Lateral Conductivity Research Articles

Nanoscale Heat Transport of Vertically Aligned Carbon Nanotube Bundles for Thermal Management Applications.

Electronic devices continue to shrink in size while increasing in performance, making excess heat dissipation challenging. Traditional thermal interface materials (TIMs) such as thermal grease and pads face limitations in thermal conductivity and stability, particularly as devices scale down. Carbon nanotubes (CNTs) have emerged as promising candidates for TIMs because of their exceptional thermal conductivity and mechanical properties. However, the thermal conductivity of CNT films decreases when integrated into devices due to defects and bundling effects. This study employs a novel cross-sectional approach combining high-vacuum scanning thermal microscopy (SThM) with beam-exit cross-sectional polishing (BEXP) to investigate the nanoscale morphology and thermal properties of vertically aligned CNT bundles at low and room temperatures. Using appropriate thermal transport models, we extracted effective thermal conductivities of the vertically aligned nanotubes and obtained 4 W m-1 K-1 at 200 K and 37 W m-1 K-1 at 300 K. Additionally, non-negligible lateral thermal conductance between CNT bundles suggests more complex heat transfer mechanisms in these structures. These findings provide unique insights into nanoscale thermal transport in CNT bundles, which is crucial for optimizing novel thermal management strategies.

Impact of Oxide Charges on The Minority Carrier Response in MOS(p) Devices With Al2O3/SiO2 Gate Stacks under Strong Inversion Condition

Admittance measurement, including capacitance and conductance, is very useful to analyze the electrical characteristics of metal-oxide-semiconductor (MOS) systems. These techniques offer insights into various device properties, including interface trap density and minority carrier lifetime in the substrate. It is essential to note that, apart from the gate area, the oxide region beyond the device could significantly influence measurement results [1]-[2]. In this work, a compact model proposed in [3] was used to clarify an unusual minority carrier response time observed in experimental data. The results proved the heightened sensitivity of device alternating current (AC) characteristics to oxide charges in the outer region. Additionally, the dependencies of oxide thickness and quality on the transition frequency (ωm) of devices were explored.The MOS (Al/AlOx/SiO2/p-Si) structure illustrated in Fig. 1 was employed in this study. Aluminum oxide region is under the gate electrode, while silicon oxide (SiO2) covers the entire wafer. Table 1 summarizes samples (S1 to S5) with consistent aluminum oxide thickness but diverse SiO2 thickness. Fig 2. shows the process flow and the anodic oxidation (ANO) system. By tilting the wafer at a specific angle during ANO, a high-quality SiO2 layer with different thicknesses on a single wafer could be obtained. Fig 3(a) to (d) illustrate the capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics of devices with varying SiO2 thicknesses. All devices exhibit low-frequency capacitance characteristics in strong inversion regions with thickness-dependent minority carrier response, particularly at 10kHz. Additionally, devices show different thicknesses depending on G-V characteristics at 1MHz and 10kHz. Fig 4(a) and (b) illustrate the Cinv/Cox ratio for varied oxide thicknesses and Gm/ω characteristics under strong inversion bias (VG = +3V). Gm means the measurement conductance. Following established research [3], peak Gm/ω magnitudes would occur at ωm. Table 2 reveals microsecond-range response times (τR) at ωm, considerably faster than conventional silicon minority carrier lifetimes (usually 1 ms to 100 ms). Moreover, decreasing oxide thickness shifts the ωm toward lower values.To explain this observed phenomenon, the environment outside the devices should be taken into consideration. Fig 5(a) and (b) show the schematic diagram and AC signal model proposed in [1] and [2]. Oxide charges in the outer region would deplete majority carriers and invert the p-type silicon surface to an n-type inversion layer. As a result, the lateral depletion region (Cd, out) and conductive channel (Rs) are formed outside the device, which are functions of substrate doping concentration and the effective oxide charges. The detailed model derivation is discussed in [2]. For this reason, an AC signal applied on the gate would extend outside the device for about a millimeter to a micrometer, affecting measuring results. Based on the model, the effective charges in the SiO2 could be extracted by measuring results. The thicker oxide has more oxide charges, as shown in Fig 6(a). Fig 6(b) and (c) show the modeling results of the Cinv/Cox ratio versus different oxide thicknesses and the Gm/ω-ω plot, which are very close to the experimental results. By simplifying the conductance formula (Gm), Gm reveals an inverse proportional to lateral effective conductance (GLeff) at low frequency (e.g., 10 kHz) and a direct proportional at high frequency (e.g., 1 MHz). Thicker SiO2 devices possess more oxide charges, leading to a greater lateral coupling effect, resulting in a greater GLeff compared to thinner devices. This elucidates the observed variations in Gm-V characteristics at 1 MHz and 10 kHz. Figures 7(a) and (b) display TCAD-simulated C-V and ωm for devices with varying oxide charge densities, confirming that minor changes in oxide charges result in noticeable differences in minority carrier responses in the strong inversion region. Fig 8(a) and (b) show the TCAD simulated results for devices with low doping substrate. For low doping substrates, oxide charges play a much more important role under AC operation.In summary, the study established a correlation between oxide charge densities and thicknesses. The origin of the faster minority carrier response and the peak shift in Gm/ω- ω plot were thoroughly explained and validated by TCAD simulation. Oxide charges were found to play a crucial role, especially in low-doping substrates, offering insights for advanced IC fabrication.[1] E. H. Nicollian and A. Goetzberger, IEEE Transactions on Electron Devices, vol. 12, no. 3, pp. 108-117, 1965.[2] K. C. Chen, K. W. Lin, S. W. Huang, J. Y. Lin, and J. G. Hwu, IEEE Journal of the Electron Devices Society, vol. 10, pp. 960-969, 2022.[3] S. Monaghan et al., IEEE Transactions on Electron Devices, vol. 61, no. 12, pp. 4176-4185, 2014. Figure 1

