Systems for measuring the bidirectional reflectance distribution function (BRDF) are intended to be able to measure a variety of sample scattering distributions-from close-to-specular to diffuse, from polarised to unpolarised. Measuring the BRDF involves taking the ratio of measurements of both the amount of light incident on the sample and the amount of light that is reflected by the sample. Detectors used in these systems have a finite sized aperture, and so the different sample scattering distributions will have different distributions of light falling on the detector, and this distribution will also be different from the distribution of light during the incident beam measurement. An ideal detector with a perfectly uniform response is unlikely in reality. For BRDF measurements, it is generally assumed that the response of the detector is the same for both the incident and scattered beams, so even for imperfect detectors, the response of the detector will drop out when the ratio is taken. However, if for some reason the response of the detector differs between the two ratioed quantities, then it will induce an error in the measured ratio. A difference in the response of the detector in the MSL goniospectrophotometer between the collimated and polarised incident beam and the diffuse and unpolarised scattered beam has been identified. Having identified this issue, two different approaches have been taken to avoid the error in our measurements. Firstly, a correction factor was calculated from a detailed model of the detector, using ray tracing. Secondly, a new detector with an integrating sphere in the position of the photodiode was designed to avoid the differing response. To validate these approaches, we compared measurements made using the new sphere detector with corrected measurements made using the original detector, and demonstrate that these agree within the limits of uncertainty.

In recent years, a growing demand for the capability of performing accurate measurements of the bidirectional transmittance distribution function (BTDF) has been observed in industry, research and development, and aerospace applications. However, there exists no calibration and measurement capabilities-entry for BTDF in the database of the Bureau International des Poids et Mesures and to date no BTDF comparison has been conducted between different national metrology institutes (NMIs) or designated institutes (DIs). As a first step to a possible future key comparison and to test the existing capabilities of determining this measurand, two interlaboratory comparisons were performed. In comparison one, five samples of three different types of optical transmissive diffusers were measured by five NMIs and one DI. By specific sample choice, the focus for this study lay more on orientation-dependent scatter properties. In comparison two, where one NMI, one DI, one university, and three industrial partners investigated their measurement capabilities, the dependence on the orientation was not assessed, but two additional samples of the same material and different thickness were measured. Results of the two comparisons are presented, giving a good overview of existing experimental solutions, and showing specific sample-related problems to be solved for improved future BTDF measurements.

Measurements of both hemispherical reflectance and the bidirectional reflectance distribution function (BRDF) are of interest to a wide range of industries including computer graphics, remote sensing, lighting design, and cosmetics. The scale of directional reflectance is often realised at national metrology institutes using goniospectrophotometers, and by integrating BRDF measurements made over the hemisphere, the scale of hemispherical reflectance can also be realised. This paper describes the measurement model for BRDF and hemispherical reflectance using the MSL goniospectrophotometer, which uses rotation stages to adjust the angle of the sample. The measurement model is applied to measurements of a white Spectralon sample and a white ceramic tile to demonstrate the performance of the instrument. The relative standard uncertainty in the BRDF of a white Spectralon sample at 550 nm is less than 0.1% for in-plane measurements, while the relative standard uncertainty in the hemispherical reflectance of a white Spectralon sample at 560 nm is 0.27%.

In recent years, there has been a growing interest in the measurements of the bidirectional reflectance distribution function (BRDF) in industry and research and development. However, there is currently no dedicated key comparison to demonstrate the scale conformity. To date, scale conformity has been proved only for classical in-plane geometries, in comparisons between different national metrology institutes (NMIs) and designated institutes (DIs). This study aims at expanding that with nonclassical geometries, including, for the first time, to the best of our knowledge, two out-of-plane geometries. A total of four NMIs and two DIs participated in a scale comparison of the BRDF measurements of three achromatic samples at 550 nm in five measurement geometries. The realization of the scale of BRDF is a well-understood procedure, as explained in this paper, but the comparison of the measured values presents slight inconsistencies in some geometries, most likely due to the underestimation of measurement uncertainties. This underestimation was revealed and indirectly quantified using the Mandel-Paule method, which provides the interlaboratory uncertainty. The results from the presented comparison allow the present state of the BRDF scale realization to be evaluated, not only for classical in-plane geometries, but also for out-of-plane geometries.

