Elevated Sample Temperatures Research Articles

Noise Optimization for MKIDs With Different Design Geometries and Material Selections

The separation and optimization of noise components is critical to microwave-kinetic inductance detector (MKID) development. We analyze the effect of several changes to the lumped-element inductor and interdigitated capacitor geometry on the noise performance of a series of MKIDs intended for millimeter-wavelength experiments. We extract the contributions from two-level system noise in the dielectric layer, the generation-recombination noise intrinsic to the superconducting thin-film, and system white noise from each detector noise power spectrum and characterize how these noise components depend on detector geometry, material, and measurement conditions such as driving power and temperature. We observe a reduction in the amplitude of two-level system noise with both an elevated sample temperature and an increased gap between the fingers within the interdigitated capacitors for both aluminum and niobium detectors. We also verify the expected reduction of the generation-recombination noise and associated quasiparticle lifetime with reduced inductor volume. This study also iterates over different materials, including aluminum, niobium, and aluminum manganese, and compares the results with an underlying physical model.

A thermally robust method of sample sealing for capillary DLS

Capillary Dynamic Light Scattering (DLS), has recently been introduced as a simple and enabling technique that increases the measurement range of traditional DLS analysis with minimized sample volumes (Ruseva et al., 2018). The previously published protocol for the preparation of samples for analysis within a capillary called for sealing of the capillary end using a clay compound (Ruseva et al., 2019). This material is not, however, compatible with organic solvents, nor with elevated sample temperatures. To extend the uses of capillary DLS to more complex assays like thermal aggregation studies, a new sealing method is demonstrated using a UV curing compound. This further motivates the use of capillary DLS to minimize volumes of destroyed precious samples in pharmaceutical development assays to study thermal kinetics.•Use of UV curing compound to seal capillaries used in DLS to preserve low volumes of sample.

Correcting thermal-emission-induced detector saturation in infrared spectroscopy.

We found that temperature-dependent infrared spectroscopy measurements (i.e., reflectance or transmittance) using a Fourier-transform spectrometer can have substantial errors, especially for elevated sample temperatures and collection using an objective lens. These errors can arise as a result of partial detector saturation due to thermal emission from the measured sample reaching the detector, resulting in nonphysical apparent reduction of reflectance or transmittance with increasing sample temperature. Here, we demonstrate that these temperature-dependent errors can be corrected by implementing several levels of optical attenuation that enable convergence testing of the measured reflectance or transmittance as the thermal-emission signal is reduced, or by applying correction factors that can be inferred by looking at the spectral regions where the sample is not expected to have a substantial temperature dependence.

Hugoniot elastic limit of single-crystal tantalum at normal and elevated temperatures subjected to extreme strain rates

Large-scale nonequilibrium molecular dynamic simulations of impact-induced shock propagation in defect-free single-crystal Ta along the [001] direction is presented, paying particular attention to the formation of elastic-plastic two-wave structures. Plastic deformation and elastic limits of Ta single crystals for various crystal orientations were investigated in a recent paper [R. Ravelo et al., Phys. Rev. B 88, 134101 (2013)]. In the present paper, a comprehensive study on the Hugoniot elastic limit (HEL) and its dependence on associated physical parameters is reported. The observed attenuation of an elastic precursor in a stress-wave profile led to proposing wide-range scaling relations for HEL decay applicable for ultrahigh strain rates. The influence of a lateral dimension on the spatial profile of a stress wave and time profile of free surface velocity (FSV) in the distinct appearance of a spike-valley feature and its consequence on scaling relations is investigated. Further, it is shown that the commonly used method of calculating HEL from a FSV profile is inadequate for submicron-thick samples at high strain rates. The necessary modifications are incorporated that resulted in comparable HEL values by two complimentary approaches of stress and FSV profiles. Simulations carried out for increasing impact strength revealed a power law dependence of HEL with strain rate. A methodology based on extrapolation of stress decay law and strain rate scaling constructed by us is proposed here for prediction of HEL pertaining to larger length samples. Very good agreement between the predicted values and available experimental results makes the modeling robust and applicable for a wide range of strain rates and length scales. Finally, the study is extended for elevated sample temperatures up to melting. Interestingly, yield strength is shown to follow an increasing trend up to a certain temperature, beyond which it decreases. An empirical relation is proposed here for expressing temperature dependence of HEL that explains the observed yield strength anomaly. Results are justified through thermal analysis of shear stress and evolution of dislocation density.