Synergistic Electrocatalysts Impact Efficient and Durable Oxygen Evolution Catalysis for Proton Exchange Membrane Water Splitting

Low-temperature water electrolysis can rapidly produce environmentally sustainable or green hydrogen, and is a prospective means of storing energy from renewable but intermittent power sources, such as wind and solar, in future clean energy infrastructure (1-4). Commercial water electrolysis either use liquid alkaline electrolyte or proton exchange membrane electrolyte (1). The proton exchange membrane water electrolysis (PEMWE) offers more advantages than the alkaline counterpart, such as higher purity of H2, lower resistance losses, more compact design, and what the most important is the compatible with the intermittent of the renewable energy (1-2). The grant challenge remaining in PEMWE is the development of the highly active, cost effective and stable catalysts for oxygen evolution reaction (OER), which is very sluggish requiring large amounts of precious metal as the catalysts, such as Ir, Ru and their oxides (1).In PEM water electrolysis cells, the catalysts should have high surface areas and high porosities that exposit sufficient active sites available to the reactants and electrolyte, as well as transferring the bubble out of the catalyst surface to ensure a fast mass transfer (5). Also, the OER is dependent on the inherent conductivity of the catalysts or the supports (1). For example, poor electronic conductivity within the catalyst layer will result in poor lateral conductivity across the catalyst layer, thus catalyst not in the vicinity of the porous transport layer will not participate in the reaction. To enable the widespread penetration of the PEMWE technologies, it is urgently to reduce the Ir loading to the sustainable level (~ 0.3 mg/cm2) compared with the current commercial usage (2-6 mg/cm2). Alternatively, to develop precious metal free catalyst with high efficiency and sustained durability (5).In this presentation, we will describe a method of preparing highly active yet stable synergistic electrocatalysts for oxygen evolution reaction for PEMWE. The new catalysts contain IrCoOx/ RuCoOx cluster and La&Li co-doped Co3O4 fiber which was derived from cobalt zeolitic imidazolate framework as precursor. The OER activities of the catalysts were first tested in O2 saturated acidic electrolyte by ring disk electrode (RDE), which displayed high mass activity 26-50 times that of commercial Ir and RuO2. The catalysts were fabricated into membrane electrode assemble and measured under real PEM water electrolysis condition. The cells demonstrated 2 A/cm2@1.76 V @0.25 ± 0.05 mgIr/cm2 loading, and negligible degradation after ~250 h chronoamperometric measurements at 2 A/cm2 (6), which meets the target set by US DOE for OER catalysts for PEMWE.The characterizations of the fresh and post-electrochemical samples were investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), X-ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS), transmission electron microscopy (TEM), Raman spectroscopy and BET surface analysis. We also performed DFT simulation on the OER reaction pathways over Ir and Co sites of different facets parallelly on basis of the TEM results. The result reveals the synergy between Ir/Ru and Co resulting in the enhanced catalytic activities of both IrCoOx /RuCoOx and LaLi@Co3O4 toward OER.Acknowledgments:This work was supported by Overseas Outstanding Youth Fund project, shanghai Jiao Tong university, Shanghai, China; Shanghai Pujiang talent Plan, Shanghai, China; Argonne National Laboratory through Maria Goeppert Mayer Fellowship, US; State Key Laboratory of Metal Matrix Composites, shanghai Jiao Tong university, Shanghai, China. The works performed at Hydrogen research center, shanghai Jiao Tong university, and Argonne National Laboratory’s Center for Nanoscale Materials and Advanced Photo Source.Reference: K. Ayers et al., Annu. Rev. Chem. Biomol. Eng. 10, 219–239 (2019).M. Carmo, D. L. Fritz, J. Mergel, D. Stolten, Int. J. Hydrogen Energy 38, 4901–4934 (2013).M. T. M. Koper, J. Electroanal. Chem. 660, 254–260 (2011).R. D. L. Smith et al., Science 340, 60–63 (2013).Chong et al., Science 380, 609–616 (2023).Chong et al., Adv. Energy Mater. 2023, 2302306.

