In situ deposition of metal coatings

Ceramic powder particles were metal coated by in situ deposition from decomposable compounds. The ceramic powder and a decomposable metal compound were mixed by tumbling and then heat treated in argon or in hydrogen to deposit the metal. Cermets with continuous metal matrices were obtained by hot pressing metal-coated powders or by in situ decomposition to form the metal during hot pressing. Tungsten-coated Eu₂O₃ powders were obtained by thermal decomposition of W(CO)₆ or by hydrogen reduction of WO₃. Europia-tantalum cermets were made by decomposition of tantalum hydride during hot pressing. Particles of Eu₂O₃ were coated with rhenium by decomposition of ReCl₃ or ReO_x and with molybdenum from the oxide. Cobalt and platinum coatings were deposited on ZrO₂-Y₂O₃ particles by decomposition of the chlorides. The uniformity of metal deposition depends on the mixing and on the particle size of the decomposable compound. The concurrent chemical reaction appears to enhance distribution of the metal by surface diffusion during the heat treatment that results in deposition. The extent of adherence or chemical bonding can be varied through the rate of deposition.     

In situ and ex situ stress measurements of YF3 single layer optical coatings deposited by electron beam evaporator

Yttrium fluoride (YF₃) is a material with good potential as a single-layer anti-reflection (AR) coating deposited onto glass substrates. YF₃ is a possible candidate to replace more studied fluorides such as MgF₂ or ThF₄ the latter being radioactive. For thin-film photovoltaic solar cells, depositing such layers could be a cost-effective way of improving the transmission of light to the p–n junction. However, long-term stability of these AR coatings is an important issue to be considered. This paper is concerned with the residual stress of YF₃ single layers deposited onto glass substrates, being a potential failure mechanism. The measured stress values are correlated to the structure of the layers, using ex situ characterization techniques, such as X-ray diffraction (XRD) and atomic force microscopy (AFM), in an attempt to explain the observed changes. Three substrate temperatures were investigated during deposition, namely 25, 115, and 210 °C. Intrinsic stress of up to 197 MPa has been observed in amorphous YF₃ single layers deposited by electron beam evaporation, at ambient temperature. At a substrate temperature of 210 °C, the intrinsic stress decreased to 67 MPa in the YF₃ layer, developing an orthorhombic structure. Adsorptive stress is an important issue encountered in YF₃ layers, directly related to a low packing density. The in situ stress measurements were carried out using a novel optical approach with a laser-fiber system, briefly introduced here. The residual stress values measured with this novel optical system were compared to two ex situ stress measurement techniques. The optical performance of the YF₃ single layers was also assessed using a spectrometer ex situ and in situ by the interferometry capability of the novel in situ monitoring device.     

2007 topical meeting on optical interference coatings: manufacturing problem

Measurements are described on the experimental filters submitted to the Third Optical Thin Film Manufacturing Problem in which the object was to produce multilayers with a measured colorimetric performance that is as close as possible to that specified. The perceived colors of the coating, when illuminated with randomly polarized light incident at 7 degrees by a source representing average daylight with a correlated color temperature of approximately 6500 K, were to be yellow and blue, respectively, in light reflected from its two surfaces, and the color was to appear white when viewed in transmission mode. Eleven teams from 7 different countries submitted a total of 18 samples.     

2010 topical meeting on optical interference coatings: manufacturing problem

For the 2010 Manufacturing Problem, the participants were required to produce a filter that had normal incidence transmittances of 0.001, 0.01, 0.1, and 0.96, respectively, in four separate 60?nm wide bands in the 400 to 700?nm wavelength region. The problem is not unlike those that need to be routinely solved in the telecommunication industry. Nine groups submitted a total of 11 different filters for the contest. The number of layers in the filters received ranged from 28 to 678, and the total metric thicknesses varied between 4,038 and 22,513?nm. The transmittances of the filters were measured at two independent laboratories. Some of the performances were quite close to the specifications.     

Comparison of algorithms used for optical characterization of multilayer optical coatings

Two algorithms used for the on-line and off-line characterization of multilayer optical coatings are experimentally compared using test samples produced by two different deposition processes and different monitoring approaches. One of these algorithms, called the triangular algorithm, demonstrates its superiority in all considered situations. We performed experiments with multilayer samples formed by high-density thin films, which allowed us to neglect possible errors in the film refractive indices and concentrate only on errors in the thicknesses of the layers of the produced coatings.     

