Search

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. [ABSTRACT FROM AUTHOR]

The electrodeposition of MoS2 from dichloromethane (CH2Cl2) using tetrabutylammonium tetrathiomolybdate ([NnBu4]2[MoS4]) as a single source precursor is presented. The electrodeposition of MoS2 from CH2Cl2 requires addition of a proton donor to the electrolyte and trimethylammonium chloride (Me3NHCl) was used for this purpose. Electrochemical Quartz Crystal Microbalance (EQCM) experiments have been employed for a detailed study of the electrochemical mechanism and to study the role of the proton donor. EQCM reveals cathodic electrodeposition of MoS2 and anodic deposition of MoS3 as well as an additional corrosion process where the deposited MoS3 strips back into solution. The electrodeposited MoS2 films are amorphous in nature. All the films were found to be homogeneous in composition across the electrode area and to be reproducible between experiments. Annealing of the as-deposited films under a sulfur atmosphere results in crystalline MoS2 as confirmed by energy dispersive X-ray spectroscopy (EDX), Raman spectroscopy and X-ray diffraction. The deposited films were smooth and planar, as observed with scanning electron microscopy (SEM), indicating a layer-by-layer growth typical of transition metal dichalogenides. [ABSTRACT FROM AUTHOR]

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) × 10−4Ω 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. [ABSTRACT FROM AUTHOR]

The electrodeposition of germanium antimony telluride (GST) alloys from a single non-aqueous plating bath based on tetrabutylammonium chlorometallate precursors is presented. The system provides a case-study for plating bath optimization in order to produce complex functional materials. GST deposits in the amorphous phase and the film composition and morphology can be readily adjusted by tuning the three precursor concentrations and the electrodeposition potential. Adjustment of the precursor concentrations allows the preparation of deposits ranging from the binaries (GeSb, GeTe, Sb2 Te3) to ternaries with a wide range of compositions, including the standard Ge2Sb2Te5 composition - more commonly known as GST-225 - which is widely used in the solid state memory industry. In this paper we present a detailed study discussing the complex interplay between the deposition of germanium, antimony and tellurium and how adjusting the concentrations of their chlorometallates allows control over the composition and also the morphology of the deposits. We also highlight the benefits that arise from the wide separation in the deposition potentials for the three precursors, and in particular the ability to control the composition through modulation of the deposition potential. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The identification and optimization of tunable dielectric materials exhibiting low loss characteristics in the GHz frequencies are essential in the development of low power devices for microwave applications. We have applied a combinatorial synthetic methodology employing multiple atomic evaporative sources to produce compositional gradient thin film (Ba,Sr)(Ti,Mn)O3 perovskites. High throughput screening chips of both capacitive and waveguide structures are used to measure the compositional dependence of the dielectric properties of the fully characterised thin film materials. The co-planar waveguides are shown to allow measurements at frequencies exceeding 10 GHz. Using this methodology, we have identified (Ba,Sr)(Ti,Mn)O3 compositions which exhibit good tunability with low losses at microwave frequencies: for a single device with a 10 V DC bias one can achieve a 12° phase shift with excellent transmission characteristics, and an insertion loss of ∼3.2 dB. We show that small changes in composition can result in a significant change in dielectric characteristics and device performance, and that the experimental protocol developed provides a powerful methodology for the development of materials and microwave devices. [ABSTRACT FROM AUTHOR]

