Optical Reflectance Measurements Research Articles

Structural, Optical and Optoelectrical Properties of CuAlSnS4 Thin Films

The present study used chemical deposition to deposit thin copper aluminum tin sulfide (CATS4) layers onto clean glass substrates. X-ray diffraction analysis was utilized to explore the crystalline structure of the CATS4 films, which refers to the CATS4 films having a cubic crystal structure. Energy-dispersive X-ray analysis showed the presence of Cu, Al, Sn, and S peaks in the CATS4 films, and their atomic ratio is close to 1:1:1:4. Spectrophotometric measurements of optical transmittance and reflectance spanning the 400–2500 nm spectral range were performed to describe the optical properties of the CATS4 layers. The CATS4 films demonstrated a direct energy gap transition between 1.42 and 1.31 eV. Further, increasing the layer thickness enhanced the refractive index and Urbach energy of the CATS4 films. The inspected CATS4 films showed better optoelectrical properties with increasing thickness, including improved optical conductivity, optical resistivity, optical carrier concentration, relaxation time, and optical mobility. Increasing the thickness of the CATS4 films increased their nonlinear optical indices. Additionally, the hot probe apparatus verified the p-type semiconducting characteristics of CATS4 films.

Quantum control of exciton wave functions in 2D semiconductors.

Excitons-bound electron-hole pairs-play a central role in light-matter interaction phenomena and are crucial for wide-ranging applications from light harvesting and generation to quantum information processing. A long-standing challenge in solid-state optics has been to achieve precise and scalable control over excitonic motion. We present a technique using nanostructured gate electrodes to create tailored potential landscapes for excitons in 2D semiconductors, enabling in situ wave function shaping at the nanoscale. Our approach forms electrostatic traps for excitons in various geometries, such as quantum dots, rings, and arrays thereof. We show independent spectral tuning of spatially separated quantum dots, achieving degeneracy despite material disorder. Owing to the strong light-matter coupling of excitons in 2D semiconductors, we observe unambiguous signatures of confined exciton wave functions in optical reflection and photoluminescence measurements. This work unlocks possibilities for engineering exciton dynamics and interactions at the nanometer scale, with implications for optoelectronic devices, topological photonics, and quantum nonlinear optics.

Advancing energy storage and supercapacitor applications through the development of Li+-doped MgTiO3 perovskite nano-ceramics.

Perovskite oxide materials, specifically MgTiO3 (MT) and Li-doped MgTiO3 (MTxLi), were synthesized via a sol-gel method and calcination at 800°C. This study explores the impact of varying Li doping levels (x = 0, 0.01, 0.05, and 0.1) on the crystalline structure and properties of MgTiO3. X-ray diffraction analysis revealed a well-defined rhombohedral MgTiO3 phase. Optical diffuse reflectance measurements provided insights into energy gap values, refractive index, and dielectric constant. Li+ doping enhanced the electrical properties of MgTiO3, with a notable phase transition observed at 50°C. The study investigated impedance and AC conductivity under varying temperature and frequency conditions (25-120°C, 4 Hz to 8 MHz). Electrochemical analysis through cyclic voltammetry and electrochemical impedance spectroscopy confirmed highly electrocatalytic properties for MTxLi, particularly when modified onto screen-printed electrodes. This work not only advances the understanding of Li-doped MgTiO3 nanostructures but also highlights their significant potential for direct electrochemical applications, particularly in the realm of energy storage.

Energy Spectrum and Properties of SiC: Using Two-Photon Absorption for Different Harmonics

This paper describes a methodology for studying the energy spectrum and characteristics of Silicon Carbide (SiC) semiconductor materials, utilizing various harmonics for two-photon absorption (TPA). The approach involves developing theoretical models to simulate the energy levels and transitions of SiC, based on the TPA process. By analyzing the resulting spectra obtained by varying the harmonic order, the energy spectrum, and properties of SiC are explored. In this work also includes a comparison of the energy spectrum and properties of SiC for single and two-photon absorption, providing insights into the distinctive features of SiC under these conditions. In particularly absorption co-efficient of the material was calculated from optical transmittance and reflectance measurements at room temperature (300 K) in the wavelength range of 200 -900 nm. In addition, Gaussian functions centered at different energies were modeled using TPA in SiC materials and their contribution to the Harmonic Generation (HG) signal was calculated.

