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Graphite is one of the most chemically inert materials. Its elementary constituent, monolayer graphene, is generally expected to inherit most of the parent material’s properties including chemical inertness. Here, we show that, unlike graphite, defect-free monolayer graphene exhibits a strong activity with respect to splitting molecular hydrogen, which is comparable to that of metallic and other known catalysts for this reaction. We attribute the unexpected catalytic activity to surface corrugations (nanoscale ripples), a conclusion supported by theory. Nanoripples are likely to play a role in other chemical reactions involving graphene and, because nanorippling is inherent to atomically thin crystals, can be important for two-dimensional (2D) materials in general.

Spin defects in hexagonal boron nitride (hBN) are promising quantum systems for the design of flexible two-dimensional quantum sensing platforms. Here we rely on hBN crystals isotopically enriched with either

Spin defects in hexagonal boron nitride (hBN) are promising quantum systems for the design of flexible two-dimensional quantum sensing platforms. Here we rely on hBN crystals isotopically enriched with either $^{10}$B or $^{11}$B to investigate the isotope-dependent properties of a spin defect featuring a broadband photoluminescence signal in the near infrared. By analyzing the hyperfine structure of the spin defect while changing the boron isotope, we first unambiguously confirm that it corresponds to the negatively-charged boron-vacancy center (${\rm V}_{\rm B}^-$). We then show that its spin coherence properties are slightly improved in $^{10}$B-enriched samples. This is supported by numerical simulations employing cluster correlation expansion methods, which reveal the importance of the hyperfine Fermi contact term for calculating the coherence time of point defects in hBN. Using cross-relaxation spectroscopy, we finally identify dark electron spin impurities as an additional source of decoherence. This work provides new insights into the properties of ${\rm V}_{\rm B}^-$ spin defects, which are valuable for the future development of hBN-based quantum sensing foils., Comment: 8 pages, 5 figures

We visualized negative refraction of phonon polaritons, which occurs at the interface between two natural crystals. The polaritons—hybrids of infrared photons and lattice vibrations—form collimated rays that display negative refraction when passing through a planar interface between the two hyperbolic van der Waals materials: molybdenum oxide (MoO 3 ) and isotopically pure hexagonal boron nitride (h 11 BN). At a special frequency ω 0 , these rays can circulate along closed diamond-shaped trajectories. We have shown that polariton eigenmodes display regions of both positive and negative dispersion interrupted by multiple gaps that result from polaritonic-level repulsion and strong coupling.

Two-dimensional electron systems subjected to a perpendicular magnetic field absorb electromagnetic radiation via the cyclotron resonance (CR). Here we report a qualitative breach of this well-known behaviour in graphene. Our study of the terahertz photoresponse reveals a resonant burst at the main overtone of the CR, drastically exceeding the signal detected at the position of the ordinary CR. In accordance with the developed theory, the photoresponse dependencies on the magnetic field, doping level, and sample geometry suggest that the origin of this anomaly lies in the near-field magnetoabsorption facilitated by the Bernstein modes, ultra-slow magnetoplasmonic excitations reshaped by nonlocal electron dynamics. Close to the CR harmonics, these modes are characterized by a flat dispersion and a diverging plasmonic density of states that strongly amplifies the radiation absorption. Besides fundamental interest, our experimental results and developed theory show that the radiation absorption via nonlocal collective modes can facilitate a strong photoresponse, a behaviour potentially useful for infrared and terahertz technology., 27 pages, 22 figures

Boron nitride (BN) layers with sp(2) bonding have been grown by metal organic chemical vapor deposition on AlN underlayers, which are deposited on c-plane sapphire substrates. Two different boron precursors were employed-trimethylboron and triethylboron-while ammonia was used as the nitrogen precursor. The BN obtained epitaxial BN films contain ordered rhombohedral (rBN) and partially ordered turbostratic (tBN) stackings as evidenced by x-ray diffraction analysis. We discriminatively identify the PL signatures of the rBN and tBN from those typical of the hexagonal (hBN) and Bernal stackings (bBN). The optical signature of tBN appears at 5.45eV, and it intercalates between the two recombination bands typical of rBN at 5.35eV (strong intensity) and 5.55eV(weaker intensity). The analogs of the high intensity band at 5.35eV in rBN sit at 5.47eV for hBN and at 5.54eV for bBN. Funding Agencies|network GaNeX [ANR-11-LABX-424 0014]; BONASPES project [ANR-19-CE30 0007]; ZEOLIGHT project [ANR-19-CE08-0016]; Universite de Montpellier; Swedish Research CouncilSwedish Research CouncilEuropean Commission [2017-04164]; Swedish Foundation for Strategic Research (SSF)Swedish Foundation for Strategic Research [IS14-0027]; Carl Tryggers Foundation for Scientific Research [CTS 14:189]; Swedish Government Strategic Research Area in Materials Science on Advanced Functional Materials at Linkoping University [2009-00971]; Office of Naval ResearchOffice of Naval Research [N00014-20-1-2474, 428]; National Science FoundationNational Science Foundation (NSF) [CMMI 429, 1538127]

