Large-Scale and Galvanic Replacement Free Synthesis of Cu@Ag Core-Shell Nanowires for Flexible Electronics.

Copper nanowires (CuNWs) are considered a promising alternative to indium tin oxide due to their cost-effectiveness as well as high conductivity and transparency. However, the practical applications of copper-based conductors are greatly limited due to their rapid oxidation in atmosphere. Herein, a facile adsorption and decomposition process is developed for galvanic replacement free and large-scale synthesis of highly stable Cu@Ag core-shell nanowires. First, Ag-amine complex ([Ag(NH2R)2]+) as silver source adsorbs on CuNWs surface, and Cu@Ag-amine complex core-shell structure is formed. After that, Ag-amine complex is easily decomposed to pure Ag shell through a simple thermal annealing under air. By adjusting the concentration of Ag-aminein CuNWs solution, Cu@Ag core-shell nanowires with different thickness of silver shell can be easily obtained. The obtained core-shell nanowires exhibit high stability for at least 500 h at high temperature (140 °C) and high humidity (85 °C, 85% RH) due to the protection of Ag shell. More importantly, the conductivity and transparency of Cu@Ag nanowires-based conductors is similar to that of pure CuNWs. The large-scale and facile synthesis of Cu@Ag core-shell nanowires provides a new method to prepare stable metallic core-shell nanowires.

Association between oral health-related quality of life and depressive symptoms in Chinese college students: Fitness Improvement Tactics in Youths (FITYou) project.

BACKGROUND: This study aimed to investigate a gender-specific association between oral health-related quality of life (OHRQoL) and depressive symptoms in college students, as there are limited relevant studies conducted among youths. METHODS: In 2017, a cross-sectional study of 3461 Chinese college students was conducted in Shenyang, China. OHRQoL and depressive symptoms were screened by a 14-item oral health impact profile questionnaire and a Self-rating Depression Scale, respectively. A multivariable logistic regression analysis was performed to examine the association of OHRQoL with depressive symptoms. RESULTS: The number of youths reported to have depressive symptoms was 20.7%. A univariate analysis showed that categories with a OHRQoL score over 6 were more likely to have a higher prevalence of depressive symptoms compared to the category with a score of 0 (male: ORs [95% CI]: 3.10, 2.05-4.68, P < 0.001; female: ORs [95% CI]: 3.11, 2.38-4.05, P < 0.001). Similar results were observed after adjusting for sociodemographic, anthropometric, and lifestyle-related covariates (male: ORs [95% CI]: 3.07, 1.98-4.76, P < 0.001; female: ORs [95% CI]: 2.90, 2.21-3.81, P < 0.001). CONCLUSIONS: College students who have higher OHRQoL tend to have a lower prevalence of depressive symptoms.

Low Temperature Sintering Cu6 Sn5 Nanoparticles for Superplastic and Super-uniform High Temperature Circuit Interconnections.

Brittle intermetallics such as Cu6 Sn5 can be transformed into low cost, nonbrittle, superplastic and high temperature-resistant interconnection materials by sintering at temperatures more than 200 °C lower than its bulk melting point. Confirmed via in situ TEM heating, the sintered structure is pore-free with nanograins, and the interface is super-uniform.

Three-Dimensional Stretchable and Transparent Conductors with Controllable Strain-Distribution Based on Template-Assisted Transfer Printing.

Although stretchable transparent conductors, stemmed from the strategies of both conductive composite and structural design of nonstretchable conductors, have been extensively studied, these conductors either suffer from low stretchability or require a complex fabrication process, which drastically limits their practical applications. Here, we propose a novel strategy combining the design of substrates and a simple template-assisted transfer printing process to fabricate three-dimensional (3D) transparent conductors. The strategy not only eliminates the complex and costly fabrication processes but it also endows conductors with high stretchability and long-term stability, thanks to the controllable strain distribution as well as the seamless connection between the conductor layer and the substrate. These newly designed 3D conductors achieve a low sheet resistance of 1.0 Ω/sq with a high transmittance of above 85% and remain stable without obvious resistance change during 1000 stretching-relaxation cycles until 60% strain, which are superior to most reported conductors. A large-area stretchable heater based on the 3D conductor realizes the temperature fluctuation below 10% even under a large strain, thus showing huge application prospects in the field of wearable healthcare electronics. The simple solution-processed fabrication method and high performance such as stretchability and low resistance change over a large strain range promote the practical applications of these newly designed 3D conductors.

Highly Conductive Ag Paste for Recoverable Wiring and Reliable Bonding Used in Stretchable Electronics.

Stretchable wiring and stretchable bonding between a rigid chip/component and a stretchable substrate are two key factors for stretchable electronics. In this study, a highly conductive stretchable paste has been developed with commercial Ag microflakes and poly(dimethylsiloxane), which can be used to fabricate stretchable wirings and bondings under a low curing temperature of 100 °C with printing method. Herein, recoverabilities as to recovery time and recovery resistance of the wirings are defined and discussed. The effect of Ag composition and the tensile strain rate on the recoverability of the wirings are also examined. The wiring with a low resistivity of 8.7 × 10-5 Ω cm shows much better recoverability than nanowire-based wirings due to the flake nature of the Ag particles. When stretched to 50 and 100% of strain, the resistance of the patterned wiring increases by only 10 and 110%, respectively. Moreover, the resistance of the wiring during 20% tensile cyclic test remains within 1.1 times even after 1000 cycles, thus demonstrating significant durability. The paste was utilized to fabricate conductive tracks and stretchable bondings to assemble a rigid chip to fabricate a stretchable demo. When stretched to 50% of strain, resistance of the wiring was increased by 90%. It is anticipated that the newly developed paste will be used to fabricate various stretchable wirings, bondings, and packaging structures by a simple printing process, thus enabling mass production of stretchable electronic devices.

