Self-limiting Growth Mechanism Research Articles

Self-limiting material growth triggered and tunable by force through piezocharge-induced mineralization.

Controlling the growth of material is crucial in material processing for desired properties. Current approaches often involve sophisticated equipment for controlling precursors and monitoring material formation. Here we report a self-limiting material growth mechanism controlled by the experienced mechanical loading without the need for precise control over precursors or monitoring material growth. Material formation that reduces the driving force for growth is hypothesized to result in a saturation thickness that is dependent on the maximum driving force. Analytical relations based on the growth model are derived and verified using a piezoelectric substrate immersed in an electrolyte solution under fixed frequency cyclic loading to attract surrounding mineral ions to form mineral layers. Accumulating mineral layers decrease the driving force for further growth and the material eventually reaches a saturation thickness. This allows for loading force to control the saturation thickness of the self-limiting material growth. Experimental data supports the predicted exponential relations, offering guides to predict the saturation thickness and control the growth profile. The findings are envisioned to contribute to the fundamental understanding of the self-limiting material growth mechanism and could benefit a range of applications including coatings for orthopedic implants as well as marine surface and underwater vehicles.

Highly Uniform Array of Hexagonally Symmetric Micro‐Pyramid Structures for Scalable and Single Quantum Dot Emitters (Adv. Mater. Interfaces 8/2023)

Uniform Single Quantum Dot Emitters Controlling the position, size and shape of group III-nitride quantum dots is critical for the development of scalable single quantum emitters operable at room temperature. In article number 2202085, Yong-Hoon Cho and colleagues present a methodology for highly uniform, site-controlled GaN micro-pyramidal structures with a high degree of hexagonal symmetry by adjusting growth conditions under the self-limited growth mechanism. By successively growing a thin InGaN layer on the uniform pyramidal arrays with growth rate anisotropy, high-performance single photon emission from the apex of each pyramid can be achieved with suppressed background emission from side quantum wells of the pyramids.

Synthesis of component-controllable monolayer MoxW(1-x)S2ySe2(1-y) alloys with continuously tunable band gap and carrier type.

Alloying can effectively modify electronic and optical properties of two-dimensional (2D) transition metal dichalcogenides (TMDs). However, efficient and simple methods to synthesize atomically thin TMD alloys need to be further developed. In this study, we synthesized 25 monolayer MoxW(1-x)S2ySe2(1-y) alloys by using a new liquid phase edge epitaxy (LPEE) growth method with high controllability. This straightforward approach can be used to obtain monolayer materials and operates on a self-limiting growth mechanism. The process allows the liquid solution to come into contact with the two-dimensional grains only at their edges, resulting in epitaxy confined only along the in-plane direction, which produces exclusively monolayer epitaxy. By controlling the weight ratio of MoS2/WSe2 (MoSe2/WS2), 25 monolayer MoxW(1-x)S2ySe2(1-y) alloys with different atomic ratios can be obtained on sapphire substrates, with band gap ranging from WS2 (1.55 eV) to MoSe2 (1.99 eV) and a continuously broad spectrum ranging from 623 nm to 800 nm. By adjusting the alloy composition, the carrier type and carrier mobility of alloy-based field-effect transistors can be modulated. In particular, the adjustable conductivity of MoxW(1-x)S2ySe2(1-y) alloys from n-type to bipolar type is achieved for the first time. This general synthetic strategy provides a foundation for the development of monolayer TMD alloys with multiple components and various 2D materials.

A chemiresistive biosensor for detection of cancer biomarker in biological fluids using CVD-grown bilayer graphene.

