Effect Of Mask On The Imaging Characteristics Of Silver Superlens

The resolution of ideal imaging systems and lithography systems are determined by diffraction limit. With the widely researched of surface plasmon and the improving of processing precision, evanescent wave is contributed by surface plasmon coupling transmission characteristics and local enhancement features which is used in imaging to overcome the diffraction limit. So, it is possible to achieve the resolution of sub-wavelength.Basing on a superlens imaging system mainly composed of a single layer of silver plate,we use the finite-element method to perform full wave simulations of the near field imaging of metal plate superlens. The influence of Cr mask thickness, duty ratios and line width on the quality of metal superlens image and image distance shift are studied. Meanwhile, we simulate the transmittance of Si O2-Media-Air structure of transverse magnetic wave mode with optical transfer function and further study the influence of mask material on the metal superlens image quality and image distance shift with the finite-element method. The main work and conclusions of the paper are as following:1. Thickness, duty ratios and line width of Cr mask influence on the imaging quality of metal superlens and image distance shift are studied. The results show that the contrast of the imaging is increasing with the increasing thickness of the mask and tends to stability when the thickness exceeds 50 nm. The image plane is closer to the Ag superlens with the increasing thickness of the mask. When the line width of grating increases, variation ranges of contrast ration and image plane both increases, however the former is more obvious. when the thickness of mask is fixed, the image plane is far away from the Ag superlens with the increasing line width of grating. The contrast of the imaging is decreased with the increasing deficiency of T-top phenomena. However, the deficiency influence on the shift of image distance is not obvious.2. The influences of mask material on the image quality of metal superlens and image distance shift are studied. Chromium, gold, platinum, titanium, tungsten and silicon are chosen as mask material, respectively. Among these materials, the contrast of the imaging is the highest with silicon mask,close to 1, and it is almost not affected by the thickness of the mask. When the mask material are chromium, gold, platinum, titanium or tungsten,the distance between the image plane and Ag superlens becomes shorter with the increasing thickness of the mask. However, for silicon as the mask material,its distance goes further with increasing the thickness of the mask.The research can provides a methods and some information for design and optimizing metal plate superlens imaging and lithography systems to obtain higher resolution nanopatterns.