The Performance of EDXS at Elevated Sample Temperatures Using a MEMS-Based In Situ TEM Heating System

Since the development of MEMS heating holders, dynamic in-situ experiments at elevated temperatures may be complemented by X-ray spectrometry for chemical analysis. Although the amount of IR radiation is small when compared to furnace holders, the influence of IR radiation emitted from the heating device on the quality of the X-ray spectra is significant. In this work, we systematically examine the influence of infrared (IR) radiation generated by MEMS-based in situ heating systems (DENSsolutions single- and double-tilt holders) on the results and interpretation of energy-dispersive X-ray (EDX) spectra through simulation and measurement. Focal points of interest in this study are the influence of holder geometry, shadowing and orientation with respect to the different emission characteristics of IR and X-ray photons and their interaction with a side-entry and a multi-detector system. IR photons substantially contribute to count rates, dead time, electronic noise levels, energy resolution, and detection efficiency of semiconductor detectors. At higher sample temperatures, they ultimately limit the feasibility of EDXS for elemental characterization and especially the traceability of low-Z elements. This work provides a quantitative insight into the influence of all relevant parameters related to in situ heating experiments on the spectral quality. Bearing this in mind, we aim to provide a guide to optimizing in situ heating experiments with respect to chemical EDXS analysis.

FaVAD: A software workflow for characterization and visualizing of defects in crystalline structures

The analysis of defects and defect dynamics in crystalline materials is important for fundamental science and for a wide range of applied engineering. With increasing system size the analysis of molecular-dynamics simulation data becomes non-trivial. Here, we present a workflow for semi-automatic identification and classification of defects in crystalline structures, combining a new approach for defect description with several already existing open-source software packages. Our approach addresses the key challenges posed by the often relatively tiny volume fraction of the modified parts of the sample, thermal motion and the presence of potentially unforeseen atomic configurations (defect types) after irradiation. The local environment of any atom is converted into a rotation-invariant descriptive vector (‘fingerprint’), which can be compared to known defect types and also yields a distance metric suited for classification. Vectors which cannot be associated to known structures indicate new types of defects. As proof-of-concept we apply our method on an iron sample to analyze the defects caused by a collision cascade induced by a 10 keV primary-knock-on-atom. The obtained results are in good agreement with reported literature values. Program summaryProgram Title: Fingerprinting and Visualization Analyzer of Defects (FaVAD).CPC Library link to program files:https://doi.org/10.17632/bmv9kxkzg3.1Developer’s repository link:http://gitlab.mpcdf.mpg.de/NMPP/favad.gitLicensing provisions: GPLv3.Programming language: Python 3, Fortran 90, and C++.Nature of problem: The analysis of damage and damage evolution in crystalline materials is important for fundamental science and for a wide range of applied engineering. Defects in materials on an atomic level are commonly analyzed by Wigner–Seitz or topology Voronoi tessellation based methods. However, these approaches exhibit specific shortcoming, especially at elevated sample temperatures. In order to improve upon that, a more robust and quantifiable identification and classification approach of known as well as of unpredicted defect structures is desirable.Solution method: A fingerprint-like method is proposed to analyze in detail the damage in a material augmented with a probabilistic interpretation. It is based on the calculation of a descriptor vector for each atom in the sample. These vectors represent in a compact form the individual environments of the atoms.For standard types of defects (i.e. interstitial atoms) the corresponding descriptor vectors can be precomputed and used for rapid classification. Unexpected or less common defect types can be identified by applying a principal component analysis to the descriptor vectors. Vacancies in the material are identified by computing the radii of the largest empty spheres which can be embedded into the sample, followed by a thresholding process. This new method is easy to use and requires only modest computational resources.Finally, the classified defects are visualized using the open source software VisIt.Additional comments including restrictions and unusual features: The descriptor vectors are computed using the command line interface of QUIP with the Gaussian Approximation potential (GAP) package. The analysis of the sample is done using Python scripts which make extensive use of the NumPy package. A modified KDTree2 code is employed to calculate the location of single vacancies and voids. The program VisIt is used for the visualization of the classified point defects in the sample. We provide a Dockerfile for automatically creating a portable Docker container which installs all the programs together with a Python script to analyze as an example a damaged iron molecular dynamics sample. A shell script to install the programs locally in a Linux-based server or desktop environment is included also.

