Growth Rate Of Nanowires Research Articles

Electrodeposition of 3D Au1-XAgx Nanowire Networks – Influence of Ag on the Electrochemical Properties

We present the synthesis of free-standing Au1-xAgx alloy nanowire networks with controlled geometry and atomic composition, by ion track nanotechnology and electrodeposition, and their electrochemical characterization.Polycarbonate polymer templates with interconnected nanochannels are fabricated by sequential irradiation from four directions with 1-2 GeV Au ions at the UNILAC accelerator of GSI, followed by selective chemical etching of the ion tracks. [1] Au1-xAgx alloy nanowires are subsequently synthesized by potentiostatic electrodeposition inside the channels. Nanowire growth rate and atomic composition are tuned by varying the deposition potential and the electrolyte composition. The technique provides precise control of the nanowire size, interconnectivity, and composition. [2,3,4] By dissolving the polymer template, free standing nanowire networks are obtained showing good mechanical stability. Geometry, crystallinity, and composition of the alloy Au1-xAgx nanowires were analysed by TEM, EDX, and XPS. The results demonstrate that the Ag molar fraction can be precisely adjusted between 10% and 90%.The electrochemically active surface area was determined by measuring the double layer capacitance of the nanowire network surface, and is in good agreement with the calculated theoretical surface area. The 3D network exhibit surface areas up to 200 times larger than their planar counterpart, which makes them highly interesting for catalytic processes. Their electrochemical activity in alkaline solution is investigated by cyclic voltammetry in 0.1 M KOH electrolyte, and will be discussed in this presentation.[1] M.E. Toimil-Molares, Beilstein Journal of Nanotechnology, 3.1, 860-883 (2012).[2] M. Rauber, I. Alber, S. Müller et al. Nano Letters, 11.6, 2304-2310 (2011).[3] L. Burr, I. Schubert, W. Sigle et al. The Journal of Physical Chemistry C, 119.36, 20949-20956 (2015).[4] M. Li, N. Ulrich, I. Schubert et al. RSC Advances, 13, 4721-4728 (2023).

Selective-area growth of GaN and AlGaN nanowires on N-polar GaN templates with 4° miscut by plasma-assisted molecular beam epitaxy

In this study, selective area growth (SAG)s of AlGaN/GaN nanowires (NWs) on miscut N-polar GaN templates were studied and compared with that grown on Ga-polar templates using plasma-assisted molecular beam epitaxy (MBE). The SAG of N-polar AlGaN/GaN NWs demonstrated higher growth rate and more growth selectivity than that of Ga-polar AlGaN/GaN NWs. Additionally, lateral growth rate of N-polar NWs was significantly lower than Ga-polar NWs. Compared to the pyramidal shaped top surfaces of Ga-polar NWs, the N-polar GaN NWs had flat head top surfaces. The combination of higher growth selectivity, larger growth window, negligible lateral growth, and flat head, makes N-polar (Al,Ga)N NWs attractive for a variety of applications including UV LEDs and detectors as well as quantum sensing.

Effect of Temperature on the Growth Rate of Semiconductor Nanowires

Effect of Temperature on the Growth Rate of Semiconductor Nanowires

Kinetics of Catalyst-Free and Position-Controlled Low-Pressure Chemical Vapor Deposition Growth of VO2 Nanowire Arrays on Nanoimprinted Si Substrates.

In the present article, the position-controlled and catalytic-free synthesis of vanadium dioxide (VO2) nanowires (NWs) grown by the chemical vapor deposition (CVD) on nanoimprinted silicon substrates in the form of nanopillar arrays was analyzed. The NW growth on silicon nanopillars with different cross-sectional areas was studied, and it has been shown that the NWs' height decreases with an increase in their cross-sectional area. The X-ray diffraction technique, scanning electron microscopy, and X-ray photoelectron spectroscopy showed the high quality of the grown VO2 NWs. A qualitative description of the growth rate of vertical NWs based on the material balance equation is given. The dependence of the growth rate of vertical and horizontal NWs on the precursor concentration in the gas phase and on the growth time was investigated. It was found that the height of vertical VO2 NWs along the [100] direction exhibited a linear dependence on time and increased with an increase in the precursor concentration. For horizontal VO2 NWs, the height along the direction [011] varied little with the growth time and precursor concentration. These results suggest that the high-aspect ratio vertical VO2 NWs formed due to different growth modes of their crystal faces forming the top of the growing VO2 crystals and their lateral crystal faces related to the difference between the free energies of these crystal faces and implemented experimental conditions. The results obtained permit a better insight into the growth of high-aspect ratio VO2 NWs and into the formation of large VO2 NW arrays with a controlled composition and properties.

