Similar bandgap has been observed in graphene layers on metal substrates by local probe measurements; however, this phenomenon has not been observed in graphene layers on a near-insulating substrate. Here, we present bulk bandgap-like features in a graphene layer epitaxially grown on an h-BN substrate using scanning tunneling spectroscopy. We observed edge states at zigzag edges, edge resonances at armchair edges, and bandgap-like features in the bulk.Securing a semiconducting bandgap is essential for applying graphene layers in switching devices. Theoretical studies have suggested a created bulk bandgap in a graphene layer by introducing an asymmetry between the A and B sub-lattice sites. A recent transport measurement demonstrated the presence of a bandgap in a graphene layer where the asymmetry was introduced by placing a graphene layer on a hexagonal boron nitride ( In a recent transport study, the presence of a minigap at the neutral point in a graphene layer on an h-BN substrate was confirmedSince its first successful isolation, graphene has been considered as a material suitable for future application in signal-switching devices with spin-sensitive transport1341h-BN, the valley degree of freedom was found to remain intact58911131415In a graphene layer mechanically placed on et al.2223h-BN may better mimic those for a freestanding graphene layer than those for a graphene layer on a metal surface. One may notice that most theoretical predictions were done for a freestanding graphene layer.Scanning tunneling microscopy (STM) is an ideal tool for both imaging local geometric structures and observing local electronic structures. While the above theoretical predictions were derived for a free-standing graphene layer, most previous STM studies were performed with graphene flakes epitaxially grown or drop-cast on metal substrates. Energy gaps of 0.2–0.3 eV were reported in a GNR that was drop-cast on Au(111)h-BN ML on a Cu(111) surface. Edge states of the graphene layer and bulk gap-like features were observed in this pure and well-defined heterostructure.In this study, we performed atomically resolved electronic structure measurements in epitaxially grown GNIs on an epitaxially grown h-BN ML grown on a Cu(111) substrate. After growing approximately half of the h-BN ML on a Cu(111) surface using borazine (B3H6N3), the incoming graphene precursor gas (ethylene) was decomposed on the exposed half of the Cu(111) surface. Most graphene layers were grown on the exposed Cu substrate, while some were grown as GNIs on the h-BN layer. h-BN layer, which showed moiré patterns with many different periods, similar to earlier resultsh-BN surface is ≈1/1000 times than that achieved on a Cu(111) surface. A large dosage (>108 L) of precursor gas was used to grow graphene layers on h-BN263–104 L of ethylene, small GNIs were nucleated on the h-BN surface. The produced GNIs on the h-BN surface were scarce, but they were pure and contained no traces of impurities. The GNIs grown on h-BN were usually located near the h-BN or Cu step edges, as shown in h-BN is usually featureless at a sample bias of −3–3 eV. h-BN at a sample bias of 0.7 V, revealing a featureless flat island. As the bias was increased to 4.0 V, moiré patterns under the top-layer graphene became visible, as shown in We produced a graphene layer on an h-BN/Cu(111), as demonstrated by the different shifts of surface peaks due to different charge transfer from Cu substrate to overlayers: ≈−0.3 eV for graphene, and ≈−0.2 eV for h-BN. A weak dip at ≈−0.4 eV originated from the Dirac point in the graphene layer on Cu(111). In addition to the shifted Cu surface states, the h-BN spectrum had no distinctive features other than ≈4 eV bandgap of the h-BN layer (not shown in h-BN was rather different from that on Cu(111), as shown in 8The identity of the grown layers was confirmed by the STS spectra. The spectra in 2829h-BN, as illustrated in h-BN layer, many defects are present, unlike for free-standing or epitaxial graphene layers on a metal surface. Considering this observation, the zigzag edges seem to be energetically more stable than armchair edges in the graphene layer on h-BN. The spectra change to the bulk spectra with a short decay length near the zigzag edges  modulates within a period of 10–16 lattice constants  and S6 b31h-BN using a tight-binding calculation; the simulated image is very similar to the observed STM image. In a GNR with zigzag edge terminations, the tight-binding calculation predicted a flat band at the Fermi level between 2/3kXΓ and kXΓ in momentum space where kXΓ = 3/4kXΓ and kXΓ is the crystal momentum in the direction from Γ to X in the first Brillouin zone. Unlike GNR, in the case of a GNI with a long zigzag edge, the states at the Dirac point are expected to be reduced but still presentdI/dV at the Fermi level is higher at the edge than in the bulk near the Fermi level), suggesting presence of the edge state. Therefore, the difference between the edge and the bulk is more meaningful than small features at ≈0.05 eV, ≈0.10 eV and ≈0.15 eV at the edge (location 1). dI/dV) subtracted from the bulk dI/dV. These difference spectra clearly show the presence of the edge state at this zigzag edge. The measured edge state at the Fermi level decreases with increasing distance from the edge. The height, and therefore, the strength of the edge state decreases with increasing distance from the zigzag edge. A gap-like feature is visible near the Fermi level, and the size of this gap does not vary with distance from the edge of the bulk stripe. The peak-to-peak energy gap was estimated to be ≈(0.09 ± 0.01) eV, as shown in dI/dV subtracted from the bulk dI/dV, is plotted in dI/dV versus distance. An ab initio calculation was performed to calculate the edge state at five equal distances from the zigzag edge with a periodic boundary of 4 nm ; left side of k = 2/3kXΓ), showing a semiconducting character  single crystal was cleaned by repeated Ar+ sputtering and annealing cycles. Sub-monolayer h-BN was grown using borazine (B3H6N3) at 10‒5 Pa while the sample was maintained at a temperature of 1000 K. Ethylene (C2H4) at 10‒3 Pa was introduced to form graphene on the half-monolayer h-BN-covered Cu(111) surface at 1100 K. The sample was maintained at that temperature for 2 h and then cooled at a rate of 30 K/s. All STM and STS measurements were conducted at approximately 4.9 K. STM imaging was performed under constant current mode, whereas STS was performed under constant height mode.The graphene on the t in the model Hamiltonian was fitted using the measured energy gap and a hopping parameter of t = −2.88 eV. The effective wavevector k adapted to the observed decay length of the edge state was obtained from the analytical solution for the states localized at the zigzag edge. Certain commercial equipment, instruments, or materials are identified in this paper in order to specify the experimental and theoretical procedures adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the materials or equipment identified are necessarily the best available for the purpose.Density functional theory (DFT) calculations were performed within the generalized gradient approximation (GGA) using the Vienna ab initio simulation package (VASP). The projector-augmented wave potentials, as implemented in VASP, were employed to describe DOS at atom centers. The energy cutoff for the plane-wave basis set was adjusted to 400 eV in the GGA. The model structures were optimized until the Hellman–Feynman forces acting on the atoms became lesser than 0.01 eV/Å. To include the weak van der Waals interactions between adsorbates and graphene, we adopted Grimme’s DFT-D2 correction based on a semi-empirical GGA-type theory. For Brillouin zone sampling, we used a 27 × 27 × 1 grid in the Monkhorst-Pack special k-point scheme. In addition to the DFT calculation, we also performed a tight-binding calculation with the Hubbard−model Hamiltonian for zigzag GNRs with various widths (3.4–34 nm). The ratio of the on-site repulsive potential U to the hopping parameter How to cite this article: Hwang, B. et al. Energy Bandgap and Edge States in an Epitaxially Grown Graphene/h-BN Heterostructure. Sci. Rep.6, 31160; doi: 10.1038/srep31160 (2016).


