Highly sensitive sensor arrays are in high demand for prospective applications in remote sensing and imaging. Measuring microscopic deflections of compliant micromembranes and cantilevers is developing into one of the most versatile approaches for thermal, acoustic and chemical sensing. Here, we report on an innovative fabrication of compliant nanocomposite membranes with nanoscale thickness showing extraordinary sensitivity and dynamic range, which makes them candidates for a new generation of membrane-based sensor arrays. These nanomembranes with a thickness of 25-70 nm, which can be freely suspended over large (hundred micrometres) openings are fabricated with molecular precision by time-efficient, spin-assisted layer-by-layer assembly. They are designed as multilayered molecular composites made of a combination of polymeric monolayers and a metal nanoparticle intralayer. We demonstrate that these nanocomposite membranes possess unparalleled sensitivity and a unique autorecovering ability. The membrane nanostructure that is responsible for these outstanding properties combines multilayered polymer/nanoparticle organization, high polymer-chain orientation, and a pre-stretched state.

Nanoscale uniform films containing gold nanoparticle and polyelectrolyte multilayer structures were fabricated by the using spin-assembly or spin-assisted layer-by-layer (SA-LbL) deposition technique. These SA-LbL films with a general formula [Au/(PAH-PSS)nPAH]m possessed a well-organized microstructure with uniform surface morphology and high surface quality at a large scale (tens of micrometers across). Plasmon resonance peaks from isolated nanoparticles and interparticle interactions were revealed in the UV-visible extinction spectra of the SA-LbL films. All films showed the strong extinction peak in the region of 510-550 nm, which is due to the plasmon resonance of the individual gold nanoparticles redshifted because of a local dielectric environment. For films with sufficient density of gold nanoparticles within the layers, the second strong peak was consistently observed between 620 and 660 nm, which is the collective plasmon resonance from intralayer interparticle coupling. Finally, we suggested that, for certain film designs, interlayer interparticle resonance might be revealed as an independent contribution at 800 nm in UV-visible spectra. The observation of independent and concurrent individual, intralayer, and interlayer plasmon resonances can be critical for sensing applications, which involve monitoring of optomechanical properties of ultrathin optically active compliant membranes.

Layer-by-layer (LbL) assembly, [1] which is based on alternating electrostatic adsorption of oppositely charged organic and inorganic materials (polyelectrolytes, [1] dendrimers, [2] proteins, [3] clays, [4] and nanoparticles [5,6] ) has been applied for the fabrication of a wide variety of functional ultrathin organized films. [7] These films with tunable internal multilayered organization have potential applications in nanoelectronic, optoelectronic, and magnetic technologies, as well as for opto-mechanical, chemical, and bio-sensing, and nanotribology.[7±9]Recently, the new approach of spin self-assembly [10] or spinassembly [11] was suggested, which combined the spin coating and LbL techniques to make a cost-and time-efficient technology for the fabrication of multilayered films from polyelectrolytes, dendrimers, and inorganic nanoparticles on planar substrates.[10±13] It has been shown that, in the framework of this approach, fast and efficient layer deposition under shear forces resulted in well-ordered multilayered structures with modest non-uniformity of the films and some properties different from ªconventionalº LbL films. However, this approach was not pushed to the limit and used to fabricate multilayered, nanoparticle-containing, truly nanoscale LbL films with exceptional mechanical parameters in the most demanding free-suspended or free-standing state where overall integrity and stability of the nanoscale films with macroscopic lateral dimensions play a critical role. Free-standing organized organic±inorganic films are considered as prospective sensing compliant membranes for photo-, opto-, and thermal microdevices. [14] To date, several different approaches were implemented for the fabrication of free-standing nanoscale films from polymers and inorganic nanoparticles: cast films, [15] ªgrowth fromº reactions on the patterned surface, [16] crosslinking of amphiphilic Langmuir films, [17] and the deposition of LbL multilayers onto a sacrificial or pH sensitive substrate.[18±20] However, all these approaches included slow (from hours to days), multistep routines, e.g., in the Langmuir approach: monolayer formation, deposition, and crosslinking. Moreover, the multilayer LbL films are either limited to modestly thin (100±300 nm) polymer films or thick (300±5000 nm) composite organic±inorgan-ic (with inorganic particles, platelets, fibers) films with variable uniformity. Usually, the thinner LbL films were extremely fragile. Thus, corresponding composite films must be made relatively thick to accommodate filler irregularities. The mechanical characteristics achievable for these films are characterized by the elastic modulus values of several gigapascal and ultimate tensile strength of 40±70 MPa with a record value for carbon-nanotube-reinforced films of 220 GPa. [19] In this communication, we report the fabrication of compliant, highly uniform, extremely robust, smooth, and long-living free-standing nanoscale membranes with excellent mechanical characteristics from polyelectrolyte multilayers with a c...

Freely suspended nanocomposite layer‐by‐layer (LbL) nanomembranes composed of a central layer of gold nanoparticles sandwiched between polyelectrolyte multilayers are fabricated via spin‐assisted LbL assembly. The diameter of the circular membranes is varied from 150 to 600 μm and the thickness is kept within the range of 25–70 nm. The micro‐ and nanomechanical properties of these membranes are studied using a combination of resonance‐frequency and bulging tests, and point‐load nanodeflection experiments. Our results suggest that these freely suspended nanomembranes, with a Young's modulus of 5–10 GPa are very robust and can sustain multiple significant deformations. They are very sensitive to minor variations in pressure, surpassing ordinary semiconductor and metal membranes by three to four orders of magnitude and therefore have potential applications as pressure and acoustic microsensors.

No abstract