Scholarly Publications - Physics
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Item Open Access Instability and information production around Kerr black holes: effects on entropy and the shadow(Springer, 2025-11-06) Tavlayan, Aydın; Tekin, BayramMassless or massive particles in unstable orbits around a Kerr black hole exhibit exponentially unstable motion when perturbed. They either plunge into the black hole or escape to infinity after making some oscillations around the equatorial plane. This exponentially unstable motion causes information production. In the case of the photons that escape to infinity, it was recently suggested that this information can be used to resolve the subring structure of the shadow image and obtain more precise data about the black hole mass and spin (Johnson et al. in Sci Adv 6(12):eaaz1310, 2020). Here, we extend this method to obtain more precise results by including the non-equatorial contributions to the Lyapunov exponents. For massive particles plunging into the Kerr black hole, we show that the associated Kolmogorov–Sinai entropy derived from the Lyapunov exponents can be interpreted in the context of black hole thermodynamics and obeys Bekenstein’s bound on the entropy of a physical system. Thus, the perturbed unstable orbits, either ending inside the black hole or at the observer’s screen, have physical consequences.Item Open Access Recent advances in GaN-based semiconductor lasers(Institute of Physics Publishing Ltd., 2025-07-17) Zhao, Chunyu; Tan, Swee Tiam; Demir, Hilmi VolkanIII-nitride semiconductor lasers have made remarkable progress in recent years, particularly thanks to their ability to be tuned from the ultraviolet to the infrared. This comprehensive review explores the latest developments in GaN-based semiconductor lasers, with a specific focus on edge-emitting laser, vertical-cavity surface-emitting laser, photonic crystal or nanocrystal surface-emitting laser, and whispering gallery mode laser diodes. The review delves into each laser type’s distinctive properties and potential applications, evaluating their performance while identifying current challenges. Finally, this review aims to shed light on challenges and prospects in GaN-based laser development.Item Open Access Floquet non-Bloch formalism for a non-Hermitian ladder: from theoretical framework to topolectrical circuits(American Physical Society, 2025-12-24) Roy, Koustav; Halder, Dipendu; Gogoi, Koustabh; Tanatar, Bilal; Basu, SaurabhPeriodically driven systems intertwined with non‐Hermiticity open a rich arena for topological phases that transcend conventional Hermitian limits. The physical significance of these phases hinges on obtaining the topological invariants that restore the bulk‐boundary correspondence, a task well explored for static non-Hermitian (NH) systems, while it remains elusive for the driven scenario. Here, we address this problem by constructing a generalized Floquet non‐Bloch framework that analytically captures the spectral and topological properties of time-periodic NH systems. Employing a high-frequency Magnus expansion, we analytically derive an effective Floquet Hamiltonian and formulate the generalized Brillouin zone for a periodically driven quasi-one-dimensional system, namely, the Creutz ladder with a staggered complex potential. Our study demonstrates that the skin effect remains robust (despite the absence of nonreciprocal hopping) across a broad range of driving parameters, and is notably amplified in the low-frequency regime due to emergent longer-range couplings. We further employ a symmetric time frame approach that generates chiral-partner Hamiltonians, whose invariants, when appropriately combined, account for the full edge-state structure. To substantiate the theoretical framework, we propose a topolectrical circuit (TEC) that serves as a viable experimental setting. Apart from capturing the skin modes, the proposed TEC design faithfully reproduces the presence of distinct Floquet edge states, as revealed through the voltage and impedance profiles, respectively. Thus, our work not only offers a theoretical framework for exploring NH-driven systems but also provides an experimentally feasible TEC architecture for realizing these phenomena stated above in a laboratory.Item Open Access Design and simulation of SWIR nBn-InGaAs photodetector with AlGaAs barrier(EDP Sciences, 2025-09-22) Tok, Çaǧrı; Satılmış, Mert; Keleş, Habibe; Oǧuz, Fikri; Sarı, Hüseyin; Özbay, EkmelThe article discusses the simulation of an nBn-InGaAs photodetector using Silvaco TCAD at 300 K, focusing on optimizing the barrier performance and reducing the valence band offset. It explores the device’s electrical and optical behaviors, including dark current, photocurrent, and capacitance. The results show a peak responsivity of 0.91 A/W at 1.55 