Polystyrene Nanosphere Array Research Articles

Fabrication and Optical Properties of Au-Coated Polystyrene Nanosphere Arrays with Controlled Gaps

Large area monolayer of self-assembled polystyrene sphere (PS) arrays were formed by an interface self-assembly method and the gap of PS was adjusted by O2 plasma treatment (OPT). After different duration of OPT, the spacing between the PSs varied from 5 to 88 nm. Then, 20 nm Au film was deposited on the PS arrays by electron beam deposition. The absorption peaks of Au-coated PS array red-shifted obviously by changing the gap of PS. The new absorption peaks emerged when the gap of the PS decreased to about 20 nm. The surface plasmon resonance (SPR) was employed to explain the absorption proportion of this Au-PS structure. These micro-nano structures exhibit tunable SPR bands, which may be useful to the applications in some research fields, such as biosensing, single molecule detection, and novel optoelectronic devices.

Irregular shaping of polystyrene nanosphere array by plasma etching

The morphology of nanospheres is crucial for designing the nanofabrication in the nanosphere lithography. Here, by plasma etching, the controllable tailoring of the nanosphere is realized and its morphology dependence on the initial shape, microscopic roughness, and the etching conditions is investigated quantitatively. The results show that the shape evolution strongly depends on the etching gas, power, and process duration. Particularly, the aspect ratio (diameter/height) significantly increases with violent etching, turning the spherical shape into tiny ellipsoidal nanoparticles. The findings are practical to the protocol of non-uniform etching of nanoobjects and provide the useful design tool for the device fabrication at nanoscale.

Enhanced light output from light emitting diodes with two-dimensional cone-shape nanostructured surface

A simple, inexpensive and high throughput approach for creating two-dimensional cone-shaped nanostructures is reported. A self-assembled array of polystyrene nanospheres is employed as the primary mask to fabricate such structures on AlGaInP red light emitting diodes, resulting in over two times increase of light output power. An orderly array of cones show higher intensity emitted in the forward direction than one that is randomly arranged.

Tailoring the perpendicular exchange bias in [Pt/Co/CoO]n multilayer by tensile stress on curved substrate

The effects of the tensile stress on exchange bias of [Pt/Co/CoO]n multilayer are investigated by depositing the magnetic film onto the ordered curved substrate composed of a polystyrene nanosphere monolayer film. The square ratio of the loop decreases first and increases then with the reduction of tensile stress when the nanosphere size increases. The square ratio and exchange bias field are enhanced significantly when 60 nm polystyrene nanosphere arrays are chosen as the substrate, which is ascribed to the increased interfacial uncompensated antiferromagnetic spins created by the periodical knots between neighbor spheres and the formation of the entire domain wall. In addition, the easy axis of [Pt/Co/CoO]n multilayer is tailored when the CoO sublayer thickness changes, which is due to the gradual development of a tilted anisotropy. When CoO is 1.9 and 2.6 nm, the exchange coupling with tilted magnetic easy axis is obtained in the 45° direction.

Perpendicular exchange bias of [Pt/Co]n/CoO multilayer on ordered nanosphere arrays

Polystyrene nanosphere arrays are used as the substrate for [Pt/Co]nCoO multilayer deposition. The effects of nanosphere size and CoO thicknesses on the magnetic properties of [Pt/Co]nCoO multilayer nanocaps are investigated. With decreasing nanosphere diameter, the nanocaps exhibit systematic variations of coercivity, exchange bias field, and switching field distribution. The switching field distribution is broadened and the coercivity is enhanced when the nanosphere sizes decrease, which are ascribed to the magnetic dipole-dipole interaction of the isolated nanocaps when the thickness of multilayer is far below the nanosphere radius. The mixture formation and the anisotropy direction changes of Co and CoO interface play an important role in the variation of the exchange bias field when the multilayer film is deposited on the nanosphere with diameter of 60 nm.

Nonlinear dependence between the surface reflectance and the duty-cycle of semiconductor nanorod array

The nonlinear dependence between the duty-cycle of semiconductor nanorod array and its surface reflectance minimization is demonstrated. The duty-cycle control on thin-SiO2 covered Si nanorod array is performed by O(2-) plasma pre-etching the self-assembled polystyrene nanosphere array mask with area density of 4 × 10(8) rod/cm(-2). The 120-nm high SiO2 covered Si nanorod array is obtained after subsequent CF4/O2 plasma etching for 160 sec. This results in a tunable nanorod diameter from 445 to 285 nm after etching from 30 to 80 sec, corresponding to a varying nanorod duty-cycle from 89% to 57%. The TM-mode reflection analysis shows a diminishing Brewster angle shifted from 71° to 54° with increasing nanorod duty-cycle from 57% to 89% at 532 nm. The greatly reduced small-angle reflectance reveals a nonlinear trend with enlarging duty-cycle, leading to a minimum surface reflectance at nanorod duty-cycle of 85%. Both the simulation and experiment indicate that such a surface reflectance minimum is even lower than that of a uniformly SiO2 covered Si substrate on account of its periodical nanorod array architecture with tuned duty-cycle.

