Susobhan Das
@aalto.fi
Postdoctoral Researcher
Aalto University
RESEARCH INTERESTS
Nonlinear optics
2D-Materials
Nanophotonics
Plasmonics
Metamaterial
Electromagnetics
Optical Imaging
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Juan C. Arias‐Muñoz, Henri Kaaripuro, Yi Zhang, Susobhan Das, Henry A. Fernandez, and Zhipei Sun
Wiley
AbstractInterlayer interactions are one of the crucial parameters of two‐dimensional (2D) layered materials‐based junctions. Understanding the limits of interlayer coupling and defining the “maximum building block thickness” in artificially stacked 2D layered materials are key tasks that hold significant importance, not only in fundamental physics, but also in practical applications such as electronics, photonics, and optoelectronics. Here, the interlayer coupling limits are optically investigated of a model 2D layered semiconductor, MoS2, revealing the evolution of distinct interaction mechanisms between layers via artificial stacking. As the total thickness increases, a reduction in the stacking angle influence on the properties of the homojunctions is reflected in the photoluminescence and second harmonic generation responses. The results show that the effective coupling limit for vertically stacked 2D metamaterials resides in three‐layer flakes. The findings pave the way to advanced and complex devices of 2D superlattices for photonics and optoelectronics.
Md Gius Uddin, Susobhan Das, Abde Mayeen Shafi, Lei Wang, Xiaoqi Cui, Fedor Nigmatulin, Faisal Ahmed, Andreas C. Liapis, Weiwei Cai, Zongyin Yang,et al.
Springer Science and Business Media LLC
AbstractMiniaturized spectrometers are of immense interest for various on-chip and implantable photonic and optoelectronic applications. State-of-the-art conventional spectrometer designs rely heavily on bulky dispersive components (such as gratings, photodetector arrays, and interferometric optics) to capture different input spectral components that increase their integration complexity. Here, we report a high-performance broadband spectrometer based on a simple and compact van der Waals heterostructure diode, leveraging a careful selection of active van der Waals materials- molybdenum disulfide and black phosphorus, their electrically tunable photoresponse, and advanced computational algorithms for spectral reconstruction. We achieve remarkably high peak wavelength accuracy of ~2 nanometers, and broad operation bandwidth spanning from ~500 to 1600 nanometers in a device with a ~ 30×20 μm2 footprint. This diode-based spectrometer scheme with broadband operation offers an attractive pathway for various applications, such as sensing, surveillance and spectral imaging.
Abde Mayeen Shafi, Md Gius Uddin, Xiaoqi Cui, Fida Ali, Faisal Ahmed, Mohamed Radwan, Susobhan Das, Naveed Mehmood, Zhipei Sun, and Harri Lipsanen
Wiley
AbstractMolybdenum ditelluride (MoTe2) exhibits immense potential in post‐silicon electronics due to its bandgap comparable to silicon. Unlike other 2D materials, MoTe2 allows easy phase modulation and efficient carrier type control in electrical transport. However, its unstable nature and low‐carrier mobility limit practical implementation in devices. Here, a deterministic method is proposed to improve the performance of MoTe2 devices by inducing local tensile strain through substrate engineering and encapsulation processes. The approach involves creating hole arrays in the substrate and using atomic layer deposition grown Al2O3 as an additional back‐gate dielectric layer on SiO2. The MoTe2 channel is passivated with a thick layer of Al2O3 post‐fabrication. This structure significantly improves hole and electron mobilities in MoTe2 field‐effect transistors (FETs), approaching theoretical limits. Hole mobility up to 130 cm−2 V−1 s−1 and electron mobility up to 160 cm−2 V−1 s−1 are achieved. Introducing local tensile strain through the hole array enhances electron mobility by up to 6 times compared to the unstrained devices. Remarkably, the devices exhibit metal–insulator transition in MoTe2 FETs, with a well‐defined critical point. This study presents a novel technique to enhance carrier mobility in MoTe2 FETs, offering promising prospects for improving 2D material performance in electronic applications.
Sourov Chandra, Alice Sciortino, Susobhan Das, Faisal Ahmed, Arijit Jana, Jayoti Roy, Diao Li, Ville Liljeström, Hua Jiang, Leena‐Sisko Johansson,et al.
