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Ruthenium may replace copper interconnects in next-generation very-large-scale integration (VLSI) circuits. However, interfacial bonding between Ru interconnect wires and surrounding dielectrics must be optimized to reduce thermal boundary resistance (TBR) for thermal management. In this study, various adhesion layers are employed to modify bonding at the Ru/SiO

The lithium-ion capacitor (LIC) is a novel energy storage device, pairing battery-type anodes with capacitor-type cathodes, capable of delivering high energy and power densities. The anode material...

Lithium–sulphur batteries (LSBs) have been drawing rapidly increasing research attention because of the low cost and high theoretical capacity of sulphur. The applications of LSBs however are hampered by poor stability caused by the shuttle effects of lithium polysulphides (LiPS), poor conductivities of sulphur, and sluggish redox kinetics of LiPS. Here, an advantageous carved N-doped carbon nanobox structure triply functionalized with an FeCoNi trimetallic sulphide was developed as a high performance sulphur host for LSBs. The strong chemical interactions toward LiPS, half-metallic conductivities, and catalytic activities toward redox reactions of LiPS, enabled through functionalization with FeCoNi trimetallic sulphide, work together to resolve the critical issues of LSBs. Moreover, the carved N-doped carbon nanobox structure serves as a nanoreactor that helps retain LiPS at cathodes and offers a confined space for fast local redox reactions. The triply functionalized carved N-doped carbon nanoboxes (S-FeCoNi@C-CNB) lead to high performance LSBs, delivering a high capacity of 1238 mA h g−1 at 0.1C and maintaining a decent capacity of 655 mA h g−1 at 2C. The LSB exhibits excellent stability with a low capacity decay rate of 0.049% per cycle over 200 cycle operations at 1C, indicating the success of S-FeCoNi@C-CNB in suppressing the shuttle effect.

In microthermoelectric generators (μTEGs), parasitic thermal resistance must be suppressed to increase the temperature difference across thermocouples for optimum power generation. A thermally conductive (TC) layer is typically used in μTEGs to guide the heat flow from the heat source to the hot junction of each thermocouple. In this study, we investigate the effect of the thermal boundary resistance (TBR) in metal/dielectric TC layers on the power generation of silicon nanowire (SiNW) μTEGs. We prepared various metal/adhesion/dielectric TC layers using different metal, adhesion, and dielectric layers and measured the thermal resistance using the frequency-domain thermoreflectance method. We found that the thermal resistance was significantly different, mainly due to the TBR of the metal/dielectric interfaces. Interface characterization highlights the significant role of the interfacial bonding strength and interdiffusion in TBR. We fabricated a prototype SiNW-μTEG with different TC layers for testing, finding that the power generation increased significantly when the thermal resistance of the TC layer was lowered. This study helps to understand the underlying physics of thermal transport at interfaces and provides a guideline for the design and fabrication of μTEGs to enhance power generation for effective energy harvesting.

We present a computational approach for identifying the important descriptors of the ionic conductivities of lithium solid electrolytes. Our approach discriminates the factors of both bulk and grain boundary conductivities, which have been rarely reported. The effects of the interrelated structural (e.g. grain size, phase), material (e.g. Li ratio), chemical (e.g. electronegativity, polarizability) and experimental (e.g. sintering temperature, synthesis method) properties on the bulk and grain boundary conductivities are investigated via machine learning. The data are trained using the bulk and grain boundary conductivities of Li solid conductors at room temperature. The important descriptors are elucidated by their feature importance and predictive performances, as determined by a nonlinear XGBoost algorithm: (i) the experimental descriptors of sintering conditions are significant for both bulk and grain boundary, (ii) the material descriptors of Li site occupancy and Li ratio are the prior descriptors for bulk, (iii) the density and unit cell volume are the prior structural descriptors while the polarizability and electronegativity are the prior chemical descriptors for grain boundary, (iv) the grain size provides physical insights such as the thermodynamic condition and should be considered for determining grain boundary conductance in solid polycrystalline ionic conductors., GRAPHICAL ABSTRACT

