Kinetic Controlled Chirality Transfer and Induction in 2D Hydrogen-Bonding Assemblies of Glycylglycine on Au(111).

Chirality transfer is of vital importance that dominates the structure and functionality of biological systems and living matters. External physical stimulations, e.g. polarized light and mechanical forces, can trigger the chirality symmetry breaking, leading to the appearance of the enantiomeric entities created from a chiral self-assembly of achiral molecule. Here, several 2D assemblies with different chirality, synthesized on Au(111) surface by using achiral building blocks - glycylglycine (digly), the simplest polypeptide are reported. By delicately tuning the kinetic factors, i.e., one-step slow/rapid deposition, or stepwise slow deposition with mild annealing, achiral square hydrogen-bond organic frameworks (HOF), homochiral rhombic HOF and racemic rectangular assembly are achieved, respectively. Chirality induction and related symmetry broken in assemblies are introduced by the handedness (H-bond configurations in principle) of the assembled motifs and then amplified to the entire assemblies via the interaction between motifs. The results show that the chirality transfer and induction of biological assemblies can be tuned by altering the kinetic factors instead of applying external forces, which may offer an in-depth understanding and practical approach to peptide chiral assembly on the surfaces and can further facilitate the design of desired complex biomolecular superstructures.

Night Vision Anti-Halation Method Based on Infrared and Visible Video Fusion.

In order to address the discontinuity caused by the direct application of the infrared and visible image fusion anti-halation method to a video, an efficient night vision anti-halation method based on video fusion is proposed. The designed frame selection based on inter-frame difference determines the optimal cosine angle threshold by analyzing the relation of cosine angle threshold with nonlinear correlation information entropy and de-frame rate. The proposed time-mark-based adaptive motion compensation constructs the same number of interpolation frames as the redundant frames by taking the retained frame number as a time stamp. At the same time, considering the motion vector of two adjacent retained frames as the benchmark, the adaptive weights are constructed according to the interframe differences between the interpolated frame and the last retained frame, then the motion vector of the interpolated frame is estimated. The experimental results show that the proposed frame selection strategy ensures the maximum safe frame removal under the premise of continuous video content at different vehicle speeds in various halation scenes. The frame numbers and playing duration of the fused video are consistent with that of the original video, and the content of the interpolated frame is highly synchronized with that of the corresponding original frames. The average FPS of video fusion in this work is about six times that in the frame-by-frame fusion, which effectively improves the anti-halation processing efficiency of video fusion.

Complex supramolecular tessellations with on-surface self-synthesized C60 tiles through van der Waals interaction.

Supramolecular tessellation with self-synthesized (C60)7 tiles is achieved based on a cooperative interaction between co-adsorbed C60 and octanethiol (OT) molecules. Tile synthesis and tiling take place simultaneously on a gold substrate leading to a two-dimensional lattice of (C60)7 tiles with OT as the binder molecule filling the gaps between the tiles. This supramolecular tessellation is featured with simultaneous on-site synthesis of tiles and self-organized tiling. In the absence of specific functional groups, the key to ordered tiling for the C60/OT system is the collective van der Waals (vdW) interaction among a large number of molecules. This bicomponent system herein offers a way for the artificial synthesis of 2D complex vdW supramolecular tessellations.

[The Role of Virtual Reality Technology in Medical Education in the Context of Emerging Medical Discipline].

According to Healthy China, a national strategy of the Government of China, new requirements were put forward for high-quality medical education, high-level surgical research, and precise clinical diagnosis and treatment. In the context of Emerging Medical Discipline, a strategic blueprint of medical education in China, this paper reviews the concept and core value of virtual reality (VR) and its significant role in the medical industry. On that basis, we explore the role of VR technology in medical training against the background of Emerging Medicine Discipline. Furthermore, typical cases are presented to help analyze and illustrate in detail the important role of VR technology in the teaching and training of stomatological and clinical procedures, skills assessment, online self-directed training, and clinical thinking skills training. We herein summarize useful information from past experience so as to help build innovative models of medical education in the context of Emerging Medical Discipline.

On-surface synthesis of size- and shape-controlled two-dimensional Aun nanoclusters using a flexible fullerene molecular template.