Electrodeposition of Three-Dimensional Au Nanowire Networks and Their Application As Catalysts for Methanol Electro-Oxidation

In this talk we will first present the synthesis of free-standing, stable gold nanowire network with controlled morphology and geometry by ion-track technology and electrodeposition. Etched ion-track membranes with interconnected nanochannels are produced by sequential GeV heavy ion irradiation of polymer foils from four directions, and subsequent etching and enlargment of the created ion-tracks. Au nanowire networks with three different nanowire diameters are synthesized by potentiostatic electrodeposition in the templates. Nanowire growth rate and homogeneity are tuned by varying the deposition potential. The electrochemical surface area was determined for each sample by CV analysis of surface oxide reduction reaction charge transfer. We will also discuss the catalytic performance of these Au nanowire networks towards methanol electro-oxidation, acting as an electrode in a half-cell setup. High current density and high catalytic activity were recorded. The Au nanowire networks provided up to 200 times higher peak current density than a flat Au electrode, along with excellent long term cyclability, which the current density drops only 5% over 200 CV cycles. SEM studies of the morphology and crystallinity of the nanowires before and after the methanol oxidation reaction will also be presented in the talk.Figure 1. (a) SEM image of Au nanowire network, (b) Cyclic Voltammograms recorded for a of Au nanowire network in 0.1 M KOH with (solid line) and without (dash line) 1 M MeOH. Figure 1

Enhancing the incorporation of Sn in vapor–liquid–solid GeSn nanowires by modulation of the droplet composition

We report on the influence of the liquid droplet composition on the Sn incorporation in GeSn nanowires (NWs) grown by the vapor−liquid−solid (VLS) mechanism with different catalysts. The variation of the NW growth rate and morphology with the growth temperature is investigated and 400 °C is identified as the best temperature to grow the longest untapered NWs with a growth rate of 520 nm min−1. When GeSn NWs are grown with pure Au droplets, we observe a core–shell like structure with a low Sn concentration of less than 2% in the NW core regardless of the growth temperature. We then investigate the impact of adding different fractions of Ag, Al, Ga and Si to Au catalyst on the incorporation of Sn. A significant improvement of Sn incorporation up to 9% is obtained using 75:25 Au–Al catalyst, with a high degree of spatial homogeneity across the NW volume. Thermodynamic model based on the energy minimization at the solid–liquid interface is developed, showing a good correlation with the data. These results can be useful for obtaining technologically important GeSn material with a high Sn content and, more generally, for tuning the composition of VLS NWs in other material systems.

Implementing the Reactor Geometry in the Modeling of Chemical Bath Deposition of ZnO Nanowires.

The formation of nanowires by chemical bath deposition is of great interest for a wide variety of optoelectronic, piezoelectric, and sensing devices, from which the theoretical description of their elongation process has emerged as a critical issue. Despite its strong influence on the nanowire growth kinetics, reactor size has typically not been taken into account in the theoretical modeling developed so far. We report a new theoretical description of the axial growth rate of nanowires in dynamic conditions based on the solution of Fick’s diffusion equations, implementing a sealed reactor of finite height as a varying parameter. The theoretical model is applied in various chemical bath deposition conditions in the case of the growth of ZnO nanowires, from which the influence of the reactor height is investigated and compared to experimental data. In particular, it is found that the use of reactor heights smaller than 2 cm significantly decreases the ZnO nanowires’ axial growth rate in typical experimental conditions due to the faster depletion of reactants. The present approach is further used predictively, showing its high potential for the design of batch reactors for a wide variety of chemical precursors and semiconductor materials in applied research and industrial production.

