Element-specific Analysis Research Articles

New Insights into the ORR Catalysis on Pt Alloy Nanoparticles from an Element Specific d-Band Analysis.

Bolstered by their unique atomic structures and tailored compositions, nanoalloys exhibit extraordinary properties making them ideal materials to solve challenges in energy storage and conversion catalysis. However, a quantitative description of the structure-property relationships using an accurate descriptor-based model for nanoalloys, ranging from bimetallic to multimetallic compositions, is needed to drive efficient material design toward high-performance catalysis. In this work, we highlight the electronic property and catalytic activity relationship from an element specific d-band analysis of Pt-based alloy catalysts using X-ray absorption near-edge spectroscopy (XANES). Using a series of L10-MPt/Pt (M = Fe, Co, Ni) core/shell alloy catalysts with well-defined atomic structures, we quantified subtle differences in the Pt d-electron states and correlated the Pt d-band structure to their superior catalytic activity toward the oxygen reduction reaction (ORR). Our analysis used the upper d-band edge position as a predictive descriptor for the mass activity toward the ORR instead of the commonly used d-band center position. Together with density functional theory calculations and Nørskov d-band theory, the upper d-band edge position for the Pt states, derived from experimental measurements, elucidates new physical insights into the ORR performance of the L10-MPt/Pt core/shell catalysts. An element specific Pt d-band analysis using XANES overcomes challenges in traditional X-ray photoelectron spectroscopy-based valence d-band analysis, which cannot distinguish signals from independent elements in nanoalloys. Thus, the insights from the element specific d-band analysis presented in this work are a promising approach to determine structure-property relationships in a variety of transition metal nanoalloys and will be useful in the design of future high-performance catalysts.

Automated, 3-D and Sub-Micron Accurate Ablation-Volume Determination by Inverse Molding and X-Ray Computed Tomography.

Ablation of materials in combination with element‐specific analysis of the matter released is a widely used method to accurately determine a material's chemical composition. Among other methods, repetitive ablation using femto‐second pulsed laser systems provides excellent spatial resolution through its incremental removal of nanometer thick layers. The method can be combined with high‐resolution mass spectrometry, for example, laser ablation ionization mass spectrometry, to simultaneously analyze chemically the material released. With increasing depth of the volume ablated, however, secondary effects start to play an important role and the ablation geometry deviates substantially from the desired cylindrical shape. Consequently, primarily conical but sometimes even more complex, rather than cylindrical, craters are created. Their dimensions need to be analyzed to enable a direct correlation with the element‐specific analytical signals. Here, a post‐ablation analysis method is presented that combines generic polydimethylsiloxane‐based molding of craters with the volumetric reconstruction of the crater's inverse using X‐ray computed tomography. Automated analysis yields the full, sub‐micron accurate anatomy of the craters, thereby a scalable and generic method to better understand the fundamentals underlying ablation processes applicable to a wide range of materials. Furthermore, it may serve toward a more accurate determination of heterogeneous material's composition for a variety of applications without requiring time‐ and labor‐intensive analyses of individual craters.

First-principles calculation of electroacoustic properties of wurtzite (Al,Sc)N

We study the electroacoustic properties of aluminum scandium nitride crystals ${\mathrm{Al}}_{1\ensuremath{-}x}{\mathrm{Sc}}_{x}\mathrm{N}$ with the metastable wurtzite structure by means of first-principles calculations based on density functional theory. We extract the material property data relevant for electroacoustic device design, namely, the full tensors of elastic and piezoelectric constants. Atomistic models were constructed and analyzed for a variety of Sc concentrations $0\ensuremath{\le}x\ensuremath{\le}50$%. The functional dependence of the material properties on the scandium concentration was extracted by fitting the data obtained from an averaging procedure for different disordered atomic configurations. We give an explanation of the observed elastic softening and the extraordinary increase in piezoelectric response as a function of Sc content in terms of an element-specific analysis of bond lengths and bond angles.

Effect of Fatigue on Functional Movement Screening Performance in Dancers.

