Sequential Growth Process Research Articles

Confinement of excited states in two-dimensional, in-plane, quantum heterostructures

Two-dimensional (2D) semiconductors are promising candidates for optoelectronic application and quantum information processes due to their inherent out-of-plane 2D confinement. In addition, they offer the possibility of achieving low-dimensional in-plane exciton confinement, similar to zero-dimensional quantum dots, with intriguing optical and electronic properties via strain or composition engineering. However, realizing such laterally confined 2D monolayers and systematically controlling size-dependent optical properties remain significant challenges. Here, we report the observation of lateral confinement of excitons in epitaxially grown in-plane MoSe2 quantum dots (~15-60 nm wide) inside a continuous matrix of WSe2 monolayer film via a sequential epitaxial growth process. Various optical spectroscopy techniques reveal the size-dependent exciton confinement in the MoSe2 monolayer quantum dots with exciton blue shift (12-40 meV) at a low temperature as compared to continuous monolayer MoSe2. Finally, single-photon emission (g2(0) ~ 0.4) was also observed from the smallest dots at 1.6 K. Our study opens the door to compositionally engineered, tunable, in-plane quantum light sources in 2D semiconductors.

Coral‐tentacle‐inspired antifouling membrane spacer: A natural solution for biofouling prevention

AbstractFouling of membrane spacers leads to increased pressure drop and reduced lifespan of membrane modules. Cleaning these fouled spacers is challenging due to strong foulant‐membrane spacer interactions. To address this issue, we introduce a novel spacer, PP‐N‐F, inspired by coral's antifouling properties. This spacer features on‐demand antifouling capabilities through a sequential growth process of functional polymer brushes on its surface. It not only possesses lower surface free energy characteristics than polypropylene spacers, but also exhibits controllable morphological changes similar to swaying coral tentacles. Temperature control strengthens the interfacial hydration layer, mitigating the trade‐off between anti‐adsorption and hydrophobicity of fluorinated surface. The temperature‐responsive surface changes enhance foulant desorption efficiency. Compared to a commercial spacer, PP‐N‐F shows an 89.3% reduction in foulant adsorption and a 61.7% decrease in pressure drop increment after 48 h cross‐flow filtration experiments. This work provides valuable insights for advanced anti‐fouling membrane module design.

Self-Assembly of Mixed-Dimensional GeS1- x Sex (1D Nanowire)-(2D Plate) Van der Waals Heterostructures.

The integration of dissimilar materials into heterostructures is a mainstay of modern materials science and technology. An alternative strategy of joining components with different electronic structure involves mixed-dimensional heterostructures, that is, architectures consisting of elements with different dimensionality, for example, 1D nanowires and 2D plates. Combining the two approaches can result in hybrid architectures in which both the dimensionality and composition vary between the components, potentially offering even larger contrast between their electronic structures. To date, realizing such heteromaterials mixed-dimensional heterostructures has required sequential multi-step growth processes. Here, it is shown that differences in precursor incorporation rates between vapor-liquid-solid growth of 1D nanowires and direct vapor-solid growth of 2D plates attached to the wires can be harnessed to synthesize heteromaterials mixed-dimensional heterostructures in a single-step growth process. Exposure to mixed GeS and GeSe vapors produces GeS1- x Sex van der Waals nanowires whose S:Se ratio is considerably larger than that of attached layered plates. Cathodoluminescence spectroscopy on single heterostructures confirms that the bandgap contrast between the components is determined by both composition and carrier confinement. These results demonstrate an avenue toward complex heteroarchitectures using single-step synthesis processes.

Synthesis of cube-rod-tube triblock asymmetric nanostructures for enhanced heterogeneous catalysis.

A triblock asymmetric nanostructure composed of a core-shell Fe2O3@SiO2 cube as the head, SiO2 rod as the body and SiO2 tube as the tail is fabricated via a sequential growth process combining solution-liquid-solid and droplet soft templating mechanisms, which can be used as a nano stir bar with accelerated catalytic performance.

Large area planar photocathode for MCP-based photodetectors

We report on the principle, design, fabrication, and characterization of a large-area planar bialkali photocathode. Sequential photocathode growth process was investigated, and the growth parameters, especially the initial antimony layer thickness, were optimized. The source arrangement and configuration were also simulated and the preferred configuration was chosen for numerical and experimental studies. Photocathode with average QE of 18% and activation area of ∼40 square inches was experimentally demonstrated, making it a candidate for MCP-based photodetector applications. Further improvements were also discussed to enhance the uniformity and QE value of the photocathodes.