A database of full-body CT scans and associated lifestyle and health data from decedents who underwent an autopsy at the Office of the Medical Investigator (OMI) is under construction. The dataset has 68 metadata fields containing data from the OMI's database and interviews with next of kin. Some metadata fields could be mapped to existing standards, but the majority of fields required some modifications to current standards or the creation of new standards.

Settlement patterns in the pre-contact period in the Valley of Mexico are often characterized by the collapse and regeneration of civilizations, creating a series of power vacuums over time. How did these abrupt political changes affect population structures throughout the region? Can population structure in the Valley of Mexico be best characterized as population replacement, population continuity, or both? In this chapter, biological distances are compared with distances representing population continuity and replacement models. Biological distances based on dental morphological observations represent samples from Valley of Mexico populations from the Preclassic (1200 BC to AD 200) to the Late Postclassic (AD 1200–1520) periods. The results in this chapter support a population replacement model in the Valley of Mexico, confirming archaeological and ethnohistoric accounts of migration patterns. Population replacement is most evident during the transition from the Classic to Postclassic periods and throughout the Postclassic period.

The present study was undertaken to determine if boron phosphide (BP) crystals could be produced by a simple technique, close-spaced vapor transport (CVST). This technique has proven very successful in achieving very high growth rates for a wide variety of materials including ZnSe, AlN, and SiC. Both silicon (100) and sapphire substrates were used for the CSVT growth. The resulting films were characterized by Raman spectroscopy. Sublimation of BP powder from 1050 to 1450 °C in an argon atmosphere produced a range of deep orange colour, single and polycrystalline BP crystals. The crystal size increased and the crystal density decreased with increasing temperature. Well-faceted crystals were produced at an intermediate temperature of 1200 °C. At temperatures higher then 1450 °C no BP crystals were grown. Only a fibrous mass of fine whiskers, loosely attached to the substrate were produced. The peak position of the Raman LO mode of the BP crystals was shifted to higher wavenumbers than the BP powder source, suggesting that the crystals were compressively strained. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This comparison of methods for assessing the development of muscle insertion sites, or entheses, suggests that three-dimensional (3D) quantification of enthesis morphology can produce a picture of habitual muscle use patterns in a past population that is similar to one produced by ordinal scores for describing enthesis morphology. Upper limb skeletal elements (humeri, radii, and ulnae) from a sample of 24 middle-aged adult males from the Pottery Mound site in New Mexico were analyzed for both fibrous and fibrocartilaginous enthesis development with three different methods: ordinal scores, two-dimensional (2D) area measurements, and 3D surface areas. The methods were compared using tests for asymmetry and correlations among variables in each quantitative data set. 2D representations of enthesis area did not agree as closely as ordinal scores and 3D surface areas did regarding which entheses were significantly asymmetrical. There was significant correlation between 3D and 2D data, but correlation coefficients were not consistently high. Intraobserver error was also assessed for the 3D method. Cronbach's alpha values fell between 0.68 and 0.73, and error rates for all entheses fell between 10% and 15%. Marginally acceptable intraobserver error and the analytic versatility of 3D images encourage further investigation of using 3D scanning technology for quantifying enthesis development.

The dielectric response function of epitaxial B(12)As(2) films on 4H-SiC was determined at room temperature and at 10 K in the spectral region of 3.6-9.8 eV, i.e., in the vacuum ultraviolet (VUV) spectral region, by synchrotron ellipsometry. The experimental dielectric function was simulated with the critical point parabolic band model. The parameters of the dispersive structures were derived by numerical fitting of the experimental data to the proposed model. New high energy optical transitions are resolved at 5.95, 7.8 and 8.82 eV and their lineshape and origin are discussed. The temperature dependence of the critical point energies and transition strengths was determined, and the excitonic effect is considered.