However, the low active material utilization, low sulphur loading and poor cycling stability restrict their practical applications. Herein, we present an effective strategy to obtain Li/polysulphide batteries with high-energy density and long-cyclic life using three-dimensional nitrogen/sulphur codoped graphene sponge electrodes. The nitrogen/sulphur codoped graphene sponge electrode provides enough space for a high sulphur loading, facilitates fast charge transfer and better immobilization of polysulphide ions. The hetero-doped nitrogen/sulphur sites are demonstrated to show strong binding energy and be capable of anchoring polysulphides based on first-principles calculations. As a result, a high specific capacity of 1,200 mAh g There is intensive research underway into the cathode development of lithium–sulphur batteries. Here, the authors report a lithium–sulphur battery using nitrogen/sulphur codoped graphene structure which displays excellent electrochemical performance with high sulphur loading. Desphrinkage 0% during2S5 or Cs+ to suppress the polysulphide shuttle and passivate the lithium-metal surface17192021−2 and the sulphur content in the electrode is <70 wt. %, which are not enough to satisfy the demands for high-energy density batteries5122324Much effort has been devoted to solving these issues: improving the electrical conductivity of the sulphur electrode by integrating with carbon materials or conductive polymers891011121315et al.et al.2829Moreover, flat current collectors face the challenge of increasing the electrode thickness due to the easy delamination of active materials and limitation in lithium diffusion kinetics. Therefore, three-dimensional (3D) battery electrode design has recently been explored as an effective way to enhance the energy per surface area of batteries26−2 when the graphene sponge is employed as a 3D current collector. The interconnected graphene network facilitates fast electron and ion transfer. The sulphur and/or nitrogen doping could facilitate fast charge transfer, increase the affinity between the polysulphide species and the carbon-based framework, facilitate better immobilization of the polysulphide ions, and promote the Li2S/polysulphide/S reversible conversion to improve the electrochemical performance of Li–S batteries192122−1 at 0.2C rate, a high-rate capacity of 430 mAh g−1 at 2C rate and excellent cycling stability for 500 cycles with nearly 100% Coulombic efficiency for the N,S-codoped graphene electrode.Instead of adopting solid sulphur as the precursor followed by melt-diffusion or liquid infiltration methods, the dissolved lithium polysulphide systems have recently been proved to make active materials distribute more uniformly, improve sulphur utilization, alleviate electrode structure variation and facilitate the kinetics of the Li–S redox reaction573233342S, GO/urea and GO/thiourea as precursors followed by freeze-drying. Na2S, urea and thiourea were employed as sulphur, nitrogen and nitrogen/sulphur sources, as well as reducing agents for GO during the hydrothermal assembly process. After freeze-drying, the morphology of the samples was retained and no obvious shrinkage/expansion is observed. The size and shape of the graphene-based sponges can be adjusted by controlling the concentration of GO, reaction temperature and the volume/shape of the used autoclaves. The freeze-dried N,S-codoped graphene sponge is light and can stand stably on the top of a dandelion without deforming it at all . The N2 adsorption–desorption isotherms of all the graphene-based sponges show a main adsorption at a relative pressure >0.9 with a small hysteresis loop  is used to evaluate the degree of defects in carbon materials, and a higher ratio indicates an increased amount of defects that is proportional to the extent of reductionID/IG=0.93), the ID/IG ratio increases to 0.99, 1.03, 1.07 and 1.16 for rGO, S-doped graphene, N-doped graphene and N,S-codoped graphene sponges, respectively, suggesting the removal of oxygen-containing groups and the insertion of heteroatoms into the graphene network with more structural defectsID/IG ratio is indicative of the enhanced reduction, which is in agreement with the electrical conductivity tests of these sponges  and Raman spectroscopy . GO show sponges .2 carbon increases and becomes narrower , as shown in narrower , indicatrrower 22, which crrower 22, 46, 47.rrower 22, the thr2S6 solution was used as a reference, the rGO, S-doped graphene, N-doped graphene and N,S-codoped graphene sponges were immersed into the Li2S6 solution for 2 h and the concentration variation of Li2S6 solution was analysed. The typical peaks of the polysulphide solution located at 260, 280, 300 and 340 nm , and the semicircles located in the higher and lower frequency regions, respectively, correspond to the surface film resistance (Rf) and the charge-transfer resistance (Rct) of the batteriesZw) and space charge capacitance (CPE′)Rct of the N,S-codoped graphene electrode is much smaller than those of the rGO, S-doped graphene and N-doped graphene electrodes (2122−1). Compared with the rGO, S-doped graphene and N-doped graphene electrodes, the discharge/charge profiles of the N,S-codoped graphene electrode have an obvious higher discharge plateau at ∼2.32 V (reduction of sulphur to long-chain lithium polysulphides) and a longer plateau at ∼2.10 V (formation of short-chain lithium polysulphides) with corresponding charge plateaus at ∼2.30 and ∼2.45 V (transformation from Li2S2/Li2S to long-chain lithium polysulphides and then to sulphur)To show whether the doped heteroatoms of S and/or N on the graphene have a positive effect on the performance of Li–S batteries, these graphene sponges were cut into slices, compressed and directly used as free-standing electrodes for a series of electrochemical measurements. Different from two-dimensional graphene materials, 3D interconnected porous graphene sponges can provide multidimensional electron transport pathways and easily accessible active sites. Therefore, electrochemical impedance spectroscopy was used to analyse the kinetics of the electrochemical reactions. ectrodes , which c−1, and the capacity is retained at 822 mAh g−1 after 100 cycles with nearly 100% Coulombic efficiency, which is much higher than that of the rGO, S-doped graphene and N-doped graphene electrodes with values of 495 mAh g−1, 646 mAh g−1 and 705 mAh g−1, respectively. Lithium nitrate (LiNO3) is added to promote the formation of a stable passivation film, and the capacity decay at the initial few cycles is partially due to the LiNO3 decomposition and the formation of a SEI film on the lithium anode surface54−1, and the voltage plateau at ∼1.6 V is attributed to the reduction of LiNO3 on the carbon and lithium surface−1 after 100 cycles, demonstrating its little contribution to the overall capacity. To demonstrate the rate capabilities of these electrodes, the current density was changed from 0.2 to 2C rate, as shown in −1, 912 mAh g−1, 675 mAh g−1 and 430 mAh g−1, indicating a high charge/discharge capability. However, the rGO electrode shows almost no capacity at 2C rate, demonstrating poor rate performance. When the current density was reduced back to 0.5C rate, the discharge capacity can be recovered to 878 mAh g−1 for the N,S-codoped graphene electrode, indicating that the electrode structure remains stable after the high-current-density test. Even after the rate capability test, the N,S-codoped graphene electrode still shows excellent long-cyclic performance with higher capacity (550 mAh g−1) and retention (63%) compared with the rGO , S-doped graphene  and N-doped graphene  electrodes at a current density of 0.5C rate up to 500 cycles. The capacity decay is only 0.078% per cycle for the N,S-codoped graphene electrode, much better than those of the rGO, S-doped graphene and N-doped graphene electrodes with decay rates of 0.179%, 0.124% and 0.121% per cycle, respectively. These results imply that the nitrogen- and sulphur-doped 3D porous graphene sponge could not only facilitate fast electron/ion transfer, but also interact strongly with lithium polysulphides to significantly enhance the rate performance and long-term cyclic stability.The cycle performances of these electrodes were first tested at a small current density of 0.2C rate, as shown in −2 by adding more Li2S6 catholyte into the N,S-codoped graphene electrode with the help of a graphene-coated separator, which has been confirmed as a very useful approach to obtain high-performance Li–S batteries2829−1 at 0.2C rate, and the reversible discharge capacity could reach ca. 500 mAh g−1 at a large current density of 2C rate  the 3D graphene network and graphene layer can accommodate the volume change of the active material during cycling; and (iv) the chemical binding between the sulphur/nitrogen heteroatoms and lithium polysulphide/Li2S reduces the active material loss, realizing long cycle life and high-energy/power density Li–S batteries.To further improve the energy density of the whole battery system and satisfy the demands of high-energy batteries, the active material loading was increased from 4.6 to 8.5 mg cm 2C rate . In addi0 cycles . The adv2S) deposition is present on the surface of rGO and the corresponding metallic lithium surface is rough with many coarse lithium agglomerations  is influenced by the incorporation of N and/or S atoms into the graphene lattice. Here we used a small LiSH molecule to model the Li–S end. This model is simple but should be sufficient enough to demonstrate the influence of doping particularly on the binding interaction of the terminal Li+ cation with a doped graphene sheet, although lithium polysulphides may also exist as complex clusters5758+, we also considered Li2S adsorption at a few selected dopant sites, as shown in 2S and LiSH, implying that it would be reasonable and feasible to use LiSH for the purpose of supporting our experimental observations. For a reference, we first considered the binding of LiSH to a pristine graphene sheet and a 1,3-dioxolane (DOL) molecule, which is widely used for the electrolyte in a Li–S cell. As shown in Eb=0.78 eV, in good agreement with the previous DFT resultsEb is given by ELiSH+EGr−ELiSH/Gr, where ELiSH, EGr and ELiSH/Gr represent the total energies of an isolated LiSH, pristine (or doped) graphene and LiSH adsorbed graphene, respectively. Our calculations also predict that the Li of LiSH can be strongly bound to the O site of DOL with Eb=0.93 eV (Eb than that for the graphene case (0.78 eV) may suggest that lithium polysulphides would dissolve into the DOL-based electrolyte instead of adsorbing on the graphene surface, consistent with the existing experimental observations10To better understand the doping effect, density functional theory (DFT) calculations were performed to examine how the binding strength of the Li–S end of linear lithium polysulphides . On the other hand, the quaternary N doping  eV, as compared with the separately doped cases  between 10° and 70° at a scan rate of 0.04° s−1. Raman spectra were collected with a 488 nm laser under ambient conditions with a WITEC Alpha300 S micro-Raman system at room temperature. XPS analysis was performed on a Kratos Analytical spectrometer at room temperature with monochromatic AlKα  radiation. Ultraviolet–visible absorption spectroscopy analysis was performed to evaluate the polysulphide adsorption capability of rGO, S-doped graphene, N-doped graphene and N,S-codoped graphene sponges. About 4 mg each of rGO, S-doped graphene, N-doped graphene and N,S-codoped graphene sponges were separately added into four sealed vials of Li2S6 solution , and the Li2S6 solution without adding anything was used as a control. After absorption for 2 h, the ultraviolet–visible absorption spectra of these solutions were collected with an Evolution 300 UV–vis spectrophotometer with baseline correction. The electrical conductivity of the electrodes was measured by a standard four-point probe resistivity measurement system . Three measurements were taken at different positions on the sample, and the average value was taken.SEM observations were carried out on a FEI Quanta 650 SEM operated at 20 kV. STEM was performed with a Hitachi S-5500 SEM, and EDS was used for collecting elemental signals and mapping. XRD patterns were collected with a Philips X-ray diffractometer with Cu Kα radiation  and LiNO3  in DME  and DOL  (1:1 by volume). The polysulphide catholyte was prepared by chemically reacting sublimed sulphur  and an appropriate amount of Li2S  in the blank electrolyte to form Li2S6 (1.0 M) in the solution. The solution was then stirred at 50 °C in an Ar-filled glove box overnight to produce a brownish-red Li2S6 catholyte solution.The blank electrolyte