Synthesizing nano-clusters with a well-defined size, shape, and composition is an important and challenging goal in nanotechnology. Here we report the application of a single layer C60 molecule as an effective molecular template for the synthesis of size- and shape-selected two-dimensional gold clusters (Aun) on a graphite substrate. This molecular template facilitates the preferential formation of Au19 clusters with a selectivity as high as 90%. Density-functional-theory (DFT) calculations found an energy minimum associated with C60-stabilized two-dimensional Au19 clusters.

Squared peak-to-peak algorithm for the spectral interrogation of short-cavity fiber-optic Fabry-Perot sensors.

The cavity length of short-cavity Fabry-Perot (FP) sensors cannot be effectively interrogated using the conventional peak-to-peak method if the spectrum of the exciting source is not wide enough. In this paper, we propose a squared peak-to-peak algorithm for interrogation of short-cavity fiber-optic FP sensors. By squaring the DC-filtered reflection spectrum of an FP sensor in the frequency domain, we produce an additional peak, with which the cavity length of a sensor can be estimated using the same calculations as performed with the conventional peak-to-peak method. For investigation of the feasibility of this technique, we conducted simulations and practical experiments analyzing fiber-optic FP sensors with cavity lengths in the range of 15-25 µm. The maximum error in cavity length estimated using the proposed algorithm in experiments was 0.030 µm.

Bridge-bonded methylthiolate on Au(111) observed with the scanning tunneling microscope.

We report the discovery of bridge-bonded methylthiolate, SCH3, along the step edges of the Au(111) surface. Real-space imaging with a scanning tunnelling microscope reveals the presence of bridge-bonded SCH3 along both the [11[combining macron]0] and the [112[combining macron]] oriented step edges. The nearest neighbour distances of SCH3 along these steps are 2a and , respectively. The Au(111) terrace is covered with the usual CH3SAuSCH3 staples. The bridge-bonded alkanethiolate is expected to play a rather significant role in the formation of thiol-passivated Au nanoclusters because of the high fraction of atoms in similar low-coordination sites.

Orientational Epitaxy of van der Waals Molecular Heterostructures.

The shape of individual building blocks is an important parameter in bottom-up self-assembly of nanostructured materials. A simple shape change from sphere to spheroid can significantly affect the assembly process due to the modification to the orientational degrees of freedom. When a layer of spheres is placed upon a layer of spheroids, the strain at the interface can be minimized by the spheroid taking a special orientation. C70 fullerenes represent the smallest spheroids, and their interaction with a sphere-like C60 is investigated. We find that the orientation of the C70 within a close-packed C70 layer can be steered by contacting a layer of C60. This orientational steering phenomenon is potentially useful for epitaxial growth of multilayer van der Waals molecular heterostructures.

Controlled Manipulation of Magic Number Gold-Fullerene Clusters Using Scanning Tunneling Microscopy.

We report controlled manipulation of magic number gold-fullerene clusters, (C60) m-(Au) n, on a Au(111) substrate at 110 K using scanning tunneling microscopy (STM). Each cluster consists of a two-dimensional gold island of nAu atoms confined by a frame of mC60 molecules. Using STM, C60 molecules are extracted from the molecular frame one at a time. The extraction is conducted by driving the STM tip into the cluster, leading to one of the molecules being squeezed out of the frame. Unlike at room temperature, the extracted molecules do not move away from the cluster because of the lack of thermal energy at 110 K; they are found to be attached to the outside of the frame. Reversible manipulation is also possible by pushing an extracted molecule back into the frame. This reversible manipulation is possible only for molecules from the edge of the cluster.

Probing Phase Evolutions of Au-Methyl-Propyl-Thiolate Self-Assembled Monolayers on Au(111) at the Molecular Level.

A self-assembled monolayer (SAM) consisting of a mixture of CH3S-Au-SCH3, CH3S-Au-S(CH2)2CH3, and CH3(CH2)2S-Au-S(CH2)2CH3 was studied systematically using scanning tunneling microscopy and density functional calculations. We find that the SAM is subjected to frequent changes at the molecular level on the time scale of ∼minutes. The presence of CH3S or CH3S-Au as a dissociation product of CH3S-Au-SCH3 plays a key role in the dynamical behavior of the mixed SAM. Slow phase separation takes place at room temperature over hours to days, leading to the formation of methyl-thiolate-rich and propyl-thiolate-rich phases. Our results provide new insights into the chemistry of the thiolate-Au interface, especially for ligand exchange reaction in the RS-Au-SR staple motif.