Lateral electrical conductivity variations along the Main Himalayan thrust in the northwestern Himalayas: Insights from 3D Magnetotelluric forward modeling

Understanding the arc parallel variation on the geometry of the Main Himalayan Thrust (MHT) is as important as understanding the arc perpendicular variation in the Himalayas. The geometric variability of the MHT holds significant implications for the occurrence of major and great earthquakes. Three-dimensional magnetotelluric (MT) forward modeling enables the investigation of potential crustal models along the MHT in northwest Himalayas. MT impedance tensors were computed utilizing the 3D forward modeling code MTD3FWD. Previously established MT resistivity and seismic velocity models from various sectors of the northwestern Himalayas were employed as inputs for generating the resistivity mesh necessary for 3D forward modeling. The computed impedance tensors by 3D forward computation were cross-referenced with the original published MT data to validate their accuracy. A lateral resistivity cross section is also derived from the 3D forward model along the sub-Himalaya and lesser-Himalaya region to study the lateral heterogeneity. The lateral resistivity cross-section reveals significant heterogeneity within the crust, marked by both high and low-resistive structures and a possible lateral ramp along the MHT. The geometry of the lateral MHT showcases a gradual incline within the Himachal sector and a steep ramp within the Garhwal and Kumaun sectors in the northwestern Himalayas. The crustal architecture exhibits distinct nearly-vertical resistive and conductive features beneath the study area. Consequently, the crust within this region is characterized by considerable heterogeneity, influenced by a network of subsurface faults and ridges. The Delhi Haridwar Ridge, which exhibits high resistivity, plays a significant role in dictating the lateral dip of the MHT and exerting control over seismic activity patterns in the region.

Orientation-Dependent Photoconductivity of Quasi-2D Nanocrystal Self-Assemblies: Face-Down, Edge-Up Versus Randomly Oriented Quantum Wells.

Here, strongly orientation-dependent lateral photoconductivity of a CdSe monolayer colloidal quantum wells (CQWs) possessing short-chain ligands is reported. A controlled liquid-air self-assembly technique is utilized to deliberately engineer the alignments of CQWs into either face-down (FO) or edge-up (EO) orientation on the substrate as opposed to randomly oriented (RO) CQWs prepared by spin-coating. Adapting planar configuration metal-semiconductor-metal (MSM) photodetectors, it is found that lateral conductivity spans ≈2 orders of magnitude depending on the orientation of CQWs in the film in the case of utilizing short ligands. The long native ligands of oleic acid (OA) are exchanged with short-chain ligands of 2-ethylhexane-1-thiol (EHT) to reduce the inter-platelet distance, which significantly improved the photoresponsivity from 4.16, 0.58, and 4.79mAW-1 to 528.7, 6.17, and 94.2mAW-1, for the MSM devices prepared with RO, FO, and EO, before and after ligands exchange, respectively. Such CQW orientation control profoundly impacts the photodetector performance also in terms of the detection speed (0.061 s/0.074 s for the FO, 0.048 s/0.060 s for the EO compared to 0.10 s/0.16 s for the RO, for the rise and decay time constants, respectively) and the detectivity (1.7×1010, 2.3×1011, and 7.5×1011 Jones for the FO, EO, and RO devices, respectively) which can be further tailored for the desired optoelectronic device applications. Attributed to charge transportation in colloidal films being proportional to the number of hopping steps, these findings indicate that the solution-processed orientation of CQWs provides the ability to tune the photoconductivity of CQWs with short ligands as another degree of freedom to exploit and engineer their absorptive devices.