Carbon-coated Li4Ti5O12 (LTO) has been prepared using polyimide (PI) as a carbon source via the thermal imidization of polyamic acid (PAA) followed by a carbonization process. In this study, the PI with different structures based on pyromellitic dianhydride (PMDA), 4,4′-oxydianiline (ODA), and p-phenylenediamine (p-PDA) moieties have been synthesized. The effect of the PI structure on the electrochemical performance of the carbon-coated LTO has been investigated. The results indicate that the molecular arrangement of PI can be improved when the rigid p-PDA units are introduced into the PI backbone. The carbons derived from the p-PDA-based PI show a more regular graphite structure with fewer defects and higher conductivity. As a result, the carbon-coated LTO exhibits a better rate performance with a discharge capacity of 137.5 mAh/g at 20 C, which is almost 1.5 times larger than that of bare LTO (94.4 mAh/g).

Various factors affect the interfacial thermal resistance (ITR) between two materials, making ITR prediction a high-dimensional mathematical problem. Machine learning is a cost-effective method to address this. Here, we report ITR predictive models based on experimental data. The physical, chemical, and material properties of ITR are categorized into three sets of descriptors, and three algorithms are used for the models. Those descriptors assist the models in reducing the mismatch between predicted and experimental values and reaching high predictive performance of 96%. Over 80,000 material systems composed of 293 materials were inputs for predictions. Among the top-100 high-ITR predictions by the three different algorithms, 25 material systems are repeatedly predicted by at least two algorithms. One of the 25 material systems, Bi/Si achieved the ultra-low thermal conductivity in our previous work. We believe that the predicted high-ITR material systems are potential candidates for thermoelectric applications. This study proposed a strategy for material exploration for thermal management by means of machine learning.

Lithium sulfur batteries (LSBs) are regarded as one of the most promising energy storage devices because of their ultrahigh theoretical energy densities (2500 Wh kg-1), low cost, and environmental friendliness. Nevertheless, several detrimental drawbacks, including shuttling effects caused by soluble lithium polysulfides (LiPS), sluggish conversion kinetics between LiPS, and poor conductivities of sulfur, prevent commercialization of LSBs. To takle the above issues, MOF-derived cobalt disulfide/nitrogen-doped carbon (NC) composite polyhedrons linked with multi-walled carbon nanotubes (MWCNTs), CoS2@NC/MWCNT, were developed as an effective sulfur host for LSBs. It was fabricated through first in-situ growth of nanoporous ZIF-67 on surface treated MWCNTs, followed by carbonization and sulfurization. CoS2@NC/MWCNT combines the advantages of outstanding conductivities of MWCNTs, excellent chemical adsorption of NC and CoS2 toward LiPS, and high catalytic efficiency of CoS2 toward LiPS conversion, effectively addressing the shuttling, sluggish conversion, and low conductivity issues. The CoS2@NC/MWCNT electrode delivered a high specific capacity of 1133 mAh g-1 at 0.1 C and maintained a decent specific capacity of 607 mAh g-1 at 2.0 C. Its cycling stability is excellent, with a capacity retention rate of 77% after 300 cycles at 1.0 C, i.e., an average capacity decay rate of 0.078% per cycle. The cycling stability was further improved through increasing N-doping levels of the carbons for enhanced chemical adsorption toward LiPS and through incorporation of inter-linked reduced graphene oxide sheets as a physical barrier to reduce the diffusion loss of LiPS, achieving even smaller capacity decay rates of 0.066 and 0.064 % per cycle, respectively.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Heat transfer at interfaces plays a critical role in material design and device performance. Higher interfacial thermal resistances (ITRs) affect the device efficiency and increase the energy consumption. Conversely, higher ITRs can enhance the figure of merit of thermoelectric materials by achieving ultra-low thermal conductivity via nanostructuring. This study proposes a dataset of descriptors for predicting the ITRs. The dataset includes two parts: one part consists of ITRs data collected from 87 experimental papers and the other part consists of the descriptors of 289 materials, which can construct over 80,000 pair-material systems for ITRs prediction. The former part is composed of over 1300 data points of metal/nonmetal, nonmetal/nonmetal, and metal/metal interfaces. The latter part consists of physical and chemical properties that are highly correlated to the ITRs. The synthesis method of the materials and the thermal measurement technique are also recorded in the dataset for further analyses. These datasets can be applied not only to ITRs predictions but also to thermal-property predictions or heat transfer on various material systems., Measurement(s)material entity • interface • Material DescriptionTechnology Type(s)machine learning • digital curation Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.11618253