A chemiresistive biosensor is described for simple and selective detection of miRNA-21. We developed chemical vapor deposition (CVD) and low-damage plasma treatment (LDPT)-treated bilayer graphene composite of graphene oxide/graphene (GO/GR) for the determination of a reliable biomarker. We have successfully overcome the self-limiting growth mechanism by using CVD method to grow more than one layer of graphene on copper foil. In addition, LDPT can be used to form GO/GR structures for chemiresistive biosensor applications. Due to the direct formation of BLGR (bilayer graphene), the coupling between graphene layers is theoretically superior to that of stacked BLGR, which is also confirmed by the blue shift of the characteristic peak of graphene in Raman spectroscopy. The shift is about double compared with that of stacked BLGR. Based on the results, the limit of detection for the target miRNA-21 was calculated to be 5.20 fM and detection rage is calculated as 100 fM to 10 nM, which is obviously better performance. Compared with previous work, this chemiresistive biosensor has good selectivity, and stability towards detection of miRNA-21. The ability to detect miRNA-21 in different biological fluids was almost identical to that in pH 7.4 phosphate-buffered saline (PBS). Thus, the proposed bilayer GO/GR of modified chemiresistive biosensor may potentially be applied to detect cancer cells in clinical examinations.Graphical abstract Supplementary InformationThe online version contains supplementary material available at 10.1007/s00604-022-05463-7.

In situ visualization of hierarchical agglomeration growth during electrochemical deposition of Cu nanocrystals in an open ionic liquid cell

Metal nanoparticles have important applications in batteries, fuel cells, electrocatalysis, and sensing. However, their growth mechanisms are still unclear. Here the growth mechanism of Cu nanoparticles during electrochemical deposition was characterized via an in situ transmission electron microscopy observation in an open ionic liquid cell. We revealed a hierarchical agglomeration growth (HAG) mechanism, namely, single Cu atoms were formed first due to electrochemical reduction of Cu2+ ions. The single Cu atoms then agglomerated into nanoclusters, which subsequently recrystallized into small nanocrystals. The small nanocrystals agglomerated into larger nanocrystals, and then formed a porous nanocrystals network with an average grain size of 10 nm. The large Cu nanoparticles are single crystals with numerous multiple twins. A self-limiting grain growth mechanism governed by the Cu2+ ion limited diffusion was also found. Our study demonstrates the possibility of observing nanoparticle growth under realistic electrochemical conditions, which may have important applications in tailoring the nanoparticle size and shape for practical applications.

Strong and robust polarization anisotropy of site- and size-controlled single InGaN/GaN quantum wires

Optical polarization is an indispensable component in photonic applications, the orthogonality of which extends the degree of freedom of information, and strongly polarized and highly efficient small-size emitters are essential for compact polarization-based devices. We propose a group III-nitride quantum wire for a highly-efficient, strongly-polarized emitter, the polarization anisotropy of which stems solely from its one-dimensionality. We fabricated a site-selective and size-controlled single quantum wire using the geometrical shape of a three-dimensional structure under a self-limited growth mechanism. We present a strong and robust optical polarization anisotropy at room temperature emerging from a group III-nitride single quantum wire. Based on polarization-resolved spectroscopy and strain-included 6-band k·p calculations, the strong anisotropy is mainly attributed to the anisotropic strain distribution caused by the one-dimensionality, and its robustness to temperature is associated with an asymmetric quantum confinement effect.

Control of the 3-Fold Symmetric Shape of Group III-Nitride Quantum Dots: Suppression of Fine-Structure Splitting.

Controlling the in-plane symmetry of wide-bandgap semiconductor quantum dots (QDs) is essential for room temperature quantum photonic applications using polarization entangled photon pairs. Herein, we report the formation of 3-fold symmetric group III-nitride QDs at the apex of a triangular pyramid via a self-limited growth mechanism. We employed the in-plane rotational symmetry of the c-plane of a Wurtzite crystal and the large built-in piezoelectric field to reduce fine-structure splitting. The QDs exhibit emission that is distinguishable from that of sidewall quantum wells, and the biexciton-exciton cascade possesses a single-photon nature. We observed the relatively low optical polarization anisotropy and small fine structure splitting under the measurement limit (270 μeV) with the 3-fold symmetric QD. In contrast with current strategies that consider group III-nitride QDs as strongly polarized single-photon emitters, our approach for controlling the QD symmetry provides a new perspective on such QDs, as polarization-entangled photon pairs.

Photoelectrochemistry of Self-Limiting Electrodeposition of Ni Film onto GaAs.