Operando X-Ray Diffraction Studies of Co Oxide Model Catalysts during Alcohol Oxidation and Oxygen Evolution Reaction

Green energy technology involving hydrogen generation requires developing catalyst materials of commercial viability, good stability and high reactivity for the electrochemical water splitting. Transition-metal oxides such as Co3O4 are among the best precious-metal-free electrode materials for the anodic oxygen evolution reaction (OER) in alkaline electrolysis [1]. Moreover, these spinel-type transition metal oxides are an important class of catalysts for the selective oxidation of organic compounds. Previous in situ and operando surface X-ray diffraction studies of epitaxial Co oxide films by our group showed pronounced changes in the near-surface structure of these catalysts. In particular, a sub-nm CoOx(OH)y skin layer starts forming in the pre-OER potential range which is accompanied by a volume change of the Co3O4 lattice [2]. In a more recent work, where we systematically explored the relationship between the effective thickness of this skin layer and the OER activity, we found clear evidence that the entire skin layer serves as a three-dimensional reactive zone for the OER [3]. Since the skin layer formation already starts several 100 mV negative of the onset of the OER, it is not induced by the catalytic reaction itself, but rather reflects the oxides’ electrochemistry, and may thus be expected also for other electrocatalytic processes, especially other electrocatalytic oxidation reactions which occur in a similar potential range. These oxide materials are not only of interest for OER, but also for the electrochemical oxidation of other compounds, such as alcohols [4]. However, data on the oxides’ structure in the presence of organic compounds does not exist at present. Obtaining such data is of great interest for understanding the mutual influence of oxide-electrolyte interface structure and electrocatalytic activity. In addition, the vast majority of publications on Co oxide oxidation processes, in particular all in situ and operando studies, have been performed up to now at room temperature only, and, thus, the catalytic performance of these materials at higher temperatures remains unknown. As electrolyzers and industrial (electro-) catalytic processes typically operate at elevated temperatures, such data are of considerable interest. Here, we present results of first potential-dependent structural studies of epitaxial Co3O4(111) and CoOOH(001) films electrodeposited on Au(111) single crystal substrates during ethylene glycol oxidation (EG Ox) in 0.1 M NaOH solution and compare those with the behavior found on the same samples in EG-free electrolyte. Ethylene glycol oxidation is a highly suitable reaction for such studies, as it occurs at potentials prior to the onset of the OER [4]. The samples were investigated as a function of electrode potential and temperature by operando surface X-ray diffraction at beamline P23 of PETRA III, DESY. The EG Ox was studied by successively increasing the EG concentration from 0 to 0.1, 0.5 and 2 M, which allows direct quantitative comparison of the potential-dependent structural changes. These studies of the oxides’ structure and electrochemical reactivity were performed at different temperatures in the range of 25 - 70°C. In all cases significant skin layer formation and accompanying changes in the oxide lattice strain were observed. The structural data are correlated with the results of cyclic voltammetry and optical reflectivity measurements that were recorded in parallel with the X-ray diffraction measurements. Together, they provide insights into the potential-dependent evolution of the skin layer thickness and strain and into the stability of the oxides in dependence of EG concentration and temperature. First results indicate that at elevated temperatures larger skin layer thicknesses and strain changes occur. Furthermore, the structural properties recover completely upon cooling back down to room temperature, suggesting that these effects are highly reversible. In the presence of EG, the reversible skin layer formation and changes in the Co3O4 bulk lattice were also observed, even though these structural changes appear to be less pronounced under alcohol oxidation conditions, especially at higher EG concentration. These studies will contribute to an in-depth understanding of the near surface structure of these Co oxide thin films during liquid phase oxidation catalysis, which is a prerequisite for the design of new, abundant and superior catalysts based on transition metal oxides for catalytic selective oxidation processes.We acknowledge financial support by the Deutsche Forschungsgemeinschaft via special research area TRR 247, project B10 (project no. 388390466).[1] A. Bergmann et al., Nature Catalysis 2018, 1, 711 - 719[2] F. Reikowski et al., ACS Catal. 2019, 9, 3811 - 3821[3] T. Wiegmann et al., ACS Catal. 2022 [4] S. N. Sun et al, J. Electrochem. Soc. 2016, 163, H99

Machine Learning Designed and Experimentally Confirmed Enhanced Reflectance in Aperiodic Multilayer Structures

