Precise description of the interaction between molecular oxygen and metal surfaces is one of the most challenging topics in quantum chemistry. In this work, we use low-temperature scanning tunneling microscopy (STM) to identify and characterize an adsorption state of molecular oxygen that coordinates to three Ag atoms (μ3) on Ag(100). Surprisingly, μ3-O2 cannot be identified as a stable configuration with generalized gradient approximation (GGA)-level density functional theory (DFT) calculations. Through inelastic electron tunneling spectroscopy (IETS), we identify three vibrational modes of individual μ3-O2 and assign them to out-of-plane hindered rotation (HR) at 38.0 meV, in-plane HR at 32.4 meV, and in-plane hindered translation (HT) at 22.0 meV. We determine the barrier for rotational isomerization of μ3-O2 to be 69.3 meV from tunneling electrons-induced rotations. The inability of theory to predict the experiment stems most likely from self-interaction errors inherent to GGA-DFT, which leads to an inaccurate description of localized charges. We speculate that the μ3-O2 configuration represents a formal molecular oxygen anion and assign the ±11 meV excitation in the IETS to a transition between spin-orbit states of the surface-bound anion.

Nitrogen (N)-doped graphene is a promising candidate for semiconducting devices and catalysts or sensor applications due to its controllable properties depending on the atomic structure of nitrogen defects. Therefore, it is important to control the doping configurations and understand the corresponding properties in order to utilize nitrogen-doped graphene for the applications. We investigated the nitrogen defects formed in graphene grown on the Pt(111) surface using pyridine precursors. In this study, we used scanning tunneling microscopy (STM) and atomic force microscopy (AFM) simultaneously to compare the atomic structures of defects with their electronic structures. We identified two different types of nitrogen defects: graphitic-N and pyridinic-N defects. Atomic resolution of AFM imaging confirmed the atomic arrangement of each defect, which was not clearly resolved in the STM imaging. In addition, the results of theoretical calculations using density functional theory were consistent with our experimental results and helped in identifying the defects. Moreover, we imaged the dissociated pyridine precursor prior to forming graphene, which provided insight into the growth mechanism and explained the density of nitrogen defects.

A simple spontaneous deposition kit for 210Po determination using alpha spectrometry was newly designed, and polonium deposition characteristics under various physicochemical conditions were evaluated using it. The high -purity silver disc (99.99%) showed high deposition efficiencies of over 85.1% in the HCl concentration range of 0.01-6 M. Optimal physicochemical factors were determined to be a temperature of 90 degrees C, deposition time of 90 min, and the use of ascorbic acid as a reducing agent in an amount similar to that of the interfering element (Fe).

This Special Publication represents the work of researchers at professional conferences, as reported by NIST employees in Fiscal Year 2020 (October 1, 2019–September 30, 2020).

Since daily drinking water is one of the major source for the ingestion of radiotoxic 222Rn and 226Ra, the demand for a simple method to determine these two radionuclides has significantly increased. In the present study, a rapid, simple sequential analysis method for determining 222Rn and 226Ra in drinking water using a liquid scintillation counter was developed. The method employs solvent extraction and correction equations for the effect of native 222Rn for 226Ra analysis. Validation and examination of applicability for drinking water analysis were conducted using 222Rn-injected water and 226Ra standard source. Minimum required counting times for examining drinking water on Quantulus 1220 and Hidex 300SL were estimated via minimum detectable activity depending on the counting time. In addition, the correction method, including an equation for reducing analysis time by more than 10 days, was suggested based on the analytical results for different elapsed times between sampling and measurement.

