- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Vital role of Ar ambient pressure in controlled properties of nanocrystalline CdS thin films
摘要： A report on the manipulation of structural, optical, and electrical properties of nanocrystalline CdS (ncCdS) thin films in the framework of varying Ar ambient pressure in pulsed laser deposition (PLD) is presented here. Increase in Ar ambient pressure results in reduction of crystallite size which in turns increases the structural imperfections and structural phase transformation of ncCdS thin films. The most significant observation here is the bleaching of multiphonon Raman modes (MRMs) particularly LO + 2E2, 2LO + 2E2, etc. in ncCdS thin films. An acute investigation on the reason of bleaching of LO + 2E2, 2LO + 2E2, etc. modes is carried out here and concluded that it is due to the fading of E2 mode with increasing Ar pressure as confirmed by low-frequency micro-Raman measurements. UV–visible absorption and photoluminescence spectroscopies are used to examine the optical properties like bandgap and possible electronic transitions in ncCdS thin films. Further, transport properties of ncCdS thin films are investigated using Hall measurement and I–V characteristics.
关键词： electrical properties,optical properties,Ar ambient pressure,structural properties,pulsed laser deposition,nanocrystalline CdS thin films
更新于2025-09-23 15:21:01
-
Control of the size and luminescence of carbon nanodots by adjusting ambient pressure in laser ablation process
摘要： A femtosecond pulse laser was used to fabricate carbon nanodots (CDs), of which the particle size and photoluminescence (PL) properties could be effectively controlled by adjusting ambient pressure. By increasing the reaction pressure, the particle size of CDs gradually decreased and finally reached less than 1 nm at 4 MPa. Simultaneously, the fluorescence intensity of the CDs first increased and then decreased by further increasing the pressure. By examining the PL dynamics and the chemical structure of the CDs, we found that the PL change of products was attributed to the quantity change of functional groups attached to the CDs due to the surface area change of the carbonic core.
关键词： laser ablation,ambient pressure,photoluminescence,particle size,carbon nanodots
更新于2025-09-19 17:13:59
-
Laser ionization ion mobility spectrometric interrogation of acoustically levitated droplets
摘要： Acoustically levitated droplets have been suggested as compartmentalized, yet wall-less microreactors for high-throughput reaction optimization purposes. The absence of walls is envisioned to simplify up-scaling of the optimized reaction conditions found in the microliter volumes. A consequent pursuance of high-throughput chemistry calls for a fast, robust and sensitive analysis suited for online interrogation. For reaction optimization, targeted analysis with relatively low sensitivity suffices, while a fast, robust and automated sampling is paramount. To follow this approach, in this contribution, a direct coupling of levitated droplets to a homebuilt ion mobility spectrometer (IMS) is presented. The sampling, transfer to the gas phase, as well as the ionization are all performed by a single exposure of the sampling volume to the resonant output of a mid-IR laser. Once formed, the nascent spatially and temporally evolving analyte ion cloud needs to be guided out of the acoustically confined trap into the inlet of the ion mobility spectrometer. Since the IMS is operated at ambient pressure, no fluid dynamic along a pressure gradient can be employed. Instead, the transfer is achieved by the electrostatic potential gradient inside a dual ring electrode ion optics, guiding the analyte ion cloud into the first stage of the IMS linear drift tube accelerator. The design of the appropriate atmospheric pressure ion optics is based on the original vacuum ion optics design of Wiley and McLaren. The obtained experimental results nicely coincide with ion trajectory calculations based on a collisional model.
关键词： Ion mobility spectrometry,Acoustic levitation,Ambient pressure laser ionization,Ion optics
更新于2025-09-16 10:30:52
-
Mitigation of porosity defects in fiber laser welding under low vacuum
摘要： Laser welding trials were conducted under low vacuum to reduce porosity defects. The effect of vacuum on the characteristics of porosity was quantitatively evaluated using 3D micro-CT. To explore the mechanisms of porosity formation at atmospheric pressure and porosity defects mitigation under vacuum, the weld pool and fluid flow behaviors were directly observed by placing a transparent glass plate on one side of the weld pool. The results showed that the vacuum condition was favorable for reducing porosity, especially process porosity. It was also found that the weld pool size and fluid flow were totally different at atmospheric pressure and under vacuum. At atmospheric pressure, bubbles were trapped in the vortex induced by two opposing fluid flows, failed to escape from the weld pool and finally formed pores. Under vacuum, suppression of vapor plume and reduction in the boiling point led to a deeper keyhole and a thinner weld pool, resulting in an upward flow in the rear weld pool. In this case, the bubbles could escape easily from the weld pool with the help of the upward flow.
关键词： 3D micro-computed tomography,Fluid flow,Low vacuum,Laser welding,Porosity,Ambient pressure
更新于2025-09-12 10:27:22
-
Monolithic silicon carbide with interconnected and hierarchical pores fabricated by reaction‐induced phase separation
摘要： Hierarchically porous silicon carbide (SiC) monoliths were fabricated based on polycarbosilane (PCS), divinyl benzene (DVB), and decalin, by a sequence of procedures including catalyst-free hydrosilylation reaction-induced phase separation, ambient-pressure drying, calcination, and HF etching. The influences of ratios of each component on the phase separation were systematically studied. It was found that isotactic polypropylene added as a nonreactive additive could effectively tailor the microstructure and improve the mechanical properties of SiC monoliths. The resultant SiC monoliths mainly consisted of β-SiC nanocrystals, and possessed low bulk density (0.7 g/cm3), high porosity (78%), large specific area (100.6 m2/g), high compressive strength (13.5 ± 1.6 MPa), and hierarchical pores (macropores around 350 nm, mesopores around 4 nm and 20 nm). These properties make SiC monoliths promising materials for catalyst/catalyst support, gas separator, and the reinforcement of high-temperature composites.
关键词： nanocrystal,reaction induced phase separation,hierarchical pore,ambient pressure drying,SiC monolith
更新于2025-09-09 09:28:46