High Spatial Resolution 2D Imaging of Current Density and Pressure for Graphene Devices under High Pressure Using Nitrogen-Vacancy Centers in Diamond.

Current density imaging is helpful for discovering interesting electronic phenomena and understanding carrier dynamics, and by combining pressure distributions, several pressure-induced novel physics may be comprehended. In this work, noninvasive, high-resolution two-dimensional images of the current density and pressure gradient for graphene ribbon and hBN-graphene-hBN devices are explored using nitrogen-vacancy (NV) centers in diamond under high pressure. The two-dimensional vector current density is reconstructed by the vector magnetic field mapped by the near-surface NV center layer in the diamond. The current density images accurately and clearly reproduce the complicated structure and current flow of graphene under high pressure. Additionally, the spatial distribution of the pressure is simultaneously mapped, rationalizing the nonuniformity of the current density under high pressure. The current method opens a significant new avenue to investigate electronic transport and conductance variations in two-dimensional materials and electrical devices under high pressure as well as for nondestructive evaluation of semiconductor circuits.

Guiding the Formation of Metal-Organic Structures of 1,4-Diaminoanthraquinone through Surface-Based Cu Atoms.

The gradual guidance of the formation of metal-organic structures through surface-based Cu atoms for 1,4-diaminoanthraquinones (DAQs) has been studied by scanning tunneling microscopy (STM) at room temperature. On the Ag(110) surface, the transition from a hydrogen-bond network structure to metal-organic coordination structures of DAQs can be induced by introducing foreign copper atoms. Due to the weak interaction between DAQs and Ag(110), thermal treatment easily leads to the desorption of DAQs from the surface. To address this challenge, Cu(111) is selected as the substrate. Under thermal driving and in the presence of copper adatoms, the hydrogen-bond network structure of DAQs on the surface gradually undergoes a transition into a metal-coordinated structure, eventually leading to the formation of metal-organic complexes through amino dehydrogenation. It is demonstrated that the construction of a metal-organic coordination structure on metal surfaces is a result of the competition among factors such as metal atoms, functional groups of molecules, surface chemical activity, and temperature.

Phase Transitions of Naphthalene-2,3-carbonitride Steered by Solvent Effects and Metal Ion Concentration Variation.

The delicate regulation of structural phase transition can provide advanced approaches for fabricating desired and well-organized nanoarchitectures on surfaces. Introduction of metal ions into pure organic systems can facilitate the phase transition from hydrogen-bonded structures to metal-organic structures by coordinating with organic molecules. However, it remains a challenge to attain a phase transition dominated by variable metal coordination configurations through adjustment of the metal ion concentration. Herein, we report the phase transitions of naphthalene-2,3-carbonitride (2,3-DCN) molecules on highly oriented pyrolytic graphite (HOPG) under varying solvents and Cu2+ ion concentrations. By integrating data from scanning tunneling microscopy imaging and density functional theory calculations, it is demonstrated that phase transitions of 2,3-DCN occur through forming diverse coordination configurations where Cu2+ ions can coordinate with 2,3-DCN and 1-nonanoic acid or Cl- ions to form different ligand components with a coordination number of 4 when varying the molar ratios of 2,3-DCN to Cu2+ ion in the 1-nonanoic acid solvent. However, in the case of 1-heptanoic acid as a solvent, the self-assembly structure of 2,3-DCN only changes via the alteration of hydrogen bonding sites and Cu2+ ions do not coordinate with 2,3-DCN molecules. These findings provide valuable insights into the coordination behavior of metal ions in different solvents.

Insights into the Rearrangement of the Molecular Assembly Structure of 6-Aminonicotinic Acid in Its Hydrated Environment.

Water, as a ubiquitous and essential component of life, is known to have a significant impact on the structure and function of organic molecules. In this study, we investigate the role of water in the phase transition of organic molecular assembly structures by scanning tunneling microscopy at room temperature. The results show that the -O-H···O hydrogen induced by water molecules can lead to a significant structural transition in the molecular assembly, specifically through selective weakening of -C-H···O between 6-aminonicotinic acid and the formation of new -O-H···O bonds between 6-aminonicotinic acid and water molecules. Subsequent thermal treatment of these molecular assembly structures reveals that the formation of -N-H···O hydrogen bonds induced by water molecules has created a different pathway for the phase transition of the molecular assembly structure. This knowledge has important implications for the design of organic molecules with specific nanostructures that can be controlled through hydration.