Silicon nanocone formation via low-energy helium ion sputtering

In this study, the effect of low-energy (100 eV) He+ ion irradiation on Si surface morphology is explored. Si (100) and (111) samples were irradiated with 100 eV He+ ions at an elevated sample temperature of 600 °C and to fluences in the range 5.0 × 1019–2.0 × 1020 ions cm–2. Through a combination of high ion flux and high sample temperature, it was found that continued He+ ion irradiation facilitates the formation of homogeneously populated, high aspect ratio silicon nanocones (NCs) (∼50–100 nm base and ∼200–400 nm height). The resulting surface morphology is shown to have excellent antireflective properties, suggesting potential application toward enhanced light absorption in photovoltaic and other optical applications. Furthermore, similar irradiations at reduced sample temperature show comparable structuring mechanisms but with smaller cone diameter. These results indicate that NC size and number density (and related wavelength-dependent reflectivity properties) may be tailored by carefully tuning ion irradiation conditions. Utilizing very low-energy He+ ions as the irradiating species, these studies also demonstrate an added benefit to limiting metallic surface contamination through reduced probability of sputtering in-vacuum components.

A colorimetry based, semi-automated portable sensor device for the detection of arsenic in drinking water

A portable colorimetric device is presented for arsenic ion detection in drinking water. The main purpose of this device – which was developed to complement a commercial water dearsenating station demanding regular (weekly to monthly) regeneration runs depending on its saturation – is to provide regular field measurements and easy, semi-automatic operation designed specifically for untrained, typically illiterate users e.g. the population of developing countries. The device exploits a commercially available, well established reagent kit, which is widely used in arsenic field-testing in many developing countries. The hereby presented custom-designed microfluidic system enhances the user-friendliness, the functionality and reliability of the test-strip based kit. The response for total inorganic arsenic ion concentrations (As(III) and As(V)) is linear in the 5–20μg/l (ppb) range with a sensitivity of 1μg/l, thus the device is capable to distinguish drinkable water based on the World Health Organization (WHO) guidelines of 10μg/l. The average relative standard deviation of the measurements is 8% in the linear range and it is below 2% for higher arsenic concentrations (above 20μg/l). The hardware construction of the device and the custom microfluidic system is presented in detail. The effect of elevated water sample temperature on the kinetics and performance of the device was also investigated in order to reduce the required time for the measurements. Stable and reliable arsenic concentration values were obtained after 60min at 22°C (ambient temperature) and after only 25min at 50°C water sample temperature, but at a cost of an increased relative standard deviation to 16%, in the linear range.

The Effect of Elevated Water Sample Temperature on the Performance Of A Custom-developed Colorimetric Arsenic Sensor

A custom-developed colorimetric device is presented for arsenic ion detection in drinking water. The device utilizes standard reagents, which are used in arsenic field-testing kits, in its custom microfluidic system. The response for arsenic concentrations is linear in the 5-20μg/l (ppb) range, thus our device is capable to distinguish drinkable water based on the World Health Organization (WHO) guidelines1 limit of 10 μg/l. The effect of elevated water sample temperature on the kinetics and performance of the device is investigated in order to reduce the required time for the measurements. Stable and reliable arsenic concentration values were obtained after 25 min at 50 oC water sample temperature.

Alterations in Human Liver Metabolome during Prolonged Cryostorage.

