Aktive Thermosonde zur Messung des Energieeinstromes

A active thermal probe for the measurement of the energy influx A continuously working active thermal probe for the determination of the energy influx at plasma‐technological processes is presented. The principle of mesurement is based on the compensation of the incoming energy influx. Key benefits are the application for continuous measurement and the suitability for thin film deposition. A calibration is not needed. At selected positions of the reactor the energy influx to the probe can be measured and the correlation with properties of the growing layer or the treated surface, respectively, can be determined. Since the thermal probe reacts sensitively to the process parameters at the substrate surface it is very well qualified for control and monitoring of layer growth or surface treatment processes. The probe is a ost‐efficient, particularly suitable device for quality control in plasma‐technological applications.     

A novel thermal probe design for the measurement of energy influx in RF remote plasma

A novel design of a thermal probe to measure the energy influx of RF plasma has been achieved. This probe utilises one-dimensional steady-state conduction through the probe's cylindrical body and has the ability of controlling its exposed surface's temperature. The probe is fully instrumented so that the temperature field within it is known. This temperature field will serve as an indicator of achieving steady-state conduction as well as securing the needed data to calculate the energy influx of the RF plasma. Experimental results show that the plasma energy influx varied from 0.3 kW/m² to 2.2 kW/m² for RF power ranging from 15 W to 300 W, respectively. The variation of the energy influx with the RF power was found to follow a linear profile and a simple relation is proposed to model this variation for the considered plasma. Error analysis has been carried out to estimate the experimental uncertainties in the resulting energy influx values. The resulting uncertainties are found to be within the acceptable range for such applications.     

Measurement of total energy flux density at a substrate during TiOx thin film deposition by using a plasma jet system

The total energy flux density delivered to an electrically isolated substrate in a low-pressure pulsed DC hollow cathode plasma jet sputtering system during TiO₂ thin film deposition has been quantified. The plasma source was operated in constant average current mode and in a mixture of argon and oxygen or only in pure argon working gas. A titanium nozzle served as the hollow cathode. The total energy flux density measurements were made using a planar calorimeter probe. The main results from the calorimeter probe showed clearly that the total energy flux density at the electrically isolated substrate decreases significantly with duty cycle from 100% (DC mode) to 10% at a given pulsing frequency 2.5 kHz. A local maximum at duty cycle 60% for only pure argon operation has been observed. In addition, the voltage waveforms on the hollow cathode and before the ballast resistor have been saved for pulsed DC measurements for both pure argon and argon + oxygen mixture. A similar transient phenomenon on the cathode voltage and discharge current as observed recently in mid-frequency pulsed DC magnetron discharge has been discovered in the hollow cathode plasma jet sputtering system. We can conclude from these preliminary measurements that the main asset of the pulsed DC hollow cathode plasma jet discharge as distinct from the DC driving of the same plasma system lies in the possibility to reduce or to increase energy influx on the floating substrate within the change of duty cycle.     

Heating of polymer substrate by discharge plasma in radiofrequency magnetron sputtering deposition

The substrate used for the thin film deposition in a radiofrequency magnetron sputtering deposition system is heated by the deposition plasma. This may change drastically the surface properties of the polymer substrates. Deposition of titanium dioxide thin films on polymethyl methacrylate and polycarbonate substrates resulted in buckling of the substrate surfaces. This effect was evaluated by analysis of atomic force microscopy topography images of the deposited films. The amount of energy received by the substrate surface during the film deposition was determined by a thermal probe. Then, the results of the thermal probe measurements were used to compute the surface temperature of the polymer substrate. The computation revealed that the substrate surface temperature depends on the substrate thickness, discharge power and substrate holder temperature. For the case of the TiO₂ film depositions in the radiofrequency magnetron plasma, the computation indicated substrate surface temperature values under the polymer melting temperature. Therefore, the buckling of polymer substrate surface in the deposition plasma may not be regarded as a temperature driven surface instability, but more as an effect of argon ion bombardment.     

The analyses of an SiF4 plasma in an R.F. glow discharge for preparing fluorinated amorphous silicon thin films

The measurements of plasma parameters, such as an electron energy and an electron energy distribution function using a probe method, and of the optical emission spectroscopy for observing the chemical reactions in a plasma were studied for characterizing the glow discharge SiF₄ plasma. The probability of a basic dissociation process of the SiF₄ molecule by the electron impact was supported by the optical emission and also by the electron energy in the plasma. The discussions as to the electron energy distribution function in an r.f. glow discharge plasma suggest that a mean electron energy obtained by a double-probe method may not be very critical.The contribution of atomic hydrogen radicals and the probable reactions responsible for the deposition in the gas phase and/or on the substrate surface are also discussed.     

