Self-directed growth of molecular nanostructures on silicon

Unraveling pnicogen bonding cooperativity: Insights from molecular electrostatic potential analysis

A theoretical investigation on the cooperativity of a series of binary, ternary, and quaternary complexes interconnected by pnicogen bonds has been conducted using calculations at the M06-2X/aug-cc-pVTZ level of density functional theory. By measuring changes in the molecular electrostatic potential (MESP) at the nucleus of interacting atoms in all of the complexes, it is possible to quantify the substantial reorganization of the electron density triggered by the formation of pnicogen bonds. The positive change in MESP, indicating a loss of electron density from the donor molecule in a dimer, facilitates the acceptance of electron density from a third molecule, resulting in the formation of a ternary complex with a stronger pnicogen bond compared to the one present in the binary complex. Similarly, the acceptor molecule in a dimer with a negative change in MESP showed an enhanced tendency to donate electron density to an electron-deficient third molecule. The MESP analysis provided valuable insights into the donor/acceptor characteristics of pnicogen bonds within the quaternary complexes. The proposed MESP hypotheses are consistent with the positive cooperativity observed in the pnicogen-bonded clusters. To quantify the changes in MESP, both at the donor atom (ΔVdonor ) and the acceptor atom (ΔVacceptor ), for all pnicogen bonds in the cluster, the total change in MESP (ΔΔVn ) was measured as ΔΔVn  = ∑(ΔVdonor )-∑(ΔVacceptor ). Remarkably, ΔΔVn exhibited a strong linear relationship with the sum of the bond energies of the pnicogen bonds in the cluster. This establishes the MESP analysis as a robust approach for understanding the strength and cooperative behavior of pnicogen-bonded clusters. Additionally, the MESP features provided clear evidence of pnicogen bond formation, further supporting the reliability of this approach.

Non-covalent interactions in the monohydrated complexes of 1,2,3,4-tetrahydroisoquinoline

The eleven monohydrates of 1, 2, 3, 4-tetrahydroisoquinoline (THIQ) are analyzed through natural bond orbital (NBO) analysis and QTAIM methods employing M06-2X functional in DFT and MP2 methods. Here, the role of OH bonds as an acceptor and donor is critically analyzed. The role of lone pairs of O is critically monitored in two of the complexes, where N-H···O hydrogen bonds are present. The relative contributions of rehybridisation and hyperconjugation are compared in detail. Popelier criteria are satisfied in all the complexes barring a few exceptions involving weak hydrogen bonds. At the bond critical points (BCP), four monohydrates show higher values of electron density (ρ_C) and negative values of total electron energy density (H_C), while Laplacian [Formula: see text] remains positive. These complexes satisfy the criteria of partial covalency. All these are O-H⋅⋅⋅N-type bonds. Remaining h-bonds are weaker in nature. These are also confirmed by the smaller values of ρ_C at the respective BCP. The variation of potential energy density (V_C) among the complexes seems to be the most important factor in determining the nature of non-covalent interactions.

A computational study on acetaminophen drug complexed with Mn+, Fe2+, Co+, Ni2+, and Cu+ ions: structural analysis, electronic properties, and solvent effects

In the present research, the cation-π interactions in acetaminophen-M complexes (M = Mn⁺, Fe²⁺, Co⁺, Ni²⁺, and Cu⁺) are investigated using density functional theory (DFT/ωB97XD) in the gas phase and solution. The results show that the absolute values of energy are reduced in going from the gas phase to the solution. Based on the obtained data, the complexes in water are the most stable. The natural bond orbital (NBO) and the atoms in molecules (AIM) analyses are also applied to achieve more details about the nature of interactions. These results are useful for understanding the role of the drug-receptor interactions in the complexes. According to AIM outcomes, the cation-π interactions are the closed-shell and may indicate the partially covalent nature in the complexes. A comprehensive analysis is also performed on the conceptual DFT parameters of the complexes to evaluate their electronic properties. Our findings show increasing the stability and decreasing the reactivity of the complexes in the solution phase with respect to the gas phase. These interactions are ubiquitous in biological systems, and their importance in theoretical models led us to study such important interactions. The results of this study may be useful for the design and synthesis of a variety of supramolecular complexes with the desired properties.

