Browsing by Author "Ishraq, Aqiq"

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Kaktüs and its impact on Turkish feminism
(Bilkent University, 2015) Ishraq, Aqiq; Hakimi, Hamza; Ishraq, Marzana; Dang, Mayuri; Jabbarov, Rustam
Open Access
Laser nano-structuring deep inside silicon using bessel beams
(2021-01) Ishraq, Aqiq
Current nano-fabrication methods for silicon (Si), while excellent, are limited to its surface. Novel laser-lithography methods are emerging to introduce subsurface (inchip) functionality to Si, however, the state-of-the-art is at the microfabrication level, with resolution limited to > 1 µm. Multiple challenges exist for breaking this fabrication barrier, such as the diffraction-limit and complex limiting nonlinear effects inside silicon. This thesis demonstrates the first nanofabrication capability deep inside silicon, achieved without altering the wafer above or below fabricated structures, with confinement in one- and two-dimensions at the nanoscale. We achieve this by exploiting nonlinear energy localization due to structured laser beams and also a new seeding-type effect. The approach is based on pre-formed laser-written inchip structures enabling the controlled formation of even smaller features. We also demonstrate laser polarization as a new parameter for in-chip fabrication control. Further, by exploiting a combination of parameters, including pulse energy, Bessel beam phase pattern, polarization and the laser focusing conditions, we demonstrate the first in-chip structures that are beyond the diffraction limit in terms of feature size, with resolution down to 120 nm ± 25 nm, thus, improving the state-of-the-art by about an order of magnitude. In order to demonstrate a proof-of-concept optical element, we fabricated the first in-chip nano-gratings, shown to be operating with an efficiency approaching 90%. This new nanofabrication capability, demonstrated for the important technological material silicon, may have significant implications for nano-photonics, micro/nano-fluidics, photonic-electronic integration, and micro/nano-electromechanical systems (MEMS/NEMS)-type systems.
Open Access
Laser nanofabrication deep inside silicon wafers
(IEEE, 2021-09-30) Sabet, Rana Asgari; Ishraq, Aqiq; Tokel, Onur
Here, we introduce the first controlled nanofabrication capability in the bulk of silicon wafers. We exploit smart use of Bessel beams and demonstrate "in-chip" nano-structuring with features lower than 250 nm.
Open Access
Laser nanofabrication inside silicon with spatial beam modulation and anisotropic seeding
(NATURE PORTFOLIO, 2024-07-16) Sabet, Rana Asgari; Ishraq, Aqiq; Saltık, Alperen; Bütün, Mehmet; Tokel, Onur
Nanofabrication in silicon, arguably the most important material for modern technology, has been limited exclusively to its surface. Existing lithography methods cannot penetrate the wafer surface without altering it, whereas emerging laser-based subsurface or in-chip fabrication remains at greater than 1 mu m resolution. In addition, available methods do not allow positioning or modulation with sub-micron precision deep inside the wafer. The fundamental difficulty of breaking these dimensional barriers is two-fold, i.e., complex nonlinear effects inside the wafer and the inherent diffraction limit for laser light. Here, we overcome these challenges by exploiting spatially-modulated laser beams and anisotropic feedback from preformed subsurface structures, to establish controlled nanofabrication capability inside silicon. We demonstrate buried nanostructures of feature sizes down to 100 +/- 20 nm, with subwavelength and multi-dimensional control; thereby improving the state-of-the-art by an order-of-magnitude. In order to showcase the emerging capabilities, we fabricate nanophotonics elements deep inside Si, exemplified by nanogratings with record diffraction efficiency and spectral control. The reported advance is an important step towards 3D nanophotonics systems, micro/nanofluidics, and 3D electronic-photonic integrated systems. The authors report controlled laser nanofabrication inside silicon. The dimensional barrier is overcome by spatially modulated lasers and anisotropic feedback from preformed structures. Features down to 100 nm is achieved, improving the state-of-the-art by an order-of-magnitude.