We demonstrate, both by experiments and by data informatics, an alternative strategy to achieve ultralow thermal conductivity in a dense solid. The interfacial thermal resistance (ITR) prediction of the machine learning model is implemented in a nanoscale field. The size dependence on ITR is considered and applied to the interface design of nanostructuring. The Bi/Si system was selected from 2025 kinds of interfaces through the interface thermal resistance prediction model by machine learning. The BiSi nanocomposite, which was composed of crystallized Bi and amorphous Si, was designed with various parameters by a laboratory-built combinatorial sputtering system. Electrically conductive, thermally insulating BiSi nanocomposites were reported for the first time and have a thermal conductivity as low as 0.16 W m–1 K–1. The ultralow thermal conductivity is attributed to the high ratio between the interfacial surface area and the volume because of the small Bi particle size and high Si/Bi atomic ratio. By intr...

Interfacial thermal resistance (ITR) at metal/nonmetal interfaces is a crucial issue affecting the efficiency of electronic devices. We investigated the ITR of Ni/Al2O3 and W/Al2O3 interfaces under the influence of bidirectional heat fluxes, with the heat flowing from the metal to the nonmetal and vice versa, using the time domain thermoreflectance technique. An asymmetric ITR was first experimentally observed such that the ITR was larger by a factor of 1.4–1.9 when the heat was applied from the nonmetal side, relative to the metal side. The additional interfacial electron–phonon couplings induced by the temperature difference between the hot electrons and phonons, which occur upon heating from the metal side, could be one of the plausible reasons causing the asymmetry. The thermal contribution of the interfacial electron–phonon coupling is found to be comparable with the phonon–phonon coupling. This new approach may allow us to elucidate thermal rectification at metal/nonmetal interfaces, thus leading to the development of light-controlled thermal diodes.

In this study, the graphene-modified Al foils are prepared to assemble lithium ion batteries (LIBs) through a three-step approach comprising: (1) deposition of the polyamic acid (PAA) on the Al substrate; (2) curing the PAA to form the polyimide (PI)-coated Al foils; (3) converting the PI into porous graphene by CO2 laser irradiation. With integration of the PI derived graphene (PDG) in the LIBs, the inserted PDG layer can enhance the adhesion and interface resistance between the active layer and Al electrode. The LiNi0.5Mn1.5O4 (LNMO)//Li4Ti5O12 (LTO) full cells with PDG layer are also fabricated to evaluate the effect of the modified layer on the cell performance. Compared to the pristine Al electrode, the modified current collector can improve the rate performance and reduce the temperature rise during the charge/discharge process leading to better cycling stability.

Electronic states of active sites of catalysts play a key role in determining electrocatalytic performances. Engineering electronic states through decoration of functional entities is an effective way to advance catalyst design. In this work, Au nanocrystal decorated Fe, Co, and Ni based trimetallic metal organic frameworks (MOFs) (termed Au/(FCN)MOFs), grown in-situ on nickel plates (NP), are developed as high performance oxygen evolution reaction (OER) electrocatalysts. At optimal Au nanocrystal decoration, the Au/(FCN)MOF/NP electrode achieves significantly improved OER performances over the (FCN)MOF/NP electrode, lowering η10 and η500 from 242 and 340 mV to 216 and 290 mV, respectively, Tafel slope from 42.1 to 31.7 mV dec−1, and current density decay from 6 to 5% after 50 h operations at an initial current density of 160 mA cm-2. The enhancement is attributed to the significantly elevated oxidation states of Fe, Co, and Ni, induced by decoration of the Au nanocrystals of high electronegativity, as evidenced with high-resolution X-ray photoelectron spectroscopy and in-situ Raman spectroscopy studies. Furthermore, the main active metal centers are identified with in-situ X-ray absorption spectroscopy study to be Ni and Co, with Fe playing a supporting role to help Ni acquire high valence states to realize enhanced OER activities.