In Situ Synthesis and Dual Functionalization of Nano Silicon Enabled by a Semisolid Lithium Rechargeable Flow Battery

Nanosized silicon has attracted considerable attentions as a new-generation anode material for lithium-ion batteries (LIBs) due to its exceptional theoretical capacity and reasonable cyclic stability. However, serious side reactions often take place at the nanosized silicon/electrolyte interface in LIBs, where critical electrochemical properties such as initial Coulombic efficiency (ICE) are compromised. On the basis of this feature, a new method is developed to synthesize nanosilicon-based particles in a facile, scalable way, which are endowed with the function of prelithiation and storage stability in air. A semisolid lithium rechargeable flow battery (SSFB) technology is used for the first time to convert the micrometer-sized silicon raw material into an amorphous-nanosilicon-based material (ANSBM), as a result of the pulverization process induced by the repeated lithiation/delithiation cycles. The particle size is successfully reduced from 1-4 μm to around 30 nm after cycles in the flow battery. Bulk functionalization of the nano silicon is introduced by the unbalanced lithiation/delithiation cyclic process, which endows ANSBM with a unique prelithiation capability universally applicable to different anode systems such as nanosized Si, SiO_x, and graphite, as evidenced by the significantly improved ICEs. Superior air stability (10% relative humidity) is exhibited by ANSBM due to surface functionalization by the stable interfacial layer encapsulated by electron-conductive carbon. The outcome of this work provides a promising way to synthesize dual-functionalized nano silicon with good electrochemical performance in terms of improved capacity and increased initial Coulombic efficiency when it is composited with other typical anode materials.

Pervasive orientational and directional locking at geometrically heterogeneous sliding interfaces

Understanding the drift motion and dynamical locking of crystalline clusters on patterned substrates is important for the diffusion and manipulation of nano- and microscale objects on surfaces. In a previous work, we studied the orientational and directional locking of colloidal two-dimensional clusters with triangular structure driven across a triangular substrate lattice. Here we show with experiments and simulations that such locking features arise for clusters with arbitrary lattice structure sliding across arbitrary regular substrates. Similar to triangular-triangular contacts, orientational and directional locking are strongly correlated via the real- and reciprocal-space Moiré patterns of the contacting surfaces. Due to the different symmetries of the surfaces in contact, however, the relation between the locking orientation and the locking direction becomes more complicated compared to interfaces composed of identical lattice symmetries. We provide a generalized formalism which describes the relation between the locking orientation and locking direction with arbitrary lattice symmetries.

The Effect of Deposition Time on the Surface Coverage of Sublimation Deposited Solid-Phase Glycine and Proline Molecules Measured by Scanning Tunneling Microscopy

The effect of deposition time on the surface coverage of sublimation deposited solid-phase glycine and proline molecules onto a Ge(100) surface was studied at room temperature using scanning tunneling microscopy (STM). The STM images obtained at various coverages of glycine and proline adsorbed on the Ge(100) surface showed that (i) the adsorption rate for both molecules gradually decreased with increasing deposition time, obeying the Langmuir adsorption model, and (ii) the coverage of glycine on the Ge(100) surface is higher than that of proline under the same deposition conditions, which may be due to the differences in their molecular weight or molecular sticking probability.

Ultratrace Nitroaromatic Vapor Detection via Surface-Enhanced Fluorescence on Carbazole-Terminated Black Silicon

Detection of nitroaromatic compounds (NACs) is an important applied task for environmental monitoring, medical diagnostics, and forensic analysis. However, detection of NAC vapors is challenging owing to their low vapor pressure and relatively weak sensitivity of the existing detection techniques. Here, we propose a novel concept to design fluorescence (FL) detection platforms based on chemical functionalization of nanotextured dielectric surfaces exhibiting resonant light absorption, trapping, and localization effects. We demonstrate highly-efficient NAC vapor sensor with selective FL-quenching response from monolayers of carbazole moieties covalently bonded to a spiky silicon surface, "black" silicon, produced over the centimeter-scale area using simple reactive ion etching. The sensor is shown to provide unprecedented ppt (10^-12) range limits of detection for several NAC vapors. Easy-to-implement scalable fabrication procedure combined with simple and versatile functionalization techniques applicable to all-dielectric surfaces make the suggested concept promising for realization of various gas sensing systems for social and environmental safety applications.