Computational investigation on the disturbed thermal plasma for improving the reliability of electrostatic diagnosis

For measuring the current-voltage (I-V) characteristic curve with respect to flowing plasmas, a Langmuir probe, a conducting object, should be inserted to the region directly, and the interaction between the probe and the flowing plasma is not avoidable. This interaction can cause the serious problem for plasma diagnostics due to aerodynamic and thermal disturbances generated by inserting the metallic probe. In spite of the problem related to the disturbances, the conventional probe theory assumes a connection between the measured probe currents and parameters of the undisturbed plasma. Unfortunately, the simplicity of the operating scheme is not reflected by the appropriate theories for the disturbed plasma. Also, the disturbed region should be affected by the size of the inserted probe, and this calls for a small probing object not to perturb the global state of the plasma. The main purpose of this paper is to know the disturbances of the original temperature and velocity fields, which are called as thermal and aerodynamic disturbances, of the entire free-burning arc disturbed by the inserted metallic probe with the turbulent model.     

Langmuir probe diagnostics of microwave electron cyclotron resonance (ECR) plasma

A Langmuir probe diagnostics is done on the microwave ECR generated plasma in a 2.45 GHz, 1.5 kW facility set up in our laboratory (for thin film deposition) by inserting a probe in the plasma close to substrate location (640 mm away from main ECR zone). A program using Graphical User Interface (GUI) was used for data analysis of I-V probe characteristics to obtain the radial electron energy distribution function (EEDF) in plasma. Plasma parameters such as charged particle density (n_e and n_i), electron temperature (T_e), plasma potential (V_pl) and floating potential (V_float) were estimated at substrate location for two incident microwave power levels at a fixed operating pressure. These parameters were estimated by different methods like orbital motion limited (OML) theory, electron energy distribution function (EEDF) and conventional method. The results obtained by the different methods are compared and observed differences are explained. The results indicate that even though the diffusion of plasma at the substrate location is mainly forced by particle collisions that lead to radial plasma uniformity, it still shows a non-Maxwellian behavior for the electrons with two groups having different energies.     

Study of the delamination of diamond coatings under thermal stress

The influence of the thickness of CVD diamond coatings on the adhesion to a substrate, after cooling down from deposition temperature to room temperature, has been studied experimentally and theoretically. Diamond layers have been deposited at 850°C on W substrates by microwave plasma enhanced CVD. Cooling down of the substrate-diamond coating system to room temperature induces thermal stresses, due to different thermal expansion coefficients of coating and substrate. For thick diamond coatings a total and sudden delamination could be observed as a consequence of these stresses. On the contrary thin coatings, produced under identical circumstances, adhered well. These phenomena have been modelled and explained by the use of an energetic criterion for the delamination of a two-layer system under thermal stress. From the model a critical thickness of the coating can be calculated. Above this critical thickness, delamination will suddenly occur. The calculations also predict that for intermediate coating thicknesses delamination can easily be induced by external causes.     

Tailoring the composition of self-assembled Si(1-x)C(x) quantum dots: simulation of plasma/ion-related controls

Precise control of composition and internal structure is essential for a variety of novel technological applications which require highly tailored binary quantum dots (QDs) with predictable optoelectronic and mechanical properties. The delicate balancing act between incoming flux and substrate temperature required for the growth of compositionally graded (Si(1-x)C(x); x varies throughout the internal structure), core-multishell (discrete shells of Si and C or combinations thereof) and selected composition (x set) QDs on low-temperature plasma/ion-flux-exposed Si(100) surfaces is investigated via a hybrid numerical simulation. Incident Si and C ions lead to localized substrate heating and a reduction in surface diffusion activation energy. It is shown that by incorporating ions in the influx, a steady-state composition is reached more quickly (for selected composition QDs) and the composition gradient of a Si(1-x)C(x) QD may be fine tuned; additionally (with other deposition conditions remaining the same), larger QDs are obtained on average. It is suggested that ionizing a portion of the influx is another way to control the average size of the QDs, and ultimately, their internal structure. Advantages that can be gained by utilizing plasma/ion-related controls to facilitate the growth of highly tailored, compositionally controlled quantum dots are discussed as well.     

Two regimes of heat exchange between a metal particle and a nonequilibrium plasma

A theoretical model is developed for the process of energy exchange between a spherical drop and a nonequilibrium plasma. It is demonstrated that, in a certain range of the plasma parameters, a quasistationary temperature of the drop can be maintained in two different heat exchange regimes. In one of these, the energy flux from plasma to drop is compensated by cooling due to the thermal emission of electrons; in the other, the energy supply is equilibrated by intensive evaporation of the drop material. The two regimes, characterized by certain quasistationary temperatures, are separated by a temperature interval featuring unstable states of the system. The particular realization of one or another quasistationary regime is determined by the initial temperature of the drop.     

