One-dimensional Substrate Research Articles

Peak effect and dynamics of stripe- and pattern-forming systems on a periodic one-dimensional substrate.

We examine the ordering, pinning, and dynamics of two-dimensional pattern-forming systems interacting with a periodic one-dimensional substrate. In the absence of the substrate, particles with competing long-range repulsion and short-range attraction form anisotropic crystal, stripe, and bubble states. When the system is tuned across the stripe transition in the presence of a substrate, we find that there is a peak effect in the critical depinning force when the stripes align and become commensurate with the substrate. Under an applied drive, the anisotropic crystal and stripe states can exhibit soliton depinning and plastic flow. When the stripes depin plastically, they dynamically reorder into a moving stripe state that is perpendicular to the substrate trough direction. We also find that when the substrate spacing is smaller than the widths of the bubbles or stripes, the system forms pinned stripe states that are perpendicular to the substrate trough direction. The system exhibits multiple reentrant pinning effects as a function of increasing attraction, with the anisotropic crystal and large bubble states experiencing weak pinning but the stripe and smaller bubble states showing stronger pinning. We map out the different dynamic phases as a function of filling, the strength of the attractive interaction term, the substrate strength, and the drive, and demonstrate that the different phases produce identifiable features in the transport curves and particle orderings.

Role of finite probe size in measuring growth exponent in film deposition

We use computer simulations to investigate the effects of the tip diameter of an electrostatic force microscope (EFM) operating at a constant force on the extraction of the growth exponent β during film growing in a one-dimensional substrate. Laplace’s equation is solved in the EFM simulation using the finite element method to determine the electrostatic force between the tip and the film interface. Importantly, for EFM tips with sufficiently large apex diameters, the topographies calculated with EFM and those computed with the transformed mean height profile (TMHP) method, where the interface is divided into bins of the same tip diameter size and the average height within each bin is used to transform the original interface, are almost identical. This was shown in the context of lattice models of the Kardar–Parisi–Zhang (KPZ) and Villain–Lai–Das–Sarma (VLDS) classes. The global roughness of the film surface, W, scales with the diameter of the EFM tip, ε, as W/a=(ε/a)αg[Ψ], where a is the lattice parameter, α is the KPZ/VLDS roughness exponent, and g is a universal scaling function of the argument Ψ≡t/(ε/a)z, where t and z are the reduced time of deposition and the KPZ/VLDS dynamic exponent, respectively. These results provide a limit for ε from which a KPZ/VLDS growth exponent can be reliably determined with EFM at a constant force. When the EFM tip diameter is larger than the surface correlation length, a misleading effective growth exponent consistent with uncorrelated growth is found.

Bidirectional flow of two-dimensional dusty plasma under asymmetric periodic substrates driven by unbiased external excitations

Collective transport properties of a one-dimensional (1D) asymmetric periodic substrate modulated two-dimensional (2D) dusty plasma driven by an unbiased sinusoidal excitation force are investigated using Langevin dynamical simulations. It is discovered that by changing the amplitude and frequency of the unbiased sinusoidal external excitations, as well as the depth of the 1D asymmetric periodic substrate, both the direction and speed of the persistent particle flow can be adjusted, i.e., both the flow rectification and its reversal of the ratchet effect of the steady drift motion for particles are achieved using various excitations. For the studied 2D dusty plasma under the 1D asymmetric periodic substrate, when the amplitude of the excitation increases from zero, the magnitude of the overall drift velocity increases from zero to its first maximum in the easy direction of the 1D asymmetric periodic substrate, next decreases gradually back to zero, and then increases from zero to its second maximum in the hard direction of the 1D asymmetric periodic substrate before finally gradually decaying. It is found that, as the frequency of the excitation and the depth of the 1D asymmetric periodic substrate change, the maximum overall drift velocity also varies, exhibiting a similar variation trend as that for the change of the excitation amplitude. The observed ratchet effect in both the easy and hard directions of 1D asymmetric periodic substrate for 2D dusty plasma is attributed to the combination of the spatial symmetry breaking of the 1D asymmetric periodic substrate and the inertial effects of particles, which is further confirmed by the three different presented diagnostics.