Tissue metabolomics requires high sample quality that crucially depends on the biobanking storage protocol. Hence, we systematically analyzed the influence of realistic storage scenarios on the liver metabolome with different storage temperatures and repeated transfer of samples between storage and retrieval environments, simulating the repeated temperature changes affecting unrelated samples stored in the same container as the sample that is to be retrieved. By cycling between storage (-80 °C freezer, liquid nitrogen, cold nitrogen gas) and retrieval (room temperature, -80 °C), assuming three cycles per day and sample, we simulated biobank storage between 3 months and 10 years. Liver tissue metabolome was analyzed by liquid chromatography/mass spectrometry. Most metabolite concentrations changed <5% for the first "year" of time-compressed biobanking simulation, predominantly due to hydrolysis of peptides and lipids. Interestingly, storage temperature affected metabolite concentrations only little, while there was a linear dependence on the number of temperature change cycles. Elevated sample temperature during (prolonged) retrieval time led to a distinctly different signature of metabolite changes that were induced by cycling. Our findings allow giving recommendations for optimized storage protocols and provide signatures that allow detection of deviations from protocol.

Temperature- and Component-Dependent Degradation of Perovskite Photovoltaic Materials under Concentrated Sunlight.

We report on accelerated degradation testing of MAPbX3 films (X = I or Br) by exposure to concentrated sunlight of 100 suns and show that the evolution of light absorption and the corresponding structural modifications are dependent on the type of halide ion and the exposure temperature. One hour of such exposure provides a photon dose equivalent to that of one sun exposure for 100 hours. The degradation in absorption of MAPbI3 films after exposure to 100 suns for 60 min at elevated sample temperature (∼45-55 °C), due to decomposition of the hybrid perovskite material, is documented. No degradation was observed after exposure to the same sunlight concentration but at a lower sample temperature (∼25 °C). No photobleaching or decomposition of MAPbBr3 films was observed after exposure to similar stress conditions (light intensity, dose, and temperatures). Our results indicate that the degradation is highly dependent on the hybrid perovskite composition and can be light- and thermally enhanced.

ChemInform Abstract: Understanding Automotive Exhaust Catalysts Using a Surface Science Approach: Model NOx Storage Materials

AbstractReview: 56 refs.

Understanding Automotive Exhaust Catalysts Using a Surface Science Approach: Model NOx Storage Materials

The structure–reactivity relationships of model BaO-based NOx storage/reduction catalysts were investigated under well controlled experimental conditions using surface science analysis techniques. The reactivity of BaO toward NO2, CO2, and H2O was studied as a function of BaO layer thickness [0 < θBaO < 30 monolayer (ML)], sample temperature, reactant partial pressure, and the nature of the substrate the NOx storage material was deposited onto. Most of the efforts focused on understanding the mechanism of NO2 storage either on pure BaO, or on BaO exposed to CO2 or H2O prior to NO2 exposure. The interaction of NO2 with a pure BaO film results in the initial formation of nitrite/nitrate ion pairs by a cooperative adsorption mechanism predicted by prior theoretical calculations. The nitrites are then further oxidized to nitrates to produce a fully nitrated surface. The mechanism of NO2 uptake on thin BaO films (<4 ML), BaO clusters (<1 ML) and mixed BaO/Al2O3 layers are fundamentally different: in these systems initially nitrites are formed only, and then converted to nitrates at longer NO2 exposure times. These results clarify the contradicting mechanisms presented in prior studies in the literature. After the formation of a nitrate layer the further conversion of the underlying BaO is slow, and strongly depends on both the sample temperature and the NO2 partial pressure. At 300 K sample temperature amorphous Ba(NO3)2 forms that then can be converted to crystalline nitrates at elevated temperatures. The reaction between BaO and H2O is facile, a series of Ba(OH)2 phases form under the temperature and H2O partial pressure regimes studied. Both amorphous and crystalline Ba(OH)2 phases react with NO2, and initially form nitrites only that can be converted to nitrates. The NO2 adsorption capacities of BaO and Ba(OH)2 are identical, i.e., both of these phases can completely be converted to Ba(NO3)2. In contrast, the interaction of CO2 with pure BaO results in the formation of a BaCO3 layer that prevents to complete carbonation of the entire BaO film under the experimental conditions applied in these studies. However, these “carbonated” BaO layers readily react with NO2, and at elevated sample temperature even the carbonate layer is converted to nitrates. The importance of the metal oxide/metal interface in the chemistry on NOx storage-reduction catalysts was studied on BaO(<1 ML)/Pt(111) reverse model catalysts. In comparison to the clean Pt(111), new oxygen adsorption phases were identified on the BaO/Pt(111) surface that can be associated with oxygen atoms strongly adsorbed on Pt atoms at the peripheries of BaO particles. A simple kinetic model developed helped explain the observed thermal desorption results. The role of the oxide/metal interface in the reduction of Ba(NO3)2 was also substantiated in experiments where Ba(NO3)2/O/Pt(111) samples were exposed to CO at elevated sample temperature. The catalytic decomposition of the nitrate phase occurred as soon as metal sites opened up by the removal of interfacial oxygen via CO oxidation from the O/Pt(111) surface. The temperature for catalytic nitrate reduction was found to be significantly lower than the onset temperature of thermal nitrate decomposition.

