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Hybrids made of defective nanodiamonds interacting with DNA nucleobases
摘要： The characteristics of hybrids made of a defective nanodiamond and a biomolecule unit are investigated in this work. Focus is given on the interaction between the nanodiamond and a DNA nucleobase. The latter is placed close to the former in two different arrangements, realizing different bonding types. The nanodiamond includes a negatively charged nitrogen-vacancy center and is hydrogen terminated. Using quantum-mechanical calculations, we could elucidate the structural and electronic properties of such hybrids. Our study clearly identifies the importance of the relative orientation of the two components, the nanodiamond and the nucleobase, in the complex in controlling the electronic properties of the resulting hybrid. The position of the defect at the center or closer to its interface with the nucleobase further controls the electronic orbitals around the defect center, hence its optical activity. In the end, we discuss the relevance of our work in biosensing.
关键词： electronic structure,defects,DFT,DNA,nanodiamond
更新于2025-09-23 15:22:29
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Semiconducting B<sub>13</sub>C<sub>2</sub> system: Structure search and DFT-based analysis
摘要： DFT calculation on Boron Carbide in B13C2 stoichiometry using a 15-atom unit cell necessarily results in metallic ground state regardless of the crystal structure. This is because such a unit cell consists of odd number of electrons, and hence complete filling of the top most band(s) of nonzero occupancy is impossible. This is in contrast to the observed semiconducting nature. If the crystal structure of B13C2 is made of a 30-atom unit cell which cannot be reduced to a 15 atom cell, there is a possibility of obtaining either a metallic or a semiconducting state as such a cell consists of an even number of electrons. In this work the evolutionary algorithm based structure search using 30-atom unit cells has yielded a previously unreported semiconducting system of B13C2 with unique bonding pattern. The mechanical and dynamical stability of the system have been properly established through the computation of elastic constants and phonon spectra. Its bond lengths, elastic moduli, hardness and infrared spectrum are in good agreement with experimental data.
关键词： Boron Carbide,elastic constants,evolutionary algorithm,DFT,phonon spectra,semiconducting,structure search,B13C2
更新于2025-09-23 15:22:29
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Syntheses, X-Ray Crystal Structures, Emission Properties and DFT Calculations of Monoprotonated Polypyridines
摘要： Monoprotonated compounds [(L)HPF6] were prepared by the reaction of (L = bpy, phen, dpphen, bqn and ppy) with concentrated HCl in water. Monoprotonated pyridine rings are hydrogen bonded intramolecularly to the adjacent pyridine ring and intermolecularly to the adjacent PF6- in compounds. These hydrogen bonds restrain the nonradiative decay to produce intense emission. Density functional theory was applied to interpret the planarity in compounds. The attachment of one proton to the nitrogen in [(dpphen)HPF6] and [(bqn)HPF6] leads to the strong emission in acetonitrile (Φ = 0.046 and 0.097, respectively). In particular, the attachment of one proton to the ppy nitrogen results in exhibiting a strong emission with a large quantum yield (Φ = 0.264).
关键词： crystal structure,DFT calculations,blue emission,monoprotonated polypyridine
更新于2025-09-23 15:22:29
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Phase Transition in Two-dimensional Tellurene under Mechanical Strain Modulation
摘要： We carry out computational simulations based on density functional theory (DFT) to investigate different phases of two-dimensional (2-D) tellurene. These phases are classified by their characteristic space groups and symmetry elements. Correlations of these phases to the bulk crystalline tellurium structure are also illustrated. Our specific interests include mechanical property calculations for different phases and the possible phase transitions between them. Simulation results show that these 2-D Te phases have very different elastic moduli due to their different atomic bonding and relaxed structures. Moreover, compression along the in-plane directions facilitates the α → β phase transition, while in-plane tensile strains always make the α-phase more stable than the β-phase. However, the energy difference between the two phases is comparable to or even much smaller than the thermal energy kT, depending on the in-plane strain direction. We find that further increase of the tensile strain along the chain direction beyond a critical value, ca. 12%, may lead to a possible α → γ phase transition. As the tensile strain is above 15%, the γ-phase will be more stable than the α-phase, accompanied by a further reduced transition energy barrier.