A numerical study of the droplet impact dynamics on a two-dimensional random rough surface

Considerable efforts had been devoted to investigating numerically the droplet impact dynamics on a superhydrophobic surface, whereas most of these numerical simulations were restricted to the two-dimensional (2D) axisymmetric coordinate system with the one-dimensional (1D) substrate surface. In this work, a three-dimensional (3D) computational fluid dynamics (CFD) model, which intergrew a 2D random rough surface, was proposed to investigate the droplet impact dynamics, and the multi-phase flow issue was solved by the Navier–Stokes equations. It is remarkable that the 3D CFD model revealed several significant dynamic details that were not easily captured in a 2D axisymmetric coordinate system or practical experiments. For instance, the 3D CFD model provided a unique perspective to understand the varying dynamic behaviors of impinged droplet in terms of the velocity streamline and dynamic viscosity analyses. Herein, the dynamic viscosity diagram revealed that the sprawl droplet on the 2D random rough surface was classified as the Cassie state, while as the Wenzel state for the smooth surface, which also explained the better bouncing behaviors of the droplet from the random rough surface. Accordingly, we suggested a visual way to evaluate the solid–liquid contact area surrounded by the triple-phase contact line. The effects of finger protrusion and central cavity growth from the sprawl droplet on the vortex generation were further analyzed on the ground of the velocity amplitude distribution and streamline data. The present work can provide early guidance to inquire into the impact dynamics of droplets on the random rough surface.

Flocking dynamics mediated by weighted social networks.

We study the effects of animal social networks with a weighted pattern of interactions on the flocking transition exhibited by models of self-organized collective motion. We consider variations of traditional models of collective motion in which interactions between individuals are mediated by static complex weighted networks, representing patterns of social interactions. For a model representing dynamics on a one-dimensional substrate, application of a heterogeneous mean-field theory provides a phase diagram as function of the heterogeneity of the network connections and the correlations between weights and degree. In this diagram we observe two phases, one corresponding to the presence of a transition and other to a transition suppressed in an always ordered system, already observed in the nonweighted case. Interestingly, a third phase, with no transition in an always disordered state, is also obtained. These predictions, numerically recovered in computer simulations, are also fulfilled for the more realistic Vicsek model, with movement in a two-dimensional space. Additionally, we observe at finite network sizes the presence of a maximum threshold for particular weight configurations, indicating that it is possible to tune weights to achieve a maximum resilience to noise effects. Simulations in real weighted animal social networks show that, in general, the presence of weights diminishes the value of the flocking threshold, thus increasing the fragility of the flocking state. The shift in the threshold is observed to depend on the heterogeneity of the weight pattern.

Transport properties in multilayer adsorption of dimers.

In this paper, we study the transport properties (percolation and conductivity) of a two-dimensional structure created by depositing dimers on a one-dimensional substrate where multilayer deposition is allowed. Specifically, we are interested in studying how the mentioned properties vary as a function of the height of the multilayer. The critical parameters of the percolation transition are calculated using finite-size scaling analysis, obtaining the scaling laws for the probability of percolation and the conductivity of the system. To calculate the electrical conductivity of the multilayer, we use the Frank-Lobb algorithm.

Evaporation of pure and binary droplets on curved substrates

We investigate the evaporation of pure ethanol, water and ethanol-water binary sessile droplets on one-dimensional cylindrical substrates using shadowgraphy and infrared imaging techniques. Our results demonstrate that pure ethanol has a greater spread and a smaller contact angle on curved substrates, whereas pure water and binary droplets exhibit a smaller spread on the curved substrates. The top views of the droplet taken using the infrared imaging system demonstrate that a pure ethanol droplet does not preserve a spherical cap profile on the curved substrate, whereas a binary mixture does, which explains the difference in wetting dynamics on curved and flat substrates. Moreover, three-dimensional solid modelling is conducted to obtain the evolution of the morphology of the pure and binary droplets during evaporation. For all binary compositions, we observe that the droplet perimeter remains constant on flat and curved substrates, resulting in identical overall evaporation times on flat and curved substrates.

Integration of multiple electronic components on a microfibre towards an emerging electronic textile platform.

Electronic fibres have been considered one of the desired device platforms due to their dimensional compatibility with fabrics by weaving with yarns. However, a precise connecting process between each electronic fibre is essential to configure the desired electronic circuits or systems. Here, we present an integrated electronic fibre platform by fabricating electronic devices onto a one-dimensional microfibre substrate. Electronic components such as transistors, inverters, ring oscillators, and thermocouples are integrated together onto the outer surface of a fibre substrate with precise semiconductor and electrode patterns. Our results show that electronic components can be integrated on a single fibre with reliable operation. We evaluate the electronic properties of the chip on the fibre as a multifunctional electronic textile platform by testing their switching and data processing, as well as sensing or transducing units for detecting optical/thermal signals. The demonstration of the electronic fibre suggests significant proof of concepts for the realization of high performance with wearable electronic textile systems.