Exciton Fate in Semiconductor Nanocrystals at Elevated Temperatures: Hole Trapping Outcompetes Exciton Deactivation

The tens-of-percent photoluminescence (PL) quantum yields routinely obtained for colloidally prepared CdSe semiconductor nanocrystals (NCs) decrease substantially with temperature elevation. While such PL efficiency loss has direct consequences for applications ranging from light-emitting diodes and lasers to photovoltaics under solar concentration, the origin of this loss is currently not established, hindering synthetic efforts to design materials with robust performance. Here, for the first time, we utilize transient absorption and ultrafast PL in addition to static PL and time-correlated single photon counting, to characterize CdSe core-only and CdSe/ZnS core/shell NCs up to temperatures as high as 800 K. For multiple particle sizes, loss of PL efficiency as a function of temperature elevation is more severe and less reversible for core-only NCs than for core/shell NCs. Ultrafast measurements performed at elevated sample temperatures indicate that thermally activated trapping of individual carriers dominates the nonradiative loss of excitons. Through a combination of spectroscopic techniques, we identify the primary carrier loss process as hole trapping in particular. These findings support the notion that extrinsic trapping effects out-compete intrinsic exciton deactivation at high temperature and point to realizable improvements in thermally robust optoelectronic performance.

Structural and electrical evolution of He ion irradiated hydrocarbon films observed by conductive atomic force microscopy

Polymer-like hydrocarbon films are irradiated with 100keV He ion at the fluences of 1.0×1015–1.0×1017ions/cm2 or at the irradiation temperature ranging from 25 to 600°C. Conductive atomic force microscopy (CAFM) has been used to evaluate the nanoscale electron conducting properties of these irradiated hydrocarbon films. Nanoscale and conducting defects have been formed in the hydrocarbon films irradiated at a relatively high ion fluence (1.0×1017ions/cm2) or an elevated sample temperature. Analysis indicates that He ion irradiation results in the evolution of polymer-like hydrocarbon into a dense structure containing a large fraction of sp2 carbon clusters. The sp2 carbon clusters formed in irradiated hydrocarbon films can contribute to the formation of filament-like conducting channels with a relatively high local field-enhancing factor. Measurements indicate that the growth of nanoscale defects due to He ion irradiation can result in the surface swelling of irradiated hydrocarbon films at a relatively high ion fluences or elevated temperature.