Wiley
Juan Arias Muñoz, Henri Kaaripuro, Yi Zhang, Susobhan Das, Andreas C. Liapis, and Zhipei Sun
Optica Publishing Group
We investigate artificially stacked few-layer MoS2 homojunctions with linear and nonlinear optical spectroscopies, observing various coupling effects in the layers.
Juan Arias Muñoz, Henri Kaaripuro, Yi Zhang, Susobhan Das, Andreas C. Liapis, and Zhipei Sun
Optica Publishing Group
We investigate artificially stacked few-layer MoS2 homojunctions with linear and nonlinear optical spectroscopies, observing various coupling effects in the layers.
Yi Zhang, Xueyin Bai, Juan Arias Muñoz, Yunyun Dai, Susobhan Das, Yadong Wang, and Zhipei Sun
Springer Science and Business Media LLC
AbstractLight modulation is of paramount importance for photonics and optoelectronics. Here we report all-optical coherent modulation of third-harmonic generation (THG) with chiral light via the symmetry enabled polarization selectivity. The concept is experimentally validated in monolayer materials (MoS2) with modulation depth approaching ~100%, ultra-fast modulation speed (<~130 fs), and wavelength-independence features. Moreover, the power and polarization of the incident optical beams can be used to tune the output chirality and modulation performance. Major performance of our demonstration reaches the fundamental limits of optical modulation: near-unity modulation depth, instantaneous speed (ultra-fast coherent interaction), compact footprint (atomic thickness), and unlimited operation bandwidth, which hold an ideal optical modulation solution for emerging and future nonlinear optical applications (e.g., interconnection, imaging, computing, and quantum technologies).
Yadong Wang, Fadil Iyikanat, Xueyin Bai, Xuerong Hu, Susobhan Das, Yunyun Dai, Yi Zhang, Luojun Du, Shisheng Li, Harri Lipsanen,et al.
American Chemical Society (ACS)
High-harmonic generation (HHG), an extreme nonlinear optical phenomenon beyond the perturbation regime, is of great significance for various potential applications, such as high-energy ultrashort pulse generation with outstanding spatiotemporal coherence. However, efficient active control of HHG is still challenging due to the weak light–matter interaction displayed by currently known materials. Here, we demonstrate optically controlled HHG in monolayer semiconductors via the engineering of interband polarization. We find that HHG can be efficiently controlled in the excitonic spectral region with modulation depths up to 95% and ultrafast response speeds of several picoseconds. Quantitative time-domain theory of the nonlinear optical susceptibilities in monolayer semiconductors further corroborates these experimental observations. Our demonstration not only offers an in-depth understanding of HHG but also provides an effective approach toward active optical devices for strong-field physics and extreme nonlinear optics.
Abde Mayeen Shafi, Susobhan Das, Vladislav Khayrudinov, Er-Xiong Ding, Md Gius Uddin, Faisal Ahmed, Zhipei Sun, and Harri Lipsanen
American Chemical Society (ACS)
Abde Mayeen Shafi, Faisal Ahmed, Henry A. Fernandez, Md Gius Uddin, Xiaoqi Cui, Susobhan Das, Yunyun Dai, Vladislav Khayrudinov, Hoon Hahn Yoon, Luojun Du,et al.
American Chemical Society (ACS)
Mixed-dimensional heterostructures combine the merits of materials of different dimensions; therefore, they represent an advantageous scenario for numerous technological advances. Such an approach can be exploited to tune the physical properties of two-dimensional (2D) layered materials to create unprecedented possibilities for anisotropic and high-performance photonic and optoelectronic devices. Here, we report a new strategy to engineer the light–matter interaction and symmetry of monolayer MoS2 by integrating it with one-dimensional (1D) AlGaAs nanowire (NW). Our results show that the photoluminescence (PL) intensity of MoS2 increases strongly in the mixed-dimensional structure because of electromagnetic field confinement in the 1D high refractive index semiconducting NW. Interestingly, the 1D NW breaks the 3-fold rotational symmetry of MoS2, which leads to a strong optical anisotropy of up to ∼60%. Our mixed-dimensional heterostructure-based phototransistors benefit from this and exhibit an improved optoelectronic device performance with marked anisotropic photoresponse behavior. Compared with bare MoS2 devices, our MoS2/NW devices show ∼5 times enhanced detectivity and ∼3 times higher photoresponsivity. Our results of engineering light–matter interaction and symmetry breaking provide a simple route to induce enhanced and anisotropic functionalities in 2D materials.
