role in industrial as well as in many house hold applications. There are many ways to form such thin films, namely self assembly, Langmuir Blodgett films, electro-deposition, vacuum evaporation, sputtering, laser deposition etc. These techniques are used depending upon the targets, substrates and many more. The properties and the quality of the thin film can be analyzed with various techniques like electrochemistry, spectroscopy, etc.

Experimental:
In this project week I used Pulse Laser Deposition (PLD) technique to form thin films of Polycarbonate (PC), which were characterized by FTIR spectroscopy. During the laser deposition bulk polymer targets are irradiated by the laser beam. As target, PC was used. The ablated material was deposited on silicon substrate surface. These substrates were cleaned in an ultrasonic bath in acetone, then rinsed with methanol and finally dried well before mounting in the vacuum chamber.

Schematic representation of the PLD is shown below.

The properties of laser deposited polymer thin films depends on many factor like laser power, vacuum or pressure of the chamber, substrates and many more. We were interested to study the characteristics of the polymer thin film by pressure in the chamber. To describe the modifications of the films, two series were deposited using different laser power. The deposited films were characterized by using FTIR; the spectrum shows interesting features of the polymer thin film. The following table describes the experiments performed and the spectrum will give the idea how variation in chamber pressure and laser power will change the quality of the polymer thin film. Further studies like TGA and SEM will give more insight in to the thin film.

At higher laser energy, with 10,000 pulses at 5Hz/s

Substrates	1	2	3	4	5	6
Vacuum(mbar)	6x10^-6	1.2x10^-3	0.102	0.25	0.5	1

At lower laser energy with 10,000 pulses at 5Hz/s.

Substrates	1	2	3	4	5	6	7	8	9
Vacuum(mbar)	3x10^-7	1x10^-3	0.1	0.267	0.5		0.350	0.445	0.793

As an example the IR spectra in fig. 1 and fig. 2 (films deposited with 230 mJ/cm²) shows that there is a prominent change in the intensities of 2800-2900 cm^-1 region i.e. for methylene and methyl stretches and 1200 cm^-1 region for CH₂ bending modes as the vacuum decreases from 6x10^-6 to 1.0 mbar.

Nov 15 2003

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