Dance is associated with a high risk of injury, with fatigue identified as a contributing factor. Functional movement screening (FMS) has been used to identify alterations in normal movement which may contribute to injury risk, though this test is not normally performed in a fatigued state. The aim of this study was to determine whether fatigue induced by the dance aerobic fitness test (DAFT) results in changes in FMS scores with implications for performance and injury risk. Forty-one university dancers completed the FMS before and immediately after completion of the DAFT. Rate of perceived exertion and heart rate were quantified as measures of fatigue. Post-DAFT, the mean FMS composite score (15.39±1.86) was significantly less (p≤0.01) than the pre-exercise score (16.83±1.83). Element-specific analysis revealed that the deep squat, non-dominant lunge, and dominant inline lunge scores were all significantly impaired post-DAFT (all p≤0.01). The identification of changes in quality of movement in a fatigued state suggests that movement screening should also be performed post-exercise to enhance screening for injury risk. The influence of dance-specific fatigue was FMS element-specific. Specifically, the deep squat and inline lunge were most susceptible to fatigue, with implications for injury risk and performance and reflective of the high level of neuromuscular control required.

Vibrations and chemical states of iron ions in soda‐lime glasses determined by element‐specific X‐ray analyses

We systematically study medium‐range structures including more than three neighboring atoms around iron ions (Fe2+ and Fe3+) in soda‐lime glass samples with low iron oxide concentrations (MFe2O3) and a wide number ratio of Fe2+ to all iron ions (Fe2+/ΣnFe). The precise medium‐range structures around iron ions in glass have not yet been revealed because of a lack of the appropriate measurement methods. To avoid this problem, we used element‐specific nuclear resonant inelastic scattering (NRIS) with synchrotron X‐rays to observe the vibrations of iron ions (57Fe). The vibrations are related to medium‐range structures with more than three neighboring atoms and to the potential asymmetry and the coordination environment, around iron ions. The NRIS method has high sensitivity and can measure over a wide concentration range. Linear combination fitting of the X‐ray absorption fine structure spectra, which measures only the first neighbors but is a faster than using the NRIS method, was also used additionally. A systematically produced set of glasses with 0.015–5 wt% MFe2O3 and 0–0.85 Fe2+/ΣnFe was measured with these methods. It was found that the soda‐lime glass possessed two different medium‐range structures with different iron ion valences (~2+ or ~3+), which were determined by the Fe2+/ΣnFe, and that these structures were generated during production of the glass. Moreover, these medium‐range structures were the same from 0.015 to 5 wt% MFe2O3.

Chemical and Structural Investigation of Pt-Ni Extended Surface Catalyst Electrodes

Typical carbon-supported platinum (Pt) nanoparticle catalysts suffer from having only moderate specific activities relative to bulk Pt, as well as activity losses caused by various degradation processes. [1] Extended surface Pt catalysts are a promising alternative to the current state-of-the-art catalysts, particularly if high surface areas are achieved. Recently, we have developed Pt-Ni extended surface catalysts with surface areas >90 m2/gmPt and improvements in mass activity, specific activity, and durability. [2] However, as-synthesized materials are susceptible to dissolution of the Ni from the core of the Pt-Ni nanowire (NW) and therefore exhibit serious performance losses due to Ni ions binding to proton sites in the ionomer. Through a series of post-synthesis treatments involving annealing and subsequent acid leaching to optimize material structure and composition, the NW specific activity and durability were significantly improved. [3] Current efforts focus on performance optimization of the catalyst layer in membrane electrode assemblies (MEAs), which in addition to detailed information on the as-synthesized and treated catalysts, also requires investigation of these materials when part of an electrode. Structure, composition, and morphology were determined with initial 2D characterization of the NWs and electrodes using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) via scanning transmission electron microscopy (STEM), and X-ray photoelectron spectroscopy (XPS), as well as synchrotron techniques including X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies. Beyond these methods, transmission X-ray microscopy (TXM) allowed for high resolution, non-destructive, element-specific analysis of the electrode structure with 2-D and 3-D visualization. Catalyst composition/structure and electrode fabrication conditions were varied to explore opportunities and limitations of in situ characterization of the electrodes with these low Pt loadings extended surface catalysts. R. Borup, J. Meyers, B. Pivovar, Y.S. Kim, R. Mukundan, N. Garland, D. Myers, M. Wilson, F. Garzon, D. Wood, P. Zelenay, K. More, K. Stroh, T. Zawodzinski, J. Boncella, J.E. McGrath, M. Inaba, K. Miyatake, M. Hori, K. Ota, Z. Ogumi, S. Miyata, A. Nishikata, Z. Siroma, Y. Uchimoto, K. Yasuda, K.I. Kimijima, N. Iwashita, Scientific aspects of polymer electrolyte fuel cell durability and degradation, Chemical Reviews, 107 (2007) 3904-3951.S.M. Alia, B.A. Larsen, S. Pylypenko, D.A. Cullen, D.R. Diercks, D. R.; K.C. Neyerlin, S.S. Kocha, B.S. Pivovar, Acs Catal 4(2014) 1114-1119.S.M. Alia, C. Ngo, S. Shulda, M.-A. Ha, A.A. Dameron, J.N. Weker, K.C. Neyerlin, S.S. Kocha, S. Pylypenko, B.S. Pivovar, Exceptional Oxygen Reduction Reaction Activity and Durability of Platinum–Nickel Nanowires through Synthesis and Post-Treatment Optimization, ACS Omega, 2 (2017) 1408-1418.