Dynamic characteristics of terahertz hot-electron graphene FET bolometers: Effect of electron cooling in channel and at side contacts

We analyze the operation of the hot-electron FET bolometers with the graphene channels (GCs) and the gate barrier layers. Such bolometers use the thermionic emission of the hot electrons heated by incident-modulated THz radiation. The hot electrons transfer from the GC into the metal gate. As the THz detectors, these bolometers can operate at room temperature. We show that the response and ultimate modulation frequency of the GC-FET bolometers are determined by the efficiency of the hot-electron energy transfer to the lattice and the GC side contacts due to the 2DEG lateral thermal conductance. The dependences of these mechanisms on the band structure and geometrical parameters open the way for the GC-FET bolometers optimization, in particular, for the enhancement of the maximum modulation frequency.

The mechanism by which thermal coupling leads to an asymptotic maldistribution stability boundary for flow boiling in parallel channels

Phase change heat transfer processes are attractive for the efficient thermal management of advanced semiconductor devices, with flow boiling in parallel microchannel heat sinks being one promising solution. However, there are several implementation challenges associated with two-phase flow in parallel microchannels, particularly flow maldistribution, which can adversely affect performance and reliability. Two-phase flow models can be useful in predicting and understanding the instability mechanisms that leads to maldistribution, such that parametric performance trends and safe regions of operation can be identified. Channel-to-channel thermal coupling has been shown to alleviate maldistribution, but it is not yet understood why this effect is limited to some critical lateral thermal conductance above which there is no further benefit. In the current work, a two-phase flow model with a lumped thermal capacitance representation of the heat sink wall is developed to identify the mechanism for this asymptotic maldistribution stability boundary for thermally coupled microchannels. The lumped model allows the nature of stability boundary to be explained via a scaling analysis of the eigenvalues. In such systems, it is identified that a single eigenvalue determines the occurrence of flow maldistribution. Scaling analysis shows that, for small values of thermal conductance, this eigenvalue becomes a quadratic function of thermal coupling, which enhances the stability of microchannels and moves the stability boundary. However, for large values of thermal conductance, the eigenvalue is dependent only on the fluid properties, leading to a limit at which thermal coupling can no further improve stability or affect the stability boundary. The lumped model developed in this work enables mechanistic understanding of the role of channel-to-channel thermal coupling on mitigating flow maldistribution and therefore may offer important guidance on the design of flow boiling systems and heat sinks.

Beam divergence of RF negative hydrogen ion sources for fusion

Neutral beam injectors (NBI) for fusion facilities have strict requirements on the beam divergence (7 mrad for the ITER NBI at 1 MeV). Measurements of the single beamlet divergence of RF negative ion sources (at lower beam energy < 100 keV) show significantly higher values (9–15 mrad), also larger than filament arc sources at similar beam energies. This opened up questions whether the higher divergence is caused by different measurement or evaluation techniques, whether it is a direct cause of the RF source, e.g. due to a higher temperature of negative ions or an oscillating extraction meniscus, and whether it is a problem at all after full acceleration. In a joint effort between the labs modeling and diagnostic capabilities at the NNBI test facilities have been strongly extended and evaluation methods benchmarked. Particularly challenging is the strong increase in beamlet divergence at a lower filling pressure, seen both in filament arc and RF sources.Beside the source and beam investigations carried out in SPIDER (with selected, isolated apertures rather than the total of 1280 apertures) at Consorzio RFX, the IPP test facilities ELISE (640 apertures) and BATMAN Upgrade (70 apertures) contribute to the physics understanding of the beam optics in RF sources. The determination of the beam divergence is not straight-forward because effects originating from measuring the divergence of multiple beamlets (Beam Emission Spectroscopy) and/or constraints from the individual diagnostic (lateral heat conductance in CFC tiles) lead to difficulties. Still, the divergence requirement is not met at the limited total beam energy available at ELISE and BATMAN Upgrade (< 60kV). However, variation of the beam energy show a decrease of the divergence for higher energies and beam simulation for the ITER NBI accelerator predict that the divergence requirement will be met after full acceleration of the negative ion beam.

Interdigitated‐back‐contacted silicon heterojunction solar cells featuring novel MoOx‐based contact stacks

