Focused on silicon surface in water, superimposed multiple shots of linearly polarized 800-nm, 100-fs, 10-Hz laser pulses at lower fluence than the single-pulse ablation threshold are shown to produce two kinds of periodic nanostructures with almost constant periods of 150 nm and 400 nm. Surface plasmon polaritons excited in the surface layer illustrates well the formation of nanostructures and its dynamic properties observed. Pump and probe measurements of the ultrafast change in surface reflectivity during the interaction have demonstrated that the multiple low-fluence fs pulses are crucial to the nanostructuring through the accumulation of non-thermal bonding structure change and the subsequent nanoscale ablation.

Pulsed laser ablation of Ge 2 Sb 2 Te 5 target materials at approximately 400 Pa of ambient argon gas produces amorphous nanoparticles with a size distribution of from 4 to 30 nm. Thermal treatment of the nanoparticles in their aerosol states crystallizes the particles to both a hexagonal structure and a face-centered cubic structure at 300 C, while only a face-centered cubic structure results at 400 C. The crystallized nanoparticles were then size-classified by a differential mobility analyzer to produce size-and structure-controlled Ge 2 Sb 2 Te 5 nanoparticles. The particles are revealed to consist of germanium, antimony and tellurium by composition analysis using energy dispersive X-ray spectroscopy.

We discuss the effect of ArF (λ laser =193 nm) and KrF (λ laser =248 nm) excimer laser irradiation of InP/InGaAs/InGaAsP quantum well (QW) microstructures on surface morphology of the top InP layer. The irradiation was carried out in air with lasers delivering up to 700 pulses of fluence from 82 to 142 mJ/cm 2 . We observe the formation of nano-cone structures having their period increasing from 450 to 1080 nm for KrF laser, and from 675 to 875 nm for ArF laser, in proportion to the laser fluence and pulse number. The chemical and structural modification of the laser irradiated surface has resulted in the enhancement of the QW photoluminescence emission up to 1.4 times when compared to the non-processed material. Thus, the excimer laser processing of the surface of InP capped InGaAs/InGaAsP QW microstructures using relatively low pulse fluence, has been found attractive for the fabrication of enhanced optical emission semiconductor devices.Keywords: InP/InGaAs/InGaAsP quantum well microstructures, excimer laser irradiation, surface morphology, nano-structure formation, atomic force microscopy, photoluminescence IntroductionLaser processing of semiconductor materials has attracted continuous interest due to its potential in delivering microfabrication solutions of interest for advanced photonic and electronic devices. Due to the relatively low thermal and chemical stability of III-V compound semiconductors, laser irradiation at a relatively moderate pulse fluence can alter the surface morphological, chemical and physical properties of these materials [1]. For instance, the formation of nano-cone arrays was observed on the surface of InGaAs cap of the InGaAs/InGaAsP/InP quantum well (QW) microstructure irradiated with an excimer laser [2]. Following the annealing in a rapid thermal annealing (RTA) furnace, the laser irradiated sites exhibited an enhanced photoluminescence (PL) emission from InGaAs QWs. The sub-micrometer surface features have also been observed on the surface of bulk InP [3] and diamond-like films [4] irradiated with femtosecond (fs) lasers, which illustrates that the formation of surface nanostructures does not require a strong thermal component typical of nanosecond lasers [5]. It has also been reported that the irradiation of bulk InP with a low fluence (F ≈ 80 mJ/cm 2 ) of a nanosecond UV laser (λ = 337 nm) leads to the formation of mounds and increased surface roughness of this material in proportion to the number of irradiating laser pulses [6].Excimer lasers offer wafer level processing and these tools have been successfully applied by the microelectronics industry for sub-micrometer resolution photolithography. We have been investigating the application of 308 [2], 248 [7] and 193 nm [8] excimers for surface modification and bandgap engineering of III-V quantum semiconductors. This approach is attractive for