Search

Silica thin films with vertical nanopores are useful to control access to electrode surfaces and may act as templates for growth of nanomaterials. The most effective method to produce these films, electrochemically assisted surfactant assembly, also produces aggregates of silica particles. This paper shows that growth with an AC signal superimposed onto the potential avoids the aggregates and only very small numbers of single particles are found. This finding is linked to better control of the diffusion field of hydroxide ions that are responsible for particle growth. The resultant films are smooth, with very well-ordered hexagonal pore structures.\ud \ud

The square pyramidal WSeCl4 monomer and its complexes with neutral donor ligands are described, including [WSeCl4(SenBu2)], which is a single source CVD precursor for highly oriented WSe2 thin films.

Memristors are emerging as promising candidates for practical application in reservoir computing systems that are capable of temporal information processing. Here, we experimentally implement a physical reservoir computing system using resistive memristors based on three-dimensional (3D)-structured mesoporous silica (mSiO2) thin films fabricated by a low cost, fast and vacuum-free sol–gel technique. The in situ learning capability and a classification accuracy of 100% on a standard machine learning dataset are experimentally demonstrated. The volatile (temporal) resistive switching in diffusive memristors arises from the formation and subsequent spontaneous rupture of conductive filaments via diffusion of Ag species within the 3D-structured nanopores of the mSiO2 thin film. Besides volatile switching, the devices also exhibit a bipolar non-volatile resistive switching behavior when the devices are operated at a higher compliance current level. The implementation of mSiO2 thin films opens the route to fabricate a simple and low cost dynamic memristor with a temporal information process functionality, which is essential for neuromorphic computing applications.

Two‐terminal memristor has emerged as one of the most promising neuromorphic artificial electronic devices for their structural resemblance to biological synapses and ability to emulate many synaptic functions. In this work, a memristor based on the back‐end‐of‐line (BEOL) material silicon carbide (SiC) is developed. The thin film memristors demonstrate excellent binary resistive switching with compliance‐free and self‐rectifying characteristics which are advantageous for the implementation of high‐density 3D crossbar memory architectures. The conductance of this SiC‐based memristor can be modulated gradually through the application of both DC and AC signals. This behavior is demonstrated to further emulate several vital synaptic functions including paired‐pulse facilitation (PPF), post‐tetanic potentiation (PTP), short‐term potentiation (STP), and spike‐rate‐dependent plasticity (SRDP). The synaptic function of learning‐forgetting‐relearning processes is successfully emulated and demonstrated using a 3 × 3 artificial synapse array. This work presents an important advance in SiC‐based memristor and its application in both memory and neuromorphic computing.

We report on the development of hybrid organic−inorganic material-based flexible memristor devices made by a fast and simple electrochemical fabrication method. The devices consist of a bilayer of poly(methyl methacrylate) (PMMA) and Te-rich GeSbTe chalcogenide nanoscale thin films sandwiched between Ag top and TiN bottom electrodes on both Si and flexible polyimide substrates. These hybrid memristors require no electroforming process and exhibit reliable and reproducible bipolar resistive switching at low switching voltages under bothflat and bending conditions. Multistate switching behavior can also be achieved by controlling the compliance current (CC). We attribute the switching between the high resistance state (HRS) and low resistance state (LRS) in the devices to the formation and rupture of conductive Ag filaments within the hybrid PMMA/GeSbTe matrix. This work provides a promising route to fabricate flexible memory devices through an electrodeposition process for application in flexible electronics.

In this paper, an atomic layer deposited memristor based on Al2O3/MoO3 bi-layer structure is reported. Compared with the single layer MoO3 based device, the bi-layer memristor demonstrates the improved bipolar switching behaviors including better endurance, higher ON/OFF ratio, and higher uniformity of the programming voltages. Space-charge-limited current (SCLC) model is used to explain the current conduction in our memristor. The formation and rupture of conductive oxygen vacancy-based filaments are illustrated as the proposed mechanism for the observed resistive switching behavior.