was prepared by dissolving an appropriate amount of lithium trifluoromethanesulfonate (LiCF2 and a mass of 0.9–1.4 mg. About 12 μl of Li2S6 catholyte (1.0 M) was added into each of the rGO, S-doped graphene, N-doped graphene and N,S-codoped graphene electrodes, corresponding to a sulphur loading of 4.6 mg cm−2. The Celgard 2500 separator was then placed on top of the electrode, followed by adding 30 μl of the blank electrolyte. Finally, the lithium-metal foil anode was placed on the separator as the anode. An Arbin battery cycler was used to perform the galvanostatic cycling measurements at 1.5–2.8 V (versus Li/Li+) at room temperature. The current density set for tests was referred to the mass of sulphur in the cathode and was varied from 0.2C to 2C rate. For the high sulphur loading cathode, 22 μl of Li2S6 catholyte (1.0 M) was added into the N,S-codoped graphene electrodes, corresponding to a sulphur loading of 8.5 mg cm−2. The graphene-coated separator was used to place on the top of the sulphur cathode followed by adding 50 μl of the blank electrolyte. Electrochemical impedance spectroscopy measurements were performed with a Solartron Impedance Analyzer (Solartron 1260A) in the frequency range of 1 MHz to 0.1 Hz with an AC voltage amplitude of 5 mV at the open-circuit potential. For the cycled samples, the cycled cells were disassembled inside an Ar-filled glove box, and the electrodes were rinsed with 1,2-dimethoxyethane solvent to remove the lithium salt and dried inside the glove box at room temperature before analysis.The Li/dissolved polysulphide cells (CR2032 coin cells) were assembled in an Ar-filled glove box. The rGO, S-doped graphene, N-doped graphene and N,S-codoped graphene sponges were dried at 120 °C under vacuum overnight before using. These samples were cut, compressed and shaped into rectangular plates to be used as the current collectors with an area of 0.5 cmAb initio Simulation Package (VASP)z) direction to avoid interactions between graphene and its periodic images. To model N and/or S dopant atoms at graphene edges and vacancies, we employed a graphene flake consisting of 37C atoms in a periodic simulation box of dimensions 20 × 20 × 15 Å; dangling C bonds were passivated by H atoms. A gamma-centred 2 × 2 × 1 Monkhorst–Pack mesh of k points was used for the Brillouin zone integration. All atoms were fully relaxed until the residual forces on constituent atoms became smaller than 0.02 eV Å−1. We used the semi-empirical approach proposed by GrimmeThe atomic configurations and binding energies reported herein were calculated using DFT within the Perdew–Berke–Ernzerhof generalized gradient approximation (GGA-PBE)How to cite this article: Zhou, G. et al. Long-life Li/polysulphide batteries with high sulphur loading enabled by lightweight three-dimensional nitrogen/sulphur codoped graphene sponge. Nat. Commun. 6:7760 doi: 10.1038/ncomms8760 (2015).Supplementary Figures 1-13 and Supplementary Tables 1-4


Sn/Te and the evaporation conditions. It is shown that as-deposited layers with RSn/Te ranging from 0.4 to 0.9 exhibit excellent characteristics as humidity sensors operating at room temperature—very high sensitivity, good selectivity, fast response and short recovery period. Ageing tests have shown that the layers possess good long-term stability. Results obtained regarding the type of the water adsorption on the layers' surface help better understand the relation between preparation conditions, structure, composition and humidity sensing properties.In this paper the humidity sensing properties of layers prepared by a new method for obtaining doped tin oxide are studied. Different techniques—SEM, EDS in SEM, TEM, SAED, AES and electrical measurements—are used for detailed characterization of the thin layers. The as-deposited layers are amorphous with great specific area and low density. They are built up of a fine grained matrix, consisting of Sn- and Te-oxides, and a nanosized dispersed phase of Te, Sn and/or SnTe. The chemical composition of both the matrix and the nanosized particles depends on the ratio R The fir2 sensing layers are their insufficient long-term stability and poor selectivity, i.e., the ability to detect a gas among a mixture of many gases. One possibility to improve these parameters is doping with suitable dopants—metals or other oxides  was measured at intervals of 2 s. The hysteresis of the sensor was measured in the humidity chamber at 25 °C. The resistance variation of the sensor was followed with increasing humidity from 30% to 75% and then with decreasing humidity from 75% to 30%, with steps of 10% RH.As a measure for the sensitivity of the sensing layers the change in their electrical resistance (R [Ω]) as a function of the relative humidity (RH [%]) was used. The resistance was measured within the interval RH = 30%–100% at temperatures of 25 to 80 °C in a test humidity chamber equipped with temperature and RH controller . The measurement of R [Ω] of the layers was performed with a multichannel ohmmeter (MCOM), product of National Instruments . The data acquisition and processing, as well as the control of the ohmmeter, were computerized using LabView software. The experiments concerning the response time and recovery period (kinetic measurements) were performed using saturated solutions of NaOH and . They contained twenty parts of oxygen, ten parts of tellurium and eight parts of tin . The solid state reaction between Sn and TeO2 during the co-evaporation resulted in the formation of eight parts of SnO2, two parts of TeO2 and eight parts of elemental Te. After removal of the elemental Te by the ion beam, the O:Te:Sn-ratio changed to 66.7:6.7:26.7%. As seen in As mentioned above, Auger-electron spectroscopy was used to investigate the homogeneity of the Sn-O-Te layers. However, the direct application of the method is not possible because of the high mobility of the elemental Te present in the layers according to 3.2.3.2.1.3 is much lower than the respective values for the bulk materials TeO2, Te, Sn and SnO2—between 5.7 and 7.3 g/cm3 [Sn/Te ranging from 0.4 to 1.3. As can be seen, the electrical resistance of layers with RSn/Te = 0.4–0.9 decreases with increasing relative environmental humidity spanning 3–4 decades of resistance, the response curve reveals a close exponential relationship between resistance and RH and can be linearized by taking the logarithm of the resistance. Layers with RSn/Te = 1.3 do not show the same dependence, i.e., only layers with RSn/Te < 1 possess high sensitivity to humidity.As the Sn-O-Te layers obtained have a nanosized structure, low density and high specific area respectively  have unambiguously confirmed that with increasing atomic ratio RSn/Te (up to 1.3) the amount of TeO2 decreases and the amount of Sn-oxides and elemental Te increases. At RSn/Te < 1 the layers consist of a mixture of Sn oxides (SnO2 and some SnO) and TeO2, doped with very finely dispersed elemental Te. Obviously, there exists an optimum ratio between the products of the redox reaction (RSn/Te = 0.7–0.9), which causes the high sensitivity towards humidity at room temperature. It is known that the presence of a second oxide at a level of 2–10 wt.% and of other dopants in SnO2-based sensors leads to improved gas response and shifts the maximum of sensitivity to lower operation temperature [Sn/Te in the range of 0.7–0.9 is probably related also to the non-stoichiometry of SnO2, which favors the adsorption of the specific oxygen adsorbate As we have already mentioned, during the vacuum co-deposition of TeOn oxides ,5,9. InvThe release of electrons leads to decreased resistance with increasing humidity. It should be stressed however, that, as noted by other authors too, the mechanism of gas impact on the electrical properties of mixed oxides is much more complicated as compared with homogenous oxides and its detailed understanding needs a more comprehensive study.etc. [The lack of sensitivity to humidity of thermally treated layers is due to significant changes in the in-depth distribution of the layers' components and in the structure .10 Ω). One of the ways to overcome this problem is the additional doping with some metals (in our case with Pt). The doping with 2–3 at.% Pt leads to a resistance decrease of one order of magnitude (shown in the same figure) compared with the undoped layers, without any changes in sensitivity [It is important to note that the high sensitivity to humidity is observed only at room temperature (25 °C). As seen in sitivity . Therefo3, H2SO4, HCl, bases—NH4OH and ethanol) at room temperature was checked. No change in the resistance was observed, i.e., the layers exhibit a very high selectivity.To study the selectivity of the humidity sensitive Sn-O-Te layers their sensitivity towards different vapors  in the presence of moisture [The results presented in this paper demonstrate the applicability of the method developed at our Institute for preparing nanosized doped SnOmoisture . A shortThe layer preparation method allows the introduction of finely dispersed dopants in order to obtain materials sensitive to other reduction gases. It is compatible with conventional microelectronics technologies and after optimization the sensors can be integrated on one chip with field-effect transistors or with entire subsystems for data processing.


Two dimensional atomically thin crystals of graphene and its insulating isomorph hexagonal boron nitride (h-BN) are promising materials for spintronic applications. While graphene is an ideal medium for long distance spin transport, h-BN is an insulating tunnel barrier that has potential for efficient spin polarized tunneling from ferromagnets. Here, we demonstrate the spin filtering effect in cobalt|few layer h-BN|graphene junctions leading to a large negative spin polarization in graphene at room temperature. Through nonlocal pure spin transport and Hanle precession measurements performed on devices with different interface barrier conditions, we associate the negative spin polarization with high resistance few layer h-BN|ferromagnet contacts. Detailed bias and gate dependent measurements reinforce the robustness of the effect in our devices. These spintronic effects in two-dimensional van der Waals heterostructures hold promise for future spin based logic and memory applications. Two dimensional 2D) crystals of graphene (Gr) and hexagonal boron nitride (h-BN) have gained immense attention in recent years because of their exciting properties for nanoelectronics1D crystal456789429151617Recently h-BN has been shown to be a promising 2D material for tunnel barrier applications591966781023In this article we report an inversion of spin signal with large magnitude of spin polarization in non-local graphene spin valves with h-BN|cobalt (Co) high resistance (HR)–low resistance (LR) injector-detector (with different h-BN thickness) combination tunnel contacts. Through systematic nonlocal pure spin transport and Hanle spin precession measurements on devices having different interface barrier conditions, we associate the negative spin polarization with HR h-BN|Co contacts. The characteristic polarization and spatial spin filtering across such contacts leads to relatively large magnitude of spin signal in these devices. We further establish the robustness of the sign of polarization through bias and gate dependent measurements. Our results show the possibility of manipulating the sign and magnitude of spin polarization due to different interface conditions with thickness of h-BN barriers. The large and negative spin polarization using such high resistance (HR) h-BN|Co contacts observed in graphene non-local spin valves indicates spin filtering effects and opens avenues for efficient 2D vdWH spintronic devices.2 substrates. A layer of CVD h-BN |h-BN vdWH devices with ferromagnetic Co contacts. A schematic representation of realizing injection and detection contacts with different h-BN thicknesses along with an optical microscope image of an actual device is presented in CVD h-BN  was tranchniques . DetailsRi = 170 kΩ μm2) and a low resistance (LR) detector (Rd = 25 kΩ μm2). Such a difference in contact resistance is a characteristic feature of CVD h-BN tunnel barriers due to a spatial thickness distribution, which is mostly 1–2 layers with some patches of higher thickness (~3 layers) as reported previously92 substrates  characterization of the injection and detection contacts in a three-terminal configurationbstrates . This thbstrates , which ibstrates . The chator Rd =  kΩ μm2. NLV) for parallel and anti-parallel configurations of the injection and detection ferromagnetic electrodes. This gives a measure of the induced spin splitting (Δμ) in graphene and hence the spin polarization of the