Dimensional Design for Surface-Enhanced Raman Spectroscopy.

Surface-enhanced Raman spectroscopy (SERS) is a vibrational spectroscopy technique that enables specific identification of target analytes with sensitivity down to the single-molecule level by harnessing metal nanoparticles and nanostructures. Excitation of localized surface plasmon resonance of a nanostructured surface and the associated huge local electric field enhancement lie at the heart of SERS, and things will become better if strong chemical enhancement is also available simultaneously. Thus, the precise control of surface characteristics of enhancing substrates plays a key role in broadening the scope of SERS for scientific purposes and developing SERS into a routine analytical tool. In this review, the development of SERS substrates is outlined with some milestones in the nearly half-century history of SERS. In particular, these substrates are classified into zero-dimensional, one-dimensional, two-dimensional, and three-dimensional substrates according to their geometric dimension. We show that, in each category of SERS substrates, design upon the geometric and composite configuration can be made to achieve an optimized enhancement factor for the Raman signal. We also show that the temporal dimension can be incorporated into SERS by applying femtosecond pulse laser technology, so that the SERS technique can be used not only to identify the chemical structure of molecules but also to uncover the ultrafast dynamics of molecular structural changes. By adopting SERS substrates with the power of four-dimensional spatiotemporal control and design, the ultimate goal of probing the single-molecule chemical structural changes in the femtosecond time scale, watching the chemical reactions in four dimensions, and visualizing the elementary reaction steps in chemistry might be realized in the near future.

Substrate induced freezing, melting and depinning transitions in two-dimensional liquid crystalline systems.

We use molecular dynamics simulations to investigate the ordering phenomena in two-dimensional (2D) liquid crystals over the one-dimensional periodic substrate (1DPS). We have used Gay-Berne (GB) potential to model the interaction between a pair of liquid crystalline (LC) particles. The underlying substrate potential with which the GB particles interact varies sinusoidally in one direction only. At a given temperature and density of the GB system, we varied the substrate's periodicity (as) but fixed the substrate strength. We observed that with a small value of as, an underlying substrate helps to stabilize a disordered LC nematic phase to a 2D solid phase. However, for an intermediate range of as, the system melts and transitions to a modulate-smectic. Finally, with a further increase in as, the system undergoes a structural depinning transition and returns to an LC nematic phase like a free system with no substrate. We argue that a three-way interplay of the energies arising from orientation-dependent particle-particle and particle-substrate interaction makes it possible for the system to undergo substrate-periodicity-dependent multiple phase transitions in the GB LC system.

Growth of ordered two-dimensional cobalt phthalocyanine films on a one-dimensional substrate

The growth of Co phthalocyanine (CoPc) films on the one-dimensional Si(111)(4 × 1)-In surface is studied using scanning tunneling microscopy (STM). At low CoPc coverages, the molecules are highly mobile on the surface. Only when the coverage approaches the saturation coverage, the molecules stabilize each other and a highly ordered two-dimensional CoPc monolayer forms. Based on the STM images, a structure model for this film could be developed, with the molecules selectively adsorbing on the In chains with a (4 × 4) periodicity.

Bifurcation study for a surface-acoustic-wave-driven meniscus

A thin-film model for a meniscus driven by Rayleigh surface acoustic waves (SAW) is analysed, a problem closely related to the classical Landau-Levich or dragged-film problem where a plate is withdrawn at constant speed from a bath. We consider a mesoscopic hydrodynamic model for a partially wetting liquid, were wettability is incorporated via a Derjaguin (or disjoining) pressure and combine SAW driving with the elements known from the dragged-film problem. For a one-dimensional substrate, i.e., neglecting transverse perturbations, we employ numerical path continuation to investigate in detail how the various occurring steady and time-periodic states depend on relevant control parameters like the Weber number and SAW strength. The bifurcation structure related to qualitative transitions caused by the SAW is analysed with particular attention on the {appearance and interplay of Hopf bifurcations where branches of time-periodic states emerge. The latter correspond to the regular shedding of liquid ridges from the meniscus. The obtained information is relevant to the entire class of dragged-film problems.