Self-catalyzed copper-silver complex inks for low-cost fabrication of highly oxidation-resistant and conductive copper-silver hybrid tracks at a low temperature below 100 °C.

Cu-Ag complex inks are developed for printing conductive tracks of low cost, high stability, and high conductivity on heat-sensitive substrates such as polyethylene terephthalate (PET) substrates. The inks show an obvious self-catalyzed characteristic due to the in situ formation of fresh metal nanoparticles which promote rapid decomposition and sintering of the inks at a low temperature below 100 °C. The temperature is 40-60 °C lower than those of general Cu complex inks and 100-120 °C lower than those of general Cu/Ag particle inks. Highly conductive Cu-Ag tracks of 2.80 × 10-5 Ω cm and 6.40 × 10-5 Ω cm have been easily realized at 100 °C and 80 °C, respectively. In addition, the printed Cu-based tracks not only show high oxidation resistance at high temperatures of up to 140 °C (the maximum tolerable temperature of current PET substrate) but also show excellent stability at high humidity of 85% because of the very uniform Cu-Ag hybrid structure. The printable tracks exhibit great potential application in various wearable devices fabricated on textiles, papers, and other heat-sensitive substrates.

Bottom-Up Electrodeposition of Large-Scale Nanotwinned Copper within 3D Through Silicon Via.

This paper is the first to report a large-scale directcurrent electrodeposition of columnar nanotwinned copper within through silicon via (TSV) with a high aspect ratio (~4). With this newly developed technique, void-free nanotwinned copper array could be fabricated in low current density (30 mA/cm²) and convection conditions (300 rpm), which are the preconditions for copper deposition with a uniform deep-hole microstructure. The microstructure of a whole cross-section of deposited copper array was made up of (111) orientated columnar grains with parallel nanoscale twins that had thicknesses of about 22 nm. The hardness was also uniform along the growth direction, with 2.34 and 2.68 GPa for the top and bottom of the TSV, respectively. The gelatin additive is also first reported hereas a key factor in forming nanoscale twins by adsorbing on the cathode surface, in order to enhance the overpotential for cathodic reaction during the copper deposition process.

Highly Stable Transparent Conductive Electrodes Based on Silver-Platinum Alloy-Walled Hollow Nanowires for Optoelectronic Devices.

In industrial manufacturing, alloying can contribute to the passivation of active metals and markedly improve their corrosion resistance. This inspires us to solve the current critical problem of Ag nanowires (Ag NWs) that have poor stability against chemical and electrochemical corrosion. These problems have seriously limited the applications of Ag NWs in optoelectronic devices where they are used for transparent conductive electrodes. Here, a kind of transparent conductive electrode based on Ag@Pt alloy-walled hollow nanowires (Ag@Pt AHNWs) is successfully fabricated by introducing 12 mol % Pt into long Ag NWs to form Ag@Pt alloy. The as-synthesized electrodes exhibit better optical transmittance (82% at the wavelength of 550 nm) under high electrical conductivity (28.73 Ω/sq-1), high thermal stability up to 400 °C for 11 h, and remarkable mechanical flexibility (remaining stable after 5000 cycles bending), as well as high resistance against chemical and electrochemical corrosion. The Ag@Pt AHNWs electrodes are further applied in a primary bifunctional polyaniline electrochemical device, and the device shows promising flexibility, noticeable multicolor performances, and high specific capacitance because of the remarkable mechanical flexibility and electrochemical stability of Ag@Pt AHNWs. This work will provide an optional approach for the preparation of other metal nanomaterial electrodes with high stability.

Printable and Flexible Copper-Silver Alloy Electrodes with High Conductivity and Ultrahigh Oxidation Resistance.

Printable and flexible Cu-Ag alloy electrodes with high conductivity and ultrahigh oxidation resistance have been successfully fabricated by using a newly developed Cu-Ag hybrid ink and a simple fabrication process consisting of low-temperature precuring followed by rapid photonic sintering (LTRS). A special Ag nanoparticle shell on a Cu core structure is first created in situ by low-temperature precuring. An instantaneous photonic sintering can induce rapid mutual dissolution between the Cu core and the Ag nanoparticle shell so that core-shell structures consisting of a Cu-rich phase in the core and a Ag-rich phase in the shell (Cu-Ag alloy) can be obtained on flexible substrates. The resulting Cu-Ag alloy electrode has high conductivity (3.4 µΩ·cm) and ultrahigh oxidation resistance even up to 180 °C in an air atmosphere; this approach shows huge potential and is a tempting prospect for the fabrication of highly reliable and cost-effective printed electronic devices.