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From thin film solar cells to metal–oxide–semiconductor (MOS) devices in leading edge integrated circuits, the electronic structure at and near the interfaces between component materials determines the most important fundamental operating characteristics of those devices such as turn-on voltage, power dissipation, and off-state current leakage. Fermi level location at buried interfaces, semiconductor (SC) band bending, charge transfer, oxide defects, and work functions of the constituent materials all contribute to device performance. This paper describes how these important parameters can be determined by employing femtosecond photovoltage spectroscopy, an extension of ultraviolet photoelectron spectroscopy (UPS) using ultrafast lasers. While standard UPS is fundamentally a surface-sensitive spectroscopy, pump/probe techniques add a new dimension to this venerable spectroscopy, permitting the accurate extraction of the underlying band bending in SCs. When combined with the valence band edge location of the SC and oxide, and determination of the system Fermi level, full characterization of the electronic structure of a MOS stack can be obtained providing key insights on device operating properties. This approach can be extended to study key device materials in emerging areas of artificial intelligence and quantum computing. In each case, surprising new details were uncovered that led to performance optimization of these technologically important devices.
Recent discovery of ferroelectricity in doped HfO2 has reignited research interest in the ferroelectric field-effect transistor (FeFET) as emerging embedded nonvolatile memory with the potential for neuro-inspired computing. This paper reviews two major aspects for its application in neuro-inspired computing: ferroelectric devices as multilevel synaptic devices and the circuit primitive design with FeFET for in-memory computing. First, the authors survey representative FeFET-based synaptic devices. Then, the authors introduce 2T-1FeFET synaptic cell design that improves its in situ training accuracy to approach software baseline. Then, the authors introduce the FeFET drain–erase scheme for array-level operations, which makes the in situ training feasible for FeFET-based hardware accelerator. Finally, the authors give an outlook on the future 3D-integrated 2T-1FeFET design.
Recent applications require vertical chip stacking to increase the performance of many devices without the need of advanced node components. Image sensors and vision systems will embed more and more smart functions, for instance, image processing, object recognition, and movement detection. In this perspective, the combination of Cu-to-Cu direct hybrid bonding technology with Through-Silicon-Via (TSV) will allow 3D interconnection between pixels and the associated computing and memory structures, each function fabricated on a separate wafer. Wafer-to-wafer hybrid bonding was achieved with multi-pitch design—1–4 μm—of single levels of Cu damascene patterned on 300 mm silicon substrates. Defect-free bonding, as far as the extreme edge of the wafer, was demonstrated on a stack with three wafers. Middle wafers thinning was done with grinding only and with a thickness uniformity (TTV) <2 μm to an ultimate thinning as low as 3 μm. Alignment performance was characterized by post-bonding for two superposed hybrid bonding interfaces. In our set of wafers, modeling the alignment with translation, rotation, and scaling components enables us to optimize the residuals down to 3σ < 100 nm. A process flow of thin TSV with a fine pitch of 2 μm for high-density vertical interconnect through a three-wafer stack was developed. Via-last TSV architecture was adopted with 1 μm TSV diameter and 10 μm thickness. Lithography, etching solutions, Ti/TiN barrier deposition, and void-free Cu filling solutions were demonstrated. TSV cross sections after CMP and connections with top and bottom Cu damascene lines show good profile control. Process developments are matured and can be reliably used in the fabrication of an electrical test vehicle including vertical interconnects associating multi-wafers stacking with a hybrid bonding process and high-density thin TSV applicable to low pitches (<5 μm).
Conventional computed tomography (CT) remains the workhorse of cross-sectional medical imaging. But dual- and multi-energy CT allows for more specific material decomposition, enabling distinct advantages in the clinical setting. In this review, we describe the basic principles behind material decomposition in dual- and multi-energy CT, outline the techniques used to acquire images, and explore how enhanced material decomposition leads to improved patient care. We also explore areas of active research and future directions, including photon-counting CT, that have the potential to revolutionize CT in clinical use.
From the 1918 influenza pandemic (H1N1) until the recent 2019 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, no efficient diagnostic tools have been developed for sensitive identification of viral pathogens. Rigorous, early, and accurate detection of viral pathogens is not only linked to preventing transmission but also to timely treatment and monitoring of drug resistance. Reverse transcription-polymerase chain reaction (RT-PCR), the gold standard method for microbiology and virology testing, suffers from both false-negative and false-positive results arising from the detection limit, contamination of samples/templates, exponential DNA amplification, and variation of viral ribonucleic acid sequences within a single individual during the course of the infection. Rapid, sensitive, and label-free detection of SARS-CoV-2 can provide a first line of defense against the current pandemic. A promising technique is non-linear coherent anti-Stokes Raman scattering (CARS) microscopy, which has the ability to capture rich spatiotemporal structural and functional information at a high acquisition speed in a label-free manner from a biological system. Raman scattering is a process in which the distinctive spectral signatures associated with light-sample interaction provide information on the chemical composition of the sample. In this prospective, we briefly discuss the development and future prospects of CARS for real-time multiplexed label-free detection of SARS-CoV-2 pathogens.