Isothermal structural evolution of CL-20/HMX cocrystals under slow roasting at 190 °C.

As a new type of energetic material, cocrystal explosives demonstrate many excellent properties, such as high energy density and low sensitivity, due to the interaction between the molecules of the two components. The known decomposition temperature is 235 °C for CL-20/HMX cocrystals at a faster heating rate. CL-20 molecules could separate from the cocrystal matrix and decompose at a higher temperature, much lower than the decomposition temperature. The current work provided deep insight into the isothermal structural evolution of CL-20/HMX cocrystals with slow roasting at 190 °C. We found that the initial decomposition originates from separating CL-20 molecules from the surface along the (010) plane of the cocrystals. The gas products, such as NO2 and NO, escape from the largest exposed surface of the (010) plane and generates microbubbles and microholes. At the same time, the residual HMX molecules form δ-phase HMX crystals and shrink the volume by 72%. By increasing the time held at 190 °C, the decomposition of CL-20 molecules and recrystallization of the residual HMX molecules form a gully-like structure on the (010) plane of the CL-20/HMX cocrystal. After a long time at 190 °C, the CL-20 component completely decomposes, and all HMX molecules recrystallize in the δ-HMX form. The interaction between HMX and CL-20 molecules makes the decomposition rate of the CL-20/HMX cocrystal much slower than that of the CL-20 pure crystal with a similar decomposition activation energy during isothermal heating. This work can help to deeply understand the safety of CL-20/HMX cocrystal explosives at a temperature lower than the recognized decomposition temperature.

Three-Bit Digital Comparator Based on Intracell Diffusion of Silver Single Atom.

Using a single atom to construct electronic components is a promising route for the microminiaturization of electronic instruments. However, effective control of the intrinsic property in a molecular/atomic prototype component is full of challenges. Here, we present that the intracell diffusion behavior of a target Ag single atom within a unit cell of Si reconstruction is controllably modulated by constructing Ag nanoclusters and arrays in the neighboring cells. Moreover, a three-bit digital comparator device is fabricated on the basis of the diffusion time of a Ag single atom that can be effectively regulated by using the intercoupling between the target Ag monomer and the surrounding metal arrays.

Research of exosome in bone metastasis through dual aptamer recognition based entropy-driven amplification.

Sensitive and accurate detection of exosome will greatly facilitate the early diagnosis of diverse diseases, such as cancers. Herein, a novel dual aptamer recognition based entropy-driven amplification was established for accurate analysis of exosomes. There are two main procedures in the proposed biosensor, including dual aptamer based recognition of exosome and entropy-driven catalytic system based signal recycling. In the recognition process, designed SMBs-S1 probe and S2-S4 probe complex, containing a CD63 aptamer and an EpCAM aptamer, respectively, are utilized for cooperated identification of exosomes. S4 probe was then released from S2-S4 probe complex through chain replacement of S5. The released S4 probe triggers entropy-driven catalytic system based signal recycling and endow the method a superior sensitivity. Impressively, owing to the cooperated identification of CD63 and EpCAM protein, the method exhibited a superior specificity and stayed stable under the interference of free CD63 and/or EpCAM protein. We believe that the sensitive, accurate strategy will provide a powerful tool for multiple biomarkers analysis and related clinical applications.

Orthorhombic-to-Hexagonal Phase Transition of REF3 (RE = Sm to Lu and Y) under High Pressure.

For the famous functional REF3 family, there exist two typical structures, that is, orthorhombic phase and hexagonal phase. In the present work, high pressure behaviors of the orthorhombic phase REF3 (RE = Sm to Lu and Y) were investigated by experimental methods and first-principles calculations. The pressure-induced phase transitions of GdF3, TbF3, YbF3, and LuF3 were studied by using in situ photoluminescence measurements in the diamond anvil cell. At room temperature, all these four compounds follow the phase transition route from orthorhombic to hexagonal phase at 5.5-20.6 GPa. The pressure ranges of phase transition are 5.5-9.3, 8.4-11.9, 13.5-20.3, and 14.8-20.6 GPa for GdF3, TbF3, YbF3, and LuF3, respectively. In combination with first-principles calculations, we infer that all orthorhombic REF3 members from Sm-Lu and Y obey the same orthorhombic-to-hexagonal phase transition rules under high pressures. For lanthanide trifluorides, the transition pressures increase as zero pressure volumes of REF3 in the orthorhombic phase become smaller. As the calculation results show, this is because the difference in value of energy from the two structures is larger. This work not only provides precise structural change but also benefits the understanding of two typical structures for rare-earth trifluorides, which may play a significant role in the applications of REF3.

