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Black A, Abdelazim NM, Noori YJ, Han Y, Zhelev N, Thomas S, Zhang W, Reid G, Beanland R, de Groot CHK, Bartlett PN. Toward a Procedure for the Template Free Growth of Te Nanowires Across an Insulator by Electrodeposition. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2024; 128:18634-18640. [PMID: 39502806 PMCID: PMC11533211 DOI: 10.1021/acs.jpcc.4c05915] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/01/2024] [Revised: 10/09/2024] [Accepted: 10/11/2024] [Indexed: 11/08/2024]
Abstract
In this work, we present a method for direct, site-selective growth of tellurium nanowires by electrochemical deposition. The Te nanowires were grown laterally between two specially designed nanoband electrodes across a gap, and over a dielectric material, forming a lateral device structure directly. The resulting wires are crystalline and phase pure, as evidenced by Raman spectroscopy, EDS (energy dispersive X-ray spectroscopy), and ADF-STEM (annular dark field scanning transmission electron microscopy). The precise conditions for lateral growth of the nanowires were investigated and the fabrication of an electronic device from the as-deposited material, without the need for any transfer process or further contact fabrication, is demonstrated.
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Kapur O, Guo D, Reynolds J, Newbrook D, Han Y, Beanland R, Jiang L, de Groot CHK, Huang R. An ultra high-endurance memristor using back-end-of-line amorphous SiC. Sci Rep 2024; 14:14008. [PMID: 38890324 PMCID: PMC11189404 DOI: 10.1038/s41598-024-64499-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2024] [Accepted: 06/10/2024] [Indexed: 06/20/2024] Open
Abstract
Integrating resistive memory or neuromorphic memristors into mainstream silicon technology can be substantially facilitated if the memories are built in the back-end-of-line (BEOL) and stacked directly above the logic circuitries. Here we report a promising memristor employing a plasma-enhanced chemical vapour deposition (PECVD) bilayer of amorphous SiC/Si as device layer and Cu as an active electrode. Its endurance exceeds one billion cycles with an ON/OFF ratio of ca. two orders of magnitude. Resistance drift is observed in the first 200 million cycles, after which the devices settle with a coefficient of variation of ca. 10% for both the low and high resistance states. Ohmic conduction in the low resistance state is attributed to the formation of Cu conductive filaments inside the bilayer structure, where the nanoscale grain boundaries in the Si layer provide the pre-defined pathway for Cu ion migration. Rupture of the conductive filament leads to current conduction dominated by reverse bias Schottky emission. Multistate switching is achieved by precisely controlling the pulse conditions for potential neuromorphic computing applications. The PECVD deposition method employed here has been frequently used to deposit typical BEOL SiOC low-k interlayer dielectrics. This makes it a unique memristor system with great potential for integration.
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Soulé S, Moehl GE, Huang R, Noori YJ, Kiang KS, Kees de Groot CH, Beanland R, Smith DC, Hector AL. Confining the growth of mesoporous silica films into nanospaces: towards surface nanopatterning. NANOSCALE ADVANCES 2022; 4:1105-1111. [PMID: 36131765 PMCID: PMC9417874 DOI: 10.1039/d1na00654a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Accepted: 01/10/2022] [Indexed: 06/15/2023]
Abstract
The combination of lithographic methods and sol gel bottom-up techniques is a promising approach for nanopatterning substrates. The integration and scalable fabrication of such substrates are of great interest for the development of nanowire-based materials opening potentialities in new technologies. We demonstrate the deposition of ordered mesoporous silica into nanopatterned silica substrates by dip coating. Using scanning electron microscopy and grazing incidence small angle X-ray scattering, the effect of the sol composition on the pore ordering was probed. Optimising the sol composition using anodic alumina membranes as confined spaces, we showed how the pH controlled the transformation from circular to columnar mesophase. Vertical mesopores were obtained with very good repeatability. The effect of the sol chemistry on the surfactant curvature was then shown to be similar in nanopatterned substrates made by e-beam lithography.
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Robinson F, Sethi V, de Groot CHK, Hector AL, Huang R, Reid G. Low-Pressure CVD of GeE (E = Te, Se, S) Thin Films from Alkylgermanium Chalcogenolate Precursors and Effect of Deposition Temperature on the Thermoelectric Performance of GeTe. ACS APPLIED MATERIALS & INTERFACES 2021; 13:47773-47783. [PMID: 34606236 DOI: 10.1021/acsami.1c14237] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The homologous series [GenBu3(EnBu)] (E = Te, Se, S; (1), (3) and (4)) and [GenBu2(TenBu)2] (2) have been synthesized as mobile oils in excellent yield (72-93%) and evaluated as single-source precursors for the low-pressure chemical vapor deposition (LPCVD) of GeE thin films on silica. Compositional and structural characterizations of the deposits have been performed by grazing-incidence X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, and Raman spectroscopy, confirming the phase purity and stoichiometry. Electrical characterization via variable-temperature Hall effect measurements is also reported. Given the strong interest in GeTe and its alloys for thermoelectric applications, variable-temperature Seebeck data were also investigated for a series of p-type GeTe films. The data show that it is possible to tune the thermoelectric response through intrinsic Ge vacancy regulation by varying the deposition temperature, with the highest power factor (40 μW/K2cm@629 K) and effective ZT values observed for the films deposited at higher temperatures.