The “one-to-many” problem is a typical challenge that faced by many machine learning aided inverse nanophotonics designs where one target optical response can be achieved by many solutions (designs). Although novel training approaches, such as tandem network, and network architecture, such as the mixture density model, have been proposed, the critical problem of solution degeneracy still exists where some possible solutions or solution spaces are discarded or unreachable during the network training process. Here, we report a solution to the “one-to-many” problem by employing a conditional generative adversarial network (cGAN) that enables generating sets of multiple solution groups to a design problem. Using the inverse design of a transmissive Fabry–Pérot-cavity-based color filter as an example, our model demonstrates the capability of generating an average number of 3.58 solution groups for each color. These multiple solutions allow the selection of the best design for each color which results in a record high accuracy with an average index color difference ΔE of 0.44. The capability of identifying multiple solution groups can benefit the design manufacturing to allow more viable designs for fabrication. The capability of our cGAN is verified experimentally by inversely designing the RGB color filters. We envisage this cGAN-based design methodology can be applied to other nanophotonic structures or physical science domains where the identification of multi-solution across a vast parameter space is required.

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.

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.

The red-brown [(WSCl4)2{µ-RS{CH2)2SR}] (R = Me, Ph, iPr) and [(WSCl4)2{µ-MeS{CH2)3SMe}] have been made by reaction of WSCl4 with the thioether in a 2:1 molar ratio, in anhydrous CH2Cl2 solution, and characterised by microanalysis, IR, UV/Vis and 1H NMR spectroscopy. The X-ray structures of the four dithioether complexes reveal square pyramidal WSCl4 units and bridging dithioethers with W=S trans to thioether sulfur. Paramagnetic W(V) complexes, [WSCl3{RS{CH2)2SR}] (R = Me, iPr), have been made similarly using a 1: ≥1 ratio of reactants or longer reaction times. The W(VI) complexes, [WSCl4(SMe2)] and [WSCl4(SeMe2)], are also described. Analogous complexes of WOCl4, [(WOCl4)2{RS(CH2)2SR}] (R = Ph, iPr), have been made similarly from WOCl4, but reactions using MeS(CH2)nSMe (n = 2, 3) led to reduction to W(V), forming [WOCl3{MeS{CH2)nSMe], both of which were identified crystallographically. Curiously, they are geometric isomers: [WOCl3{MeS(CH2)3SMe}] has the dithioether trans Cl/Cl whereas in [WOCl3{MeS(CH2)2SMe}] it is trans O/Cl. Remarkably, low pressure chemical vapour deposition (CVD) experiments using the dinuclear W(VI) species, [(WSCl4)2{iPrS(CH2)2SiPr}], as a single source precursor produced thin films of 4H-WS2, identified by grazing incidence X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy; the tungsten thiochloride complex is the first single source low pressure CVD precursor for WS2. In contrast, the mononuclear W(V) complex, [WSCl3{iPrS(CH2)2SiPr}], does not deposit WS2 under similar conditions.

In this work, we report on the fabrication of resistive random-access memory cells based on electrodeposited GeSbTe material between TiN top and bottom electrodes in a crossbar architecture. The cells exhibit asymmetric bipolar resistive switching characteristics under the same SET and RESET compliance current (CC), showing highly uniform and reproducible switching properties. A multi-state switching behavior can be also achieved by varying the sweeping voltage and CC. Unlike phase-change switching, the switching between the high-resistance state and the low-resistance state in these cells can be attributed to the formation and rupture of conductive Te bridge(s) within the Te-rich GeSbTe matrix upon application of a high electric field. The results point toward the usage of the electrodeposition method to fabricate advanced functional device structures for application in non-volatile memory.

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.