AbstractMachine learning (ML) methods have gained widespread attention in optimizing nanostructures for target transport properties and discovering unexpected physics. Here, an ML method is developed to discover and experimentally confirm binary CeO2‐MgO aperiodic multilayers (AMLs) for thermal barrier coatings with significantly enhanced reflectance. The effect of varying AML design parameters like total thickness, average period, and randomness in layer thicknesses, on the spectral and total reflectance is demonstrated. Introducing aperiodicity in layer thicknesses is shown to lead to a broadband increase in spectral reflectance due to photon localization. Since the number of possible AML structures increases exponentially with total thickness, a Genetic Algorithm optimizer is developed to efficiently discover AMLs with enhanced reflectance, for total thicknesses of 5–50 µm. Surprisingly, all the optimized structures show an odd number of layers with a CeO2 layer at both ends, deviating from the traditional way of designing binary superlattices with paired layers. The optimized AML and a reference periodic superlattice of 5 µm thickness are fabricated by Pulsed Laser Deposition and characterized by optical reflectance measurements. The fabricated AML, despite considerable fabrication uncertainty, still enhances the reflectance to 48% from 40% of the reference superlattice, validating the effectiveness of our ML‐based optimization process.

Optical Transitions of a Single Nodal Ring in SrAs_{3}: Radially and Axially Resolved Characterization.

SrAs_{3} is a unique nodal-line semimetal that contains only a single nodal ring in the Brillouin zone, uninterrupted by any trivial bands near the Fermi energy. We performed axis-resolved optical reflection measurements on SrAs_{3} and observed that the optical conductivity exhibits flat absorption up to 129meV in both the radial and axial directions, confirming the robustness of the universal power-law behavior of the nodal ring. The axis-resolved optical conductivity, in combination with theoretical calculations, further reveals fundamental properties beyond the flat absorption, including the overlap energy of the topological bands, the spin-orbit coupling gap along the nodal ring, and the geometric properties of the nodal ring such as the average ring radius, ring ellipticity, and velocity anisotropy. In addition, our temperature-dependent measurements revealed a spectral weight transfer between intraband and interband transitions, indicating a possible violation of the optical sum rule within the measured energy range.

Assessment of thermal maturity in Lower Cambrian organic-rich shale in south China using integrated optical reflectance and Raman spectroscopy of pyrobitumen

It is challenging to accurately determine the thermal maturity of Lower Cambrian overmature shale, which is widely distributed in South China. In this study, we report an integrated method of measuring optical reflectance and Raman spectroscopy of pyrobitumen to determine the thermal maturity of Lower Cambrian organic-rich shales that contained a highly aromatized organic matter chemical structure. The optical reflectance measurement was conducted on large-particle-size angular pyrobitumen to eliminate the interference of clay mineral matrix, and the Raman spectrum analysis is a statistical response of a highly thermally evolved pyrobitumen chemical structure. Raman analysis compensates for the limitation of optical anisotropy interference in optical reflectance measurements. There is a good agreement between optically measured pyrobitumen reflectance (PBRo) and pyrobitumen reflectance calculated by Raman parameters (RmcPBRo), reflecting only minimal effects of optical anisotropy on the average optical reflectance (PBRo) values of pyrobitumen with fine or irregular mosaic texture, further indicating reliability of this integrated method for analyzing overmature shale. Thermal maturity varies significantly in the Lower Cambrian organic-rich shales, ranging from 2.60 to 2.92% EqVRo in the western Hubei province (WHBP), 2.98–3.49% EqVRo in the southern Shaanxi province (SSXP), 3.20–3.38% EqVRo in the southern Sichuan province (SSCP) and 4.06–4.31% EqVRo in the southeastern Chongqing (SECQ). The degree of aromatization and the structural order of organic matter (OM) are abruptly intensified when thermal maturity reaches about 3.5–3.7% EqVRo, as indicated by the deconvolution of the D and G bands in the Raman spectrum of pyrobitumen. The abrupt change in chemical structure of OM provides evidence for further dividing the early and late stages of overmaturation at a boundary of 3.5–3.7% EqVRo. The Lower Cambrian organic-rich shales distributed in the Cambrian shale gas breakthrough areas are normally at the early stage of overmaturation (2.0% < EqVRo < 3.5–3.7%). Development of paleo-uplifts in the Cambrian shale gas breakthrough areas led to relatively shallow burial depth of Lower Cambrian shale distributed on the peripheral areas of paleo-uplifts and created favorable shale gas preservation condition with only rare and small-scale faults.

