Well-defined Contacts Research Articles

Inside-Out Design of Zinc-Binding Proteins with Non-Native Backbones.

The de novo design of functional proteins requires specification of tertiary structure and incorporation of molecular binding sites. Here, we develop an inside-out design strategy in the molecular modeling program Rosetta that begins with amino acid side chains from one or two α-helices making well-defined contacts with a ligand. A full-sized protein is then built around the ligand by adding additional helices that promote the formation of a protein core and allow additional contacts with the ligand. The protocol was tested by designing 12 zinc-binding proteins, each with 4-5 helices. Four of the designs were folded and bound to zinc with equilibrium dissociation constants varying between 95 nM and 1.1 μM. The design with the tightest affinity for zinc, N12, adopts a unique conformation in the folded state as assessed with nuclear magnetic resonance (NMR) and the design model closely matches (backbone root-mean-square deviation (RMSD) < 1 Å) an AlphaFold model of the sequence. Retrospective analysis with AlphaFold suggests that the sequences of many of the failed designs did not encode the desired tertiary packing.

Graphene/MoSi2X4: A class of van der Waals heterojunctions with unique mechanical and optical properties and controllable electrical contacts

The key solution to achieve high-performance nano-electronic devices depends on solving the contact resistance problem at the metal–semiconductor interface. Here, we construct graphene/ MoSi2X4 (X=N, P, As) van der Waals heterojunctions and investigate their mechanical, electronic, and optical properties systematically, especially focusing on their electrical contact features. It is found that such intrinsic heterojunctions hold a low Schottky barrier height (SBH) and better electrical contact behavior. Particularly, the more ideal electrical contact can be realized by vertical strain and electric field regulations. For example, vertical strain can cause a transition between n-type and p-type Schottky contacts, even leading to a switching from p-type Schottky to p-type Ohmic contacts for graphene/MoSi2X4 (X=P, As) vdWHs, and an applied electric field can make a conversion from Schottky contacts (n-, p-type) to well-defined Ohmic contacts (n-, p-type) for all heterojunctions. Furthermore, physical regulations can induce high-concentration carrier doping in graphene, up to 1013 cm−2, under external electric field, which provides new possibility to design graphene/MoSi2X4-based high-gain transistors. And also shown is that these heterojunctions also possess a reasonable Poisson ratio and high stiffness features, robustly enough to withstand geometrical deformation and mechanical damage, indicating that they are suitable as electrode and nano-device materials.

Trends of adequate hypertensive patients from 2017 to 2019 in Portuguese Primary Health Care

BackgroundArterial hypertension (AHT) adequate monitoring implies, follow-up, non-pharmacological and pharmacological therapeutic measures in the General Practice (GP). The Primary Health Care Identity Card (BI-CSP) platform collects wide-nation data, disaggregatable down to the level of the Regional Health Administration (RHA) and the Health Centres Cluster (HCC). We intended to study the trends of the indicator ‘Proportion of hypertensive patients with adequate monitoring’, April to June, 2017 to 2020, at the nationwide total and by RHA.MethodsCross-sectional observational study, of a sample of randomised HCC of each RHA. Data from April to June, 2017 to 2020, were collected from the BI-CSP for the health indicator. Trends were calculated for 2017 to 2019, for 2017 to 2020 and for the mean of the period 2017 to 2019 and 2020, nationwide and by RHA.ResultsAt nation-wide level, a trends of Δ = +20.03 for 2017 and 2019, of Δ = -0.06 for 2017 and 2020 and of Δ = -0.18 for the mean of the triennial 2017–2019 period and 2020. At the RHA level, positive trends existed between 2017 and 2019. The trends between 2017 and 2020 were distinctively negative, more marked in the North (Δ = -27.33) but still positive for Algarve (Δ = +55.78).ConclusionsThe positive trends from 2017 to 2019 disappeared with the COVID19 pandemics. Harmful outcomes in the long term are so to be expected. RHA differences mean health inequities. Portuguese GP need new tactics to tackle the strategy of adequate control of AHT: Pro-activity in face-to-face consultations at well-defined times and distance contacts.