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Thomas S, Greenacre VK, Smith DE, Noori YJ, Abdelazim NM, Hector AL, de Groot CHK, Levason W, Bartlett PN, Reid G. Tungsten disulfide thin films via electrodeposition from a single source precursor. Chem Commun (Camb) 2021; 57:10194-10197. [PMID: 34519740 DOI: 10.1039/d1cc03297f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
We report a simple process for the electrodeposition of tungsten disulfide thin films from a CH2Cl2-based electrolyte using a tailored single source precursor, [NEt4]2[WS2Cl4]. This new precursor incorporates the 1 : 2 W : S ratio required for formation of WS2, and eliminates the need for an additional proton source in the electrolyte to remove excess sulfide. The electrochemical behaviour of [NEt4]2[WS2Cl4] is studied by cyclic voltammetry and electrochemical quartz crystal microbalance techniques, and the WS2 thin films are grown by potentiostatic electrodeposition.
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Ye S, Yan X, Husain MK, Saito S, de Groot CHK, Tsuchiya Y. Direct observation of surface charge redistribution in active nanoscale conducting channels by Kelvin Probe Force Microscopy. NANOTECHNOLOGY 2021; 32:325206. [PMID: 33930886 DOI: 10.1088/1361-6528/abfd55] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2020] [Accepted: 04/30/2021] [Indexed: 06/12/2023]
Abstract
Surface-exposed uniformly doped silicon-on-insulator channels are fabricated to evaluate the accuracy of Kelvin Probe Force Microscopy (KPFM) measured surface potential and reveals the role of surface charge on the exposed channel operated in the ambient environment. First, the quality of the potential profile probed in the vacuum environment is assessed by the consistency of converted resistivity from KPFM result to the resistivity extracted by the other three methods. Second, in contrast to the simulated and vacuum surface potential profile and image, the ambient surface potential is bent excessively at the terminals of the channel. The excessive bending can be explained by the movement of surface charge under the drive of geometry induced strong local electric field from the channel and results in non-uniform distribution. The dynamic movement of surface charges is proved by the observation of time-dependent potential drift in the ambient measurement. The result suggests the surface charge effect should be taken into account of the measurement of the surface potential in the ambient environment and the design of charge sensitive devices whose surfaces are exposed to air or in ambient conditions in their operation.
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Robinson F, Newbrook DW, Curran P, de Groot CHK, Hardie D, Hector AL, Huang R, Reid G. Low temperature CVD of thermoelectric SnTe thin films from the single source precursor, [ nBu 3Sn(Te nBu)]. Dalton Trans 2021; 50:998-1006. [PMID: 33355323 DOI: 10.1039/d0dt03760e] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
This work has demonstrated that the single source precursor [nBu3Sn(TenBu)], bearing n-butyl groups and containing the necessary 1 : 1 Sn : Te ratio, facilitates growth of continuous, stoichiometric SnTe thin films. This single source CVD precursor allows film growth at significantly lower temperatures (355-434 °C at 0.01-0.05 Torr) than required for CVD from SnTe powder. This could be advantageous for controlling the surface states in topological insulators. The temperature-dependent thermoelectric performance of these films has been determined, revealing them to be p-type semiconductors with peak Seebeck coefficient and power factor values of 78 μV K-1 and 8.3 μW K-2 cm-1, respectively, at 615 K; comparing favourably with data from bulk SnTe. Further, we have demonstrated that the precursor facilitates area selective growth of SnTe onto the TiN regions of SiO2/TiN patterned substrates, which is expected to be beneficial for the fabrication of micro-thermoelectric generators.
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Noori YJ, Thomas S, Ramadan S, Smith DE, Greenacre VK, Abdelazim N, Han Y, Beanland R, Hector AL, Klein N, Reid G, Bartlett PN, Kees de Groot CH. Large-Area Electrodeposition of Few-Layer MoS 2 on Graphene for 2D Material Heterostructures. ACS APPLIED MATERIALS & INTERFACES 2020; 12:49786-49794. [PMID: 33079533 DOI: 10.1021/acsami.0c14777] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Heterostructures involving two-dimensional (2D) transition metal dichalcogenides and other materials such as graphene have a strong potential to be the fundamental building block of many electronic and optoelectronic applications. The integration and scalable fabrication of such heterostructures are of the essence in unleashing the potential of these materials in new technologies. For the first time, we demonstrate the growth of few-layer MoS2 films on graphene via nonaqueous electrodeposition. Through methods such as scanning and transmission electron microscopy, atomic force microscopy, Raman spectroscopy, energy- and wavelength-dispersive X-ray spectroscopies, and X-ray photoelectron spectroscopy, we show that this deposition method can produce large-area MoS2 films with high quality and uniformity over graphene. We reveal the potential of these heterostructures by measuring the photoinduced current through the film. These results pave the way toward developing the electrodeposition method for the large-scale growth of heterostructures consisting of varying 2D materials for many applications.
