Conferences and exhibitons

The International Conference on Plasma Surface Engineering will take place for the 16^th time this year. The biennial PSE conference is a well-established forum for discussing the challenges, recent developments and new knowledge in the field of plasma as well as ion- and particle-beam assisted surface modification and thin film technologies. It is equally about the basics and applications of plasma technology. The main focus of this year's PSE is ”MEMS in our everyday life” and the role of plasma processes in the development of these microelectromechanical systems MEMS.

The Fraunhofer IST participates in the exhibition of the conference on September 18 - 19 as part of the joint booth of the competence network INPLAS and provides numerous contributions to the scientific conference program:

 

Monday, September 17, 2018

Plenary Lecture, 2:20 - 3:05 pm

Chair: Günter Bräuer

 

Tuesday, September 18, 2018

Poster Session, 7:00 - 10:00 pm

Poster - Plasma treatment and cleaning

”Artificial Neural Networks for the Prediction of Plasma Nitration Results”

Markus Mejauschek, Pierre Landgraf, Jörg Pribbenow, Weber Martin, Hanno Paschke, Günter Bräuer, Thomas Lampke

Plasma nitriding is a state-of-the-art thermochemical treatment, which the processing industry uses for hardening of the surface layer of tools and components. In the past, the potential to generate optimal results was not fully exploited. For this purpose, a prediction tool which calculates appropriate nitriding parameters adapted for the required properties of the component or tool is to be developed. The aim is to perform optimized nitriding treatments taking into account for example the chemical composition, hardness and nitriding depth. The prediction tool uses artificial neural networks (ANN). ANN usually consist of neurons which are connected and combined in an input layer, hidden layer and output layer. In order to train the network, the weight distribution of the connections, the number of hidden neurons and the neuron activation functions are varied. The aim of the ANN is to generate an output of different simulated hardness profiles depending on the chemical composition of the steel and the process parameters. In order to test the network, real-life trial results that are not incorporated into the training of the network will be used to confirm the results. This shows the accuracy of the prediction. The data base for the calculations and the training of the prediction tool are 42 variants of different nitriding processes. These are carried out using 12 different steels that differ fundamentally in their chemical composition. The composition and the process parameters have a decisive influence on the nitriding result. This generates varying hardness depth profiles in regards to the type of hardness gradient, surface hardness and the nitriding hardness depth. The data provided is used for initial training of the artificial neural network and evaluation of the predictions. Additionally, microstructural investigations enable for further analysis.

 

Wednesday, September 19, 2018

Poster Session, 3:15 - 4:45 pm

Poster - Protective and tribological coatings

”Correlation between process parameters and layer formation during plasma nitriding and boriding of nickel based alloys”

Julian Vogtmann, Günter Bräuer, Peter Kaestner, Martin Weber

In principle nickel based alloys are used for applications where the material is exposed to a high mechanical and thermal stress. Examples for these conditions are turbine blades and hot forming tools. Forming tools are additionally strained tribologically which leads to high wear because of the low hardness of nickel based alloys. In order to meet this challenging environment and ensure a long durability of tools, surface modifications are necessary. Hard coatings like DLC are not suitable for forming tools at high temperatures. Therefore plasma nitriding and boriding represent good alternatives for surface hardening Ni-based alloys. Three different nickel based alloys were plasma nitrided and borinded with various parameters. The nitrided layers of the samples were 5 to 15 μm thick and reached hardnesses up to 1700 HV. Plasma boriding was carried out in a H2-Ar-BCl3 atmosphere for two hours. The Temperature was varied between 500 and 800 °C. The samples were characterized by cross-sections, EDX-analysis, hardness profiles, adhesion of compound layer and tribometer tests. The cross-sections show a compact boride layer of 20 to 60 μm thickness mainly consisting of a mixture of hard nickel and chromium borides. The measurements yield a hardness of approximately 3000 HV directly under the surface and a sufficient adhesion of the boride layer to the ground material. The tribometer testing revealed a low friction coefficient and great wear resistance. Generally this investigation shows that nickel based alloys can be plasma nitrided and borided within a relativ wide array of process parameters. Plasma boriding has advantages over diffusion treatments using boron containing paste. Especially better controls of the surface properties through process parameters and less effort for perand post-processing are considerable. Additionally, if a borided tool is in contact with air at high temperatures, boronoxyd can form at the surface which is known as a dry-film lubricant.

