Dust-Sized High-Power-Density Photovoltaic Cells on Si and SOI Substrates for Wafer-Level-Packaged Small Edge Computers.

Advancement in microelectronics technology enables autonomous edge computing platforms in the size of a dust mote (<1 mm), bringing efficient and low-cost artificial intelligence close to the end user and Internet-of-Things (IoT) applications. The key challenge for these compact high-performance edge computers is the integration of a power source that satisfies the high-power-density requirement and does not increase the complexity and cost of the packaging. Here, it is shown that dust-sized III-V photovoltaic (PV) cells grown on Si and silicon-on-insulator (SOI) substrates can be integrated using a wafer-level-packaging process and achieve higher power density than all prior micro-PVs on Si and SOI substrates. The high-throughput heterogeneous integration unlocks the potential of large-scale manufacturing of these integrated systems with low cost for IoT applications. The negative effect of crystallographic defects in the heteroepitaxial materials on PV performance diminishes at high power density. Simultaneous power delivery and data transmission to the dust mote with heteroepitaxially grown PV are also demonstrated using hand-held illumination sources.

Diffusion-Controlled Porous Crystalline Silicon Lithium Metal Batteries.

Nanostructured porous silicon materials have recently advanced as hosts for Li-metal plating. However, limitations involve detrimental silicon self-pulverization, Li-dendrites, and the ability to achieve wafer-level integration of non-composite, pure silicon anodes. compo. Herein, full cells featuring low-resistance, wafer-scale porous crystalline silicon (PCS) anodes are embedded with a nanoporous Li-plating and diffusion-regulating surface layer upon combined wafer surface cleaning (SC) and anodization. LL Lithiophilic surface formation is illustrated via correlation of surface groups and X-ray structure. Low-cost SC-PCS anodes require no composite formulation, and pre-lithiation enables sustainable Li-metal plating/stripping on the lithiophilic surface and in SC-PCS bulk nanostructure. Anodization time and C-rate determined competitive full cell performance: NMC811 | 4800 s SC-PCS: 195 mAh/g (99.9% coulombic efficiency [C.E.], C/3, 50 cycles), 165 mAh/g, 587 Wh/kg (97.1% C.E., C/3 and C/2 rate, 350 cycles), 24 Ω∗cm2 SC-PCS-resistivity (900 cycles); 160 µm LCO | 500 s SC-PCS: 102 mAh/g (94.1% C.E., 1C, 350 cycles).

High-speed logic integrated circuits with solution-processed self-assembled carbon nanotubes.

As conventional monolithic silicon technology struggles to meet the requirements for the 7-nm technology node, there has been tremendous progress in demonstrating the scalability of carbon nanotube field-effect transistors down to the size that satisfies the 3-nm node and beyond. However, to date, circuits built with carbon nanotubes have overlooked key aspects of a practical logic technology and have stalled at simple functionality demonstrations. Here, we report high-performance complementary carbon nanotube ring oscillators using fully manufacturable processes, with a stage switching frequency of 2.82 GHz. The circuit was built on solution-processed, self-assembled carbon nanotube arrays with over 99.9% semiconducting purity, and the complementary feature was achieved by employing two different work function electrodes.

Cardiorespiratory Fitness and All-Cause Mortality in Men With Emotional Distress.

OBJECTIVE: Mental health and emotional disorders are often associated with higher mortality risk. Whether higher cardiorespiratory fitness (CRF) reduces the risk for all-cause mortality in individuals with emotional distress is not well known. PATIENTS AND METHODS: Participants were 5240 men (mean age 46.5±9.5 years) with emotional distress (including depression, anxiety, thoughts of suicide, or a history of psychiatric or psychological counseling) who completed an extensive medical examination between 1987 and 2002, and were followed for all-cause mortality through December 31, 2003. Cardiorespiratory fitness was quantified as maximal treadmill exercise test duration and was grouped for analysis as low, moderate, and high. Cox proportional hazards regression was used to calculate hazard ratios (HRs) and 95% CIs. RESULTS: During a median of 8.7 years (range, 1.0-16.9 years) and 46,217 person-years of follow-up, there were 128 deaths from any cause. Age- and examination year-adjusted all-cause mortality rates per 10,000 person-years according to low, moderate, and high CRF groups were 64.7 (95% CI, 44.9-89.3), 28.0 (95% CI, 23.8-31.5), and 19.6 (95% CI, 17.1-21.6) (trend P<.001) in men who reported any emotional distress. Overall, the multivariable-adjusted HRs and 95% CIs across incremental CRF categories were 1.00 (referent), 0.54 (0.32-0.90), and 0.47 (0.26-0.85), linear trend P =.03. CONCLUSION: Among men with emotional distress, higher CRF is associated with lower risk of dying, independent of other clinical mortality predictors. Our findings underscore the importance of promoting physical activity to maintain a healthful level of CRF in individuals with emotional distress.