Co|h-BN tunnel contacts. The different shape anisotropies of the ferromagnetic contacts ensure distinct switching fields for each of them. In contrast to the normally observed NL spin signal in graphene spin valves  configuration as depicted in the inset of shown in , we obseRNL) by spin precession in a perpendicular magnetic field . We have also found similar spin lifetime in graphene devices prepared with TiO2 tunnel barrier and in other studies4262V−1s−1. The actual tunnel resistances (not Resistance × contact Area) in our device iR and dR >> iR and dR are the actual contact resistances of injector and detector contacts and the channel spin resistance28L and resistance where tal data , we obtaP is considered to be quite large for graphene spin valve devices32NLΔRand P with injection bias current and voltages, exhibiting a decreasing trend at higher bias. It is worth mentioning that the spin lifetime and diffusion constant were seen to be fairly independent of the bias  due to an effective increase in the thickness of h-BN by one layer29Pd ≈ 15%  is responsible for the negative sign of the spin polarization, we performed measurements on a series of devices with different combinations of tunnel resistances. In 2. The normal sign for a spin valve signal in LR-TR combinations 2 also show a normal spin signal without any inversionBased on the sign of the observed spin signal, we group these devices into two categories. First kind, with inverted spin valve signal that has been observed exclusively in devices with a HR-LR contact combination , which pTo understand the robustness of the spin signal inversion, we further studied the influence of the applied injection current bias and gate voltage on the spin signal of our devices at room temperature. gV), which controls the carrier density in graphene, on the sign of the spin signal is examined. In NLΔR for both HR-LR and LR-LR devices in the range gV = ±40 V. In both cases we observe a decrease in the magnitude of NLΔR by 10–15% for higher gV (higher carrier concentration). This behavior is in agreement with theoryTR is much higher than the graphene channel resistance ChR. In such regime, a decreasing trend in the magnitude of NLΔR at higher gate voltage gV is usually observed in lateral spin valve devices. Throughout the gV sweep range, we observe a negative NLΔR for the HR-LR device, which shows that the observed negative spin polarization in a HR Co|h-BN|Gr tunnel contact is stable against variation of carrier density in graphene.Next, the effect of a gate voltage  interfaces4647et al. predicted82O3, MgO have been observed to bear a positive spin polarization2O3-Ta2O3, SrRuO3 and Fe3O4 barriers have also shown negative spin polarization4350515253Spin resolved conductance across the junctions of 2D crystals with ferromagnets has been the subject of recent theoretical and experimental interest due to their atomically thin nature. Karpan In conclusion, we have observed an inversion of spin signal in non-local graphene spin valves with ferromagnetic tunnel contacts with h-BN barrier. Through controlled experiments on several devices having different injector-detector contact resistances, we confirm that the high resistance Co|h-BN junctions with negative spin polarization lead to the observed inversion of spin signal. The effect is found to be robust as established through systematic bias and gate voltage dependent measurements. The enhanced polarization with thicker h-BN junctions indicates considerable spin filtering of spatial nature. These findings bring out the significance of CVD h-BN as a novel spin tunnel barrier, well beyond its use as a 2D insulating barrier that can provide interface resistance for addressing the conductivity mismatch problem. It also demonstrates the possibility of achieving different polarization with different thicknesses of h-BN offering different spin dependent interface conditions and spin filtering. The possibility of high spin polarization in thicker multilayer h-BN together with better quality graphene would be a key ingredient for efficiency in future graphene spintronic devices. In addition, the novel spin filtering effects of ferromagnetic tunnel contacts with thicker h-BN barriers can be explored for engineering spintronic devices with other 2D crystals56572. Graphene flakes are exfoliated on a cleaned SiO2/Si substrate with predefined Ti/Au markers by repeated peeling of highly oriented pyrolytic graphite (HOPG) using the conventional scotch tape technique. The graphene flakes were selected using a combination of optical and atomic-force microscopy. The CVD h-BN layer used as tunnel barrier in our experiment, was grown by chemical vapor deposition (CVD) on a copper foil and has high crystalline quality with ~90% coverage (procured from Graphene supermarket). The CVD h-BN is placed on graphene by wet chemical etching and transfer processes, respectively. The h-BN surface is first covered with PMMA, and then isolated from the Cu substrate by etching in a FeCl3 solution. The h-BN/PMMA layer is washed with 10% HCl and deionized water, and subsequently transferred onto the chip containing graphene flakes. The chip is then baked at 150 °C and washed with acetone to remove the PMMA. The resulting chip containing a h-BN|graphene heterostructure is annealed at 400° C in Ar/H2 atmosphere. The annealing improves the adhesion between the h-BN and graphene and ensures the removal of possible residues of resist remaining from the transfer process of h-BN. The h-BN layer is patterned in regions covering graphene flakes by electron beam lithography and subsequent Ar-etching. In the 2nd step of e-beam lithography, electrodes were patterned and cobalt of 65 nm deposited by electron beam evaporation at a rate of 2 Å/sec at a pressure of <5 × 10−7 mbar with sample being placed in normal position without any specific tilt of the sample stage. The ferromagnetic Co deposition was followed by deposition of 20 nm thick Au capping layer without breaking the vacuum to protect them from possible oxidation. The electrical and spin transport measurements were performed in a liquid helium cryostat with a superconducting magnet.The Graphene devices with Co|h-BN tunnel contacts were prepared on a highly doped Si substrate with 285 nm SiOHow to cite this article: Kamalakar, M. V. et al. Inversion of Spin Signal and Spin Filtering in Ferromagnet|Hexagonal Boron Nitride-Graphene van der Waals Heterostructures. Sci. Rep.6, 21168; doi: 10.1038/srep21168 (2016).


HSP70) gene polymorphisms in the susceptibility to IPF is unknown. The aim of this study was to explore the association between HSP70 polymorphisms and IPF susceptibility in the Mexican population.Idiopathic pulmonary fibrosis (IPF) is a fatal lung disease of unknown etiology. Genetic variation within different major histocompatibility complex (MHC) loci contributes to the susceptibility to IPF. The effect of 70 kDa heat shock proteins (HSPA1L (rs2075800), +2437 of HSP HSPA1L A>G (rs2227956), +190 of HSPA1A G>C (rs1043618) and +1267 of HSPA1B G>A (rs1061581).Four HSP70 single nucleotide polymorphisms (SNPs) were evaluated using real time PCR assays in 168 IPF patients and 205 controls: +2763 C>T of HSPA1B (rs1061581) GA and AA genotypes were associated with a lower risk of IPF compared with GG . Similarly, HSPA1L (rs2227956) AG genotype  and the dominant model AG + GG genotypes were also associated with a lower risk of IPF . In contrast, the HSPA1L (rs2075800) TT genotype was associated with susceptibility to IPF .The analysis of the recessive model revealed a significant decrease in the frequency of the genotype HSPA1B AA (rs1061581) in IPF patients  when compared to controls. Using a multivariate logistic regression analysis in a codominant model the HSPA1 (rs1043618) polymorphisms are associated with a decreased risk of IPF.Our findings indicate that HSPA1B (rs1061581), HSPA1L (rs2227956) and The online version of this article (doi:10.1186/s12890-015-0127-7) contains supplementary material, which is available to authorized users. MUC5B  in both studied groups. No significant differences in the distribution of haplotypes between IPF patients and healthy controls were detected. To calculate linkage disequilibrium in the control group the Haploview 4.2 program was used [HSPA1B (rs1061581) with HSP1AL (rs2075800) and HSPA1B (rs1061581) with HSPA1A (rs1043618).Finally, we also performed a haplotype analysis Table  and we fwas used . In Fig.HSP70 polymorphisms is unknown [HSPA1B 1267A/G polymorphism [HSP70 genes in IPF patients and healthy controls from Mexican ancestry. The most striking findings confirmed by a multivariate analysis were that the GA and AA genotypes of the HSPA1B (rs1061581) polymorphism were associated with a lower risk of IPF. Also, AG genotype and the AG + GG genotypes (in a dominant model) of the SNP HSPA1L (rs2227956) were also associated with a lower risk to develop IPF. On the other hand, the HSPA1L (rs2075800) TT genotype was significantly associated with susceptibility to IPF.Hsp70s, together with their Hsp40 co-chaperones, are the most prominent chaperone families that participate in chaperone-assisted proteosomal degradation of misfolded proteins . Previou unknown . Interesmorphism . Likewismorphism . In thisHSPA1L gene and leads to an amino acid change at position 493 from a non-polar hydrophobic Met to a polar neutral Thr. Amino acid 493 is present in the 18 kDa peptide-binding domain on the beta sheet that forms the floor of the peptide binding groove [HSPA1L polymorphic G allele translates to a Met residue, an hydrophilic amino acid that may affect the interaction of the HSP70 with hydrophobic proteins and consequently impairs its ability to assemble and transport proteins within cells [HSPA1B AG/GG genotype, which seem to protect from IPF, have an increased risk of cancer [HSPA1A, HSPA1B-179 C>T and HSPA1B 1267 A>G have been linked with significant alterations in the mRNA and protein expression [HSP70-HOM +2437 A>G (Met493Thr), affecting the substrate specificity and chaperone activity of HSP-70 HOM, has been described [HSP70 gene-disease associations in IPF are unclear. In this context, strong evidence has revealed the accumulation of unfolded and misfolded proteins with severe endoplasmic reticulum (ER) stress in alveolar epithelial cells lining areas of fibrosis [HSPA1B 1267 A>G polymorphism in the differential expression of HSPA1B mRNA [The polymorphism rs2227956 is located in the coding region of the g groove . The HSPin cells , 39. Intf cancer . Previoupression , 26. Alsfibrosis . It is pA1B mRNA . In addip = 0.005). In comparison with former data of associated functional polymorphisms [HSPA1B [In our study, the combination of the two genotypes associated with protection was only found in healthy controls and not in IPF patients (orphisms , 27, 44, [HSPA1B .HSP70 polymorphisms association with the protection to IPF with a statistical power greater that 80 %, even with the stringently defined number of IPF cases studied. Another limitation was the imbalanced distribution of males and females among IPF and control group. In this regard, a possible bias of the genetic association analysis may be due to the gender disparities. However, in previous genetic-association studies of MHC genes, no marked differences in the MHC genes frequencies have been detected between males and females from Mexican ancestry [To determine whether the associations described in the three models of inheritance are independent of LD between the SNPs analyzed, a multivariate analysis was performed. As a result we confirmed that these associations are independent of LD. The differences in the association with IPF between the three models of inheritance may indicate that the segregation of one or two genotypes of protection or risk act independently, either as protective or risk IPF factors, respectively. The present study has some limitations and replications in other populations are needed to verify these findings, since polymorphisms suggesting fibrosis protection are relatively rare. Notwithstanding, we were able to confirm ancestry . FurtherHSP70 SNPs genotypes between Mexicans and other ethnic groups (Additional file HSPA1L gene is the most common genotype, whereas CC genotype is the least frequent genotype in Italian Caucasians [HSPA1L with rs2227956 are similar in all population groups. Likewise, for the HSPA1A rs1043618 gene, the GG genotype is more frequent in Chinese, Taiwanese, Polish [Finally, we compared the frequencies of ucasians  and Croaucasians  subjectsucasians  and Taiwucasians  as well , Polish , 51 and HSPA1L and HSPA1B genes may influence the susceptibility of developing IPF in our population. Additional investigations with other populations are needed to confirm the significance of our findings and the functionality properties of these polymorphisms.In summary, the present study suggests that genetic variation in the