Exposure of mass-selected bimetallic Pt-Ti nanoalloys to oxygen explored using scanning transmission electron microscopy and density functional theory.

The response of nanoparticles to exposure to ambient conditions and especially oxidation is fundamental to the application of nanotechnology. Bimetallic platinum-titanium nanoparticles of selected mass, 30 kDa and 90 kDa, were produced using a magnetron sputtering gas condensation cluster source and deposited onto amorphous carbon TEM grids. The nanoparticles were analysed with a Cs-corrected Scanning Transmission Electron Microscope (STEM) in High Angle Annular Dark Field (HAADF) mode. It was observed that prior to full Ti oxidation, Pt atoms were dispersed within a Ti shell. However, after full oxidation by prolonged exposure to ambient conditions prior to STEM, the smaller size 30 kDa particles form a single Pt core and the larger size 90 kDa particles exhibit a multi-core structure. Electron beam annealing induced a single core morphology in the larger particles. First principles density functional theory (DFT) calculations were employed to calculate the lowest energy structure of the Pt-Ti nanoparticles with and without the presence of oxygen. It was demonstrated that, as the concentration of oxygen increases, the lowest energy structure changes from dispersed Pt to multiple Pt cores and finally a single Pt core, which is in good agreement with the experimental observations.

Tip-triggered Thermal Cascade Manipulation of Magic Number Gold-Fullerene Clusters in the Scanning Tunnelling Microscope.

We demonstrate cascade manipulation between magic number gold-fullerene hybrid clusters by channelling thermal energy into a specific reaction pathway with a trigger from the tip of a scanning tunnelling microscope (STM). The (C60)m-Aun clusters, formed via self-assembly on the Au(111) surface, consist of n Au atoms and m C60 molecules; the three smallest stable clusters are (C60)7-Au19, (C60)10-Au35, and (C60)12-Au49. The manipulation cascade was initiated by driving the STM tip into the cluster followed by tip retraction. Temporary, partial fragmentation of the cluster was followed by reorganization. Self-selection of the correct numbers of Au atoms and C60 molecules led to the formation of the next magic number cluster. This cascade manipulation is efficient and facile with an extremely high selectivity. It offers a way to perform on-surface tailoring of atomic and molecular clusters by harnessing thermal energy, which is known as the principal enemy of the quest to achieve ultimate structural control with the STM.

Surface-induced symmetry reduction in molecular switching: asymmetric cis-trans switching of CH3S-Au-SCH3 on Au(111).

The cis-trans isomerization of CH3S-Au-SCH3 driven by the tip of the scanning tunneling microscope is investigated at 77 K. CH3S-Au-SCH3 anchored on the Au(111) surface with the S-Au-S axis parallel to the substrate functions as a molecular switch due to the flipping of the CH3 groups. The bonding between CH3S-Au-SCH3 and Au(111) leads to asymmetric isomerization where one of the two methyl groups flips much more effectively than the other, despite the symmetry of CH3S-Au-SCH3. Our findings suggest the possibility of constructing similar molecular switches that can be operated at room temperature and a potential route for fine-tuning of molecular switches in future nanoscale electro-mechanical devices.

Critical assessment of the evidence for striped nanoparticles.

There is now a significant body of literature which reports that stripes form in the ligand shell of suitably functionalised Au nanoparticles. This stripe morphology has been proposed to strongly affect the physicochemical and biochemical properties of the particles. We critique the published evidence for striped nanoparticles in detail, with a particular focus on the interpretation of scanning tunnelling microscopy (STM) data (as this is the only technique which ostensibly provides direct evidence for the presence of stripes). Through a combination of an exhaustive re-analysis of the original data, in addition to new experimental measurements of a simple control sample comprising entirely unfunctionalised particles, we show that all of the STM evidence for striped nanoparticles published to date can instead be explained by a combination of well-known instrumental artefacts, or by issues with data acquisition/analysis protocols. We also critically re-examine the evidence for the presence of ligand stripes which has been claimed to have been found from transmission electron microscopy, nuclear magnetic resonance spectroscopy, small angle neutron scattering experiments, and computer simulations. Although these data can indeed be interpreted in terms of stripe formation, we show that the reported results can alternatively be explained as arising from a combination of instrumental artefacts and inadequate data analysis techniques.