Mapping the SERS Efficiency and Hot-Spots Localization on Gold Film over Nanospheres Substrates

Noble metal films deposited over two-dimensional arrays of polystyrene nanospheres constitute a confirmed class of efficient and cost-effective substrates for surface enhanced Raman scattering (SERS). In this paper, we perform scanning confocal SERS microscopy to investigate the spatial (lateral) variations of the SERS enhancements on gold films over nanospheres (AuFoN) substrates. By constructing SERS imaging maps with a resolution down to the diffraction limit, the local SERS efficiency is found to vary on two different scales. First, the local SERS efficiency is periodically modulated (intensity ratios of 2−3) by the periodic AuFoN surface topography (as demonstrated by correlation with atomic force microscopy imaging of the same sample area); second, randomly distributed SERS hot-spots are observed, at which the SERS intensity is 1 to 2 orders of magnitude larger than at adjacent regions. Furthermore, these hot-spots exhibit fluctuating behavior, characteristic of single-molecule SERS sensitivity. The...

Improved deposition of large scale ordered nanosphere monolayers via liquid surface self-assembly

An improvement to the method of creating close-packed polystyrene nanosphere arrays on silicon via liquid surface self-assembly has been attained via modification of the deposition technique. This modification facilitates consistent and large area deposition of high quality close-packed polystyrene nanosphere monolayers on silicon substrates that was achieved in this work. This technique has the potential to be used for photonics applications such as creating low cost, large area antireflective surfaces in solar cells.

Convective assembly of two-dimensional nanosphere lithographic masks

We report the implementation in our laboratory of a simple variant device to control the convective assembly of colloidal particles on solid substrate. The device allows the control over the volume of solution, rate of withdrawal, height of the deposition plate relative to the substrate and the portion of the substrate to be covered with solution. Ordered array of polystyrene nanospheres of 450 nm diameter were successfully deposited on glass and used as reliable lithographic masks.

Reply to “Comment on ‘Size-dependent scaling of perpendicular exchange bias in magnetic nanostructures’ ”

Our observation of size-dependent scaling effects at room temperature in exchange-biased multilayers grown onto arrays of polystyrene nanospheres [Phys. Rev. B 75, 012413 (2007)] does not conflict with the observation by Baltz et al. of a crossover to thermally activated spin reversal in the antiferromagnetic layer upon patterning [Phys. Rev. Lett. 94, 117201 (2005)]. We mention a few dissimilarities between the two systems that might account for a different behavior at room temperature.

Gold Films Deposited over Regular Arrays of Polystyrene Nanospheres as Highly Effective SERS Substrates from Visible to NIR

Gold nanostructured films of various thicknesses (15, 30, and 60 nm) are deposited over regular arrays of polystyrene nanospheres in an attempt to evaluate their potential as SERS-active substrates. Atomic force microscopy is used to topographically characterize the substrates as well as to ensure the thickness of the deposited gold films. The optical response of the prepared substrates recommends their use in SERS experiments with multiple laser lines from visible and NIR spectral domains. The assessment of the substrates' SERS activity is performed by using the 532, 633, and 830 nm excitation lines and different average enhancement factor (EF) values are obtained depending on the film thickness and employed laser line. The 60 nm gold nanostructured film generates the greatest local electromagnetic field confinement under NIR excitation and consequently gives rise to maximum SERS enhancement. The large tunability of surface plasmon excitation combined with the advantage of relatively high exhibited average EF values obtained under NIR excitation recommends these substrates as outstanding candidates for upcoming investigations of biological relevant molecules.

Fabrication of Size-Tunable Gold Nanoparticles Array with Nanosphere Lithography, Reactive Ion Etching, and Thermal Annealing

Two-dimensional ordered arrays of gold (Au) nanoparticles were fabricated using two different variants of the nanosphere lithography technique. First, ordered arrays of polystyrene nanospheres on Si substrate were used as deposition masks through which gold films were deposited by electron beam evaporation. After the removal of the nanospheres, an array of triangular Au nanodisks was left on the Si substrate. After thermal annealing at increasing temperature, systematic shape transition of the nanostructures from original triangular Au nanodisks to rounded nanoparticles was observed. This approach allows us to systematically vary the size and morphology of the particles. In the second and novel technique, we made use of reactive ion etching to simultaneously reduce the dimension of the masking nanospheres and create arrays of nanopores on the substrate prior to the deposition of the Au films. These samples were subsequently annealed, which resulted in size-tunable and ordered Au nanoparticle arrays with the nanoparticles nested in the nanopores of the templated substrate. With the nanoparticles anchored in the nanopores, the substrate could be useful as a template for growth of other nanomaterials.