Biomimetic subwavelength antireflective gratings on GaAs

Chih-Hung Sun,

 

1 Brian J. Ho,1 Bin Jiang,2 and Peng Jiang1,*

OPTICS LETTERS / Vol. 33, No. 19 / October 1, 2008 p 2224-2226

Purpose of Study-

The authors developed a simple effective method in order to make a patterned surface that decreases the reflectivity of a surface.  In this manuscript they apply this method to GaAs wafers.

Methods-

Silica colloidal spheres are dispersed on a wafer using a simple spin-coating technique.  The size of the colloids can be controlled by varing the speed of the spin-coater.  In order to apply this method to GaAs surfaces, a single-layer reduction technique was employed.  Once the silica has  been deposited, a PDMS stamp is created.   Using the stamp as a mold, they are able create a template to form a patterned polymer film.

Key Findings-

• Subwavelength antireflective gratings can be easily formed on a variety of substrates.
• Silica colloids can be uniformily dispersed across a substrate, and be used to create a pattern template.

Fabrication of Thermosensitive Polymer Nanopatterns through Chemical Lithography and Atom Transfer Radical Polymerization

Qiang He, Alexander Kuller, Michael Grunze, and Junbai Li

Langmuir 2007, 23, 3981-3987

Purpose

The authors present a simple, one=step method to create a template in order to control surface-initiated polymerization to create a tunable surface.  Chemical lithography was used to create the template, and atom transfer radical polymerization (ATRP) was used to create well defined regions of polymer brushes.

Methods

A NBT SAM was formed on gold and then patterned via irradiated by electron-flood gun through a suitable mask or was written with a LEO 150 SEM with a Raith pattern generator, which results in an intralayer cross-linking and conversion of the terminal nitro groups into amino groups.  The binding of BIBB into the amino sites gives a SAM that bears surface initiator.  Exposure to an N-isopropylacrylamide (NIPAM) and the radical polymerization results in a polymer brush layer at the irradiated regions

 

Key Findings

·         Utilizing chemical lithography in conjunction with surface-initiated ATRP enables precise control of polymer growth, both spatially (tunable patterns) and vertically (polymer brush thickness).

·         The thickness of the polymer brushes can are tunable by the reaction time allotted for polymerization.

·         This technique can be applied to a variety of polymers including “smart” polymers.

·         Line, as well as, circular features can be created using this technique.

Definitions

NBT – 4’-nitro-1,1’-biphenyl-4-thiol

BIBB – bromoisobutyryl bromide

Molecular Structure Analysis in a Dip-Coated Thin Film of Poly(2-perfluorooctylethyl acrylate) by Infrared Multiple-Angle Incidence Resolution Spectrometry

Masaya Matsunaga, Toshio Suzuki, Kiyoshi Yamamoto, and Takeshi Hasegawa

 

Macromolecules 2008, 41, 5780-5784

 

Purpose of the Study

 

The authors use infrared spectroscopy to determine structural and conformational details of a polymer adsorbed to a silicon substrate.

 

Methods and Procedures

 

Polymer films were prepared via dip-coating a silicon substrate with a thin film of poly(2-perfluorooctylethyl acrylate).  The samples were subjugates to infrared-multiple angle incidence resolution spectrometry (IR-MAIRS).  For comparison, the x-ray diffraction pattern of poly(2-perfluorooctylethyl acrylate) powder was also collected.  Using the diffraction patterns, infrared spectra, and appropriate models, the polymer structure and confirmation on the surface can be determined.

 

Key Results

 

• Infrared Spectroscopy can be used to determine structural and conformational properties of non-crystalline materials.
• Using IR-MAIRS, both transmittance and reflective-absorbance IR spectra can be collected on the same sample; thus, taking advantage of selectively observed parallel and normal vibrations ,respectively.
• The poly(2-perfluorooctylethyl acrylate) films investigated are oriented with the perfluoronated side-chains, with a length of 1.6 nm) normal to the surface.  The tilt angle of the carbonyl group is ~37^o.

Networked Gold-Nanoparticle Coatings on Polyethylene: Charge Transport and Strain Sensitivity

Tobias Vossmeyer,* Carsten Stolte, Michael Ijeh, Andreas Kornowski, and Horst Weller

 

Adv. Funct. Mater.  2008, 18, 1611-1616.

 

Purpose of Study

 

Gold nanoparticles assembled into a matrix using dithiol chemistry have potential applications in strain sensing.  The authors want to determine the effects of mechanical strain on the electrical response of layered gold nanoparticles tethered using a dithiol ligand using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electrical conductivity measurements.

 

Methods

 

Gold nanoparticles modified with 1,9 nonanedithiol ligands were deposited onto a functionalized low density polyethylene (LDPE) substrate.  Charge transport properties were measured at varying temperatures of the LDPE/Au samples.  The thermal expansion of the polyethylene film induced a mechanical strain on the gold nanoparticles.  Topography of the LDPE/Au layers were characterized using SEM and TEM images.

 

Key Findings

 

• Gold nanoparticles can be deposited layer-by-layer via self-assembly onto oxidized LDPE.
• Results are consistent with previously reported values for gold nanoparticles on other substrates.
• The relaxation and expansion response of the gold nanoparticles to strain cycling is fully reversible and reproducible under the conditions of the experiment with a guage sensitivity factor of 11-20.