µm and a junction capacitance of 9 pF at −5 V. Adding an anti-reflection coating notably improved the optical performance, highlighting the structure’s potential for efficient infrared photodetection.Item Embargo Electrolyte-free potassium ions intercalated in 2D layered metal oxide for imitating spatiotemporal biological neural dynamics(Elsevier Ltd, 2025-06) Noh, Gichang; Kim, Jeongho; Woo, Dong Yeon; Kim, Min-gyu; Yoo, Hyeri; Jeong, Han Beom; Jo, Yooyeon; Park, Eunpyo; Lee, Dae Kyu; Kim, Min Jee; Jo, Min-kyung; Kim, In Soo; Kasırga, Talip Serkan; Ha, Dong Han; Kim, Soo Young; Hwang, Gyu Weon; Kim, Sangtae; Lee, Chul-Ho; Yang, Heejun; Jeong, Hu Young; Kang, Kibum; Kwak, Joon YoungAlkali ions are crucial to physiological neural activities and their dynamics can be implemented in various iontronics. For the host materials for alkali ions, 2D layered materials have become the preferred choice thanks to their facilitating ion accommodation and movement between layers. Nevertheless, challenges such as the need for external electrolytes, pre-fabrication for ion intercalation, and thermodynamic stability during ion movements still persist. Consequently, the comprehensive understanding of the electrical dynamics associated with alkali ion movement has rarely been demonstrated in 2D layered materials so far. Here, we engineered an electrolyte-free high-crystalline 2D layered MnO₂ nanoplate with potassium ions by metal–organic chemical vapor deposition. The combination of potassium ions and layered MnO₂ exhibits electrically induced ion migration coupled with a subsequent phase transition, resulting in negative differential resistance. Furthermore, the material's distinct hybrid plasticity, driven by its ion dynamics, provides a sophisticated platform for sequential motion recognition, valuable for assessing continuous motion across varied subjects. Finally, we demonstrate the broad applicability of our 2D K-MnO₂ and highlight its versatility in spatiotemporal ion modulation within three-terminal structures, showing potential for future advancements.Item Embargo Electro-optical evaluation of Cu¹⁺ and Cu²⁺ states in copper-doped CdSe colloidal quantum wells(American Chemical Society, 2026-01-29) Yu, Junhong; Wang, Ke; Han, Yadong; Lian, Zhenzhong; Hou, Songyan; Cao, Chang; Demir, Hilmi Volkan; Jasieniak, Jacek J.; Sharma, ManojResolving the ambiguous oxidation state of copper dopants responsible for the large Stokes-shifted emission in CdSe colloidal quantum wells (CQWs) is critical for harnessing their emerging optoelectronic properties. Employing carrier injection to tune the population distribution between Cu¹⁺/Cu²⁺ centers and in situ monitoring of the copper-related emission (CE), we have revealed that the CE band undergoes blueshifting, intensity quenching, and line width broadening with gradually increased Cu²⁺ states. Time-resolved CE dynamics and intragap absorption further confirm that Cu²⁺ states generate narrow, inefficient emission with minimal Stokes shifts due to trap-mediated Auger recombination, reduced radiative center energy spanning, and Fermi-level shifts. Accordingly, we identify Cu¹⁺ as the dominant species that produces the bright, broad CE band with its hallmark large Stokes shift. This work not only presents mechanistic clarifications but also provides an effective approach to electrically modulate defect emissions in CQWs.Item Unknown Implications of Mexican hat-like band structure on thermoelectric properties(TUBITAK, 2025-07-29) Hilal, Muhammad; Gülseren, OğuzElectronic band structure of low dimensional materials significantly impacts their thermoelectric performance. A Mexican hat-like band structure, characterized by a ring-shaped extremum in momentum space, offers distinct advantages due to its singularity in the density of states at the band edge and its ability to enhance energy-dependent transport. This work investigates a two-dimensional tight-binding model hamiltonian that incorporates both nearest-neighbor (t1 ) and next-nearest-neighbor (t2 ) hopping. The ratio of the hopping amplitudes, ξ = t2 /t1 , serves as a tunable parameter that modulates the shape and depth of the Mexican hat dispersion. We use an analytical expression for the energy band of the form ε(k) = εv − α(k2 − kc2)2 , and demonstrate how the curvature α, the radius of the Fermi ring kc , and the valley height ε0 evolve with ξ. Using the Landauer formalism within the constant relaxation time approximation, we compute various properties, including the energy surface, band structures, density of states, transmission spectra, transport moments (L0 , L1 , L2 ), and thermoelectric properties such as electrical conductivity (σ ), Seebeck coefficient (S ), electronic thermal conductivity (κel ), power factor (PF), and figure of merit (ZT ) as functions of the chemical potential