Dip‐pen nanolithography (DPN) is a low‐cost, versatile bench‐top method for directly patterning materials on surfaces with sub‐50 nm resolution; it involves the use of a cantilever tip to transfer a selected ink onto various surfaces to create predefined patterns. Many parameters may influence DPN quality, due to the variety of deposited and surface materials and the chemical interactions between them. DPN tip deposition of liquid inks is not yet well understood, due to the lack of thorough study of the various parameters that need to be controlled in order to achieve uniform patterning. In this research, the printing of polydimethylsiloxane (PDMS) lines and the control of their physical dimensions are investigated; the applied parameters are different humidity levels, n‐hexane dilution proportions and different tip velocities. Numerous experiments accompanied by atomic force microscope measurements are conducted in order to derive a recommended recipe for the required dimensions of the printable lines. A practical aspect of the research is to assess the potential of the application of DPN for the fabrication of various optical devices, such as gratings and waveguides. In order to validate the theoretical results, PDMS printing over silicon is used to successfully produce an optical diffraction grating.
Our understanding of processes involved in two-photon photoemission (2PPE) from surfaces can be tested when we try to exercise control over the electron emission. In the past, coherently controlled 2PPE has been demonstrated using very short pulses and single crystal surfaces. Here we show that by applying polarization pulse shaping on surfaces, it is possible to vary both the angular distribution of the emitted photoelectrons and the total photoemission yield. The presented 2PPE experimental setup introduces pulse shaping in the visible range, which is a unique property that allows control of polarization. We relate the ability to use polarization as a means of control to the surface corrugation.
Resonant cavity-assisted enhancement of optical absorption was a photodetector designing concept emerged about two and half decades ago, which responded to the challenge of thinning the photoactive layer while outperforming the efficiency of the monolithic photodetector. However, for many relevant materials, meeting that challenge with such a design requires unrealistically many layer deposition steps, so that the efficiency at goal hardly becomes attainable because of inevitable fabrication faults. Under this circumstance, we suggest a new approach for designing photodetectors with absorber layer as thin as that in respective resonant cavity enhanced ones, but concurrently, the overall detector thickness being much thinner, and topmost performing. The proposed structures also contain the cavity-absorber arrangement but enclose the cavity by two dielectric one-dimensional grating-on-layer structures with the same grating pitch, instead of the distributed Bragg reflectors typical of the resonant cavity enhancement approach. By design based on the in-house software, the theoretical feasibility of such ∼ 7.0µm − 8.5µm thick structures with ∼ 100% efficiency for a linearly polarized (TE or TM) mid-infrared range radiation is demonstrated. Moreover, the tolerances of the designed structures' performance against the gratings' fabrication errors are tested, and fair manufacturing tolerance while still maintaining high peak efficiency along with a small deviation of its spectral position off initially predefined central-design wavelength is proved. In addition, the electromagnetic fields amplitudes and Poynting verctor over the cavity-absorber area are visualized. As a result, it is inferred that the electromagnetic fields' confinement in the designed structure, which is a key to their upmost efficiency, is two-dimensional combining in-depth vertical resonant-cavity like confinement, with the lateral microcavity like one set by the presence of gratings.
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