Correlation Between Intracoronary Vascular Ultrasound Indexes in Patients with Coronary Heart Disease.

Background: Coronary atherosclerosis is a serious and progressive condition characterized by the accumulation of plaques, consisting of fat, cholesterol, and other substances, within the arteries that supply blood to the heart. These plaques can harden and narrow the arteries, leading to reduced blood flow to the heart muscle. Objective: The primary objective of this study is to investigate the correlation between specific cardiovascular parameters and intracoronary vascular ultrasound indexes in patients diagnosed with coronary heart disease. This investigation aims to explore the relationships between intracoronary vascular ultrasound measurements and three key cardiovascular parameters: epicardial fat pad thickness, mono-platelet polymer levels, and small dense low-density lipoprotein cholesterol (sdLDL-C) levels. Methods: In this investigation, we applied a comprehensive method to evaluate atherosclerotic plaque characteristics in patients with diverse stages of coronary heart disease (CHD), contrasting these profiles with those of healthy individuals. Our study included 80 acute myocardial infarction (AMI) patients, 145 with unstable angina pectoris (UAP), 175 with stable angina pectoris (SAP), and 100 controls. We utilized intravascular ultrasound (IVUS), an advanced imaging technique that surpasses traditional angiography by providing detailed, high-resolution images of both the coronary artery lumen and wall, including plaque composition. This approach is pivotal for assessing plaque stability, a key factor in the risk of rupture and subsequent cardiovascular events, indicated by features like lipid-rich cores and thin fibrous caps. During IVUS, we quantified parameters such as plaque area, load, and the remodeling index, the latter offering insights into vascular adaptation to plaque buildup. Additionally, we conducted a correlation analysis between IVUS indices and three cardiovascular markers: epicardial fat pad thickness, monocyte-platelet aggregates, and sdLDL-C levels. The goal was to ascertain the predictive value of these markers in tandem with IVUS for determining the stability of coronary artery atherosclerotic plaques. This integrative approach enhances understanding of plaque formation and destabilization, potentially informing more effective CHD prevention and management strategies. Results: Our study revealed distinct variations in key parameters across patient groups with different forms of CHD and healthy controls. Notably, we observed significant differences in gender distribution, hypertension, and diabetes mellitus prevalence among these groups. In terms of IVUS indexes and cardiovascular parameters, the SAP group exhibited markedly different results compared to the AMI and UAP groups. Specifically, the SAP patients showed the lowest values for EMMA, plaque area, plaque burden, reconstruction index, and positive remodeling. Additionally, they exhibited the thickest fibrous caps. In contrast, the AMI and UAP groups presented similar outcomes in these aspects. Regarding the epicardial fat pad thickness, the positive rate of monocyte-platelet aggregates, and the levels of sdLDL-C, there were no significant differences between the AMI and UAP groups. However, these parameters were notably higher in the AMI and UAP groups compared to the SAP group. Crucially, we established a significant correlation between the thickness of the epicardial fat pad, the positive rate of monocyte-platelet aggregates, and the sdLDL-C levels with plaque loading rate and remodeling index. These correlations underscore the potential utility of these parameters as indicators of plaque stability and cardiovascular risk in patients with CHD. This highlights the complexity of atherosclerotic disease progression and underscores the importance of a multifaceted approach to assessing and managing CHD. Conclusion: Our research delineates the critical role of the remodeling index, epicardial fat pad thickness, monocyte-platelet aggregates, and sdLDL-C levels as key prognostic tools for assessing coronary plaque stability in coronary artery disease (CAD). These biomarkers collectively provide an enhanced perspective on plaque vulnerability, an essential aspect in the genesis of acute coronary events. Clinically, these findings are pivotal. They offer a refined approach to CAD management and risk evaluation, allowing for the precise identification of patients at increased risk of plaque rupture, a precursor to acute coronary syndromes. This precision facilitates the adoption of more individualized treatment strategies, focusing on aggressive interventions for high-risk patients and more conservative management for those with stable plaques.