Catalytic Activity and Stability of Oxides: The Role of Near-Surface Atomic Structures and Compositions

Electrocatalysts play an important role in catalyzing the kinetics for oxygen reduction and oxygen evolution reactions for many air-based energy storage and conversion devices, such as metal-air batteries and fuel cells. Although noble metals have been extensively used as electrocatalysts, their limited natural abundance and high costs have motivated the search for more cost-effective catalysts. Oxides are suitable candidates since they are relatively inexpensive and have shown reasonably high activity for various electrochemical reactions. However, a lack of fundamental understanding of the reaction mechanisms has been a major hurdle toward improving electrocatalytic activity. Detailed studies of the oxide surface atomic structure and chemistry (e.g., cation migration) can provide much needed insights for the design of highly efficient and stable oxide electrocatalysts. In this Account, we focus on recent advances in characterizing strontium (Sr) cation segregation and enrichment near the surface of Sr-substituted perovskite oxides under different operating conditions (e.g., high temperature, applied potential), as well as their influence on the surface oxygen exchange kinetics at elevated temperatures. We contrast Sr segregation, which is associated with Sr redistribution in the crystal lattice near the surface, with Sr enrichment, which involves Sr redistribution via the formation of secondary phases. The newly developed coherent Bragg rod analysis (COBRA) and energy-modulated differential COBRA are uniquely powerful ways of providing information about surface and interfacial cation segregation at the atomic scale for these thin film electrocatalysts. In situ ambient pressure X-ray photoelectron spectroscopy (APXPS) studies under electrochemical operating conditions give additional insights into cation migration. Direct COBRA and APXPS evidence for surface Sr segregation was found for La1-xSrxCoO3-δ and (La1-ySry)2CoO4±δ/La1-xSrxCoO3-δ oxide thin films, and the physical origin of segregation is discussed in comparison with (La1-ySry)2CoO4±δ/La1-xSrxCo0.2Fe0.8O3-δ. Sr enrichment in many electrocatalysts, such as La1-xSrxMO3-δ (M = Cr, Co, Mn, or Co and Fe) and Sm1-xSrxCoO3, has been probed using alternative techniques, including low energy ion scattering, secondary ion mass spectrometry, and X-ray fluorescence-based methods for depth-dependent, element-specific analysis. We highlight a strong connection between cation segregation and electrocatalytic properties, because cation segregation enhances oxygen transport and surface oxygen exchange kinetics. On the other hand, the formation of cation-enriched secondary phases can lead to the blocking of active sites, inhibiting oxygen exchange. With help from density functional theory, the links between cation migration, catalyst stability, and catalytic activity are provided, and the oxygen p-band center relative to the Fermi level can be identified as an activity descriptor. Based on these findings, we discuss strategies to increase a catalyst's activity while maintaining stability to design efficient, cost-effective electrocatalysts.

Element-specific structural analysis of Si/B4C using resonant X-ray reflectivity. Corrigendum

Errors in the article by Nayak, Pradhan & Lodha [J. Appl. Cryst. (2015), 48, 786–796] are corrected.