An organic/inorganic white-light emitting F8T2 (9,9-dioctylfluorene-co-bithiophene)/GaN heterojunction is reported. The white-light emission is produced by hybridizing the blue light (464 nm) emitted from the GaN MQWs and the yellow/green light (500–650 nm) emitted at the F8T2/p-GaN interface by electroluminescence (EL). The yellow/green light emission in the F8T2 layer is resulted from the carrier accumulation and Frenkel excitons at the F8T2/p-GaN junction interface. It is concluded that the energy barrier and large mobility discrepancy at the F8T2/p-GaN junction interface cause carriers accumulating in the F8T2 side near the F8T2/p-GaN interface. The accumulated carriers at the F8T2/p-GaN interface form Frenkel excitons by Coulombic interaction. Then, the Frenkel excitons recombine to radiate the yellow/green emission in the F8T2 layer. The International Commission on Illumination (CIE) coordinate of the white-light emitted from the present device is at (0.28, 0.30), which is very close to the standard white light (0.33, 0.33).

Highly mesoporous silicon nanoparticles of sizes less than 150 nm and porosity greater than 50% were successfully synthesized and composited with N-doped carbon (m-Si@NDC) as high performance anode materials for lithium ion based energy storage. The small size, large porosity, and composition with N-doped carbon coating layer of the highly mesoporous silicon nanoparticles offer much improved cycling volume expansion/shrinkage stability and overall conductivities, and create nano-sized reservoirs for lithium ions to enable local, fast lithiation/delithiation for much enhanced lithium ion based energy storage performances. The m-Si@NDC anode delivered a high specific capacity of 2,482 mAh g−1 at 0.2 A g−1 and maintained a decent specific capacity of 797 mAh g−1 at a high current density of 8 A g−1. The lithium ion capacitor, assembled by coupling the m-Si@NDC anode with a glucose derived carbon nanosphere (GCNS) cathode of an ultrahigh specific surface area of 1,451 m2 g−1, m-Si@NDC//GCNS, delivered a high energy density of 210 Wh kg−1 at a power density of 0.32 kW kg−1, and maintained a decent energy density of 70.1 Wh kg−1 at a high power density of 36.1 kW kg−1. The stability of m-Si@NDC//GCNS is also outstanding, exhibiting an energy density retention of 89% after a 20,000 cycle operation at a current density of 8 A g−1. The N-doped carbon coated small highly mesoporous silicon nanoparticles prove to be an outstanding nanostructure for anodes of lithium ion based energy storage.

Lithium ion capacitors (LICs), lately evolved energy storage devices which integrate the merits of both lithium ion batteries (LIBs) and supercapacitors (SCs) for high energy and power densities, have attracted substantial research attention in recent years. Here, a Prussian blue analogue nanocube templating process was developed to produce N-doped carbon nanoboxes (N-CNB) as high performance anode materials for lithium ion based energy storage. The N-CNB exhibited high specific capacities and excellent rate capability and cycling performances as an anode. If paired with glucose derived carbon nanospheres (GCNS) cathodes, the N-CNB//GCNS LIC delivered a high energy density of 77.5 Wh kg−1 at the power density of 311.3 W kg−1 and maintained a decent energy density of 40.4 Wh kg−1 at a high power density of 112 kW kg−1. Its cycling performances were outstanding, reaching an ultrahigh, over 100%, capacity retention of 138% after a 40,000 cycle operation at 10 A g−1, attributable to the continuous electrochemical activation of the electrode materials. The success of the present LIC can be attributed to the advantageous nanobox structure in serving as nano-reservoirs for Li-ion to enable local, fast lithiation/delithiation and in buffering the volume expansion/shrinkage during lithiation/delithiation cycles.

