Prism coupling technique investigation of elasto-optical properties of thin polymer films

Ay, F.; Kocabas, Askin; Kocabaş, Coşkun; Aydınlı, Atilla; agan, S.

doi:10.1063/1.1812823

Cited by 55 publications

(24 citation statements)

References 32 publications

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“…Birefringence measurements of spun coat and annealed PS films (150 kg=mol, 2:3 m) have established out-ofplane alignment on oxide coated wafers [16]. Additional studies have shown that the thermal conductivity of polymer microscale films can increase by a factor 4-8 in the direction of alignment [14].…”

Section: Prl 106 175501 (2011) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 99%

Experimental Verification of the Formation Mechanism for Pillar Arrays in Nanofilms Subject to Large Thermal Gradients

2011

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The free surface of molten nanofilms is known to undergo spontaneous formation of periodic protrusions when exposed to a large transverse thermal gradient. Early time measurements of the array pitch and growth rate in polymer melts confirm a formation process based on a long wavelength thermocapillary instability and not electrostatic attraction or acoustic phonon driven growth as previously believed. We find excellent agreement with theoretical predictions provided the nanofilm out-of-plane thermal conductivity is several times larger than bulk, an enhancement suggestive of polymer chain alignment. DOI: 10.1103/PhysRevLett.106.175501 PACS numbers: 81.16.Dn, 47.55.nb, 66.70.Hk, 68.35.bm For the past decade, researchers have been exploring the effects of large thermal gradients on molten nanofilms in the hope of harnessing pillar instabilities for generating microarrays [1][2][3][4]. When the free surface of a molten nanofilm is exposed to large thermal gradients, periodic protrusions form and grow toward the cooler target until contact is achieved. There is significant interest in this phenomenon since external field gradients can be used to generate three dimensional nanostructures directly from the melt, which after solidification exhibit ultra smooth surfaces befitting the most demanding optical applications. Controlled growth of desired shapes, however, requires identification of the dominant growth mechanism, the material and geometric properties affecting structure formation, and the principles that establish the minimum feature size.Three different mechanisms have been proposed as the source of instability: electrostatic attraction from surface induced charge between the film and overlying substrate (SC model [2,5]), internal film pressure caused by interfacial reflections of low frequency acoustic phonons (AP model [3,6]), and thermocapillary flow from temperature variations along the interface which draw fluid toward cooler regions (TC model [7,8]). The first two mechanisms rely on properties specific to polymeric films. The thermocapillary mechanism is applicable to any liquid nanofilmit represents an extreme limit of (Bénard) Marangoni instability for long wavelength fluctuations in which gravitational effects are absent and thermocapillary forces overcome stabilization by capillary forces. Previous experimental investigations have confronted limitations imposed by the typical setup shown in Fig. 1(a), namely, no direct measure of the thermal gradient within the narrow gap, lack of parallelism between opposing substrates, and lack of visualization during structure formation and growth. In fact, all measurements to date have relied on solidified formations resulting from prolonged contact with the cooler target.We find that physical contact with the overlying substrate results in smaller wavelengths from fluid reorganization. While this ultimately reduces the array pitch, it compromises direct comparison to models based on linear stability analysis, which also require amplitude fluctuations small i...

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Section: Prl 106 175501 (2011) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 99%

Experimental Verification of the Formation Mechanism for Pillar Arrays in Nanofilms Subject to Large Thermal Gradients

2011

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“…24 The deviation is of the order of 10 −4 and depends on the viscoelastic properties of the polymer. 25 Shorter wavelengths can support higher numbers of modes than the longer ones.…”

Section: Resultsmentioning

confidence: 99%

Polarization-dependent optical characterization of poly(phenylquinoxaline) thin films

Ksianzou¹,

Velagapudi²,

Grimm³

et al. 2006

Journal of Applied Physics

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Linear optical properties of two types of poly͑phenylquinoxaline͒ ͑PPQ͒ are studied by multiwavelength prism coupling technique and optical absorption spectroscopy. Surface roughness measurements are done using atomic force microscopy. PPQs form smooth films of high optical quality having refractive indices above 1.7 in the visible and near infrared spectral ranges. Enhanced birefringence of ⌬n ϳ 0.04 has been observed in both PPQ films prepared by spin coating. Sellmeier coefficients are derived for the wavelength range starting from 0.532 to 1.064 m for both TE and TM polarizations. Quantum chemical calculations both on the semiempirical and on the ab initio level are carried out in order to calculate the first-order molecular polarizability tensors of the polymer repeat units. From the obtained tensor elements, theoretical values for both the average refractive indices and the maximum expectable birefringence are calculated. Based on these values a more detailed interpretation of the experimental findings is carried out. The dispersion of refractive index is quantified by the value of Abbe's constant ͑ d ͒. In our case the value d Ϸ 11 indicates high dispersion in the visible spectral range. The imaginary part k of the complex refractive index n * = n − ik reaches values of k ഛ 10 −3 in the wavelength range from 0.5 to 1 m.

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“…This eliminates the possibility of stress induced artefacts in the measurement of refractive indices. This is especially important in the refractive index measurements of soft materials such as some polymers [2]. We applied this technique to measure the refractive index of SiON slab waveguides with a precision of the order of 10 −4 .…”

Section: Discussionmentioning

confidence: 99%

“…In the prism coupling approach, adjustment of the gap between the prism and the waveguide is critical and requires significant pressure, with the associated possibility of damage to the waveguide or the prism [1,2]. Also, the bulky nature of the prism makes it unsuitable for applications in integrated devices.…”

Section: Introductionmentioning

confidence: 99%

An elastomeric grating coupler

Kocabas¹,

Ay²,

Dâna³

et al. 2005

J. Opt. A: Pure Appl. Opt.

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We report on a novel nondestructive and reversible method for coupling free space light to planar optical waveguides. In this method, an elastomeric grating is used to produce an effective refractive index modulation on the surface of the optical waveguide. The external elastomeric grating binds to the surface of the waveguide with van der Waals forces and makes conformal contact without any applied pressure. As a demonstration of the feasibility of the approach, we use it to measure the refractive index of a silicon oxynitride film. This technique is nondestructive, reversible, low cost and can easily be applied to the characterization of optical materials for integrated optics.

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Prism coupling technique investigation of elasto-optical properties of thin polymer films

Cited by 55 publications

References 32 publications

Experimental Verification of the Formation Mechanism for Pillar Arrays in Nanofilms Subject to Large Thermal Gradients

Experimental Verification of the Formation Mechanism for Pillar Arrays in Nanofilms Subject to Large Thermal Gradients

Polarization-dependent optical characterization of poly(phenylquinoxaline) thin films

An elastomeric grating coupler

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