Gallium arsenide (GaAs) provides a suitable bandgap (1.43eV) for solar spectrum absorption and allows a larger photovoltage compared to silicon, suggesting great potential as a photoanode toward water splitting. Photocorrosion under water oxidation condition, however, leads to decomposition or the formation of an insulating oxide layer, which limits the photoelectrochemical performance and stability of GaAs. In this work, a self-limiting electrodeposition method of Ni on GaAs is reported to either generate ultra-thin continuous film or nanoislands with high particle density by controlling deposition time. The self-limiting growth mechanism is validated by potential transients, X-ray photoelectron spectroscopy composition and depth profile measurements. This deposition method exhibits a rapid nucleation, forms an initial metallic layer followed by a hydroxide/oxyhydroxide nanofilm on the GaAs surface and is independent of layer thickness versus deposition time when coalescence is reached. A photocurrent up to 8.9mA cm-2 with a photovoltage of 0.11V is obtained for continuous ultrathin films, while a photocurrent density of 9.2mA cm-2 with a photovoltage of 0.50V is reached for the discontinuous nanoislands layers in an aqueous solution containing the reversible redox couple K3 Fe(CN)6 /K4 Fe(CN)6 .

Study of VO2 thin film synthesis by atomic layer deposition

Vanadium dioxide emerges as an appealing material for smart thermal management and electrical/optical switching owing to its abrupt semiconductor-to-metal transition (SMT) at near room temperature. The application potential of this material should be leveraged by the implementation of the atomic layer deposition (ALD), a method that enables an unequaled control over the thickness and film conformality on complex substrate structures by virtue of self-limiting growth mechanism. Here, the vanadium oxide thin films are synthesized from vanadyl (V) triisopropoxide (VTOP) as the vanadium precursor and H2O as the reactant. The thermal decomposition threshold of VTOP was observed at 90 °C, and temperature window with a constant growth rate was observed at 50–90 °C. The saturation behavior of the ALD half reactions was demonstrated at 80 °C, yielding the optimized ALD cycle conditions of 8 s VTOP/15 s purge/6 s H2O/15 s purge with a growth rate of 0.047 nm/cycle. The as-grown amorphous films convert into VO2 via a 4-h heat treatment under 10−5 mbar at 550 °C. The formed VO2 features a sudden and reversible change in the total hemispherical reflectance in UV-VIS-NIR region at 68 °C, confirming its SMT behavior. The conversion process induces, however, a surface roughening, which was considerably suppressed by a postdeposition treatment in plasma environment prior the annealing treatment.

Controlled synthesis of uniform multilayer hexagonal boron nitride films on Fe2B alloy.

Two-dimensional (2D) hexagonal boron nitride (h-BN) is highly appreciated for its excellent insulating performance and absence of dangling bonds, which could be employed to maintain the intrinsic properties of 2D materials. However, controllable synthesis of large scale multilayer h-BN is still very challenging. Here, we demonstrate chemical vapor deposition (CVD) growth of multilayer h-BN by using iron boride (Fe2B) alloy and nitrogen (N2) as precursors. Different from the self-limited growth mechanism of monolayer h-BN on catalytic metal surfaces, with sufficient B source in the bulk, Fe2B alloy promotes the controllable isothermal segregation of multilayer h-BN by reacting with active N atoms on the surface of the substrate. Microscopic and spectroscopic characterizations prove the high uniformity and crystalline quality of h-BN with a highly orientated layered lattice structure. The achievement of large scale multilayer h-BN in this work would facilitate its applications in 2D electronics and optoelectronics in the future.

Low-Temperature Wafer-Scale Deposition of Continuous 2D SnS2 Films.

Semiconducting 2D materials, such as SnS2 , hold immense potential for many applications ranging from electronics to catalysis. However, deposition of few-layer SnS2 films has remained a great challenge. Herein, continuous wafer-scale 2D SnS2 films with accurately controlled thickness (2 to 10 monolayers) are realized by combining a new atomic layer deposition process with low-temperature (250 °C) postdeposition annealing. Uniform coating of large-area and 3D substrates is demonstrated owing to the unique self-limiting growth mechanism of atomic layer deposition. Detailed characterization confirms the 1T-type crystal structure and composition, smoothness, and continuity of the SnS2 films. A two-stage deposition process is also introduced to improve the texture of the films. Successful deposition of continuous, high-quality SnS2 films at low temperatures constitutes a crucial step toward various applications of 2D semiconductors.