Indium tin oxide (ITO) has become a very useful plasmonic and nonlinear optical material because of its highly tunable electrical and optical properties and strong optical nonlinearity. In this work, the authors conducted detailed fabrication process studies by using high-temperature reactive sputtering to finely tune the optical properties of ITO thin films, particularly the epsilon-near-zero (ENZ) wavelength in the near and mid-IR spectrum. Sputtered ITO thin films are characterized by using spectroscopic ellipsometry, surface profilometry, Hall measurements, and 4-point probe testing. Additionally, the effect of post-deposition annealing of ITO films is also investigated.
This study investigated a new strategy for fabricating porous scaffolds with the self-folding ability and controlled release of growth factors (GFs) via 3D printing. The scaffolds were a bilayer structure comprising a poly(D,L-lactide-co-trimethylene carbonate) scaffold for providing the shape morphing ability and a gelatin methacrylate scaffold for encapsulating and delivering GF. The structure, shape morphing behavior, GF release, and its effect on stem cell behavior were studied for new scaffolds. The results suggest that these scaffolds have great potential for regenerating tissues such as blood vessels. This work also contributes to developments of 3D printing in tissue engineering.
Barium titanate (BTO) is a ferroelectric perovskite with potential in energy storage applications. Previous research suggests that BTO dielectric constant increases as nanoparticle diameter decreases. This report recounts an investigation of this relationship. Injection-molded nanocomposites of 5 vol% BTO nanoparticles incorporated in a low-density polyethylene matrix were fabricated and measured. Finite-element analysis was used to model nanocomposites of all BTO sizes and the results were compared with experimental data. Both indicated a negligible relationship between BTO diameter and dielectric constant at 5 vol%. However, a path for fabricating and testing composites of 30 vol% and higher is presented here.
Tracing the flow of solid matter during an explosion requires a rugged tag that can be measured by a unique identifiable signature. Silica-covered semiconductor quantum dots (QDs) provide a unique and tunable photoluminescent signature that emits from within a sacrificial outer layer. Five types of silica-covered zinc sulfide QDs were synthesized and covalently bound to commercial luminescent powders. The combination of five dots and five powders enables a matrix of 25 unique tags. The tracers are shown to be tolerant of environments associated with chemical explosives and provides a unique tag to evaluate debris fields.
This work investigated the photophysical pathways for light absorption, charge generation, and charge separation in donor–acceptor nanoparticle blends of poly(3-hexylthiophene) and indene-C60-bisadduct. Optical modeling combined with steady-state and time-resolved optoelectronic characterization revealed that the nanoparticle blends experience a photocurrent limited to 60% of a bulk solution mixture. This discrepancy resulted from imperfect free charge generation inside the nanoparticles. High-resolution transmission electron microscopy and chemically resolved X-ray mapping showed that enhanced miscibility of materials did improve the donor–acceptor blending at the center of the nanoparticles; however, a residual shell of almost pure donor still restricted energy generation from these nanoparticles.
The understanding of adhesion and survival behavior of bacterial pathogens on implant surfaces are critical to control and reduce implant-associated infections. Herein, the authors investigate the interactions of Staphylococcus aureus, one of the most prevalent causes of implant infections, with Mg–4Zn–0.5Ca implants. It was found that within 60 min of exposure, 99.1% of adherent bacteria were inactivated. The combination of unique mechanical properties, biodegradation kinetics, and antimicrobial characteristics of Mg–4Zn–0.5Ca alloy makes it a promising candidate for future implant applications.
Obtaining a good statistical representation of material microstructures is crucial for establishing robust process–structure–property linkages and machine learning techniques can bridge this gap. One major difficulty in leveraging recent advances in deep learning for this purpose is the scarcity of good quality data with enough metadata. In machine learning, similarity metric learning using Siamese networks has been used to deal with sparse data. Inspired by this, the authors propose a Siamese architecture to learn microstructure representations. The authors show that analysis tasks such as the classification of microstructures can be done more efficiently in the learned representation space.
The development of thermoelectric measurement technology at nanoscale is a challenging task. Here, a novel MEMS-based dual temperature control (DTC) measurement method for thermoelectric properties of individual nanowires was proposed. Different from conventional thermal bridge testing devices, this DTC thermoelectric testing device can obtain the thermoelectric properties by independently control ambient temperature and temperature difference between two ends of the nanowires through two separate resistance thermometers without auxiliary heating devices. The reliability of the model and the testing accuracy were verified by accurately measuring the thermal conductivity, electrical conductivity, and the absolute value of the Seebeck coefficient of VO2 nanowires.