Molecular dynamics of hydrogen molecules (H-2) on surfaces and their interactions with other molecules have been studied with the goal of improvement of hydrogen storage devices for energy applications. Recently, the dynamic behavior of a H-2 at low temperature has been utilized in scanning tunnelling microscopy (STM) for sub-atomic resolution imaging within a single molecule. In this work, we have investigated the intermolecular interaction between H-2 and individual vanadyl phthalocyanine (VOPc) molecules on Au(111) substrates by using STM and non-contact atomic force microscopy (NC-AFM). We measured tunnelling spectra and random telegraphic noise (RTN) on VOPc molecules to reveal the origin of the dynamic behavior of the H-2. The tunnelling spectra show switching between two states with different tunnelling conductance as a function of sample bias voltage and RTN is measured near transition voltage between the two states. The spatial variation of the RTN indicates that the two-state fluctuation is dependent on the atomic-scale interaction of H-2 with the VOPc molecule. Density functional theory calculations show that a H-2 molecule can be trapped by a combination of a tip-induced electrostatic potential well and the potential formed by a VOPc underneath. We suggest the origin of the two-state noise as transition of H-2 between minima in these potentials with barrier height of 20-30 meV. In addition, the bias dependent AFM images verify that H-2 can be trapped and released at the tip-sample junction.

New reference materials (RMs), zirconium silicate, bauxite and phosphogypsum, were produced and characterized according to an ISO guide. The homogeneity of the three RMs was evaluated using X-ray fluorescence (XRF), and characterizations of the three candidate materials were performed through a collaborative study with nine expert radioanalytical laboratories. The assigned radionuclides are 230Th, 232Th, 234U, 235U, and 238U for zirconium silicate; 230Th, 232Th, 234U, and 238U for bauxite; and 226Ra, 230Th, 234U, and 238U for phosphogypsum.

The operational parameters of an alpha spectrometer equipped with a planar silicon semiconductor detector were characterized by measuring a mixed alpha source. The full width at half maximum (FWHM) decreased with increasing conversion gain (CG) and sample-to-detector distance (SDD) and was constant beyond an SDD of 21 mm. Although the FWHM was minimum at 4096 CG, peak-shape analysis showed that 1024 CG and 2048 CG are more appropriate than 4096 CG for alpha spectrum analysis. In practical measurement with SDD less than 5 mm, a sample thickness difference of 1 mm caused a relative error in detection efficiency of 11 %.

Vertical and horizontal distributions of 137Cs were investigated in sediment cores of the crater lake, Baengnokdam of Mt. Halla, Korea. The activities of 137Cs in sediments were in the range of minimum detectable activity 0.2–214 Bq kg−1 in the 0–100 cm layer. The inventories of 137Cs were in the range of 7.4–29.7 kBq m−2. The higher total inventories of 137Cs were observed in the middle of Baengnokdam of Mt. Halla, indicating that higher 137Cs in soil sediments of the middle of Baengnokdam of Mt. Halla can be strongly adsorbed on mud.

Several studies have documented the characteristics of seasonal, decadal, and spatial variations of tritium in different regions including North America, Australia, and Europe. However, long-term data such as these studies were not yet reported for Northeast Asia. In this study, we document the extensive spatial-temporal monitoring data of tritium levels in precipitation measured at 16 stations in Korea over the last 20 years, including the long-term trend since 1961 by using measured and estimated data. The long-term variation of tritium concentrations in the Korean precipitation follows the global trend, reaching the maximum in 1963 owing to nuclear bomb testing, followed by a consistent level since the late 1990s. Tritium concentrations in precipitation from 1998 to 2017 were maximum in spring (April) due to tropopause folding and minimum in summer (July) due to the dominant inflows of marine air. The tritium concentrations in precipitation were lower toward the coastal stations, due to the influence of marine moisture for all seasons. Our results characterize the differences in tritium levels in groundwater recharging areas for different periods in this region. These results will serve as important tritium reference data for hydrology studies in Northeast Asia, which is an important region for understanding global hydrological cycles.