The development of Bi2Te3 thin films has huge potential in the pursuit of efficient thermoelectric micro/nanodevices due to their high Seebeck coefficient, high electrical conductivity and low thermal conductivity. The optimization of experimental parameters of Bi-Te thin films produced by co-evaporation will be investigated in this study. Co-evaporation is a low cost, easy-to-control process which can be used for high throughput and is scalable. We found that an optimal Te/Bi ratio of 1.5 with good thermoelectric properties can be directly synthesized by Bi and Bi2Te3 co-evaporation. Compared to the conventional Bi/Te co-evaporation process, high temperature annealing or substrate heating is not necessary for the process mentioned in this paper, which is a desirable feature when using polymer-based substrates, organic/inorganic hybrid thermoelectric generators, and flexible devices since they have relatively low tolerance to heat. The optimized Bi2Te3 thin films, which are mixed phases of Bi2Te3, Bi3Te4 and Te, possess high carrier concentration (6.65 × 1020 cm−3), low electrical resistivity (3.17 × 10−3 Ωcm), and extremely low thermal conductivity (0.59 W/mK) at room temperature on a smooth surface (roughness

Ni dopants typically exist as Ni 2+ oxidation state in metal oxides. We report that as Ni is co-doped with P in Ni(P):SnO 2 , P promotes Ni 2+ into Ni 3+ , which acts as acceptor and coverts n-type SnO 2 to p-type conduction. Significant hole concentration (4.5 × 10 18 cm −3 ) of p-type Ni(P):SnO 2 can be obtained. The chemical state of Ni 3+ in Ni(P):SnO 2 is verified by ultra-violet and x-ray photoelectron spectroscopy. With the developed p-Ni(P):SnO 2 , transparent p-Ni(P):SnO 2 /i-SnO 2 /n-ITO p-i-n structure was fabricated and characterized: low leakage-current (8.41 × 10 −5 A at −5 V), turn-on voltage (4.68 eV), good transmittance (85%), and small ideality-factor (1.73).

Maskless H2SO4 wet-etching on sapphire substrates creates three-dimensional pyramidal pattern on sapphire surface. Alunogen self-forming mask grows in H2SO4 etching generating a dynamic self-masking action, which fabricates 3-dimensional pyramidal pattern on the etched sapphire wafers. The slope and size of the pyramids are controlled by rate ratio (k) between alunogen growth rate and c-plane etching rate. Constant k results in flat facet side-planes of sapphire pyramids and varying k in etching produce curved side-planes of the sapphire pyramid. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0051506ssl] All rights reserved.

The polarization and surface reactivity of the ZnO nanorods (NRs) grown on the (0001) N-polar GaN substrate and the (0001) Ga-polar GaN substrate by hydrothermal process were studied. We found tha...

The electrical properties of transparent Al-doped tin oxide (SnO 2 ), N-doped SnO 2 , and AlN-doped SnO 2 thin films were studied. The Al-doped tin oxide (SnO 2 ) thin films all show n-type conduction regardless the annealing condition. The n-type conduction of the as-deposited N-doped SnO 2 , and AlN-doped SnO 2 thin films could be converted to p-type conduction by annealing the films at an elevated temperature of 450 °C. XPS analysis verified that the substitution of N ions in the O ion sites in the annealed N-doped SnO 2 and AlN-doped SnO 2 thin films were responsible for the n–p conduction transition. The conduction of the annealed N-doped SnO 2 and AlN-doped SnO 2 thin films could be converted back to n-type conduction by thermally annealing the films at higher temperature, over 450 °C. The p–n conduction transition is related with the outgassing of N ions in the p-type N-doped SnO 2 and AlN-doped SnO 2 thin films. Remarkably, we found that the Al content can retard the outgassing of N ions in the p-type N-doped SnO 2 and AlN-doped SnO 2 thin films and prolong the p–n conduction transition temperature above 600 °C. XPS analysis revealed that the formation of the Sn N Al bond improved the stability of the N ions in the AlN-doped SnO 2 thin films. I – V curve of the p-type AlN-doped SnO 2 /n-type fluorine-doped SnO 2 junction exhibited clear p–n junction characteristics, a low leakage current under the revised bias (1.13 × 10 −5 A at −5 V), and a low turn-on voltage (3.24 V). p-Type AlN-doped SnO 2 /n-type fluorine-doped SnO 2 junction exhibited excellent transmittance (over 90%) in the visible region (470–750 nm).