Self-assembled alkanethiol monolayers on gold surfaces: resolving the complex structure at the interface by STM.

The surface properties of metals and metal oxides can be modified by adding a single layer of organic molecules. A most popular route for depositing such a molecular layer is via the formation of self-assembled monolayers (SAMs). The molecules that form SAMs have a functionality which binds to the surface and the adsorption is self-regulated to terminate at exactly one single molecular layer. The very first example, which has become the most widely studied system, of SAMs on metal surfaces consists of chemisorbed alkylthiolate on gold. Despite the simplicity in the preparation of alkanethiol SAMs and the seemingly straightforward structure of such SAMs, the detailed bonding between the sulfur head group and gold is still subject to debate. Experimental and theoretical effort in the last six years has led to a much improved understanding of this classical system of SAMs. In this review, we will highlight the most recent progress in the study of the interfacial structure of alkanethiol SAMs on gold. We focus on the important phenomenon of phase transition that occurs from n-propanethiol to n-butanethiol, and propose a unified structural model to explain how the (3 × 4) phase for short chain alkanethiol monolayers (methyl-, ethyl- and propylthiolate monolayers) changes into the (3 × 2√3)-rect./c(4 × 2) phase for long chain molecular monolayers.

Cooperative assembly of magic number C60-Au complexes.

We report the assembly of magic number (C60)m-(Au)n complexes on the Au(111) surface. These complexes have a unique structure consisting of a single atomic layer Au island wrapped by a self-selected number (seven, ten, or twelve) of C(60) molecules. The smallest structure consisting of 7 C60 molecules and 19 Au atoms, stable up to 400 K, has a preferred orientation on the surface. We propose a globalized metal-organic coordination mechanism for the stability of the (C(60))(m)-(Au)n complexes.

Mixed methyl- and propyl-thiolate monolayers on a Au(111) surface.

Mixed methyl- and propyl-thiolate self-assembled monolayers (SAMs) are prepared on a Au(111) surface by exposing the gold substrate to methyl-propyl-disulfide vapor at room temperature. Scanning tunneling microscopy imaging of such SAMs reveals a (3 × 4) phase consisting of CH3-S-Au-S-CH3, CH3-S-Au-S-(CH2)2CH3, and CH3-(CH2)2-S-Au-S-(CH2)2CH3. Partial desorption of methyl-thiolate occurs when samples are thermally annealed to 373 K, leading to the formation of a striped phase consisting of primarily CH3-(CH2)2-S-Au-S-(CH2)2CH3.

The striped phases of ethylthiolate monolayers on the Au(111) surface: a scanning tunneling microscopy study.

Striped phases of ethylthiolate monolayers, corresponding to surface coverage in between 0.2 ML and 0.27 ML, were studied using high-resolution scanning tunneling microscopy. Striped phases consist of rows of Au-adatom-diethythiolate (AAD) aligned along the [112] direction. In the perpendicular [110] direction, the AAD rows adjust their spacing according to the surface coverage. A (5√3 × âˆš3)-R30° striped phase with 0.27 ML thiolate and a (6√3 × âˆš3)-R30° striped phase with 0.23 ML thiolate, both with long-range order, are found. A localized (5 × âˆš3)-rect. phase is also found as a minority phase embedded in the 5√3 × âˆš3)-R30° phase. This (5 × âˆš3)-rect. phase can be constructed using di-Au-adatom-tri-thiolate species.

Adsorption and electron-induced dissociation of ethanethiol on Au(111).

Dissociation of ethanethiol and the formation of Au-adatom-diethylthiolate rows on the Au(111) surface were investigated using scanning tunneling microscopy (STM) at low temperature. Ethanethiol molecules physisorb on Au(111) at 120 K by sequentially occupation of the elbow site, the fcc domain before covering the whole surface with a semiliquid layer without long-range order. Scanning the physisorbed layer with a sample bias higher than +1.2 V leads to dissociation via cleaving the H-S bond. One of the dissociation products, ethylthiolate, forms a double-row structure with the rows aligned in one of the [112(-)] directions. These double rows arise from the Au-adatom-dithiolate species: CH(3)CH(2)S-Au-SCH(2)CH(3).