Accelerated Electron-Hole Separation at the Organic-Inorganic Anthracene/Janus MoSSe Interface.

Organic light-absorbing materials with two-dimensional semiconductor layers as contact electrodes are promising for efficient and flexible low-cost solar cells. Considering anthracene as an absorber and a MoSSe Janus monolayer, we use non-adiabatic molecular dynamics to show that electron transfer from anthracene to MoSSe is faster on the Se side than the S side. The transfer from anthracene to MoS and MoSe monolayers takes intermediate times.

Dimer Coupling Energies of the Si(001) Surface.

The coupling energies between the buckled dimers of the Si(001) surface were determined through analysis of the anisotropic critical behavior of its order-disorder phase transition. Spot profiles in high-resolution low-energy electron diffraction as a function of temperature were analyzed within the framework of the anisotropic two-dimensional Ising model. The validity of this approach is justified by the large ratio of correlation lengths, ξ_{∥}^{+}/ξ_{⊥}^{+}=5.

Urchin-like hierarchical ruthenium cobalt oxide nanosheets on TiCT MXene as a binder-free bifunctional electrode for overall water splitting and supercapacitors.

Synthesizing efficient electrode materials for water splitting and supercapacitors is essential for developing clean electrochemical energy conversion/storage devices. In the present work, we report the construction of a ruthenium cobalt oxide (RuCoO)/TiCT MXene hybrid by electrophoretic deposition of TiCT MXene on nickel foam (NF) followed by RuCoO nanostructure growth through an electrodeposition process. Owing to the strong interactions between RuCoO and TiCT sheets, which are verified by density functional theory (DFT)-based simulations, RuCoO/TiCT MXene@NF can serve as a bifunctional electrode for both water splitting and supercapacitor applications.

Dependence of electron transfer dynamics on the number of graphene layers in π-stacked 2D materials: insights from ab initio nonadiabatic molecular dynamics.

Recent time-resolved transient absorption studies demonstrated that the rate of photoinduced interfacial charge transfer (CT) from Zn-phthalocyanine (ZnPc) to single-layer graphene (SLG) is faster than to double-layer graphene (DLG), in contrast to the expectation from Fermi's golden rule. We present the first time-domain non-adiabatic molecular dynamics (NA-MD) study of the electron injection process from photoexcited ZnPc molecules into SLG and DLG substrates. Our calculations suggest that CT occurs faster in the ZnPc/SLG system than in the ZnPc/DLG system, with 580 fs and 810 fs being the fastest components of the observed CT timescales, respectively.

Size- and orientation-selective si nanowire growth: thermokinetic effects of nanoscale plasma chemistry.

A multiscale, multiphase thermokinetic model is used to show the effective control of the growth orientation of thin Si NWs for nanoelectronic devices enabled by nanoscale plasma chemistry. It is shown that very thin Si NWs with [110] growth direction can nucleate at much lower process temperatures and pressures compared to thermal chemical vapor deposition where [111]-directed Si NWs are predominantly grown. These findings explain a host of experimental results and offer the possibility of energy- and matter-efficient, size- and orientation-controlled growth of [110] Si NWs for next-generation nanodevices.

Plasma-enabled graded nanotube biosensing arrays on a Si nanodevice platform: catalyst-free integration and in situ detection of nucleation events.

Low-temperature plasmas in direct contact with arbitrary, written linear features on a Si wafer enable catalyst-free integration of carbon nanotubes into a Si-based nanodevice platform and in situ resolution of individual nucleation events. The graded nanotube arrays show reliable, reproducible, and competitive performance in electron field emission and biosensing nanodevices.

Kinetics of low-pressure, low-temperature graphene growth: toward single-layer, single-crystalline structure.

Graphene grown on metal catalysts with low carbon solubility is a highly competitive alternative to exfoliated and other forms of graphene, yet a single-layer, single-crystal structure remains a challenge because of the large number of randomly oriented nuclei that form grain boundaries when stitched together. A kinetic model of graphene nucleation and growth is developed to elucidate the effective controls of the graphene island density and surface coverage from the onset of nucleation to the full monolayer formation in low-pressure, low-temperature CVD. The model unprecedentedly involves the complete cycle of the elementary gas-phase and surface processes and shows a precise quantitative agreement with the recent low-energy electron diffraction measurements and also explains numerous parameter trends from a host of experimental reports.