Механизм роста монослоя на верхней грани Ga-каталитических нитевидных нанокристаллов GaAs и GaP

The growth mechanism of monolayer on the top facet of Ga-catalyzed GaAs and GaP nanowires is investigated. Within the framework of a theoretical model, the maximal monolayer coverage due to the material in the catalyst droplet, the nanowire growth rate and the content of group V atoms in the droplet are found depending on the growth conditions. The estimates of the phosphorus re-evaporation coefficient from neighboring nanowires and substrate are obtained by comparing the theoretical and experimental growth rate of Ga-catalyzed GaP nanowires.

Growth mechanism of monolayer on the top facet of Ga-catalyzed GaAs and GaP nanowires

The growth mechanism of monolayer on the top facet of Ga-catalyzed GaAs and GaP nanowires is investigated. Within the framework of a theoretical model, the maximal monolayer coverage due to the material in the catalyst droplet, the nanowire growth rate and the content of group V atoms in the droplet are found depending on the growth conditions. The estimates of the phosphorus re-evaporation coefficient from neighboring nanowires and substrate are obtained by comparing the theoretical and experimental growth rate of Ga-catalyzed GaP nanowires. Keywords: III-V nanowires, vapor-liquid-solid growth mechanism, nucleation

Unusually-high growth rate (∼2.8 μm/s) of germania nanowires and its hierarchical structures by an in-situ continuous precursor supply

Low-dimensional nanostructured semiconductors are becoming the promising materials for high-performance nanophotonics, nanoelectronics, and quantum devices. To enable these applications, it requires an efficient methodology to control the dimension of these materials during synthesis processes, and to achieve mass production of these materials with high reproducibility, perfect crystallinity, and low production cost. In this study, an ultra-fast, facile synthesis strategy is presented for reproducible monocrystalline hexagonal germania (GeO2) nanowires (NWs) and hierarchical structures. These GeO2 nanostructures were grown by one-step-annealing of the Ni film-covered GeSn epilayers in a rapid thermal annealing (RTA) system without any gaseous or liquid Ge sources. It was found that after short annealing for 60 s at 675 °C, the long GeO2 NWs of more than 170 μm are obtained, indicating that the growth rate is several magnitude orders higher than that of the common chemical vapor deposition (CVD) methods. The mechanism of the growth was studied by changing the growth temperature, catalyst type, and surface oxidation. The results indicate that this record-fast growth (>2.8 μm/s) of NW is due to the continuously generated in-situ GeO vapors from the Ni-catalyst decomposition of supersaturated GeSn epilayer. This work presents a rapid, and low-cost method to synthesis high-density GeO2 NW and its hierarchical structures which have the potential applications for optoelectronic communication/detection, superhydrophobic surfaces, photocatalyst, and sensing.

Self-consistent modeling of MBE self-catalyzed GaAs nanowire growth

Self-catalyzed GaAs nanowires are synthesized by molecular beam epitaxy at various arsenic fluxes and growth temperatures. The growth of GaAs nanowires is simulated considering the kinetics of material transport inside the catalyst droplet. The re-evaporation coefficient of arsenic is estimated for the given growth conditions. Calculated nanowire growth rate is in satisfactory agreement with the experimental data.

Morphology characterization and growth of GaAs nanowires on Selective-area substrates

Gold (Au)-catalyzed and catalyst-free gallium arsenide (GaAs) nanowires (NWs) were grown on GaAs substrates with mask patterns by metal–organic chemical vapor deposition (MOCVD). Catalyst-free GaAs NWs with hexagonal prism morphology were observed by scanning electron microscopy (SEM). The growth rate of catalyst-free GaAs NWs was reduced to nearly 5.5% of that of NWs grown using a vapor–liquid–solid (VLS) mechanism. By coating Au as a catalyst on selective-area substrates with the same thickness of Au film, an increased growth was observed. The diameter of the Au-catalyzed NWs grown on selective-area substrates was roughly reduced to 40%, resulting in multiple NWs being squeezed into the same hole. GaAs NWs with cylindrical geometry on selective-area substrates were produced by adjusting the thickness of the Au film, and thus, a single NW could be contained in one hole as the Au film thickness increased.