at room temperature. Additionally, we evaluate PF and ZT as functions of temperature. Our results indicate that increasing ξ sharpens the density of states near the band edge, enhances the Seebeck coefficient, and improves the overall thermoelectric response. These findings emphasize the significance of band engineering by modulating hopping parameters as a viable strategy for optimizing next-generation thermoelectric materials.Item Unknown The origin of gate degradation under HTRB operation: Buffer engineering to suppress impact ionization in GaN HEMT(Institute of Electrical and Electronics Engineers Inc., 2025-12-15) Soydan, Mahmut Can; Joya, Amir Ali; Ghobadi, Amir; Özbay, EkmelThis study investigates the origin of gate degradation in AlGaN/GaN HEMTs under high-temperature reverse bias (HTRB) conditions and proposes a buffer engineering strategy to mitigate this degradation. Transmission electron microscopy (TEM) analysis reveals the presence of a thin oxide layer between the gate and AlGaN contact. It is found that the holes generated through impact ionization (under high electric fields of HTRB operation), are directed toward the gate due to the intense local electric field under the gate and the field plate overhang, and are accumulated under this energetic barrier. Consequently, these trapped holes cause gate degradation and increased gate leakage. To address this issue, impact ionization, as the initial forcing mechanism of the degradation, is suppressed via thinning the channel GaN (C-GaN) layer. This improvement is attributed to the suppression of the local electric field near the gate region in thin C-GaN HEMTs. Additionally, the impact of C-GaN thinning on breakdown characteristics and RF performance is discussed. Overall, the findings provide insights into the root cause of gate degradation and offer a buffer engineering strategy to minimize gate degradation under deep off-state stress. This approach enhances the reliability of future high-power and high-frequency GaN HEMTs, contributing to their long-term performance in demanding applications.Item Unknown Upper bounds on focusing light through multimode fibers(American Physical Society, 2025-11-04) Ammar, Amna; Şener, Sarp Feykun; Ercan, Mert; Yılmaz, HasanWavefront shaping enables precise control of light propagation through multimode fibers (MMFs), facilitating diffraction-limited focusing for applications such as high-resolution single-fiber imaging and high-power fiber amplifiers. While the theoretical intensity enhancement at the focal point is dictated by the number of input degrees of freedom, practical constraints - such as phase-only modulation and experimental noise - impose significant limitations. Despite its importance, the upper bounds of enhancement under these constraints remain largely unexplored. In this work, we establish a theoretical framework to predict the fundamental limits of intensity enhancement with phase-only modulation in the presence of noise-induced phase errors, and we experimentally demonstrate wavefront shaping that approaches these limits. Our experimental results confirm an enhancement factor of 5000 in a large-core MMF, approaching the theoretical upper bound, enabled by noise-tolerant wavefront shaping. These findings provide key insights into the limits of phase-only control in MMFs, with profound implications for single-fiber imaging, optical communication, high-power broad-area fiber amplification, and beyond.Item Embargo Lasing from brillouin zone folding guided resonances(American Chemical Society, 2025-09-25) Chua, Matthew R.; Ding, Lu; Liang, Xiao; Dabard, Corentin; Wang, Wudeng; Akhil, Syed; Durmusoglu, Emek Goksu; Tjiptoharsono, Febiana; Demir, Hilmi Volkan; Paniagua-Domínguez, Ramón; Kuznetsov, Arseniy I.High-quality factor (Q-factor) nanophotonic cavities are critical components in applications such as lasing and nonlinear optics. However, to obtain out-of-plane lasing emission and a low lasing threshold, the lasing mode must fulfill the contradictory requirement of coupling to the light cone while maintaining a high Q-factor. One relatively unexplored method to design such modes consists of using a Brillouin Zone folding guided resonance (BZF-GR) as the high Q-factor mode for lasing. In such a design, guided modes are “folded” into the light cone via periodic perturbations, allowing fine control of the Q-factor throughout momentum space. In this paper, we experimentally demonstrate the use of such a BZF-GR to achieve vertical emission lasing from a nanophotonic cavity with colloidal quantum dots as a gain medium. The lowest lasing threshold fluence under nanosecond pump is (20.4 ± 0.3) μJ cm–2. When considering the absorption, this value falls to (4.08 ± 0.08) μJ cm–2. This work presents a method of designing lasing modes that may be further