A hyphenated SMPS–ICPMS coupling setup: Size-resolved element specific analysis of airborne nanoparticles

Physical and chemical characterization of gas borne particles in the nanometer to sub‐micrometer size range includes knowledge about particle size distribution and chemical composition, possibly with a high time resolution. However, most of the available techniques are offline methods and/or not able to provide such physical and chemical information simultaneously. Scanning Mobility Particle Sizer (SMPS) is a well-established and widely used technique for determining size distribution and number concentration of such particles, within scan durations of a few minutes. Inductively Coupled Plasma Mass Spectrometry (ICPMS) is a highly sensitive multi-element technique, allowing the determination of elemental composition with excellent detection limits and a wide dynamic concentration range. In this work, SMPS and ICPMS were coupled to one hyphenated system which allows achieving on-line and simultaneously size and chemical information with SMPS-typical time resolutions. A Rotating Disk Diluter was used as sample introduction interface, and the SMPS flow concept was re-designed to fulfill the requirements of both different analytical methods. The developed setup was successfully tested with a model aerosol containing airborne silver nanoparticles. Proper SMPS operation under argon atmosphere instead of air was validated. The presented setup was applied to scan the particle size range from 7 to 156nm within 120s. Similar sensitivities and efficiencies compared to that of state-of-the-art SMPS and ICPMS instruments were achieved.

Bonding properties of thiolate-protected gold nanoclusters and structural analogs from X-ray absorption spectroscopy

Abstract Subnanometer, atomically precise thiolate-protected gold nanoclusters represent an important advancement in our understanding of thiolate-protected gold nanoparticles and thiolate-gold chemistry. Aside from being a link between larger gold nanoparticles and small gold complexes, gold nanoclusters exhibit extraordinary molecule-like optical, electronic, and physicochemical properties that are promising for next-generation imaging agents, sensing devices, or catalysts. The success in elucidating a number of unique thiolate-gold surface and gold core structures has greatly improved our understanding of thiolate-gold nanoclusters. Nevertheless, monitoring the structural and electronic behavior of thiolate-protected gold nanoclusters in a variety of media or environments is crucial for the next step in advancing this class of nanomaterials. Not to mention, there are a number of thiolate-protected gold nanoclusters with unknown structures or compositions that could reveal important insights on application-based properties such as luminescence or catalytic activity. This review summarizes some of the recent contributions from X-ray absorption spectroscopy (XAS) studies on the intriguing bonding properties of thiolate-protected gold nanoclusters and some structural analogs. Advantages from XAS include a local structural, site- and element-specific analysis, suitable for ultra-small particle sizes (1–2 nm), along with versatile experimental conditions.

Element-Specific Analysis of the Growth Mechanism, Local Structure, and Electronic Properties of Pt Clusters Formed on Ag Nanoparticle Surfaces

Bimetallic nanoparticles (NPs) consisting of small Pt clusters on the surface of larger metal NPs are potential catalysts that combine the advantages of reduced cost, high surface area, and a strong alloying interaction between Pt and the substrate. Herein we report the preparation of a series of small Pt clusters deposited on the surface of Ag NPs with systematically varied compositions (Ag93Pt7, Ag81Pt19, Ag72Pt28, and Ag65Pt35) via a galvanic replacement reaction. UV–vis spectroscopy, transmission electron microscopy, and inductively coupled plasma optical emission spectroscopy are used to provide evidence of NPs formation and evaluate their gross structural and compositional characteristics. Extended X-ray absorption fine structure (EXAFS) measurements at the Pt L3- and Ag K-edges are then used to elucidate the structural evolution of small surface Pt clusters as the Pt concentration is increased, allowing the formation mechanism of the bimetallic NPs to be deduced. X-ray absorption near-edge structure (XANES) provides further information regarding the electronic properties of the bimetallic NPs from both Ag and Pt perspectives. Finally, the Pt L3-edge XANES spectra are used in conjunction with ab initio calculations to verify the accuracy of structural models based on the EXAFS fitting results and to provide insight into the size-dependent nature of the Ag–Pt bonding interaction.

