Download APL – Supplemental Material

APL – Supplemental Material
Detailed description of sample preparation
1. Electron Beam Lithography (EBL)
Due to the insulating nature of the substrate, the EBL to pattern the 250 nm thick Poly(methil methacrylate) mask (PMMA)
is performed in low vacuum with a chamber pressure of 40 Pa. Arrays of 40 lines, 500 nm wide and 200 µm long, are
exposed with an electron polarization of 30 kV and a 300 µC/cm2 dose, then developed in standard MIBK:IPA 1:3 dilution.
2. Plasma polymerization and fluorescent ptA deposition
Plasma polymerization is a well known technique in the domain of biomedical applications mainly concerning protein
immobilization or cell adhesion processes [1-2]. In this work, a plasma polymerization procedure has been explored in order
to obtain Plasma-Polymerized Acrylic Acid functional films (PPAAc) on the top of the multilayer that are 30 nm thick.
These filems expose at the surface carboxylic groups (-COOH) that can react with the amino groups (-NH2) of AlexaFluor
546 Protein A. No extra step such as the use of N-hydroxysuccinimide (NHS) and 1-ethyl-3-(3-dimethyl aminopropyl)
carbodiimide (EDC) as reaction catalyst is needed.
Plasma treatments were carried out at room temperature in a PECVD reactor made of a stainless-steel vacuum chamber with
cylindrical geometry (diameter = 320 mm; height = 200 mm), where two horizontal parallel plates of 15 cm in diameter act
as electrodes. These are placed at 4 cm far away from each other. The gas mixture (Acrylic Acid vapors and Argon) was
uniformly distributed in the reactor by the upper showerhead electrode (with pinholes diameter of 2 mm). This electrode
was externally connected to a 13.56 MHz RF power supply. Argon was used as gas carrier (flow = 20 sccm), which bubbled
into liquid Acrylic Acid in order to enhance vapors formation (Acrylic Acid Vapor Pressure = 3.1 Torr @ 20C°) that were
subsequently driven into the chamber. A function generator was used to properly vary the on/off time of the plasma
discharge. After plasma deposition, the sample has been incubated with AlexaFluor 546 Protein A 0.1mg/ml for 30 minutes
and deeply washed with phosphate buffered saline (PBS pH=7.4) and deionized water.
3. Plasma enhanced chemical vapor deposition
The 1DPC was grown in a capacitively-coupled plasma enhanced chemical vapor deposition (PECVD) system, using silane
(SiH4), ammonia (NH3) and carbon dioxide (CO2) as precursors for the incorporation of Si, N, and O respectively. For the
deposition of a-SixO1-x layers, hydrogen (H2) was used as diluter. The deposition system consisted of a cylindrically shaped
steel vacuum chamber, equipped with planar parallel electrodes of 144 cm2. The bottom electrode was connected to a 13.56
MHz radio frequency generator through a matching network, while the upper electrode, on which the substrates were
located, was grounded. The pumping system consisted of a turbomolecular and a mechanical pump in sequence, with
nominal pumping speeds of 400 l/s and 25 m3/h respectively. Before the deposition of the multilayer structure, the chamber
was evacuated to a base pressure of 10-7 mbar. The 1DPC was grown at a substrate temperature of 220 °C.
For the growth of the a-SixN1-x layers, the total gas flow was set to 75 sccm and the reactive gas flow ratio
[NH3]/([SiH4]+[NH3]) to 80%, without any hydrogen dilution. The pressure was set to 450 mTorr and the RF power density
to 20.8 mW/cm2. For the growth of the a-SixO1-x layers, the total gas flow was set to 141 sccm and the reactive gas flow
ratio [CO2]/([SiH4]+[CO2]) to 97.6%, while the hydrogen dilution [H2]/([SiH4]+[CO2]+[H2]) was set to 71%. The pressure
was set to 600 mTorr and the RF power density to 104 mW/cm2. Before deposition, the substrates were cleaned in a
ultrasonic bath for about 5 min, then rinsed in isopropyl alcohol and deionized water, and finally dried flowing dry nitrogen
on their surface.
4. Experimental details
The light source used to produce Fig. 2B is a Doric Lenses fibered high-brightness white LED. The emission spectrum
ranges from about 400 to 800 nm. The numerical aperture is 0.22. The light beam is first collimated and spatially filtered
before being directed onto the sample. The reflected light is then spatially filtered by means of a diaphragm and than
focused and injected into a collection fiber by using a low NA lens. The broadening of the angularly resolved reflectance
results from a convolution with an angular acceptance of 0.2 deg.