developed for use in low-threshold nanoscale lasers.Item Open Access Side-emitting optical fibers of colloidal quantum wells for application in curved-surface lighting and sensing(American Chemical Society, 2025-03-04) Adelpour, Zahra; Shabani, Farzan; Sadeghi, Mojtaba; Khaligh, Aisan; Rahman, Mahmudur; Karaboğa, Fırat; Ünal, Emre; Ordu, Mustafa; Demir, Hilmi VolkanAs specialized optical fibers, side-emitting optical fibers (SEOFs) are designed to emit light from their sides rather than their ends for possible applications in curved-surface lighting and sensing. In this study, we propose and demonstrate an in situ decoration of SEOFs with colloidal quantum wells (CQWs) for the first time. The proposed method enables the homogeneous distribution of CQWs in the polymeric matrix of the fiber with high side-emission efficiency, which is based on a simple yet effective method of CQW sheet coating. Two different structures of CQWs, a red-emitting CdSe/CdZnS core/shell and a green-emitting CdSe/CdS core/crown, were synthesized and employed in SEOFs. Accordingly, carefully tuned concentrations of CQWs were incorporated within the hollow-core optical fibers, and the side-scattered light from the fibers was systematically characterized and analyzed. The results confirm excellent side-emitting characteristics that are highly dependent on the optical fiber structure and CQW absorption spectrum. The average quantum yield values of 51 ± 5% and 34.5 ± 5% for different concentrations of red and green CQWs relative to their solution form were measured in our experiment, which is associated with polymeric medium, cluster formation, and fiber tower temperature. The findings pave the way for developing high-performance optical fiber devices based on CQW-doped SEOFs capable of efficient and precise light emission targeting a wide variety of applications ranging from three-dimensional curved-surface lighting to sensing.Item Open Access GaN-on-SiC broadband driver amplifier for C- and X-band applications(John Wiley and Sons Inc, 2025-06-12) Hannan, Abdullah; Aras, Erdem; Gürdal, Armağan; Urfalı, Emirhan; Zafar, Salahuddin; Nawaz, Muhammad Imran; Özbay, EkmelA GaN-on-SiC-based broadband driver amplifier operating in the C- and X-bands from 5 to 12 GHz has been demonstrated. The MMIC has a typical small signal gain of 29.7 dB with a ±1.4 dB gain ripple. The input and output return losses are better than 10.5 and 8.8 dB, respectively. The average Psat is approximately 2.65 W with an OIP3 of 37.7 dBm, while the large signal gain is 22 dB. This design is distinguished by its low output power ripple and the low large signal gain fluctuations observed across the full frequency range of interest. Consistent load impedance matching at the output stage for the whole frequency range enabled an output power ripple less than ±1.1 dB and a large signal gain ripple less than ±0.6 dB at 10 dBm input power. This allowed for an output power density of at least 2.68 W/mm across the broad frequency range of 5–12 GHz. The typical power-added efficiency is 26.4%. To the best of the authors' knowledge, this DA design exhibits the best combination of gain, output power density, gain ripple, output power ripple and output return loss in this frequency band.Item Open Access Modal gain tailoring by flat stamping of thin colloidal films(AIP Publishing LLC, 2025-05-20) Azizov, Ruslan; Zhu, Jinlong; Talianov, Pavel; Işık, Furkan; Demir, Hilmi Volkan; Makarov, SergeyPost-synthetic tailoring and improvement of the light-emitting material properties is an important direction for optimization of solution processible LEDs and recently emerged laser diodes based on nanocrystals. In this study, we demonstrate modal gain engineering by flat stamping light-emitting films of core/alloyed shell CdSe/CdZnS nanoplatelets. This film modification approach affects the volume density occupation (D) of the emitters in the film and allows for control of the layer thickness while keeping surface roughness low and uniformity high. The achieved level of control of the mode confinement factor (Г) and optical gain is promising for better integration with resonators and multilayered structures. Careful accounting of such parameters makes it possible to achieve higher D values and increase the modal gain up to ∼2.39 times in comparison with standard spin-coating films. The modal gain enhancement and the Г factor control allow us to maximize the optical gain in light-emitting devices and facilitate low-threshold lasing.Item Open Access Highly photosensitive colloidal quantum well based nanocrystal skins assisted by orientation control(American Chemical Society, 2025-11-17) Işık, Furkan; Bozkaya, Taylan; Bozkaya, İklim; Delikanlı, Savaş; Canımkurbey, Betül; Demir, Hilmi VolkanColloidal quantum wells (CQWs) exhibit superior optical characteristics, including