High-Resolution Element Specific Analysis with Scanning Tunneling Microscope Assisted by Synchrotron Radiation Light

High-Resolution Element Specific Analysis with Scanning Tunneling Microscope Assisted by Synchrotron Radiation Light

Element-specific analysis of the magnetic anisotropy in Mn-based antiferromagnetic alloys from first principles

The magnetic anisotropy energy (MAE) and element-specific contributions to the MAE have been studied for Mn-based antiferromagnetic alloys with layered L${1}_{0}$ structure within the framework of the local spin-density approximation and the fully relativistic torque method. It is found that the contribution to the total MAE from nonmagnetic $3d$ and $4d$ elements in MnNi and MnPd alloys are comparable to the contribution of the magnetic Mn atoms. In the $3d$-$5d$ MnIr and the $4d$-$5d$ MnRh alloys the Ir and Rh contributions are found to be dominating. The origin of this nonzero contribution into the MAE from the atom with zero spin moment is linked to the nontrivial atomic spin density distribution, which gives a zero moment only on average. We also find and discuss the strong dependence of the total and element-specific contributions to the MAE on the state of magnetic order.

X-ray fluorescence spectrometry-based approach to precision management of bioavailable phosphorus in soil environments

Purpose Managing declining nutrient use efficiency in crop production has been a global priority to maintain high agricultural productivity with finite non-renewable nutrient resources, in particular phosphorus (P). Rapid spectroscopic methods increase measurement density of soil nutrients and improve the accuracy of rates of additional P inputs. Materials and methods Soil P was measured by a multielement energy-dispersive X-ray fluorescence spectroscopic (XRFS) method to estimate the spatial distribution of soil total (XRFS-P) and bioavailable P in a Fluvisol occurring on a 20-ha contiguous area comprised of seven elongated field strips under a wheat–maize rotation near the Quzhou Agricultural Experiment Station in the North China Plain. Results and discussion Soil XRFS-P was highly variable along the length of the field strips and across the entire area after decades of continuous cultivation. A linear relationship existed between XRFS-P and bicarbonate-extractable P or Mehlich 3-extractable P, allowing a description of the spatial distribution of bioavailable P based on XRFS, in both directions of a two-dimensional grid covering the entire area (p<0.05). Distinct management zones were identified for more precise placement of additional P. Conclusions Direct element-specific analysis and a high sample throughput make XRFS an indispensable component of a new approach to sustainably manage P, and other macronutrients of low atomic number Z such as K, Ca, or Cl in production fields, based on their site-specific variations in the soil. Concerning P, this rapid precision approach provides a promising avenue to manage soil P as a regionalized variablewhilepreventingzonesofdeficiencyorsurplus Pthat can affect plant productivity or potential loss from a field, respectively.

Microwave‐Hydrothermal Synthesis of Nanostructured Zinc‐Copper Gallates

AbstractZinc gallate is an important semiconductor for manifold applications, e.g. in field emission displays or as a photocatalyst for water splitting. In addition to these interesting properties, zinc gallate is also an excellent matrix material that can be furthermore tuned through the incorporation of guest cations to form functional solid solutions with new optical and catalytic properties. We present a convenient microwave‐hydrothermal synthesis of nanostructured Cu2+‐substituted ZnGa2O4 spinels and their characterization with respect to morphology, chemical composition, structural, magnetic and optical properties. The microwave‐based approach offers a straightforward and one‐step access to nanostructured zinc gallate‐based materials and related compounds as a new preparative advantage. As the properties of mixed spinel‐based solid solutions strongly depend on the distribution of the guest ions between the different lattice sites, we have employed a wide range of analytical techniques to investigate the physico‐chemical properties of the obtained copper‐containing zinc gallate materials. The element specific EXAFS analysis at the Cu K‐ and Zn K‐edge shows a difference in the coordination environments with Zn mostly situated on the tetrahedral sites of the spinel lattice whereas Cu is located on the octahedral sites of the nanostructured ZnGa2O4:Cu2+ materials.

ASAXS study on the formation of core–shell Ag/Au nanoparticles in glass

Nanosized metal particles of various configurations embedded in surface regions ofglass have great potential as nonlinear optical materials for photonic devices.We have prepared Ag/Au nanoparticles in core–shell configuration in soda-limesilicate glass by double-ion implantation and investigated their structuralcharacteristics by anomalous small-angle x-ray scattering (ASAXS) and transmissionelectron microscopy. Measurements at x-ray energies slightly below the AuL3 edge indicate the formation of bimetallic Ag/Au shells in some of the nanoparticles forhigh-dose ion implantation. An element-specific analysis of the ASAXS results allowed usnot only to validate and quantify the core–shell structure, but simultaneously alsothe composition of the shells. Hollow nanoparticles were found for an Au–Agimplantation sequence, whereas an Ag–Au sequence generates a diluted core composition.The shift of the maximum position of optical absorption of the samples due tosurface plasmon resonance of bimetallic nanoparticles, as monitored by opticalspectroscopy, revealed the considerable influence of the respective particle configuration.

