Fabrication Of Metal Wrinkles On Carbon Structures And Its Application In SERS

It is well known that when a thin stiff film subjects to a compressive stress that is bigger than a critical value, the film will buckle and wrinkles will arise. Such a phenomenon is usually considered to be a failure of structure. Recently, some researchers found that different kinds of buckling patterns can be formed by utilizing this phenomenon, based on which, they propose new methods to fabricate micro-scale structures. Inspired from the above progress, we propose to integrate buckling patterns in thin film with micro-scale structure. Through such a fabrication method, micro-nano hierarchical structures, i.e., nano-scale buckling patterns on micro-scale substrate can be readily obtained. The fabrication method does not require expensive equipments; it is suitable for high efficiency and low cost fabrication of micro-nano hierarchical structure; the obtained structure can be used in many applications, including solar cell, SER.S substrate, etc. The main research contents are described as follows.First, a fabrication process is proposed to obtain micro-nano hierarchical structure. We use a negative photoresist SU-8and a positive photoresist AZ9260to fabricate cylinder array with65μm diameter and hemi-sphere array with20μm diameter by photolithography, respectively; after that, Ti film whose thickness ranges from20nm to1μm is sputtered onto the substrate surface by magnetron sputtering; after sputtering, pyrolysis is carried out in reducing atmosphere according to specific temperature curve ranging from400℃to900℃, during which, the photoresist substrate is reduced to carbon and shrinks and nano-scale buckling pattern on micro-scale substrate is obtained.Second, experments are carried out and it is proved that buckling pattern in metal film is formed during the pyrolysis of substrate from photoresist to carbon and the film is well adhered to the substrate in that process. The Fourier transform method and atomic force microscope are used to characterize the wavelength and amplitude of buckling patterns, respectively, and the relationship between the size of buckling patterns (the wavelength and amplitude) and the process parameters (film thickness and carbonization temperature) is discussed.Third, A5nm thick Ti film is used in this process to get nano-scale buckling pattern as a template, and the silver film with thickness ranging from50nm to600nm is sputtered to obtain SERS substrate; Rhodamine6G (R6G) is used as probe molecule to evaluate the enhancement of the as-prepared SERS substrate:10μL of10-7mol/L R6G ethanol solution is dipped onto the as-prepared substrate with9mm2area and the peaks of R6G can be easily observed from its Raman spectrometer. Comparing the SERS substrates of different silver film thickness, we find out that the SERS substrate with200nm silver film has the highest enhancement factor. Comparing with planer silver substrate, the average enhancement factor of SERS substrate with200nm silver film measured from15positions is106and the standard derivation of the highest peak value is31.3%, R6G with concertration10"9mol/L can be detected on the SERS substrate. The SERS substrate can be used to detect melamine, it is proved that the Raman signal of melamine with concentration of0.25mg/L can be obtained from SERS substrate which meet the national standard.