Schottky Contacts on Polarity-Controlled Vertical ZnO Nanorods.

Polarity-controlled growth of ZnO by chemical bath deposition provides a method for controlling the crystal orientation of vertical nanorod arrays. The ability to define the morphology and structure of the nanorods is essential to maximizing the performance of optical and electrical devices such as piezoelectric nanogenerators; however, well-defined Schottky contacts to the polar facets of the structures have yet to be explored. In this work, we demonstrate a process to fabricate metal-semiconductor-metal device structures from vertical arrays with Au contacts on the uppermost polar facets of the nanorods and show that the O-polar nanorods (∼0.44 eV) have a greater effective barrier height than the Zn-polar nanorods (∼0.37 eV). Oxygen plasma treatment is shown by cathodoluminescence spectroscopy to affect midgap defects associated with radiative emissions, which improves the Schottky contacts from weakly rectifying to strongly rectifying. Interestingly, the plasma treatment is shown to have a much greater effect in reducing the number of carriers in O-polar nanorods through quenching of the donor-type substitutional hydrogen on oxygen sites (HO) when compared to the zinc-vacancy-related hydrogen defect complexes (VZn-nH) in Zn-polar nanorods that evolve to lower-coordinated complexes. The effect on HO in the O-polar nanorods coincides with a large reduction in the visible-range defects, producing a lower conductivity and creating the larger effective barrier heights. This combination can allow radiative losses and charge leakage to be controlled, enhancing devices such as dynamic photodetectors, strain sensors, and light-emitting diodes while showing that the O-polar nanorods can outperform Zn-polar nanorods in such applications.

Determining the structure of a layer under 2D-cover: the case of Pb underneath epitaxial graphene on Ru(0001)

Intercalation of solid and molecular species underneath 2D materials is one of the hottest topics in physics and chemistry nowadays – being important from the point of view of well-defined 2D materials-metals contacts formation, as well as performing catalytic reactions under cover. The confined space available for the intercalated layer’s formation often favours unique structural arrangements which are, however, difficult to study directly using conventional surface science techniques. We used directional elastic peak electron spectroscopy (DEPES) in combination with low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) to determine the structure of a Pb layer underneath epitaxial graphene (Gr) on Ru(0001). The results reveal that Pb forms a (√7×√7)R19.1° structure underneath Gr, which is similar to that formed by Pb on clean Ru(0001). As DEPES measurements utilize conventional LEED/AES optics commonly available in surface science laboratories, our approach can be adapted by other groups for the determination of the structure of various layers under 2D-covers.

In-Situ Transmission Electron Microscopy Imaging of Aluminum Diffusion in Germanium Nanowires for the Fabrication of Sub-10 nm Ge Quantum Disks

The thermal activated solid state reaction forming aluminum–germanium nanowire (NW) heterostructures is a promising system as very sharp and well-defined one-dimensional contacts can be created bet...

Maskless Arbitrary Writing of Molecular Tunnel Junctions.

Since fabricating geometrically well-defined, noninvasive, and compliant electrical contacts over molecular monolayers is difficult, creating molecular-scale electronic devices that function in high yield with good reproducibility is challenging. Moreover, none of the previously reported methods to form organic-electrode contacts at the nanometer and micrometer scales have resulted in directly addressable contacts in an untethered form under ambient conditions without the use of cumbersome equipment and nanolithography. Here we show that in situ encapsulation of a liquid metal (eutectic Ga-In alloy) microelectrode, which is used for junction formation, with a convenient photocurable polymeric scaffold enables untethering of the electrode and direct writing of arbitrary arrays of high-yielding molecular junctions under ambient conditions in a maskless fashion. The formed junctions function in quantitative yields and can afford tunneling currents with high reproducibility; they also function at low temperatures and under bent. The results reported here promise a massively parallel printing technology to construct integrated circuits based on molecular junctions with soft top contacts.