AbstractThe fabrication process of interdigitated‐back‐contacted silicon heterojunction (IBC‐SHJ) solar cells has been significantly simplified with the development of the so‐called tunnel‐IBC architecture. This architecture utilizes a highly conductive (p)‐type nanocrystalline silicon (nc‐Si:H) layer deposited over the full substrate area comprising pre‐patterned (n)‐type nc‐Si:H fingers. In this context, the (p)‐type nc‐Si:H layer is referred to as blanket layer. As both electrodes are connected to the same blanket layer, the high lateral conductivity of (p)nc‐Si:H layer can potentially lead to relatively low shunt resistance in the device, thus limiting the performance of such solar cells. To overcome such limitation, we introduce a thin (&lt;2 nm) full‐area molybdenum oxide (MoOx) layer as an alternative to the (p)nc‐Si:H blanket layer. We demonstrate that the use of such a thin MoOx minimizes the shunting losses thanks to its low lateral conductivity while preserving the simplified fabrication process. In this process, a novel (n)‐type nc‐Si:H/MoOx electron collection contact stack is implemented within the proposed solar cell architecture. We assess its transport mechanisms via electrical simulations showing that electron transport, unlike in the case of tunnel‐IBC, occurs in the conduction band fully. Moreover, the proposed contact stack is evaluated in terms of contact resistivity and integrated into a proof‐of‐concept front/back‐contacted (FBC) SHJ solar cells. Contact resistivity as low as 100 mΩcm2 is achieved, and fabricated FBC‐SHJ solar cells obtain a fill factor above 81.5% and open‐circuit voltage above 705 mV. Lastly, the IBC‐SHJ solar cells featuring the MoOx blanket layer are fabricated, exhibiting efficiencies up to 21.14% with high shunt resistances above 150 kΩcm2. Further optimizations in terms of layer properties and fabrication process are proposed to improve device performance and realize the efficiency potential of our novel IBC‐SHJ solar cell architecture.

Ice templated honeycomb-like porous copper foam to improve the anisotropic thermal transfer property of phase change composites

This study explores the use of copper foam (CF) as a thermally conductive scaffold for phase change materials (PCMs), enhancing shape stability. Employing the ice template method (ITM), we fabricate a CF with a low-density, honeycomb structure and anisotropy from flake copper powders. The resulting phase change composites (PCCs), infused with paraffin wax (PW), showcase high thermal conductivity and shape retention compared to pure PW, with anisotropic heat flow due to directional channels in the CF. With a 34.4 wt% filling ratio, the PCCs achieve axial and lateral thermal conductivities of 2.85 W m−1 K−1 and 1.51 W m−1 K−1, respectively, and a thermal storage enthalpy of 158.18 J g−1. This work presents a novel method for advanced thermal energy storage and management, indicating the promise of ITM-derived CF in high-performance PCCs for diverse applications.

Significant conductivity enhancement in Al-rich n-AlGaN by modulation doping

Enhancing the conductivity in Al-rich n-AlGaN is a key issue for realizing AlGaN-based ultraviolet light-emitting diodes (UV-LEDs) with low operating voltage and high wall-plug efficiency, especially in a planar geometry of flip–chip configuration. An approach of modulation doping is herein proposed, where an alternating-layer structure consisting of Si-doped and unintentionally doped AlGaN is assembled to achieve the spatial separation of electron activation and transport. As massive electrons diffuse from the AlGaN:Si layer into the neighboring i-AlGaN ones and then drift, the ionized-donor scattering is effectively weakened, leading to a significant enhancement of mobility as well as conductivity. An impressive electrical property of n-Al0.6Ga0.4N with a lateral conductivity of 201.7 S/cm is realized as a consequence, being 2.1 times of that in the continuously doped one. Furthermore, the operating voltage of 280 nm UV-LEDs is correspondingly reduced by 0.1–0.2 V at 100 mA by adopting modulation-doped n-AlGaN in the n-cladding layer.

Comparison of multi-coil and multi-frequency frequency domain electromagnetic induction instruments

IntroductionCharacterization of the shallow subsurface in mountain catchments is important for understanding hydrological processes and soil formation. The depth to the soil/bedrock interface (e.g., the upper ~5 m) is of particular interest. Frequency domain electromagnetic induction (FDEM) methods are well suited for high productivity characterization for this target as they have short acquisition times and do not require direct coupling with the ground. Although traditionally used for revealing lateral electrical conductivity (EC) patterns, e.g., to produce maps of salinity or water content, FDEM inversion is increasingly used to produce depth-specific models of EC. These quantitative models can be used to inform several depth-specific properties relevant to hydrological modeling (e.g. depths to interfaces and soil water content).Material and methodsThere are a number of commercial FDEM instruments available; this work compares a multi-coil device (i.e., a single-frequency device with multiple receiver coils) and a multi-frequency device (i.e., a single receiver device with multiple frequencies) using the open-source software EMagPy. Firstly, the performance of both devices is assessed using synthetic modeling. Secondly, the analysis is applied to field data from an alpine catchment.ResultsBoth instruments retrieved a similar EC model in the synthetic and field cases. However, the multi-frequency instrument displayed shallower sensitivity patterns when operated above electrically conductive grounds (i.e., 150 mS/m) and therefore had a lower depth of investigation. From synthetic modeling, it also appears that the model convergence for the multi-frequency instrument is more sensitive to noise than the multi-coil instrument.ConclusionDespite these limitations, the multi-frequency instrument is smaller and more portable; consequently, it is easier to deploy in mountainous catchments.