Sequential Growth of High Quality Sub-10 nm Core-Shell Nanocrystals: Understanding the Nucleation and Growth Process Using Dynamic Light Scattering.

Monodisperse sub-10 nm core-shell nanocrystals have been extensively studied owing to their important applications in catalysis, bioimaging, nanomedicine, and so on. In this work, an amorphous shell component crystallization strategy has been proposed to prepare high quality sub-10 nm NaYF4:Yb/Er@NaGdF4 core-shell nanocrystals successfully via a sequential growth process. The dynamic light scattering technique has been used to investigate the secondary nucleation and growth process forming the core-shell nanocrystals. The size and morphology evolution of the core-shell nanocrystals reveals that the secondary nucleation of the shell component is unavoidable after hot-injecting the shell precursor at high temperatures, which was followed by dissolution and recrystallization (an Ostwald ripening process) to partially produce the core-shell nanocrystals. The present study demonstrates that the size of seed nanocrystals and the injection temperature of the shell component precursor play a vital role in the formation of core-shell nanostructures completely. This work will provide an alternative strategy for precisely controlling the fabrication of sub-10 nm core-shell nanostructures for various applications.

Enhanced red upconversion emission of Ho3+ in NaYF4 nanocrystals

Hexagonal-phase NaYF4:Yb3+/Ho3+ nanocrystals (with size of 20 nm) were successfully prepared by a modified solution-based method. Under 980 nm near- infrared (NIR) excitation, the upconversion (UC) emission was tuned from green to red in NaYF4:Yb3+/Ho3+ nanocrystals by introducing Ce3+ ions. The corresponding red to green (R/G) emission ratio of Ho3+ increased by approximately 10-fold as the Ce3+ concentration increased to 14%. However, the overall UC emission intensity gradually decreased. A series of core–shell structures for NaYF4:Yb3+/Ho3+/Ce3+@NaYF4:Yb3+ nanocrystals codoped with different Yb3+ ion concentrations in the shell was successfully fabricated by a sequential growth process to further enhance the red UC emission intensity. When the Yb3+ concentration from the shell of NaYF4:Yb3+ was increased from 0% to 20%, the UC emission intensity of the core–shell nanocrystals first increased and then decreased. Moreover, the highest UC emission intensity was obtained in the core–shell nanocrystals with 10% Yb3+. Experimental results indicated red UC was enhanced due to the resonance energy transfer between adjacent Ho3+ and Ce3+ and Yb3+ and Ho3+ ions. These nanocrystals with red UC emission have great potential in the biological field and multicolor applications.

Epitaxial growth of ultrathin layers on the surface of sub-10nm nanoparticles: the case of β-NaGdF4:Yb/Er@NaDyF4 nanoparticles.

Upconversion core–shell nanoparticles have attracted a large amount of attention due to their multifunctionality and specific applications. In this work, based on a NaGdF4 sub-10 nm ultrasmall nanocore, a series of core–shell upconversion nanoparticles with uniform size doped with Yb3+, Er3+ and NaDyF4 shells with different thicknesses were synthesized by a facile sequential growth process. NaDyF4 coated upconversion luminescent nanoparticles showed an obvious fluorescence quenching under excitation at 980 nm as a result of energy resonance transfer between Yb3+, Er3+ and Dy3+. NaGdF4:Yb,Er@NaDyF4 core–shell nanoparticles with ultrathin layer shells exhibited a better T1-weighted MR contrast.

Sequential Growth of NaYF4:Yb/Er@NaGdF4 Nanodumbbells for Dual-Modality Fluorescence and Magnetic Resonance Imaging.

Upconversional core-shell nanostructures have gained considerable attention due to their distinct enhanced fluorescence efficiency, multifunctionality, and specific applications. Recently, we have developed a sequential growth process to fabricate unique upconversion core-shell nanoparticles. Time evolution of morphology for the NaYF4:Yb/Er@NaGdF4 nanodumbbells has been extensively investigated. An Ostwald ripening growth mechanism has been proposed to illustrate the formation of NaYF4:Yb/Er@NaGdF4 nanodumbbells. The hydrophilic NaYF4:Yb/Er@NaGdF4 core-shell nanodumbbells exhibited strong upconversion fluorescence and showed higher magnetic resonance longitudinal relaxivity (r1 = 7.81 mM-1 s-1) than commercial contrast agents (Gd-DTPA). NaYF4:Yb/Er@NaGdF4 nanodumbbells can serve as good candidates for high efficiency fluorescence and magnetic resonance imaging.

