Sven Bornholdt

Effect of surface treatments on the properties and morphological change of dental zirconia

STATEMENT OF PROBLEM Creating a rough surface for bonding with airborne-particle abrasion with alumina may damage the surface of zirconia. Other treatment methods for creating a bonding surface without causing damage require investigation. PURPOSE The purpose of this in vitro study was to find ways of treating the zirconia surface without causing flaws, debris, pits, microcracks, or tetragonal to monoclinic phase transformation. MATERIAL AND METHODS Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramic surfaces were treated with gas plasma, argon-ion bombardment, 150-μm abrasive zirconia particles, and abrasive 150-μm alumina particles; untreated surfaces were used as the control group. X-ray diffraction (XRD) and confocal Raman spectroscopy were used to study the phase transformation. The roughness of specimens was measured with a confocal 3D laser scanning microscope. Modification of surface topography was analyzed with field emission scanning electron microscopy (FESEM), and the flexural strength was measured with a universal testing machine. Statistical analyses were performed with 1-way ANOVA, followed by comparison of means with the Tukey honest significant difference test. The standard deviation was calculated with descriptive statistics. RESULTS The sintered Y-TZP ceramic used in this study showed 2 phases, tetragonal and cubic. Specimens abraded with 150-μm alumina particles showed a higher monoclinic volume fraction (VmXRD=8.68%) and roughness (Ra=0.91μm) than specimens abraded with 150-μm zirconia particles (VmXRD=1.22%, Ra=0.08μm). One-way ANOVA indicated a significance difference in roughness among groups (P<.01). No phase transformation was observed in specimens treated with argon-ion bombardment or plasma. According to the Raman results, the volume fraction of the monoclinic phase for the specimens treated with airborne-particle abrasion depended on the distance from the ceramic surfaces and decreased with the increase in this distance. A slightly higher flexural strength was observed for untreated specimens (1009 MPa), followed by specimens treated with gas plasma (1000 MPa) and those airborne-particle abraded with 150-μm zirconia particles (967 MPa). The flexural strength of other specimens was lower (940 MPa for specimens abraded with 150-μm alumina particles and 916 MPa for specimens subjected to argon-ion bombardment). One-way ANOVA analysis indicated no significant difference in flexural strengths among all groups (P>.2). FESEM measurements showed that airborne-particle abrading Y-TZP surfaces with 150-μm alumina particles caused more damage to this area than the other methods. CONCLUSIONS Y-TZP ceramic surfaces treated with zirconia particles, argon-ion bombardment, and gas plasma were damaged less in comparison with surfaces abraded with alumina particles.

Characterization of the energy flux toward the substrate during magnetron sputter deposition of ZnO thin films

The characterization of energy influxes from plasma to substrate during sputter deposition of ZnO films is presented and discussed. Measurements were carried out in a triple rf magnetron sputter deposition system using calorimetric probes in various Ar/N2 and Ar/H2 mixtures at typical substrate positions. By variation of the probe bias the different contributions originating from the kinetic energy of charge carriers, the recombination of charge carriers (electrons and ions) at the surface as well as the contributions from the impact of neutral sputtered particles and subsequent film growth were determined. Radial scans in the substrate plane were recorded to obtain information about inhomogeneities in the total energy influx.The results show that the crystallinity reaches its optimum at that Ar/N2 ratio where the influence of the bombarding ions reaches its lowest value, indicating the destructive character of ion impact. Radial measurements indicate the influence of the magnetic field on the homogeneity of the energy influx caused by the superposition of the three (balanced) magnetic configurations. The superposition leads to an ?unbalanced character? resulting in a lowering of the electron trapping. The admixture of H2 leads to a drastic increase in the energy influx due to molecule formation at the (substrate/probe) surface.

