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The tensile mechanical behavior of tetragonal zirconia micro/nano-fibers and beams was studied with push-to-pull (PTP) devices equipped in an in situ nanoindenter. The small-volume ceramics generally experienced linear elastic deformation before fracture. Polycrystalline and oligocrystalline micro/nano-fibers exhibit a tensile strength of ∼0.9–1.4 GPa, while single-crystal beams exhibit a much higher tensile strength (∼2.1–3.2 GPa). The tensile strength of the small-volume zirconia is found comparable to the corresponding compressive strength, which indicates the large discrepancy between the tensile and compressive strength observed in bulk zirconia becomes insignificant at micro/nano-scales. No martensitic transformation induced shape memory strain was detected in the zirconia fibers and beams. Further variation in dopant concentration and crystal orientation was explored for single-crystal beams and their significance in controlling the tensile strength was discussed. Our work offers a new insight into the mechanical behavior of tetragonal zirconia-based ceramics at small scales. The authors would like to acknowledge the funding support under project agreements PA 9013103290.

In this article, we demonstrate the Ti/TiN/Al (15/50/50 nm) ohmic contact on InGaP/GaAs heterojunction bipolar transistors (HBTs) epitaxially grown on 200-mm Si substrate. We study the rapid thermal annealing (RTA) effect of the metal stack on both n-type InGaAs and p-type GaAs. The dc characteristics of the HBT devices fabricated using the Ti/TiN/Al metal contacts have been analyzed. Contact resistances (R-c)

This article describes a novel method for improving image resolution achieved using time-resolved photon emission techniques. Instead of directly generating images from photon counting, all detected photons are displayed as a point cloud in 3D space and a new higher-resolution image is generated based on probability density functions associated with photon distributions. Unsupervised learning algorithms identify photon distribution patterns as well as fainter emission sources.

Transient liquid phase (TLP) bonding is a promising solution for high temperature (HT) electronic devices as high-quality bonds can be formed at a temperature much lower than the melting point of the resulted joint. In this work, Ag-rich Ag–Sn TLP bonding was evaluated as a potential die attach solution for HT (250 °C) electronic applications. The influence of varying the Ag content on the mechanical strength of the Ag–Sn TLP joint was investigated through room temperature (RT) and HT shear tests. The study was complemented with X-ray imaging of any void formation, and scanning electron microscope (SEM)/energy-dispersive X-ray spectroscopy (EDX) spectra for composition and morphology analysis. It is shown that the Ag-rich joint comprises Ag and Ag3Sn intermetallic compound (IMC), and no obvious void was observed. The shear strengths of the joints measured at both RT and 250 °C have satisfied the requirement for HT applications. In addition, the fractured surfaces after the shear test showed that the failure of Ag-rich joints occurred mostly in the Ag3Sn IMC region. Furthermore, the shear strength improved with increasing Ag content (up to 81.5 at.%) in the bond.

Alumina particles are investigated as a potential catalyst for phthalonitrile polymerization and as a property enhancer. In this work, extensive characterizations were conducted on alumina-filled resorcinol-based phthalonitrile to differentiate between the catalytic effect and the filler effect. Thermal gravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy suggest the occurrence of chemical interaction between alumina fillers and phthalonitrile, which provides an insight into the better performance of alumina-filled phthalonitrile resins. This hypothesis is further supported by the additional Al-N peak observed in the X-ray photoelectron spectroscopy (XPS) analysis when alumina is added to phthalonitrile before curing, as well as the presence of an exothermic peak in the differential scanning calorimetry (DSC) analysis that indicates the catalytic polymerization of phthalonitrile. This catalytic phenomenon observed by the addition of alumina fillers is beneficial for the improvement of the conventionally slow curing process of phthalonitrile and, more importantly, is coupled with observable enhancement of thermomechanical properties of the composite. Agency for Science, Technology and Research (A*STAR) Published version This study is supported under the RIE2020 Industry Alignment Fund−Industry Collaboration Projects (IAF-ICP) Funding Initiative, as well as cash and an in-kind contribution from Rolls-Royce Singapore Pte Ltd.

The scientific community has recognized that copper can kill bacteria; however, the effect of the particle size, concentration, and oxidation state on antibacterial activity remains unclear for copper and its nanoparticles (NPs), in particular. In this study, copper NP coatings with extremely fast and sustained antibacterial activity are reported. It is found that coating with cuprous oxide (Cu2O) NPs (∼150 nm) and coating with metallic copper NPs (∼50 nm) on commonly used fabrics for cleaning and masks can kill bacteria within 45 s. Our bacterial study was conducted using Staphylococcus aureus as a Gram-positive bacterium and Klebsiella pneumoniae and Pseudomonas aeruginosa as Gram-negative bacteria. Scanning electron micrographs suggest bacterial damage, and bacterial DNA harvested after interaction with copper-coated fabrics indicates DNA fragmentation. On top of this, significantly higher levels of 8-hydroxy-2′-deoxyguanosine are also detected in DNA after interaction with coated fabrics, signifying that both copper and Cu2O NPs rapidly induce oxidative stress. Furthermore, cumulative inoculations with K. pneumoniae for 144 h show excellent sustained bacterial killing in the presence of Cu2O NPs. Using a combination of detailed physical and chemical analysis of the NPs and a study of how bacteria interact with the coated substrate, it is possible to establish the parameters that resulted in speedy and robust antibacterial properties in Cu2O-coated fabrics. This study offers a rational strategy on how to slow down or even halt the transmission of infectious pathogens. Ministry of Education (MOE) This research was supported by the Ministry of Education, Singapore, under its Academic Research Fund Tier 1 (Project RG98/19). Y.-H.G. acknowledges financial support given by Kuprion, Inc. (USA), for this work.