Nanotip-assisted photoreduction of silver nanostructures on chemically patterned ferroelectric crystals for surface enhanced Raman scattering

Nanotips made of metal and semiconductor have been widely utilized in versatile applications to strengthen the electric field through lightning rod effect and localized surface plasmon resonance (LSPR) effect. Here, we present the utilization of ferroelectric nanotips to assist photoreduction of silver nanostructures for surface enhanced Raman scattering (SERS). Ferroelectric nanotips with spontaneous polarization posses the unique feature of producing the permanent electrostatic field without requiring external excitation, which differs from the present nanotips requiring electrical and optical excitation. The enhanced electrostatic field promotes the formation of silver nanoparticles by reducing the effect of Stern layer and accelerating the movement of photoelectrons and silver ions to the template surface. Experimental results show that sharp ferroelectric nanotips facilitate the formation of large-diameter nanoparticles with strong LSPR action. Compared to the conventional ferroelectric templates, the SERS substrates using nanotip-equipped ferroelectric templates produce 5.51 times larger Raman intensity, which can be further increased by >10.76 times by increasing the reaction time. The proposed SERS substrate owns the limit of detection <10-8 M and the enhancement factor of 2.3 × 109. The presented ferroelectric nanotips with permanent electrostatic field would open promising applications in the versatile areas, such as nanomaterial fabrication and optoelectronic devices.

Molecular Surface Functionalization of Carbon Materials via Radical-Induced Grafting of Terminal Alkenes

Formation of functional monolayers on surfaces of carbon materials is inherently difficult because of the high bond strength of carbon and because common pathways such as SN2 mechanisms cannot take place at surfaces of solid materials. Here, we show that the radical initiators can selectively abstract H atoms from H-terminated carbon surfaces, initiating regioselective grafting of terminal alkenes to surfaces of diamond, glassy carbon, and polymeric carbon dots. Nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS) demonstrate formation of self-terminating organic monolayers linked via the terminal C atom of 1-alkenes. Density functional theory (DFT) calculations suggest that this selectivity is at least partially thermodynamic in origin, as significantly less energy is needed to abstract H atoms from carbon surfaces as compared to typical aliphatic compounds. The regioselectivity favoring binding to the terminal C atom of the reactant alkenes arises from steric hindrance encountered in bond formation at the adjacent carbon atom. Our results demonstrate that carbon surface radical chemistry yields a versatile, selective, and scalable approach to monolayer formation on H-terminated carbon surfaces and provide mechanistic insights into the surface selectivity and regioselectivity of molecular grafting.

Hexacene generated on passivated silicon

On-surface synthesis represents a successful strategy to obtain designed molecular structures on an ultra-clean metal substrate. While metal surfaces are known to favor adsorption, diffusion, and chemical bonding between molecular groups, on-surface synthesis on non-metallic substrates would allow the electrical decoupling of the resulting molecule from the surface, favoring application to electronics and spintronics. Here, we demonstrate the on-surface generation of hexacene by surface-assisted reduction on a H-passivated Si(001) surface. The reaction, observed by scanning tunneling microscopy and spectroscopy, is probably driven by the formation of Si-O complexes at dangling bond defects. Supported by density functional theory calculations, we investigate the interaction of hexacene with the passivated silicon surface, and with single silicon dangling bonds.

How a tertiary diamine molecule chelates the silicon dimers of the Si(001) surface: a real-time scanning tunneling microscopy study

