Zn and ZnO nanoparticles were produced by a pulsed Nd:YAG laser ablation method in the absence of any surfactants and/or catalysts in deionized (DI) water via pulsed laser ablation in liquid (PLAL). In this paper, we present direct evidence for the production of Zn(II) ions induced from the plasma plume during the process of PLAL for the first time. Investigation of the absorption and emission spectra of zinc tetra(p-sulfonatophenyl) porphyrin (ZnTSPP) formed via the laser ablation on a Zn metal plate in TSPP solution showed a significant fluorescence quenching of ZnTSPP. This fluorescence quenching of ZnTSPP was further investigated with an aid of theoretical calculations. Based on these experimental and theoretical results, a plausible mechanism for the production of Zn and ZnO nanoparticles is proposed.

The rutile-type TiO2 powders originally whitish and micrometer in size were successfully reduced in size with accompanied structure, composition and optical property change to become dark bluish by pulsed laser ablation in liquid under 532 nm excitation and 400 mJ per pulse at a specified water depth (5 or 15 mm) for up to 30 min. Transmission electron microscopic observations indicated the newly formed anatase nanoparticles are ca. 5 nm in size with spindle-like shape having well-developed {101} faces and -(001) facets for mutual coalescence into unity. The -(001)-specific coalescence twin of anatase was also observed. There are also amorphous nanoparticles in association with anatase, minor brookite and relic rutile with 2 x (110) superstructure. The resultant colloidal TiO2 nanoparticles are (Ti3+, Ti2+, H+) co-signified according to optical spectroscopic results and have a bimodal minimum band gaps 3.12 and 2.66 eV due to nanocrystals and amorphous phase, respectively, for potential optocatalytic applications in UV-visible range.

Pulsed laser ablation on an Al target in water spiked with 0.05 and 1 M NaOH was employed to fabricate epitaxial β-NaAlO 2 and γ-Al 2 O 3 nanoparticles for X-ray diffraction and electron microscopic and spectroscopic characterizations. A higher NaOH concentration in the pulsed laser ablation in liquid (PLAL) process caused a higher content of NaAlO 2 3 4/5H 2 O and β-NaAlO 2 besides the predominant γ-Al 2 O 3 nanoparticles. Upon settling on the silica substrate at room temperature, the NaAlO 2 3 4/5H 2 O tended to develop as micrometer sized plates for the sample fabricated under a relatively low (i.e., 0.05 M) NaOH concentration. However, the crystal structures, d-spacings, mismatch strain, and morphology of the coexisting phases are almost the same for the samples fabricated under different NaOH concentrations. The β-NaAlO 2 phase (denoted as N), presumably derived from NaAlO 2 3 5/4H 2 O, was found to form intimate intergrowth with the defective γ-Al 2 O 3 following the crystallographic relationship (011) γ //(110) N ; [111] γ //[001] N and alternatively (101) γ //(110) N ; [141] γ // [001] N . The epitaxial composite phases have a significant internal compressive stress, (OH -, Na þ ) cosignature, and a mixed charge state of Al þ , Al 2þ , and Al 3þ and hence a smaller band gap (ca. 5.3 eV) for potential applications in the UV region.

Nanosized (5 to 10 nm) amorphous and crystalline nanocondensates, i.e., metallic α-phase of Zn-Cu alloy in face-centered cubic structure and (Zn,H)-codoped cuprite (Cu2O) with high-pressure-favored close-packed sublattice, were formed by pulsed laser ablation on bulk Cu65Zn35 in water and characterized by X-ray/electron diffractions and optical spectroscopy. The as-fabricated hybrid nanocondensates are darkish and showed photoluminescence in the whole visible region. Further dwelling of such nanocondensates in water caused progressive formation of a rice-like assembly of (Zn,H)-codoped tenorite (CuO) nanoparticles with (001), (100), and {111} preferred orientations, (111) tilt boundary, yellowish color, and minimum bandgap narrowing down to ca. 2.7 eV for potential photocatalytic applications.

No abstract

The properties of two-dimensional (2D) materials are readily affected by their surroundings. Therefore, the underlying substrates and surrounding materials always disturb the pristine properties of 2D materials. Herein, we describe how the pristine properties of suspended 2D materials can be precisely extracted from Raman and photoluminescence (PL) spectra with great signal enhancements by taking advantage of both air gap suspension and nanocavity enhancement effects. The modes of the Raman emission lines were enhanced to almost the same degree when the 2D materials were positioned over the nanocavity: the 2D/G peaks of suspended single-layer graphene (SLG) and the E 1 2g /A 1g peaks of MoS 2 were significantly enhanced almost equally. Moreover, recording Raman and PL spectra at different positions of the suspended 2D materials was a very powerful tool for observing charge transfer between the pristine 2D materials and the surrounding materials. We also found that the residual holes of the suspended SLG could be neutralized by aluminum (Al) at certain positions. By employing the air cavity structure, we could readily locate the charge neutrality point of the suspended 2D materials. In addition, the PL intensity of MoS 2 could be greatly enhanced when using the same nanocavity. The great enhancements in the PL signals from the suspended 2D materials allowed us to further investigate the spectral weights of both the A 0 exciton and A − trion peaks when MoS 2 was suspended or supported upon various metal films. This approach may open up new doors for techniques allowing precise characterization of abundant information from pristine and suspended 2D materials.

No abstract

No abstract