Manufacture and characterization of optical coatings with incorporated copper island films

Copper island films have been prepared by thermal evaporation in vacuum and characterized by in situ as well as ex situ spectrophotometry. The parallel investigation of the island morphology by means of transmission electron microscopy allowed us to establish a clear correlation between film structure and optical properties. The effective optical constants of the copper island films could be determined by means of a fit of their ex situ transmission and reflection spectra. The effective optical constants have been used for designing and preparing optical multilayer coatings applicable for attenuator or color filter specifications. Measured characteristics of the multilayer coatings are in very good agreement with the calculated spectra.     

双介孔SiO2的原位合成及表征

以富含大孔或大介孔结构的硅胶为原料,在其上通过原位晶化合成具有小介孔-大介孔双孔分布的复合SiO2,并利用N2吸附-脱附、X射线衍射、扫描电镜、透射电子显微镜等手段对SiO2的物化性能和孔分布进行了表征。结果表明,所制备的样品具有双孔分布,孔径分别在3和45nm左右;小介孔的孔结构与MCM-41介孔类似,负载于硅胶表面及大孔孔壁上;大介孔的孔径较硅胶孔径有所减小,但未被完全填充堵塞。通过改变TEOS/大孔硅胶及CTAB/TEOS的配比可以实现对双介孔SiO2孔分布的调控。     

Topical meeting on optical interference coatings (OIC'2001): manufacturing problem

Measurements are presented of the experimental filters submitted to the first optical thin-film manufacturing problem posed in conjunction with the Topical Meeting on Optical Interference Coatings, in which the object was to produce multilayers with spectral transmittance and reflectance curves that were as close as possible to the target values that were specified in the 400- to 600-nm spectral region. No limit was set on the overall thickness of the solutions or the number of layers used in their construction. The participants were free to use the coating materials of their choice. Six different groups submitted a total of 11 different filters for evaluation. Three different physical vapor deposition processes were used for the manufacture of the coatings: magnetron sputtering, ion-beam sputtering, and plasma-ion-assisted, electron-beam gun evaporation. The solutions ranged in metric thickness from 758 to 4226 nm and consisted of between 8 and 27 layers. For all but two of the samples submitted, the average rms departure of the measured transmittances and reflectances from the target values in the spectral region of interest was between 0.98% and 1.55%.     

In situ TEM creation and electrical characterization of nanowire devices

We demonstrate the observation and measurement of simple nanoscale devices over their complete lifecycle from creation to failure within a transmission electron microscope. Devices were formed by growing Si nanowires, using the vapor-liquid-solid method, to form bridges between Si cantilevers. We characterize the formation of the contact between the nanowire and the cantilever, showing that the nature of the connection depends on the flow of heat and electrical current during and after the moment of contact. We measure the electrical properties and high current failure characteristics of the resulting bridge devices in situ and relate these to the structure. We also describe processes to modify the contact and the nanowire surface after device formation. The technique we describe allows the direct analysis of the processes taking place during device formation and use, correlating specific nanoscale structural and electrical parameters on an individual device basis.     

Transparent thin-film characterization by using differential optical sectioning interference microscopy

We propose an optical thin-film characterization technique, differential optical sectioning interference microscopy (DOSIM), for simultaneously measuring the refractive indices and thicknesses of transparent thin films with submicrometer lateral resolution. DOSIM obtains the depth and optical phase information of a thin film by using a dual-scan concept in differential optical sectioning microscopy combined with the Fabry-Perot interferometric effect and allows the solution of refractive index and thickness without the 2pi phase-wrapping ambiguity. Because DOSIM uses a microscope objective as the probe, its lateral resolution achieves the diffraction limit. As a demonstration, we measure the refractive indices and thicknesses of SiO2 thin films grown on Si substrate and indium-tin-oxide thin films grown on a glass substrate. We also compare the measurement results of DOSIM with those of a conventional ellipsometer and an atomic force microscope.     

Combined in situ and ex situ optical data analysis of magnesium fluoride coatings deposited by plasma ion assisted deposition

The combination of in situ spectrophotometry during film deposition and ex situ spectrophotometry allows insight into the depth distribution of optical losses in plasma ion assisted deposition coatings. An adapted optical characterization strategy for absorbing coatings using only in situ transmittance data has been developed and is exemplified in application to magnesium fluoride coatings. Measurements and simulation results strongly indicate an increased absorption caused by local understoichiometry of the fluoride material close to the fused silica substrate.     

In situ synthesis of TiC/Ti coatings by reactive plasma spraying

ABSTRACT

Sucrose, as a precursor of carbon, and titanium powders were used to prepare TiC powders by a spray-drying/precursor-pyrolysis method. Using the powders, TiC/Ti composite coatings were deposited by reactive plasma spraying. The results show that submicron-sized TiC is formed. The TiC phases have three kinds of crystal morphology: spherical TiC with a diameter of about 600?nm, dendrite TiC with a primary dendrite spacing of about 450?nm and a secondary arm spacing of about 150?nm, and cellular-dendrite TiC with a width of about 120?nm and a length of about 600?nm. The TiC/Ti coatings exhibit high microhardness and excellent wear resistance, which is about 2–3 times and about 200 times higher than that of TC4 alloys, respectively.     

