SELF-POLYMERIZATION OF NANO-FIBRES AND NANO-MEMBRANES INDUCED BY TWO-PHOTON ABSORPTION
M. Malinauskas, G. Bičkauskaitė, M. Rutkauskas, D. Paipulas, V. Purlys, and R. Gadonas
Department of Quantum Electronics and Laser Research Centre, Vilnius University, Saulėtekio 10, LT-10223 Vilnius, Lithuania
E-mail: mangirdas.malinauskas@ff.vu.lt

Received 20 December 2009; revised 8 March 2010; accepted 19 March 2010

Laser Two-Photon Polymerization (LTPP) is a technique enabling formation of 3D nanostructures in photosensitive resins with sub-wavelength resolution and unmatched flexibility. However, controllable fabrication of sub-100 nm features by this technique is still a challenge. Self-polymerization, also known as non-local polymerization, is considered to be promising in this ultra-high resolution structure formation. Recent observation of fragile self-polymerized fibres with diameter within tens of nanometres (nano-fibres) encourages the use of self-polymerization to produce nanometre scale structures other than fibres and to define the conditions for controllable fabrication. “X”-shaped polymerized supports are used as rigid structures to produce suspended self-polymerized features of different nature (shape and dimensionality) in-between the walls of “X”. By laser writing lines parallel to the substrate and perpendicular to the long symmetry axis of “X” under different conditions, self-formation of periodic nano-fibres (diameter <100 nm) and nano-membranes is induced in acrylate photopolymer AKRE37. Depending on introduced exposure dose, spatial density threshold behaviour of non-structure, nano-fibre, nano-membrane, and laser written lines is deduced. Preliminary model including laser intensity, concentration of radicals, collapse force, and distance between supports as variables having threshold effect on final self-polymerized structure’s geometry is proposed to explain non-local self-polymerization.

Keywords: femtosecond laser, multi-photon absorption polymerization, acrylate photopolymer, self-assembly, nanotechnology

DVIFOTONE SUGERTIMI INDUKUOTA NANOGIJŲ IR NANOMEMBRANŲ SAVIPOLIMERIZACIJA
M. Malinauskas, G. Bičkauskaitė, M. Rutkauskas, D. Paipulas, V. Purlys, R. Gadonas
Vilniaus universitetas, Vilnius, Lietuva

Aštriai sufokusuoto pluošto židinyje vyksta dvifotonė sugertis, kuri inicijuoja fotopolimere lokalizuotą polimerizacijos reakciją. Po ryškinimo tirpiklyje išlieka tik eksponuota medžiagos dalis, todėl galima gaminti trimates mikrostruktūras. Pastaruoju metu pastebėta gijos formos darinių savipolimerizacija. Tokios nanostruktūros savaime susidaro tarp tvirtų polimerinių atramų, kai atstumas tarp jų yra mažesnis už kritinį (D_kr ~ 1 μm). Šiame darbe tiriamas ir aiškinamas nanogijų (skersmuo <100 nm) ir nanomembranų (storis 100 nm) savipolimerizacijos reiškinys akrilatiniame fotopolimere AKRE37. Sufokusuoto femtosekundinio lazerio (80 fs, 800 nm, 80 MHz) pluoštu generuojami radikalai tarp suformuotos „X“ pavidalo atramos sienų rašant lygiagrečias linijas, kai intensyvumas yra artimas slenkstiniam polimerizacijos intensyvumui. Nustatytos sąlygos (vidutinė lazerio galia ir linijų tankis), reikalingos savaime susipolimerizavusiems dariniams (nanogijoms ir nanomembranoms) gauti. Pasiūlytas apibendrintasis modelis, nusakantis savipolimerizacijos sąlygas – lazerio šviesos intensyvumą, radikalų koncentraciją, darinio tvirtumą ir kritinį atstumą tarp atramų.