TY - JOUR A1 - Yadavalli, Nataraja Sekhar A1 - Linde, Felix A1 - Kopyshev, Alexey A1 - Santer, Svetlana T1 - Soft matter beats hard matter - rupturing of thin metallic films induced by mass transport in photosensitive polymer films JF - ACS applied materials & interfaces N2 - The interface between thin films of metal and polymer materials play a significant role in modern flexible microelectronics viz., metal contacts on polymer substrates, printed electronics and prosthetic devices. The major emphasis in metal polymer interface is on studying how the externally applied stress in the polymer substrate leads to the deformation and cracks in metal film and vice versa. Usually, the deformation process involves strains varying over large lateral dimensions because of excessive stress at local imperfections. Here we show that the seemingly random phenomena at macroscopic scales can be rendered rather controllable at submicrometer length scales. Recently, we have created a metal polymer interface system with strains varying over periods of several hundred nanometers. This was achieved by exploiting the formation of surface relief grating (SRG) within the azobenzene containing photosensitive polymer film upon irradiation with light interference pattern. Up to a thickness of 60 nm, the adsorbed metal film adapts neatly to the forming relief, until it ultimately ruptures into an array of stripes by formation of highly regular and uniform cracks along the maxima and minima of the polymer topography. This surprising phenomenon has far-reaching implications. This is the first time a direct probe is available to estimate the forces emerging in SRG formation in glassy polymers. Furthermore, crack formation in thin metal films can be studied literally in slow motion, which could lead to substantial improvements in the design process of flexible electronics. Finally, cracks are produced uniformly and at high density, contrary to common sense. This could offer new strategies for precise nanofabrication procedures mechanical in character. KW - metal/polymer interface KW - rupturing of metal film KW - forces generated during surface relief grating formation KW - in situ atomic force microscopy KW - azobenzene KW - two beam interferometry Y1 - 2013 U6 - https://doi.org/10.1021/am4006132w SN - 1944-8244 VL - 5 IS - 16 SP - 7743 EP - 7747 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Yadavalli, Nataraja Sekhar A1 - Korolkov, Denis A1 - Moulin, Jean-Francois A1 - Krutyeva, Margarita A1 - Santer, Svetlana T1 - Probing opto-mechanical stresses within azobenzene-containing photosensitive polymer films by a thin metal film placed above JF - ACS applied materials & interfaces N2 - Azo-modified photosensitive polymers offer the interesting possibility to reshape bulk polymers and thin films by UV-irradiation while being in the solid glassy state. The polymer undergoes considerable mass transport under irradiation with a light interference pattern resulting in the formation of surface relief grating (SRG). The forces inscribing this SRG pattern into a thin film are hard to assess experimentally directly. In the current study, we are proposing a method to probe opto-mechanical stresses within polymer films by characterizing the mechanical response of thin metal films (10 nm) deposited on the photosensitive polymer. During irradiation, the metal film not only deforms along with the SRG formation but ruptures in a regular and complex manner. The morphology of the cracks differs strongly depending on the electrical field distribution in the interference pattern, even when the magnitude and the kinetics of the strain are kept constant. This implies a complex local distribution of the opto-mechanical stress along the topography grating. In addition, the neutron reflectivity measurements of the metal/polymer interface indicate the penetration of a metal layer within the polymer, resulting in a formation of a bonding layer that confirms the transduction of light-induced stresses in the polymer layer to a metal film. KW - surface relief grating KW - opto-mechanical stresses KW - bonding layer at the metal/polymer interface KW - rupturing of metal film KW - metal/multilayered graphene/polymer interfaces KW - azobenzene Y1 - 2014 U6 - https://doi.org/10.1021/am501870t SN - 1944-8244 VL - 6 IS - 14 SP - 11333 EP - 11340 PB - American Chemical Society CY - Washington ER -