Results show that among the commonly native point defects in graphene, only the single vacancy 5–9 and divacancy 555–777 have the desirable electronic structures to trap N-containing groups and to mediate the subsequent dehydrogenation processes. The local structure of the defective graphene in combining with the thermodynamic and kinetic effect plays a crucial role in dominating the complex atomic rearrangement to form graphitic-N which heals the corresponding defect perfectly. The importance of the symmetry, the localized force field, the interaction of multiple trapped N-containing groups, as well as the catalytic effect of the temporarily formed bridge-N are emphasized, and the predicted doping configuration agrees well with the experimental observation. Hence, the revealed mechanism will be helpful for realizing the targeted synthesis of N-graphene with reduced defects and desired properties.Nitrogen-doped graphene (N-graphene) has attractive properties that has been widely studied over the years. However, its possible formation process still remains unclear. Here, we propose a highly feasible formation mechanism of the graphitic-N doing in thermally treated graphene with ammonia by performing  Chemical doping is a powerful technique to tailor the properties of carbon materials12325623613146101617Nitrogen-doped graphene (N-graphene) can be fabricated by either direct-synthesis456171927912131621224567121329162268216172151012131756821et al. have reported that a high ratio of graphitic-N/pyridinic-N can provide a promising activity for ORRFor the N-graphene obtained in some experiments56712131719662762417281013et al.3), most of the N-dopants (80%) are graphitic-Ns. It is intuitively clear that graphitic-N forms by merging N atoms into the defect region of graphene. First principles calculations have also proved that the occurrence of N-doping at defects of graphene is energetically favorable2732Post-treatment of graphene with N-precursors has been proved a practical means to achieve high-quality N-graphene which is enriched in graphitic-N but small amounts of defects712ab initio molecular dynamics (ab-MD) simulations at experimental conditions, we investigate the interaction of the widely used N-precursor of NH3 with the graphene of different structures. A highly feasible formation mechanism of graphitic-N is revealed, the defect-configuration relationship is established, the dynamics of the simultaneous formation of graphitic-N and the healing of the defect is visualized, and the important factors which dominate the formation process is emphasized. Thus, our simulations give new insights in N-graphene chemistry and will certainly help to achieve the targeted synthesis of N-graphene with reduced defects and desired doping structures.In this work, by performing As a precondition to occur N-doping, N-sources should be trapped by graphene. We first examined the possibility to trap N atoms at the perfect region of graphene at experimental conditions. A temperature range from 700 to 1000 °C with a step of 50 °C has been used in the simulations, and the snapshots for 850 °C are plotted in Structural defects like Stone-Wales (SW), vacancies, nanoholes, grain boundaries, as well as the edges of graphene are known to possess a relative higher activity2627From the structural point of view, to heal a divacancy requires two adatoms. We have carried out simulations to study the interaction of two N atoms with a DV(5-8-5) and DV(555-777), respectively. Remarkably, only the DV(555-777) has trapped the two N atoms as expected see . Traject3 in thermal treatment experiments is complicated, which may involve various reactions and the products of -NH2, -NH-, and -N are possible. N atom is only the simplest model for the possible N-sources. We continued our simulations to investigate the interaction of a DV(555-777) and SV(5-9) with the N-containing groups of NH3, -NH2, and -NH-, respectively.In sharp contrast to the widespread intuition that a variety of defects in graphene can provide rich active sites for N-doping, our simulations demonstrate clearly that among the commonly native point defects of graphene, only the SV(5-9) and DV(555-777) have the ability to trap N atom, but it seems not always result in the formation of graphitic-Ns. Moreover, the decomposition of NH2 and -NH- can be well trapped by the defect, but the NH3 can not, suggesting that the occurrence of the first step of NH3 decomposition in the thermal treatment experiments does not need the help of the defect. Our simulations also show that although the -NH2 and -NH- can be trapped by the defect, both of them can not dehydrogenate at all, even the simulation time has been extended to 3 ps. It is well known that without dehydrogenation, the formation of N-doping is impossible.The results for DV(555-777) are given in 2 appears at 100 fs, it moves to the defect region and reacts with the first one to form a -NH- and a NH3. The formed NH3 drifts freely above the surface and runs out of the sight as expected. While the formed -NH- adsorbs tightly at the bridge-site of the first 5–7 pair as shown in 2. The formed atomic-N transforms to a pyridinic-N due to merged into the 5–7 pair. Instead of drifting away, he -NH2 moves quickly to the second second 5–7 pair to adsorb on a top-site.We extended our simulations to consider the possible dehydrogenation from the interaction of N-containing groups, and the results are given in 2 → -NH- → atomic-N” route.Remarkably, a DV(555-777) can trap multiply N-containing groups which induce a two-step dehydrogenation process that leads to the formation of an atomic-N. It can be simply represented by the “-NH2 at the third round moves away from the surface of graphene. Surprisingly, although to heal a DV(555-777) requires only two adatoms, as many as three atomic-Ns can be formed at the vicinity.We found that the process continues as more N-containing groups appear at the reaction region, making as many as three atomic-Ns to be formed at the vicinity of a DV(555-777). One can see in As the simulation proceeds further, we found the significance of the coexistence of three atomic-Ns at a divacancy. It is that a complex atomic rearrangement process can be induced, directly resulting in the formation of graphitic-Ns and the healing of the defect. The entire process involves the rotation, break, and formation of multiply bonds as shown in It is worthy of noting that the third N has the same species (bridge-N) at the initial and final stages of the rearrangement. While As a catalyst, the bridge-N should be active and unstable at experimental conditions. This is why bridge-N has never been observed in the N-graphene obtained in experiments. We have performed density functional theory (DFT) calculations and found that the energy barrier for process of “bridge-N → top-N → bridge-N” is about 1.15 eV when considered vdW corrections. This means that the bridge-N migration at the surface of graphene can occur easily at macroscopic time range of the real thermal treatment experiments, but the probability to find the migration in fs-ps time range simulations should be very small. Thus we have only considered what will happen when two bridge-Ns have moved close to each other. The results displayed in 2 → -NH- → atomic-N”, and the result is also basically the same, namely a single graphitic-N (with a configuration of N1) is formed eventually that heals the defect perfectly.We have further extended our simulations to consider the possible formation of graphitic-N at the defect of SV(5-9) and the snapshots are given in Our simulations show that among the native point defects of graphene, only the SV(5-9) and DV(555-777) have the ability to trap N-containing groups and to mediate the subsequent N-doping process. This can be well understood by analyzing the localized force field of the defects.Unambiguously, there exist two major localized force fields at a defect: a strain field (S-field) caused by lattice-disorder and an electronic field (E-field) generated due to the existence of dangling bonds. From a structural point of view, a SW(55-77) is formed by the rotation of a C-C bond of 90° at the perfect region of graphene, thus only the S-field presents at the vicinity. Our simulations show that the S-field of SW(55-77) is not large enough to trap N-containing groups at experimental conditions. But for SV(5-9), it is formed by missing a C atom. There exist three dangling bonds at the vicinity. It undergoes a Jahn-Teller distortion which can lead to the saturation of two of the three dangling bonds, but one dangling bond always remains owing to geometrical reasons. Thus both the S-field and the E-field exist at a SV(5-9), resulting in the localized force field which is large enough to trap N-containing groups.et al.While for DV(5-8-5) and DV(555-777), they both form by missing a pair of C atoms. Self-saturations let no unsaturated C atoms but only lattice-disorder present at the defect. It is well known that a DV(555-777) can be formed from a DV(5-8-5) by the rotation of a C-C bond of 90° 26We noticed that the trapped N atom adsorbs on the top-site of SV(5-9) see , but on 2 and -NH- can not dehydrogenate when only considered the interaction of the N-containing group with graphene, in consistent with the observations of previous studies8272 → -NH- → atomic-N” is revealed in our simulations. It is clear that multiply N-containing groups can be trapped by a SV(5-9) or a DV(555-777), and the interaction between them demonstrates the same route of dehydrogenation at the two defects. This means that the revealed dehydrogenation route is independent on the type of the defects but dominated by the interaction of N-containing groups.Our simulations show that the -NHOur simulations show that without the third atomic-N, the two atomic-Ns can not launch the complex atomic rearrangement process and the N-doping of D3h symmetry. First principles calculations have confirmed that the localized force field of a DV(555-777) extends widely at the vicinity in D3h symmetryD3h symmetry allows three atomic-Ns to be formed at the vicinity of a DV(555-777). The symmetry plays a crucial role in determining the number of the formed atomic-Ns and mediating the formation of It is well known that a DV(555-777) contains four disordered C atoms of, one locates at the center and the other three surround it, resulting in the formation of three 5–7 pairs in 1 and two graphitic-Ns quasi-adjacently occupied the same sublattice (A) of graphene result in the doping configuration of et al.3 are Experimental measurements show that the formed graphitic-Ns can either distribute randomly between the two sublattices of graphene71 and Our ab-MD simulations have certainly resolved this long-lasting issue. Basis on our simulations, the relationship between the native point defects of graphene and the doping configurations of the graphitic-N can be established. Namely, SV(5-9) and DV(555-777) mediate to the formation of N1 or a The finding from our ab-MD simulations is of importance. It reveals for the first time that the DV(555-777) is a favorable active site for N-doping. This is also a somewhat expected result when considering the observation from previous studiesab initio molecular dynamic simulations, we have found a new mechanism for substitutional nitrogen-doping in thermally treated graphene that satisfactorily explains the experimental observations and will be helpful for realizing targeted synthesis of nitrogen-graphene with reduced defects and desired doping configurations.In conclusion, by performing 3 molecule and its decomposing products of -NH2, -NH-, and -N were used as the possible N-containing groups for N-doping. The initial position of the containing group was set to 3.6 Å away from the graphene layer to ensure the elimination of direct chemical interactions. In this case, vdW forces play the dominant role at the initial stage of simulations.A large supercell (15 × 15 × 1) containing 450 C atoms see  was adopζ polarization (DZP) numerical atomic orbital basis sets with the energy cut-off of 80 meV were adopted. The real-space integration was done on the mesh defined by 200 Ry kinetic energy cutoff. Each step was achieved with the tolerance of density matrix (DM) of 1.0−4. The snapshots of the simulations were grabbed using VMD programThe simulations were carried out using ab initio package SIESTA 3.2How to cite this article: Li, X.-F. et al. Unraveling the formation mechanism of graphitic nitrogen-doping in thermally treated graphene with ammonia. Sci. Rep.6, 23495; doi: 10.1038/srep23495 (2016).