Accurate and traceable measurements of transmittance haze are required for quality control in various different industries, such as optoelectronics, automobiles, and agriculture. Transmittance haze is defined as the fraction of light transmitted through a material that deviates from the incident beam by more than 2.5 ∘ . Various documentary standards specify the use of an integrating sphere with a prescribed geometry for the measurement of transmittance haze. This paper uses goniometric measurements of the bidirectional transmittance distribution function (BTDF) to calculate transmittance haze according to the definition and demonstrates that the sphere-based realisation of transmittance haze specified in the documentary standards does not agree with the definition, with the difference being up to 20% for some samples. The BTDF measurements are also used to simulate the integrating sphere haze, allowing the sensitivity of the sphere haze to errors in the integrating sphere geometry to be calculated.

Goniometric measurements are essential for the determination of many optical quantities, and quantifying the effects of errors in the rotation axes on these quantities is a complex task. In this paper, we show how a measurement model for a four-axis goniometric system can be developed to allow the effects of alignment and rotation errors to be included in the uncertainty of the measurement. We use three different computational methods to propagate the uncertainties due to several error sources through the model to the rotation angles and then to the measurement of bidirectional reflectance and integrated diffuse reflectance, a task that would otherwise be intractable. While all three methods give the same result, the GTC Python package is the simplest and intrinsically provides a full uncertainty budget, including all correlations between measurement parameters. We then demonstrate how the development of a measurement model and the use of GTC has improved our understanding of the system. As a consequence, taking advantage of negative correlations between measurements in different geometries allows us to minimise the total uncertainty in integrated diffuse reflectance, lowering the standard uncertainty from 0.0029 to 0.0015.

Most members of the ferromagnetic rare-earth nitride series display doping control over electron transport, with nitrogen vacancies being the most common donor. This paper reports the control and characterization of vacancies in one of the fourteen in the series, DyN. Electrical transport and optical spectra in films with controlled concentrations of vacancies show a pair of in-gap impurity levels ∼ 0.4 eV below the conduction band minimum and a third impurity level that lies nearly coincident with the conduction band minimum. Electron transport is found to be activated for concentrations ≤1019 cm−3, with signatures of extended state conduction at the Fermi level for higher concentrations.

New approaches to synthesize decorative black coatings on metallic surfaces are of significant research and commercial interest to manufacturing industries. In this work, decorative hard black coatings were deposited on a titanium surface by carbon ion implantation at ambient temperature. A 10 keV C+ beam was implanted on a Ti substrate to a fluence of 1-1.25 x 10(18) C cm(-2). Rutherford backscattering spectrometry and transmission electron microscopy results show that the implantation resulted in a bi-layered coating structure with a similar to 50 nm amorphous carbon layer at the surface followed by a similar to 50 nm amorphous titanium carbide intermixing layer deposited on top of a crystalline Ti surface. Raman spectroscopy confirms the formation of carbide intermixing layer and shows that the amorphous carbon layer has 15-20% sp(3) content. Nanoindentation measurements show that the surface hardness of the implanted surface has increased by 72%, from 3.7 to 6.6 GPa, upon carbon implantation. Scratch tests further demonstrate a reduction in coefficient of friction in the implanted surface by 25%, signifying an improvement in wear-resistance of the coated materials. Colorimetry measurements reveal that carbon implantation reduces the luminosity of the Ti surface from 77 to 49 and chromaticity from 4.67 to 1.36, confirming incorporation of black color on Ti surface. The results demonstrate that C implantation onto a Ti surface at high fluence results in a black coating with high surface hardness and wear-resistance that can be employed in decorative surface applications for manufacturing industries.