Optisch dünne Schichten mit kontrollierten Eigenschaften durch plasmaunterstütztes Magnetronsputtern

Optical thin films with controlled properties by plasma enhanced magnetron puttering A new reactive magnetron sputter process was investigated in which an additional plasma source was implemented to support the magnetron sputter process. The plasma source is determined by high ion current density and moderate ion energy. At the beginning of the work, extensive investigations of the interaction of the magnetron with the plasma source during the deposition process were performed. Also, the plasma parameters in the region of the substrate were determined. A stable process which can be controlled very precicely was obtained with the set‐up used here. In the following, different oxide materials such as zirconia (ZrO₂) and titania (TiO₂) were deposited and investigated. It shows that because of the precise process control, different optical and morphological properties can be directly influenced by tuning the ion‐to neutral fraction of the process.     

Realization of thermally durable close-packed 2D gold nanoparticle arrays using self-assembly and plasma etching

Realization of thermally and chemically durable, ordered gold nanostructures using bottom-up self-assembly techniques are essential for applications in a wide range of areas including catalysis, energy generation, and sensing. Herein, we describe a modular process for realizing uniform arrays of gold nanoparticles, with interparticle spacings of 2?nm and above, by using RF plasma etching to remove ligands from self-assembled arrays of ligand-coated gold nanoparticles. Both nanoscale imaging and macroscale spectroscopic characterization techniques were used to determine the optimal conditions for plasma etching, namely RF power, operating pressure, duration of treatment, and type of gas. We then studied the effect of nanoparticle size, interparticle spacing, and type of substrate on the thermal durability of plasma-treated and untreated nanoparticle arrays. Plasma-treated arrays showed enhanced chemical and thermal durability, on account of the removal of ligands. To illustrate the application potential of the developed process, robust SERS (surface-enhanced Raman scattering) substrates were formed using plasma-treated arrays of silver-coated gold nanoparticles that had a silicon wafer or photopaper as the underlying support. The measured value of the average SERS enhancement factor (2?×?10(5)) was quantitatively reproducible on both silicon and paper substrates. The silicon substrates gave quantitatively reproducible results even after thermal annealing. The paper-based SERS substrate was also used to swab and detect probe molecules deposited on a solid surface.     

Analysis of the energy input during wire coating from a cylindrical magnetron source

In order to deposit thin films on a substrate several techniques can be used, e.g. chemical vapour deposition, atomic layer deposition or sputter deposition, depending on their specific advantages and disadvantages due to the related application. A significant parameter is the energy incident upon the substrate by the specific technique, especially when the heat capacitance of the substrate is low. Within this paper we analyse the energy transported into a thin wire (few 10 μm in diameter) during a dynamic inline aluminium sputter process in a cylindrical magnetron source. The evoked heating is important for the tensile strength of the wire and uniformity of the sputtered layer. Therefore, mathematical models were created to estimate the energy input into the wire supported by monte-carlo-simulations of the sputtering process using the TRIM-simulation (Transport and Range of Ions in Matter). Measurements with a Langmuir probe and the corresponding deposition rate were used to quantify these models, showing that at an aluminium coating process of a gold wire, the significant energy input is only due to electrons and ions of the processing gas (argon). Using the heat equation based on the sputtering apparatus' parameters, it was also possible to determine the energy input into the wire with in situ electrical resistance measurements. Both methods did show similar results, whereby the resistance results were more stable. The determined energy input made it possible to calculate the temperature profile during the wire-coating process which can be useful for estimations about film diffusion and process optimisation.     

Laser pulsing of field evaporation in atom probe tomography

The processes by which field evaporation in an atom probe is momentarily stimulated by impingement of a laser beam on a specimen are considered. For metals, the dominant and perhaps only sensible mechanism is energy absorption leading to thermal pulsing, which has been well established. The energy of a laser beam is absorbed in a thin optical skin depth on the surface of the specimen. For materials with a band gap such as semiconductors and dielectrics, it is found that energy absorption in a thin surface layer dominates the process as well and leads to similar thermal pulsing. The relative amount of surface absorption versus volume absorption can strongly influence the heat flow and therefore the mass spectrum of the specimen. Thus it appears for very different reasons that all materials behave similarly in response to laser pulsing in atom probe tomography.     