Crystallographic texture engineering in ceramics is essential to achieve direction-specific properties. Current texture engineering methods are time-consuming, energy extensive, or can lead to unnecessary diffusion of added dopants. Herein, we explore ultrafast high-temperature sintering (UHS) to prepare dense and textured alumina using templated grain growth (TGG). From a slurry containing alumina microplatelets coated with Fe3O4 nanoparticles dispersed in a matrix of alumina nanoparticles, green bodies with oriented microplatelets were prepared using magnetic assisted slip casting (MASC). The effects of the sintering temperature, time and heating rate on the density and microstructure of the obtained ceramics were then studied. We found that TGG occurs for a temperature range between 1640 and 1780 °C and 10 s sintering time. Sintering at 1700 °C for 10 s led to dense and textured alumina with anisotropic grains thanks to the Fe3O4 coating, which did not have the time to diffuse. The highest texture and relative density were obtained with a heating rate of ~5,500 °C/min, leading to texture-dependent anisotropic mechanical properties. This study opens new avenues for fabricating textured ceramics in ultra-short times. National Research Foundation (NRF) Submitted/Accepted version This research was funded by the National Research Foundation of Singapore (award NRF-NRFF12-2020-0002). The authors would like to acknowledge with thanks the financial support of the work by the project with PA number of DSOCL 21115, Singapore.

Much attention has been drawn to the Ni-Sn transient liquid phase (TLP) bonded joints for high-temperature electronic packaging applications since their inception. A comparative study of Ni-Sn TLP bonded joints with different interlayers was conducted. The evolution of microstructure and mechanical properties of joints with different bonding times was also investigated. In addition, the high-temperature (300 °C) thermal reliability of the Ni-Sn TLP bonded joints was explored with aging times from 0 h to 100 h. The results show that electroplated Ni-Sn TLP bonded joints exhibited a slightly higher average shear strength than those prepared using Sn foil and Sn96.5Ag3.5 paste. Also, the average shear strength of the electroplated Ni-Sn TLP bonded joints was greatly improved when the bonding time increased from 0.5 h to 5 h, while there was a continuous decrease in the average shear strength as the aging time was increased from 4 h to 100 h. During aging, the Ni/Ni3Sn2 interface was the preferential site for the nucleation of newly formed Ni3Sn2 intermetallic compounds (IMCs). Furthermore, the cross-sectional microstructure of the shear fractured joints after aging from 4 h to 100 h indicates that the shear fractures propagated through both the Ni3Sn4 IMCs and the Ni3Sn2/Ni3Sn4 interface. National Research Foundation (NRF) Submitted/Accepted version The work was investigated with the support of Rolls-Royce@NTU Corporate Laboratory, Nanyang Technological University and the National Research Foundation (NRF).

The use of optical techniques for attacking integrated circuits (ICs) is increasingly being reported, particularly the nefarious extraction data from embedded SRAM. Such attacks can provide access to highly sensitive information such as encryption keys and bypass various security measures. Attackers usually exploit one of several interactions between light and semiconductors to generate logic-state images that reflect data in memory. Thermal laser stimulation (TLS) and laser probing via electro-optical frequency mapping (EOFM) have been reported in the literature, but photoelectric laser stimulation (PLS) gets little attention. Considering the potential advantages of PLS over other techniques (e.g., less power is required to generate current-voltage changes and the effect can be triggered at shorter wavelengths, which can lead to improved spatial resolution), the authors set out to determine if logic state images can be generated from various types of devices with PLS and assess the strengths and limitations for each case. The results of the investigation are presented in this paper.

Current and next-generation high power devices require a new set of materials with higher electrical and thermal conductivity to efficiently spread and remove increased waste heat. Kuprion's ActiveCopper technology enables the formation of bulk copper joints at typical soldering temperatures, yet the resulting interconnects are stable up to 500°C or more. This technology has been developed for a number of applications including die attach, thermal vias, and a replacement for WCu heat spreaders. Die attach materials can be dispensed, screened, or stenciled like traditional solder pastes followed by a solder-like thermal profile in a reflow oven under an inert atmosphere. Sintering can be achieved with or without pressure. Thermal vias are generated by stenciling an ActiveCopper paste directly into open circuit board cavities up to 4 mm in diameter followed by hot pressing under conditions similar to those used for traditional PCB manufacture. The resulting copper vias have thermal conductivity up to 330 W/mK, are solder compatible with or without further surface finish, and show excellent bonding to electroplated copper on the via sidewalls. Near net shape heat spreaders akin to WCu or AlSiC can also be generated via hot pressing or injection molding. The CTE of vias and spreaders can be tuned by adjusting the formulation of the original paste. ActiveCopper technology enables the design of all-Copper systems that can handle the increased thermal demands of next-generation electronics while avoiding failure modes attributed to intermetallic formation. Copper also presents an advantage over silver-based systems which show increased migration, dendritic growth, and voiding under higher thermal and electrical loads.