Scattering characterization of nanopigments in metallic coatings using hyperspectral optical imaging

We have determined the reflectance spectra of colored metallic coatings with high spatial resolution by using a hyperspectral imaging system. Reflectance spectra were converted to color coordinates revealing characteristic color maps in the color space. Principal-component analysis was applied to decorrelate the spatial variability of the reflectance spectra. We found that the eigenvalue spectra follow different power laws. The scaling exponent was analyzed by considering random-walk-type processes. An estimation of the Hurst exponent was done, suggesting anomalous diffusion from multiple light scattering. The results show that hyperspectral imaging combined with principal-component analysis provides a valuable method for nondestructive testing of complex turbid media.     

In situ TEM near-field optical probing of nanoscale silicon crystallization

Laser-based processing enables a wide variety of device configurations comprising thin films and nanostructures on sensitive, flexible substrates that are not possible with more traditional thermal annealing schemes. In near-field optical probing, only small regions of a sample are illuminated by the laser beam at any given time. Here we report a new technique that couples the optical near-field of the laser illumination into a transmission electron microscope (TEM) for real-time observations of the laser-materials interactions. We apply this technique to observe the transformation of an amorphous confined Si volume to a single crystal of Si using laser melting. By confinement of the material volume to nanometric dimensions, the entire amorphous precursor is within the laser spot size and transformed into a single crystal. This observation provides a path for laser processing of single-crystal seeds from amorphous precursors, a potentially transformative technique for the fabrication of solar cells and other nanoelectronic devices.     

In situ optical inspection of electrochemical migration during THB tests

In order to get more information about the process of electrochemical migration (ECM), a novel in situ optical inspection system was developed and tested. The optical inspection system is applicable for real time in situ investigation to observe water condensation and dendrite growth during Thermal Humidity Bias (THB) tests. In this paper, a real time observation of water condensation and dendrite growth is studied on immersion silver (iAg), bare copper (Cu) and galvanic tin (gSn) interdigital (double comb) patterns prepared on FR4 substrate during Dew Point THB test. The real time in situ optical investigations were verified by real time voltage measurements, which are presented in the paper as well. The result shows that the water condensation mainly starts on the metal surface, which is an unexpected phenomenon since the preliminary condition of ECM is the presence of a continuous moisture film between the metallization stripes, e.g. on the surface of the insulation board material.     

In situ optical testing of infrared lenses for high-performance cameras

We propose to evaluate infrared lenses with a dedicated analyzer having the same mechanical interface as the usual cameras. The proposed analysis is based on a wavefront measurement and allows a diagnostic of possible internal defects of the analyzed lens. The infrared lens analyzer described is constituted with a quadriwave lateral shearing interferometer and works with a blackbody light. We describe the response of this interferometer and an innovative method to obtain the wavefront under test. We finally present the experimental analysis of long-wavelength infrared lenses and the particular case of a modified lens that generates a large spherical aberration.     

Topical meeting on optical interference coatings (OIC'2001): design contest results

A gain-flattening filter (GFF) for minimum manufacturing errors (12 designs submitted) and dense wavelength-division multiplex (DWDM) filters for low group-delay (GD) variation (9 designs submitted) was the subject of a design contest held in conjunction with the Optical Interference Coatings 2001 topical meeting of the Optical Society of America. Results of the contest are given and evaluated. It turned out that the parameter space for GFFs with optimum performance when manufacturing errors are not considered is much different from that when manufacturing errors are considered. DWDM filter solutions with low GD variation are possible.     

Laboratory simulation of a turbulent layer: optical and in situ characterization

Up to now only a few numerical or experimental simulations of atmospheric turbulent layers have been performed in the laboratory. These are devoted mainly to show the validity of Kolmogorov behavior but are not suitable to implement in an optical bench to test light propagation. Here we present a small size experimental simulation of an optical turbulent layer. With optical and in situ measurements, we managed to determine its characteristics: the mean variance of the refractive-index fluctuations integrated over the thickness of the turbulent flow and longitudinal and transverse structure functions of angles of arrival. From these measurements we found that the power spectrum of the refractive index is well fitted by a Von Karman function with an outer scale of 91 mm and an inner scale of 4.7 mm. Moreover, the temporal stationarity of these parameters indicates the reproducibility of this simulated turbulent flow.