Phase change memories (PCM) is an emerging type of non-volatile memory that has shown a strong presence in the data-storage market. This technology has recently attracted significant research interest in the development of non-Von Neumann computing architectures such as in-memory and neuromorphic computing. Research in these areas has been primarily motivated by the scalability potential of phase change materials and their compatibility with industrial nanofabrication processes. In this work, we are presenting our development of crossbar phase change memory arrays through the electrodeposition of GeSbTe (GST). We show that GST can be electrodeposited in microfabricated TiN crossbar arrays using a scalable process. Our phase switching test of the electrodeposited materials have shown that a SET/RESET resistance ratio of 2-3 orders of magnitude is achievable with a switching endurance of around 80 cycles. These results represent the first phase switching of electrodeposited GeSbTe in microfabricated crossbar arrays. Our work paves the way towards developing large memory arrays involving electrodeposited materials for passive selectors and phase switching devices. It also opens opportunities for developing a variety of different electronic devices using electrodeposited materials., Comment: 9 pages, 5 figures

Dynamic structural color provides an additional time dimension in contrast to the static one, enriching the information load and functionalities. As a phase change material, vanadium dioxide offers great opportunities to implement dynamic structural color as its insulator-metal transition. Nevertheless, the multiple states also place a barrier to the efficient design of the structure configurations. This work firstly reports the dynamic structural color inverse design of asymmetric Fabry-Pérot cavity through a parameter-based conditional generative adversarial networks approach. The proposed structure attains a gamut as large as 117% of sRGB in the insulator state and can produce a 5% color coverage variation via the phase change of VO2 layer. By using the trained conditional generative adversarial networks, the inverse design accuracy with the average color difference ΔE of 0.98 is achieved. A monochromatic pattern is designed by the trained networks to demonstrate different color dynamics of the various structures.

Structural color based on Fabry–Perot (F-P) cavity enables a wide color gamut with high resolution at submicroscopic scale by varying its geometrical parameters. The ability to design such parameters that can accurately display the desired color is therefore crucial to the manufacturing of F-P cavities for practical applications. This work reports the first inverse design of F-P cavity structure using deep learning through a bidirectional artificial neural network. It enables the production of a significantly wider coverage of color space that is over 215% of sRGB with extremely high accuracy, represented by an average Δ E 2000 value below 1.2. The superior performance of this structural color-based neural network is directly ascribed to the definition of loss function in the uniform CIE 1976-Lab color space. Over 100,000 times improvement in the design efficiency has been demonstrated by comparing the neural network to the metaheuristic optimization technique using an evolutionary algorithm when designing the famous painting of “Haystacks, end of Summer” by Claude Monet. Our results demonstrate that, with the correct selection of loss function, deep learning can be very powerful to achieve extremely accurate design of nanostructured color filters with very high efficiency.

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.

The ever-increasing demand for renewable energy and zero carbon dioxide emission have been the driving force for the development of thermoelectric generators with better power generation performance. Alongside with the effort to discover thermoelectric materials with higher figure-of-merit, the geometrical and structural optimisation of thermoelectric generators are also essential for maximized power generation and efficiency. This work demonstrates for the first time the application of artificial neural network, a deep learning technique, in forward modelling the maximum power generation and efficiency of a thermoelectric generator and its application in the generator design and optimisation. After training using a dataset containing 5000 3-D finite element method based simulations, the artificial neural networks with 5 layers and 400 neurons per layer demonstrate extremely high prediction accuracy over 98% and are able to operate under both constant temperature difference and heat flux conditions while taking into account of the contact electrical resistance, surface heat transfer and other thermoelectric effects. Coupling with genetic algorithm, the trained artificial neural networks can optimise the leg height, leg width, fill factor and interconnect height of the thermoelectric generator for different operating and contact resistance conditions. With almost identical optimised values obtained, our neural networks can realise geometrical optimisation within 40 s for each operating condition, which is averagely over 1,000 times faster than the optimisation performed by finite element method. The up-front computational time for the neural network can be recovered when more than 2 optimisations are needed. The successful application of this data-driven approach in this work clearly represents a new and cost-effective avenue for conducting system level design and optimisation of thermoelectric generators and other energy harvesting technologies.

