Effective Cooling Generates Efficient Emission: Blue, Green, and Red Light-Emitting Si Nanocrystals

Abstract

Nanosecond pulsed laser ablation of bulk silicon crystal upon the excitation of 532 nm was conducted in supercritical CO 2 to generate silicon nanocrystals, whose properties were studied by seven experimental methods. According to the photoluminescence spectra and fluorescence microscope images, emissions of near-ultraviolet, violet, blue, green, and red were observed in air, at room temperature, and without cooling in liquid nitrogen or a helium cryogenic system. A preferable emission channel of carriers, generated by photoexcitation of Si/SiO 2 of core/shell structure, was responsible for interface states with defect sites. This luminescence process caused color changes and intensity increase, enhanced by a factor of 100, where thermal properties of supercritical CO 2 were maximized, due to critical anomaly. It was found that colors and intensities of photoluminescence of silicon nanocrystals are controlled by a cooling rate during ablation, whose quantity is manipulated by the supercritical fluid pressure.

Aluminum Nano-polycrystalline Substance with Ferromagnetics and Application to High-Frequency Core Inductor

“…Producing any kind of nanoparticle with a diameter close to 2 nm in liquids is easily possible. It has been proven in various papers in which scanning transmission electron microscope (STEM) analyses were performed, and the structures and sizes have already been observed [12][13][14]. The size of the produced nanoparticles is not changed by materials.…”

“…The size of the produced nanoparticles is not changed by materials. Additionally, the proof of the mean size, i.e., the size of the produced Si nanoparticles needed for them to emit violet light, should be lower than 2 nm, and the bandgap energy enhanced by the size effect must be larger than 2 eV [12][13][14].…”

“…Bulk Al is normally known to be non-magnetic. However, authors fabricated Al nanoparticles with a mean diameter of less than 20 nm from Al oxide (alumina) particles [12][13][14][15][16], and obtained Al nano-polycrystalline structures using the Al nanoparticles [15]. SQUID measurements of the magnetic hysteresis revealed that the Al nano-polycrystalline structure was ferromagnetic.…”

“…SQUID measurements of the magnetic hysteresis revealed that the Al nano-polycrystalline structure was ferromagnetic. Using this method, sintered Al nano-polycrystalline structures from Al oxide powder can be easily fabricated at low cost in a short time [12][13][14][15][16][17]. These nano-metals with small poly-crystalline structures are novel materials, and their magnetic and mechanical properties, aside from some of the electrical properties, have not yet been clarified.…”

Amorphous and Crystalline Silicon Films from Soluble Si-Si Network Polymers

“…As an alternative method, laser ablation of bulk c-Si in supercritical CO 2 after excitation with a 532-nm nanosecond pulsed laser yielded nc-Si that could produce blue, green, and red emitters. (Saitow & Yamamura, 2009). As we have demonstrated, controlled vacuum pyrolysis using a single SNP source material, possibly including GNP source material, should offer a new, environmentally friendly, safer process to efficiently produce red-green-blue-near infrared emitters, thin films for TFTs, and solar cells because the required technology is largely compatible with XeCl excimer laser annealing and the crystallization process for making poly-Si TFTs from aSi thin films deposited using the SiH 4 -Si 2 H 6 CVD process.…”