The patterning of silicon surfaces by organic molecules emerges as an original way to fabricate innovative nanoelectronic devices. In this regard, we have studied how a diamine, N,N,N',N'-tetramethylethylenediamine (TMEDA, (CH₃)₂N-[CH₂]₂-N(CH₃)₂), chelates the silicon dimers of the Si(001)-2 × 1 surface. Starting from very low coverage to surface saturation (at 300 K), we used real-time scanning tunneling microscopy (STM) in a scanning-while-dosing approach. The images show that the molecules can adopt two bonding configurations: the cross-trench (CT) configuration by bridging two adjacent dimer rows, and the end-bridge (EB) configuration by chelating two adjacent dimers in the same row. However, while CT dominates over EB at low coverage, the percentage of EB adducts steadily increases, until it becomes largely dominant at high molecular coverage. Above a critical coverage θ_mol of ∼0.13 monolayer (ML), a sudden change in the molecular imprints is seen, likely due to a change in the tunneling conditions. The EB stapling of two adjacent dimers in a row via a dual-dative bond (as shown by XPS) is achieved efficiently by the TMEDA molecule with a very high chemical selectivity. The EB is a unique configuration in amine adsorption chemistry, as it leads to the formation of a pair of first-neighbor, doubly-occupied dangling bonds. Further reactivity of the EB site with other molecules remains to be explored, and possible reaction schemes are envisaged.

Half-flat vs. atomically flat: Alkyl monolayers on morphologically controlled Si(100) and Si(111) have very similar structure, density, and chemical stability

Chemists have long preferred the Si(111) surface for chemical functionalization, as a simple aqueous etch can be used to produce ideal, atomically flat H/Si(111) surfaces for subsequent reactions. In contrast, industry-standard etches produce rough H/Si(100) surfaces terminated by nanohillocks. The recent discovery of an aqueous etch that produces morphologically controlled H/Si(100) surfaces with a near atomically flat or "half-flat" morphology challenges the assumption that Si(111) is an inherently preferable starting point for chemical functionalization. This study shows that alkyl functionalization of morphologically controlled, "half-flat" Si(100) surfaces by terminal alkenes produces dense, tightly packed monolayers that are essentially identical to those on atomically flat Si(111). The striking similarity between the infrared spectra on these two surfaces - in terms of absolute absorbance, line shape and position, and polarization dependence - strongly suggests that alkyl monolayers on morphologically controlled Si(111) and Si(100) have essentially identical structures. The principle difference between the two surfaces is the amount of residual H at the Si/organic interface, a difference that is dictated by the structure of the Si(100) surface. Alkyl monolayers on morphologically controlled Si(111) and Si(100) surfaces were shown to be equally resistant to harsh oxidants. As a result, there appears to be no chemical reason to prefer one surface over the other, at least for functionalization with terminal alkenes.

Two-dimensional self-assembly of diacetylenic acid derivatives and their light-induced polymerization on HOPG surfaces

The effect of UV illumination time on the polymerization efficiency and the structural change of DA-25.

Power Laws in Adsorption and the Characterization of Heterogeneous Substrates

The adsorption of particles with repulsive nearest-neighbour interactions was studied through Monte Carlo simulation on bivariate surfaces characterized by patches of weak and strong adsorbing sites of size l. Patches were either arranged in a deterministic chessboard structure or in a random way. Quantities were identified which scale obeying power laws as a function of the scale length l. The consequences of these findings were discussed for the determination of the energetic topography of the surface from adsorption measurements.

Monte Carlo Simulation of the Adsorption of Binary Gas Mixtures on Heterogeneous Surfaces

The adsorption of a gaseous mixture containing particles A and B was studied via lattice-gas simulations on homogeneous and heterogeneous bivariate surfaces characterized by a chessboard topography of strong and weak adsorbing sites. The effects of lateral interactions among adsorbed particles and of heterogeneity on the adsorption isotherms and differential heats of adsorption were analyzed.

The results displayed a rich variety of behaviours and their analysis contributes to the understanding of mixed-gas adsorption at a molecular level.