Md Gius Uddin, Susobhan Das, Abde Mayeen Shafi, Vladislav Khayrudinov, Faisal Ahmed, Henry Fernandez, Luojun Du, Harri Lipsanen, and Zhipei Sun
Wiley
Engineering of the dipole and the symmetry of materials plays an important role in fundamental research and technical applications. Here, a novel morphological manipulation strategy to engineer the dipole orientation and symmetry of 2D layered materials by integrating them with 1D nanowires (NWs) is reported. This 2D InSe -1D AlGaAs NW heterostructure example shows that the in-plane dipole moments in InSe can be engineered in the mixed-dimensional heterostructure to significantly enhance linear and nonlinear optical responses (e.g., photoluminescence, Raman, and second harmonic generation) with an enhancement factor of up to ≈12. Further, the 1D NW can break the threefold rotational symmetry of 2D InSe, leading to a strong optical anisotropy of up to ≈65%. These results of engineering dipole orientation and symmetry breaking with the mixed-dimensional heterostructures open a new path for photonic and optoelectronic applications.
Mingde Du, Xiaoqi Cui, Hoon Hahn Yoon, Susobhan Das, MD Gius Uddin, Luojun Du, Diao Li, and Zhipei Sun
American Chemical Society (ACS)
van der Waals (vdW) heterostructures based on two-dimensional (2D) semiconducting materials have been extensively studied for functional applications, and most of the reported devices work with sole mechanism. The emerging metallic 2D materials provide us new options for building functional vdW heterostructures via rational band engineering design. Here, we investigate the vdW semiconductor/metal heterostructure built with 2D semiconducting InSe and metallic 1T-phase NbTe2, whose electron affinity χInSe and work function ΦNbTe2 almost exactly align. Electrical characterization verifies exceptional diode-like rectification ratio of >103 for the InSe/NbTe2 heterostructure device. Further photocurrent mappings reveal the switchable photoresponse mechanisms of this heterostructure or, in other words, the alternative roles that metallic NbTe2 plays. Specifically, this heterostructure device works in a photovoltaic manner under reverse bias, whereas it turns to phototransistor with InSe channel and NbTe2 electrode under high forward bias. The switchable photoresponse mechanisms originate from the band alignment at the interface, where the band bending could be readily adjusted by the bias voltage. In addition, a conceptual optoelectronic logic gate is proposed based on the exclusive working mechanisms. Finally, the photodetection performance of this heterostructure is represented by an ultrahigh responsivity of ∼84 A/W to 532 nm laser. Our results demonstrate the valuable application of 2D metals in functional devices, as well as the potential of implementing photovoltaic device and phototransistor with single vdW heterostructure.
Xiaoqi Cui, Mingde Du, Susobhan Das, Hoon Hahn Yoon, Vincent Yves Pelgrin, Diao Li, and Zhipei Sun
Royal Society of Chemistry (RSC)
On-chip dielectric platform using van der Waals materials is experimentally demonstrated for light propagation, emission, and detection, indicating its great potential for faster, smaller, and more efficient photonic integrated circuits.
Yadong Wang, Fadil Iyikanat, Habib Rostami, Xueyin Bai, Xuerong Hu, Susobhan Das, Yunyun Dai, Luojun Du, Yi Zhang, Shisheng Li,et al.
Wiley
Electronic states and their dynamics are of critical importance for electronic and optoelectronic applications. Here, we probe various relevant electronic states in monolayer MoS2 , such as multiple excitonic Rydberg states and free-particle energy bands, with a high relative contrast of up to 200 via broadband (from ∼1.79 to 3.10 eV) static third-harmonic spectroscopy, which is further supported by theoretical calculations. Moreover, we introduce transient third-harmonic spectroscopy to demonstrate that third-harmonic generation can be all-optically modulated with a modulation depth exceeding ∼94% at ∼2.18 eV, providing direct evidence of dominant carrier relaxation processes, associated with carrier-exciton and carrier-phonon interactions. Our results indicate that static and transient third-harmonic spectroscopies are not only promising techniques for the characterization of monolayer semiconductors and their heterostructures, but also a potential platform for disruptive photonic and optoelectronic applications, including all-optical modulation and imaging. This article is protected by copyright. All rights reserved.