A Novel Approach to the Layer-Number-Controlled and Grain-Size-Controlled Growth of High Quality Graphene for Nanoelectronics

Thermal chemical vapor decomposition of methane on copper is the most widely employed technique for high quality and large area graphene growth. Graphene growth by this technique tends to be limited to a monolayer owing to the surface mediated self-limiting growth mechanism, and hence, it is difficult to obtain continuous bilayers and multilayers. We report the layer-controlled growth of high quality and large area polycrystalline graphene on copper foil in a hot filament chemical vapor deposition (HFCVD) reactor and demonstrate that graphene can be grown with a controlled grain size in the range of 5–16 μm. The field effect hole mobilities of the largest grain monolayer and bilayer graphene and the thickest few-layer graphene are 4310 ± 348, 2745 ± 276, and 2472 ± 185 cm2V–1s–1, respectively, which are comparable to that of high quality polycrystalline graphene and suitable for future nanoelectronics. The results of the systematic parametric study hereby presented indicate that graphene adlayers grow on ...

Ni foam assisted synthesis of high quality hexagonal boron nitride with large domain size and controllable thickness

The scalable synthesis of two-dimensional (2D) hexagonal boron nitride (h-BN) is of great interest for its numerous applications in novel electronic devices. Highly-crystalline h-BN films, with single-crystal sizes up to hundreds of microns, are demonstrated via a novel Ni foam assisted technique reported here for the first time. The nucleation density of h-BN domains can be significantly reduced due to the high boron solubility, as well as the large specific surface area of the Ni foam. The crystalline structure of the h-BN domains is found to be well aligned with, and therefore strongly dependent upon, the underlying Pt lattice orientation. Growth-time dependent experiments confirm the presence of a surface mediated self-limiting growth mechanism for monolayer h-BN on the Pt substrate. However, utilizing remote catalysis from the Ni foam, bilayer h-BN films can be synthesized breaking the self-limiting effect. This work provides further understanding of the mechanisms involved in the growth of h-BN and proposes a facile synthesis technique that may be applied to further applications in which control over the crystal alignment, and the numbers of layers is crucial.

Rapid Formation of Black Holes in Galaxies: A Self-limiting Growth Mechanism

Abstract We present high-quality fluid dynamical simulations of isothermal gas flows in a rotating barred potential. We show that a large quantity of gas is driven right into the nucleus of a galaxy when the model lacks a central mass concentration, but the inflow stalls at a nuclear ring in comparison simulations that include a central massive object. The radius of the nuclear gas ring increases linearly with the mass of the central object. We argue that bars drive gas right into the nucleus in the early stages of disk galaxy formation, where a nuclear star cluster and perhaps a massive black hole could be created. The process is self-limiting, however, because inflow stalls at a nuclear ring once the mass of gas and stars in the nucleus exceeds ∼1% of the disk mass, which shuts off rapid growth of the black hole. We briefly discuss the relevance of these results to the seeding of massive black holes in galaxies, the merger model for quasar evolution, and the existence of massive black holes in disk galaxies that lack a significant classical bulge.

Multiferroic heterostructures of Fe3O4/PMN-PT prepared by atomic layer deposition for enhanced interfacial magnetoelectric couplings

In this work, multiferroic heterostructures have been prepared by in situ growing oxide magnetic films on ferroelectric single crystal substrates using atomic layer deposition (ALD). Strong interfacial mechanical coupling between the magnetic and ferroelectric phases has been created, arising from the formation of chemical bonds at the interface due to the nature of layer-by-layer self-limiting growth mechanism of the ALD technique. An enhanced magnetoelectric (ME) coupling has been achieved, which allows an electric field to robustly switch magnetic anisotropy up to 780 Oe. In addition, electrical impulse non-volatile tuning of magnetism has also been realized through partially coupled ferroelectric/ferroelastic domain switching. The ALD growth of magnetic oxide films onto ferroelectric substrates provides an effective platform for the preparation of multiferroic heterostructures at low temperatures with an improved ME coupling, demonstrating a great potential for applications in 3D spintronics, microelectronics and data storages.