Theneutral complexes [GaCl3(EnBu2)] (E = Se or Te), [(GaCl3)2{nBuE(CH2)nEnBu}] (E = Se, n= 2; E = Te, n= 3), and [(GaCl3)2{tBuTe(CH2)3TetBu}] are conveniently prepared byreaction of GaCl3with the neutral EnBu2in a 1:1 ratio or with nBuE(CH2)nEnBu or tBuTe(CH2)3TetBu in a 2:1 ratio andcharacterized by IR/Raman and multinuclear (1H, 71Ga, 77Se{1H}, and 125Te{1H}) NMR spectroscopy, respectively, all of which indicate distortedtetrahedral coordination at Ga. The tribromide analog, [GaBr3(SenBu2)], was prepared andcharacterized similarly. A crystal structure determination on [(GaCl3)2{tBuTe(CH2)3TetBu}] confirms this geometrywith each pyramidal GaCl3fragment coordinated to one Tedonor atom of the bridging ditelluroether, Ga–Te = 2.6356(13)and 2.6378(14) Å. The nBu-substitutedligand complexes serve as convenient and very useful single sourceprecursors for low pressure chemical vapor deposition (LPCVD) of singlephase gallium telluride and gallium selenide, Ga2E3, films onto SiO2and TiN substrates. The compositionand morphology were confirmed by SEM, EDX, and Raman spectroscopy,while XRD shows the films are crystalline, consistent with cubic Ga2Te3(F4̅3m) and monoclinic Ga2Se3(Cc), respectively. Hall measurements on films grown on SiO2show the Ga2Te3is a p-type semiconductorwith a resistivity of 195 ± 10 Ω cm and a carrier densityof 5 × 1015cm–3, indicative ofa close to stoichiometric compound. The Ga2Se3is also p-type with a resistivity of (9 ± 1) × 103Ω cm, a carrier density of 2 × 1013cm–3, and a mobility of 20–80 cm2/V·s. Competitive deposition of Ga2Te3onto a photolithographically patterned SiO2/TiN substrateindicates that film growth onto the conducting and more hydrophobicTiN is preferred. [ABSTRACT FROM AUTHOR]

The distorted octahedral complexes [SnCl4{nBuSe(CH2)nSenBu}] (n= 2or 3),(1) and (2), obtained from reaction of SnCl4with the neutral bidentate ligands and characterized by IR/Ramanand multinuclear (1H, 77Se{1H} and 119Sn) NMR spectroscopy and X-ray crystallography, serve asvery effective single source precursors for low pressure chemicalvapor deposition (LPCVD) of microcrystalline, single phase tin diselenidefilms onto SiO2, Si and TiN substrates. Scanning ElectronMicroscopy (SEM) and Atomic Force Microscopy (AFM) imaging show hexagonalplate crystallites which grow perpendicular to the substrate surfacein the thicker films, but align mostly parallel to the surface whenthe quantity of reagent is reduced to limit the film thickness. X-raydiffraction (XRD) and Raman spectroscopy on the deposited films areconsistent with hexagonal SnSe2(P3̅m1; a= b= 3.81 Å; c= 6.13 Å), with strong evidence for preferred orientationof the crystallites in thinner (0.5–2 μm) samples, consistentwith crystal plate growth parallel to the substrate surface. Hallmeasurements show the deposited SnSe2is a n-type semiconductor.The resistivity of the crystalline films is 210 (±10) mΩcm and carrier density is 5.0 × 1018cm–3. Very highly selective film growth from these reagents onto photolithographicallypatterned substrates is observed, with deposition strongly preferredonto the (conducting) TiN surfaces of SiO2/TiN patternedsubstrates, and onto the SiO2surfaces of Si/SiO2patterned substrates. A correlation between the high selectivityand high contact angle of a water droplet on the substrate surfacesis observed. [ABSTRACT FROM AUTHOR]

Smart radiative cooling devices based on thermochromic materials such as vanadium dioxide (VO 2 ) are of practical interest for temperature regulation and artificial homeostasis, i.e., maintaining stable equilibrium conditions for survival, both in terrestrial and space applications. In traditional solar reflector configurations, solar absorption in the VO 2 layer is a performance limiting factor due to the multiple reflections of sunlight in the stack. Here, we demonstrate a visually transparent, smart radiator panel with reduced solar absorption. An Al-doped ZnO transparent conducting oxide layer acts as a frequency selective infrared back-reflector with high transmission of solar radiation. In this study we make use of high-quality VO 2 thin films deposited using atomic layer deposition and optimized annealing process. Patterning of the VO 2 layer into a metasurface results in a further reduction of the solar absorption parameter α to around 0.3, while exhibiting a thermal emissivity contrast Δ ε of 0.26 by exploiting plasmonic enhancement effects. The VO 2 metasurface provides a visual spectrum transmission of up to 62%, which is of interest for a range of applications requiring visual transparency. The transparent smart metasurface thermal emitter offers a new approach for thermal management in both space and terrestrial radiative cooling scenarios., (© 2022 Kai Sun et al., published by De Gruyter, Berlin/Boston.)

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., (© 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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.