Mg incorporation induced microstructural evolution of reactively sputtered GaN epitaxial films to Mg-doped GaN nanorods

Mg-doped GaN films/nanorods were grown epitaxially on c-sapphire by reactive co-sputtering of GaAs and Mg at different N2 percentages in Ar–N2 sputtering atmosphere. Energy dispersive x-ray spectroscopy revealed that the Mg incorporation increases with increase of Mg area coverage of GaAs target, but does not depend on N2 percentage. In comparison to undoped GaN films, Mg-doped GaN displayed substantial decrease of lateral conductivity and electron concentration with the initial incorporation of Mg, indicating p-type doping, but revealed insulating behaviour at larger Mg content. Morphological investigations by scanning electron microscopy have shown that the films grown with 2%–4% Mg area coverages displayed substantially improved columnar structure, compared to undoped GaN films, along with rough and voided surface features at lower N2 percentages. With increase of Mg area coverage to 6%, the growth of vertically aligned and well-separated nanorods, terminating with smooth hexagonal faces was observed in the range of 50%–75% N2 in sputtering atmosphere. High-resolution x-ray diffraction studies confirmed the epitaxial character of Mg-doped GaN films and nanorods, which displayed complete c-axis orientation of crystallites and a mosaic structure, aligned laterally with the c-sapphire lattice. The catalyst-free growth of self-assembled Mg-doped GaN nanorods is attributed to increase of surface energy anisotropy due to the incorporation of Mg. However, with further increase of Mg area coverage to 8%, the nanorods revealed lateral merger, suggesting enhanced radial growth at larger Mg content.

Charge balance in OLEDs: Optimization of hole injection layer using novel p‐dopants

AbstractCharge balance is one of the most important factors for realizing high performance organic light emitting devices (OLEDs). In this work, we provide a novel strategy to improve the charge balance in OLEDs by optimizing the hole injection layer (HIL) as well as the electron transporting layer (ETL) and thereby controlling the charge carrier supplies in the device. First, we develop a p‐dopant material (PD02), with a lowest unoccupied molecular orbit (LUMO) of −4.63 eV, much shallower than that of the commercial material (PD01) of which the LUMO is −5.04 eV. Nevertheless, this enables us to modulate the supply of holes to the emissive layer through tuning doping concentration. We demonstrate that device performances are significantly improved by employing such a scheme. With a 23% molar doping of PD02, a bottom emission red OLED achieves an external quantum efficiency (EQE) of over 30%, an operating voltage of 3.4 V and a LT95 ~15,000 h at 10 mA/cm2, with a Digital Cinema Initiative P3 (DCI‐P3) chromaticity of CIE (X, Y) = (0.68, 0.32). Moreover, the efficiency roll‐off is suppressed up till ~3500 cd/m2, a desirable feature in display applications. The lateral conductivity of by using such HIL is also found to be much lower than that of PD01, resulting in reduced crosstalk among RGB pixels. Next, a new electron transporting material (ETM‐02) with a deep LUMO of −2.86 eV is also introduced to further optimize the charge balance. Although devices with ETM‐02 shows lower voltage and higher EQE, lifetime is compromised. In order to improve lifetime, additional fine tuning of the charge balance is essential. Finally, a second p‐dopant PD03 with a LUMO of −4.91 eV is added to the HIL to further extend the modulation flexibility in the hole injection. A double‐layer HIL consisting of 8 nm of HTM:16% PD02 and 2 nm of HTM:3% PD03, where the former is in contact with anode, is adopted in the device structure. The bottom emission deep red device achieve EQE over 30%, an operating voltage of 3.2 V and an improved LT95 ~13,000 h at 10 mA/cm2 with a BT.2020 range chromaticity of CIE (X, Y) = (0.701, 0.299). In the double HIL configuration, the introduction of PD03 provides one more parameter for tuning and therefore improves the overall device performances.

Bolometric IR photoresponse based on a 3D micro-nano integrated CNT architecture.