Lead-210 is a useful tracer in environmental studies for a wide range of applications, particularly in atmospheric research and geochronology. Liquid scintillation counting (LSC) is a commonly used measurement method for 210Pb analysis. In the present work, to increase detection efficiency, an improved LSC technique for 210Pb determination was developed. After adding lead carrier, samples were decomposed with mineral acid in closed digestion vessels. Using extraction chromatography with Sr resin, 210Pb was selectively separated and precipitated as lead oxalate. Following re-dissolution, the solution was mixed with a scintillation cocktail and measured by a liquid scintillation counter. In this study, all the spectral regions with peaks of 210Pb, 210Bi, and 210Po were used to calculate the activity of 210Pb; this is in contrast to the existing method, which divides the spectra into three regions according to energy level, and then selects only the 210Pb region. The method in this study also addresses a procedure for correcting blank values to account for 210Pb activity in the Pb2+ carrier. This measurement technique, using the spectral regions of 210Pb, 210Bi, and 210Po, exhibited more than twice the detection efficiency of the conventional method using only the 210Pb spectrum region. This measurement technique is expected to be a useful method for 210Pb analysis of environmental samples that show low activity, and when sample amounts are limited.

This study was conducted to analyze the status and to evaluate the geochemical characteristics of the constructional aggregate using its mineral compositions and major component contents in Gangwon area. In 2016, Gangwon Province produced 22,659 m(3)/year aggregate which is 6.4 times bigger than 2005 production. In 2018, 140 companies were registered as the aggregate suppliers in Gangwon Province. The aggregate products are used in manufacturing remicon (40.3 %), road subbase (15.3 %), and ascon (8.1 %). In this study, the aggregate was classified into sand and gravel and 117 samples were collected from 85 aggregate companies to analyze mineral compositions and major component compositions. Sand and gravel are mainly composed of quartz (14.3 similar to 84.3%), plagioclase (0 similar to 42.9%), K-feldspar (0 similar to 31.1%), muscovite (0 similar to 24.8%), and biotite(0.4 similar to 20.3%). Sand did not show any tendency of variation against with SiO2 content change, but in gravel, Al2O3, K2O and Na2O were increased with SiO2 content increase and CaO and L.O.I. decreased. Because this study was conducted on the products which were mixture of the samples that had experienced different geological processes, there was a limit to understanding the petrogenesis, evolution, and weathering of the rocks.

We studied the geometric and local electronic structure of a Se-adsorbed Au(111) surface. The reconstructed herringbone structure disappeared and the Au(111) surface states were attenuated with Se adsorption on the Au(111) surface, as explained by density functional theory calculations. Electron interference patterns were observed on the exposed Au (111) surface due to electron scattering by potential barriers formed by Se adsorbates. A strong bound state from the Se p-orbital on top of the Se clusters with quantum confinement effects were observed using scanning tunneling microscopy and spectroscopy.

To determine the seasonal variations in the removal efficiency of fine aerosols (PM2.5) in the Northeast Asia, we analyzed 7Be data collected for the surface air and precipitation over 20 years in Korea. The 7Be activity concentrations in the surface air were relatively higher in spring owing to tropopause folding but lower in summer owing to efficient removal by precipitation. The monthly 7Be concentrations decreased as the precipitation amounts increased showing a negative correlation (r2 = 0.34) against the precipitation amount. These results indicate that the concentrations of 7Be and fine aerosols are mainly controlled by the same washout effect, although the sources are different. The mean depositional velocities of fine aerosols, based on the 7Be mass balance model, showed a large seasonal variation, with its maximum value (1.9 cm s-1) in July and minimum value (0.22 cm s-1) in March. The 7Be depositional velocity reflects the net deposition of fine aerosols excluding moisture effects. Thus, the concentrations of fine aerosols can occur as high as five-fold in the dry season, if the input terms of fine aerosols remain the same. Our results imply that precipitation plays a critical role in the seasonal changes in the concentrations of fine aerosols, providing much clean air in the summer monsoon season in the Northeast Asia.

The observation of surface phonon dispersion using local probes can provide important information related to local structural and thermal properties. In this study, surface phonon modes on a Cu(100) surface were measured using the inelastic tunneling spectroscopy of scanning tunneling microscopy (STM-IETS) with atomically sharp tips. Different phonon modes were selectively measured depending on the structures of the probing tips or the surfaces. Two different surface phonon modes, at 19.0 meV on a clean Cu(100) surface and at 13.5 meV on an oxygen-adsorbed Cu(100) surface, are explained by the selection rules. Additionally, the spatial variation in STM-IETS showed surface stress relaxation.