SWCNT networks on nanoporous silica catalyst support: morphological and connectivity control for nanoelectronic, gas-sensing, and biosensing devices.

Effective control of morphology and electrical connectivity of networks of single-walled carbon nanotubes (SWCNTs) by using rough, nanoporous silica supports of Fe catalyst nanoparticles in catalytic chemical vapor deposition is demonstrated experimentally. The very high quality of the nanotubes is evidenced by the G-to-D Raman peak ratios (>50) within the range of the highest known ratios. Transitions from separated nanotubes on smooth SiO(2) surface to densely interconnected networks on the nanoporous SiO(2) are accompanied by an almost two-order of magnitude increase of the nanotube density.

Nanoscale plasma chemistry enables fast, size-selective nanotube nucleation.

The possibility of fast, narrow-size/chirality nucleation of thin single-walled carbon nanotubes (SWCNTs) at low, device-tolerant process temperatures in a plasma-enhanced chemical vapor deposition (CVD) is demonstrated using multiphase, multiscale numerical experiments. These effects are due to the unique nanoscale reactive plasma chemistry (NRPC) on the surfaces and within Au catalyst nanoparticles. The computed three-dimensional process parameter maps link the nanotube incubation times and the relative differences between the incubation times of SWCNTs of different sizes/chiralities to the main plasma- and precursor gas-specific parameters and explain recent experimental observations.

Plasma effects in semiconducting nanowire growth.

Three case studies are presented to show low-temperature plasma-specific effects in the solution of (i) effective control of nucleation and growth; (ii) environmental friendliness; and (iii) energy efficiency critical issues in semiconducting nanowire growth. The first case (related to (i) and (iii)) shows that in catalytic growth of Si nanowires, plasma-specific effects lead to a substantial increase in growth rates, decrease of the minimum nanowire thickness, and much faster nanowire nucleation at the same growth temperatures. For nucleation and growth of nanowires of the same thickness, much lower temperatures are required.

Thin single-walled carbon nanotubes with narrow chirality distribution: constructive interplay of plasma and Gibbs-Thomson effects.

Multiscale, multiphase numerical modeling is used to explain the mechanisms of effective control of chirality distributions of single-walled carbon nanotubes in direct plasma growth and suggest effective approaches to further improvement. The model includes an unprecedented combination of the plasma sheath, ion/radical transport, species creation/loss, plasma-surface interaction, heat transfer, surface/bulk diffusion, graphene layer nucleation, and bending/lift-off modules. It is shown that the constructive interplay between the plasma and the Gibbs-Thomson effect can lead to the effective nucleation and lift-off of small graphene layers on small metal catalyst nanoparticles.

Minimizing the Gibbs-Thomson effect in the low-temperature plasma synthesis of thin Si nanowires.

An advanced combination of numerical models, including plasma sheath, ion- and radical-induced species creation and plasma heating effects on the surface and within a Au catalyst nanoparticle, is used to describe the catalyzed growth of Si nanowires in the sheath of a low-temperature and low-pressure plasma. These models have been used to explain the higher nanowire growth rates, low-energy barriers, much thinner Si nanowire nucleation and the less effective Gibbs-Thomson effect in reactive plasma processes, compared with those of neutral gas thermal processes. The effects of variation in the plasma sheath parameters and substrate potential on Si nanowire nucleation and growth have also been investigated.

Low- and high-temperature controls in carbon nanofiber growth in reactive plasmas.

A numerical growth model is used to describe the catalyzed growth of carbon nanofibers in the sheath of a low-temperature plasma. Using the model, the effects of variation in the plasma sheath parameters and substrate potential on the carbon nanofiber growth characteristics, such as the growth rate, the effective carbon flux to the catalyst surface, and surface coverages, have been investigated. It is shown that variations in the parameters, which change the sheath width, mainly affect the growth parameters at the low catalyst temperatures, whereas the other parameters such as the gas pressure, ion temperature, and percentages of the hydrocarbon and etching gases, strongly affect the carbon nanofiber growth at higher temperatures.