The second technique is based on monitoring of potassium concentration in urine. High level of potassium concentration denotes clear occurrence of dehydration. Furthermore, a Wireless Body Area Network (WBAN) was developed for this sensor platform to manage data transfer among devices and the internet. The WBAN coordinator controls the sensor devices and collects and stores the measured data. The collected data is particular to individuals and can be shared with physicians, emergency systems or athletes' coaches. Long-time monitoring of activity and potassium concentration in urine can help maintain the appropriate water intake of elderly people or athletes and to send warning signals in the case of near dehydration. The created sensor system was calibrated and tested in laboratory and real conditions as well. The measurement results are discussed.A non-invasive solution for monitoring of the activity and dehydration of organisms is proposed in the work. For this purpose, a wireless standalone chemical sensor platform using two separate measurement techniques has been developed. The first approach for activity monitoring is based on humidity measurement. Our solution uses new humidity sensor based on a nanostructured TiO From this point of view, interest in wearable portable and hand-held sensors to provide health monitoring functions has increased in the last decades. These sensors are currently in the form of developmental point of care platforms. A number of such sensors with a controlling device can be integrated as a wearable Wireless Body Area Network (WBAN), which can be used for computer-assisted monitoring of chronic diseases, diabetes, asthma, heart attacks or dehydration state as well –8.Water is the most important substance for the human organism and the quantity of fluids influences the correct function of all body cells . The watDehydration of the organism leads to disruption of the cells and brain work and reduces the functioning of metabolic processes. The first symptoms of dehydration appear at the loss of about 2% of the body fluids ,10. Exisetc. [in-situ or wearable sensors, e.g., for human biological processes monitoring [2 films [Sweating process monitoring can be interpreted as a personal activity and it can be determined through the measurements of humidity level close to skin surface as perspiration rate. Activity is also related to water metabolism and it can impact dehydration significantly, but it is difficult to determine dehydration from these data. Therefore, an activity monitor is an additional sensor helping to better understand data from urine sensor and giving feedback to a person in time to avoid dehydration. The sensor should be safe for human body and stable in a salt atmosphere during a long period of time . Metal oxide semiconductor sensors, which also have fast response time, low drift of the parameters and don't have hysteresis, meet these requirements –22. Receetc. –22. Nanonitoring –25 closenitoring ,27, nanonitoring ,29, nanonitoring , nanocomnitoring –33, micr[2 films , titaniu[2 films , nanopow[2 films ,37, nano[2 films  and nano[2 films  or sol-g[2 films  techniqu2 sensor was developed. This sensor has increased sensitivity in the high humidity conditions which occur near the human skin. It uses sensitive element based on array of titanium oxide nanopillars formed by an electrochemical anodizing method.In this work, we propose and develop a sensor platform for non-invasive dehydration detection and monitoring. It is extremely important for elderly people or athletes to prevent serious health problems or sudden death . The pla2 sensor for relative humidity measurement, is innovative. Therefore, the major part of this article is primarily focused on TiO2 sensor development and fabrication due to its novelty and benefits.The concept of wireless sensor platform which combines mentioned sensors for this purpose, as well newly developed TiO2.2.1.The dehydration monitoring system is based on an electrode sensitive to potassium and a device for measurement and wireless data transfer. Potassium concentration is measured by a standard potassium ion selective electrode obtained from Elektrochemické detektory s.r.o.  with potentiometric output according to the calibration curve. The voltage is converted into data values in the form of digital numbers by a standalone wireless battery powered electronic circuit after each measurement see . The meaThe potassium ion selective electrode had been conditioned before use in a 0.5 mmol/L KCl  aqueous solution for 1 h. The calibration of the system was performed using KCl solutions with a concentration in the range between 1 mg/L and 10 g/L with addition of urea in the concentrations of 0%, 0.5%, 1%, 1.5% and 2% . All so2.2.The activity monitor is based on determination of skin perspiration rates during daily activities. Sweating depends on the effort expended in activities. Humidity close to the skin increases with the effort of the person and ambient conditions. It is necessary to have two humidity and two temperature sensors with a certain distance between them and the skin in measurements to calculate perspiration rate.2/h), calculated with a well-known mathematical model [S·(dm/dt) is the evaporation rate (g/m2/h), D′ is the constant 0.67 × 10−3 (g/m/h·Pa), (∂p/∂x) is the vapor pressure gradient in (Pa/m). From this equation, we can calculate the rate of sweat evaporation close to the skin surface and then interpolate the total amount of evaporated water as the result of integration over time.The water transport through the skin, the so called transepidermal water loss  was used for temperature stabilization of the anodization process. Millipore water was used for the preparation of electrolytes and sample washing. Anodization of aluminum and titanium layers was performed in a 0.9 M aqueous solution of oxalic acid in the galvanic static mode with the current density of 4 mA/cm2 and the voltage of 30 V on stationary stage of porous alumina growing. When the anodization front reached the titanium underlayer and all aluminum was fully consumed, the anodization voltage began to increase and its growth continued up to a certain limited value at 37 V. Then the anodizing mode was automatically switched to the constant voltage mode for electrochemical anodization of titanium underlayer to continue. The titanium anodization process took about 40 min. After reaching the constant minimum value of anode current (less than 50 μA/cm2) [The nanostructured TiO μA/cm2)  the proc3, 35 mL/L H3PO4 solution kept at 65 °C for 15 min thus opening the array of titanium oxide nanopillars. A photoresist mask for the formation of gold electrodes that provide electrical contact to the sensor structure was prepared by photolithographic techniques on the surface of Ti/TiO2 layer. The mask was made in the form of an inter-digital structure with an electrode width of 100 microns and spacing of 50 microns  close to the skin surface at a distance of 5–7 mm (skin RH sensor). The second commercial resistive humidity sensor HS-15P is located on the opposite side of the sensing unit. This sensor was intended to measure ambient relative humidity (ambient RH sensor). The DS18B20U sensor with digital output has been used for skin temperature measurements. All components of the sensing unit are integrated in the box, which can be fixed on the arm of the person  with an operation voltage between 15 and 25 keV. X-ray diffraction (XRD) analysis was performed at the Department of Condensed Matter Physics  using a laboratory assembled diffractometer equipped with Cu X-ray tube, Siemens high voltage generator, Soller slit, graphite monochromator, and a Radicon scintillation detector. Before analysis, all samples were washed in flowing Millipore water for a few minutes three times and then dried in a stream of warm air.The surface and cross section morphology of the nanostructured TiO2 (RH of 33%), K2CO3 (RH of 43%), Mg(NO3)2 (RH of 57%), NaCl (RH of 75%), KCl (RH of 85%), and K2SO4 (RH of 97%) [2 sensors were aged in the atmosphere of 97% RH vapor for 8 h.Relative humidity (RH) measurements of the developed nanostructured sensor were done by using saturated salts solutions providing stable air humidity near the surface. These solutions include: LiCl (relative humidity (RH) of 11%), MgCl of 97%) . The sen2 and commercial HS-15P) by using saturated salt solutions. After the calibration, necessary adjustment of electronics was done because of different impedance values of the new and commercial sensors. Then, the portable part of the system was tested with the help of four volunteers during standard life activity and sport exercises. During testing each volunteer wore the perspiration sensor module on the arm  × 1010 pil/cm2. Each pillar has a smaller lower part diameter and a bigger upper part diameter as seen from cross section image  all crystals were not transformed from the anatase to the rutile phase configuration. The interatomic d-spacing measurements also revealed that the size of the spacing of the main TiO0 nm see . These d3.3.2 sensor were performed in a closed chamber filled with saturated salt solutions in the range of humidity from 11% to 97% according to the methodology described above (Section 2.4). A special electronic module was developed for conversion of sensor impedance value into a voltage signal changing from 3 V to 0 V. The maximum of the signal corresponds to the minimal value of RH data and vice versa the minimum of the voltage signal matches the maximum RH value. The results of RH measurements for fabricated TiO2 sensors are shown in The relative humidity (RH) measurements of TiO2 based sensors are presented in the Responses of three individual TiO2O molecule adsorbed in a vacancy would provide a geometrically particularly well-suited adsorption site for O–H interaction and dissociation. The nanostructured morphology of the sensing layer offers more possibilities for the formation of oxygen vacancies which helps improve the adsorption-desorption process as well. Adsorption of water molecules is going on in a few layers and the growth of a multilayer provides the formation of hydronium ions. Hydronium ion interactions between the absorbed species and the bridging oxygen atoms of the TiO2 sensing layer are expected to facilitate proton transfer with a corresponding increase of electrical conductivity. This process is reversible at room temperature and depends on the humidity level of ambient air, which means that when the humidity level rises a higher concentration of mobile protons increases the electrical conductivity [The sensing mechanism of the semiconducting titanium oxide is based on the adsorption of the surrounding water molecules by the nanomorphology surfaces. Adsorption occurs at exposed fivefold coordinated Ti sites in each case with the hydrogen atoms pointing away from the surface. An Huctivity ,45,46.3.4.2 based and commercial HS-15P, ) was done using saturated salt solutions (see Section 2.4). The calibration results presented in 2-based sensor has a better sensitivity in the higher humidity region and the commercial HS-15P sensor has lower sensitivity balanced in the whole studied humidity range.Before testing the whole wearable system, the calibration of both humidity sensors  were detected during one month after calibration. In the case of the commercial sensor the maximum error was determined to be about 4% RH in the whole range. Calibration constants were determined for the sensors and these values were actualized in the perspiration sensor device.The TiOents see . For ambThe measured current consumption of the perspiration sensor module is shown in 2 skin sensor, the red line corresponds to data obtained from the commercial ambient sensor and the green line corresponds to the water loss calculation.A typical measurement water loss diagram for a male volunteer during an 8-h period can be seen in 2 skin surfaces showed losses of 740 mL of fluids by body perspiration for the 8-h testing time. The skin surface area can be set in the system software according to the age, gender and physical features of the person.Both sensors (skin and ambient) show a high RH value for the male volunteer  during tThe female volunteer  had an aThe analysis of water loss figures showed some influence of the ambient RH sensor from the volunteer sweating during long sport activities. It depends on the distance between the ambient and skin sensors, which is 1.5 cm. However, during long perspiration periods the relative humidity level of the ambient air on the distance of about 2–3 cm around human body can increase. It can be seen from the values of ambient sensor , stationary computer or hospital server, and sent through any network to medical specialists for monitoring and analysis of water balance (metabolism) of the organism.2 layer consists mostly of a crystalline rutile phase, constructed to ensure fast adsorption—desorption process of water molecules. Based on electrochemical technology, as well as with the use of microelectronic methods, a prototype of the planar relative humidity sensor has been designed and manufactured. The conversion from impedance to the voltage signal of sensor response has linear characteristics with a low response time in the range of relative humidity from 33% to 97%.A special designed nanostructured titanium oxide sensing layer, fabricated by anodization techniques, was used for measurements of relative humidity level near the human skin surface. The semiconducting TiOThe obtained results are promising for further applications in different fields such as fitness, medical or military services and the fabricated system has a low cost and high efficiency.