Regulatory mechanism of miR-20a-5p in neuronal damage and inflammation in lipopolysaccharide-induced BV2 cells and MPTP-HCl-induced Parkinson's disease mice.

BACKGROUND: Parkinson's disease (PD) is a prevailing neurodegenerative disorder increasingly affecting the elderly population. The involvement of microRNAs (miRNAs) in PD has been confirmed. We sought to explore the molecular mechanism of miR-20a-5p in PD. METHODS: Lipopolysaccharide (LPS)-induced BV2 cell model and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP-HCl)-induced PD mouse model were established. miR-20a-5p, inducible nitric oxide synthase (iNOS), interleukin (IL)-6, tumour necrosis factor (TNF)-α, transforming growth factor (TGF)-ß1, and IL-10 expression in BV2 cells was examined by reverse transcription - quantitative polymerase chain reaction. Cell viability was assessed by MTT assay. The apoptotic rate and levels of Bcl-2, Bax, cleaved caspase-3, and signal transducer and activator of transmission (STAT)3 were examined by flow cytometry and Western blot. Bioinformatics software predicted the potential binding sites of miR-20a-5p and STAT3. Dual-luciferase experiment verified the binding relationship. Iba1-positive and tyrosine hydroxylase (TH)-positive cell numbers in substantia nigra pars compacta were detected by immunohistochemistry. The effect of miR-20a-5p on motor function in MPTP-induced PD mice was detected by Rota-rod test, Pole test, Traction test and Beam-crossing task. RESULTS: miR-20a-5p was under-expressed in LPS-induced BV2 cells. Overexpression of miR-20a-5p increased the viability of LPS-induced BV2 cells and reduced apoptosis rates. Moreover, overexpression of miR-20a-5p reduced cleaved caspase-3, Bax, iNOS, IL-6, and TNF-α and increased Bcl-2 and TGF-ß1, and IL-10. miR-20a-5p targeted STAT3. STAT3 overexpression partially reversed miR-20a-5p overexpression-mediated effects on LPS-induced BV2 cell viability, apoptosis, and inflammatory responses. miR-20a-5p overexpression inhibited MPTP-induced STAT3 and α-synuclein levels, microglia activation, and inflammatory response, and reduced the loss of TH-positive cells in mice. miR-20a-5p overexpression ameliorated MPTP-induced dyskinesia in PD model mice. CONCLUSION: miR-20a-5p alleviates neuronal damage and suppresses inflammation by targeting STAT3 in PD.

Friction properties of black phosphorus: a first-principles study.

Based on the first-principle, the friction anisotropy, structural super-lubricity and oxidation induced ultra-low friction of black phosphorus at atomic scale under different loads have been studied. The results show that the interface friction of black phosphorus is anisotropic, that is, the friction along the armchair direction is greater than that along the zigzag direction. Moreover, the friction between the black phosphorus interfaces shows a structural superlubricity property, and the incommensurate interface friction is approximately one thousandth of the commensurate interface friction, which is mainly due to the less electronic charge and the smaller amplitude of electronic charge change between the incommensurate interfaces during the friction process. In addition, the oxidation of black phosphorus is beneficial for lubrication between interfaces.

Theoretical exploration of the structural, electronic and optical properties of g-C3N4/C3N heterostructures.

Integration of graphene-like carbon nitride materials is essential for nanoelectronic applications. Using density-functional theory (DFT), we systematically investigate the structural, electronic and optical properties of a s-triazine-based g-C3N4/C3N heterostructure under different modified conditions. The g-C3N4/C3N van der Waals heterostructure (vdWH) formed has an indirect bandgap with type-II band alignment and the band structures can be tuned from type-II band alignment to type-I band alignment by applying biaxial strains and external electric fields (Efield). Compared to single transition metal (TM) atoms at g-C3N4/C3N surfaces, the TM atoms anchored in the interlayer region exhibit more stability, and the corresponding bandgaps are changed from 0.19 eV to 0.61 eV. In addition, the g-C3N4/C3N heterostructure has a strong absorption coefficient in the ultraviolet-visible light region along the x direction. It is found that compressive strain has a large influence on the absorption coefficient of the g-C3N4/C3N system. With the increased compressive strain, the absorption spectra in the visible light region disappeared. Tensile strain has a slight effect on the absorption range, but causes a red shift of the absorption spectrum. In comparison, the light absorption coefficient of the g-C3N4/C3N system remains almost unchanged under the Efield conditions. In summary, the formation of a s-triazine-based g-C3N4/C3N heterostructure has shown potential for applications in nanoelectronic and optoelectronic devices.