Retraction of "Thermodynamic Self-Limiting Growth of Heteroepitaxial Islands Induced by Nonlinear Elastic Effect".

We investigate nonlinear elastic effect (NLEF) on the growth of heteroepitaxial islands, a topic of both scientific and technological significance for their applications as quantum dots. We show that the NLEF induces a thermodynamic self-limiting growth mechanism that hinders the strain relaxation of coherent island beyond a maximum size, which is in contrast to indefinite strain relaxation with increasing island size in the linear elastic regime. This self-limiting growth effect shows a strong dependence on the island facet angle, which applies also to islands inside pits patterned in a substrate surface with an additional dependence on the pit inclination angle. Consequently, primary islands nucleate and grow first in the pits and then secondary islands nucleate at the rim around the pits after the primary islands reach the self-limited maximum size. Our theory sheds new lights on understanding the heteroepitaxial island growth and explains a number of past and recent experimental observations.

Wafer-scale Thermodynamically Stable GaN Nanorods via Two-Step Self-Limiting Epitaxy for Optoelectronic Applications

We present a method of epitaxially growing thermodynamically stable gallium nitride (GaN) nanorods via metal-organic chemical vapor deposition (MOCVD) by invoking a two-step self-limited growth (TSSLG) mechanism. This allows for growth of nanorods with excellent geometrical uniformity with no visible extended defects over a 100 mm sapphire (Al2O3) wafer. An ex-situ study of the growth morphology as a function of growth time for the two self-limiting steps elucidate the growth dynamics, which show that formation of an Ehrlich-Schwoebel barrier and preferential growth in the c-plane direction governs the growth process. This process allows monolithic formation of dimensionally uniform nanowires on templates with varying filling matrix patterns for a variety of novel electronic and optoelectronic applications. A color tunable phosphor-free white light LED with a coaxial architecture is fabricated as a demonstration of the applicability of these nanorods grown by TSSLG.