Single-Molecule Rotational Switch on a Dangling Bond Dimer Bearing

One of the key challenges in the construction of atomic-scale circuits and molecular machines is to design molecular rotors and switches by controlling the linear or rotational movement of a molecule while preserving its intrinsic electronic properties. Here, we demonstrate both the continuous rotational switching and the controlled step-by-step single switching of a trinaphthylene molecule adsorbed on a dangling bond dimer created on a hydrogen-passivated Ge(001):H surface. The molecular switch is on-surface assembled when the covalent bonds between the molecule and the dangling bond dimer are controllably broken, and the molecule is attached to the dimer by long-range van der Waals interactions. In this configuration, the molecule retains its intrinsic electronic properties, as confirmed by combined scanning tunneling microscopy/spectroscopy (STM/STS) measurements, density functional theory calculations, and advanced STM image calculations. Continuous switching of the molecule is initiated by vibronic excitations when the electrons are tunneling through the lowest unoccupied molecular orbital state of the molecule. The switching path is a combination of a sliding and rotation motion over the dangling bond dimer pivot. By carefully selecting the STM conditions, control over discrete single switching events is also achieved. Combined with the ability to create dangling bond dimers with atomic precision, the controlled rotational molecular switch is expected to be a crucial building block for more complex surface atomic-scale devices.

Van der Waals molecular interactions in the organic functionalization of graphane, silicane, and germanane with alkene and alkyne molecules: a DFT-D2 study

Density functional theory with the addition of a semi-empirical dispersion potential was applied to the conventional Kohn-Sham energy to study the adsorption of alkene and alkyne molecules on hydrogen-terminated two-dimensional group IV systems (graphane, silicane, and germanane) by means of a radical-initiated reaction. In particular, we investigated the interactions of acetylene, ethylene, and styrene with those surfaces. Although we had studied these systems previously, we included van der Waals interactions in all of the cases examined in the present work. These forces, which are noncovalent interactions, can heavily influence different processes in molecular chemistry, such as the adsorption of organic molecules on semiconductor surfaces. This unified approach allowed us to perform a comparative study of the relative reactivities of the various organic molecule/surface systems. The results showed that the degree of covalency of the surface, the lattice size, and the partial charge distribution (caused by differences in electronegativity) are all key elements that determine the reactivity between the molecules and the surfaces tested in this work. The covalent nature of graphane gives rise to energetically favorable intermediate states, while the opposite polarities of the charge distributions of silicane and germanane with the organic molecules favor subsequent steps of the radical-initiated reaction. Finally, the lattice size is a factor that has important consequences due to steric effects present in the systems and the possibility of chain reaction continuation. The results obtained in this work show that careful selection of the substrate is very important. Calculated energy barriers, heats of adsorption, and optimized atomic structures show that the silicane system offers the best reactivity in organic functionalization.

Towards 1D nanolines on a monolayered supramolecular network adsorbed on a silicon surface

The growth of 3D extended periodic networks made up of π-conjugated molecules on semi-conductor surfaces is of interest for the integration of nano-components in the future generations of smart devices. In the work presented in this article, we successfully achieved the formation of bilayered networks on a silicon surface including 1D-isolated nanolines in the second layer. Firstly, we observed the formation of a 2D large-scale supramolecular network in the plane of a silicon surface through the deposition of tailored molecules. Then using the same molecules, a second-layer, based on 1D nanolines, grew above the first layer, thanks to a template effect. Mono- or bi-layered networks were found to be stable from 100 K up to room temperature. These networks were investigated by scanning tunnel microscopy imaging under an ultra-high vacuum (UHV-STM).

Multiscale Self-Assembly of Silicon Quantum Dots into an Anisotropic Three-Dimensional Random Network

Multiscale self-assembly is ubiquitous in nature but its deliberate use to synthesize multifunctional three-dimensional materials remains rare, partly due to the notoriously difficult problem of controlling topology from atomic to macroscopic scales to obtain intended material properties. Here, we propose a simple, modular, noncolloidal methodology that is based on exploiting universality in stochastic growth dynamics and driving the growth process under far-from-equilibrium conditions toward a preplanned structure. As proof of principle, we demonstrate a confined-but-connected solid structure, comprising an anisotropic random network of silicon quantum-dots that hierarchically self-assembles from the atomic to the microscopic scales. First, quantum-dots form to subsequently interconnect without inflating their diameters to form a random network, and this network then grows in a preferential direction to form undulated and branching nanowire-like structures. This specific topology simultaneously achieves two scale-dependent features, which were previously thought to be mutually exclusive: good electrical conduction on the microscale and a bandgap tunable over a range of energies on the nanoscale.