 

Session 16 - (Plasma enhanced) chemical vapour deposition (PE)CVD II

5:55 - 6:15 pm

”Influence of the structure of 3D printed scaffolds on film deposition with an atmospheric plasma jet”

Thomas Neubert, Maria Cámara Torres, Veysel Zeren, Kristina Lachmann, Michael Thomas, Ravi Sinha, Carlos Domingues Mota, Alessandro Patelli, Lorenzo Moroni

An interesting new approach for the regeneration of lost bone fragments is the implantation of 3D-printed biodegradable polymer scaffolds. These polymer scaffolds replace the bone fragments until new bone cells form mineralized tissue that grows and matures into new bone inside the porous structure. To achieve good cell adhesion and growth, the surface chemistry of the scaffold material is important. Previous works show that plasma polymerized layers with nucleophilic and electrophilic groups promote cell growth for pre-osteoblasts. Because of its porous structure, it is not possible to coat the whole surface of the scaffold with conventional dielectric barrier discharge (DBD) deposition techniques. For this reason, we investigated chemical vapor deposition processes using an atmospheric plasma jet. This type of process provides the possibility for higher penetration depth into the scaffold structure as well as the option to integrate the deposition process in the 3D printing process of the scaffold. The plasma jet was powered with high voltage (HV) and radiofrequency (RF) and can be pulsed to achieve a good retention of precursor molecules. To achieve nucleophilic plasma polymer films (3-aminopropyl)trimethoxysilane (APTMS) was used as a precursor. A mixture of vinyltrimethoxysilane (VTMOS) and maleic anhydride (MAA) was used to deposit water stable electrophilic layers. The group density and the depth of the film formation into the scaffold structure were investigated by ATR-FTIR-spectroscopy and dyeing techniques. A variation of certain structure parameters of the scaffolds, e.g. diameter of the filaments, pore size, were investigated to optimize the film deposition with regard to an integration of the coating procedure into the 3D printing process.

 

Thursday, September 20, 2018

Session 19 - HiPIMS I

11:55 am – 12:15 pm

”How to transfer HIPIMS processes using different cathodes and machines”

Ralf Bandorf, Dominic Spreemann, Holger Gerdes, Michael Vergöhl, Günter Bräuer

HIPIMS processes have reached industrial level and there is a number of commercial HIPIMS solutions on the market. Nevertheless, the most efforts in development are still made using lab scale systems and cathodes. Exploiting these results and successfully transferring them to larger scale quite often presents a major challenge. In many cases the current, or better the peak current (peak current density) attached to the cathode is referred as the main parameter for scaling. Transferring processes between different cathodes and therefore different magnetic configuration will influence the electrical parameters applied to the cathode. Even more critical is shifting the coating system. This paper addresses issues concerning the transfer between different cathodes and coating systems. Instead of focusing on the electrical parameters applied at the cathode the situation at the substrate position is observed. Plasma properties like electron and ion density or electron temperature, as well as the ion to neutral ratio of the film forming species are used to characterize the process conditions for the film formation. Tailoring the input parameters at the cathode to reach comparable situation at the substrate is discussed. Finally, results of film growth and morphology are shown as first indication of proper choice for a successful approach for process scaling and transfer.

 

Session 20 - Other plasma based surface processing technologies

12:15  – 12:35 pm

”Plasmaboriding of high-alloyed tool steels – a new approach for wear reduction on highly loaded forming tools”

Martin Weber, Markus Mejauschek, Paschke Hanno, Günter Bräuer, Peter Kaestner, Julian Vogtmann, Jacob Wessel

Boriding of low alloy steels with powder or a paste-like precursor is well understood and has been studied for many years. The process involves boron diffusing into the material surface at temperatures above 750° C. Very hard and wear-resistant boride layers with a larger layer thickness are formed compared to conventional hard coatings. A disadvantage of this process is the resulting residues of the precursor on the material surface, which must be laboriously removed and then disposed of. To get around this, gas boriding processes with BCL3precursor and additional plasma support were developed. However, the problem here was the formation of pores and the technology was not suitable for the successful treatment of high-alloy steels. With a new boriding process, it was possible to produce almost non-porous boride layers on various high-alloyed steels at temperatures of 700 - 750° C. This could be achieved by changing the process gas composition and changing the gas supply. The use of the BCL3 precursor could be significantly reduced. With the new process, coating thicknesses between 10 and 20 μm with good adhesion can be achieved after a process time of two hours. Depending on the tool steel used and the process parameters, the layer hardness is between 1800 and 2500 HV. After boriding, the edge zone has a columnar structure which has disappeared after post-hardening of the steels according to the specifications of the material manufacturers. In Chromium-alloyed tool steels a fine-grained edge zone with chrome boride precipitates could be observed. Ball-on disk-tests against steel and aluminum demonstrate a very good friction and wear behavior.