The Application of Atomic Layer Deposition in Lithium-Ion Batteries

Lithium-ion batteries (LIBs) have been considered a promising energy storage system for various applications such as electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs). Intensive studies have been focused on improving LIBs in terms of power and energy density, cycling lifetime, safety characteristics, and cost. Atomic layer deposition (ALD) emerges as a powerful technique for addressing these issues due to its exclusive advantages over other thin film deposition techniques. Based on a self-limiting growth mechanism, ALD enables ultra uniform and conformal deposition of thin films and provides exquisite control of the thin film thickness down to angstrom. The advantages stand out more on high-aspect-ratio three-dimensional (3D) substrates due to the nature of the gas phase reactions [1, 2]. In LIBs, We first employed ALD to design nanocomposites used as electrode or solid-state electrolyte (SSE) materials, which can further be applied in the fabrication of 3D all-solid-state microbatteries [3]. Another application of ALD in LIBs is to deposit the ultra thin film on the electrode material as a surface modification in order to promote the performance of LIBs [4]. Our work also focuses on the development of lithium phosphate and lithium tantalum as SSE by ALD [5, 6]. The ALD processes have been established for both materials. LiOtBu is used as the lithium source. The as prepared thin films exhibit an amorphous structure. Electrochemical measurements are applied to characterize the ionic conductivity of these two thin films, which reaches an order of 10-8 scm-1. In addition, our work summarizes our recent study of engineering electrode/electrolyte interfaces by ALD. The complete surface coating acts an effective protection from the undesired side reactions (metal dissolutions in some cathode materials) and thus improves the capacity retention [6, 7]. The negligible thickness of the thin film allows ions to pass through. Besides, ALD prepared SSE (LiTaO3) as coating layers even benefits the transporting of lithium ions compared with simple binary oxide coatings such as Al2O3. [4] Furthermore, coatings with good toughness restrain the volume change of the electrode materials upon cycling, preventing pulverization. [8] We have been purposely developing different materials by ALD and combining them with LIBs. Lithium protection via ALD is another focus of our research. With fairly high energy density, lithium metal suffers from parasitic reactions with solvents, contaminations, and shuttled active species in the electrolyte. It has been reported that applying a thin chemical protection layer is a practical solution towards stabilizing lithium metal anodes in battery performances [9]. It has proven that ALD is a critical resort in the advances of next-generation LIBs in the future. [1] X. Meng, X. Yang, X. Sun, Adv. Mater. 2012, 24, 3589–3615 [2] J. Liu, X. Sun, Nanotechnology 2015, 26, 024001 [3] J. Liu, M. Banis, Q. Sun, A. Lushington, R. Li, T. K Sham, X. Sun, Adv. Mater. 2014, 26, 6472-6477 [4] X. Li, J. Liu, M. Banis, A. Lushington, R. Li, M. Cai, X. Sun, Energy Environ. Sci. 2014, 7, 768-778 [5] B. Wang, J. Liu, Q. Sun, R. Li, T. K Sham, X. Sun, Nanotechnology 2014, 25, 504007 [6] J. Liu, M. Banis, X. Li, A. Lushington, M. Cai, R. Li, T. K. Sham, X. Sun, J. Phys. Chem. C 2013, 117, 20260-20267 [7] B. Xiao, J. Liu, Q. Sun, B. Wang, M. Banis, D. Zhao, Z. Wang, R. Li, X. Cui, T. K. Sham, X. Sun, Adv. Sci. 2015, 1500022 [8] D. Wang, J. Yang, J. Liu, X. Li, R. Li, M. Cai, T. K. Sham, X. Sun, J. Mater. Chem. A 2014, 2, 2306-2312 [9] A. Kozen, C. Lin, A. J. Pearse, M. A. Schroeder, X. Han, L. Hu, S. Lee, G. W. Rubloff, Malachi Noked, ACS. Nano. 2015, 9, 5884-5892

Thermodynamic Self-Limiting Growth of Heteroepitaxial Islands Induced by Nonlinear Elastic Effect.

We investigate nonlinear elastic effect (NLEF) on the growth of heteroepitaxial islands, a topic of both scientific and technological significance for their applications as quantum dots. We show that the NLEF induces a thermodynamic self-limiting growth mechanism that hinders the strain relaxation of coherent island beyond a maximum size, which is in contrast to indefinite strain relaxation with increasing island size in the linear elastic regime. This self-limiting growth effect shows a strong dependence on the island facet angle, which applies also to islands inside pits patterned in a substrate surface with an additional dependence on the pit inclination angle. Consequently, primary islands nucleate and grow first in the pits and then secondary islands nucleate at the rim around the pits after the primary islands reach the self-limited maximum size. Our theory sheds new lights on understanding the heteroepitaxial island growth and explains a number of past and recent experimental observations.

An etching phenomenon exhibited by chemical vapor deposited graphene on a copper pocket

What causes graphene etching is still controversial. Here we report a special etching phenomenon on the outer surface of a copper (Cu) pocket, while large-size graphene domains grow slowly on the inner surface. A systematic study along a time axis was conducted to investigate this etching process through isotope-tracing. When millimeter-size graphene domains on the inner surface joined together, the original monolayer graphene with a few residual multilayers stayed behind on the outer surface, indicating that multilayer graphene formed in the interim subsequently disappeared. Combined with our previous work, we conclude that the etching phenomenon is analogous to a counter diffusion process that keeps a stable monolayer of graphene on both sides of the Cu foil. Low C solubility and poor C saturation in Cu appear to drive this counter diffusion and help keep the stable state. Furthermore, we used a fast-growth process to break this stable state and realized 85% coverage rates of bilayer graphene growth on the outer surface of a Cu pocket. This work sheds light on the graphene diffusion mechanism and self-limited growth mechanism on Cu substrates.