Зависимость скорости роста и структуры III-V нитевидных нанокристаллов от площади сбора адатомов на поверхности подложки

A theoretical analysis is presented for the growth rate and structure of III-V nanowires depending on the collection area of group III adatoms on the substrate surface. An expression for the maximum possible nanowire vertical growth rate is obtained and different reasons are analyzed for its suppression in different technologies. It is shown that the maximum growth rate is proportional to the collection area and inversely proportional to the squared nanowire radius. It is demonstrated that self-catalyzed GaAs nanowires grow or shrink radially at large or small adatom collection areas, respectively, having the zincblende crystal phase in both cases. The wurtzite phase forms in GaAs nanowires growing only axially at the intermediate adatom collection areas.

Limits of III–V Nanowire Growth

The growth kinetics of III–V semiconductor nanowires by a vapor–liquid–solid method is theoretically analyzed. The analysis includes three concurrent processes—the deposition rate of an element of group V, penetration of atoms of group III into the droplet taking into account surface diffusion, and nucleation at the liquid–solid interface. A generalized formula for the vertical growth rate of nanowires is obtained, and it can be limited by one of the three processes. Various growth conditions with Au and Ga catalysts depending on the fluxes of elements of groups III and V and the nanowire radius are analyzed.

In-situ reflectometry to monitor locally-catalyzed initiation and growth of nanowire assemblies

We investigate in-situ laser reflectometry for measuring the axial growth rate in chemical vapor deposition of assemblies of well-aligned vertical germanium nanowires grown epitaxially on single crystal substrates. Finite difference frequency domain optical simulations were performed in order to facilitate quantitative analysis and interpretation of the measured reflectivity data. The results show an insensitivity of the reflected intensity oscillation period to nanowire diameter and density within the range of experimental conditions investigated. Compared to previous quantitative in-situ measurements performed on III–V nanowire arrays, which showed two distinct rate regimes, we observe a constant, steady-state nanowire growth rate. Furthermore, we show that the measured reflectivity decay can be used to determine the germanium nanowire nucleation time with good precision. This technique provides an avenue to monitor growth of nanowires in a variety of materials systems and growth conditions.

In Situ Transmission Electron Microscopy Measurements of Ge Nanowire Synthesis with Liquid Metal Nanodroplets in Water.

The growth of Ge nanowires in water inside a liquid transmission electron microscope (TEM) holder has been demonstrated at room temperature. Each nanowire growth event was stimulated by the incident electron beam on otherwise unsupported liquid Ga or liquid In nanodroplets. A variety of conditions were explored, including liquid metal nanodroplet surface condition, liquid metal nanodroplet size and density, formal concentration of dissolved GeO2, and electron beam intensity. The cumulative observations from a series of videos recorded during growth events suggested the following points. First, the conditions necessary for initiating nanowire growth at uncontacted liquid metal nanodroplets in a liquid TEM cell indicate the process was governed by solvated electrons generated from secondary electrons scattered by the liquid metal nanodroplets. The attained current densities were comparable to those achieved in conventional electrochemical liquid-liquid-solid (ec-LLS) growths outside of a TEM. Second, the surface condition of the liquid metal nanodroplets was quite influential on whether nanowire growth occurred and surface diffusion of Ge adatoms contributed to the rate of crystallization. Third, the Ge nanowire growth rates were limited by the feed rate of Ge to the crystal growth front rather than the rate of crystallization at the liquid metal/solid Ge interface. Estimates of an electrochemical current for the reduction of dissolved GeO2 were nominally in line with currents used for Ge nanowire growth by ec-LLS outside of the TEM. Fourth, the Ge nanowire growths in the liquid TEM cell occurred far from thermodynamic equilibrium, with supersaturation values of 104 prior to nucleation. These collective points provide insight on how to further control and improve Ge nanowire morphology and crystallographic quality by the ec-LLS method.