Formation of stable polonium monolayers with tunable semiconducting properties driven by strong quantum size effects.

Elemental two-dimensional (2D) materials have attracted extraordinary interest compared with other 2D materials over the past few years. Fifteen elements from group IIIA to VIA have been discussed experimentally or theoretically for the formation of 2D monolayers, and the remaining few elements still need to be identified. Here, using first-principles calculations within density functional theory (DFT) and ab initio molecular dynamics simulations (AIMDs), we demonstrated that polonium can form stable 2D monolayers (MLs) with a 1T-MoS2-like structure. The band structure calculations revealed that polonium monolayers possess strong semiconducting properties with a band gap of ∼0.9 eV, and such semiconducting properties can well sustain up to a thickness of 4 MLs with a bandgap of ∼0.1 eV. We also found that polonium monolayers can be achieved through a spontaneous phase transition of ultrathin films with magic thicknesses, resulting in a weaker van der Waals interaction of ∼32 meV Å-2 between each three atomic layers. Also, the underlying physics comes from layered Peierls-like distortion driven by strong quantum size effects. Based on these intriguing findings, a suitable substrate on which the polonium monolayer can be grown through an epitaxial growth technique is proposed for further experiments. Our work not only extends completely the puzzle of elemental 2D monolayer materials from group IIIA to VIA, but also presents a new formation mechanism of 2D materials beyond the database of bulk materials with layered van der Waals interactions.

Comparative Study of NO and CO Oxidation Reactions on Single-Atom Catalysts Anchored Graphene-like Monolayer.

Noble metal single-atom catalysts (NM-SACs) anchored at novel graphene-like supports has attracted enormous interests. Gas sensitivity, catalytic activity, and d-band centers of single NM (Pt and Pd) atoms at graphenylene (graphenylene-NM) are investigated using first-principle calculations. The adsorption geometries of gas reactants on graphenylene-NM sheets are analyzed. It is found that the adsorption energies of reactant species on graphenylene-Pt are larger than those on graphenylene-Pd, because the d-band center of the Pt atom is closeser to the Fermi level. The NO and CO oxidation reactions on graphenylene-NM are investigated via four catalytic mechanisms, including Langmuir-Hinshelwood (LH), Eley-Rideal (ER), New ER (NER), and termolecular ER (TER). The results show that the NO and CO oxidations via LH and TER mechanisms can occur owing to the relatively small energy barriers. Moreover, the interaction of 2NO+2CO via ER mechanism is the energetically more favorable reaction. Although the NO oxidation via the NER mechanism has rather low energy barriers, the reaction is unlikely to occur due to the low adsorption energy of O2 compared with CO and NO. This research may provide guidance for exploring the catalytic performance of SACs on graphene-like materials to remove toxic gas molecules.

Simple transabdominal minimally invasive direct coronary artery bypass surgery with right gastroepiploic artery.

For three patients with isolated right coronary artery disease who had drug resistance and were intolerant to interventional therapy, simple transabdominal small incision bypass grafting of the right gastroepiploic artery and the posterior descending branch of the right coronary artery was conducted without cardiopulmonary. All three patients were discharged smoothly without complications, and were followed up for three months, during which time the myocardial bridges were unobstructed and the cardiac functions were good. The surgery needs no thoracotomy and the injury is small, and avoids influences of sternum and pericardium adhesion on other cardiac surgery in the future. The risk of median sternotomy can be avoided for patients undergoing reoperation for coronary artery bypass surgery.

Enhanced removal of cadmium from wastewater with coupled biochar and Bacillus subtilis.