Waterproof bioelectrodes enable long-term biological monitoring and the assessment of performances of athletes in water. Existing gel electrodes change their electrical properties even when covered with a waterproof film. Here, the authors present the poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/poly(styrene-butadiene-styrene) (SBS) bi-layer nanosheet and waterproof film for a comfortable waterproof bioelectrode. PEDOT:PSS/SBS is fully foldable with a conductivity loss of only 5%. This foldable nanosheet electrode provides a reliable electrical connection between the skin and the wire. The waterproof film-covered bioelectrode enables continuous monitoring of electrocardiograms in water, showing a signal-to-noise ratio of 21.5 dB for the R wave and 17.5 dB for the T wave, comparable to atmospheric measurements, and sensing a change in heart rate from 79 to 131 bpm during bathing.
The enhanced reducibility of the surface of ceria relative to the bulk has long been established. Several studies also show that ceria nanoparticles with different facets exhibit different catalytic activities. Despite consensus that the activity is correlated with the surface Ce3+ concentration, experimental measurements of this concentration as a function of termination are lacking. Here, X-ray absorption near-edge spectroscopy (XANES) is used to quantify the Ce3+ concentration in films with (001), (110), and (111) surface terminations under reaction relevant conditions. While an enhanced Ce3+ concentration is found at the surfaces, it is surprisingly insensitive to film orientation.
UV-initiated crosslinking of electrospun poly(ethylene) oxide (PEO)/chitosan (CS) nanofibers doped with zinc oxide nanoparticles (ZnO-NPs) was performed using pentaerythritol triaclyrate (PETA) as the photoinitiator and crosslinker agent. The influence of the addition of PETA to the PEO/CS diameter and crosslinking of nanofibers was evaluated. The effect of irradiation time on the morphology and swelling properties of the crosslinked nanofibers were investigated. For ZnO-NPs, the minimum inhibitory concentrations were found at 1 mg/mL, and the minimum bactericidal concentrations at 2 mg/mL for all the strains tested. The nanofibrous hydrogel antibacterial effect was tested. This material enters the realm of fibrous hydrogels which have potential use in several applications as in the biomedical area.
The authors report results of the studies relating to the synthesis of nanodot zirconia that has been utilized for the fabrication of electrochemical biosensing platform for the detection of CYFRA-21-1 biomarker, secreted in saliva samples of oral cancer patients. For the synthesis of nanodot zirconia (ndZrO2), the hydrothermal process was used and further functionalized with 3-aminopropyl triethoxysilane (APTES). Electrophoretic deposition technique was employed for its deposition onto the ITO electrode. The EDC-NHS reaction was used for anti-CYFRA-21-1 immobilization and bovine serum albumin (BSA) was used for blocking of the nonspecific binding sites. The fabricated biosensing platform (BSA/anti-CYFRA-21-1/APTES/ndZrO2/ITO) exhibited a wide linear detection range (0.5–50 ng/mL) with excellent sensitivity (0.53 μA mL/ng cm2).
In this work, RF-sputtered metallic tin (Sn) film was sulfurized through di-tert-butyl-disulfide vapor at 350 °C for 150, 180, 210, and 240 min. According to the Raman spectra analysis, 210 min was sufficient to form dominantly SnS film. X-ray diffraction and X-ray photoelectron spectroscopy (XPS) studies of SnS film were evaluated. The n-type window layers CdS and high transmittance Cd(S,O) were deposited by chemical bath deposition through two different baths without and with TX-100 surfactant, respectively. XPS analysis of CdS and Cd(S,O) films was carried out. SnS solar cells formed in the superstrate solar cell device configuration. The photovoltaic performances were evaluated.
This work investigates the antifungal effect of plasma polymer films produced by low-pressure RF-generated plasma system using acrylic acid, 2–hydroxyethyl methacrylate, and diethyl phosphite (DEP). Unmodified and plasma-modified polystyrene (PS) microplate wells were tested by 30 biofilm-positive Candida spp. isolated from blood samples and two control strains using a quantitative plaque assay method. Regardless of the precursors and plasma parameters, biofilm formation was inhibited for all plasma-modified microplate wells. The most significant anti-biofilm effect was observed on PS modified by DEP at 90 W plasma power with the inhibition of all Candida species’ biofilm formation.
An amorphous aluminum oxide supercapacitor can store a large amount of electric storge on the uneven surfaces with AlO6 clusters. The amount of stored electricity increases with decreasing convex diameter d and depth of valley h. The nondestructive detection of AlO6 clusters on a surface with (Al0.91Y0.09)O1.66 oxide layer at a depth of 0.5 μm was determined based on a 3505 cm−1 peak band in the Fourier transform-infrared (FT-IR) spectrum and one 1047 cm−1 peak in the microRaman spectrum. The discharging time (T) could be expressed as T = 1.388 × 100.019 I. Thus, we can evaluate the amount of electricity by the nondestructive detection methods such as FT-IR and the microRaman spectra.