 

Plenary Lecture, 2:20 - 3:05 pm

Chair: Michael Thomas

 

Poster Session, 3:15 - 4:45 pm

Poster - HiPIMS

”Microwave plasma assisted chemical vapor deposition of silica”

Holger Gerdes, Ralf Bandorf, Rolf Schäfer, Thomas Schütte, Michael Vergöhl, Günter Bräuer

Silica coatings are part in many optical and electrical applications. Especially, in electrical applications, e. g. as insulator the thin films have to be deposited defect-free. One solution for depositing silica is reactive sputtering, but this process needs usually active process control and leads to low deposition rates compared to CVD. Therefore, CVD-processes are favored in industrial applications. Especially microwave excitation offers a tool for cost efficient production. In this presentation, we will focus on microwave processes using a parabolic microwave source for deposition of SiO2-films. The working pressure was varied, as well as the source power and amount of HMDSO/TMS-gas. The plasma is characterized by optical emission spectroscopy. The deposited films are characterized with respect to their electrical (i. e. insulation) and optical properties. Furthermore, the characterization is complemented by SEM investigations of the topography and morphology of the films with top view and fracture cross section.

 

Session 21 - Atmospheric and in liquids plasma

Keynote Lecture, 4:45 - 5:15 pm

”Plasma Printing: Area-selective functionalization of surfaces at atmospheric pressure – Plasma sources and applications”

Michael Thomas, Kristina Lachmann, Marko Eichler, Antje Dohse, Claus-Peter Klages

The paper will give an overview on area-selective surface treatment using microplasmas at atmospheric pressure. In this so-called plasma printing process dielectric barrier discharges (DBD) are ignited inside microcavities, which are formed temporarily during the treatment by the contact of a suitably designed »plasma stamp« with the substrate surface. In the last two decades different plasma sources have been developed and patented in order to modify or coat different types of substrates for various applications. For semiconductor applications a localized plasma treatment of wafers was optimized so that wafer bonding can be performed at temperatures as low as 200 °C rather than at 1000 °C necessary in today’s standard processes. In the field of biomedical applications area-selective deposition of differentcoatings with specific chemical functionalities have been applied to control the adhesion of biomolecules like proteins, cells, or anti-bodies. In recent years the stamp technology was transferred to a reel-to-reel system allowing now line speeds up to 10 m/min. One of the most promising applications is the additive electroless metallization after area-selective surface treatment of polymers. By using N2/H2 gas mixtures more than 10 nitrogen-containing functional groups per nm2 can be grafted to the surface, forming a seed layer for the subsequent electroless processes. Flexible printed circuits and biosensors were produced using copper and palladium, respectively, with resolutions down to 25 μm. The latest development is a combined process of plasma printing and gravure printing of security products such as Guilloches or color shift devices. The wettability of different nano inks was adapted to the treated surfaces. Graphene-containing nano inks were optimized so that they contract to the plasma-treated regions on BOPP. The sharp border between plasma treated and untreated areas leads to a high-resolution gravure-printing process with resolutions below 10 μm.

 

Session 23 - Properties of technological plasmas

6:15 - 6:35 pm

”3D modelling of bipolar magnetron sputtering plasma discharges”

Andreas Pflug, Michael Siemers, Thomas Melzig, Michael Vergöhl

Dual rotatable magnetron sputtering sources are state of the art in large area coating technology and are nowadays also being used for deposition of precision interference coatings. For the latter, a precise uniformity control on flat as well as on curved moving substrates is mandatory. The design of optimized deposition setups including uniformity masks and specialized substrate holders usually requires time consuming experimental iterations. Thus, a simulation tool capable of predicting the film thickness distribution and optimizing the geometrical setup is desirable. Based on known erosion profiles on the sputter targets, the angularly resolved particle flux profile close to the substrate can be obtained via Direct Simulation Monte Carlo (DSMC) method. This enables subsequent computation of the film thickness profile on curved substrates in different positions. However, in a bipolar pulse magnetron discharge a uniform plasma density distribution cannot always be presumed and a proper determination of the sputter erosion profiles is not trivial. In order to get a more detailed picture on possible plasma non-uniformities in dual cylindrical magnetron discharges, we present 3D Particle-in-Cell Monte-Carlo (PIC-MC) simulations of the plasma discharge in Argon. Due to numerical constraints, the PIC-MC simulations are performed at lower plasma density compared to real discharges but nevertheless represent the relative plasma density profile in a reasonable approximation. The impact of different parameters such as total pressure, magnet tilting angle and electrical pulse shape on the plasma distribution is shown, and the results are compared with experimental findings.

 

Session 24 - HiPIMS II

Chair:  Holger Gerdes