Shortcomings of individual biochar or microbial technologies often exist in heavy metal removal from wastewater and may be circumvented by coupled use of biochar and microorganisms. In this study, Bacillus subtilis and each of three biochars of different origins (corn stalk, peanut shell, and pine wood) were coupled forming composite systems to treat a cadmium (Cd, 50 mg/L) wastewater formulated with CdCl2 in batch tests. Biochar in composite system enhanced the activity and Cd adsorption of B. subtilis. Compared with single systems with Cd removal up to 33%, the composite system with corn stalk biochar showed up to 62% Cd removal, which was greater than the sum of respective single B. subtilis and biochar systems. Further analysis showed that the removal of Cd by the corn stalk composite system could be considered to consist of three successive stages, that is, the biochar-dominant adsorption stage, the B. subtilis-dominant adsorption stage, and the final biofilm formation stage. The final stage may have provided the composite system with the ability to achieve prolonged steady removal of Cd. The biochar-microorganism composite system shows a promising application for heavy metal wastewater treatment.

A sensitive and reversible staining of proteins on blot membranes.

A modified, sensitive and reversible method for protein staining on nitrocellulose (NC) and polyvinylidine fluoride (PVDF) membranes was developed in Western blotting. The method employed Congo red staining to visualize proteins on different blot membranes. Staining of proteins with Congo red dye is more faster procedures. According to the experimental results, approximate 20 ng proteins could be detected in 3 min in room temperature. The staining on the proteins is easily reversible with Congo red destaining solution for NC and PVDF membranes, so that the blot membranes can be reused for Western blotting. In addition, we confirmed that the staining method is fully compatible with Western blot detection. NC and PVDF membranes treatment with Congo red staining does not interfere with conventional chemiluminescent substrates of peroxidase. As compared to MemCode reversible protein stain kits from Pirece Biotechnology, the staining technique is more sensitive, lower of cost, convenient and not adversely affecting subsequent Western blotting results. On the other hand, the stain is more sensitive than the Ponceau S staining. Therefore, Congo red staining is a promising and ideal alternative for current protein stain. Besides, the binding modes of Congo red or Ponceau S stain were investigated using various 2D and 3D molecular docking and demonstrated potential molecular basis for sensitivity of Congo red staining are higher than Ponceau S.

BN cluster-doped graphdiyne as visible-light assisted metal-free catalysts for conversion CO2 to hydrocarbon fuels.

Carbon dioxide electrochemical reduction reaction (CO2RR) under ambient conditions provides an intriguing picture for conversion of CO2 to useful fuels and chemicals. Here by means of density functional theory (DFT) computations, the formation configuration and CO2RR catalytic activity of boron nitrogen cluster-doped graphdiyne (BN-doped GDY) were systematically investigated. The band structure and optical adsorption spectra reveal that BN-doped GDY exhibits semiconductor with the band gap of 0.902 eV and shows photothermal effect under visible and even infrared light irradiation. The BN-doped GDY could act as a hot spot to enhance CO2RR. The adsorption configurations of various reaction intermediates indicate that boron atoms are active sites, which can be further confirmed by charge analysis. Based on thermodynamic analysis, the reaction pathways and onset potentials were studied as compared with Cu(111) surface. For the production of CO, the onset potential for BN-doped GDY (-1.06 V) is higher than that for Cu(111) surface. While for the reduction of CO2 to HCOOH, CH4, CH3OH, and C2H4 on BN-doped GDY, the onset potentials are lower than that on Cu(111) surface, which are -0.57 V, -0.62 V, -0.57 V, and -0.82 V, respectively. Moreover, the onset potential of competitive hydrogen evolution reaction on BN-doped GDY is high to -0.82 V, which shows us a good selectivity towards to CO2RR rather than HER. Our results may pave a new avenue for the conversion of CO2 into high-value fuels and chemicals.

Single-atom metal-modified graphenylene as a high-activity catalyst for CO and NO oxidation.