Tunable band-stop filters based on graphene with periodically modulated chemical potentials are proposed. Periodic graphene can be considered as a plasmonic crystal. Its energy band diagram is analyzed, which clearly shows a blue shift of the forbidden band with increasing chemical potential. Structural design and optimization are performed by an effective-index-based transfer matrix method, which is confirmed by numerical simulations. The center frequency of the filter can be tuned in a range from 37 to 53 THz based on the electrical tunability of graphene, while the modulation depth (−26 dB) and the bandwidth (3.1 THz) of the filter remain unchanged. Specifically, the bandwidth and modulation depth of the filters can be flexibly preset by adjusting the chemical potential ratio and the period number. The length of the filter (~750 nm) is only 1/9 of the operating wavelength in vacuum, which makes the filter a good choice for compact on-chip applications. Graphene, a monolayer of carbon atoms arranged in a two-dimensional honeycomb lattice, has attracted much attentions in recent years for its constant light absorption13479919202223252728Plasmonic filters are essential for information processing systems and have been widely investigated3031323331et al. proposed a wavelength selector by coupling a graphene ribbon with a graphene disket al. proposed to place a uniformly doped graphene monolayer on a silicon gratinget al. proposed a free-standing periodically-stacked graphene nanoribbon waveguide with patterned chemical potentialBand-stop filters that selectively eliminate undesired information and suppress interfering signals, play an important role in broadband communications and information storageIn this report, we propose a type of tunable band-stop filters based on graphene monolayers with periodically modulated chemical potential that can be treated as graphene plasmonic crystals (GPCs). Investigating the energy band diagram of the GPC, one can find a blue shift of the forbidden band with increasing chemical potential. An effective-index-based transfer matrix method (EIB-TMM) is adopted to calculate the transmission and optimize the design of the GPC filter, which are in good agreement with our numerical simulations. Such a method can greatly promote the efficiency of calculations. The center frequency of the filter can be tuned from 37 to 53 THz with a stable modulation depth as high as −26 dB and a fixed bandwidth (3.1 THz) based on the electrical tunability of graphene. Bandwidth and modulation depth can be preset freely by adjusting the chemical potential ratio and the period number. The length of the filter is only 750 nm, just 1/9 of the operating wavelength in vacuum, which makes it a very good candidate for integrated plasmonic devices.The dispersion relation of the GPs in a graphene sheet can be described as the quasi-static form41σg is the complex surface conductivity of the graphene monolayer, εeff is the effective environment permittivity and neff = β/k0 is the effective refractive index for the GP mode which is inversely proportional to σg.where σg of a graphene monolayer is described by the Kubo formulation42σg = σintra + σinter, where σintra corresponds to the intraband electron-phonon scatteringIn the THz frequency region, the complex surface conductivity σinter is given byand the interband transition contribution e is the elementary charge, kB is Boltzmann’s constant, T is the ambient temperature, ħ is the reduced Planck constant, ω is the photon frequency, n and vf are the charge density and the Femi velocity of the graphene respectively, and μ of graphene on a silica substrate could reach 40000 cm2V−1s−1 at room temperature2V−1s−1. To improve the credibility of the calculation results, 10000 cm2V−1s−1 is adopted as the carrier mobility in our studyHere μc is the only variable of neff for a specific GP mode. A graphene monolayer with a periodic μc acts as a GPC. When broadband GPs, which can be excited by tip scattering couplingd1 and d2 have different chemical potentials under a backgate bias voltage. The silica layer not only couples with the graphene but also ensures the tuning feasibility of the chemical potential of graphene. When a gate voltage is applied to the device, the charge density of the graphene is inversely proportional to the thickness of the silica layer d asεd is the permittivity of silica. Thus the chemical potential ratio r = μc2/μc1 between two regions is equal to d2 is fixed at 130 nm and r is regulated by d1. The permittivity of silica is assumed as 3.9 and the period of the GPC is D = 2w = 50 nm. It is worth emphasizing that the influence of the silicon grating on the GPs could be eliminated since the thickness of the silica layer is always larger than 100 nm.According to r = 1.25. Bloch wave vector reaches a maximum on both edges of the forbidden band and decreases as frequencies are away from the forbidden band. As shown in μc1. Larger μc1 causes wider bandwidths for the allowed and the forbidden bands. In particular, high-order forbidden bands appear when μc1 is small enough.By using the characteristic equation (see methods), we can calculate the forbidden band of the GPC as shown in N can be described as4546The EIB-TMM is adopted to calculate the transmission and optimize the design of the GPC filters. When the GPs propagate along the graphene, reflection and transmission will occur at each interface. As an analogy of a one dimensional photonic crystal, the transfer matrix of the GPC with a period number δj = k0neff,jw and j = 1, 2). The transmission of the GPs is47where where N = 15 are shown in μc1 increases from 0.3 to 0.6 eV, the center frequency experiences a blue shift from 37 to 53 THz, showing a 16 THz tunability range. Particularly, the modulation depth and the bandwidth in the tuning process remain approximately stable around −26 dB and 3.1 THz, respectively. The flexible tunability, stable modulation depth and bandwidth greatly enhance the application potential of such band-stop filters. We notice that a high-order stop band appears in the transmission spectrum when μc1 is 0.3 eV, which is attributed to the high-order forbidden band of the GPC mentioned above.Transmission spectra with the same parameters as in E|2) distributions (side view) at the pass band and the stop band frequencies of the filter with μc1 = 0.4 eV are shown in Near-field intensity .


