(Color online) Illumination system (not to scale). A glass slide, in some cases coated with an APTES layer, is covered with an aqueous solution that forms silver nanoparticles upon exposure to light. A microscope objective is used to focus a 532 nm laser beam and illuminate a section of the glass–liquid interface in order to deposit silver nanoparticles on the substrate.
Particle counting masks. (a) and (b) Original SEM images processed in Gwyddion software for particle counting. (c) Mask used for the center particles generated with solution 5. The agglomerated particles are counted as one; hence, the size of the particles is overestimated. On the other hand, the area coverage is calculated correctly. (d) Mask used for the region 10 μm to the right of the center of the deposition generated with solution 6. Since the particles are small and separated, the counting and size calculation methods are reliable.
(Color online) APTES coating: APTES mixed with water reacts replacing one or more of the silicon-oxygen bonds with silicon-hydroxyl chains and protonating the ammonia group. When in contact with the glass slide, APTES reacts with the hydroxyl groups on the substrate to form a strong bond through oxygen. The protonated ammonia group attracts the newly formed silver nanoparticle since they are capped by citrate ions.
Density comparison with and without APTES coating. (a) Deposition of silver obtained by illumination of a glass–liquid interface without any coating on the glass. The image was taken on the densest region of the deposit. (b) Deposition of silver obtained by illumination of a glass–liquid interface in which the glass slide has been coated with APTES. The percentage of coverage of the substrate by the silver particles in the uncoated surface is 34% in the densest area; the coverage of the coated slide is approximately 100%.
Silver nanoparticles structure comparison. (a) Silver nanoparticles formed by an illumination of 10 W/cm2. (b) Silver nanoparticles formed by an illumination of 60 W/cm2. It can be seen that the particles formed with higher intensities are round, and the particles made with lower intensities are platelike in shape and standing vertically on the substrate.
Flat platelike structures. Particles formed at the edge of the deposition using an illumination intensity (average power density) of 60 W/cm2 for 100 s [same as Fig. 5(b) ]. The particles formed have platelike shape but, compared to the ones shown in Fig. 5 , these plates are laying flat on the substrate. Due to the nature of the Gaussian beam illumination the local intensity (local power density) forming these particles should be less than 0.3 W/cm2.
Comparison of nanoparticles deposited using the same dose. Nanoparticles found in the center of the deposition with illuminations of (a) 60 W/cm2 for 100 s, (b) 42 W/cm2 for 150 s, (c) 26 W/cm2 for 4 min, and (d) 10 W/cm2 for 10 min. The shape of the particles is a strong function of intensity, and not necessarily of total dose.
(Color online) Mapping the deposit's silver content. (a) SEM of the deposited area. (b) Map of the Ag Lα1 peak. The EDS map shows that the ring formed by platelike particles contains more silver than the other regions of the deposition.
Average diameter, diameter standard deviation (SSD), and coverage percentage for each solution measured in a region about 30 μm from the center of the deposition.
Article metrics loading...
Full text loading...