Charge Transport through a Single Molecule of trans-1-bis-Diazofluorene [60]fullerene

Fullerenes have attracted interest for their possible applications in various electronic, biological, and optoelectronic devices. However, for efficient use in such devices, a suitable anchoring group has to be employed that forms well-defined and stable contacts with the electrodes. In this work, we propose a novel fullerene tetramalonate derivate functionalized with trans-1 4,5-diazafluorene anchoring groups. The conductance of single-molecule junctions, investigated in two different setups with the mechanically controlled break junction technique, reveals the formation of molecular junctions at three conductance levels. We attribute the conductance peaks to three binding modes of the anchoring groups to the gold electrodes. Density functional theory calculations confirm the existence of multiple binding configurations and calculated transmission functions are consistent with experimentally determined conductance values.

Temperature-Dependent Charge Transport through Individually Contacted DNA Origami-Based Au Nanowires.

DNA origami nanostructures have been used extensively as scaffolds for numerous applications such as for organizing both organic and inorganic nanomaterials, studying single molecule reactions, and fabricating photonic devices. Yet, little has been done toward the integration of DNA origami nanostructures into nanoelectronic devices. Among other challenges, the technical difficulties in producing well-defined electrical contacts between macroscopic electrodes and individual DNA origami-based nanodevices represent a serious bottleneck that hinders the thorough characterization of such devices. Therefore, in this work, we have developed a method to electrically contact individual DNA origami-based metallic nanowires using electron beam lithography. We then characterize the charge transport of such nanowires in the temperature range from room temperature down to 4.2 K. The room temperature charge transport measurements exhibit ohmic behavior, whereas at lower temperatures, multiple charge transport mechanisms such as tunneling and thermally assisted transport start to dominate. Our results confirm that charge transport along metallized DNA origami nanostructures may deviate from pure metallic behavior due to several factors including partial metallization, seed inhomogeneities, impurities, and weak electronic coupling among AuNPs. Besides, this study further elucidates the importance of variable temperature measurements for determining the dominant charge transport mechanisms for conductive nanostructures made by self-assembly approaches.

Effect of electron injection in copper-contacted graphene nanoribbons

For practical electronic device applications of graphene nanoribbons (GNRs), it is essential to have abrupt and well-defined contacts between the ribbon and the adjacent metal lead. By analogy with graphene, these contacts can induce electron or hole doping, which may significantly affect the I/V characteristics of the device. Cu is among the most popular metals of choice for contact materials. In this study, we investigate the effect of in situ intercalation of Cu on the electronic structure of atomically precise, spatially aligned armchair GNRs of width N = 7 (7-AGNRs) fabricated via a bottom-up method on the Au(788) surface. Scanning tunneling microscopy data reveal that the complete intercalation of about one monolayer of Cu under 7-AGNRs can be facilitated by gentle annealing of the sample at 80 °C. Angle-resolved photoemission spectroscopy (ARPES) data clearly reflect the one-dimensional character of the 7-AGNR band dispersion before and after intercalation. Moreover, ARPES and core-level photoemission results show that intercalation of Cu leads to significant electron injection into the nanoribbons, which causes a pronounced downshift of the valence and conduction bands of the GNR with respect to the Fermi energy (ΔE ~ 0.5 eV). As demonstrated by ARPES and X-ray absorption spectroscopy measurements, the effect of Cu intercalation is restricted to n-doping only, without considerable modification of the band structure of the GNRs. Post-annealing of the 7-AGNRs/Cu/Au(788) system at 200 °C activates the diffusion of Cu into Au and the formation of a Cu-rich surface Au layer. Alloying of intercalated Cu leads to the recovery of the initial position of GNR-related bands with respect to the Fermi energy (EF), thus, proving the tunability of the induced n-doping. [Figure not available: see fulltext.] (Less)

Selective Localization of Shanks to VGLUT1-Positive Excitatory Synapses in the Mouse Hippocampus.