Micro-thermoelectric generators are attractive for autonomous sensor systems. This work reports an approach for fabricating thin film micro-thermoelectric generators via selective chemical vapor deposition. The approach utilizes our single-source precursors, which enable the production of high-quality thermoelectric materials, as exemplified by Sb2Te3 in this work. It also allows great control over the thermoelectric properties of the as-deposited Sb2Te3 by simply varying the deposition temperature. A competitive power factor of 16.5 μW/(cm·K2) can be obtained for a Sb2Te3 film deposited at 364 °C, with the highest estimated ZT value of 0.65. The selective deposition over the conductive TiN surface enables the fabrication of a prototype single-leg thermoelectric generator, which produces a maximum power of 0.27 nW, with a temperature gradient of only 0.11 K while reducing 87% of tellurium consumption.

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.

The red-brown [(WSCl4)2{μ-RS(CH2)2SR}] (R = Me, Ph, iPr) and [(WSCl4)2{μ-MeS(CH2)3SMe}] have been made by reaction of WSCl4 with the thioether in a 2 : 1 molar ratio, in anhydrous CH2Cl2 solution, and characterised by microanalysis, IR, UV/Vis and 1H NMR spectroscopy. The X-ray structures of the four dithioether complexes reveal square pyramidal WSCl4 units and bridging dithioethers with W[double bond, length as m-dash]S trans to thioether sulfur. Paramagnetic W(v) complexes, [WSCl3{RS(CH2)2SR}] (R = Me, iPr), have been made similarly using a 1 : ≥1 ratio of reactants or longer reaction times. The W(vi) complexes, [WSCl4(SMe2)] and [WSCl4(SeMe2)], are also described. Analogous complexes of WOCl4, [(WOCl4)2{RS(CH2)2SR}] (R = Ph, iPr), have been made similarly from WOCl4, but reactions using MeS(CH2)nSMe (n = 2, 3) led to reduction to W(v), forming [WOCl3{MeS(CH2)nSMe], both of which were identified crystallographically. Curiously, they are geometric isomers: [WOCl3{MeS(CH2)3SMe}] has the dithioether trans Cl/Cl whereas in [WOCl3{MeS(CH2)2SMe}] it is trans O/Cl. Remarkably, low pressure chemical vapour deposition (CVD) experiments using the dinuclear W(vi) species, [(WSCl4)2{iPrS(CH2)2SiPr}], as a single source precursor produced thin films of 4H-WS2, identified by grazing incidence X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy; the tungsten thiochloride complex is the first single source low pressure CVD precursor for WS2. In contrast, the mononuclear W(v) complex, [WSCl3{iPrS(CH2)2SiPr}], does not deposit WS2 under similar conditions.

Poly(N-isopropylacrylamide) (PNIPAm) is widely used to fabricate cell sheet surfaces for cell culturing, however copolymer and interpenetrated polymer networks based on PNIPAm have been rarely explored in the context of tissue engineering. Many complex and expensive techniques have been employed to produce PNIPAm-based films for cell culturing. Among them, spin coating has demonstrated to be a rapid fabrication process of thin layers with high reproducibility and uniformity. In this study, we introduce an innovative approach to produce anchored smart thin films both thermo- and electro-responsive, with the aim to integrate them in electronic devices and better control or mimic different environments for cells in vitro. Thin films were obtained by spin coating of colloidal solutions made by PNIPAm and PAAc nanogels. Anchoring the films to the substrates was obtained through heat treatment in the presence of dithiol molecules. From analyses carried out with AFM and XPS, the final samples exhibited a flat morphology and high stability to water washing. Viability tests with cells were finally carried out to demonstrate that this approach may represent a promising route to integrate those hydrogels films in electronic platforms for cell culture applications.

The inherently rapid ligand substitution kinetics associated with the novel and chemically compatible precursors, [MCl3(EnBu2)3] (M = Sb, Bi; E = Se, Te), enable CVD growth of ternary Bi2(Se1-xTex)3 and (Bi1-ySby)2Te3 thin films with very good compositional, structural and morphological control, for the first time. X-ray diffraction data follow Vegard’s law and Raman bands shift linearly with the atom substitutions, indicating very well-distributed solid solutions.