Pressure effects on the thermal decomposition of the LLM-105 crystal.

Thermal mechanical responses under high temperature and high pressure are basic information to understand the performance of energetic materials. In this work, the pressure effects on the thermal decay of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) are explored. Up to the initial pressure of 4.6 GPa, the pressure dependent decomposition boundary is built and no phase transition occurs until the decomposition of the LLM-105 crystal. The decomposition temperature is significantly lifted via a weak loading pressure. The experimental measurement confirms the decomposition products, including NO2, CO2 and NH3, which are predicted by the density functional tight-binding molecular dynamics method. The calculation described the details of thermal decay in the initial stages under high pressure. The sudden drop in the shifts of the Raman modes associated with hydrogen bonds under high pressure indicates the strengthening of the intermolecular hydrogen bonds and the occurrence of intermolecular hydrogen transfer prior to crystal decomposition. The simulation supported the existence of intermolecular hydrogen transfer and provided the transfer path and decomposition mechanism. All of these jobs not only contribute significantly to the understanding of thermal decomposition of energetic materials as a function of pressure, but also contribute to the understanding of sensitivity mechanisms and safety issues.

Directing on-surface polymerization via a substrate-directed molecular template.

Using a template to control the on-surface polymerization process is valuable for building functional molecular nanostructures. Here, the role of the symmetric matching between a halogen-ligand component (H2TBrPP) and the substrate for the fabrication of a regular metal-organic structure on Cu(111) and Cu(100) surfaces was studied using scanning tunnelling microscopy (STM). Considering the formation of short-range order polymers on the Au(111) surface via the process of debromination due to the weak directing effect from the substrate to the precursors, a bilayer of ordered assembled structure of H2TBrPP/Au(111) has been fabricated and the molecules in the top layer are guided by the first-layer molecules. Owing to the steering effect of the substrate-directed molecular template, the H2TBrPP components in the top layer were polymerized into ordered molecular chain arrays along the given direction that is determined by the initial close-packed assembled structure of H2TBrPP components during the post-annealing treatment.

Inference of a "Hot Ice" Layer in Nitrogen-Rich Planets: Demixing the Phase Diagram and Phase Composition for Variable Concentration Helium-Nitrogen Mixtures Based on Isothermal Compression.

Van der Waals (vdW) chemistry in simple molecular systems may be important for understanding the structure and properties of the interiors of the outer planets and their satellites, where pressures are high and such components may be abundant. In the current study, Raman spectra and visual observation are employed to investigate the phase separation and composition determination for helium-nitrogen mixtures with helium concentrations from 20 to 95% along the 295 K isothermal compression. Fluid-fluid-solid triple-phase equilibrium and several equilibria of two phases including fluid-fluid and fluid-solid have been observed in different helium-nitrogen mixtures upon loading or unloading pressure. The homogeneous fluid in helium-nitrogen mixtures separates into a helium-rich fluid (F1) and a nitrogen-rich fluid (F2) with increasing pressure. The triple-phase point occurs at 295 K and 8.8 GPa for a solid-phase (N2)11He vdW compound, fluid F1 with around 50% helium, and fluid F2 with 95% helium. Helium concentrations of F1 coexisted with the (N2)11He vdW compound or δ-N2 in helium-nitrogen mixtures with different helium concentrations between 40 and 50% and between 20 and 40%, respectively. In addition, the helium concentration of F2 is the same in helium-nitrogen mixtures with different helium concentrations and decreases upon loading pressure. Pressure-induced nitrogen molecule ordering at 32.6 GPa and a structural phase transition at 110 GPa are observed in (N2)11He. In addition, at 187 GPa, a pressure-induced transition to an amorphous state is identified.

Realization of Electron Antidoping by Modulating the Breathing Distortion in BaBiO3.