Members of the Shank family of multidomain proteins (Shank1, Shank2, and Shank3) are core components of the postsynaptic density (PSD) of excitatory synapses. At synaptic sites Shanks serve as scaffolding molecules that cluster neurotransmitter receptors as well as cell adhesion molecules attaching them to the actin cytoskeleton. In this study we investigated the synapse specific localization of Shank1-3 and focused on well-defined synaptic contacts within the hippocampal formation. We found that all three family members are present only at VGLUT1-positive synapses, which is particularly visible at mossy fiber contacts. No costaining was found at VGLUT2-positive contacts indicating that the molecular organization of VGLUT2-associated PSDs diverges from classical VGLUT1-positive excitatory contacts in the hippocampus. In light of SHANK mutations in neuropsychiatric disorders, this study indicates which glutamatergic networks within the hippocampus will be primarily affected by shankopathies.

Solution Structure of a Nonribosomal Peptide Synthetase Carrier Protein Loaded with Its Substrate Reveals Transient, Well-Defined Contacts.

Nonribosomal peptide synthetases (NRPSs) are microbial enzymes that produce a wealth of important natural products by condensing substrates in an assembly line manner. The proper sequence of substrates is obtained by tethering them to phosphopantetheinyl arms of holo carrier proteins (CPs) via a thioester bond. CPs in holo and substrate-loaded forms visit NRPS catalytic domains in a series of transient interactions. A lack of structural information on substrate-loaded carrier proteins has hindered our understanding of NRPS synthesis. Here, we present the first structure of an NRPS aryl carrier protein loaded with its substrate via a native thioester bond, together with the structure of its holo form. We also present the first quantification of NRPS CP backbone dynamics. Our results indicate that prosthetic moieties in both holo and loaded forms are in contact with the protein core, but they also sample states in which they are disordered and extend in solution. We observe that substrate loading induces a large conformational change in the phosphopantetheinyl arm, thereby modulating surfaces accessible for binding to other domains. Our results are discussed in the context of NRPS domain interactions.

Measuring and Modeling Flash Temperatures at Magnetic Recording Head–Disk Interfaces for Well-Defined Asperity Contacts

High-speed impacts of magnetic recording heads with small asperity defects on disk surfaces have long been a major source for reliability failures for disk drives. Consequently, determining the contacting stresses and flash temperatures that occur during these impacts is an important step toward understanding the wear and eventual failure mechanisms associated with these impacts. Here we report measurements and modeling of the flash temperatures that occur when a magnetic recording head impacts an asperity at disk-drive-like conditions (at speeds 9–15 m/s and with a few nanometers of interference). The asperities considered here have a well-defined shape with radii of curvature at their summits = 100–200 µm. One surprising result of our measurements is that the flash temperature does not increase monotonically with increasing interference, which would be expected if the flash temperature is solely from frictional heating. To explain this result, we have developed an analytical model where, in addition to frictional heating, we include the effect of contact cooling through the contact zone of the heat generated by the thermal contact sensor and the heater used for clearance control. From this modeling, we are able to estimate that fairly high coefficients of friction (µ = 0.8–3.9) occur between the magnetic recording heads and these types of asperities. These results provide not only precise understanding of the flash temperatures generated by high-speed impacts with asperities, but also insight into the contact stresses and potential wear mechanisms that occur during these contacts.

Nanoscale resistive switching memory device composed of NiO nanodot and graphene nanoribbon nanogap electrodes

We report a nanoscale resistive random access memory (RRAM) device consisting of a NiO nanodot and graphene nanoribbon (GNR) nanogap electrodes. The GNR nanogap was established by an electroburning process induced by applying voltage ramp stress between the two ends of the GNR. A NiO nanodot was then deposited between the nanogapped GNR electrodes by an elaborately controllable dip pen lithography method using a nickel carbonate [Ni2(CO3)(OH)2] solution. The nanoscale GNR/NiO/GNR RRAM device exhibited reliable unipolar resistive switching characteristics with low SET/RESET voltages and currents, which might be the result of its miniaturized size and well-defined Ohmic contacts between the NiO nanodot and GNR electrodes.