Susobhan Das, Yadong Wang, Yunyun Dai, Shisheng Li, and Zhipei Sun
Springer Science and Business Media LLC
AbstractThe light–matter interaction in materials is of remarkable interest for various photonic and optoelectronic applications, which is intrinsically determined by the bandgap of the materials involved. To extend the applications beyond the bandgap limit, it is of great significance to study the light–matter interaction below the material bandgap. Here, we report the ultrafast transient absorption of monolayer molybdenum disulfide in its sub-bandgap region from ~0.86 µm to 1.4 µm. Even though this spectral range is below the bandgap, we observe a significant absorbance enhancement up to ~4.2% in the monolayer molybdenum disulfide (comparable to its absorption within the bandgap region) due to pump-induced absorption by the excited carrier states. The different rise times of the transient absorption at different wavelengths indicate the various contributions of the different carrier states (i.e., real carrier states in the short-wavelength region of ~<1 µm, and exciton states in the long wavelength region of ~>1 µm). Our results elucidate the fundamental understanding regarding the optical properties, excited carrier states, and carrier dynamics in the technologically important near-infrared region, which potentially leads to various photonic and optoelectronic applications (e.g., excited-state-based photodetectors and modulators) of two-dimensional materials and their heterostructures beyond their intrinsic bandgap limitations.
Yadong Wang, Susobhan Das, Fadil Iyikanat, Yunyun Dai, Shisheng Li, Xiangdong Guo, Xiaoxia Yang, Jinluo Cheng, Xuerong Hu, Masood Ghotbi,et al.
American Chemical Society (ACS)
All-optical control of nonlinear photonic processes in nanomaterials is of significant interest from a fundamental viewpoint and with regard to applications ranging from ultrafast data processing to spectroscopy and quantum technology. However, these applications rely on a high degree of control over the nonlinear response, which still remains elusive. Here, we demonstrate giant and broadband all-optical ultrafast modulation of second-harmonic generation (SHG) in monolayer transition-metal dichalcogenides mediated by the modified excitonic oscillation strength produced upon optical pumping. We reveal a dominant role of dark excitons to enhance SHG by up to a factor of ∼386 at room temperature, 2 orders of magnitude larger than the current state-of-the-art all-optical modulation results. The amplitude and sign of the observed SHG modulation can be adjusted over a broad spectral range spanning a few electronvolts with ultrafast response down to the sub-picosecond scale via different carrier dynamics. Our results not only introduce an efficient method to study intriguing exciton dynamics, but also reveal a new mechanism involving dark excitons to regulate all-optical nonlinear photonics.
Yunyun Dai, Yadong Wang, Susobhan Das, Shisheng Li, Hui Xue, Ahmadi Mohsen, and Zhipei Sun
American Chemical Society (ACS)
Two-dimensional transition-metal dichalcogenide monolayers have remarkably large optical nonlinearity. However, the nonlinear optical conversion efficiency in monolayer transition-metal dichalcogenides is typically low due to small light–matter interaction length at the atomic thickness, which significantly obstructs their applications. Here, for the first time, we report broadband (up to ∼150 nm) enhancement of optical nonlinearity in monolayer MoS2 with plasmonic structures. Substantial enhancement of four-wave mixing is demonstrated with the enhancement factor up to three orders of magnitude for broadband frequency conversion, covering the major visible spectral region. The equivalent third-order nonlinearity of the hybrid MoS2-plasmonic structure is in the order of 10–17 m2/V2, far superior (∼10–100-times larger) to the widely used conventional bulk materials (e.g., LiNbO3, BBO) and nanomaterials (e.g., gold nanofilms). Such a considerable and broadband enhancement arises from the strongly confined electric field in the plasmonic structure, promising for numerous nonlinear photonic applications of two-dimensional materials.
Ville Hynninen, Sourov Chandra, Susobhan Das, Mohammad Amini, Yunyun Dai, Sakari Lepikko, Pezhman Mohammadi, Sami Hietala, Robin H. A. Ras, Zhipei Sun,et al.