Herein, the adsorption behaviors and interactions of different gas species on single-metal atom-anchored graphenylene (M-graphenylene, M = Mn, Co, Ni, and Cu) sheets were investigated by first-principles calculations. At first, the single metal atom tends to adsorb on the hollow or bridge site of graphenylene, and the formed M-graphenylene systems exhibit varied magnetic properties. The reactants (NO, CO, O2, O, CO2, and NO2) adsorbed on the Mn-, Co-, and Ni-graphenylene sheets exhibit higher stability than those adsorbed on the Cu-graphenylene sheet. Moreover, the co-adsorption configurations of NO-O2, CO-O2, 2NO, and 2CO on the M-graphenylene sheets were comparably studied, which are considered as the initial states for NO and CO oxidation. It was found that the energy barriers for the formation of OONO and OOCO complexes on Mn-graphenylene by the Langmuir-Hinshelwood (LH) mechanism are larger than those in the case of Co-graphenylene (<0.4 eV). The possible reactions for the oxidation of 2CO by the 2NO molecules on the M-graphenylene sheets were also considered, because of the adsorbed NO molecules are more stable than the CO and O2 molecules. Furthermore, the energy barrier for the oxidation of CO on Mn-graphenylene via the Eley-Rideal (ER) mechanism (2NO + 2CO → 2CO2 + N2) is smaller (<0.3 eV) than those in the cases of other substrates. These results illustrate that the single-metal atom-modified graphenylene can be used as a potential novel carbon-based catalyst with high activity.

Graphdiyne coordinated transition metals as single-atom catalysts for nitrogen fixation.

The reduction of N2 molecules to NH3 is a very challenging task in chemistry. The electrocatalytic nitrogen reduction reaction (NRR) is a promising technology for NH3 synthesis. By using first-principles calculation, a new class of single-atom catalysts (SACs), graphdiyne coordinated single transition metal atoms (TM@GDY, TM = Sc-Zn, Y-Cd, and La-Hg) were designed, and the NRR catalytic character of TM@GDY was systematically investigated. The results demonstrated that some TM@GDY (TM = Ti, V, Fe, Co, Zr, Rh, and Hf) monolayers exhibit better NRR activities than a Ru(0001) stepped surface. There is an obvious linear correlation between the limiting potential and the atomic N adsorption energy, which confirms that the N adsorption energy may be a descriptor for evaluation of the NRR catalytic performance. The V@GDY monolayer possesses the best NRR catalytic character with the lowest limiting potential of -0.67 V and the potential-limiting step (PLS) of *N2→ *NNH for both alternating and distal mechanisms. Our results highlight a new family of efficient and stable TM@GDY catalysts and provide useful guidelines for SAC development and practical applications.

Formation Mechanism, Geometric Stability and Catalytic Activity of a Single Iron Atom Supported on N-Doped Graphene.

Based on density functional theory (DFT) calculations, the formation geometries, stability and catalytic properties of single-atom iron anchored on xN-doped graphene (xN-graphene-Fe, x=1, 2, 3) sheet are systemically investigated. It is found that the different kinds and numbers of gas reactants can effectively regulate the electronic structure and magnetic properties of the 3 N-graphene-Fe system. For NO and CO oxidation reactions, the coadsorption configurations of NO/O2 and CO/O2 molecules on a reactive substrate as the initial state are comparably analyzed. The NO oxidation reactions through the Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms have relatively smaller energy barriers than those of the CO oxidation processes. In comparison, the preadsorbed 2NO reacting with 2CO molecules (2NO+2CO→2CO2 +N2 ) through ER reactions (<0.4 eV) are energetically more favorable processes. These results can provide beneficial references for theoretical studies on NO and CO oxidation and designing graphene-based catalyst for toxic gas removal.

A computational study of CO oxidation reactions on metal impurities in graphene divacancies.