Correlation‐Driven Magnetic Frustration and Insulating Behavior of TiF3

The halide perovskite TiF3, renowned for its intricate interplay between structure, electronic correlations, magnetism, and thermal expansion, is investigated. Despite its simple structure, understanding its low‐temperature magnetic behavior has been a challenge. Previous theories propose antiferromagnetic ordering. In contrast, experimental signatures for an ordered magnetic state are absent down to 10 K. The current study has successfully reevaluated the theoretical modeling of TiF3, unveiling the significance of strong electronic correlations as the key driver for its insulating behavior and magnetic frustration. In addition, frequency‐dependent optical reflectivity measurements exhibit clear signs of an insulating state. The analysis of the calculated magnetic data gives an antiferromagnetic exchange coupling with a net Weiss temperature of order 25 K as well as a magnetic response consistent with a S = 1/2 local moment per Ti3+. Yet, the system shows no susceptibility peak at this temperature scale and appears free of long‐range antiferromagnetic order down to 1 K. Extending ab initio modeling of the material to larger unit cells shows a tendency for relaxing into a noncollinear magnetic ordering, with a shallow energy landscape between several magnetic ground states, promoting the status of this simple, nearly cubic perovskite structured material as a candidate spin liquid.

Location deviation correction method based oncross-correlation spectrum in OFDR.

A location deviation compensation algorithm based on cross-correlation spectrum is proposed for optical frequency domain reflection (OFDR) measurement. The strain and the imperfect repeatability of the laser source may cause a location deviation of the OFDR measurement system, resulting in a demodulation error. This paper proposes to use the peak-to-average ratio (PAR) to measure the quality of the correlation results and achieve compensation, which achieves efficient compensation for location deviation. Compared to other compensation methods, this algorithm can deal with the complex location deviation with better demodulation accuracy and stability. Through a strain measurement experiment, we demonstrate that the demodulation error caused by location deviation is largely eliminated. As a result, the spatial resolution of the system is improved from 8cm to 2cm, and the maximum measurement range is expanded to 5000µε.

Laser-induced coherent longitudinal acoustics phonons in thin films observed by ultrafast optical reflectivity and ultrafast x-ray diffraction

Femtosecond laser excitation of crystal materials can produce coherent longitudinal acoustic phonons (CLAPs), which possess the capability to interact with various quasiparticles and influence their dynamics. The manipulation of CLAPs' behavior is thus of significant interest for potential applications, particularly in achieving ultrafast modulations of material properties. In this study, we present our findings on the propagation of laser-induced CLAPs at thin-film interfaces and heterojunctions using ultrafast optical reflectivity and ultrafast x-ray diffraction measurements. We observe that CLAPs can efficiently propagate from a LaMnO3 thin-film to its SrTiO3 substrate due to the matching of their acoustic impedance, and the oscillation period increases from 54 to 105 GHz. In contrast, in ultrafast x-ray diffraction experiments, we discover that CLAPs are partially confined within an Au (111) thin film due to the mismatch of acoustic impedance with the substrates, leading to an oscillation period of 122 ps. However, interestingly, when examining La0.7Ca0.175Sr0.125MnO3/Ba0.5Sr0.5TiO3 bilayers, no oscillations are observed due to the favorable impedance matching between the layers. Our findings demonstrate that acoustic impedance can serve as an effective means to control coherent phonons in nanometer-thin films and may also play a crucial role in phonon engineering at interfaces or heterostructures.

Correlating Optical Microspectroscopy with 4×4Transfer Matrix Modeling for Characterizing Birefringent Van der Waals Materials.

Van der Waals materials exhibit intriguing properties for future electronic and optoelectronic devices. As those unique features strongly depend on the materials' thickness, it has to be accessed precisely for tailoring the performance of a specific device. In this study, a nondestructive and technologically easily implementable approach for accurate thickness determination of birefringent layered materials is introduced by combining optical reflectance measurements with a modular model comprising a 4×4 transfer matrix method and the optical components relevant to light microspectroscopy. This approach is demonstrated being reliable and precise for thickness determination of anisotropic materials like highly oriented pyrolytic graphite and black phosphorus in a range from atomic layers up to more than 100nm. As a key feature, the method is well-suited even for encapsulated layers outperforming state of-the-art techniques like atomic forcemicroscopy.

