In this study, the size effect of copper particles on the flash light sintering of copper (Cu) ink was investigated using Cu nanoparticles (20-50 nm diameter) and microparticles (2 μm diameter). Also, the mixed Cu nano-/micro-inks were fabricated, and the synergetic effects between the Cu nano-ink and micro-ink on flash light sintering were assessed. The ratio of nanoparticles to microparticles in Cu ink and the several flash light irradiation conditions (irradiation energy density, pulse number, on-time, and off-time) were optimized to obtain high conductivity of Cu films. In order to precisely monitor the milliseconds-long flash light sintering process, in situ monitoring of electrical resistance and temperature changes of Cu films was conducted during the flash light irradiation using a real-time Wheatstone bridge electrical circuit, thermocouple-based circuit, and a high-rate data acquisition system. Also, several microscopic and spectroscopic characterization techniques such as scanning electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy were used to characterize the flash light sintered Cu nano-/micro-films. In addition, the sheet resistance of Cu film was measured using a four-point probe method. This work revealed that the optimal ratio of nanoparticles to microparticles is 50:50 wt%, and the optimally fabricated and flash light sintered Cu nano-/micro-ink films have the lowest resistivity (80 μΩ cm) among nano-ink, micro-ink, or nano-micro mixed films.

No abstract

In this work, bimodal Cu nano-inks composed of two different sizes of Cu nanoparticles (NPs) (40 and 100 nm in diameter) were successfully sintered with a multi-pulse flashlight sintering technique. Bimodal Cu nano-inks were fabricated and printed with various mixing ratios and subsequently sintered by a flash light sintering method. The effects of the flashlight sintering conditions, including irradiation energy and pulse number, were investigated to optimize the sintering conditions. A detailed mechanism of the sintering of bimodal Cu nano-ink was also studied via real-time resistance measurement during the sintering process. The sintered Cu nano-ink films were characterized using x-ray photoelectron spectroscopy and scanning electron microscopy. From these results, it was found that the optimal ratio of 40-100 nm NPs was found to be 25:75 wt%, and the optimal multi-pulse flash light sintering condition (irradiation energy: 6 J cm, and pulse duration: 1 ms, off-time: 4 ms, and pulse number: 5) was found. The optimally sintered Cu nano-ink film exhibited the lowest resistivity of 5.68 μΩ cm and 5B adhesion level.

No abstract

The electrochemical performance of pure Pt and Pt-based alloy nanoparticle catalysts with various Pt, Ru and Mo concentrations is investigated. Pure Pt, Ru, and Mo are first deposited on multi-walled carbon nanotubes (MWCNTs) using a E-beam evaporator (MEP5000, SNTEK), and Pt-based alloy nanoparticles are subsequently formed on the MWCNTs via flash light irradiation. Several microscopic and spectroscopic techniques, including X-ray diffractometry, scanning electron microscopy, and Raman spectroscopy are employed to characterize the catalysts. Cyclic voltammetry experiments are also performed to measure the electrochemical reactions of the Pt-based alloy nanoparticle/MWCNT catalysts. To verify the experimental results, a computational simulation analysis is conducted using molecular dynamics and the application of density functional theory. From the experimental and analytical findings, it is concluded that the Pt 43 -Ru 43 -Mo 14 /MWCNT structure exhibits the best electrochemical performance for the oxidation of methanol.The phenomenon of CO poisoning is a critical problem in the field of direct methanol fuel cells (DMFCs). CO poisoning occurs at pure Pt catalyst sites on the DMFC anode during the methanol oxidation reaction. The oxidation of methanol to carbon dioxide proceeds via a six-electron transfer process as follows: 1-4 Pt + CH 3 OH → Pt(CO) ads + 4H + + 4e − [1.1] Pt + H 2 O → Pt(OH) ads + H + + e − [1.2] Pt(CO) ads + Pt(OH) ads → CO 2 + 2Pt + H + + e − [1.3]Strongly adsorbed CO can gradually occupy all active Pt sites according to reaction 1.1. In order to remove the Pt(CO) ads species, the production of Pt(OH) ads by reaction 1.2 is needed so that reaction 1.3 may occur. However, the formation of Pt(OH) ads is difficult due to its high electrochemical potential (0.7 V vs. reversible hydrogen electrode (RHE)). A promising approach to solve this issue is to form M(OH) ads (M = metal) species that have a low electrode potential. For example, water dissociation can occur on Ru sites with the formation of Ru(OH) ads species at a potential as low as 0.2 V vs. RHE. 3 Various metals (e.g., Ru, Ni, Mo, Sn, Rh, Pd) that are compatible with Pt have been proposed for the fabrication of binary, ternary, and quaternary catalysts. [5][6][7][8][9][10][11][12][13][14][15][16][17] In particular, Pt-Ru-Mo is considered to be one of the best Pt-based alloy catalysts. 18-21 However, the synthesis of this metal alloy is quite challenging when compared to the fabrication of pure metal nanoparticles due to the difficulty in forming a uniform material. Furthermore, controlling the concentration of each metal in the metal alloy nanoparticles is important. For example, it has been reported that excessive concentrations of Mo has a deleterious effect on methanol oxidation. [21][22][23] In this study, we fabricated Pt-Ru-Mo/MWCNT catalysts with various metal atomic ratios in a short period of time (millisecond) using the flash light irradiation method under ambient conditions at room temperature. 14,15 The optimum atomic ratio of...