Based on the density functional theory calculations, the formation geometry, electronic properties, and catalytic activity of metal impurities in divacancy graphene (M-DG, M = Mo, Fe, Co, and Ni) were systematically investigated. It has been found that the reactive gases have different stabilities on M-DG substrates, and these quite stable substrates exhibit high catalytic activity for CO oxidation by comparing the traditional Eley-Rideal (ER) and Langmuir-Hinshelwood (LH), as well as the new termolecular ER (TER) mechanisms. For the Co-DG substrate, the coadsorption of O2 and CO as a starting step is an energetically more favorable process, whereas the dissociation reaction of O2 molecules on Mo-DG substrate has a much smaller energy barrier, and the generation of atomic oxygen is active for CO oxidation. These results indicate that the varied adsorption behaviors of reactive gases on M-DG substrates can determine the catalytic pathways and energy barriers, which give us insight into the surface reactivity of graphene-metal composite catalysis in energy-related devices.

Tuning the adsorption and interaction of CO and O2 on graphene-like BC3-supported non-noble metal atoms.

Research into suitable substrate-supported single-atom catalysts has become a major challenge for electrochemical sensors and energy devices. Firstly, we investigate the adsorption properties of metal atoms (MA = Fe, Co, Ni, Cu and Al) on pristine and defective BC3 sheets through using first-principles calculations. It is found that the MA-doped BC3 configurations (MA-BC3) are quite stable at high temperature and the positively charged MAs as surface active sites can effectively regulate the stability of reactive gases. Secondly, the adsorption of individual O2 molecules is more stable than that of CO molecules, which can modify the electronic and magnetic properties of MA-BC3 systems. Moreover, the possible reaction processes of CO oxidation on the Fe-BC3 substrate are comparably analyzed through the Eley-Rideal (ER) and Langmuir-Hinshelwood (LH) mechanisms. In the LH mechanism, the coadsorbed O2 and CO as starting materials start to form an OOCO complex with a smaller energy barrier (0.38 eV), which is an energetically more favorable process than that of the OOCO (0.65 eV) or CO3 complex (0.42 eV) formed through ER mechanisms. This result indicates that the functionalized MA-BC3 sheets have low cost and high activity.

Theoretical study on geometric, electronic and catalytic performances of Fe dopant pairs in graphene.

The formation geometries, electronic structures and catalytic properties of monovacancy and divacancy graphene sheets with two embedded Fe dopants (2Fe-MG and 2Fe-DG) have been systematically investigated using the first-principles calculations. It was found that the configuration of 2Fe-DG is slightly more stable than that of 2Fe-MG sheets and the two doped Fe atoms in graphene (2Fe-graphene) as active sites could regulate the stability of gas molecules. In addition, the adsorption of O2 and CO molecules could modulate the electronic and magnetic properties of 2Fe-graphene systems. Moreover, the adsorption behaviors of reactants could determine the reaction pathway and energy barrier of the catalytic oxidation of CO. On the 2Fe-graphene substrates, the adsorptive decomposition of O2 molecules (<0.20 eV) and the subsequent Eley-Rideal (ER) reaction (2Oads + 2CO → CO2) (<0.60 eV) have low energy barriers. In comparison, the CO3 complex is quite stable and its formation needs to overcome a higher energy barrier (>0.90 eV). Hence, the dissociation of O2 as an initial step is an energetically more favored process. These results provide valuable guidance for the design of functionalized graphene-based devices.

Catalytic conversion of CHx and CO2 on non-noble metallic impurities in graphene.

Density functional theory (DFT) was applied to investigate the geometric, electronic, and magnetic properties of CHx (x = 0, 1, 2, 3, 4) species on non-noble metal embedded graphene (NNM-graphene). It was found that the different stabilities of CHx species can modify the electronic structures and magnetic properties of NNM-graphene systems. The carbonaceous reforming reactions include conversion of CHx (x = 0, 1, 2 and 3) species by hydrogen molecules (H2) to form CHx+2 species or oxidation of C atoms by oxygen molecules to form CO2. In the hydrogenation reactions, deposited C atoms can be converted easily into CHx species overcoming small energy barriers. In comparison, coadsorption of C and O2 to generate CO2 encounters relatively larger energy barriers on the NNM-graphene. Hence, the coadsorption of CHx and H2 as the starting state is energetically more favorable and formation of CHx species can reduce amounts of carbon deposition. Among the NNM-graphene substrates studied, moderate adsorption energies and low reaction barriers of CHx species are more likely to occur on the Co-graphene surface, thus the hydrogenation reaction is able to inhibit carbon deposition on the NNM-graphene surface while maintaining high activity.