Tunable Subnanometer Gaps in Self-Assembled Monolayer Gold Nanoparticle Superlattices Enabling Strong Plasmonic Field Confinement.

Nanoparticle superlattices produced with controllable interparticle gap distances down to the subnanometer range are of superior significance for applications in electronic and plasmonic devices as well as in optical metasurfaces. In this work, a method to fabricate large-area (∼1 cm2) gold nanoparticle (GNP) superlattices with a typical size of single domains at several micrometers and high-density nanogaps of tunable distances (from 2.3 to 0.1 nm) as well as variable constituents (from organothiols to inorganic S2-) is demonstrated. Our approach is based on the combination of interfacial nanoparticle self-assembly, subphase exchange, and free-floating ligand exchange. Electrical transport measurements on our GNP superlattices reveal variations in the nanogap conductance of more than 6 orders of magnitude. Meanwhile, nanoscopic modifications in the surface potential landscape of active GNP devices have been observed following engineered nanogaps. In situ optical reflectance measurements during free-floating ligand exchange show a gradual enhancement of plasmonic capacitive coupling with a diminishing average interparticle gap distance down to 0.1 nm, as continuously red-shifted localized surface plasmon resonances with increasing intensity have been observed. Optical metasurfaces consisting of such GNP superlattices exhibit tunable effective refractive index over a broad wavelength range. Maximal real part of the effective refractive index, nmax, reaching 5.4 is obtained as a result of the extreme field confinement in the high-density subnanometer plasmonic gaps.

Investigations on black silicon nanostructures fabricated by reactive ion etching on highly curved surfaces

A large amount of valuable research on black silicon (b-Si) nanostructures has pushed its use further into application in recent years. However, the research results to be found are all related to plane substrates. For an investigation of b-Si structures on curved surfaces, they were fabricated on hemispherical silicon lenses using inductively coupled plasma reactive ion etching. It was possible to achieve different structure morphologies according to the selected etching parameters, analogous to their fabrication on Si wafers. Scanning electron microscopy inspections of the structure morphology were carried out to study the homogeneity across the lens surface as well as the orientation of the structures. Simulations of the bent electric field within the etching chamber and the resulting ion trajectories explain the underlying etching process that creates structures approximately perpendicular to the curved lens surface. Optical reflectance measurements confirm the findings on homogeneity and orientation.

Local piezoelectric doping of monolayer WSe2

We report non-contact local doping of a monolayer WSe2 transferred onto a piezoelectric substrate having surface potential wells (SPWs) induced by structural inhomogeneities. We used epitaxial GaN and InP/GaInP2 structures, in which there are SPWs ∼0.2 V deep and 0.1–2 μm in size. Using surface topography and potential scanning probe microscopy, as well as optical reflectance, photoluminescence, and Raman spectroscopy measurements, we observed strong enhancement of charged exciton emission and Raman intensity in the SPW regions of the monolayer WSe2, which indicate on piezoelectric doping at a level n ≥ 1012 cm−2 on a length scale ∼0.2–1 μm. Our results can be used to create electron/hole quantum puddles with anyon states in transition metal dichalcogenides, promising for the development of room temperature and magnetic-field-free fault-tolerant topological quantum computing.

Comparison of a commercially available veterinary digital refractometer to analogue refractometer and laboratory chemistry analyzer in the evaluation of canine serum total protein.

To assess the agreement between measurements of total protein (TP) concentrations in canine serum samples between a commercially available veterinary digital refractometer (DR), an analog handheld refractometer (AR), and a laboratory-based chemistry analyzer (LAB). An additional objective was to assess the effects of various potential interferents (ie, hyperbilirubinemia, increased BUN, hyperglycemia, hemolysis, and lipemia) on DR measurements. 108 canine serum samples. Serum samples were measured in duplicate on the DR, which reported TP concentration, assessed via optical reflectance and critical angle measurement. These serum samples were also assessed on the AR and LAB for comparison. Serum samples with grossly visible lipemia, hemolysis, and icterus were noted. Medical records were retrospectively assessed to determine concentrations of BUN, glucose, and bilirubin. Method comparisons among the various data generated by the analyzers were completed using linear regression, Bland Altman, and calculation of intraclass coefficients. Mean bias between DRTP and LABTP in samples without potential interferents was 0.54 g/dL with 95% limits of agreement of -0.17 to 1.27 g/dL. One-third of DRTP samples without potential interferents had > 10% difference from their LABTP comparison. Interferents, particularly marked hyperglycemia, can result in inaccurate measurements on the DR. There was a statistically significant difference between DRTP and LABTP measurements. TP measurements in samples with any potential interferent, particularly hyperglycemia, should be assessed cautiously on DR and AR.