The growth mechanisms of ZnO nanorods (NRs) on sputtered Al-doped ZnO (AZO) and V-doped AZO (V:AZO) thin films are studied in this work. Firstly, the microstructure of the AZO and V:AZO thin films was investigated by XRD. We found that V-dopants retard the crystallization (grain growth) and enlarge the d-spacing of the (0002) plane of the V:AZO thin films. ZnO NRs were prepared on the AZO and V:AZO thin film substrates by the hydrothermal method. Vertically aligned ZnO NRs were grown on the pure AZO thin film substrate. With incorporating V-dopants, the growth direction of ZnO NRs grown on the V:AZO thin films is highly influenced by the concentration of the V-doping. The V-doping causes the random growth direction of ZnO NRs. XRD and SEM analysis indicate that the growth behavior of ZnO NRs depends on the microstructure of the surface grains of the AZO and V:AZO thin film substrates. A growth mechanism of ZnO NRs on the AZO and V:AZO thin film substrates is proposed in this work.

The conductivity stability of aluminum-doped zinc oxide (AZO) films was evaluated in the ambient with different humidity. We found that the conductivity of AZO films is sensitive to the humidity and degrades remarkably in high humidity ambient (90 ± 5% relative humidity) at 60 °C. Hall measurement results show that the conductivity degradation is due to the drop in the carrier concentration, while the carrier mobility is found to remain relatively constant in the high humidity ambient. XPS (X-ray photoelectron spectroscopy) analysis reveals that the oxygen-vacancies in the AZO thin films were greatly reduced in the high-humidity ambient. So, we believe that the high-humidity ambient causes the decrease in the oxygen vacancies and eventually resulted in the decrease in the concentration of the free carriers in the AZO thin films. In this study, a mechanism is proposed to explain the humidity-assist reduction in the oxygen vacancies in the humidity-tested AZO films. In addition, we report that the electrical properties of AZO film can be stabilized by coating a Cr layer on the AZO thin film surface.

Creating a pyramidal structure on an n-GaN surface is considered the most effective approach for maximizing light extraction of n-side-up GaN-based light-emitting diodes (LEDs). This letter shows that the light extraction efficiency of a pyramidal n-GaN surface can be further enhanced by growing ZnO nano-rods (NRs) specifically on the tips of the pyramids on the n-GaN surface. Using tip-only ZnO NRs, the light-output power of an n-side-up LED with a pyramidal n-GaN surface can be further enhanced by 49.6% at 250 mA. This improved light extraction efficiency is due to the multiple facets on the ZnO NRs.

Using the diffusivity discrepancy between Al and N in the SnO2 phase, N-doped n+ and Al-doped p+ degenerate regions were created at the interface by annealing an AlN/SnO2 bilayer. Current–voltage (I–V) characteristics of the p+-AlN:SnO2/n+-SnO2 junction indicate distinct tunnel diode characteristics, such as the tunneling mode, negative differential resistance, and turn-on mode. The overall transmittance of the p-AlN:SnO2/n-SnO2 tunnel diode is higher than 80% in the visible region. In a certain wavelength region, the transmittance of the p-AlN:SnO2/n-SnO2 tunnel diode is even higher than 90%. This shows that a transparent p-AlN:SnO2/n-SnO2 tunnel diode has great potential for use in a broad range of invisible electronics.

This study produced transparent p-type AlN-doped SnO2 thin films by annealing sputtered sandwich SnO2/AlN/SnO2 thin films. Both Al3+-Sn4+ and N3−O2− substitution reactions—which are the main sources for the hole carriers—were identified by XPS analysis. The hole concentration of the p-type AlN:SnO2 thin films was as high as 1.074 × 1019 cm−3. Using the produced p-AlN:SnO2 thin film, transparent p-AlN:SnO2/n-SnO2:In2O3 p-n junctions were fabricated and characterized as follows: (1) A low leakage current (2.97 × 10−5 A at −5 V); (2) a 2.17 eV turn-on voltage; and (3) a low ideality factor (12.2).