Thin films for transparent electronic devices

Isocyanate functionalized graphene / P3HT based nanocomposites for electronic devices

We developed a method for the preparation of isocyanate functionalized graphene -regioregular poly 3-hexyl tiophene (rr-P3HT) nanocomposites is presented. Graphite oxide preparedby the Hummer's method and half blocked tetrametyl xylylene isocyanate (Et-TMXDI) are the precursors for the new obtained isocyanate functionalized graphene. Fourier transform infrared spectroscopy, UV-Vis spectroscopy, X-ray diffraction, Atomic force microscopy, Scaning electron microscopy and Raman spectroscopy were used to characterize the functionalized graphene. The isocyanate functionalized graphene facilitates the self-assembling of P3HT polymer in highly oriented nanowires.Thin films of functionalized graphene - rrP3HT nanocomposites obtained by spinning and  dip coating processes were investigated and used for organic field effect transistors (OFETs).

IRGO improve p-p stacking of P3HT nanowires

AFM images (topography) of diluted chloroform/dichlorbenzene solution of IRGO/P3HT deposited on Si substrate; P3HT nanowires have a radial orientation with center in IRGO flake

• Solution processable isocyanate functionalized graphene/P3HT nanocomposites are useful for spinning and dip coating processes.
• IRGO/P3HT nanocomposites materials exhibit good dispersability and high storage stability.
• The fabrication process is simple and compatible with silicon technology.
• The IRGO improve p- p stacking of P3HT nanowires leading an improvement of mobility

increase of the mobility: 0.02 cm2V-1s-1 / P3HT based OFETs  à 0.1 cm2V-1s-1 /IRGO-P3HT based OFETs

PN II project (2009-2011) -Program Ideas „Multifunctional molecular architectures for organic electronics and nanotechnology- theoretical and experimental studies”. Contract No. 617/2009

The nanocomposites have been  obtained from commercial polymers (PMMA, PVA) and dopants: metal (Ag), metal oxide nanoparticles (TiO2, ZrO2) or organic materials (Rhodamine, Alq3) by chemical routes and sol-gel processes. The optical properties of these materials depend on the   composition, metal/oxide concentration, particle size and dispersion homogeneity. Micro/nano pattering techniques based on combination of electron beam lithography and replication techniques have been developed to obtain structures with applications in micro-optics.

	XTEM image of PMMA-TiO2 film (dTiO2 = 5-10 nm). TiO2 nanoparticles are uniform dispersed in the film.
Dispersion of the refractive index    of PMMA-TiO2 film
Real and imaginary refractive index of Ag – PVA film
XTEM  images of Ag-PVA  film (d Ag =  5 - 30 nm)
Dispersion of the refractive index    of dye doped PMMA films	Surface plasmon enhanced emission from RhB doped PMMA/Au strips at l=600 nm (excitation with l=530 nm) - application in biosensing and OLEDs

PN II Project (2007-2010), “Development of soft lithography techniques for micro and nano-photonics” – LISOFT.
PN II project (2009-2011-Program Ideas „Multifunctional molecular architectures for organic electronics and nanotechnology- theoretical and experimental studies”. Contract No. 617/2009
Contact person: Dr. Paula Obreja

3D Electron beam lithography in for μ- and n-optics

3D-profile structures with feature size in the submicron range, for applications in photonics (photonic crystals, optical waveguides, and holograms) were obtained by EBL in multi-layer resist systems. If the polymers that compose the multi-layers have different charge sensitivity and/or different dissolution rate, the remaining structure after exposure and development will have a 3D profile. T-shape and suspended structures can be obtained in by-layer systems PMMA950K /PMMA495K  PMMA 950K/LOR and /PMMA950K/ PMMA35K. The exposure parameters and the development process were optimized and calibrated for each type of structures.

IMT core program Convert- project PN 09 29 02 05- cooperation with Microphysical characterization laboratory (EBL,SEM).

This technique is versatile, inexpensive and can transfer patterns into functional materials and onto a number of surfaces. Replica molding was used to replicate:

• micro-optical components with different feature size (dots, rectangular structures, pillars, optical resonators);
•  components for micro-fluidic applications;
•  to generate nano-components in polymers with 30-100 nm resolution.

PN II Project (2007-2010), “Development of soft lithography techniques for micro and nano-photonics” - LISOFT.
Contact person: Dr. Paula Obreja

Transparent Thin Film Transistors (TTFT )  on quartz substrate  using as active channel n-ZnO and  as gate dielectric SiO

Graphene/P3HT based OFET

Substrate (gate): high coductivity Si Gate dielectric:  SiO2 300nm-thick Interdigitated gold electrodes for drain and source (bottom contact configuration). Active layer : spin-coating IRGO-P3HT solution in chloroform DCB in glove box under N2 athmosphere + annealing  (160oC for 15 minutes in the oven under nitrogen).
Examples of plots of the square root of saturation source-drain current as a function of the gate voltage VGS for FETs based on P3HT and P3HT–IRGO nanocomposite: (a) FET with IDT electrodes, L= 8 μm, W=72.75 mm; (b) FET with L=30 μm, W = 3mm. Net photocurrent (Iph= IDS(light)-IDS(dark)) under illumination((VGS=-20V):
DUV R~9 mA/W / l= 240 nm	White light

PN II project (2009-2011) -Program Ideas „Multifunctional molecular architectures for organic electronics and nanotechnology- theoretical and experimental studies”. Contract No. 617/2009

Dye laser with Bragg grating on Rh6G doped PMMA