关键词： phase transition,elastic modulus,Tellurene,strain engineering,density functional theory (DFT),2-D materials
更新于2025-09-23 15:22:29
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Enhanced NLO activity of organic 2-methyl-5-nitroaniline crystal: Experimental and computational investigation with and without silver addition
摘要： The nonlinear optical (NLO) material, 2-methyl-5-nitroaniline (M5NA), is synthesized and the crystals are grown by slow evaporation technique. The theoretical vibrational spectral analyses are done for the first time for M5NA using B3LYP computational method with the basis set cc-pVTZ. Natural Bond Orbital (NBO) and Atoms In Molecules (AIM) analyses are carried out for obtaining the charge transfer interactions and the Hirshfeld surface analysis with the fingerprint plot is performed for finding out the intermolecular interaction sites of the molecule. Using the theoretical and experimental IR and Raman spectra, the vibrations of M5NA are estimated. Changes in the linear and nonlinear optical properties with the addition of silver nanoparticles are studied from the UV–vis absorption spectra and the Z-Scan curves. A comparison of the hyperpolarizability values is done with pure and silver-added M5NA.
关键词： NLO,HOMO-LUMO,DFT,Vibrational spectroscopy,Silver nanoparticles
更新于2025-09-23 15:22:29
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Two novel rhodamine-based fluorescent probes for the rapid and sensitive detection of Fe3+: Experimental and DFT calculations
摘要： Fe3+ ions play an important role in both biological and environmental field. In this work, two novel rhodamine-based colorimetric and fluorescent probes (RBA2 and RBA3) were designed and synthesized for the efficient detection of Fe3+. Upon the addition of Fe3+, the fluorescence intensity of RBA2 and RBA3 enhanced 108-fold and 222-fold, respectively. RBA2 and RBA3 exhibited a low detection limit which could achieve 12.8 nM and 11.0 nM. In addition, the binding modes of RBA2 and RBA3 with Fe3+ were proved to be 1:1 stoichiometry in the complexes by Job’s plot, ESI-MS and 1H NMR results. The complexing ability of RBA3 with Fe3+ excessed to that of RBA2 that was determined by the binding association constants, and highly consistent with DFT calculations results. Furthermore, RBA2 and RBA3 were further utilized to detect Fe3+ in living cells and real water samples, indicating their promising prospects in biological and environmental field.
关键词： Cell imaging,DFT calculation,Binding ability,Naked eye,Fe3+
更新于2025-09-23 15:22:29
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Graphene Nucleation Preference at CuO Defects Rather Than Cu2O on Cu(111): A Combination of DFT Calculation and Experiment
摘要： It is well-known that reducing the nucleation density is an effective way to enhance the growth quality of graphene. In this work, we explore the mechanism of graphene nucleation and growth around CuO defects on a Cu(111) substrate by using density functional theory (DFT) combined with the nudged elastic band (NEB) method. The defect formation mechanism at the initial nucleation stage is also studied. Our calculation results of the C adsorption energy and the reaction barrier of C–C dimer formation illustrate that the initial nucleation of graphene could be promoted by artificially introducing CuO defects on a Cu(111) surface and the nucleation on the clean Cu(111) substrate could thus be suppressed. These conclusions have been verified by graphene growth experiments using a chemical vapor deposition (CVD) method. Further studies showed that graphene grown around CuO “seed crystals” could maintain its structural integrity without significantly producing defective carbon rings. This work provides fundamental understanding and theoretical guidance for controllable preparing large dimension and high quality graphene by artificially introducing CuO seeds.