Wiley
Because of their lightweight structure, flexibility, and immunity to electromagnetic interference, polymer optical fibers (POFs) are used in numerous short-distance applications. Notably, the incorporation of luminescent nanomaterials in POFs offers optical amplification and sensing for advanced nanophotonics. However, conventional POFs suffer from nonsustainable components and processes. Furthermore, the traditionally used luminescent nanomaterials undergo photobleaching, oxidation, and they can be cytotoxic. Therefore, biopolymer-based optical fibers containing nontoxic luminescent nanomaterials are needed, with efficient and environmentally acceptable extrusion methods. Here, such an approach for fibers wet-spun from aqueous methylcellulose (MC) dispersions under ambient conditions is demonstrated. Further, the addition of either luminescent gold nanoclusters, rod-like cellulose nanocrystals or gold nanocluster-cellulose nanocrystal hybrids into the MC matrix furnishes strong and ductile composite fibers. Using cutback attenuation measurement, it is shown that the resulting fibers can act as short-distance optical fibers with a propagation loss as low as 1.47 dB cm-1 . The optical performance is on par with or even better than some of the previously reported biopolymeric optical fibers. The combination of excellent mechanical properties (Young's modulus and maximum strain values up to 8.4 GPa and 52%, respectively), low attenuation coefficient, and high photostability makes the MC-based composite fibers excellent candidates for multifunctional optical fibers and sensors.
Yunyun Dai, Yadong Wang, Susobhan Das, Hui Xue, Mohsen Ahmadi, Shisheng Li, and Zhipei Sun
IEEE
Nanoscale nonlinear optics provides a host of fascinating phenomena ( e.g. , saturable absorption), remarkably useful for photonic applications. [1] - [3] Recently, two-dimensional (2D) transition-metal dichalcogenides (TMDs) have attracted tremendous interest due to their fascinating optical nonlinearity [4] - [6] , such as the gate-tunability, showing the great potential for diverse on-chip nonlinear optical devices. [7] However, the applications of TMDs are limited due to the low conversion efficiency at their atomic thickness. Plasmonics provides an excellent platform for enhancing light-matter interactions in TMDs, deserving further investigation (e.g., wave mixing).
Xueyin Bai, Shisheng Li, Susobhan Das, Luojun Du, Yunyun Dai, Lide Yao, Ramesh Raju, Mingde Du, Harri Lipsanen, and Zhipei Sun
Royal Society of Chemistry (RSC)
Abnormal anti-pyramid MoS2/WS2 vertical heterostructures were synthesized by a facile single-step chemical vapour deposition.
Yadong Wang, Masood Ghotbi, Susobhan Das, Yunyun Dai, Shisheng Li, Xuerong Hu, Xuetao Gan, Jianlin Zhao, and Zhipei Sun
Royal Society of Chemistry (RSC)
We have demonstrated broadband difference frequency generation with monolayer MoS2, showing possibility of using two-dimensional layered materials for optical parametric generation, amplification and oscillation.
Yunyun Dai, Yadong Wang, Susobhan Das, Hui Xue, Xueyin Bai, Eero Hulkko, Guangyu Zhang, Xiaoxia Yang, Qing Dai, and Zhipei Sun
American Chemical Society (ACS)
Monolayer transition-metal dichalcogenides show strong optical nonlinearity with great potential for various emerging applications. Here we demonstrate the gate-tunable interband resonant four-wave mixing and sum-frequency generation in monolayer MoS2. Up to 80% modulation depth in four-wave mixing is achieved when the generated signal is resonant with the A exciton at room temperature, corresponding to an effective third-order optical nonlinearity |χ(3)eff| tuning from (∼12.0 to 5.45) × 10–18 m2/V2. The tunability of the effective second-order optical nonlinearity |χ(2)eff| at 440 nm C-exciton resonance wavelength is also demonstrated from (∼11.6 to 7.40) × 10–9 m/V with sum-frequency generation. Such a large tunability in optical nonlinearities arises from the strong excitonic charging effect in monolayer transition-metal dichalcogenides, which allows for the electrical control of the interband excitonic transitions and thus nonlinear optical responses for future on-chip nonlinear optoelectronics.