Theoretical formulations and simulations of one-dimensional inhibition kinetics of ethanologenic microorganisms in batch fermenters

The utilization of bio-based technology for energy has piqued researchers' curiosity around the world. As a result, bioethanol fermentation has been a hot topic of research for many scientists since it uses less energy and chemicals, produces fewer harmful by-products and emissions, and has environmentally favorable applications. The modeling and simulations of one-dimensional product and substrate inhibitions for sorghum, maize, and cassava extracts are discussed in this paper. Because it provides an edge over other methodologies, mechanistic modeling techniques are used. Models of substrate and product inhibitions in one dimension (1-D) are constructed. These 1-D models are then confirmed using parameter estimates before being employed in the work's simulations. For each dynamic model constructed, model fitness coefficients (α) are calculated. For the product, the exponential inhibition model, sorghum extract data has the best model fitness coefficient (α = 0.4088), for product sudden stop inhibition model and cassava extract data gives the best model fitness coefficient (alpha = 0.4417) for product exponential model. The projected yield increases for substrate exponential inhibition with sorghum extract data, substrate linear inhibition with maize extract data, and substrate linear inhibition with cassava extract data are 74%, 27%, and 25%, respectively. This unique framework has offered the industry a wide choice of kinetics models to choose from to alleviate inhibitions in fermentation systems and maximize yield and productivity in the bioethanol fermentation process.Article HighlightsThe modeling of inhibitions namely linear, sudden stop, and exponential in batch fermentation processes are presented in this article.Model fitness coefficient analysis showed the product as a primary inhibitor and substrate as a secondary inhibitor during the processThe cassava and maize processes described linear inhibition model and sorghum fermentation showed exponential product inhibition model.

Substrate effect on the electronic properties of graphene on vicinal Pt(1 1 1)

The atomic structure and electronic properties of monolayer graphene on a curved multi-nano-vicinal Pt (111) substrate are investigated with a low-energy electron diffraction, scanning tunneling microscopy and angle-resolved photoemission spectroscopy. Despite graphene grows continuously over the terraces and step bunching areas, the spatial periodicity also varies by varying the vicinal angle of the substrate. This superperiodicity has been evidenced by splitting of first order Pt spots in LEED and from STM. The photoemission spectroscopy unravels that the linearly dispersing π band of graphene is affected by the step periodicity as evidenced by the opening of bandgaps. The gaps opening occurs at the intersection of the main graphene band with Umklapp bands due to the superperiodicity of the one-dimensional nanostructured substrate. The energy and momentum locations of the minigaps change with the superperiodicity, which is related to the spatial periodicity and vicinal angle of the substrate. Our results show a simple way to tune the electronic properties of epitaxial graphene by tuning the substrate vicinality.

Structure and dynamical properties of two-dimensional dusty plasmas on one-dimensional periodic substrates

In the presence of the substrate, various structural and dynamical properties of two-dimensional dusty plasma (2DDP) were investigated using Langevin dynamical simulations. This paper reviews a series of results of the structural and dynamical properties of 2DDP modified by one-dimensional periodic substrates (1DPSs) as follows. First, when the depth of the 1DPS increases gradually, it is found that the static structural order of 2DDP along each potential well of the 1DPS increases first and then decreases gradually. When the width of the 1DPS increases gradually, the particle arrangement in each potential well of the 1DPS changes from one straight row gradually to two rows, including the stable zigzag structure. Second, when there are two rows in each potential well of the 1DPS, the phonon spectra are split into two branches, corresponding to the breathing and sloshing modes, respectively. In addition, due to the pure repulsion between dust particles, from the obtained phonon spectra, the sloshing wave propagates backward at small wave numbers. Third, the calculated mean square displacement shown that, at the intermediate timescale between the initial ballistic and final diffusive motions, the particle motion tends to be more subdiffusive while the depth of the 1DPS increases. While the width of the 1DPS increases gradually, the long-time diffusive motion first increases, then decreases, and finally increases again, exhibiting the oscillation-like diffusion, due to the stable zigzag structure. Finally, when an external direct-current driving force is applied on all particles of 2DDP, three different depinning phases are discovered, which are the pinned, disordered plastic flow, and moving ordered states, respectively, as the driving force increases from zero. In addition, the continuous/discontinuous property of the phase transition between these different depinning states is investigated, showing that the transition property is modulated by the depth of the applied 1DPS.

Continuous and discontinuous transitions in the depinning of two-dimensional dusty plasmas on a one-dimensional periodic substrate.