Selective area formation of GaN nanowires on GaN substrates by the use of amorphous Al x O y nucleation layer

Examples are presented that application of amorphous Al x O y nucleation layer is an efficient way of controlling spatial distribution of GaN nanowires grown by plasma-assisted molecular beam epitaxy. On GaN/sapphire substrates Al x O y stripes induce formation of GaN nanowires while a compact GaN layer is formed outside the stripes. We show that the ratio of nanowire length h to the thickness of the compact layer d can be tailored by adjusting impinging gallium and nitrogen fluxes. Calculations of the h/d aspect ratio were performed taking into account dependence of nanowire incubation time on the growth parameters. In agreement with calculations we found that the value of h/d ratio can be increased by increasing the N/Ga flux ratio in the way that the N-limited growth regime determines nanowire axial growth rate while growth of compact layer remains Ga-limited. This ensures the highest value of the h/d aspect ratio. Local modification of GaN growth kinetics caused by surface diffusion of Ga adatoms through the boundary separating the Al x O y stripe and the GaN/sapphire substrate is discussed. We show that during the nanowire incubation period gallium is transported out of the Al x O y stripe, which delays nanowire nucleation onset and leads to reduced length of GaN nanowires in the vicinity of the stripe edge. Simultaneously the growth on the GaN/sapphire substrate is locally enhanced, so the planar GaN layers adopts a typical edge shape of mesa structures grown by selective area growth. Ga diffusion length on a-Al x O y surface of ∼500 nm is inferred from our results.

Influence of growth parameters on the morphology of GaAs nanowires grown on Si (111) by molecular beam epitaxy

We report on the impact of Ga and As flux on GaAs nanowires (NWs) morphology grown by Ga assisted molecular beam epitaxy on epi-ready Si (111) substrates. The results are presented in terms of growth rate, density and diameter of NWs. It is demonstrated that an increase in the As flux by a factor of 4 results in an increase in the growth rate of GaAs NWs by a factor of 3.4. It is perceived that while the average diameter of the GaAs NWs is more sensitive to the increase in the Ga flux, the amount of As flux is important for having longer NWs with a tapering around 1.0%. However, a tapering around -1.4% in GaAs NWs is obtained under high As/Ga flux ratio of 80. Besides, it is revealed that relatively high As/Ga flux ratio consumes the Ga droplets at the tip of the GaAs NWs which results in the change of NW diameter. Above all, it is shown that a change in growth mechanism from vapor-liquid-solid to vapor-solid occurs in the case of high As/Ga ratio which appears at the bottom region of GaAs NWs.

Facile, wafer-scale compatible growth of ZnO nanowires via chemical bath deposition: assessment of zinc ion contribution and other limiting factors.

ZnO is a highly promising, multifunctional nanomaterial having various versatile applications in the fields of sensors, optoelectronics, photovoltaics, photocatalysts and water purification. However, the real challenge lies in producing large scale, well-aligned, highly reproducible ZnO nanowires (NWs) using low cost techniques. This large-scale production of ZnO NWs has stunted the development and practical usage of these NWs in fast rising fields such as photocatalysis or in photovoltaic applications. The present article shows an effective, simple approach for the uniform, aligned growth of ZnO NWs on entire silicon wafers (sizes 3 or 4 inches), using a low-temperature Chemical Bath Deposition (CBD) technique. In addition to this, a systematic study of the substrate size dependent growth of NWs has been conducted to better understand the effect of the limitation in the deposition rate of Zn2+ ions on the growth of NWs. The growth rate of ZnO NWs is seen to have a strong relationship with the substrate size. Also, the loading efficiency of the Zn2+ ions is higher in ZnO NWs grown on a 3-inch silicon wafer in comparison to those grown on a small piece. An in-depth time dependent growth study conducted on entire 3-inch wafers to track the morphological evolution (length, diameter and number of the NWs) reveals that the growth rate of the length of the NWs reaches a saturation state in a short time span of 20 min. Assessment of the overall homogeneity of the NWs grown on the 3-inch wafer and simultaneous growth on two entire 4-inch silicon wafers has also been demonstrated in this article. This demonstration of large-scale, well-aligned controllable, aligned growth of ZnO NWs on entire silicon wafers is a first step towards NW based devices especially for applications such as photovoltaic, water purification, photocatalysis or biomedical applications.

Лимитирующие режимы роста III-V нитевидных нанокристаллов

Theoretical analysis is presented for vapor-liquid-solid growth of III-V nanowires in the presence of three competing processes of the group V deposition, surface diffusion of group III adatoms and nucleation of islands at the liquid-solid interface. A generalized equation for the nanowire growth rate is obtained which can be limited of one of the three processes depending on the growth environment. Different regimes of vapor-liquid-solid growth of III-V nanowires are analyzed depending on the group III and V influxes and nanowire radius.