Steffen Wilbrandt

The incorporation of metal clusters into thin organic dye layers as a method for producing strongly absorbing composite layers: an oscillator model approach to resonant metal cluster absorption

We present data on the NIR/VIS/UV optical constants of thin composite layers, built up from a copper phthalocyanine matrix with embedded metal clusters. The metal clusters (copper, gold and silver) have diameters on a nanometre scale and act as strong absorption centres. In particular, local plasmon resonances and metal interband transitions could be observed from a fit of the experimentally determined dielectric functions by means of a Lorentzian multi-oscillator model. Average dipole transition matrix elements with respect to a single metal cluster have been estimated from the oscillator parameters.

In situ optical characterization and reengineering of interference coatings.

A new optical monitoring system has been developed that allows recording of transmission spectra in the wavelength range between 400 and 920 nm of a growing optical coating during deposition. Several kinds of thin film sample have been prepared by use of a hybrid monitoring strategy that is essentially based on a combination of quartz monitoring and in situ transmission spectra measurements. We demonstrate and discuss the applicability of our system for reengineering procedures of high-low stacks and measurements of small vacuum or thermal shifts of optical coatings.

Mixed oxide coatings for optics

Material mixtures offer new possibilities for synthesizing coating materials with tailored optical and mechanical properties. We present experimental results on mixtures of HfO2, ZrO2, and Al2O3, pursuing applications in UV coating technology, while the mixtures are prepared by magnetron sputtering, ion beam sputtering, plasma ion-assisted deposition (PIAD), and electron beam evaporation without assistance. The properties investigated include the refractive index, optical gap, thermal shift, and mechanical stress. The first high reflectors for UV applications have been deposited by PIAD.

Computational manufacturing of optical interference coatings: method, simulation results, and comparison with experiment

Virtual deposition runs have been performed to estimate the production yield of selected oxide optical interference coatings when plasma ion-assisted deposition with an advanced plasma source is applied. Thereby, deposition of each layer can be terminated either by broadband optical monitoring or quartz crystal monitoring. Numerous deposition runs of single-layer coatings have been performed to investigate the reproducibility of coating properties and to quantify deposition errors for the simulation. Variations of the following parameters are considered in the simulation: refractive index, extinction coefficient, and film thickness. The refractive index and the extinction coefficient are simulated in terms of the oscillator model. The parameters are varied using an apodized normal distribution with known mean value and standard deviation. Simulation of variations in the film thickness is performed specific to the selected monitoring strategy. Several deposition runs of the selected oxide interference coatings have been performed to verify the simulation results by experimental data.

Plasma ion assisted deposition of hafnium dioxide using argon and xenon as process gases

Hafnium dioxide films have been produced by plasma ion assisted electron beam evaporation, utilizing argon or xenon as working gases. The optical constants of the layers have been investigated by spectrophotometry, while X-ray reflection measurements (XRR), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM) have been performed with selected samples. The correlation between structural and optical properties is discussed. With respect to optical quality, the application of xenon as working gas results in coatings with higher refractive index and smaller surface roughness than the application of argon. This effect is attributed to a more efficient momentum transfer from high energetic working gas ions or atoms to hafnium atoms during deposition.

All-oxide broadband antireflection coatings by plasma ion assisted deposition: design, simulation, manufacturing and re-optimization

A new all-oxide design for broadband antireflection coatings with significantly reduced impact of deposition errors to the final reflectance is presented. Computational manufacturing including re-optimization during deposition has been used in the design work to account for maximum insensibility of the design with respect to deposition errors typical for plasma ion assisted deposition PIAD. Repeated deposition runs with the deducted monitoring and re-optimization strategy verify the validity of the simulations and the stability of the derived design solution.

Deposition and spectral performance of an inhomogeneous broadband wide-angular antireflective coating

Gradient index coatings and optical filters are a challenge for fabrication. In a round-robin experiment, basically the same hybrid antireflection coating for the visible spectral region, combining homogeneous refractive index layers of pure materials and linear gradient refractive index layers of material mixtures, has been deposited. The experiment involved three different deposition techniques: electron-beam evaporation, ion-beam sputtering, and radio frequency magnetron sputtering. The material combinations used by these techniques were Nb(2)O(5)/SiO(2), TiO(2)/SiO(2), and Ta(2)O(5)/SiO(2), respectively. The spectral performances of samples coated on one side and on both sides have been compared to the corresponding theoretical spectra of the designed profile. Also, the reproducibility of results for each process is verified. Finally, it is shown that ion-beam sputtering gave the best results in terms of deviation from the theoretical performance and reproducibility.

Hybrid optical coating design for omnidirectional antireflection purposes

We present a new design for an omnidirectional antireflection coating for the visible spectral range. In contrast to classical designs, it combines homogeneous layers and linear gradient index layers into one hybrid design with a full thickness of approximately 500 nm. The coating may be practically produced based on silicon dioxide as low index material and niobium pentoxide as high index material, while intermediate indices may be obtained from corresponding mixtures.

All-optical in-situ analysis of PIAD deposition processes

In the case of plasma ion assisted deposition (PIAD) processes either quartz crystal monitoring or optical monitoring are commonly applied to control thickness of the layers. For several oxide layer materials the final stoichiometry of the deposited film is extremely sensitive to the oxygen gas inlet during the deposition process. It is well known, that under these circumstances, variations in the reaction gas flow or in deposition rates may cause unwanted variations of the stoichiometry of the coating. Finally this results in film inhomogeneities and increased absorption losses, which cannot be identified early enough and reliably by in-situ transmission spectroscopy alone. For this reason, the correlation between optical performance of the coating and emission spectra of the APS-plasma measured by a separate analyzer has been investigated. The synchronization in recording in-situ transmission spectra and plasma emission spectra was achieved by developing a common trigger unit for both spectrum analyzers. From the correlation between spectrophotometry and emission spectroscopy, we expect an earlier and more reliable assignment of absorption losses and inhomogeneities to instabilities in the process parameters of the deposition process.

Characterization of metal-oxide thin films deposited by plasma-assisted reactive magnetron sputtering

For single layers of SiO2, Nb2O5, and Ta2O5 that are deposited by plasma-assisted reactive magnetron sputtering (PARMS), we present measurement results for basic optical and mechanical properties, in particular, optical index, intrinsic film stress, thermal shift of spectral transmittance, and microroughness. We find high refractive indices combined with low intrinsic film roughness, moderate compressive stress, and almost a vanishing shift, indicate high potential for the production of high-performance optical coatings. The high thickness accuracy and process stability are exemplified by the measured spectral performance of multilayer stacks with about 200 single layers. OCIS codes: 310.1860, 310.6860. doi: 10.3788/COL201008S1.0073.