Orientation and stability of a bi-functional aromatic organic molecular adsorbate on silicon

In this work we combine scanning tunneling microscopy, near-edge X-ray absorption fine structure spectroscopy, X-ray photoemission spectroscopy and density functional theory to resolve a long-standing confusion regarding the adsorption behaviour of benzonitrile on Si(001) at room temperature.

A theoretical guide for fabricating a conductive molecular wire on a silicon surface via an in situ surface polymerization reaction

It has been a long-standing goal to make conductive molecular wires or linear polymer chains on traditional semiconductors or insulator substrates to satisfy the ongoing miniaturization in electronic devices. Here, we have proposed a surface in situ polymerization reaction for a pre-absorbed molecule, 4-hydrazinyl-3-(pyridin-4-ylmethyl)-benzaldehyde (HPyMB), to produce a conductive molecular wire on a silicon surface. Our first-principles calculations show that HPyMB molecules can absorb alternatively on the exposed Si atoms created via ultrahigh vacuum scanning tunneling microscopy on a hydrogen passivated H-Si(001)2 × 1 surface along the [110] direction. The adsorption is exothermic and its generated energy is sufficient for the following intermolecular dehydration polymerization reaction to overcome the activation energy barriers and thereafter form a molecular wire on the surface. This polymerized molecular wire is mechanically stable since it is chemically bonded onto the surface. After polymerization, the system becomes conductive due to the charge transfer from the molecule-surface bonds to their pyridine rings. More importantly, by removing 1.1 electrons from the system, the surface polymer chain is the sole conductive channel. Furthermore, its conducting nature remains robust even under a large external electric field. Our findings open a new window for the fabrication of conductive molecular wires or polymer chains on semiconductor surfaces, and provide insights into the mechanism behind the molecular wire conductivity.

Contact effects and quantum interference in engineered dangling bond loops on silicon surfaces

Dangling bond structures created on H-passivated silicon surfaces offer a novel platform for engineering planar nanoscale circuits, compatible with conventional semiconductor technologies. In this investigation we focus on the electronic structure and quantum transport signatures of dangling bond loops built on H-passivated Si(100) surfaces contacted by carbon nanoribbons, thus leading to a two-terminal planar, nanoscale setup. The computational studies were carried out to rationalize the influence of the local atomic-scale contacts of the dangling bond system to the mesoscopic electrodes as well as the possibility of revealing quantum interference effects in the dangling bond loops. Our results reveal a strong sensitivity of the low-energy quantum transmission to the loop topology and to the atomistic details of the electrode-loop contact. Varying the length of the loop or the spatial position of at least one of the electrodes has a drastic impact on the quantum interference pattern; depending on whether constructive or destructive interference within the loop takes place, the conductance of the system can be tuned over several orders of magnitude, thus suggesting the possibility of exploiting such quantum mechanical effects in the design of two-dimensional, atomic-scale electronic devices such as logic gates.

Propanoate grafting on (H,OH)-Si(0 0 1)-2 × 1

We have examined the reactivity of water-covered Si(0 0 1)-2 × 1, (H,OH)-Si(0 0 1)-2 × 1, with propanoic (C2H5COOH) acid at room temperature. Using a combination of spectroscopic techniques probing the electronic structure (XPS, NEXAFS) and the vibrational spectrum (HREELS), we have proved that the acid is chemisorbed on the surface as a propanoate. Once the molecule is chemisorbed, the strong perturbation of the electronic structure of the hydroxyls, and of their vibrational spectrum, suggests that the molecule makes hydrogen bonds with the surrounding hydroxyls. As we find evidence that surface hydroxyls are involved in the adsorption reaction, we discuss how a concerted or a radical-mediated reaction (involving the surface silicon dangling bonds) could lead to water elimination and formation of the ester.

Reaction pathways for pyridine adsorption on silicon (0 0 1)

Density functional theory is used to describe the reactions of chemisorption of pyridine on the silicon (0 0 1) surface. Adsorption energies of six relevant structures, and the activation energies between them are reported. We consider in detail the dative to tight-bridge transition for which conflicting results have been reported in the literature, and provide a description of the formation of inter-row chains observed in high-coverage experiments. We demonstrate that the choice of DFT functional has a considerable effect on the relative energetics and of the four DFT functionals considered, we find that the range-separated hybrid ωB97X-D functional with empirical dispersion provides the most consistent description of the experiment data.