Unique Upconversion Core–Shell Nanoparticles with Tunable Fluorescence Synthesized by a Sequential Growth Process

A facile sequential growth process is developed to synthesize uniform lanthanide-doped upconversion (UC) core–shell nanoparticles with controlled nanostructures and enhanced UC fluorescence, which provides an important tool for their extensive applications in the near future. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

A Model for the Universe that Begins to Resemble a Quantum Computer

This article presents a sequential growth model for the Universe that acts like a quantum computer. The basic constituents of the model are a special type of causal set (causet) called a c-causet. A c-causet is defined to be a causet that has a unique labeling. We characterize c-causets as those causets that form a multipartite graph or equivalently those causets whose elements are comparable whenever their heights are different. We show that a c-causet has precisely two c-causet offspring. It follows that there are 2n c-causets of cardinality n + 1. This enables us to classify c-causets of cardinality n + 1 in terms of n-bits. We then quantize the model by introducing a quantum sequential growth process. This is accomplished by replacing the n-bits by n-qubits and defining transition amplitudes for the growth transitions. We mainly consider two types of processes, called stationary and completely stationary. We show that for stationary processes, the probability operators are tensor products of positive rank-one qubit operators. Moreover, the converse of this result holds. Simplifications occur for completely stationary processes. We close with examples of precluded events.

Facile synthesis of β-NaGdF4:Yb/Er@CaF2 nanoparticles with enhanced upconversion fluorescence and stability via a sequential growth process

β-NaGdF4:Yb,Er@CaF2 core–shell nanoparticles: β-NaGdF4:Yb/Er nanoparticles coated with an ultrathin layer of CaF2 have been achieved via a sequential growth process.

An Isometric Dynamics for a Causal Set Approach to Discrete Quantum Gravity

We consider a covariant causal set approach to discrete quantum gravity. We first review the microscopic picture of this approach. In this picture a universe grows one element at a time and its geometry is determined by a sequence of integers called the shell sequence. We next present the macroscopic picture which is described by a sequential growth process. We introduce a model in which the dynamics is governed by a quantum transition amplitude. The amplitude satisfies a stochastic and unitary condition and the resulting dynamics becomes isometric. We show that the dynamics preserves stochastic states. By "doubling down" on the dynamics we obtain a unitary group representation and a natural energy operator. These unitary operators are employed to define canonical position and momentum operators.

Growing metal trees on tubular semiconductor land: TiO2/(Zn,Sn)Pd heterostructures with high SERS and photocatalytic activity

By using sacrificial ZnO nanorods, a self non-uniform electric field was established to yield the aqueous growth of 〈111〉 oriented, single-crystalline (Zn,Sn)-doped Pd nanodendrites on TiO2 nanotubes for synthesizing three-dimensional hydrophobic heterostructures. Structural analyses revealed that primary dendrite arms grew along a 〈111〉 direction group; symmetric branches were built on the basal plane of the arms but sprouted in another [111] direction, similar to a twin structure. Sequential growth processes different from a diffusion-limited aggregation model were suggested, including the dissolution of ZnO nanorods for forming a self non-uniform electric field, the protruding of primary arms towards a Zn2+ concentrated zone, and then the development of branches through a cation depletion zone. A strong surface enhanced Raman scattering and high photocatalytic activity, owing to the strong surface plasmon resonance on the large-surface symmetric structures and the inhibited recombination of photogenerated electron–hole pairs, suggested the high potential of the heterostructures for applications in self-cleaning photocatalysts and nano-optoelectronic devices.

A Dynamics for Discrete Quantum Gravity

This paper is based on the causal set approach to discrete quantum gravity. We first describe a classical sequential growth process (CSGP) in which the universe grows one element at a time in discrete steps. At each step the process has the form of a causal set (causet) and the "completed" universe is given by a path through a discretely growing chain of causets. We then quantize the CSGP by forming a Hilbert space $H$ on the set of paths. The quantum dynamics is governed by a sequence of positive operators $\rho_n$ on $H$ that satisfy normalization and consistency conditions. The pair $(H,\brac{\rho_n})$ is called a quantum sequential growth process (QSGP). We next discuss a concrete realization of a QSGP in terms of a natural quantum action. This gives an amplitude process related to the sum over histories" approach to quantum mechanics. Finally, we briefly discuss a discrete form of Einstein's field equation and speculate how this may be employed to compare the present framework with classical general relativity theory.