To elucidate the influence of polarization in diffuse reflectometry, we performed a series of measurements in several bidirectional geometries and determined the Stokes parameters of the diffusely reflected radiation. Different types of matte reflection standards were used, including several common white standards and ceramic colour standards. The dependence of the polarization on the sample type, wavelength and geometry have been studied systematically, the main influence factors have been identified: The effect is largest at large angles of incidence or detection and at wavelengths where the magnitude of the reflectance is small. The results for the colour standards have been modelled using a microfacet-based reflection theory which is derived from the well-known model of Torrance and Sparrow. Although the theory is very simple and only has three free parameters, the agreement with the measured data is very good, all essential features of the data can be reproduced by the model.

The field of spectral radiance factor (SRF) measurements has seen growing interest in recent years. Scale conformity has so far only been established between the national metrology institutes (NMIs) of Germany and the USA. This study aims at a bigger, multilateral scale comparison. For this purpose, a total of six NMIs participated in a scale comparison of goniospectrophotometers based on neutral and colored diffusely reflecting ceramics samples. In addition, two universities, providing a home-built gonioreflectometer and two widely used commercially available color measurement instruments, respectively, were involved. The wavelength range of the scale comparison covers the visible wavelength range from 380 nm to 780 nm. Results indicate systematic issues and that the uncertainty evaluation of the NMIs requires further work; although for the greatest part of the covered spectral range the agreement is good.

We present a study of the structural, conducting, magnetic, and optical properties of YbN thin films. Magnetic measurements reveal an antiferromagnetic Curie-Weiss temperature dependence. We find the temperaturedependent resistivity and carrier concentration to be indicative of YbN being semiconducting in nature. Along with this we observe an absorption onset at 1.5 eV, found from optical transmission and reflection measurements. This apparent combination of antiferromagnetism and semiconductivity present in YbN makes it unique among the rare earth nitrides, a series dominated by ferromagnetic semiconductors.

Andreas Hope et al.; 12th International Conference, Otaniemi, Espoo, Helsinki (Finland), 24-27 June, 2014; http://newrad2014.aalto.fi/

The European Metrology Research Program (EMRP) is a metrology-focused program of coordinated Research & Development (R&D) funded by the European Commission and participating countries within the European Association of National Metrology Institutes (EURAMET). It supports and ensures research collaboration between them by launching and managing different types of project calls. Within the EMRP Call 2012 "Metrology for Industry", the joint research project (JRP) entitled "Multidimensional Reflectometry for Industry" (xD-Reflect) was submitted by a consortium of 8 National Metrology Institutes (NMIs) and 2 universities and was subsequently funded. The general objective of xD-Reflect is to meet the demands from industry to describe the overall macroscopic appearance of modern surfaces by developing and improving methods for optical measurements which correlate with the visual sensation being evoked. In particular, the project deals with the "Goniochromatism", "Gloss" and "Fluorescence" properties of dedicated artifacts, which will be investigated in three main work packages (WP). Two additional transversal WP reinforce the structure: "Modelling and Data Analysis" with the objective to give an irreducible set of calibration schemes and handling methods and "Visual Perception", which will produce perception scales for the different visual attributes. Multidimensional reflectometry involves the enhancement of spectral and spatial resolution of reference gonioreflectometers for BRDF measurements using modern detectors, conoscopic optical designs, CCD cameras, line scan cameras, and modern light sources in order to describe new effects like sparkle and graininess/coarseness. More information and updated news concerning the project can be found on the xD-Reflect website http://www.xdreflect.eu/.