Effect of surface modifications on the bond strength of zirconia ceramic with resin cement resin

OBJECTIVES Purpose of this in vitro study was to evaluate the effect of surface modifications on the tensile bond strength between zirconia ceramic and resin. METHODS Zirconia ceramic surfaces were treated with 150-μm abrasive alumina particles, 150-μm abrasive zirconia particles, argon-ion bombardment, gas plasma, and piranha solution (H2SO4:H2O2=3:1). In addition, slip casting surfaces were examined. Untreated surfaces were used as the control group. Tensile bond strengths (TBS) were measured after water storage for 3 days or 150 days with additional 37,500 thermal cycling for artificial aging. Statistical analyses were performed with 1-way and 3-way ANOVA, followed by comparison of means with the Tukey HSD test. RESULTS After storage in distilled water for three days at 37 °C, the highest mean tensile bond strengths (TBS) were observed for zirconia ceramic surfaces abraded with 150-μm abrasive alumina particles (TBS(AAP)=37.3 MPa, TBS(CAAP)=40.4 MPa), and 150-μm abrasive zirconia particles (TBS(AZP)=34.8 MPa, TBS(CAZP)=35.8 MPa). Also a high TBS was observed for specimens treated with argon-ion bombardment (TBS(BAI)=37.8 MPa). After 150 days of storage, specimens abraded with 150-μm abrasive alumina particles and 150-μm abrasive zirconia particles revealed high TBS (TBS(AAP)=37.6 MPa, TBS(CAAP)=33.0 MPa, TBS(AZP)=22.1 MPa and TBS(CAZP)=22.8 MPa). A high TBS was observed also for specimens prepared with slip casting (TBS(SC)=30.0 MPa). A decrease of TBS was observed for control specimens (TBS(UNT)=12.5 MPa, TBS(CUNT)=9.0 MPa), specimens treated with argon-ion bombardment (TBS(BAI)=10.3 MPa) and gas plasma (TBS(GP)=11.0 MPa). A decrease of TBS was observed also for specimens treated with piranha solution (TBS(PS)=3.9 MPa, TBS(CPS)=4.1 MPa). A significant difference in TBS after three days storage was observed for specimens treated with different methods (p<0.001). Thermal cycling significantly reduced TBS for all groups (p<0.001) excluding groups: AAP(p>0.05), CAAP(p>0.05) and SC(p>0.05). However, the failure patterns of debonded specimens prepared with 150-μm abrasive zirconia particles were 96.7% cohesive. CONCLUSION Treatment of zirconia ceramic surfaces with abrasive zirconia particles is a promising method to increase the tensile bond strength without significant damage of the ceramic surface itself. An alternative promising method is slip casting.

Energy fluxes in a radio-frequency magnetron discharge for the deposition of superhard cubic boron nitride coatings

Energy flux measurements by a calorimetric probe in a rf-magnetron plasma used for the deposition of super-hard c-BN coatings are presented and discussed. Argon as working gas is used for sputtering a h-BN target. Adding a certain amount of N2 is essential for the formation of stoichiometric BN films, since a lack of nitrogen will lead to boron rich films. Subsequently, the contributions of different plasma species, surface reactions, and film growth to the resulting variation of the substrate temperature in dependence on nitrogen admixture are estimated and discussed. In addition, SRIM simulations are performed to estimate the energy influx by sputtered neutral atoms. The influence of magnetron target power and oxygen admixture (for comparison with nitrogen) to the process gas on the total energy flux is determined and discussed qualitatively, too. The results indicate that variation of the energy influx due to additional nitrogen flow, which causes a decrease of electron and ion densities, electron temperature and plasma potential, is negligible, while the admixture of oxygen leads to a drastic increase of the energy influx. The typical hysteresis effect which can be observed during magnetron sputtering in oxygen containing gas mixtures has also been confirmed in the energy influx measurements for the investigated system. However, the underlying mechanism is not understood yet, and will be addressed in further investigations.