关键词： CuO,Cu2O,Graphene,DFT,Nucleation
更新于2025-09-23 15:21:21
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Apply DFT Integrated Enhanced EBAC Methodology on Defect Isolations
摘要： Design for test (DFT) has been widely applied to digital circuit failure analysis (FA) in semiconductor industries. The FA methods based on DFT involve layer-by-layer checks using a polisher and an SEM for defect identification and localization. Yet these methods have limitations with high risks of sample damages. Besides, they are highly dependent on the technical proficiencies of operators and, thus, they are not effective for precise defect isolations. This problem has been aggravated, especially at advanced nodes. The nano-probing electron beam absorbed current (EBAC) has significant advantages on precisely locating defects. This technique is to directly identify specific defects without layer-by-layer checks. Therefore, it can minimize sample damages during sample pretreatment. EBAC is an efficient technique to isolate the defects when the circuit is at the floating condition. Because the ground lines exist almost everywhere in a chip and they are for, e.g., electronic static discharge charge releases or connecting with sources for pickup, EBAC becomes a natural option for us. However, due to poor EBAC images, EBAC’s applications are restricted when the circuits under test have grounding paths. In this paper, we propose two enhanced EBAC analysis methods, based on the DFT and EBAC integrated system, for the defect isolations with grounded connections. It is the first time the DFT and EBAC integrated system is reported, and we successfully demonstrated EBAC applicability by real FA cases.
关键词： Design for test (DFT),Grounding line,Fault isolation,Electron beam absorbed current (EBAC),Failure analysis (FA)
更新于2025-09-23 15:21:21
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Defect-associated adsorption of monoethanolamine on TiO2(1 1 0): An alternative way to control the work function of oxide electrode
摘要： Controlling defects is one of the basic strategies for tailoring electronic structure of materials, which has not been explored that much yet for organic-inorganic hybrid systems. In this study, we investigated the control of work function of oxide electrode by defect-associated adsorption of molecules at the single-molecule level by means of scanning tunneling microscopy and first principle calculations. The equilibrium adsorption configuration of monoethanolamine (MEA, HO(CH2)2NH2), an effective coating for lowering the work function of an oxide electrode, varies as a function of surface coverage at TiO2(1 1 0) surfaces. Our results showed that defects at the oxide surface and intermolecular interactions dominate the stable configuration of adsorbates as well as work function of the system. The dissociative adsorption at Ov was found to be more efficient at lowering the work function of TiO2(1 1 0) surface, suggesting that defect control can be used to improve the performance of organic-inorganic hybrid systems.
关键词： STM,Work function,DFT,TiO2(1 1 0),Defect,Monoethanolamine
更新于2025-09-23 15:21:21
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Novel A2-D-A1-D-A2 type NIR absorbing symmetrical squaraines based on 2, 3, 3, 8-tetramethyl-3H-pyrrolo [3, 2-h] quinoline: Synthesis, photophysical, electrochemical, thermal properties and photostability study
摘要： Two novel acceptor–donor-acceptor-donor-acceptor type pi-conjugated symmetrical squaraine dyes, denoted by PQSQ 1 and PQSQ 2 based on 2, 3, 3, 8-tetramethyl -3H-pyrrolo [3,2-h] quinoline were successfully synthesized for the first time to arrive absorption and emission at NIR region. These dyes comprise indolenines as electron donor units, squaryl ring as a central electron acceptor and pyridines as terminal electron acceptor units. The relationship between molecular structures and photophysical properties of these dyes was studied in comparison with their parent compounds (ISQ and N-Et ISQ). These novel squaraine dyes displayed an intense absorption within the range 671 to 692 nm in polar to non- polar solvents respectively with good molar extinction coefficients (? 105 Lmol-1cm-1). Compared to their parent squaraines, both dyes showed red-shifted absorption (33 - 44 nm) as well as emission (38 - 59 nm) due to the electron-accepting ability of the ancillary pyridine acceptors and extended pi-conjugation. These dyes exhibited negative solvatochromism and Reichardt's ET (30) scale was applied to propose a quantitative relationship of the relative stability of ground and excited-state of these squaraines with solvent polarity. The electrochemical and computational properties of these symmetrical squaraines were investigated with the help of cyclic voltammetry and density functional theory (DFT). Moreover, PQSQ 1-2 exhibited high thermal and photo-stability. These A2-D-A1-D-A2 type dyes showed improved photostabilities compared to their parent D-A-D type dyes.
关键词： 2, 3, 3, 8-tetramethyl -3H-pyrrolo [3, 2-h] quinoline,NIR absorbing dyes,acceptor-donor-acceptor-donor-acceptor,squaraines,DFT computations,red shift
更新于2025-09-23 15:21:21