Cross-linked polymer replica of a nanoimprint mold at 30 nm half-pitch

This letter reports the demonstration of a photocurable polymer process for replicating the master mold for nanoimprint lithography. The cross-linked polymer mold was fabricated directly with high fidelity from a master by imprinting and photocuring a low viscosity liquid prepolymer film spun onto a substrate. The surface of the cross-linked polymer mold can be treated using an O(2) plasma, and then vapor primed with a low surface energy mold release layer for repeatable imprinting. The imprinting results demonstrated that the cross-linked polymer mold could be faithfully used for both thermal and photocurable nanoimprint lithography.     

Novel long laminar plasma sprayed hybrid structure thermal barrier coatings for high-temperature anti-sintering and volcanic ash corrosion resistance

1.Introduction The artificial-designed segmentation cracks in the ceramic layer of the thermal barrier coatings is an excellent choice by using the atmospheric plasma spray (APS) method under a low cost on the applications of aircraft engines or gas turbine engines.The residual thermal stress energy of the coatings with a certain inter-space of vertical cracks during the thermal cycling test is released through the cracks.The coating with vertical cracks was found out to be superior to other coatings with conventional lamellar structure[1].This process by using the atmospheric plasma spray method usually deposited a dense layer of YSZ (usual thickness of 0.5-1.5 mm) and heating the substrate over 773 K with an auxiliary device previously,even for a complex curved surface of the vanes.     

Relation between the plasma characteristics and physical properties of functional zinc oxide thin film prepared by radio frequency magnetron sputtering process

The ZnO thin film was deposited on a glass substrate by a RF reactive magnetron sputtering method. Results showed that plasma density, electron temperature, deposition rate and estimated ion bombardment energy increase with increasing applied RF power. Three distinct power regimes were observed, which are strongly correlated with plasma properties. In the low-power regime, the largest grain size was observed due to slow deposition rate. In the medium-power regime, the smallest grain size was found, which is attributed to insufficient time for the adatoms to migrate on substrate surface. In the high-power regime, relatively larger grain size was found due to very large ion bombardment energy which enhances the thermal migration of adatoms. Regardless of pure ZnO thin film or ZnO on glass, high transmittance (> 80%) in the visible region can be generally observed. However, the film thickness plays a more important role for controlling optical properties, especially in the UV region, than the applied RF power. In general, with properly coated ZnO thin film, we can obtain a glass substrate which is highly transparent in the visible region, is of good anti-UV characteristics, and is highly hydrophobic, which is highly suitable for applications in the glass industry.     

镀铬/高能束复合表面处理研究进展

根据高能束对镀铬涂层及其界面强化机制的不同,镀铬/高能束表面复合技术可分为两类:高能束强化镀铬涂层复合技术和高能束预处理基体/镀铬复合技术.前者典型代表有激光表面强化或等离子体氮化/镀铬涂层;后者主要代表是激光预淬火基体/镀铬复合表面处理.综合阐述了上述3种典型的复合处理技术的原理、目的及实际综合效果;通过试验初步探讨了激光预淬火基体/镀铬复合技术延长镀铬身管寿命的主要机理.     

Measurement of the thermal conductivity of molten semiconductors

The thermal conductivity of molten InSb in the temperature range between 800 and 870 K was measured by the transient hot-wire method using a ceramic probe. The probe was fabricated from a tungsten wire printed on an alumina substrate and coated with a thin alumina layer. The thermal conductivity was found to be about 18 W· m^–·K^–at the melting point and increased moderately with increasing temperature. The thermal conductivity of alumina used as the substrate for the probe was also measured in the same temperature range.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.On leave from NEC Corporation.     

Dynamic-stiffening-induced aggravated cracking behavior driven by metal-substrate-constraint in a coating/substrate system

Air plasma sprayed thermal barrier coatings(APS-TBCs)saw their wide application in high-temperaturerelated cutting-edge fields.The lamellar structure of APS-TBCs provides a significant advantage on thermal insulation.However,short life span is a major headache for APS-TBCs.This is highly related to the property changes and passive behaviors of the coatings during thermal service.Herein,a finite element model was developed to investigate the dynamic stiffening and substrate constraint on total spallation process.Results show that the stiffening accelerates the crack propagation of APS-TBCs.The driving force for crack propagation,which is characterized by strain energy release rate(SERR),is significantly enlarged.Consequently,the crack starts to propagate when the SERR exceeds the fracture toughness.In addition,the changing trends of SERR and crack propagation features are highly associated with temperatures.A higher temperature corresponds to more significant effect of stiffening on substrate constraint.In brief,temperature-dependent stiffening significantly aggravates the substrate constraint effect on APS-TBCs,which is one of the major causes for the spallation.Given that,lowering stiffening degree is essential to maintain high strain tolerance,and to further extend the life span of APS-TBCs.This understanding contributes to the development of advanced TBCs in future applications.