Electrochemical metallization ReRAMs (ECM) - Experiments and modelling: General discussion

This paper presents a method for the electrodeposition of stoichiometric, crystalline HgTe, which provides advantages over conventional HgTe preparation techniques, such as physical and chemical vapor deposition, in a number of ways; e.g. fast deposition rates (2 mm/hr) and the ability to reliably produce stoichiometric or near-stoichiometric material. The HgTe is prepared in a dichloromethane based plating bath using [NnBu4]2[TeCl6] and [NnBu4]2[HgCl4] as the precursors for Te and Hg, respectively. The paper details the electrochemical behavior of the plating bath and its components, together with a detailed characterization of the morphology, crystallinity and composition of the prepared HgTe.

Reaction of activated germanium with nBu2Te2 in THF solution was shown to be more effective for the preparation of the germanium(iv) tellurolate compound, [Ge(TenBu)4], than reaction of GeCl4 with LiTenBu in a 1 : 4 molar ratio in THF. The product was characterised by 1H, 13C{1H} NMR spectroscopy and microanalysis and evaluated as a single source precursor for the low pressure chemical vapour deposition of GeTe thin films. Depending upon deposition conditions, either dull grey films (predominantly elemental Te) or highly reflective (GeTe) films were obtained from the pure precursor. Grazing incidence X-ray diffraction shows that the highly reflective films are comprised of the rhombohedral α-GeTe phase, while scanning electron microscopy and energy dispersive X-ray analysis reveal rhomb-shaped crystallites with a 49(1) : 51(1)% Ge : Te ratio. This structure is also confirmed from Raman spectra. Van der Pauw measurements show ρ = 3.2(1) × 10-4 Ω cm and Hall electrical measurements indicate that the GeTe thin films are p-type, with a mobility of 8.4(7) cm2 V-1 s-1 and carrier concentration of 2.5(2) × 1021 cm-3. The high p-type concentration is most likely a result of the substantial Ge vacancies in its sub-lattice, in line with the EDX elemental ratios.

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.

We report on the fabrication of memory devices based on a nanoporous GeSbTe layer electrodeposited inbetween TiN and Ag electrodes. It is shown that devices can operate along two distinct electrical modes consisting of a volatile or a non-volatile resistance switching mode upon appropriate preconditioning procedures. Based on electrical measurements conducted in both switching modes and physical analysis performed on a device after electrical stress, resistance switching is attributed to the formation/dissolution of a conductive filament from the Ag electrode into the GST layer whereas the volatile/non-volatile resistance switching is attributed to the presence of an interface layer between the GST and the Ag top electrode. Due to their simple, low-cost and low-temperature fabrication procedure, these devices could be advantageously exploited in flexible electronic applications or embedded into the back-end of line CMOS technology.

Thermoelectric generators are attractive for autonomous sensor systems where regular battery replacement would not only cause an increase in the maintenance costs and discontinuity in the operation, but also destroy the concept of a truly autonomous system. Micro-thermoelectric generators utilise thin films of material for energy harvesting which can greatly reduce the amount of material used, which is especially important for rare elements such as tellurium. Thin films of Bi2Te3 were successfully prepared via a single source precursor CVD method. The thermoelectric performance of these films is improved by alloying a Bi2Se3 precursor to deposit ternary Bi2Te3-xSex. The composition of the ternary system is tuned to optimise the combination of carrier concentration and mobility to give a three-fold enhancement of the thermoelectric power factor at 300 K, and six-fold enhancement at 500 K, with respect to Bi2Te3. This improvement from the substitution of Te with Se is believed to be due to donor effects, as well as point defects caused by this substitution.