Suppression of electron–vibron coupling in graphene nanoribbons contacted via a single atom

Graphene nanostructures, where quantum confinement opens an energy gap in the band structure, hold promise for future electronic devices. To realize the full potential of these materials, atomic-scale control over the contacts to graphene and the graphene nanostructure forming the active part of the device is required. The contacts should have a high transmission and yet not modify the electronic properties of the active region significantly to maintain the potentially exciting physics offered by the nanoscale honeycomb lattice. Here we show how contacting an atomically well-defined graphene nanoribbon to a metallic lead by a chemical bond via only one atom significantly influences the charge transport through the graphene nanoribbon but does not affect its electronic structure. Specifically, we find that creating well-defined contacts can suppress inelastic transport channels.

Upper Paleozoic coal measures and unconventional natural gas systems of the Ordos Basin, China

Upper Paleozoic coal measures in the Ordos Basin consist of dark mudstone and coal beds and are important source rocks for gas generation. Gas accumulations include coal-bed methane (CBM), tight gas and conventional gas in different structural areas. CBM accumulations are mainly distributed in the marginal area of the Ordos Basin, and are estimated at 3.5 × 1012 m3. Tight gas accumulations exist in the middle part of the Yishan Slope area, previously regarded as the basin-centered gas system and now considered as stratigraphic lithologic gas reservoirs. This paper reviews the characteristics of tight gas accumulations: poor physical properties (porosity < 8%, permeability < 0.85 × 10−3 μm2), abnormal pressure and the absence of well-defined gas water contacts. CBM is a self-generation and self-reservoir, while gas derived from coal measures migrates only for a short distance to accumulate in a tight reservoir and is termed near-generation and near-reservoir. Both CBM and tight gas systems require source rocks with a strong gas generation ability that extends together over wide area. However, the producing area of the two systems may be significantly different.

Atypical Self-Activation of Ga Dopant for Ge Nanowire Devices

In this Letter we report the atypical self-activation of gallium (Ga) implanted by focused ion beam (FIB) into germanium nanowires (Ge-NWs). By FIB implantation of 30 keV Ga(+) ions at room temperature, the Ge-NW conductivity increases up to 3 orders of magnitude with increasing ion fluence. Cu(3)Ge heterostructures were formed by diffusion to ensure well-defined contacts to the NW and enable two point I/V measurements. Additional four point measurements prove that the conductivity enhancement emerges from the modification of the wires themselves and not from contact property modifications. The Ga distribution in the implanted Ge-NWs was measured using atom probe tomography. For high ion fluences, and beginning amorphization of the NWs, the conductivity decreases exponentially. Temperature dependent conductivity measurements show strong evidence for an in situ doping of the Ge-NWs without any further annealing. Finally the feasibility of improving the device performance of top-gated Ge-NW MOSFETs by FIB implantation was shown.

Single-Molecule Conductance of Pyridine-Terminated Dithienylethene Switch Molecules

We have investigated the conductance of individual optically switchable dithienylethene molecules in both their conducting closed configuration and nonconducting open configuration, using the technique of repeatedly formed break-junctions. We employed pyridine groups to link the molecules to gold electrodes in order to achieve relatively well-defined molecular contacts and stable conductance. For the closed form of each molecule, we observed a peak in the conductance histogram constructed without any data selection, allowing us to determine the conductance of the fully stretched molecules. For two different dithienylethene derivatives, these closed-configuration conductances were (3.3 ± 0.5) × 10(-5)G(0) and (1.5 ± 0.5) × 10(-6)G(0), where G(0) is the conductance quantum. For the open configuration of the molecules, the existence of electrical conduction via the molecule was evident in traces of conductance versus junction displacement, but the conductance of the fully stretched molecules was less than the noise floor of our measurement. We can set a lower limit of 30 for the on/off ratio for the simplest dithienylethene derivative we have investigated. Density functional theory calculations predict an on/off ratio consistent with this result.

Geoperspective Oil and Gas in the Netherlands – Is there a future?