An experimental and theoretical study on the dielectric-response function of icosahedral B{sub 12}As{sub 2} in the spectral region between 1.24 and 9.8 eV is presented. Comprehensive experimental information on the energy band structure from the analysis of features in the optical dispersion was complemented by spin-orbit first-principles calculations. The lowest indirect band gap width is 3.2 eV; the two lowest direct interband transitions are at 3.46 and 3.9 eV. High-energy critical points are assigned to specific electron transitions in the Brillouin zone and their dimensionality was determined. The static dielectric constant of B{sub 12}As{sub 2} is uniaxially anisotropic with values of 7.84 and 9.02 for polarization perpendicular and parallel to the trigonal axis. Hole and electron effective masses are derived from the band dispersions.

Few human variants are truly population specific, with 100% frequency in one group and 0% in others. However, for traits to be of use in forensic identification they must be as specific to a population as possible. Forensically, several dental morphological traits have been described as useful for determining an unknown individual's ancestry. For these traits to be of value, they should occur in their associated group in proportions statistically different from all other groups. Furthermore, ancestral groups not associated with the trait should have no significant frequency differences among them. To test this, frequencies of dental morphological traits listed in the forensic literature as useful for ancestry determination were compared among samples of African Americans, European Americans, Hispanic Americans, and Native Americans (n=1625). chi2 tests were conducted on dichotomized frequencies of ten trait observations, including incisor shoveling, Carabelli's trait, canine mesial ridge, and cusp seven. Results were mixed. For example, Native Americans have statistically different frequencies of shovel shaping from all other groups. However, statistical differences are seen among other groups as well. Only canine mesial ridge was consistently different in African Americans and not different among the other three groups. Unfortunately, this trait is not common in any group (2-21%), so lack of the trait is not indicative of ancestry. Overall, these commonly used traits may not be of much actual value in ancestry determination. Combining these traits with other observations and more sophisticated statistical tools may be of more practical value.

Historically, forensic anthropology has concentrated on race determination using skeletal morphological variation. Conversely, dental anthropology has been concerned with worldwide patterns of dental morphological variation. This paper represents a synthesis of the goals of forensic anthropology with the methods of dental anthropology. Dentitions of modem African Americans (n = 110) and European Americans (n = 155) were observed using methods based on the Arizona State University dental morphology standards. Of 136 characters observed, eight were found with frequencies that were very different between the groups. Based on these eight characteristics, probability tables were created for determining an individual's social race, using both Bayesian prediction and logistic regression. These tables are applicable for determining the probability that an unknown individual can be categorized as African American or European American. This method was tested on 40 individuals known to belong in one of these two ancestral groups. Correct assignment of race was made in 90% of cases.

The thermal conductivity of icosahedral boron arsenide (B12As2) films grown on (0001) 6H–SiC substrates by chemical vapor deposition was studied by the 3ω technique. The room temperature thermal conductivity decreased from 27.0 to 15.3 W/m K as the growth temperature was decreased from 1450 to 1275 °C. This is mainly attributed to the differences in the impurity concentration and microstructure, determined from secondary ion mass spectrometry and high resolution transmission electron microscopy, respectively. Callaway’s theory was applied to calculate the temperature-dependent thermal conductivity, and the results are in good agreement with the experimental data. Seebeck coefficients were determined as 107 μV/K and 136 μV/K for samples grown at 1350 °C with AsH3/B2H6 flow ratio equals to 1:1 and 3:5, respectively.

B12As2/SiC pn heterojunction diodes based on the radiation-hard B12As2 deposited on (0001) n-type 4H–SiC via chemical vapor deposition were demonstrated. The diodes exhibit good rectifying behavior with an ideality factor of 1.8 and a leakage current as low as 9.4×10−6 A/cm2. Capacitance-voltage measurements using a two-frequency technique showed a hole concentration of ∼1.8–2.0×1017 cm−3 in B12As2 with a slight increase near the interface due to the presence of an interfacial layer to accommodate lattice mismatch. Band offsets between the B12As2 and SiC were estimated to be ∼1.06 eV and 1.12 eV for conduction band and valance band, respectively.