A new 3D micro-nano integrated M-shaped carbon nanotube (CNT) architecture was designed and fabricated. It is based on vertically aligned carbon nanotube arrays composed of low-density, mainly double-walled CNTs with simple lateral external contacts to the surroundings. Standard optical lithography techniques were used to locally tailor the width of the vertical block structure. The complete sensor system, based on a broadband blackbody absorber region and a high-resistance thermistor region, can be fabricated in a single chemical vapor deposition process step. The thermistor resistance is mainly determined by the high junction resistances of the adjacent aligned CNTs. This configuration also provides low lateral thermal conductivity and a high temperature coefficient of resistance (TCR). These properties are advantageous for new bolometric sensors with high voltage responsivity and broadband absorption from the infrared (IR) to the terahertz spectrum. Preliminary performance evaluations have shown current and voltage responsivities of 2 mA/W and 30 V/W, respectively, in response to IR (980 nm) absorption for a 20 × 20 μm2 device. The device exhibits an exceptionally fast response time of ≈0.15 ms, coupled with a TCR of -0.91 %/K. These attributes underscore its high operating speed and responsivity, respectively. In particular, the device maintains excellent thermal stability and reliable operation at elevated temperatures in excess of 200 °C, extending its potential utility in challenging environmental conditions. This design allows for further device miniaturization using optical lithography techniques. Its unique properties for mass production through large-scale integration techniques make it important for real-time broadband imaging systems.

Ultra-Low Loading IrO2 on Porous Transport Layer for Catalysis of Proton Exchange Membrane Water Electrolysis

Proton Exchange Membrane Water Electrolysis (PEMWE) is a commercial technology with specific advantages such as high-power density and rapid start-up times, which makes it a perfect match to produce hydrogen from intermittent renewable energy sources (green H2). [1] However, very scarce materials, such as iridium and platinum, are currently used as catalysts and protection coatings to withstand the harsh operating conditions in PEMWE. Iridium is the anode catalyst in the state-of-the-art PEMWE, with loadings in the range 1-2 mg/cm2. This metric translates into using 200-500 kg of iridium per GW, which accounts for roughly 10% of the global iridium production per year. Reducing iridium usage in PEMWE is critical to realize the 10-100 GW/year growth in green H2 power. [2,3]To significantly reduce the Ir loading, while maintaining the lateral conductivity, we coated the iridium catalyst by atmospheric spatial Atomic Layer Deposition (sALD) on titanium porous transport layer (PTL), which acts as the electrically conductive substrate. The coating renders ultra-low iridium loadings, which is 100-200 times less iridium than the state-of-the-art catalyst coated membrane technology, while retaining ca. 60-80% of the performance (in terms of current density), with durability demonstrated up to 100 h (see Figure 1). We will also show here that protection coatings on the titanium PTL are beneficial to yield good durability with these ultra-low loadings of iridium and demonstrated that sALD has the potential to produce non-PGM based protection coatings.[1] Barbir, F. Solar Energy 78 (2005) 661-669.[2] Gavrilova, A., Wieclawska, S.M. “Towards a green future. Part 2” (2021). TNO report 21-12158.[3] Minke, C., Suermann, M., Bensmann, B., & Hanke-Rauschenbach, R. J. Hydrogen Energy 46 (2021) 23581-23590. Figure 1

Parameterization of a National Groundwater Model for New Zealand

Groundwater is a vital source of water for humanity, with up to 50% of global drinking water and 43% of irrigation water being derived from such sources. Quantitative assessment and accounting of groundwater is essential to ensure its sustainable management and use. TopNet-GW is a parsimonious groundwater model that was developed to provide groundwater simulation at national, regional, and local scales across New Zealand. At a national scale, the model can help local government authorities estimate groundwater resource reliability within and between regions. However, as many catchments are ungauged, the model cannot be calibrated to local conditions against observed data. This paper, therefore, describes a method to derive an a priori, reach-scale groundwater model parameter set from national-scale hydrogeological datasets. The parameter set includes coefficients of lateral (kl) and vertical (kr) conductivity and effective aquifer storage (S). When the parameter set was used with the TopNet-GW model in the Wairau catchment in the Marlborough region (South Island, New Zealand), it produced a poor representation of peak river flows but a more accurate representation of low flows (overall NSE 0.64). The model performance decreased in the smaller Opawa catchment (NSE 0.39). It is concluded that the developed a priori parameter set can be used to provide national groundwater modeling capability in ungauged catchments but should be used with caution, and model performance would benefit greatly from local scale calibration. The parameter derivation method is repeatable globally if analogous hydrological and geological information is available and thus provides a basis for the parameterization of groundwater models in ungauged catchments. Future research will assess the spatial variability of parameter performance at a national scale in New Zealand.