Pressure tuning of optical reflectivity in LuH2

Recently, the claim of room-temperature superconductivity in nitrogen-doped lutetium hydride at near-ambient conditions has attracted tremendous attention. Criticism of the work rises shortly, while further explorations are needed to settle the dispute. One of the intriguing observations is the pressured-induced color change, which has been reproduced in the lutetium dihydride LuH2 while its mechanism remains unclear. Through optical reflectivity measurements of LuH2 in the visible to near-infrared region, we observe strong light absorption next to the sharp plasmon resonance, which continuously shifts to higher energies with increasing pressure. It gives rise to the increased reflection of red light and suppressed reflection of blue light. Our work sheds light on resolving the puzzles regarding the pressure induced color change in LuH2.

Electrically addressable tungsten doped phase change device in a through pixel configuration

In this paper, we propose and demonstrate electrical switching of a 4% tungsten-doped Ge2Sb2Te5 (W-GST) pixel in a lateral configuration without the need for an auxiliary resistive heater. The phase transition between an amorphous and poly-crystalline state is achieved by Joule heating directly through the 4 μm × 4 μm × 350 nm active volume of the chalcogenide phase change pixel. While undoped GST would be challenging to switch in a lateral configuration due to very large resistance in the amorphous state, W-GST allows for switching at reasonable voltage levels. The pixel temperature profile is simulated using finite element analysis methods to identify the pulse parameters required for a successful electrical actuation. Experimentally, a 1550 nm light source is used for in-situ optical reflection measurements in order to verify the crystallization and re-amorphization of the pixel. As a result of the W doping, we identify volatile and non-volatile regimes with respect to bias voltage and pulse width during crystallization. During amorphization, we observe irreversible material failure after one complete cycle using in-situ optical monitoring, which can be attributed to a migration or segregation process. These results provide a promising path toward electrically addressed devices that are suitable for optical applications requiring amplitude modulation in a reflective geometry, such as spatial light modulators.

Optical spectroscopy of bulk single crystals of VOx and TiOx

We successfully grew bulk single crystals of ${\mathrm{VO}}_{x}$ and ${\mathrm{TiO}}_{x}$ with a sodium-chloride structure by the floating-zone method, and we performed optical reflectivity measurement and pump-probe spectroscopy to clarify the electronic structure of these series of compounds and their $x$ dependence. We found that optical spectra can be discussed on the basis of the Mott-Hubbard model, although a disorder arising from the deficiencies of Vi or Ti and O plays an important role in the electronic structure as well as their $x$ dependence.

Dielectric Spectroscopy of Calcium Titanate Processed by Spark Plasma Sintering.

Calcium titanate (CaTiO3) powder was compacted by spark plasma sintering (SPS). The resulting products were subjected to the phase stability study and dielectric characterization. The change in temperature of SPS between 1100 °C and 1250 °C had a clear and straightforward effect on density, porosity, relative permittivity, loss tangent, and DC resistivity. Since the SPS itself introduces certain oxygen deficiency into Ti-perovskites, all samples were annealed after SPS. However, this post-processing did not mask the effects of the SPS regime. Optical reflectance measurements were completed to compare and quantify the sample coloration and support the dielectric results with corresponding optical band gap estimations. Subtle changes in the CaTiO3 crystal lattice arrangement, completed between 1150 °C and 1250 °C and documented in the literature for conventionally sintered samples, could not be confirmed for SPS-prepared calcium titanate. The novelty of this research work is in producing very stable dielectric ceramics and an indication of the SPS processing parameters suitable for this. The best sample showed at 1 MHz frequency the combination of relative permittivity 370, loss tangent 0.008, and DC resistivity 3 × 1012 Ωm.