The tensile mechanical behaviour of tetragonal zirconia micro/nano-fibers and beams were studied with a push-to-pull (PTP) device equipped in an in-situ nanoindenter. Polycrystalline and oligocrystalline micro/nano-fibers exhibited some degree of plastic strain before fracture with the tensile strength ranging from ~0.9 GPa to 1.4 GPa. Single-crystal beams generally experienced linear elastic deformation with tensile strength of ~2.1-3.4 GPa. No martensitic transformation induced shape memory strain was detected in the zirconia fibers and beams. Further variation of dopant concentration and crystal orientation was explored for single-crystalline beams and their significance in controlling the tensile strength was assessed and discussed.

Alumina toughened zirconia (ATZ), aluminum (Al) and titanium (Ti) particulate fillers were added to carbon fiber-reinforced polycarbonate composites (PC–CF) at the percolation threshold (20 vol.%) to form a hybrid composite with multi-dimensional fillers. Experiments indicate that the storage modulus and yield strength were increased by a maximum of 148% and 8%, respectively. In contrast, mechanical properties of the composite deteriorated when additional 1-dimensional (1D) chopped carbon fibers were incorporated in any amount. Using the Hashin–Shtrikman and Suquet analysis to remove the influence of filler material property, it was shown that the stiffening and strengthening occurred because 0D particles could be dispersed in the interstitial sites of the PC–CF composite more easily than 1D fibers without causing significant agglomeration. Theoretical predictions from previous studies and electrical conductivity measurements support this premise. Employment of this novel strategy produced polycarbonate hybrid composites with specific strengths exceeding that of magnesium alloys, steel and some aluminum alloy grades, as well as combinations of strength and density not found in current engineering materials. Submitted/Accepted version This work was funded with Temasek Labs Seed Grant (TLSP-19-05), which C.Q. Lai is grateful for.

3D printing of transparent ceramics has attracted great attention recently but faces the challenges of low transparency and low printing resolution. Herein, magnesium aluminate spinel transparent ceramics with transmittance reaching 97% of the theoretical limit have been successfully fabricated by stereolithography based 3D printing method assisted with hot isostatic press for the first time and the critical factors governing the transparency are revealed. Various transparent spinel lenses and microlattices have been printed at a high resolution of ~100-200 µm. The 3D printed spinel lens has demonstrated fairly good optical imaging ability and the printed Diamond microlattices as a transparent photocatalyst support for TiO2 have significantly enhanced its photocatalytic efficiency compared with opaque counterparts. Compared with the other 3D printed transparent materials such as silica glass and organic polymers, the printed spinel ceramics have the advantages of broad optical window, high hardness, excellent high-temperature stability and chemical resistance and therefore, have great potentials to be used in various optical lens/windows and photocatalyst support for the applications in harsh environment. Agency for Science, Technology and Research (A*STAR) Accepted version The authors would like to acknowledge with thanks the financial support of the work by A*STAR AME IRG grant with project number of A1883c0009. H.W. would like to thank Dr. Yuezhong Wang for discussion. Z.D. would like to thank Dr. Lai Wenn Jing and Mr. Sean Looi for insightful discussion and thanks Yida Zhao and Dr. Zhang Hao for drawing the 3D lattice model and some of the SEM analysis.

Carbon nanotubes (CNTs) with three different diameter ranges (10–20, 40–60, and 60–100 nm) were doped into tin-silver-copper (SAC) solder, to study the performance of the composite SAC-CNTs solder materials – as well as the effect of the size of the CNTs. It was found that all the CNTs-doped composite solder samples displayed refined microstructure, inhibited interfacial intermetallic compound (IMC) growth, and reinforced mechanical strength – while the melting point of the composite solder was close to that of the pristine solder. The reinforcement in mechanical strength was due to the doped CNTs pinned at the solder grain boundaries, which acted as second-phase particles that refined the microstructure and increased the dislocation density. The adsorbed CNTs destroyed the integrity of the interfacial IMCs, leading to reduced growth rate. Among these composite solders, CNTs with a diameter of 40–60 nm provided superior performance in refining the microstructure, lowering the IMC growth rate by 30.9% – and reinforcing the ball shear strength by 15.3% and the hardness by 16.1%. This size effect on the performance of composite solders was due to the various surface energy values for CNTs – that led to the agglomeration and adsorption of CNTs in the solder matrix and interfacial IMCs.