Undoped ZnO thin films with tunable electrical properties have been achieved by adjusting the O2 plasma time in the plasma enhanced atomic layer deposition process. The structural, compositional and electrical properties of the deposited ZnO films were investigated by various characterization techniques. By tuning the plasma exposure from 2 to 8s, both resistivities and carrier concentrations of the resultant ZnO films can be modulated by up to 3 orders of magnitude. Forming-free TiN/ZnO/TiN resistive memory devices have been achieved by choosing the ZnO film with the plasma exposure time of 6s. This deposition method offers a great potential for producing other un-doped metal oxides with tunable properties as well as complex multilayer structures in a single deposition. Display Omitted

The thriving of the Internet of Things is set to increase the demand for low-power wireless sensing devices. Thin-film thermoelectric generators are ideal as a sustainable power source for Internet of Things devices as they allow for low maintenance and energy autonomy. This work presents a model to estimate the performance of a thin-film thermoelectric generator. Verified by finite-element method simulation, the results from the model show that increasing the interconnect electrical conductivity and reducing the device pitch increases the power density. The power density can also be increased by increasing the fill factor and reducing the thermal conductivity of the insulating materials. A new corrugated thin-film thermoelectric generator design is proposed in this work that allows for higher fill factors than conventional square designs where a limit on the minimum feature size is imposed, as is the case with photolithography.

The molecular Sn(iv) complexes, [SnCl

A series of alkylchalcogenostibines, Me2SbSenBu, MeSb(SenBu)2, Sb(SenBu)3 and MeSb(TenBu)2, have been designed and synthesised as potential precursors for chemical vapour deposition (CVD) by reaction of nBuELi (E = Se, Te) with the appropriate halostibine, Me3−nSbCln (n = 1, 2, 3), and characterised by 1H, 13C{1H} and 77Se{1H} or 125Te{1H} NMR spectroscopy as appropriate. MeSb(SenBu)2 and MeSb(TenBu)2 are very effective single source precursors for the low pressure CVD of high quality crystalline thin films of Sb2Se3 and Sb2Te3, respectively, confirmed by scanning electron microscopy, energy dispersive X-ray spectroscopy, Raman spectroscopy and thin film X-ray diffraction. Hall conductivity, carrier mobility, carrier density and, in the case of Sb2Te3, Seebeck coefficient measurements reveal electronic characteristics comparable with Sb2E3 deposited by atomic layer deposition or molecular beam epitaxy, suggesting materials quality and performance suitable for incorporation into electronic device structures. Choice of substrate and deposition conditions were found to significantly affect the morphology and preferred orientation of Sb2Te3 crystallites, enabling deposition of films with either 〈1 1 0〉 or 〈0 0 1〉 alignment. Use of micro-patterned substrates allowed selective deposition of crystalline 2D micro-arrays of Sb2Te3 onto exposed TiN surfaces only.

Resistive random access memory based on TiN/HfOx/TiN has been fabricated, with the stoichiometry of the HfOx layer altered through control of atomic layer deposition (ALD) temperature. Sweep and pulsed electrical characteristics were extracted before and after 60Co gamma irradiation. Monoclinic HfOx deposited at 400°C did not result in resistive switching. Deposition at 300°C and 350°C resulted in cubic HfOx which switched successfully. Both stoichiometric HfO2 and sub-oxides HfO2-x result in similar memory characteristics. All devices are shown to be radiation hard up to 10 Mrad(Si), independent of stoichiometry.

Cu/amorphous-SiC (a-SiC) electrochemical metallization memory cells have been fabricated with two different counter electrode (CE) materials, W and Au, in order to investigate the role of CEs in a non-oxide semiconductor switching matrix. In positive bipolar regime with Cu filaments forming and rupturing, the CE influences the OFF state resistance and minimum current compliance. Nevertheless, a similarity in SET kinetics is seen for both CEs, which differs from previously published SiO2 memories, confirming that CE effects are dependent on the switching layer material or type. Both a-SiC memories are able to switch in the negative bipolar regime, indicating Au and W filaments. This confirms that CEs can play an active role in a non-oxide semiconducting switching matrix, such as a-SiC. By comparing both Au and W CEs, this work shows that W is superior in terms of a higher ROFF/RON ratio, along with the ability to switch at lower current compliances making it a favourable material for future low energy applications. With its CMOS compatibility, a-SiC/W is an excellent choice for future resistive memory applications.