6 research outputs found
Optical Trapping-Formed Colloidal Assembly with Horns Extended to the Outside of a Focus through Light Propagation
We
report optical trapping and assembling of colloidal particles at a
glass/solution interface with a tightly focused laser beam of high
intensity. It is generally believed that the particles are gathered
only in an irradiated area where optical force is exerted on the particles
by laser beam. Here we demonstrate that, the propagation of trapping
laser from the focus to the outside of the formed assembly leads to
expansion of the assembly much larger than the irradiated area with
sticking out rows of linearly aligned particles like horns. The shape
of the assembly, its structure, and the number of horns can be controlled
by laser polarization. Optical trapping study utilizing the light
propagation will open a new avenue for assembling and crystallizing
quantum dots, metal nanoparticles, molecular clusters, proteins, and
DNA
Optical Trapping-Formed Colloidal Assembly with Horns Extended to the Outside of a Focus through Light Propagation
We
report optical trapping and assembling of colloidal particles at a
glass/solution interface with a tightly focused laser beam of high
intensity. It is generally believed that the particles are gathered
only in an irradiated area where optical force is exerted on the particles
by laser beam. Here we demonstrate that, the propagation of trapping
laser from the focus to the outside of the formed assembly leads to
expansion of the assembly much larger than the irradiated area with
sticking out rows of linearly aligned particles like horns. The shape
of the assembly, its structure, and the number of horns can be controlled
by laser polarization. Optical trapping study utilizing the light
propagation will open a new avenue for assembling and crystallizing
quantum dots, metal nanoparticles, molecular clusters, proteins, and
DNA
Optical Trapping-Formed Colloidal Assembly with Horns Extended to the Outside of a Focus through Light Propagation
We
report optical trapping and assembling of colloidal particles at a
glass/solution interface with a tightly focused laser beam of high
intensity. It is generally believed that the particles are gathered
only in an irradiated area where optical force is exerted on the particles
by laser beam. Here we demonstrate that, the propagation of trapping
laser from the focus to the outside of the formed assembly leads to
expansion of the assembly much larger than the irradiated area with
sticking out rows of linearly aligned particles like horns. The shape
of the assembly, its structure, and the number of horns can be controlled
by laser polarization. Optical trapping study utilizing the light
propagation will open a new avenue for assembling and crystallizing
quantum dots, metal nanoparticles, molecular clusters, proteins, and
DNA
Reflection Microspectroscopic Study of Laser Trapping Assembling of Polystyrene Nanoparticles at Air/Solution Interface
We present the formation of a single
nanoparticle assembly with
periodic array structure induced by laser trapping of 200 nm polystyrene
nanoparticles at air/solution interface of the colloidal heavy water
solution. Their trapping and assembling behavior is observed by monitoring
transmission and backscattering images and measuring reflection spectra
under a microscope. Upon the laser irradiation into the solution surface
layer, nanoparticles are gathered at and around the focal spot, and
eventually a nanoparticle assembly with the size much larger than
the focal volume is formed. The assembly gives structural color in
visible range under halogen lamp illumination, indicating that constituent
nanoparticles are periodically arrayed. Reflection spectra of the
assembly show a reflection band, and its peak position is gradually
shifted to short wavelength and the bandwidth becomes narrow with
time, depending on the distance from the focal spot. After the laser
is switched off, red-shift is observed in the reflection band. These
results indicate that nanoparticles are rearranged into a densely
packed periodic array during laser irradiation and diffused out to
the surrounding solution after turning off the laser. These dynamics
are discussed from the viewpoints of the attractive optical trapping
force and the electrostatic repulsive force among nanoparticles
Reflection Microspectroscopic Study of Laser Trapping Assembling of Polystyrene Nanoparticles at Air/Solution Interface
We present the formation of a single
nanoparticle assembly with
periodic array structure induced by laser trapping of 200 nm polystyrene
nanoparticles at air/solution interface of the colloidal heavy water
solution. Their trapping and assembling behavior is observed by monitoring
transmission and backscattering images and measuring reflection spectra
under a microscope. Upon the laser irradiation into the solution surface
layer, nanoparticles are gathered at and around the focal spot, and
eventually a nanoparticle assembly with the size much larger than
the focal volume is formed. The assembly gives structural color in
visible range under halogen lamp illumination, indicating that constituent
nanoparticles are periodically arrayed. Reflection spectra of the
assembly show a reflection band, and its peak position is gradually
shifted to short wavelength and the bandwidth becomes narrow with
time, depending on the distance from the focal spot. After the laser
is switched off, red-shift is observed in the reflection band. These
results indicate that nanoparticles are rearranged into a densely
packed periodic array during laser irradiation and diffused out to
the surrounding solution after turning off the laser. These dynamics
are discussed from the viewpoints of the attractive optical trapping
force and the electrostatic repulsive force among nanoparticles
Optically Evolved Assembly Formation in Laser Trapping of Polystyrene Nanoparticles at Solution Surface
Assembling
dynamics of polystyrene nanoparticles by optical trapping
is studied with utilizing transmission/reflection microscopy and reflection
microspectroscopy. A single nanoparticle assembly with periodic structure
is formed upon the focused laser irradiation at solution surface layer
and continuously grows up to a steady state within few minutes. By
controlling nanoparticle and salt concentrations in the colloidal
solution, the assembling behavior is obviously changed. In the high
concentration of nanoparticles, the assembly formation exhibits fast
growth, gives large saturation size, and leads to dense packing structure.
In the presence of salt, one assembly with the elongated aggregates
was generated from the focal spot and 1064 nm trapping light was scattered
outwardly with directions, while a small circular assembly and symmetrical
expansion of the 1064 nm light were found without salt. The present
nanoparticle assembling in optical trapping is driven through multiple
scattering in gathered nanoparticles and directional scattering along
the elongated aggregates derived from optical association of nanoparticles,
which dynamic phenomenon is called optically evolved assembling. Repetitive
trapping and release processes of nanoparticles between the assembly
and the surrounding solution always proceed, and the steady state
at the circular assembly formed by laser trapping is determined under
optical and chemical equilibrium