Effects of Hydrogen Dilution on ZnO Thin Films Fabricated via Nitrogen-Mediated Crystallization

Hydrogenated ZnO thin films have been successfully deposited on glass substrates via a nitrogen mediated crystallization (NMC) method utilizing RF sputtering. Here we aim to study the crystallinity and electrical properties of hydrogenated NMC-ZnO films in correlation with substrate temperature and H2 flow rate. XRD measurements reveal that all the deposited films exhibit strongly preferred (001) orientation. The integral breadth of the (002) peak from the hydrogenated NMC-ZnO films is smaller than that of the conventional hydrogenated ZnO films fabricated without nitrogen. Furthermore, the crystallinity and surface morphology of the hydrogenated NMC-ZnO films are improved by increasing substrate temperature to 400 °C, where the smallest integral breadth of (002) 2θ–ω scans of 0.83° has been obtained. By utilizing the hydrogenated NMC-ZnO films as buffer layers, the crystallinity of ZnO:Al (AZO) films is also improved. The resistivity of AZO films on NMC-ZnO buffer layers decreases with increasing H2 flow rate during the sputter deposition of buffer layers from 0 to 5 sccm. At a H2 flow rate of 5 sccm, 20-nm-thick AZO films with low resistivity of 1.5×10-3 Ω cm have been obtained.

Comparison of calorimetric plasma diagnostics in a plasma downstream reactor

The energy influx in a non-equilibrium plasma in the afterglow of a plasma downstream reactor has been measured by two different calorimetric probe types. The radio frequency discharge is investigated for oxygen (10–100%)–argon (90–0%) mixtures at relatively high gas flow rates (750–3000 sccm) and pressures (100–350 Pa). The main process parameters influencing the energy influx are the plasma power, the system pressure and the total gas flow rate. Even though the size, geometry and material composition of the used probe types are different, comparable energy flux values are achieved. Depending on the process parameters, energy fluxes between around 100 and 3500 W m−2 are found and the variation of the pressure and total gas flow rate suggests a highly flow-dependent plasma density distribution in the reactor.

Calorimetric Probes for Energy Flux Measurements in Process Plasmas

This chapter gives an overview of the method of calorimetric probes which are used for characterizing the interaction between low-temperature plasmas and substrates in materials processing. Although the focus is on low-temperature non-equilibrium plasmas most of the concepts can also be transferred to thermal plasmas or are in fact adopted from fusion research. An introductory section showing the importance and complexity of plasma wall interactions is followed by a section providing an overview and comparison of various probe concepts, which have been developed in the last decades. Special focus is on the type of probes which are similar to the probes used by J.A. Thornton (In fact, Thornton was not the first, to use this type of probe. From his work from 1978 [1], one can follow the citations back to the work of Jackson in 1969, who used equation (6.7) for the determination of the power dissipated by a copper block located at substrate position in a sputtering discharge [2]) who was one of the pioneers connecting plasma characteristics with resulting surface properties. Thereafter, a short section gives a basic overview of the different contributions to the total energy influx and which are of importance for the plasma wall interaction. The last section shows different examples of applications of calorimetric probes. It demonstrates the applicability and flexibility of these types of probes for characterization of different low-temperature plasmas. The examples mainly focus on complex plasmas, where the variety of the involved processes also causes a specific plasma wall interaction. Such complex situations can be found in systems where reactive gases or gas mixtures, nano or micro particles (dust), magnetic fields or large surface to volume ratios are involved.

Plasma Treatment of Polyethylene Powder Particles in Hollow Cathode Glow Discharge

Polyethylen (PE) is widely used in the production of foils, insulators, packaging materials, plastic bottles etc. Untreated PE is hydrophobic due to its unpolar surface. Therefore, it is hard to print or glue PE and the surface has to be modified before converting.In the present experiments a hollow cathode glow discharge is used as plasma source which is mounted in a spiral conveyor in order to ensure a combines transport of PE powder particles. With this set‐up a homogeneous surface treatment of the powder is possible while passing the glow discharge. The plasma treatment causes a remarkable enhancement of the hydrophilicity of the PE powder which can be verified by contact angle measurements and X‐ray photoelectron spectroscopy.