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Cicvarić K, Meng L, Newbrook DW, Huang R, Ye S, Zhang W, Hector AL, Reid G, Bartlett PN, de Groot CHK. Thermoelectric Properties of Bismuth Telluride Thin Films Electrodeposited from a Nonaqueous Solution. ACS OMEGA 2020; 5:14679-14688. [PMID: 32596605 PMCID: PMC7315573 DOI: 10.1021/acsomega.0c01284] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Accepted: 05/05/2020] [Indexed: 05/20/2023]
Abstract
We report the thermoelectric properties of Bi2Te3 thin films electrodeposited from the weakly coordinating solvent dichloromethane (CH2Cl2). It was found that the oxidation of porous films is significant, causing the degradation of its thermoelectric properties. We show that the morphology of the film can be improved drastically by applying a short initial nucleation pulse, which generates a large number of nuclei, and then growing the nuclei by pulsed electrodeposition at a much lower overpotential. This significantly reduces the oxidation of the films as smooth films have a smaller surface-to-volume ratio and are less prone to oxidation. X-ray photoelectron spectroscopy (XPS) shows that those films with Te(O) termination show a complete absence of oxygen below the surface layer. A thin film transfer process was developed using polystyrene as a carrier polymer to transfer the films from the conductive TiN to an insulating layer for thermoelectrical characterization. Temperature-dependent Seebeck measurements revealed a room-temperature coefficient of -51.7 μV/K growing to nearly -100 μV/K at 520 °C. The corresponding power factor reaches a value of 88.2 μW/mK2 at that temperature.
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Sun K, Xiao W, Ye S, Kalfagiannis N, Kiang KS, de Groot CHK, Muskens OL. Embedded Metal Oxide Plasmonics Using Local Plasma Oxidation of AZO for Planar Metasurfaces. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2020; 32:e2001534. [PMID: 32419202 DOI: 10.1002/adma.202001534] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2020] [Revised: 04/19/2020] [Accepted: 04/27/2020] [Indexed: 06/11/2023]
Abstract
New methods for achieving high-quality conducting oxide metasurfaces are of great importance for a range of emerging applications from infrared thermal control coatings to epsilon-near-zero nonlinear optics. This work demonstrates the viability of plasma patterning as a technique to selectively and locally modulate the carrier density in planar Al-doped ZnO (AZO) metasurfaces without any associated topographical surface profile. This technique stands in strong contrast to conventional physical patterning which results in nonplanar textured surfaces. The approach can open up a new route to form novel photonic devices with planar metasurfaces, for example, antireflective coatings and multi-layer devices. To demonstrate the performance of the carrier-modulated AZO metasurfaces, two types of devices are realized using the demonstrated plasma patterning. A metasurface optical solar reflector is shown to produce infrared emissivity equivalent to a conventional etched design. Second, a multiband metasurface is achieved by integrating a Au visible-range metasurface on top of the planar AZO infrared metasurface. Independent control of spectral bands without significant cross-talk between infrared and visible functionalities is achieved. Local carrier tuning of conducting oxide films offers a conceptually new approach for oxide-based photonics and nanoelectronics and opens up new routes for integrated planar metasurfaces in optical technology.
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Huang R, Kissling GP, Kashtiban R, Noori YJ, Cicvarić K, Zhang W, Hector AL, Beanland R, Smith DC, Reid G, Bartlett PN, de Groot CHK. Towards a 3D GeSbTe phase change memory with integrated selector by non-aqueous electrodeposition. Faraday Discuss 2019; 213:339-355. [PMID: 30411749 DOI: 10.1039/c8fd00126j] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
We have recently reported a new method for the electrodeposition of thin film and nanostructured phase change memory (PCM) devices from a single, highly tuneable, non-aqueous electrolyte. The quality of the material was confirmed by phase cycling via electrical pulsed switching of both 100 nm nano-cells and thin film devices. This method potentially allows deposition into extremely small confined cells down to less than 5 nm, 3D lay-outs that require non-line-of-sight techniques, and seamless integration of selector devices. As electrodeposition requires a conducting substrate, the key condition for electronic applications based on this method is the use of patterned metal lines as the working electrode during the electrodeposition process. In this paper, we show the design and fabrication of a 2D passive memory matrix in which the word lines act as the working electrode and nucleation site for the growth of confined cells of Ge-Sb-Te. We will discuss the precursor requirement for deposition from non-aqueous, weakly coordinating solvents, show the transmission electron microscopy analysis of the electrodeposition growth process and elemental distribution in the deposits, and show the fabrication and characterisation of the Ge-Sb-Te memory matrix.
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