Probing the average size of self-assembled metal nanoparticles using x-ray standing waves

We report application of x-ray standing-wave field for characterization of average vertical size of metal nanoparticles dispersed on a substrate surface with accuracies better than 1 nm. This method is applied to analyze the distribution of Fe, Co, and Au nanoparticles on Si substrate and W/C multilayer substrates. Results demonstrate that the method is a valuable tool to evaluate the surface morphology of nanoparticles over a large surface area. Unlike conventional probes such as atomic force microscopy or microinterferometry, the present method provides element-specific analysis. It also has the advantage of being able to examine nanoparticles in a liquid medium, or buried inside a coating layer. We anticipate that the proposed method has great potential to infer the internal structure of nanoparticles.

A new approach for the determination of silicon in airborne particulate matter using electrothermal atomic absorption spectrometry

In this work a new procedure for element specific analysis of silicon in airborne particulate matter is presented. The method is based on a preliminary treatment of the aerosol samples with nitric acid and perchloric acid leading to a mineralization of the organic sampling substrate, dissolution of soluble material and a homogeneous suspension of the remaining non-soluble sample fraction. ETAAS measurement of the derived slurries was performed using a Zr-treated graphite tube which prevents the formation of stable silicon carbide during sample measurement. Losses of volatile silicon species during sample pyrolysis were overcome by using Co(II) as matrix modifier and a pyrolysis temperature of only 300 °C. Furthermore this low pyrolysis temperature prevents charring of organic material which enables accurate ETAAS analysis. The method including the developed pretreatment procedure was evaluated using the Standard reference material ® 2709 (San Joaquin Soil) from NIST (National Institute of Standards and Technology, Gaithersburg, MD, USA). Suitability for measurement of Si in airborne particulate matter with an aerodynamic diameter ≤10 μm (PM10) was demonstrated by the analysis of selected aerosol samples and comparison of derived results with the findings obtained for the same samples after microwave digestion and subsequent ETAAS measurement. Finally the developed procedure was applied for the analysis of silicon in PM10 collected at an urban site in Vienna (Austria). Matrix matched calibration has been used for quantification of derived absorption signals. With the use of 20 μL sample injection volume for ETAAS analysis an instrumental detection limit of 52.2 μg L −1 was obtained, which translates to method detection limits of approximately 0.52 μg m −3 when considering the volumes of air collected per investigated aerosol sample. The reproducibility of analysis given as the relative standard deviation was 4.4% ( n = 12). Derived concentrations for Si in PM10 varied between 0.8 and 7.2 μg m −3 which is in good accordance with the literature findings.

Investigation of metal nanoparticles on a Si surface using an x-ray standing wave field

An x-ray standing wave field generated under total external reflection condition is used to characterize the average vertical dimension of metal nanoparticles as well as their nature of dispersion on a flat surface. This approach is applied to characterize the distribution of Fe nanoparticles deposited on a silicon surface using a solution dip method. The atomic force microscopy results on these nanoparticles reinforce our interpretation. The authors believe that the present method has a strong utility in characterizing, over a large area, the morphology of the surfaces coated with nanoparticles. The method also provides element specific analysis for the nanoparticulate matter.

Substrate-dependent bonding distances of PTCDA: A comparative x-ray standing-wave study on Cu(111) and Ag(111)

We study the adsorption geometry of 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) on Ag(111) and Cu(111) using X-ray standing waves. The element-specific analysis shows that the carbon core of the molecule adsorbs in a planar configuration, whereas the oxygen atoms experience a non-trivial and substrate dependent distortion. On copper (silver) the carbon rings resides 2.66 A (2.86 A) above the substrate. In contrast to the conformation on Ag(111), where the carboxylic oxygen atoms are bent towards the surface, we find that on Cu(111) all oxygen atoms are above the carbon plane at 2.73 A and 2.89 A, respectively.