Binding of a Benzoate Dye-Molecule Analogue to Rutile Titanium Dioxide Surfaces

Scanning tunneling microscopy (STM) has been used to investigate the adsorption of benzoic acid on the rutile TiO2(110)(1 × 1) and the reconstructed TiO2(110)(1 × 2) surfaces. Benzoic acid binds to both surfaces dissociatively via a bridging geometry to two Ti5c sites. At a slightly elevated sample temperature during deposition onto the (110) (1 × 1) surface, a well-ordered (2 × 1) overlayer was formed at saturated benzoate coverage. On the reconstructed (110) (1 × 2) surface, benzoate was observed to adsorb between the (1 × 2) strands leading to a (2 × 2) superstructure at higher coverage. Elongation along the [110] direction in the STM images indicates a rotation of the benzene ring of 90° relative to the carboxylate group, which is reasonably explained by hydrogen bond interactions between terminating O-atoms on the surface and H-atoms of the ring.

In situ Raman spectroscopy of H2 interaction with WO3 films

It is well known that WO(3) interacts efficiently with H(2) gas in the presence of noble metals (such as Pd, Pt and Au) at elevated temperatures, changing its optical behaviors; and that its crystallinity plays an important role in these interactions. For the first time, we investigated the in situ Raman spectra changes of WO(3) films of different crystal phases, while incorporating Pd catalysts, at elevated temperatures in the presence of H(2). The Pd/WO(3) films were prepared using RF sputtering and subsequently annealed at 300, 400 and 500 °C in air in order to alter the dominant crystal phase. The films were then characterized using SEM, XRD, XPS, and both UV-VIS and Raman spectroscopy. In order to fundamentally study the process, the measurements were conducted when films were interacting with 1% H(2) in synthetic air at elevated sample temperatures (20, 60, 100 and 140 °C). We suggest that the changes of Raman spectra under such conditions to be mainly a function of the crystal phase, transforming from monoclinic to a mix phase of monoclinic and orthorhombic achieved via increasing the annealing temperature. The as-deposited sample consistently shows similar Raman spectra responses at different operating conditions upon H(2) exposure. However, increasing the annealing temperature to 500 °C tunes the optimum H(2) response operating temperature to 60 °C.

Liquid state DNP using a 260 GHz high power gyrotron

Dynamic nuclear polarization (DNP) at high magnetic fields (9.2 T, 400 MHz (1)H NMR frequency) requires high microwave power sources to achieve saturation of the EPR transitions. Here we describe the first high-field liquid-state DNP results using a high-power gyrotron microwave source (20 W at 260 GHz). A DNP enhancement of -29 on water protons was obtained for an aqueous solution of Fremy's Salt; in comparison the previous highest value was -10 using a solid-state microwave power source (maximum power 45 mW). The increased enhancements are partly due to larger microwave saturation and elevated sample temperature. These experimentally observed DNP enhancements, which by far exceed the predicted values extrapolated from low-field DNP experiments, demonstrate experimentally that DNP is possible in the liquid state also at high magnetic fields.

Formation of Rh−Au Core−Shell Nanoparticles on TiO2(110) Surface Studied by STM and LEIS

Rh-Au core-shell nanoparticles were fabricated on TiO(2)(110) surface by physical vapor deposition (PVD) of Rh followed by exposure of Au at elevated sample temperature (500 K). The morphology of the bimetallic particles was checked by scanning tunneling microscopy (STM). The chemical composition of the particles was characterized by low energy ion scattering (LEIS) method. It was shown that the "seeding + growing" method described previously for growth of monometallic particles in narrow size distribution (Berko, A. et al. J. Catal. 1999, 182, 511) can also be applied for fabrication of bimetallic nanoparticles. The large mean free path of surface diffusion of gold on the oxide support makes the accumulation of Au possible exclusively on the Rh seeds formed in the first step of the procedure. By performing careful STM and LEIS experiments, it was proven that, for appropriate Au and Rh coverages, the postdeposited Au completely and uniformly covers the Rh nanoparticles.

Electrical insulation properties of sputter‐deposited SiO2, Si3N4 and Al2O3 films at room temperature and 400 °C

AbstractIn this paper the breakdown field strength and resistivity of sputter‐deposited Al2O3, SiO2 and Si3N4 layers are investigated in the temperature range between room temperature and 400 °C. All the investigated layers showed excellent insulation properties, even at elevated sample temperature. One example of industrial application is the deposition of electrical insulation layers onto the membranes of pressure sensors using cluster type sputter equipment