giant oscillator strengths and high absorption cross sections, making them attractive for light-sensing applications. In this study, we fabricated light-sensitive nanocrystal skin (LS-NS) devices using a single-layer edge-up oriented CQW film as the active absorber and achieved a significant enhancement in the performance by leveraging the controlled orientation of the self-assembled CQWs. The LS-NS devices with edge-up oriented CQW film show eight times higher sensitivity and three times higher voltage build-up compared to LS-NS devices with spin-coated CQW films. Such enhancements are due to the trapping of the holes on the edges of the CQWs because of defect-ridden edges, which helps hopping of the holes localized within close proximity to the metal–CQW interface. The LS-NS device with edge-up CQW film exhibited a record-high photovoltage buildup of 600 mV, three times greater than the highest previously reported value for similar LS-NS architectures.Item Open Access Room-temperature exciton-polariton-driven self-phase modulation in planar perovskite waveguides(American Chemical Society, 2025-04-01) Glebov, Nikita V.; Masharin, Mikhail A.; Yulin, Alexei; Mikhin, Alexey; Miah, Md Rumon; Demir, Hilmi Volkan; Krizhanovskii, Dmitry N.; Kravtsov, Vasily; Samusev, Anton K.; Makarov, Sergey V.Optical nonlinearities are crucial for advanced photonic technologies since they allow photons to be managed by photons. Exciton-polaritons resulting from strong light-matter coupling are hybrid in nature: they combine the small mass and high coherence of photons with strong nonlinearity enabled by excitons, making them ideal for ultrafast all-optical manipulations. Among the most prospective polaritonic materials are halide perovskites since they require neither cryogenic temperatures nor expensive fabrication techniques. Here, we study strikingly nonlinear self-action of ultrashort polaritonic pulses propagating in planar MAPbBr3 perovskite slab waveguides. Tuning the input pulse energy and central frequency, we experimentally observe various scenarios of its nonlinear evolution in the spectral domain, which include peak shifts, narrowing, or splitting driven by self-phase modulation, group velocity dispersion, and self-steepening. The theoretical model provides complementary temporal traces of pulse propagation and reveals the transition from the birth of a doublet of optical solitons to the formation of a shock wave, both supported by the system. Our results presented here represent an important step in ultrafast nonlinear on-chip polaritonics in perovskite-based systems.Item Open Access Improvement in ASM and GaN HEMT model for RF applications(Institute of Electrical and Electronics Engineers Inc., 2026-11-26) Hannan, Abdullah; Gürbüz, Abdulkadir; Nawaz, Muhammad Imran; Darwish, Haitham; Aras, Erdem; Özbay, EkmelGallium nitride (GaN) high electron mobility transistors (HEMTs) are widely used in high-frequency and high-power applications because of their exceptional electrical properties. Accurate modeling of HEMT is crucial for reliable circuit design, particularly as the device dimension scales. The measurement-based models are reliable but dependent on the periphery and do not offer flexibility to the designer. These can be used to design impedance-matching networks and perform small signal simulations only of the complete MMIC design. In this work, we have proposed an improvement in advanced Spice model for HEMT (ASM-HEMT) for better S22 performance at low frequencies by implementing an additional series RC network to address the parasitic path between the drain and the source through the buffer. Also, an electromagnetic (EM)-based modeling approach for obtaining scalable extrinsic parasitics is described. Equations are developed as a function of the number of gate fingers and gate widths from extrinsic parasitics of the gate, the drain, and the source. The proposed model was validated by fabricating six different peripheries of HEMTs. The S-parameters were verified from 400 MHz to 26.5 GHz for the quiescent bias of 28 V and 100 mA/mm. Large-signal validation for output power and power-added efficiency (PAE) was also performed on devices with the sizes of 6×100 μ m, 8×100 μ m, and 10×100 μ m, confirming the accuracy of the model under large-signal excitation. This work provides a comprehensive and scalable modeling solution for GaN HEMTs, suitable for advanced RF and microwave circuit design.Item Embargo An extensive thermal conductivity measurement method based on atomic force microscopy(Elsevier Ltd., 2025-11-15) Kasırga, Talip Serkan; Köker, BerkeHeat transport in low-dimensional solids can significantly differ from their bulk counterpart due to various size-related effects. This offers rich heat transport phenomena to emerge. However, finding an appropriate