arXiv subjects

Ihor Pavlov

Publications and source records attributed to Ihor Pavlov.

4 recordsLinked to original sources

arXiv2025

Controlling Competing Feedback Mechanisms for Programmable Patterns via Nonlinear Laser Lithography

Controlling laser-induced pattern formation remains a long-standing challenge. A key advance was recognising the pivotal role of intrinsic feedback mechanisms in self-organisation, which enabled self-similar patterns with long-range order through nonlinear laser lithography. This concept was recently leveraged to surpass the diffraction limit. However, demonstrated structures in laser-induced pattern formation have been relatively simple and material-specific, as they rely on a single assumed formation mechanism for each material. Here, we reveal the coexistence of competing feedback mechanisms that drive distinct chemical and ablative processes, resulting in patterns with different symmetries. We show that one mechanism can be selectively activated, while completely suppressing the other, by tuning the laser parameters independently of the material. The competing mechanisms break surface symmetries in distinct lateral and vertical directions, and the selection can be dynamically inverted in situ, leading to rich surface chemistries and morphologies. We demonstrate the potential for applications through the maskless and ambient-air fabrication of complex composite patterns on diverse materials and substrates. These include seamlessly stitched superhydrophilic and superhydrophobic domains, structural colour, and a holographic temperature sensor. Combining programmable mechanism selection with recent demonstrations of sub-10 nm features could enable the maskless fabrication of composite structures that rival the capabilities of nanofabrication techniques.

physics.optics↗

arXiv2023

Development of a Selective Wet-Chemical Etchant for 3D Structuring of Silicon via Nonlinear Laser Lithography

Recently-demonstrated high-quality three-dimensional (3D) subsurface laser processing inside crystalline silicon (c-Si) wafers opens a door to a wide range of novel applications in multidisciplinary research areas. Using this technique, a novel maskless micro-pillars with precise control on the surface reflection and coverage are successfully fabricated by etching the laser processed region of c-Si wafer. To achieve this, a particular selective wet chemical etching is developed to follow subsurface laser processing of c-Si to reveal the desired 3D structures with smooth surfaces. Here, we report the development of a novel chromium-free chemical etching recipe based on copper nitrate, which yields substantially smooth surfaces at high etch rate and selectivity on the both laser-processed Si surface and subsurface, i.e., without significant etching of the unmodified Si. Our results show that the etch rate and surface morphology are interrelated and strongly influenced by the composition of the adopted etching solution. After an extensive compositional study performed at room temperature, we identify an etchant with a selectivity of over 1600 times for laser-modified Si with respect to unmodified Si. We also support our findings using density functional theory calculations of HF and Cu adsorption energies, indicating significant diversity on the c-Si and laser-modified surfaces.

physics.app-ph↗

arXiv2017

The alignment of nematic liquid crystal by the Ti layer processed by nonlinear laser lithography

It is well known that the alignment of liquid crystals can be realized by rubbing or photoalignment technologies. Recently nonlinear laser lithography was introduced as a fast, relatively low-cost method for large area nano-grating fabrication based on laser-induced periodic surface structuring. In this letter for the first time the usage of the nonlinear laser lithography as a perspective method of the alignment of nematics was presented. By nonlinear laser lithography, microgrooves with about 1 μm period were formed on Ti layer. The microstructured Ti layer was coated with oxidianiline-polyimide film with annealing of the polymer followed without any further processing. Aligning properties of microstructured Ti layers were examined with combined twist LC cell. The dependencies of the twist angle of LC cells and azimuthal anchoring energy of layers on scanning speed and power of laser beam during processing of the Ti layer were the focus of our studies as well. The maximum azimuthal anchoring energy, obtained for pure microstructured Ti layer, is comparable with photoalignment technology. It was found that the deposition of polyimide film on microstructured Ti layer leads to the gain effect of the azimuthal anchoring energy. Also, AFM study of aligning surfaces was carried out.

cond-mat.soft↗

arXiv2017

Switching between normal and anomalous Laser Induced Periodic Surface Structures

We report on the studies of switching mechanism between normal and anomalous laser induced periodic surface structures. We have shown that for high loss metals the switching mechanism between normal and anomalous modes relays on an interplay between two different feedbacks inherent into the structure formation process: long range, low intensity dipole-like scattering of light along the surface, which governs anomalous ripples parallel to the laser polarization, and short range, high intensity plasmon-polariton wave, which is initiated by near field dipole radiation and responsible for creation of ripples perpendicular to the polarization, i. e. normal structure. By managing these two feedbacks, we demonstrated creation of both normal and anomalous laser induced periodic surface structures on the same surface. In contrast to the previous studies, we have shown that the thermal oxidation mechanism can form both normal and anomalous types of the structure, while the ablation mechanism is involved only during the normal structure formation. Unlike the formation of oxidation type anomalous structure, the formation of ablation type normal structure does not have inherent negative feedback, which is self-regulating nano-ripples formation. This feedback needs to be applied artificially, by regulating scanning speed and pulse energy at a given repetition rate of the laser. With implementation of nonlinear laser lithography technique for ablation type of normal laser induced periodic surface structures we demonstrated large area high regular nano-grating formation on different surfaces with extremely high industrially acceptable speed.

physics.optics↗