Energetics and kinetics of Cu atoms and clusters on the Si(111)-7 × 7 surface: first-principles calculations.

Exploring the properties of noble metal atoms and nano- or subnano-clusters on the semiconductor surface is of great importance in many surface catalytic reactions, self-assembly processes, crystal growth, and thin film epitaxy. Here, the energetics and kinetic properties of a single Cu atom and previously reported Cu magic clusters on the Si(111)-(7 × 7) surface are re-examined by the state-of-the-art first-principles calculations based on density functional theory. First of all, the diffusion path and high diffusion rate of a Cu atom on the Si(111)-(7 × 7) surface are identified by mapping out the total potential energy surface of the Cu atom as a function of its positions on the surface, supporting previous experimental hypothesis that the apparent triangular light spots observed by scanning tunneling microscopy (STM) are resulted from a single Cu atom frequently hopping among adjacent adsorption sites. Furthermore, our findings confirm that in the low coverage of 0.15 monolayer (ML) the previously proposed hexagonal ring-like Cu6 cluster configuration assigned to the STM pattern is considerably unstable. Importantly, the most stable Cu6/Si(111) complex also possesses a distinct simulated STM pattern with the experimentally observed ones. Instead, an energetically preferred solid-centered Cu7 structure exhibits a reasonable agreement between the simulated STM patterns and the experimental images. Therefore, the present findings convincingly rule out the tentative six-atom model and provide new insights into the understanding of the well-defined Cu nanocluster arrays on the Si(111)-(7 × 7) surface.

Van der Waals Effects on semiconductor clusters.

Van der Waals (vdW) interactions play an important role on semiconductors in nanoscale. Here, we utilized first-principles calculations based on density functional theory to demonstrate the growth mode transition from prolate to multiunit configurations for Gen (n = 10-50) clusters. In agreement with the injected ion drift tube techniques that "clusters with n < 70 can be thought of as loosely bound assemblies of small strongly bound fragments (such as Ge7 and Ge10 )," we found these stable fragments are connected by Ge6 , Ge9 , or Ge10 unit (from bulk diamond), via strong covalent bonds. Our calculated cations usually fragment to Ge7 and Ge10 clusters, in accordance with the experiment results that the spectra Ge7 and Ge10 correspond to the mass abundance spectra. By controlling a germanium cluster with vdW interactions parameters in the program or not, we found that the vdW effects strengthen the covalent bond from different units more strikingly than that in a single unit. With more bonds between units than the threadlike structures, the multiunit structures have larger vdW energies, explaining why the isolated nanowires are harder to produce. © 2015 Wiley Periodicals, Inc.

Geometric stability and reaction activity of Pt clusters adsorbed graphene substrates for catalytic CO oxidation.

The geometric stabilities, electronic structures and catalytic properties of tetrahedral Pt4 clusters anchored on graphene substrates are investigated using the first-principles methods. It is found that the small Pt4 clusters adsorbed on pristine graphene substrates easily interconvert between structural isomers by the small energy barriers, while the structural interconversion of Pt4 clusters on the defective graphene and oxygen-doped graphene (O-graphene) have the large energy barriers. Compared to other graphene substrates, the Pt4 clusters supported on the O-graphene substrate (Pt4/O-graphene) have the least geometrical distortion and the high symmetry of the Pt4 cluster can enhance the sensitivity of reactive gases. Moreover, the sequential reactions of CO oxidation on Pt4/O-graphene are investigated for comparison. Compared with the coadsorption reaction of CO and O2 molecules, the dissociative adsorption of O2 as a starting step has a small energy barrier (0.07 eV) and is followed through the Eley-Rideal reaction with an energy barrier of 0.42 eV (CO + Oads → CO2). The results provide valuable guidance for fabricating graphene-based catalysts as anode materials, and explore the microscopic mechanism of the CO oxidation reaction on atomic-scale catalysts.