Strain-driven mound formation of substrate under epitaxial nanoparticles.

We observe the growth of crystalline SiC nanoparticles on Si(001) at 900 °C using in situ electron microscopy. Following nucleation and growth of the SiC, there is a massive migration of Si, forming a crystalline Si mound underneath each nanoparticle that lifts it 4-5 nm above the initial growth surface. The volume of the Si mounds is roughly five to seven times the volume of the SiC nanoparticles. We propose that relaxation of strain drives the mound formation. This new mechanism for relieving interfacial strain, which involves a dramatic restructuring of the substrate, is in striking contrast to the familiar scenario in which only the deposited material restructures to relieve strain.

Creation of a transient vapor nanogap between two fluidic reservoirs for single molecule manipulation.

We introduce a new experimental technique for manipulating a segment of a charged macromolecule inside a transient nanogap between two fluidic reservoirs. This technique uses an FPGA-driven nanopositioner to control the coupling of a nanopipette with the liquid surface of a fluidic cell. We present results on creating a transient nanogap, triggered by a translocation of double-stranded DNA between a nanopipette and a fluidic cell, and measure the probability to find the molecule near the tip of the nanopipette after closing the gap. The developed platform will enable testing of our recent theoretical predictions for the behavior of charged macromolecule in a nanogap between two fluidic reservoirs.

Principle of direct van der Waals epitaxy of single-crystalline films on epitaxial graphene.

There are numerous studies on the growth of planar films on sp(2)-bonded two-dimensional (2D) layered materials. However, it has been challenging to grow single-crystalline films on 2D materials due to the extremely low surface energy. Recently, buffer-assisted growth of crystalline films on 2D layered materials has been introduced, but the crystalline quality is not comparable with the films grown on sp(3)-bonded three-dimensional materials. Here we demonstrate direct van der Waals epitaxy of high-quality single-crystalline GaN films on epitaxial graphene with low defectivity and surface roughness comparable with that grown on conventional SiC or sapphire substrates. The GaN film is released and transferred onto arbitrary substrates. The post-released graphene/SiC substrate is reused for multiple growth and transfer cycles of GaN films. We demonstrate fully functional blue light-emitting diodes (LEDs) by growing LED stacks on reused graphene/SiC substrates followed by transfer onto plastic tapes.

High-performance air-stable n-type carbon nanotube transistors with erbium contacts.

So far, realization of reproducible n-type carbon nanotube (CNT) transistors suitable for integrated digital applications has been a difficult task. In this work, hundreds of n-type CNT transistors from three different low work function metals-erbium, lanthanum, and yttrium-are studied and benchmarked against p-type devices with palladium contacts. The crucial role of metal type and deposition conditions is elucidated with respect to overall yield and performance of the n-type devices. It is found that high oxidation rates and sensitivity to deposition conditions are the major causes for the lower yield and large variation in performance of n-type CNT devices with low work function metal contacts. Considerable improvement in device yield is attained using erbium contacts evaporated at high deposition rates. Furthermore, the air-stability of our n-type transistors is studied in light of the extreme sensitivity of these metals to oxidation.

Epitaxial graphene nanoribbon array fabrication using BCP-assisted nanolithography.

A process for fabricating dense graphene nanoribbon arrays using self-assembled patterns of block copolymers on graphene grown epitaxially on SiC on the wafer scale has been developed. Etching masks comprising long and straight nanoribbon array structures with linewidths as narrow as 10 nm were fabricated, and the patterns were transferred to graphene. Our process combines both top-down and self-assembly steps to fabricate long graphene nanoribbon arrays with low defect counts. These are the narrowest nanoribbon arrays of epitaxial graphene on SiC fabricated to date.