thermometry method for thermal conductivity measurements at the reduced size and dimensionality of the samples is a challenge. Here, we propose and study the feasibility of a nanoscale resolution thermal conductivity measurement method based on bolometric thermometry implemented on an atomic force microscopy (AFM). The local heat exchange between the AFM tip and the sample occurs at a suspended section of the sample, and thermal modeling of the measured electrical resistance change resulting from the bolometric effect in the sample provides a unique value for thermal conductivity. As we illustrate via thermal simulations, the proposed method can measure thermal conductivity with thermal disturbance to the sample in as little as 0.2 K at ∼20 nm lateral resolution. Our in-depth analysis shows the feasibility and extensive applicability of the proposed AFM-based bolometric thermometry method, which we coin as mechanical bolometric thermometry (MBT), on low-dimensional materials, both in diffusive and ballistic heat transport regimes from cryogenic to above-room temperature. Consequently, the proposed method can lead to a deeper experimental understanding of fundamental questions in nanoscale and low-dimensional heat transport phenomena in many different material classes, as well as Fourier and non-Fourier heat transfer regimes.Item Open Access Subwavelength phase engineering deep inside silicon(Institute of Physics Publishing Ltd., 2025-08-20) Bütün, Mehmet; Saltık, Alperen; Tokel, OnurRecent advances in three-dimensional laser writing have enabled direct nanostructuring deep within silicon, unlocking a volumetric design space previously inaccessible to surface-bound nanophotonic devices. Here, we introduce subwavelength phase engineering inside crystalline silicon, offering a novel strategy for integrated photonics. We design and numerically demonstrate a volumetric metaoptic monolithically embedded within the bulk, achieving full 2π phase control at telecommunication wavelengths, with simulated transmission efficiencies reaching 90%. The architecture is guided by a semi-analytical Fabry-Pérot model and validated through full-wave simulations. Arrays of 250 nm-wide metaatoms spaced at 300-410 nm pitch yield a focusing efficiency of 70%. With the wafer surface left pristine, this platform can potentially enable co-integration with electronics, MEMS/NEMS, and conventional metasurfaces. Moreover, the method is directly transferable to other transparent dielectrics compatible with ultrafast laser writing. These results establish a CMOS-compatible blueprint for three-dimensional nanophotonics and multi-level integration within the wafer.Item Embargo Spin-glass phases and multichaos in the Ashkin–Teller model(Elsevier, 2026-01) Saray, Alican; Berker, A. NihatThe global phase diagram of the Ashkin–Teller spin glass is calculated in d=3 spatial dimensions by renormalization-group theory. Depending on the value of the positive or negative four-spin interaction, qualitatively different topologies are found for the spin-glass phase diagram in the usual variables of temperature and fraction of antiferromagnetic nearest-neighbor interactions. Two different spin-glass phases occur. Both spin-glass phases are chaotic. One spin-glass exhibits phase reentrance that is reverse from the reentrances seen in previous spin-glass phase diagrams. Seven different phases: Ferromagnetic and antiferromagnetic, entropic ferromagnetic and entropic antiferromagnetic, spin-glass and entropic spin-glass, and disordered phases occur. The entropic ferromagnetic phase unusually but understandably occurs at temperatures above one spin-glass phase. A random disorder line is identified and no phase transition occurs on this line. Our calculation is exact on the d = 3 hierarchical lattice and Migdal–Kadanoff approximate on the cubic lattice.Item Open Access Thermal management to break the heat trap: scalable lithography-free multilayer films for radiative cooling(IEEE, 2025-07-02) Khalichi, Bahram; Osgouei, Ataollah Kalantari; Ghobadi, Amir; Özbay, EkmelThis work presents a high-performance, lithography-free multilayer absorber/emitter for passive radiative cooling. The proposed structure exhibits a strong absorption resonance around 9 $μm$, aligning with the atmospheric transparency window to maximize thermal emission. The structure achieves a temperature reduction of −10.93°C at 20°C ambient temperature under purely radiative cooling conditions $(h_c = 0 W/m²K)$. As convective heat transfer increases, the cooling effect remains strong, reaching 6.68°C for $h_c = 3 W/m²K$ and 11.30°C for $h_c = 6 W/m²K$. The proposed scalable, cost-effective, and fabrication-friendly approach represents a significant advancement in energy-efficient cooling technologies for industrial and thermal management applications.