The recent proposal of antidoping scheme breaks new ground in conceiving conversely functional materials and devices; yet, the few available examples belong to the correlated electron systems. Here, we demonstrate both theoretically and experimentally that the main group oxide BaBiO3 is a model system for antidoping using oxygen vacancies. The first-principles calculations show that the band gap systematically increases due to the strongly enhanced Bi-O breathing distortions away from the vacancies and the annihilation of Bi 6s/O 2p hybridized conduction bands near the vacancies. Our further spectroscopic experiments confirm that the band gap increases systematically with electron doping, with a maximal gap enhancement of ∼75% when the film's stoichiometry is reduced to BaBiO2.75. These results unambiguously demonstrate the remarkable antidoping effect in a material without strong electron correlations and underscores the importance of bond disproportionation in realizing such an effect.

Polymorphic Pairing Configurations of Guanine and Cytosine at the Water-HOPG Interface.

A series of nucleobases guanine (G) and cytosine (C) pairing configurations have been fabricated on highly oriented pyrolytic graphite (HOPG) surface by controlling the molar ratio of G and C in water solution. Watson-Crick (WC) base pairing governs the association of C and G nucleobases when the molar ratio of C/G is adjusted to 1:1. Nucleobase-rich is preferentially hydrogen-bonded to the sites exposed around WC motifs with the adjustment of the C/G molar ratio. At a higher C/G molar ratio imbalance, the pairing configurations depend on the combination of interspace and sites of hydrogen binding between G and C bases. The systematic analysis of the high-resolution STM images and DFT calculations reveal that hydrogen bonding plays a dominant role in the formation of these pairing configurations and that the competition between the priority and diversity of hydrogen-bonded configurations bonding between G and C is the key for the pairing structural polymorphism.

Enhanced luminescence of Si(111) surface by localized surface plasmons of silver islands.

The role of silver localized surface plasmons (LSPs) on the luminescence of a Si(111)-(7 × 7) surface has been investigated by scanning tunneling microscopy (STM) with a silver tip at 77 K. On a bare Si(111)-(7 × 7) surface, a characteristic peak at 1.85 eV dominates the STM-induced luminescence spectrum, although the luminescence intensity is extremely weak. Once Ag atoms are deposited onto the Si surface to form islands with a few atomic layers, it is found that the intensity of the characteristic peak from the Si surface underneath the Ag islands is significantly enhanced by about one order. In addition to the luminescence from the Si surface, light emission originating from the irradiation decay of the Ag plasmons is also detected. Such great enhancement of the luminescence from the Si surface is attributed to the strong coupling between the surface states of the Si and the LSPs of the Ag islands.

Development of a novel ssDNA aptamer targeting cardiac troponin I and its clinical applications.

Cardiac troponin I (cTnI) is a specific biomarker of acute myocardial infarction (AMI). However, cTnI detection kits prepared with antibodies have many defects. Nucleic acid aptamers are sequences of single-strand DNA or RNA that can overcome the deficiency of antibodies. Herein, sandwich ELONA methods were established based on aptamers. Two selected ssDNA aptamers (Apt3 and Apt6) showed high binding affinity and sensibility (Apt3: Kd = 1.01 ± 0.07 nM, Apt6: k = 0.68 ± 0.05) and did not bind to the same domain of cTnI. Therefore, these two aptamers can be applied to the ELONA methods. The detection range of cTnI using the dual-aptamer sandwich ELONA method was 0.05-200 ng/mL, and the bioanalytical method verification results can meet the national standard of Chinese Pharmacopoeia (2020 Edition). There was no difference between results of the dual-aptamer sandwich ELONA method and the diagnostic results of serum obtained from 243 people (P = 0.39, P ˃ 0.05). The sensitivity and specificity of the ELONA with cTnI in serum were 96.46% and 93.85%, respectively. Compared with the FICA kit, which is clinically used, the consequences of ELONA method are closer to the diagnostic results. This study suggests that the aptamers Apt3 and Apt6 have high affinity and strong specificity and that the dual-aptamer sandwich ELONA method has a wide detection range and can be used to determine cTnI in serum, with potential applications in the diagnosis of AMIs.

Surface-mediated construction of diverse coordination-dominated nanostructures with 4-azidobenzoic acid molecule.