A very low potential electrochemical detection of l-cysteine based on a glassy carbon electrode modified with multi-walled carbon nanotubes/gold nanorods

A nanohybrid platform built with multi-walled carbon nanotubes and gold nanorods, prepared via a cationic surfactant-containing seed-mediated sequential growth process, in aqueous solution, on a glassy carbon substrate has been successfully developed to be used in the electrocatalytic oxidation of l-cysteine (Cys). The nanohybrid was characterized by transmission electron microscopy, Raman spectroscopy and electrochemical measurements. Cyclic voltammetry results had shown that the modified electrode allows the oxidation of Cys at a very low anodic potential (0.00V vs. Ag/AgCl). The kinetic constant kcat for the catalytic oxidation of Cys was evaluated by chronoamperometry and provided a value of 5.6×104Lmol−1s−1. The sensor presents a linear response range from 5.0 up to 200.0µmolL−1, detection limit of 8.25nmolL−1 and a sensitivity of 120nALµmol−1.

A facile route to Si nanowire gate-all-around field effect transistors with a steep subthreshold slope

We present a facile CMOS-compatible fabrication of lateral gate-all-around (GAA) field effect transistors (FETs) based on concentric Si-SiO₂/N(++)Si core-multi-shell nanowires (NWs). Si-SiO₂/N(++)Si core-multi-shell NWs were prepared by sequential Si NW growth, thermal oxidation and Si deposition processes in a single chamber. The GAA NW FET was then fabricated using the Si core, SiO₂ inner-shell, N(++) Si outer-shell as a channel, gate dielectric, and gate electrode, respectively. A one-step wet etching process was able to define the gate and source-drain contact regions. The SiNW GAA FET clearly exhibits a geometry-dependent gating effect and a steep subthreshold slope due to the low interface trapped charge density at the interface of the Si core and the SiO₂ shell. Our proposed SiNW GAA structures offer new opportunities for low-energy-consumption digital device applications.

Models for Discrete Quantum Gravity

We first discuss a framework for discrete quantum processes (DQP). It is shown that the set of q-probability operators is convex and its set of extreme elements is found. The property of consistency for a DQP is studied and the quadratic algebra of suitable sets is introduced. A classical sequential growth process is "quantized" to obtain a model for discrete quantum gravity called a quantum sequential growth process (QSGP). Two methods for constructing concrete examples of QSGP are provided.

Characterization of spatial networklike patterns from junction geometry

We propose a method for quantitative characterization of spatial networklike patterns with loops, such as surface fracture patterns, leaf vein networks, and patterns of urban streets. Such patterns are not well characterized by purely topological estimators: also patterns that both look different and result from different morphogenetic processes can have similar topology. A local geometric cue--the angles formed by the different branches at junctions--can complement topological information and allow the quantification of the large scale spatial coherence of the pattern. For patterns that grow over time, such as fracture lines on the surface of ceramics, the rank assigned by our method to each individual segment of the pattern approximates the order of appearance of that segment. We apply the method to various networklike patterns and find a continuous but sharp dichotomy between two classes of spatial networks: hierarchical and homogeneous. The former class results from a sequential growth process and presents large scale organization, and the latter presents local, but not global, organization.

High electron emission from branched tree-like carbon nanotubes suitable for field emission applications

Fabrication of branched tree-like carbon nanostructures has been carried out by means of a sequential hydrogenation and growth process in a direct-current plasma enhanced chemical vapor deposition unit. The field emission characteristic of the tree-like structures has been investigated showing a dramatic improvement with respect to vertical nanotubes. The fabrication process consists of the growth of vertical nanotubes, hydrogenation treatment, encapsulation and a secondary treatment and growth. The secondary growth takes advantage of the tip growth mechanism and is seeded on top of the initial nanotubes. The emission characteristic of the evolved nanostructures is expected to promote considerably due to a field enhancement as observed from the emission characteristics of the nanostructures. A preliminary field emission display has been realized at pixel level.