Langevin dynamical simulations are performed to study the depinning dynamics of two-dimensional dusty plasmas on a one-dimensional periodic substrate. From the diagnostics of the sixfold coordinated particles P_{6} and the collective drift velocity V_{x}, three different states appear, which are the pinning, disordered plastic flow, and moving ordered states. It is found that the depth of the substrate is able to modulate the properties of the depinning phase transition, based on the results of P_{6} and V_{x}, as well as the observation of hysteresis of V_{x} while increasing and decreasing the driving force monotonically. When the depth of the substrate is shallow, there are two continuous phase transitions. When the potential well depth slightly increases, the phase transition from the pinned to the disordered plastic flow states is continuous; however, the phase transition from the disordered plastic flow to the moving ordered states is discontinuous. When the substrate is even deeper, the phase transition from the pinned to the disordered plastic flow states changes to discontinuous. When the depth of the substrate further increases, as the driving force increases, the pinned state changes to the moving ordered state directly, so that the disordered plastic flow state disappears completely.

Oscillation-like diffusion of two-dimensional liquid dusty plasmas on one-dimensional periodic substrates with varied widths

The long-time diffusion of two-dimensional dusty plasmas on a one-dimensional periodic substrate with varying widths is investigated using Langevin dynamical simulations. When the substrate is narrow and the dust particles form a single row, the diffusion is the smallest in both directions. We find that as the substrate width gradually increases to twice its initial value, the long-time diffusion of the two-dimensional dusty plasmas first increases, then decreases, and finally increases again, giving an oscillation-like diffusion with varying substrate widths. When the width increases to a specific value, the dust particles within each potential well arrange themselves in a stable zigzag pattern, greatly reducing the diffusion and leading to the observed oscillation in the diffusion with the increase in the width. In addition, the long-time oscillation-like diffusion is consistent with the number of dust particles that are hopping across the potential wells of the substrate.

Quasi-aligned nanorod arrays composed of Nickel–Cobalt nanoparticles anchored on TiO2/C nanofiber arrays as free standing electrode for enzymeless glucose sensors

Nickel-based enzymeless glucose sensors have been extensively explored. However, poor conductivity and severe aggregation of nickel-base nanocomposites often reduce the performance of its practical applications. Herein, free-standing TiO2/C core-shell nanofiber arrays (TiO2/C NFAs) were fabricated directly on a titanium foil to serve as the one-dimensional (1D) conductive substrate. Nickel-cobalt binary nanoparticles were then deposited on the nanofibers to form the NiCo/TiO2/C NFAs for enzymeless glucose sensing. The NiCo/TiO2/C NFAs exhibit much improved sensitivity and excellent stability towards glucose determination, with a wide linear range from 1 μM to 7658 μM, and a high sensitivity of 975.3 μA mM−1 cm−2. The detection limit is calculated to be 0.6 μM (S/N = 3). The NiCo/TiO2/C NFAs also show excellent selectivity with minimal interference from the coexistent species. The superior analytical performance should be attributed to the large specific surface area of the 1D nanostructure, direct electron transfer pathway via the free standing TiO2/C NFAs, and high activity of the binary Ni–Co electrocatalyst.

Depinning dynamics of two-dimensional dusty plasmas on a one-dimensional periodic substrate.

We investigate the depinning dynamics of two-dimensional dusty plasmas driven over one-dimensional periodic substrates using Langevin dynamical simulations. We find that, for a specific range of substrate strengths, as the external driving force increases from zero, there are three different states, which are the pinned, the disordered plastic flow, and the moving ordered states, respectively. These three states are clearly observed using different diagnostics, including the collective drift velocity, static structural measures, the particle trajectories, the mean-squared displacements, and the kinetic temperature. We compare the observed depinning dynamics here with the depinning dynamics in other systems.

Phonon spectra of two-dimensional liquid dusty plasmas on a one-dimensional periodic substrate

We investigate the phonon spectra of two-dimensional liquid dusty plasmas on a one-dimensional periodic substrate using numerical simulations. The propagation of the waves across the potential wells of the substrate is inhibited due to the confinement of the dust particles by the substrate minima. If the substrate wells are narrow or deep, one-dimensional chains of particles are formed in each minima, and the longitudinal motion of an individual chain dominates the propagation of waves along the potential wells of the substrate. Increasing the width or decreasing the depth of the substrate minima allows the particles to buckle into a zig-zag structure, and the resulting spectra develop two branches, one for sloshing motion and one for breathing motion. The repulsion between neighboring dust particles produces backward propagation of the sloshing wave for small wave numbers.