This research is the first empirical attempt to calculate the various components of the hidden bias associated with the sampling strategies routinely-used in human genetics, with special reference to surname-based strategies. We reconstructed surname distributions of 26 Italian communities with different demographic features across the last six centuries (years 1447–2001). The degree of overlapping between "reference founding core" distributions and the distributions obtained from sampling the present day communities by probabilistic and selective methods was quantified under different conditions and models. When taking into account only one individual per surname (low kinship model), the average discrepancy was 59.5%, with a peak of 84% by random sampling. When multiple individuals per surname were considered (high kinship model), the discrepancy decreased by 8–30% at the cost of a larger variance. Criteria aimed at maximizing locally-spread patrilineages and long-term residency appeared to be affected by recent gene flows much more than expected. Selection of the more frequent family names following low kinship criteria proved to be a suitable approach only for historically stable communities. In any other case true random sampling, despite its high variance, did not return more biased estimates than other selective methods. Our results indicate that the sampling of individuals bearing historically documented surnames (founders' method) should be applied, especially when studying the male-specific genome, to prevent an over-stratification of ancient and recent genetic components that heavily biases inferences and statistics. The question of how representative is a sample of a given population is particularly critical in human genetic research, where data collection is strongly affected by ethical and social factors. The choice of the sampling strategy can affect the estimation of a number of relevant parameters and, accordingly, the inferences one can make about either the groups or the genetic variants under study. The ideal goal is to achieve the best compromise among recruitment costs, statistical power and representativeness. To make a sample an unbiased proxy of the underlying population, either for genetic screening, genotype-phenotype association studies or evolutionary reconstructions, its composition should minimize close kinship, ambiguous individual ancestry assignments, and the side effects of population stratification.Most of present-day human populations have experienced recent admixture to some extent  and geneUsing surnames to select research subjects has the advantage that family names are cultural markers typically transmitted from fathers to sons in most human societies. The distributions and mode of inheritance of surnames mirror the non-recombinant markers of the male specific regions of the Y chromosome (MSY). The main difference between surnames and MSY sequences is the nature of the transmitted units which are predominantly, if not exclusively, identical by descent for MSY markers and identical by state (polyphyly) other than by descent (monophyly) for surnames. In addition, the depth of the genealogical reconstruction is largely unbounded for MSY markers, while for surnames it is limited to the time since such family names have been stabilized as markers of inheritance (around 1200–1800 AD in Western societies). Such differences have been invoked to explain deviations from neutral expectations when surnames were used to estimate consanguinity or gene propagation , 10. NonA number of reasons makes the Italian population an ideal case-study for surnames-related research: Italians show one of the highest surname diversity in the world  with a mThe present work aims at first comparing different surname-based sampling strategies, to estimate the bias associated with each method. In order to do this, we reconstructed the surname distributions of 26 Italian communities with different demography in the time interval encompassing the 1447–2001 AD. The degree of overlapping between “reference core” surname distributions, obtained from analyzing the oldest historical frames, and the distributions obtained from sampling present-day surnames by probabilistic (random) and selective  methods was quantified at different geographic scales . Whenever possible, jackknife re-sampling and comparisons between different data sources and models, with low and high levels of kinship, were applied to weigh the various sources of the sampling bias.Twenty-six Italian communities belonging to 11 provinces and 8 regions were analyzed : four ofStato delle anime), baptismal , and marriage  sacramental registers. The present-day distributions of surnames from the same communities were extracted from the digitalized versions of the 1993 complete national phone directory [We reconstructed the earlier distributions of surnames from either three kinds of historical records: census , single-digit mismatches (i.e. “Marino/Marini”) and double surnames (i.e. “Albertini Marchesani = Albertini”). In presence of doubtful cases, a stringent criterium was adopted in order to minimize the bias due to mutational events . Overall, such a method tends to inflate the degree of overlapping between “founding” and present-day distributions and, hence, to underestimate the sampling bias. The lemmatization process was applied separately to each community. The complete database is provided in In order to validate the use of different sources, as either historical or recent references, we recovered and compared the surname distributions from SEAT and ISTAT records in the community of Cerchio , as well the surname distributions from marriage and baptismal acts in the community of Montecarlo .x is the number of the k surnames which are in common between the historical and current repository and Nk is the size of the current repository. SDB ranges from 1, no surname shared, to 0, all the surnames of the current repository are shared with the historical repository. A “low-kinship” (LK) model, namely when only one individual per surname was considered, and a “high-kinship” model (HK), when using the entire set of surnames and their bearers, were applied to each pairwise comparison. Under HK, k was intended as the total number of surnames, allowing multiple counts for the same type; under LK, k was intended as the number of different surnames, one for type. Being our null hypothesis the adhesion of the sampled surnames to the oldest surname distribution of each community, as occurs when collecting according to the founding surnames method, the SDB rate expectation is zero under both models.For each strategy we measured the sampling-dependent bias (SDB) according to the formula:To estimate how far the departures of SDB from zero are exclusively due to genetic drift we simulated the evolution of the 26 studied communities under both a growth (observed relative growth rates) and a stationary model (null growth rate) by the Markov chain Monte Carlo method implemented in the software ASHEs , 17. ForTo estimate how far SDB is affected by sample size, we performed a total of 201 jackknife re-samplings of twenty, fifty and, when possible, one hundred individuals out of every dataset, using PopTools version 3.2.5 .STATISTICA v. 6.0  and XLSTAT (Addinsoft) were utilized to perform the Chi-square tests, the correlation analyses and to create graphics.When simulating by the random sampling criterion (R), the entire list of surnames of the recent repository (SEAT or ISTAT) was considered as starting set. When selecting samples by a spatial distribution criterion , we chose only those surnames whose geographic origin was unambiguously centered within a single province (the metropolises Milan and Rome excluded), as shown in the SEAT 1993-derived GENS database [2 = 0.87, P<0.01 and R2 = 0.82, P<0.01 respectively) and did not differ significantly . The fact that Cerchio and Montecarlo are communities with intermediate size and growth rate would suggest that, for most of the investigated communities, the availability of data sources exerted a negligible effect on the estimate of the intrinsic bias (SDB).Bivariate analyses of present-day surname lists obtained from ISTAT (2001) and SEAT (1993) records in the community of Cerchio  and of “As a rule, the comparisons between “founder” and present-day lists of surnames showed a low level of concordance independently of the applied sampling strategy and the kinship model . RegardiThe percentage of shared surnames sampled with a random strategy (R) was predictably low under a LK model  as well as under a HK model . Instead, it was somewhat surprising to observe the same features when applying the grandparents’ criterion (GP): surnames sharing ranged from 3 to 47% (SDB = 0.53–0.97) under the LK and from 6 to 95% (SDB = 0.05–0.94) under the HK.The frequency-based criterion (FQ) showed the highest degree of uncertainty: surnames sharing, in fact, ranged from 4 to 100% (SDB = 0.00–0.96) under both the LK and the HK. The criterion based on locally-spread surnames (LS), on the other hand, showed the lowest bias: the overlapping degree varying from 22 to 65% under the LK (SDB = 0.35–0.78) and from 41 to 86% under the HK (SDB = 0.14–0.59). In this case preserved patrilineages approach the estimated proportion of “autochthony” of Italian surnames at the province level  and theSimulations performed under growth and stationary models allowed us to measure the expected bias accumulated by lineage sorting alone (genetic drift), from foundation to present times. As shown in A more accurate analysis was done by evaluating the dependence of SDB by the type of the community –S6 Figs.t) > 500 . Similarly, we found that the higher the difference between the intrinsic bias calculated under the HK and LK methods (ΔSDB), the lower the value of S/N in the “founding” list, here used as a crude estimate of early population diversity [2 = 0.35, P = 0.02), the FQ  and the GP  sampling strategies but not for the LS criterion . The same tendency was observed between ΔSDB and isonymy, here intended as the random component of inbreeding  (data not shown). Interestingly, Nonantola , despite being not geographically isolated and with a size in the order of thousands, showed the highest ΔSDB when sampling by the FQ criterion. In this case, the retention of frequency-based surname legacies is more easily explained by its hosting a “Partecipanza”, a social-economic entity where rights over common lands have been long transmitted strictly following residency and patrilineal genealogies [A second observation is the generally lower SDB values scored using HK compared to LK sampling criteria, with a more pronounced trend in small communities. The drop of SDB was significantly lower in communities with present-day size  and, vice versa, overestimates SDB in regions represented by large open cities (Apulia). Missing or overabundance of data prevented us to extend the analysis to higher levels than municipality, respectively for the GP and LS method. Nonetheless, a breakdown of SDB is expected when locally spread surnames are assigned at the regional and, of course, at the Country level.When the sampling bias was calculated at the level of mid (region) and macro (Country) area, the overall patterns observed at the municipality level held for the R and FQ sampling methods under both the LK and HK models (data not shown). Deviations are mainly due to the proportion of closed The mean values of the percentage of “founder” surnames (1-SDB), calculated after randomly re-sampling twenty, fifty and one hundred individuals out of the complete list of present-day surnames, were not appreciably different under the LK  and HK  models. However, the range of values decreased geometrically by increasing the sample size.The outputs of random Jackknife resampling for the S/N parameter are shown in The identification of the most reliable sampling strategy, among the many available for human genetic studies, could be of great utility. Conversely, an improper collection of samples from the population may introduce hidden confounding factors. With this perspective, we calculated the various sources of bias associated with common methods of sample recruitment: those employing family names as ancestry markers. Sampling by surnames is in fact one of the most accurate and cost-efficient ways to assess the genetic composition of historical populations, despite the fact that family names behave as a single locus transmitted along only one parental lineage, and the fact that mismatches are expected in Y-DNAs due to illegitimate paternities and adoptions .A main result of our analyses is that the fidelity to the ancestral composition of the population (measured from 1447–1775) by samples selected from current lists of surnames is variable but generally low whatever is the size of the sample, the selection strategy, the primary source of data, the geographic scale, or type of the community. As expected, lineage sorting accounts for the deviations from fidelity only partially and in very closed communities.Despite the use of a relaxed lemmatization, biases lower than 40%, intending this term as the complement to one of the degree of overlapping between “founding” and present-day lists of family names (SDB), have been observed only in small mountainous hamlets as far as a close parenthood among participants was admitted (high-kinship model). The selection of unrelated donors is usually associated with a substantial increase of the bias other than to higher costs of recruitment and, in remote areas, a lower sample size. Low kinship in most cases means rates of bias much higher than 50%, unless the first quartile method is applied in stable communities where cultural  or geographic (mountain terrain) barriers preserved family names with high frequency over long periods of time.Population stratification due to recent fluctuations in allele frequencies over time thus appears a foremost level of apportionment of the overall genetic variance. While typically not recognized because of the lack of contribution of bio-demographic data to genetic sampling designs, the diachronic variance would play a crucial role in the representativeness of a population sample and, hence, to its utility in biological research.The proportion of ancestry from ancient and recent demography can vary widely between individuals, leading to step-ups of the internal structure of the population which, in turn, may easily introduce either spurious results (type I and II errors) in genetic association studies or distortions in historical and evolutionary reconstructions. The latter case has been demonstrated by Manni et al.  who founHere, we demonstrated that sampling criteria could easily affect population parameters resulting in inflated (random methods) or deflated (selective methods) estimates of diversity.The most efficient method to correct population parameters for the diachronic bias is to select individuals bearing historically documented surnames (“founders” method). Alternative but equally time-demanding methods, such as those based on surname distribution (LS) and residency (GP), are heavily influenced by recent gene flows and appeared to be efficient only in specific contexts, as macro geographic scales and alpine villages. Moreover, they generally result in a reduction of the maximum gatherable sample size down to a hundred or even less. Consequently, their use in population genetics is limited by the poor statistical power, and is very limited or impracticable in genotype-phenotype association studies. In these latter cases a truly random sampling under a HK model, despite it carrying a high SDB, is able to give samples of suitable size at affordable costs.Among the various features used to define a human community both geographically and demographically, altitude was found the best proxy of the bias inherent to most of the sampling procedures in the modern Italian population.We can conclude that sampling individuals bearing historically documented surnames should be the method of choice to buffer the stratification of ancient and recent genetic components of the sampled population. Nonetheless, the selection of “founders”, while excluding misleading results from markers of the male specific fraction of the Y chromosome, does not prevent that recent population reshufflings heavily driven by women mobility could bias inferences and statistics based on the variability at autosomal, X-chromosome and mitochondrial markers.S1 Fig(TIF)Click here for additional data file.S2 FigYellow lines, simulated SDB values with population growth; yellow diamonds, simulated SDB values with constant population size.(TIF)Click here for additional data file.S3 FigHK, high-kinship model; LK, low-kinship model.(TIF)Click here for additional data file.S4 FigHK, high-kinship model; LK, low-kinship model.(TIF)Click here for additional data file.S5 FigHK, high-kinship model; LK, low-kinship model.(TIF)Click here for additional data file.S6 FigHK, high-kinship model; LK, low-kinship model.(TIF)Click here for additional data file.S7 Fig(TIF)Click here for additional data file.S8 Fig(TIF)Click here for additional data file.S9 Fig(TIF)Click here for additional data file.S1 Dataset(XLSX)Click here for additional data file.