Characterization of surface morphology and crystal defects is reported for homoepitaxial 4H‐SiC films grown at high rates (35–40μm∕h) using methyltrichlorosilane (CH3SiCl3), as single precursor. The ratio of hydrogen to argon (H2∕Ar) in the carrier gas was varied to determine the effect of hydrogen on the surface morphology and the crystalline defects. Due to hydrogen’s reaction with the graphite heater, adjusting the H2∕Ar ratio effectively changed the C∕Si ratio in the gas phase; thereby, influencing surface roughness and dislocation density. Low H2∕Ar ratios of 0.1 and 0.125 produced smooth surfaces without step bunching. Higher H2∕Ar ratios of 0.2 and 0.33 enhanced the conversion of basal plane dislocations into threading edge dislocations and reduced the density of basal plane dislocations to approximately 600cm−2. However, at these H2∕Ar ratios, macrosteps formed on the surface and the roughness increased. Micropipes from substrate dissociated into closed-core threading screw dislocations in the films grown with H2∕Ar ratio in the range of 0.1–0.2. At H2∕Ar ratio of 0.33, micropipes propagated into the film, generating hollow-core threading screw dislocations.

T HE article on "The Mountains about Tatsienlu" (Geogr. J., vol. 75, PP. 345-353) deals with the majority of travellers who have been in a position to discuss these mountains, but the names of Potanin, Prince Henry of Orleans, Doctors Tafel and Assmy, Captain St6tzner, General Pereira, L. M. King, and Dr. Heim are omitted. The author also seems unaware that in a biography of the late Dr. Z. Loftis, of Batang, published about I9I0, a vivid description of the Tatsienlu Mountains is on record. The present writer published a paper, "The Gangka-a peak in Eastern Tibet" (J. West China Border Research Soc., vol. 3, pp. I57-6 I) before seeing the article in the Journal. The following comments upon the accounts of the travellers quoted may be of interest. Kingdon Ward's remarks are approximately correct; he is also near the mark when he suggests 20,000 feet for the Tatsienlu Range. The "Ta Hsiang" of Gordon's account does not mean the "Great Elephant," but the "Premier Pass"; and I know the Tzu Mei more particularly as a col and a non-Chinese hamlet 4 miles south of the Gang Kar lamasery. The name may be loosely applied to some adjacent mountains, but not seriously to any system continuous with the Gang Kar [the "Kunka" of the original article] complex. I do not know of any feature in the locality indicated by the sketchmap that could claim the name "Tzu Mei" (Tibetan: T'si Min). Regarding Gill's account, the Gang Kar is not seen from the valley roads on the T'ung side of the Gi La or Cheto; what he saw when looking back the first time was the short Tatsienlu range. The Ka Ji (Kashi La), 50 to 60 miles westward of Tatsienlu, gives just such a view as Gill describes. But my belief is that he was speaking of the Zhara (Jara) and looking at the Gang Kar! In the narrative of Szechenyi's Expedition there is again a description of a journey towards the Cheto col. But on, or near, the summit the narrative becomes confused. In the first place, on the Pass there is no vista of specially arresting mountains, and even the higher saddles or lower plateaux would only reveal an ordinary snow-field and a rather poor view of the Zhara. From the Ka Ji however it is possible to admire not only the great rim of the Gang Kar complex, but also an intrusion of serrated peaks which run between the T'ung and the Che Ch'u from the Hai Tzu Shan to Tatsienlu. This may explain the suggested confusion. In any case the most northern peak of the great rim is the Zhara and the southern one the Gang Kar. About 90 miles north of the Gi La, just east of Taofu or Dawo, we have crossed the YalungT'ung divide above glaciers and near snow peaks. To the north-west-again perhaps 00oo miles-on the left bank of the Yalung is another snow peak, the Kawalori of Coales, which is detached from the snow-clad Kanze system on the right bank of the same river. Returning again to Loczy's "Bo Kunka" we find that this name, so pronounced, is the one given to-day in every case where the southern peak is concerned, and this traveller's description, also, is admirable. Evidently Kreitner's "Kunka Range" (literally "Snow Mountains") east-north-east of the main peak is also correct, or nearly so.