The coordination reactions of 4-Azidobenzoic Acid (ABA) molecules on different active surfaces are studied by scanning tunneling microscopy and density functional theory calculations. ABA molecules deposited on Ag(111)/Ag(100)/Cu(100) held at room temperature lead to the decomposition of azide groups and the release of a N2 molecule per ABA molecule. Two residual segments of ABA molecules can interact with one Ag/Cu adatom to form a coordination dimer through the N-Ag/Cu-N coordination bond on different substrates. Different orientations with different symmetries can result in different nanostructures based on the dimers. Interestingly, the residual segments of ABA molecules can generate four Cu adatoms as the coordination center on Cu(100) to form a novel coordination complex after annealing, which is the first report for trapping four adatoms as a coordination center. The number and the species of adatoms captured can be changed to alter coordination structures. It expounds that various regulatory effects of different substrates lead to the diversity of nanostructures dominated by coordination bonds.

Wide-range ratiometric upconversion luminescence thermometry based on non-thermally coupled levels of Er in high-temperature cubic phase NaYF4: Yb, Er.

Wide-range optical thermal sensing is achieved here based on the two-photon upconversion luminescence of the high-temperature (HT) cubic phase NaYF4:Yb, Er. In the range of room temperature to 973 K, the single-phase sample exhibits two bands of green and red emission with different dependences on the temperature. The CIE chromaticity diagram shows that the color point moves from deep red (0.6357, 0.3501) at room temperature to the yellow region (0.4379, 0.475) at 600 K and then to the green region (0.318, 0.669) at 973 K. It reveals that HT cubic phase NaYF4:Yb, Er is the promising ratiometric and colorimetric luminescent thermometer. The relative sensitivity decreases slightly up to 673 K and then increases with the increasing temperature. The lattice expansion of the HT cubic phase alters the crystal symmetry around the activator ion and further increases the green-to-red emission ratio.

Observations of Gradual Chiral Self-Recognition of Adsorbed Aromatic Compound.

The self-assembly of two-dimensional chiral 1 H,5 H-benzo(1,2- d:4,5- d')bistriazole (H2bbta) on a Ag(110) surface was investigated by ultra-high-vacuum scanning tunneling microscopy. The gradual formation of ordered structures by H2bbta molecules with the same chirality recognizing each other was observed as the annealing temperature was increased from 300 to 333 K. When the sample was annealed at 355 K, the homochiral structures were converted to coexisting structures containing λ-H2bbta and δ-H2bbta in a ratio of 6:1. Density functional theory (DFT) calculations revealed that thermally driven and intermolecular interactions induced chiral self-recognition to form enantiomorphous H2bbta structures in which N-H···N hydrogen bonds and C-H···N hydrogen bonds are the main attractive forces.

Assembling fullerene into nanostructures over micrometer scale with atomic precision.

Assembling large organic molecules into predesigned structures for nanoscale devices is a long-standing challenge. Here, we present the atom-scale precise repositions of individual fullerene molecules and molecule transportation over the micrometer scale on a Si(111) surface via reproducible and reversible vertical manipulation by a scanning tunneling microscopy tip. A two-rod abacus consisting of ten fullerene molecules was used to perform arithmetic operations with double digits. This opens the door for the use of larger organic molecules displaying intrinsic characteristics as complex molecular devices with novel functions.

Effect of pressure gradient and new phases for 1,3,5-trinitrohexahydro-s-triazine (RDX) under high pressures.

Herein, pressure-induced phase transitions of RDX up to 50 GPa were systematically studied under different compression conditions. Precise phase transition points were obtained based on high-quality Raman spectra with small pressure intervals. This favors the correctness of the theoretical formula for detonation and the design of a precision weapon. The experimental results indicated that α-RDX immediately transformed to γ-RDX at 3.5 GPa due to hydrostatic conditions and possible interaction between the penetrating helium and RDX, with helium gas as the pressure-transmitting medium (PTM). Mapping of pressure distribution in samples demonstrates that the pressure gradient is generated in the chamber and independent of other PTMs. The gradient induced the first phase transition starts at 2.3 GPa and completed at 4.1 GPa. The larger pressure gradient promoted phase transition in advance under higher pressures. Experimental results supported that there existed two conformers of AAI and AAE for γ-RDX, as proposed by another group. δ-RDX was considered to only occur in a hydrostatic environment around 18 GPa using helium as the PTM. This study confirms that δ-RDX is independent of PTM and exists under non-hydrostatic conditions. Evidence for a new phase (ζ) was found at about 28 GPa. These 4 phases have also been verified via XRD under high pressures. In addition to this, another new phase (η) may exist above 38 GPa, and it needs to be further confirmed in the future. Moreover, all the phase transitions were reversible after the pressure was released, and original α-RDX was always obtained at ambient pressure.