Solid Oxide Cell Performance: Spatially Resolved Oxygen Electrode Stability

Solid Oxide Cell (SOC) electrolysis will play an important role in the electrification of the chemical, fertilizer, and fuel industries, contributing to the reduction of their reliance on fossil fuel feedstocks. The integration of high temperature steam and CO2-electrolyzers in industrial processes with readily available waste heat and renewable electricity allows for highly efficient green hydrogen production and methods for CO2 utilization.The development of next generation SOC electrolyzer technology at TNO aims to provide high performance and low-cost technological options for the electrification of the aforementioned chemicals and fuels industries. The ambition of the SOC technology development program is to assist the whole value chain, from cell manufacturing to end-users, by increasing the economic viability of the technology. In line with this ambition, the TNO R&D activities regarding SOC technology concentrate on cell and stack technology development coupled with techno-economic and business case studies on SOC technology integration in the industrial environment. Improvements in SOC performance and durability for electrolysis applications are of great importance for the successful industrial implementation of the technology. Hydrogen Europe targets for 2030 aim at low stack degradation rates of 0.5%/khr at thermoneutral voltage, while delivering current densities of at least 1.5 A/cm2. Therefore, lifetime improvements at high current density are one of the vocal points of SOC development efforts, which calls for a good understanding of the degradation phenomena and analytical methods to investigate the material stability in the SOC during electrolysis operation.In this contribution, the current status of SOC development and testing within TNO will be presented. Several aspects of TNO SOC performance characteristics will be discussed, with a focus on water electrolysis performance and lifetime behaviour during endurance tests of several thousand hours. Excellent water electrolysis performance of the TNO SOC cells is observed at thermoneutral voltage (1.3 V), achieving current density values of 1.75 A/cm2 at an operating temperature of 750 ºC. Lifetime assessment and material degradation of the SOC will be discussed, with a focus on the analysis of observed degradation phenomena in the oxygen electrode material. As oxygen electrode degradation can be critical for SOC performance in a stack environment, it is important to have a good understanding of the degradation processes and the ability to monitor them. At TNO, a novel high-resolution 2D mapping of the lateral conductivity of the oxygen electrode have been used as an effective tool for quality control and validation of the air electrode development. Additionally, the combination of 2D sheet resistance mapping, SEM-EDX and XRD techniques (Figure 1) provides a powerful combination of tools to obtain a spatially resolved (3D) view of the localized degradation observed in the oxygen electrode after several thousand hours of water electrolysis. Figure 1

The geoelectric field coast effect: Results from two dimensional finite element method and analytic solutions

The geoelectric fields induced during geomagnetic disturbances (GMD) may affect the normal operation of technological systems at the Earth’s surface. The non-uniform Earth conductivity structure, especially large lateral conductivity contrasts, can lead to the enhancement of geoelectric fields near boundaries such as a coastline. In this paper, we give an overview of the applicability of a two-dimensional finite element method (2D-FEM) for studying lateral variations of the Earth’s conductivity, which can be considered as one of magnetotelluric sounding forward modelling methods, including both the E and the H polarization cases. Then the spatial distribution of the geoelectric field near a continent-ocean boundary is calculated with different models. This is compared with analytic solutions for simple models to verify the accuracy of the FEM modelling, which is calculated by using the ANSOFT software. More realistic scenarios are then developed to emphasize the advantages of FEM. The factors influencing the coast effect are discussed. Results show that frequency, the shape of seafloor boundaries, and the depth of ocean have a significant impact on the geoelectric fields. Therefore, these factors should attract more attention when assessing risk for man-made conducting systems located within the coastal influence range.

Solid Oxide Cell Performance: Spatially Resolved Oxygen Electrode Stability

Several aspects of TNO SOC performance characteristics will be discussed, with a focus on steam electrolysis performance and lifetime behaviour during endurance tests of several thousand hours. Excellent steam electrolysis performance of the TNO SOE cells is observed at thermoneutral voltage, achieving current density values of −1.7 A/cm2 at an operating temperature of 750 °C. Lifetime assessment and material degradation of the SOC will be discussed, with a focus on the analysis of observed degradation phenomena in the oxygen electrode material. As oxygen electrode degradation can be critical for SOC performance in a stack environment, it is important to have a good understanding of the degradation processes and the ability to monitor them. At TNO, a novel approach of high-resolution 2D mapping of the lateral conductivity of the oxygen electrode has been used as an effective tool for quality control and validation of the oxygen electrode development. Additionally, the combination of 2D sheet resistance mapping, SEM-EDX and XRD techniques provides a powerful combination of tools to obtain a spatially resolved (3D) view of the localized degradation observed in the oxygen electrode after several thousand hours of steam electrolysis.