Electric field induced hydrogenation of silicene

The electric field can act as a catalyst to reduce the energy barrier of H₂ molecule dissociative adsorption on silicene, thus facilitating the hydrogenation of silicene.

Formation of stable nitrene surface species by the reaction of adsorbed phenyl isocyanate at the Ge(100)-2 × 1 surface

The reaction of phenyl isocyanate (PIC) following adsorption at the Ge(100)-2 × 1 surface has been investigated both experimentally and theoretically by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy, temperature-programmed desorption, quantum chemical calculations, and molecular dynamics simulations. PIC initially adsorbs by [2 + 2] cycloaddition across the C═N bond of the isocyanate, as previously reported, but this initial product converts to a second product on the time scale of minutes at room temperature. The experimental and theoretical results show that the second product formed is phenylnitrene (C6H5N) covalently bonded to the germanium surface via a single Ge-N bond. This conclusion is further supported by FTIR spectroscopy experiments and density functional theory calculations using phenyl isocyanate-(15)N and phenyl-d5 isocyanate.

Density functional theory study of the organic functionalization of hydrogenated silicene

Silicene, the silicon analogous of graphene, is a newly synthesized two-dimensional nanomaterial, with unique features and promising potential applications. In this paper we present density functional theory calculations of the organic functionalization of hydrogenated silicene with acetylene, ethylene, and styrene. The results are compared with previous works of the adsorption on H-Si[111]. For styrene, binding energies for the intermediate and final states as well as the energy barrier for hydrogen abstraction are rather similar for the two systems. On the other hand, results for acetylene and ethylene are surprisingly different in H-silicene: the abstraction barrier is much smaller in H-silicene than in H-Si[111]. These differences can be understood by the different electrostatic potentials due to the presence of the H atoms at the bottom of the silicene bilayer that allows the delocalization of the spin density at the reaction intermediate state.

Density functional theory study of the organic functionalization of hydrogenated silicene

Silicene, the silicon analogous of graphene, is a newly synthesized two-dimensional nanomaterial, with unique features and promising potential applications. In this paper we present density functional theory calculations of the organic functionalization of hydrogenated silicene with acetylene, ethylene, and styrene. The results are compared with previous works of the adsorption on H-Si[111]. For styrene, binding energies for the intermediate and final states as well as the energy barrier for hydrogen abstraction are rather similar for the two systems. On the other hand, results for acetylene and ethylene are surprisingly different in H-silicene: the abstraction barrier is much smaller in H-silicene than in H-Si[111]. These differences can be understood by the different electrostatic potentials due to the presence of the H atoms at the bottom of the silicene bilayer that allows the delocalization of the spin density at the reaction intermediate state.

Organic vapor passivation of silicon at room temperature

A simple, inexpensive, efficient, and scalable method to create air-stable organic surface passivation layers on silicon using a vapor-phase treatment is demonstrated. A variant of initiated chemical vapor deposition is used to synthesize a thin film that acts as both a passivation layer and an antireflective coating. The lowest surface recombination velocity reported to date is achieved and maintained during prolonged exposure to air.

Dispersive Electronic States of the π-Orbitals Stacking in Single Molecular Lines on the Si(001)-(2×1)-H Surface

One-dimensional (1D) molecular assemblies have been considered as one of the potential candidates for miniaturized electronic circuits in organic electronics. Here, we present the quantitative experimental measurements of the dispersive electronic feature of 1D benzophenone molecular assemblies on the Si(001)-(2×1)-H. The well-aligned molecular lines and their certain electronic state dispersion were observed by scanning tunneling microscopy (STM) and angle-resolved ultraviolet photoemission spectroscopy (ARUPS), respectively. Density functional theory (DFT) calculations reproduced not only the experimental STM image but also the dispersive features that originated from the stacking phenyl π-orbitals in the molecular assembly. We obtained the effective mass of 2.0me for the hole carrier along the dispersive electronic state, which was comparable to those of the single-crystal molecules widely used in organic electronic applications. These results ensure the one-dimensionally delocalized electronic states in the molecular lines, which is requisitely demanded for a charge-transport wire.