We report measurements of the optical response of polycrystalline DyN thin films. The frequency-dependent complex refractive index in the near IR-visible-near UV was determined by fitting reflection/transmission spectra. In conjunction with resistivity measurements these identify DyN as a semiconductor with 1.2 eV optical gap. When doped by nitrogen vacancies it shows free carrier absorption and a blue-shifted gap associated with the Moss-Burstein effect. The refractive index of 2.0+/-0.1 depends only weakly on energy. Far infrared reflectivity data show a polar phonon of frequency 280 cm-1 and dielectric strength delta epsilon= 20.

Analysis of CIPM international comparisons is increasingly being carried out using a model-based approach that leads naturally to a generalized least-squares (GLS) solution. While this method offers the advantages of being easier to audit and having general applicability to any form of comparison protocol, there is a lack of consensus over aspects of its implementation. Two significant results are presented that show the equivalence of three differing approaches discussed by or applied in comparisons run by Consultative Committees of the CIPM. Both results depend on a mathematical condition equivalent to the requirement that any two artefacts in the comparison are linked through a sequence of measurements of overlapping pairs of artefacts. The first result is that a GLS estimator excluding all sources of error common to all measurements of a participant is equal to the GLS estimator incorporating all sources of error, including those associated with any bias in the standards or procedures of the measuring laboratory. The second result identifies the component of uncertainty in the estimate of bias that arises from possible systematic effects in the participants' measurement standards and procedures. The expression so obtained is a generalization of an expression previously published for a one-artefact comparison with no inter-participant correlations, to one for a comparison comprising any number of repeat measurements of multiple artefacts and allowing for inter-laboratory correlations.

The Schott series of NG glasses are frequently used to manufacture neutral density transmittance standards for validation of spectrophotometer systems as well as for comparisons of regular spectral transmittance scales. A study has been made of the temperature and temporal dependence of transmittance in these types of filters. The temperature dependence of transmittance is found to scale as −ln(T). The filter transmittance was found to vary significantly with time shortly after manufacture but appears to be stabilizing nine months after beginning measurements.

A one-dimensional model based on classical nucleation and growth has been developed as a diagnostic tool for predicting the impact of different process conditions and nozzle geometries on particle size distributions produced from supersonic quenching of magnesium vapours. The model was validated against experimental data for water and SF6, showing good qualitative agreement with the data. For the cases in the study—magnesium concentration from 1 to 20mol% and the inlet temperature varying from 1600 to 1900K—the model predicts that 99% of the condensation is due to growth of particles nucleated during an initial high nucleation rate stage. The ultimate average particle size is therefore dependent on the magnitude of the nucleation rate during that initial stage of nucleation and to the degree of subsequent growth of those particles which are, in turn, a complex function of the conditions in the nozzle. The distribution of condensate size is somewhat sensitive to the inlet temperature of nozzle, increasing the temperature from 1600 to 1900K increases the mean size of the condensate by 25%. The molar concentration of magnesium in the gas affects the final particle size but this does not follow a simple trend. The size distribution of particles predicted from the model is very sensitive to changes in surface tension and sticking coefficient, highlighting the need for a more rigorous treatment of these parameters.

The diffusion length of carriers in semiconductors is a significant parameter determining the suitability of a material for device applications. Here we describe a simple new technique to measure diffusion length and apply it to a study of two types of disordered GaN. We find the diffusion length to be of the order of microns in nanocrystalline GaN and hundreds of microns in amorphous GaON. Experimentally the method involves the defocussing of a laser spot between two contacts. The results are supported by numerical modelling of the carrier concentrations in the experiment.

We report the growth of $\mathrm{GdN}$ thin films and a study of their structure and magnetic and conducting properties. It is demonstrated that they are semiconducting at ambient temperature with nitrogen vacancies the dominant dopant. The films are ferromagnetic below $68\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, and a significant narrowing of the band gap is signaled by more than a doubling of its conductivity. The conductivity in the low-temperature ferromagnetic state remains typical of a doped semiconductor, supporting the view that this material is semiconducting in its ground state and that no metal-insulator transition occurs at the Curie temperature.