AbstractThe impact of oil and, in particular, gas fields discovered in the Dutch subsurface has been very significant. However, 50 years after the discovery of the giant Groningen gas field the Netherlands has become very mature for exploration of oil and gas, and the gas volume left to be discovered in conventional traps is insignificant compared to what has been found already. The total portfolio of conventional prospects held by the industry contains several 100s of billions of cubic metres (bcm), as reported by the Ministry of Economic Affairs, but many of these prospects are unattractive to drill because of their small size or other geologically unfavourable aspects. Hence, for planning purposes of future national gas production the risk should be taken into account that the size of the conventional portfolio is overestimated. The major E&amp;P companies have reduced their exploration efforts and the number of wells drilled as well as the size and total volume of discovered gas reserves has seen a steady decline over the last 10 years. Some surprises may still be in store and can occasionally add a welcome addition of gas. But the follow-up potential of new play and trapping concepts has been disappointing for many years now, and it is concluded that this is unlikely to be different in the future. Remaining conventional discoveries will mainly be in small near-field targets that as a result of technological advances made in the last few decades can be drilled with high confidence, despite their small volumes.This leaves the so-called unconventional gas (UG) resources for a real and significant increase in the exploration potential of the Netherlands. UG resources occur outside conventional structural or stratigraphic traps in tight (low permeability) rocks and are of regional or sub-regional extent, without well-defined hydrocarbon-water contacts. The potential for Basin Centred Gas, Shale Gas and Coal Bed Methane is reviewed. As, according to present-day technology, development of UG requires very dense drilling at low costs with well spacing of a few 100s of metres, only the onshore potential can be commercial, even in the longer term.Recent geological uplift is a characteristic for all North American commercial UG developments. Uplift helps bringing the resources close to the surface and facilitates development of fractures, which are essential for achieving commercial flow rates. This significantly reduces the area where commercial UG resources may occur in the Netherlands. In addition, sweet spots, where commercial flow rates and ultimate recovery per well can be achieved, represent only a fraction of the total ‘play area’. The UG plays in the Dutch subsurface remain to be proven, and there is still a significant technical risk associated with these plays, on top of the commercial risk. Therefore, despite potentially enormous in-place gas volumes in these unconventional plays, recoverable volumes are much less. If UG resources can be proven and are commercially developable, their cumulative volume potential is estimated by us in the order of a few tens to one or two hundreds bcm of recoverable gas at best. Finally, as UG resources produce at very low rates and require large numbers of wells to develop, the environmental impact in a densely populated country like the Netherlands is enormous, and needs to be seriously considered, already in the exploration phase.In a mature area like the Netherlands, industry focus should be on technology development to reduce risk, increase recovery, reduce cost and minimize surface impact. Cooperation between Operators to build multi-well campaigns is therefore strongly recommended to reduce mobilisation cost. In addition, government incentives should be targeted at the development phase, in order to increase economic attractiveness for difficult reservoirs, both conventional and unconventional. In this way State and industry will both be able to maximize their returns on the remaining potential for gas and oil in the next two to three decades.

Study of SERS Chemical Enhancement Factors Using Buffer Layer Assisted Growth of Metal Nanoparticles on Self-Assembled Monolayers

Highly controlled morphology Au nanoparticle films can be formed on the surfaces of self-assembled monolayers (SAMs) by vapor deposition at cryogenic temperatures (approximately 10 K) with intervening condensed Xe layers on the SAMs serving as a buffer to reduce the kinetic energy of the Au atoms impinging on the surface (buffer layer assisted growth or BLAG). Under these conditions pristine Au nanoparticles (AuNp) of a uniform shape and size were deposited onto two SAMs differing only by their terminal groups, 4-benzenedithiol (BDT) and 4-methylbenzenethiol (MBT), to form -S/Au and -CH(3)/Au interfaces with essentially identical AuNp overlayer morphologies. A surface enhanced Raman (SERS) enhancement factor ratio EF(BDT)/EF(MBT) of approximately 130 was observed uniformly across the surfaces (approximately <10% variation). Since equal electromagnetic contributions to the SERS enhancements are expected from the two identically structured Au overlayer films, the observed SERS intensity ratio accordingly reflects a pure chemical enhancement (CE) contribution arising from the -S/Au relative to the -CH(3)/Au interface and thereby provides the first quantitative experimental data for the magnitude of the SERS CE for well-defined Au-molecule contacts.